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专业英语(中)课堂练习.ppt

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Theenginelathe,oneoftheoldestmetalremovalmachines,hasanumberofusefulanddesirableattributes.Todaytheselathesareusedprimarilyinsmallplantswheresmallerquantitiesratherthanlargeproductionrunsareencountered. Tolerancesfortheenginelathedependprimarilyontheskilloftheoperator.Thedesignengineermustbecarefulinusingtolerancesofanexperimentalpartthathasbeenproducedontheenginelathebyaskilledoperator.Inredesigninganexperimentalpartforproduction,economicaltolerancesshouldbeused. Theenginelathehasbeenreplacedintoday’sproductionplantsbyawidevarietyofautomaticlathessuchasturretlathes,automaticscrewmachines,andautomatictracer(仿形)lathes.Intheassemblyofmachinery,whentwoshaftsarenotinlineorareafewthousandthsofaninchoutofparallel,theyareforcedintoconnectionbyrigidcouplings.Theresultingstressesintheshaftsbecomereversingstresseswhentheshaftsarerotated.Thecorrection,whenperfectalignmentcannotbeeconomicallyattained,istouseflexiblecouplingswhichcanminimizetheharmfuleffectsofshafts.在机器的装配过程中，当两轴不在一条直线上或者在平行度上相差千分之几英寸时，采用刚性联轴器强使他们连接在一起。当轴旋转时，轴上所产生的应力就是一个方向不断改变的应力。通常情况下，在无法经济地实现两轴线之间的精确找正对准时，可以使用弹性联轴器来减少轴的有害影响。Grindingisoneofthemostwidelyusedmethodoffinishingpartstoextremelyclosetolerancesandlowsurfaceroughness.Currently,therearegrinders（磨床）foralmosteverytypeofgrindingoperations.Particulardesignfeaturesofapartdictateto（决定了）alargedegreethetypeofgrindingmachinerequired.Whereprocessingcostsareexcessive,partsredesignedtoutilizealessexpensive,higheroutputgrindingmethod（高效磨削方法）maybewellworthwhile.Grindingisoneofthemostwidelyusedmethodoffinishingpartstoextremelyclosetolerancesandlowsurfaceroughness.Currently,therearegrinders（磨床）foralmosteverytypeofgrindingoperations.Whereprocessingcostsareexcessive,partsredesignedtoutilizealessexpensive,higheroutputgrindingmethod（高效磨削方法）maybewellworthwhile.