>> P.42
A39∆δ=α∆tE…………………………………(29)where, ∆δ: Reductionofradialclearance, mm α: Coefficientoflinearexpansionforbearingsteel ≒12.5×10-61/°C ∆t: Temperaturedifferencebetweentheouterringandtheinnerringplusrollingelementsconsideredasoneunit, ° C E: Borediameterofouterring,mmThetemperaturedifference∆tisconsideredtobe5〜10°Cundernormaloperatingconditionsand15〜 20°Cathighrotationalspeeds.Therefore,whenthetemperaturedifferenceisgreat,acorrespondinglylargerradialinternalclearancemustbeselected.FitPurposeoffitToachievethebestperformanceofneedlerollerbearings,itisimportantthatthebearingringsarecor-rectlyfittedontotheshaftandintothehousing.Thepurposeoffitistoprovidetheappropriateamountofinterferencerequiredbetweentheinnerringandtheshaftorbetweentheouterringandthehousing,topreventharmfulmutualslippage.Iftheinterferenceisinsufficient,itwillcauseaharmfulrelativedisplacement,knownascreep,betweenthefittedsurfacesinthecircumferentialdirection.Thismayleadtoabnormalwearoffittedsurfaces,intru-sionofwearparticlesintothebearing,generationofabnormalheat,vibration,etc.Therefore,asuitablefitmustbeselected.Table20NatureofradialloadandfitNatureoftheloadFitInnerringRotatingconditionsOuterringRotatingloadoninnerringStationaryloadonouterringRotatingloadonouterringStationaryloadoninnerringDirectionallyndeterminateladTheloaddirectionisnotfixed,includingcaseswheretheloaddirectionisfluctuat-ingorthereisanunbal-ancedload.Innerring:RotatingOuterring:StationaryLoaddirection:FixedInnerring:StationaryOuterring:RotatingLoaddirection:RotatingwithouterringInnerring:StationaryOuterring:RotatingLoaddirection:FixedInnerring:RotatingOuterring:StationaryLoaddirection:RotatingwithinnerringInnerring:RotatingorstationaryOuterring:RotatingorstationaryLoaddirection:NotfixedInterferencefitClearancefitInterferencefitClearancefitInterferencefitInterferencefit
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