制造技術專業(yè)英語翻譯樣本

資料內(nèi)容僅供您學習參考，如有不當或者侵權，請聯(lián)系改正或者刪除。7.1NATUREOFPLASTICDEFORMATIONPlasticdeformationisthedeformationwhichispermanentandbeyondtheelasticrangofthematerialoften,metalsareworkedbypfasticdeformationbecauseofthebeneficialeffectthatisimpartedtothemechanicalpropertiesbyit.Thenecessarydeformationinametalcanbeachievedbyapplicationoflargeamountofmechanicalforceonlyorbyheatingthemetalandthenapplyingasmallforce.7.1塑性變形本質(zhì)塑性變形是超過彈性變形范圍之后的一種永久變形。一般,金屬采用塑性變形加工是因為能夠經(jīng)過其獲得良好的機械性能。金屬所需要的變形能夠只經(jīng)過施加大量的機械力或者經(jīng)過加熱金屬而且施加少量的應力來獲得。Thedeformationofmetals,whichiscausedbythedisplacementoftheatomsisachievedbyoneorbothoftheprocessescalledslipandtwinning.Thedetailsofthemicroscopicdeformationmethodscanbefoundinthetextbooksof'metallurgy.Onthemacroscopicscale,whenplastic,deformationoccursthemetalappearstoflowinthesolidstatealongspecificdirections,whicharedepedentonthetypeofprocessingandthedirectionofappliedforce.Thecrystalsorgrainsofthemetalareelongatedinthedirectionofmetalflow.Thisflowofmetalcanbeseenundermicroscopeafterpolishingandsuitableetchingofthementalsurface.Thesevisiblelinesarecalledfibreflowlines,somerepresentativespecimensofwhicharepresentedinfig金屬的變形是由原子排列引起的,這種排列是由被稱作滑移和孿生過程中的一種或者兩者共同作用造成的。微觀的變形方式能夠從冶金學課本中找到。在微觀范圍內(nèi),當塑性變形產(chǎn)生的時候,在固體內(nèi)部金屬的流動傾向于特定的方向,這個方向取決于加工類型和應力方向。在金屬流動方向上金屬晶體或者晶粒將會延長。經(jīng)過顯微鏡觀察拋光和蝕刻后的表面,能夠看到這種金屬的流動方式。這些可見的線條叫做纖維流線。Sincethegrainsareelongatedinthedirectionofflow,wheywouldbeabletooffermoreresistancetostressesactingacrossthem.Asaresult,themechanicallyworkedmetalscalledwroughtproductswouldbeabletoachievebettermechanicalstrengthinspecificorientation,thatoftheflowdirection.sinceitispossiblesibletocontroltheseflowlinesinanyspecificdirectionbycarefulmanipulationoftheappliedforcesasshowninFig.7.1,itispossibletoachieveoptimummechanicalproperties.Themetal,ofcourse,wouldbeweakalongtheflowlines.因為晶粒在流動方向上被拉長了,這樣她們就更能夠抵抗作用于其上的應力。因此,在被稱為鍛造產(chǎn)品的機械加工零件的金屬流動方向上會獲得優(yōu)良的強度。這是因為,只要小心謹慎地控制應力,就能讓纖維流線朝著任何一個方向流動而且獲得最佳的機械性能。當然,金屬在沿著纖維線的方向也會變得疲軟。Thewastageofmaterialinmetal-workingprocessesiseithernegligibleorverysmall,andtheproductionrateisingeneralveryhigh.thesetwofactorsgiverisetotheeconomyinproduction材料的浪費在金屬加工過程中是很少的,甚至能夠忽略不計,而且其生產(chǎn)率一般來說是非常高的。這兩個因素使其在生產(chǎn)上更為經(jīng)濟。7.1.1HotWorkingandColdWorkingThemetal-workingprocessesaretraditionallydividedintohot-workingandcold-workingprocesses.Thedivisionisonthebasisoftheamountofheatingappliedtothemetalbeforeapplyingthemechanicalforce.7.1.1冷加工和熱加工傳統(tǒng)的金屬加工工藝分為熱加工和冷加工。這種區(qū)分是基于機械應力施加前金屬的受熱程度。Thoseprocesses,workingabovetherecrystallizationtemperature,aretermedhot-workingprocesseswhereasthosebelowaretermedcold-workingprocesses在這些加工工藝中,加熱溫度在再結(jié)晶溫度以上的叫做熱加工,在再結(jié)晶溫度以下的叫做冷加工。Undertheactionofheatandforcewhentheatomsreachacertainhigherenergylevel,thenewcrystalsstartformingwhichistermedasrecrystallization.Recrystallizationdestroystheoldgrainstructuredeformedbymechanicalworkingandentirelynewcrystals,whicharestrain-freeareformed,thegrains,infact,startnucleatingatthepointsofseverestdeformation.RecrystallzationtemperatureasdefinedbytheAmericanSocietyofMetalsis”theapproximateminimumtemperatureatwhichcompleterecrystallizationofacoldworkedmetaloccurswithinaspecifiedtime”.在加熱和應力的作用下,當原子達到某一更高能量的等級的時候,新的晶粒就開始形成的過程叫做再結(jié)晶。再結(jié)晶破壞了由機械作用構成的原有晶體結(jié)構,而且產(chǎn)生了無應變的新的晶體。事實上,新的晶粒是在嚴重變形的時候開始形核的。再結(jié)晶溫度是由美國金屬學會這樣定義的”在一定的時間段內(nèi),冷加工金屬完成再結(jié)晶時的最小溫度”。Therecrystallizationtemperaturegenerallyvariesbetweenone-thirdtohalfthemeltingpointofmostofthemetals.Typicalvaluesofrecrystallisationtemperaturesaregivenintable7.1,therecrystallizationtemperaturealsodependsontheamountofcoldworkamaterialhasalreadyreceived.thehigherthecoldworkthelowerwouldtherecrystallizationtemperatureasshowninFig7.2大多數(shù)的金屬再結(jié)晶溫度一般在金屬熔點的三分之一到二分之一內(nèi)。表7.1給出了具有代表性的再結(jié)晶溫度值。再結(jié)晶溫度取決于材料已經(jīng)改變的冷加工量。冷加工量越高,再結(jié)晶溫度越低,如圖7.2所示。Inhotworking,theprocessmaybecarriedabovetherecrystallizationtemperaturewithorwithoutactualheating.Forexample,forleadandtin,therecrystallizationtemperatureisbelowtheroomtemperatureandhenceworkingofthesemetalsatroomtemperatureisalwayshotworking.Similarlyforsteels,therecrystallizationtemperatureisoftheorderof1000℃,andthereforeworkingbelowthattemperatureisstillcoldworkingonly.在熱加工中,在加熱或者不加熱的實際條件下再結(jié)晶可能在再結(jié)晶溫度以上發(fā)生。例如,鉛和錫,它們的再結(jié)晶溫度都在室溫以下,因此室溫下的加工都屬于熱加工。同樣,鋼也是一樣的,鋼的再結(jié)晶溫度達到1000攝氏度,因此,在這溫度以下的加工都是冷加工。Inhotworking.,thetemperatureatwhichtheworkingiscompletedisimportantsinceanyextraheatleftafterworkingwillaidinthegraingrowth,thusgivingpoormechanicalproperties.TheeffectoftemperatureofcompletionofhotworkingisshownschematicallyinFig.7.3.AsimpleheatingisshowninA,wherethegrainsstartgrowingafterthemetalsizewouldbelargerthanwhenstartedinA.Afterheating,whenthemetalisworked,becauseofrecrystallization,thegrainsizeisreduced.Thisismadeofpossiblebecausetheworkingofmetalgivesrisetoalargenumberofnucleationsitesforthenewcrystalstoform.Butifthehotworkingiscompletedmuchabovetherecrystallizationtemperatureasin.C,thegrainsizestartsincreasingandfinallymayendupasacoarsegrainsize.Thisincreaseinsizeofthegrainsoccursbyaprocessofcoalescenceofadjoininggrainsandisafunctionoftimeandtemperature.Thisisnotgenerallydesirable.IfthehotworkingiscompletedjustabovetherecrystallizationtemperatureasinDthentheresultantgrainsizewouldbefine.ThesameisschematicallyshownforhotrollingoperationinFig.7.4.在熱加工中,加工完成后的溫度是很重要的,因為加工完成后任何余熱都能讓晶粒長大,這樣會得到很差的機械性能。熱加工最后溫度的影響如圖表7.3。如A中的一個簡單加熱過程,當溫度超過再結(jié)晶溫度后,晶粒就開始長大。當在沒有熱加工的條件下冷卻時,如B,晶粒最后的尺寸將會比A開始的時候大。加熱之后,由于再結(jié)晶作用,當金屬加工的時,晶粒尺寸就會減小。金屬的加工將會增加在大量的形核點形成新核的可能性?？墒?熱加工的最后溫度比再結(jié)晶溫度高太多的話,如C,晶粒的尺寸就開始增大而且最后會得到粗大的晶粒尺寸。晶粒的尺寸的增大是經(jīng)過合并相鄰晶粒的過程發(fā)生的,這是時間和溫度相互作用的結(jié)果。一般情況下,這都不是我們想要的。如果熱加工的最終溫度在再結(jié)晶溫度以上,如D,這樣得到的細小的晶粒尺寸。HOTWorkingAdvantages1.Asthematerialisabovetherecrystallizationtemperature,anyamountofworkingcanbeimpartedsincethereisnostrain-hardeningtakingplace.2.Atahightemperature,thematerialwouldhavehigheramountofductilityandthereforethereisnolimitontheamountofhotworkingthatcanbedoneonamaterial.Evenbrittlematerialcanbehotworked.3.Sincetheshearstressgetsreducedathighertemperatures,hotworkingrequiresmuchlessforcetoachievethenecessarydeformation.熱加工益處1.當材料溫度在再結(jié)晶溫度以上時,加工量的多少都是能夠的,因為這時候沒有加工硬化的產(chǎn)生。2.在較高溫度下,材料將會有較高的韌性,因此材料的熱變形量沒有限制。即使脆性材料也能夠進行熱加工。3.因為在較高溫度下剪切應力將會減小,熱加工中少量的應力就能獲得所需的變形。4.熱加工中,晶粒的繼續(xù)改良是有可能的,如果溫度和加工率得到適當?shù)目刂?將會獲得優(yōu)良的晶粒尺寸和良好的機械性能。Disadvantages1.Somemetalscannotbehotworkedbecauseoftheirbrittlenessathightemperatures.2.Highertemperaturesofmetalgiverisetoscalingofthesurfaceandasaresult,thesurfacefinishobtainedispoor.Also,thereisapossibilityofthedecarburizationofskininsteelsduetothehightemperature.3.Becauseofthethermalexpansionofmetals,thedimensionalaccuracyinhotworkingisharttoachievesinceitisdifficulttocontrolthetemperatureofworkpieces.4.Handlingandmaintainingofhotmetalisdifficultandtroublesome.弊處1.由于在較高溫度下材料脆性的原因,一些金屬不能進行熱加工。2.高溫下,金屬表面比例將會增大,這樣將會導致最后得到的表面質(zhì)量很差。而且,由于高溫會使鋼表面有脫碳的可能性。3.由于金屬內(nèi)熱擴散的原因,控制工件的溫度是很困難的,因此在熱加工中很難獲得精確的尺寸。4.操作和維持加熱金屬是很困難和麻煩的。Coldworkingadvantages1.Coldworkingincreasesthestrengthandhardnessofthematerialduetostrainhardeningwhichwouldbebeneficialinsomesituation.Table7.3givessomecomparativevaluesforthepropertiesobtainedafterhotworkingandcoldworking.Further,thereisnopossibilityofdecarburizationofthesurface..2.Sincetheworkingisdueinthecoldtate,nooxidewouldformonthesurfaceandconsequently,goodsurfacefinishobtained.3.Betterdimensionalaccuracyisachieved.4Itisfareasiertohandlecoldpartsandalsoiseconomicalforsmallersize.冷加工益處1.由于加工硬化的原因,冷加工將會增加材料的強度和硬度,這在某些方面是有利的。圖表7.3給出了熱加工和冷加工后獲得的性能的一些比較值。而且,冷加工不會有表面脫碳的可能性。2.因為加工是在冷態(tài)下完成的,因此表面不會產(chǎn)生氧化物,最后會得到良好的表面質(zhì)量。3.能獲得良好的尺寸精確性。較小尺寸的冷態(tài)零件更容易控制,而且也很經(jīng)濟Disadvantages1.Sincethematerialhashigheryieldstrengthatlowertemperatures,theamountofdeformationthatcanbegiventoislimitedbythecapabilityofthepressesorhammersused.2.Sincethematerialgetsstrainhardened,themaximumamountofdeformationthatcanbegivenislimited.Anyfurtherdeformationcanbegivenafterannealing.3.Somematerialswhicharebrittlecannotbecoldworked.弊處1.因為低溫下材料擁有較高的屈服強度,因此變形量將會受到壓力機和錘頭能力的限制。2.因為加工硬化的原因,最大變形量也會受到限制,任何后續(xù)的變形都需經(jīng)過退火。一些脆性材料不能進行冷加工。7.2.1PrincipleRollingisaprocesswherethemetaliscompressedbetweentworotatingrollsforreducingitscross-sectionalarea.Thisisoneofmostwidelyusedofallthemetalworkingprocesses,becauseofitshigherproductivityandlowcost.Rollingwouldbeabletoproducecomponentshavingconstantcrosssectionthroughoutitslength.manyshapessuchasI,T,Landchannelsectionsarepossibleasshowninfig.7.6,butnotverycomplexshapes.Itisalsopossibletoproducespecialsectionssuchasrailwaywagonwheelsbyrollingindividualpieces.7.2輥軋輥軋是在兩根旋轉(zhuǎn)輥之間對金屬施加壓力使其橫截面積減少的一種工藝。由于較高的生產(chǎn)率和較低的花費使其廣泛應用于各種金屬加工工藝。輥軋能夠生產(chǎn)在沿長度方向上擁有恒定截零件。如圖7.6是中的I、T、L和槽型等許多形狀,可是不能生產(chǎn)復雜的形狀。它也能夠經(jīng)過輥軋單獨的零件來制造特定截面的零件,如鐵路貨車車輪。Rollingisnormallyahot-workingprocessunlessspecificallymentionedascoldrolling.Themetalistakenintorollsbyfrictionandsubsequentlycompressedtoobtainthefinialshape.Thethicknessofthemetalthatcanbedrawnintorollsdependontheroughnessoftherollsurface.Rougherrollswouldbeabletoachievegreeterreductionthansmootherrolls.Buttherollsurfacegetsembeddedintotherolledmetalthusproducingroughsurface.除非特別提出將其作為冷加工,不然輥軋一般都屬于熱加工。輥軋經(jīng)過摩擦力和之后的壓力將金屬放入旋轉(zhuǎn)輥中來獲得最終的形狀。金屬最終拉伸的厚度取決于輥的表面粗糙度。粗糙的旋轉(zhuǎn)輥比光滑的輥更能得到較少的橫截面,可是旋轉(zhuǎn)輥表面會嵌Thereductionthatcouldbeachievedwithagivensetofrollisdesignedasthe”angleofbite”andisshowninFig.7.5.ThisdependsonthetypeofrollingandtheconditionsoftherollsanshowninTable7.4.Thevolumeofthemetalthatenterstherollingstandshouldbethesameasthatleavingitexceptininitialpasseswhentheremightbesomelossduetofillingofvoidsandcavitiesintheingots.Sincetheareaofthecrosssectiongetsdecreased,themetalleavingtherollswouldbeatahighervelocitythanwhenitentered.Initially,whenthemetalenterstherolls,thesurfacespeedofrollsishigherthanthatoftheincomingmetal,whereas,themetalvelocityattheexitishigherthanofthesurfacespeedofrolls.Betweentheentranceandexit,thevelocityofthemetaliscontinuouslychanging,whereastherollvelocityremainsconstant.Somewhereinthecontactlength,thevelocitiesofthemetalandrollsaresame,whichisdesignatedasneutralplaneinFig.7.5.橫截面的減少能夠經(jīng)過一套設計有軋入角的旋轉(zhuǎn)輥獲得,如圖7.5。這取決于輥軋類型和輥軋條件,如表7.4。金屬進入輥軋機和離開輥軋機的體積應該保持不變,除了最初經(jīng)過輥軋機填充鑄錠中的空位和型腔時會使體積減少。由于橫截面積的減少,金屬離開輥軋機的速度會比進入時的高。金屬開始進入輥軋機的時表面速度比將要進入的金屬高,然而,在出口處的金屬速度比旋轉(zhuǎn)輥的速度高。在出口與入口之間,金屬的速度持續(xù)變化的,可是旋轉(zhuǎn)輥的速度卻保持恒定。在接觸長度上,金屬和旋轉(zhuǎn)輥的速度保持一致,這個地方被設計為中性平面,如圖7.5。Thepressureonrollsgraduallybuildsupformtheentrytotheneutralpointwhereitishighestandthendecreasetillitreachestheexit.Theroll-separatingforcewhichseparatesthetworollsapartcanbeobtainedbymultiplyingtheaveragerollpressurewiththetotalcontactarea.Theaveragerollpressurecanbedecreasedbyreducingthemaximumpressure,whichisafunctionofthecontactlength,itispossibletodecreasetheroll-separatingforce.Thisinturn,canbeachievedbyreduction.Thesmallerrollswouldnothaveenoughregiditytosupportalargeroll-separatingforce.Hence,backuprollsareattachedtothesmallrollstoprovidethenecessaryrigidity.Thoughhigherfrictionbetweenrollsandthemetalisrequiredforincreasingthereducitionachieved,italsoincreasestherollseparatingforce.輥上的壓力從進入部分到中點逐漸增大,其中中點的最大,然后到出口部分一直變小。分離兩個輥的卷分離力能夠經(jīng)過輥的平均壓力和總的接觸面積的乘積得到。經(jīng)過加少最大壓力能夠減小接觸長度上的平均壓力,這也有可能減小卷分離力。反過來說,也能夠經(jīng)過減小輥的直徑來獲得,因為,減少相同的量,較小的輥比較大的輥擁有減小的接觸長度。較小的輥用于減少量較大和卷分離力較大的冷軋的情況下。可是小輥沒有足夠的剛度來支撐較大的卷分離力,因此,支撐輥被附加在小輥上已提供所需的剛度。雖然輥和金屬間較大摩擦力能夠增大減少量,可是這也會增加卷分離力。7.2.2RollingStandArrangementThearrangementofrollsinarollingmill,alsocalledrollingstand,variesdependingontheapplication.ThevariouspossibleconfigurationsarepresentedinFogs.7.7and7.8.Thenamesoftherollingstandarrangementsaregenerallygivenbythenumberofrollsemployed.ThefirstoneinFig.7.7a,the2-highnonreversingrollingstandarrangement,isthemostcommononarrangement.Inthis,therollsalwaysmoveinonlyonedirection.ThearrangementshowninFig.7.7bisa2-highreversingrollingstand,wherethedirectionofrollrotationcanbereversed.Thistypeofstandisparticularlyusefulinreducingthehandlingofthehotmetalinbetweentherollingpasses.WhenallthemetalhasreachedtherightsideoftheFig7.7,thedirectionoftherollsisreversedandthemetalisallowedtoenterintothenextpass.Thesestandsaremoreexpensivecomparedtothenonreversibletypebecauseofthereversibledriveneeded.7.2.2軋鋼架布置輥軋機軋輥的布置也叫軋鋼機架因應用的不同而不同。如圖7.7和7.8是幾種可能的布置。軋鋼機架布局是經(jīng)過所應用的軋輥的數(shù)量來命名的。圖7.7(a)的第一個圖是二輥不可逆軋鋼機架的布置,這是最常見的布置。在這種布置中,軋輥只會朝著一個方向運動。圖7.7(b)是軋輥只能旋轉(zhuǎn)能夠倒轉(zhuǎn)的二輥不可逆軋鋼機布置。這種機架主要用于減少加熱金屬經(jīng)過輥軋機時的操作。當所有金屬到達圖7.7的右邊時,軋輥的旋轉(zhuǎn)方向就會倒轉(zhuǎn)過來,金屬就有能夠經(jīng)過下一個通道。因為需要反轉(zhuǎn)驅(qū)動,因此這種鋼架比不倒轉(zhuǎn)的鋼架更貴。The3-highrollingstandarrangementshowninFig.7.7isusedforrollingoftwocontinouspassesinarollingsequencewithoutreversingthedrives.Afterallthemetalhaspassedthroughthebottomrollset,theendofthemetalisenteredintotheothersetoftherollsforthenextpass.Forthispurpose,atable-tiltingarrangementisrequiredtobringthemetaltothelevelwiththerolls.三輥軋機的布置如圖7.7(c)。這種布置用于在軋制次序中不需要反轉(zhuǎn)驅(qū)動的兩個連續(xù)通道的軋制。當所有的金屬都經(jīng)過軋制機的尾部的時候,金屬的末端進入另一個軋制機的通道。為此,需要一個傾斜板布置將金屬帶到輥軋機的水平位置。A4-highrollingstandshowninFig.7.7isessentiallya2-highrollingmill,butwithsmall-sizedrolls.Theothertuorollsarethebackuprollsforprovidingthenecessaryrigiditytothesmallrolls.AbetterbackupcanbeprovidedtothesmallrollswithaclusterarrangementofrollsasshowninFig.7.7.Fortherollingarrangementsrequiringlargereduction,anumberoffreerotatingwheelsinsteadofasinglesmallroll,arefixedtoalargebackuprollintheplanetaryrollingmillarrangementshowninFig.7.8.四輥軋機鋼架布置如圖7.7(d),它的本質(zhì)其實是一個擁有小軋輥的二輥軋機。其它兩個軋輥是為小軋輥提供所需剛度的支撐軋輥。如圖7.7(e)是能夠為帶有一串軋輥的小軋輥機提供支撐的布置。對于需要大量縮減量的軋制機布置來說,大量的自由旋轉(zhuǎn)輪代替了單獨的小軋輥,這些旋轉(zhuǎn)輪被安在行星軋制機中的大支撐軋輥上,如圖7.8。Sincethefinalshaperequiredcannotbeobtainedinasinglepass,therollingmillsaregenerallyarrangedwithrollswhichhavemorethanonepassmachinedintothemsothatthematerialcomingoutofonepassisthentobefedbacktotheotherpassbyreversingtherolldirectionorbyarrangingtherollingmillsintandem.Itisgeneralpracticetomaintaintensioninthestripbetweenthestandsintheinterestofkeepingitflatandalsotocontrolthethicknessclosely.Thisalsohelpsinreducingtheroll-separatingforce.因為在單通道中不能獲得所需的最終形狀,軋制機上安排有制造出不止一個通道的輥輪,這樣從一個通道出來的材料就能經(jīng)過反轉(zhuǎn)輥的方向和聯(lián)合的輥軋機將其返回到另一個通道。一般通保證鋼架上帶的拉力來保持它的平直,而且緊密地控制它的厚度。這樣也有助于減小卷分離力。Thesteelcomingoutofablastfurnaceoraremeltingshopisintheformofaningotwhichhasacrosssectionoftheorderof600*600mm.Theseingotsarefurtherprocessedinrollingmillstlproducetheintermediateshapessuchasblooms,slabsandbillets.Bloomsaregenerallysquarecrosssectionsvaryingfrom150*150mmto400*400mm.Slabsarerectangularcrosssectionswithwidthsvaryingfrom500to1800mmandthicknessesvaryingfrom50to300mm.Billetsarerectangularcrosssectionswithsizesvaryingfrom40*40mmto150*150mm.從鼓風爐或者熔煉車間出來的鋼都是橫截面是600×600mm的鑄錠。這些鑄錠之后會被輥軋機制成像初軋方坯、板坯和坯錠。初軋方坯的橫截面一般是在150×150mm到400×400mm之間。板坯矩形橫截面的寬度是在500到1800mm之間,厚度從50到300mm之間不等。Theingotobtainedbycastingwouldnormallyhavedefectssuchasshrinkagecavities,blowholhesandslaginclusions.Whentheingotisrolled,theshrinkagecavity(calledpipe)istowardstheend,whichisthencroppedafterafewinitialpassestoreducethedefectsinthedefectsinthefinishedproduct.經(jīng)過鑄造獲得的初軋方坯一般帶有縮孔、氣眼、夾渣等缺陷。當初軋方坯被軋制的時候,縮孔會移到末端,為了在最終的產(chǎn)品中減少這些缺陷,在最后經(jīng)過的時候會將其末端剪掉Thebloomingandslabbingmillswhichproducebloomsandslabsfromtheingotsaregenerallythereversible2-highrollingstands.Themetalisturned90degreesintheinitialpassestoenablethematerialtobeuniformlycompressedfromallsides,sothatanyoftheinternalvoidssuchasblowholesareeliminatedandtheslaginclusionsaresegregated.能夠?qū)⒊踯埛脚髦瞥砂迮骱团麇V的軋制機一般是二輥軋鋼機架。為了使材料各個方向能均勻受壓,金屬在經(jīng)過軋制機前被彎成90度,因此,像氣眼這樣的空隙就能被排除夾渣也會被分離。Therollsaregenerallymanufacturedofchilledcastiron,carbonsteelandalloysteels.Thesoftrollswithhardnessrangeof150to250BHNareusedinroughingstandsoftheheavysectionmillsandbilletmills.Thesemi-hardrollswith250to400BHNareusedinroughingstandsofrailstructuremills,andfinishingstandsofheavysectionmilsandbilletmills.Hardrollswith400to600BHNareusedtomakefinishingstandsofsheets,railwaystructuresandbackingrollsforsmalldiameterrolls.Thesemaysometimeshavearollsurfaceofhardalloysuchastungstencarbide.Theextrahardrollswith600to800BHN,areusedforcoldrolling.Thesmallerrollsinthiscategorymaybemadeofhardmaterialsliketungstencarbide.輥軋一般見來制作冷硬鑄鐵、碳鋼和合金鋼。硬度在150到250BHN之間的軟輥被用在大型鋼材軋制機的粗軋機架和鋼坯軋機上。硬度在250到400BHN之間的半硬輥一般見在鐵路結(jié)構軋制機的粗軋鋼架上。硬度在400-600BHN之間的硬輥用來制作精軋板、鐵路結(jié)構件和支撐輥的上,支撐輥一般是小直徑輥。這些零件一般會有硬合金輥的表面形狀,如碳化鎢。硬度在600-800BHN的超硬輥用于冷軋。這種小直徑輥就是用像碳化鎢這樣的硬質(zhì)材料做的。7.2.3RollingLoadRigorouscalculationoftherollingloadrequirestheunderstandingofplasticitytheory,whichisbeyondthescopeofthisbook.Thenecessaryequationsderivedfromtheapplicationoftheoriesarepresentedbelow.Thereaderisadvisedtorefertothesebooksfordetailedanalysis.Thefollowingexpressionsarevalidforrollingofflatsurfaces.7.2.3軋制載荷嚴格計算軋制載荷需要很好地理解塑形理論,這超出了本書的范圍。軋制載荷能夠從下面給出的公式得出。建議讀者參考本書中的詳細分析。下面的公式對軋制表面適用。Thepressureonrollsstartsfromtheentrypointandcontinuestobuilduptilltheneutralpoin.Similarlytheexitpressureiszeroattheexitpointandincreasestowardstheneutralpoint.Atanysection,betweentheentrypointandexitpointintherollsasshowninFig.7.9,thepressureactingontherollsisgivenbysuperscript-indicatingthepressurefromtheentrysidewhileindicatesthepressurefromtheexitside.軋制壓力從進入點到中心點逐漸增大。在出口點的壓力是0,而且到中心點的力逐漸增大。在進入點與出口點中任何一個區(qū)域i上,如圖7.9,作用在輥上的壓力經(jīng)過進入邊直接標出的力加上出口邊指出的力得到。Toidentifytheneutralplaneposition,thetwoexpressionsfortherollpressurep-andp+shoulebeequatedasthepressuresfrombothends--peakattheneutralplane.為了確定中性面的位置,軋輥的壓力p-和p+的兩個公式應該和兩端的壓力公式相等——在中性面到達最大。Thesolutionoftheaboveequationsrequireacomputerprogramtocompletelysolvealltheequationsthroughanumberofiterationsbeforethevaluesconverge.上述問題的解決方法需要計算機在數(shù)值收斂之前經(jīng)過許多迭代次數(shù)來解決。Anapproximateexpressionconsideringrollingsimilartoplanestraintosettingprocess,whichgivesareasonablycloseresult,similartothoseobtainedbytheearlieranalysisisgivenbyAltanetalasfollows.考慮到軋制工序平面應力和鐓粗幾乎一樣的公式,這個公式給出了一個合理的近似值,和這些公式相同的公式由Altan早前的分析給出。7.2.4RollPassesThefinalrolledproductssuchasplates,flats,sheets,roundsandsectionsareobtainedinanumberofpassesstartingfrombilletsorslabs.Forrollingtheflatproducts,plaincylindricalrollsareusedbutforsections,groovedrollsareused.Thetypeofgroovingdoneisdecidedbythefinalsectiondesired.Theroll-passsequencecanbebroadlycategorisedintothreetypes.BreakdownpassesTheseareusedforreducingthecross-sectionalareanearertowhatisdesired.Thesewouldbethefirsttobepresentinthesequence.RoughingpassesInthesepassesalso,thecross-sectiongetsreduced,butalongwithit,theshapeoftherolledmaterialcomesnearertothefinalshape.FinishingpassesThesearethefinalpasses,whichgivetherequiredshapeoftherolledsection.Generally,thefinishingpassfollowsaleaderpass.7.2.4軋制孔型最終軋制產(chǎn)品如板條,薄片,板料,圓形和管形是從坯料或者厚板經(jīng)過許多孔型得到的。對軋制板條產(chǎn)品,會用到普通外圓輥,可是對于截面,要用到帶槽軋輥。帶槽軋輥類型是經(jīng)過所要獲得的最終界面決定的。軋制孔型順序大致地分為三類。分散孔型這用在經(jīng)過減少橫截面積到所獲得的形狀。這在序列中排在第一位。粗軋在這些孔型中,橫截面積也會減小,可是沿長度方向,材料形狀接近最終形狀。精軋這是得到所需形狀的最后軋制。一般來說,精軋需要一個成品前孔。DraughtInordertodesigntheroll-passschedule,thefirsttobeconsideredisthedraughtofelongationineachofthepasses.Thetotalelongationcanbecalculatedbydividingtheinitialareaofthecrosssectionbythefinalareaofcrosssectionoftherolledproduct.壓縮量為了設計軋制孔型的順序,首先考慮的是每一個孔型的壓縮量和伸長率。總的伸長率能夠經(jīng)過最初橫截面積除以產(chǎn)品最終橫截面積。Theelongationcanbedefinedastotalforallthepassesorthatforeachpassseparately.Draughtofanygivenpassspecifiesthereductionachievedinthedimensions.Considerarectangle,asshowninFig.7.10,asreducedfromA*Btoa*bmm.Then,Draught=A+B-(a+b)伸長量能夠定義為總的伸長長度或者每一單獨的伸長量。任何孔型壓縮量的指定減少量都能夠經(jīng)過標注尺寸獲得。Ifweknowthemeandraughttobeprovidedineachpassthenthenumberofpassescanbeestimated.Butthedraughtprovidedineachpassalsodependsontheworkmaterial,angleofbite,rollstrength,poweroftherollingmillandtheconditionoftherolls.如果我們知道每一孔型所給出的壓縮量的意思,那么就能夠計算出孔型數(shù)量?？墒?每一孔型所提供的壓縮量取決于工件材料、軋入角、軋輥強度、軋制機的功率和軋制條件。Besides,thedraughtsofallthepassesinthesequencearenotsame.Normally,intheinitialpasses,itisnecessarytoreduceasmuchcross-sectionalareaaspossible.Thismeansthatthemaincriterionforchoosingthedraughtisthereforetobetheangleofbiteorthemaximumsizetherollscanpullunderthem.Inrollingplainshapessuchasplatesorsheetsorintermediatepasses,itisthestrengthoftherollsortheavailablepowerofthemotors,whichlimitthedraught.Forfinishingpasses,rollwearmaybethelimitingfactorindecidingthedraught.Particularlyforsectionsofcomplexshapessuchasrails,itisnecessarytoreducetherollweartoaminimumtoobtainaccuratedimensionsandgoodsurfacefinish.另外,軋制次序中,不是所有的孔型的壓縮量都一樣。一般來說,在最初孔型中,有必要盡可能減少橫截面積。這就意味著,壓縮量選擇的主要標準是輥能夠牽引其的咬入角和最大尺寸。在平面形狀軋制中,如板條,板料或者預軋孔型中,軋輥的強度和機器的可用功率7.2.5BreakDownPassesTheprincipalbreakdownpasssequencesare(a)Box-pass series(b)Diamond-square series(c)Oval-square seriesThesebreakdownpasssequencesareSchematicallyshowninFig.7.11.7.2.5分散孔型主要的分散孔型是(a)箱型孔系類(b)菱形系統(tǒng)孔型(c)橢圓方孔型這些分散孔型如圖7.11.Box-PassSeriesBoxpassesaregenerallyusedforinitialmediumandlargesectionsofbloomingandbilletmills.Therollsofboxpassseriesarestronger.Theycanbeusedfordifferentsizesbyscrewingdownthetoproll.TheyprovideforeffectivedescalingandensureuniformdraughtalongtheWidthOfthebar.However,themainproblemsWiththesearethesmallerelongation(1.05to1.15)andinaccuratesquareproducedbecausethesidespreadisnotcontrolled.Theyaregenerallyusedforlagerproducts.箱型孔系列箱型孔型最初用在中等和大型截面的初軋機和鋼坯軋機上。箱型孔型系列的軋輥是非常堅硬的。經(jīng)過擰緊她們能夠用在不同的頂端機上。她們能有效地消除鐵銹而且確保棒料在寬度方向上的統(tǒng)一壓縮量。當然,主要的問題是較小壓縮量(1.05to1.15)和由于不能控制金屬邊界流動伸展而產(chǎn)生的不準確的方形鋼坯。因此它們一般用徉大型零件上。Diamond-SquareSeriesInthis,thesquareproducedinalargerrollisturnedoverby90degreesandpassedthroughthediamondrolls,theoutputofwhichisagainturnedoverby90degreesandputthroughsmallersquarerollsasshowninFig.7.11(b).Theadvantagesofthisseriesaretheslowcoolingoftheentirematerial,accuratesquarethatarepossibleandlargerelongationsthatcanbeachieved(1.20to1.45).Becauseofthesespecificadvantages,theseareextensivelyusedinthefinishingpassesofthecomparativelysmallersectionssuchasbillets.Thematerialbeingconfinedfully,thesetypeofpassedgiveagoodstabilityandalsouniformdeformationofthematerial.Thetwoprinciplesthataregenerallyuseindesigningthediamond-squareseriesistokeeptheheightofonepassequaltothewidthofthenextpassortheheightofonepasslessthanthewidthofthenextpass.Thedisadvantagewiththeseriesisthattherollgetsweakenedbecauseofthedeepimpressionsmadeintotherolls.菱形系統(tǒng)孔型在這種孔型中,方鋼在大型軋制機上被反轉(zhuǎn)了90度并經(jīng)過菱形的軋制機。從軋制機上出來的材料又被反轉(zhuǎn)了90度,然從小型的軋制機上經(jīng)過,如圖7.11(b)。這種孔型系列的好處是能夠緩慢地冷卻材料,獲得精確的方鋼和較大的壓縮量(1.20to1.45)。由于這些特別的好處,相比較小型截面如鋼坯而言,其廣泛應用于精致孔型中。材料被完全地限制,因此這種類型的孔型能給材料良好的穩(wěn)定性和均勻的變形量。在設計菱形系統(tǒng)系列孔型時,需要用到兩個重要的準則,要使前一個孔型的高度等于下一個孔型的寬度或者前一孔型的高度要小于后一孔型的寬度。這種系類孔型不利之處是,由于較深的壓痕壓入軋輥使得乳輥變得疲軟。Over-SquareSeriesInthisseriesthediamondisreplacedbyovalshape.Thestockaftergoingthroughtheovalpass,isturnedoverby90degreesintosquarepass,theoutputofwhichisthenturnedoverby45degreestofeedintothenextovalpass.Themainadvantageofthisseriesisthelargeelongationthatcanbeobtained(1.35to1.80)comparedtotheotherbreakdownpassed,rhemainproblemofthisarethedifficultytoguidethestockinovalpass,thenonuniformityofthedeformationalongthewidthoftherollandhigherrollwearinovalpass.Whenhigher-reductionsareused,thematerialislikelytogiverisetosurfacedefectcalledfoldbecauseofthewearingoftheovalpassatpointsofmaximumreductionwhichcannotbeeliminated.TheovalpasshassomeothervariantsasshowninFig.7.12橢圓方孔型在這種系列中,橢圓形取代了錐形。坯料經(jīng)過橢圓道后.被反轉(zhuǎn)90度進入方形道中,輸出量被反轉(zhuǎn)90度進給到下一個橢圓形道中。這種系列和其它箱型孔類型相比的主要好處就是能夠得到較大的壓縮量(1.35to1.80)。其產(chǎn)生的主要問題是難以將坯料引進橢圓通道中,在沿軋制機寬度方向上的變形量不均勻,在橢圓通道中軋制機的磨損量很大。當減少量很大的時候,由于在最大減少量點的地方橢圓孔型的磨損量不能消除,材料就會產(chǎn)生叫做褶皺的表面缺陷。其它一些不同的橢圓形孔型如圖7.12.7.2.6Roll-PassSequencesDesigningrollpassedisafairlycomplexandskilledart,theexplanationofwhichisbeyondthescopeofthebook.Tothisend,specialistliteratureisavailablethedetailsofwhicharepresentedinreferencesattheendofthischapter.Here,wewillonlyrefertosomesalientpointstobeconsideredinthedesignoftherollpasses.7.2.6軋孔型順序設計軋制孔型是一種相當并需要技巧的技術。設計說明也超出了本書的范圍。為此,本章的最后列出了有用的設計細節(jié)的專門文獻,以供參考。這里,我們只列出了在孔型設計中一些考慮到的突出點。Beforedecidingontheactualsequence,itisnecessarytoconsidertherequirementsofthefinalproduct.Sincehotrollingisfinishedatahightemperatureoftheorderof900to1100'Cdependingonthematerial,thedimensionofthefinishingpassshouldtakeintoaccountthelinearexpansionofthemetaltobeused,atthistemperature.在決定實際順序之前,有必要考慮成品的要求。因為熱軋是在900到1100度高溫下完成的,這個溫度主要取決于材料,在這樣地溫度下,成品的尺寸需要將所用金屬的線性膨脹考慮進去。PassScheduleforBloomsTher