8-paper-Temperature Stability in Coating Pots as a

TemperatureStabilityinCoatingPotsasaFunctionofPowerSupplyTechnologyBillRovinsDirector,GalvanizingandHeatingTechnologiesInductothermCorp.Rancocas,NewJerseyU.S.A.PresentedattheTheSecondBaosteelBiennialAcademicConferenceMay25-26,20062TEMPERATURESTABILITYINGALVANIZINGPOTSASAFUNCTIONOFPOWERSUPPLYTECHNOLOGYBillRovinsDirector,GalvanizingandStripHeatingTechnologiesInductothermCorp.MassHeating&CoatingRancocas,NewJerseyU.S.A.Tel.:[phone]ext.323Fax:[phone]E-mail:[e-mail]:Theuseoftapchangerandsolid-statepowersuppliesforinductorsonceramiclinedcoatingpotsisdiscussedwithparticularemphasisontemperaturestability.Inaddition,thecorelesscoatingpotanditsinherenttemperaturestabilityispresented.Havingathoroughunderstandingofthevariouspowersupplyandpottechnologiesavailabletodaywillbebeneficialforgalvanizersindeterminingthebestchoicefortheirparticularprocesses.Keywords:coatingpots;galvanizing;temperaturestability;tapchanger;solid-state;corelesspots0.INTRODUCTIONOverthelastdozenyears,fluidflowandtemperaturedistributionincontinuousgalvanizingbathshasbeenstudiedandreported.[1,2]Watermodelinghasbeenusedtodetermineflowpatternsastheyrelatetoaluminumdistributioninthebath.[3]Numericalmodelinghasbeenusedtoexaminetheimpactofflowpatternsondrosspickuponthestrip.[4]Bothhavebeenusedinconjunctionwithbathsamplingtoinvestigatethemovementofdrossparticlesinthebath.[5]Numericalmodelinghasalsobeenusedtoseehowingotchargingconfigurationaffectsbathflowfromthemeltingingots.[6]Morerecently,particularfocuswasplacedontherolethatthe“pulsing”ofinductorsplaysoninducingtransienteffectsonflowpatternsandtemperaturedistributionsinthecontinuousgalvanizingbath.[2]Therearebasicallytwotypesofpowersuppliesusedtopowerzincchannelinductorstoday–tapchangerandsolid-state.Itiswellknownintheindustrythatsolid-statepowersuppliesallowgreaterpottemperaturestabilitythantapchangerpowersuppliesinthisapplication.Theauthorseekstotakethisastepfurtherbyverifyingthatthesmoothoperationofsolid-statepowersupplies,ascomparedtothe“pulsing”oftapchangerpowersupplies,decreasestheamountofbathtemperaturefluctuationsinthevicinityofthestrip.31.BACKROUNDMostofthechannelpotsinexistencetodayusetapchangertypepowersupplies.Thistypeofpowersupplyusestheselectionoftapsonanauto-transformertoprovidediscreetchangesinpowerlevel.Onehightapandonelowtapareselectedsuchthattheybrackettheaveragepowerrequirementforthegivenlineconditions.Acontactorcyclesbackandforthbetweenthetwotapsasdictatedbyatemperaturecontrollerusingfeedbackfromabaththermocouple.Becausethecontactorisanelectro-mechanicaldevice,ithasafinitelifespan.Thisimposesapracticallimitonthedegreeofbathtemperatureregulationavailable,typically+/-3degreesC.Otherwise,prematurefailureofthecontactorispossible.Solid-statepowersuppliesofferstep-lesscontrolwithouttheuseofmovingparts.ThisprovidesahigherdegreeofreliabilityalongwithahigherdegreeofbathtemperatureregulationbecauseoftruePIDcontrol.Regulationofthebathtemperaturetowithin+/-1degreeC.iseasilyachievable.2.BATHSAMPLINGMETHODInordertoverifytheauthor’shypothesis,bathtemperaturemeasurementsweretakenintwochannelcoatingpotsrunningwithsimilarlineconditions.Onepothadthreeinductorspoweredbysolid-statepowersupplies,andtheotherpothadtwoinductorspoweredbytapchangerpowersupplies.Acomparisonofthelineconditionsappearsinthetablebelow:Table1ComparisonofLineParametersforTwoPotswithDifferentTypesofPowerSuppliesPropertyPotw/solid-statep.s.Potw/tapchangerp.s.AlloyGIGIIngotSize2400lbs.(1091kg)1130kgStripwidth60.38”(1534mm)1200mmStripthickness0.035”(0.89mm)0.5mmLinespeed385FPM(117m/min.)145m/min.Coatingweight67g/m2eachside60g/m2eachsideStriptemperatures.p.880F.(471C.)500C.Bathtemperatures.p.865F.(463C.)460C.Thetype‘K’thermocoupleswerepositionedinthetwopots,respectively,asshowninthefollowingtwofigures:4Figure1ThermocouplePlacementinPotwithInductorsPoweredbySolid-StatePowerSuppliesFigure2ThermocouplePlacementinPotwithInductorsPoweredbyTapChangerPowerSupplies5Thermocouples#1-4wereconnectedtoaYokogawachartrecorderwithadigitalreadout.Thecustomer’sbaththermocoupleswereconnectedtotheinputoftheHoneywelltemperaturecontrollersuppliedwiththeequipment.Thermocouples#1and#2werelocated12”infrontofthethroatopeningoncenterlinescorrespondingtothecenterandoneouterlegoftheinductorchannel.Thermocouples#3and#4wereplacedcloselybehindthesnout,enteringthebathatthesameangleasthesnoutandstrip.TemperatureandkWreadingsweretakeneverytwominutesandthetimesatwhichingotswerechargedintothepotwerenoted.3.RESULTSANDDISCUSSIONThefollowinggraphshowstheresultsofthemeasurementstakenonthepotwithinductorspoweredbytapchangerpowersupplies:Graph1TemperatureResponseofChannelPotwithTapChangerPowerSuppliesAsthereaderwillnote,thereisaverydiscernablepatterntotherecordedtemperaturesinresponsetothe“pulsing”oftheinductors.Anaveragetemperaturevariationof6degreesF.occurswithasystemtimeconstantofapproximately30minutesforthecoatingpot.Thenextgraphshowstheresultsofthemeasurementstakenonthepotwithinductorspoweredbysolid-statepowersupplies:ChannelPotwith(2)Ta