Designation:D2858–70(Reapproved1997)e1AnAmericanNationalStandardStandardTestMethodforThermalConductivityofElectricalGradeMagnesiumOxide1ThisstandardisissuedunderthefixeddesignationD2858;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(e)indicatesaneditorialchangesincethelastrevisionorreapproval.e1NOTE—Section13wasaddededitoriallyinOctober1997.1.Scope1.1Thismethodcoversthedeterminationofthermalcon-ductivityofcompacted,granular,electricalgrademagnesiumoxide(MgO)underconditionswhichsimulatetheuseofthismaterialasinsulationintubularheatingunits.1.2Thevaluesstatedininch-poundunitsaretoberegardedasthestandard.2.ReferencedDocuments2.1ASTMStandards:B344SpecificationforDrawnorRolledNickel-ChromiumandNickel-Chromium-IronAlloysforElectricalHeatingElements2D2755TestMethodofSamplingandReductiontoTestWeightofElectricalGradeMagnesiumOxide3D2771TestMethodsforCompactionDensityofElectricalGradeMagnesiumOxide33.SummaryofTestMethod3.1ThesampleofMgOiscompactedwithinthecylindricalspaceformedbyatubularsheathandaconcentric,inner,hollowrod.Therodisheatedelectricallytoproduceatemperaturegradientacrosstheinsulation.Thermalconductiv-ityiscalculatedfrommeasurementsofinternalandexternaltemperatures,wattageappliedtotheunit,andthedimensionsoftheunit.4.Significance4.1Thermalconductivityoftheinsulationaffectstheinter-naltemperatureoftubularheatingunits;therefore,itinfluenceselectricalleakageandlifeoftheheaters.5.Apparatus5.1FillingMachine,vibratory-type,withsuitableloadingdevices.45.2SwagingMachine,5with11.8-mm(0.465-in.)and11.4-mm(0.450-in.)dieswith6-degthroatangle(12degincluded).5.3MetalLathe,orothersuitableequipmentforcuttingtestunittolength.5.4SpotWeldingMachine.5.5A-cVoltmeter,10Vnominal,61%offullscale,5.6A-cAmmeter,300Anominal,61%offullscale.5.7Thermocouple,26-gage,ANSITypeK,withappropriatepotentiometer(s)andthermocoupleswitch.5.8Variablea-cPower...
