>> P.59
A56ABCDEFGHIJKLMFrictionandAllowableRotationalSpeedFrictionComparedwithslidingbearings,thestarting(static)frictionforrollingbearingsissmall,andthedifferencebetweenthestarting(static)frictionandthekineticfrictionisalsosmall.Thelossofpowerandtempera-tureriseinmachinesarethusreduced,improvingthemechanicalefficiency.Frictionaltorqueisinfluencedbythebearingtype,bearingload,rotationalspeed,lubricantcharacteris-tics,etc.Itvariesaccordingtothelubricantwhenoperatedunderlight-loadsandhigh-speedconditions,andaccordingtotheloadwhenoperatedunderheavy-loadsandlow-speedconditions.Frictionaltorqueofrollingbearingsiscomplicatedbecauseitisinfluencedbyvariousfactors,butforconvenience,itcanbeexpressedapproximatelybythefollowingequations.・RadialbearingsM=μP……………………(37)・ThrustbearingsM=μP……………………(38)where,M:Frictionaltorque, N-mmμ:CoefficientoffrictionP:Bearingload, Nd:Bearingborediameter, mmdm:Meanvalueofbearingboreandoutsidediameters, mmTheapproximatecoefficientsoffrictionofIKOBearingsunderoperatingconditions,inwhichlubrica-tionandmountingarecorrectandwhereloadsarerel-ativelylargeandstable,areshowninTable40.AllowablerotationalspeedAstherotationalspeedofrollingbearingsisincreased,thebearingtemperaturealsoincreasesduetotheheatgeneratedatthecontactsurfacesbetweenthecage,racewaysandrollingelements,untilitfinallyleadstobearingseizure.Itisthereforenecessarytomaintaintherotationalspeedofabear-ingbelowacertainlimitvaluetoensuresafeopera-tionforlongperiods.Thislimitvalueiscalledtheallowablerotationalspeed.Sincetheamountofheatgeneratedisapproximatelyproportionaltotheslidingspeedatthecontactarea,thisslidingspeedisanapproximateguideindicatingthelimitofthebearingrotationalspeed.Theallowablerotationalspeedofbearingsthusvariesaccordingtothebearingtype,size,bearingload,methodoflubrication,radialclearance,andothersuchfactors.Theallowablerotationalspeedsshowninthetableofdimensionsareempiricalvalues.Theyarenotabsolutevaluesandcanbechangedaccordingtothebearinguseconditions.Dependingonthestructureandaccuracyaroundthebearing,thelubricantandthelubricationmethod,itispossibleforsomebear-ingstobeoperatedatmorethantwicetheallowablerotationalspeedgiveninthetablewithouttrouble.d2dm2Table40CoefficientoffrictionBearingseriesNeedlerollerbearingswithcageFullcomplementneedlerollerbearingsThrustneedlerollerbearingsThrustrollerbearingsμ0.0010〜0.00300.0030〜0.00500.0030〜0.00400.0030〜0.00401N=0.102kgf=0.2248lbs.1mm=0.03937inch
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