金属圆锯片的动态特性及锯切降噪王太勇,张纪锁,张策(机械工程系)摘要基于声振理论与实验分 析技术,系统研究了金属锯切过程的动态特性,提出快速方便地估算任一夹紧比下弹性圆板结构动 态特性的算法。进而探索了减振降噪措施,取得明显降噪效果。关键词:
金属锯切噪声,圆锯结构 ,
动态特性,降噪中图法分类号:TB535RESEARCHONDYNAMICBEHAVI OURANDNOISEREDUCTIONOFMETALCUTTINGSAWPLATES ¥WangTaiyong;ZhangJisuo;ZhangCe(Dept.ofMech anicalEng.)Abstract:Basedupontheoreticaland experimentalmethodsofacousticsandvibration, thedynamiccharacteristicsofcuttingprocesses havebeenresearchedsystematically,andasimpli fiedmethodofquicklyestimatingthemodalparame tersofelasticcircularplatestructuresundercl ampinghasalsobeenadvanced.Furthermore,wetry thebesttoexploreeffectivelythenoise-reducin gwaysinthesawingprocess.Infact,satisfactory resultshavebeenachievedinpractice.Keywords: metalsawingnoise,sawplatestructures,dynamic behaviour,noisereductionInmetallurgicalindu stry,metalsawingnoisemayreach120dBormore,it isimperativetotakeeffectivemeasurestoreduce theharmfulnoise.UPtillnow,littleworkinthisf ieldhasbeendonebecauseofthetransientexcitat ionsandtheircomplicatedmechanism.Butalotofr esearchworkonwoodsawingplateshavebeendonein USandmanyothercountriesbecauseoftherelative lystableandsoftexcitations,etc[1'2j.Therear eatleastfourbasicwaysinwhichcircularsawspro ducenoise[3):l)Aerodynamicnoiseiscausedwhen thecircularsawplaterotatesandeddiesareshedp eriodicallyfromtheteeth.Theactualnoisegener atedbytheeddiesthemselvesisquitesmallasthee fficiencyofnoisegenerationisverylow.Theaero dynamicnoiseisduemainlytothealternatingpres sureexertedontheairbytheteethoftheplate.2)V ibrationofsawplateconsistsmainlyofresonantv ibrationandforcedvibration.Thesheddingofedd iescanexciteresonantlateralvibrationinthesa wplatewhich,inturn,radiatesnoise.Modalpatte rnsarecomplexandthevibrationedestsmainlyint heouterthirdofthesawplate.Intheprocessofcut ting,theteethforcetheplatetovibrate.Athighf requenciesmostofthenoisefromthesawplateisdu etoplatevibration.3)Noisefromtheworkpiececa nvaryconsiderably,particularlyifalargesheet ofmaterialwithlowdampingisbeingcut,becausei tsradiationefficiencycanbehigh.4)Motorandtr ansmissionnoiseisminimalfornormalelectricmo torsandbeltdrive(ifany).Anysignificantnoise isprobablyduetowornbearingsandcanbefixedeas ily.AshighfrequenciescontributemoretotheAwe ightednoiselevels,mostofthenloudnessnofnois eisusuallyradiatedfromthesawplate.1DynamicC haracteristicsofSawPlateStructuresInthispap er,weanalyzemainlythesawplatestructureafl00 0mmX6mmXac500mm(platediameterXthicknessXcla mpingdiameter),whichiscommonlyusedinmetallu rgicalindustry.Withthecoordinationamongmeth odsoffiniteelement,theimpulseexcitationtest andsandmodeexcitationtest,alotofeffectivere sultshavebeenachieved:1)Inclampingactions,s awplatestructureshaveverydensemodaldistribu tionandverylittledamping,andeachmodalshapec onsistsregularlyofnodaldiametersandnodalcir cles.Themainmodesconsistonlyofnodaldiameter s.Onlyonenodalcirclebeginstobefoundonthe16t hmodalshape.Eachmodalfrequencywithnodaldiam etersgetsthedualmodalshapes,butReceivedApr. 28,1994.RevisedSep.27,1994.Bornin1962,male, Dr,associateprof.practicallateralrestrainin gattoothpositionmakesonemodalfrequencyofthe dualmodesgettinghigherthanever[4j.2)Insandm odeexcitationtestswetrytoimitatethepractica lsawingexcitationbypositioningtheexciteratt hecuttingpoint.Ithasbeenprovedthatthenodald iametermodesaremuchmoresensitivethannodalci rcleones.Theyarethemainreasontoproduceinten sivevibrationandnoise.Fig.lpresentsthestati sticalrelationsbetweenmodalfrequenciesandth enodaldiameternumbersinresponse.Theyaccordq uitewellwithexponentialfunctionsorthesecond aryfunctions[sj.Fig.1Relationsbetweenmodalf requenciesandthenodaldiameters3)Rigidityoff langesandtheclampingforceinfluencesobviousl ythemodalfrequencies:largerflangesmakethefi rstseveralmodalfrequencieshigherlstrongercl ampingforcecanmakeallmodalfrequencieshigher Irigidityoftheflangesinfluencesobviouslythe uppergrademodes,strongrigiditymakesthesefre quenciesalittlebitlower[51.4)Forear1lycalcu latingthemodalf.requencesandthemodalshapesofsawplatestructuresunderclamping,basinguponelasticdynamicsandfiniteelementtheories,wehaveadvanced'aneasilyused,fastestimatingform
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