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Ⅲ-7FrictionLubricationFrictionoflinearmotionrollingguideThestaticfriction(start-upfriction)oflinearmotionrollingguidesismuchlowerthanthatofconventionalplainguides.Also,thedifferencebetweenstaticfrictionanddynamicfrictionissmall,andfrictionalresistancevarieslittlewhenvelocitychanges.Theseareexcellentfeaturesoflinearmotionrollingguides,andaccountfortheirabilitytoreducepowerconsumption,suppressoperatingtemperaturerise,andincreasetravelingspeed.Sincefrictionalresistanceandvariationaresmall,highspeedresponsecharacteristicstomotioncommandsandhighaccuracypositioningcanbeachieved.FrictioncoefficientThefrictionalresistanceoflinearmotionrollingguidesvarieswiththeirmodel,appliedload,velocityandcharacteristicsoflubricant.Generally,lubricantorsealsaremajorfactorsindeterminingthefrictionalresistanceinlightloadorhighspeedoperation,whiletheamountofloadisthemajorfactorinheavyloadorlowspeedoperation.Thefrictionalresistanceoflinearmotionrollingguidesdependsonvariousfactors,butgenerallythefollowingformulaisused.F=μP(3)where,F:Frictionalresistance,Nμ:DynamicfrictioncoefficientP:Appliedload,NForsealedguides,sealresistanceisaddedtotheabovevalue,butthisresistancevariesgreatlydependingontheinterferenceamountofseallipandlubricationconditions.Wherethelubricationandmountingconditionarecorrectandtheloadismoderate,thefrictioncoefficientsoflinearmotionrollingguideinoperationarewithintherangeshowninTable5.Generally,frictioncoefficientislargeundersmallload.Table5FrictioncoefficientSeriesnameDynamicfrictioncoefficientμ(1)CrossedRollerWay0.0010～0.0030LinearSlideUnit0.0010～0.0020LinearBallSpline0.0020～0.0040LinearBushing0.0020～0.0030StrokeRotaryBushing0.0006～0.0012RollerWay0.0020～0.0040FlatRollerCage0.0010～0.0030Note(1)Thesefrictioncoefficientsdonotincludeseal.ObjectivesoflubricationTheobjectivesofapplyinglubricantforlinearmotionrollingguidesistokeepraceways,rollingelements,etc.inalinearmotionrollingguidefrommetalcontact,andtherebyreducefrictionandwearpreventingheatgenerationandseizure.Whenanadequateoilfilmisformedattherollingcontactareabetweentheracewaysandrollingelements,thecontactstressduetoloadcanbereduced.Tomanagetheformationofadequateoilfilmisimportantforensuringthereliabilityoflinearmotionrollingmechanism.SelectionoflubricantToobtainthefullperformanceoflinearmotionrollingguides,itisnecessarytoselectanappropriatelubricantandlubricationmethodbyconsideringthemodel,loadandvelocityofeachlinearmotionrollingguide.However,ascomparedwithplainguides,lubricationoflinearmotionrollingguidesismuchsimpler.Onlyasmallamountoflubricationoilisneededandreplenishmentintervalislonger,somaintenancecanbegreatlyreduced.Greaseandoilarethetwomostcommonlyusedlubricantsforlinearmotionrollingguides.GreaselubricationForlinearmotionrollingguides,lithium-soapbasegrease(ConsistencyNo.2ofJIS)iscommonlyused.Forrollingguidesoperatingunderheavyloadconditions,greasecontainingextremepressureadditivesisrecommended.Incleanandhigh-vacuumenvironments,wherelowdustgeneratingperformanceandlowvaporizationcharacteristicsarerequired,greasescontainingasynthetic-baseoilorasoapotherthanthelithium-soapbaseareused.Forapplicationsintheseenvironments,dueconsiderationisnecessarytoselectagreasethatissuitablefortheoperatingconditionsoflinearmotionrollingguideandachievessatisfactorylubricationperformanceatthesametime.Table6Pre-packedgreaselistSeriesnamePre-packedgreaseC-LubeLinearBallSplineMAGLinearBallSplineGAlvaniaEPGrease2[ShellLubricantsJapanK.K.]GreasereplenishmentintervalThequalityofanygreasewillgraduallydeteriorateasoperatingtimepasses.Therefore,periodicreplenishmentisnecessary.Greasereplenishmentintervalvariesdependingontheoperatingconditions.Asixmonthintervalisgenerallyrecommended,andifthemachineoperationconsistsofreciprocatingmotionswithmanycyclesandlongstrokes,replenishmenteverythreemonthisrecommended.Inaddition,linearmotionrollingguidesinwhichthelubricationpart"C-Lube"isbuiltdeliverlong-termmaintenancefreeperformance.Thiseliminatestheneedforlubricationmechanismandworkloadwhichusedtobenecessaryforlinearmotionrollingguidesandsignificantlyreducesmaintenancecost.
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