ASTM_A_937_-_A_937M_-_12.pdf

Designation:A937/A937M12Standard Test Method forDetermining Interlaminar Resistance of Insulating CoatingsUsing Two Adjacent Test Surfaces1This standard is issued under the fixed designation A937/A937M;the number immediately following the designation indicates the yearof original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers a means of testing the inter-laminar resistance of electrically insulating coatings as appliedto adjacent laminations of flat-rolled electrical steel,underpredetermined conditions of voltage,pressure and temperature.It indicates the effectiveness of surface coatings on electricalsheet steels for limiting interlaminar losses in electrical ma-chinery.The interlaminar resistance is measured directly inunits of resistance(k).1.2 This test method is particularly useful for,but notlimited to,electrical steels coated with inorganic insulatingcoatings.1.3 The values and equations stated in customary(cgs-emuand inch-pound)or SI units are to be regarded separately asstandard.Within this standard,SI units are shown in brackets.The values stated in each system may not be exact equivalents;therefore,each system shall be used independently of the other.Combining values from the two systems may result in noncon-formance with this standard.1.4 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2A34/A34M Practice for Sampling and Procurement Testingof Magnetic MaterialsA717/A717M Test Method for Surface Insulation Resistivityof Single-Strip Specimens3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 bad contacta contact which results in a voltage dropin excess of 0.6 V as described in 6.1.3.3.1.2 exposed test surfacethe insulating top surface of thetop lamination or the insulating bottom surface of the bottomlamination of the test specimen.3.1.3 four-terminal measuring technique,often referred toas four-probe measuring techniquea common method tomeasure resistance when a high degree of accuracy is re-quired.3In this standard,the circuit configuration for thistechnique is referred to as a four-probe configuration.In thetwo-surface tester,this configuration features two probes con-nected to the top lamination test surface and two probesconnected to the bottom lamination test surface.One of theprobes in each pair carries the measuring current,and the otherprovides a contact for the voltage measurement.Because of theextremely high impedance of the measuring circuit,very littlecurrent flows through the voltage contacts,and thus very littlevoltage is produced across the contacts to influence the truereading,that is,any effect from contact resistance is avoided orreduced to a negligible amount.The two-surface tester hasprovision to check the integrity of the contacts made betweenthe probes and the test surfaces.3.1.4 interlaminar resistancethe average resistance of twoadjacent insulating surfaces in contact with each other,underconditions specified in this standard.3.1.5 surface insulation resistivitythe effective resistivityof a single insulating layer tested between applied bare metalcontacts and the base metal of the insulated test specimen,asper Test Method A717/A717M.3.1.6 test specimentwo electrical steel laminations,eachhaving a minimum size of 25 25 cm 250 250 mm andeach having an electrically insulating coating on both sides.The two electrical steel laminations are placed one on top ofthe other for the interlaminar resistance measurement,Fig.1.3.1.7 two-surface testerthe apparatus used in this testmethod.1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Subcommittee A06.01 on TestMethods.Current edition approved Nov.1,2012.Published December 2012.Originallyapproved in 1995.Last previous edition approved in 2006 as A937/A937M06.DOI:10.1520/A0937_A0937M-12.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3Harris,F.K.,Electrical Measurements,Robert E.Krieger Publishing Company,Huntington,New York,1975,pp.220224.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.Summary of Test Method4.1 The test method measures the average resistance of twoadjacent insulating surfaces.Intimate physical contact of thesesurfaces is achieved via test heads which force a definedsurface area into contact under a specified pressure