Static Electricity Causes and Cures

Contents

WhatIsStaticElectricity? 4

HowIsStaticCreated? 5

WhatFactorsAffectStaticElectricity? 6

MethodsOfElimination 7

ModesOfOperationofStaticEliminators 8

AddressingCommonElectrostaticProblems 14

OverviewOfSolutions 15

Glossary,TribolelectricSeries 18

AboutMeech 19

Static Electricity Causes and Cures

AboutMeech:

Staticelectricitycausesproductivity,qualityandsafetyproblemsthroughoutindustry.Intheformofelectrostaticattractionorrepulsionitgeneratesdustcontaminationandproductmisbehaviour.Asanelectrostaticdischargeitgivesshockstooperators,startsfiresanddestroyselectroniccomponentsbythemillion.

Meechhasspecialisedinindustrialelectrostaticsforover40years.Thisexperienceenablesustodevelopproductswhichmatchthechangingneedsofourcustomers.TheMeechrangeencompassesfourtechnologiesandincludesover40products.

Ourmissionistodevelopeffectiveanddurableproductsthatarerelevanttoourcustomers’needs;tomaintainthehighestlevelsofresponseandserviceandtodevelopthebestpossiblesupportsystemforourclientsinourfieldofelectrostatics.

AsthefirstspecialistmanufacturerofstaticeliminationequipmentworldwidetobeapprovedasanISO9002registeredcompany,wetakeourcommitmenttoqualityseriously.

Theinternationalqualityapprovalscoveringsome,orallofourproductsinclude:

Static Electricity - Causes and Cures

Qualityproductsmustbesupportedbygoodservice.MeechDistributorsthroughouttheworldshareourcommitmenttoqualityandparticipateinourcontinuoustrainingprogramme.Thiskeepstheminformedaboutdevelopmentsinapplicationsandtechnologysotheycanofferthehighestlevelofcustomerserviceandsupport.

Introduction

Thepurposeofthisbookletistolookatwhatstaticis,howitoccurs,themethodsavailabletocounteractitandhowMeechusesthesemethodsinavarietyofindustrialapplications.Itisnotintendedtobeanexacting,scientificreferencemanual;insteaditsaimistoanswerthemostcommonlyaskedquestionsaboutstaticelectricityposedbyDistributorsandCustomersalike.

Tounderstandthisbookletitishelpfultofamiliariseyourselfwiththevarioustermswhichcanbefoundintheglossaryattheendofthisbooklet.


WhatIsStaticElectricity?

Whenamaterialorobjectholdsanetelectricalcharge,eitherpositiveornegative,itissaidtohaveastaticcharge.Thetermstaticisarelativeoneasinmanycasesstaticchargeswillslowlydecreaseoveraperiodoftime.Thelengthoftimethatthistakesisdependentontheresistanceofthematerial.Forpracticalpurposesthetwoextremescanbetakenasplasticsandmetal.Plasticsgenerallyhaveveryhighresistivities.Thisallowsthemtomaintainstaticchargesforlongperiodsoftime;ontheotherhandmetalshaveverylowresistancesandanearthedmetalobjectwillholditschargeforanimperceptiblysmallperiodoftime.Staticelectricityisusuallymeasuredinvolts.Whilstmainsvoltagesof220voltsACareconsidereddangerous,levelsofstaticelectricityof100kVarecommon.Thevoltagepresentonamate-rialisdependentontwofactors;theamountofchargeonthematerialandthecapacitanceofthematerial.ThesimplerelationshipisQ=CVwhereQisthecharge,VthevoltageandCthecapacitanceofthematerial.Itcanbeseenthatforagivenchargeona

material,thelowerthecapacitancethehigherthevoltageandviceversa.Plasticsgenerallyhaveverylowcapacitivevaluesandhenceasmallchargecanproduceveryhighvoltages.Converselymetalstendtohavehighcapacitivevaluesandthereforearelativelyhighchargewillproducelowvoltages.Thisiswhy,inpractice,problemswithstaticelectricityaremostnoticeablewhenworkingwithplastic,asitisthevoltagelevelwhichcausestheattractionofdust,operatorshockandmisbehaviourofmaterials.

Therearetwomaintypesofstaticelectricity,volumetricandsurface.Volumetricstaticchargesarechargeimbalanceswithinthebodyofamaterialwhereassurfacestaticelectricityisonlypresentontheveryoutersurfaceofamaterial.

Inpracticenearlyallthestaticelectricityproblemsfoundinindustryrelatetosurfacecharges.Whilstthereisnowayofneutralisingvolumetricstaticchargestheyrarelycauseaproblemandtheireffectsarenormallyminimalwhencomparedtosurfacestaticcharges.


HowIsStaticCreated?

Therearethreemaincausesofstaticelectricity;friction,separationandinduction.

FrictionAstwomaterialsarerubbedtogethertheelectronsassociatedwiththesurfaceatomsoneachmaterialcomeintoverycloseproximitywitheachother.Thesesurfaceelectronscanbemovedfromonematerialtoanother.ThedirectioninwhichtheelectronstraveleitherfromMaterialAtoMaterialBorviceversadependsontheTriboelectricSeries(Seepage18).MaterialsonthepositivesideoftheTriboelectricSerieswilltendtogiveuptheirsurfaceelectronsandbecomepositivelychargedwhilstconverselymaterialsonthenegativesideoftheseriestendtogainelectronsandhenceanegativecharge.Theharder

thetwomaterialsarepressedtogetherthegreatertheexchangeofelectronsandhenceahigherchargeisgenerated.

Apracticalexampleisifapieceofpolytheneisrubbedonanyloncarpetwithgentleforceamoderatenegativechargewillbegeneratedonthepolythene,whereasiftheforceisincreasedalargernegativechargewillbeachieved.Thespeedoftherubbingactionalsohasthateffectonthelevelofcharge,thefastertherubbingthehigherthelevelofcharge.Thisisduetothesurfaceelectronsgainingheatenergygeneratedbythefriction.Thisextraenergyallowsthemtobreaktheiratomicbondsandtransfertootheratoms.


Contact+Friction+Separation

SeparationThemethodofchargingbyseparationissimilartothatoffriction.WhentwomaterialsareincontactthesurfaceelectronsareincloseproximitytoeachotheranduponseparationhaveatendencytoadheretoonematerialortheotherdependentupontheirrelativepositionsontheTriboelectricSeries.

Thefastertheseparationofthematerials,thehigherchargegeneratedandconversely,theslowertheseparationthelowerthecharge.AcommonexampleisofaPVCwebmovingoveraTefloncoatedroller,asthematerialsseparatetheelectronswilltendtoadheretotheTeflon,generatinganetnegativechargeontheTeflonandanetpositivechargeonthePVC.

InductionWhilstofinteresttechnically,inductiondoesnotplayasignificantroleinourfield.Staticchargescanbegeneratedwhenmaterialsareinthepresenceofastrongelectricfield.Thesurfaceofamaterialincloseproximitytoahighpositivevoltagewilltendtobecomepositivelycharged.Themethodofchargingiscausedbyionisationoftheairbetweenthesurfaceofthematerialandthevoltagesourcewhichcarriessurfaceelectronsawayfromthematerialtothesource,(ionisationisexplainedinmethodsofelimination).Anexampleofinductionisoperatorsworkingnearchargedmaterials.Theoperatorwillhimselfbecomechargedandontouchinganearthedobjectwilldischargetoit,givingtheoperatoranelectricshock-oftenmistakenforashockfromthemainssupply.


Contact+Pressure+Separation

WhatFactorsAffectStaticElectricity

Amongthemanyfactorsthataffectthegenerationandmaintenanceofastaticchargearehumidity,thetypeofmaterial,repetitionandchangeintemperature.

TypeOfMaterialSomematerialsaremorereadilychargedthanothers.Forexamplematerialssuchasacetatewillgainachargeveryreadilywhilstglasswillgainachargelessreadily.AlsotherelativepositionofmaterialsontheTriboelectricSerieswilldeterminewhetheramaterialchargespositivelyornegativelydependentontheothermaterialwithwhichithascomeintocontact.Forexamplehardrubber,whenrubbedagainstnylon,willbecomenegativelychargedwhilstwhenitisrubbedagainstpolythenewillbecomepositivelycharged.

HumidityGenerallyspeakingthedryertheenvironment,thehigherthelevelofstaticchargeandconverselythehigherthehumidity,thelowerthestaticcharge.Inrelativetermswaterisasignificantlybetterconductorof

electricitythanmostplastics.Atmospherichumiditydepositssmallquantitiesofwateronallsurfacesintheirenvironmentandhencesurfacestaticchargesonmaterialshaveatendencytodissipatetoearthbycurrentflowthroughthesurfacemoisture.

RepetitionRepeatedactionssuchasfrictionorseparationwillincreasethelevelofchargefoundonamaterial.ForexampleaplasticwebmovingoveraseriesofTeflonrollerswillincreaseitssurfacechargeaftereveryroller.

BatteryEffectThecombinationofmanychargeditemscanleadtoextremelyhighcharges.Forinstanceindividualsheetsofplasticwithrelativelylowsurfacechargeswhenstackedtogethercangenerateextremelyhighvoltages.

ChangeInTemperatureAsamaterialcoolsdownithasatendencytogeneratecharge.Theactionofthecoolingistoleaveanetchargeonthematerialthroughoutits


entirevolume.Ifthematerialisaverygoodinsulatortheinternal(volumetric)staticchargecanbemaintainedforextremelylongperiodsoftime.Howeverovertimethischargenormallymigratestothesurfaceatwhichpointitbecomesasurfacestaticcharge.Anexampleofthisisaninjectionmouldingwhichisseeminglyneutralwhenhotbutcansubsequentlybefoundtohavealargesurfacechargeoncecool.

MethodsofElimination

Thefundamentalprincipleforneutralisationofstaticchargesisthesamewhateverthetechniqueused.Whereamaterialhasapositivesurfacechargeelectronsmustbedeliveredtothesurfacetobringthechargebackintobalance.Wherethesurfacechargeisnegativetheexcesselectronsmustberemovedfromthesurfacetoneutralisethecharge.Thedeliveryorremovalofelectronscanbedonebyoneofthethreefollowingmethods,either

1. Movementofelectronsthroughthematerialitself.

2. Movementofelectronsthroughanothermaterialincontactwiththesurface.

3. Movementofelectronsthroughionisationofthesurroundingair.

Thereisinactualfactafourthmethod,sparking,whichoccurswhenthesurfacevoltageissufficientlyhightocausetheairtobecomeconductive.Howevertheoccurrenceofsparkingisnormallyduetothelackofapplicationofothermethods!

HumidityAspreviouslynotedmoistureon(orwithin)amaterialwilltendtoleachawaystaticchargesdowntoearth.Forexamplepapergenerallyhasarelativelyhighmoisturecontentanddoesnotmaintainparticularlyhighlevelsofstatic.Howeverifthepaperisparticularlydrystaticcanbecomeasevereproblem.


PassiveIonisationThecloseproximityofaconductortoachargedobjectwilltendtodischargeit.ForexampleMeechModel974CarbonFibreBrusheswillreducestaticchargesinmaterialspassedincloseproximitytothebrush.

RadioactiveIonisationRadioactivesourcessuchaspoloniumcauseionisationofthesurroundingairwhichwillneutralisesurfacestaticcharges.MeechdonotsupplyRadioactiveEliminators.

Adrawbackofradioactiveeliminatorsisthefactthattheyareonlyavailableonannualleases.Theradioactivesourcelosesitseffectivenessovertimeandrequiresreplacementonanannualbasis.

ActiveElectricalIonisationByusinghighvoltageACorDC,ionisedaircanbeproducedwhichcanthenbeusedtoneutralisesurfacecharges.TheuseofACorDCsystemsisapplicationdependent.Furtherinformationonthisisavailableintheapplicationssectionlaterinthebooklet,fromtheMeechManualorfromourtechnicalsalesstaff.


Brush Casing Connectedto earth

Ionisation at brush tips

Surface with smallresidual positive charge

Surface with highpositive charge

Direction of material

Negative Ions

Passive Eliminator Brush

Diagram1

ModesOfOperationOfStaticEliminators

PassiveEliminatorsAchargedobjectwillgenerateanelectricfieldbetweenitselfandanysurroundingearthedobject(orindeedanyobjectofdifferingvoltage).InthecaseoftheMeech974passiveeliminatorthefieldisbetweenthesurfaceandthetipsoftheCarbonFibreorStainlessSteelearthedbrush.SeeDiagram1.Thefinepointattheendoftheindividualbristlescausestheelectricfieldtobehighlyconcentratedatthispoint.Whenthestrengthofthiselectricfieldreachesasufficientvalue,ionisationoftheairmoleculessurroundingthetipoccurs.

IntheexampleinDiagram1thepositivechargeonthesurfaceofthematerialwillcauseelectronsfromthetipofthebrushtojumptosurroundingairmoleculeswhichwillthenhaveanetnegativechargeandarethusnegativeions.

Fromthesimplerulethatoppositechargesattract,thenegativeionwillbedrawntothepositivelychargedSurfaceofthematerial.Whentheionreachesthesurfacetheextraelectronthemoleculeiscarryingisdrawnfromthemoleculeanddeliveredtothe

surfaceofthematerial.Whenthisprocesshasoccurredinsufficientquantitythepositivechargeonthesurfacewillbereduced.Inthisprocesstherewillcomeatimewhentheelectricfieldgeneratedbetweenthesurfaceandthetipofthebrushisnolongersufficienttocauseionisationoftheairandnofurtherneutralisationtakesplace.Intheinstanceofanegativelychargedsurfacetheoppositeproceduretakesplace.

Passiveeliminatorsarethususefulforreducinghighlevelsofstaticcharge,tensofkV’sdowntolevelsofafewkV’s.Howeverbytheirverynaturetheyarenotabletocompletelyneutralisethesurfacecharge.

RadioactiveEliminatorsRadioactiveeliminatorsemploypolonium210orotherlowlevelradioactivesource.Intheprocessofradioactivedecayalphaparticlesareemittedtothesurroundingatmosphere.Thesehighspeedparticlescollidewiththeairmoleculesandindoingsocausetheairtobecomeionised.Thisionisedairthenneutralisesnearbysurfacesinsimilarfashiontothepassiveeliminators.


ACEliminatorsACEliminatorsoperateatsupplyfrequency.Themainsvoltage,110or240etc.isgreatlyincreasedusingaferro-resonatingtransformer,MeechModel904,togeneratevoltagesofbetween4.5and7kV.Thishighvoltageisfedtotheionisingpins,whilstthecasingofthebarisconnectedtoearth.SeeDiagram2.Ifwelookatthepositivecycleoftheinputwaveformwewillseethattheelectrodepinwillbeatapositivevoltagecomparedtothecasing.Thisgeneratesastrongelectricfieldbetweenthetwowhichishighlyconcentratedatthesharppointoftheelectrodepin.Thisinsimilarfashiontothepassivebargeneratespositiveionsatthepinpoint.Thesemolecules

arethenrepelledfromthepinduetotheirlikecharge.

Onthenegativehalfofthecycletheoppositeoccursandnegativeionsarecreatedatthepinpoint.Theseagainarerepelledfromtheelectrodepinduetotheirlikevoltage.Thusaroundtheionisingpinacloudofpositiveandnegativeionsisproduced.Intheabsenceofoutsideinfluencesthepositiveandnegativeionsareattractedtoeachotherortoanearbyearth,suchasthecasingofthebarornozzle,andwouldeitherneutraliseeachotherorbedissipatedtoearth.Howeverwiththepresenceofanearbystaticchargeanionwillbeattractedtoonoppositechargeonthesurfaceofthematerial.Atthesurface


Bar Casing Connected to earth

HT AC Supply toElectrode Pin

Ionising Bar

Ionisation at Electrode Point

Surface with noresidual charge



Diagram2

ofthematerialtheelectronswillbeexchangedandthesurfacewillbeneutralised.

Astheionisationatthebarisnotdependentuponthesurfacechargeandionsareproducedregardlessoftheproximityofasurfacecharge,completeneutralisationofasurfacecanbeachieved.Thisisasignificantadvantageoverthepassiveeliminators.Thespeedatwhichchargescanbeneutralisedisdependentupontherateofionproductionandspeedofrepulsionoftheionsfromtheemitterpins,whichinturnisdependentonthevoltageatthepin.TheModel915Barrunningat7.0kVgivesgreaterperformancethanwhenrunningat5kV.

PulsedDCEliminatorsPulsedDCEliminatorsliketheirACcounterpartsproduceionisedairbyusinghighvoltage.WhereastheACunitsoperateatsupplyfrequencythePulsedDCunitsoperateatlowerfrequencies,inthecaseoftheMeechModel977v3between0.5-20Hz.The977v3alsofeaturesavariableoutputvoltagefrom6-14kVpeaktopeak.Theionisingbarconsistsofaseriesofemittersconnectedalternatelytothenegativeandpositiveoutputsofthe977v3.Seediagram3.Thecasingof

thebarismadeofplasticandhencethereisnoproximityearth.Theoutputfromthepowersupplyiseffectivelyasquarewaveswitchingfromnegativetopositiveatthechosenfrequency.Lookingatthepositivehalfofthewaveformthecontrollerswitchesonthehighoutputvoltageconnectedtothepositiveemitters.Thisthensetsupanelectricfieldbetweentheemitterandthesurroundingearthedobjects.Atthesharppointoftheemitterthisfieldisextremelystrong,andinsimilarfashiontotheACeliminators,positiveionsareproduced.Thesimilarchargeoftheionandtheemitterdrivestheionsawayfromthebar.

Onthenegativehalfofthecyclethepowersupplydeliversahighnegativevoltagetothealternatesetofemitters.AgaininsimilarfashiontotheACeliminatorsnegativeionsareproducedattheemitterpoint.Astaticallychargedobjectinthevicinityoftheionisingbarwillattractorrepeltheions,dependentupontheirrelativepolarities.Whentheionsreachthestaticallychargedsurface,neutralisationtakesplaceinasimilarmannerasdescribedintheACEliminatorssection.ThelowfrequencyofoperationlendsPulsedDCequipmenttolongrangeneutralisation.Therelativelylong


durationofeachhalfofthecyclecauselarge“clouds”ofionsofalternatingpolaritytobeemittedfromthebar.Thisdistancebetweenthepositiveandnegativeionsclosetothebargreatlyreducestherateofre-combination,(positiveandnegativeionscomingtogetherandcancellingeachotherout).Atlongdistancesfromthebar,lessionsaredeliverabletoastaticallychargedsurfaceandhencethespeedofneutralisationisreduced.HencewhenutilisingPulsedDCequipmentondynamicapplications,suchasmovingwebs,thoughtmustbegiventodistanceatwhichthebarwillbemountedfromthetargetsurface.

AnadditionalfeatureofthePulsedDCsystemisthattheoutputwaveformcanbealteredandthedurationofthenegativeandpositivesectionofthewaveformcanbeincreasedordecreased.Forinstanceifthechargetobeneutralisedisknowntobepositivethedurationofthenegativepartoftheoutputcanbeincreasedandconverselythepositivepartofthewaveformreduced.Thiswillincreasetheproductionofnegativeionsanddecreasetheproductionofpositiveions,makingthesystemmoreefficientatneutralisingthepositivecharge.Insimilarfashionforaknownnegativechargetheoutputcanbebiasedtowardspositiveionproduction.


Pulsed DC Ionising Bar

Ionisation at Electrode Points

Surface with noresidual charge



Negative Ions attracted to positive charge over long distance

Positive Ions not attracted to surface charge.

Dedicated positive andnegative emitter pins

Diagram3:

OtherAspects

MeasurementInordertoselectthecorrectequipmentforagivenapplicationitisimportanttoknowthemagnitude,andinsomeinstances,thepolarityofthechargetobeneutralised.IncaseswhereACeliminatorsaretobeuseditisimportanttoknowthemagnitudeofthestaticchargesothatthecorrecteliminatorbarcanbeselected.IncaseswherePulsedDCequipmentistobeused,boththemagnitudeandthepolarityofthestaticchargeareimportanttoallowthepowerandbiasoftheoutputtobesetcorrectly.Whilstitisquitedifficulttomeasuretheactualamountofsurfacechargethesurfacevoltagecanbemeasuredbylookingattheelectricfielditgenerates.

TheMeechModel983v2measurestheelectricfieldgeneratedbyastati-callychargedobject,theunitofwhichisvoltspermetre.Bymeasuringthefieldataknowndistancethesurfacevoltagecanthenbededuced.InthecaseoftheMeechModel983v2,theunitiscalibratedforadistanceof150mmfromthesurfaceofthechargedobject.Thesurfacevoltageanditspo-larityisthendisplayedonthescreen.

HighAccuracyBalancedNeutralisationInthemajorityofapplicationsthereductionofastaticchargetoafewhundredvoltsisnormallysufficienttoeliminatedustattractionandmisbehaviouroftheproduct.Howeverintheelectronicsindustrystaticchargesofafewhundredvoltscanhavedisastrousconsequenceswithmodernmicro-processorchips.Intheseinstancesitisimportanttoensurethattheionisationdeliveredbytheneutralisationsystemisbalanced.InsuchcasestheMeechSeries200rangeofproductsisrecommended.Thishasbeenspecificallydevelopedforuseintheelectronicsindustry.Forexample,theModels221and225Ionisedairblowersconstantlymonitortheionouputtoensureveryexactneutralisation.Productscanbeneutralisedtowithinafewvoltsofearthpotential.Thisgreatlyreducestheriskofdamagetocomponentsby,intermsofstaticcharges,relativelylowvoltages.


StaticGenerationAswellasneutralisingstaticitisalsopossibletogeneratestaticchargesinmaterialsbytheuseofhighvoltages.Bypassingmaterialsthroughintenseelectricfieldsitispossibletochargematerialseitherpositivelyornegatively.Thischargecanbeofassistanceinamanufacturingprocess.Acommonusageofstaticgenerationisinhighfrequencyweldingapplicationswhereinducedstaticchargesareusedtotemporarilybondoneitemtoanothertoholdtheminplaceduringtheweldingprocess.ForfurtherinformationonstaticgenerationapplicationspleaseconsulteithertheMeechManualorMeechStaticEliminatorsHeadOffice.


AddressingCommonElectrostaticProblems

IdentificationoftheproblemTherearefourmaintroublesomedifficultiesarisinginindustry,derivingfromelectrostaticcharges,withafifthaffectingonlytheelectronicsindustrybutwithveryseriousandcostlyconsequences.

Electrostaticattraction(ESA)Airborneparticlesareattractedtochargedsurfacesorindeedchargedairborneparticlesareattractedtoasurfacewhichcouldbetotallyfreeofanycharge.Thisproblemeffectsmostplasticbasedindustriesinoneformoranother,spoilingfinishesofpaintedproductsandcausingrejectsinqualityinthefood,pharmaceuticalandmedicalindustries.

Intheprintingindustrydustattractiondamagesprintfinishesorindeedprintingplates.Thefilmindustryalsosufferswithlowqualityprintsandpoorresolutionprojectionsinthecinemas.

Themicroscopicnatureofsemiconductormanufacturecanbeaffectedbythisproblem.

MaterialMisbehaviourThisisanotherformofESA.However,insteadofthecontaminationofproducts,theproblemmanifestsitself


intheformoftheproductitself,usuallywebs,fibresorsheets,stickingtothemselvesorequipment,misroutingorrepelling.Automatedprocessesareparticularlypronetothisproblem.

Operator/PersonnelShocksThisisbecomingincreasinglysignificantascompanieslooktoimprovedsafetystandards.Whilstshockscanbepainfultheeffectsareusuallyquitesafeandshortlived.However,inextremecases,thedebilitatingeffectscancausepersonnelcollisionorentrapmentwithassociatedmachineryorcaneveninitiateafireoranexplosioninhazardousareas.

ElectrostaticDischarge(ESD)Thisproblemisassociatedtoelectronicsassembly,installationandfieldserviceandalsoelectroniccomponentmanufacture.

Voltagesaslowas5voltswhichhavenorealmeaninginotherindustries,cancausecatastrophicfailureofelectroniccomponentsormuchworse,latentdamagewhichresultsinfieldfailure,byfarthemostcostlyintermsofrepairandmanufacturers’reputation.

OverviewOfSolutions

Electrostatic attraction (ESA)

Avarietyofequipmentisavailabletoresolvethisprobleminmanydifferentways.Someexamplesfollow:

A.InjectionMoulding-NeutralisationBathecomponentsinionisedair.OftenusingACIonisedairblowersorPulsedDCbars.

Thismethodwillnotremoveattractedparticlesbutwillhelppreventchargingandthuspreventattractionofdust.

B.InjectionMoulding-ParticleRemovalWhereparticleshavealreadybeenattractedtheycanberemovedeffectivelybytheuseofhighvelocityionisedair.ThiscanbeachievedforsmallcomponentswithMeechnozzlesorguns,largercomponentsbytheuseof957aircurtainsandwithextremelylargecomponentstheMeechJetStreamsystem.Note:Theuseofordinarycompressedairwilloftenfailtoremovedust.Itcanalsoworsentheproblembygeneratingfurtherstaticchargesonthematerial.

C.WebsSingleordoubledsidedwebcleanerscouldbedeployedinthissituationorhighvelocityblowoffsystems,aircurtainsetc.,

D.SilkScreenPrinting-LongRangeLongrangePulsedDCBarscanbeusedtoeliminatechargedscreenswithoutcausingdrying.Ionisinggunsoraircurtainscanremoveattractedparticlesfromsubstratespreprinting.

E.SemiConductors-LongRangePulsedDCcanbeusedforthissituation-standaloneorusingairassistfromHEPAfilters.

Material Misbehaviour

A.WebsMostcommonlysolvedusingACionisingbars.TheModel915baroffersthepowertocopewithfast,highly-chargedwebs.

Barscanbepositionedeithersideofawebtoachievethebestresults,usuallyatthepointwheretheproblemoccurs,orjustpriortothisposition.Anexamplewouldbewhereawebexitsarollerorattheexitrollersofaflatbagmakingmachine.

B.SheetsTwomajorproblemsexistwithsheets-theycanrepelorsticktogetherwhencollating.Ionisingbarsora935blowercanbeplacedabovetheprocesstoeliminatethestaticchargesonthesheetsandallowtheprocesstocontinue.


Onsheetfeeders,staticattractioncausesmultiplesheetpick-upratherthanthesinglesheetsrequired.Meech957aircurtainscanbeusedinthissituationtocreateabladeofionisedairwhichpenetratesthetoplayersofsheetsallowingfreeseparation.

C.ComponentStickingAndRepellingOnconveyorsorbowlfeeders,smallplasticcomponentscansticktothebeltorinsidethetrackofthebowlfeeder:thisleadstodowntimeandineffectiveproductionflow.Wherecomponentsrepeleachothertheycanjumpofforoutofthedeliverysystem.

Deployingionisingbars,longrangepreferably(ACbarswithairassistorPulsedDC)canresolvethisproblem.Meech935blowersmayalsobeusedinthissituation.

Wherelargercomponentsareconcerned,repellingcancausecomponentstofalloverwhilstinprocesstransporte.g.blowmouldedbottlesonconveyors.Theparrisonsonblowmouldingmachinesalsocanrepeleachothercausingqualityproblems.

935ionisingblowersaregenerallyusedontransportsystems.LongrangePulsedDCequipmentisexceptionallyusefulforcontrollinhgthechargesonparisons.

Operator/Personnel Shocks

Thisproblemcanoccurintwowaysandcanberesolvedintwoways.

1. Personnelcanreceiveshocksfromextremelyhighlychargedmaterialasitdischargesthroughthemtoearth.

2. Operatorscanthemselvesbecomechargedbyhandlingorbeingincloseproximitytohighlychargedmaterial.Whentheoperatorispresentedwithapathtoearth,usuallymetalobjectsoramachine,theydischargeviolentlyoftenbelievingtheyhavehadamainsshock.

TheproblemcanbeaddressedbyeitherneutralisingthematerialwithbarsorblowersorbycontinuouslyneutralisingtheoperatorwithlongrangePulsedDCbars.Inextremecasesbothmethodscanbecombined.


Inallofthesesituationsionisationisrecognisedasasolutionandsometimesasasupplementtotraditionalmethods.

Thisisaveryspecialisedareafor200rangeofequipment.Series200whichMeechhasdevelopedtheseriesproductsarecleanroomfriendlyandgivehighlyaccurate,fastneutralisation.

TriboelectricSeries

Thepositionintheseriesindicatestherelativepolaritythatislikelytooccurwhentwoofthematerialsarerubbedtogetherbutdoesnotnecessarilydictatethelikelymagnitudeofthecharges.

Electrostatic Discharge (ESD)

Theelectronicsindustrypredominantlyaddressesthisproblembytheuseofconductiveorstaticdissipativematerialsintheworkplaceandinpackaging.

Allofthesematerialsareearthbondedtothesameelectricalpotentialthuseliminatingthepossibilityofpotentialdifferencesandsubsequentdischarges.

Howevertherearemanyareasinelectronicswheresuchmaterialscannotbeusedpractically.

CleanRoomsThematerialscancausecontamination.Alsothelaminarairflowscangeneratestatic.

Powering-UpTestingPCB’sandcomponentsmayshortoutandpresentanelectricshockhazard.

AutoAssemblyThemovementandseparationwithintheequipmentgeneratesitsownstaticcharges.

ProductAssemblyWherePCB’sareassembledintoequipmentmadefromordinarystaticgenerativematerials


Glossary

Capacitance:Ameasureoftheabilityofasubstancetoholdcharge.

Coulomb:Theunitofmeasureofelectricalcharge.

Conductance:Thehighertheconductanceofamaterialtheeasierchargewillflowthroughit.Metalsareveryconductive.

Electron:Asmallatomicparticlewithanegativecharge(1.6x1019

coulombs).


Ion:Amoleculeoratomwithanelectricalimbalance(anegativeionhasanexcessofelectrons,apositiveionhasadeficitofelectrons).

Resistance:Thehighertheresistanceofamaterialtheharderitisforchargetoflowthroughit.Insulatorssuchasplasticsareveryresistive.

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Static Electricity Causes and Cures - Meech

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Transcript of Static Electricity Causes and Cures - Meech