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ASTM A 977/A 977M Document Information:
Title
Standard Test Method for Magnetic Properties of High-Coercivity Permanent Magnet Materials Using Hysteresigraphs
ASTM International
Publication Date:
Nov 1, 2007
Scope:
This test method covers how to determine the magnetic
characteristics of magnetically hard materials (permanent magnets),
particularly their initial magnetization, demagnetization, and
recoil curves, and such quantities as the residual induction,
coercive field strength, knee field, energy product, and recoil
permeability. This test method is suitable for all materials
processed into bulk magnets by any common fabrication technique
(casting, sintering, rolling, molding, and so forth), but not for
thin films or for magnets that are very small or of unusual shape.
Uniformity of composition, structure, and properties throughout the
magnet volume is necessary to obtain repeatable results. Particular
attention is paid to the problems posed by modern materials
combining very high coercivity with high saturation induction, such
as the rare-earth magnets, for which older test methods (see Test
Method A 341) are unsuitable. An applicable international standard
is IEC Publication 60404-5.
The magnetic system (circuit) in a device or machine generally
comprises flux-conducting and nonmagnetic structural members with
air gaps in addition to the permanent magnet. The system behavior
depends on properties and geometry of all these components and on
the operating temperature. This test method describes only how to
measure the properties of the permanent magnet material. The basic
test method incorporates the magnetic specimen in a magnetic
circuit with a closed flux path. Test methods using ring samples or
frames composed entirely of the magnetic material to be
characterized, as commonly used for magnetically soft materials,
are not applicable to permanent magnets.
This test method shall be used in conjunction with Practice A
34/A 34M.
The values and equations stated in customary (cgs-emu or
inch-pound) or SI units are to be regarded separately as standard.
Within this test method, SI units are shown in brackets except for
the sections concerning calculations where there are separate
sections for the respective unit systems. The values stated in each
system may not be exact equivalents; therefore, each system shall
be used independently of the other. Combining values from the two
systems may result in nonconformance with this test method.
The names and symbols of magnetic quantities used in this test
method, summarized in Table 1, are those generally accepted by the
industry.
This test method is useful for magnet materials having
Hci values between about 100 Oe and 35 kOe [8
kA/m and 2.8 MA/m], and Br values in the
approximate range from 500 G to 20 kG [50 mT to 2 T].
High-coercivity rare-earth magnet test specimens may require much
higher magnetizing fields than iron-core electromagnets can
produce. Such samples must be premagnetized externally and
transferred into the measuring yoke. Typical values of the
magnetizing fields, Hmag, required for
saturating magnet materials are shown in Table A2.1.
This standard does not purport to address all of the safety
concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and
health practices and determine the applicability of regulatory
limitations prior to use.
Keywords:
- coercive field strength
- coercivity
- hysteresigraph
- induction
- magnetic
- magnetic material
- magnetic test
- permanent magnets
- permeameter
- remanence
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