1、Designation: A 937/A 937M 06Standard Test Method forDetermining Interlaminar Resistance of Insulating CoatingsUsing Two Adjacent Test Surfaces1This standard is issued under the fixed designationA 937/A 937M; the number immediately following the designation indicates the yearof original adoption or,
2、in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon (e) 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 elect
3、rically 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. Th
4、e interlaminar resistance is measured directly inunits of resistance (kV).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 rega
5、rded 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 Th
6、is 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 Documen
7、ts2.1 ASTM Standards:2A 34/A 34M Practice for Sampling and Procurement Test-ing of Magnetic MaterialsA 717/A 717M Test Method for Surface Insulation Resis-tivity of Single-Strip SpecimensA 718 Test Method for Surface Insulation Resistivity ofMulti-Strip Specimens33. Terminology3.1 Definitions of Ter
8、ms Specific to This Standard:3.1.1 bad contacta contact which results in a voltagedrop in 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
9、measuring technique, often referred toas four-probe measuring techniquea common method tomeasure resistance when a high degree of accuracy is re-quired.4In this standard, the circuit configuration for thistechnique is referred to as a four-probe configuration.Inthetwo-surface tester, this configurat
10、ion 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
11、 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 t
12、he integrity of the contacts made betweenthe probes and the test surfaces.3.1.4 interlaminar resistancethe average resistance oftwo adjacent insulating surfaces in contact with each other,under conditions specified in this standard.3.1.5 surface insulation resistivitya) the effective resistiv-ity of
13、 a single insulating layer tested between applied baremetal contacts and the base metal of the insulated testspecimen, as per Test Method A 717/A 717M; b) the resistanceof a unit area per test strip calculated from a measurement ofthe electrical resistance of a stack of strips as per Test MethodA 71
14、8.3.1.6 test specimentwo electrical steel laminations, eachhaving a minimum size of 25 3 25 cm 250 3 250 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. 1.1This
15、 test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of SubcommitteeA06.01 on TestMethods.Current edition approved Nov. 1, 2006. Published November 2006. Originallyapproved in 1995. Last previous edition approved in 2001 as A 937/A 937M
16、01.2For 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.3Withdrawn.4Harris, F. K., Electrical Measurements, Robert
17、 E. Krieger Publishing Company,Huntington, New York, 1975, pp. 220224.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.7 two-surface testerthe apparatus used in this testmethod.4. Summary of Test Method4.1 The test method measures
18、 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. For theinterlaminar resistance measurement, electrical contact is es-tablished between the test
19、 specimen and a constant directcurrent source using metallic contacts (drill bits). The testerutilizes two sets of metallic contacts which penetrate theexposed test surfaces into the base metal, to form a four-probeconfiguration, Fig. 1. A continuous electrical path is formedbetween the contacts and
20、 constant current source when themetallic contacts penetrate through the coating on the exposedtest surfaces to the underlying base metal, and the insulatingsurfaces are held in intimate contact by the test head. Whencurrent flows in the circuit, the dc voltage developed in thecircuit may be easily
21、measured by means of a digital voltmeter.A block diagram of the two-surface test system is illustrated inFig. 2.NOTE 1The current range settings for the two-surface tester are 1-Adc and 10-A dc, thus enabling the resistance to be read directly from thevoltmeter. The current select switch is designed
22、 to shift the decimal pointappropriately so as to provide a resistance reading in units of kV.5. Significance and Use5.1 This test method is particularly suitable for qualitycontrol in the application of insulating coatings. This testmethod measures the interlaminar resistance of insulatingcoatings,
23、 as defined in 3.1.4. Interlaminar resistance is themeasure of the insulating quality of the coating. Interlaminarresistance is reported in units of kV.5.2 The interlaminar resistance determined in accordancewith this test method is not the same quantity determined byTest Method A 717/A 717M or Test
24、 Method A 718.5.3 This test method is particularly useful for electricalsteels coated with inorganic insulating coatings having surfaceFIG. 1 Schematic Illustration of Four-Probe ConfigurationA 937/A 937M 062insulation resistivities in excess of 0.3 kVcm230 kVmm2when tested using Test Method A 717/A
25、 717M (a Franklincurrent less than 0.02 A). This test method can readily beextended to any range of insulation resistivity that the equip-ment comprising the two-surface tester allows. For the equip-ment specified herein, the maximum measurable resistance is1200 kV for the 10-A current setting and 1
26、2 000 kV for the1-A current setting; the maximum voltage for the test systemis 12 V.5.4 Repeat readings on the same set of two electrical steellaminations using different contact positions, as well as thetesting of multiple laminations from the same lot of electricalsteel, are recommended. Several r
27、eadings are suggested be-cause the coating thickness may vary across the surface of agiven electrical steel lamination. Additionally, the coatingthickness may vary across several laminations taken from thesame lot of electrical steel. Such variations in coating thicknessare likely to yield variation
28、s in the measured interlaminarresistance. The required number of readings depends on thenature of the coating and the accuracy required.6. Apparatus6.1 The two-surface tester measures the resistance betweentwo laminations that are in intimate contact with one another asshown in Fig. 1. The two-surfa
29、ce tester shall consist of twopressure pads, each of which is mounted to one of the heads ofa hydraulic or pneumatic press. The diameter of each pressurepad is 3.57 cm 35.7 mm, giving a nominal area of 10 cm21000 mm2. The diameter of the pressure head is 11.50 cm115 mm. Each pressure head circumscri
30、bes two metalliccontacts (drill bits) which are used to make contact with the testspecimen. A schematic diagram of the pressure head, pads andmetallic contacts is shown in Fig. 3. Commercially availablerollnut actuators, which convert rotary to linear motion, can beused to house and rotate the drill
31、 bit through the coating on theexposed surfaces of the test specimen, Fig. 4.6.1.1 The associated measuring equipment, which may beremotely located, includes an electronic voltmeter with adigital readout, a source of constant current, a contact checkunit, a calibration module and a display unit. A b
32、lock diagramFIG. 2 Block Diagram of Two-Surface Test SystemA 937/A 937M 063of the electronic system for the two-surface tester is shown inFig. 2. A computer compatible interface, although not manda-tory, is recommended for data collection and analysis. Thisfunction is a standard feature on many comm
33、ercial electronicvoltmeters.6.1.1.1 The two-surface tester measures the interlaminarresistance as follows: The constant current source of the testerforces a constant current through the insulation. The voltagewhich results is measured by a suitable voltmeter. The resis-tance of the insulation is the
34、n determined by Ohms law. Theresults are communicated to the operator via a display.6.1.2 Constant Direct Current SourceThe use of a sourcewhich supplies constant measuring current, independent ofsurface resistance, is recommended. The use of a properlyadjusted dc constant current source enables res
35、istance to beread directly in units of resistance (kV).6.1.2.1 In the two-surface tester, constant direct current issupplied using a feedback circuit incorporating a high gainoperational amplifier. Current is set by means of an adjustableresistor. Once set, the current is held constant by means of t
36、hefeedback control circuit. The test system is configured suchthat an indicator light will turn on if the current goes out ofregulation.6.1.2.2 Furthermore, the test system described herein isequipped with two constant current range settings, 10 and1 A. For interlaminar resistance values less than 1
37、200 kV, the10-A range is suitable. For interlaminar resistance valuesgreater than 1200 kV, the 1-A range is recommended tooptimize the accuracy of the measurement. This system isequipped with an indicator light that warns the operator if thecurrent range is not appropriate for a given specimen (beca
38、usethe current goes out of regulation).6.1.2.3 Because the current source setting is an exactmultiple of ten, the resistance of the test specimen is numeri-cally equal to the voltage reading to within a multiple of ten.Therefore, the resistance, in kV, may be directly read on thevoltmeter. The decim
39、al point is properly positioned by thecurrent range select switch.FIG. 3 Diagram of Pressure Head AssemblyA 937/A 937M 0646.1.3 Contact Check UnitThe contact check unit serves toverify the integrity of the contacts and to ensure that badcontacts do not interfere with the coating resistance measure-m
40、ent. The contact resistance is measured using the four-probeconfiguration shown in Fig. 1. Note that there are two currentprobes and two voltage probes. The contact resistance ismeasured at the start of a test by temporarily connecting thevoltage contacts together with a switch. This causes current
41、tobe diverted as shown in Fig. 5. The contacts are consideredacceptable if the voltage across either pair of probes is less than5 % of the product of the maximum measurable resistance forthe selected current and the selected current, that is, anassociated voltage drop of 0.6 V for either current ran
42、ge.(Specifically, V = i 3 R. For a current setting of 1 A and amaximum measurable resistance of 12 000 kV; 0.05 3 (1A 3 12 000 kV) = 0.6 V. Similarly, 0.05 3 (10 A 3 1200kV) = 0.6 V.) If either contact shows a voltage drop in excessof 0.6 V, a bad contact indicator light is lit and the measure-ment
43、of interlaminar resistance is inhibited. The penetrationsmay be reestablished until satisfactory results are obtained. Ifthe measurable voltage drop is less than 0.6 V, subsequentinterlaminar resistance measurement is enabled.6.1.3.1 Once suitable contact resistance values are obtained,the switch co
44、nnecting the voltage contacts is opened, andcurrent is redirected to flow through the insulation instead ofthe switch, Fig. 6. The interlaminar resistance can then bemeasured.6.1.4 Calibration ModuleThe calibration module is pro-vided to allow precise calibration of the two-surface tester. Themodule
45、 is simply a set of precision resistors, and some variableresistors which may be connected to the two-surface tester bymeans of cables. The calibration module substitutes preciselyknown values of resistance for the insulation under test. It alsosubstitutes a variable contact resistance for each of t
46、he upperand lower contacts, allowing the operation of the contactFIG. 4 Schematic Diagram of Metallic Contact/Rollnut Actuator AssemblyNOTEWhen the switch of the Contact Check Unit (Item CFig. 2)isin the “closed” position, the voltage contacts are temporarily connected.The voltage drop across contac
47、ts between 1 and 3, and between 2 and 4is evaluated. A “bad contact” indicator light is triggered if this voltagedrop is in excess of 0.6 V. The measurement of the coatings interlaminarresistance is inhibited under “bad contact” conditions.FIG. 5 Current Path During the Contact Check ProcessA 937/A
48、937M 065resistance system to be independently verified. By selecting theappropriate jumper, a precision resistor is substituted for theinsulation. The meter reading should correctly read the valueselected by the jumper (provided that it is within the range ofmeasurable resistances for the given curr
49、ent setting).7. Sampling7.1 Specimens shall be representative of the coated electri-cal steel in the final condition to be used in the application.Specimens shall be prepared in an appropriate manner whichassures representative sampling as described in Practice A 34/A 34M.8. Test Specimen8.1 A test specimen consists of two laminations in intimatecontact. For measuring interlaminar resistance as defined in3.1.4, each lamination should have a minimum size of25 3 25 cm 250 3 250 mm; each having an electricallyinsulating coating on both sides
