流体机械原理英语

圆锥收敛模具中的液流流动 3.1 简介 3.1.1 目的 关于圆锥收敛模具中金属液流流动的研究覆盖了诸如划线、开式挤压、静液挤压以及封闭腔挤压等工艺。 图1所示为一个钢坯及模具。钢坯由各向同性材料制成，不同材料的特性将在后面加以考虑分析。在下面的简化中，钢坯为一半径为Ro的圆柱型棒料，将该棒料压入圆锥收敛模具中，使其半径还原为Rf。减小值可以通过模具入口处及出口处钢坯的横截面予以测得。 三个与该还原过程相关的变量描述如下： 1. 减小量可通过半径比Ro/Rf、面积比Ro^2/Rf^2, 面积减小值：r= ... ..., 面积减小比: r%=..., 或有效/对数应变[ ... ]来测得。(公式我就不帮你翻译了，麻烦您自己抄一下吧) 2.半锥角， 划线过程中模具角的一半，相对较小，一般为6E-12E，开式挤压中可能达到20E, 对于封闭腔挤压，模具可能是方的，数值可能达到90E。 3.第三个变量为模具与棒料间的摩擦力。

3.2.THEEXPERIMENTALAPPROACH3.2实验途径3.2.1TheEquipment3.2.1设备Adrawbench(Fig.<2>)maybeusedtomeasuretheforcerequiredinwiredrawing.可以用一台冷拔机（图2）来测量拉丝所需的力。Theworkpiece,therodpassingthroughthedie,hasitsfrontend,thenarrowend,heldbygrips.把通过模具的工件（金属杆）的前端，即窄的一端，用夹具保持住。Thegripsarepulledbyahydraulicsystem-acylinderwithpiston-orbyothermeans.夹具由液压系统（一套带活塞的液压缸）或其他方法牵引。Theforceappliedistransmittedthroughaloadcell(Fig.<3>).施加的力通过一个负荷传感器传递（图3）。InaloadcellstraingaugesareappliedtothetensilerodtoproduceaWheatstonebridgeinwhichthevoltagedifferential,properlycalibrated,providesameasureofthedrawingforce.FordetailsseeReference[1].在负荷传感器中，应变规被加到拉伸杆上，以产生一个惠斯登电桥，其中被很好定标的电压差动就提供了拉丝力的量度。关于详细情况，参见文献【1】。2.2RecordingoftheReadings2.2读数的记录Themeasureofdrawingforceisproducedcontinuouslyonarecorder,oronanoscillographasafunctionofgripdisplacement,i.e.,lengthofwiredrawn.拉丝力的量度是作为夹具位移（即被拉金属丝的长度）的函数，在记录仪上或示波器上连续产生的。Updatedinstrumentationmaydigitizetheforcevs.displacementreadingsandrecordthemontape,disk,orothermemoryunitonamicrocomputer.现代化的仪器可以使力和位移关系的读数数字化，并将它们记录到磁带、硬盘或微机的其他存储装置上。Figure<4>representsarecordofasinglerunofawirethroughadie.图4示出了金属丝单程通过模具的记录。Withtheapplicationofmotiontothehydraulicpiston,theloadonthewirerises;thesteepslopeofthecurve,duetotheelasticstretchingofthesystemwithincreasingforce,andotherfactors,suchasthesettlingoftheridgesofthegripsbitingintotheworkpiece,occursbeforeanywireisdrawnthroughthedie.随着向液压活塞施加运动，金属丝上的负荷就上升；在任何金属丝被拉丝通过模具之前就会发生以下现象，即曲线出现很陡的斜率，这是因为系统随着力的增加出现弹性伸长，以及其他因素的关系，这些因素包括夹具脊的固定咬入工件等。Thepeakofthecurveisduetotwofactors.曲线的峰是由于两个因素。Onecomprisestheinertiaforces;thesuddenapplicationofforceacceleratesthewirefromstandstilltofullspeedinashorttime.一个是惯性力；力的突然施加加快了金属丝在短时间内从静止到全速的速度。Anothercauseofthepeakisthatatstandstillandslowspeeds,frictionishigherthanfrictionatfullydevelopedspeeds.曲线峰的另一个起因是，在静止和低速下的磨擦要高于全速前进速度下的磨擦。Astheinertiaforcesubsidesandfrictionreduces,thedrawingforcedropstoitssteady-stateconstantvaluefortheconstantspeeddrawing.随着惯性力的下降和磨擦的降低，拉丝力降到其恒速拉丝时的稳态恒定值。Thismeasureofsteady-statedrawingforceshouldordinarilybetakenastheforcereading.稳态拉丝力的这一度量通常应被取作力的读数。Whenthedrawingforceisdividedbythecross-sectionareaofthewireemergingfromthedie,theresultisthedrawingstressforthespecificcombinationofreduction,coneangle,andfriction.当拉丝力除以从模具中出来的金属丝的横截面时，其结果就是缩小量、锥角和磨擦特定组合下的拉丝应力。

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