Bearing Selection - AHR International

1 Bearing Selection14 Equivalent Load "P"As previously stated radial and axial loads must be considered separately for split roller bearings. For the calculation of theoretical life only radial loads are = Radial LoadsThe value of Fr is that calculated from standard mechanical formulae, the impact of additional forces resulting from external influences must also be = FactorUnder the influence of the above conditionsP = Fr x FzThe required theoretical Bearing life is based upon a number of factors, including reliability, accessibility and service considerations. Generally life values should be as follows:Dynamic LoadingSelection of SRB split roller bearings must take into account the effects of both radial and axial loads.

2 These loads must be considered independently of each Load ConsiderationsThe basic rating life of a Bearing can be derived from the formulae laid down in ISO281:1990L10 = (C/P) 10/3 (106 Revolutions) (i)In the majority of cases where the speed remains constant then the life can be expressed in hours from the formulaL10h = (106) x L10 (ii) 60 x nSubstituting (i) L10h = (106) x C 10/3 (ii) 60 x n P L10 = Basic Rating Life (90% reliability), 106 Revolutions L10h = Basic Rating Life (90% Reliability)

3 , HoursC = Bearing Dynamic Capacity, kNn = Speed, min-1P = Equivalent Bearing LoadThis calculation assumes for the load components considered for an individual Bearing , that the shaft system is a beam resting on rigid, moment free supports. Elastic deformations in the Bearing , housing or machine structure are not taken into Used Intermittently 500 to 2,000 hoursOccasional Use 5,000 to 10,000 hoursNormal Operation 20,000 to 50,000 hoursContinuous Operation 75,000 to 100,000 hoursHigh Reliability > 100,000 hoursLoad ConditionFactor FzSteady to Shock or Out of Balance to Shock or Vibration to to Life Values 15a3 FactorThe a3 factor considers all operational parameters that influence fatigue life.

4 The most obvious of these is lubrica-tion. The highest life values are achieved where a state of hydrodynamic lubrication exists, in this state no metal to metal contact effectiveness of lubricant due to decreasing film thickness or effects of contamination will reduce the a3 to the interrelationships between materials adjust-ment factor a2 and operating adjustment factor a3, a common factor a23 is frequently used. a23 Factora23 = a2 + a3 The a23 factor can be taken from fig 1:V1 = Rated Viscosity (Depends on Bearing size and operating speed)V = Operating Viscosity (Depends on original viscosity and operating temperature)Adjusted Life CalculationThe L10 fatigue life calculation is based upon the rating life of a large number of identical bearings expressed as a number of revolutions operating at a constant speed.

5 This rating life is reached or exceeded by 90% of these before the first evidence of fatigue above definition applies to bearings operating under optimum conditions. Variations in operating conditions will lead to changes in the life of these allows for an adjusted life calculation: Lhna = a1 x a2 x a3 x L10hWhere Lhna = Adjusted LifeL10h = Rating Life in Hoursa1 = Life adjustment factor, failure probability other than 10%a2 = Life adjustment factor, material propertiesa3 = Life adjustment factor, operating conditionsa1 FactorIn cases where a failure rate other than 10% is required, then an a1 factor as in the table below.

6 Should be A1a2 FactorThis factor takes into account the material FactorFailure Probability % 10 5 4 3 2 1 Factor a1 Life Adjustment FactorValues for V and V1 are obtained from the following graphs:Where D = Bearing outside diameter d = Bearing Bore n Shaft speed (RPM)V1 is then read off the vertical Loading In situations where bearings rotate slowly (<10 rpm), oscil-late slowly, are stationary for prolonged periods, or subject to high shock loads, it is important to check that no perma-nent deformations occur between rolling elements and raceways at peak basic static load rating is defined in ISO 76:1987 and refers to the contact stress at the centre of the most heavily loaded rolling element/raceway contact area.

7 For roller bearings this value is 4000 Mpa. This will result in a perma-nent deformation of of the roller required static load rating can be determined from:Co = Fs. PoCo = Basic Static Load Rating Po = Equivalent Static Load Fs = Static Safety FactorGuidelines for the Static Safety Factor Fs can be found in the table below:Nature of DutySmooth no Vibration > > > for Duty Low Medium HighUsing the operating temperature and nominal lubricant viscosity, the value for operating viscosity, V, is read off the horizontal Ratings17 mmHeavy SeriesDynamic Cr (kN/lb)Max RPM inchStatic Cor (kN/lb)Axial Ca (kN/lb) Shaft (d)

8 Bearings Ratings mm 35 4045 5060 6570 7580 90100 105110 115120 130135 140150 155160 170 180190 200220 230240 250260 280300 305320 330340 350360 380400 420 440 460480 500 530 560 580 600 Light Series 13/16 11/2111/16 223/16 21/2211/16 333/16 31/2311/16 443/16 41/2411/16 553/16 51/2511/16 667/16 61/2611/16 771/4 881/2 991/2 10101/2 11111/2 12121/2 1314 15 16 17 18 19 20 21 22 23 24 5400 4630 3940 3310 2790 2340 1970 1740 1570 1450 1320 1220 1070 930 820 730 650 590 540 500 460 430 410 380 360 340 330 310 300 65 1461383 18659103 23155138 31024187 42039288 64745316 71040363 81606422 94869459 103187583 131064524 117800614 138033659 148149696 156467794 178498929 208848920 206824967 2173901011 2272821054 2369491095 2461661134 2549331291 2902281336 3003451377 3095621419 3190041591 3576711638 368237 68 1528787 19558115 25853161 36194231 51931366 82280427 95993496 111505585 131513664 149273792 178049828 186142990 2225611062 2387471182 2657241376 3093371665 3743071674 3763301824 4100521975 4439982125 4777192275 5114402427 5456112800 6294652974 6685823150 7081483324 7472653759 8450573956 889344

9 33002 Dynamic Cr (kN/lb)Max RPM inchStatic Cor (kN/lb)Axial Ca (kN/lb) Shaft (d)Bearings Ratings mmMedium SeriesDynamic Cr (kN/lb)Max RPM inchStatic Cor (kN/lb)Axial Ca (kN/lb) Shaft (d)Bearings RatingsAxial load ratings (Ca) assume the use of EP additives or oil lubrication, otherwise use 50% of loads and speeds may be permissible. Please contact SRB Technical Services. 100 105110 120125 130135 140150 155160 170175 180190 200220 230240 260280 300 320 340 360380 400 420 440460 500 530 560 580 600 311/16 443/16 41/2415/16 553/16 51/2511/16 667/16 611/1663/4 771/4 881/2 991/2 1011 12 13 14 15 16 17 18 20 21 22 23 24 1820 1640 1500 1340 1220 1110 1030 880 760 700 620 560 500 460 420 360 340 310 280 270 653 146800656 147475753 169281827 1859171037 2331271015 2281811275 2866311423 3199031665 3743071694 3808261936 4352302114 4752462718 6110312686 6038373195 718265 3187 7164663501 787056 4324 972074 4448

10 9999504443 998826 783 176025801 180072974 2189641084 2436931325 2978721326 2980971767 3972381958 4401762455 5519062519 5662943115 7002803194 7180404093 9201434421 9938815238 1177550 5813 13068156091 1369312 7603 1709223 8781 19740488918 2004847 56382 67982 78009 86012400 89924 45 5055 6570 7580 90100 105110 115120 130135 140150 155160 170180 190 200220 230240 260270 280300 305320 330340 360380 400 420 440 460480 500 530 560 580 600 111/16 223/16 21/2211/16 333/16 31/2311/16 443/16 41/2411/16 553/16 51/2511/16 667/16 61/2611/16 771/4 881/2 991/2 10101/2 11111/2 12121/2 1314 15 16 17 18 19 20 21 22 23 24 4350 3680 3080 2520 2130 1820 1600 1450 1320 1200 1120 960 850 750 670 610 550 500 460 430 400 380 360 340 330 310 300 290 121 27202168 37768258 58001297 66768388 87226454 102063525 118025600 134885730 164111842 189289927 2083981013 2277321138 2558331240 2787631476 3318181569 3527251723 3873461989 4471451800 4046562105 4732232324 5224562215 4979522445 5496582320 5215572556 5746122683 6031632740 6159772770 622721 127 28551190 42714300 67443353 79358491 110381592