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1、Forminghigh-strengthmaterialsByArtHedrickJanuary31,2002Variousshapedefectscanbeencounteredinflat-rolledferrousandnonferrousstrip.Knowingtheirmechanicsandoriginsandhowtocorrectthemcanbeveryusefulintimesofneed.Figure1ObjectFabricatorsencountervariousshapedefectsinflat-rolledfer
2、rousandnonferrousstrip,somesimpleandsomecomplex.Howdothesedefectsoriginate?Whatmethodsandmachinescanfabricatorsusetocorrectthem?SimpleShapeDefectsSimpleshapedefectsarecharacterizedbylengthvariationsacrossthethicknessofthestrip.CoilSet.Coilsetisthemostbasicandcommonofallshaped
3、efects.Itiscausedbyalengthdifferentialfromthetoptobottomsurfaceofthestripinthelengthwisedirection(seeFigure1).Itcancomefromapreviousbendingoperation(forinstance,theexitpasslinerollinaslittinglineisnotoriousforputtinginreversecoilset)orjustfromcoilingthecoilinacoldmill,ahotmil
4、l,orevenonatensionlevelline.Thisconditioncanbecorrectedbyreverse-bendingthematerial,whichstretchestheshortsurfaceandcompressesthelongsurface.Forthiscorrectiontobepermanent,thematerialmustbebentpastitsyieldpoint,whichiscommonlyreferredtoasitsyielddiameter.Theyielddiameterofama
5、terialcanbecalculatedusingthefollowingformula:Dy=tE/Ywhere:Dy=yielddiameter,inchest=materialthickness,inchesE=modulusofelasticity,poundspersquareinchY=materialyieldstrength,PSIThemodulusofelasticityisabasicmaterialpropertythatdefinesitsstiffness.Ahighnumberindicatesthemateria
6、lisstiff,whilealownumberindicatesitisnot.Steelhasamodulusofelasticityofabout30,000,000PSIandisconsiderablystifferthanaluminum,whichhasamodulusofelasticityof10,000,000PSI.Figure3ObjectForexample,analuminumstripthatis1/8in.thickwitha40,000-PSIyieldstrengthmustbebenttoa31-1/4-in
7、.diametertoreachthepointatwhichanyfurtherbendingwillcausepermanentset.Ontheotherhand,a1/8-in.-thick,40,000-PSI-yield-strengthsteelstripwouldneedtobebentonlytoa93-3/4-in.diametertoreachthesameplasticpoint.Tohavethesameeffect,aluminummustbebenttoamuchtighterdiameterthansteel,wh
8、ichrequiresmoreworkandmorepower.Ifthesteelinthisexamplehada120,000-P
