1. Mechanical DesignRolling Contact bearingsRolling contact bearings6.1 Types of rolling contact bearings Friction between moving parts can not be eliminated entirely, but often it isreduced most effectively by using some form of rolling bearings. There aremany types of rolling contact bearings which suit different applications. Themost common types are, See fig.(6.1): 1.Ball bearings1.1. Single row ball bearing1.2. Double row ball bearing1.3. Self alignment ball bearing1.4. Angular contact ball bearing1.5. Thrust ball bearing 2. Roller contact bearings2.1. Taper roller bearing2.2. Straight roller bearing2.3. Conical roller bearing2.4. Concave roller bearing2.5. Thrust roller bearing2.6. Needle bearingsRoller thrustBall thrust bearing Spherical roller Radial taperedBall bearing Rollerbearingthrust bearingroller bearingFig. (6.1) Cut view of different types of rolling contact bearingsThe loading on roller contact bearings can beclassified into three groups: 1. Solely radial loading 2. Solely axial loading 3. Combined radial and axial loadingBall and roller bearings aremanufactured in several series, the most popularones are shown in fig (6.2). Within each of theseExtra Light MediumHeavyseries is a wide range of different bearing sizes. lightHeavy series bearings have the greater load Fig. (6.2) Series of ballcarrying capacity but extra light series bearings bearingsrun at higher speeds, assuming the bearings havethe same bore diameter and of similar internal construction. Dr. Salah Gasim AhmedYIC1 2. Mechanical DesignRolling Contact bearings6.2 Standardisation of ball bearings: Through the effort of the society of Automotive Engineers (SAE) themanufacturers of radial ball bearings have adopted the international standarddimensions, according to which the light series is designated by the number200, the medium by 300 and the heavy by 400. The last two digits of a standardbearing number designate the bore diameter which comes in multiple of 5 mm,see fig. (6.3)6.3 Main parts of a typical ball bearing6309Bearing type Series number Bore diameter Fig. (6.3) Bearing designation numberThe main parts of a typical ball bearing are :1. The outer ring, (outerrace).BallBall2. The inner ring ,(inner retainerrace).3. Therolling elements,(ball).4. The ball retainer (the cage)See fig. (6.4)6.4 Selection of ball bearings:Inner In selecting a ball bearing from ring Outer ringtrade catalogue for specific installationthree main points must be considered:1. The bearing must be of the series Fig. (6.4) Main parts of a typical ball bearing best suited to the installation, in regard to both capacity and dimensions.2. The type of bearing selected, radial, thrust or combined must be suitable for the type of imposed load.3. The size of the bearing must be such as to give the required length of service with sufficient assurance. In the majority of applications ball bearings have to resist some combinationof radial and thrust loads. The bearing rating is always referred to a radial load.There for the combined load must be reduced to an equivalent radial load. Dr. Salah Gasim AhmedYIC2 3. Mechanical Design Rolling Contact bearings Various catalogues give different methods of reduction. In general the equivalent load Fe may be computed by the equation:Fe = XFr + YFa (6.1) Where, Fe : equivalent radial load Fr : actual radial load Fa : actual axial load X and Y are coefficients which depends on the ratio Fa/Fr. For most bearings The values given in table (6.1) are suitable.Table (6.1) Values of X and Ye of bearingYXp groove 1.5 1ular contact1 0.5aligning 2.50.5Experiments have shown that the life of a ball bearing is a function of the load it carries. It also showed that the service life of a ball bearing is inversely proportional to the value of the load it carries raised to power 3. In other words it can be expressed by the equationLn = (C) 3 (6.2) Fe Where, C: dynamic specific capacity of bearing. Ln: Life of bearing in millions of revolution. Fe : Equivalent loadTable (6.4) shows the dynamic specific capacity for SKF bearings. SKF engineers introduced speed factor and life factor which can be taken from fig. (6.5) and fig. (6.6) respectively. The required dynamic capacity can be obtained from the equation: f s Fe f hFc ≥ (6.3) fn Wherefs: safety factorfn : speed factorfh : life factorFc : dynamic capacity of the bearingBearing lifeLife in working Class of machine hours 1Instruments and apparatus that are used only seldom.Dr. Salah Gasim AhmedYIC 3 4. Mechanical DesignRolling Contact bearings Demonstration apparatus, mechanisms for operating sliding doors2 Aircraft engines 2000 - 1000 Machines used for short periods or intermittently and whose brake down would not have serious consequences; hand tools, lifting tackles in38000 - 4000 workshops, hand operated machines, generally agricultural machines, cranes in erecting shops, domestic machines Machines working intermittently and where breakdown would have serious consequences.4Auxiliary machines in power stations, conveyor plant 12000 - 8000 for flow production, lifts cranes for piece goods; machine tools used infrequently Machine for use 8 hours per day and fully utilized:5 20000 - 12000 .stationary electric motors, general purpose gear units Machine for use 8 hours per day and fully utilized:6machines for engineering industry generally: cranes30000 - 20000 for bulk goods, ventilating fans, countershafts Machines for continuous use 24 hours per day: Separators, compressors, pumps, mine hoist,7 60000 - 40000 stationary electric machines, machines in continuousoperations on board naval ships Machines required to work ith high degree of reliability 24 hours per day: pulp and paper8machinery; public power plants, mine pumps, pumps 200000 - 100000 in water works, machinery in continuous operation onboard merchant ships6.5 Installation of ball bearings:In the installation of ball bearings the following points must beconsidered separately: 1. The shaft must be designed to take the inner ring (race)., see fig. (6.7) 2. A suitable mounting must be designed for the outer ring (race). 3. Lubrication must be provided for the bearing 4. Methods of sealing the lubricant and preventing penetration of foreignmatter must be provided. Dr. Salah Gasim AhmedYIC4 5. Mechanical Design Rolling Contact bearingsExample 1 Determine the load capacity of a single row deep-groove SKF bearing –SKF 10, medium series, that must run 2000 hours at 700 rpm.Solution:From table (6.4) C = 10400 lbFig. (6.7) A method of fastening ball bearing to a shaftFrom fig.(6.5) fn = 0.36From fig.(6.6) fh = 1.58 f s Fe f hHence from equation (6.3) Fc ≥ fnFc f nFe =fs fhTake safety factor fs = 110400 x0.36 Fe =1x1.58 Fe = 2370Example 2A shaft is supported by two bearings. One of the bearings carries a radialload of 200 lb and an axial load of 500 lb with minor shocks. The shaft runs at230 rpm and operates 10 hours per day for 5 days per week. Select a suitable Dr. Salah Gasim Ahmed YIC5 6. Mechanical DesignRolling Contact bearingsball bearing with a service life of 2 years if the diameter of the shaft can bevaried between 3 16 and 3 1 . 152Solution…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..……………………..…………………………………………………………………………………………..…………………….. Dr. Salah Gasim AhmedYIC6 7. Mechanical Design Rolling Contact bearingsExercises1. The main shaft in a reduction gear-box is shown in fig.(1). The shaft is to besupported by two deep groove ball bearing at A and D. In addition to theradial loads the shaft carries an axial load of 175 lb. Determine the bearingsloads and select suitable single row deep groove bearings if the shaft rotatesat 1200 rpm and operates 7 hours per day, five days a week for five years.Take factor of safety = 1.5. The maximum diameter of the shaft at both endsshould not exceed 30 mm 100 lb2 in250 lb 3 in1 in A Gear B 175 lb Gear CD Fig.(1)2. Select suitable deep groove ball bearings for the spindle of a woodworking machine revolving at 1200 rpm. One bearing is subjected to a radial load of 600 lb and the other carries a radial load of 820 lb. An axial load of 310 lb is acting along the machine spindle. The machine is to be used 8 hours per day and 5 days a week, and a service life of 10 years is desired. The diameter of the spindle is 2 in. and can be turned down slightly.3. A reduction gear-box is shown in fig.(2). It consists of two helical gears fixed to shafts X and Y. Shaft X is supported by two single row deep groove ball bearings. On shaft X, the bearings and the helical gear are located as follows: The distance between the centre of pulley and centre of bearing A = 35 mm, The distance between the centre of pulley and centre of helical gear = 90 mm, The distance between the centre of pulley and centre of bearing B = 135 mm. Dr. Salah Gasim Ahmed YIC7 8. Mechanical DesignRolling Contact bearingsThe helical gear exerts the following loads on shaft X:Radial load= 100 lbTangential load = 150 lbAxial load= 50 lb Bearing A Shaft XBearing B Shaft Y Fig.(2)4. Determine the bearings loads and select suitable single row deep groove bearings if the shaft rotates at 1500 rpm and operates 8 hours per day, seven days a week for five years. Take factor of safety = 1.55. A shaft supported by two ball bearings: A and B is shown in fig. (3). The shaft carries two pulleys with radial loads 250 lb and 600 lb. An axial load of 300 lb is acting along the shaft in the direction indicated by the arrow. The shaft runs at speed of 1500 rpm for 8 hours per day and 5 days a week, and a 2 inch2 inch1 inch 600 Lb300 LbBearing A Bearing B250 Lb Fig. (3) service life of 10 years is desired. The minimum diameter of the shaft is not less than 1 inch. Select suitable ball bearings. Dr. Salah Gasim AhmedYIC8 9. Mechanical Design Rolling Contact bearings6. Determine the load capacity of a single row deep-groove SKF bearing – SKF 15, heavy series, that must run 3000 hours at 600 rpm. Fig. (4) shows a shaft supported by two ball bearings and runs at 1000 rpm. A radial and axial loads act on the shaft with minor shocks. If the shafts operate for 16 hours per day and total service life required is 3 years select suitable bearings for the shaft. The minimum diameter off both ends of the shaft is not less than 9 mm.7. Select suitable ball bearings for the spindle of a woodworking machinerevolving at 1200 rpm. One bearing is subjected to a radial load of 600 lb900 lb8 inch 4 inch150 lb BA Fig. (4)and a thrust load of 450 lb; the other carries only a radial load of 650 lb. Themachine is to be used 8 hour per day and 5 days a week, and a service lifeof 10 years is desired. The diameter of the spindle is 2 in. and can be turneddown slightly.8. A ball bearing is to be used on a drill press operating at 3000 rpm with a 250 lb maximum thrust load and 500 lb radial load. The press will be operated five 8-hour days a week but will be idle 20% of the time. Determine thr type and size of the bearing (a) if it should last 1 year. (b) if it should last 2 years.9. Determine the radial capacity of an SKF 6211-Z bearing running at 500 rpm and carrying an axial load of 500 lb, for 2 years of continuous service.10.A shaft is supported by two bearings 16 in apart and carries a bevel gear of 7.75 in pitch diameter. The gear is at 6 in from one end of the shaft. The gear produces a radial load of 2150 lb and a thrust load of 625 lb when rotating at 525 rpm. .Determine : (a) The shaft diameter if the shaft is made of SAE1045 steel and (b) The proper type and size of ball bearings to be used on each end of the shaft. The desired life is 2 years at 50 hour/week. Dr. Salah Gasim Ahmed YIC9 10. Mechanical DesignRolling Contact bearings Table (6.2) Safety factors for MRB ball bearings Safety factor, life Safety factor, life of 5 to 10 years of 10 to 20 years Load conditions Intermittent 10 hours per dayContinuousContinuous Steady load0.5 ------ 1 1.523 Light shock1 ------- 22.534 Moderate shock 2 ------- 33.545 Severe shock 3-------- 44.556Table (6.1) Values of X and Yf bearing Y Xroove1.51r contact 10.5gning2.5 0.5 Table (6.3) Over-all dimensions of radial ball bearingsSAE (Bore of inner race (d Outside diameter D mm (Width B (mm Bearing 200 300400200 300 400 Numbermm inseriesseries series seriesseriesseries 00 10 0.3937 3035…… 911…… 01 12 0.4724 3237……1012…… 02 15 0.5906 3542……1113…… 03 17 0.6693 4047 62 121417 04 20 0.7874 4752 72 141519 05 25 0.9843 5262 80 151721 06 30 1.1811 6272 90 161923 07 35 1.3780 7280100 172125 08 40 1.5748 8090110 182327 09 45 1.7717 85 100120 192529 10 50 1.9685 90 110130 202731 11 55 2.1654100 120140 212933 12 60 2.3622110 130150 223135 13 65 2.5591120 140160 233337 14 70 2.7559125 150180 243542 15 75 2.9528130 160190 253745 16 80 3.1496140 170200 263948 17 85 3.3465150 180210 284152 18 90 3.5433160 190225 304354 19 95 3.7402170 200……3245…… 20100 3.9370180 215……3447…… 21105 4.1339190 225……3649…… 22110 4.3307200 240……3850……Dr. Salah Gasim AhmedYIC 10 11. aligningroovegroove Angulacontact-row self-deep- deep--rowrow Table (6.4)Specific dynamic capacity of SKF ball bearings, in Poundsrowgr-Double Double Single- Single-0 00 00 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 03 4 23423 4 2 3 4………… 0 50 6 4…… 0 2 2…… …………………… 7110 0 5 ……0 4 1 0 0 8…… 0 6 8…… ……………………Mechanical Design11110 3 6 ……0 5 2 0 6 9…… 0 4 0 …………………………Dr. Salah Gasim Ahmed11120 2 1 ……0 0 6 0 6 3…… 0 0 6 0 0 8 ………… …… ……212230 4 2 ……0 6 1 0 5 7 ……0 5 5 0 0 5 …… ……0 0 7 ……22234 20 5 2…… 0 2 3 0 5 6 0 0 3 0 0 8 0 0 0……0 8 2 0 0 8 0 0 2323636 2 3 60 5 00 0 10 5 2 0 0 8 0 0 5 0 0 3 0 0 8 0 0 4 30 0 2 0 0 8 0 5 34 6347571 3 4 70 0 80 5 00 0 3 0 0 7 0 0 5 0 0 1 0 0 3 0 0 0 40 5 2 0 0 7 0 0 34 7459791 4 5 90 0 10 5 00 0 9 0 5 90 0 0 10 0 00 0 2 10 0 6 70 0 1 0 5 9 0 0 6 06 846 1811 5 6 10 5 6 0 0 4 0 0 0 5 0 0 00 0 2 30 0 00 0 6 40 0 0 20 0 7 0 0 0 0 0 9 27 159 1912 5 9 10 5 6 0 0 0 2 0 5 80 0 4 0 0 0 6 40 5 60 0 0 70 0 5 70 0 00 0 4 00 0 3 48 151 1912 61 1 drives0 0 4 0 0 0 7 2 0 5 30 0 0 2 0 0 3 7 0 0 8 1 0 0 3 90 0 5 70 5 30 0 0 20 0 6 61 171 1 112 71 10 0 0 2 0 0 3 5 0 0 80 0 7 3 0 0 0 9 0 0 3 4 0 0 0 20 0 5 00 0 80 0 7 30 0 3 81 181 1 123 81 10 0 7 2 0 0 3 6 0 5 60 0 3 5 0 0 8 0 0 0 6 5 0 0 0 5……0 0 0 0 0 0 3 50 0 0 01 191 2 1211 20 0 3 5 0 0 0 00 0 4 0 0 0 0 7 0 0 0 6 0 0 0 7 0 0 5 7……0 0 0 1 0 0 0 70 0 5 51 2 11 2 1211 20 0 3 6 0 0 8 20 0 0 1 0 0 6 8 0 0 0 8 0 0 0 8 0 0 5 0……0 0 4 1 0 0 0 90 0 0 71 2 11 2 1311 20 0 0 8 0 0 5 50 0 2 2 0 0 8 0 ……0 0 6 9 0 0 5 3……0 0 7 2 0 0 8 0 ……1 2 12 13120 0 0 0 0 0 5 70 0 7 3 0 0 4 2 ……0 0 4 0 0 0 5 3……0 0 3 4 0 0 8 2 ……2 2 12 23120 0 8 2 0 0 0 10 0 6 5 0 0 5 4 ……0 0 2 3 0 0 5 5……0 0 6 6 0 0 5 4 ……2 3 12 23120 0 5 5 …… 0 0 6 7 0 0 5 6 ……0 0 5 8 …… ……0 0 6 7 0 0 5 6 ……2 12 2120 0 5 7 …… 0 0 6 9 0 0 5 0 ……0 0 0 2 …… ……0 0 6 9 0 0 5 2 ……2 13 3130 0 0 1 …… 0 0 6 1 0 0 5 2 ……………… …… …… 0 0 5 4 ……3 2330 0 5 3 …… 0 0 0 4 0 0 5 7 ……………… ……0 0 0 4 0 0 0 9 ……3 2323Belt………… ………………………… ……0 0 5 7…… ……2YIC 11………… ………………………… ……0 0 0 1 0 0 0 8 ……34………… ………………………… ……0 0 5 3…… ……3………… ………………………… ……0 0 0 9 0 0 5 8 ……35………… ………………………… ……0 0 5 1 …………4 12. Number SAE0 0 2 0 0 5 6 8 1 5 1Mechanical Design 0 9 20 5 2Dr. Salah Gasim Ahmed 01 30 0 4 01 40 3 8 01 50 4 2 02 60 0 1 03 70 5 3 03 80 5 2 04 90 5 7 04 00 0 1 15 drives 10 0 2 16 20 0 1 17 30 5 6 17 40 0 5 18 50 0 3 19 60 0 8 19 7 0 0 8 1 1 1 8 0 0 9 2 1 1 9…… 1 0 0 0 3 6 2 1 1…… 2 2 0 0 4 0 2 2Belt 4 …… 2YIC 12 6 …… 2 8 …… 2 0 …… 3 2 …… 3 13. Number SAE0 0 2 0 0 5 6 8 1 5 1Mechanical Design 0 9 20 5 2Dr. Salah Gasim Ahmed 01 30 0 4 01 40 3 8 01 50 4 2 02 60 0 1 03 70 5 3 03 80 5 2 04 90 5 7 04 00 0 1 15 drives 10 0 2 16 20 0 1 17 30 5 6 17 40 0 5 18 50 0 3 19 60 0 8 19 7 0 0 8 1 1 1 8 0 0 9 2 1 1 9…… 1 0 0 0 3 6 2 1 1…… 2 2 0 0 4 0 2 2Belt 4 …… 2YIC 12 6 …… 2 8 …… 2 0 …… 3 2 …… 3 14. Number SAE0 0 2 0 0 5 6 8 1 5 1Mechanical Design 0 9 20 5 2Dr. Salah Gasim Ahmed 01 30 0 4 01 40 3 8 01 50 4 2 02 60 0 1 03 70 5 3 03 80 5 2 04 90 5 7 04 00 0 1 15 drives 10 0 2 16 20 0 1 17 30 5 6 17 40 0 5 18 50 0 3 19 60 0 8 19 7 0 0 8 1 1 1 8 0 0 9 2 1 1 9…… 1 0 0 0 3 6 2 1 1…… 2 2 0 0 4 0 2 2Belt 4 …… 2YIC 12 6 …… 2 8 …… 2 0 …… 3 2 …… 3