1、Designation:D 2900 90(Reapproved 1997)e1An American National StandardStandard Test Method forAccelerated Life Test of Electrical Grade Magnesium Oxideas Used in Sheathed-Type Electric Heating Elements1This standard is issued under the fixed designation D 2900;the number immediately following the des
2、ignation indicates the year oforiginal adoption or,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 Octo
3、ber 1997.1.Scope1.1 This test method covers the accelerated life testing ofelectrical grade magnesium oxide(MgO)under conditionsinvolving thermal cycling to an elevated temperature.The testdetermines both the rate at which electrical insulation imped-ance(Note 1)or test current through the insulatio
4、n changeswith time and the time span resulting in complete failure of atest cell incorporating the sample under test.NOTE1At test temperatures,capacitive and inductive reactance arenegligible,and therefore impedance values are considered essentiallyresistive.1.2 This standard does not purport to add
5、ress all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.For specific safetyprecaution,see 9.4.1.1.3 The values stat
6、ed in acceptable metric units are to beregarded as the standard.2.Referenced Documents2.1 ASTM Standards: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 Grad
7、e Magnesium Oxide33.Summary of Test Method3.1 The specimen of magnesium oxide is loaded into a testcell,which is formed into an operative heater of specificconstruction.The test cell is thermally cycled by internalheating under conditions designed to accelerate deteriorationand promote failure in a
8、period of several months.Electricalresistance of the insulation is measured periodically.The totallength of time the test cell operates before failure occurs isrecorded as its life.4.Significance and Use4.1 The insulating quality of the magnesium oxide at hightemperature and during the life span of
9、a heating unit is a mostsignificant aspect of the material to the user.Accordingly,ameans is specified for determining the insulating quality in arelatively short time,with magnesium oxide being the onlyintended variable.5.Apparatus5.1 Loading Machine,vibratory-type,with suitable loadingdevices.45.2
10、 Rolling Machine,capable of roll reducing to 6.35 mm(0.250 in.)diameter through five passes of 7.62 mm(0.300 in.),7.24 mm,(0.285 in.),6.86 mm,(0.270 in.),6.60 mm(0.260in.),and 6.35 mm(0.250 in.),with no subsequent sizing rolls.55.3 Fusion or Spot Welding Machine.5.4 Variable A-C Power Source,(approx
11、imately 124 V)with voltage-regulation to 61V and meter for measuring.5.5 Variable A-C Test Voltage,supply of approximately 600V max.5.6 Voltmeter,A-C,1000 V/V,600 V full-scale deflection.65.7 Thermocouple,ANSI Type K,No.26 B&S gage,0.408mm(0.0159 in.)in diameter with appropriate potentiometer.5.8 Mi
12、lliammeter,A-C rectifier type 0-10 ma full scaledeflection.5.9 Voltage Divider,Rheostat,50W,500 V.6.MaterialsNOTE2To reduce the number of variables from one test to another,it1This method is under the jurisdiction of ASTM Committee D-9 on Electricaland Electronic Insulating Materials and is the dire
13、ct responsibility of SubcommitteeD09.14 on Electric Heating Unit Insulation.Current edition approved August 31,1990.Published October 1990.Originallypublished as D 2900 70.Last previous edition D 2900 84.2Annual Book of ASTM Standards,Vol 03.04.3Annual Book of ASTM Standards,Vol 10.02.4A suitable lo
14、ading machine is a three-station Oakley loader,manufactured byOakley Industries,Inc.,7315 N.Linder Ave.,Skokie,IL.5A suitable rolling machine is an Oakley rolling machine,manufactured byOakley Industries,Inc.,7315 Linder Ave.,Skokie,IL.Although roll reducing ispreferred,swaging is optional.Suggested
15、 sizes of reduction are 7.62 mm(0.300 in.)7.24 mm(0.285 in.),6.86 mm(0.270 in.),6.60 mm(0.260 in.),and 6.35 mm(0.250in.)If swaging is used,the sheath tube length must be increased about 3%and thehelix resistance increased about 4%.A suitable swaging is a Size 4 Torringtonmachine manufactured by the
16、Torrington Co.,59 Field St.,Torrington,CT.6A suitable voltmeter is a type DP2X manufactured by the General Electric Co.1AMERICAN SOCIETY FOR TESTING AND MATERIALS100 Barr Harbor Dr.,West Conshohocken,PA 19428Reprinted from the Annual Book of ASTM Standards.Copyright ASTM NOTICE:This standard has either been superseded and replaced by a new version or withdrawn.Contact ASTM International(www.astm.org)for the latest information is recommended that a stockpile of materials be maintained for makingl
