>> P.223
Ⅲ-3LoadRatingandLifeLifeoflinearmotionrollingguidesEveninnormaloperationalstatus,alinearmotionrollingguidewillreachtheendofitslifeafteracertainperiodofoperations.Asrepeatedloadisconstantlyappliedontoaracewayandrollingelementsofthelinearmotionrollingguide,thisleadstoleprousdamage(scale-likewearfragments)calledfatigueflakingduetorollingcontactfatigueofmaterials,itwillbeunusableattheend.Totaltravelingdistancebeforeoccurrenceofthisfatigueflakingonaracewayorrollingelementsiscalledthelifeoflinearmotionrollingguide.Asthelifeoflinearmotionrollingguidemayvarydependingonmaterialfatiguephenomenon,ratinglifebasedonstatisticcalculationisused.RatinglifeRatinglifeoflinearmotionrollingguidereferstothetotaltravelingdistance(1)90%ofagroupofthesamelinearmotionrollingguidecanoperatewithoutlinearmotionrollingguidematerialdamagesduetorollingcontactfatiguewhentheyareoperatedindividuallyunderthesameconditions.Note(1)StrokeRotaryBushingisrepresentedastotalnumberofrotations.BasicdynamicloadratingCBasicdynamicloadratingreferstoloadwithcertaindirectionandsizethatislogicallyendurableforratinglifeindicatedinTable1whenagroupofthesamelinearmotionrollingguidesisoperatedindividuallyunderthesameconditions.Table1LoadratingSeriesRatinglifeCrossedRollerWayRollerWay&FlatRollerCage100×103mLinearSlideUnitLinearBallSplineLinearBushing50×103mStrokeRotaryBushing106rotationsBasicstaticloadratingC0Basicstaticloadratingreferstostaticloadgeneratingacertaincontactstressatthecenterofcontactpartsoftherollingelementsandaracewayundermaximumload,whichistheloadattheallowablelimitfornormalrollingmotion.Generally,itisusedconsideringstaticsafetyfactor.AllowableloadFAllowableloadreferstoloadofsmoothrollingmotiononcontactsurfacetowhichmaximumcontactstressisappliedandthesumofwhoseelasticdeformationofrollingelementsandracewayissmall.Therefore,useappliedloadwithintheallowableloadrangeifverysmoothrollingmotionandhighaccuracyarerequired.DynamictorqueratingTDynamictorqueratingreferstoatorquewithacertaindirectionandsizewithwhich90%ofagroupofthesamelinearballsplinescanrun50x103mwithoutmaterialdamagesduetorollingcontactfatiguewhentheyareoperatedindividually.StatictorqueratingT0StaticmomentratingT0,TX,TYStatictorqueratingandstaticmomentratingrefertostatictorqueormomentloadgeneratingacertainlevelofcontactstressatthecenterofcontactpartsofrollingelementsandaracewayunderthemaximumloadwhenthetorqueormomentload(seeFig.1)areloaded,whichisthetorqueormomentloadattheallowablelimitfornormalrollingmotion.Generally,itisusedconsideringstaticsafetyfactor.LoaddirectionandloadratingLinearmotionrollingguideisusedwithitsloadratingcorrectedinaccordancetotheloaddirection.Basicdynamicloadratingandbasicstaticloadratingindicatedinthedimensiontableshouldbecorrectedbeforeuse.Asthevaluestobecorrectedvarydependingonseries,pleaseseeanexplanationforeachseries.
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