>> P.41
1N=0.102kgf=0.2248lbs.1mm=0.03937inchABCDEFGHIJKLM∆C=∆F+∆E………………………………(24)where,∆C:Amountofreductionoftheradialclearance,mm∆F:Amountofexpansionoftheout-sidediameterofinnerring,mm∆E:Amountofshrinkageoftheborediameterofouterring,mm1Amountofexpansionoftheoutsidediameterofinnerring∆F=∆de………………………………(25)dF・Withhollowshaft・Withsolidshaft∆F=∆de ……(26)1-(d/F)2(di/d)21-(di/d)2dF:Effectiveinterferenceofinnerring, mmwhere,∆ded:Borediameterofinnerring, mmF:Outsidediameterofinnerring, mmdi:Borediameterofhollowshaft, mm2Amountofshrinkageoftheborediameterofouterring………………………………(27)ED∆E=∆De・Withsteelhousing(D0≠∞)・Withsteelhousing(D0=∞)……(28)1-(D/D0)21-(E/D)2(D/D0)2ED∆E=∆Dewhere,∆DeDED0:Effectiveinterferenceofouterring, mm:Outsidediameterofouterring, mm:Borediameterofouterring, mm:Outsidediameterofhousing, mmReductionofradialclearancesduetotemperaturedifferencesbetweeninnerandouterringsFrictionalheatgeneratedbyrotationisdissipatedthroughtheshaftsandhousingsaswellasthroughoilandair.Undergeneraloperatingconditions,heatdis-sipationislargeronthehousingsidecomparedwiththatontheshaftside,andthetemperatureoftheouterringisusuallylowerthanthatoftheinnerring.Duringoperation,thetemperatureoftherollingele-mentsisthehighest,followedbythatoftheinnerringandthatoftheouterring.Theamountofthermalexpansion,therefore,varies,andtheradialclearancesarereduced.Thisreducedradialclearanceiscalledtheeffective(internal)clearance,andtheamountofreductionisobtainedbythefollowingequation:A38Selectionofclearancefit,thesetobearingfactorsgreatlytootheyareRadialclearancesofneedlerollerbearingschangeaccordingtemperaturedifferencebetweenbearingringsandrollingelements,loads,influencebearinglife,etc.,andaccuracy,noise,generationofheat,etc.Ifradiallarge,noiseandvibrationwillclearancesaretoosmall,abnormallygreatincrease,andifforcesareexertedonthecontactareasbetweenracewaysandrollingelements,resultinginabnormal-lyhighheatgenerationandadecreaseinbearinglife.theclearanceprovidedTherefore,beforemountingshouldbesuchthatitwillbecomezeroorslightlylargerwhenthebearinghasreachedsteady-stateoperationandtemperaturehasbecomeconstant(saturationtemperature).However,itisdifficulttoachievethisidealstateforallbearings.Undergeneraloperatingconditions,bearingswithCNclearancearemostwidelyused,andaremanufac-turedfittedaccordingtoTables21and22.WhenradialinternalclearancesotherthanCNareused,refertoTable19.toprovidesatisfactoryperformancewhentheidealcase,theinTable19ExamplesofselectingradialinternalclearancesotherthanCNclearanceOperatingconditionsSelectionofclearanceWhenheavyloadsareapplied,andamountofinterferenceisgreat.loadsandshockWhendirectionallyindeterminateloadsareapplied,andatightfitisrequiredforbothinnerandouterrings.Whentemperatureofinnerringismuchhigherthanthatofouterring.Whenshaftdeflectionand/ormountingerrortothehousingaregreat.Whenlessnoiseandvibrationarerequired.Whenaloosefitisrequiredforbothinnerandouterrings.Whenpreloadisrequired.C3orlargerclearanceC2orsmallerclearanceReductionofradialclearancesbyfittheintohousings,respectively,theradialclearancesarereduced.innerorouterringsareinterferencefittedWhentheyontoshaftsandtoelasticdeformation.Astheexpandorshrinkdueresult,Thesereducedradialclearancesarecalledresidual(internal)clearances.Theamountofreductionisobtainedbythefollowingequation,anditisgenerally70to90%oftheinterfer-enceamount.
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