UltrasonicCleaning:FundamentalTheoryandApplicationAbstract

Apresentationdescribingthetheoryofultrasonicsandhowultrasonictechnologyisappliedtoprecisioncleaning.Thispresentationwillexploretheimportanceandapplicationofultrasonicsinprecisioncleaningalongwithexplanationsofultrasoniccleaningequipmentanditsapplication.Processparametersforultrasoniccleaningwillbediscussedalongwithproceduresforproperoperationofultrasoniccleaningequipmenttoachievemaximumresults.

Introduction

Cleaningtechnologyisinastateofchange.Vapordegreasingusingchlorinatedandfluorinatedsolvents,longthestandardformostofindustry,isbeingphasedoutintheinterestoftheecologyofourplanet.Atthesametime,cleaningrequirementsarecontinuallyincreasing.Cleanlinesshasbecomeanimportantissueinmanyindustrieswhereitneverwasinthepast.Inindustriessuchaselectronicswherecleanlinesswasalwaysimportant,ithasbecomemorecriticalinsupportofgrowingtechnology.Itseemsthateachadvanceintechnologydemandsgreaterandgreaterattentiontocleanlinessforitssuccess.Asaresult,thecleaningindustryhasbeenchallengedtodelivertheneededcleanlinessandhasdonesothroughrapidinnovationoverthepastseveralyears.Manyoftheseadvanceshaveinvolvedtheuseofultrasonictechnology.

Thecleaningindustryiscurrentlyinastruggletoreplacesolventdegreasingwithalternativeenvironmentallyfriendlymeansofcleaning.Althoughsubstitutewaterbased,semiaqueousandpetroleumbasedchemistriesareavailable,theyareoftensomewhatlesseffectiveascleanersthanthesolventsandmaynotperformadequatelyinsomeapplicationsunlessamechanicalenergyboostisaddedtoassuretherequiredlevelsofcleanliness.Ultrasonicenergyisnowusedextensivelyincriticalcleaningapplicationstobothspeedandenhancethecleaningeffectofthealternativechemistries.Thispaperisintendedtofamiliarizethereaderwiththebasictheoryofultrasonicsandhowultrasonicenergycanbemosteffectivelyappliedtoenhanceavarietyofcleaningprocesses.

WhatisUltrasonics?

Ultrasonicsisthescienceofsoundwavesabovethelimitsofhumanaudibility.Thefrequencyofasoundwavedeterminesitstoneorpitch.Lowfrequenciesproduceloworbasstones.Highfrequenciesproducehighortrebletones.Ultrasoundisasoundwithapitchsohighthatitcannotbeheardbythehumanear.Frequenciesabove18Kilohertzareusuallyconsideredtobeultrasonic.Thefrequenciesusedforultrasoniccleaningrangefrom20,000cyclespersecondorkilohertz(KHz)toover100,000KHz.Themostcommonlyusedfrequenciesforindustrialcleaningarethosebetween20KHzand50KHz.Frequenciesabove50KHzaremorecommonlyusedinsmalltabletopultrasoniccleanerssuchasthosefoundinjewelrystoresanddentaloffices.

TheTheoryofSoundWaves

Inordertounderstandthemechanicsofultrasonics,itisnecessarytofirsthaveabasicunderstandingofsoundwaves,howtheyaregeneratedandhowtheytravelthroughaconductingmedium.Thedictionarydefinessoundasthetransmissionofvibrationthroughanelasticmediumwhichmaybeasolid,liquid,oragas.SoundWaveGenerationAsoundwaveisproducedwhenasolitaryorrepeatingdisplacementisgeneratedinasoundconductingmedium,suchasbyashockeventorvibratorymovement.Thedisplacementofairbytheconeofaradiospeakerisagoodexampleofvibratorysoundwavesgeneratedbymechanicalmovement.Asthespeakerconemovesbackandforth,theairinfrontoftheconeisalternatelycompressedandrarefiedtoproducesoundwaves,whichtravelthroughtheairuntiltheyarefinallydissipated.Weareprobablymostfamiliarwithsoundwavesgeneratedbyalternatingmechanicalmotion.Therearealsosoundwaveswhicharecreatedbyasingleshockevent.Anexampleisthunderwhichisgeneratedasairinstantaneouslychangesvolumeasaresultofanelectricaldischarge(lightning).Anotherexampleofashockeventmightbethesoundcreatedasawoodenboardfallswithitsfaceagainstacementfloor.Shockeventsaresourcesofasinglecompressionwavewhichradiatesfromthesource.

TheNatureofSoundWaves

ThediagramaboveusesthecoilsofaspringsimilartoaSlinkytoytorepresentindividualmoleculesofasoundconductingmedium.Themoleculesinthemediumareinfluencedbyadjacentmoleculesinmuchthesamewaythatthecoilsofthespringinfluenceoneanother.Thesourceofthesoundinthemodelisattheleft.Thecompressiongeneratedbythesoundsourceasitmovespropagatesdownthelengthofthespringaseachadjacentcoilofthespringpushesagainstitsneighbor.Itisimportanttonotethat,althoughthewavetravelsfromoneendofthespringtotheother,theindividualcoilsremainintheirsamerelativepositions,beingdisplacedfirstonewayandthentheotherasthesoundwavepasses.Asaresult,eachcoilisfirstpartofacompressionasitispushedtowardthenextcoilandthenpartofararefactionasitrecedesfromtheadjacentcoil.Inmuchthesameway,anypointinasoundconductingmediumisalternatelysubjectedtocompressionandthenrarefaction.Atapointintheareaofacompression,thepressureinthemediumispositive.Atapointintheareaofararefaction,thepressureinthemediumisnegative.

CavitationandImplosion

Inelasticmediasuchasairandmostsolids,thereisacontinuoustransitionasasoundwaveistransmitted.Innonelasticmediasuchaswaterandmostliquids,thereiscontinuoustransitionaslongastheamplitudeorloudnessofthesoundisrelativelylow.Asamplitudeisincreased,however,themagnitudeofthenegativepressureintheareasofrarefactioneventuallybecomessufficienttocausetheliquidtofracturebecauseofthenegativepressure,causingaphenomenonknownascavitation.Cavitationbubblesarecreatedatsitesofrarefactionastheliquidfracturesortearsbecauseofthenegativepressureofthesoundwaveintheliquid.Asthewavefrontspass,thecavitationbubblesoscillateundertheinfluenceofpositivepressure,eventuallygrowingtoanunstablesize.Finally,theviolentcollapseofthecavitationbubblesresultsinimplosions,whichcauseshockwavestoberadiatedfromthesitesofthecollapse.Thecollapseandimplosionofmyriadcavitationbubblesthroughoutanultrasonicallyactivatedliquidresultintheeffectcommonlyassociatedwithultrasonics.Ithasbeencalculatedthattemperaturesinexcessof10,000Fandpressuresinexcessof10,000PSIaregeneratedattheimplosionsitesofcavitationbubbles.

BenefitsofUltrasonicsintheCleaningandRinsingProcesses

Cleaninginmostinstancesrequiresthatacontaminantbedissolved(asinthecaseofasolublesoil),displaced(asinthecaseofanonsolublesoil)orbothdissolvedanddisplaced(asinthecaseofinsolubleparticlesbeingheldbyasolublebindersuchasoilorgrease).Themechanicaleffectofultrasonicenergycanbehelpfulinbothspeedingdissolutionanddisplacingparticles.Justasitisbeneficialincleaning,ultrasonicsisalsobeneficialintherinsingprocess.Residualcleaningchemicalsareremovedquicklyandcompletelybyultrasonicrinsing.

Inremovingacontaminantbydissolution,itisnecessaryforthesolventtocomeintocontactwithanddissolvethecontaminant.Thecleaningactivitytakesplaceonlyattheinterfacebetweenthecleaningchemistryandthecontaminant.(Figure1)

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Figure1

Asthecleaningchemistrydissolvesthecontaminant,asaturatedlayerdevelopsattheinterfacebetweenthefreshcleaningchemistryandthecontaminant.Oncethishashappened,cleaningactionstopsasthesaturatedchemistrycannolongerattackthecontaminant.Freshchemistrycannotreachthecontaminant.(Figure2)

Figure2

Ultrasoniccavitationandimplosioneffectivelydisplacethesaturatedlayertoallowfreshchemistrytocomeintocontactwiththecontaminantremainingtoberemoved.Thisisespeciallybeneficialwhenirregularsurfacesorinternalpassagewaysaretobecleaned.(Figure3)

Figure3

UltrasonicsSpeedsCleaningbyDissolution

Somecontaminantsarecomprisedofinsolubleparticleslooselyattachedandheldinplacebyionicorcohesiveforces.Theseparticlesneedonlybedisplacedsufficientlytobreaktheattractiveforcestoberemoved.(Figure4)

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Figure4

Cavitationandimplosionasaresultofultrasonicactivitydisplaceandremovelooselyheldcontaminantssuchasdustfromsurfaces.Forthistobeeffective,itisnecessarythatthecouplingmediumbecapableofwettingtheparticlestoberemoved.(Figure5)

Figure5

ComplexContaminants

Contaminationscanalso,ofcourse,bemorecomplexinnature,consistingofcombinationsoilsmadeupofbothsolubleandinsolublecomponents.Theeffectofultrasonicsissubstantiallythesameinthesecases,asthemechanicalmicroagitationhelpsspeedboththedissolutionofsolublecontaminantsandthedisplacementofinsolubleparticles.Ultrasonicactivityhasalsobeendemonstratedtospeedorenhancetheeffectofmanychemicalreactions.Thisisprobablycausedmostlybythehighenergylevelscreatedashighpressuresandtemperaturesarecreatedattheimplosionsites.Itislikelythatthesuperiorresultsachievedinmanyultrasoniccleaningoperationsmaybeatleastpartiallyattributedtothesonochemistryeffect.

ASuperiorProcess

Intheaboveillustrations,thesurfaceofthepartbeingcleanedhasbeenrepresentedasaflat.Inreality,surfacesareseldomflat,insteadbeingcomprisedofhills,valleysandconvolutionsofalldescription.Figure6showswhyultrasonicenergyhasbeenproventobemoreeffectiveatenhancingcleaningthanotheralternatives,includingspraywashing,brushing,turbulation,airagitation,andevenelectrocleaninginmanyapplications.Theabilityofultrasonicactivitytopenetrateandassistthecleaningofinteriorsurfacesofcomplexpartsisalsoespeciallynoteworthy.

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Figure6

UltrasonicEquipment

Tointroduceultrasonicenergyintoacleaningsystemrequiresanultrasonictransducerandanultrasonicpowersupplyorgenerator.Thegeneratorsupplieselectricalenergyatthedesiredultrasonicfrequency.Theultrasonictransducerconvertstheelectricalenergyfromtheultrasonicgeneratorintomechanicalvibrations.

UltrasonicGenerator

Theultrasonicgeneratorconvertselectricalenergyfromthelinewhichistypicallyalternatingcurrentat50or60Hztoelectricalenergyattheultrasonicfrequency.Thisisaccomplishedinanumberofwaysbyvariousequipmentmanufacturers.Currentultrasonicgeneratorsnearlyallusesolidstatetechnology.

Therehavebeenseveralrelativelyrecentinnovationsinultrasonicgeneratortechnologywhichmayenhancetheeffectivenessofultrasoniccleaningequipment.Theseincludesquarewaveoutputs,slowlyorrapidlypulsingtheultrasonicenergyonandoffandmodulatingorsweepingthefrequencyofthegeneratoroutputaroundthecentraloperatingfrequency.Themostadvancedultrasonicgeneratorshaveprovisionsforadjustingavarietyofoutputparameterstocustomizetheultrasonicenergyoutputforthetask.

SquareWaveOutput

Applyingasquarewavesignaltoanultrasonictransducerresultsinanacousticoutputrichinharmonics.Theresultisamultifrequencycleaningsystemwhichvibratessimultaneouslyatseveralfrequencieswhichareharmonicsofthefundamentalfrequency.Multifrequencyoperationoffersthebenefitsofallfrequenciescombinedinasingleultrasoniccleaningtank.

Pulse

Inpulseoperation,theultrasonicenergyisturnedonandoffataratewhichmayvaryfromonceeveryseveralsecondstoseveralhundredtimespersecond.

Thepercentageoftimethattheultrasonicenergyisonmayalsobechangedtoproducevariedresults.Atslowerpulserates,

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morerapiddegassingofliquidsoccursascoalescingbubblesofairaregivenanopportunitytorisetothesurfaceoftheliquidduringthetimetheultrasonicenergyisoff.Atmorerapidpulseratesthecleaningprocessmaybeenhancedasrepeatedhighenergyburstsofultrasonicenergyoccureachtimetheenergysourceisturnedon.

FrequencySweep

Insweepoperation,thefrequencyoftheoutputoftheultrasonicgeneratorismodulatedaroundacentralfrequencywhichmayitselfbeadjustable.

Variouseffectsareproducedbychangingthespeedandmagnitudeofthefrequencymodulation.Thefrequencymaybemodulatedfromonceeveryseveralsecondstoseveralhundredtimespersecondwiththemagnitudeofvariationrangingfromseveralhertztoseveralkilohertz.Sweepmaybeusedtopreventdamagetoextremelydelicatepartsortoreducetheeffectsofstandingwavesincleaningtanks.Sweepoperationmayalsobefoundespeciallyusefulinfacilitatingthecavitationofterpenesandpetroleumbasedchemistries.AcombinationofPulseandsweepoperationmayprovideevenbetterresultswhenthecavitationofterpenesandpetroleumbasedchemistriesisrequired.

FrequencyandAmplitude

Frequencyandamplitudearepropertiesofsoundwaves.Theillustrationsbelowdemonstratefrequencyandamplitudeusingthespringmodelintroducedearlier.Inthediagram,ifAisthebasesoundwave,Bwithlessdisplacementofthemedia(lessintensecompressionandrarefaction)asthewavefrontpasses,representsasoundwaveoflessamplitudeorloudness.Crepresentsasoundwaveofhigherfrequencyindicatedbymorewavefrontspassingagivenpointwithinagivenperiodoftime.

UltrasonicTransducers

Therearetwogeneraltypesofultrasonictransducersinusetoday:Magnetostrictiveandpiezoelectric.Bothaccomplishthesametaskofconvertingalternatingelectricalenergytovibratorymechanicalenergybutdoitthroughtheuseofdifferentmeans.

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Magnetostrictive

Magnetostrictivetransducersutilizetheprincipleofmagnetostrictioninwhichcertainmaterialsexpandandcontractwhenplacedinanalternatingmagneticfield.

Alternatingelectricalenergyfromtheultrasonicgeneratorisfirstconvertedintoanalternatingmagneticfieldthroughtheuseofacoilofwire.Thealternatingmagneticfieldisthenusedtoinducemechanicalvibrationsattheultrasonicfrequencyinresonantstripsofnickelorothermagnetostrictivematerialwhichareattachedtothesurfacetobevibrated.Becausemagnetostrictivematerialsbehaveidenticallytoamagneticfieldofeitherpolarity,thefrequencyoftheelectricalenergyappliedtothetransduceris1/2ofthedesiredoutputfrequency.Magnetostrictivetransducerswerefirsttosupplyarobustsourceofultrasonicvibrationsforhighpowerapplicationssuchasultrasoniccleaning.

Becauseofinherentmechanicalconstraintsonthephysicalsizeofthehardwareaswellaselectricalandmagneticcomplications,highpowermagnetostrictivetransducersseldomoperateatfrequenciesmuchabove20kilohertz.Piezoelectrictransducers,ontheotherhand,caneasilyoperatewellintothemegahertzrange.

Magnetostrictivetransducersaregenerallylessefficientthantheirpiezoelectriccounterparts.Thisisdueprimarilytothefactthatthemagnetostrictivetransducerrequiresadualenergyconversionfromelectricaltomagneticandthenfrommagnetictomechanical.Someefficiencyislostineachconversion.Magnetichysteresiseffectsalsodetractfromtheefficiencyofthemagnetostrictivetransducer.

Piezoelectric

Piezoelectrictransducersconvertalternatingelectricalenergydirectlytomechanicalenergythroughuseofthepiezoelectriceffectinwhichcertainmaterialschangedimensionwhenanelectricalchargeisappliedtothem.

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Electricalenergyattheultrasonicfrequencyissuppliedtothetransducerbytheultrasonicgenerator.Thiselectricalenergyisappliedtopiezoelectricelement(s)inthetransducerwhichvibrate.Thesevibrationsareamplifiedbytheresonantmassesofthetransduceranddirectedintotheliquidthroughtheradiatingplate.Earlypiezoelectrictransducersutilizedsuchpiezoelectricmaterialsasnaturallyoccurringquartzcrystalsandbariumtitanatewhichwerefragileandunstable.Earlypiezoelectrictransducerswere,therefore,unreliable.Todaystransducersincorporatestronger,moreefficientandhighlystableceramicpiezoelectricmaterialswhichweredevelopsasaresultoftheeffortsoftheUSNavyanditsresearchtodevelopadvancedsonartranspondersinthe1940s.Thevastmajorityoftransducersusedtodayforultrasoniccleaningutilizethepiezoelectriceffect.

UltrasonicCleaningEquipment

Ultrasoniccleaningequipmentrangesfromthesmalltabletopunitsoftenfoundindentalofficesorjewelrystorestohugesystemswithcapacitiesofseveralthousandgallonsusedinavarietyofindustrialapplications.Selectionordesignoftheproperequipmentisparamountinthesuccessofanyultrasoniccleaningapplication.

Thesimplestapplicationmayrequireonlyasimpleheatedtankcleanerwithrinsingtobedoneinasinkorinaseparatecontainer.Moresophisticatedcleaningsystemsincludeoneormorerinses,addedprocesstanksandhotairdryers.Automationisoftenaddedtoreducelaborandguaranteeprocessconsistency.

Thelargestinstallationsutilizeimmersibleultrasonictransducerswhichcanbemountedonthesidesorbottomofcleaningtanksofnearlyanysize.Immersibleultrasonictransducersoffermaximumflexibilityandeaseofinstallationandservice.

Heatedtankcleaningsystems(figure7)areusedinlaboratoriesandforsmallbatchcleaningneeds.

Figure7

Small,selfcontainedcleaners(figure8)areusedindoctorsofficesandjewelrystores.

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Figure8

Consolecleaningsystems(figure9)integrateultrasoniccleaningtank(s),rinsetank(s)andadryerforbatchcleaning.SystemscanbeautomatedthroughtheuseofaPLCcontrolledmaterialhandlingsystem.

Figure9

Awiderangeofoptionsmaybeofferedincustomdesignedsystems,aspicturedinfigure10.Largescaleinstallationsorretrofittingofexistingtanksinplatinglines,etc.,canbeachievedthroughtheuseofmodularimmersibleultrasonictransducers.Ultrasonicgeneratorsareoftenhousedinclimatecontrolledenclosures.

Figure10

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MaximizingtheUltrasonicCleaningProcess

ProcessParameters

Effectiveapplicationoftheultrasoniccleaningprocessrequiresconsiderationofanumberofparameters.Whiletime,temperatureandchemicalremainimportantinultrasoniccleaningastheyareinothercleaningtechnologies,thereareotherfactorswhichmustbeconsideredtomaximizetheeffectivenessoftheprocess.Especiallyimportantarethosevariableswhichaffecttheintensityofultrasoniccavitationintheliquid.

MaximizingCavitation

Maximizingcavitationofthecleaningliquidisobviouslyveryimportanttothesuccessoftheultrasoniccleaningprocess.Severalvariablesaffectcavitationintensity.

Temperatureisthemostimportantsingleparametertobeconsideredinmaximizingcavitationintensity.Thisisbecausesomanyliquidpropertiesaffectingcavitationintensityarerelatedtotemperature.Changesintemperatureresultinchangesinviscosity,thesolubilityofgasintheliquid,thediffusionrateofdissolvedgassesintheliquid,andvaporpressure,allofwhichaffectcavitationintensity.Inpurewater,thecavitationeffectismaximizedatapproximately160F.

Theviscosityofaliquidmustbeminimizedformaximumcavitationeffect.Viscousliquidsaresluggishandcannotrespondquicklyenoughtoformcavitationbubblesandviolentimplosion.Theviscosityofmostliquidsisreducedastemperatureisincreased.

Formosteffectivecavitation,thecleaningliquidmustcontainaslittledissolvedgasaspossible.Gasdissolvedintheliquidisreleasedduringthebubblegrowthphaseofcavitationandpreventsitsviolentimplosionwhichisrequiredforthedesiredultrasoniceffect.Theamountofdissolvedgasinaliquidisreducedastheliquidtemperatureisincreased.

Thediffusionrateofdissolvedgassesinaliquidisincreasedathighertemperatures.Thismeansthatliquidsathighertemperaturesgiveupdissolvedgassesmorereadilythanthoseatlowertemperatures,whichaidsinminimizingtheamountofdissolvedgasintheliquid.

Amoderateincreaseinthetemperatureofaliquidbringsitclosertoitsvaporpressure,meaningthatvaporouscavitationismoreeasilyachieved.Vaporouscavitation,inwhichthecavitationbubblesarefilledwiththevaporofthecavitatingliquid,isthemosteffectiveformofcavitation.Astheboilingtemperatureisapproached,however,thecavitationintensityisreducedastheliquidstartstoboilatthecavitationsites.

CavitationintensityisdirectlyrelatedtoUltrasonicPoweratthepowerlevelsgenerallyusedinultrasoniccleaningsystems.Aspowerisincreasedsubstantiallyabovethecavitationthreshold,cavitationintensitylevelsoffandcanonlybefurtherincreasedthroughtheuseoffocusingtechniques.

CavitationintensityisinverselyrelatedtoUltrasonicFrequency.Astheultrasonicfrequencyisincreased,cavitationintensityisreducedbecauseofthesmallersizeofthecavitationbubblesandtheirresultantlessviolentimplosion.Thereductionincavitationeffectathigherfrequenciesmaybeovercomebyincreasingtheultrasonicpower.

ImportanceofMinimizingDissolvedGas

Duringthenegativepressureportionofthesoundwave,theliquidistornapartandcavitationbubblesstarttoform.Asanegativepressuredevelopswithinthebubble,gassesdissolvedinthecavitatingliquidstarttodiffuseacrosstheboundaryintothebubble.Asnegativepressureisreducedduetothepassingoftherarefactionportionofthesoundwaveandatmosphericpressureisreached,thecavitationbubblestartstocollapseduetoitsownsurfacetension.Duringthecompressionportionofthesoundwave,anygaswhichdiffusedintothebubbleiscompressedandfinallystartstodiffuseacrosstheboundaryagaintoreentertheliquid.Thisprocess,however,isnevercompleteaslongasthebubblecontainsgassincethediffusionoutofthebubbledoesnotstartuntilthebubbleiscompressed.Andoncethebubbleiscompressed,theboundarysurfaceavailablefordiffusionisreduced.Asaresult,cavitationbubblesformedinliquidscontaininggasdonotcollapseallthewaytoimplosionbutratherresultinasmallpocketofcompressedgasintheliquid.Thisphenomenoncanbeusefulindegassingliquids.Thesmallgasbubblesgrouptogetheruntiltheyfinallybecomesufficientlybuoyanttocometothesurfaceoftheliquid.

MaximizingOverallCleaningEffect

CleaningChemicalselectionisextremelyimportanttotheoverallsuccessoftheultrasoniccleaningprocess.Theselectedchemicalmustbecompatiblewiththebasemetalbeingcleanedandhavethecapabilitytoremovethesoilswhicharepresent.Itmustalsocavitatewell.Mostcleaningchemicalscanbeusedsatisfactorilywithultrasonics.Someareformulatedespeciallyforusewithultrasonics.However,avoid

thenonfoamingformulationsnormallyusedinspraywashingapplications.Highlywettedformulationsarepreferred.Manyofthenewpetroleumcleaners,aswellaspetroleumandterpenebasedsemiaqueouscleaners,arecompatiblewithultrasonics.Useoftheseformulationsmayrequiresomespecialequipmentconsiderations,includingincreasedultrasonicpower,tobeeffective.

Figure11

Temperaturewasmentionedearlierasbeingimportanttoachievingmaximumcavitation.Theeffectivenessofthecleaningchemicalisalsorelatedtotemperature.Althoughthecavitationeffectismaximizedinpurewateratatemperatureofapproximately160F,optimumcleaningisoftenseenathigherorlowertemperaturesbecauseoftheeffectthattemperaturehasonthecleaningchemical.Asageneralrule,eachchemicalwillperformbestatitsrecommendedprocesstemperatureregardlessofthetemperatureeffectontheultrasonics.Forexample,althoughthemaximumultrasoniceffectisachievedat160F,mosthighlycausticcleanersareusedatatemperaturesof180Fto190Fbecausethechemicaleffectisgreatlyenhancedbytheaddedtemperature.Othercleanersmaybefoundtobreakdownandlosetheireffectivenessifusedattemperaturesinexcessofaslowas140F.Thebestpracticeistouseachemicalatitsmaximumrecommendedtemperaturenotexceeding190F

Degassingofcleaningsolutionsisextremelyimportantinachievingsatisfactorycleaningresults.Freshsolutionsorsolutionswhichhavecooledmustbedegassedbeforeproceedingwithcleaning.Degassingisdoneafterthechemicalisaddedandisaccomplishedbyoperatingtheultrasonicenergyandraisingthesolutiontemperature.Thetimerequiredfordegassingvariesconsiderably,basedontankcapacityandsolutiontemperature,andmayrangefromseveralminutesforasmalltank

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toanhourormoreforalargetank.Anunheatedtankmayrequireseveralhourstodegas.Degassingiscompletewhensmallbubblesofgascannotbeseenrisingtothesurfaceoftheliquidandapatternofripplescanbeseen.

Figure12

TheUltrasonicPowerdeliveredtothecleaningtankmustbeadequatetocavitatetheentirevolumeofliquidwiththeworkloadinplace.Wattspergallonisaunitofmeasureoftenusedtomeasurethelevelofultrasonicpowerinacleaningtank.Astankvolumeisincreased,thenumberofwattspergallonrequiredtoachievetherequiredperformanceisreduced.Cleaningpartsthatareverymassiveorthathaveahighratioofsurfacetomassmayrequireadditionalultrasonicpower.Excessivepowermaycausecavitationerosionorburningonsoftmetalparts.Ifawidevarietyofpartsistobecleanedinasinglecleaningsystem,anultrasonicpowercontrolisrecommendedtoallowthepowertobeadjustedasrequiredforvariouscleaningneeds.PartExposuretoboththecleaningchemicalandultrasonicenergyisimportantforeffectivecleaning.Caremustbetakentoensurethatallareasofthepartsbeingcleanedarefloodedwiththecleaningliquid.Partsbasketsandfixturesmustbedesignedtoallowpenetrationofultrasonicenergyandtopositionthepartstoassurethattheyareexposedtotheultrasonicenergy.Itisoftennecessarytoindividuallyrackpartsinaspecificorientationorrotatethemduringthecleaningprocesstothoroughlycleaninternalpassagesandblindholes.

Conclusion

Properlyutilized,ultrasonicenergycancontributesignificantlytothespeedandeffectivenessofmanyimmersioncleaningandrinsingprocesses.Itisespeciallybeneficialinincreasingtheeffectivenessoftodayspreferredaqueouscleaningchemistriesand,infact,isnecessaryinmanyapplicationstoachievethedesiredlevelofcleanliness.Withultrasonics,aqueouschemistriescanoftengiveresultssurpassingthosepreviouslyachievedusingsolvents.Ultrasonicsisnotatechnologyofthefutureitisverymuchatechnologyoftoday.

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