毕业设计（论文）-混凝土泵车支腿部分的设计

图书分类号：密级：全套图纸加V信153893706或扣3346389411毕业设计(论文)混凝土泵车支腿部分的设计DESIGNOFTHECONTRETEPUMPTRUCKSTABILIZER学生姓名学院名称机电工程学院专业名称机械设计制造及其自动化指导教师20XX年6月2日徐州工程学院毕业设计(论文)·式中—混凝土泵车工作时垂直液压缸的最大闭锁力，辐射式支腿垂直液压缸的等于泵送工作时的最大支腿反力，=160921.2N。计算=8(MPa)垂直液压缸的收放时间为60s液压缸流量Q==()0.784=3.69L/min（2）其他液压缸的选择后支腿摆动油缸的选择：工作负载F=N=0.13622=362.2N内径的计算D=式中P＝5Mpa，=2.5，0.95代入数据，则D＝0.015（m）根据工程机械用液压缸内径系列，选取D=80mm活塞杆直径dd=0.717D=50mm最小导向长度H导向长度应满足H≥+=450/20+80/2=50(mm)导向套滑动面长度A取活塞杆直径的(0.61.0)倍,A取50mm；活塞宽度B为液压缸内径的(0.61.0)倍,B取50mm。壁厚计算≥PD/2[]=1.04(mm)选用10mm。缸筒外径的确定D1=D+2=80+20=100(mm)缸底厚度1≥0.433D2=2.65(mm)取1=10mm。水平液压缸的收放时间为30s。液压缸流量Q==2.75L/min前支腿摆动油缸的选择：工作负载F=N=0.13990=399N内径的计算D=式中P＝5Mpa，=2.5，0.95代入数据，则D＝0.015（m）根据工程机械用液压缸内径系列，选取D=80mm活塞杆直径dd=0.717D=50mm最小导向长度H导向长度应满足H≥+=800/20+80/2=100(mm)导向套滑动面长度A取活塞杆直径的(0.61.0)倍,A取50mm；活塞宽度B为液压缸内径的(0.61.0)倍,B取50mm。壁厚计算≥PD/2[]=1.04(mm)选用10mm。缸筒外径的确定D1=D+2=80+20=100(mm)缸底厚度1≥0.433D2=2.65(mm)取1=10mm。前支腿摆动液压缸的收放时间为30s。液压缸流量Q==4.28L/min前支腿伸缩油缸的选择：工作负载F=N=0.11678=167.8N内径的计算D=式中P＝5Mpa，=2.5，0.95代入数据，则D＝0.015（m）根据工程机械用液压缸内径系列，选取D=63mm活塞杆直径dd=0.717D=50mm最小导向长度H导向长度应满足H≥+=1200/20+63/2=100(mm)导向套滑动面长度A取活塞杆直径的(0.61.0)倍,A取50mm；活塞宽度B为液压缸内径的(0.61.0)倍,B取50mm。壁厚计算≥PD/2[]=1.04(mm)选用6mm。缸筒外径的确定D1=D+2=63+12=75(mm)缸底厚度1≥0.433D2=2.65(mm)取1=10mm。前支腿摆动液压缸的收放时间为30s。液压缸流量Q==2.76L/min（3）液压泵的选型与计算液压泵的主要参数是：额定工作压力和额定输出流量。确定液压泵的最大工作压力式中—缸或马达的最大工作压力—系统工作时的总压力损失，包括直管中的沿途损失，弯管、各种接头和阀的损失，对一般中高压，流量较大的液压系统取为2MPa。则14+2=16MPa确定液压泵的出口流量＝1.1(3.69*4+2.35*2+4.28*2+2.76*2)=33.54(L/min)又由条件,,选择CBQ－F532齿轮泵，属于高压齿轮泵，采用铝合金壳体和DU轴承机构，具有体积小、重量轻、转速高、寿命长等优点。排量为32mL/r，额定转速为2500r/min，额定压力为20MPa，驱动功率为26KW。（4）阀的选择根据压力和流量选择阀如下：节流阀选择C-175-C-11,联接方式为管式。溢流阀选择DBD·H15G10电磁换向阀选用DSG型9.5液压系统性能验算(1)液压系统压力损失的验算验算液压系统压力损失的目的是为正确调整系统的工作压力，使执行元件输出的力满足设计要求，并可根据压力损失的大小分析判断系统设计是否符合要求。液压系统中的压力损失包括：油液通过管道时的沿程损失、局部损失和流经阀类元件时局部损失，即：上式中沿程损失和局部损失可按下式计算式中：、d—直管长度和内径v—液流平均速度—液压油的重度、—沿程阻力系数和局部阻力系数=10m,d=0.02m,=9009.8=8820,=0.5,=0.021,代入上式可得：=0.22MPa=0.06MPa流经标准阀类元件时的压力损失值与其额定流量、额定压力损失和实际通过的流量有关，其近似关系式为=6MPa式中：和的值可以从产品目录或样品本上查出在液压系统工作循环中，不同动作阶段的压力是不同的，必须分别计算。当已知液压系统的压力损失后，就可以确定溢流阀的调整压力，它必须大于工作压力和总压力损失之和，即=0.28MPa14+0.17=14.17MPa(2)液压系统总效率的验算㈠根据系统的压力损失，确定管路的压力效率，又称管路的当量机械效率㈡管路系统中各个阀的泄露量和溢流量之和称为管路系统的容积损失，用表示，则管路系统的容积效率为式中：—当系统中无蓄能器时，为最大工作流量㈢管路系统的总效率为㈣液压传动系统的总效率，要考虑液压泵、管路系统、液压缸或液压马达各部分的能量损失，它们的总和用符号表示，则系统的总效率为式中：———液压泵的输入功率—液压系统总的能量损失———液压泵的总效率———管路系统的总效率———液压缸和液压马达的总效率(3)液压系统发热温升的计算液压系统工作时，所损失的能量必然转化为热能，使液压系统的油温升高，油温升高后会产生许多不良后果，如油温上升，油液粘度很快下降，泄露增大，容积效率降低；油温升高还会使油液形成胶状物质，堵塞元件小孔和缝隙，使液压系统不能正常工作等，因此，对液压系统的发热温升，必须进行验算并予以控制，对不同的液压系统，因其工作条件不同，允许的最高温度也不相同工程机械正常工作温度50～80最高允许工作温度70～80油的温升〈=35～40kW式中：P—液压系统的实际输入功率，即液压泵的实际输入功率，为26kW—系统的总效率液压系统所产生的热量，一部分使油液和系统的温度上升，另一部分热量经过冷却表面散发到空气中，当系统产生的热量和散发的热量相等时，系统达到了热平衡状态，油温不再上升，而稳定在某一温度上。当产生的热量Q，全部被冷却表面所散发时，即式中：—散热系数，当通风很差时为8.5～9.32；当通风良好时为15.13～17.46；当风扇冷却时为23.3；循环水冷却为110.5～147.6。可选16。—油箱散热面积—液压系统油液的温升由上式可得：计算时，如果油箱三边的结构尺寸比例为1：1：1到1：2：3时，而且油位为油箱高0.8时，其散热面积的近似计算式式中：V—油箱的有效容积计算所得的温升，加上环境温度，应不超过油液的最高允许温度，如果超过允许值，必须适当增加油箱散热面积或采用冷却器来降低油温即可满足要求。结论至此，我已顺利设计完混凝土泵车的支腿部分，设计中采用了现在市场上最常用的辐射式支腿型式，并通过中心范围的计算求解，得出了泵车的最小跨距范围，并且通过数学方法对支腿的展开角度进行了优化设计，使支腿可以最大限度的发挥作用，稳定性达到设计要求；并且利用四点支撑和三点支撑的方法进行了支腿竖直反力的求解，并利用求得的竖直反力对支腿的强度进行了校核，经过计算材料的强度可以满足泵车的工作需要；液压部分选择了电磁阀来控制支腿油缸的动作，方便实现自动化控制，在垂直支腿油缸上安装了双向液压锁，避免工作时出现缩腿现象，在行走时又避免油缸在重力作用下自动伸出，并且双向液压锁与支腿垂直油缸直接相连接防止油管老化爆裂出现危险；液压系统的有关部件工作性能也通过计算证明是符合要求的。我设计绘制了混凝土泵车支腿，以及垂直支腿油缸，所设计的支腿部分基本符合工况要求，并且具有结构简单、经济、操作安全等优点。

致谢到今天我的毕业设计已经圆满的完成了。在此，我要特别感谢我的指导老师仇文宁老师，在这段时间内他给了我莫大的帮助，正由于他的热心地帮助和指导，我的毕业设计才能够顺利的完成。仇老师严谨治学的态度和精神也是我在这次设计过程中学到的宝贵的财富。大学四年的学习和生活即将告别。感谢这四年来各位老师对我的教诲，各位同学给我的帮助！感谢与我共同走过大学的朋友们、同学们！感谢所有帮助过我的老师、同学、朋友，同时祝愿你们在以后的日子里，开心、快乐！

参考文献[1]马永辉.工程机械液压系统设计[Z].北京：机械工业出版社，1985.[2]郑红.混凝土泵车的稳定性分析[A].本溪冶金高等专科学校报，2001.[3]张艳伟.混凝土泵车支腿反力计算及基于ANSYS的支腿结构分析[D].中国机械工程学报。2004[4]朱文坚，黄平，吴昌林.机械设计[M].北京：高等教育出版社，2005.[5]徐景.机械设计手册[M].北京：机械工业出版社，1992.[6]李壮云，葛宜远.液压元件与系统[M].北京：机械工业出版社，2000.[7]朱宏涛.液压与气压传动[M].北京：清华大学出版社，2005.[8]杜国森.液压元件产品样本[M].北京：机械工业出版社，2000.[9]何存兴.液压传动与气压传动[M].武汉：华中科技大学出版社,2000.[10]单耀祖.材料力学[M].北京：高等教育出版社,2003.[11]郝振铎.垂直支腿油缸的设计[R].液压动力报，1985。[12]姜校林、欧沩槟.凝土泵车支腿展开角度的优化设计[R].建筑机械，2004。

附录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.译文：演讲2.6：结构钢的焊接性演讲简要讨论焊接工艺的基础，然后测试决定结构钢焊接性的因素。摘要焊接的基本过程方面在这里被讨论。然后把重点放在冶金参数对结构钢的焊接性的影响。一种钢如果被认为有良好的焊接性，如果焊接处有足够的强度和韧性。凝固裂纹，热影响区液化开裂氢致开裂，层状撕裂，再热裂解在这里被描述。这些是焊点不利影响的表现。采取的减少这些影响的措施被测试。1.导言1.1焊接工艺简介焊接是材料加入过程，焊缝可以通过高温、高压或两者共同产生。在本文中，只讨论高温产生焊缝。因为这是到目前为止最常用焊接结构钢的方法。这基本上是这样一个过程：激烈的热源用于工件表面以实现熔化。同时将“料”添加到熔融熔池，以连接之间的缝，生产所需的焊缝形状和尺寸并冷却。最常见的焊接工艺为钢结构使用电弧，保持焊棒和工件产生强烈的热源。如果得不到很好的保障，熔融金属在熔池随时可以接触大气中中的氧气和氮气，这样会导致凝固焊缝金属中间有孔和脆性。这种技术被用于避免融池吸收空气，主要用于焊接工艺加入结构钢在下面更详细的介绍。1.2主要焊接工艺A.手动材料电弧焊接在这个过程中，焊机采用了金属电极棒与熔矿物涂层，在持有人连接到电力供应。一个电弧在电极和焊点区域产生，形成回路，电极表面区域和工件都是电弧熔体。电磁力产生电弧，帮助失液电极上熔融面积工件的情况下两个金属保险丝，形成熔池。电极涂层的焊剂贡献直接熔池，防止了金属反应，其中完善熔化金属。焊剂也提供了一个气态的气氛阻止吸收大气中的气体由焊缝金属。有有很多类型的电极。主要不同点是在焊剂涂层。三个主要类别的电极如下所示：金红石型：通用电极，应用在不需要严格控制的机械性能的场合。这些电极含有高比例的二氧化钛在焊剂涂层。基本型：这些电极产生比金红石型焊缝更好的强度和韧性。电极有一个涂层，其中包含碳酸钙和其他碳酸盐岩和萤石。纤维素型：这种的电极类型所产生的电弧是非常精确的。这些电极在他们的涂层有很高比例的可燃有机材料。B.埋弧焊（saw）这个过程中采用了裸丝电极和焊剂的补充分被加入以颗粒或粉末状态加入电弧和熔池。焊剂保护熔融金属形成一层炉渣和它也使电弧稳定。这一过程主要是用于一个机械系统的焊接连续长度的焊丝从一个线圈，而焊接铅是沿着焊缝，一个埋弧焊机可以吃几条焊丝。一个接着另一个，所以一个多线运行焊缝可以做出。埋弧焊比手工焊接产生更一致的焊点，但它是不适合难以进入的领域。C.气体保护焊在这个过程中，裸丝电极被使用，保护气体充满电弧和熔池周围。这种气体，防止由空气污染电极和熔池。这个工艺过程中有三个主要变化，如下所示：MIG(金属惰性气体)焊接，氩气或氦气用来作为屏蔽气体。这种工艺一般用于废铁结束的焊接。MAG（金属活性气体）焊接，二氧化碳（通常是混合氩）用来作为屏蔽气体。这种工艺一般用于碳钢和碳锰钢。TIG（钨惰性气体）焊接，氩气或氦气用于屏蔽气体以及电弧之间工件和非消耗品钨电极。这个工艺一般用于薄板的工作和精密焊接。1.3焊接缝的设计与准备有两个基本类型的焊接缝称为对接焊接缝和角焊缝[1]。这两个焊缝类型，如图1所示。实际焊缝的形状是由将要结合的形状决定的。焊缝准备的类型，要看焊接的工艺个制作的工艺。例如不同的焊接准备工作正在如图2所示；该焊缝要设置形成这样一种方式：这是方便双方的焊接工艺和焊接位置。详细的焊缝形状的设计可用热充分分配，并协助控制焊缝金属的渗透，从而产生一个完善的焊缝。操作者导致的缺陷，如缺乏渗透与融合，这些难以避免。如果焊缝筹备和设计良好的焊接条件可以防止这些。1.4焊接热循环对微观结构的影响焊接过程中所涉及激烈的热，影响焊缝金属及原金属和接近融合的边界的微观结构（边界之间的固体和液体金属）。因此，焊接周期影响焊缝的力学性能。熔融熔池迅速冷却，由于金属被加入作为一个有效率的散热片。这冷却的结果，在焊缝金属中有一个冷铸态组织。在焊接结构钢中，焊接钎料通常不具有与母材料金属相同的成分。如果成分相同，快速冷却可能会导致硬脆阶，如马氏体，在焊缝金属的微观结构。这个问题的避免方法是采用焊接钎料碳含量比较母质底。母板金属接近熔化的熔池迅速加热到达一个由融合边界决定的温度。接近融合的边界，定点温度接近熔点或已经到达熔点。而材料，只有几毫米的距离，可能只能达到几百摄氏度。母质接近融合边界加热到奥氏体相场。由于冷却，这一地区的变换到一个不同于其余的母材微观结构。在这一区域的冷却速度通常是快速，因此有一种向低温结构转型倾向，如贝氏体，马氏体，这比大部份的母金属更硬，更脆。这一区域被称为热影响区（HAZ.）焊接热影响区的微观结构受