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外文翻译--机械.doc

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外文翻译--机械.doc

附录附录1英文原文RollingContactBearingsTheconcernofamachinedesignerwithballandrollerbearingsisfivefoldasfollowsalifeinrelationtoloadbstiffness,i.e.deflectionsunderloadcfrictiondwearenoise.Formoderateloadsandspeedsthecorrectselectionofastandardbearingonthebasisofaloadratingwillbecomeimportantwhereloadsarehigh,althoughthisisusuallyoflessmagnitudethanthatoftheshaftsorothercomponentsassociatedwiththebearing.Wherespeedsarehighspecialcoolingarrangementsbecomenecessarywhichmayincreasefricitionaldrag.Wearisprimarilyassociatedwiththeintroductionofcontaminants,andsealingarrangementsmustbechosenwithregardtothehostilityoftheenvironment.Becausethehighqualityandlowpriceofballandrollerbearingdependsonquantityproduction,thetaskofthemachinedesignerbecomesoneofselectionratherthandesign.Rollingcontactbearingsaregenerallymadewithsteelwhichisthroughhardenedtoabout900HV,althoughinmanymechanismsspecialracesarenotprovidedandtheinteractingsurfacesarehardenedtoabout600HV.Itisnotsurprisingthat,owingtothehighstressesinvolved,apredominantformoffailureshouldbemetalfatigue,andagooddealofworkisbasedonacceptvaluesoflifeanditisgeneralpracticeinbearingindustrytodefinetheloadcapacityofthebearingasthatvaluebelowwhich90percentofabatchwillexceedlifeofonemillionrevolutions.Notwithstandingthefactthatresponsibilityforbasicdesignofballandrollerbearingsrestswithhebearingmanufacturer,themachinedesignermustformacorrectappreciationofthedutytobeperformedbythebearingandbeconcernednotonlywithbearingselectionbutwiththeconditionsforcorrectinstallation.Thefitofthebearingracesontotheshaftorontothehousingsisofcriticalimportancebecauseoftheircombinedeffectontheinternalclearanceofthebearingaswellaspreservingthedesireddegreeofinterferencefit.Inadequateinterferencecaninduceserioustroublefromfrettingcorrosion.Theinnerraceisfrequentlylocatedaxiallybyagainstashoulder.Aradiusatthispointisessentialfortheavoidanceofstressconcentrationandballracesareprovidedwitharadiusorchamfertofollowspaceforthis.Wherelifeisnotthedeterminingfactorindesign,itisusualtodeterminemaximumloadingbytheamounttowhichabearingwilldeflectunderload.Thustheconceptofstaticloadcarryingcapacityisunderstoodtomeantheloadthatcanbeappliedtoabearing,whichiseitherstationaryorsubjecttoslightswivelingmotions,withoutimpairingitsrunningqualitiesforsubsequentrotationalmotion.Thishasbeendeterminedbypracticalexperienceastheloadwhichwhenappliedtoabearingresultsinatotaldeformationof0.0025mmforaball25mmindiameter.Thesuccessfulfunctioningofmanybearingsdependsuponprovidingthemwithadequateprotectionagainsttheirenvironment,andinsomecircumstancestheenvironmentmustbeprotectedfromlubricantsorproductsofdeteriorationofthebearingdesign.Moreover,sealswhichareappliedtomovingpartsforanypurposeareofinteresttotribologistsbecausetheyarecomponentsofbearingsystemsandcanonlybedesignedsatisfactorilyonbasisoftheappropriatebearingtheory.Notwithstandingtheirimportance,theamountofresearcheffortthathasbeendevotedtotheunderstandingofthebehaviorofsealshasbeensmallwhencomparedwiththatdevotedtootheraspectsofbearingtechnology.LathesLathesarewidelyusedinindustrytoproduceallkindsofmachinedparts.Somearegeneralpurposemachines,andothersareusedtoperformhighlyspecializedoperations.EnginelathesEnginelathes,ofcourse,aregeneralpurposemachineusedinproductionandmaintenanceshopalloverthetheworld.Sizedrangerfromsmallbenchmodelstohugeheavydutypiecesofequipment.Manyofthelargerlathescomeequippedwithattachmentsnotcommonlyfoundintheordinaryshop,suchasautomaticshopforthecarriage.TracerorDuplicatingLathesThetracerorduplicatinglatheisdesignedoproduceirregularlyshapedpartsautomatically.Thebasicoperationofthislatheisasfallows.Atemplateofeitheraflatorthreedimensionalshapeisplacedinaholder.Aguideorpointerthenmovesalongthisshapeanditsmovementcontrolsthatofthecuttingtool.Theduplicationmayincludeasquareortaperedshoulder,grooves,tapers,andcontours.Worksuchasmotorshafts,spindles,pistons,rods,caraxles,turbineshafts,andavarietyofotherobjectscanbeturnedusingthistypeoflathe.TurretLathesWhenmachiningacomplexworkpieceonageneralpurposelathe,agreatdealoftimeisspentchangingandadjustingtheseveraltoolsthatareneededtocompletethework.Oneofthefirstadaptationsoftheenginelathewhichmadeitsuitabletomassproductionwastheadditionofmultitoolinplaceofthetailstock.Althoughmostturretshavesixstations,somehaveasmanyaseight.Highproductionturretlathesareverycomplicatedmachineswithawidevarietyofpoweraccessories.Theprincipalfeatureofallturretlathes,however,isthatthetoolscanperformaconsecutiveserialsofoperationsinpropersequence.Oncethetoolshavebeensetandadjusted,littleskillisrequiretorunoutduplicateparts.AutomaticScrewMachineScrewmachinesaresimilarinconstructiontoturretlathes,exceptthattheirheadsaredesignedtoholdandfeedlongbarsofstock.Otherwise,theirislittledifferentbetweenthem.Botharedesignedformultipletooling,andbothhaveadaptationsforidenticalwork.Originally,theturretlathewasdesignedasachuckinglatheformachiningsmallcasting,forgings,andirregularlyshapedworkpieces.Thefirstscrewmachinesweredesignedtofeedbarstockandwireusedinmakingsmallscrewparts.Today,however,theturretlatheisfrequentlyusedwithacollectattachment,andtheautomaticscrewmachinecanbeequippedwithachucktoholdcastings.Thesinglespindleautomaticscrewmachine,asitsnameimplies,machinesworkononlyonebarofstockatatime.Abar16to20feetlongisfeedthroughtheheadstockspindleandisheldfirmlybyacollect.Themachiningoperationsaredonebycuttingtoolsmountedonthecrossslide.Whenthemachineisinoperation,thespindleandthestockarerotatedatselectedspeedsfordifferentoperations.Ifrequired,rapidreversalofspindledirectionisalsopossible.Inthesinglespindleautomaticscrewmachine,aspecificlengthofstockisautomaticallyfedthroughthespindletoamachiningarea.Atthispoint,theturretandcrossslidemoveintopositionandautomaticallyperformwhateveroperationsarerequired.Afterthemachinedpieceiscutoff,stockisagainfedintothemachiningareaandtheentirecycleisrepeated.Multiplespindleautomaticscrewmachineshavefromfourtoeightspindleslocatedaroundaspindlecarrier.Longbarsofstock,supportedattherearofthemachine,passthoughthesehollowspindlesandaregrippedbycollects.Withthesinglespindlemachines,theturretindexesaroundthespindle.Whenonetoolontheturretisworking,theothersarenot.Withamultiplespindlemachine,however,thespindleitselfindex.Thusthebarsofstockarecarriedtothevariousendworkingandsideworkingtools.Eachtooloperatesinonlyoneposition,buttollsoperatesimultaneously.Therefore,fourtoeightworkpiecescanbemachinedatthesametime.VerticalTurretLathesAverticalturretisbasicallyaturretlathethathasbeenstoodonitsheadstockend.Itisdesignedtoperformavarietyofturningoperations.Itconsistsofaturret,arevolvingtable,andasideheadwithasquareturretforholdingadditionaltools.Operationsperformedbyanyofthetoolsmountedontheturretorsideheadcanbecontrolledthroughtheuseofstops.MachiningCentersManyoftodaysmoresophisticatedlathesarecalledmachiningcenterssincetheyarecapableofperforming,inadditiontothenormalturningoperations,certainmillinganddrillingoperations.Basically,amachiningcentercanbethoughtofasbeingacombinationturretlatheandmillingmachine.Additionalfeaturesaresometimesincludedbytheversatilityoftheirmachines.NumericalControlOneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrolNC.PriortotheadventofNC,allmachinetoolsweremanuallyoperatedandcontrolled.Amongthemanylimitationsassociatedwithmanualcontrolmachinetools,perhapsnoneismoreprominentthanlimitationofoperatorskills.Withmanualcontrol,thequalityoftheproductisdirectlyrelatedtoandlimitedtotheskillsoftheoperator.Numericalcontrolrepresentsthefirstmajorstepawayfromhumancontrolofmachinetools.Numericalcontrolmeansthecontrolofmachinetoolsandothermanufacturingsystemsthroughtheuseofprerecorded,writtensymbolicinstructions.Ratherthanoperatingamachinetool,anNCtechniciantooltobenumericallycontrolled,itmustbeinterfacedwithadeviceforacceptinganddecodingtheprogrammedinstructions,knownasareader.Numericalcontrolwasdevelopedtoovercomethelimitationofhuman

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