搜索
附录附录1英文原文RollingContactBearingsTheconcernofamachinedesignerwithballandrollerbearingsisfivefoldasfollows:(a)lifeinrelationtoload;(b)stiffness,ie.deflectionsunderload;(c)friction;(d)wear;(e)noise.Formoderateloadsandspeedsthecorrectselectionofastandardbearingonthebasisofaloadratingwillbecomeimportantwhereloadsarehigh,althoughthisisusuallyoflessmagnitudethanthatoftheshaftsorothercomponentsassociatedwiththebearing.Wherespeedsarehighspecialcoolingarrangementsbecomenecessarywhichmayincreasefricitionaldrag.Wearisprimarilyassociatedwiththeintroductionofcontaminants,andsealingarrangementsmustbechosenwithregardtothehostilityoftheenvironment.Becausethehighqualityandlowpriceofballandrollerbearingdependsonquantityproduction,thetaskofthemachinedesignerbecomesoneofselectionratherthandesign.Rolling-contactbearingsaregenerallymadewithsteelwhichisthrough-hardenedtoabout900HV,althoughinmanymechanismsspecialracesarenotprovidedandtheinteractingsurfacesarehardenedtoabout600HV.Itisnotsurprisingthat,owingtothehighstressesinvolved,apredominantformoffailureshouldbemetalfatigue,andagooddealofworkisbasedonacceptvaluesoflifeanditisgeneralpracticeinbearingindustrytodefinetheloadcapacityofthebearingasthatvaluebelowwhich90percentofabatchwillexceedlifeofonemillionrevolutions.Notwithstandingthefactthatresponsibilityforbasicdesignofballandrollerbearingsrestswiththebearingmanufacturer,themachinedesignermustformacorrectappreciationofthedutytobeperformedbythebearingandbeconcernednotonlywithbearingselectionbutwiththeconditionsforcorrectinstallation.Thefitofthebearingracesontotheshaftorontothehousingsisofcriticalimportancebecauseoftheircombinedeffectontheinternalclearanceofthebearingaswellaspreservingthedesireddegreeofinterferencefit.Inadequateinterferencecaninduceserioustroublefromfrettingcorrosion.Theinnerraceisfrequentlylocatedaxiallybyagainstashoulder.Aradiusatthispointisessentialfortheavoidanceofstressconcentrationandballracesareprovidedwitharadiusorchamfertofollowspaceforthis.Wherelifeisnotthedeterminingfactorindesign,itisusualtodeterminemaximumloadingbytheamounttowhichabearingwilldeflectunderload.Thustheconceptofstaticload-carryingcapacityisunderstoodtomeantheloadthatcanbeappliedtoabearing,whichiseitherstationaryorsubjecttoslightswivelingmotions,withoutimpairingitsrunningqualitiesforsubsequentrotationalmotion.Thishasbeendeterminedbypracticalexperienceastheloadwhichwhenappliedtoabearingresultsinatotaldeformationof0.0025mmforaball25mmindiameter.Thesuccessfulfunctioningofmanybearingsdependsuponprovidingthemwithadequateprotectionagainsttheirenvironment,andinsomecircumstancestheenvironmentmustbeprotectedfromlubricantsorproductsofdeteriorationofthebearingdesign.Moreover,sealswhichareappliedtomovingpartsforanypurposeareofinteresttotribologistsbecausetheyarecomponentsofbearingsystemsandcanonlybedesignedsatisfactorilyonbasisoftheappropriatebearingtheory.Notwithstandingtheirimportance,theamountofresearcheffortthathasbeendevotedtotheunderstandingofthebehaviorofsealshasbeensmallwhencomparedwiththatdevotedtootheraspectsofbearingtechnology.LathesLathesarewidelyusedinindustrytoproduceallkindsofmachinedparts.Somearegeneralpurposemachines,andothersareusedtoperformhighlyspecializedoperations.EnginelathesEnginelathes,ofcourse,aregeneral-purposemachineusedinproductionandmaintenanceshopalloverthetheworld.Sizedrangerfromsmallbenchmodelstohugeheavydutypiecesofequipment.Manyofthelargerlathescomeequippedwithattachmentsnotcommonlyfoundintheordinaryshop,suchasautomaticshopforthecarriage.TracerorDuplicatingLathesThetracerorduplicatinglatheisdesignedoproduceirregularlyshapedpartsautomatically.Thebasicoperationofthislatheisasfallows.Atemplateofeitheraflatorthree-dimensionalshapeisplacedinaholder.Aguideorpointerthenmovesalongthisshapeanditsmovementcontrolsthatofthecuttingtool.Theduplicationmayincludeasquareortaperedshoulder,grooves,tapers,andcontours.Worksuchasmotorshafts,spindles,pistons,rods,caraxles,turbineshafts,andavarietyofotherobjectscanbeturnedusingthistypeoflathe.TurretLathesWhenmachiningacomplexworkpieceonageneral-purposelathe,agreatdealoftimeisspentchangingandadjustingtheseveraltoolsthatareneededtocompletethework.Oneofthefirstadaptationsoftheenginelathewhichmadeitsuitabletomassproductionwastheadditionofmulti-toolinplaceofthetailstock.Althoughmostturretshavesixstations,somehaveasmanyaseight.High-productionturretlathesareverycomplicatedmachineswithawidevarietyofpoweraccessories.Theprincipalfeatureofallturretlathes,however,isthatthetoolscanperformaconsecutiveserialsofoperationsinpropersequence.Oncethetoolshavebeensetandadjusted,littleskillisrequiretorunoutduplicateparts.AutomaticScrewMachineScrewmachinesaresimilarinconstructiontoturretlathes,exceptthattheirheadsaredesignedtoholdandfeedlongbarsofstock.Otherwise,theirislittledifferentbetweenthem.Botharedesignedformultipletooling,andbothhaveadaptationsforidenticalwork.Originally,theturretlathewasdesignedasachuckinglatheformachiningsmallcasting,forgings,andirregularlyshapedworkpieces.Thefirstscrewmachinesweredesigned