1、Designation:D 2858 70(Reapproved 1997)e1An American National StandardStandard Test Method forThermal Conductivity of Electrical Grade Magnesium Oxide1This standard is issued under the fixed designation D 2858;the number immediately following the designation indicates the year oforiginal adoption or,
2、in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.e1NOTESection 13 was added editorially in October 1997.1.Scope1.1 This method covers the determin
3、ation of thermal con-ductivity of compacted,granular,electrical grade magnesiumoxide(MgO)under conditions which simulate the use of thismaterial as insulation in tubular heating units.1.2 The values stated in inch-pound units are to be regardedas the standard.2.Referenced Documents2.1 ASTM Standards
4、:B 344 Specification for Drawn or Rolled Nickel-Chromiumand Nickel-Chromium-Iron Alloys for Electrical HeatingElements2D 2755 Test Method of Sampling and Reduction to TestWeight of Electrical Grade Magnesium Oxide3D 2771 Test Methods for Compaction Density of ElectricalGrade Magnesium Oxide33.Summar
5、y of Test Method3.1 The sample of MgO is compacted within the cylindricalspace formed by a tubular sheath and a concentric,inner,hollow rod.The rod is heated electrically to produce atemperature gradient across the insulation.Thermal conductiv-ity is calculated from measurements of internal and exte
6、rnaltemperatures,wattage applied to the unit,and the dimensionsof the unit.4.Significance4.1 Thermal conductivity of the insulation affects the inter-nal temperature of tubular heating units;therefore,it influenceselectrical leakage and life of the heaters.5.Apparatus5.1 Filling Machine,vibratory-ty
7、pe,with suitable loadingdevices.45.2 Swaging Machine,5with 11.8-mm(0.465-in.)and11.4-mm(0.450-in.)dies with 6-deg throat angle(12 degincluded).5.3 Metal Lathe,or other suitable equipment for cutting testunit to length.5.4 Spot Welding Machine.5.5 A-c Voltmeter,10 V nominal,61%of full scale,5.6 A-c A
8、mmeter,300 A nominal,61%of full scale.5.7 Thermocouple,26-gage,ANSI Type K,with appropriatepotentiometer(s)and thermocouple switch.5.8 Variable a-c Power Source,capable of handling 250Aat8 V.6.Materials6.1 Degreasing AgentAcetone or similar solvent.6.2 Hollow Rod,80 Ni-20 Cr alloy,in accordance with
9、Specification B 344,4.06+0.08,0.00 mm(0.160+0.003,0.000 in.)in outside diameter,0.89+0.08,0.00 mm(0.035+0.003,0.000 in.)in wall thickness,and 410 6 0.8 mm(166132in.)long,and straight within 0.42 mm/m(0.005 in./ft).6.3 Rubber Plugs,11.00 mm(0.430 in.)in outside diameter,3.18 mm(0.125 in.)in inside di
10、ameter,and 12.70 mm(0.500in.)long.6.4 Sheath Tubing,Incoloy 8006or equivalent,bright aswelded,12.70 6 0.08 mm(0.500 6 0.003 in.)in outsidediameter,0.89 6 0.08 mm(0.035 6 0.003 in.)in wallthickness,3606 0.8-mm(14 6132in.)long,and straightwithin 0.43 mm/m(0.005 in./ft).1This test method is under the j
11、urisdiction of ASTM Committee D-9 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.14 on Electric Heating Unit Insulation.Effective Feb.27,1970.2Annual Book of ASTM Standards,Vol 03.04.3Annual Book of ASTM Standards,Vol 10.02.4A suitable filling ma
12、chine is a three station Oakley loader,available fromOakley Industries,Inc.,7315 N.Linder Ave.,Skokie,IL.5Swaging machines found suitable for this purpose are size 4 swaging machines,available from either Torrington Co.,59 Field St.,Torrington,CT,or Fenn Mfg.Co.,200 Fenn Road.,Newington,CT.6Incoloy,
13、800t is a registered trademark of the International Nickel Co.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.NOTICE:This standard has either been superceded and replaced by a new version or discontinued.Contact ASTM International(www.ast
14、m.org)for the latest information.7.Sampling7.1 Obtain a sample of MgO in accordance with TestMethods D 2755.8.Test Sample8.1 A sample size of approximately 150 g is required foreach test unit.9.Procedure9.1 Clean the sheath and rod in the degreasing agent.Aftercleaning,handle the rod only at the end
15、s.9.2 Assemble the sheath and the rod with the loadingdevices to maintain the rod centrally within the sheath andeffect bottom closure.9.3 Using a vibratory filling machine,load the sample intothe sheath,taking about 2 min to fill the unit.9.4 Pour out the first load of sample and discard.NOTE1The i
16、nitial load serves as the final cleaning step by mildlyabrading the metal components.9.5 Refill the unit as before.9.6 Remove the top filling device and remove the sample toa depth of approximately 4.8 mm(316in.).Force the rubberplug over the end of the rod and firmly down inside the tube.Invert the tube and repeat the process at the bottom end.9.7 Swage the tube through a 11.80-mm(0.465-in.)die byfirst inserting one end and pushing through smoothly to within25 mm(1 in.)of the other end,removing
