轧机机械专业毕业设计外文翻译

1RollingObjectiveToperformrollingprocessonanleadbarinordertoobservethechangeinboththecross-sectionalareaandthegeneralshape.Theory1.DefinitionFlatrollingorRollingisdefinedasthereductionofthecross-sectionalareaofthemetalstock,orthegeneralshapingofthemetalproducts,throughtheuseoftherotatingrolls[1].Itallowsahighdegreeofclosed-loopautomationandveryhighspeeds,andisthuscapableofprovidinghigh-quality,closetolerancestartingmaterialforvarioussecondarysheetmetalworkingprocessesatalowcost[1].2.SchematicDrawingofRollingProcess2Figure1.RollingProcess[2]TherollsrotateasillustratedinFigure1.topullandsimultaneouslysqueezetheworkbetweenthem.ThebasicprocessshowninFigure1isflatrolling,usedtoreducethethicknessofarectangularcrosssection.Figure2.Variousconfigurationsofrollingmills:(a)twohigh,(b)threehigh,(c)fourhigh,(d)clustermill,and(e)tandemrollingmill[2].Variousrollingmillconfigurationsareavailabletodealwiththevarietyofapplicationsandtechnicalproblemsintherollingprocess.Thebasicrollingmillconsistsoftwooppositerotatingrollsandisreferredtoasatwo-highrollingmill(Figure2a).Inthethree-highconfigurationFigure2(b),therearethreerollsinaverticalcolumn,andthedirectionofrotationofeachrollremainsunchanged.Toachieveaseriesofreductions,theworkcanbeapassedthroughfromeithersidebyraisingorloweringthestripaftereachpass.The3equipmentinathree-highrollingmillbecomesmorecomplicated,becauseanelevatormechanismisneededtoraiseandlowerthework[2].Roll-workcontactlengthisreducedwithalowerrollradius,andthisladstolowerforces,torque,andpower.Thefour-highrollingmillusestwosmallerdiameterrollstocontacttheworkandtwobackingrollsbehindthem.Anotherrollconfigurationthatallowssmallerworkingrollsagainsttheworkistheclusterrollingmill.Toachievehigherthroughputratesinstandardproducts,atandemrollingmillisoftenused.Thisconfigurationconsistsofaseriesofrollingstands.Witheachrollingstep,workvelocityincreases,andtheproblemofsynchronizingtherollspeedsateachstandissignificant[2].3.GeneralOverviewofProcessTheprimaryobjectivesoftheflatrollingprocessaretoreducethecross-sectionoftheincomingmaterialwhileimprovingitspropertiesandtoobtainthedesiredsectionattheexitfromtherolls.Theprocesscanbecarriedouthot,warm,orcold,dependingontheapplicationandthematerialinvolved.Therolledproductsareflatplatesandsheets.Rollingofblooms,slabs,billets,andplatesisusuallydoneattemperaturesabovetherecrystallizationtemperature(hotrolling).Sheetandstripoftenarerolledcoldinordertomaintainclosethicknesstolerances.Basicallyflatrollingconsistsofpassingmetalbetweentworollsthatrevolveinopposite4directions,thespacebetweentherollsbeingsomewhatlessthanthethicknessoftheenteringmetal.Becausetherollsrotatewithasurfacevelocityexceedingthespeedoftheincomingmetal,frictionalongthecontactinterfaceactstopropelthemetalforward.Themetalissqueezedandelongatedandusuallychangedincrosssection.Theamountofdeformationthatcanbeachievedinasinglepassbetweenagivenpairofrollsdependonthefrictionconditionsalongtheinterface.Iftoomuchisdemanded,therollswillsimplyskidoverstationerymetal.Toolittledeformationperpassresultsinexcessivecost.Rollinginvolveshighcomplexityofmetalflowduringtheprocess.Fromthispointofview,rollingcanbedividedintothefollowingcategories[3]:Uniformreductioninthicknesswithnochangeinwidth:Here,thedeformationisinplanestrain,thatis,inthedirectionsofrollingandsheetthickness.Thistypeoccursinrollingofstrip,sheet,orfoil.Uniformreductioninthicknesswithanincreaseinwidth:Here,thematerialiselongatedintherollingdirection,isspreadinthewidthdirection,andiscompresseduniformlyinthethicknessdirection.Thistypeoccursintherollingofblooms,slabs,andthickplates.Moderatelynon-uniformreductionincrosssection:Here,themetaliselongatedintherollingdirection,isspreadinthewidthdirection,andisreducednon-uniformlyinthethicknessdirection.Highlynon-uniformreductionincrosssection:Here,thereductioninthethickness5directionishighlynon-uniform.Aportionoftherolledsectionisreducedinthicknesswhileotherportionsmaybeextrudedorincreasedinthickness.Asaresult,inthewidthdirectionmetalflowmaybetowardthecenter[3].HotRollingThedistinctivemarkofhotrollingisnotacrystallizedstructure,butthesimultaneousoccurrenceofdislocationpropagationandsofteningprocesses,withorwithoutrecrystallizationduringrolling.Thedominantmechanismdependsontemperatureandgrainsize.Ingeneral,therecrystallizedstructurebecomesfinerwithlowerdeformationtemperatureandfastercoolingratesandmaterialofsuperiorpropertiesareobtainedbycontrollingthefinishingtemperature[1].Hotrollingoffersseveraladvantages[1]:1)Flowstressesarelow,henceforcesandpowerrequirementsarerelativelylow,andevenverylargeworkpiecescanbedeformedwithequipmentofreasonablesize.2)Ductilityishigh;hencelargedeformationscanbetaken.3)Complexpartshapescanbegenerated.Theupperlimitforhotrollingisdeterminedbythetemperatureatwhicheithermeltingorexcessiveoxidationoccurs.Generally,themaximumworkingtemperatureislimitedto50°Cbelowthemeltingtemperature.Thisistoallowthepossibilityofsegregatedregionsoflower6meltingmaterial[4].ColdRollingColdrolling,intheeverydaysense,mea