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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
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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:
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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.
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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.
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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.
Static Electricity - Causes and Cures
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
Static Electricity - Causes and Cures
Bar Casing Connected
to earth
HT AC Supply toElectrode Pin
Ionising Bar
Ionisation atElectrode Point
Surface with noresidual charge
Surface with highpositive charge
Direction of material
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.
Static Electricity - Causes and Cures
Pulsed DC Ionising Bar
Ionisation atElectrode Points
Surface with noresidual charge
Surface with highpositive charge
Direction of material
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.
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StaticGeneration
Aswellasneutralisingstaticitisalso
possibletogeneratestaticchargesinmaterialsbytheuseofhighvoltages.
Bypassingmaterialsthroughintense
electriceldsitispossibletocharge
materialseitherpositivelyor
negatively.Thischargecanbeof
assistanceinamanufacturingprocess.
Acommonusageofstaticgenerationisinhighfrequencywelding
applicationswhereinducedstatic
chargesareusedtotemporarilybond
oneitemtoanothertoholdthemin
placeduringtheweldingprocess.For
furtherinformationonstaticgeneration
applicationspleaseconsulteithertheMeechManualorMeechStatic
EliminatorsHeadOfce.
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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
Static Electricity - Causes and Cures
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.
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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.
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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.
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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
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Glossary
Capacitance:Ameasureoftheability
ofasubstancetoholdcharge.
Coulomb:Theunitofmeasureof
electricalcharge.
Conductance:Thehigherthe
conductanceofamaterialtheeasier
chargewillowthroughit.Metalsare
veryconductive.
Electron:Asmallatomicparticlewitha
negativecharge(1.6x1019
coulombs).
Static Electricity - Causes and Cures
Ion:Amoleculeoratomwithan
electricalimbalance(anegativeion
hasanexcessofelectrons,apositive
ionhasadecitofelectrons).
Resistance:Thehighertheresistance
ofamaterialtheharderitisforcharge
toowthroughit.Insulatorssuchas
plasticsareveryresistive.
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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
email:[email protected]
Meech Elektrostatik SA
AvCGrandprez27B4970,Stavelot
Belgium
Tel:+3280862983Fax:+3280862821
email:[email protected]
Meech CE
2151FtSzchenyit.46
Hungary
Tel:+3627535075Fax:+3627535076
email:[email protected]
Meech China
Room1105,No.5Building,SIPPC1111ZhennanRd,PutuoDistrict
Shanghai200331China
Tel:+86216608198066081981Fax:+862166081982
email:[email protected]