1、Designation: A976 18Standard 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 oforiginal adoption or, in
2、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 electri-cal steels according to the
3、ir composition, relative insulatingability, and functionality. The purpose of this classification is toassist users of insulating coatings by providing general infor-mation about the chemical nature and use of the coatings, aswell as to provide important data concerning limits to their use,that is,
4、relative insulating ability, punchability, temperaturestability, weldability, and fabricability. Specific surface insula-tion resistivity values for each coating are not included in thisclassification. The user is referred to the flat-rolled electricalsteel specifications noted in 1.2 should more de
5、tailed informa-tion concerning surface insulation resistivity values be re-quired.1.2 This classification is to be used in conjunction with thevarious specifications for flat-rolled electrical steels under thejurisdiction of Committee A06, including Specifications A345,A677, A683, A726, A840, A876,
6、and A1086. However, inthose instances in which the coating descriptions and charac-teristics differ between this classification and any of thespecifications, this classification shall supersede the specifica-tion.1.3 The values stated in SI units are to be regarded asstandard. The values given in pa
7、rentheses are mathematicalconversions to customary (cgs-emu and inch-pound) unitswhich are provided for information only and are not consideredstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of thi
8、s standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Deci
9、sion on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2A340 Terminology of Symbols and Definitions Relating toMagnetic TestingA345 Speci
10、fication for Flat-Rolled Electrical Steels forMagnetic ApplicationsA677 Specification for Nonoriented Electrical Steel FullyProcessed TypesA683 Specification for Nonoriented Electrical Steel, Semi-processed TypesA717/A717M Test Method for Surface Insulation Resistivityof Single-Strip SpecimensA726 S
11、pecification for Cold-Rolled Magnetic LaminationQuality Steel, Semiprocessed TypesA840 Specification for Fully Processed Magnetic Lamina-tion Steel (Withdrawn 2011)3A876 Specification for Flat-Rolled, Grain-Oriented, Silicon-Iron, Electrical Steel, Fully Processed TypesA937/A937M Test Method for Det
12、ermining InterlaminarResistance of Insulating Coatings Using Two AdjacentTest SurfacesA1086 Specification for Thin-Gauge Nonoriented ElectricalSteel Fully Processed Types3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 interlaminar resistance, nthe average resistance oftwo adja
13、cent insulating surfaces in contact with each other, inaccordance with Test Method A937/A937M.3.1.2 stress-relief anneal, nheat treatment that improvesthe magnetic properties of electrical steel by relieving internalstresses which are introduced during fabrication of magneticcores.1This classificati
14、on is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Subcommittee A06.02 onMaterial Specifications.Current edition approved Oct. 1, 2018. Published October 2018. Originallypublished in 1997. Last previous edition approved in 2013 as A976 13. DO
15、I:10.1520/A0976-18.2For 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.3The last approved version of this histori
16、cal standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision
17、 on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.1.3 surface insulation resistivity, nthe effective resistiv-ity of a single insulating layer tested between applied baremetal
18、 contacts and the base metal of the insulated testspecimen, in accordance with Test Method A717/A717M.3.2 Definitions for other terms and symbols used in thisspecification are defined in Terminology A340.4. Significance and Use4.1 This classification establishes categories of insulatingcoatings base
19、d on their chemical nature, relative insulatingability, and typical applications. These categories describegeneral physical and chemical characteristics of the coatingsthat are useful in making broad estimates of their insulatingability and suitability for various applications.5. Basis of Classifica
20、tion5.1 The insulating coatings are categorized according togeneral composition, relative insulating ability, and function-ality (Table 1). The purpose of this classification is to create anomenclature for the various coating types. It is not the intentof this classification to specify coating requi
21、rements. Specificproperties required by coating users should be negotiated withthe steel producer.5.2 To reduce confusion regarding the various categories ofcoatings, this classification follows the “C” type of designationinitially used by the American Iron and Steel Institute fordescribing insulati
22、ng coatings.4The “C” is included in thecoating designation because insulating coatings for electricalsteels have been historically referred to as “coreplate” coatings.This classification includes new coatings and test methods notincluded in the most recent edition of the AISI classification.Note tha
23、t the electrical steel committee of theAISI is no longeractive, and the 1983 edition of the coating classificationdocument was the last edition of the coating classification to bepublished.56. Test Methods6.1 The surface insulation resistivity of an insulating layermay be measured using Test Methods
24、 A717/A717M. In thistest method, ten metallic contacts of fixed area are applied toone of the surfaces of the test specimen, and electrical contactis made with the base metal by two drills (Fig. 1 and Fig. 2).The effectiveness of the coating (surface insulation) then isindicated by a measurement of
25、the average electrical currentflowing between the contacts and the base metal under speci-fied applied voltage. This current value often is referred to asthe “Franklin Current” and may be used directly as an indicatorof the quality of the insulation. Specifically, a Franklin Currentof zero correspon
26、ds to a perfect insulator.AFranklin Current of1 ampere corresponds to a perfect conductor. If desired, anapparent surface insulation resistivity value for the insulatinglayer may be calculated as follows:Ri5 6.45 $1/I! 2 1% in cm2/lamination (1)orRi5 645 $1/I! 2 1% in mm2/lamination (2)where:Ri= sur
27、face insulation resistivity of test sample (two sur-faces in series) in cm2/lamination or mm2/lamination andI = ammeter reading inA(also known as Franklin Current).Note that this test method often is referred to as the Franklintest. The Franklin test is a widely used method for evaluatingthe effecti
28、veness of surface insulation on electrical steels.6.2 The average resistance of two adjacent insulating sur-faces in contact with each other, interlaminar resistance, maybe measured using Test Method A937/A937M. Because theinterlaminar resistance is influenced by coating-to-coatingcontact, this test
29、 method is particularly useful for providing anestimate of the interlaminar resistance in a stacked or woundcore in which coated surfaces are in contact with each other.Furthermore, this test method is particularly useful for electri-cal steels coated with insulating coatings having surfaceinsulatio
30、n resistivities in excess of 300 cm2,or30kmm2,(that is, less than 0.02 A when measured according to TestMethod A717/A717M). In this Two-Surface test method,intimate physical contact of these surfaces is achieved bymeans of test heads that force a defined surface area intocontact under a specified pr
31、essure. For the interlaminar resis-tance measurement, electrical contact is established betweenthe test specimen and a constant direct current source usingmetallic contacts. The tester uses two sets of metallic contacts,which penetrate the exposed test surfaces into the base metal,to form a fourprob
32、e configuration (Fig. 3). A continuouselectrical path is formed between the contacts and the constantcurrent source when the metallic contacts penetrate through thecoating on the exposed test surfaces to the underlying basemetal. When current flows in the circuit, the dc voltagedeveloped in the circ
33、uit is measured with a voltmeter. Theresistance of the insulation is then determined by Ohms law.7. Keywords7.1 coatings; coreplate; Franklin test; insulation; insulatingcoatings; interlaminar resistance; steels; surface insulationresistivity; TwoSurface test; varnishes4Steel Products Manual on Flat
34、Rolled Electrical Steel, American Iron andSteel Institute, 1101 17th St., N.W., Washington, DC 200364700, January 1983.5Loudermilk, D. S. and Murphy, R. A., “Overview of Technology of InsulatingCoatings for GrainOriented and Nonoriented Electrical Steels,” Fifteenth AnnualConference on Properties an
35、d Applications of Magnetic Materials, Illinois Instituteof Technology, Chicago, IL, May 1996.A976 182TABLE 1 Classification of Insulating Coatings for Electrical SteelsCoatingNameACoating Description/CharacteristicsC-0 Oxide that is formed naturally on the steel surface during mill processing. This
36、oxide layer is thin, tightly adherent, and provides 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
37、 may be enhanced by controlling the atmosphere to 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
38、 of the heat-treating cycle. This coatingusually is 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 an
39、d used on grain-oriented electrical steel. The coating 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 coa
40、ting is very abrasive, and hence, is not typically 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 acc
41、eptable Franklin test current for this coating.C-3 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 r
42、equired Franklin test current is subject to agreement 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 i
43、s suitable for operating temperatures up to about 180C (350F).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
44、 will withstand normal stress-relief annealing temperatures, 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-A Thin film of C-4-type coating use
45、d primarily for preventing 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 coa
46、ting was known as C-4-AS 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 inorga
47、nic components have been 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 s
48、teels, nonoriented electrical 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
49、 coatings are used for applications 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 840C (1550F) 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 320-540C (600-1000F) us
