ASTM A596/A596M-95(1999)

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Designation: A 596/A 596M – 95 (Reapproved 1999)
Standard Test Method for
Direct-Current Magnetic Properties of Materials Using the
Ballistic Method and Ring Specimens
This standard is issued under the fixed designation A 596/A 596M; 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 standard. Within this test method, the SI units are shown in
brackets except for the sections concerning calculations where
1.1 This test method covers dc ballistic testing for the
there are separate sections for the respective unit systems. The
determination of basic magnetic properties of materials in the
values stated in each system are not exact equivalents; there-
form of ring, toroidal, link, double-lapped Epstein cores, or
fore, each system shall be used independently of the other.
other standard shapes which may be cut, stamped, machined,
Combining values from the two systems may result in noncon-
or ground from cast, compacted, sintered, forged, or rolled
formance with this method.
materials. It includes tests for normal induction and hysteresis
1.8 This standard does not purport to address all of the
taken under conditions of steep wavefront reversals of the
safety concerns, if any, associated with its use. It is the
direct-current magnetic field strength.
responsibility of the user of this standard to establish appro-
1.2 This test method shall be used in conjunction with
priate safety and health practices and determine the applica-
Practice A 34/A 34M.
bility of regulatory limitations prior to use.
1.3 This test method is suitable for a testing range from very
low magnetic field strength up to 200 or more Oe [15.9 or more
2. Referenced Documents
kA/m]. The lower limit is determined by integrator sensitivity
2.1 ASTM Standards:
and the upper limit by heat generation in the magnetizing
A 34/A 34M Practice for Sampling and procurement Test-
winding. Special techniques and short duration testing may
ing of Magnetic Materials
extend the upper limit of magnetic field strength.
A 340 Terminology of Symbols and Definitions Relating to
1.4 Testing under this test method is inherently more accu-
Magnetic Testing
rate than other methods. When specified dimensional or shape
A 341/A 341M Test Method for Direct Current Magnetic
requirements are observed, the measurements are a good
Properties of Materials Using D-C Permeameters and the
approximation to absolute properties. Test accuracy available is
Ballistic Test Methods
primarily limited by the accuracy of instrumentation.
A 343 Test Method for Alternating-Current Magnetic Prop-
1.5 This test method permits a choice of test specimen to
erties of Materials at Power Frequencies Using the
permit measurement of properties in any desired direction
Wattmeter-Ammeter-Voltmeter Method and 25-cm Epstein
relative to the direction of crystallographic orientation without
Test Frame
interference from external yoke systems.
A 773/A 773M Test Method for dc Magnetic Properties of
1.6 The symbols and abbreviated definitions used in this test
Materials Using Ring and Permeameter Procedures with
method appear in Fig. 1 and Sections 5, 6, 9, and 10. For the
dc Electronic Hysteresigraphs
official definitions see Terminology A 340. Note that the term
2.2 IEC Standard:
flux density used in this document is synonymous with the term
Publication 404-4, Magnetic Materials—Part 4: Methods of
magnetic induction.
Measurement of the D-C Magnetic Properties of Solid
1.7 The values stated in either customary (cgs-emu and
Steels, IEC, 1982
inch-pound) units or SI units are to be regarded separately as
This test method is under the jurisdiction of ASTM Committee A06 on
Magnetic Properties and is the direct responsibility of Subcommittee A06.01 on Test
Methods. Annual Book of ASTM Standards, Vol 03.04.
Current edition approved Feb. 15, 1995. Published April 1995. Originally Available from American National Standards Institute, 11 W. 42nd St., 13th
published as A 596 – 69. Last previous edition A 596 – 89. Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
A 596/A 596M – 95 (1999)
4.2 The basic quality of materials having directionally
sensitive properties cannot be tested satisfactorily with rings or
laminations. With them it is necessary to use Epstein speci-
mens cut with their lengths in the direction of specific interest
or to use long link-shaped or spirally wound toroidal core test
specimens whose long dimensions are similarly located. The
acceptable minimum width of strip used in such test specimens
is also sensitive to the material under test. At present, it is
believed that the grain-oriented silicon steels should have a
strip width of at least 3 cm [30 mm].
4.3 Unless ring specimens are large in diameter, it is difficult
to provide a sufficient number of primary turns needed to reach
the highest magnetic field strength. In general, magnetic
materials tend to have nonuniform properties throughout the
body of the test specimen; for this reason, uniformly distrib-
uted test windings and uniform specimen cross-sectional area
are highly desirable to suppress nonuniform behavior to a
NOTE 1—
tolerable degree.
A —Multirange ammeter, main-magnetizing current circuit
A —Multirange ammeter, hysteresis-current circuit
N —Magnetizing (primary) winding
5. Apparatus
N —Flux-sensing (secondary) winding
5.1 The apparatus shall consist of as many of the compo-
F—Electronic integrator
R —Main current control rheostat nents described in 5.2-5.10 as are required to perform the
R —Hysteresis current control rheostat
2 desired test. The basic circuit is shown in Fig. 1.
S —Reversing switch
5.2 Balance and Scales:
S —Shunting switch for hysteresis current control rheostat
5.2.1 The balance used to weigh the test specimen shall be
FIG. 1 Basic Circuit Using Ring-Type Cores
capable of weighing to an accuracy of better than 0.1 %.
5.2.2 The micrometer, caliper, or other length-measuring
device used in the determination of magnetic path length and
3. Significance and Use
cross-sectional area shall be capable of measuring to an
3.1 Test methods using suitable ring-type specimens are
accuracy of better than 0.1 %.
the preferred methods of determining the basic magnetic
5.3 dc Power Supply—The preferred source of dc current is
properties of a material caused by the absence of demagnetiz-
a high quality linear power supply of either unipolar or bipolar
ing effects and are well suited for specification acceptance,
operation. The power supply must exhibit high stability and
service evaluation, and research and development.
very low ripple to achieve the most accurate results. Program-
3.2 Provided the test specimen is representative of the bulk
mable bipolar operational amplifier power supplies have
material as is usually the case for thin strip and wire, this test
proven to be very satisfactory for this type of testing. Other
is also suitable for design purposes.
stable sources of dc current such as storage batteries are
3.3 When the test specimen is not necessarily representative
permitted.
of the bulk material such as a ring machined from a large
5.4 Main-Current-Control Rheostat R —When nonpro-
forging or casting, the results of this test method may not be an
grammable sources of dc current such as storage batteries are
accurate indicator of the magnetic properties of the bulk
used, rheostats must be used to control the current. These
material. In such instances, the test results when viewed in
rheostats must have sufficient power rating and heat-dissipating
context of past performance history will be useful for judging
capability to handle the largest test current without undesirable
the suitability of the current material for the intended applica-
changes in resistance and, therefore, magnetizing current
tion.
during conduct of the test.
5.5 Hysteresis-Current-Control Rheostat R —The
4. Interferences
hysteresis-current-control rheostat, when required, must have
4.1 This test method has several important requirements.
the same power rating and resistance as the main-current-
Unless adequate inside diameter to outside diameter ratios are
control rheostat.
maintained in the test specimens, the magnetic field strength
5.6 Main-Current Ammeter A —Measurement of the mag-
will be excessively nonuniform throughout the test specimen
netizing current can be accomplished with either a dc ammeter
and the measured parameters cannot be represented as material
or a combination of a precision shunt resistor and dc voltmeter.
properties.
The meters and shunt resistor, if used, must have an accuracy
of at least 0.25 %. To improve test accuracy multirange digital
ammeters or voltmeters are preferred. Autoranging capability
is desirable for convenience but is not essential for this test
Lloyd, M. G., “Errors in Magnetic Testing with Ring Specimens,’’ Technical
method. If analog meters are used, the ranges must be such that
News Bulletin, National Institute for Standards and Technology, Vol 5, 1909, p. 435
(S108). all test readings are made in the upper two thirds of the scale.
A 596/A 596M – 95 (1999)
5.7 Hysteresis-Current Ammeter, A —The hysteresis- properties evaluation with relatively unoriented materials pro-
current measuring system shall conform to the requirements in vided the uncertainty in determination of true-path (effective)
5.6. In general, a separate measuring system is not required length is less than 5 % of the total path length. When this
since the main current ammeter (A ) can also be used to uncertainty in path length (shortest or longest relative to the
measure the hysteresis current. mean-path length) exceeds 5 %, the test values should be
5.8 Reversing Switch, S —Because of the low resistance reported as core properties and not basic material properties.
nature of the magnetizing circuit, it is imperative that high 6.4 The test specimen may be constructed of solid laminated
quality switches be used. Changes in switch resistance upon or strip materials and in any of the shapes described in 1.1.
reversal will cause deviation from the cyclically magnetized 6.5 Test specimen cores made from strip may be laminated,
condition which, if excessive, will impair test accuracy and machined, spirally wound, or Epstein specimens (the method
precision. Experience has shown that mercury switches are the of selection for Epstein specimens is described in Test Method
best suited for this application. Knife blade switches or A 343, Appendix 3). When the material is to be tested half
mechanical or electrically operated contractors can also be transverse and half longitudinal, the material shall be cut into
used provided the requirement for uniform and equal contact Epstein strips or square laminations of adequate dimensional
resistance can be maintained. Because of the presence of ratio.
leakage currents in the open condition, solid state relays are not 6.6 Test specimens used for basic material evaluation shall
permitted. The difficulties inherent in the use of main current be cut, machined, ground, slit, or otherwise formed to have a
reversing switches can be minimized by use of linear power cross section that remains sufficiently uniform that its nonuni-
supplies capable of accepting a remote programming signal. formity will not materially affect the accuracy of establishing
Such power supplies are permitted provided that the magne- and measuring flux density, B, or magnetic field strength, H,in
tizing current is equal (to within 0.1 %) in either polarity when the test specimen.
normal induction testing is conducted, current reversals can be 6.7 When required for material properties development, the
conducted with no overshoot or oscillation and the magnetizing test specimen shall have received a stress relief or other heat
current is truly zero for the zero current programming signal. treatment after preparation. This heat treatment is subject to
5.9 Hysteresis Switch, S (When Required)—This switch agreement between manufacturer and purchaser, manufacturers
should conform to requirements in 5.8. recommendation, or the recommended heat treatment provided
5.10 Integrator, F—Because of their superior accuracy, by the appropriate ASTM standard for the material. The heat
stability, and ease of operation, electronic charge integrators treatment used shall be reported with the magnetic test results.
are the preferred means of measuring magnetic flux. Integra-
7. Calibration of Integrator
tors using either operational amplifier and capacitor feedback
7.1 Practical operating experience has shown that provided
(analog integrator) or pulse counting are permitted. The accu-
a proper warmup period is allowed, electronic integrators
racy of the integrator must be better than 1 % full scale. If
require infrequent calibration and unlike ballistic galvanom-
analog display meters are used to read the value of flux, the
eters, calibration is not an integral part of this test method.
measurement should be made on the upper two thirds of the
scale. Analog integrators must have drift adjust circuitry and When calibration is required, it can be accomplished with
−6
either a mutual inductor or a volt-second source. Because of
the drift should not exceed 100 Maxwell-turns [10 Wb-turns]
per minute on the most sensitive range. It is also desirable that their traceability to the fundamental units of voltage and time,
volt-second sources are the preferred means of calibration. The
the integrator have appropriate scaling circuitry to permit direct
reading of either flux (f) or flux density (B). Ballistic galva- accuracy of either the mutual inductor or volt-second source
must be better than the rated full-scale accuracy of the
nometers or moving coil fluxmeters are allowed provided the
1 % full-scale accuracy requirement is met. integrator.
6. Test Specimen 8. Procedure
6.1 When the test specimen represents a test lot of material, 8.1 In Fig. 1, the dc power source supplies magnetizing
its selection shall conform to the requirements of Practice current measured by ammeter A or A . Rheostats R and R
1 2 1 2
A 34/A 34M or of an individual specification. and switches S and S determine the magnitude and direction
1 2
6.2 To qualify as a test specimen suitable for evaluation of of the current as required by various operations. In general,
material properties the effective ratio of mean diameter to three types of switching opera
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