金属(jīnshǔ)轧制基础Rolling轧制(zházhì)Theprocessissimilartotherollingofdough(面团(miàntuán)）witharollingpin（擀面杖）toreduceitsthickness.Rolling,whichaccountsforabout90%ofallmetalsproducedbymetalworkingprocesses,wasfirstdevelopedinthelate1500s.Thebasicoperationisflatrolling.扁平孔型轧制,orsimplyrolling,wheretherolledproductsareflatplateandsheet.Sheetsaregenerallylessthan6mmthick.Theyareusedforautomobileandaircraftbodies,appliances(仪表(yíbiǎo)),foodandbeverages(饮料）containers,andkitchenandofficeequipment.Flat-andShape-RollingProcessesMECHANICSOFROLLINGFlat-Rolling扁平孔型(kǒnꞬxínꞬ)轧制Thevelocityofthestripishighestattheexitfromtherollgap;wedenoteitasVfthere.Becausethesurfacespeedoftherollisconstant,thereisrelativeslidingbetweentherollandthestripalongthearcofcontactintherollgap,L.Atonepointalongthecontactlength,calledtheneutralpointorno-slippoint中性点Therollspullthematerialintotherollgapthroughanetfrictionalforceonthematerial.ItcanbeseenthatthisnetfrictionalforcemustbetotherightinFig.13.2b;consequently,thefrictionalforcetotheleftoftheneutralpointmustbehigherthanthefrictionforcetotheright.Becausetherollsapplypressureonthematerialinordertoreduceitsthickness,aforceperpendiculartothearcofcontact(Fig.13.2c)isneeded.TherollforceinflatrollingcanbeestimatedfromtheformulawhereListheroll-stripcontactlength,wisthewidthofthestrip,andYangistheaveragetruestressofthestripintherollgap.Equation(13.2),ideally,isforafrictionlesssituation.ReducingRollForce.Four-HighRollingMillGeometricConsiderationsRollBendingSpreading展宽(zhǎnkuān)ofaStripFLAT-ROLLINGPRACTICEColdrollingiscarriedoutatroomtemperature(Section1.7)and,comparedtohotrolling,producessheetandstripwithmuchbettersurfacefinish(becauseoflackofscale),dimensionaltolerances,andmechanicalproperties(becauseofstrainhardening).冷轧是在室温下对材料(cáiliào)进行轧制。与热轧相比，冷轧产品尺寸精度高，表面光洁，机械强度高。冷轧变形抗力大，适于轧制塑性好，尺寸小的线材、薄板材等。/Packrolling（迭板轧制(zházhì)）isaflat-rollingoperationinwhichtwoormorelayersofmetalarerolledtogether;thisprocessimprovesproductivity.Aluminumfoil,forexample,ispac