ASTM A977-97

1.1 This test method describes 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 fields, knee field, energy products, and recoil permeability. This test method is suitable for all materials processed into bulk magnets by an 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 A341) are unsuitable. An applicable international standard is IEC Publication 404-5.

1.2 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 temperature. The tests described here measure only the properties of the permanent magnet material. The basic test method incorporates the magnet 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 to magnetically soft materials, are not applicable to permanent magnets.

1.3 This test method shall be used in conjunction with Practice A 34.

1.4 the preferred units and the corresponding values appearing in this test method are customary (cgs-emu) units. SI units are indicated in parentheses. When necessary, derivations of separate equations, conversion factors or the inclusion of SI values, or both, in the text of tables is specified in the text.

1.5 The names and symbols of magnetic quantities used in this test method, summarized in Table 1, are the currently preferred by U.S. industry.

1.6 This test method is useful for magnet materials having Hci values between 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 2T). High coercivity rare-earth magnet test specimens may require much higher magnetizing fields that iron-core electromagnets can product. 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 1.

1.7 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.