1、Designation: A937/A937M 06 A937/A937M 12Standard 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 ad
2、option 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 interlaminar resistance
3、 of electrically insulating coatings as applied toadjacent laminations of flat-rolled electrical steel, under predetermined conditions of voltage, pressure and temperature. It indicatesthe effectiveness of surface coatings on electrical sheet steels for limiting interlaminar losses in electrical mac
4、hinery. Theinterlaminar 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 ar
5、e 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 innonconformance with this sta
6、ndard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenc
7、ed Documents2.1 ASTM Standards:2A34/A34M Practice for Sampling and Procurement Testing of Magnetic MaterialsA717/A717M Test Method for Surface Insulation Resistivity of Single-Strip SpecimensA718 Test Method for Surface Insulation Resistivity of Multi-Strip Specimens33. Terminology3.1 Definitions of
8、 Terms Specific to This Standard:3.1.1 bad contacta contact which results in a voltage drop in excess of 0.6 V as described in 6.1.3.3.1.2 exposed test surfacethe insulating top surface of the top lamination or the insulating bottom surface of the bottomlamination of the test specimen.3.1.3 four-ter
9、minal measuring technique, often referred to as four-probe measuring techniquea common method to measureresistance when a high degree of accuracy is required.3 In this standard, the circuit configuration for this technique is referred toas a four-probe configuration. In the two-surface tester, this
10、configuration features two probes connected to the top lamination testsurface and two probes connected to the bottom lamination test surface. One of the probes in each pair carries the measuringcurrent, and the other provides a contact for the voltage measurement. Because of the extremely high imped
11、ance of the measuringcircuit, very little current flows through the voltage contacts, and thus very little voltage is produced across the contacts to influencethe true reading, that is, any effect from contact resistance is avoided or reduced to a negligible amount. The two-surface testerhas provisi
12、on to check the integrity of the contacts made between the probes and the test surfaces.3.1.4 interlaminar resistancethe average resistance of two adjacent insulating surfaces in contact with each other, underconditions specified in this standard.1 This test method is under the jurisdiction of ASTM
13、Committee A06 on Magnetic Properties and is the direct responsibility of Subcommittee A06.01 on Test Methods.Current edition approved Nov. 1, 2006Nov. 1, 2012. Published November 2006 December 2012. Originally approved in 1995. Last previous edition approved in 20012006as A937/A937M 01.A937/A937M06.
14、 DOI: 10.1520/A0937_A0937M-06. 10.1520/A0937_A0937M-12.2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 H
15、arris, F. K., Electrical Measurements, Robert E. Krieger Publishing Company, Huntington, New York, 1975, pp. 220224.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may n
16、ot be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor
17、Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.5 surface insulation resistivitya) the effective resistivity of a single insulating layer tested between applied bare metalcontacts and the base metal of the insulated test specimen, as per Test Method A717/A717M; b) the resista
18、nce of a unit area pertest strip calculated from a measurement of the electrical resistance of a stack of strips as per Test Method A718.3.1.6 test specimentwo electrical steel laminations, each having a minimum size of 25 25 cm 250 250 mm and eachhaving an electrically insulating coating on both si
19、des. The two electrical steel laminations are placed one on top of the other forthe interlaminar resistance measurement, Fig. 1.3.1.7 two-surface testerthe apparatus used in this test method.4. Summary of Test Method4.1 The test method measures the average resistance of two adjacent insulating surfa
20、ces. Intimate physical contact of thesesurfaces is achieved via test heads which force a defined surface area into contact under a specified pressure. For the interlaminarresistance measurement, electrical contact is established between the test specimen and a constant direct current source usingmet
21、allic contacts (drill bits). The tester utilizes two sets of metallic contacts which penetrate the exposed test surfaces into the basemetal, to form a four-probe configuration, Fig. 1. A continuous electrical path is formed between the contacts and constant currentsource when the metallic contacts p
22、enetrate through the coating on the exposed test surfaces to the underlying base metal, and theinsulating surfaces are held in intimate contact by the test head. When current flows in the circuit, the dc voltage developed in thecircuit may be easily measured by means of a digital voltmeter. A block
23、diagram of the two-surface test system is illustrated inFig. 2.NOTE 1The current range settings for the two-surface tester are 1-A dc and 10-A dc, thus enabling the resistance to be read directly from thevoltmeter. The current select switch is designed to shift the decimal point appropriately so as
24、to provide a resistance reading in units of k.FIG. 1 Schematic Illustration of Four-Probe ConfigurationA937/A937M 1225. Significance and Use5.1 This test method is particularly suitable for quality control in the application of insulating coatings. This test methodmeasures the interlaminar resistanc
25、e of insulating coatings, as defined in 3.1.4. Interlaminar resistance is the measure of theinsulating quality of the coating. Interlaminar resistance is reported in units of k.5.2 The interlaminar resistance determined in accordance with this test method is not the same quantity determined by TestM
26、ethod A717/A717M or Test Method A718.5.3 This test method is particularly useful for electrical steels coated with inorganic insulating coatings having surface insulationresistivities in excess of 0.3 kcm2 30 kmm2 when tested using Test Method A717/A717M (a Franklin current less than 0.02A). This te
27、st method can readily be extended to any range of insulation resistivity that the equipment comprising the two-surfacetester allows. For the equipment specified herein, the maximum measurable resistance is 1200 k for the 10-A current settingand 12 000 k for the 1-A current setting; the maximum volta
28、ge 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 testingof multiple laminations from the same lot of electrical steel, are recommended. Several readings are suggested because the coatingthickness
29、may vary across the surface of a given electrical steel lamination. Additionally, the coating thickness may vary acrossseveral laminations taken from the same lot of electrical steel. Such variations in coating thickness are likely to yield variationsin the measured interlaminar resistance. The requ
30、ired number of readings depends on the nature of the coating and the accuracyrequired.6. Apparatus6.1 The two-surface tester measures the resistance between two laminations that are in intimate contact with one another asshown in Fig. 1. The two-surface tester shall consist of two pressure pads, eac
31、h of which is mounted to one of the heads of aFIG. 2 Block Diagram of Two-Surface Test SystemA937/A937M 123hydraulic or pneumatic press. The diameter of each pressure pad is 3.57 cm 35.7 mm, giving a nominal area of 10 cm2 1000mm2. The diameter of the pressure head is 11.50 cm 115 mm. Each pressure
32、head circumscribes two metallic contacts (drill bits)which are used to make contact with the test specimen. A schematic diagram of the pressure head, pads and metallic contacts isshown in Fig. 3. Commercially available rollnut actuators, which convert rotary to linear motion, can be used to house an
33、d rotatethe drill bit through the coating on the exposed surfaces of the test specimen, Fig. 4.6.1.1 The associated measuring equipment, which may be remotely located, includes an electronic voltmeter with a digitalreadout, a source of constant current, a contact check unit, a calibration module and
34、 a display unit. A block diagram of theelectronic system for the two-surface tester is shown in Fig. 2. A computer compatible interface, although not mandatory, isrecommended for data collection and analysis. This function is a standard feature on many commercial electronic voltmeters.6.1.1.1 The tw
35、o-surface tester measures the interlaminar resistance as follows: The constant current source of the tester forcesa constant current through the insulation. The voltage which results is measured by a suitable voltmeter. The resistance of theinsulation is then determined by Ohms law. The results are
36、communicated to the operator via a display.6.1.2 Constant Direct Current SourceThe use of a source which supplies constant measuring current, independent of surfaceresistance, is recommended. The use of a properly adjusted dc constant current source enables resistance to be read directly in unitsof
37、resistance (k).6.1.2.1 In the two-surface tester, constant direct current is supplied using a feedback circuit incorporating a high gain operationalamplifier. Current is set by means of an adjustable resistor. Once set, the current is held constant by means of the feedback controlcircuit. The test s
38、ystem is configured such that an indicator light will turn on if the current goes out of regulation.6.1.2.2 Furthermore, the test system described herein is equipped with two constant current range settings, 10 and 1 A. Forinterlaminar resistance values less than 1200 k, the 10-A range is suitable.
39、For interlaminar resistance values greater than 1200k, the 1-A range is recommended to optimize the accuracy of the measurement. This system is equipped with an indicator lightthat warns the operator if the current range is not appropriate for a given specimen (because the current goes out of regula
40、tion).FIG. 3 Diagram of Pressure Head AssemblyA937/A937M 1246.1.2.3 Because the current source setting is an exact multiple of ten, the resistance of the test specimen is numerically equalto the voltage reading to within a multiple of ten. Therefore, the resistance, in k, may be directly read on the
41、 voltmeter. Thedecimal point is properly positioned by the current range select switch.6.1.3 Contact Check UnitThe contact check unit serves to verify the integrity of the contacts and to ensure that bad contactsdo not interfere with the coating resistance measurement. The contact resistance is meas
42、ured using the four-probe configurationshown in Fig. 1. Note that there are two current probes and two voltage probes. The contact resistance is measured at the start ofa test by temporarily connecting the voltage contacts together with a switch. This causes current to be diverted as shown in Fig.5.
43、 The contacts are considered acceptable if the voltage across either pair of probes is less than 5 % of the product of the maximummeasurable resistance for the selected current and the selected current, that is, an associated voltage drop of 0.6 V for either currentrange. (Specifically, V = i R. For
44、 a current setting of 1 A and a maximum measurable resistance of 12 000 k; 0.05 (1A 12 000 k) = 0.6 V. Similarly, 0.05 (10 A 1200 k) = 0.6 V.) If either contact shows a voltage drop in excess of 0.6 V,FIG. 4 Schematic Diagram of Metallic Contact/Rollnut Actuator AssemblyNOTE 1When the switch of the
45、Contact Check Unit (Item CFig. 2) is in the “closed” position, the voltage contacts are temporarily connected. Thevoltage drop across contacts between 1 and 3, and between 2 and 4 is evaluated. A “bad contact” indicator light is triggered if this voltage drop is in excessof 0.6 V. The measurement of
46、 the coatings interlaminar resistance is inhibited under “bad contact” conditions.FIG. 5 Current Path During the Contact Check ProcessA937/A937M 125a bad contact indicator light is lit and the measurement of interlaminar resistance is inhibited. The penetrations may bereestablished until satisfactor
47、y results are obtained. If the measurable voltage drop is less than 0.6 V, subsequent interlaminarresistance measurement is enabled.6.1.3.1 Once suitable contact resistance values are obtained, the switch connecting the voltage contacts is opened, and currentis redirected to flow through the insulat
48、ion instead of the switch, Fig. 6. The interlaminar resistance can then be measured.6.1.4 Calibration ModuleThe calibration module is provided to allow precise calibration of the two-surface tester. The moduleis simply a set of precision resistors, and some variable resistors which may be connected
49、to the two-surface tester by means ofcables. The calibration module substitutes precisely known values of resistance for the insulation under test. It also substitutes avariable contact resistance for each of the upper and lower contacts, allowing the operation of the contact resistance system to beindependently verified. By selecting the appropriate jumper, a precision resistor is substituted for the insulation. The meter readingshould correctly read the value selected by the jumper (provided that it is with
