ASTM A937/A937M-06
(Test Method)Standard Test Method for Determining Interlaminar Resistance of Insulating Coatings Using Two Adjacent Test Surfaces
Standard Test Method for Determining Interlaminar Resistance of Insulating Coatings Using Two Adjacent Test Surfaces
SIGNIFICANCE AND USE
This test method is particularly suitable for quality control in the application of insulating coatings. This test method measures the interlaminar resistance of insulating coatings, as defined in 3.1.4. Interlaminar resistance is the measure of the insulating quality of the coating. Interlaminar resistance is reported in units of kΩ.
The interlaminar resistance determined in accordance with this test method is not the same quantity determined by Test Method A 717/A 717M or Test Method A 718.
This test method is particularly useful for electrical steels coated with inorganic insulating coatings having surface insulation resistivities in excess of 0.3 kΩ·cm2 [30 kΩ·mm2] when tested using Test Method A 717/A 717M (a Franklin current less than 0.02 A). This test method can readily be extended to any range of insulation resistivity that the equipment comprising the two-surface tester allows. For the equipment specified herein, the maximum measurable resistance is 1200 kΩ for the 10-μA current setting and 12 000 kΩ for the 1-μA current setting; the maximum voltage for the test system is 12 V.
Repeat readings on the same set of two electrical steel laminations using different contact positions, as well as the testing of multiple laminations from the same lot of electrical steel, are recommended. Several readings are suggested because the coating thickness may vary across the surface of a given electrical steel lamination. Additionally, the coating thickness may vary across several laminations taken from the same lot of electrical steel. Such variations in coating thickness are likely to yield variations in the measured interlaminar resistance. The required number of readings depends on the nature of the coating and the accuracy required.
SCOPE
1.1 This test method covers a means of testing the interlaminar resistance of electrically insulating coatings as applied to adjacent laminations of flat-rolled electrical steel, under predetermined conditions of voltage, pressure and temperature. It indicates the effectiveness of surface coatings on electrical sheet steels for limiting interlaminar losses in electrical machinery. The interlaminar resistance is measured directly in units of resistance (k).
1.2 This test method is particularly useful for, but not limited to, electrical steels coated with inorganic insulating coatings.
1.3 The values and equations stated in customary (cgs-emu and inch-pound) or SI units are to be regarded separately as standard. 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 nonconformance with this standard.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
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Designation:A937/A937M −06
StandardTest Method for
Determining Interlaminar Resistance of Insulating Coatings
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Using Two Adjacent Test Surfaces
This standard is issued under the fixed designationA937/A937M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope A718Test Method for Surface Insulation Resistivity of
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Multi-Strip Specimens
1.1 This test method covers a means of testing the inter-
laminar resistance of electrically insulating coatings as applied
3. Terminology
to adjacent laminations of flat-rolled electrical steel, under
3.1 Definitions of Terms Specific to This Standard:
predeterminedconditionsofvoltage,pressureandtemperature.
3.1.1 bad contact—acontactwhichresultsinavoltagedrop
It indicates the effectiveness of surface coatings on electrical
in excess of 0.6 V as described in 6.1.3.
sheet steels for limiting interlaminar losses in electrical ma-
chinery. The interlaminar resistance is measured directly in 3.1.2 exposed test surface—the insulating top surface of the
units of resistance (kΩ). top lamination or the insulating bottom surface of the bottom
lamination of the test specimen.
1.2 This test method is particularly useful for, but not
3.1.3 four-terminal measuring technique, often referred to
limited to, electrical steels coated with inorganic insulating
as four-probe measuring technique—a common method to
coatings.
measure resistance when a high degree of accuracy is re-
1.3 The values and equations stated in customary (cgs-emu
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quired. In this standard, the circuit configuration for this
and inch-pound) or SI units are to be regarded separately as
technique is referred to as a four-probe configuration.Inthe
standard. Within this standard, SI units are shown in brackets.
two-surface tester, this configuration features two probes con-
Thevaluesstatedineachsystemmaynotbeexactequivalents;
nected to the top lamination test surface and two probes
therefore,eachsystemshallbeusedindependentlyoftheother.
connected to the bottom lamination test surface. One of the
Combining values from the two systems may result in noncon-
probesineachpaircarriesthemeasuringcurrent,andtheother
formance with this standard.
providesacontactforthevoltagemeasurement.Becauseofthe
1.4 This standard does not purport to address all of the
extremely high impedance of the measuring circuit, very little
safety concerns, if any, associated with its use. It is the
current flows through the voltage contacts, and thus very little
responsibility of the user of this standard to establish appro-
voltage is produced across the contacts to influence the true
priate safety and health practices and determine the applica-
reading,thatis,anyeffectfromcontactresistanceisavoidedor
bility of regulatory limitations prior to use.
reduced to a negligible amount. The two-surface tester has
provision to check the integrity of the contacts made between
2. Referenced Documents
the probes and the test surfaces.
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2.1 ASTM Standards:
3.1.4 interlaminar resistance—theaverageresistanceoftwo
A34/A34MPractice for Sampling and Procurement Testing
adjacent insulating surfaces in contact with each other, under
of Magnetic Materials
conditions specified in this standard.
A717/A717MTestMethodforSurfaceInsulationResistivity
3.1.5 surface insulation resistivity—a) the effective resistiv-
of Single-Strip Specimens
ity of a single insulating layer tested between applied bare
metal contacts and the base metal of the insulated test
specimen, as per Test Method A717/A717M; b) the resistance
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This test method is under the jurisdiction of ASTM Committee A06 on
of a unit area per test strip calculated from a measurement of
MagneticPropertiesandisthedirectresponsibilityofSubcommitteeA06.01onTest
the electrical resistance of a stack of strips as per Test Method
Methods.
A718.
Current edition approved Nov. 1, 2006. Published November 2006. Originally
approved in 1995. Last previous edition approved in 2001 as A937/A937M–01.
DOI: 10.1520/A0937_A0937M-06.
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For referenced ASTM standards, visit the ASTM website, www.astm.org, or Withdrawn. The last approved version of this historical standard is referenced
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM on www.astm.org.
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Standards volume information, refer to the standard’s Document Summary page on Harris,F.K., Electrical Measurements,RobertE.KriegerPublishingCompany,
the ASTM website. Huntington, New York, 1975, pp. 220–224.
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