static electricity causes and cures booklet

7/31/2019 Static Electricity Causes and Cures Booklet

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Static Electricity

Causes and Cures


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Contents

WhatIsStaticElectricity? 4

HowIsStaticCreated? 5

WhatFactorsAffectStaticElectricity? 6

MethodsOfElimination 7ModesOfOperationofStaticEliminators 8

AddressingCommonElectrostaticProblems 14

OverviewOfSolutions 15

Glossary,TribolelectricSeries 18

AboutMeech 19

Static Electricity

Causes and Cures


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AboutMeech:

Staticelectricitycausesproductivity,qualityandsafetyproblemsthroughout

industry.Intheformofelectrostatic

attractionorrepulsionitgenerates

dustcontaminationandproduct

misbehaviour.Asanelectrostatic

dischargeitgivesshockstooperators,

startsresanddestroyselectroniccomponentsbythemillion.

Meechhasspecialisedinindustrial

electrostaticsforover40years.This

experienceenablesustodevelop

productswhichmatchthechanging

needsofourcustomers.TheMeechrangeencompassesfourtechnologies

andincludesover40products.

Ourmissionistodevelopeffectiveanddurableproductsthatarerelevantto

ourcustomersneeds;tomaintainthe

highestlevelsofresponseandservice

andtodevelopthebestpossible

supportsystemforourclientsinour

eldofelectrostatics.

Astherstspecialistmanufacturerof

staticeliminationequipmentworldwide

tobeapprovedasanISO9002

registeredcompany,wetakeour

commitmenttoqualityseriously.

Theinternationalqualityapprovalscoveringsome,orallofourproducts

include:

Static Electricity - Causes and Cures


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Qualityproductsmustbesupported

bygoodservice.MeechDistributors

throughouttheworldshareour

commitmenttoqualityandparticipate

inourcontinuoustrainingprogramme.

Thiskeepstheminformedabout

developmentsinapplicationsand

technologysotheycanofferthe

highestlevelofcustomerserviceand

support.

Introduction

Thepurposeofthisbookletistolook

atwhatstaticis,howitoccurs,the

methodsavailabletocounteractitand

howMeechusesthesemethodsina

varietyofindustrialapplications.Itis

notintendedtobeanexacting,

scienticreferencemanual;insteadits

aimistoanswerthemostcommonly

askedquestionsaboutstaticelectricity

posedbyDistributorsandCustomers

alike.

Tounderstandthisbookletitishelpful

tofamiliariseyourselfwiththevarious

termswhichcanbefoundinthe

glossaryattheendofthisbooklet.



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WhatIsStaticElectricity?

Whenamaterialorobjectholdsa

netelectricalcharge,eitherpositive

ornegative,itissaidtohaveastatic

charge.Thetermstaticisarelative

oneasinmanycasesstaticcharges

willslowlydecreaseoveraperiodof

time.Thelengthoftimethatthistakes

isdependentontheresistanceofthe

material.Forpracticalpurposesthe

twoextremescanbetakenas

plasticsandmetal.Plasticsgenerally

haveveryhighresistivities.This

allowsthemtomaintainstaticcharges

forlongperiodsoftime;ontheother

handmetalshaveverylowresistances

andanearthedmetalobjectwillhold

itschargeforanimperceptiblysmall

periodoftime.

Staticelectricityisusuallymeasured

involts.Whilstmainsvoltagesof220

voltsACareconsidereddangerous,

levelsofstaticelectricityof100kVare

common.

Thevoltagepresentonamate-

rialisdependentontwofactors;the

amountofchargeonthematerialand

thecapacitanceofthematerial.The

simplerelationshipisQ=CVwhere

Qisthecharge,VthevoltageandC

thecapacitanceofthematerial.Itcan

beseenthatforagivenchargeona

material,thelowerthecapacitance

thehigherthevoltageandviceversa.

Plasticsgenerallyhaveverylow

capacitivevaluesandhenceasmall

chargecanproduceveryhigh

voltages.Converselymetalstend

tohavehighcapacitivevaluesand

thereforearelativelyhighchargewill

producelowvoltages.Thisiswhy,in

practice,problemswithstaticelectricity

aremostnoticeablewhenworkingwith

plastic,asitisthevoltagelevelwhich

causestheattractionofdust,operator

shockandmisbehaviourofmaterials.

Therearetwomaintypesofstatic

electricity,volumetricandsurface.

Volumetricstaticchargesarecharge

imbalanceswithinthebodyofa

materialwhereassurfacestatic

electricityisonlypresentonthevery

outersurfaceofamaterial.

Inpracticenearlyallthestatic

electricityproblemsfoundinindustry

relatetosurfacecharges.Whilstthere

isnowayofneutralisingvolumetric

staticchargestheyrarelycausea

problemandtheireffectsarenormally

minimalwhencomparedtosurface

staticcharges.



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HowIsStaticCreated?

Therearethreemaincausesofstatic

electricity;friction,separationand

induction.

Friction

Astwomaterialsarerubbedtogether

theelectronsassociatedwiththe

surfaceatomsoneachmaterialcome

intoverycloseproximitywitheach

other.Thesesurfaceelectronscanbe

movedfromonematerialtoanother.

Thedirectioninwhichtheelectrons

traveleitherfromMaterialAto

MaterialBorviceversadependson

theTriboelectricSeries(Seepage18).

Materialsonthepositivesideofthe

TriboelectricSerieswilltendtogive

uptheirsurfaceelectronsandbecome

positivelychargedwhilstconversely

materialsonthenegativesideofthe

seriestendtogainelectronsand

henceanegativecharge.Theharder

thetwomaterialsarepressedtogether

thegreatertheexchangeofelectrons

andhenceahigherchargeis

generated.

Apracticalexampleisifapieceof

polytheneisrubbedonanyloncarpet

withgentleforceamoderate

negativechargewillbegeneratedon

thepolythene,whereasiftheforceis

increasedalargernegativechargewill

beachieved.Thespeedoftherubbing

actionalsohasthateffectonthelevel

ofcharge,thefastertherubbingthe

higherthelevelofcharge.Thisisdue

tothesurfaceelectronsgainingheat

energygeneratedbythefriction.This

extraenergyallowsthemtobreaktheir

atomicbondsandtransfertoother

atoms.


Contact+Friction+Separation


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Separation

Themethodofchargingbyseparation

issimilartothatoffriction.Whentwomaterialsareincontactthesurface

electronsareincloseproximityto

eachotheranduponseparationhave

atendencytoadheretoonematerial

ortheotherdependentupontheir

relativepositionsontheTriboelectric

Series.

Thefastertheseparationofthe

materials,thehigherchargegenerated

andconversely,theslowerthe

separationthelowerthecharge.A

commonexampleisofaPVCweb

movingoveraTeoncoatedroller,as

thematerialsseparatetheelectrons

willtendtoadheretotheTeon,

generatinganetnegativechargeon

theTeonandanetpositivechargeon

thePVC.

Induction

Whilstofinteresttechnically,induction

doesnotplayasignicantroleinoureld.Staticchargescanbegenerated

whenmaterialsareinthepresenceof

astrongelectriceld.Thesurfaceof

amaterialincloseproximitytoahigh

positivevoltagewilltendtobecome

positivelycharged.Themethodof

chargingiscausedbyionisationoftheairbetweenthesurfaceofthematerial

andthevoltagesourcewhichcarries

surfaceelectronsawayfromthe

materialtothesource,(ionisationis

explainedinmethodsofelimination).

Anexampleofinductionisoperators

workingnearchargedmaterials.Theoperatorwillhimselfbecomecharged

andontouchinganearthedobjectwill

dischargetoit,givingtheoperatoran

electricshock-oftenmistakenfora

shockfromthemainssupply.


Contact+Pressure+Separation


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WhatFactorsAffectStaticElectricity

Amongthemanyfactorsthataffect

thegenerationandmaintenanceof

astaticchargearehumidity,thetype

ofmaterial,repetitionandchangein

temperature.

TypeOfMaterial

Somematerialsaremorereadily

chargedthanothers.Forexample

materialssuchasacetatewillgaina

chargeveryreadilywhilstglasswill

gainachargelessreadily.Alsothe

relativepositionofmaterialsonthe

TriboelectricSerieswilldetermine

whetheramaterialchargespositively

ornegativelydependentontheother

materialwithwhichithascomeinto

contact.Forexamplehardrubber,

whenrubbedagainstnylon,will

becomenegativelychargedwhilst

whenitisrubbedagainstpolythene

willbecomepositivelycharged.

Humidity

Generallyspeakingthedryerthe

environment,thehigherthelevel

ofstaticchargeandconverselythe

higherthehumidity,thelowerthestatic

charge.Inrelativetermswaterisa

signicantlybetterconductorof

electricitythanmostplastics.

Atmospherichumiditydepositssmall

quantitiesofwateronallsurfacesin

theirenvironmentandhencesurface

staticchargesonmaterialshavea

tendencytodissipatetoearthby

currentowthroughthesurface

moisture.

Repetition

Repeatedactionssuchasfriction

orseparationwillincreasethelevel

ofchargefoundonamaterial.For

exampleaplasticwebmovingovera

seriesofTeonrollerswillincreaseits

surfacechargeaftereveryroller.

BatteryEffect

Thecombinationofmanycharged

itemscanleadtoextremelyhigh

charges.Forinstanceindividualsheets

ofplasticwithrelativelylowsurface

chargeswhenstackedtogethercan

generateextremelyhighvoltages.

ChangeInTemperature

Asamaterialcoolsdownithasa

tendencytogeneratecharge.The

actionofthecoolingistoleaveanet

chargeonthematerialthroughoutits



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entirevolume.Ifthematerialisavery

goodinsulatortheinternal(volumetric)

staticchargecanbemaintainedforextremelylongperiodsoftime.

Howeverovertimethischarge

normallymigratestothesurfaceat

whichpointitbecomesasurfacestatic

charge.Anexampleofthisisan

injectionmouldingwhichisseemingly

neutralwhenhotbutcansubsequentlybefoundtohavealargesurface

chargeoncecool.

MethodsofElimination

Thefundamentalprinciplefor

neutralisationofstaticchargesisthesamewhateverthetechniqueused.

Whereamaterialhasapositive

surfacechargeelectronsmustbe

deliveredtothesurfacetobringthe

chargebackintobalance.Wherethe

surfacechargeisnegativetheexcess

electronsmustberemovedfromthe

surfacetoneutralisethecharge.The

deliveryorremovalofelectronscan

bedonebyoneofthethreefollowing

methods,either

1. Movementofelectronsthroughthe

materialitself.

2. Movementofelectronsthrough

anothermaterialincontactwith

thesurface.

3. Movementofelectronsthrough

ionisationofthesurroundingair.

Thereisinactualfactafourthmethod,

sparking,whichoccurswhenthe

surfacevoltageissufcientlyhighto

causetheairtobecomeconductive.

Howevertheoccurrenceofsparking

isnormallyduetothelackof

applicationofothermethods!

Humidity

Aspreviouslynotedmoistureon(or

within)amaterialwilltendtoleach

awaystaticchargesdowntoearth.

Forexamplepapergenerallyhasa

relativelyhighmoisturecontentand

doesnotmaintainparticularlyhigh

levelsofstatic.Howeverifthepaper

isparticularlydrystaticcanbecomea

severeproblem.



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PassiveIonisation

Thecloseproximityofaconductortoa

chargedobjectwilltendtodischargeit.ForexampleMeechModel974

CarbonFibreBrusheswillreduce

staticchargesinmaterialspassedin

closeproximitytothebrush.

RadioactiveIonisation

Radioactivesourcessuchaspoloniumcauseionisationofthesurrounding

airwhichwillneutralisesurfacestatic

charges.Meechdonotsupply

RadioactiveEliminators.

Adrawbackofradioactiveeliminators

isthefactthattheyareonlyavailable

onannualleases.Theradioactive

sourcelosesitseffectivenessover

timeandrequiresreplacementonan

annualbasis.

ActiveElectricalIonisation

ByusinghighvoltageACorDC,

ionisedaircanbeproducedwhich

canthenbeusedtoneutralisesurface

charges.TheuseofACorDCsystems

isapplicationdependent.Further

informationonthisisavailableinthe

applicationssectionlaterinthe

booklet,fromtheMeechManualor

fromourtechnicalsalesstaff.


Brush Casing Connected

to earth

Ionisation at

brush tips

Surface with smallresidual positive charge

Surface with highpositive charge

Direction of material

Negative Ions

Passive Eliminator Brush

Diagram1


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ModesOfOperationOfStatic

Eliminators

PassiveEliminators

Achargedobjectwillgeneratean

electriceldbetweenitselfandany

surroundingearthedobject(orindeed

anyobjectofdifferingvoltage).Inthe

caseoftheMeech974passive

eliminatortheeldisbetweenthe

surfaceandthetipsoftheCarbon

FibreorStainlessSteelearthedbrush.

SeeDiagram1.Thenepointatthe

endoftheindividualbristlescauses

theelectriceldtobehighly

concentratedatthispoint.Whenthe

strengthofthiselectriceldreaches

asufcientvalue,ionisationoftheairmoleculessurroundingthetipoccurs.

IntheexampleinDiagram1the

positivechargeonthesurfaceofthe

materialwillcauseelectronsfromthe

tipofthebrushtojumpto

surroundingairmoleculeswhichwillthenhaveanetnegativechargeand

arethusnegativeions.

Fromthesimplerulethatopposite

chargesattract,thenegativeionwill

bedrawntothepositivelycharged

Surfaceofthematerial.Whentheion

reachesthesurfacetheextraelectron

themoleculeiscarryingisdrawnfrom

themoleculeanddeliveredtothe

surfaceofthematerial.Whenthis

processhasoccurredinsufcient

quantitythepositivechargeonthe

surfacewillbereduced.Inthis

processtherewillcomeatimewhen

theelectriceldgeneratedbetween

thesurfaceandthetipofthebrushis

nolongersufcienttocauseionisation

oftheairandnofurtherneutralisation

takesplace.Intheinstanceofa

negativelychargedsurfacethe

oppositeproceduretakesplace.

Passiveeliminatorsarethususefulfor

reducinghighlevelsofstaticcharge,tensofkVsdowntolevelsofafew

kVs.Howeverbytheirverynature

theyarenotabletocompletely

neutralisethesurfacecharge.

RadioactiveEliminators

Radioactiveeliminatorsemploy

polonium210orotherlowlevel

radioactivesource.Intheprocessof

radioactivedecayalphaparticlesare

emittedtothesurrounding

atmosphere.Thesehighspeed

particlescollidewiththeairmolecules

andindoingsocausetheairto

becomeionised.Thisionisedairthenneutralisesnearbysurfacesinsimilar

fashiontothepassiveeliminators.



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ACEliminators

ACEliminatorsoperateatsupply

frequency.Themainsvoltage,110or240etc.isgreatlyincreasedusinga

ferro-resonatingtransformer,Meech

Model904,togeneratevoltagesof

between4.5and7kV.Thishigh

voltageisfedtotheionisingpins,

whilstthecasingofthebaris

connectedtoearth.SeeDiagram2.

Ifwelookatthepositivecycleofthe

inputwaveformwewillseethatthe

electrodepinwillbeatapositive

voltagecomparedtothecasing.This

generatesastrongelectriceld

betweenthetwowhichishighly

concentratedatthesharppointofthe

electrodepin.Thisinsimilarfashiontothepassivebargeneratespositive

ionsatthepinpoint.Thesemolecules

arethenrepelledfromthepindueto

theirlikecharge.

Onthenegativehalfofthecyclethe

oppositeoccursandnegativeionsare

createdatthepinpoint.Theseagain

arerepelledfromtheelectrodepindue

totheirlikevoltage.

Thusaroundtheionisingpinacloudof

positiveandnegativeionsisproduced.

Intheabsenceofoutsideinuences

thepositiveandnegativeionsare

attractedtoeachotherortoanearby

earth,suchasthecasingofthebaror

nozzle,andwouldeitherneutralise

eachotherorbedissipatedtoearth.

Howeverwiththepresenceofa

nearbystaticchargeanionwillbeattractedtoonoppositechargeonthe

surfaceofthematerial.Atthesurface


Bar Casing Connected

to earth

HT AC Supply toElectrode Pin

Ionising Bar

Ionisation atElectrode Point

Surface with noresidual charge



Diagram2


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ofthematerialtheelectronswillbe

exchangedandthesurfacewillbe

neutralised.

Astheionisationatthebarisnot

dependentuponthesurfacecharge

andionsareproducedregardlessof

theproximityofasurfacecharge,

completeneutralisationofasurface

canbeachieved.Thisisasignicant

advantageoverthepassive

eliminators.Thespeedatwhich

chargescanbeneutralisedis

dependentupontherateofion

productionandspeedofrepulsionof

theionsfromtheemitterpins,which

inturnisdependentonthevoltageat

thepin.TheModel915Barrunningat7.0kVgivesgreaterperformancethan

whenrunningat5kV.

PulsedDCEliminators

PulsedDCEliminatorsliketheirAC

counterpartsproduceionisedairby

usinghighvoltage.WhereastheAC

unitsoperateatsupplyfrequency

thePulsedDCunitsoperateatlower

frequencies,inthecaseoftheMeech

Model977v3between0.5-20Hz.The

977v3alsofeaturesavariableoutput

voltagefrom6-14kVpeaktopeak.

Theionisingbarconsistsofaseriesof

emittersconnectedalternatelytothenegativeandpositiveoutputsofthe

977v3.Seediagram3.Thecasingof

thebarismadeofplasticandhence

thereisnoproximityearth.Theoutput

fromthepowersupplyiseffectivelyasquarewaveswitchingfromnegative

topositiveatthechosenfrequency.

Lookingatthepositivehalfofthewave

formthecontrollerswitchesonthe

highoutputvoltageconnectedtothe

positiveemitters.Thisthensetsup

anelectriceldbetweentheemitter

andthesurroundingearthedobjects.

Atthesharppointoftheemitterthis

eldisextremelystrong,andinsimilar

fashiontotheACeliminators,positive

ionsareproduced.Thesimilarcharge

oftheionandtheemitterdrivesthe

ionsawayfromthebar.

Onthenegativehalfofthecyclethe

powersupplydeliversahighnegative

voltagetothealternatesetof

emitters.Againinsimilarfashionto

theACeliminatorsnegativeionsare

producedattheemitterpoint.

Astaticallychargedobjectinthe

vicinityoftheionisingbarwillattractor

repeltheions,dependentupontheir

relativepolarities.Whentheionsreach

thestaticallychargedsurface,

neutralisationtakesplaceinasimilar

mannerasdescribedintheAC

Eliminatorssection.

ThelowfrequencyofoperationlendsPulsedDCequipmenttolongrange

neutralisation.Therelativelylong



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durationofeachhalfofthecycle

causelargecloudsofionsof

alternatingpolaritytobeemittedfromthebar.Thisdistancebetweenthe

positiveandnegativeionsclosetothe

bargreatlyreducestherateof

re-combination,(positiveandnegative

ionscomingtogetherandcancelling

eachotherout).

Atlongdistancesfromthebar,less

ionsaredeliverabletoastatically

chargedsurfaceandhencethespeed

ofneutralisationisreduced.Hence

whenutilisingPulsedDCequipment

ondynamicapplications,suchas

movingwebs,thoughtmustbegiven

todistanceatwhichthebarwillbe

mountedfromthetargetsurface.

AnadditionalfeatureofthePulsed

DCsystemisthattheoutputwave

formcanbealteredandthedurationofthenegativeandpositivesection

ofthewaveformcanbeincreasedor

decreased.Forinstanceifthecharge

tobeneutralisedisknowntobe

positivethedurationofthenegative

partoftheoutputcanbeincreased

andconverselythepositivepartofthe

waveformreduced.

Thiswillincreasetheproductionof

negativeionsanddecreasethe

productionofpositiveions,makingthe

systemmoreefcientatneutralising

thepositivecharge.Insimilarfashion

foraknownnegativechargethe

outputcanbebiasedtowardspositiveionproduction.


Pulsed DC Ionising Bar

Ionisation atElectrode Points

Surface with noresidual charge



Negative Ions attractedto positive charge overlong distance

Positive Ionsnot attractedto surface charge.

Dedicated positive andnegative emitter pins

Diagram3:


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OtherAspects

Measurement

Inordertoselectthecorrect

equipmentforagivenapplicationitis

importanttoknowthemagnitude,and

insomeinstances,thepolarityofthe

chargetobeneutralised.Incases

whereACeliminatorsaretobeusedit

isimportanttoknowthemagnitudeof

thestaticchargesothatthecorrect

eliminatorbarcanbeselected.In

caseswherePulsedDCequipmentis

tobeused,boththemagnitudeand

thepolarityofthestaticchargeare

importanttoallowthepowerandbias

oftheoutputtobesetcorrectly.Whilst

itisquitedifculttomeasuretheactual

amountofsurfacechargethesurface

voltagecanbemeasuredbylookingat

theelectricelditgenerates.

TheMeechModel983v2measures

theelectriceldgeneratedbyastati-

callychargedobject,theunitofwhich

isvoltspermetre.Bymeasuringthe

eldataknowndistancethesurface

voltagecanthenbededuced.Inthe

caseoftheMeechModel983v2,the

unitiscalibratedforadistanceof150

mmfromthesurfaceofthecharged

object.Thesurfacevoltageanditspo-

larityisthendisplayedonthescreen.

HighAccuracyBalancedNeutralisationInthemajorityofapplicationsthe

reductionofastaticchargetoafew

hundredvoltsisnormallysufcientto

eliminatedustattractionand

misbehaviouroftheproduct.However

intheelectronicsindustrystatic

chargesofafewhundredvoltscanhavedisastrousconsequenceswith

modernmicro-processorchips.In

theseinstancesitisimportantto

ensurethattheionisationdeliveredby

theneutralisationsystemisbalanced.

InsuchcasestheMeechSeries200

rangeofproductsisrecommended.Thishasbeenspecicallydeveloped

foruseintheelectronicsindustry.For

example,theModels221and225

Ionisedairblowersconstantly

monitortheionouputtoensurevery

exactneutralisation.Productscan

beneutralisedtowithinafewvoltsof

earthpotential.Thisgreatlyreduces

theriskofdamagetocomponentsby,

intermsofstaticcharges,relatively

lowvoltages.



17/24

StaticGeneration

Aswellasneutralisingstaticitisalso

possibletogeneratestaticchargesinmaterialsbytheuseofhighvoltages.

Bypassingmaterialsthroughintense

electriceldsitispossibletocharge

materialseitherpositivelyor

negatively.Thischargecanbeof

assistanceinamanufacturingprocess.

Acommonusageofstaticgenerationisinhighfrequencywelding

applicationswhereinducedstatic

chargesareusedtotemporarilybond

oneitemtoanothertoholdthemin

placeduringtheweldingprocess.For

furtherinformationonstaticgeneration

applicationspleaseconsulteithertheMeechManualorMeechStatic

EliminatorsHeadOfce.



18/24

AddressingCommon

ElectrostaticProblems

Identicationoftheproblem

Therearefourmaintroublesome

difcultiesarisinginindustry,deriving

fromelectrostaticcharges,withafth

affectingonlytheelectronicsindustry

butwithveryseriousandcostly

consequences.

Electrostaticattraction(ESA)

Airborneparticlesareattractedto

chargedsurfacesorindeedcharged

airborneparticlesareattractedtoa

surfacewhichcouldbetotallyfreeof

anycharge.Thisproblemeffectsmost

plasticbasedindustriesinoneformor

another,spoilingnishesofpaintedproductsandcausingrejectsinquality

inthefood,pharmaceuticaland

medicalindustries.

Intheprintingindustrydust

attractiondamagesprintnishesor

indeedprintingplates.Thelm

industryalsosufferswithlowqualityprintsandpoorresolutionprojections

inthecinemas.

Themicroscopicnatureof

semiconductormanufacturecanbe

affectedbythisproblem.

MaterialMisbehaviourThisisanotherformofESA.However,

insteadofthecontaminationof

products,theproblemmanifestsitself


intheformoftheproductitself,

usuallywebs,bresorsheets,sticking

tothemselvesorequipment,

misroutingorrepelling.Automated

processesareparticularlypronetothis

problem.

Operator/PersonnelShocksThisisbecomingincreasingly

signicantascompanieslookto

improvedsafetystandards.Whilst

shockscanbepainfultheeffectsare

usuallyquitesafeandshortlived.

However,inextremecases,the

debilitatingeffectscancause

personnelcollisionorentrapmentwithassociatedmachineryorcaneven

initiateareoranexplosionin

hazardousareas.

ElectrostaticDischarge(ESD)

Thisproblemisassociatedto

electronicsassembly,installationand

eldserviceandalsoelectroniccomponentmanufacture.

Voltagesaslowas5voltswhichhave

norealmeaninginotherindustries,

cancausecatastrophicfailureof

electroniccomponentsormuchworse,

latentdamagewhichresultsineld

failure,byfarthemostcostlyintermsofrepairandmanufacturers

reputation.


19/24

OverviewOfSolutions

Electrostatic attraction (ESA)

Avarietyofequipmentisavailableto

resolvethisprobleminmanydifferent

ways.Someexamplesfollow:

A.InjectionMoulding-Neutralisation

Bathecomponentsinionisedair.Often

usingACIonisedairblowersorPulsedDCbars.

Thismethodwillnotremoveattracted

particlesbutwillhelppreventcharging

andthuspreventattractionofdust.

B.InjectionMoulding-Particle

RemovalWhereparticleshavealreadybeenattractedtheycanberemoved

effectivelybytheuseofhighvelocity

ionisedair.Thiscanbeachievedfor

smallcomponentswithMeechnozzles

orguns,largercomponentsbytheuse

of957aircurtainsandwithextremely

largecomponentstheMeech

JetStreamsystem.Note:Theuseofordinarycompressedairwilloftenfail

toremovedust.Itcanalsoworsenthe

problembygeneratingfurtherstatic

chargesonthematerial.

C.Webs

Singleordoubledsidedweb

cleanerscouldbedeployedinthissituationorhighvelocityblowoff

systems,aircurtainsetc.,

D.SilkScreenPrinting-LongRangeLongrangePulsedDCBarscanbe

usedtoeliminatechargedscreens

withoutcausingdrying.Ionisingguns

oraircurtainscanremoveattracted

particlesfromsubstratespreprinting.

E.SemiConductors-LongRange

PulsedDCcanbeusedforthissituation-standaloneorusingair

assistfromHEPAlters.

Material Misbehaviour

A.Webs

MostcommonlysolvedusingAC

ionisingbars.TheModel915baroffersthepowertocopewithfast,

highly-chargedwebs.

Barscanbepositionedeitherside

ofawebtoachievethebestresults,

usuallyatthepointwheretheproblem

occurs,orjustpriortothisposition.

Anexamplewouldbewhereawebexitsarollerorattheexitrollersofa

atbagmakingmachine.

B.Sheets

Twomajorproblemsexistwithsheets

-theycanrepelorsticktogetherwhen

collating.Ionisingbarsora935blower

canbeplacedabovetheprocesstoeliminatethestaticchargesonthe

sheetsandallowtheprocessto

continue.



20/24

Onsheetfeeders,staticattraction

causesmultiplesheetpick-uprather

thanthesinglesheetsrequired.Meech957aircurtainscanbeused

inthissituationtocreateabladeof

ionisedairwhichpenetratesthetop

layersofsheetsallowingfree

separation.

C.ComponentStickingAndRepellingOnconveyorsorbowlfeeders,small

plasticcomponentscansticktothe

beltorinsidethetrackofthebowl

feeder:thisleadstodowntimeand

ineffectiveproductionow.Where

componentsrepeleachothertheycan

jumpofforoutofthedeliverysystem.

Deployingionisingbars,longrange

preferably(ACbarswithairassistor

PulsedDC)canresolvethisproblem.

Meech935blowersmayalsobeused

inthissituation.

Wherelargercomponentsare

concerned,repellingcancause

componentstofalloverwhilstin

processtransporte.g.blowmoulded

bottlesonconveyors.Theparrisons

onblowmouldingmachinesalsocan

repeleachothercausingquality

problems.

935ionisingblowersaregenerally

usedontransportsystems.Long

rangePulsedDCequipmentisexceptionallyusefulforcontrollinhgthe

chargesonparisons.

Operator/Personnel Shocks

Thisproblemcanoccurintwoways

andcanberesolvedintwoways.

1. Personnelcanreceiveshocks

fromextremelyhighlycharged

materialasitdischargesthrough

themtoearth.

2. Operatorscanthemselves

becomechargedbyhandlingorbeingincloseproximitytohighly

chargedmaterial.Whenthe

operatorispresentedwithapath

toearth,usuallymetalobjectsor

amachine,theydischarge

violentlyoftenbelievingtheyhave

hadamainsshock.

Theproblemcanbeaddressedby

eitherneutralisingthematerialwith

barsorblowersorbycontinuously

neutralisingtheoperatorwithlong

rangePulsedDCbars.Inextreme

casesbothmethodscanbecombined.



21/24

Inallofthesesituationsionisationis

recognisedasasolutionand

sometimesasasupplementtotraditionalmethods.

Thisisaveryspecialisedareafor

200rangeofequipment.Series200

whichMeechhasdevelopedtheseries

productsarecleanroomfriendlyand

givehighlyaccurate,fastneutralisation.

TriboelectricSeries

Thepositionintheseriesindicatesthe

relativepolaritythatislikelytooccur

whentwoofthematerialsarerubbedtogetherbutdoesnotnecessarily

dictatethelikelymagnitudeofthe

charges.

Electrostatic Discharge (ESD)

Theelectronicsindustrypredominantlyaddressesthisproblembytheuseof

conductiveorstaticdissipative

materialsintheworkplaceandin

packaging.

Allofthesematerialsareearthbonded

tothesameelectricalpotentialthuseliminatingthepossibilityofpotential

differencesandsubsequent

discharges.

Howevertherearemanyareasin

electronicswheresuchmaterials

cannotbeusedpractically.

CleanRoomsThematerialscancause

contamination.Alsothelaminarair

owscangeneratestatic.

Powering-UpTestingPCBsand

componentsmayshortoutand

presentanelectricshockhazard.

AutoAssemblyThemovementand

separationwithintheequipment

generatesitsownstaticcharges.

ProductAssemblyWherePCBsare

assembledintoequipmentmadefrom

ordinarystaticgenerativematerials



22/24

Glossary

Capacitance:Ameasureoftheability

ofasubstancetoholdcharge.

Coulomb:Theunitofmeasureof

electricalcharge.

Conductance:Thehigherthe

conductanceofamaterialtheeasier

chargewillowthroughit.Metalsare

veryconductive.

Electron:Asmallatomicparticlewitha

negativecharge(1.6x1019

coulombs).


Ion:Amoleculeoratomwithan

electricalimbalance(anegativeion

hasanexcessofelectrons,apositive

ionhasadecitofelectrons).

Resistance:Thehighertheresistance

ofamaterialtheharderitisforcharge

toowthroughit.Insulatorssuchas

plasticsareveryresistive.


23/24


24/24

Meech International

2NetworkPointRangeRoad,Witney

OX290YD,UK

Tel:+44(0)1993706700Fax:+44(0)1993776977

email:[email protected]

Meech Static Eliminators USA Inc.

2915NewparkDriveNorton,OH44203

USA

Tel:+13305642000/18002324210Fax:+13305642005


Meech Elektrostatik SA

AvCGrandprez27B4970,Stavelot

Belgium

Tel:+3280862983Fax:+3280862821


Meech CE

2151FtSzchenyit.46

Hungary

Tel:+3627535075Fax:+3627535076


Meech China

Room1105,No.5Building,SIPPC1111ZhennanRd,PutuoDistrict

Shanghai200331China

Tel:+86216608198066081981Fax:+862166081982


static electricity causes and cures booklet

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