ASTM A976-97
(Classification)Standard Classification of Insulating Coatings by Composition, Relative Insulating Ability and Application
Standard Classification of Insulating Coatings by Composition, Relative Insulating Ability and Application
SCOPE
1.1 This document classifies insulating coatings according to their composition, insulating ability, and functionality. The purpose of this classification is to assist users of insulating coatings by providing general information about the chemical nature and use of the coatings, as well as to provide important data concerning limits to their use, that is, relative insulating ability, punchability, temperature stability, weldability, and fabricability. Specific surface insulation resistivity values for each coating are not included in this classification. The user is referred to the flat-rolled electrical steel specifications noted in 1.2 should be more detailed information concerning surface insulation resistivity values be required.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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Designation: A 976 – 97
Standard Classification of
Insulating Coatings by Composition, Relative Insulating
Ability and Application
This standard is issued under the fixed designation A 976; the number immediately following the designation indicates the year of
original adoption or, 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. Scope Magnetic Applications
A 677 Specification for Nonoriented Electrical Steel Fully
1.1 This document classifies insulating coatings according
Processed Types
to their composition, insulating ability, and functionality. The
A 677M Specification for Nonoriented Electrical Steel,
purpose of this classification is to assist users of insulating
Fully Processed Types (Metric)
coatings by providing general information about the chemical
A 683 Specification for Nonoriented Electrical Steel, Semi-
nature and use of the coatings, as well as to provide important
processed Types
data concerning limits to their use, that is, relative insulating
A 683M Specification for Nonoriented Electrical Steel,
ability, punchability, temperature stability, weldability, and
Semiprocessed Types (Metric)
fabricability. Specific surface insulation resistivity values for
A 717/A 717M Test Method for Surface Insulation Resis-
each coating are not included in this classification. The user is
tivity of Single Strip Specimens
referred to the flat-rolled electrical steel specifications noted in
A 726 Specification for Cold Rolled Magnetic Lamination
1.2 should more detailed information concerning surface insu-
Quality Steel, Semiprocessed Types
lation resistivity values be required.
A 726M Specification for Cold Rolled Magnetic Lamina-
1.2 This classification is to be used in conjunction with the
tion Quality Steel, Semiprocessed Types (Metric)
various specifications for flat-rolled electrical steels under the
A 840 Specification for Fully Processed Magnetic Lamina-
jurisdiction of Committee A-6, including Specifications A 345,
tion Steel
A 677, A 677M, A 683, A 683M, A 726, A 726M, A 840,
A 840M Specification for Fully Processed Magnetic Lami-
A 840M, A 876, and A 876M. However, in those instances in
nation Steel (Metric)
which the coating descriptions and characteristics differ be-
A 876 Specification for Flat Rolled, Grain Oriented, Sili-
tween this classification and any of the specifications, this
con Iron, Electrical Steel, Fully Processed Types
classification shall supersede the specification.
A 876M Specification for Flat Rolled, Grain Oriented, Sili-
1.3 This standard does not purport to address all of the
con Iron, Electrical Steel, Fully Processed Types (Metric)
safety concerns, if any, associated with its use. It is the
A 937 Test Method for Determining Interlaminar Resis-
responsibility of the user of this standard to establish appro-
tance of Insulating Coatings Using Two Adjacent Test
priate safety and health practices and determine the applica-
Surfaces
bility of regulatory limitations prior to use.
1.4 The values stated in either customary (cgs-emu and
3. Terminology
inch-pound) units or SI units are to be regarded separately as
3.1 Definitions of Terms Specific to This Standard:
standard. Within the text, the SI units are shown in brackets.
3.1.1 interlaminar resistance, n—the average resistance of
The values stated in each system are not exact equivalents;
two adjacent insulating surfaces in contact with each other, in
therefore, each system shall be used independently of the other.
accordance with Test Method A 937.
Combining values from the two systems may result in noncon-
3.1.2 quality anneal, n—heat treatment used for quality
formance with this specification.
control purposes and grading in accordance with the magnetic
2. Referenced Documents property requirements of the particular electrical steel grade.
The anneal is made under conditions that ensure that the steel
2.1 ASTM Standards:
reaches a temperature of 1450-1550°F (790-850°C) for ap-
A 345 Specification for Flat-Rolled Electrical Steels for
proximately 1 h, and with conditions that favor decarburiza-
tion. The atmosphere shall contain sufficient moisture to be
highly decarburizing but should not excessively oxidize the
This classification is under the jurisdiction of ASTM Committee A-6 on
steel strips (Epstein strips for magnetic property evaluation).
Magnetic Properties and is the direct responsibility of Subcommittee A06.02 on
Material Specifications.
Current edition approved Oct. 10, 1997. Published March 1998.
Annual Book of ASTM Standards, Vol 03.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
A 976
An atmosphere meeting these conditions approximately 20 % 5.2 To reduce confusion regarding the various categories of
hydrogen, 80 % nitrogen and has a dew point of +55°F (+ 13 coatings, this classification follows the “C” type of designation
°C). Care must be taken to ensure that the steel strips retain initially used by the American Iron and Steel Institute for
their flatness and the strip edges have ready access to the heat describing insulating coatings. The “C” is included in the
treatment atmosphere. coating designation because insulating coatings for electrical
3.1.3 stress-relief anneal, n—heat treatment that improves steels have been historically referred to as “coreplate” coatings.
the magnetic properties of electrical steel by relieving internal This classification includes new coatings and test methods not
stresses which are introduced during fabrication of magnetic included in the most recent edition of the AISI classification.
cores. Note that the electrical steel committee of the AISI is no longer
3.1.4 surface insulation resistivity, n—the effective resistiv- active, and the 1983 edition of the coating classification
ity of a single insulating layer tested between applied bare document was the last edition of the coating classification to be
metal contacts and the base metal of the insulated test published.
specimen, in accordance with Test Method A 717/A 717M.
6. Test Methods
6.1 The surface insulation resistivity of an insulating layer
may be measured using Test Methods A 717/A 717M. In this
test method, ten metallic contacts of fixed area are applied to
one of the surfaces of the test specimen, and electrical contact
is made with the base metal by two drills (Fig. 1 and Fig. 2).
The effectiveness of the coating (surface insulation) then is
indicated by a measurement of the average electrical current
flowing between the contacts and the base metal under speci-
fied applied voltage. This current value often is referred to as
the “Franklin Current” and may be used directly as an indicator
of the quality of the insulation. Specifically, a Franklin Current
of zero corresponds to a perfect insulator. A Franklin Current of
1 ampere corresponds to a perfect conductor. If desired, an
apparent surface insulation resistivity value for the insulating
layer may be calculated as follows:
R 5 6.45 $~1/I!21% in V·cm /lamination (1)
i
or
FIG. 1 Apparatus of Surface Insulation Resistivity Measurement
for Franklin Test
R 5 6.45 $~1/I!21%/in @V·mm /lamination# (2)
i
where:
R = surface insulation resistivity of test sample (two sur-
i
2 2
faces in series) in V·cm /lamination or [V·mm /
lamination] and
I = ammeter reading (also known as Franklin Current).
Note that this test method often is referred to as the Franklin
test. The Franklin test is a widely used method for evaluating
FIG. 2 Diagram of Connections for Contacts and Resistors for
Franklin Test the effectiveness of surface insulation on electrical steels.
6.2 The average resistance of two adjacent insulating sur-
4. Significance and Use
faces in contact with each other, interlaminar resistance, may
be measured using Test Method A 937. Because the interlami-
4.1 This classification establishes categories of insulating
nar resistance is influenced by coating-to-coating contact, this
coatings based on their chemical nature, relative insulating
test method is particularly useful for providing an estimate of
ability, and typical applications. These categories describe
the interlaminar resistance in a stacked or wound core in which
general physical and chemical characteristics of the coatings
coated surfaces are in contact with each other. Furthermore,
that are useful in making broad estimates of their insulating
this test method is particularly useful for electrical steels coated
ability and suitability for various applications.
with insulating coatings having surface insulation resistivities
2 2
5. Basis of Classification
in excess of 300 V·cm [30 kV·mm ] (that is, less than 0.02 A
5.1 The insulating coatings are categorized according to
general composition, relative insulating ability, and function-
ality (Table 1). The purpose of this classification is to create a
Steel Products Manual on Flat–Rolled Electrical Steel, American Iron and
Steel Institute, 1101 17th St., N.W., Washington, DC 20036–4700, January 1983.
nomenclature for the various coating types. It is not the intent
Loudermilk, D. S. and Murphy, R. A., “Overview of Technology of Insulating
of t
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