Active Standard ASTM A977 / A977M | Developed by Subcommittee: A06.01
Book of Standards Volume: 03.04
Historical (view previous versions of standard)
Significance and Use
4.2 When a test specimen is cut or fabricated from a larger magnet, the magnetic properties measured on it are not necessarily exactly those of the original sample, even if the material is in the same condition. In such instances, the test results must be viewed in context of part performance history.
4.3 Tests performed in general conformity to this test method and even on the same specimen, but using different test systems, may not yield identical results. The main source of discrepancies are variations between the different test systems in the geometry of the region surrounding the sample, such as, size and shape of the electromagnet pole caps (see Annex A1 and Appendix X1), air gaps at the specimen end faces, and especially the size and location of the measuring devices for H and B or for their corresponding flux values (Hall-effect probes, inductive sensing coils). Also important is the method of B calibration, for example, a volt-second calibration of the fluxmeter alone versus an overall system calibration using a physical reference sample. The method of B and H sensing should be indicated in test reports (see Section 9).
1.1 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 A341/A341M) are unsuitable. An applicable international standard is IEC Publication 60404-5.
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 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.
1.3 This test method shall be used in conjunction with Practice A34/A34M.
1.4 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.
1.5 The names and symbols of magnetic quantities used in this test method, summarized in Table 1, are those generally accepted by the industry.
1.6 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.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
A34/A34M Practice for Sampling and Procurement Testing of Magnetic Materials
A340 Terminology of Symbols and Definitions Relating to Magnetic Testing
A341/A341M Test Method for Direct Current Magnetic Properties of Materials Using D-C Permeameters and the Ballistic Test Methods
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
Magnetic Materials Procedure Association StandardMMPANo.0100–00 Standard Specifications for Permanent Magnet Materials
International Electrotechnical Commission DocumentPublication60404-5 Magnetic Materials- Part 5: Permanent Magnet (Magnetically Hard) Materials - Methods of Measurement of Magnetic Properties
ICS Number Code 29.030 (Magnetic materials)