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BASIC

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BASIC

    BASIC

CHINESEJ0URNAL0FMECHANICALENGINEERNG?45?

    spectrumiscontinuousanditsfrequencydistributionfollowsthe famousPlancklaw.

    1.5Broadeningofspectralline

    Amongtheaboveclassesofradiation.spectrallineofline spectrumtendstobroadenorfrequencyshiftbecauseofthe interactionbetweentheradiatingparticlesandsurroundingparticles. Thereareseveraltypesofspectrallinebroadening.Themain broadeningincludesStarkbroadeningandDopplerbroadening. Starkbroadeningtakesplacewhenradiatin2particlesareinfluenced bysurroundingchargedparticles(ionsandelectrons).Therelative motionbetweentheradiatingparticlesanddirectionofobservation causesDopplerbroadening.Thehigherthetemperature,the strongertheBrowmanmotionoftheradiatingparticles,thusthe moreobvioustheDopplerbroadening.

    Spectralcharacteristicsofeachclassofradiationdeterminethe applicationofeachspectruminformationinweldingarc.Among them,linespectrumhasbroadapplicationwhilecontinuousspec. trumandspectrallinesbroadeninghavetheirownuniqueapplica. tions.

    2BASICTHEoRYoFWELDINGARC

    SPECTRALINFoRMATIoN

    Thearccolumn.wheremanyweldingarcphenomenatake

    placeandpass,isakindofplasmaandaccountsformostpartof weldingarcvolume.Inweldingarcspectralinformationtechno1.

    ogy,thearccolumnanditsambientareawhereradiationappears aretheobjectstobeinvestigated.Basedontheviewofplasma physicsandspectroscopy,whentheinvestigatedobject(called system)isincompletethermodynamicequilibrium(CTE)orlocal thermodynamicequilibrium(LTE1.thefollowingequationswill comeintoexisten[3-81.

    Theequationofspectrallineemissivityisdescribedasfol

    lows.

    "Whenaparticlesuchasanatomjumpsfromhighenergylevel tolowenergyleveln,thespectrallineemissivitythatcorre- spondstocertainwavelengthcanbeexpressedasfollows =

    gmnxexp(]

    wheresistheemissivityofcertainspectralline,Amisthe transitionprobabilityfromenergylevelmton,hisplankconstant, isthefrequencyofthespectralline,gmisthestatisticweight ofenergylevelm,Z(isthepartitionfunctionofatom,noisthe numberdensityofatom,E,nisthepotentialenergyofenergylevel ,Tisthetemperature,andKisBoltzmannconstant.

    Boltzmanndistributionequation

    n=z(rKT]?.)IJ?

    wherenmistheatomnumberdensityofenergylevelm.Other symbolsareidem.

    Sahadistributionequation

    =×T(27~meKT)3/2

    n

    p

    (-KT],z(,),(3)

    wherenr+listheionnumberdensityofllevelionization,r/,isthe ionnumberdensityofrlevelionization,meisthemassofelectron,

andneisthenumberdensityofelectron.

    Forfirstlevelionization,theEq.(3)canbewrittenas :

    0

    2Z(T)l(2nmeKT)

    z(r)h

    (]?

    Forthedissociationreactionofdiatomicgasmolecule A2A+A,accordingtothelawofmassaction,thedissociation equationisgivenas

    =

    Z(h](]/(5)

    wherenisthenumberdensityofmolecule,nistheatomic numberdensityofdissociationmolecule,nisthepartitionfunc

    tionofmolecule,isthepartitionfunctionofatom,mAisthemass ofatom,andED.

    istheenergyofdissociation.

    Thenumberofpositivechargeisequaltothatofnegative chargeinarcplasma,sothequasineutralequationcomesintoexis

    tence

    n.=?n+2?+3?"+..?(6)

    wherer/f,r/fandistheionnumberdensityofelementi whoseionizationlevelisfrom1to3.

    Theplasmapressurepfollowstheequationofstate P=?,,(7)

    wherepisthepressureoftheplasma,istheparticlenumberden

    sityofjparticle,Jincludeatom,molecule,electronandion,and isthecorrectionquantityofp.

    ForBremsstrahlungradiation,thedistributionofBrem

    sstrahlungemissivitywithfrequencycanbewrittenas

Uf=6.37x10-53e

    niZ2(K)-'/2~exp(]

    wheretheunitofUfisW?m?Hz-,isthenumberdensityof

    ion,Zistheionchargenumber,istheelectrontemperature,and isGauntfacton

    Forrecombinationradiation,radiantphotonenergyhfcanbe expressedas

    hf=+(9)

    wherehisthePlanckconstant.fisthefrequencyofradiationpho. ton,isthekineticenergyofelectronwhichiscontinuous,andEi istheionizationenergywhichisdiscrete.Recoml~linationradiation isacontinuousspectrumwichst.Becausetheionizationenergy

    ishigh,thephotonenergyofrecombinationradiationishigh.Re

    combinationradiationspectrummainlydistributesinvaCUUlTIultra- violetarea.

    TheequationofStarkbroadening

    ?2=2.50x10o'1/2(10)

    where?2isthewholewidthathalf-highofStarkbroadening outlineofHlineanda1,2isthehalf-widthathalf-highofStark broadeninglineoutlineinducinginone.

    TheequationofDopplerbroadening

    =

    (

    where?卵2isthewholewidthathalf-highofDopplerbroaden. inglineoutline,isthetemperatureofheavyparticle,isthe massofradiationparticle,andcisthelightspeedinvacuum,20is wavelengthoflinecenter.

    ThePlanckequationofblackbodyradiation

    e(,=2nhc2

exp[[j?J(12)

    wheree,Tb)iStheradiationpowerperunitofwavelengthand ereawhentheblackbodytemperatureisTbandcentralwavelength is.isthewavelength,cisthelightspeedinvacuum.andTbis thetemperatureoftheblackbody.

    Thetwelveequationsaboveareselectedfromtheequations ofplasmaphysicsandspectroscopy.Theseequationspresentthe relationshipbetweendifferentradiationvolumeandvariousstate

CHINESEJ0URNAL0FM|ECHANICALENGINEERING?47?

    onspectrometer(Fig.1(71).Thesecondmethodisbasedoninter. ferencefilter,generallywhichiSutilizedasaspectra1sensor (Fig.2ll'J,.Theadvantagesofthefirstmethodareitsabundant informationquantityandhighprecision,however,itsbiggervol

    umeandexpensivepricebringsomedisadvantages.Thismethod isfitforlaboratorystudy.Thesecondmethodtakesadvantagesof smallervolume,simplestructureandconvenienceforuse,which issuitableforrealtimetestingandcontrollingonline. Fig.1Diagramoftheexperimentalapparatusforarcspectrummeasuringandcontrolling

    Fig.2Photographofarcspectralsensorwith

    interferencefilterinsideforcontrolling

    weldingmetaldroplettransfer

    4APPLICATIoNEXAMPLES0FWELDING

    ARCSPECTRALINF0RMATIoN

    4.1Applicationinmeasuringtemperature,componentand densi~ofarcplasma

    Fig.3showedthedistributionoftemperatureandcompo. nentinAH,arcmeasuredbyspectra1method.FromFig.3wecan seethattheuniformmixedgasesAr+H,becomenotuniformafter

    enteringarcspaceandthedensityoffH,1incenteriShigherthan thedensityinbrimofarccolumnt'..Thisresultpointsoutthat theexistanceofhydrogeninarciSmuchharmfu1becausetheY concentrateinthehightemperaturecentralereaanddivideintoH andH.SOthatitiSveryeasytoenterweldingpoo1andproduce hydrogenporosityintheweldingseam.

    ThetemperatarefieldofAN7arcmeasuredbyspectral methodiSshowedinFig.4t/-I.ThestudyshowedthatwiththeN contentincreasinginarcspace,thetemperaturefiledbecomesnar- rowerandnarrowerandhighertemperatureregionshiftingtoward positiveelectrode.WhenN,?50%.thehighest.temperatureregion fallsintothesideofpositiveelectrode(Fig.4,.ThisphenomenoniS verybeneficiaItohemingworkpiece.ThisiSthereasonwhyArN7

    arcisgoodtoweldcopperandstainlessstee1.

    

    

    

    

    

    

    

    

    (a)Distributionofvariousparticlenumber

    densitywitharctemperature

    RadiUSr/mm

    fb)Distributionoftemperaturealongdirection

    ofradius

    1.2

    1.0

    0.8

0.6

    0.4

    0.2

    (c)Distributionoftheratioofargontohydrogenandthe

    distributionofhydrogenequivalentdensityH2 alongdirectionofradius Fig.3Temperatureandcomponentdistribution

    ofAr+H2arcmeasuredbyspectralmethod

    一鲁..一一\+H.s.

    一暑..H\+《皇BEjz

    —一口.

    .B^ln..{i0J

LIJunyue,etal:Basictheoryandapplicationsofweldingarcspectralinformation

    0

    2

    8

    l3.

    4

    \

    

    ,

    (-)

    :

    ,,//,

    //g1

    ,

    ,

    ,

    :,\,,//

O

    l2

    8

    l3

    4

    2l(+)0

    Distance

    (a)TemperaturefieldofAr+l0%N2

    ()

    ,

    I

    I/'1"1'1'

    I

    '

    /

    2

    21(+1O12

    Distanced/mm

    (b)TemperaturefieldofAr+50%N2

    Fig.4TemperaturefieldofAr+N2arCmeasured

    byspectralmethod

    4.2Applicationinrealtimemeasuringandcontrollingarc

    atmosphere

    Accordingtothestudyabove,acompacttypedeviceusedin monitoringhydrogeninarcspacewasdeveloped.Thisdevice usesinterferometricfilter(narrowbandfilter)toobtainneeded radiationspectralsignalandmonitorthehydrogeninarcspace. Whenhydrogendensityexceedsacertainnumericvalue,thede

    viceCangiveanalarmandsendoutasignaltooperatortoCOntrol arcatmosphere.Inthisway,thearcatmospherecanbecontroled

    automatically.Theschematicdiagramofthedevicecanbeseenin Fig.5r7,13-151

    4.3Applicationinarcweldingpoolimagingandseam tracking

    Thespectralmethodcanbeusedinarcweldingpoolimaging ThismethodiSmainlyapplyingthedifferenceofarcspectrum distributioninspace.Fig.6showsapartofweldingarcspectro

    gramofGTAW.FromFig.6wecanseethatspectrallinesof metalelementMnandFemainlydistributeinbottomofarcspace whereclosedupweldingpoo1.however,theAratomspectralline distributesalongallthearCcolumn.Theintensityofspectralline ofAratomiSbiggestincenterportion.TheArionspectralline mainlydistributedinupperportionofarccolumn(closedup tungstenelectrode)whosetemperatureiSthehighest.Therefore. selectingspecialspectralwindowsandshootingangle.theweld. ingpoolimageandweldingseamcouldbeshot(Fig.7l1.This

    methodcanbeusedinvisualtrackingofweldingseam.L. [=》墨—

    }l当呈一

    rferometricfilter尝呈舌一

    f盆量2

    .

    [=》毒茎—1,

    Fig.5Schematicdiagramofspectralmonitorofhydrogen pollutioninweldingarc

    Fig.6ApartofweldingarCspectrogramofGTAW

    (a)Weldingpoolimage

    (b)Resultofimageprocessing

    Fig.7Weldingpoolimageandresult

    ofimageprocessingshotbyspectral

sensingtechnology

    4.4Applicationinaccuratecontrolofmetaldroplet

    transfer

    Fig.81iSoscillogramofweldingcurrentandmetaldroplet transferspectralsignalinpulsedGMAW.FromFig.8wecansee thatthereareone(Fig.8a),two(Fig.8b)orthree(Fig.8c)pulses inspectralsignalcorrespondingeverycurrentpulse.Thesepulses 080

CHINESEJ0URNAL0FMECHANICALENGINEERING?49?

    indicatethatthereareone.twoorthreemetaldropletstransferred ineverycurrentpulse.Thesespectralsignalscanbeusedtoaccu- ratelycontrolmetaldroplettransferofonedroplet.twodropletsor threedropletsinapulse.calledonepulseonedroplettransfer

    f0PODT).onepulse.twodroplettransfer(OPTDT)andone pulse.threedropletstransfer(OPTHDT)(Fig.9LandFig.10L"J1. Fig.9isafieldphotographofmetaldroplettransferrealtime

    controlbyarcspectralsignalinpulsedGMAW,inwhichthereisa smallcompacttypespectralsensordevelopedinthisstudy.The sensorisinstalledbesideofweldingtorch.Inweldingprocess.the sensorrea1.timecollectsarcspectralsignalandfeedbacktocon- troltheoutputofweldingpowersupplywithsinglechipprocessor conolsystem.Inthisway,theaccuratecontrolofmetaldroplet transferhasbeenrealized.Fig.10isanoscillogramofcontrol result.IntheFig.10.wecanseethatthereisonefFig.10a)ortwo (Fig.10b)pulsesofspectralsignalcorrespondingeverycurrent pulseorvoltagepulse.thatistosay,theformerisOPODTandthe laRerisOPTDMoreover.pulsesareorderlyandeven.Fig.10 indicatesthatthemetaldroplettransfercontrolisveryaccurate.

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