1、Designation: A 976 03Standard Classification ofInsulating Coatings for Electrical Steels by Composition,Relative Insulating Ability and Application1This standard is issued under the fixed designation A 976; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This document classifies insulating coatings for electri-cal steels according to
3、their 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 i
4、s, 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
5、 detailed 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 A 345,A 677, A 683, A 726, A 840
6、, and A 876. However, in thoseinstances in which the coating descriptions and characteristicsdiffer between this classification and any of the specifications,this classification shall supersede the specification.1.3 The values stated in customary (cgs-emu and inch-pound) units are to be regarded as
7、standard. The values givenin parentheses are mathematical conversions to SI units whichare 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 and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 345 Specification for Flat-Rolled Electrical Steels forMagnetic ApplicationsA 677 Specification for Nonoriented Electr
9、ical Steel FullyProcessed TypesA 683 Specification for Nonoriented Electrical Steel, Semi-processed TypesA 717/A 717M Test Method for Surface Insulation Resis-tivity of Single Strip SpecimensA 726 Specification for Cold Rolled Magnetic LaminationQuality Steel, Semiprocessed TypesA 840 Specification
10、for Fully Processed Magnetic Lamina-tion SteelA 876 Specification for Flat Rolled, Grain Oriented, Sili-con Iron, Electrical Steel, Fully Processed TypesA 937/A 937M Test Method for Determining InterlaminarResistance of Insulating Coatings Using Two AdjacentTest Surfaces3. Terminology3.1 Definitions
11、 of Terms Specific to This Standard:3.1.1 interlaminar resistance, nthe average resistance oftwo adjacent insulating surfaces in contact with each other, inaccordance with Test Method A 937/A 937M.3.1.2 stress-relief anneal, nheat treatment that improvesthe magnetic properties of electrical steel by
12、 relieving internalstresses which are introduced during fabrication of magneticcores.3.1.3 surface insulation resistivity, nthe effective resistiv-ity of a single insulating layer tested between applied baremetal contacts and the base metal of the insulated testspecimen, in accordance with Test Meth
13、od A 717/A 717M.4. Significance and Use4.1 This classification establishes categories of insulatingcoatings based on their chemical nature, relative insulatingability, and typical applications. These categories describegeneral physical and chemical characteristics of the coatingsthat are useful in m
14、aking broad estimates of their insulatingability and suitability for various applications.1This classification is under the jurisdiction of ASTM CommitteeA06 onMagnetic Properties and is the direct responsibility of Subcommittee A06.02 onMaterial Specifications.Current edition approved Oct. 1, 2003.
15、 Published November 2003. Originallypublished in 1997. Last previous edition approved in 1997 as A 976 97.2For 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 standa
16、rds Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Basis of Classification5.1 The insulating coatings are categorized according togeneral composition, relative insulating ability, and func
17、tion-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 requirements. Specificproperties required by coating users should be negotiated withthe steel producer.5.2 To reduce confus
18、ion regarding the various categories ofcoatings, this classification follows the “C” type of designationinitially used by the American Iron and Steel Institute fordescribing insulating coatings.3The “C” is included in thecoating designation because insulating coatings for electricalsteels have been
19、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 that the electrical steel committee of the AISI is no longeractive, and the 1983 edition of the coating classificationdoc
20、ument was the last edition of the coating classification to bepublished.46. Test Methods6.1 The surface insulation resistivity of an insulating layermay be measured using Test Methods A 717/A 717M. In thistest method, ten metallic contacts of fixed area are applied toone of the surfaces of the test
21、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 the average electrical currentflowing between the contacts and the base metal under speci-fied applied voltage. Thi
22、s 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 corresponds to a perfect insulator. A Franklin Current of1 ampere corresponds to a perfect conductor. If desired, anapparent
23、 surface insulation resistivity value for the insulatinglayer may be calculated as follows:Ri5 6.45 $1/I!21% in Vcm2/lamination (1)orRi5 645 $1/I!21% in Vmm2/lamination (2)where:Ri= surface insulation resistivity of test sample (two sur-faces in series) in Vcm2/lamination or Vmm2/lamination andI = a
24、mmeter reading in A (also known as Franklin Cur-rent).Note that this test method often is referred to as the Franklintest. The Franklin test is a widely used method for evaluatingthe effectiveness of surface insulation on electrical steels.6.2 The average resistance of two adjacent insulating sur-fa
25、ces in contact with each other, interlaminar resistance, maybe measured using Test Method A 937/A 937M. Because theinterlaminar resistance is influenced by coating-to-coatingcontact, this test method is particularly useful for providing anestimate of the interlaminar resistance in a stacked or wound
26、core 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 surfaceinsulation resistivities in excess of 300 Vcm2(30 kVmm2)(that is, less than 0.02 A when measured according to TestMet
27、hod A 717/A 717M). 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 pressure. For the interlaminar resis-tance measurement, electrical contact is established betweenthe test s
28、pecimen 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 fourprobe configuration (Fig. 3). A continuouselectrical path is formed between the contacts and the constantcurr
29、ent 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 circuit is measured with a voltmeter. Theresistance of the insulation is then determined by Ohms law.3Steel P
30、roducts Manual on FlatRolled Electrical Steel, American Iron andSteel Institute, 1101 17th St., N.W., Washington, DC 200364700, January 1983.4Loudermilk, D. S. and Murphy, R. A., “Overview of Technology of InsulatingCoatings for GrainOriented and Nonoriented Electrical Steels,” Fifteenth AnnualConfe
31、rence on Properties and Applications of Magnetic Materials, Illinois Instituteof Technology, Chicago, IL, May 1996.FIG. 1 Apparatus of Surface Insulation Resistivity Measurementfor Franklin TestFIG. 2 Diagram of Connections for Contacts and Resistors forFranklin TestA976032TABLE 1 Classification of
32、Insulating Coatings for Electrical SteelsCoatingNameCoating Description/CharacteristicsC-0 Oxide that is formed naturally on the steel surface during mill processing. This oxide layer is thin, tightly adherent, and provides sufficient insulating qualityfor most small cores. The oxide layer will with
33、stand 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 be more or less oxidizing to thesurface. It is not appropriate to assert a max
34、imum 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 is bluish to gray in color and used for various electrical steel applications.
35、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 coating is formed from thereaction of the annealing separator with the steel surf
36、ace 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 used for stamped laminations.The primary application of this coating is air-co
37、oled 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 Organic varnish/enamel coating that is applied to the steel surface and cured
38、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 agreement betweenthe producer and user. This coating generally improves the punchabil
39、ity 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 350F (180C).C-4 Coating formed by chemical treating or phosphating of the steel
40、 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 temperatures, but somereduction of surface insulation resistivity may occur during
41、 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 semiprocessed nonoriented electrical steel or cold-rolled motor lamination steel duringqu
42、ality 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-5 Inorganic or mostly inorganic coating similar to C-4, to which ceramic fillers or film-forming inorganic components have been added to inc
43、rease 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 electrical steels,
44、 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 applications r
45、equiring 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 t
46、o 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 statorwinding insulation during rebuilding of motors. The coating
47、 can be used in air-cooled or oil-immersed cores.In some cases, organic components may be added to C-5 coatings to enhance punchability. The applications, use, and properties of such coatings aresimilar to those of inorganic C-5 coatings. The user should consult the producer if there are particular
48、concerns with coating off-gassingduring welding or elevated temperature exposure of the coated steel.C-5-AS Thin film of C-5-type coating used primarily for preventing sticking of semiprocessed nonoriented electrical steel and cold-rolled motor lamination steelduring quality anneals. This coating of
49、ten is referred to as “anti-stick.” It is not appropriate to assert a maximum acceptable Franklin test currentfor this coating.C-6 Organic-based coating to which inorganic fillers have been added to increase the insulating ability of the coating. The coating is applied to the steel surfaceand cured by heating. C-6 coatings typically are used for fully processed nonoriented electrical steels. It is appropriate to designate a maximum Franklintest current for this type of coating. The required Franklin test current is subject to agreement between the producer and u
