ASTM A937/A937M-12

5.1 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.

5.2 The interlaminar resistance determined in accordance with this test method is not the same quantity determined by Test Method A717/A717M.

5.3 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 A717/A717M (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.

5.4 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.

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 (kΩ).

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.

1.4 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.