Designing With Engineering Plastics

June 10, 2018 | Author: Scott Anderson | Category: Polyethylene, Wear, Combustion, Plastic, Carbon
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2x 4 5 ° 3 0 + 0 , 5 2 0 + 0 , 5 Ø 7 0 , 0 5 + 0 , 1 Ø 5 0 , 0 5 + 0 , 1 2 Ø 6 8 2 x 4 5 º Designing with engineering Plastics Titel Konstruieren 27.10.2004 10:19 Uhr Seite 1 Licharz on the web Certified quality management according to DIN EN ISO 9001 : 2000 DIN EN ISO 9001:2000 Certificate No 01 100 040034 Konstr. Kunststoffe engl.7/04 27.10.2004 7:32 Uhr Seite 2 3 C o n t e n t s Contents Polyamides (PA) 6-10 Oilamid ® 11-13 Calaumid ® 612 / Calaumid ® 1200 14-15 Calaumid ® 612-Fe / Calaumid ® 1200-Fe 16 Polyacetal (POM) 17-19 Polyethylene terephthalate (PET) 20-21 Polyethylene (PE) 22-24 Polypropylene (PP) 25-26 Polyvinyl chloride (PVC) 27-28 Polyvinylidene fluoride (PVDF) 29 Polytetrafluoroethylene (PTFE) 30-31 Polyetheretherketone (PEEK) 33 Polysulphone (PSU) 34 Polyether imide (PEI) 35 Tolerances 105-113 Machining guidelines 114-118 Physical material standard values and chemical resistances 119-133 Information on how to use this documentation / Bibliography 134 Foreword – Engineering plastics as design materials 4 Material overview 5 Structure and properties of plastic 36-43 Behaviour in fire 44-45 Resistance to radiation and weathering 46-47 Storage information 48 Plastic friction bearings 49-60 Plastic sliding panels 61-64 Plastic castors 65-75 Plastic rope pulleys 76-85 Plastic gear wheels 86-100 Plastic spindle nuts 101-104 Konstr. Kunststoffe engl.7/04 27.10.2004 7:32 Uhr Seite 3 Engineering plastics are becoming increasingly popular in machine and plant construction as design engineers recognise their advantages and economic significance. The use and development of materials is subject to continuous change. This also applies to plastics. Many machined parts that were manufactured exclusively from conventional metals just ten years ago are now being made from modern engineered plastics. We can expect this change to continue in the future – perhaps at an even faster pace than we have experi enced to date. Thi s change can be attri buted to the enormous ri se i n the number of en- gi neeri ng pl asti cs avai l abl e al ong wi th thei r many di fferent modi fi cati ons, characteri sti cs and possi bl e appl i cati ons. Due to thei r speci f i c properti es, many pl asti cs are equal or superi or i n many ways to conventi onal desi gn materi al s. In many cases, engi neeri ng pl asti cs have al ready replaced conventional materials due to their superior performance properties. The main advantages of engineering plastics in comparison to conventional metals are: weight reduc- tion, resistance to wear, good vibration absorption and the fact that plastics are easier to machine. Additionally, their high level of chemical resistance, the increasing thermal stability of several types of plastic and improved recycling possibilities are further positive arguments for choosing engineering plastics. The task of design engineers will increasingly be to find an optimal material for a specific applica- tion while keeping production costs down. Often there is a lack of awareness regarding the actual volume prices of plastics compared to conventional metal materials. Even high quality modified polyamides can be less expensive than many types of metals. In addition, the much lower quantity of chips when plastics are machined is another factor that influences the price /performance ratio in comparison to metals. The experi ence that LICHARZ has gai ned duri ng the l ast 40 years i n manufacturi ng, processi ng and utilizing engineering plastics for machine and equipment design, automotive industry appli- cations and other areas has made LICHARZ one of the leading companies in this industry in Euro- pe (world wide???). Over the years, we have come to focus on applications that are subject to slip and wear stresses and have achieved extensive success. The majority of semi-finished products as describes in this document, especially all variants of cast polyamides, and finished parts, are produced in our plant or manufactured by us on cutting edge CNC controlled machines. In order to make i t easi er for desi gn engi neers and users to determi ne whi ch pl asti c i s best for their specific applications, we have summarised our experience in the form of material descriptions and design and machining information in this brochure. Please do not hesitate to contact us with any questions you may have. 3rd edition, July 2004 Foreword 4 Konstr. Kunststoffe engl.7/04 27.10.2004 7:33 Uhr Seite 4 5 Material overview The most important engineering plastics are Polyamide (PA) Polyacetal (POM) Polyethyleneterephthalate (PET) Many different material modifications of these engineering plastics are used in components that are subject to sliding and wear loads. Other materials are only used occasionally for sliding applications and mainly for applications where there is chemical demand. These include Polyethylene (PE) Polypropylene (PP) Polyvinylchloride (PVC) Polyvinylidenefluoride (PVDF) Polytetrafluoroethylene (PTFE) High-performance plastics are another group of modern materials that are characterised by their high level of rigidity and stability at high temperatures. The disadvantage is the high price, which in some cases can be as much as 30 times the cost of engineering plastics. High-performance plastics include Polyetheretherketone (PEEK) Polysulphone (PSU) Polyether imide (PEI) Konstr. Kunststoffe engl.7/04 27.10.2004 7:33 Uhr Seite 5 Polyamides (PA) Konstr. Kunststoffe engl.7/04 27.10.2004 7:33 Uhr Seite 6 7 P A Polyamides are subdivided into various basic types. The most important are PA 6, PA 66 and PA 12. The differences in physical properties are in the composition and structure of the molecule chains. In the manufacture of semi -fi ni shed products, a di sti ncti on i s made between moul ded and extruded materials. The key properties of polyamide are: • High mechanical stability, hardness, rigidity and toughness • High mechanical damping properties • Good fatigue resistance • Very high wear resistance • Good sliding and emergency running properties • Good machining properties Because of the hi gher crystal l i ni ty, semi -fi ni shed products manufactured by casti ng have much better physical properties than extruded polyamides. Extruded Polyamides Polyamide 6 i s the best known extruded pol yami de. PA 6 offers a good combi nati on of mechani cal stabi l i ty, i mpact resi stance and dampi ng, but compared to PA 6 G i t has much l ower wear resi stance, absorbs more moi sture and has l ess di mensi onal stabi l i ty. Appl i cati ons: parts that are subject to shock and impact, gear wheels, hammer heads. Colour: natural, black Polyamide 66 is used in smaller applications. Compared to PA 6 it is harder and is more resistant to wear, howe- ver, it does have less impact resistance. Applications: friction bearings, sliding panels. It has similar mechanical properties to PA 6 G, which is much less expensive and is generally used instead of PA 66. Colour: natural Polyamide 12 has very good i mpact behavi our, i t i s tough and, because of i ts very l ow water absorpti on, i t i s di mensi onal l y stabl e. It i s avai l abl e i n smal l quanti ti es as semi -fi ni shed products, but i s not generally considered for construction applications due to its high price (3-4 times more expensive than PA 6). Polyamides (PA) Konstr. Kunststoffe engl.7/04 27.10.2004 7:33 Uhr Seite 7 8 P A The so-called monomer moulding process, in which semi-finished products are created by means of a control l ed chemi cal reacti on, i s a si gni fi cant i mprovement compared to conventi onal extrusion or injection moulding processes and is especially important for the performance of this material. Typical physical properties are improved in a targeted manner. Range of cast polyamide materials PA 6 G Cast pol yami de for components i n machi ne and equi pment desi gns that are subject to wear (standard quality). Colours: natural, black, blue Oilamid ® PA 6 G with integrated lubrication, self-lubricating effect, improved wear resistance. Colours: black, yellow, natural PA 6 G/WS Essenti al l y si mi l ar to the standard qual i ty but better protected wi th a thermal stabi l i ser agai nst thermal-oxidative degradation. Colour: natural PA 6 G/MoS Essentially similar to the standard quality, but this type has a higher degree of crystallinity due to molybdenum sulphide constituents. Colour: black Calaumid ® 612 Co-polyamide based on PA 6/12-G with higher impact and shock resistance, less water absorption and improved creep resistance compared to pure PA 6 G. Also available as Calaumid ® 612-Fe with a steel core (see separate material description). Colour: natural Calaumid ® 1200 Cast polyamide based on laurin lactam. Very good impact behaviour, toughness, excellent dimen- sional stability, lowest water absorption, very good creep resistance, hydrolysis resistance, good chemical resistance. PA 12 G is far superior to extruded PA 12 in every respect. Also available as Calaumid ® 1200-Fe with a steel core (see separate material description). Colour: natural Cast polyamides Konstr. Kunststoffe engl.7/04 27.10.2004 7:33 Uhr Seite 8 9 P A PA 6 G i s a bei ge col oured, fi rm, homogeneous, stress-rel i eved materi al wi th a hi gh degree of crystal l i ni ty. Speci fi c properti es are al so devel oped through modi fi cati on, speci al setti ngs and additives. Material properties PA 6 G offers tried and tested characteristic material properties: Hi gh abrasi on and wear resi stance at l ow to medi um speeds compared to cast i ron, steel or bronze – especially under rough conditions (sand, dust). Vibration and noise absorption Prol ongs the l i fe of machi ne parts through the vi sco-el asti ci ty of the pl asti c and compl i es wi th environmental requirements, e.g. noise absorption via PA 6 G rollers, gear wheels, etc. Low weight Wi th a speci fi c wei ght of 1.15 g/cm 3 , PA 6 G onl y wei ghs approx. 13% of the same vol ume of bronze, 15% of steel and 43% of aluminium, which means less centrifugal force and imbalance in rotating parts. Chemical resistance Against weak acids and alkalis as well as all conventional organic solvents. Very good sliding properties characterise PA 6 G as a traditional friction bearing material for machine parts that are subject to a l ot of wear, such as beari ng bushes, sl i di ng panel s, gui de panel s, gear wheel s and sprocket wheels and rollers. Because of the low coefficient of friction, lubrication is often unnecessary or only an initial lubrication is required when the parts are being installed. Stability of physical properties The property values of PA 6 G are influenced by temperature and moisture. When temperatures increase or water is absorbed, tensile and compressive strength are reduced, modulus of elasticity and hardness are reduced, while impact resistance and expansion increase. PA 6 G Konstr. Kunststoffe engl.7/04 27.10.2004 7:33 Uhr Seite 9 10 P A Dimensional stability Thi s i s al so dependent on temperature and moi sture. However, the hi gh crystal l i ni ty of PA 6 G reduces moisture absorption considerably. Water is only absorbed very slowly. The rate of absorp- tion reduces progressively with the depth of penetration. Guiding values for moisture Saturation level in a standard climate (23°C/50% RH) depending on type: 1.5 – 2%. Li near deformati on due to moi sture absorpti on: approx. 0.15 – 0.20% per 1% water absorbed. Linear deformation due to temperature changes: approx. 0.1% per 10°C temperature difference. Machining PA 6 G can easi l y be machi ned on equi pment that i s normal l y used for metal and wood pro- cessing. To prevent deformation, material should be removed equally from all sides. If material is to be removed unevenl y i t i s recommended that the workpi ece be pre-worked, anneal ed and stored for 24 hours before the final processing work is carried out. Because of the notch sensitivity of plastics in general, sharp-edged transitions should be avoided. PA 6 G Notch impact resistance of polyamide 6 G at low temperatures Notch impact resistance of polyamide 6 G with different water contents Water absorption of pol yami de 6 G i n water at room temperature and standard climate (Test piece: standard small rod) 1 2 3 4 5 0 -150 -120 -80 -40 0 -200 N o t c h i m p a c t r e s i s t a n c e ( K J / m 2 ) Temperature °C 10 9 8 7 6 5 4 3 2 1 0 10 0 10 1 10 2 10 3 10 4 W a t e r c o n t e n t [ % ] Days in water at room temperature in standard climate 10 20 30 40 0,5 1 1,5 2 0 0 N o t c h i m p a c t r e s i s t a n c e ( K J / m 2 ) Water content (%) Konstr. Kunststoffe engl.7/04 27.10.2004 7:34 Uhr Seite 10 Oilamid ® Konstr. Kunststoffe engl.7/04 27.10.2004 7:34 Uhr Seite 11 12 O i l a m i d ® Oilamid is a high-molecular thermoplastic based on PA 6 G. Oilamid has a fine crystalline structure with high wear-resistant and self-lubricating properties. The high level of wear resistance and the extraordi nary sl i di ng properti es are speci fi cal l y devel oped by addi ng oi l , sol i d l ubri cants and stabilisers. Increased abrasion and wear resistance The oil is added before the polymerisation process and gives the material a self-lubricating effect. The coeffi ci ent of fri cti on i s reduced by 50%, whi ch makes Oi l ami d an i deal desi gn materi al for hi ghl y l oaded, sl ow movi ng, dry-runni ng sl i di ng el ements wi th up to 10 ti mes more wear resistance than unfilled polyamide. At slow to medium speeds, and especially in rough conditions (sand, dust), Oilamid has considerably more abrasion and wear resistance than cast iron, steel or bronze. Generally a pv factor is given as a load limit for sliding elements. Oilamid can work under hi gher l oads and speeds than PA 6 G. The i nfl uence on the l evel of sl i di ng abrasi on i s subject to the parameters of the surface roughness of the metal l i c mati ng component, surface pressure, sl i di ng speed, sl i di ng surface temperature and l ubri cati on. Because of i ts l ow coeffi ci ent of friction, Oilamid has a low rate of abrasion and is suitable for dry-running in special applications. Vibration and noise absorption Oi l ami d’s vi brati on and noi se absorpti on prol ongs the l i fe of machi ne parts through the vi sco- elasticity of the plastic and complies with environmental requirements, e.g. noise absorption via Oilamid gear wheels and rollers. Excellent sliding properties Due to i ts l ubri cati on supporti ng effect, Oi l ami d i s becomi ng an i mportant fri cti on beari ng material for machine and equipment parts such as bearing bushes, sliding panels, guide panels, guide curves, gear wheels and sprocket wheels. Oilamid ® 5 2 3 4 10 0,15 0,2 0,02 0,03 0,1 0,05 0,3 0,07 1,0 Polyamide 6 G Oilamid ® 0,4 0,6 0,8 1,5 0,15 1,00 0,10 0,20 0,30 0,40 0,50 0,60 1,50 0,80 2,00 3,00 4,00 5,00 6,00 8,00 10,00 Circumferential speed m/s B e a r i n g l o a d M P a Konstr. Kunststoffe engl.7/04 27.10.2004 7:34 Uhr Seite 12 13 O i l a m i d ® Sliding abrasion as a function of the bearing load Load within the permissible pv range; lubrication: dry-running; sliding surface temperature: 80 ºC; surface roughness of the steel counterpart Rz = 2µm For sliding elements that are intended to be used in dry-running applications, it is recommended that they are gi ven an i ni ti al l ubri cati on to al l evi ate break-i n l oadi ng. The coeffi ci ent of sl i di ng friction of Oilamid remains stable as the pressure increases. The stick-slip behaviour is better than other thermoplastics. Because of the low coefficients of sliding friction, the friction heat of Oilamid sliding elements is l ower than other pol yami de grades, whi ch means that they can operate at hi gher l oads and speeds. Polyamide 6 G Oilamid ® 5 6 7 8 9 10 11 12 0,11 0,10 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,6 0,4 0,2 POLYAMIDE 6 G 0 0,5 1,0 1,5 OILAMID ® Polyamide 6 G Oilamid 30 20 10 0 40 50 60 70 80 90 100 1 0 0,2 0,4 0,6 1,2 1,4 1,6 1,8 2,0 0,8 Coefficient of sliding friction of polyamide 6 G and Oilamid Friction ring ST 50 K (v = 1m/s) Surface temperature after 1 hour Sliding friction of polyamide 6 G and Oilamid friction ring ST 50 K (v=1m/s) M e a n c o e f f i c i e n t o f s l i d i n g f r i c t i o n Surface pressure [MPa] W e a r , [ µ m / k m ] Bearing load [MPa ] Surface pressure [MPa] S u r f a c e t e m p e r a t u r e Konstr. Kunststoffe engl.7/04 27.10.2004 7:34 Uhr Seite 13 Calaumid ® /Calaumid ® -Fe Konstr. Kunststoffe engl.7/04 27.10.2004 7:34 Uhr Seite 14 15 C a l a u m i d ® Calaumid ® Calaumid 612 is a co-polyamide based on PA 6/12 G. Compared to pure PA 6 G, shock and impact resi stance are hi gher i n Cal aumi d 612, moi sture absorpti on i s l ower and creep resi stance i s improved. Because of these material properties Calaumid 612 is especially suitable for use in areas where increased shock loads are expected or where higher fatigue resistance and flexibility are re- quired. Typical applications are: • Gear wheels • Toothed racks • Pinions • Outrigger float pads Calaumid 1200 is the trade name for PA 12 G, which is also manufactured from the raw material laurin lactam in a pressureless monomer moulding process. The seamless transition from polyme- ri sati on to crystal l i sati on creates a hi gh-crystal l i ne structure. Thi s produces materi al properti es that are far superior to extruded PA 12. Advantages of Calaumid 1200 compared to other polyamides: • Low water absorption compared to other polyamides • Thi s makes i t di mensi onal l y stabl e and reduces the effects of water content on mechani cal properties to an absolute minimum • Good creep resistance, even at high temperatures • Good shock and notch impact resistance, also at temperatures as low as –50°C • Good resistance to hydrolysis and chemicals in the pH 2-14 range • Temperature stability from –60 to +110°C • Good slip and abrasion resistance • Resistant to stress cracking • Low specific weight The combination of these properties makes Calaumid 1200 an ideal material for gear components, especially if steel hubs are being moulded in during manufacture. These properties are not completely achieved by other thermoplastics or bronze. Dependence of the mechanical properties on the water content for Calaumid 1200 0 0,5 1,0 1,5 2,0 Mass % 70 60 50 40 MPa 0 0,5 1,0 1,5 2,0 Mass % 2800 2400 2200 1600 MPa 2000 1800 2600 -40 0 40 80 120 ºC 2600 1800 1400 8 1000 600 2200 MPa Y i e l d s t r e s s M o d u l u s o f e l a s t i c i t y ( b e n d i n g ) M o d u l u s o f e l a s t i c i t y Water content Temperature Water content Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 15 16 C a l a u m i d ® - F e Calaumid-Fe Calaumid-Fe is moulded in a pressureless process in a form-fit and non-positive manner around a 2 to 2.5mm deep knurled steel core. Combinations with aluminium, stainless steel and brass are also possible. The plastic can be either Calaumid 612 or Calaumid 1200. The combi nati on of the pl asti c outsi de and the metal core i s especi al l y sui tabl e for opti mi sed torque transmission for component parts such as • Spur wheels • Worm wheels • Bevel wheels • Sprocket wheels • Castors, guide rollers and rope pulleys • Cam disks The combi nati on of a steel core and a pl asti c casi ng uni tes the uni que properti es of steel and plastic that are so highly valued in design. The shaft-hub connection is calculated in the same way as steel, thus offering the possibility of a high degree of power transmission. The advantages of Calaumid-Fe: • Maintains the time-tested metallic shaft-hub connection • Runs quietly • Weight advantage compared to pure steel designs • Good noise absorption and vibration behaviour • Good dry and emergency running properties • Optimum power transmission (calculated like steel) • Precise bearing seat, high degree of fitting accuracy • High degree of true running Calaumid F Fe-Kern Material: Calaumid ® -FeV Steel core: Ø60mm x 38mm Calaumid disk: Ø140mm x 38mm Knurl: Axial and circumferential knurl, DIN 82-RKE 2.0 Material steel: Machining steel 9 SMn 28K Max. axial load: 100 kN F Material: Calaumid ® -FeV Steel core: Ø80mm x 20mm Calaumid disk: Ø200mm x 33mm Knurl: Axial and circumferential knurl, DIN 82-RKE 2.0 Material steel: Machining steel 9 SMn 28K Max. torque: 4,45 kNm Axial load experiment Torque transmission test Result of axial load: Result of torque transmission: Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 16 POM/PET Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 17 18 P O M Polyacetal (POM) Pol yacetal i s a hi gh crystal l i ne thermopl asti c wi th a hi gh l evel of stabi l i ty and ri gi di ty as wel l as good sl i di ng properti es and wear resi stance wi th a l ow l evel of moi sture absorpti on. Its good di mensi onal stabi l i ty, excepti onal fati gue resi stance and excel l ent machi ni ng properti es make pol yacetal a versati l e desi gn materi al al so for compl ex components. POM sati sfi es hi gh surface finish requirements. Stabi l i ty, ri gi di ty and di mensi onal stabi l i ty can be further i mproved by addi ng gl ass fi bres as a filler, although this decreases sliding properties. A distinction is made between homopolymers (POM-H) and copolymers (POM-C); homopolymers have a higher density, hardness and stability due to their higher degree of crystallinity. However, copol ymers have a hi gher i mpact resi stance, greater abrasi on resi stance and better thermal / chemical stability. The polyacetal semi-finished products that we offer – from which we also manufacture finished products– are produced from copolymers in an extrusion process. Main properties • High stability • High rigidity • High hardness • Good impact resistance, also at low temperatures • Low level of moisture absorption (at saturation 0.8%) • Good creep resistance • High dimensional stability • Resistant to hydrolysis (up to +60°C) • Physiologically safe Colours: POM – C : natural/black POM – C + GF: black Slip Sliding properties POM-C has excel l ent sl i di ng properti es and good wear resi stance. Together wi th i ts other out- standing properties, POM-C is well suited for sliding applications with medium to high loads. This also applies to applications where high levels of humidity or wetness are to be expected. Because of the cl ose stati c and dynami c coeffi ci ents of fri cti on, l ow start-up moments can be implemented. This does not apply to the types filled with glass as their sliding properties are much less than the unfilled types. Weathering effects POM-C is not resistant to UV rays. UV rays, in combination with atmospheric oxygen, oxidise the surface, and discolouration occurs or the surface becomes matt. If the material is subject to the effects of UV rays for a long time, it tends to become brittle. Chemical resistance POM i s resi stant to weak aci ds, weak and strong al kal i ne sol uti ons, organi c sol vents and petrol , benzole, oils and alcohols. POM-C is not resistant to strong acids (pH < 4) or oxidising materials. Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 18 19 P O M Behaviour in fire POM-C is rated as normal flammable. When the source of ignition is removed, POM-C continues to burn, formi ng dropl ets. Duri ng thermal decomposi ti on, formal dehyde can form. The oxygen index (= the oxygen concentration required for combustion) at 15% is very low compared to other plastics. Areas of use • General machine engineering • Vehicle construction • Precision mechanics • Electrical industry • Information technology Applications • Spring elements • Bushes • Gear wheels • Sliding elements • Insulators • Pump components • Casing parts • Valves and valve bodies • Counter parts • Precision parts Machining POM-C develops a fragmented chip and is thus ideally suited for machining on automatic lathes, but i t i s al so possi bl e to machi ne i t on cutti ng machi ne tool s. The semi -fi ni shed products can be dri l l ed, mi l l ed, sawed, pl aned and turned on a l athe. It i s al so possi bl e to cut threads or i nsert threaded parts in the material. Generally no cooling or lubricating emulsion is necessary. To limit material deformation due to internal residual stress in semi-finished products, the parts should always be machined from the geometrical centre of the semi-finished product, removing an even quantity of material from all sides. If maxi mum di mensi onal stabi l i ty i s demanded from the fi ni shed components, the parts to be manufactured shoul d be rough pre-machi ned and stored for an i nteri m peri od or heat treated. The parts can then be completed. More detailed information on interim storage and heat treat- ment, as wel l as other i nformati on about machi ni ng, i s provi ded i n the chapter on “ Machi ni ng guidelines” . Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 19 20 P E T Polyethyleneterephthalate (PET) The molecule structure of polyethyleneterephthalate can be produced either as an amorphous or semi-crystalline thermoplastic. The amorphous type is crystal clear with lower mechanical stability and inferior sliding properties. The semi-crystalline types, on the other hand, have a high level of hardness, rigidity and stability wi th excel l ent sl i di ng properti es and l ow sl i di ng abrasi on. Because of i ts good creep resi stance, low level of moisture absorption and excellent dimensional stability, the material is ideally suited for compl ex parts wi th the hi ghest demands on di mensi onal stabi l i ty and surface fi ni sh. For the reasons mentioned above, only the semi-crystalline type is suitable for sliding applications. The wear resistance and sliding properties of PET-GL have been improved compared to pure PET by adding a special, homogeneously distributed solid lubricating agent. The pol yethyl ene terephthal ate semi -fi ni shed products that we offer – and from whi ch we al so manufacture all finished products – are manufactured from semi-crystalline types in an extrusion process. Main properties • High stability • High rigidity • High hardness • Low moisture absorption (at saturation 0.5%) • Very good creep resistance • Very high dimensional stability • Constantly low sliding friction • Very little sliding abrasion • Resistant to hydrolysis (up to +70°C) • Physiologically safe Colours PET: natural, black PET-GL: light grey Sliding properties PET has excellent sliding properties, very good wear resistance and, in combination with its other properti es, i s an excel l ent materi al for hi ghl y l oaded sl i di ng appl i cati ons. Thi s al so appl i es to applications where high levels of humidity or wetness are expected. The modi fi ed type PET-GL i s especi al l y sui tabl e for hi ghl y l oaded sl i di ng appl i cati ons i n dry running operations due to its integrated solid lubricating agent. The solid lubricating agent “ self lubricates” the PET-GL, which gives it excellent sliding properties and highest wear resistance with a much hi gher l oad-beari ng strength (pv l i mi ti ng val ue) compared to pure PET. It al so prevents the stick-slip effect. The other properties are equal to those of pure PET. Weathering effects PET i s not resi stant to UV rays. The materi al surface changes when subjected to UV rays i n com- bination with atmospheric oxygen. If the material is to be subjected to UV rays for longer periods, a black coloured type is recommended. Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 20 21 P E T 21 Chemical resistance PET is resistant to weak acids and alkaline solutions, salt solutions, perchlorinated and fluorinated hydrocarbons, oi l s, fuel s, sol vents and surface-acti ve substances. Strong pol ar sol vents have an irreversible swelling effect. PET is not resistant to strong acids or alkaline solutions, esters, ketones or chlorinated hydrocarbons. Behaviour in fire PET is rated as normal flammable. When the source of ignition is removed, PET continues to burn, forming droplets. The oxygen index (the oxygen concentration required for combustion) at 23% is average compared to other plastics. Areas of use Applications • General machine engineering • Ratchet wheels • Vehicle construction • Bushes • Precision mechanics • Gear wheels • Electrical industry • Sliding elements • Information technology • Insulators • Casing parts • Counter components • Precision bearings • Cam disks Machining PET develops a brittle, flowing chip and is suitable for machining on automatic lathes, but it can al so be machi ned on cutti ng machi ne tool s. The semi -fi ni shed products can be dri l l ed, mi l l ed, sawed, planed and turned on a lathe. It is also possible to cut a thread into the material or insert a threaded element. Generally no cooling or lubricating emulsion is necessary. Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 21 Plastics that are highly resistant to chemicals Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 22 23 Polyethylene is a semi-crystalline thermoplastic with high toughness and chemical resistance, rather low mechanical strength in comparison to other plastics and cannot be used at high temperatures. The i ndi vi dual pol yethyl enes di ffer i n regard to thei r mol ar mass (mol ecul ar wei ght), whi ch i s i mportant f or the respecti ve physi cal properti es. Thi s means that i n addi ti on to the common properties that all types have, certain ones have type-specific properties. The polyethylene semi-finished products that we offer – from which we also manufacture finished products – consist of high density polyethylene types produced by extrusion or moulding proces- ses. Main properties • Low density compared to other materials (0.94 g/cm 3 ) • High impact resistance, also at low temperatures • Minimum water absorption (< 0.01%) • Excellent chemical resistance • High corrosion resistance • Anti-adhesive • Very good electrical insulator • High vibration absorption • Physiologically safe (does not apply to regenerate semi-finished products) Colours PE – HD: natural, black PE – HMW: natural, green PE – UHMW: natural, green, black Other colours on request. Sliding properties PE-HD (PE 300; molar mass approx. 200,000 g/mol) is very suitable for welding due to its relatively l ow mol ar mass; however, i t i s not abrasi on resi stant and has l ow stabi l i ty val ues. Thi s l eads to a high level of sliding abrasion, which excludes its use in sliding applications. PE-HMW (PE 500; molar mass approx. 500,000 g/mol) has better sliding properties because of its higher molar mass and is also more abrasion resistant than PE-HD. In combination with its good toughness, it is suitable for use in low stress components that are not subject to any high degree of sliding abrasion. PE-UHMW (PE 1000; mol ar mass approx. 4,500,000 g/mol ). Because of i ts hi gh mol ar mass i t has very good wear resi stance, bendi ng strength and i mpact resi stance and good noi se absorbti on. Due to its excellent sliding properties and low sliding abrasion, it is the ideal material for lightly loaded components. Both PE-HMW und PE-UHMW are al so avai l abl e as regenerated materi al , al though i t must be noted that the respective physical properties are slightly reduced. Chemical resistance Al l PE types are resi stant to aci ds, al kal i ne sol uti ons, sal ts and sal t sol uti ons, al cohol s, oi l s, fats, waxes and many solvents. Aromatics and halogenated hydrocarbons cause swelling. All PE types are not resi stant to strong oxi di si ng materi al s (e.g. ni tri c aci d, chromi c aci d or hal ogens), and there is a danger of stress corrosion cracking. Polyethylene (PE) P E Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 23 24 P E Weathering effects As a general rule, no PE types are resistant to UV rays. This does not apply to the black coloured types, which are resistant to UV rays (also in combination with atmospheric oxygen). Behaviour in fire All PE types are rated as normal flammable. When the source of ignition is removed they continue to burn and form drops. However, apart from carbon dioxide, carbon monoxide and water, only smal l quanti ti es of carbon bl ack and mol ecul ar consti tuents of the pl asti c devel op as confl ag- ration gases. The oxygen index (the oxygen concentration required for combustion) at 18% is low compared to other plastics. Areas of use Applications PE-HD PE-HD • Electroplating industry • Component parts in chemical plant construction • Chemical industry • Fittings • Chemical apparatus construction • Inserts • Stacking boxes PE-HMW PE-HMW • Food industry • Cutting table surfaces • Meat processing industry • Agitator blades • Sporting venue construction • Wall linings in refrigeration rooms • Impact bands • Knife blocks PE-UHMW PE-UHMW • Electroplating industry • Rope pulleys, guide rollers • General machine engineering • Sprocket wheels and pinions • Coal processing • Gear wheels • Packaging industry • Chain guides • Conveying technology • Slides • Paper industry • Suction plates • Electrical industry • Knife-over roll coaters • Chute linings for silos • Conveyor trough linings • Abrasion protection strips Machining In addition to the good welding properties of PE-HD and PE-HMW, all PE types can also be machined on machine tools. The semi-finished products can be drilled, milled, sawed, planed and turned on a lathe. It is also possible to cut a thread into the material or insert a threaded element. As a rule, no cooling or lubricating emulsion is necessary. Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 24 25 P P Polypropylene is a semi-crystalline thermoplastic with high rigidity and very good chemical resi- stance. Characteristic for polypropylene is a CH3 side-group in the monomer structural unit, which can be aligned in various spatial positions during polymerisation. The various spatial alignments are significant for the physical properties and differ according to the following: • Isotactic (regular, one-sided alignment in the macromolecule) • Syndiotactic (regular, double-sided alignment in the macromolecule) • Atactic (irregular, random alignment in the macromolecule) Alignment A distinction is also made between homopolymers and copolymers; copolymers are tougher but have less mechanical and chemical stability. As the physical properties improve considerably with the increase in the isotactic concentration in the pol ymer, i sotacti c pol ypropyl ene homopol ymers shoul d be the fi rst choi ce for use i n the techni cal area. The pol ypropyl ene semi -fi ni shed products that we offer – from whi ch we al so manufacture finished products – are produced by extrusion or moulding processes. Main properties • Low density compared to other materials (0,91 g/cm 3 ) • Minimum water absorption (< 0.01%) • Excellent chemical resistance, also to solvents • High corrosion resistance • Relatively high surface hardness • Very good electrical insulator • Physiologically safe Colours Natural (white), grey (≈ RAL 7032) Other colours available on request. Slip properties PP-H is subject to strong sliding abrasion and is thus not suitable for use in sliding applications. Chemical resistance PP-H is resistant to acids, alkaline solutions, salts and salt solutions, alcohols, oils, fats, waxes and many solvents. Aromatics and halogenated hydrocarbons cause swelling. PP-H is not resistant to strong oxidising materials (e.g. nitric acid, chromic acid or halogens) and there is a danger of stress corrosion cracking. Behaviour in fire PP-H i s rated as normal fl ammabl e. When the source of i gni ti on i s removed PP-H conti nues to burn, formi ng dropl ets. However, apart from carbon di oxi de, carbon monoxi de and water, onl y smal l quanti ti es of carbon bl ack and mol ecul ar consti tuents of the pl asti c devel op as confl ag- ration gases. The oxygen index (the oxygen concentration required for combustion) at 18% is low compared to other plastics. Polypropylene (PP) Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 25 26 P P Weathering effects PP-H i s not resi stant to UV rays. UV rays, i n combi nati on wi th atmospheri c oxygen, oxi di se the surface and discolouration occurs. If the material is exposed to the effects of UV rays for a longer period, this will cause irreparable damage and decomposition of the surface. Areas of use Applications • Electroplating industry • Pump parts • Chemical industry • Component parts in chemical apparatus construction • Machine engineering • Fittings • Stamping/punching plants • Valve bodies • Product holders for electroplating processes • Punching pads Machining In addition to its good welding properties, PP-H can also be machined on machine tools. The semi- finished products can be drilled, milled, sawed, planed and turned on a lathe. It is also possible to cut a thread i nto the materi al or i nsert a threaded el ement. General l y no cool i ng or l ubri cati ng emulsion is necessary. During cutting, it is very important to ensure that the tools that are used are always adequately sharp. Bl unt tool s cause the surface to heat, whi ch can cause “ smeari ng” and consequentl y unacceptable surface finishes. Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 26 27 P V C Polyvinylchloride (PVC) Polyvinylchloride – hard (PVC-U) is an amorphous thermoplastic with no added plasticiser. It has a hi gh hardness and ri gi di ty. Accordi ng to DIN 16 927 the materi al i s cl assi fi ed as normal shock resi stant, however i ts toughness val ues border on bei ng rated as hi ghl y shock resi stant, whi ch gi ves i t a hi gh degree of saf ety i n regard to the desi gn of components. The pol yvi nyl chl ori de semi -fi ni shed products that we offer – from whi ch we al so manufacture fi ni shed products – are produced i n extrusi on or moul di ng processes. Main properties • Hard surface • High rigidity • Low water absorption • Excellent chemical resistance • Fire resistant (UL 94 V 0) • Easily thermoformed • Can be bonded • Good cutting properties Colours grey (≈ RAL 7011), black, red, transparent Other colours available on request. Sliding properties PVC-U i s not subject to any major sl i di ng abrasi on and i s thus sui tabl e for use i n sl i di ng appl i - cations. Weathering effects PVC-U i s not resi stant to the effects of UV rays. In combi nati on wi th atmospheri c oxygen, the surface oxidises and discolouration occurs. If the material is exposed to UV rays and atmospheric oxygen for longer periods, irreparable damage and decomposition of the surface will occur. Food law suitability PVC-U does not compl y wi th the requi rements of the German Federal Insti tute for Ri sk Assess- ment (BgVV) or the FDA and may not be used for manufacturing consumer goods that come into direct contact with food. Chemical resistance PVC-U i s resi stant to aci ds, al kal i ne sol uti ons, al cohol s, oi l s, fats, al i phati c hydrocarbons and petrol. PVC-U is not resistant to benzole, chlorinated hydrocarbons, ketones or esters. In combination with strong oxidising materials (e.g. nitric acid or chromic acid), there is a danger of stress corrosion cracking. Behaviour in fire PVC is rated as fire resistant in the highest category, even without additives. When the source of ignition is removed, PVC is self-extinguishing. The oxygen index (the oxygen concentration required for combustion) at 40% is very high com- pared with other plastics. Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 27 28 P V C Areas of use Applications • Electroplating industry • Pump parts • Machine engineering • Fittings • Filling plants • Valve bodies • Photo industry • Component parts in chemical plant construction • Feed tables • Machine and equipment covering Machining In addition to its good welding properties and the possibility of bonded connections, PVC-U can al so be machi ned on machi ne tool s. The semi -fi ni shed products can be dri l l ed, mi l l ed, sawed, pl aned and turned on a l athe. It i s al so possi bl e to cut a thread i nto the materi al or i nsert a threaded element. Generally no cooling or lubricating emulsion is necessary. During processing it is very important to ensure that the tools that are used are always adequately sharp. If this is not the case, the high temperatures caused by the blunt cutting edge can cause the material to decompose and, in combination with atmospheric moisture, can cause small quanti- ties of hydrochloric acid to form as aerosols. In addition, because of its hard-brittle properties, we recommend that elastomer or thermoplastic washers are used for PVC-U component parts that are to be fastened by screwi ng. The use of washers such as this reduces the danger of transmitting high stresses by tightening the screws and the stress cracking around the edge of the drilled hole that this causes. Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 28 29 P V D F Polyvinylidenefluoride (PVDF) Pol yvi nyl i denefl uori de i s a hi gh crystal l i ne thermopl asti c wi th good mechani cal , thermal and electrical properties. As a fluoroplastic, polyvinylidene fluoride has excellent chemical resistance wi thout the di sadvantages of l ow mechani cal val ues and di ffi cul t workabi l i ty of other fl uoro- plastics. Our polyvinylidene semi-finished products – from which we also manufacture all finished products – are manufactured in extrusion or moulding processes. Main properties • Low density in comparison to other • High chemical resistance fluoroplastics • Good hydrolytic stability • Good mechanical stability compared to • Weather resistant other fluoroplastics • Radiation resistant • Can be used continuously at high temperatures • Good electric insulator (+140°C in air) • Fire resistant (UL 94 V 0) • Absorbs practically no water • Physiologically safe • Good dimensional stability • High abrasion resistance Colours natural (white to ivory) Sliding properties PVDF has good sliding properties, is resistant to wear and is very suitable for chemically stressed sliding applications that are also subjected to thermal influences. However, in constructive design, the relatively high coefficient of thermal expansion should be considered. Resistance to radiation / Weathering effects PVDF i s resi stant to both b-rays and g-rays as wel l as UV rays i n connecti on wi th atmospheri c oxygen. Hence PVDF i s i deal for use i n the pharmaceuti cal and nucl ear i ndustri es and under weathering effects. Chemical resistance PVDF i s resi stant to aci ds and al kal i ne sol uti ons, sal ts and sal t sol uti ons, al i phati c and aromati c hydrocarbons, alcohols and aromatics. PVDF is not resistant to ketones, amines, fuming sulphuric aci d, ni tri c aci d or to several hot al kal i s (concentrati on rel ated). Di methyl formami de and dimethyl acetamide dissolve PVDF.. Behaviour in fire Even without additives, PVDF is rated in the highest category as fire resistant. When the source of ignition is removed, PVDF extinguishes itself. At 78%, the oxygen index (= the concentration of oxygen required for combustion) is very high compared to other plastics. Areas of use Applications • Chemical and petrochemical industries • Pump parts • Pharmaceutical industry • Fittings and fitting components • Textile industry • Valves and valve components • Paper industry • Seals • Food industry • Friction bearings • Component parts in plant/apparatus engineering Machining In addition to its good welding suitability, PVDF can also be machined on machine tools. With the respecti ve surface treatment, PVDF can be bonded wi th a speci al sol vent adhesi ve. Fl uorop ol ymers decompose at temperatures above approx. 360°C and form hi ghl y aggressi ve and toxi c hydrofl uori c aci d. As pol ymer dust can form when the materi al i s bei ng machi ned, smoki ng should not be permitted at the workplace. Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 29 30 P T F E Polytetrafluoroethylene is a high crystalline thermoplastic with excellent sliding properties, anti- adhesive surfaces, excellent insulation properties, an almost universal chemical resistance and an exceptionally broad temperature deployment spectrum. However, this is offset by low mechanical strength and a hi gh speci fi c wei ght compared to other pl asti cs. To i mprove the mechani cal properties, polytetrafluoroethylene is compounded with fillers such as glass fibre, coal or bronze. The polytetrafluoroethylene semi-finished products that we offer – from which we also manufac- ture all finished parts – are produced in pressure sintering and ram extrusion processes, films are produced in a peel process. Main properties • Excellent sliding properties • Highest chemical resistance, also to solvents (limited with PTFE + bronze) • Resistant to hydrolysis (limited with PTFE + bronze) • High corrosion resistance (limited with PTFE + bronze) • Broad temperature deployment spectrum (-200°C to +260°C) • Resistant to weathering • Does not absorb moisture • Physiologically safe (not PTFE + coal /+ bronze) • Good electrical insulator (not PTFE + coal /+ bronze) • Good thermal insulator (not PTFE + coal /+ bronze) • Anti-adhesive • Virtually unwettable with liquids • Fire resistant Colours PTFE pure: weiß PTFE + glass: light grey PTFE + coal: black PTFE + bronze: brown Sliding properties PTFE has excel l ent sl i di ng properti es and because of i ts very cl ose stati c and dynami c abrasi on values, it prevents the “ stick-slip effect” . However, due to its low mechanical strength, PTFE has high sliding abrasion and a tendency to creep (cold flow). Hence, unfilled PTFE is only suitable for sl i di ng appl i cati ons wi th l ow mechani cal l oad. Its l oad beari ng capaci ty can be constructi vel y i mproved by equi ppi ng the sl i di ng el ement wi th several chambers. It must be ensured that the chamber is fully enclosed so that the slip lining cannot escape (“ flow out” ). PTFE + glass has worse slip properties than pure PTFE due to the filler, but it can bear much higher loads. Sliding abrasion and the coefficient of elongation are reduced, while creep resistance and dimensional stability increase. The glass particles embedded in the material cause higher wear on the mating part than pure PTFE. PTFE + coal has similarly good slip properties as pure PTFE, but because of the addition of a filler, it has much better mechanical stability. As with glass as a filler, sliding abrasion and the coefficient of elongation are reduced while creep resistance and dimensional stability increase. Sliding ele- ments filled with coal can be used for applications that are occasionally or constantly surrounded by water. PTFE + bronze has the best mechanical values of all filled PTFE types and is very suitable for sliding applications. The filler causes the lowest sliding abrasion of all PTFE types. In addition to this, ther- mal conducti vi ty, and consequentl y the di ssi pati on of fri cti on heat from the fri cti on beari ng, i s considerably improved compared to other sliding materials, which leads to a longer life. Polytetrafluoroethylene (PTFE) Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 30 31 P T F E Weathering effects Al l PTFE types are very resi stant to UV rays, even i n combi nati on wi th atmospheri c oxygen. No oxidation or discolouration has been observed. Chemical resistance Unfilled PTFE is resistant to almost all media apart from elemental fluorine, chlorotrifluoride and molten or dissolved alkali metals. Halogenated hydrocarbons cause minor, reversible swelling. In the case of filled PTFE, due to the filler one can reckon with a lower chemical resistance, although it is the filler that forms the reaction partner to the medium, not the PTFE. As a rule, it can be said that the types filled with coal are not much less resistant than pure PTFE. The types filled with glass are resistant to acids and oxidising agents but less resistant to alkalis. The types filled with bronze have a much lower chemical resistance than pure PTFE. Before using filled PTFE types in chemically burdened environments, their resistance to the respec- tive medium should always be tested. Behaviour in fire PTFE is rated as fire resistant in the highest category. It does not burn when an ignition source is added. The oxygen index (the oxygen concentration required for combustion), at 95% is one of the highest compared to other plastics. Areas of use Applications • Chemical industry • Friction bearings • Machine engineering • Bearing bushes • Precision mechanics • Shaft seals • Electrical industry • Piston rings • Textile industry • Valve seats/seat rings • Paper industry • Insulators • Food industry • Flat seals • Aerospace industry • O rings • Building and bridge construction • Test jacks • Thread guides • Anti-adhesive liners Machining PTFE is difficult to weld and that only by using a special process. It can be machined on machine tools. The semi-finished products can be drilled, milled, sawed, planed and turned on a lathe. It is al so possi bl e to cut a thread i nto the materi al or i nsert a threaded el ement. PTFE can also be bonded when the surface has been suitably treated by etching with special etching fluid. Up to approx. 19°C, PTFE i s subject to a phase transi ti on whi ch i s normal l y accompani ed by an increase in volume of up to 1.2%. This means that finished parts that are dimensionally stable at 23°C can have consi derabl e di mensi onal devi ati ons at temperatures bel ow 19°C. Thi s must be consi dered i n the desi gn and di mensi oni ng of PTFE components. When the materi al i s bei ng machined, attention must be paid that good heat dissipation is guaranteed for parts with mini- mum tolerances, otherwise the good insulation properties can lead to dimensional deviations in finished parts after cooling because of the heat build-up and thermal expansion. Fluoropolymers decompose above approx. 360°C forming highly aggressive and toxic hydrofluoric aci d. As pol ymer dust can form when the materi al i s bei ng machi ned, smoki ng shoul d not be permitted at the workplace. Konstr. Kunststoffe engl.7/04 27.10.2004 7:35 Uhr Seite 31 High performance plastics Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 32 33 Pol yetheretherketone i s a semi -crystal l i ne thermopl asti c wi th excel l ent sl i di ng properti es, very good mechani cal properti es, even under thermal l oad and an excel l ent resi stance to chemi cal s. The high continuous working temperature rounds out the profile of this high-performance plastic and makes i t a vi rtual l y uni versal l y useabl e desi gn materi al for hi ghl y stressed parts. The pol yetheretherketone semi -fi ni shed products that we offer – from whi ch we al so manufacture finished parts – are produced in extrusion or moulding processes. Main properties • High continuous working temperature • High dimensional stability (+250°C in air) • Excellent chemical resistance • High mechanical strength • Resistant to hydrolysis • High rigidity • Good electrical insulator • High creep resistance, also at high temperatures • Radiation resistant • Good sliding properties • Physiologically safe • High wear resistance • Fire resistant (UL 94 V 0) Colour natural (≈ RAL 7032), black Sliding properties PEEK ideally combines good sliding properties with high mechanical strength and thermal stabi- lity as well as excellent chemical resistance. Because of this, it is suitable for sliding applications. Modified types containing carbon fibre, PTFE and graphite – with highest wear resistance, a low coeffi ci ent of fri cti on and a hi gh pv l i mi ti ng val ue – are avai l abl e for component parts that are subject to especially high abrasion and wear. Resistance to weathering PEEK is resistant to X rays, b-rays and g-rays. Hence PEEK is ideal for use in the pharmaceutical and nuclear industries. PEEK is not resistant to UV rays in combination with atmospheric oxygen. Chemical resistance PEEK i s resi stant to non-oxi di si ng aci ds, concentrated al kal i ne sol uti ons, sal t sol uti ons, cl eani ng agents or paraffin oils. It is not resistant to oxidising agents such as concentrated sulphuric acid, nitric acid or hydrogen fluoride. Behaviour in fire PEEK is rated fire resistant in the highest category. When the source of ignition is removed PEEK is self-extinguishing. The oxygen index (the oxygen concentration required for combustion) is 35%. Areas of use Applications • Chemical and petrochemical industries • Gear wheels • Pharmaceutical industry • Friction bearings • Food industry • Bobbins • Nuclear industry • Fittings (e.g. casing for hot water meters) • Aerospace industry • Valves • Defence technology • Piston ring • Parts for car engines (e.g. bearing cages) Machining In addition to its good welding and bonding properties PEEK can be easily machined. The semi- fi ni shed products can be dri l l ed, mi l l ed, sawed, pl aned and turned on a l athe. It i s al so possi bl e to cut a thread into the material or insert a threaded element. Generally no cooling or lubricating emulsion is necessary. Polyetheretherketone (PEEK) P E E K Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 33 34 P S U Pol ysul phone i s an amorphous thermopl asti c wi th hi gh mechani cal stabi l i ty and ri gi di ty and remarkably high creep resistance across a wide temperature range and high continuous working temperature for an amorphous pl asti c. In addi ti on, pol ysul phone i s transparent because of i ts amorphous molecule structure. Its very good resistance to hydrolysis and very good dimensional stabi l i ty round out the profi l e. The pol ysul phone semi -fi ni shed products that we offer – from which we also manufacture finished parts – are produced by extrusion. Main properties • High continuous working temperature (+160°C in air) • Very good resistance to hydrolysis (suitable for repeated steam sterilisation) • High toughness, also at low temperatures • High dimensional stability • Good electrical insulator • High mechanical stability • High rigidity • High creep resistance across a wide temperature range • Good resistance to radiation • Physiologically safe • Fire resistant (UL 94 V 0) Colour Natural (honey yellow, translucent) Sliding properties PSU is subject to strong sliding abrasion and is thus unsuitable for sliding applications. Resistance to radiation/weathering effects PSU is resistant to X rays, b-rays, g-rays and microwaves. Hence PSU is ideally suited for use in the pharmaceutical, food and nuclear industries. Chemical resistance PSU is resistant to inorganic acids, alkaline solutions and salt solutions, as well as cleaning agents and paraffi n oi l s. It i s not resi stant to ketones, esters, chl ori nated hydrocarbons or aromati c hy- drocarbons. Behaviour in fire PSU is rated as fire resistant in the highest category. When the source of ignition is removed, PSU i s sel f-exti ngui shi ng. The oxygen i ndex (the oxygen concentrati on requi red for combusti on) i s 30%. Areas of use Applications • Electro-technology • Bobbins • Electronics • Inspection glasses • Vehicle construction • Sealing rings • Equipment engineering • Equipment casing • Aerospace industry • Insulating sleeves Machining In addi ti on to i ts good wel di ng and bondi ng properti es PSU can be easi l y machi ned. The semi - fi ni shed products can be dri l l ed, mi l l ed, sawed, pl aned and turned on a l athe. It i s al so possi bl e to cut a thread into the material or insert a threaded element. Generally no cooling or lubricating emulsion is necessary. Polysulphone (PSU) Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 34 35 P E I Polyetherimide is an amorphous thermoplastic with high mechanical stability and rigidity as well as remarkabl y hi gh creep resi stance across a wi de temperature range and hi gh conti nuous worki ng temperature for an amorphous pl asti c. In addi ti on, pol yether i mi de i s transparent because of its amorphous molecule structure. Its very good resistance to hydrolysis and very good dimensional stability round out the profile. The polyetherimide semi-finished products that we offer – from which we also manufacture finished parts – are produced by extrusion. Main properties • High continuous working temperature (+170°C in air) • High mechanical stability • High rigidity • High creep resistance across a broad temperature range • High dimensional stability • Very good resistance to hydrolysis (suitable for repeated steam sterilisation) • Good electrical insulator • Good resistance to radiation • Physiologically safe • Fire resistant (UL 94 V 0) Colour Natural (amber, translucent) Sliding properties PEI is subject to strong sliding abrasion and is thus unsuitable for sliding applications. Resistance to radiation/weathering effects PEI i s resi stant to x-rays, b-rays and g-rays as wel l as UV-rays i n combi nati on wi th atmospheri c oxygen. Hence PEI is ideally suited for use in the pharmaceutical and nuclear industries and under weathering effects. Chemical resistance PEI‘s resi stance shoul d be tested before i t i s used wi th ketones, aromati c hydrocarbons or hal o- genated hydrocarbons. Alkaline reagents with pH values > 9 should be completely avoided. Behaviour in fire PEI is rated as fire resistant in the highest category, also without additives. When the source of ig- nition is removed, PEI is self-extinguishing. The oxygen index (the oxygen concentration required for combustion), at 47% is very high compared to other plastics. Areas of use Applications • Electro-technology • Bobbins • Electronics • Inspection glasses • Vehicle construction • Equipment casing • Equipment engineering • Insulating sleeves Polyetherimide (PEI) Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 35 Structure and properties of plastics ( CH 2 ) 5 HN – CO – – – – –– [NH – (CH 2 ) 6 – NH – (CO – CH 2 ) 4 – CO ] n –– 2 –– [NH – (CH 2 ) 11 – CO] n –– Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 36 37 S t r u c t u r e a n d p r o p e r t i e s 1. Fundamentals In general terms, pl asti cs are macromol ecul ar compounds manufactured from exi sti ng natural substances by chemical conversion or by synthesising products from the chemical decomposition of coal , petrol eum or natural gas. The raw materi al pl asti c fusi ons produced by conversi on or synthesis are usually formed into semi-finished products or finished products by applying tempe- rature and pressure. These processes i ncl ude, among others, i njecti on moul di ng and extrusi on. Exceptions to this are the polyamide semi-finished products manufactured by Licharz in static and centrifugal moulding processes, as these methods work without pressure. 2. Structure 2.1 Classification Usually plastics are classified in two main groups – thermoplastics and duroplastics. • When they are heated to an adequate degree, thermoplastics soften until they are melted and then harden again on cooling. Forming and reforming thermoplastics is based on this repeata- bl e process. Provi ded the heati ng does not cause excess thermal stress l eadi ng to chemi cal decomposition, there is no change to the macromolecules. • Because of thei r mol ecul ar structure, duroplastics cannot be reformed after they have been originally formed, not even at high temperatures. The original formation is based on a chemical reacti on of i ntermedi ates – most of whi ch are not macromol ecul ar – to cl osel y cross-l i nked macromolecules. In DIN 7724, pl asti cs are cl assi fi ed accordi ng to thei r behavi our when subjected to di fferent temperatures. This leads to the following classification: • Plastomers (= thermoplastics) are non-cross-linked plastics that react energy-elastically (metal- elastically) within their service temperature range, and which soften and melt from a material- specific temperature onwards. • Thermoplastic elastomers are physi cal l y or chemi cal l y coarse-meshed, cross-l i nked pl asti cs or pl asti c mi xtures. In thei r normal servi ce temperature range they behave entropy-el asti cal l y (rubber-elastically) but at high temperatures they soften to the point of melting. • Elastomers are coarse-grai ned, temperature-stabl e, cross-l i nked pl asti cs whi ch are entropy- elastic (rubber-elastic) in their service temperature range. They can be formed reversibly and do not flow until they reach their decomposition temperature range. • Duromers (= duroplastics) are close-meshed, cross-linked plastics, which react energy-elastically (metal -el asti cal l y) i n thei r servi ce temperature range and whi ch do not fl ow unti l they reach their decomposition temperature range. 2.2 Structure and form of the macromolecules Apart from a few excepti ons, the pl asti cs that are produced today are general l y based on the ability of carbon to form long chains through atomic bonds. As opposed to ion bonds, the outer shell of the carbon atom fills to the noble-gas configuration with eight electrons. Bond partners can be compl ete atom groups or si ngl e atoms such as hydrogen, oxygen, ni trogen, sul phur or carbon. Structure and properties of plastics Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 37 38 S t r u c t u r e a n d p r o p e r t i e s Through synthesi s many i ndi vi dual smal l mol ecul es (= monomers) of one or more starti ng pro- ducts are bonded together chemically into macromolecules (= polymers). As a rule, the resulting chai ns are between 10 -6 and 10 -3 mm l ong. The si ze of the macromol ecul es i s expressed by the degree of pol ymeri sati on n or by the mol ecul ar wei ght. As i t i s not possi bl e to achi eve a homo- geneous di stri buti on of the chai n l ength i n pol ymeri sati on, the val ues are gi ven as averages. In technology, it is usual to state a measure for the viscosity (e.g. melt index, M.F.I.) instead of the de- gree of polymerisation or the molecular weight. The higher n is, the higher the viscosity. In the formati on of macromol ecul es a di sti ncti on i s made between l i near, branched and cross- linked molecule structures. Li near or branched macromol ecul es produce thermopl asti cs, weak cross-l i nked ones produce elastomers and strongly cross-linked macromolecules produce duromers. As Li charz has speci al i sed i n the manufacture and marketi ng of semi -fi ni shed products and fi ni shed parts from thermopl asti cs (pl astomers), we wi l l onl y consi der the thermopl asti c group and its various sub-groups in the following. There is adequate literature available that deals with the other groups of plastics. 2.3 Molecular bonding force The coherence of macromolecules is based on chemical and physical bonding forces. For polymer materials these are: • the primary valency forces as a chemical bonding force • the secondary valency force (van der Waals forces) as a physical bonding force The pri mary val ency forces are essenti al l y responsi bl e for the chemi cal properti es of the pl asti c, while the secondary valency forces are responsible for the physical properties and the alignment of the macromolecules. 2.3.1 Primary valency forces The pri mary val ency forces that are generated by the bond di stance and the bondi ng energy come from the atomic bond of the polymers. The smaller the bond distance between the indivi- dual atoms i n the pol ymer chai n, the hi gher the bondi ng energy. The bondi ng energy i s al so increased with the number of bonds of the individual atoms. • If the monomers are bonded wi th one another at two poi nts (bi functi onal ) thi s forms a threadl i ke, l i near macromolecule. • If the i ndi vi dual monomers are bonded at more than two points this produces molecule branches. • If monomers are mai nl y bonded wi th one another at three points (trifunctional) this forms a spatial, weakly or strongly cross-linked macromolecule. Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 38 39 S t r u c t u r e a n d p r o p e r t i e s 2.3.2 Secondary valency forces (Secondary bonding forces) The secondary valency forces come from the intermolecular bonds. They consist of three forces: 1. Dispersion forces are the forces of attraction between the individual molecules in the substance. These are greater the cl oser the mol ecul es are to one another. In the crystal l i ne ranges of the semi -crystal l i ne plastics, these forces are especially high because of this. This explains their mechanical superiority compared to amorphous plastics. Increasi ng the di stances between the mol ecul es drasti cal l y reduces the forces. One reason for increasing distances could be vibration caused by heating the polymer material. But intercalating foreign atoms between the molecules (e.g. solvent or water) can also increase the distance. By intercalating plasticisers in the molecule chain, this effect can be used to produce plastics that are rubber-elastic at room temperature. 2. Dipole forces are not found in all plastics. They only occur if the ato- mi c bond has a strong overwei ghti ng to one si de due to the al i gnment of the atoms i n the gal vani c seri es. Thi s can onl y happen i f di ssi mi l ar partners form a bond. The more electronegative atom of a bond draws the electron pair towards itself (➛polarisation) and a dipole is formed. The neighbouring polarised groups attract one another because of the unequal electrical charges. Polymer materials with a dipole character are generally less soluble (with the exception of strong pol ar sol vents) and soften at hi gher temperatures than pol ymer materi al s wi thout a di pol e character. PVC is the most significant polymer material with a dipole character. 3. Hydrogen bridges These are bonds of opposite oxygen and hydrogen molecules of different molecule chains due to thei r hi gh affi ni ty to one another. Thi s type of bond i s the most stabl e of al l secondary val ency bonds. The hydrogen bridges are only dissolved with very strong forces and immediately reform themselves as soon as the displacement forces cease, rather like Velcro. The excellent properties, l i ke a hi gh mel ti ng poi nt or extraordi nary toughness, of vari ous pol ymer materi al s such as polyamides are due to hydrogen bridges. Other purel y physi cal i ntermol ecul ar bonds are entangl ement, l oopi ng of chai ns or bondi ng i n the semi -crystal l i ne ranges. These are descri bed as network poi nts that al l ow mol ecul e- interlocking power transmission. In very thin and symmetrical molecule chains, the secondary valency powers are generally not so pronounced, apart from mol ecul e parts i n the semi -crystal l i ne ranges. The mol ecul e chai ns of polymer materials such as this can easily slide past one another if they are subject to mechanical stress. These materials have very good sliding properties, but at the same time they are subject to hi gh wear due to abrasi on, and they have a hi gh tendency to creep. Exampl es of thi s are PE-UHMW and PTFE. - + - + - + - + + - + - + - + - Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 39 40 S t r u c t u r e a n d p r o p e r t i e s 2.4 Order of the macromolecules Thermopl asti cs are cl assi fi ed i n two groups accordi ng to the order of thei r macromol ecul es. A distinction is made between • amorphous thermopl asti cs wi th compl etel y di sordered macromol ecul es (waddi ng-l i ke structure) due to the form of the basi c uni ts and /or the al i gnment of any si de groups that exi st. Amorphous thermopl asti cs are hard, brittle and transparent. • semi -crystal l i ne thermopl asti cs wi th some hi ghl y ordered, paral l el posi - ti oned macromol ecul e chai ns that form crystal l i tes. A l arge number of crystal l i tes form so-cal l ed spherul i tes. Compl ete crystal l i sati on (➛ semi - crystal l i ne pl asti c) i s not possi bl e because of chai n l oopi ng duri ng pol y- merisation. Semi-crystalline plastics are tough and opaque to white. Semi -crystal l i ne pl asti cs have di fferent properti es than amorphous pl asti cs due to the hi gher se- condary valency forces. They soften later, can be subjected to more mechanical stress, are more resis- tant to abrasion, are tough-elastic rather than brittle and are generally more resistant to chemicals. Because of this, the semi-crystalline thermoplastics are more significant for engineering plastics. 2.5 Alignment of the molecules in the macromolecule Basically there are three different alignment possibilities of the substitute “ R” in the molecule chain. 1. Atactic Random alignment in the chain 2. Isotactic Regular, one-sided alignment in the chain 3. Syndiotactic Regularly changing alignment in the chain The polymer material can only have a crystalline structure if a regular chain alignment exists for a specific length of the complete sequence. As a result of this, the molecule alignment has a direct influence on the mechanical properties. 2.6 Homopolymers / copolymers Plastics that are polymerised from the same monomer structural elements are called homopoly- mers. Pl asti cs that consi st of two or more monomer uni ts are descri bed as copol ymers. When copolymers are being produced, the monomer units are not just mixed, but chemically integrated i nto the mol ecul e chai n. Wi th copol ymeri sati on i t i s possi bl e to i mprove speci fi c materi al properties in a targeted manner. Essentially, a distinction is made between four different types of copolymers: 1. Statistic chain structure (random distribution of the different monomer units) 2. Alternating chain structure (regular change of the different individual monomer units) 3. Block-like chain structure (regularly changing blocks of the different monomer units) 4. Graft polymers (homogeneous chai n of one uni t wi th grafted si de chai ns of a different unit) C R C Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 40 41 S t r u c t u r e a n d p r o p e r t i e s Another al ternati ve to change the properti es i s to (physi cal l y) mi x two pol ymers. The materi al s produced from this are known as polyblends. 3. Properties The above-described molecular structure of the plastics produces a range of special properties and unique characteristics. In the following, several of these will be introduced and described in more detail. 3.1 Mechanical properties The mechanical properties of plastics are primarily determined by the secondary bonding forces. The more pronounced these are, the better the mechanical properties. Because of the morphological structure of plastics, the properties are dependent on factors such as • time • temperature • moisture • chemical influences and fluctuate strongly depending on the influence of one of more factors. 3.1.1 Visco-elastic behaviour Al l pl asti cs have a more or l ess pronounced vi sco-el asti ci ty. Mechani cal stress di ssol ves the secondary bonds i n the mol ecul e structure, and the mol ecul e chai ns sl i de past one another. The l onger the stress i s appl i ed, the further the chai ns move away from each other. Thi s means that compared to metal l i c materi al s, pl asti cs deform when subjected to hi gh stress over a l ong peri od (r cold flow). When maximum expansion has been reached, the pl asti c sol i di fi es agai n and expansi on i s reduced. The weaker the secondary bonds i n the macromol ecul e are, the more pronounced these properties are. A simple molecule structure with no entangled side-groups, or a low degree of crystallinity in the plastic, encourages the chains to glide past one another. Thi s deformati on i s further promoted by thermal i nfl uences. The mol ecul es are sti mul ated to vi brate whi ch l eads to greater di stances between the chai ns and consequentl y to weaker secondary bonds. Hence, stability values for dimensioning component parts cannot be used as a single point value, but rather they must be included in the static calculation in relation to stress time and thermal effects. 3.1.2 Moisture absorption In particular plastics produced by polycondensation (r polymerisation with the cleavage of e.g. water) have a tendency to absorb water from the surroundings via inward diffusion. This process is a reversible balanced reaction in which the more water which is available, the more the plastics absorb. The intercalated water molecules increase the distance between the molecule chains and seconds days T e n s i l e f o r c e Expansion r r Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 41 42 S t r u c t u r e a n d p r o p e r t i e s weaken the secondary bonds. The chai ns become more mobile, which results in a reduction in mechanical values and an increase in elasticity as well as swelling. In the case of pol yami des the hydrogen bri dges do not just ensure excellent mechanical properties such as good abrasion resistance, mechanical stability and toughness, they also lead to intercalation of water in the molecule chains. As both water and the pol yami de mol ecul es are capabl e of formi ng hydrogen bri dges when the water has di ffused i nto the molecule chain, it separates the existing hydrogen bridge and occupies the free valences. The water molecules make the pol ymer chai n sl i ghtl y more mobi l e whi ch gi ves room for more water mol ecul es. Thi s process conti nues unti l the saturati on poi nt has been reached. When the water concen- tration in the surroundings falls again, the process is reversed. Water absorption is favoured by increasing temperatures and hi gh ambi ent moi sture. By absorbi ng water, the pol yami des become more tough-elastic and less solid and rigid. For appl i cati ons i n whi ch these properti es are requi red, i t i s possi bl e to i ncrease the water concentrati on by stori ng the materials in hot water (r conditioning). For water absorpti on through atmospheri c moi sture, i t shoul d be noted that the process i n thi ck-wal l ed component parts onl y takes pl ace cl ose to the surface and that general l y no water absorption – with the described results – should be expected in the inner area of the component part. 3.1.3 Chemical influences Chemi cal s can attack and separate the pri mary and secondary bonds of the mol ecul e chai ns, which can be seen by swelling or decomposition of the plastic. Swelling of the plastic is caused by the chemi cal di ffusi ng i nto the mol ecul e structure, l eadi ng to a l oss of stabi l i ty. In a purel y chemical attack, the loss of stability can occur with no noticeable increase in volume or weight. The inward diffusion of the foreign molecules reduces the secondary valency powers to such an extent that the i nternal stresses i n the materi al or external forces can cause (stress) cracki ng (r stress corrosion cracking). 3.2 Chemical resistance Compared to metallic materials, plastics have a high resistance to chemicals. This can be attributed to the fact that the mol ecul es are l i nked through atomi c bondi ng. Because of thei r physi cal nature, the secondary valency powers only play a subordinate role. Most plastics are resistant to many acids and alkaline solutions as well as aqueous salt solutions and solvents. However, oxidising acids and organic solvents can be a problem in many cases, but this problem can be resolved by using special plastics. Resistance to chemicals decreases as the temperature and exposure time increase. This can be seen by an increase in weight and volume as well as a decline in mechanical values. A lack of resistance to a speci fi c medi um can general l y be seen by a swel l i ng of the pl asti c wi th no appreci abl e chemical attack, or in a chemical attack with medium to severe swelling. R i g i d i t y Water content E x p a n s i o n Water content r r r r Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 42 43 S t r u c t u r e a n d p r o p e r t i e s 3.3 Electrical properties Because of the atomi c bondi ng of thei r mol ecul es, pl asti cs, unl i ke metal l i c materi al s wi th i on bonds, do not have free electrons and are thus classified as non-conductors. However, the insulati- on properties can be greatly reduced or even completely negated through water absorption and / or the addition of metallic fillers, graphite or carbon black. Many plastics are suitable for use in high-frequency areas as their dielectric losses are very low and they only heat up a little. Losses in the area of application should be • for high frequency insulators e r . tan d < 10 -3 • for high frequency heating e r . tan d > 10 -2 Pl asti cs general l y have a surface resi stance of >10 8 Ω. In the event of fri cti on wi th a second non-conductor, thi s l eads to el ectrostati c chargi ng due to el ectron transfer at the boundary surface. Pl asti cs are not sui tabl e for use i n expl osi on protected areas wi thout any conductance additives, as sparks can be caused when they touch earthed objects. 3.4 Dimensional stability Increasi ng heat or i ntercal ati on of forei gn mol ecul es (e.g. water or sol vent) i n the chai n com- pound of the molecule chains increases the distance between the chains. This causes the volume of the pl asti c components to change, resul ti ng i n a change i n i ts di mensi ons. Vi ce versa, as the surroundings become colder, or when the water concentration decreases, the volume is reduced which is accompanied by the corresponding shrinking and size reduction. Pl asti cs are general l y formed or reformed to semi -fi ni shed products from the melt. As a rule, the semi-finished products we manufacture are thi ck-wal l ed products wi th hi gh vol u- mes, such as sol i d rods, sl abs and bl ocks. As pl asti cs are bad heat conductors, the edges of the products cool much quicker than the core. However, because of heat expansion, this has a greater volume than the edges. The outer area has al ready sol i di fi ed wi th a l oss of vol ume and the associ ated shrinking. The shrinking of the core causes inner stresses that “ freeze” as the product cool s. These stresses can be mi ni - mi sed by heat treatment (r anneal i ng, si mi l ar to stress-free anneal i ng of steel ). However, some resi dual stress can remai n. These decrease over a peri od of ti me due to the vi sco-el asti c behavi our of the pl asti cs (r relaxation). These resi dual stresses can be rel eased by one-si ded machi ni ng or heati ng and can become obvious through dimensional changes or distortion. The above-described properties of the plastics are more or less pronounced and can be compen- sated and kept under control relatively easily with constructive measures. But they must be ade- quately considered in the design of components. The following chapters deal with special issues such as behaviour in fire, storage, material-compliant tolerances in components and many other factors. Warm core Solidified jacket Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 43 44 B e h a v i o u r i n f i r e 1. Behaviour of plastics in fire and fire ratings Generally, plastics are organic substances or modifications of organic substances, which, like other organi c substances are threatened by chai n breakage, cl eavage of substi tutes and oxi dati on at high temperatures. Therefore, apart from a few exceptions, plastics are more or less combustible which is something that can be a serious technical problem in the specific use of plastics. 1.1 Combustibility If plastics are heated locally or over large surfaces to above their specific decomposition tempe- rature, they release volatile, low molecular constituents. In many cases together with the ambient oxygen, these form a flammable gas mixture which can ignite if an ignition source is added and an adequate supply of oxygen is available. The amount of heat that is fed in and the volume of the combustible surface that this can affect are both very si gni fi cant for the evol uti on of a fi re and the course of the fi re. Another deci si ve factor is the atmospheric oxygen concentration. For instance, it is possible that a large quantity of heat which affects a large volume with a large surface area but a lack of oxygen only leads to pyrolytic cleavage in the beginning (r release of hi ghl y fl ammabl e, vol ati l e and l ow mol ecul ar consti tuents). If one adds oxygen i n the ri ght concentration, under unfavourable conditions this can result in a deflagration or an explosion. However, wi th the same vol umes and a l ower heat i nput, as wel l as an adequatel y hi gh oxygen concentration, the same substance only burns slowly. Because of this behaviour, it is very difficult, if not impossible, to make any fire-technical forecasts. 1.2 Conflagration gases As with the combustion of other substances, when plastics burn they produce various conflagra- tion gases. As a rule, these are said to be highly toxic. This is not absolutely correct as, on the one hand, the toxicity depends on the type and quantity of the plastic involved in the fire and, on the other, all conflagration gases resulting from a (substance-independent) fire should be regarded as toxic. One example is the conflagration gases resulting from the incineration of polyethylene, which, in addi ti on to smal l quanti ti es of soot and l ow mol ecul ar pl asti c consti tuents, al most excl usi vel y contai n carbon monoxi de, carbon di oxi de and water. Thi s i s comparabl e wi th the confl agrati on gases that occur when wood or stearine are burned. On the other hand, when pol yvi nyl chl ori de i s burned, there i s a danger of chl ori ne bei ng rel eased, whi ch i n combi nati on wi th atmospheri c moi sture or exti ngui shi ng water forms to hydrochloric acid. Many plastics produce a lot of soot when they burn, which makes it difficult for the fire brigades to reach the source of the fire. These plastics include the polyolefins PE and PP as well as styrene plastics such as PS and ABS. This must be considered for designs in fire-critical areas. Behaviour in fire Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 44 45 B e h a v i o u r i n f i r e 1.3 Behaviour in fire Al most al l pl asti cs are combusti bl e. Excepti ons to thi s are PTFE and si l i cones, whi ch are vi rtual l y non-combustible. Most plastics continue to burn after they have been ignited and the source of ignition has been removed. Several extinguish when the ignition source is removed, while others cannot be i gni ted. In many cases, the pl asti c mel ts due to the heat of combusti on and forms burning droplets which can promote the spread of the fire. The degree of combustibility can be reduced by adding the corresponding additives. Additives based on the following mechanisms are used: • Endothermy The temperature of the plastic is reduced by the decomposition or vaporisation of the additive. Thi s i s possi bl e for exampl e wi th water stores (al umi ni um hydroxi de) or phosphorous com- pounds being added to the plastic. • Radical bonding The radicals that form during the fire are bonded by the additive, which slows down the thermal decomposition and consequently the release of flammable, volatile constituents. • Formation of heavy gases Heavy gases are formed through the thermal effects on the additive, preferably halogens, which shield the plastic from atmospheric oxygen and thus prevent oxidation. But the use of fire retarding additives does not make plastics non-combustible. Only plastics that are regarded as being non-flammable are suitable for applications that demand non-combustibi- lity of the plastic. 1.4 Fire ratings Often, to assess how pl asti cs behave i n fi re, i mpreci se terms such as “ hi ghl y fl ammabl e” or “ fi re resi stant” or “ non combusti bl e” are used. These terms i nadequatel y refl ect the actual behavi our of the pl asti cs and onl y provi de a l i mi ted i nference for the usabi l i ty of a pl asti c for a specific application. To assess how plastics behave in fire in the areas of electro-technology, traffic, bui l di ng, etc. there are currentl y approx. 700 nati onal and i nternati onal test methods. In the el ectri cal sector the method UL 94 HB or UL 94 V from Underwri ters Laboratori es (USA) has become the most wi del y accepted. These tests refer to the burni ng ti me and the burni ng behaviour of plastics. In test UL 94 V a di sti ncti on i s made between cl assi fi cati ons V0 to V2, V0 bei ng the most favourable rating. Another possi bi l i ty of compari ng the fl ammabi l i ty of pl asti cs i s the oxygen i ndex. In a control l abl e O 2 /N 2 mi xture a verti cal pl asti c sampl e i s i gni ted and the mi ni - mum vol ume of O 2 requi red to burn the pl asti c i s measured. Thi s test al so al l ows the effects of fl ame retardants to be observed. The di agram opposi te contai ns several oxygen i ndi ces for com- parison. Index val ues ≤ 21% can l ead to continued burning after the sour- ce of ignition has been removed. PA 6 PA 66 POM PET PC PE PP PVC PVDF PTFE PSU PEI PEEK Oak (as a comparison) 0 10 20 30 40 50 60 70 80 90 100 Oxygen index (%) Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 45 46 R e s i s t a n c e t o r a d i a t i o n a n d w e a t h e r i n g Resistance to radiation and weathering 1. Plastics’ resistance to radiation and weathering Changes i n pl asti cs due to weatheri ng effects and hi gh-energy rays are often descri bed as »aging«, with reference to the process of biological degradation. This is quite an accurate descrip- tion since plastics, as organic materials, do not just have an analogy to natural substances in their constituents but also in their macromolecular structure. The paral l el s are al so obvi ous by the fact that we often speak of the “ l i fe” of a pl asti c product. The durati on i s determi ned by the decomposi ti on of the pl asti c. It may be rel ati vel y l ong com- pared to other natural substances, but it is still limited. 1.1 Radiation The majori ty of pl asti cs are subject to decomposi ti on or a cross-l i nki ng of the macromol ecul ar structure when affected by hi gh-energy radi ati on. The changes i n the mol ecul ar structure that actually occur depend on the atmospheric oxygen. When oxygen is present, generally oxidative decomposition of the plastic occurs. This is especially the case when the dose of radiation is small, the surface area of the product is large and the walls are thin. Under these prerequisites, the atmospheric oxygen has sufficient time to diffuse into the plastic and to occupy the valences that are made free by the radiation. In the absence of oxygen, the plastic is partially decomposed by the main chains breaking up and parti al l y cross-l i nked. General l y decomposi ti on and cross-l i nki ng reacti ons happen at the same time, although one of the reactions is stronger. In any case, the changes in the plastics caused by radiation are accompanied by a loss of mechani- cal properti es such as mechani cal stabi l i ty, ri gi di ty and hardness or bri ttl eness. Pl asti cs that are subject to cross-l i nki ng can experi ence a change i n properti es even l eadi ng to a rubber-el asti c condi ti on. Besi des thi s, duri ng both the cross-l i nki ng and decomposi ti on of the pl asti cs, smal l amounts of gaseous substances such as carbon monoxide or carbon dioxide are released. Attention should be paid to the fact that the described changes are very gradual and that there is no sudden, unannounced change in properties. The effects of radiation on plastics depend on the geometry of the component, dosage, mechani cal stress, temperature and the surroundi ng medium. Therefore, it is not possible to make a generalised statement about the damaging doses for individual plastics. 1.2 Weathering effects Weatheri ng resi stance i s mai nl y eval uated by the vi sual change of the surface. However, thi s leaves the question unanswered as to how the mechanical values change. On the one hand, it can- not be ruled out that plastics which are not subject to any great visual changes have a serious loss of mechanical properties and, on the other hand, plastics with considerable visual changes suffer no great l oss of mechani cal properti es. But to eval uate weatheri ng resi stance correctl y, the mechanical properties must be a measured. Some results of weathering are a decline in stability and hardness as well as an increase in elasticity or brittleness. The surface of the plastic can appear bleached or oxidatively decomposed or stress cracks can form. The changes i n pl asti cs as a resul t of weatheri ng are mai nl y caused by thermal and photo-oxi - dative reactions as well as by the intercalation of water molecules in the plastic’s chain structure. UV rays and warmi ng by di rect sunl i ght l ead to chai n decomposi ti on and free val ences that are saturated by oxygen diffusing inwards. The surface becomes yellow or bleached. In the case of semi -crystal l i ne pl asti cs there coul d be secondary crystal l i sati on resul ti ng i n increased hardness and rigidity. Consequently these plastics are also more brittle and lose a large part of thei r el asti ci ty. Frozen resi dual stresses from the manufacturi ng process can rel ax and Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 46 47 R e s i s t a n c e t o r a d i a t i o n a n d w e a t h e r i n g cause deformati on through the effects of warmi ng – si mi l ar to an anneal i ng process. Thi s i s especially serious for thin-walled finished parts. By absorbing water, the plastics become tough-elastic and stability and rigidity decline, which can also be a problem with thin-walled finished parts. Weatheri ng resi stance can be i mproved wi th addi ti ves – i n a si mi l ar way that fi re retardant additives are used. However, it is not possible to provide a complete protection against decompo- sition caused by the effects of weathering. Unfortunately no valid testing standard or standard parameters are defined regarding artificial weatheri ng and i ts vari abl es that coul d be used to compare resi stances. However i t can be sai d that pl asti cs that have been col oured wi th carbon bl ack or stabi l i sed agai nst UV rays wi th addi ti ves are more stabl e agai nst l i ght and weatheri ng effects than l i ght col oured or natural coloured grades. Exceptions to this are PVDF and PTFE, which have outstanding resistance to light and weathering effects even without colouring or additives. When eval uati ng weatheri ng resi stance, i t shoul d al so be remembered that changes caused by weathering effects are generally in the surface areas of the product. Deeper layers are usually not attacked, so that thick-walled parts are less affected by change than thin-walled parts. Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 47 48 S t o r a g e i n f o r m a t i o n Storage information Information for material-related handling of plastics at receipt and in storage The material properties and special features of plastics described in the previous sections clearly illustrate that plastic products can suffer unwanted quality losses due to environmental effects. Therefore to mai ntai n the hi gh qual i ty and functi onal i ty of our products – al so over l onger periods – several factors should be considered when handling and storing them. 1. Pl asti cs become bri ttl e at l ow temperatures and become hard, l ess el asti c and sensi ti ve to impact. In this condition the danger of breaking or splitting through external forces is very high – especi al l y for fi ni shed products. Col d pl asti c products shoul d never be thrown, shaken or dropped. 2. The properti es of pl asti cs can change due to weatheri ng effects. The materi al properti es can suffer i rreversi bl e negati ve effects through sunl i ght, atmospheri c oxygen and moi sture (e.g. bleaching and/or oxidation of the surface, water absorption, etc.). If the products are subject to di rect sunl i ght or one-si ded heat, there i s a danger of permanent deformati on through heat expansi on and rel eased i nternal resi dual stresses. Therefore fi ni shed products shoul d not be stored outdoors and semi-finished products should be stored outdoors for as short a period as possible. 3. Pl asti cs have scratch sensi ti ve surfaces. Sharp edges on shel ves, nai l s i n pal l ets, l arge di rt parti cl es between the products and other sharp objects can cause scratches and/or grooves, which in turn can cause breakage and notching. When transporting and storing plastic products i t shoul d be ensured that the surface remai ns scratch and groove free and that no rough particles are allowed to adhere to the surface. 4. Not all plastics are equally resistant to chemicals, solvents, oils or fats. Several are attacked by these substances, whi ch can l ead to surface opaci ty, swel l i ng, decomposi ti on and permanent changes i n the mechani cal properti es. Therefore, substances that can attack and damage plastics must be kept away from the products during storage. 5. Plastics are subject to reversible dimensional changes when affected by extreme temperature fl uctuati ons due to shri nki ng or expansi on. Di mensi on checks can onl y be carri ed out i mme- diately on receipt of the goods if the products are at room temperature (≈ +23°C). Products with a hi gher or l ower temperature coul d produce i ncorrect measured val ues due to shri nkage or expansion of the plastic. Too warm/cold products must be stored temporarily in a dry place and be brought up/down to room temperature before dimensions are checked. 6. Because of the producti on process, pl asti cs, and fi ni shed products manufactured from them, can have resi dual stresses, i n spi te of anneal i ng. These have a tendency to rel ax when the products are stored for long periods and subjected to temperature effects (e.g. direct sunlight). Pol yami des al so tend to absorb water when the humi di ty i s hi gh, whi ch i n turn causes the vol ume to i ncrease. These processes are general l y accompani ed by di mensi onal and shape changes due to deformation. Therefore for long-term storage we recommend closed boxes and constant conditions (≈ standard climate +23°C/50% RH). The expected dimensional and shape changes are thus kept to a minimum and generally have no effect on the function of the product. Konstr. Kunststoffe engl.7/04 27.10.2004 7:36 Uhr Seite 48 Plastic friction bearings Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 49 50 P l a s t i c f r i c t i o n b e a r i n g s 1. Use of thermoplastics for friction bearings Requirements for a friction bearing material such as • Good sliding and emergency running properties • Wear resistance • Pressure resistance • Long life • Heat deflection temperature are easily fulfilled by today’s modern thermoplastics. Plastics are especially used where • Dry running or mixed friction occurs • Special plastic-specific properties are required • Low manufacturing costs are advantageous even with low quantities The following plastic-specific properties are especially valued: • Good sliding properties • Low coefficients of friction • High wear resistance • Good damping properties • Low weight • Good dry and emergency running properties • Corrosion resistance • Chemical resistance • Low maintenance after initial one time lubrication • Physiologically safe in some cases Disadvantages such as low heat conductivity, temperature-dependent stability values, relatively high heat expansion, creeping when subject to long-term stress and in some cases the tendency to absorb moisture can be kept under control to a great extent by material-related design measures. 1.1 Materials Of the large number of plastics that are available, those with semi-crystalline or high crystalline molecular structures are most suitable for use as sliding elements. Several materials belonging to this group, and how they have been modified for slide applications, are listed in Table 1. Plastic friction bearings Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 50 51 P l a s t i c f r i c t i o n b e a r i n g s Material Short description Property Polyamide 6 cast PA 6 G High abrasion resistance Polyamide 6 cast PA 6 G + MoS 2 Higher crystallinity than PA 6 G + Molybdenum disulphide Oilamid ® PA 6 G + OIL Highest abrasion resistance, low coefficient of friction Calaumid ® 1200 PA 12 G High abrasion resistance, high load bearing strength Polyamide 6 PA 6 Medium abrasion resistan Polyamide 66 PA 66 High abrasion resistance Polyacetal (Copolymer POM Medium abrasion resistance, compression resistant Polyethylene terephthalate PET High abrasion resistance, low coefficient of friction Polyethylene terephthalate PET-GL High abrasion resistance, very low coefficient and lubricant of friction Polyethylene UHMW PE - UHMW Low coefficient of friction, low rigidity, acid-resistant Polytetrafluoroethylene PTFE Very good sliding properties, low rigidity Polytetrafluoroethylene Partially good sliding properties and glass fibre PTFE + Glass good rigidity Polytetrafluoroethylene PTFE + Coal Very good sliding properties, good rigidity and coal Polyetheretherketone PEEK High pv, high loadability, high price Polyetheretherketone PEEK - GL Best sliding properties modified highest pv value and highest price Table1: Friction bearing materials and properties 1.2 Manufacture Friction bearings can be manufactured by machining or injection moulding. Polyamide bearings manufactured by i njecti on moul di ng are much l ess wear resi stant than those produced by machi ni ng due to thei r amorphous proporti ons i n the mol ecul ar structure. The fi ne crystal l i ne structure of the l ow stress pol yami de semi -fi ni shed products manufactured by casti ng guarantees optimum wear resistance. Compared to i njecti on moul ded fri cti on beari ngs, machi ned beari ngs al l ow hi gh di mensi onal preci si on. The hi gh machi ni ng performance of conventi onal machi ne tool s, l athes and CNC processi ng centres al l ow the cost-effecti ve manufacturi ng of i ndi vi dual parts as wel l as smal l to medi um si zed batches. Fl exi bl e, al most l i mi tl ess desi gn possi bi l i ti es, especi al l y for thi ck wal l ed parts are another advantage of machined friction bearings. 1.3 Sliding abrasion/mating Sliding abrasion is primarily dependent on the material and surface properties of the mating component. The most favourable mating component for plastic has pro- ven to be hardened steel with a minimum hardness of 50 HRc. If surfaces with a lower hardness are used there i s a danger of rough ti ps breaki ng off and causi ng i n- creased plastic/metal abrasion in friction bearings. The influence of surface roughness on sliding abrasion and the sliding friction coefficient can be evaluated in di fferent ways. For the more abrasi on resi stant, l ess roughness sensi ti ve pl asti cs (e.g. PA and POM) i t can C o e f f i c i e n t o f s l i d i n g f r i c t i o n µ Average depth of roughness µm POM PA Figure 1 0,2 0 2 4 6 0,4 0,6 Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 51 52 P l a s t i c f r i c t i o n b e a r i n g s be observed that the sliding friction coefficient i s rel ati vel y hi gh, especi al l y for parti cul arl y smooth surfaces (Figure 1). As the roughness i ncreases, i t i s reduced to a mi ni mum and then i ncreases agai n i n the further course. The sl i di ng abrasi on becomes higher with increasing roughness. On the other hand, the more abrasi on sus- cepti bl e pl asti cs (e.g. PE-UHMW, PTFE) show a steadi l y i ncreasi ng sl i di ng fri cti on coeffi ci ent wi th i ncreasi ng roughness. The range i n whi ch the sliding friction coefficient improves with increasing roughness is minimal. The sliding abrasion increases with increasing roughness. The model idea to explain this behaviour assumes that abrasion in friction bearings takes over a l ubri cati ng functi on. It can be observed that a favourabl e sl i di ng condi ti on exi sts when the quantity and form of abrasion are optimum. With the plastics that are less sensitive to roughness, adhesion forces and adhesive bridges have an effect in the low roughness range of the mating component. Due to the smooth surface, there i s no great abrasi on that can take over the l ubri cati ng functi on. As roughness i ncreases, the movement-hi nderi ng forces decrease so that the sl i di ng fri cti on coeffi ci ent i mproves wi th i n- creasi ng abrasi on. From a speci fi c degree of roughness, the pl asti c begi ns to abrade, whi ch re- quires higher movement forces. The amount of abrasion exceeds the optimum. Because of these mechanisms, the sliding friction coefficient deteriorates. As the opti mum abrasi on vol ume i s very smal l wi th the pl asti cs that are sensi ti ve to roughness, these pl asti cs onl y have a very narrow range i n whi ch the sl i di ng behavi our can be i mproved by abrasi on. Wi th i ncreasi ng roughness, the effects of the abrasi on become predomi nant. It i s no l onger possi bl e to i mprove the sl i di ng behavi our. On the other hand, by thi s token the sl i di ng behaviour only worsens due to a lack of abrasion on materials that have mating components with an extremely smooth surface. The surface roughness of the plastics plays no role in this observation, as they are soft compared to the metallic mating component and quickly adapt to its contact pattern. Hence, important for choosing the surface quality of the steel sliding surface is the question whether the functionality of the sliding element is affected by either the amount of sliding abrasion or the sliding friction coefficient. For combination with plastic friction bearings, the mating components in Table 2 with the associated surface grades can be recommended: Table 2: Recommended surface qualities for mating components Low surface hardness and smal l er/greater surface roughnesses than those speci fi ed promote sliding abrasion in the bearing and thus shorten its useful life. PA 6 G PA 12 G PA 6 PA 66 PA 12 POM PET PE- PTFE UHMW Mating Hardness component HRc min. 50 50 50 50 50 50 50 50 50 hardened steel R z [µm] 2 – 4 2 – 4 2 – 4 2 – 4 2 – 4 1 – 3 0,5 – 2 0,5 – 2 0,2 – 1 Mating Material POM POM POM POM POM PA PA/POM PA/POM PA/POM/PET component thermo- R z [µm] 10 10 10 10 10 10 10 10 5 plastic Average depth of roughness µm PET PE-UHMW 0,6 0,4 0,2 Figure 2 0 2 4 6 C o e f f i c i e n t o f s l i d i n g f r i c t i o n µ Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 52 53 P l a s t i c f r i c t i o n b e a r i n g s In addi ti on to the above-menti oned factors, runni ng speed, surface pressure and temperature also have an effect on sliding abrasion. High running speeds, surface pressure and temperatures also increase sliding abrasion. The following table contains guiding values for the sliding abrasion of plastics. Table 3: Sliding abrasion of plastics Material Sliding abrasion Material Sliding abrasion in µm/km in µm/km Oilamid ® 0,05 POM-C 8,9 PA 6 G 0,1 PET 0,35 PA 6 0,23 PET-GL 0,1 PA 66 0,1 PE-UHMW 0,45 PA 12 0,8 PTFE 21,0 The stated values depend on the sliding system and can also change due to changes in the sliding system parameters. 1.4 Lubrication/dry running At present there are no general val i d l ubri cati on rul es for pl asti c fri cti on beari ngs. The same l ubri cants that are used for metal l i c fri cti on beari ngs can al so be used for pl asti c beari ngs. It i s advisable to use a lubricant despite the good dry running properties of plastics, as the lubricant reduces the coefficient of friction and thus the frictional heat. In addition, continuous lubrication also helps dissipate heat from the bearing. Lubricating the friction bearings gives them a higher l oad beari ng capaci ty and reduces wear, whi ch i n turn gi ves them l onger l i fe. However, i f the bearings are to be used in a very dusty application it is advisable not to use any lubrication, as the dust parti cl es become bonded i n the l ubri cant and can form an abrasi ve paste whi ch causes consi derabl e wear. The pl asti c beari ng materi al s recommended i n the tabl e on page 53 are resistant to most commonly used lubricants. An alternative to external lubrication are plastics with self-lubricating properties such as OILAMID and PET-GL. Due to the l ubri cants that are i ntegrated i nto the pl asti c, these materi al s have the l owest wear rates as wel l as excel l ent dry and emergency runni ng properti es. When desi gn reasons require to do so, it is also possible to operate plastic friction bearings without lubrication. However, attention must be paid that the load values are within the pv values stated in Table 4. In any case, a one ti me l ubri cati on shoul d be carri ed out duri ng i nstal l ati on i f possi bl e, even i f the beari ngs wi l l run dry. Thi s consi derabl y i mproves the start-up behavi our and can prol ong the l i fe of the product. It i s al so possi bl e to l ubri cate the beari ngs subsequentl y at i nterval s to be determined empirically. 1.5 Contamination/corrosion The steel shaft of fri cti on beari ngs that are operated i n dry runni ng condi ti ons i s i n danger of corroding due to migrating moisture. When the surface of the mating component is damaged by corrosion, this increases sliding abrasion and can cause the bearing to malfunction prematurely. Thi s can be prevented by seal i ng the beari ng agai nst moi sture. Other effecti ve measures are to pl ate the mati ng component wi th chromi um or to manufacture the mati ng component from stainless steel. Because of their low coefficients of sliding friction, plastic friction bearings tend to suffer much less from frictional corrosion than metallic bearing materials. Wear caused by frictional corrosion can be reduced even further by l ubri cati on. Compared to metal l i c beari ng materi al s, wear i n pl asti c fri cti on beari ngs caused by contami nati on such as dust or abrasi on i s much l ower, as plastics, and especially polyamides, have the ability to embed dust particles and thus prevent the Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 53 54 P l a s t i c f r i c t i o n b e a r i n g s abrading effects. When operating in environments with high dust levels, it is recommended that the beari ng i s fi tted wi th l ubri cati on grooves. The l ubri cant contai ned there bi nds the dust particles and keeps them away from the slide zone. 1.6 Load limits Load l i mi ts for thermopl asti c fri cti on beari ngs are defi ned by the compressi ve strength and beari ng temperature. The beari ng temperature i s di rectl y rel ated to the runni ng speed and the ambi ent temperature, and, wi th dynami cal l y stressed fri cti on beari ngs, al so to the durati on of operati on. The mati ng components, thei r surface qual i ty and the chosen type of operati on (l ubri cated or unl ubri cated) al so have an effect on the beari ng temperature of a thermopl asti c friction bearing. Tabl e 4 contai ns gui di ng val ues for i ndi vi dual pl asti cs. For stati cal l y l oaded beari ngs or fri cti on bearings with very low running speeds, the figures for sustained pressure loading can be applied. For dynami cal l y l oaded beari ngs, usual l y the pv val ue (product of surface pressure and average running speed) is used as a characteristic variable. It must be noted that this value is not a material characteristic value, as the load limit of the plastics depends on the above-mentioned variables. Table 4: Material guiding values Sustained pressure load static MPa Not equipped with cham- bers, Deformation < 2% 23 20 24 15 18 10 22 35 33 5 5 12 57 68 Equipped with cham- bers; Deformation < 2% 70 60 - 50 60 43 74 80 75 20 20 - 105 120 Coefficient of friction µ 0,36 0,18 0,40 0,38 0,35 0,32 0,30 (average value) - - - - - - 0,30 0,25 0,2 0,29 0,08 0,1 - 0,11 Dry running on steel 0,42 0,23 0,60 0,42 0,42 0,38 0,38 pv-guiding value MPa . m/s Dry running / Installation lubrication V = 0,1 m/s 0,13 0,23 0,12 0,11 0,13 0,08 0,15 0,15 0,25 0,08 0,05 0,40 0,34 0,66 V = 1,0 m/s 0,08 0,15 0,10 0,07 0,08 0,10 0,10 0,15 0,05 0,22 0,42 Continuously lubricated 0,50 0,50 0,35 0,40 0,50 0,50 0,50 0,50 0,50 0,40 0,40 0,50 1,0 1,0 Coefficient of thermal expansion +20°C bis +60°C in 10 -5 . K -1 8 8 10 9 8 10 10 8 8 18 20 11 5 4,5 Maximum permissible bearing temperature in continuous operation (RF< 80%) +90 +90 +90 +80 +90 +80 +90 +80 +90 +50 +160 +200 +250 +250 Moisture absorption in % at 23°C/50% RF 2,2 1,8 0,9 2,1 3,1 0,8 0,2 0,2 0,2 0 0 0 0,2 0,14 when saturated in water 7,0 7,0 1,4 10 9 1,5 0,8 0,5 0,4 < 0,01 < 0,01 < 0,01 0,45 0,3 P A 6 G O i l a m i d ® C a l a u m i d ® 1 2 0 0 P A 6 P A 6 6 P A 1 2 P O M - C P E T P E T - G L P E - U H M W P T F E P T F E C o a l P E E K P E E K - G L Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 54 55 2. Constructional design 2.1 Bearing play When desi gni ng fri cti on beari ngs, a di sti ncti on i s made between operati ng pl ay h 0 , i nstal l ati on play h e and manufacturing play h f (see Figure 3). • The operati ng pl ay (basi c pl ay or mi ni mum pl ay) h 0 is the minimum clearance that must exist under the most unfavourable conditions to prevent the bearing from sticking. • The i nstal l ati on pl ay h e i s the cl earance i n an installed but not yet warm operating state. • The manufacturi ng pl ay h f i s the measure des- cribing the excess size that the internal diameter of the beari ng must have compared to the shaft di ameter to ensure operati ng pl ay under ope- rating conditions. The requi red operati ng beari ng pl ay h 0 can be seen i n Di agram 1. If gui di ng requi rements are hi gher, the beari ng pl ay can be l ess. Li terature recommends the fol l owi ng as a cal cul ati on basis h 0 = 0,015Md w where h 0 = operating bearing play in mm d w = spindle diameter in mm However, for ari thmeti cal determi nati on, the preci se operati ng condi ti ons must be known, as otherwi se the temperature and moi sture effects cannot be taken fully into account. 2.2 Wall thickness/bearing width The wall thickness of thermoplastic friction bearings is very important in regard to the good insulati- on properties of the plastics. To ensure adequate heat dissipation and good dimensional stability, the fri cti on beari ng wal l must be thi n. However, the beari ng wal l thi ckness al so depends on the amount and type of load. Bearings with high circumferential speeds and/or high surface pressures should have thin walls, while those with high impact loads should be thicker. Diagram 2 shows the bearing wall thicknesses that we recommend in relation to the shaft diameter and the type of load. Where thermopl asti c fri cti on beari ngs are to be used as a repl acement for beari ngs made from other materi al s, the wal l thi cknesses are general l y defi ned by the exi sti ng shafts and beari ng housi ngs. In cases such as thi s, attenti on shoul d be pai d that the mi ni mum wal l thicknesses in Diagram 2 are maintained. To prevent a bui l d-up of heat i n the centre of the fri cti on beari ng i t shoul d be ensured that it is in the range of 1 – 1.5 d w when the beari ng wi dth i s bei ng determi ned. Expe- ri ence has shown that a beari ng wi dth of approx. 1.2 d w is ideal to prevent an accumu- lation of heat in the middle of the bearing. D h e h f h o h e Figure 3: Diagram of different bearing play 0 0 10 30 50 100 150 200 0,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 Internal diameter of bearing in mm h 0 i n % i n r e l a t i o n t o i n t e r n a l d i a m e t e r o f b e a r i n g H i g h i m p a c t l o a d i n g N o rm a l lo a d in g High running speed B e a r i n g w a l l t h i c k n e s s i n m m Shaft diameter in mm 0 20 40 60 80 100 120 140 160 180 200 220 240 260 0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 Diagram 1: Required operating bearing play Diagram 2: Recommended bearing wall thickness P l a s t i c f r i c t i o n b e a r i n g s Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 55 56 P l a s t i c f r i c t i o n b e a r i n g s 2.3 Allowances For fri cti on beari ngs that are to be used i n envi ronments wi th hi gh temperatures, a certai n di mensi onal change due to thermal expansi on shoul d be al l owed for when the beari ng i s bei ng dimensioned. The expected dimensional change is calculated from ∆l = s L . k w [mm] where ∆l = dimensional change s L = bearing wall thickness k W = correction factor for heat expansion The correction factor k W for the respective max. ambient temperatures is shown in Diagram 3. The calculated dimensional change must be added to the operating bearing play. If it is foreseeable that polyamide friction bearings are to be used permanently under conditions wi th i ncreased humi di ty or water spl ashi ng, an addi ti onal di mensi onal change due to moi sture absorption must be taken into account. The expected dimensional change is calculated from ∆l = s L . k F [mm] where ∆l = dimensional change s L = bearing wall thickness k F = correction factor for moisture absorption Di agram 4 shows the correcti on factor k F for the respective max. humidity The cal cul ated di mensi onal change must be added to the operating bearing play. The two values are determined and added for operating conditions that require a correction due to temperature and moisture. The total is the required allowance. 2.4 Design as slit bearing bush For use in extreme moisture and temperatu- re condi ti ons, a beari ng bush wi th an axi al sl i t runni ng at an angl e of 15° -30° to the shaft axi s has proven to be the best sol uti - on. The slit absorbs the circumferential expansion of the bearing bush so that a diameter chan- ge caused by the effects of temperature or moisture does not have to be considered when calculating bearing play. Only the wall thickness change has to be included, although 20 40 60 80 100 0,04 0,03 0,02 0,01 0 Bearing temperature in °C C o r r e c t i o n f a c t o r k w 50 60 70 80 90 100 Relative humidity in % 0,06 0,05 0,04 0,03 0,02 0,01 0 C o r r e c t i o n f a c t o r k F 0 50 100 150 200 250 300 350 Bearing diameter in mm 16 14 12 10 8 6 4 2 0 W i d t h o f s l i t i n m m Diagram 3: Correction factor k w Diagram 5: Width of slit Diagram 4: Correction factor k F 1,5% of U L 1% of U L Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 56 57 P l a s t i c f r i c t i o n b e a r i n g s thi s i s mi nor compared to the change i n di ameter caused by circumferential expansion. In l ubri cated beari ngs, the sl i t can al so ful fi l the rol e of a l ubri cant depot and col l ect abrasi on particles. The width of the slit depends on the diameter of the bearing and the requirements of the operating conditions. We recommend a slit approx. 1 – 1.5% of the circumference of the friction bearing. 2.5 Fixing In practice it has proved expedient to press over- di mensi onal fri cti on beari ngs i nto a beari ng bore. When it is being set in, the bearing bush is compressed by the amount of the oversi ze. Therefore this oversize must be considered as an al l owance to the operati ng beari ng pl ay on the i nternal di ameter of the bush. Di agram 6 shows the required oversize. As a result of temperature increases, the stresses i n the beari ng become greater and there i s a danger of rel axati on when i t cool s. Thi s can l ead to a si tuati on where the force of pressure i s no l onger adequate to keep the fri cti on beari ng i n the beari ng seat under pressure. Because of thi s we recommend an addi ti onal safeguard for temperatures above 50°C wi th a securi ng form-fi t element commonly used in machine engineering. 3. Calculating dynamically loaded friction bearings As opposed to friction bearings that are only burdened by a static normal force, statically loaded fri cti on beari ngs are al so subjected to a tangenti al force. Thi s l eads to an i ncrease i n transverse stress in the plastic and consequently to higher material stress. 3.1 Continuous operation General l y the pv val ue (the product of the average surface pressure and the average runni ng speed) is used as a characteristic value for the dynamic load bearing capacity of friction bearings. To calculate the dynamic load bearing capacity of radial bearings, it is necessary to determine the pv duration value. The average surface pressure for radial bearings is where F = bearing load in N d W = shaft diameter in mm L = bearing width in mm 0,007 0,006 0,005 0,004 0,003 0,002 0,001 20 40 60 80 100 120 140 160 180 0 Outer diameter of the friction bearing P r e s s - f i t o v e r s i z e p e r m m D a d w S L L D Radial bearing [MPa] F p = d w . L Diagram 6: Required press-fit oversize Figure 5: Radial bearing 15°- 30° [mm] [mm] Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 57 58 P l a s t i c f r i c t i o n b e a r i n g s The average running speed for radial bearings is d w . π . n v = –––––––– [m/s] 60000 where d W = shaft diameter in mm n = speed in min -1 Hence pv duration for dynamic loading for radial bearings without lubrication is r F i r d w . p . n i pv duration =e––––––e . e–––––––––– e [MPa . m/s] qd w . L t q 60000 t The cal cul ated pv durati on val ue shoul d be l ess or equal to the materi al -speci fi c pv val ue shown i n Table 4. 3.2 Intermittent operation The dynamic load bearing capacity of thermoplastic friction bearings is very much dependent on the heat that builds up during operation. Accordingly, friction bearings in intermittent operation wi th a decreasi ng duty cycl e become i ncreasi ngl y l oadabl e. Thi s i s accounted for by usi ng a correction factor for the relative duty cycle (= ED). Under these conditions, the following applies to radial bearings in intermittent operation pv duration pv int = ––––––––- f where f = correction factor for ED The relative duty cycle ED is defined as the ratio of the load duration t to the total cycle time T in percent. For thermopl asti c fri cti on beari ngs, the total cycl e time is defined as T = 60 min. The total of all individual l oads duri ng these 60 mi nutes forms the l oad dura- tion. This calculated value can then be used to determine the correction factor f from Diagram 7. It should be noted that every load duration t, over and above 60 min. (regardless of whether this only happens once), is to be evaluated as continuous loading. 3.3 Determining sliding abrasion It i s a very compl ex matter to determi ne the sl i di ng abrasi on beforehand i n order to determi ne the expected life of a friction bearing. Generally it is not possible to record the external conditions adequatel y, or condi ti ons change duri ng operati on i n a manner that cannot be predetermi ned. However, it is possible to calculate the expected sliding abrasion sufficiently accurately to provide a rough estimate of the life of a bearing. Roughness, pressure and temperature proportions are aggregated to form an equation based on simplified assumptions. t ED= . 100 [%] T 0% 50% 100% Relative duty cycle ED 1,2 1,0 0,8 0,6 0,4 0,2 0 C o r r e c t i o n f a c t o r f Diagram 7: Correction factor f Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 58 59 P l a s t i c f r i c t i o n b e a r i n g s Hence sliding abrasion ∆S is r c F c F– c 0 i ∆S = 10p N (S 0 + S 1 . R V . + S 2 . R 2 V ) . e1 - ––– + 400 d 0 e. r 2 g [µm/km] q c 0 t where S 0 = measured and experience value S 1 = measured and experience value S 2 = measured and experience value c 0 = measured and experience value c F = sliding surface temperature in °C R V = average depth of roughness in µm p N = maximum compression in MPa r 2 = grooving direction factor g = smoothing factor The grooving direction factor r 2 is only used in the equation if the sliding direction corresponds to the direction of the processing grooves of the metallic mating component. This takes account of the influence of the different degrees of roughness during the relative movement of the metallic mating component in the same direction and vertically to the direction of the processing grooves. The smoothing factor g describes the smoothing of the metallic mating component through the abrasion of rough tips and/or the filling of roughness troughs with abraded plastic material. Using an approximation equation the maximum compression p N is 16 F p N = –––– . ––––––––– [MPa] 3p d w . L where F = bearing load in N d W = shaft diameter in mm L = bearing width in mm where p N 6(0,8 bis 1,0) may not exceed j D (compressive strength of the respective plastic). The measured and experi ence val ues can be seen i n Tabl e 5, the groovi ng di recti on factors i n Table 6. We do not have any measured or experience values for materials other than those listed below. Material S 0 S 1 S 2 c 0 g PA 6 0,267 0,134 0 120 0,7 PA 66 0,375 0,043 0 120 0,7 PA 12 0,102 0,270 0,076 110 0,7 POM-C 0,042 0,465 0,049 120 0,8 PE-UHMW 1,085 - 4,160 4,133 60 0,7 PET 0,020 0,201 - 0,007 110 0,8 PTFE 1,353 -19,43 117,5 200 0,6 Table 5: Measured and experience values for individual plastics Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 59 60 P l a s t i c f r i c t i o n b e a r i n g s R v vertical to the direction of the processing grooves in µm PA POM-C PET PE-UHMW > 0,5 1,0 0,9 0,8 0,8 0,5 – 1 0,9 0,6 0,6 0,4 1 – 2 0,8 0,3 0,4 0,2 2 – 4 0,8 0,2 0,3 — 4 – 6 0,8 0,2 0,3 — 3.4 Determining the service life of a bearing As a rul e, a pl asti c fri cti on beari ng has reached the end of i ts servi ce l i fe when the beari ng pl ay has reached an unacceptabl y hi gh l evel . Beari ng pl ay i s made up of several factors. On the one hand there i s some deformati on due to the beari ng l oad, and on the other hand the operati ng pl ay and the wear resul ti ng from use must be consi dered. As these can onl y be ari thmeti cal l y cal cul ated i n advance and si nce the sl i di ng abrasi on cal cul ated approxi matel y at 3.3 i s used to calculate the service life, the service life itself should only be regarded as an approximate value for a rough estimate. Under these prerequisites and in combination with the running speed, the expected service life H is r h 0 i eDh per - Dh - e q 2 t H = ––––––––––––––––––– . 10 3 [h] DS . v . 3,6 where Dh per = permissible journal hollow in mm Dh = journal hollow in mm h 0 = operating play in mm DS = wear rate in µm v = running speed in m/sec To obtai n a rough approxi mati on of the actual servi ce l i fe, i t i s acceptabl e to l eave the journal hollow Dh out of the calculation, as in realistic conditions this is very small and is often within the manufacturing tolerance range. Table 6: Groove direction factors for plastics Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 60 Thermoplastic sliding pads Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 61 62 P l a s t i c s l i d i n g p a d s 1. Thermoplastic sliding pads In the same way that friction bearing bushes are used to arrange the bea- ri ngs of a shaft for rotati onal and up and down movements, the same plastics can of course be used for linear movements in the form of sliding pads. Basically all the plastics listed in the “ Friction bearings” chapter are sui tabl e for use as sl i di ng pads. However, several are especi al l y sui tabl e. These will be described in the following with their advantages. 1.1 Materials Pl asti cs that are used as sl i di ng pads requi re good sl i di ng properti es as wel l as hi gh stabi l i ty and el asti ci ty and creep resi stance. These requi re- ments are fulfilled especially well by Polyamide 6 cast. The high stability compared to other thermoplastics allows higher loads. The good elasti- city ensures that deformation is reversed when the material is subjected to impact load peaks. Assuming that the load remains below the permis- sible limit, this ensures that permanent deformation is avoided to a great extent. The oi l -fi l l ed modi fi cati on OILAMID i s avai l abl e for hi ghl y stressed sl i di ng pads. The oi l whi ch i s embedded i n the mol ecul ar structure reduces sl i di ng fri cti on by around 50% and al so consi derabl y reduces sliding abrasion. PET i s best sui ted for appl i cati ons where a hi gh l evel of moi sture i s ex- pected. The materi al has hi gh mechani cal stabi l i ty, creep resi stance, di mensi onal stabi l i ty and good sl i di ng properti es. Water absorpti on i s low and has virtually no effect on the mechanical or electrical properties. However, PET i s not as wear resi stant as pol yami des. But PET-GL i s avai l abl e as a modi fi ed grade wi th a sol i d l ubri cant. Thi s has i mproved sliding properties and much better wear resistance. 2. Design information 2.1 Friction heat As opposed to fri cti on beari ngs that operate conti nuousl y at hi gh speeds, most sliding pads and guide rails usually work under conditions that mi ni mi se the evol uti on of fri cti on heat. The runni ng speeds are rel ati vel y sl ow and operati on i s more i ntermi ttent than conti nuous. Under these conditions, it is unlikely that friction heat builds up to a level that could cause increased wear or a breakdown in the component. Plastic sliding pads Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 62 63 P l a s t i c s l i d i n g p a d s 2.2 Pressure and running speed As a rule, when dimensioning and designing sliding elements, the design engineers consider the pressure and speed ratio. If the pressure and speed ratios are unfavourable, the resulting friction heat l eads to excess wear and even to a premature breakdown of the component. However, experience in the design and operation of guide pads has shown that it is generally unnecessary to calculate the pressure and speed values due to the favourable operating conditions of sliding pads. Instead of this, the following limiting pressure values can be used as a basis for most guide rail applications. The values apply at a standard temperature of 23°C. 2.3 Lubrication Agai n the statements regardi ng dry runni ng and the use of l ubri cants from the “ Fri cti on bearings” chapter apply. Basically it must be said that installation lubrication considerably impro- ves the service life and running behaviour. The materials that have been modified with lubricant, such as Oilamid, have much longer service lives than all other plastics. 2.4 Mounting Pol yami de sl i di ng pads or gui de rai l s wi th a mechani cal sl i di ng functi on are general l y mounted on steel construc- tions. Countersunk screws or machi ne screws can be used wi thout any probl em for appl i cati ons at room temperature and normal cl i mati c condi ti ons (50% RH). For operati ng condi ti ons wi th hi gh humidity, we recommend that you con- sider using PET /PET-GL. If a hi gher ambi ent temperature i s expected, the approx.10 ti mes hi gher linear expansion of plastic compared to steel must be considered. Firmly screwed plastic rails can corrugate due to linear expansion. To prevent this from happening, the mounting points should be l ess than 100mm apart. In the case of l onger sl i di ng rai l s, one si ngl e fi xed poi nt screw i s advi sed. The other screws i n obl ong hol es shoul d be abl e to absorb the thermal expansi on. Instead of oblong holes, the rails can also be held in grooves, T-slots or similar. Changes in length caused by extreme ambient conditions have no effect on the fixing or function. For polyamide sliding pads in high performance applications such as telescopic booms on mobile cranes, we recommend special nuts that are pressed into hexagonal holes on the sliding panels. By pressing the nut into the hexagonal hole it cannot fall out or loosen. The bottom of the slide plate should be absolutely flush. PA PET Load Movement Lubrication 28 MPa 21 MPa interrupted interrupted periodic 14 MPa 10 MPa continuous interrupted periodic 3,5 MPa 2,5 MPa continuous continuous none Figure 1: Example of threaded inserts Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 63 64 P l a s t i c s l i d i n g p a d s Under full torque, the polyamide is held under pressure by the threaded insert and the insert sits on the steel support. For mountings such as this, pad thicknesses of 12 – 25mm are adequate for optimum performance. 2.5 Applications and examples of shapes Slide and guide pads in telescopic cranes, garbage presses, car body presses, road and rail vehicles, timber processing machines and plants, packaging and filling plants, transport and conveyor systems, chain guides, etc. Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 64 Plastic castors Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 65 66 P l a s t i c c a s t o r s 1. Plastics as castor materials Pl asti c wheel s and castors are i ncreasi ngl y used i n pl ants and materi al fl ow systems, repl aci ng conventional materials. This is because of advantages such as • Cost-effective manufacturing • Very quiet running • High wear resistance • Good vibration and noise damping • Low weight • Protection of the tracks • Corrosion resistance In addi ti on to the soft-el asti c wheel s made from pol yurethanes, hard el asti c wheel s and castors made from cast pol yami de, POM and PET are popul ar for hi gher l oads. However, compared to conventional metal wheel and castor materials, several plastic-specific properties must be consi- dered when calculating and dimensioning. 1.1 1.1 Materials PA 6 G, PA 6/12 G and PA 12 G have proved to be ideal materials. POM and PET can also be used. However, experience has shown that although these have a similar load bearing capacity to the cast polyamides, they are subject to much more wear. The recovery capacity of these materials is lower than that of polyamides. In dynamic operation, flattening that occurs under static loading does not form back as easily as with polyamide castors. 1.2 1.2 Differences between steel and plastic Pl asti c has a much l ower modul us of el asti ci ty than steel , whi ch l eads to a rel ati vel y greater de- formation of plastic wheels when they are subjected to loads. But at the same time, this produces a l arger pressure area and consequentl y a l ower speci fi c surface pressure, whi ch protects the track. If the loading of the wheel remains within the permissible range, the deformation quickly disappears due to the elastic properties of the plastics. In spi te of the l arger pressure area, pl asti c wheel s are not as l oadabl e as steel wheel s wi th the same di mensi ons. One reason for thi s i s that pl asti c wheel s can onl y wi thstand much smal l er compressive strain (compression) in the contact area, another reason is the transverse strain that occurs due to the very different degrees of rigidity of the castor and track materials. These hinder the wheel from deforming and have a negative influence on the compressive strain distribution in the wheel. 1.3 Manufacture There are several production processes that can be used to manufacture plastic castors. If hi gh vol umes of wheel s wi th smal l di mensi ons are to be produced, i njecti on moul di ng i s a sui tabl e method. As a rul e, for producti on-engi neeri ng reasons, l arger di mensi ons can onl y be produced by injection moulding as recessed and ribbed profile castors. It must also be noted that these only have half the load bearing capacity of a solid castor with the same dimensions. It is also a very complex procedure to calculate a castor such as this compared to a solid castor, and rolling speeds of more than 3m/s are not recommended because of production-related eccentricity. An economi c and techni cal al ternati ve to i njecti on moul di ng i s to machi ne semi -fi ni shed pro- ducts. In the small dimensional range up to Ø 100mm, the castors are manufactured on automatic lathes from rods. Sizes above this are produced on CNC lathes from blanks. Another alternative is the centrifugal moulding process. In this process, the outer contours of the castor are moulded to size and then only the bearing seat and axis holes are machined to the re- quired finished size. This allows large quantities of larger dimensions to be manufactured econo- mically. Plastic castors Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 66 67 P l a s t i c c a s t o r s With this process, running truths are achieved that allow speeds of up to 5 m/s. 1.4 Castor design In addi ti on to the four basi c castor body shapes, castors di ffer mai nl y i n the type and desi gn of thei r beari ngs. Li ke rope pul l eys, sol i d castors can al so be fi tted wi th fri cti on beari ngs. A prere- quisite is that the material-specific max. loading parameters are not exceeded. How to calculate friction bearings and the significant factors for safe operation of the bearing are contained in the chapter on »Friction bearings«. If it is not possible to use a friction bearing because the load is too high or because of other factors, the use of antifriction bearings is recommended. The chapter on »Tol erances«, sec- ti on 2.5.2 deal s wi th the materi al - rel ated desi gn of beari ng seats i n detail. Compressi on-set anti fri cti on bea- ri ngs used at temperatures above 50°C can l oosen. Thi s can be coun- teracted by design measures such as pressi ng the beari ng i nto a steel flange sleeve screwed to the body of the castor. Al ternati vel y we recom- mend the use of our Cal aumi d-Fe materi al s (PA wi th a metal core), whi ch combi nes the advantages of plastic as a castor material and steel as a bearing seat material. Because of its form and frictional connection of the steel core with the plastic, this material is also recommended for applications where driving torque has to be trans- ferred. For castor diameters > 250 mm, a lined castor design is advantageous. The plastic lining is fixed to the metal l i c core of the castor through shri nkage. Detai l s of thi s desi gn al ternati ve wi l l be described in a separate section. 2. Calculation When calculating plastic castors, several important points must be remembered. The material has vi sco-el asti c properti es, whi ch become vi si bl e through decrease i n ri gi di ty as the l oad durati on increases. The result of this is that when the contact area of the static wheel is continuously loa- ded, it becomes larger the longer this load continues. However, as a rule because of the materials’ elastic properties, they are quickly able to return to their original shape when they begin rolling. Hence, no negati ve behavi our i s to be expected duri ng operati on. But i f the permi ssi bl e yi el d stress of the materi al i s exceeded the materi al can »fl ow« and l ead to permanent deformati on. This causes increased start-up forces when the castor or wheel is restarted and eccentricity in the rol l i ng movement. Hi gh ambi ent temperatures and, especi al l y for pol yami des, hi gh humi di ty promote thi s behavi our, as they reduce the maxi mum yi el d stress. An excepti on to thi s are the PA 12 G polyamides, as they have less tendency to absorb water. It should also be noted that because of the material’s good damping properties, the body of the castor can heat up as a resul t of hi gh runni ng speeds or other l oadi ng factors. In extreme cases, temperatures can occur that cause the plastic wheel to malfunction. However, if the loads remain within the permissible limits, plastic castors and wheels will operate safely and reliably. 2.1 Calculation basics It would appear practical to apply the Hertzian relationships when calculating castors. But plastic wheels do not fulfil all the conditions for this approach. For example, there is no linear connection Figure 1: Basic castor shapes Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 67 68 P l a s t i c c a s t o r s between stress and expansion, and because of the elasticity of the material, shear stresses occur in the contact area whi l e the wheel i s rol l i ng. Neverthel ess, i t i s possi bl e to make an adequatel y precise calculation on the basis of Hertz’ theory. The compression parameter p’ is determined with the fol l owi ng cal cul ati ons. Thi s parameter i s general l y cal cul ated wi th short-ti me modul us of elasticity determined at room temperature and therefore does not reflect the actual compression i n the contact area. Because of thi s, the determi ned val ues are onl y expressi ve i n combi nati on with Diagrams 1 to 4. The cal cul ated val ues are usual l y rather hi gher than those that actual l y occur duri ng operati on and therefore contai n a certai n degree of safety. Sti l l , castors or wheel s can mal functi on as i t i s not possi bl e to consi der al l the unknown parameters that can occur duri ng operati on to an adequate extent in the calculation. For castors wi th fri cti on beari ngs, the l oad l i mi t of the fri cti on beari ng i s deci si ve. As a rul e, the full load bearing capacity of the running surface cannot be utilised, as the load limit of the friction bearing is reached beforehand (see chapter »Friction bearings«). 2.2 Cylindrical castor/flat track Under l oad, a projected contact area i s formed wi th l ength 2a and wi dth B, wi th compressi on di stri buted over the area i n a hemi el l i psoi dal form. Noti ceabl e i s that the stress i ncreases at the edges of the castor. This stress increase is generated by shear stresses that occur across the running direction. These have their origins in the elastic behaviour of the castor material. The stress increa- ses become larger the greater the differences in rigidity between the track and the castor mate- rials. As stress increase in a castor made from hard-elastic plastic is quite small and can therefore be i gnored for operati ng purposes and as the shear stresses cannot be cal cul ated wi th Hertz’ theory, these are not considered. Assuming that the track material has a much higher modulus of elasticity than the castor material and that the radii in the principal curvature level (PCL) 2 are infinite, the compression parameter p’ is where: F = wheel load in N r 11 = castor radius in mm from PCL 1 B = wheel width in mm f w = material factor PA 6 G = 25.4 PA 6 = 38 POM = 33.7 If the modul i of el asti ci ty of the castor and track materi al s are known, the fol l owi ng equati ons can be used: and 1 1 1 - v 2 1 1 - v 2 2 –– = –– –––– + ––––– E e 2 E 1 E 2 p’ = f w F r 11 . B [MPa] p’ = F . E e 2 . p . r 11 . B [MPa] r 11 F 2 a p ’ B Principal curvature level 1 2 Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 68 69 P l a s t i c c a s t o r s For identical track and castor materials E e is E E e = –––––– 1 - v 2 where F = wheel load in N E e = replacement module in MPa r 11 = castor radius in mm from PCL 1 B = wheel width in mm E 1 = modulus of elasticity of the castor body in MPa v 1 = transversal contraction coefficient of the castor body from Table 1 E 2 = modulus of elasticity of the track material in MPa v 2 = transversal contraction coefficient of the track material from Table 1 Table 1: Transversal contraction coefficients for various materials PA 6 Cast iron PA 6 G Steel with POM Ferritic approx. Austenitic GG GG GG GGG 38 Aluminium Titanium PET steels 12% Cr steels 20 30 40 to 72 alloys alloys Transversal con- 0,4 up 0,25 0,24 0,24 0,28 0,23 traction coeffi- to 0,3 0,3 0,3 up to up to up to up to 0,33 up to cient µ at 20° C 0,44 0,26 0,26 0,26 0,29 0,38 The half contact area length required to estimate flattening is calculated from 8 . F . r 11 a = ––––––––– [mm] p . E e . B where F = wheel load in N E e = replacement module in MPa r 11 = castor radius in mm from PCL 1 B = wheel width in mm 2.3 Cylindrical castor/ curved track Al so i n thi s system a projected contact area is formed with length 2a and width B, with compression distributed over the area i n a hemi el l i psoi dal form. The pre- vi ousl y descri bed stress i ncreases al so form in the edge zones. The calculation is carried out in the same way as for the “ cyl i ndri cal castor/fl at track” from secti on 2.2. However, be- cause of the second radi us i n PCL 1, a replacement radius r e is formed from the radi i r 11 and r 21 . Thi s i s used i n the equa- ti on correspondi ng to rel ati onshi ps of the modul i of el asti ci ty to cal cul ate the compression parameter. If the castor runs on a curved track the replacement radius is F p ’ r 11 r 21 2 a B Principal curvature level 1 2 Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 69 70 P l a s t i c c a s t o r s r 11 . r 21 r e = ––––––– [mm] r 11 + r 21 For castors running on a curved track the replacement radius is r 11 . r 21 r e = ––––––– [mm] r 11 - r 21 where r 11 = castor radius in mm from PCL 1 r 21 = track radius in mm from PCL 1 The replacement radius r e is also used in the equation to calculate half the contact area length a. 2.4 Curved castor/ flat track castor system The phenomenon descri bed i n secti on 2.2, where stress i ncreases at the edges, can be reduced with design changes of the shape of the wheel. If the track is furthermore slightly curved across the rol l i ng di recti on, onl y mi nor stress i ncreases are observed. It has proven practi cal to use the diameter of the wheel as the radius of the curvature. This measure also counteracts the evolution of excess edge pressure that could arise from alignment errors during assembly. A castor wi th curves i n PCL 1 and 2 forms an el l i pti cal contact area wi th axes 2a and 2b across whi ch the compressi on i s di stri buted i n the form of an el l i psoi d. The semi axi s of the el l i pti cal contact area are calculated from 1 1 a = s . 3 3 . F . r e . ––– [mm] and b = l . 3 3 . F . r e . ––– [mm] E e E e and r 11 . r 12 r e = ––––––– [mm] r 11 + r 12 where F = wheel load in N E e = replacement module in MPa s = Hertz correction value from Table 2 r e = substitute radius l = Hertz correction value from Table 2 The replacement module is determined as described in section 2.2. To determine the Hertz correction values s and l the value cos t must be determined mathmatically. r1 1 i e––- - ------ e q r 11 r 12 t cos t = –––––––––––– r1 1 i e–– - + ------e q r 11 r 12 t where r 11 = castor radius in mm from PCL 1 r 12 = Rcastor radius in mm from PCL 2 The Hertz correcti on val ues i n rel ati on to cos t can be taken from Tabl e 2. Intermedi ate val ues must be interpolated. Table 2: Hertz correction values in relation to cos t cos t 1 0,985 0,940 0,866 0,766 0,643 0,500 0,342 0,174 0 s ∞ 6,612 3,778 2,731 2,136 1,754 1,486 1,284 1,128 1 l 0 0,319 0,408 0,493 0,567 0,641 0,717 0,802 0,893 1 w ∞ 2,80 2,30 1,98 1,74 1,55 1,39 1,25 1,12 1 r 11 F B 2 a p ’ r 12 2 b Principal curvature level 1 2 Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 70 71 P l a s t i c c a s t o r s With these calculated values the compression parameter can be determined as follows: 3 . F p’ = ––––––––––––––––– [MPa] 2 . p . a . b where F = wheel load in N a = semi axis of the contact area longitudinally to the running direction b = semi axis of the contact area transversely to the running direction 2.5 Curved castor/curved track castor system Both the shape of the contact area and the calculation correspond to section 2.3. However, when the replacement radius r and the value for cos t are being calculated, it should be considered that the track also has curvature radii in PCL 1 and 2. Consequently the replacement radius for castors that roll on a curved track is 1 1 1 1 1 ––– = –––– + –––– + –––– + –––– [mm] r e r 11 r 12 r 21 r 22 and for castors that roll in a curved track 1 1 1 1 1 ––– = –––– + –––– + –––– + –––– [mm] r e r 11 r 12 -r 21 -r 22 where r 11 = castor radius in mm from PCL 1 r 12 = castor radius in mm from PCL 2 r 21 = track radius in mm from PCL 1 r 22 = track radius in mm from PCL 2 When determi ni ng cos t i t shoul d be remembered that the val ue shoul d be con- si dered i ndependentl y of whether the castor runs on or in a track. Therefore in the equation a positive value is always used for the radii. r 1 1 i r 1 1 i e––- –– e +e––- –– e q r 11 r 12 t q r 21 r 22 t cos t = ––––––––––––––––––––––––––––– r 1 1 i r1 1 i e––+ ––e +e––+ ––e q r 11 r 12 t q r 21 r 22 t To cal cul ate the semi axi s a and b and the compressi on parameter the method descri bed i n section 2.4 can be applied. 2.6 Cylindrical plastic castor lining 2.6.1 Calculation Castor l i ni ngs can onl y be cal cul ated accordi ng to the equati ons i n secti ons 2.2 to 2.5 i f speci fi c rati os between the hal f contact area l ength a, the wheel wi dth B and the hei ght of the l i ni ng h are fulfilled. The ratios h/a ≥ 5 and B/a ≥ 10 must be fulfilled as a condition. As soon as these limiting values are not met, the evolving contact area is reduced despite the same load and outer wheel dimensions. The result is that the compression of the contact area increases and becomes greater, the smaller the l i ni ng thi ckness. In spi te of thi s, i t i s possi bl e to determi ne the compressi on rati os approxi - mately. F r 11 r 21 2 a B p ’ 2 b r 12 r 22 Principal curvature level 1 2 Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 71 72 P l a s t i c c a s t o r s The half contact area length a becomes F E’ 1 . h 2 + E’ 2 . h 1 a = 3 1,5 . r e . ––– . ––––––––––––––––––––– [mm] B E’ 1 . E’ 2 For castor linings that run on a flat track r e = r 1 . For castor l i ni ngs that run on or in a curved track, the replacement radius r e i s determi ned as descri bed i n secti on 2.3. The compression parameter then becomes 9 1 rF i 2 E’ 1 . E’ 2 p’ = 3 ––– . ––– . e– e . –––– –––––––––––––– [MPa] 32 r e q B t E’ 1 . h 2 + E’ 2 . h 1 where F = wheel load in N r e = replacement radius in mm E´ 1 = calculation module of wheel material in MPa h 1 = castor lining thickness in mm E´ 2 = calculation module of track material in MPa h 2 = track thickness in mm B = wheel width in mm The cal cul ati on modul i of the materi al s must be determi ned taki ng account of the transversal contraction coefficients. E 1 (1 - v 1 ) 2 E 2 (1 - v 1 ) 2 E’ 1 = ––––––– . –––––––––– und E’ 2 = ––––––– . –––––––––– [MPa] 1 - v 2 1 1 - 2v 1 1 - v 2 2 1 - 2v 2 where E 1 = modulus of elasticity of the castor material in MPa v 1 = transversal contraction coefficient of the castor material from Table 1 E 2 = modulus of elasticity of the track material in MPa v 2 = transversal contraction coefficient of the track material from Table 1 2.6.2 Design and assembly information The shape of the pl asti c castor l i ni ngs and the metal l i c core i s general l y dependent on the type of l oad that the castor wi l l be subjected to. For castors wi th a l ow l oad where no axi al shear i s expected and where the diameter is < 400mm, it is possible to choose a core shape with no side support. The operati ng temperatures may not exceed 40°C. If i t i s expected that axi al forces may affect the castor, that the l i ni ng wi l l be subjected to hi gh pressures or that operati ng temperatures wi l l exceed 40°C for short or l ong peri ods, the l i ni ngs must be se- cured agai nst sl i di ng down by a si de col l ar on the core or wi th a fl ange. The same appl i es for cas- tor diameters ≥ 400mm. h1 F 2a p’ r 11 B B a r e s n a p - b a c k s i z e A x i a l p l a y 40 60 80 100 Operating temperature °C Aufschrumpfuntermaß in Abhängigkeit zur Betriebstemperatur 0,25 0,45 0,65 0,85 % 0,25 0,45 0,65 0,85 % 0,05 0,05 Diagram 1: Bare snap-back size and axial play in relation to operating temperature Principal curvature level 1 2 Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 72 73 P l a s t i c c a s t o r s No speci al demands are pl aced on the metal core in the area of support for the l i ni ng i n regard to surface qual i ty and di mensi onal stabi l i ty. A cl eanl y ma- chined surface and a diameter tolerance of d ± 0.05mm are adequate. Grooves in the axi al di recti on (e.g. knurl s wi th grooves paral l el to the axi s and broken tips) are permissible. Approximately 1.0 to 1.5% of d has proven to be a suitable height for the plastic lining. The lining is generally fixed to the metal core by heati ng i t and then shri nki ng i t on to the col d core. The l i ni ng can be heated ei ther wi th ci rcul ati ng hot ai r (approx. 120 to 140°C) or in a water bath (approx. 90 to 100°C). The l i ni ng i s heated to an extent that it can be easily drawn on to the col d core wi th a gap between the core and the l i ni ng al l the way around. Thi s process shoul d be carri ed out qui ckl y so that the l i ni ng does not become col d before i t si ts properly on the core. Rapid or uneven cooling should be avoided at all costs, as otherwise stresses wi l l form i n the l i ni ng. The bare snap-back si ze for manufacturi ng the l i ni ng depends on the operati ng temperature and the di ameter of the metal core. Di agram 1 shows the proporti onal bare size in relation to the diameter of the metal core for castors with a diameter of > 250mm. For castors with a securing collar/flange a slight axial play must be considered to absorb the changes in width resulting from thermal expansion. The proportional axial play in relation to the width of the lining can also be seen in Diagram 1. 2.7 Maximum permissible compression parameters Diagrams 2 to 5 show the limit loads of castor materials for various temperatures and in relation to the rolling speed. The results for compression parameters gained from the calculations have to be compared with these limits and may not exceed the maximum values. The curves in relation to the rolling speed reflect the load limits in continuous use. In intermittent operation, higher values may be permitted. Unallowable high loads must be avoided when the castor is stationary, as these could cause irreversible deformation (flattening) of the contact area. L o a d l i m i t p ’ m a x 0 1 2 20 10 30 4 3 5 40 50 60 70 80 20°C 50°C 75°C 100°C m/s 90 Load limit for ball bearing solid castors made from PA 6 G Rolling speed MPa L o a d l i m i t p ’ m a x 0 1 2 20 10 30 4 3 5 40 50 60 70 80 m/s 90 Load limit for ball bearing solid castors made from POM Rolling speed MPa 20°C 50°C 75°C 100°C Diagram 2 Diagram 3 h ø D ø d a Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 73 74 P l a s t i c c a s t o r s 3. Estimating the elastic deformation of the castor body Often the function of castors and wheels is dependent on the deformation of the running surface (flattening) while the wheel or castor is stationary. This is determined immediately after the load has taken effect wi th the modul us of el asti ci ty of the materi al . However, because of the vi sco- elastic behaviour of the plastic, the time-related deformation behaviour must be determined with the part-speci fi c creep modul us. The creep modul us i s determi ned by carryi ng out creep expe- riments with castors and can be seen in Diagrams 6 and 7. On the basis of the values determined in experiments, the time-related flattening can only be estimated with the following equations. It i s vi rtual l y i mpossi bl e to make an exact cal cul ati on due to the often unknown operati ng para- meters and the special properties of the plastic. But the values obtained from the equations allow the flattening to be determined approximately enough to assess the functioning efficiency. The following is used to estimate the cylindrical castor/cylindrical track 1,5 . w . F o A = –––––––––––––– [mm] E e . a and the cylindrical castor/flat track F r r 2 . r 11 i i o A = --––––––––––––– . e2 . ln e–––––– e+ 0,386e [mm] p . E e . B q q a t t where L o a d l i m i t p ’ m a x 20 20 40 60 40 80 100 60 80 100 °C Load limit for PA 6 G castors with static loading MPa Ambient temperature v u L o a d l i m i t p ’ m a x 20 20 40 60 40 80 100 60 80 100 °C Load limit for POM castors with static loading MPa Ambient temperature v u Diagram 4 Diagram 5 Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 74 F = wheel load in N W = Hertz correction value from Table 2 E e = modulus of elasticity or creep modulus in MPa a = semi axis of the contact area longitudinal to the running direction B = wheel width in mm r 11 = castor radius in mm from PCL 1 As in castor systems with curvature radii quite considerable shear stresses occur in the PCL 2, it is not possible to analytically estimate the systems with curvature radii in the PCL 2. These can only be determined numerically with a three-dimensional FE model. 75 P l a s t i c c a s t o r s C r e e p m o d u l u s Load time 10 -4 10 -3 10 -2 10 -1 10 -0 10 1 10 2 10 3 h Creep modulus of PA 6 G at 20 °C 500 1000 1500 2000 2500 3000 MPa C r e e p m o d u l u s Load time 10 -4 10 -3 10 -2 10 -1 10 -0 10 1 10 2 10 3 Creep modulus of POM at 20 °C 500 1000 1500 2000 2500 3000 MPa h Diagram 6 Diagram 7 Konstr. Kunststoffe engl.7/04 27.10.2004 7:37 Uhr Seite 75 Plastic sheaves Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 76 77 P l a s t i c s h e a v e s Plastic sheaves 1. Use of PA 6 G as a sheave material Steel wire ropes are important and highly stressed machine elements in conveying technology. In many cases, l arge pl ants depends on thei r functi oni ng not onl y for effi ci ency but al so safety. As opposed to other machine elements, they must be replaced before they are completely damaged. The surface pressure that occurs at the poi nt of contact between the sheave and the rope i s decisive for the service life and loadability of ropes that run over sheaves. Sheave materials with a low modulus of elasticity lead to low surface pressures and consequently to a longer service life of the rope. For this reason, thermoplastics are used to manufacture sheaves. The plasticvs need to offer the following properties: • Rope conserving elasticity • Adequate compression fatigue strength • High wear resistance • Adequate toughness, also at low temperatures • Resistance to lubricants • High resistance to weathering effects Experi ence has shown that cast pol yami de (PA 6 G) ful fi l s these requi rements more than ade- quately. Other plastics such as PE-UHMW or PVC as shock-resistant modifications are only used in special cases due to their low degree of loadability and lower wear resistance. Because of this, we will only deal with PA 6 G as a sheave material in the following. 1.1 Advantages of sheaves made from PA 6 G 1.1.1 Low rope wear Ropes that run over sheaves made from metal l i c materi al s are subject to hi gh stress due to the surface pressure that occurs between the rope and the groove. When the rope rol l s over the sheave, only the outer strands lie on the groove. The result of this is wear in the form of individual strands breaking or, more serious, rope breakage. Sheaves made from PA 6 G prevent this due to their elastic behaviour. The pressure between the rope and the rol l er i n the combi nati on steel rope/pol yami de rol l er i s around 1:10 compared to steel rope/steel roller. This can be attributed to the visco-elastic behaviour of polyamide. It is not just the outer strands that l i e i n the groove, but al most the whol e projected strand wi dth. Thi s reduces surface pressure between the rope and the roller and considerably extends the life of the rope. 1.1.2 Weight reduction Pol yami des are around seven ti mes l i ghter than steel . Because of the wei ght advantage, a con- si derabl e wei ght reducti on can be achi eved by usi ng pol yami de sheaves wi th a si mi l ar l oad bearing capacity. A mobile crane with up to 18 polyamide sheaves can save approx. 1,000kg and thus reduce the axle load. The lighter sheave weight also has a positive effect on the crane boom and considerably eases the handling and assembly of the sheaves. Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 77 78 P l a s t i c s h e a v e s 1.1.3 Damping The good damping properties of PA 6 G reduce vibration that metallic sheaves transfer from the rope via the sheave to the shaft and bearings. This conserves the rope, shaft and bearings and also reduces running noise. 1.2 Lubricating the rope The use of viscous and adhesive rope lubricants can cause the rope to stick to the sheave groove. In combi nati on wi th a dusty envi ronment or di rt parti cl es that are i ntroduced to the sheave system, thi s forms an abrasi ve paste that can cause i ncreased wear on the rope and the sheave. Therefore we recommend that the rope is lubricated with a low viscous corrosion protection oil, which keeps the rope and the sheave relatively clean. 1.3 Wear on sheaves made from PA 6 G Essentially, wear is caused on polyamide sheaves through excess mechanical stress or wheel slip, whereby the sheave groove is the most stressed point. The sheave groove is subjected to pulsating stresses as the rope rolls over it and it becomes warm at high speeds. Basically, wear on idler sheaves or sheaves that run over a taut rope is less than on driven sheaves. If stranded ropes are used, the individual strands can press into the base of the groove in highly stressed appl i cati ons. For hi ghl y stressed, non-sl i ppi ng sheaves i n combi nati on wi th an open stranded rope, the circumference of the groove base must not be an integral multiple of the wire strand. Thus, l i ke the combi ng teeth of a cog wheel , i t i s prevented that the same poi nts of the groove base are constantly in contact with a rope summit or valley. When closed ropes are used in combi nati on wi th l ubri cants, pi ts can form, whi ch are probabl y caused i n the same way as pi ts form with gear wheels. As a rule, under normal environmental conditions and when the limit load values are not exceeded, one can expect groove base wear of ≤ 0.1µm/km. 2. Construction Design information 2.1 Sheave groove profile The radius of the sheave groove should be approx. 5 – 10% larger than half the diameter of the rope. Thi s ensures that rope tol erances are adequatel y consi dered and that the rope si ts wel l i n the groove. The sheave groove depth h is given in DIN 15061 part 1 for steel sheaves as at least h min = da2. We recommend a sheave groove depth of h ≥ 1.5d for polyamide sheaves. The V angle b is dependent on the lateral fleet angle (max. permissible fleet angle in the groove direction = 4.0°). The following groove angles in combination with the fleet angle have stood the test: Fleet angle 0° - 2.5° c b = 45° Fleet angle >2.5° - 4.0° c b = 52° A groove angle of < 45° should be avoided. DIN 15061 part 1 recommends the dimensions in Table 1 as guiding values for sheave groove profiles. As a guiding value for the diameter of the rope groove base of rope disks made from cast polyamide, we recommend: D 1 = 22 · d 1 [mm] Groove angle b Rounded Rope ø d 1 m m h Groove radius r D 1 Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 78 79 P l a s t i c s h e a v e s Ø d 1 r 1 h m Ø d 1 r 1 h m Ø d 1 r 1 h m 3 1,6 8 2 21 11 35 7 39 21 60 11 4 2,2 10 2 22 12 35 7 40 21 60 11 5 2,7 12,5 2 23 12,5 35 7 41 23 60 11 6 3,2 12,5 3 24 13 37,5 8 42 23 65 11 7 3,7 15 4 25 13,5 40 8 43 23 65 11 8 4,2 15 4 26 14 40 8 44 24 65 12,5 9 4,8 17,5 4,5 27 15 40 8 45 24 65 12,5 10 5,3 17,5 4,5 28 15 40 8 46 25 67,5 12,5 11 6,0 20 5 29 16 45 8 47 25 70 12,5 12 6,5 20 5 30 16 45 8 48 26 70 12,5 13 7,0 22,5 5 31 17 45 8 49 26 72,5 12,5 14 7,5 25 6 32 17 45 8 50 27 72,5 12,5 15 8,0 25 6 33 18 50 10 52 28 75 12,5 16 8,5 27,5 6 34 19 50 10 54 29 77,5 12,5 17 9,0 30 6 35 19 55 10 56 30 80 12,5 18 9,5 30 6 36 19 55 10 58 31 82,5 12,5 19 10,0 32,5 7 37 20 55 11 60 32 85 12,5 20 10,5 35 7 38 20 55 11 – – – – 2.2 Bearings Due to the good sliding properties of PA 6 G, when sheaves are not subjected to undue stress, fric- tion bearings can be used. Decisive is the pv limiting value. If high degrees of wear are expected on the bearing with an intact sheave groove, the use of a replaceable bearing bush can prevent the sheave having to be replaced prematurely. For highly stressed sheaves, whose maximum load values are above those for a friction bearing, we recommend the installation of anti-friction bearings. These can be mounted by pressing them into a bearing seat produced according to the dimensions in Diagrams 1 and 2. If axial loads are expected on the anti-friction bearings, we recommend that the bearing is secured against falling out by securi ng el ements commonl y used i n machi ne engi neeri ng, such as ci rcl i ps accordi ng to DIN 472. The following diagram shows several possible sheave designs. 1 2 3 4 5 Design with bearing seat for antifriction bearings Design with friction bearings Table 1: Guiding values for rope groove profiles in mm according to DIN 15061 Part 1 Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 79 80 P l a s t i c s h e a v e s When calculating and dimensioning the bearings, especially friction bearings, attention should be paid that the bearing load for idler sheaves corresponds to the rope tension, but for fixed sheaves the angle of contact forms a force equal to twice the cable tension at 180°. Section 3 »Calculating sheaves« provides more information on this subject. 0,0 0,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0 10 30 50 100 150 200 225 175 125 75 40 20 0,007 0,006 0,005 0,004 0,003 0,002 0,001 0 60 100 160 200 250 180 140 80 40 20 120 Internal diameter of bearing (mm) Outer diameter of the antifriction bearing (mm) O p e r a t i n g b e a r i n g p l a y i n % B o r e s e t t i n g s i z e p e r m m o u t e r d i a m e t e r Diagram 1: Recommended bore setting size for antifriction bearing seats Diagram 2: Recommended operating bearing play for friction bearings Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 80 81 P l a s t i c s h e a v e s 3. Calculating rope pulleys sheaves For the calculation of sheaves, distinctions must be made regarding the load case, the rope used and the type of operation. A distinction is made between • Point loading on the sheave • Circumferential loading on the sheave (the sheave runs on a taut rope) (rope encircles the sheave) • The type of rope • The type of operation Open wire rope (stranded rope) Loose sheave (e.g. sheave on a cableway) Closed wire rope Fixed sheave (e.g. deflection sheaves) These criteria lead to different calculation procedures and force considerations for the individual load cases, rope types and types of operation. 3.1 Calculating the bearing compression If the rol l er beari ng i s to be executed as a fri cti on beari ng, the pv val ues i n the beari ng must be cal cul ated and compared wi th the permi ssi bl e val ues for PA 6 G. The fri cti on beari ng shoul d be considered in the same way as a press fit bearing bush. In other words, the calculation is the same as for dynamically loaded friction bearings. The expected bearing load is dependent on the type of operation of the sheave. For idler sheaves, the rope tension F s can be used as the bearing load to calculate the pv value of the rope tension. Thus the average surface pressure for radial bearings in idler sheaves is F S p = ––––––– [MPa] d W . L where F S = rope tension in N d W = shaft diameter in mm L = bearing width in mm and the average sliding speed is d W . p . n v = –––––––––– [m/s] 60000 where d W = shaft diameter in mm n = speed in min -1 Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 81 82 P l a s t i c s h e a v e s Aggregated pv duration for idler sheaves with dynamic loading becomes r F S i r d W . p . n i pv duration =u––––––––u . u––––––––––– u [MPa . m/s] q d W . L t q 60000 t In intermittent operation it is possible to correct pv duration by the process described in the section 3.2 of the chapter on »Friction bearings«. For fixed rollers, the bearing load is dependent on the angle of contact that the rope forms with the sheave. If the sheave is completely encircled (180°), the rope tension is doubled in the calcu- lations. For an angle of contact a < 180°, a resulting force F res must be calculated with the help of the angle and the cable tension. This is calculated from the triangular relationship and is F res = F S 2 - 2 . cos a [N] where F S = cable tension in N a = angle of contact For sheaves made from PA 6 G, the determi ned pv val ues may not exceed 0.13 Mpa · m/s i n dry runni ng appl i cati ons or 0.5 Mpa · m/s wi th l ubri cati on. If the cal cul ated val ues exceed these maximum values, an antifriction bearing would be advisable. 3.2 Calculating the compression between the rope and the sheave groove The main criterion for the load bearing capacity of sheaves is the compression between the rope and the sheave. To calculate the compression, the Hertz’ equations that have been modified for thi s case are used. The resul ts of the cal cul ati ons must be compared wi th the permi ssi bl e val ues for PA 6 G shown in Diagrams 3 and 4. They must be considered in combination with the speed of the rope and may not exceed these values. 3.2.1 Point contact of closed wire ropes If closed wire ropes with a small fleet angle are used (a < 10°), such as is the case with cableways, this causes concentrated loading. The area of pressure is elliptical. Under these conditions the compression parameter p’ for sheaves made from PA 6 G is calculated from the equation a FS Fres FS a Fres FS FS FS FS 2FS 180° Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 82 83 P l a s t i c s h e a v e s 63,5 r 1 i p’ =–––––– . 3 eS ––e 2 . F [MPa] y . h q Rt where y = correction value h = Hcorrection value S 1 R = total of the principle curvatures in mm -1 F = sheave load in N The sum of the pri nci pl e curvatures of the bodi es that are i n contact wi th one another i s calculated from 1 2 1 1 2 S –––=–––- –––- –––+ ––– [mm –1 ] R d r r D From the sum of the pri nci pl e curvatures, the correcti on angl e c can be used to determi ne the correction values y and h according to the following formula: 2 1 1 2 ––+ ––- ––- –– d r r D cos c = ––––––––––––––– 1 S –– R where d = rope diameter in mm r = rope curvature radius (generally negligible as it is very large compared to other radii) r = groove radius in mm D = groove base diameter The correcti on val ues y and h can be found i n Tabl e 1. If c l i es between the tabl e val ues, the correction values must be interpolated. 3.2.2 Point contact of open wire ropes It can be assumed for sheaves made from PA 6 G that because of the el asti ci ty of the sheave i n combi nati on wi th an open stranded rope, that not one si ngl e wi re from the strand l i es i n the groove but rather several wi res and that these parti ci pate i n the transmi ssi on of power. There- fore, the entire strand is regarded as a single wire and it is assumed that all loaded strands trans- mit the same power. In the calculation, a correcting factor is introduced that takes account of the power transmission of several strands (maximum 40%). With this consideration the compression parameter p‘ becomes X p’ = p’ e . 3 ––– [MPa] Z and the compression parameter p‘ e e for one single wire in combination with a PA 6 G sheave is r d 1 d 1 i 2 F p’ e = 42 . 3 e1 - ––––+ ––––e . ––– [MPa] q 2r D t d 2 1 where Table 1: Correction values y and h for different values of c c 90° 80° 70° 60° 50° 40° 30° 20° 10° 0° y 1,0 1,128 1,284 1,486 1,754 2,136 2,731 3,778 6,612 ∞ h 1,0 0,893 0,802 0,717 0,641 0,567 0,493 0,408 0,319 0 Sheave load F Sheave load F Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 83 84 P l a s t i c s h e a v e s X = correction factor in relation to p’ e , from Table 2 Z = number of outer strands d 1 = strand diameter in mm r = groove radius in mm D = groove base diameter in mm F = sheave load in N 3.2.3 Peripheral load with open wire ropes In regard to the power transmi ssi on between the rope and the sheave, the same appl i es as to concentrated l oadi ng as descri bed i n i tem 3.2.2. The onl y di fference i s that the l oad on a com- pletely encircled pulley is not a point load but a uniform load. Hence, the compression parameter p’ becomes X p’ = p’ e . ––– [MPa] Z and the compression parameter p’ e for a single wire in combination with a PA 6 G sheave is (2r - d1) . FS p’ = 55 . ––––––––––––– [MPa] 2r . d 1 . D X = correction factor in relation to p’ e from Table 2 Z = number of outer strands d 1 = strand diameter in mm r = groove radius in mm D = groove base diameter in mm F S = cable tension in N When determining the correction factor, it should be considered that when X > Z, Z = X must be i nserted i n the radi cand of the correcti on factor so that the radi cand i s 1. If the val ue of p’ e i s between the values given in the table, the value for X must be interpolated accordingly. Strand d d 1 Idler FS FS FS FS Fixed sheave Surface pressure p’ e Correction factor in MPa X ≤ 50 Z 150 6 300 4 ≥ 450 2,5 Table 2: Correction factor X Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 84 85 P l a s t i c s h e a v e s 3.3 Maximum permissible surface pressures The resul ts from the cal cul ati ons must be compared wi th the maxi mum permi ssi bl e l oad para- meters from Diagrams 3 and 4. It is not permissible to exceed these values. 20°C 50°C 75°C 100°C 0 80 40 120 140 160 200 240 280 0 1 2 3 4 5 6 m/s Diagram 3: Load limit in relation to the rope speed and ambient temperature for sheaves made from PA 6 G under peripheral loading M a x . p ’ i n M P a Diagram 4: Load limit parameter p‘max in relation to the rope speed and ambient temperature for sheaves made from PA 6 G under concentrated loading. 20°C 50°C 0 0,5 1 2 3 m/s 2,5 1,5 40 80 20 100 60 120 0 Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 85 Plastic gear wheels Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 86 P l a s t i c g e a r w h e e l s Plastic gear wheels 1. Use of plastics as a gear material Although thermoplastic gears are unsuitable for applications in high performance gears and for transmitting high power, they have opened up a broad field of application. The specific material properti es al l ow use under condi ti ons where even hi gh qual i ty metal l i c materi al s fai l . For instance, plastic gears must be used if the following are the key requirements: • Maintenance-free • High wear resistance when used in a dry-running application • Low noise • Vibration damping • Corrosion resistance • Low mass moment of inertia through low weight • Cost-effective manufacture For a plastic to be able to satisfy these requirements, it is absolutely vital that the right material is chosen and that the design is carried out in a material-related manner. 1.1 Materials Only a few thermoplastics are significant for the manufacture of gears. The plastics are described in detail in the previous chapters, so here we will only describe them in regard to tooth forming. • PA 6 Universal gear material for machine engineering; it is wear resistant and impact absorbing even when used i n rough condi ti ons, l ess sui tabl e for smal l gear wheel s wi th hi gh di mensi onal requirements. • PA 66 Is more wear resi stant than PA 6 apart from when i t i s used wi th very smooth mati ng com- ponents, more di mensi onal l y stabl e than PA 6 as i t absorbs l ess moi sture, al so l ess sui tabl e for small gear wheels with high dimensional requirements. • PA 6 G Essentially like PA 6 and PA 66, however, it is especially wear resistant due to its high degree of crystallinity. • Calaumid ® 612 / 612 – Fe (PA 6/12 G) Tough modified polyamide, suitable for use in areas with impact-like load peaks, wear resistance comparable to PA 6 G. • Calaumid ® 1200 / 1200 – Fe (PA 12 G) Tough-hard polyamide with relatively low tendency to absorb water, hence, better dimensional stability than other polyamides, especially suitable for use in areas with impact-like load peaks, excellent wear resistance. • Oilamid ® Self-lubricating properties due to oil in the plastic, hence, excellent for dry running applications and especially wear resistant. • POM – C Because of its low moisture absorbing tendency it is especially suitable for small gears with high dimensional stability demands, not so loadable in dry running applications due to its hardness, however, if permanently lubricated, POM–C gears are more loadable than polyamide ones. 87 Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 87 88 P l a s t i c g e a r w h e e l s • PE – UHMW Because of its low stability, it can only be used for gears that are not subjected to high loads, good dampi ng properti es and chemi cal resi stance, hence mai nl y sui tabl e for use i n appl i cati ons wi th mechanical vibration and in chemically aggressive environments. 1.2 Counterparts Hardened steel i s the most sui tabl e counterpart regardi ng wear and uti l i sati on of the l oad carryi ng capaci ty, as i t ensures very good di ssi pati on of fri cti on heat. In regard to surface pro- perties, the same applies as with friction bearings: the harder the steel the less wear on the wheel and pinions. As a guiding value, we recommend a maximum roughness depth of R t = 8 to 10 µm both in lubricated operation and in dry running applications. For gears that are not subject to heavy l oads, i t i s possi bl e to mate pl asti c/pl asti c. The surface roughnesses are insignificant for wear. When choosing a material, it should be remembered that the driving pinions are always subjected to a higher level of wear. Consequently, the more wear resistant material should always be chosen for the pinions (r pinion: steel, wheel: plastic or pinion: PA, wheel: POM). 1.3 Lubrication The statements made in the chapter on »Friction bearings« regarding dry running and the use of lubricants also apply here. Basically it should be noted that installation lubrication considerably i mproves the servi ce l i fe and the runni ng-i n behavi our. Materi al s that are modi fi ed wi th a l ubri cant, such as Oi l ami d, have much l onger servi ce l i ves than al l other pl asti cs, even wi thout lubrication. Continuous lubrication with oil leads to better heat dissipation and consequently to a longer life and higher levels of transmitted power. When the component i s l ubri cated wi th grease, the ci rcumferenti al speed shoul d not exceed 5 m/sec, as otherwise there is a danger that the grease will be cast off. Due to polyamide’s tendency to absorb moi sture, water l ubri ca- ti on i s not recommended for po- lyamide components. 1.4 Noise development Pl asti cs i n general have good dampi ng properti es. Thi s consi - derabl y reduces noi se on pl asti c gears compared to metal ones. The diagram opposite shows the sound i ntensi ty curves of gear mates steel/steel (a) and steel/plastic (b). It shows maxi mum di fferences of 9 dB. Hence, steel/steel is up to three times as loud as steel/plastic. 1.5 Manufacture Plastic gears are manufactured with the same machining process as metal gears (usually shaping by the generating method and automatic hobbing). As the cutting forces are very low, the profile can be manufactured in one cycle with high forward feed rates, which in turn reduces manufacturing costs. When manufacturing with high forward feed rates, corrugated surfaces can be produced. At first these gi ve an unfavourabl e i mpressi on. However, i n dry runni ng appl i cati ons the faces of the dB 80 70 60 500 1000 2000 2900 U/min a b Steel CK 45 Polyamide 6 G Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 88 89 P l a s t i c g e a r w h e e l s teeth are qui ckl y smoothed after a short runni ng-i n peri od. In l ubri cated appl i cati ons, the corrugated form acts as a lubrication pocket where the lubricant can collect – to the advantage of the gear. In other words, this corrugation is no reduction in quality. Basi cal l y when machi ni ng pl asti c gears, dependi ng on the modul e, qual i ti es of 9 to 10 can be achi eved. Regardi ng the tooth qual i ty that can be achi eved, i t shoul d be noted that the rol l i ng tooth flanks of plastic gears easily fit one another. Therefore, greater tolerances are allowed than would be the case with metal gears. This especially applies to power transmitting pinions. For the grade that is exclusively related to tangential composite error F i " and tangential tooth-to-tooth error f i " this means that up to two grades more are permitted than for similar gears made from metal . The tooth pl ay i s i ncreased by one to two grades compared to steel to compensate for temperature and moisture effects. 2. Design information The following design information is intended to assist when dimensioning new gear components. Exi sti ng data shoul d be used for gear desi gns that are i n use and whi ch have been tri ed and tested. 2.1 Width of the tooth face For pl asti c gears there i s basi cal l y no probl em i n extendi ng thei r wi dth to the same si ze as the diameter. Determining the smallest width is dependent upon the axial stability of the gear. No test results are available in regard to the connection between the life of the component and the width of the tooth face or regarding a determination of the optimum width of tooth face. Practical experience has, however, shown that the width of the tooth face should be at least six to eight times the module. For the mating components steel/plastic it is better to design the plastic gear slightly smaller than the steel pinion to make sure that the plastic gear is loaded across the entire width of the tooth face. A similar situation arises with the mating components plastic/plastic, where the dimensions of the gear on which the higher wear is expected should be slightly narrower. This prevents wear on the edges of the teeth, which could affect the running behaviour. 2.2 Module, angle of pressure and number of teeth The l oad beari ng capaci ty of pl asti c gears can be di rectl y affected by the choi ce of modul e and angle of pressure. If, while maintaining the same peripheral force, the module/angle of pressure is increased, the root-strength of the teeth increases. However, compared to steel gears, the actual i ncrease i s l ess, as the effecti ve contact rati o factor decreases and i t i s no l onger possi bl e for several teeth to engage simultaneously. A higher contact ratio factor, however, can be better for the load bearing capacity than increasing the root-strength of an individual tooth. We can derive the following connection from this (applies mainly to slow running or impact loaded gears): • Preferably a small module for tough elastic thermoplastics (increase in the contact ratio factor, r several teeth engaged simultaneously) • Preferably a large module for hard thermoplastics (increase in the root-strength of the teeth, as a higher contact ratio factor is not possible due to the inferior deformation behaviour) In the case of gears wi th a hi gh peri pheral speed, attenti on must be pai d that the movement i s not affected by the effective contact ratio factor. The angl e of pressure for i nvol ute teeth i s defi ned at 20°. Neverthel ess, i t can occasi onal l y be necessary to change the angl e of pressure (e.g. to decrease the number of teeth or reduce Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 89 90 P l a s t i c g e a r w h e e l s running noise). Angles of pressure < 20° lead to thinner and hence less loadable teeth with steep tooth profiles but low running noise. Angles of pressure > 20° produce sharper, thicker teeth with a greater root-strength and flatter profiles. In regard to the number of teeth, it should be noted for higher peripheral speeds that the ratio between the number of teeth may not be an i nteger mul ti pl e. If thi s i s the case, the same teeth always engage, which encourages wear. 2.3 Helical gearing Experi ence has shown that hel i cal pl asti c gears run qui eter wi th a smal l hel i x angl e than spur toothed types. However, the expected i ncrease i n the l oad beari ng abi l i ty i s smal l er than i s the case wi th steel gears. Al though the l ength of the face contact l i ne i ncreases and the l oad i s distributed among several teeth, the load is uneven and the teeth are deformed. This negates the advantage of helical gearing to a certain degree. As with metal gears, helical toothed plastic gears are calculated via a spur toothed spare wheel. b ≈ 10° – 20° is regarded as being a favourable helix angle. 2.4 Profile correction Profile corrections are generally necessary when • a gear pair has to be adapted to suit a specified axle base (positive or negative profile correction) • the number of teeth is not reached and this causes undercut (positive profile correction) In the appl i cati on, attenti on shoul d be pai d that i n the case of negati ve profi l e correcti on the undercut i s not too great. Thi s woul d resul t i n a greatl y mi ni mi sed root-strength of the teeth, which could reduce the life and load bearing capacity of the gear. Vice versa, in the case of positive profile correction, the thicker tooth root could cause a loss in the deformation capability and a subsequent reduction in the contact ratio factor. 2.5 Flank clearance and crest clearance Because of the hi gh thermal expansi on factors of pl asti cs when di mensi oni ng gears, attenti on must be paid to the material-related fitting of the flank and crest clearances so that a minimum flank clearance is guaranteed. When plastic gears are used, it has proven practical to maintain a minimum flank clearance of ≈ 0.04 · modulus. The built-in flank clearance is thus S e = S eo + 2l . sin a (k a . k F ) [mm] where S eo = minimum flank clearance in mm l = total distance consisting of plastic between the two rotational axes in mm a = angle of pressure k a = coefficient of elongation k F = correction factor for moisture absorption (to be used for polyamides, can be found in the chapter on »Friction bearings«) For the i nbui l t crest cl earance, a measure of 0.3 · modul e has proven to be practi cal . Thi s takes account of temperature fluctuations of up to ± 20°C and also makes adequate consideration for any inaccuracies in the toothed gears. Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 90 91 P l a s t i c g e a r w h e e l s 2.6 Power transmission The feather key and groove type of connecti on that i s general l y used i n machi ne engi neeri ng i s al so used for pl asti c gears. For a connecti on such as thi s, the fl ank of the key groove must be exami ned to ensure that i t does not exceed the permissible surface pressure. The surface pressure is M d . 10 3 p F = i . r m . h . b [MPa] where M d = transmitted torque in Nm i = number of groove flanks r m = radi us from the centre of the shaft to the centre of the bearing flank in mm h = height of the bearing flank in mm b = width of the bearing flank in mm The val ue produced from the cal cul ati on i s compared wi th Di agram 1 and may not exceed the maximum permissible values. However, i t shoul d be noted that thi s val ue contains no safety factor for shock-type loads or safety reserves. Dependi ng on the l oad, we recommend a safety factor of 1.5 to 4. Because of the notch sensitivity of plastics when key grooves are being manufactured, attention should be paid that the edges are designed with a radius. However, this is generally not possible because the usual cutting tools and feather keys are sharp edged. When l arger torques are bei ng transmi tted thi s can al so cause deformati on i n the hub. If the cal cul ati on of the fl ank pressure shoul d produce hi gh pressure val ues that are not permi ssi bl e, or i f hub deformati on i s feared, there are several possi bi l i ti es of power transmission available. One possi bi l i ty i s the non-posi ti ve connec- ti on of the wheel body wi th a steel i nsert. Thi s i s screwed to the wheel body. The di agram opposi te shows one possi bl e design solution. For fi xi ng the steel i nsert we recommend hexagon socket screws accordi ng to DIN 912, property cl ass 8.8 or better i n the following dimensions. r m b h PA 6 G/POM 30 20 10 0 0 20 40 60 80 100 MPa Ambient temperature Diagram 1: Guiding value for permissible surface pressure Tip Number Screw diameter of screws size up to 100 mm 3 M 6 up to 200 mm 4 M 8 above 200 mm 6 M 8 /M 10 Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 91 92 P l a s t i c g e a r w h e e l s For gears with relatively thin walls, it is advis- able to use hexagon socket screws with a low head according to DIN 6912, property class 8.8 or better. One al ternati ve to the use of a screwed steel fi tti ng i s to desi gn the gears i n Cal aumi d 612 Fe or Cal aumi d 1200 Fe. The metal l i c core whi ch i s connected to the pl asti c both i n a form-fit and non-positive manner enables the shaft-hub connection to be calculated and di- mensi oned l i ke a metal l i c component as usual . The form-fi t and non-posi ti ve connec- tion between the plastic casing and the metallic core is created with a knurl. 3. Calculating thermoplastic gears wheels The reasons for the premature breakdown of thermoplastic gears are generally the same damage aspects and principles that occur in metallic gears. This is why the calculation of plastic gears does not differ in principle from the known methods. The only difference is that the material-specific properties of plastics are included in the calculations in the form of correction factors. 3.1 Torque M d , peripheral force F U and peripheral speed v The torque is The peripheral force is The peripheral speed is calculated as P M d d 0 . p . n M d = 9550 . –– [Nm] F U = 2 . 10 3 . ––– [N] v = –––––––––– [m/s] n d 0 60 . 10 3 where where where P = power in kW M d = torque in Nm d 0 = reference diameter in mm n = speed in min -1 d 0 = reference diameter n = speed in min -1 in mm 3.2 Tooth body temperature c Z and tooth flank temperature c F in continuous operation As wi th al l desi gns made from thermopl asti c materi al s, temperature al so pl ays a major rol e for gears in regard to the load bearing capacity of the component. A distinction is made between the tooth body temperature c Z and the tooth flank temperature c F . The tooth body temperature i s responsi bl e for the permi ssi bl e tooth root l oadi ng and tooth deformation, whereas the tooth flank temperature is used to roughly estimate the level of wear. However, it is very difficult to determine these two temperatures accurately, as on a rotating gear wheel the heat transmission coefficient can only be estimated roughly. Consequently, any arith- meti cal determi nati on of the temperatures i s l i abl e to have a certai n amount of error. In parti - cular, when the tooth flank temperature is being calculated, quite often high values are produced which, in some cases, are even above the melting temperatures of the plastics. However, in prac- tice no melting of the tooth profile has been observed. Nevertheless, the values can be regarded as characteristic and comparison temperature values. It can be assumed that the excessive calculated values would guarantee a design which is on the safe side in any case. Calaumid Steel Knur DIN 82 – RKE 2,0 Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 92 93 P l a s t i c g e a r w h e e l s For the thermal cal cul ati on of the gears, the fri cti on heat, the heat di ssi pated from the gear wheel in the gear room and the heat that is dissipated from the gear room to the outside must be considered. Under these conditions, we get the following: i + 1 r k 2 . 17100 k 3 i c 1,2 = c U + P . m . 136 . –––––––––––– . e ––––––––––––––––– + 7,33 . ––– e [°C] z 1,2 + 5i q b . z 1,2 . (v . m) 3 4 A t where Index 1 for the pinion Index 2 for the wheel c U = ambient temperature in °C b = width of the tooth face in mm P = power in kW v = peripheral speed in m/sec µ = coefficient of friction m = module in mm z = teeth A = surface of the gear casing in m 2 i = transmission ratio z 1 /z 2 with k 2 = material-related factor z 1 = number of teeth in pinion k 3 = gear-related factor in m 2 K/W For factor k 2 the following must be included depending on the temperature to be calculated: Calculation of flank temperature: Calculation of root temperature: k 2 = 7 for mating components steel/plastic k 2 = 1.0 for mating components steel/plastic k 2 = 10 for mating components plastic/plastic k 2 = 2.4 for mating components plastic/plastic k 2 = 0 in the case of oil lubrication k 2 = 0 in the case of oil lubrication k 2 = 0 at v ^1 m/sec k 2 = 0 at v ≤ 1 m/sec For factor k 3 and the coefficient of friction µ, the following must be included independent of the temperature to be calculated: k 3 = 0 for completely open gear m 2 K/W k 3 = 0.043 to 0.129 for partially open gear in m 2 K/W k 3 = 0.172 for closed gear in m 2 K/W µ = 0.04 for gears with permanent lubrication µ = 0.4 PA/PA µ = 0.07 for gears with oil mist lubrication µ = 0.25 PA/POM µ = 0.09 for gears with assembly lubrication µ = 0.18 POM/Stahl µ = 0.2 PA/steel µ = 0.2 POM/POM 3.2.1 Tooth body temperature c Z and tooth flank temperature c F in intermittent operation Analogous to friction bearings, because of the lower amount of heat caused by friction, gears in intermittent operation are increasingly loadable the lower the duty cycle. The relative duty cycle ED is considered in the equation in section 3.2 by introducing a correction factor f. The rel ati ve duty cycl e i s defi ned as the rati o between the l oad durati on t and the overal l cycl e time T as a percentage. t ED = –– . 100 [%] T where t = total of all load times within the cycle time T in min T = cycle time in min Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 93 94 P l a s t i c g e a r w h e e l s For thermoplastic gears, the overall cycle time is defined as T = 75 min. The total of all individual l oad ti mes occurri ng wi thi n thi s 75 mi n forms the load duration t. Wi th the val ue that has been cal cul ated i n thi s manner i t i s now possi bl e to determi ne the correcti on factor f from Di agram 2. Attenti on shoul d be pai d that each l oad durati on whi ch exceeds 75 mi n (regardl ess of whether thi s i s only once) is evaluated as a continuous load. Taking account of the correction factor, the tooth flank temperature and tooth body temperature is i + 1 r k 2 . 17100 k 3 i c 1,2 = c U + P . f . m . 136 . –––––––––––– . e ––––––––––––––––– + 7,33 . ––– e [°C] z 1,2 + 5i q b . z 1,2 . (v . m) 3 4 A t The values given in section 3.2 can be used for the factors k 2 , k 3 and the coefficient of friction µ. 3.3 Calculating the root strength of teeth If the tooth root stress j F exceeds the permi ssi bl e stress j Fper under l oadi ng, i t must be assumed that the teeth will break. For this reason the tooth root stress must be calculated and compared with the permissible values. If the pinion and gear are constructed from plastic, the calculations must be carried out separately for each of them. The tooth root stress is F U j F = –––––– . K B . Y F . Y b . Y e [MPa] b . m where F U = peripheral force in N b = gear width in mm (where the width of the pinion and gear differ: use the smaller width + m as a calculation value for the wider gear) m = module in mm K B = operating factor for different types of drive operation, from Table 2 Y F = tooth shape factor from Diagram 3 Y b = hel i x factor to take account of the i ncrease i n l oad beari ng capaci ty i n hel i cal geari ng, as this is the case with plastic gears, this value is to be set as 1.0 Y e = contact ratio factor from Table 1, where Y e = 1/e a und e a = e a z1 + e a z2 1,0 20 40 60 80 100 0,8 0,6 0,4 0,2 Diagram 2: Correction factor for ED C o r r e c t i o n f a c t o r f Relative duty cycle (%) Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 94 95 P l a s t i c g e a r w h e e l s z 14 15 16 17 18 19 20 21 22 23 24 e az 0,731 0,740 0,749 0,757 0,765 0,771 0,778 0,784 0,790 0,796 0,801 z 25 26 27 28 29 30 31 32 33 34 35 e az 0,805 0,810 0,815 0,819 0,822 0,827 0,830 0,833 0,837 0,840 0,843 z 36 37 38 39 40 41 42 43 44 45 46 e az 0,846 0,849 0,851 0,854 0,857 0,859 0,861 0,863 0,866 0,868 0,870 z 47 48 49 50 51 52 53 54 55 56 57 e az 0,872 0,873 0,875 0,877 0,879 0,880 0,882 0,883 0,885 0,887 0,888 z 58 59 60 61 62 63 64 65 66 67 68 e az 0,889 0,891 0,892 0,893 0,895 0,896 0,897 0,898 0,899 0,900 0,901 z 69 70 71 72 73 74 75 76 77 78 79 e az 0,903 0,903 0,904 0,906 0,906 0,907 0,909 0,909 0,910 0,911 0,912 z 80 81 82 83 84 85 86 87 88 89 90 e az 0,913 0,913 0,914 0,915 0,916 0,917 0,917 0,918 0,919 0,919 0,920 z 91 92 93 94 95 96 97 98 99 100 101 e az 0,920 0,921 0,922 0,922 0,923 0,924 0,924 0,925 0,925 0,926 0,927 2,0 2,2 2,4 2,6 2,8 Y F 3,0 3,2 3,4 3,6 x = 0 , 0 - 0 , 0 5 - 0 , 1 - 0 , 2 - 0 , 3 - 0 , 4 - 0 , 5 - 0 , 6 0 , 0 5 0 , 1 0 ,2 0 ,3 0 ,4 0,5 0,6 0,7 0,8 15 16 18 19 20 25 30 40 50 60 80 100 200 400 17 35 45 70 90 150 300 Z x = Profile correction Mode of operation Mode of operation of the driven machine of the driving machine Even Moderate Average Strong impact impact impact Even 1,0 1,25 1,5 1,75 Moderate impact 1,1 1,35 1,6 1,85 Average impact 1,25 1,5 1,75 2,0 Strong impact 1,5 1,75 2,0 2,25 Table 1: Partial transverse contact ratio for gears without profile correction Table 2: Operating factor K B Diagram 3: Tooth formation factor Y F as a function of the number of teeth Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 95 96 P l a s t i c g e a r w h e e l s In the case of profile corrected toothed gears the factor Y e must be adjusted accordingly. The following applies: z 1 r z 2 i z 2 e a = –––––– . (tana E1 - tana A1 ) and tana A1 = tana tw . e1 + ––– e- –––tana A2 2 . p q z 1 t z 1 The value tana E1 is dependent on the The value tana A2 is dependent on the correction value correction value d K1 d K1 D 1 = –––– D 2 = ––– d G2 d G2 where where d K1 = outside diameter of pinion d K2 = outside diameter of large wheel d G2 = base diameter of large wheel d G1 = base diameter of pinion The values for tana E1 and tana A2 can be taken from Diagram 5. The effective pressure angles a tw and tan a tw are cal cul ated from the profi l e correcti on x 1,2 and the number of teeth z 1,2 where Index 1 stands for the pinion and Index 2 for the large gear. The effective pressure angles for spur gears are shown in Diagram 4. 3.4 Calculating tooth profile strength Excessive pressure on the tooth profile can cause pitting or excessive wear. The wear is particularly obvious in the root and crest of the tooth, which changes the tooth formation and consequently leads to uneven transmission of motion. In order to prevent premature failure due to excessive wear or pitting, the tooth flank pressure j H must be determined. The pressure occurring on the tooth flank is F U . (z 1 + z 2 ) j H = –––––––––––––– . K B . Z e . Z H . Z M [MPa] b . d 0 . z 2 where F U = peripheral force in N d 0 = reference diameter in mm z 1 = number of teeth in pinion K B = operating factor for different z 2 = number of teeth in large gear types of drive operation, from b = gear width in mm (where the width of Table 2 the pinion and gear differ: use the Z e = contact ratio factor the smaller width + m as a calculation Z H = zone factor value for the wider gear) Z M = material factor 35 0 0,02 0,04 0,06 0,08 30 25 20 15 Diagram 4: Effective pressure angle a tw , tana tw a tw (x 1 + x 2 )/(z 1 + z 2 ) tana tw 10 0,10 0,7 0,6 0,5 0,4 0,3 0,2 tana tw a tw , 1,0 1,1 1,2 1,3 1,4 Diagram 5: Correction diagram for transverse contact ratio D 1 , D 2 t a n a A 2 , t a n a E 1 1,0 0,8 0,6 0,4 0,2 0 Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 96 97 P l a s t i c g e a r w h e e l s The contact rati o of several teeth acts l i ke a wi deni ng of the tooth. Thi s apparent wi deni ng i s taken account of with the contact ratio factor Z e and equated for spur and helical gears. The contact ratio factor becomes 4 - ( e az1 + e az2 ) Z e = –––––––––––––––– 3 where e az1 = partial transverse contact ratio of pinion from Table 1 e az2 = parti al transverse contact rati o of l arge wheel from Table 1 The tooth formati on factor Z H takes account of the tooth flank distortion. In the case of non-profile correc- ted spur teeth wi th an angl e of pressure of a = 20° the zone factor can be approxi mated wi th Z H = 1.76. For profi l e corrected spur teeth Z H can be taken from the diagram opposite. For angl es of pressure other than 20° the fol l owi ng applies: 1 1 Z H = ––––––– . ––––––– cosa tana tw where a = normal angle of pressure tan a tw = effective pressure angle from Diagram 4 The elasticity of the plastic and consequently the effective contact surface of the tooth profile are considered with the material factor Z M . It can be said with sufficient accuracy that E 1 . E 2 Z M = 0,38 . E’ and E’ = –––––––– E 1 + E where E 1 = dynamic modulus of elasticity of the pinion E 2 = dynamic modulus of elasticity of the gear The different moduli of different materials for the pinion and gear have been taken into account. For the mati ng components pl asti c/steel the correspondi ng factor for Z M can be taken from Diagram 8. For the mating components of gears made from the same plastic the following applies: 1 Z M(K/K) = –––– . Z M(K/St) M2 If the gear and pinion are made from different plastics, the factor Z M (K/St) for the softer plastic should be used. The tooth flank temperature is determined with the help of the formula in sections 3.2 or 3.2.1. Diagram 6: Zone factor Z H with profile correction and a = 20° Z H (x 1 + x 2 )/(z 1 + z 2 ) 2,0 1,9 1,8 1,7 1,6 1,5 1,4 1,3 1,2 1,1 0 0,02 0,04 0,06 0,08 0,1 Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 97 98 P l a s t i c g e a r w h e e l s -20 Diagram 7: Dynamic modulus of elasticity Tooth flank temperature D y n a m i c m o d u l u s o f e l a s t i c i t y 0 0 20 40 60 80 100 120 140 °C POM PA 6 G 500 MPa 4500 4000 3500 3000 2500 2000 1500 1000 Diagram 8: Material factor for mating components K/St. Tooth flank temperature Z M POM PA 6 G 4 8 12 16 20 24 28 32 36 40 44 MN mm -20 0 20 40 60 80 100 120 140 °C 3.5 Safety factor S The results for j F and j H from the calculations must be compared with the permissible values. As a rule a minimum safety factor of 1.2 to 2 is advisable. The following applies: j Fmax j Hmax j Fzul = –––––– and j Hzul = –––––– S S where S = advisable safety factor j Fmax = permissible tooth root stress from Diagrams 9 and 10 in combination with the tooth temperature or S = advisable safety factor j Hmax = permissible flank pressure from Diagrams 11 to 14 in combination with the tooth temperature The following table contains several minimum safety factors in relation to operating conditions. Type of operation Minimum safety factor Normal operation 1,2 High stress reversal 1,4 Continuous operation with stress reversals ≥ 10 8 ≥ 2 The permissible tooth root stresses and flank pressures are shown in the following diagrams. Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 98 99 P l a s t i c g e a r w h e e l s 10 5 10 6 10 7 10 8 70 60 50 40 30 20 10 0 20 °C 60 °C 80 °C 100 °C Tooth temperature Diagram 9: Root strength of teeth j Fmax für POM Load alternations R o o t s t r e s s j F m a x MPa 10 5 10 6 10 7 10 8 10 9 60 50 40 30 20 10 0 60 °C 120 °C Tooth temperature 20 °C 40 °C 80 °C 100 °C Diagram 10: Root strength of teeth j Fmax for PA 6 G Load alternations R o o t s t r e s s j F m a x MPa Flank temperature (°C) 20 40 60 80 100 120 140 Diagram 11: Contact surface pressure j Hmax , PA 6 G, dry running C o n t a c t s u r f a c e p r e s s u r e j H m a x 10 5 10 6 10 7 10 8 10 9 70 60 50 40 30 20 10 0 MPa Load alternations Flank temperature (°C) 40 80 100 120 Diagram 14: Contact surface pressure j Hmax , POM, dry running C o n t a c t s u r f a c e p r e s s u r e j H m a x 140 120 100 80 60 40 20 0 10 5 10 6 10 7 10 8 10 9 20 Load alternations MPa Load alternations C o n t a c t s u r f a c e p r e s s u r e j H m a x MPa 10 5 10 6 10 7 10 8 10 9 140 120 100 80 60 40 20 0 Diagram 13: Contact surface pressure j Hmax , PA 6 G, oil lubrication 20 40 60 80 120 140 100 Flank temperature (°C) Diagram 12 : Contact surface pressure j Hmax , PA 6 G, grease lubrication Flank temperature (°C) C o n t a c t s u r f a c e p r e s s u r e j H m a x MPa 140 120 100 80 60 40 20 20 40 60 80 100 120 140 Load alternations 10 5 10 6 10 7 10 8 10 9 0 Konstr. Kunststoffe engl.7/04 27.10.2004 7:38 Uhr Seite 99 100 P l a s t i c g e a r w h e e l s 3.6 Calculating tooth distortion The tooth distortion that occurs when a load is applied acts like a pitch error during the transition from the l oaded to the unl oaded condi ti on of the tooth. As excessi ve deformati on coul d cause the gear to break down, plastic gears must be examined in regards to their compliance with the maximum permissible tooth distortion. Tooth distortion f K as a correction of the crest of the tooth in the peripheral direction becomes 3 . F U r w 1 w 2 i f K = –––––––––––– . J . e––– + –––e [mm] 2 . b . cos a 0 q E 1 E 2 t where J F = correction value from Diagram 15 w 1,2 = correction values from Diagram 16 E 1,2 = modulus of elasticity from Diagram 7 For the mating components plastic/steel the following applies: w ST _____ = 0 E ST The permissible tooth distortion is generally determined by the requirements that are placed on the gears in regard to running noise and life. Practice has shown that the running noises increase considerably from a tooth distortion f K = 0.4mm. Another parameter is the ratio between tooth distortion and module. In the form of an equation, the permissible limiting values become f Kzul ≤ 0,4 [mm] or f Kper ≤ 0,1 . m [mm] The calculated values should not exceed the limiting values. If, however, this is the case one would have to accept increased running noises and a shorter life. Diagram 15: Correction value J C o r r e c t i o n v a l u e J 14 16 18 20 25 30 40 50 100 Number of teeth z 1,2 8,6 8,2 7,8 7,4 7,0 6,6 6,2 5,8 z 1 /z 2 = 1,0 0,8 0,6 0,4 0,2 0 Diagram 16: Correction value w 1,2 C o r r e c t i o n v a l u e w 1 , 2 14 16 18 20 25 30 40 50 100 Number of teeth z 1,2 2,0 x 1,2 = - 0,6 1,6 1,2 0,8 0,4 - 0,4 - 0,2 0 0,2 0,4 0,6 0,8 1,0 Konstr. Kunststoffe engl.7/04 27.10.2004 7:39 Uhr Seite 100 Plastic spindle nuts Konstr. Kunststoffe engl.7/04 27.10.2004 7:39 Uhr Seite 101 102 P l a s t i c s p i n d l e n u t s 102 1. Plastic as a material for spindle nuts Spi ndl e nuts, i n combi nati on wi th a threaded spi ndl e, transform a turni ng moti on i nto a l i near motion. Good stability of the nut material, a large thread bearing area and high surface quality are advantages for power transmission. A trapezoidal screw thread design according to DIN 103 is advantageous and practical. Loadi ng of the thread fl anks i s the same as on a sl i di ng el ement whi ch means that i n regard to choosi ng a sui tabl e materi al for the spi ndl e nut, the mai n consi derati ons are sl i di ng and wear properties. The stability of the chosen material is decisive for safe power transmission. It should be noted that glass fibre reinforced plastics are unsuitable for the manufacture of spindle nuts. Compared to other thermoplastics, they exhibit inferior sliding and wear values. In addition, the glass fibres can cause increased wear in the mating component. The relatively high modulus of el asti ci ty of these materi al s al so hi nders deformati on of the thread duri ng stress peaks, so that the load can distribute evenly over all the threads. This results in tears in the thread and a much shorter service life compared to plastics that are not reinforced. 1.1 Materials For the manufacture of spindle nuts, cast polyamides with and without sliding additives, as well as POM, PET and PET with sliding additives have proven their worth. In regard to servi ce l i fe, l i ke al l other sl i di ng appl i cati ons, the use of materi al s wi th bui l t-i n lubrication (such as Oilamid and PET-GL) is an advantage. Compared to other plastics, they exhibit less wear and thus achieve a longer service life. 1.2 Lubrication As with all other slide applications, lubrication is not absolutely necessary, but among other things it does considerably prolong the service life of the components. It also counteracts the danger of stick-slip occurring. An i ni ti al i nstal l ati on l ubri cati on i s practi cal , as recommended for fri cti on beari ngs and sl i di ng pads, wi th a subsequent empi ri cal l ubri cati on. Thi s especi al l y appl i es to hi ghl y stressed spi ndl e nuts where attention has to be paid that the friction heat is dissipated. However, graphite should not be used as a lubricant in combination with polyamide spindle nuts, as with this combination stick-slip becomes more likely. 2. Manufacture and design The threads of spindle nuts can be machined on suitable machine tools. We recommend that they be produced on a l athe wi th the use of a l athe thread chi sel . In thi s way, i t can be ensured that there is enough play on the flanks of the thread to balance out the effects of heat expansion and moisture absorption. Generally the spindle nut and housing are connected via a feather key. The load bearing capacity of plastic nuts in this case is oriented to the admissible compression in the feather key groove. To fully utilise the load bearing capacity of the plastic thread, a form-fit connection between the outer steel housing and the plastic nut is required. Plastic spindle nuts Konstr. Kunststoffe engl.7/04 27.10.2004 7:39 Uhr Seite 102 103 P l a s t i c s p i n d l e n u t s 3. Calculating the load bearing capacity 3.1 Surface pressure in the key groove For a feather key connection, the side of the key groove must be checked to ensure that it does not exceed the permissible surface pressure. The surface pressure is M d . 10 3 P F = –––––––––––––– [MPa] i . r m . h . b where M d = transmitted torque in Nm i = number of groove flanks r m = radius from the middle of the shaft to the middle of the bearing flank in mm h = height of the bearing flank in mm b = width of the bearing flank in mm The val ue from the cal cul ati on i s compared wi th Di agram 1 and may not exceed the maxi mum value. 3.2 Surface pressure on the thread flank If we assume that all thread flanks bear the load equally, the surface pressure on the flanks is F p = –––––––––––––––––––––––– [MPa] r l i 2 z . H . ed 2 . p . –– e + l 2 q P t where F = axial load of the spindle in N P = lead in mm d 2 = flank diameter in mm l = length of nut in mm H = depth for ISO metric trapezoidal screw thread in mm according to Table 1 z = number of screw flights (in case of multiple-flights) In the case of static loading for spindle nuts made from PA, POM or PET, at 20°C approx. 12 MPa and at 80°C approx. 8 MPa can be permitted as the maximum compression. 103 PA 6 G/POM 30 20 10 0 MPa 0 20 40 60 80 100 Ambient temperature Diagram 1: Guiding values for permissible surface pressure S u r f a c e p r e s s u r e P 30° dd 2 = D 2 d 3 H Konstr. Kunststoffe engl.7/04 27.10.2004 7:39 Uhr Seite 103 104 P l a s t i c s p i n d l e n u t s 104 Table 1: ISO metric trapezoidal screw thread according to DIN 103 Thread Thread Thread diameter P H d 2 diameter P H d 2 diameter P H d 2 d = 0,5 . P = d - H d = 0,5 . P = d - H = 0,5 . P = d - H 8 1,5 0,75 7,25 36 6 3 33 75 10 5 70 10 2 1 9 40 7 3,5 36,5 80 10 5 75 12 3 1,5 10,5 44 7 3,5 40,5 85 12 6 79 16 4 2 14 48 8 4 44 90 12 6 84 20 4 2 18 52 8 4 48 95 12 6 89 24 5 2,5 21,5 60 9 4,5 55,5 100 12 6 94 28 5 2,5 25,5 65 10 5 60 110 12 6 104 32 6 3 29 70 10 5 65 120 14 7 113 3.3 Sliding friction on the thread flank As the thread fl anks can be consi dered, as a sl i di ng el ement, the pv val ue can al so be used as a guiding value for sliding friction loads for spindle nuts. For the thread flank this is n . (d 2 . p) 2 + s 2 pv = p . –––––––––––––––––– [MPa . m/s] 60000 where n = number of strokes in 1/min –1 d 2 = flank diameter in mm s = stroke length in mm As with friction bearings, the question regarding the permissible sliding friction load is a problem caused by the heat that occurs due to fri cti on. If i t can be ensured that the pl asti c nuts have sufficient time to cool down in intermittent operation, higher values can be permitted than in the case of continuous operation. However, the determined values may not exceed the maximum values given in Table 2. Table 2: pv – limiting values for spindle nuts P A 6 G O i l a m i d P O M – C P E T P E T – G L P A 6 G O i l a m i d P O M – C P E T P E T – G L Continuous operation Intermittent operation Dry running 0,15 0,23 0,15 0,15 0,25 0,23 0,34 0,23 0,23 0,37 Continuous lubrication 0,30 0,30 0,30 0,30 0,50 0,45 0,45 0,45 0,45 0,50 Konstr. Kunststoffe engl.7/04 27.10.2004 7:39 Uhr Seite 104 Tolerances Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 105 106 T o l e r a n c e s Tolerances 1. Material-related tolerances for machined plastic construction parts Plastics are often integrated into existing assemblies to replace conventional materials. As a rule, however, the producti on drawi ng i s onl y al tered i n respect to the new materi al . Often the tol erances that have been speci fi ed for the steel component are not adapted to sui t the new material. But even in the case of new designs where plastic is planned as a material, the tolerance fields that are normal for steel are still used. However, the special features of plastics extensively preclude the choice of the narrow production tolerances required for steel parts. The deci si ve factor i s not the possi bi l i ty of manufacturi ng the parts, si nce thi s i s vi rtual l y no problem with the use of modern CNC machine tools, but rather the permanent compliance with the tolerances after the manufacturing process. This applies especially to dimensions in a class of tol erances wi th very narrow fi el ds (< 0.1mm). These can change i mmedi atel y after the part i s taken from the machine table due to the visco-elastic behaviour of the plastics. In particular, the higher level of thermal expansion, volume changes due to the absorption of moisture as well as form and di mensi onal changes caused by the rel axati on of producti on-rel ated resi dual stresses are just some of the possible causes. Another problem is the fact that there is no general standard for machined plastic components. The l ack of a common basi s for materi al -rel ated tol erance for parts such as thi s often l eads to di sagreement between the customer and the suppl i er i n regard to the cl assi fi cati on of rejects and/or defects i n del i very. Choosi ng a tol erance fi el d that i s sui tabl e for the respecti ve materi al can avoid disputes and also ensure that the plastic components function and operate safely as in- tended. The following sections of this chapter are based on our many years of experience with different plastics and are intended to assist design engineers in defining tolerances. The aim is to create a standard basis and to avoid unnecessary costs caused by rejects due to off-spec tolerances. The tolerance fields that we recommend can be achieved with conventional production methods and without any additional expenditure. In general, the functioning and operating safety of the components were not limited because of the increased tolerance. Narrower tolerances than those stated here are possi bl e to a certai n extent, but woul d necessi tate unjusti fi abl y hi gh processi ng expenditure, and the materials would also require intermediate treatment (annealing) during the production process. If component parts require tolerance fields of < 0.1mm or ISO series IT 9 fits and smal l er, we wi l l be happy to advi se you i n the choi ce of a techni cal l y/economi cal l y practi cal and sustainable tolerance field. 2. Plastic-related tolerances 2.1 General tolerances The general tolerances for untoleranced dimensions can be chosen according to DIN ISO 2768 T1, tolerance class »m«. In this standard, the tolerances are defined as follows: Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 106 107 T o l e r a n c e s Table 1: Limiting dimensions in mm for linear measures (DIN ISO 2768 T1) Nominal size range in mm Tolerance 0,5 above 3 above 6 class up to 3 up to 6 f (fine) m (medium) ± 0,2 ± 0,5 ± 1,0 g (rough) v (very rough) ± 0,4 ± 1,0 ± 2,0 Nominal size range in mm Tolerance 0,5 above 3 above 6 above 30 above 120 above 400 above 1000 above 2000 class up to 3 up to 6 up to 30 up to 120 up to 400 up to 1000 up to 2000 up to 4000 f (fine) ± 0,05 ± 0,05 ± 0,1 ± 0,15 ± 0,2 ± 0,3 ± 0,5 - m (medium) ± 0,1 ± 0,1 ± 0,2 ± 0,3 ± 0,5 ± 0,8 ± 1,2 ± 2,0 g (rough) ± 0,15 ± 0,2 ± 0,5 ± 0,8 ± 1,2 ± 2,0 ± 3,0 ± 4,0 v (very rough) - ± 0,5 ± 1,0 ± 1,5 ± 2,5 ± 4,0 ± 6,0 ± 8,0 Table 2: Limiting dimensions in mm for radius of curvature and height of bevel (DIN ISO 2768 T1) Table 3: Limiting dimensions in degrees for angle measurements (DIN ISO 2768 T1) Nominal size range of the shorter leg in mm Tolerance up to 10 above 10 above 50 above 120 above 400 class up to 50 up to 120 up to 400 f (fine) ± 1° ± 30’ ± 20’ ± 10’ ± 5’ m (medium) g (rough) ± 1° 30’ ± 1° ± 30’ ± 15’ ± 10’ v (very rough) ± 3° ± 2° ± 1° ± 30’ ± 20’ In speci al cases, for l ongi tudi nal di mensi ons i t i s possi bl e to choose the tol erance cl ass »f«. However, it is important that permanent compliance with the tolerance in regard to component geometry is checked in agreement with the manufacturer. 2.2 Shape and position The general tolerances for untoleranced dimensions can be selected according to DIN ISO 2768 T2, tolerance class »K«. In this standard the tolerances are defined as follows: Table 4: General tolerances for straightness and evenness (DIN ISO 2768 T2) Nominal size range in mm Tolerance above 10 above 30 above 100 above 300 above 1000 class up to 10 up to 30 up to 100 up to 300 up to 1000 up to 3000 H 0,02 0,05 0,1 0,2 0,3 0,4 K 0,05 0,1 0,2 0,4 0,6 0,8 L 0,1 0,2 0,4 0,8 1,2 1,6 Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 107 108 T o l e r a n c e s Dimension category Plastics Comments A POM, PET, PTFE+glass, PTFE+bronze, Thermoplastics with or PTFE+coal,PC,PVC-U, PVDF, PP-H, or without reinforcement/ PEEK, PEI, PSU, HGW (laminated fillers fabric) (with low moisture absorption) B PE-HD, PE-HMW, PE-UHMW, PTFE, Soft thermoplastics and PA 6, PA 6 G, PA 66, PA 12 polyamides with moisture absorption Table 5: General tolerances for rectangularity (DIN ISO 2768 T2) Nominal size range in mm Tolerance above 100 above 300 above 1000 class up to 100 up to 300 up to 1000 up to 3000 H 0,2 0,3 0,4 0,5 K 0,4 0,6 0,8 1,0 L 0,6 1,0 1,5 2,0 Nominal size range in mm Tolerance above 100 above 300 above 1000 class up to 100 up to 300 up to 1000 up to 3000 H 0,5 K 0,6 0,8 1,0 L 0,6 1,0 1,5 2,0 Table 6: General tolerances for symmetry (DIN ISO 2768 T2) The general tolerance for run-out and concentricity for class »K« is 0.2mm. In speci al cases for shape and posi ti on i t i s possi bl e to choose tol erance cl ass »H«. The general tolerance for run-out and concentricity for class »H« is 0.1mm. However, it is important that permanent compliance with the tolerance in regard to component geometry is checked in agreement with the manufacturer. 2.3 Fits As described above, it is not possible to apply the ISO tolerance system that is usually applied to steel components. Accordi ngl y, the tol erance seri es IT 01 – 9 shoul d not be used. In addi ti on, to determine the correct tolerance series, the processing method and the type of plastic being used must be considered. 2.3.1 Dimensional categories The different plastics can be classified into two categories according to their dimensional stability. These are shown in Table 7. Table 7: Dimension categories for plastics Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 108 109 T o l e r a n c e s 2.3.2 Classification of tolerance series for milled parts Classification for milled parts with tolerances Dimension A IT 10 - 12 category: B IT 11 - 13 Table 8: ISO basic tolerances in µm according to DIN ISO 286 Nominal size ISO tolerance series (IT) range in mm 6 7 8 9 10 11 12 13 14 15 16 From up to 1-3 6 10 14 25 40 60 100 140 250 400 600 Above up to 3-6 8 12 18 30 48 75 120 180 300 480 750 Above up to 6-10 9 15 22 36 58 90 150 220 360 580 900 Above up to 10-18 11 18 27 43 70 110 180 270 430 700 1100 Above up to 18-30 13 21 33 52 84 130 210 330 520 840 1300 Above up to 30-50 16 25 39 62 100 160 250 390 620 1000 1600 Above up to 50-80 19 30 46 74 120 190 300 460 740 1200 1900 Above up to 80-120 22 35 54 87 140 220 350 540 870 1400 2200 Above up to 120-180 25 40 63 100 160 250 400 630 1000 1600 2500 Above up to 180-250 29 46 72 115 185 290 460 720 1150 1850 2900 Above up to 250-315 32 52 81 130 210 320 520 810 1300 2100 3200 Above up to 315-400 36 57 89 140 230 360 570 890 1400 2300 3600 Above up to 400-500 40 63 97 155 250 400 630 970 1550 2500 4000 2.3.3 Classification of tolerance series for turned parts Classification for turned parts with tolerances Dimension A IT 10 - 11 category: B IT 11 - 12 Table 8: ISO basic tolerances in µm according to DIN ISO 286 Nominal size ISO tolerance series (IT) range in mm 6 7 8 9 10 11 12 13 14 15 16 From up to 1-3 6 10 14 25 40 60 100 140 250 400 600 Above up to 3-6 8 12 18 30 48 75 120 180 300 480 750 Above up to 6-10 9 15 22 36 58 90 150 220 360 580 900 Above up to 10-18 11 18 27 43 70 110 180 270 430 700 1100 Above up to 18-30 13 21 33 52 84 130 210 330 520 840 1300 Above up to 30-50 16 25 39 62 100 160 250 390 620 1000 1600 Above up to 50-80 19 30 46 74 120 190 300 460 740 1200 1900 Above up to 80-120 22 35 54 87 140 220 350 540 870 1400 2200 Above up to 120-180 25 40 63 100 160 250 400 630 1000 1600 2500 Above up to 180-250 29 46 72 115 185 290 460 720 1150 1850 2900 Above up to 250-315 32 52 81 130 210 320 520 810 1300 2100 3200 Above up to 315-400 36 57 89 140 230 360 570 890 1400 2300 3600 Above up to 400-500 40 63 97 155 250 400 630 970 1550 2500 4000 Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 109 110 T o l e r a n c e s 2.4 Surface quality The degree of surface qual i ty that can be achi eved depends on the processi ng method. Tabl e 9 shows the surface qualities that can be achieved without any additional expenditure for the indi- vidual processes. Table 9: Achievable surface qualities for various machining processes Form of machining Max. achievable Average roughness Averaged depth of degree of roughness value R a (µm) roughness R z (µm) Milling N7 1,6 8 Turning N7 1,6 8 Planing N8 3,2 12,5 Sawing N8 3,2 16 It i s possi bl e to achi eve better surface qual i ti es than those shown i n Tabl e 9 i n conjuncti on wi th higher production expenditure. However, the production possibilities must be discussed with the manufacturer of the component part i n regard to the respecti ve pl asti c and the processi ng method. 2.5 Tolerances for press fits 2.5.1 Oversize for bushes To ensure that friction bearing bushes sit properly in the beari ng bore, the i nserti on of an oversi zed component has proved to be good method. The oversi ze for pl asti c bushes i s very l arge compared to metal beari ng bushes. However, due to the vi sco-el asti c behavi our of the pl asti cs, thi s i s especi al l y i mportant because of the effects of heat, as otherwi se the beari ng bush woul d become l oose i n the bore. If the maxi mum servi ce tem- perature i s 50°C, i t i s possi bl e to do wi thout an addi ti - onal securing device for the bearing bush if the oversizes from Di agram 1 are compl i ed wi th. In the case of tem- peratures above 50°C, we recommend that the bush be secured wi th a devi ce commonl y used i n machi ne en- gineering (e.g. a retaining ring according to DIN 472, see also the chapter on »Friction bearings« section 2.5). It should also be considered that when the bearing bush is being inserted, its oversize leads to it being compressed. Consequentl y the oversi ze must be consi dered as an excess to the operati ng beari ng pl ay, and the i nternal di ameter of the beari ng must be di mensi oned accordi ngl y. Di agram 2 shows the required bearing play in relation to the i nternal di ameter of the beari ng. To prevent the bearing from sticking at temperatures above 50°C, i t i s necessary to correct the beari ng pl ay by the factors shown i n the chapter on »Fri cti on bearings« section 2.3. 0,007 0,006 0,005 0,004 0,003 0,002 0,001 20 40 60 80 100 120 140 160 180 0 Outer diameter of the friction bearing in mm P r e s s - f i t o v e r s i z e p e r m m o u t e r d i a m e t e r i n m m Diagram 1: Press-fit oversize for friction bearings 0 10 30 50 100 150 200 0,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0 Internal diameter of bearing in mm O p e r a t i n g b e a r i n g p l a y i n % Diagram 2: Operating bearing play Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 110 111 T o l e r a n c e s In regard to di mensi oni ng thi n wal l ed beari ng bushes, ri ngs and si mi l ar components, i t must be noted that the measuri ng forces that are appl i ed and the deformati on that thi s causes can resul t i n i ncorrect measurements. Hence, the tol erances for the outer di ameter and wal l thi ckness shown i n Figure1 are recommended. 2.5.2 Press-fit undersize for antifriction bearings Anti fri cti on beari ngs can be i nserted di rectl y i nto the undersi zed beari ng seat for maxi mum operating temperatures of up to 50°C. If low stress and low operating temperatures are expected, no additional security is required for the bearing, but this is, however, recommended for higher stresses and operati ng temperatures. Agai n thi s i s because of the vi sco-el asti c behavi our of the pl asti cs whi ch can resul t i n a reducti on i n the compressi on force and beari ng mi grati on. The beari ng can al so be secured wi th devi ces commonl y used in machine engineering (e.g. re- tai ni ng ri ng accordi ng to DIN 472). If the bearing is to be used in areas where high temperatu- res or loads are expected, it is al- so possi bl e to pl ace a steel sl ee- ve in the bearing bore. This steel sl eeve i s fi xed i n the beari ng bore wi th addi ti onal securi ng el ements, and the beari ng i s pressed in to this ring. Di agram 3 shows the requi red temperature-related undersizes for fi xi ng the beari ng i n the bearing seat by compression. For bearing seats into which an- tifriction bearings are inserted for operation at normal temperature and load conditions, we re- commend the following press-fit undersizes and tolerances: Bearing seat diameter up to 50 mm c – 0.15 /– 0.25 mm Bearing seat diameter above 50 up to 120 mm c – 0.25 /– 0.35 mm Bearing seat diameter above 120 mm c – 0.40 /– 0.50 mm In our many years of experience, bearing seats manufactured according to the above exhibit no excessive decrease in compression force and are able to keep the antifriction bearings in position safely and securely. However, if this recommendation is taken, it should be noted that in the case of extremely small ratios between the bearing seat diameter and the outer diameter it is possible that the bearings loosen despite compliance with our recommendations. This can be attributed to the fact that the stresses caused by i nserti on can resul t i n el ongati on of the resi dual materi al . As a resul t of thi s, the beari ng seat di ameter becomes l arger and the compressi on force needed to fi x the beari ng can no longer be maintained. This behaviour is exacerbated by high temperatures and/or flexing that occurs duri ng operati on. Thi s can be negated to a certai n extent by the securi ng measures described above. 70 0 -0,2 2 , 5 - 0 , 1 0 - 0 , 1 5 Ø 4 5 ( Ø 4 0 ) + 0 , 2 5 + 0 , 1 5 Figure 1: Example of tolerance for a bearing bush 0,1 0,7 0,6 0,5 0,4 0,3 0,2 0,0 20 40 60 80 100 120 O p e r a t in g t e m p e r a t u r e 5 0 ° C Operating temperature 20 °C Antifriction bearing diameter in (mm) B o r e s e t t i n g s i z e i n m m Diagram 3: Bore setting sizes for bearing seats Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 111 112 T o l e r a n c e s 3. General information The basi c tol erances and di mensi ons stated above can onl y be sustai nabl y mai ntai ned under normal climatic conditions (23°C/50% rel. humidity). If the environmental conditions differ, they must be consi dered by appl yi ng the respecti ve correcti on factors. These can be found for the specific cases in the previous chapters. 3.1 Dimensional and volume changes under the influence of temperature In general it can be said that elongation caused by temperature is approx. 0.1% per 10 K tempe- rature change. In addition, in the case of polyamides, due to the absorption of moisture a change in volume of 0.15 – 0.20% per 1% water absorbed must be considered. Considering the material-specific coefficient of elongation, the expected elongation and volume changes due to fluctuating temperatures can be calculated approximately. Hence, the expected elongation is Dl = I . a . (u 1 – u 2 ) [mm] where DI = expected elongation l = original length in mm a = material-specific coefficient of elongation u 1 = installation temperature in °C u 2 = operating temperature in °C The expected change i n vol ume i s cal cul ated – wi th the assumpti on that the el ongati on i s not hindered in any direction – from: DV = V . b . (u 2 – u 1 ) [mm 3 ] and b = 3 . a where DV = expected change in volume V = original volume in mm 3 a = material-specific coefficient of elongation b = material-specific coefficient of volume expansion u 1 = installation temperature in °C u 2 = operating temperature in °C The material-specific coefficients of elongation can be found in Table 10. Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 112 113 T o l e r a n c e s Material Abbreviation Coefficient of elongation a 10 -5 . K -1 Polyamide 6 cast PA 6 G 7 Polyamide 6 cast CC PA 6 G-CC 8 Oilamid PA 6 G + Öl 7 Calaumid 612 PA 6/12 G 8 Calaumid 1200 PA 12 G 10 Polyamide 6 PA 6 9 Polyamide 6 + 30% glass fibre PA 6 GF30 3 Polyamide 66 PA 66 10 Polyamide 12 PA 12 12 Polyacetal POM -C 10 Polyacetal GF-filled POM -C-GF30 2,5 Polyethylene terephthalate PET 7 Polyethylene terephthalate + lubricant additive PET -GL 8 Polytetrafluoroethylene PTFE 19 Polytetrafluoroethylene + 25% glass fibre PTFE -GF25 13 Polytetrafluoroethylene + 25% coal PTFE -K25 11 Polytetrafluoroethylene + 40% bronze PTFE -B40 10 Polyethylene 500 PE-HMW 18 Polyethylene 1000 PE-UHMW 18 Polyetheretherketone PEEK 4 Polyetheretherketone modified PEEK-GL 3 Polysulphone PSU 6 Polyether imide PEI 6 Table 10: Linear coefficients of elongation of various plastics 3.2 Geometric shapes The geometri c rel ati onshi ps of a workpi ece can cause changes i n di mensi ons and shape after the machi ni ng process. Therefore, ei ther the geometri c shape has to be changed or the recom- mended tolerance series for workpieces with extreme geometric shape and wall thickness relati- onships, e.g. extreme one-sided machining, extremely thin walls, extreme wall thickness differen- ces, must be adapted accordingly. If there is any uncertainty in regard to the definition of shape, dimension or position tolerances, we would be pleased to assist. 3.3 Measuring technology It i s very di ffi cul t to measure narrow tol erances i n pl asti c workpi eces, especi al l y i n thi n-wal l ed parts. The pressure exerted on the workpiece by the measuring instrument can deform the plastic part, or the l ow coeffi ci ent of fri cti on of pl asti cs can di stort the starti ng torque of mi crometer gauges. Thi s i nevi tabl y l eads to i ncorrect measured val ues. Therefore i t i s recommended that contactless measuring systems are used. Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 113 Machining guidelines Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 114 M a c h i n i n g g u i d e l i n e s Machining guidelines 1. Machining of thermoplastics With the increasing variety of engineering plastics and the resul ti ng appl i cati ons, desi gn engi neers now have many new hori zons that were previ ousl y unthi nkabl e with conventional materials. In many cases, in addition to materi al l i mi tati ons, the onl y other l i mi t to desi gn possi bi l i ti es are the restri cti ons i mposed by the manu- facturing process. Particularly if large volume parts are required from cast polyamides and polyacetal (POM) or pol yethyl ene terephthal ate (PET), manufacturi ng processes such as i njecti on moul di ng cannot be used. Thi s appl i es equal l y to compl ex parts that requi re machining from all sides with narrow tolerances. In thi s area, machi ni ng has proven to be the best method. Highly precise parts and large components can be manufactured especi al l y economi cal l y i n smal l and medium batches by machining. For the manufacture of hi gh qual i ty products, certai n speci fi c features of pl asti cs must be consi dered when machines and tools are being chosen and used. 1.1 Machining equipment/tools No special machines or processes are required for machining. The machines that are normally used in the woodworking and metal industries with HSS tools (high performance superspeed steel) or hard metal tools can be used. The only thing to consider is that when a circular saw is used to cut plastic, hard metallic saw blades must be used. The group of glass fibre reinforced plastics is a special case. While it is possible to machine them with hard metal tools, it is very difficult to achieve economic results due to the short service life of the tools. In this case it is advisable to use diamond tipped tools, which are much more expensive than conventional tools but have a much longer service life. 1.2 Machining and clamping the workpiece Pl asti cs have l ower thermal conductance properti es than metal s, as wel l as a l ower modul us of el asti ci ty. If not handl ed properl y, the workpi ece can become extremel y warm and thermal expansi on can occur. Hi gh cl ampi ng pressures and bl unt tool s cause deformati on duri ng machining. Dimensional and shape deviations outside the tolerance range are the consequence. Satisfactory results are only achievable if several material-specific guidelines are considered when machining plastics. In detail, these guidelines are: • The highest possible cutting speed should be chosen. • Optimum chip removal must be ensured so that the chips are not drawn in by the tool. • The tools that are used must be very sharp. Blunt tools can cause extreme heat, which results in deformation and thermal expansion. • The cl ampi ng pressures must not be too hi gh as thi s woul d resul t i n deformati on of the work- piece and the clamping tool would leave marks in the workpiece. • Because of the l ow degree of sti ffness, the workpi ece must be adequatel y supported on the machine table and should lie as flat as possible. Fig. 1: Complex component made from POM 115 Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 115 • Perfect, hi gh-qual i ty surfaces can onl y be obtai ned when the machi nes operate wi th l ow vibration. If these guidelines are complied with, it is possible to obtain narrow, plastic-oriented tolerances with a high level of reproducibility without difficulty. 1.3 Cooling during machining As a rule it is not absolutely necessary to cool the workpiece during machining. If cooling is to be applied it is recommended that compressed air is used. This has the advantage that in addition to the cool i ng effect, the chi ps are removed from the worki ng area and cannot be drawn i nto the workpiece or tool. Conventional drilling emulsions can also be used for cooling and are especially recommended for deep bores and cutting threads. In addition, it is possible to achieve higher rates of forward feed and consequently, shorter running times. However, if using drilling emulsions, attention should be paid that these are completely removed after machining. This prevents oily components causing problems in subsequent processes such as bondi ng or pai nti ng, especi al l y i n the case of pol yami des where the water i n the emul si on can cause changes in the components through absorption. 2. Parameters for the individual machining processes 2.1 Sawing Pl asti cs can be sawn wi th a band saw or a ci rcul ar saw. The choi ce depends on the shape of the semi -fi ni shed product. The use of a band saw i s parti cul arl y recommended when a “ support groove” (prism) is used to cut rods and tubes and also has the advantage that the built up heat is dissipated via the long saw blade. However, the teeth of the blade must be set adequately so that the blade cannot jam. Ci rcul ar saws, on the other hand, are mai nl y used for cutti ng sheets and bl ocks wi th strai ght edges. Here, attenti on shoul d be pai d that the feed rate i s adequate so that chi ps are removed, that the saw bl ade does not jam and that the pl asti c does not overheat at the poi nt where i t i s being cut. Table 1 contains guiding values for the cutting geometry of the saw blades. PA, PE, POM, PET, PVDF, PVC Band saw Circular saw a = Clearance angle (°) 30 - 40 10 - 15 g = Effective cutting angle (°) 0 - 8 0 - 10 v = Cutting speed m/min 200 - 1000 1000 - 3500 t = Number of teeth 3 - 5 per inch 24 - 80 t α γ Table 1: Tool geometry for saw blades M a c h i n i n g g u i d e l i n e s 116 Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 116 117 M a c h i n i n g g u i d e l i n e s 2.2 Milling Mi l l i ng on conventi onal machi ni ng centres i s unprobl emati c. Wi th a hi gh cutti ng speed and medi um feed rate i t i s possi bl e to achi eve hi gh l evel s of machi ni ng performance wi th good surface quality and accuracy. In regard to the cutter geometry, we recommend the values given in Table 2. 2.3 Turning on a lathe Since most plastics produce unbroken chips, it is important to ensure that the chips are removed, as they would otherwise catch and revolve with the part being turned on the lathe. In addition, because of the low degree of stiffness of plastics, there is a great danger of longer parts sagging, and i t i s thus advi sabl e to use a steady rest. The val ues gi ven i n Tabl e 3 appl y to the cutter geometry. 2.4 Drilling Dri l l hol es can be made wi th a conventi onal HSS dri l l . If deep hol es are bei ng dri l l ed, i t must be ensured that the chips are removed, as otherwise the plastic on the walls of the hole will heat to the point of melting and the drill will “ clog” . This especially applies to deep holes. For drilled holes in thin-walled workpieces, it is advisable to choose a high drilling speed and, if applicable, a neutral (0°) effective cutting angle. This prevents the drill from sticking in the work- pi ece and hi nders the associ ated stri ppi ng of the hol e or the workpi ece bei ng drawn up by the drill. Table 4 contains the recommended values for cutting edge geometry. PA, PE PTFE POM, PET PVDF, PVC a = Clearance angle (°) 5 - 15 10 - 15 5 - 10 g = Effective cutting angle (°) 0 - 15 15 - 20 0 - 10 v = Cutting speed m/min up to 1000 up to 600 up to 1000 s 2 = Forward feed/tooth up to 0,5 up to 0,5 up to 0,5 Angle of twist in ° 0 - 40 0 - 40 0 - 40 α γ PA, PE PTFE POM,PET PVDF, PVC a = Clearance angle (°) 5 - 15 10 - 15 5 - 10 g = Effective cutting angle (°) 0 - 10 15 - 20 0 - 5 x = Setting angle (°) 0 - 45 0 - 45 0 - 45 v = Cutting speed m/min 200 - 500 100 - 300 200 - 500 s = Forward feed mm/rev. 0,05 - 0,5 0,05 - 0,3 0,05 - 0,5 a = Rate of cut mm up to 15 up to 15 up to 15 The point radius should be at least 0.5mm α γ χ a Table 2: Tool geometry for milling cutters Table 3: Tool geometry for lathe chisels Konstr. Kunststoffe engl.7/04 27.10.2004 7:40 Uhr Seite 117 118 M a c h i n i n g g u i d e l i n e s 2.5 Drilling large diameters in sections of round rod When drilling, high temperatures build up on the cutting edges, especially with highly crystalline materials such as PA 6 G, which cannot be adequately dissipated because of the good insulation properti es of the pl asti cs. The heat causes an i nternal expansi on i n the materi al , whi ch i n turn causes compressi ve stress i n the i nsi de of the rod secti on. Thi s stress can be so hi gh that the rod tears and splits. This can be avoided to a great extent if the material is machined correctly. It i s advi sabl e to pre-dri l l the hol e and compl ete i t wi th a ri ght si de tool . The pre-dri l l ed hol es should not exceed 35 mm in diameter. Drilled holes in long sections of rod must only be made from one side, as otherwise an unfavou- rabl e stress rel ati onshi p i s created when the dri l l ed hol es meet i n the mi ddl e of the bl ank rod, which can lead to the rod section cracking. In extreme cases i t may be necessary to heat the bl ank to approx. 120 – 150°C and pre-dri l l i t i n this condition. The hole can then be completed when the rod has cooled down and when an even temperature has set in throughout the blank. If these machi ni ng gui del i nes are compl i ed wi th, i t i s qui te possi bl e to manufacture compl ex products from engi neeri ng pl asti cs usi ng machi ni ng processes even when the hi ghest demands are placed on quality, accuracy and functionality. γ 1 α ϕ PA, PE PTFE POM,PET PVDF, PVC a = Clearance angle (°) 10 - 15 10 - 15 5 - 10 g 1 = Effective cutting angle (°) 3 - 5 3 - 5 3 - 5 J = Point angle (°) 60 - 90 130 60 - 90 v = Cutting speed m/min 50 - 100 100 - 300 50 - 100 s = Forward feed mm/rev. 0,1 - 0,5 0,1 - 0,3 0,1 - 0,3 The angle of twist of the drill should be at least 12 - 16° Table 4: Tool geometry for drills Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 118 Mechanical values and chemical resistances of plastics Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 119 120 M e c h a n i c a l v a l u e s Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 120 121 M e c h a n i c a l v a l u e s Parameter Condition Footnote Impact resistance DIN 53 453 Measured with an impact pendulum testing machine 0.1 DIN 51 222 1 Creep stress DIN 53 444 Stress that leads to 1% overall expansion after 1,000 h 2 Coefficient of sliding friction Hardened and ground against steel, P = 0.05 MPa, V = 0.6 m/s, t = 60° in vicinity of running area 3 Linear coefficient of elongation For temperature range from +23°C up to +60°C 4 Temperature range Experience values, determined on finished parts without load in warmed air, dependent on the type and form of heat, short-term = max. 1 h, long-term = months 5 Dielectric strength DIN 53 483 at 10 6 Hz 6 Colours POM-C natural = white PET-natural = white PVDF-natural = white to ivory (translucent) PE-natural = white PP-H natural = white (translucent) PP-H grey ≈ RAL 7032 PVC-grey ≈ RAL 7011 PEEK-natural ≈ RAL 7032 PSU-natural = honey yellow (translucent) PEI-natural = amber (translucent) 7 Units and abbreviations o.B. = without breakage 1 MPa = 1 N/mm 2 1 g/cm 3 = 1,000kg/m 3 1 kV/mm = 1MV/m none Information and conditions concerning the table “Mechanical values” The i nformati on i n the l i st i s i ntended to provi de an overvi ew of the properti es of our products and to allow a quick comparison of materials. They represent our present standard of knowledge and do not cl ai m to be compl ete. Because of the hi gh l evel of dependence on envi ronmental i nfl uences and processi ng methods, the val ues gi ven here shoul d onl y be regarded as standard values. In no way do they represent a legally binding assurance in regard to the properties of our products nor to thei r sui tabi l i ty for speci fi c appl i cati ons. Al l the val ues stated here were deter- mined from average values resulting from many individual measurements and refer to a tempe- rature of 23°C and 50% RH. For speci fi c appl i cati ons, we recommend that the sui tabi l i ty of the materi al s be fi rst tested by practical experiments. The condi ti ons under whi ch the i ndi vi dual val ues were determi ned, and any speci al features i n regard to these values, are contained in the following list with the respective footnotes: Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 121 122 Physical Material Guiding Values D e n s i t y D I N 5 3 4 7 9 Y i e l d s t r e s s D I N 5 3 4 5 5 E l o n g a t i o n a t b r e a k D I N 5 3 4 5 5 M o d u l u s o f e l a s t i c i t y r e s u l t i n g f r o m t e n s i l e t e s t D I N 5 3 4 5 7 M o d u l u s o f e l a s t i c i t y r e s u l t i n g f r o m b e n d i n g t e s t D I N 5 3 4 5 7 F l e x u r a l s t r e n g t h D I N 5 3 4 5 2 I m p a c t s t r e n g t h D I N 5 3 4 5 3 N o t c h e d - b a r i m p a c t s t r e n g t h D I N 5 3 4 5 3 B a l l i n d e n t a t i o n h a r d n e s s H 3 5 8 / 3 0 D I N 5 3 4 5 6 C r e e p r a t e s t r e s s a t 1 % e l o n g a t i o n D I N 5 3 4 4 4 2 ) No. Material Abbrev. Colours Test specimen (standard) condition 1 Polyamide 6 Cast PA 6 G natural/black/ dry blue humid 2 Polyamide 6 Cast + MoS 2 PA 6 G + MoS 2 black dry humid 3 Polyamid 6 Cast-CC PA 6 G-CC natural/black dry 4 Polyamide 6 Cast PA 6 G-WS black dry Heat stabilised humid 5 Oilamid ® PA 6 G + Öl yellow/black/ dry natural humid 6 Calaumid ® 612 PA 6 /12 G natural dry (impact resistant) humid 7 Calaumid ® 1200 PA 12 G natural dry humid 8 Polyamide 6 PA 6 natural/black dry humid 9 Polyamide 66 PA 66 natural/black dry humid 10 Polyamide 6 + Glass fibre PA 6 + GF 30 black dry humid 11 Polyamid 66 + Glass fibre PA 66 + GF 30 black dry humid 12 Polyamide 12 PA 12 natural dry 13 Polyacetal POM - C natural 7) /black dry Copolymer 14 Polyacetal POM - C GF 30 black dry Copolymer + Glass fibre 15 Polyethylen- PET natural 7) dry terephtalat 16 Polyethylenterephtalat/ PET-GL lightgrey dry lubricant additive 17 Polytetrafluoro- PTFE white dry ethylen 18 Polytetrafluoro- PTFE + 25% grey dry ethylen /Glass fibre Glass fibre 19 Polytetrafluoro- PTFE + 25% black dry ethylen /Carbon Carbon 20 Polytetrafluoro- PTFE + 40% brown dry ethylen /Brass Brass 21 Polyvinyl- PVDF natural 7) dry difluorid 22 Polyethylene 300 PE - HD natural 7) dry black 23 Polyethylene 500 PE - HMW natural 7) dry black/green 24 Polyethylene 1000 PE - UHMW natural 7) dry black/green 25 Polypropylene PP - H natural 7) /grey 7) dry 26 Polyvinylchloride PVC - U grey 7) /black/ dry red/white 27 Polycarbonate PC transparent dry 28 Polyether- PEEK natural 7) dry ketone black 29 Polyetherketone PEEK - GL black dry (modified) 30 Polysulfone PSU natural 7) dry 31 Polyether amide PEI natural 7) dry 1 2 3 4 5 6 7 8 9 10 r j zS e zR E t E B3 j bB a cU a cN H K j 1/1000 g/cm 3 MPa % MPa MPa MPa kJ/m 2 kJ/m 2 MPa MPa 1,15 80 40 3.100 3.400 140 o. B. 14 160 17 60 100 1.800 2.000 60 115 125 1,15 85 40 3.100 3.300 130 o. B. 15 150 17 60 100 1.800 2.000 50 115 115 1,15 71 140 2.800 2.700 97 o. B. - 125 - 1,15 90 30 2.500 3.000 120 o. B. 14 170 17 60 80 2.000 2.300 40 112 130 1,14 80 50 2.500 2.800 135 o. B. 15 140 17 55 120 1.500 1.800 55 115 100 1,12 80 55 2.500 2.800 135 o. B. 112 140 115 55 120 1.500 1.800 55 o. B. 100 1,03 60 55 2.200 2.400 90 o. B. 115 - 111 50 120 1.800 - - 100 1,14 70 50 2.700 2.500 130 o. B. 13 160 18 45 180 1.800 1.400 40 o. B. 70 1,14 85 30 3.000 2.900 135 o. B. 13 170 18 65 150 1.900 1.200 60 115 100 1,40 180 4 9.000 8.300 240 55 6 220 35 120 7 6.400 4.800 40 15 150 1,29 160 5 11.000 - - 50 6 240 40 1,02 50 1200 1.800 1.500 60 o. B. 115 100 14 1,41 65 40 3.000 2.900 115 o. B. 110 150 13 1,59 125 3 9.300 9.000 150 30 5 210 40 1,38 80 40 3.000 2.600 125 o. B. 14 140 13 1,43 75 5 2.200 - - 30 2 - - 2,18 25 380 750 540 6 o. B. 16 30 1,5 2,23 15 280 1.500 1.320 4 o. B. 12 31 - 2,12 15 180 - 1.275 9 - 8 38 - 3,74 14 140 1.400 1.375 8 - 11 39 - 1,78 56 22 2.000 2.000 75 o. B. 115 120 3 0,95 22 300 800 800 32 o. B. 12 40 3 0,95 28 300 850 850 40 o. B. 50 45 3 0,94 22 350 800 800 27 o. B. o. B. 40 - 0,91 32 70 1.400 1.400 45 o. B. 7 70 4 1,42 58 15 3.000 - 82 o. B. 4 130 - 1,20 60 80 2.300 2.200 95 o. B. 125 100 40 1,32 95 45 3.600 4.100 160 o. B. 7 230 - 1,48 118 3 8.100 10.000 210 25 2,5 270 - 1,24 75 150 2.500 2.700 106 o. B. 4 150 22 1,27 105 150 3.100 3.300 145 o. B. - 165 - All listed values were obtained as average values from a multitude of individual measures, and are related to a temperature of 23 °C and 50% RF. Mechanical values As of 9/2004 Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 122 123 S l i d i n g f r i c t i o n c o e f f i c i e n t a g a i n i s t s t e e l 3 ) S l i d i n g w e a r a g a i n s t s t e e l ( d r y r u n n i n g ) 3 ) M e l t i n g t e m p e r a t u r e D I N 5 3 7 3 6 T h e r m a l c o n d u c t i v i t y D I N 5 2 6 1 2 S p e c i f i c t h e r m a l c a p a c i t y C o e f f i c i e n t o f l i n e a r e x p a n s i o n 4 ) O p e r a t i n g t e m p e r a t u r e r a n g e , l o n g - t e r m 5 ) O p e r a t i n g t e m p e r a t u r e r a n g e , s h o r t - t e r m 5 ) F i r e b e h a v i o u r a f t e r U L D i e l e c t r i c c o n s t a n t 6 ) D I N 5 3 4 8 3 D i e l e c t r i c l o s s f a c t o r 6 ) D I N 5 3 4 8 3 S p e c i f i c v o l u m e r e s i s t a n c e D I N 5 3 4 8 2 S u r f a c e r e s i s t a n c e D I N 5 3 4 8 2 D i e l e c t r i c s t r e n g t h D I N 5 3 4 8 1 C r e e p c u r r e n t r e s i s t a n c e D I N 5 3 4 8 0 M o i s t u r e a b s o r p t i o n i n n a t u r a l r u b b e r u n t i l s a t u r a t e d D I N 5 3 7 1 5 W a t e r a b s o r p t i o n u n t i l s a t u r a t e d D I N 5 3 4 9 5 11 12 13 14 15 0 m V T m l c - mm/km °C W/(K·m) J/(g·K) 0,36 0,10 + 220 0,23 1,7 0,42 0,32 0,10 + 220 0,23 1,7 0,37 0,36 - + 220 0,23 1,7 0,42 0,36 0,10 + 220 0,23 1,7 0,42 0,18 0,05 + 220 0,23 1,7 0,23 0,36 0,12 + 220 0,23 1,7 0,42 0,40 - + 190 0,23 1,7 0,38 0,23 + 218 0,23 1,7 0,42 0,35 0,10 + 265 0,23 1,7 0,42 0,46 - + 220 0,25 1,5 0,52 0,45 - + 255 0,30 1,5 0,32 0,80 + 178 0,30 2,09 0,38 0,32 8,90 + 168 0,31 1,45 0,50 - + 168 0,40 1,21 0,25 0,35 + 255 0,24 1,1 0,20 0,10 + 255 0,23 - 0,08 21,0 + 327 0,23 1 0,14 1,30 + 327 0,41 - 0,12 1,0 + 327 0,70 - 0,14 0,50 + 327 0,70 - 0,30 - + 178 0,19 0,96 0,29 7,4 + 128 0,38 1,86 0,29 1,0 + 133 0,38 1,88 0,29 0,45 + 133 0,38 1,84 0,35 11,0 + 162 0,22 1,7 0,60 56,0 - 0,159 1,05 0,55 22,0 + 230 0,21 1,17 0,34 - + 340 0,25 1,06 0,11 - + 340 0,24 - 0,40 - - 0,26 1 - - - 0,22 - 16 17 18 19 20 21 22 23 24 25 26 27 28 a - - - e R tan d r D R o E d - w(H 2 O) W S - 10 -5 ·K -1 °C °C - - - Ω· cm Ω kV/mm - % % 7 - 8 - 40 + 170 HB 3,7 0,03 10 15 10 13 50 KA 3c 2,2 6,5 hard, pressure and abrasion resistant + 105 10 12 10 12 20 KA 3b can be produced in largest dimensions 7 - 8 - 40 + 160 HB 3,7 0,03 10 15 10 13 50 KA 3c 2,2 6,5 as PA 6 G, except + 105 10 12 10 12 20 KA 3b increased cristallinity 8 - 9 - 40 + 150 HB 3,7 0,03 10 15 10 13 50 KA 3c 2,5 7,5 higher impact strength than PA 6 G + 90 10 12 10 12 20 KA 3b 7 - 8 - 40 +180 HB 3,7 0,03 10 15 10 13 50 KA 3c 2,2 7 as PA 6 G, except heat + 105 10 12 10 12 20 KA 3b ageing resistant 7 - 8 - 40 + 160 HB 3,7 0,03 10 15 10 13 50 KA 3c 1,8 5,5 highest abrasion resistance, + 105 10 12 10 12 20 KA 3b low sliding friction 7 - 8 - 40 + 160 HB 3,7 0,03 10 15 10 13 50 KA 3c 2,2 7 as PA 6G, except set for + 105 10 12 10 12 20 KA 3b high impact strength 10 - 11 - 60 + 150 HB 3,7 0,03 10 15 10 13 50 KA 3c 0,9 1,4 low water absorption, very good +110 10 12 10 12 20 KA 3b long-term rupture strength 8 - 9 -30 + 140 HB 3,7 0,031 10 15 10 13 50 KA 3c 3,0 10,0 tough, good + 100 7 0,3 10 12 10 10 20 KA 3b vibration damping 9 - 10 - 30 + 150 HB 3,2 0,025 10 15 10 12 50 KA 3b 2,5 9,0 high abrasion resistance + 100 5,0 0,2 10 12 10 10 20 CTI 600 (similar to PA 6 G) 2 - 3 - 30 + 180 HB 3,7 0,021 10 15 10 14 60 KA 3c 2,1 6,3 high strength, low + 120 7,0 0,2 10 13 10 12 30 KA 3a thermal expansion 2 - 3 - 30 +180 HB 3,7 0,02 10 14 10 13 60 CTI 475 1,7 5,5 high strength, low + 120 thermal expansion 11 - 12 - 70 + 140 HB 3,1 0,03 2 x 10 15 10 13 30 KA 3b 0,8 1,5 tough, hydrolysis resistance + 70 3,6 0,06 CTI 600 negligible moisture absorption 9 - 10 - 30 + 140 HB 3,9 0,003 10 15 10 13 70 KA 3c 0,2 0,8 high strength, impact resistance + 100 KC1600 low creep behaviour 3 - 4 - 30 + 140 HB 4,8 0,005 10 15 10 13 65 KA 3c 0,17 0,6 high strength, + 110 KC1600 low thermal expansion 7 - 8 - 20 + 160 HB 3,6 0,008 10 16 10 14 60 KC 350 0,25 0,5 tough, hard, negligible cold flow, + 100 dimensionally stable 7 - 8 - 20 + 160 HB 3,6 0,008 10 16 10 14 - - 0,2 0,4 as PET, plus highest + 110 wear resistance 18 - 20 - 200 + 280 V - 0 2,1 0,0005 10 18 10 17 40 KA 3c !0,01 !0,01 high chemical resistance, + 260 KB1600 low strength 12 - 13 - 200 + 280 V - 0 2,85 0,0028 10 16 10 16 13 - !0,01 !0,01 as PTFE, except + 260 higher strength 10 - 11 - 200 + 280 V - 0 - - 10 3 10 3 2,8 - !0,01 !0,01 as PTFE, except + 260 lower wear due to sliding friction 9 - 10 - 200 + 280 V - 0 - - 10 8 10 8 - - !0,01 !0,01 higher strength than PTFE, + 260 but chemically less resistant 13 - 40 + 160 V - 0 8,0 0,165 5 x 10 14 10 13 25 CTI 600 !0,04 !0,04 resistant to UV-, b- and + 140 g-Radiation, resistant to abrasion 18 - 50 + 80 HB 2,4 0,004 110 16 10 14 47 KA 3c !0,01 !0,01 high chemical resistance + 50 low density, high abrasion 18 - 100 + 80 HB 2,9 0,0002 110 16 10 14 44 KA 3c !0,01 !0,01 as PE-HD, but far more + 50 KC1600 abrasion resistant 18 - 260 + 80 HB 3,0 0,0004 110 16 10 14 44 KA 3c !0,01 !0,01 as PE-HMW, but more abrasion + 50 KC1600 resistant at low friction values 16 0 + 100 HB 2,25 0,00033 110 16 10 14 52 KA 3c !0,01 !0,01 as PE-HD, but higher + 80 thermal strength 8 0 + 70 V - 0 3,3 0,025 10 16 10 13 39 KA 3b !0,01 !0,01 good chemical resistance + 50 hard and brittle 6 - 7 - 40 + 140 V - 2 3,0 0,006 10 17 10 15 32 KA 1 0,20 0,36 transparent, impact resistance, + 110 low cold flow 4 - 5 -40 + 310 V - 0 3,2 0,002 10 16 10 16 24 CTI 150 0,20 0,45 high temperature resistance, hydrolisis + 250 dimensionally stable 3 -40 + 310 V - 0 - - 10 5 - 24,5 - 0,14 0,3 as PEEK, except higher pv-values + 250 better sliding properties 5 - 6 - 40 + 180 V - 0 3,0 0,002 10 17 10 17 30 KA 1 0,40 0,80 can be sterilised in steam + 160 CTI 150 hydrolisis resistant, radiation resistant 5 - 6 -40 + 200 V - 0 3,0 0,003 10 18 10 17 33 CTI 175 0,75 1,35 high strength and rigidity + 170 high thermal resistance Specific properties Thermal values Electrical values Miscellaneous data All calculations, designs and technical specifications are merely for information and advice. Legally binding assurances of properties and/or results cannot be taken from this information. We recom- mend carrying out practical tests to establish the suitability of a product for a given application. Subject to errors and changes! Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 123 124 M e c h a n i c a l v a l u e s PA 6 G PA 12 G Oilamid PA 6 PA 66 PA 12 POM - C PET PET - GL PE - HMW PE - UHMW PTFE PEEK Steel St. 37 Stainless steel 1.4301 Stainless steel 1.4571 Brass PA 6 G PA 12 G Oilamid PA 6 PA 66 PA 12 POM - C PET PET - GL PE - HMW PE - UHMW PTFE PEEK Comparison of material costs (volume prices) E-modulus from tensile test in MPa (short-term value) Permissible yield stress in MPa (short-term value) 0 500 1000 1500 2000 2500 3000 3500 4000 PA 6 G PA 12 G Oilamid PA 6 PA 66 PA 12 POM - C PET PET - GL PE - HMW PE - UHMW PTFE PEEK 0 10 20 30 40 50 60 70 80 90 100 3600 750 850 800 2200 3000 3000 1800 3000 2700 2500 2200 3100 95 25 22 28 75 80 65 50 85 70 80 60 80 Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 124 125 M e c h a n i c a l v a l u e s Flexural strength in MPa (short-term value) PA 6 G PA 12 G Oilamid PA 6 PA 66 PA 12 POM - C PET PET - GL PE - HMW PE - UHMW PTFE PEEK 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 Long term service temperature in °C (in air without static stress) PA 6 G PA 12 G Oilamid PA 6 PA 66 PA 12 POM - C PET PET - GL PE - HMW PE - UHMW PTFE PEEK 0 25 50 75 100 125 150 175 200 225 250 275 Coefficient of sliding friction against steel (hardened and ground, P = 0,05 MPa, v = 0,6 m/s, t = 60 °C (in the vicinity of the running surface) PA 6 G PA 12 G Oilamid PA 6 PA 66 PA 12 POM - C PET PET - GL PE - HMW PE - UHMW PTFE PEEK 0 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 160 6 27 40 115 125 115 60 135 130 140 90 140 0,34 0,08 0,29 0,29 0,2 0,25 0,32 0,32 0,35 0,38 0,18 0,4 0,36 250 260 80 80 110 100 100 70 100 100 105 110 105 Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 125 126 M e c h a n i c a l v a l u e s Coefficient of linear expansion PA 6 G PA 12 G Oilamid PA 6 PA 66 PA 12 POM - C PET PET - GL PE - HMW PE - UHMW PTFE PEEK 0 1 2 3 4 5 6 7 8 9 10 11 12 13 18 19 (10 -5 · K -1 ) pv guiding values in MPa · m/s (dry running with integrated lubrication v = 0,1 m/s) PA 6 G PA 12 G Oilamid PA 6 PA 66 PA 12 POM - C PET PET - GL PE - HMW PE - UHMW PTFE PEEK 0 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 Water absorption until saturated in % PA 6 G PA 12 G Oilamid PA 6 PA 66 PA 12 POM - C PET PET - GL PE - HMW PE - UHMW PTFE PEEK 0 1 2 3 4 5 6 7 8 9 10 11 19 18 18 4 8 7 10 10 9 7 10 7 12 0,34 0,05 0,08 0,08 0,25 0,15 0,15 0,08 0,13 0,11 0,23 0,13 0,45 <0,01 <0,01 <0,01 0,4 0,5 0,8 1,5 9 10 7 6,5 1,4 0,10 Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 126 127 C h e m i c a l r e s i s t a n c e Information on how to use the list “Chemical resistance” The i nformati on regardi ng chemi cal resi stance i n the fol l owi ng l i st rel ates to experi ments i n which the samples were subjected to the respective media free of external stress and loading. This i s suppl emented by our practi cal experi ence and, i n most cases, many years of usi ng pl asti cs i n contact with these media. Due to the variety of media, this list is just an excerpt of the data that is avai l abl e to us. If the l i st does not contai n the medi um that you use, we woul d be happy to provide information on the resistance of our plastics on request. When using the list, please remember that factors such as: • deviating degrees of purity of the medium • deviating concentration of the medium • temperatures different to those stated • fluctuating temperatures • mechanical stress • part geometries, especially those that lead to thin walls or extreme differences in wall thickness • stresses that are created by machining • mixtures that are made up of different media • combinations of the above factors can have an effect on the chemical resistance. Neverthel ess, i n spi te of bei ng rated as a component wi th »l i mi ted resi stance«, a pl asti c component can still be superior to a metal part and can also be more practical from an economic aspect. In the case of oxidising materials such as nitric acid and polar organic solvents, despite a chemical resi stance agai nst the medi um, i n many thermopl asti cs there i s sti l l a danger of stress cracki ng. Therefore for the manufacture of parts that come into contact with such media, a process should be chosen that creates as little mechanical stress as possible in the workpiece. An alternative is to decrease the stress by annealing the semi-finished products before and during the manufacturing process. Generally it is not possible to forecast the level of resistance against mixtures of different media, even if the plastic is resistant to the individual components of the mixture. Therefore in such a case we recommend that the material is stored and aged with the respective mi xed medi um under the expected envi ronmental condi ti ons. It i s al so i mportant to remember that where parts are to be subjected to two or more media there could be an additional tempe- rature load in the area of immediate contact due to the evolving reaction heat. In spi te of the rati ng »resi stant«, i n certai n cases the surfaces of pl asti cs can become matte or discoloured, and transparent plastics can become opaque when they come into contact with the media. However, the resistance remains intact even after these surface changes. The i nformati on contai ned i n the l i sts corresponds to our present standard of knowl edge and shoul d be regarded as standard val ues. If i n doubt, or i n the case of speci fi c appl i cati ons, we recommend that the material be aged under the expected environmental conditions to test its resistance. Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 127 128 Chemical resistance 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 1 Acetal aldehyde 40 20 + + + + + + + + + + + + + + + 2 Acetamide 50 20 + + + + + + + + + + + + / / + 3 Acetone UV RT + + + + + + + + + + + + o o + 4 Acrylnitrile UV RT + + + + + + + + + + / / / / + 5 Alkyl alkohol UV RT o o o o o o o o o o / / + + + 6 Aluminium chloride 10 RT + + + + + + + + + + o o + + + 7 Formic acid 2 RT o o o o o o o o o o + + + + + 8 Formic acid UV RT L L L L o L L L L o - - o o + 9 Ammonia 10 RT + + + + + + + + + + + + - - + 10 Ammonium hydroxide 30 RT + + + + + + + + + + - - - - + 11 Ammoniumnitrate UV RT + + + + + + + + + + + + + + + 12 Aniline UV RT - - - - o - - - - o o o + + + 13 Anone 100 20 + + + + + + + + + + + / / / + 14 Antimontrichloride 10 RT - - - - - - - - - - / / / / + 15 Benzaldehyde UV RT o o o o o o o o o o + + + + + 16 Petrol, normal HÜ 40 + + + + + + + + + + + + + + + 17 Petrol, super HÜ 40 + + + + + + + + + + + + / / + 18 Benzene UV RT + + + + + + + + + + o o + + + 19 Benzene acid UV RT - - - - + - - - - + o o + + + 20 Benzyl alcohol UV RT o o o o o o o o o o + + + + + 21 Bleaching lye (12,5% AC) HÜ RT - - - - o - - - - o - - + + + 22 Borax WL RT + + + + + + + + + + + + + + + 23 Boric acid 10 RT + + + + + + + + + + + + + + + 24 Hydrobromic acid 10 RT - - - - - - - - - - - o o - + 25 Hydrobromic acid 50 RT - - - - - - - - - - - - - - + 26 Butanol UV RT + + + + + + + + + + + + + + + 27 Butyl acetate UV RT + + + + + + + + + + + + + + + / / / - + + + + - - + + - + / / / - + + + + / / + + / + / / / - + + + + - - + + - - / / / + + + + + / / + + - / / / / / + + + + - + + + o / / / / + + + + + + + + + + + / / / + + + + + + / + + / + / / / + + + + + + - o o - / / / / + + + + + + / o o - - / / / - + + + + / - + + + - / / / + + + + + + + + + - - / / / + + + + o - - + + - / / / / + + + + / / / + + - / / / / + + + + + + / + + / / / / / o + + + + - - + + - - + + + + + + + o + o + + o - + + + + o o o o - o + + o - / / / + o o o o - - + + - - / / / + + + + + + - + + / / / / / + + + + + / - + + o - / / / + + + + + + - + + - + / / / + + + + / / + + + / / / / / + + + + + + + + + + + / / / + + + + + + / + + + / / / / + + + + + + / o o / / / / / + + + + + + + + + o + / / / + + + + / / - + + - o C o n c e n t r a t i o n % T e m p e r a t u r e ° C P o l y a m i d e 6 C a s t P A 6 G P o l y a m i d e 6 C a s t , h e a t s t a b i l i s e d P A 6 G - W S P o l y a m i d e 6 C a s t / M O S P A 6 G + M o S 2 C a l a u m i d ® 6 1 2 P A 6 / 1 2 G C a l a u m i d ® 1 2 0 0 P A 1 2 G O i l a m i d ® P A 6 G + Ö l P o l y a m i d e 6 P A 6 P o l y a m i d e 6 / G l a s s f i b r e P A 6 + G F 3 0 P o l y a m i d e 6 6 P A 6 6 P o l y a m i d e 1 2 P A 1 2 P o l y a c e t a l C o p o l y m e r P O M - C P o l y a c e t a l C o p o l y m e r / G l a s s f i b r e P O M - C - G F 3 0 P o l y e t h y l e n e t e r e p h t a l a t P E T P o l y e t h y l e n e t e r e p h t a l a t e / l u b r i c a n t a d d . P E T - G L P o l y t e t r a f l u o r o e t h y l e n P T F E P o l y t e t r a f l u o r o e t h y l e n / G l a s s f i b r e P T F E + G F 2 5 % G l a s s f i b r e P o l y t e t r a f l u o r o e t h y l e n / C a r b o n P T F E + 2 5 % C a r b o n P o l y t e t r a f l u o r o e t h y l e n / B r a s s P T F E + 4 0 % B r a s s P o l y v i n y l d i f l u o r i d P V D F P o l y e t h y l e n e 3 0 0 P E - H D P o l y e t h y l e n e 5 0 0 P E - H M W P o l y e t h y l e n e 1 0 0 0 P E - U H M W P o l y p r o p y l e n e P P - H P o l y v i n y l c h l o r i d e P V C - U P o l y c a r b o n a t e P C P o l y e t h e r k e t o n e P E E K P o l y e t h e r k e t o n e m o d i f i e d P E E K - G L P o l y s u l f o n e P S U P o l y e t h e r a m i d e P E I UV = undiluted WL = aqueous solution GL = saturated solution HÜ = commercial quality RT = room temperature + = resistant o = limited resistant - = not resistant L = soluble / = not tested As of 9/2004 Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 128 129 Chemical resistance 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 + o + + + + + + + + + / / / + o + + / / + + + + + / / / / / + + + + + + + + + / / / - L + + L - o o o o + / / / / / + + / / + + + + + / / / - L + + L - o o o o + / / / + o + + + + + + + + + / / / / o + + / + o o o o + / / / / o + + o + + + + + + / / / - o + + o + + + + + + / / / / L + + - + + + + + o / / / o + + + - / / o o o o / / / - L + + - - o o o o + / / / / / + + / - o - - - + / / / + - + + + + + + + + + / / / + - + + + + + + + + + / / / / / + + / + + + + + o / / / + + + + + + + + + + + / / / + + + + + + + + + + + / / / + + + + o + + + + + + / / / - - + + - o + + + + + / / / - - + + - - o o o o o / / / + o + + - - o o o o + / / / o - L L - + + + + + + / / / - - + + + + + + + + + / / / + o + + - + + + + + + / / / + + + + - + + + + + / / / / P o l y e t h e r a m i d e P E I P o l y s u l f o n e P S U P o l y e t h e r k e t o n e / m o d i f i e d P E E K - G L P o l y e t h e r k e t o n e P E E K P o l y c a r b o n a t e P C P o l y v i n y l c h l o r i d e P V C - U P o l y p r o p y l e n e P P - H P o l y e t h y l e n e 1 0 0 0 P E - U H M W P o l y e t h y l e n e 5 0 0 P E - H M W P o l y e t h y l e n e 3 0 0 P E - H D P o l y v i n y l d i f l u o r i d e P V D F P o l y t e t r a f l u o r o e t h y l e n e / B r a s s P T F E + 4 0 % B r a s s P o l y t e t r a f l u o r o e t h y l e n e / C a r b o n P T F E + 2 5 % C a r b o n P o l y t e t r a f l u o r o e t h y l e n e / G l a s s f i b r e P T F E + G F 2 5 % G l a s s f i b r e P o l y t e t r a f l u o r o e t h y l e n e P T F E P o l y e t h y l e n e t e r e p h t a l a t e / l u b r i c a n t a d d . P E T - G L P o l y e t h y l e n e t e r e p h t a l a t P E T P o l y a c e t a l C o p o l y m e r / G l a s s f i b r e P O M - C - G F 3 0 P o l y a c e t a l - C o p o l y m e r P O M - C P o l y a m i d e 1 2 P A 1 2 P o l y a m i d e 6 6 P A 6 6 P o l y a m i d e 6 / G l a s s f i b r e P A 6 + G F 3 0 P o l y a m i d 6 P A 6 O i l a m i d ® P A 6 G + Ö l C a l a u m i d ® 1 2 0 0 P A 1 2 G C a l a u m i d ® 6 1 2 P A 6 / 1 2 G P o l y a m i d e 6 C a s t / M O S P A 6 G + M o S 2 P o l y a m i d e 6 C a s t , h e a t s t a b i l i s e d P A 6 G - W S P o l y a m i d e 6 C a s t P A 6 G T e m p e r a t u r e ° C C o n c e n t r a t i o n % L = soluble / = not tested RT = room temperature + = resistant o = limited resistant - = not resistant UV = undiluted WL = aqueous solution GL = saturated solution HÜ = commercial quality As of 9/2004 + + + o o + + + + + + + + + + RT 5 Calcium chloride 28 + + + - - - L L L - - - - - - RT 20 ‘’ ‘’ in alcohol 29 + o o - - - - - - - - - - - - RT GL Calcium hypochloride 30 + + + o + + + + + + + + + + + RT UV Chlorbenzene 31 + - - - - - - - - - - - - - - RT UV Chloroacetic acid 32 + - - - - o o o o o o o o o o RT UV Chloroform 33 + + + o o o o o o o o o o o o RT 1 Chromic acid 34 + + + - - - - - - - - - - - - RT 50 Chromic acid 35 + + + + + + + + + + + + + + + RT UV Cyclohexane 36 + + + + + + + + + + + + + + + RT UV Cyclohexanol 37 + - - + + + + + + + + + + + + RT UV Cyclohexanone 38 + + + + + + + + + + + + + + + RT UV Dibutyl phtalate 39 + - - + + + + + + + + + + + + RT UV Dichlorethane 40 + L L L L + + + + + + + + + + RT UV Dichlorethylene 41 + / / o o - - - - - - - - - - RT GL Iron(II)chlorid 42 + / / o o - - - - - - - - - - RT GL Iron(III)chlorid 43 + + + + + + - - - - + - - - - RT HÜ Vinegar 44 + + + + + + + + + + + + + + + RT 5 Acetic acid 45 + + + o o + o o o o + o o o o RT 10 Acetic acid 46 + + + - - o - - - - o - - - - 50 10 Acetic acid 47 + - - - - - - - - - - - - - - RT 95 Acetic acid 48 + - - - - - - - - - - - - - - 50 95 Acetic acid 49 + + + + + + + + + + + + + + + RT UV Ethylether 50 + - - - - L L L L L L L L L L RT WL Hydrofluoric acid 51 + + + + + o o o o o o o o o o RT UV Formaldehyde 52 + + + + + + + + + + + + + + + RT UV Glycerine 53 + + + + + + + + + + + + + + + RT HÜ Fuel 54 Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 129 130 Chemical resistance 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 55 Heptanol UV RT + + + + + + + + + + + + + + + 56 Hexane UV RT + + + + + + + + + + + + + + + 57 Isopropanol UV RT + + + + + + + + + + + + o o + 58 Potash lye 10 RT + + + + + + + + + + + + - - + 59 Potash lye 10 80 + + + + + + + + + + + + - - + 60 Potash lye 50 RT o o o o + o o o o + + + - - + 61 Ketone (aliphatic) UV RT o o o o o o o o o o + + - - + 62 Methanol 50 RT + + + + + + + + + + + o o + + 63 Methanol UV RT + + + + + + + + + + + o o + + 64 Methylene chlorid UV RT - - - - o - - - - o - - - - + 65 Mineral oil HÜ RT + + + + + + + + + + + + + + + 66 Sodium hypochloride 10 RT - - - - - - - - - - - - o o + 67 Sodium lye 10 RT + + + + + + + + + + + + o o + 68 Sodium lye 10 80 - - - - - - - - - - + + - - + 69 Sodium lye 50 RT o o o o o o o o o o + + - - + 70 Sodium lye 50 80 - - - - - - - - - - + + - - + 71 Nitrobenzene UV RT - - - - - - - - - - o o o o + 72 Nitrotoluene UV RT o o o o o o o o o o o o + + + 73 Oxalic acid 10 RT o o o o o o o o o o - - + + + 74 Phenol 90 RT L L L L L L L L L L - - - - + 75 Phenol UV 40 L L L L L L L L L L - - - - + 76 Phenol UV 60 L L L L L L L L L L - - - - + 77 Phenol UV 80 L L L L L L L L L L - - - - + 78 Phosphoric acid 10 RT - - - - - - - - - - + + + + + 79 Phosphoric acid 25 RT - - - - - - - - - - o o + + + 80 Phosphoric acid 85 RT L L L L L L L L L L - - + + + 81 Propanol UV RT + + + + + + + + + + + + + + + / / / + + + + o + + + + o + / / / + + + + + + - + + o + / / / + + + + + + - + + o / / / / + + + + + + - + + o + / / / o - - - + - - + + o - / / / + + + + + + - + + o - / / / / + + + / / / + + / / / / / + + + + + + - + + o + / / / + + + + + + - + + o + / / / + o o o o L - + + L L + + + + + + + + + + + + + + / / / + + + + o + + + + + / / / / o + + + + + o + + + o / / / o o o o + o - + + + - / / / o + + + + + - + + + - / / / o o o o + o - + + + - / / / + + + + + - L + + - - / / / / + + + + - - + + / / / / / + + + + + + + + + + + / / / + + + + + o L + + - - / / / + + + + + - L + + - - / / / o - - - - - L + + - - / / / o - - - - - L + + - - / / / + + + + + + + + + + + / / / + + + + + + + + + + + / / / + + + + + + + + + o - / / / + + + + + + + + + + + C o n z e n t r a t i o n % T e m p e r a t u r e ° C P o l y a m i d e 6 C a s t P A 6 G P o l y a m i d e 6 C a s t , h e a t s t a b i l i s e d P A 6 G - W S P o l y a m i d e 6 C a s t / M O S P A 6 G + M o S 2 C a l a u m i d ® 6 1 2 P A 6 / 1 2 G C a l a u m i d ® 1 2 0 0 P A 1 2 G O i l a m i d ® P A 6 G + Ö l P o l y a m i d e 6 P A 6 P o l y a m i d e 6 / G l a s s f i b r e P A 6 - G F 3 0 P o l y a m i d e 6 6 P A 6 6 P o l y a m i d e 1 2 P A 1 2 P o l y a c e t a l C o p o l y m e r P O M - C P o l y a c e t a l C o p o l y m e r / G l a s s f i b r e P O M - C - G F 3 0 P o l y e t h y l e n t e r e p h t a l a t e P E T P o l y e t h y l e n e t e r e p h t a l a t e / l u b r i c a n t a d d . P E T - G L P o l y t e t r a f l u o r o e t h y l e n e P T F E P o l y t e t r a f l u o r o e t h y l e n e / G l a s s f i b r e P T F E + G F 2 5 % G l a s s f i b r e P o l y t e t r a f l u o r o e t h y l e n e / C a r b o n P T F E + 2 5 % C a r b o n P o l y t e t r a f l u o r o e t h y l e n e / B r a s s P T F E + 4 0 % B r a s s P o l y v i n y l i d i f l u o r i d e P V D F P o l y e t h y l e n e 3 0 0 P E - H D P o l y e t h y l e n e 5 0 0 P E - H M W P o l y e t h y l e n e 1 0 0 0 P E - U H M W P o l y p r o p y l e n e P P - H P o l y v i n y l c h l o r i d e P V C - U P o l y c a r b o n a t e P C P o l y e e t h e r k e t o n e P E E K P o l y e t h e r k e t o n e / m o d i f i e d P E E K - G L P o l y s u l f o n e P S U P o l y e t h e r a m i d e P E I UV = undiluted WL = aqueous solution GL = saturated solution HÜ = commercial quality RT = room temperature + = resistant o = limited resistant - = not resistant L = soluble / = not tested As of 9/2004 Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 130 131 Chemical resistance 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 + + + - - - - - - - - - - - - RT 10 Nitric acid 82 + - - - - - - - - - - - - - - RT 80 Nitric acid 83 + - - - - L L L L L L L L L L RT 50 Nitric acid 84 + - - - - L L L L L L L L L L RT 80 Nitric acid 85 + o o - - - - - - - - - - - - RT 10 Hydrochloric acid 86 + o o - - - - - - - - - - - - RT 20 Hydrochloric acid 87 + - - - - L L L L L L L L L L RT 30 Hydrochloric acid 88 + o o - - - - - - - - - - - - RT 40 Sulphuric acid 89 + o o - - - - - - - - - - - - 60 40 Sulphuric acid 90 + - - - - L L L L L L L L L L RT 96 Sulphuric acid 91 + - - - - L L L L L L L L L L 60 96 Sulphuric acid 92 + + + o o + + + + + + + + + + RT UV Carbon tetrachloride 93 + + + + + + + + + + + + + + + RT UV Tolual 94 + o o o o o o o o o o o o o o RT UV Trichlorethylene 95 + + + + + + + + + + + + + + + RT 10 Hydrogen peroxide 96 + + + + + o - - - - o - - - - RT 20 Hydrogen peroxide 97 + + + o o - - - - - - - - - - RT 30 Hydrogen peroxide 98 + + + - - - - - - - - - - - - 60 30 Hydrogen peroxide 99 + + + + + + + + + + + + + + + RT UV Xylene 100 + + + + + + o o o o + o o o o RT 10 Citric acid 101 + + + - - o o o o o o o o o o 50 10 Citric acid 102 + + + + - + + + + + + / / / / / + + - - - - - - + / / / / + o o - - - - - - + / / / / + o o - - - - - - o / / / + + + + + + + + + + + / / / + + + + + + + + + + + / / / + o + + o + + + + + + / / / + + o o + + + + + + + / / / o o - - o o + + + + + / / / - L L L - + o o o o + / / / - L L L - o - - - - + / / / + + + + - - - - - - + / / / - - + + - - o o o o + / / / - L + + - - o o o o + / / / + + + + + + + + + + + / / / + + + + + + + + + + + / / / + + + + + + + + + + + / / / / / + + / o o o o o / / / / o o + + - - o o o o + / / / + o + + + + + + + + + / / / + o + + / + + + + + + / / / P o l y e t h e r a m i d e P E I P o l y s u l f o n e P S U P o l y e e t h e r k e t o n e m o d i f i e d P E E K - G L P o l y r e t h e r k e t o n e P E E K P o l y c a r b o n a t e P C P o l y v i n y l c h l o r i d e P V C - U P o l y p r o p y l e n e P P - H P o l y e t h y l e n e 1 0 0 0 P E - U H M W P o l y e t h y l e n e 5 0 0 P E - H M W P o l y e t h y l e n e 3 0 0 P E - H D P o l y v i n y l i d i f l u o r i d P V D F P o l y t e t r a f l u o r o e t h y l e n e / B r a s s P T F E + 4 0 % B r a s s P o l y t e t r a f l u o r o e t h y l e n e / C a r b o n P T F E + 2 5 % C a r b o n P o l y t e t r a f l u o r o e t h y l e n e / G l a s s f i b r e P T F E + G F 2 5 % G l a s s f i b r e P o l y t e t r a f l u o r o e t h y l e n e P T F E P o l y e t h y l e n e t e r e p h t a l a t e / l u b r i c a n t a d d . P E T - G L P o l y e t h y l e n e t e r e p h t a l a t e P E T P o l y a c e t a l - C o p o l y m e r / G l a s s f i b r e P O M - C - G F 3 0 P o l y a c e t a l - C o p o l y m e r e P O M - C P o l y a m i d e 1 2 P A 1 2 P o l y a m i d e 6 6 P A 6 6 P o l y a m i d e 6 / G l a s s f i b r e P A 6 + G F 3 0 P o l y a m i d e 6 P A 6 O i l a m i d ® P A 6 G + Ö l C a l a u m i d ® 1 2 0 0 P A 1 2 G C a l a u m i d ® 6 1 2 P A 6 / 1 2 G P o l y a m i d e 6 C a s t / M O S P A 6 G + M o S 2 P o l y a m i d e 6 C a s t , h e a t s t a b i l i s e d P A 6 G - W S P o l y a m i d e 6 C a s t P A 6 G T e m p e r a t u r e ° C C o n c e n t r a t i o n % L = soluble / = not tested RT = room temperature + = resistant o = limited resistant - = not resistant UV = undiluted WL = aqueous solution GL = saturated solution HÜ = commercial quality As of 9/2004 Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 131 Our machining capabilities: • CNC milling machines, workpiece capacity up to max. 2000 x 1000mm • 5-axis CNC milling machines • CNC lathes, chucking capacity up to max. 1560 mm diameter and 2000 mm long • Screw machine lathes up to 100mm diameter spindle swing • CNC automatic lathes up to 100mm diameter spindle swing • Gear cutting machines for gears starting at Module 0,5 • Profile milling (shaping and molding) • Circular saws up to 170mm cutting thickness and 3100mm cutting length • Four-sided planers up to 125mm thickness and 225mm width • Thickness planers up to 230mm thickness and 1000mm width Konstr. Kunststoffe engl.7/04 27.10.2004 7:41 Uhr Seite 132 We process: • Polyamide PA • Polyacetal POM • Polyethylene terephthalate PET • Polyethylene 1000 PE-UHMW • Polyethylene 500 PE-HMW • Polyethylene 300 PE-HD • Polypropylene PP-H • Polyvinyl chloride (hard) PVC-U • Polyvinylidene fluoride PVDF • Polytetrafluoroethylene PTFE • Polyetheretherketone PEEK • Polysulphone PSU • Polyether imide PEI Examples of parts: • Rope sheaves and castors • Guide rollers • Deflection sheaves • Friction bearings • Slider pads • Guide rails • Gear wheels • Sprocket wheels • Spindle nuts • Curved feed tables • Feed tables • Feed screws • Curved guides • Metering disks • Curved disks • Threaded joints • Seals • Inspection glasses • Valve seats • Equipment casings • Bobbins • Vacuum rails/panels • Stripper rails • Punch supports Konstr. Kunststoffe engl.7/04 27.10.2004 7:42 Uhr Seite 133 134 I n f o r m a t i o n o n h o w t o u s e t h i s d o c u m e n t a t i o n / B i b l i o g r a p h y Information on how to use this documentation All calculations, designs and technical details are only intended as information and advice and do not replace tests by the users in regard to the suitability of the materials for specific applications. No l egal l y bi ndi ng assurance of properti es and/or resul ts from the cal cul ati ons can be deduced from this document. The material parameters stated here are not binding minimum values, rather they shoul d be regarded as gui di ng val ues. If not otherwi se stated, they were determi ned wi th standardised samples at room temperature and 50% relative humidity. The user is responsible for the deci si on as to whi ch materi al i s used for whi ch appl i cati on and for the parts manufactured from the materi al . Hence, we recommend that practi cal tests are carri ed out to determi ne the suitability before producing any parts in series. We expressly reserve the right to make changes to this document. Errors excepted. You can downl oad the l atest versi on contai ni ng al l changes and suppl ements as a pdf fi l e at www.licharz.de. ©Copyright by Licharz GmbH, Germany Bibliography The following literature was used to compile “ Designing with plastics” : Ebeling, F.W. /Lüpke, G. Kunststoffverarbeitung; Vogel Verlag Schelter, W. /Schwarz, O. Biederbick, K. Kunststoffe; Vogel Verlag Carlowitz, B. Kunststofftabellen; Hanser Verlag Böge, A. Das Techniker Handbuch; Vieweg Verlag Ehrenstein, Gottfried W. Mit Kunststoffen Konstruieren; Hanser Verlag Strickle, E. /Erhard G. Maschinenelemente aus thermoplastischen Kunststoffen Grundlagen und Verbindungselemente; VDI Verlag Strickle, E. /Erhard G. Maschinenelemente aus thermoplastischen Kunststoffen Lager und Antriebselemente; VDI Verlag Erhard, G. Konstruieren mit Kunststoffen; Hanser Verlag Severin, D. Die Besonderheiten von Rädern aus PolymerMaterialen; Specialist report, Berlin Technical University Severin, D. /Liu, X. Zum Rad-Schiene-System in der Fördertechnik, Specialist report, Berlin Technical University Severin, D. Teaching material Nr. 701, Pressungen Liu, X. Personal information Becker, R. Personal information VDI 2545 Zahnräder aus thermoplastischen Kunststoffen; VDI Verlag DIN 15061 Part 1 Groove profiles for wire rope sheaves; Beuth Verlag DIN ISO 286 ISO coding system for tolerances and fits; Beuth Verlag DIN ISO 2768 Part 1 General tolerances; Beuth Verlag DIN ISO 2768 Part 2 General tolerances for features; Beuth Verlag Konstr. Kunststoffe engl.7/04 27.10.2004 7:42 Uhr Seite 134 Licharz GmbH Industriepark Nord D-53567 Buchholz Germany Telefon: ++49 (0) 26 83- 977 0 Telefax: ++49 (0) 26 83- 977 111 Internet: www.licharz.de E-Mail: [email protected] T U 0 1 . 0 1 . 0 9 . 0 4 . E For further information, detailed catalogs are available: • Information on Licharz machining capabilities of component parts • Brochure „ Material Guiding Values /chemical Resistance“ • Product information on semi-finished products of PA, POM und PET • Delivery programme Visit us on the internet at www.licharz.de ZL Engineering Plastics PO Box 2270 12 John Walsh Boulevard Peekskill, NY 10566 USA Phone: ++1 914 – 736 6066 Fax: ++1 914 – 736 2154 E-Mail: [email protected] ZL Engineering Plastics 8485 Unit D Artesia Boulevard Buena Park, CA 90621 USA Phone: ++1 714 – 523 0555 Fax: ++1 714 – 523 4555 E-Mail: [email protected] Headquarters: Branch offices: Licharz Ltd. Daimler Close Royal Oak Industrial Estate Daventry, NN11 8QJ Great Britain Phone: ++44 (0) 1327 877 500 Fax: ++44 (0) 1327 877 333 Internet: www.licharz.co.uk E-Mail: [email protected] Titel Rückseite 27.10.2004 10:17 Uhr Seite 1


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