补缩(冒口)系统设计1.定向凝固2.定义:铸件模数3.基本原理4.冒口的基本公式5.冒口颈6.冷铁目录Theoreticallynoshrinkageporositiesarefoundinthefollowingconditions:理论上铸件无缩孔及缩松的条件1.Themetaldoesnotshowanyshrinkagebehaviourandthemouldwallisstable.金属无任何收缩，砂型尺寸稳定Nearlyallcastingalloysdoshrinkduringsolidification.Castironcancompensatetheshrinkagebycarbonexpansion.铸铁由石墨析出膨胀来补尚金属收缩2.ThecompletecastingsolidifiesperfectlyisothermallyThevolumereductionofthecastingswithaconstantwallthicknessisfoundasexternalshrinkageinouterdimensionse.gtubes.•铸件完全绝热管状收缩。3.Theshrinkageporositiesareconstantlycompensatedbyliquidmetalfromariser液态收缩不断由冒口中的液态金属来补给。Inrealitythisistheonlyoptionleftandoneshouldlookforadirectionalsolidificationtowardstherisersforacompletedefect-freecastingM=V/SwithM=ModulusV=VolumeS=CoolingsurfaceRealModulusdiffersfromGeometricalModulusby:实际模数由下列因数影响而不同于几何形状模数•shapeofthecasting铸件形状•alloy合金•mouldmaterial模子材料Thetotaldifferencecanbeupto30%.最大能达到30%(NB:Misusuallygivenincm!)Examples:Sphere=D/6(D=diameter)Cube=L/6(L=riblength)Cylinder=Rh/(2+(R+h)(R=radius,h=height)定义:铸件模数Solidificationtimetasfunctionofmodulus:凝固时间是模数的函数•t=A2V2/S2sphere球形•t=B2V2/S2plate板型withB=1.15AAandBdependon:•thermalpropertiesofmetal•thermalpropertiesofsand•differenceinpouringandsolidificationtemperatureAssumptions:1.sandmouldisinfinity2.contacttemperaturebetweensandandmetalisidentical3.duringsolidificationthecontacttemperatureisconstant基本原理Assumptions:条件：1.solidificationtimeriser>solidificationtimepart冒口凝固时间>铸件凝固时间2deliveredvolume>shrinkagevolumeofthepart冒口提供的补充金属体积>铸件凝固收缩金属的体积3feedingdistancemustbelargeenough液态金属必须具有足够的补缩距离冒口的基本公式Mriser>1.2MpartM冒口>1.2M铸件underthefollowingconditions:-mouldisfilledatt=0s.(nomouldfilling)-temperaturesriserandpartareuniformatt=0sec.-partandrisersaresurroundedwiththesamemouldmaterialInfluenceofmouldfilling•solidificationduringmouldfilling•heatingeffectsofthemouldduringmouldfillingInfluenceofsuperheating•liquidshrinkagesolidificationtimeriser>solidificationtimepart冒口凝固时间>铸件凝固时间•duringsolidificationoftheparttheriseralsosolidifies•Naturalriserdelivers:ca.14%oftotalvolume(cilinder)•普通冒口提供：圆柱形冒口14%体积补缩ca.20%oftotalvolume(bol)•球形冒口20%体积补缩Assumptions:-metalsolidifiesexogeneously(inlayers)-samemouldmaterialofriserandpartThermalbusses:热套冒口•isolationbusdeliveresca.30%oftotalvolume•绝热套冒口提供30%的体积•exothermalbusdeliveresca.70%oftotalvolume•发热套冒口提供70%的体积deliveredvolume>shrinkagevolumeofthepart冒口提供的补充金属体积>铸件凝固收缩金属的体积Feedingdistanceisthelengthinaninfiniteplatethatcanbefeededbytheriser.补缩距离是指冒口对一无限平板补缩的长度•heatingeffectriser4M热效冒口4Mbyconductionandmetaltransport•endeffect5M•effectofcoolingblocks6MM=Modulusplate(=0.5D)M=板模数（=0.5D)Feedingdistancemustbelargeenough液态金属必须具有足够的补缩距离Mpart:Mneck:Mriser=1:1.1:1.2M件:M径:M冒口=1:1.1:1.2Parametersofinfluenceonthedimensionsoftheriserneck:影响冒口径尺寸的参数:-distancebetweentherisertothepart-冒口到铸件的距离-shapeoftheneck-冒口颈的形状-break-cores-冒口座冒口颈冷铁Purpose:shortenthesolidificationtimein(aspecificzoneof)apart目的：缩短铸件中有些部位的凝固时间Coolingsurfaceofacoolingblockisequalto2.5timesthecoolingsurfaceofsandifnogairgapiscreated.冷铁的冷却表面积应是2.5倍的铸件与砂模的接触面积thicknessofcoolingblock=min.modulusofpartatit'sposition(=0.5D)(formaximumcoolingeffect)冷铁的厚度=放置位置部分铸件的模数（=0.5D)Ruleofthumbtocorrectfortheheatingeffectduringmouldfilling:thicknessofcoolingblock=partthickness(=2Mpart)冷铁的厚度=铸件的厚度（=2M件)topreventheatcracking:为防止热裂:lengthofacoolblock=3a4xit'sthickness冷铁的长度=3,4X其厚度distancebetweencoolblocks=max.it'slength冷铁间的距离=最大为其长度
