畢業(yè)設(shè)計(jì)（論文）-混凝土泵車支腿部分的設(shè)計(jì)

圖書分類號(hào)：密級(jí)：全套圖紙加V信153893706或扣3346389411畢業(yè)設(shè)計(jì)(論文)混凝土泵車支腿部分的設(shè)計(jì)DESIGNOFTHECONTRETEPUMPTRUCKSTABILIZER學(xué)生姓名學(xué)院名稱機(jī)電工程學(xué)院專業(yè)名稱機(jī)械設(shè)計(jì)制造及其自動(dòng)化指導(dǎo)教師20XX年6月2日徐州工程學(xué)院畢業(yè)設(shè)計(jì)(論文)·式中—混凝土泵車工作時(shí)垂直液壓缸的最大閉鎖力，輻射式支腿垂直液壓缸的等于泵送工作時(shí)的最大支腿反力，=160921.2N。計(jì)算=8(MPa)垂直液壓缸的收放時(shí)間為60s液壓缸流量Q==()0.784=3.69L/min（2）其他液壓缸的選擇后支腿擺動(dòng)油缸的選擇：工作負(fù)載F=N=0.13622=362.2N內(nèi)徑的計(jì)算D=式中P＝5Mpa，=2.5，0.95代入數(shù)據(jù)，則D＝0.015（m）根據(jù)工程機(jī)械用液壓缸內(nèi)徑系列，選取D=80mm活塞桿直徑dd=0.717D=50mm最小導(dǎo)向長度H導(dǎo)向長度應(yīng)滿足H≥+=450/20+80/2=50(mm)導(dǎo)向套滑動(dòng)面長度A取活塞桿直徑的(0.61.0)倍,A取50mm；活塞寬度B為液壓缸內(nèi)徑的(0.61.0)倍,B取50mm。壁厚計(jì)算≥PD/2[]=1.04(mm)選用10mm。缸筒外徑的確定D1=D+2=80+20=100(mm)缸底厚度1≥0.433D2=2.65(mm)取1=10mm。水平液壓缸的收放時(shí)間為30s。液壓缸流量Q==2.75L/min前支腿擺動(dòng)油缸的選擇：工作負(fù)載F=N=0.13990=399N內(nèi)徑的計(jì)算D=式中P＝5Mpa，=2.5，0.95代入數(shù)據(jù)，則D＝0.015（m）根據(jù)工程機(jī)械用液壓缸內(nèi)徑系列，選取D=80mm活塞桿直徑dd=0.717D=50mm最小導(dǎo)向長度H導(dǎo)向長度應(yīng)滿足H≥+=800/20+80/2=100(mm)導(dǎo)向套滑動(dòng)面長度A取活塞桿直徑的(0.61.0)倍,A取50mm；活塞寬度B為液壓缸內(nèi)徑的(0.61.0)倍,B取50mm。壁厚計(jì)算≥PD/2[]=1.04(mm)選用10mm。缸筒外徑的確定D1=D+2=80+20=100(mm)缸底厚度1≥0.433D2=2.65(mm)取1=10mm。前支腿擺動(dòng)液壓缸的收放時(shí)間為30s。液壓缸流量Q==4.28L/min前支腿伸縮油缸的選擇：工作負(fù)載F=N=0.11678=167.8N內(nèi)徑的計(jì)算D=式中P＝5Mpa，=2.5，0.95代入數(shù)據(jù)，則D＝0.015（m）根據(jù)工程機(jī)械用液壓缸內(nèi)徑系列，選取D=63mm活塞桿直徑dd=0.717D=50mm最小導(dǎo)向長度H導(dǎo)向長度應(yīng)滿足H≥+=1200/20+63/2=100(mm)導(dǎo)向套滑動(dòng)面長度A取活塞桿直徑的(0.61.0)倍,A取50mm；活塞寬度B為液壓缸內(nèi)徑的(0.61.0)倍,B取50mm。壁厚計(jì)算≥PD/2[]=1.04(mm)選用6mm。缸筒外徑的確定D1=D+2=63+12=75(mm)缸底厚度1≥0.433D2=2.65(mm)取1=10mm。前支腿擺動(dòng)液壓缸的收放時(shí)間為30s。液壓缸流量Q==2.76L/min（3）液壓泵的選型與計(jì)算液壓泵的主要參數(shù)是：額定工作壓力和額定輸出流量。確定液壓泵的最大工作壓力式中—缸或馬達(dá)的最大工作壓力—系統(tǒng)工作時(shí)的總壓力損失，包括直管中的沿途損失，彎管、各種接頭和閥的損失，對(duì)一般中高壓，流量較大的液壓系統(tǒng)取為2MPa。則14+2=16MPa確定液壓泵的出口流量＝1.1(3.69*4+2.35*2+4.28*2+2.76*2)=33.54(L/min)又由條件,,選擇CBQ－F532齒輪泵，屬于高壓齒輪泵，采用鋁合金殼體和DU軸承機(jī)構(gòu)，具有體積小、重量輕、轉(zhuǎn)速高、壽命長等優(yōu)點(diǎn)。排量為32mL/r，額定轉(zhuǎn)速為2500r/min，額定壓力為20MPa，驅(qū)動(dòng)功率為26KW。（4）閥的選擇根據(jù)壓力和流量選擇閥如下：節(jié)流閥選擇C-175-C-11,聯(lián)接方式為管式。溢流閥選擇DBD·H15G10電磁換向閥選用DSG型9.5液壓系統(tǒng)性能驗(yàn)算(1)液壓系統(tǒng)壓力損失的驗(yàn)算驗(yàn)算液壓系統(tǒng)壓力損失的目的是為正確調(diào)整系統(tǒng)的工作壓力，使執(zhí)行元件輸出的力滿足設(shè)計(jì)要求，并可根據(jù)壓力損失的大小分析判斷系統(tǒng)設(shè)計(jì)是否符合要求。液壓系統(tǒng)中的壓力損失包括：油液通過管道時(shí)的沿程損失、局部損失和流經(jīng)閥類元件時(shí)局部損失，即：上式中沿程損失和局部損失可按下式計(jì)算式中：、d—直管長度和內(nèi)徑v—液流平均速度—液壓油的重度、—沿程阻力系數(shù)和局部阻力系數(shù)=10m,d=0.02m,=9009.8=8820,=0.5,=0.021,代入上式可得：=0.22MPa=0.06MPa流經(jīng)標(biāo)準(zhǔn)閥類元件時(shí)的壓力損失值與其額定流量、額定壓力損失和實(shí)際通過的流量有關(guān)，其近似關(guān)系式為=6MPa式中：和的值可以從產(chǎn)品目錄或樣品本上查出在液壓系統(tǒng)工作循環(huán)中，不同動(dòng)作階段的壓力是不同的，必須分別計(jì)算。當(dāng)已知液壓系統(tǒng)的壓力損失后，就可以確定溢流閥的調(diào)整壓力，它必須大于工作壓力和總壓力損失之和，即=0.28MPa14+0.17=14.17MPa(2)液壓系統(tǒng)總效率的驗(yàn)算㈠根據(jù)系統(tǒng)的壓力損失，確定管路的壓力效率，又稱管路的當(dāng)量機(jī)械效率㈡管路系統(tǒng)中各個(gè)閥的泄露量和溢流量之和稱為管路系統(tǒng)的容積損失，用表示，則管路系統(tǒng)的容積效率為式中：—當(dāng)系統(tǒng)中無蓄能器時(shí)，為最大工作流量㈢管路系統(tǒng)的總效率為㈣液壓傳動(dòng)系統(tǒng)的總效率，要考慮液壓泵、管路系統(tǒng)、液壓缸或液壓馬達(dá)各部分的能量損失，它們的總和用符號(hào)表示，則系統(tǒng)的總效率為式中：———液壓泵的輸入功率—液壓系統(tǒng)總的能量損失———液壓泵的總效率———管路系統(tǒng)的總效率———液壓缸和液壓馬達(dá)的總效率(3)液壓系統(tǒng)發(fā)熱溫升的計(jì)算液壓系統(tǒng)工作時(shí)，所損失的能量必然轉(zhuǎn)化為熱能，使液壓系統(tǒng)的油溫升高，油溫升高后會(huì)產(chǎn)生許多不良后果，如油溫上升，油液粘度很快下降，泄露增大，容積效率降低；油溫升高還會(huì)使油液形成膠狀物質(zhì)，堵塞元件小孔和縫隙，使液壓系統(tǒng)不能正常工作等，因此，對(duì)液壓系統(tǒng)的發(fā)熱溫升，必須進(jìn)行驗(yàn)算并予以控制，對(duì)不同的液壓系統(tǒng)，因其工作條件不同，允許的最高溫度也不相同工程機(jī)械正常工作溫度50～80最高允許工作溫度70～80油的溫升〈=35～40kW式中：P—液壓系統(tǒng)的實(shí)際輸入功率，即液壓泵的實(shí)際輸入功率，為26kW—系統(tǒng)的總效率液壓系統(tǒng)所產(chǎn)生的熱量，一部分使油液和系統(tǒng)的溫度上升，另一部分熱量經(jīng)過冷卻表面散發(fā)到空氣中，當(dāng)系統(tǒng)產(chǎn)生的熱量和散發(fā)的熱量相等時(shí)，系統(tǒng)達(dá)到了熱平衡狀態(tài)，油溫不再上升，而穩(wěn)定在某一溫度上。當(dāng)產(chǎn)生的熱量Q，全部被冷卻表面所散發(fā)時(shí)，即式中：—散熱系數(shù)，當(dāng)通風(fēng)很差時(shí)為8.5～9.32；當(dāng)通風(fēng)良好時(shí)為15.13～17.46；當(dāng)風(fēng)扇冷卻時(shí)為23.3；循環(huán)水冷卻為110.5～147.6。可選16?！拖渖崦娣e—液壓系統(tǒng)油液的溫升由上式可得：計(jì)算時(shí)，如果油箱三邊的結(jié)構(gòu)尺寸比例為1：1：1到1：2：3時(shí)，而且油位為油箱高0.8時(shí)，其散熱面積的近似計(jì)算式式中：V—油箱的有效容積計(jì)算所得的溫升，加上環(huán)境溫度，應(yīng)不超過油液的最高允許溫度，如果超過允許值，必須適當(dāng)增加油箱散熱面積或采用冷卻器來降低油溫即可滿足要求。結(jié)論至此，我已順利設(shè)計(jì)完混凝土泵車的支腿部分，設(shè)計(jì)中采用了現(xiàn)在市場(chǎng)上最常用的輻射式支腿型式，并通過中心范圍的計(jì)算求解，得出了泵車的最小跨距范圍，并且通過數(shù)學(xué)方法對(duì)支腿的展開角度進(jìn)行了優(yōu)化設(shè)計(jì)，使支腿可以最大限度的發(fā)揮作用，穩(wěn)定性達(dá)到設(shè)計(jì)要求；并且利用四點(diǎn)支撐和三點(diǎn)支撐的方法進(jìn)行了支腿豎直反力的求解，并利用求得的豎直反力對(duì)支腿的強(qiáng)度進(jìn)行了校核，經(jīng)過計(jì)算材料的強(qiáng)度可以滿足泵車的工作需要；液壓部分選擇了電磁閥來控制支腿油缸的動(dòng)作，方便實(shí)現(xiàn)自動(dòng)化控制，在垂直支腿油缸上安裝了雙向液壓鎖，避免工作時(shí)出現(xiàn)縮腿現(xiàn)象，在行走時(shí)又避免油缸在重力作用下自動(dòng)伸出，并且雙向液壓鎖與支腿垂直油缸直接相連接防止油管老化爆裂出現(xiàn)危險(xiǎn)；液壓系統(tǒng)的有關(guān)部件工作性能也通過計(jì)算證明是符合要求的。我設(shè)計(jì)繪制了混凝土泵車支腿，以及垂直支腿油缸，所設(shè)計(jì)的支腿部分基本符合工況要求，并且具有結(jié)構(gòu)簡(jiǎn)單、經(jīng)濟(jì)、操作安全等優(yōu)點(diǎn)。

致謝到今天我的畢業(yè)設(shè)計(jì)已經(jīng)圓滿的完成了。在此，我要特別感謝我的指導(dǎo)老師仇文寧老師，在這段時(shí)間內(nèi)他給了我莫大的幫助，正由于他的熱心地幫助和指導(dǎo)，我的畢業(yè)設(shè)計(jì)才能夠順利的完成。仇老師嚴(yán)謹(jǐn)治學(xué)的態(tài)度和精神也是我在這次設(shè)計(jì)過程中學(xué)到的寶貴的財(cái)富。大學(xué)四年的學(xué)習(xí)和生活即將告別。感謝這四年來各位老師對(duì)我的教誨，各位同學(xué)給我的幫助！感謝與我共同走過大學(xué)的朋友們、同學(xué)們！感謝所有幫助過我的老師、同學(xué)、朋友，同時(shí)祝愿你們?cè)谝院蟮娜兆永?，開心、快樂！

參考文獻(xiàn)[1]馬永輝.工程機(jī)械液壓系統(tǒng)設(shè)計(jì)[Z].北京：機(jī)械工業(yè)出版社，1985.[2]鄭紅.混凝土泵車的穩(wěn)定性分析[A].本溪冶金高等?？茖W(xué)校報(bào)，2001.[3]張艷偉.混凝土泵車支腿反力計(jì)算及基于ANSYS的支腿結(jié)構(gòu)分析[D].中國機(jī)械工程學(xué)報(bào)。2004[4]朱文堅(jiān)，黃平，吳昌林.機(jī)械設(shè)計(jì)[M].北京：高等教育出版社，2005.[5]徐景.機(jī)械設(shè)計(jì)手冊(cè)[M].北京：機(jī)械工業(yè)出版社，1992.[6]李壯云，葛宜遠(yuǎn).液壓元件與系統(tǒng)[M].北京：機(jī)械工業(yè)出版社，2000.[7]朱宏濤.液壓與氣壓傳動(dòng)[M].北京：清華大學(xué)出版社，2005.[8]杜國森.液壓元件產(chǎn)品樣本[M].北京：機(jī)械工業(yè)出版社，2000.[9]何存興.液壓傳動(dòng)與氣壓傳動(dòng)[M].武漢：華中科技大學(xué)出版社,2000.[10]單耀祖.材料力學(xué)[M].北京：高等教育出版社,2003.[11]郝振鐸.垂直支腿油缸的設(shè)計(jì)[R].液壓動(dòng)力報(bào)，1985。[12]姜校林、歐溈檳.凝土泵車支腿展開角度的優(yōu)化設(shè)計(jì)[R].建筑機(jī)械，2004。

附錄1英文原文Lecture2.6:WeldabilityofStructuralSteelsThelecturebrieflydiscussesthebasicsoftheweldingprocessandthenexaminesthefactorsgoverningtheweldabilityofstructuralsteels.SUMMARYThefundamentalaspectsoftheweldingprocessarediscussed.Thelecturethenfocusesonthemetallurgicalparametersaffectingtheweldabilityofstructuralsteels.Asteelisconsideredtoexhibitgoodweldabilityifjointsinthesteelpossessadequatestrengthandtoughnessinservice.Solidificationcracking,heataffectedzone-liquationcracking,hydrogen-inducedcracking,lamellartearing,andre-heatcrackingaredescribed.Theseeffectsaredetrimentaltotheperformanceofweldedjoints.Measuresrequiredtoavoidthemareexamined.1.INTRODUCTION1.1ABriefDescriptionoftheWeldingProcessWeldingisajoiningprocessinwhichjointproductioncanbeachievedwiththeuseofhightemperatures,highpressuresorboth.Inthislecture,onlytheuseofhightemperaturestoproduceajointisdiscussedsincethisis,byfar,themostcommonmethodofweldingstructuralsteels.Itisessentiallyaprocessinwhichanintenseheatsourceisappliedtothesurfacestobejoinedtoachievelocalmelting.Itiscommonforfurther"fillermetal"tobeaddedtothemoltenweldpooltobridgethegapbetweenthesurfacesandtoproducetherequiredweldshapeanddimensionsoncooling.Themostcommonweldingprocessesforstructuralsteelworkuseanelectricarcmaintainedbetweenthefillermetalrodandtheworkpiecetoprovidetheintenseheatsource.Ifunprotected,themoltenmetalintheweldpoolcanreadilyabsorboxygenandnitrogenfromtheatmosphere.Thisabsorptionwouldleadtoporosityandbrittlenessinthesolidifiedweldmetal.Thetechniquesusedtoavoidgasabsorptionintheweldpoolvaryaccordingtotheweldingprocess.Themainweldingprocessesusedtojoinstructuralsteelsareconsideredinmoredetailbelow.1.2TheMainWeldingProcessesa.ManualMetalArcwelding(MMA)Inthisprocess,thewelderusesametalstickelectrodewithafusiblemineralcoating,inaholderconnectedtoanelectricalsupply.Anarcisstruckbetweentheelectrodeandtheweldareawhichcompletesthereturncircuittotheelectricitysupply.Thearcmeltsboththeelectrodeandthesurfaceregionoftheworkpiece.Electromagneticforcescreatedinthearchelptothrowdropsofthemoltenelectrodeontothemoltenareaoftheworkpiecewherethetwometalsfusetoformtheweldpool.Theelectrodecoatingoffluxcontributestothecontentoftheweldpoolbydirectadditionofmetalandbymetallurgicalreactionswhichrefinethemoltenmetal.Thefluxalsoprovidesalocalgaseousatmospherewhichpreventsabsorptionofatmosphericgasesbytheweldmetal.Therearemanytypesofelectrodes.Themaindifferencesbetweenthemareinthefluxcoating.Thethreemainclassesofelectrodeareshownbelow:1.Rutile:Generalpurposeelectrodesforapplicationswhichdonotrequirestrictcontrolofmechanicalproperties.Theseelectrodescontainahighproportionoftitaniumoxideinthefluxcoating.2.Basic:Theseelectrodesproduceweldswithbetterstrengthandnotchtoughnessthanrutile.Theelectrodeshaveacoatingwhichcontainscalciumcarbonateandothercarbonatesandfluorspar.3.Cellulosic:Thearcproducedbythistypeofelectrodeisverypenetrating.Theseelectrodeshaveahighproportionofcombustibleorganicmaterialsintheircoating.b.SubmergedArcWelding(SAW)Thisprocessusesabarewireelectrodeandafluxaddedseparatelyasgranulesorpowderoverthearcandweldpool.Thefluxprotectsthemoltenmetalbyformingalayerofslaganditalsostabilisesthearc.Theprocessisusedmainlyinamechanicalsystemfeedingacontinuouslengthofwirefromacoilwhilsttheweldingleadismovedalongthejoint.ASAWmachinemayfeedseveralwires,onebehindtheother,sothatamulti-runweldcanbemade.Submergedarcweldingproducesmoreconsistentjointsthanmanualwelding,butitisnotsuitableforareasofdifficultaccess.c.GasshieldedweldingInthisprocess,abarewireelectrodeisusedandashieldinggasisfedaroundthearcandweldpool.Thisgaspreventscontaminationoftheelectrodeandweldpoolbyair.Therearethreemainvariationsofthisprocessasshownbelow:1.MIG(metal-inertgas)welding-Argonorheliumgasisusedforshielding.Thisprocessisgenerallyusedfornon-ferrousmetals.2.MAG(metal-activegas)welding-Carbondioxide(usuallymixedwithargon)isusedforshielding.Thisprocessisgenerallyusedforcarbonandcarbon-manganesesteels.3.TIG(tungsten-inertgas)-Argonorheliumgasisusedforshieldingandthearcstruckbetweentheworkpieceandanon-consumabletungstenelectrode.Thisprocessisgenerallyusedforthinsheetworkandprecisionwelding.1.3WeldedJointDesignandPreparationTherearetwobasictypesofweldedjointsknownasbuttandfilletwelds[1].SchematicviewsofthesetwoweldtypesareshowninFigure1.Theactualshapeofaweldisdeterminedbythepreparationoftheareatobejoined.Thetypeofweldpreparationdependsontheweldingprocessandthefabricationprocedure.ExamplesofdifferentweldpreparationsareshowninFigure2.Theweldjointhastobelocatedandshapedinsuchawaythatitiseasilyaccessibleintermsofboththeweldingprocessandweldingposition.Thedetailedweldshapeisdesignedtodistributetheavailableheatadequatelyandtoassistthecontrolofweldmetalpenetrationandthustoproduceasoundjoint.Operatorinduceddefectssuchaslackofpenetrationandlackoffusioncanbedifficulttoavoidifthejointpreparationanddesignpreventgoodaccessforwelding.1.4TheEffectoftheWeldingThermalCycleontheMicrostructureTheintenseheatinvolvedintheweldingprocessinfluencesthemicrostructureofboththeweldmetalandtheparentmetalclosetothefusionboundary(theboundarybetweensolidandliquidmetal).Assuch,theweldingcycleinfluencesthemechanicalpropertiesofthejoint.Themoltenweldpoolisrapidlycooledsincethemetalsbeingjoinedactasanefficientheatsink.Thiscoolingresultsintheweldmetalhavingachillcastmicrostructure.Intheweldingofstructuralsteels,theweldfillermetaldoesnotusuallyhavethesamecompositionastheparentmetal.Ifthecompositionswerethesame,therapidcoolingcouldresultinhardandbrittlephases,e.g.martensite,intheweldmetalmicrostructure.Thisproblemisavoidedbyusingweldfillermetalswithalowercarboncontentthantheparentsteel.Theparentmetalclosetothemoltenweldpoolisheatedrapidlytoatemperaturewhichdependsonthedistancefromthefusionboundary.Closetothefusionboundary,peaktemperaturesnearthemeltingpointarereached,whilstmaterialonlyafewmillimetresawaymayonlyreachafewhundreddegreesCelsius.Theparentmaterialclosetothefusionboundaryisheatedintotheaustenitephasefield.Oncooling,thisregiontransformstoamicrostructurewhichisdifferentfromtherestoftheparentmaterial.Inthisregionthecoolingrateisusuallyrapid,andhencethereisatendencytowardstheformationoflowtemperaturetransformationstructures,suchasbainiteandmartensite,whichareharderandmorebrittlethanthebulkoftheparentmetal.Thisregionisknownastheheataffectedzone(HAZ).ThemicrostructureoftheHAZisinfluencedbythreefactors:Thechemicalcompositionoftheparentmetal.Theheatinputrateduringwelding.ThecoolingrateintheHAZafterwelding.ThechemicalcompositionoftheparentmetalisimportantsinceitdeterminesthehardenabilityoftheHAZ.TheheatinputrateissignificantsinceitdirectlyaffectsthegrainsizeintheHAZ.Thelongerthetimespentabovethegraincoarseningtemperatureoftheparentmetalduringwelding,thecoarserthestructureintheHAZ.Generally,ahighheatinputrateleadstoalongerthermalcycleandthusacoarserHAZmicrostructure.ItshouldbenotedthattheheatinputratealsoaffectsthecoolingrateintheHAZ.Asageneralrule,thehighertheheatinputratethelowerthecoolingrate.Thevalueofheatinputrateisafunctionoftheweldingprocessparameters:arcvoltage,arccurrentandweldingspeed.Inadditiontoheatinputrate,thecoolingrateintheHAZisinfluencedbytwootherfactors.First,thejointdesignandthicknessareimportantsincetheydeterminetherateofheatflowawayfromtheweldduringcooling.Secondly,thetemperatureofthepartsbeingjoined,i.e.anypre-heat,issignificantsinceitdeterminesthetemperaturegradientwhichexistsbetweentheweldandparentmetal.1.5ResidualWeldingStressesandDistortionTheintenseheatassociatedwithweldingcausestheregionoftheweldtoexpand.Oncoolingcontractionoccurs.Thisexpansionandsubsequentcontractionisresistedbythesurroundingcoldmaterialleadingtoaresidualstressfieldbeingsetupinthevicinityoftheweld.Withintheweldmetaltheresidualstresstendstobepredominantlytensileinnature.Thistensileresidualstressisbalancedbyacompressivestressinducedintheparentmetal[2].AschematicviewoftheresidualstressfieldobtainedforlongitudinalweldshrinkageisshowninFigure3.ThetensileresidualstressesareuptoyieldpointinmagnitudeintheweldmetalandHAZ.Itisimportanttonotethattheresidualstressesarisebecausethematerialundergoeslocalplasticstrain.ThisstrainmayresultincrackingoftheweldmetalandHAZduringwelding,distortionofthepartstobejoinedorencouragementofbrittlefailureduringservice.Transverseandlongitudinalcontractionsresultingfromweldingcanleadtodistortionifthehotweldmetalisnotsymmetricalabouttheneutralaxisofafabrication[2].AtypicalangularrotationinasingleVbuttweldisshowninFigure4a.Therotationoccursbecausethemajorpartoftheweldisononesideoftheneutralaxisoftheplate,thusinducinggreatercontractionstressesonthatside.Thisleadstoadistortionknownascuspinginaplatefabrication,asshowninFigure4b.Welddistortioncanbecontrolledbypre-settingorpre-bendingajointassemblytocompensateforthedistortionorbyrestrainingtheweldtoresistdistortion.ExamplesofboththesemethodsareshowninFigure5.Distortionproblemsaremosteasilyavoidedbyusingthecorrectweldpreparation.Theuseofnon-symmetricaldoublesidedweldssuchasthoseshowninFigure2eand2iaccommodatesdistortion.Thedistortionfromthesmallsideoftheweld(producedfirst)isremovedwhenthelargerweldisputontheotherside.Thistechniqueisknownasbalancedwelding.Itisnotpossibletopredictaccuratelythedistortioninageometricallycomplicatedfabrication,butonebasicruleshouldbefollowed.Thisruleisthatweldingshouldpreferablybestartedatthecentreofafabricationandallsucceedingweldsbemadefromthecentreout,thusencouragingcontractionstooccurinthefreecondition.Ifdistortionisnotcontrolled,therearetwomethodsofcorrectingit;forceandheat.Thedistortionoflightsectionscanbeeliminatedsimplybyusingforce,e.g.theuseofhydraulicjacksandpresses.Inthecaseofheaviersections,localheatingandcoolingisrequiredtoinducethermalstressescounteractingthosealreadypresent.1.6ResidualStressReliefThemostcommonandefficientwayofrelievingresidualstressesisbyheating.Raisingthetemperatureresultsinaloweryieldstressandallowscreeptooccur.Creeprelievestheresidualstressesthroughplasticdeformation.Steelweldedcomponentsareusuallyheatedtoalowredheat(600C)duringstressrelievingtreatments.Theheatingandcoolingratesduringthisthermalstressreliefmustbecarefullycontrolledotherwisefurtherresidualstresspatternsmaybesetupintheweldedcomponent.Thereisasizelimittothestructureswhichcanbethermallystressrelievedbothbecauseofthesizeoftheovensrequiredandthepossibilityofastructuredistortingunderitsownweight.Itispossible,however,toheattreatindividualjointsinalargestructurebyplacingsmallovensaroundthejointsorbyusingelectricheatingelements.Othermethodsofstressreliefrelyonthermalexpansionprovidingmechanicalforcescapableofcounteractingtheoriginalresidualstresses.Thistechniquecanbeappliedin-situbutapreciseknowledgeofthelocationofthecompressiveresidualstressesisvital,otherwisethelevelofresidualstressmaybeincreasedratherthandecreased.Purelymechanicalstressreliefcanalsobeappliedprovidedsufficientisavailabletoaccommodatethenecessaryplasticdeformation.2.THEWELDABILITYOFSTRUCTURALSTEELS2.1IntroductionIfweldpreparationisgoodandoperatorinduceddefects(e.g.lackofpenetrationorfusion)areavoided,allthecommonstructuralsteelscanbesuccessfullywelded.However,anumberofthesesteelsmayrequirespecialtreatmentstoachieveasatisfactoryjoint.Thesetreatmentsarenotconvenientinallcases.Thedifficultyinproducingsatisfactoryweldedjointsinsomesteelsarisesfromtheextremesofheating,coolingandstrainingassociatedwiththeweldingprocesscombinedwithmicrostructuralchangesandenvironmentalinteractionsthatoccurduringwelding.Itisnotpossibleforsomestructuralsteelstotoleratetheseeffectswithoutjointcrackingoccurring.Thevarioustypesofcrackingwhichcanoccurandtheremedialmeasureswhichcanbetakenarediscussedbelow.2.2WeldMetalSolidificationCrackingSolidificationofthemoltenweldpooloccursbythegrowthofcrystalsawayfromthefusionboundaryandtowardsthecentreoftheweldpool,untileventuallythereisnoremainingliquid.Intheprocessofcrystalgrowth,soluteandimpurityelementsarepushedaheadofthegrowinginterface.Thisprocessisnotsignificantuntilthefinalstagesofsolidificationwhenthegrowingcrystalsinterlockatthecentreoftheweld.Thehighconcentrationofsoluteandimpurityelementscanthenresultintheproductionofalowfreezingpointliquidatthecentreoftheweld.Thisactsasalineofweaknessandcancausecrackingtooccurundertheinfluenceoftransverseshrinkagestrains.Impurityelementssuchassulphurandphosphorusareparticularlyimportantinthistypeofcrackingsincetheycauselowmeltingpointsilicidesandphosphidestobepresentintheweldmetal[3].AschematicviewofsolidificationcrackingisshowninFigure6.Weldmetalswithalowsusceptibilitytosolidificationcracking(lowsulphurandphosphorous)areavailableformoststructuralsteels,butcrackingmaystillariseinthefollowingcircumstances:a.Ifjointmovementoccursduringwelding,e.g.asaresultofdistortion.Atypicalexampleofthisisweldingaroundapatchornozzle.Iftheweldiscontinuous,thecontractionofthefirstpartoftheweldimposesastrainduringsolidificationoftherestoftheweld.b.Ifcontaminationoftheweldmetalwithelementssuchasulphurandphosphorusoccur.Atypicalexampleofthisistheweldingofarticleswithasulphurrichscale,suchasacomponentinasulphurcontainingenvironment.c.Iftheweldmetalhastobridgealargegap,e.g.poorfit-up.Inthiscasethedepthtowidthratiooftheweldbeadmaybesmall.Contractionoftheweldresultsinalargestrainbeingimposedonthecentreoftheweld.d.Iftheparentsteelisnotsuitableinthesensethatthediffusionofimpurityelementsfromthesteelintotheweldmetalcanmakeitsusceptibletocracking.Crackingsusceptibilitydependsonthecontentofalloyingelementwiththeparentmetalandcanbeexpressedinthefollowingequation:Hotcrackingsusceptibility=Note:Thehigherthenumber,thegreaterthesusceptibility.Solidificationcrackingcanbecontrolledbycarefulchoiceofparentmetalcomposition,processparametersandjointdesigntoavoidthecircumstancespreviouslyoutlined.2.3HeatAffectedZone(HAZ)Cracking2.3.1Liquationcracking(burning)TheparentmaterialintheHAZdoesnotmeltasawhole,butthetemperatureclosetothefusionboundarymaybesohighthatlocalmeltingcanoccuratgrainboundariesduetothepresenceofconstituentshavingalowermeltingpointthanthesurroundingmatrix.Finecracksmaybeproducedinthisregioniftheresidualstressishigh.Thesecrackscanbeextendedbyfabricationstressesorduringservice[3].AschematicviewofliquationcrackingisshowninFigure7.Insteelsthelowmeltingpointgrainboundaryfilmscanbeformedfromimpuritiessuchassulphur,phosphorus,boron,arsenicandtin.Aswithsolidificationcracking,increasedcarbon,sulphurandphosphorousmakethesteelmorepronetocracking.Therearetwomainwaysofavoidingliquationcracking.First,careshouldbetakentomakesurethatthesulphurandphosphoruslevelsintheparentmetalarelow.Unfortunately,manysteelspecificationspermithighenoughlevelsofsulphurandphosphorustointroduceariskofliquationcracking.Secondly,theriskofliquationcrackingisaffectedbytheweldingprocessused.Processesincorporatingarelativelyhighheatinputrate,suchassubmergedarcorelectroslagwelding,leadtoagreaterriskofliquationcrackingthan,forexample,manualmetalarcwelding.ThisisthecasesincetheHAZspendslongerattheliquationtemperature(allowinggreatersegregationoflowmeltingpointelements)andthereisagreateramountofthermalstrainaccompanyingwelding.譯文：演講2.6：結(jié)構(gòu)鋼的焊接性演講簡(jiǎn)要討論焊接工藝的基礎(chǔ)，然后測(cè)試決定結(jié)構(gòu)鋼焊接性的因素。摘要焊接的基本過程方面在這里被討論。然后把重點(diǎn)放在冶金參數(shù)對(duì)結(jié)構(gòu)鋼的焊接性的影響。一種鋼如果被認(rèn)為有良好的焊接性，如果焊接處有足夠的強(qiáng)度和韌性。凝固裂紋，熱影響區(qū)液化開裂氫致開裂，層狀撕裂，再熱裂解在這里被描述。這些是焊點(diǎn)不利影響的表現(xiàn)。采取的減少這些影響的措施被測(cè)試。1.導(dǎo)言1.1焊接工藝簡(jiǎn)介焊接是材料加入過程，焊縫可以通過高溫、高壓或兩者共同產(chǎn)生。在本文中，只討論高溫產(chǎn)生焊縫。因?yàn)檫@是到目前為止最常用焊接結(jié)構(gòu)鋼的方法。這基本上是這樣一個(gè)過程：激烈的熱源用于工件表面以實(shí)現(xiàn)熔化。同時(shí)將“料”添加到熔融熔池，以連接之間的縫，生產(chǎn)所需的焊縫形狀和尺寸并冷卻。最常見的焊接工藝為鋼結(jié)構(gòu)使用電弧，保持焊棒和工件產(chǎn)生強(qiáng)烈的熱源。如果得不到很好的保障，熔融金屬在熔池隨時(shí)可以接觸大氣中中的氧氣和氮?dú)猓@樣會(huì)導(dǎo)致凝固焊縫金屬中間有孔和脆性。這種技術(shù)被用于避免融池吸收空氣，主要用于焊接工藝加入結(jié)構(gòu)鋼在下面更詳細(xì)的介紹。1.2主要焊接工藝A.手動(dòng)材料電弧焊接在這個(gè)過程中，焊機(jī)采用了金屬電極棒與熔礦物涂層，在持有人連接到電力供應(yīng)。一個(gè)電弧在電極和焊點(diǎn)區(qū)域產(chǎn)生，形成回路，電極表面區(qū)域和工件都是電弧熔體。電磁力產(chǎn)生電弧，幫助失液電極上熔融面積工件的情況下兩個(gè)金屬保險(xiǎn)絲，形成熔池。電極涂層的焊劑貢獻(xiàn)直接熔池，防止了金屬反應(yīng)，其中完善熔化金屬。焊劑也提供了一個(gè)氣態(tài)的氣氛阻止吸收大氣中的氣體由焊縫金屬。有有很多類型的電極。主要不同點(diǎn)是在焊劑涂層。三個(gè)主要類別的電極如下所示：金紅石型：通用電極，應(yīng)用在不需要嚴(yán)格控制的機(jī)械性能的場(chǎng)合。這些電極含有高比例的二氧化鈦在焊劑涂層。基本型：這些電極產(chǎn)生比金紅石型焊縫更好的強(qiáng)度和韌性。電極有一個(gè)涂層，其中包含碳酸鈣和其他碳酸鹽巖和螢石。纖維素型：這種的電極類型所產(chǎn)生的電弧是非常精確的。這些電極在他們的涂層有很高比例的可燃有機(jī)材料。B.埋弧焊（saw）這個(gè)過程中采用了裸絲電極和焊劑的補(bǔ)充分被加入以顆?；蚍勰顟B(tài)加入電弧和熔池。焊劑保護(hù)熔融金屬形成一層爐渣和它也使電弧穩(wěn)定。這一過程主要是用于一個(gè)機(jī)械系統(tǒng)的焊接連續(xù)長度的焊絲從一個(gè)線圈，而焊接鉛是沿著焊縫，一個(gè)埋弧焊機(jī)可以吃幾條焊絲。一個(gè)接著另一個(gè)，所以一個(gè)多線運(yùn)行焊縫可以做出。埋弧焊比手工焊接產(chǎn)生更一致的焊點(diǎn)，但它是不適合難以進(jìn)入的領(lǐng)域。C.氣體保護(hù)焊在這個(gè)過程中，裸絲電極被使用，保護(hù)氣體充滿電弧和熔池周圍。這種氣體，防止由空氣污染電極和熔池。這個(gè)工藝過程中有三個(gè)主要變化，如下所示：MIG(金屬惰性氣體)焊接，氬氣或氦氣用來作為屏蔽氣體。這種工藝一般用于廢鐵結(jié)束的焊接。MAG（金屬活性氣體）焊接，二氧化碳（通常是混合氬）用來作為屏蔽氣體。這種工藝一般用于碳鋼和碳錳鋼。TIG（鎢惰性氣體）焊接，氬氣或氦氣用于屏蔽氣體以及電弧之間工件和非消耗品鎢電極。這個(gè)工藝一般用于薄板的工作和精密焊接。1.3焊接縫的設(shè)計(jì)與準(zhǔn)備有兩個(gè)基本類型的焊接縫稱為對(duì)接焊接縫和角焊縫[1]。這兩個(gè)焊縫類型，如圖1所示。實(shí)際焊縫的形狀是由將要結(jié)合的形狀決定的。焊縫準(zhǔn)備的類型，要看焊接的工藝個(gè)制作的工藝。例如不同的焊接準(zhǔn)備工作正在如圖2所示；該焊縫要設(shè)置形成這樣一種方式：這是方便雙方的焊接工藝和焊接位置。詳細(xì)的焊縫形狀的設(shè)計(jì)可用熱充分分配，并協(xié)助控制焊縫金屬的滲透，從而產(chǎn)生一個(gè)完善的焊縫。操作者導(dǎo)致的缺陷，如缺乏滲透與融合，這些難以避免。如果焊縫籌備和設(shè)計(jì)良好的焊接條件可以防止這些。1.4焊接熱循環(huán)對(duì)微觀結(jié)構(gòu)的影響焊接過程中所涉及激烈的熱，影響焊縫金屬及原金屬和接近融合的邊界的微觀結(jié)構(gòu)（邊界之間的固體和液體金屬）。因此，焊接周期影響焊縫的力學(xué)性能。熔融熔池迅速冷卻，由于金屬被加入作為一個(gè)有效率的散熱片。這冷卻的結(jié)果，在焊縫金屬中有一個(gè)冷鑄態(tài)組織。在焊接結(jié)構(gòu)鋼中，焊接釬料通常不具有與母材料金屬相同的成分。如果成分相同，快速冷卻可能會(huì)導(dǎo)致硬脆階，如馬氏體，在焊縫金屬的微觀結(jié)構(gòu)。這個(gè)問題的避免方法是采用焊接釬料碳含量比較母質(zhì)底。母板金屬接近熔化的熔池迅速加熱到達(dá)一個(gè)由融合邊界決定的溫度。接近融合的邊界，定點(diǎn)溫度接近熔點(diǎn)或已經(jīng)到達(dá)熔點(diǎn)。而材料，只有幾毫米的距離，可能只能達(dá)到幾百攝氏度。母質(zhì)接近融合邊界加熱到奧氏體相場(chǎng)。由于冷卻，這一地區(qū)的變換到一個(gè)不同于其余的母材微觀結(jié)構(gòu)。在這一區(qū)域的冷卻速度通常是快速，因此有一種向低溫結(jié)構(gòu)轉(zhuǎn)型傾向，如貝氏體，馬氏體，這比大部份的母金屬更硬，更脆。這一區(qū)域被稱為熱影響區(qū)（HAZ.）焊接熱影響區(qū)的微觀結(jié)構(gòu)受