ASTM_B_76_-_90_2018.pdf

Designation:B7690(Reapproved 2018)Standard Test Method forAccelerated Life of Nickel-Chromium and Nickel-Chromium-Iron Alloys for Electrical Heating1This standard is issued under the fixed designation B76;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method2covers the determination of theresistance to oxidation of nickel-chromium and nickel-chromium-iron electrical heating alloys at elevated tempera-tures under intermittent heating.Procedures for a constant-temperature cycle are provided.This test method is used forinternal comparative purposes only.1.2 The values stated in inch-pound units are to be regardedas standard.The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to become familiarwith all hazards including those identified in the appropriateSafety Data Sheet(SDS)for this product/material as providedby the manufacturer,to establish appropriate safety,health,and environmental practices,and determine the applicabilityof regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Significance and Use2.1 This test method is used by producers of electricalheating alloys to measure the cyclic oxidation resistance ofthese alloys.2.2 Because of the effect of the environment,design,anduse,the life values obtained from this test method may notcorrelate with that of an appliance or industrial heating unit.3.Test Panel3.1 Size and LocationThe dimensions of the test panelshall be similar to those shown in Fig.1.The test panel shall belocated in a position free from drafts of air.NOTE1The enclosure shall fit tightly on the panel and the glass slideshall fit snugly to prevent leakage of air at this point during the operationof the test,as even a slight draft of air in contact with the specimen willcause excessive variation in length of life.A screen of 40 wire mesh,0.010-in.(0.025-mm)wire diameter,market grade,may be used as a coverover the individual stations.3.2 Upper TerminalThe upper terminal shall consist of abinding post attached to a rod passing through another bindingpost or through the upper bus bar.This provides for adjustmentlaterally and vertically,as shown in Fig.1.3.3 Lower TerminalA 10-g weight shall be attached to thelower end of the specimen.Aflexible silver foil(approximately0.375 in.(9.52 mm)wide and 0.0015 in.(0.038 mm)thick)connected to the 10-g weight shall constitute the lowerterminal.NOTE2Experiments have shown that with high temperatures alloys ofnickel-chromium and nickel-chromium-iron are subject to plastic flowwhen under relatively light load.The weight specified in 3.3 does notcause appreciable increase in length during the test.4.Apparatus4.1 The test apparatus shall be similar to the requirementsspecified in 4.2 to 4.8,inclusive,and shall be connected asshown in Fig.2.4.2 Power SupplyThe transformer or motor generator setshall be capable of delivering a controlled voltage of from 10to 20 V to the circuit.It shall have a continuous currentcapacity of at least 20 A/specimen.4.3 Voltage ControlThe automatic voltage control shall becapable of maintaining across the bus bars a constant voltagewithin 60.5%.NOTE3It has been found impossible to make accurate tests withoutvoltage control,as changes in line voltage were sufficient to causeconsiderable variation in the results obtained(see Annex A1).4.4 Variable TransformerThe transformer shall be capableof adjusting the voltage across the specimen so that current is1This test method is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and is the direct responsibility of SubcommitteeB02.10 on Thermostat Metals and Electrical Resistance Heating Materials.Current edition approved Nov.1,2018.Published November 2018.Originallyapproved in 1929.Last previous edition approved in 2013 as B76 90(2013).DOI:10.1520/B0076-90R18.2Further information on this test method is given in a paper by F.E.Bash andJ.W.Harsch,“Life Tests on Metallic Resistor Materials for Electrical Heating,”Proceedings,ASTEA,American Society for Testing and Materials.Vol 29,Part II,1929,p.506.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with intern