>> P.48
A45RacewaymaterialsandheattreatmentWhenusingshaftsandhousingsasraceways,thefol-lowingmaterialsaregenerallyused.High-carbonchromiumbearingsteel SUJ2JISG4805Carburizingsteel SCM415〜421JISG4053Carburizingsteel SNCM220JISG4053Carburizingsteel SCr420JISG4053Carburizingsteel SNC415,815JISG4053Carburizingsteel S15CKJISG4051Inaddition,S50CandS55C(JISG4051)canbeusedafterthroughhardeningorinductionhardening.Thehardenedlayerproducedbytemperingat+160〜+180°Cafterhardeningmusthaveafineuniformmartensitemicrostructure.Whenhardeningtheracewaysurfacebycasehard-eningorinductionhardening,asurfacehardnessof58〜64HRCandanappropriatethicknessofthehardenedlayermustbeensured.Theminimumeffectivethicknessofthehardenedlayerafterheattreatmentandgrindingisdefinedasthedistancefromthesurfacetothedepthwherethehardnessis550HV,anditisobtainedbythefollowingequation.Eht≧0.8Dw(0.1+0.002Dw)……………(36)where,Eht: Minimumeffectivethicknessofthehardenedlayer, mm Dw:Rollerdiameter, mmGenerally,therequiredeffectivethicknessofthehardenedlayerisatleast0.3mm.DimensionsrelatedtomountingofbearingsThedimensionsofshaftandhousingrelatedtomountingoftheneedlerollerbearingsareshowninthetableofdimensionsforeachbearing.(SeeFig.13.)Theminimumvalueoftheshaftshoulderdiameterdawhichreceivestheinnerring,andthemaximumvalueofthehousingshoulderdiameterDawhichreceivestheouterring,representtheeffectiveshoulderdiame-ters(excludingthechamferedpart)whichmakeprop-ercontactwiththesidefacesoftheinnerandouterringsrespectively.Also,themaximumvalueoftheshaftshoulder(orinnerringretainingpiece)diameterdaisthedimen-sionrelatedtotheeaseofmounting/dismountingoftheshaftandinnerringto/fromthehousingandouterring.Thelargestpermissiblesinglecornerradiusrasmaxoftheshaftandhousingmustbesmallerthanthesmall-estpermissiblesinglechamferdimensionrsminofthebearingsothatthesidesurfaceofthebearingcanmakepropercontactwiththeshoulder.Table28showstherelateddimensions.Fordimensionsofthefilletreliefwhenfinishingtheshaftorhousingbygrinding,thevaluesshowninTable29arerecommended.Forotherdimensionsrelatedtomounting,seetherelatedsectionforeachbearingasrequired.Inaddition,foreaseindismountingofbearings,itisconvenienttomakenotchesintheshoulderoftheshaftorhousingtoallowtheinsertionofdismountinghooks.Fig.13DimensionsrelatedtomountingdaDa
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