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1、9/8/98AC43.13-1BSECTION4.MAGNETICPARTICLEINSPECTIONPar5-40Page5-199/8/98AC43.13-1B5-40.GENERAL.Magneticparticleinspectionisamethodfordetectingcracks,laps,seams,voids,pits,subsurfaceholes,andothersurface,orslightlysubsurface,discontinuitiesinferro-magneticmaterials.Mag

2、neticparticleinspectioncanbeusedonlyonferro-magneticmaterials(ironandsteel).Itcanbeperformedonrawmaterial,billets,finishedandsemi-finishedmaterials,welds,andin-serviceassembledordisassembledparts.Magneticparticlesareappliedoverasurfaceeitherdry,asapowder,orwet,asparti

3、clesinaliquidcarriersuchasoilorwater.Commonusesformagneticparticleinspectionare;finalinspection,receivinginspection,in-processinspection;andqualitycontrol,maintenance,andoverhaul.5-41.PRINCIPLESOFOPERATION.Magneticparticleinspectionusesthetendencyofmagneticlinesofforc

4、e,orflux,ofanappliedfieldtopassthroughthemetalratherthanthroughtheair.Adefectatornearthemetal’ssurfacedistortsthedistributionofthemagneticfluxandsomeofthefluxisforcedtopassoutthroughthesurface.(Seefigure 59.)Thefieldstrengthisincreasedintheareaofthedefectandoppositem

5、agneticpolesformoneithersideofthedefect.Finemagneticparticlesappliedtothepartareattractedtotheseregionsandformapatternaroundthedefect.Thepatternofparticlesprovidesavisualindicationofadefect.(Seefigure 510.)Figure5-9.Magneticfielddisrupted.Figure5-10.Crackdetectionby

6、magneticparticleinspection.a.Tolocateadefect,itisnecessarytocontrolthedirectionofmagnetization,andfluxlinesmustbeperpendiculartothelongitudinalaxesofexpecteddefects.Examinationofcriticalareasfordefectsmayrequirecompletedisassembly.Twomethodsofmagnetization,circularand

7、longitudinal,areusedtomagnetizethepartandinduceperpendicularfluxpaths.Partsofcomplexconfigurationmayrequirelocalmagnetizationtoensurepropermagneticfielddirectionandadequateremovalofsurfacecoatings,sealants,andothersimilarcompounds.Possibleadverseinfluenceoftheappliedo

8、rresidualmagneticfieldsondelicatepartssuchasinstruments,bearings,andmechanismsmayrequireremovalofthesepartsbeforeperformingt