static electricity causes and cures - meech

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.

Static Electricity - Causes and Cures

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.

Static Electricity - Causes and Cures

HowIsStaticCreated?

Therearethreemaincausesofstaticelectricity;friction,separationandinduction.

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

thetwomaterialsarepressedtogetherthegreatertheexchangeofelectronsandhenceahigherchargeisgenerated.

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

Static Electricity - Causes and Cures

Contact+Friction+Separation

SeparationThemethodofchargingbyseparationissimilartothatoffriction.WhentwomaterialsareincontactthesurfaceelectronsareincloseproximitytoeachotheranduponseparationhaveatendencytoadheretoonematerialortheotherdependentupontheirrelativepositionsontheTriboelectricSeries.

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

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

Static Electricity - Causes and Cures

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

Static Electricity - Causes and Cures

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.

Static Electricity - Causes and Cures

PassiveIonisationThecloseproximityofaconductortoachargedobjectwilltendtodischargeit.ForexampleMeechModel974CarbonFibreBrusheswillreducestaticchargesinmaterialspassedincloseproximitytothebrush.

RadioactiveIonisationRadioactivesourcessuchaspoloniumcauseionisationofthesurroundingairwhichwillneutralisesurfacestaticcharges.MeechdonotsupplyRadioactiveEliminators.

Adrawbackofradioactiveeliminatorsisthefactthattheyareonlyavailableonannualleases.Theradioactivesourcelosesitseffectivenessovertimeandrequiresreplacementonanannualbasis.

ActiveElectricalIonisationByusinghighvoltageACorDC,ionisedaircanbeproducedwhichcanthenbeusedtoneutralisesurfacecharges.TheuseofACorDCsystemsisapplicationdependent.Furtherinformationonthisisavailableintheapplicationssectionlaterinthebooklet,fromtheMeechManualorfromourtechnicalsalesstaff.

Static Electricity - Causes and Cures

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.

Static Electricity - Causes and Cures

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

arethenrepelledfromthepinduetotheirlikecharge.

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

Static Electricity - Causes and Cures

Bar Casing Connected to earth

HT AC Supply toElectrode Pin

Ionising Bar

Ionisation at Electrode Point

Surface with noresidual charge

Surface with highpositive charge

Direction of material

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

Static Electricity - Causes and Cures

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

AnadditionalfeatureofthePulsedDCsystemisthattheoutputwaveformcanbealteredandthedurationofthenegativeandpositivesectionofthewaveformcanbeincreasedordecreased.Forinstanceifthechargetobeneutralisedisknowntobepositivethedurationofthenegativepartoftheoutputcanbeincreasedandconverselythepositivepartofthewaveformreduced.Thiswillincreasetheproductionofnegativeionsanddecreasetheproductionofpositiveions,makingthesystemmoreefficientatneutralisingthepositivecharge.Insimilarfashionforaknownnegativechargetheoutputcanbebiasedtowardspositiveionproduction.

Static Electricity - Causes and Cures

Pulsed DC Ionising Bar

Ionisation at Electrode Points

Surface with noresidual charge

Surface with highpositive charge

Direction of material

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.

Static Electricity - Causes and Cures

StaticGenerationAswellasneutralisingstaticitisalsopossibletogeneratestaticchargesinmaterialsbytheuseofhighvoltages.Bypassingmaterialsthroughintenseelectricfieldsitispossibletochargematerialseitherpositivelyornegatively.Thischargecanbeofassistanceinamanufacturingprocess.Acommonusageofstaticgenerationisinhighfrequencyweldingapplicationswhereinducedstaticchargesareusedtotemporarilybondoneitemtoanothertoholdtheminplaceduringtheweldingprocess.ForfurtherinformationonstaticgenerationapplicationspleaseconsulteithertheMeechManualorMeechStaticEliminatorsHeadOffice.

Static Electricity - Causes and Cures

AddressingCommonElectrostaticProblems

IdentificationoftheproblemTherearefourmaintroublesomedifficultiesarisinginindustry,derivingfromelectrostaticcharges,withafifthaffectingonlytheelectronicsindustrybutwithveryseriousandcostlyconsequences.

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

Intheprintingindustrydustattractiondamagesprintfinishesorindeedprintingplates.Thefilmindustryalsosufferswithlowqualityprintsandpoorresolutionprojectionsinthecinemas.

Themicroscopicnatureofsemiconductormanufacturecanbeaffectedbythisproblem.

MaterialMisbehaviourThisisanotherformofESA.However,insteadofthecontaminationofproducts,theproblemmanifestsitself

Static Electricity - Causes and Cures

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.

Static Electricity - Causes and Cures

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.

Static Electricity - Causes and Cures

Inallofthesesituationsionisationisrecognisedasasolutionandsometimesasasupplementtotraditionalmethods.

Thisisaveryspecialisedareafor200rangeofequipment.Series200whichMeechhasdevelopedtheseriesproductsarecleanroomfriendlyandgivehighlyaccurate,fastneutralisation.

TriboelectricSeries

Thepositionintheseriesindicatestherelativepolaritythatislikelytooccurwhentwoofthematerialsarerubbedtogetherbutdoesnotnecessarilydictatethelikelymagnitudeofthecharges.

Electrostatic Discharge (ESD)

Theelectronicsindustrypredominantlyaddressesthisproblembytheuseofconductiveorstaticdissipativematerialsintheworkplaceandinpackaging.

Allofthesematerialsareearthbondedtothesameelectricalpotentialthuseliminatingthepossibilityofpotentialdifferencesandsubsequentdischarges.

Howevertherearemanyareasinelectronicswheresuchmaterialscannotbeusedpractically.

CleanRoomsThematerialscancausecontamination.Alsothelaminarairflowscangeneratestatic.

Powering-UpTestingPCB’sandcomponentsmayshortoutandpresentanelectricshockhazard.

AutoAssemblyThemovementandseparationwithintheequipmentgeneratesitsownstaticcharges.

ProductAssemblyWherePCB’sareassembledintoequipmentmadefromordinarystaticgenerativematerials

Static Electricity - Causes and Cures

Glossary

Capacitance:Ameasureoftheabilityofasubstancetoholdcharge.

Coulomb:Theunitofmeasureofelectricalcharge.

Conductance:Thehighertheconductanceofamaterialtheeasierchargewillflowthroughit.Metalsareveryconductive.

Electron:Asmallatomicparticlewithanegativecharge(1.6x1019

coulombs).

Static Electricity - Causes and Cures

Ion:Amoleculeoratomwithanelectricalimbalance(anegativeionhasanexcessofelectrons,apositiveionhasadeficitofelectrons).

Resistance:Thehighertheresistanceofamaterialtheharderitisforchargetoflowthroughit.Insulatorssuchasplasticsareveryresistive.

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