1、12FTM02AGMA Technical PaperPower Loss and AxialLoad Carrying Capacityof Radial CylindricalRoller BearingsBy S. Sndgen and W. Predki,ZOLLERN GetriebetechnikDorsten GmbHPower Loss and Axial Load Carrying Capacity of RadialCylindrical Roller BearingsDr.-Ing. Simon Sndgen and Prof. Dr.-Ing. Wolfgang Pre
2、dki, ZOLLERNGetriebetechnik Dorsten GmbHThe statements and opinions contained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractTheapplication ofcylindricalrollerbearings(CRB)iswidespreadinmechanicalengin
3、eering. CRBcancarrycomparatively high loads and are usable in high speed ranges. These bearings have been proven to bevariably applicable and economic. With lipped inner and outer rings CRB permit the transmission of axialloadsinadditiontoradialloads. Theaxialloadisinducedonthelipoftheinnerortheoute
4、rringandtransferredbytherollerendfacecontactstotheopposinglip. Incomparisontoanonlyradiallyloadedbearing,thereareadditional friction losses in the contact between the lip and the roller ends as a result of sliding.Thelimitingfactorsforthepermissibleaxialloadarehightemperatures,whichcancausesmearinga
5、ndseizing, lip fracture, fatigue failure and wear. In consequence of the axialloading,the stressesin the contactbetween the roller and the raceway rise and the fatigue durability of the bearing is reduced.At high speeds the permissible thrust load is dominantly limited by high temperatures. At low s
6、peeds thelimiting factors are lip fracture and wear.Within the examination an extensive test program with different bearing geometries is carried out. Therebythe decisive measure is the friction torque of the bearings.The friction torque of a thrust loaded radial cylindrical roller bearing is mainly
7、 dependent on the parametersspeed, load, size and design of the bearing.An analytical simulation model, which has been developed at the institute, allows calculating the lubricationconditions, the stresses within the lip - roller contact and the axial load dependent friction torque.Theintentionofthe
8、studyistoenlargetheapplicationrangeofradialcylindricalrollerbearingsbymeansofamore precise determination of the thrust load capacity and to allow more economic designs.Copyright 2012American Gear Manufacturers Association1001 N. Fairfax Street, Suite 500Alexandria, Virginia 22314October 2012ISBN: 97
9、8-1-61481-033-93 12FTM02Power Loss and Axial Load Carrying Capacity ofRadial Cylindrical Roller BearingsDr.-Ing. Simon Sndgen and Prof. Dr.-Ing. Wolfgang Predki, ZOLLERNGetriebetechnik Dorsten GmbHIntroductionCRB have a wide application range and high significance in drive engineering. Due to the li
10、ne contact CRBhave a greater radial load capacity than other rolling bearings of the same size. The possible application athighspeedandanadvantageous frictionbehavior areadditionalbenefits of radialCRB 1. Severaldesigns,whichvaryregardingthequantityandarrangementofthelipscanbedistinguished. Thelipsa
11、llowtheapplica-tion of axial loads in one (supporting bearing) or two directions (locating bearing). When axial forces areapplied, they aretransferredfrom thelip of the inner ring tothe roller end faces of theroller andfrom theretothe lip of the outer ring for example. Alternating axial loads can be
12、 supported by a bearing of the NJ-type incombination with an angle ring HJ or by a bearing of the NUP-type with a loose lip 2.DespitethefactthatcombinedloadedCRBareemployedformorethan100years,thereisnostandardforthecalculation of the axial load dependent friction torque and of the axial load capacit
13、y until now 3. There areequationsgivenintherelevantliteratureandinthebearingcatalogueswhichallowthecalculationof theaxialload dependent friction torque. Theseequations aremostly basedon empiric approaches andthe results ofthe different equations vary significantly.Lubenow4performedextensivemeasureme
14、ntsoncombinedloadedCRB. Figure 1showstheresultsfromtheequationsofSchaeffler5,SKF6,Braendlein7andthesimulationaccordingtoLubenowaswellasthemeasurementresultsaccordingto4. TheillustratedresultsarevalidforaruninbearingofthetypeNJ 210atan operation temperature of 70C and lubrication with a mineral oil o
15、f the viscosity class ISO VG 220.Figure 1. Axial load dependent friction torque T2according to different calculations methods andmeasurement results4 12FTM02The radial load amounts to Fr= 5kN whereas the axial load Fa= 4 kN is chosen. The axial load dependentfriction torque T2is illustrated in depen
16、dency of the inner ring speed n.Figure 1shows significant deviationsbetweenthedifferent determinedaxialloaddependent frictiontorques.Particularly at low speeds not only the results from the equations of the bearing manufacturers and ofBraendlein vary from the measurement results, but also the simula
17、tion results according to 4.The friction torque of thrust loaded radial cylindrical roller bearings is an important parameter for thedeterminationoftheaxialloadcarryingcapacityatmediumtohighspeeds. Thepermissiblethrustloadcanbedetermined by means of a heat balance 4. At low speeds the frictional los
18、ses decrease and therefore thetheoretically permissible thrust load strongly increases. The bearing manufacturers therefore additionallygivealimitingratioofaxialtoradialloadandalimitingaxialloadindependencyofthesizeandthedesignofthebearing.However, these details are only valid for the bearings of on
19、e manufacturer and considerable safety marginsare included.Testing programForthisinvestigation10fivedifferentdesignsofCRBinthreesizesareconsidered. Fortheevaluationofthesize effect, bearings with the bearing diameters d = 30, 50 and 80 mm are chosen. Rolling bearings areproduced in different series.
20、 These series feature varying load ratings in dependence of the outer diameter,quantity of rollingelements andthebearing width. Besides the bearingseries 22, the series 23 is examined.BearingsoftheNJ-designnormallyprovidefrictionoptimizedlipgeometries. Thelipisnotorthographictotheracewaybutinclinedw
21、iththelipangle. Furthermorethelipcanbecrowned. Thelooselipof aNUP-designand an angle ring in contradiction do not feature afriction optimizedgeometry. The evaluationof theseshallshowtheinfluenceofthelipgeometryonthefrictionbehaviorofaxialloadedCRB. Fullcomplementbearingsemploy the maximum possible n
22、umber of rolling elements, whereby the radial load is shared by a greaternumber of contacts which leads to greater load rating. These bearings can beused as a supportingbearinglike a NJ-design because they also feature three lips.The lubricant has a large influence on the friction behavior and there
23、fore on the permissible thrust load ofradialcylindricalroller bearings. Withinthis study amineraloilandapolyglycolof theviscosity class ISO VG220 are tested. Table 1 gives a summary test program.Table 1. Examined bearings and lubricantsBore reference number 06 10 16Bore diameter d =30mm d =50mm d =8
24、0mmVariantNJ2206 E.TVP2 NJ2210 E.TVP2 NJ2216 E.TVP2N2306 E.TVP2 NJ2310 E.TVP2 - -NUP2206 E.TVP2 NUP2210 E.TVP2 - -NJ2206 E.TVP2+ HJ206NJ2210 E.TVP2+ HJ210NJ2216 E.TVP2+HJ216SL182206 SL182210 - -Mineral oil Aral Degol BG 220Polyglycol Tribol 800/2205 12FTM02Allbearingsfeaturenormalclearance. Thecagem
25、aterialisPolyamide66. Thefrictiontorquemeasurementsareperformedat differentcombinations ofspeedandload. Thegapsbetweenthedifferent speedsinthelowspeed range are chosen smaller than at high speeds because the lubrication film thickness in the lip-roller-contact grows with speed. With rising lubricati
26、on film thickness the rate of mixed lubrication decreases andthehydrodynamic frictionincreases. Thefocus of this study is onthe operationwith mixedfriction, for whichreason the test speeds are chosen according to Table 2.The tests at constant speeds are supplementedby run-ups. Thetest program is com
27、pletedwith run-inandwear experiments.Friction torque measurements on rolling bearingsFor the assessment of the behavior of combined loaded CRB as well as of bearings in general, the globalmeasurefrictiontorqueisofdecisiverelevance. Ontheonehandtheresultingbearingtemperatureisdirectlydependent onthef
28、rictionandontheother handconclusions tothelubricationconditioncanbe drawn. Inthepast years extensive measurements of bearing friction torques have been performed at the Chair ofMechanical Components and Power Transmission, on different test rigs.Lubenow4aswellasKoryciak8useddeviceswhichallowedthemea
29、surementofthefrictiontorqueontheouter ring of the test bearing.For this study a new test rig has been designed, which allows the measurement of the frictionlosses of mul-tiple bearings with a torque measurement shaft. The detection of the friction torque is effected on the innerring. Figure 2 shows
30、that the result is affected by the measuring position due to the splashing of the rollingelements and the cage in the lubricant.Whilst the outer ring is standing still, the inner ring is driven with the necessary driving torque Tdrive.Thefrictionofthewholebearinghastobeovercomeandthereforethedriving
31、torqueTdrivecomplieswiththeabso-lutevalueofthemeasuredfrictiontorqueontheinnerringTIR. Duetothesplashingoftherollingelementsandthe cage the drag torque Tdragresults on the cage which is retained in the lubricant. The measured frictiontorque therefore is reduced by the amount of the drag torque. In t
32、he following the influence of the differentmeasuring techniques on the results is examined. With the help of a modified test rig, the influence of themeasuringpositiondependentonspeedandoillevelisinvestigated. Thetestingbearingsareappliedwiththeminimum radialloadaccordingto6. Whilstoperatingwithmini
33、mum lubricationthedraglosses vanish,bothmeasuring positions should show the same results. Dipping the shaft into the lubricants leads to additionaldraglosseswhichwouldinfluencetheresults. Thereforethemaximumoillevelislimitedtotheinnerringofthetest bearings. Between these extremes the levels “lowest
34、rolling element half in oil” and “lowest rollingelement in oil” are defined. Figure 3 shows the results for the minimum oil level.Table 2. Test speedsInner ring speed, n,rpm 20, 50 100, 500, 1000, 3000, 5000Figure 2. Measured friction torques of a bearing6 12FTM02Results for minimum lubricationFigur
35、e 3. Friction torque at minimum lubricationFigure 3 shows the total friction torque in dependence of the inner ring speed. The measuring results arecomparedwiththecalculationresults accordingtoSKF6. Thedeviationbetweenthemeasuredtorquesontheinnerandouterringarewithinthemeasurementprecision. Thisappr
36、ovestheassumptionthatwithdisap-pearance of the drag losses the measuring position has no influence on the results. Furthermore at lowspeeds theresults fit thecalculations accordingtoSKF verywell. At mediumandhighspeeds thecalculatedvalues arebelowthemeasuredones. Figure 4summarizes theresults forthe
37、maximumoillevel. Inadditionto the SKF results, values calculated with the method of Koryciak 8 are visualized.Figure 4showsthatwithhigheroillevelsarisingdifferenceofthemeasuredtorquescanbeobservedfromaninner ring speed of 1000rpm upwards. The measuring position on the outer ring furthermore shows a
38、goodcorrelation to the results according to Koryciak. Koryciak performed his examinations on test rigs whichdetect the friction torque on the outer rings of the test bearings. The conclusion is, that with rising oil leveldifferingfrictiontorquesaretobeobservedoninnerandouterrings. Furthermoretheresu
39、ltsshowdeviationsin the range of 100 Nmm for the examined bearing. The measurements within this study are performed atconsiderably high radial and axial loads, which lead to much higher frictions levels than observed in thischapter. Intherangeofhighfrictionlevels,greaterdeviationshavetobetakenintoac
40、count,whicheasilycanamount to several 100 Nmm. Considering this the influence of the measuring position on the results can beneglected.Results for oil level up to inner ringFigure 4. Friction torque at oil level “Up to inner ring“7 12FTM02Influence of the bearing sizeFortheexaminationofthesizeeffect
41、CRBwith30,50and80mmborediameteraretested. Table 3showstherelevant data of the NJ22-design.Drivenat constant speed, arisingbearingdiameter effects ahigher sum of velocities inthelip-roller contact.Atrisingsumofvelocitiesthelubricantfilmthicknessrisesaswell,whichmeansthatthesumofvelocitieshasgreat inf
42、luence on the friction and wear behavior of the contact. At low speeds the lip-roller contact ischaracterizedbymixedlubrication. Whilespeedinguptheportionof hydrodynamiclubricationrises. Forthisreason there is a minimum at a certain speed range. Above the speed range with minimum friction the draglo
43、ssesgrowbigger. Figure 5illustratestheseeffects. TheloadindependentlossesarerepresentedbyT0,theradial load dependent friction torque is T1and the axial load dependent friction torque is T2.Causedbythedifferingsumsofvelocities,inconnectionwithrisingbearingdiameters,thefrictionminimumisremovedtolower
44、speeds withrisingbearingdiameter. Concurrently, theaxialloaddependent frictiontorquedecreases, due to higher lubrication film thickness, with rising diameter and constant speed and load. Theaxial load dependent frictiontorque is described as the product of thenormal forcein theliproller contact, afr
45、ictioncoefficientandthelevertothebearingaxis. Thelevergrowswiththebearingdiameter,forwhichreas-on the friction torque grows as well. Figure 6 shows the result of the different effects at constant speed andaxial load.Duetothedescribedeffectsthesmallestbearingshowsthehighestaxialloaddependentfrictiont
46、orqueonthetestrig. Forthemediumsizebearingthelowestaxialloaddependentfrictiontorquecanbeobservedwhereasthe largest bearing has friction losses which range exactly between the other ones. Figure 7 shows theproportions.Table 3. Bearing geometry NJ2206, NJ 2210 and NJ2216NJ2206 NJ2210 NJ2216Bore diamet
47、er, d,mm 30 50 80Outer diameter, D,mm 62 90 140Bearing width, B,mm 20 23 33Quantity of rolling elements, n 13 16 18Rolling element diameter, dW,mm 9 11 16Rolling element width, lW,mm 13 15 24Static load rating, C0,kN 50 88 245Figure 5. Distribution of the friction torque dependent on the inner ring
48、speed8 12FTM02Figure 6. Friction coefficient and lever of the friction force on the lip of the inner ringFigure 7. Axial load dependent friction torque T2in dependent on speed and bearing sizeFor theinterpretationof Figure 7, it has tobeconsideredthat theillustratedresults areonly validfor theaxiall
49、oad dependent friction torque and that speed, temperatures and axial loads are held constant.Influence of the bearing designTheexaminedbearingdesignsarealreadyintroducedearlier. Macroscopicallythedifferenttestbearingscanbedistinguishedbythequantityandconfigurationoftheirlips. AdditionallyfullcomplementCRBandbearingsof the “heavy” series NJ23 are investigated. Table 4 shows the relevant data of the examined bearingdesigns.As to be seen in Table 4, the full complement bearing and the NJ2306 obviously differ from the remainingbear
