1、Designation: A976 03 (Reapproved 2008)A976 13Standard Classification ofInsulating Coatings for Electrical Steels by Composition,Relative Insulating Ability and Application1This standard is issued under the fixed designation A976; the number immediately following the designation indicates the year of
2、original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This document classifies insulating coatings for electrical
3、 steels according to their composition, relative insulating ability,and functionality. The purpose of this classification is to assist users of insulating coatings by providing general information aboutthe chemical nature and use of the coatings, as well as to provide important data concerning limit
4、s to their use, that is, relativeinsulating ability, punchability, temperature stability, weldability, and fabricability. Specific surface insulation resistivity values foreach coating are not included in this classification. The user is referred to the flat-rolled electrical steel specifications no
5、ted in 1.2should more detailed information concerning surface insulation resistivity values be required.1.2 This classification is to be used in conjunction with the various specifications for flat-rolled electrical steels under thejurisdiction of Committee A06, including Specifications A345, A677,
6、A683, A726, A840, and A876. However, in those instancesin which the coating descriptions and characteristics differ between this classification and any of the specifications, thisclassification shall supersede the specification.1.3 The values stated in customary (cgs-emu and inch-pound) units are to
7、 be regarded as standard. The values given inparentheses are mathematical conversions to SI units which are provided for information only and are not considered standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilit
8、yof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A340 Terminology of Symbols and Definitions Relating to Magnetic TestingA345 Specification for Flat-Roll
9、ed Electrical Steels for Magnetic ApplicationsA677 Specification for Nonoriented Electrical Steel Fully Processed TypesA683 Specification for Nonoriented Electrical Steel, Semiprocessed TypesA717/A717M Test Method for Surface Insulation Resistivity of Single-Strip SpecimensA726 Specification for Col
10、d-Rolled Magnetic Lamination Quality Steel, Semiprocessed TypesA840 Specification for Fully Processed Magnetic Lamination Steel (Withdrawn 2011)3A876 Specification for Flat-Rolled, Grain-Oriented, Silicon-Iron, Electrical Steel, Fully Processed TypesA937/A937M Test Method for Determining Interlamina
11、r Resistance of Insulating Coatings Using Two Adjacent Test Surfaces3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 interlaminar resistance, nthe average resistance of two adjacent insulating surfaces in contact with each other, inaccordance with Test Method A937/A937M.3.1.2 s
12、tress-relief anneal, nheat treatment that improves the magnetic properties of electrical steel by relieving internalstresses which are introduced during fabrication of magnetic cores.1 This classification is under the jurisdiction of ASTM CommitteeA06 on Magnetic Properties and is the direct respons
13、ibility of SubcommitteeA06.02 on MaterialSpecifications.Current edition approved Nov. 1, 2008Nov. 1, 2013. Published December 2008November 2013. Originally published in 1997. Last previous edition approved in 20032008as A976 03.A976 03 (2008). DOI: 10.1520/A0976-03R08.10.1520/A0976-13.2 For referenc
14、edASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. ForAnnual Book ofASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved version of this historical standard is referenced on www.
15、astm.org.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 not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult
16、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 Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.3 surface insulation resistivity, n
17、 the effective resistivity of a single insulating layer tested between applied bare metalcontacts and the base metal of the insulated test specimen, in accordance with Test Method A717/A717M.3.2 Definitions for other terms and symbols used in this specification are defined in Terminology A340.4. Sig
18、nificance and Use4.1 This classification establishes categories of insulating coatings based on their chemical nature, relative insulating ability, andtypical applications. These categories describe general physical and chemical characteristics of the coatings that are useful inmaking broad estimate
19、s of their insulating ability and suitability for various applications.5. Basis of Classification5.1 The insulating coatings are categorized according to general composition, relative insulating ability, and functionality(Table 1). The purpose of this classification is to create a nomenclature for t
20、he various coating types. It is not the intent of thisclassification to specify coating requirements. Specific properties required by coating users should be negotiated with the steelproducer.5.2 To reduce confusion regarding the various categories of coatings, this classification follows the “C” ty
21、pe of designationinitially used by the American Iron and Steel Institute for describing insulating coatings.4 The “C” is included in the coatingdesignation because insulating coatings for electrical steels have been historically referred to as “coreplate” coatings. Thisclassification includes new co
22、atings and test methods not included in the most recent edition of the AISI classification. Note thatthe electrical steel committee of the AISI is no longer active, and the 1983 edition of the coating classification document was thelast edition of the coating classification to be published.56. Test
23、Methods6.1 The surface insulation resistivity of an insulating layer may be measured using Test Methods A717/A717M. In this testmethod, ten metallic contacts of fixed area are applied to one of the surfaces of the test specimen, and electrical contact is madewith the base metal by two drills (Fig. 1
24、 and Fig. 2). The effectiveness of the coating (surface insulation) then is indicated by ameasurement of the average electrical current flowing between the contacts and the base metal under specified applied voltage.This current value often is referred to as the “Franklin Current” and may be used di
25、rectly as an indicator of the quality of theinsulation. Specifically, a Franklin Current of zero corresponds to a perfect insulator. A Franklin Current of 1 ampere correspondsto a perfect conductor. If desired, an apparent surface insulation resistivity value for the insulating layer may be calculat
26、ed asfollows:Ri 56.45 $1/I! 2 1% incm2/lamination (1)orRi 5645 $1/I! 2 1% inmm2/lamination (2)where:Ri = surface insulation resistivity of test sample (two surfaces in series) in cm2/lamination or mm2/lamination andI = ammeter reading in A (also known as Franklin Current).Note that this test method
27、often is referred to as the Franklin test. The Franklin test is a widely used method for evaluating theeffectiveness of surface insulation on electrical steels.6.2 The average resistance of two adjacent insulating surfaces in contact with each other, interlaminar resistance, may bemeasured using Tes
28、t Method A937/A937M. Because the interlaminar resistance is influenced by coating-to-coating contact, thistest method is particularly useful for providing an estimate of the interlaminar resistance in a stacked or wound core in whichcoated surfaces are in contact with each other. Furthermore, this t
29、est method is particularly useful for electrical steels coated withinsulating coatings having surface insulation resistivities in excess of 300 cm2 (30 kmm2) (that is, less than 0.02 A whenmeasured according to Test Method A717/A717M). In this Two-Surface test method, intimate physical contact of th
30、ese surfacesis achieved by means of test heads that 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 usingmetallic contacts. The tester us
31、es two sets of metallic contacts, which penetrate the exposed test surfaces into the base metal, toform a fourprobe configuration (Fig. 3). A continuous electrical path is formed between the contacts and the constant currentsource when the metallic contacts penetrate through the coating on the expos
32、ed test surfaces to the underlying base metal. Whencurrent flows in the circuit, the dc voltage developed in the circuit is measured with a voltmeter. The resistance of the insulationis then determined by Ohms law.4 Steel Products Manual on FlatRolled Electrical Steel, American Iron and Steel Instit
33、ute, 1101 17th St., N.W., Washington, DC 200364700, January 1983.5 Loudermilk, D. S. and Murphy, R. A., “Overview of Technology of Insulating Coatings for GrainOriented and Nonoriented Electrical Steels,” Fifteenth AnnualConference on Properties and Applications of Magnetic Materials, Illinois Insti
34、tute of Technology, Chicago, IL, May 1996.A976 132TABLE 1 Classification of Insulating Coatings for Electrical SteelsCoatingNameA Coating Description/CharacteristicsC-0 Oxide that is formed naturally on the steel surface during mill processing. This oxide layer is thin, tightly adherent, and provide
35、s sufficient insulating qualityfor most small cores. The oxide layer will withstand normal stress-relief annealing temperatures. The insulation quality is affected by the oxidizingpotential of the users anneal, that is, the oxidized surface condition may be enhanced by controlling the atmosphere to
36、be more or less oxidizing to thesurface. It is not appropriate to assert a maximum acceptable Franklin test current for this coating.C-1 User-formed oxide that is created on the steel surface by contact with an oxidizing furnace atmosphere at the end of the heat-treating cycle. This coatingusually i
37、s bluish to gray in color and used for various electrical steel applications. It is not appropriate to assert a maximum acceptable Franklintest current for this coating.C-2 Inorganic insulating coating predominantly comprised of magnesium silicate and used on grain-oriented electrical steel. The coa
38、ting is formed from thereaction of the annealing separator with the steel surface during high-temperature annealing. The resulting coating often is referred to as “mill glass”or “glass film”even though the coating is not technically a glass. The coating is very abrasive, and hence, is not typically
39、used for stamped laminations.The primary application of this coating is air-cooled or oil-immersed wound distribution transformers. This coating will withstand normalstress-relief annealing temperatures. It is not appropriate to assert a maximum acceptable Franklin test current for this coating.C-3
40、Organic varnish/enamel coating that is applied to the steel surface and cured by heating. Used for fully processed nonoriented and other electrical steels. Itis appropriate to designate a maximum Franklin test current for this type of coating. The required Franklin test current is subject to agreeme
41、nt betweenthe producer and user. This coating generally improves the punchability of the steel, and hence, is quite suitable for stamped laminations. This coatingwill not withstand typical stress-relief annealing temperatures. The coating normally is suitable for operating temperatures up to about 3
42、50F (180C).C-4 Coating formed by chemical treating or phosphating of the steel surface followed by an elevated temperature curing treatment. This type of coating is usedin applications requiring moderate levels of insulation resistance. This coating will withstand normal stress-relief annealing temp
43、eratures, but somereduction of surface insulation resistivity may occur during the anneal. It is appropriate to specify a maximum acceptable Franklin test current with a valueagreed to by the producer and user.C-4-AS Thin film of C-4-type coating used primarily for preventing sticking of semiprocess
44、ed nonoriented electrical steel or cold-rolled motor lamination steel duringquality anneals. This coating often is referred to as “anti-stick.” It is not appropriate to specify a maximum acceptable Franklin test currentfor this coating.C-4-A Thin film of C-4-type coating used primarily for preventin
45、g sticking of semiprocessed nonoriented electrical steel or cold-rolled motor lamination steel duringquality anneals. This coating often is referred to as “anti-stick.” It is not appropriate to specify a maximum acceptable Franklin test currentfor this coating.Note: This coating was known as C-4-AS
46、in previous versions of this classification. Existing references to C-4-AS in manufacturing, procurement, and otherdocuments may be directly substituted by coating C-4-A.C-5 Inorganic or mostly inorganic coating similar to C-4, to which ceramic fillers or film-forming inorganic components have been
47、added to increase theinsulating ability of the coating. The coating typically is a phosphate, chromate, or silicate coating, or combination thereof. Such coatings are appliedto the steel surface and cured by heating. The coatings can be applied to grain-oriented electrical steels, nonoriented electr
48、ical steels, and cold-rolled motor lamination steels. A C-5 coating may be applied over top of a C-2 coating for applications in which extra surface insulation is required, forexample, sheared laminations of grain-oriented electrical steel for cores of power transformers.C-5 coatings are used for ap
49、plications requiring a high-surface resistivity. It is appropriate to designate a maximum Franklin test current for this type ofcoating before stress-relief annealing. The required Franklin test current is subject to agreement between the producer and user. The coating willwithstand stress-relief annealing up to 1550F (840C) in neutral or slightly reducing furnace atmospheres, but some reduction in surface insulationresistivity may occur during the anneal. The coating will withstand burn-off treatments at 600-1000F (320-540C) used to remove statorwin
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