1、Designation: A 977/A 977M 02Standard Test Method forMagnetic Properties of High-Coercivity Permanent MagnetMaterials Using Hysteresigraphs1This standard is issued under the fixed designation A 977/A 977M; the number immediately following the designation indicates the yearof original adoption or, in
2、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. Scope1.1 This test method describes how to determine the mag-netic characteristics of magnet
3、ically hard materials (permanentmagnets), particularly their initial magnetization, demagneti-zation, and recoil curves and such quantities as the residualinduction, coercive fields, knee field, energy products, andrecoil permeability. This test method is suitable for all materi-als processed into b
4、ulk magnets by any common fabricationtechnique (casting, sintering, rolling, molding, and so forth),but not for thin films or for magnets that are very small or ofunusual shape. Uniformity of composition, structure, andproperties throughout the magnet volume is necessary to obtainrepeatable results.
5、 Particular attention is paid to the problemsposed by modern materials combining very high coercivitywith high saturation induction, such as the rare-earth magnets,for which older test methods (see Test Method A 341) areunsuitable. An applicable international standard is IEC Publi-cation 404-5.1.2 T
6、he magnetic system (circuit) in a device or machinegenerally comprises flux-conducting and nonmagnetic struc-tural members with air gaps in addition to the permanentmagnet. The system behavior depends on properties andgeometry of all these components and on the temperature. Thetests described here m
7、easure only the properties of the perma-nent magnet material. The basic test method incorporates themagnetic specimen in a magnetic circuit with a closed fluxpath. Test methods using ring samples or frames composedentirely of the magnetic material to be characterized, ascommonly used for magneticall
8、y soft materials, are not appli-cable to permanent magnets.1.3 This test method shall be used in conjunction withPractice A 34/A 34M.1.4 The values and equations stated in customary (cgs-emuor inch-pound) or SI units are to be regarded separately asstandard. Within this test method, SI units are sho
9、wn inbrackets except for the sections concerning calculations wherethere are separate sections for the respective unit systems. Thevalues 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 resul
10、t in noncon-formance with this test method.1.5 The names and symbols of magnetic quantities used inthis test method, summarized in Table 1, are those currentlypreferred by U.S. industry.1.6 This test method is useful for magnet materials havingHcivalues between about 100 Oe and 35 kOe 8 kA/m and 2.8
11、MA/m, and Brvalues in the approximate range from 500 G to20 kG 50 mT to 2 T. High-coercivity rare-earth magnet testspecimens may require much higher magnetizing fields thaniron-core electromagnets can produce. Such samples must bepremagnetized externally and transferred into the measuringyoke. Typic
12、al values of the magnetizing fields, Hmag, requiredfor saturating magnet materials are shown in Table 1.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and
13、health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:A 34/A 34M Practice for Procurement Testing and Sam-pling of Magnetic Materials2A 340 Terminology of Symbols and Definitions Relating toMagnetic Testing2A 341/A 341M Tes
14、t Method for Direct Current MagneticProperties Using dc Permeameters and the Ballistic TestMethods2E 177 Practice for Use of the Terms Precision and Bias inASTM Test Methods32.2 Magnetic Materials Procedure Association Standard:MMPA No. 010096 Standard Specifications for Perma-nent Magnet Materials4
15、1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Subcommittee A06.01 on TestMethods.Current edition approved Oct. 10, 2002. Published November 2002. Originallypublished as A 977 97. Last previous edition A 977 97.2Annual Book
16、 of ASTM Standards, Vol 03.04.3Annual Book of ASTM Standards, Vol 14.02.4Available from Magnetic Materials Producers Association, 8 S. Michigan Ave.,Suite 1000, Chicago, IL 60603.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.3 In
17、ternational Electrotechnical Commission Document:Publication 404-5 Magnetic Materials Part 5: PermanentMagnet (Magnetically Hard) Materials Methods ofMeasurement of Magnetic Properties53. Terminology3.1 Basic magnetic units are defined in Terminology A 340and MMPA Standard No. 010096. Additional def
18、initions withsymbols and units are given in Table 1 and Figs. 1-3 of this testmethod.4. Significance and Use4.1 This test method is suitable for magnet specification,acceptance, service evaluation, quality control in magnetproduction, research and development, and design.4.2 When a test specimen is
19、cut or fabricated from a largermagnet, the magnetic properties measured on it are notnecessarily exactly those of the original sample, even if thematerial is in the same condition. In such instances, the testresults must be viewed in context of part performance history.4.3 Tests performed in general
20、 conformity to this testmethod and even on the same specimen, but using different testsystems, may not yield identical results. The main source ofdiscrepancies are variations between the different test systemsin the geometry of the region surrounding the sample, such as,size and shape of the electro
21、magnet pole caps (see Annex A1and Appendix X1), air gaps at the specimen end faces, andespecially the size and location of the measuring devices for Hand B or for their corresponding flux values (Hall-effectprobes, inductive sensing coils). Also important is the methodof B calibration, for example,
22、a volt-second calibration of thefluxmeter alone versus an overall system calibration using aphysical reference sample. The method of B and H sensingshould be indicated in test reports (see Section 9).5. Measuring Methods and Apparatus5.1 Measuring Flux and Induction (Flux Density):5.1.1 In the prefe
23、rred B-measuring method, the total flux ismeasured with a sensing coil (search coil) that surrounds thetest specimen and is wound as closely as possible to thespecimen surface. Its winding length should be no more than athird of the specimen length, preferably less than one fifth, andmust be centere
24、d on the specimen. The leads shall be twistedtightly. As the flux changes in response to sweeping the appliedfield, H, the total flux is measured by taking the time integralof the voltage induced in this coil. This measurement is takenwith a fluxmeter. Modern hysteresigraphs use electronic inte-grat
25、ing fluxmeters that allow convenient continuous integra-tion and direct graphic recording of magnetization curves. Ifthe signal is large enough, high-speed voltage sampling at thecoil and digital integration is also possible.5.1.2 The magnetic induction, B, is determined by dividingthe total flux by
26、 the area-turns product, NA,oftheB-sensingcoil. For permanent magnets in general, and especially forhigh-coercivity materials, an air-flux correction is required (see5.3 and 5.4).5.1.3 The total error of measuring B shall be not greater than62%.5.1.4 The change of magnetic induction, D B = B2 B1,int
27、he time interval between the times t1and t2is given as follows:D B 5 108/AN!*t1t2edtcustomary units! (1)D B 5 1/AN!* t1t2edtSI units! (2)where:B = magnetic induction, G T;A = cross-sectional area of the test specimen,cm2m2;N = number of turns on the B-sensing coil;e = voltage induced in the coil, V;
28、t = time, s; and*t1t2edt= voltage integral = flux, V-s Weber.5.1.5 The change in the magnetic induction shall be cor-rected to take into account the air flux outside the test specimenthat is linked by the sensing coil. The corrected change, Bcorr,is given as follows:D Bcorr5 108/ AN!*t1t2edt2DH At2
29、A! /A customary units!(3)DBcorr5 1/AN!*t1t2edt2 0DH At A! /A SI units! (4)where:A = average cross-sectional area of the sensing coil,cm2m2;D H = change in field from t1until t2, Oe A/m; and0= magnetic constant 4p 10-7H/m.5.2 Determining Intrinsic Induction:5Available from International Electrotechni
30、cal Commission (IEC), 3 rue deVaremb, P.O. Box 131, CH-1211, Geneva 20, Switzerland.TABLE 1 Symbols, Quantities, and UnitsNOTE 1IEC nomenclature calls Br“remanence,” when Brrepresentsthe B at H = 0 of the outermost hysteresis loop, and it calls Br“remanentmagnetic induction” for B at H = 0 at smalle
31、r loops.Symbol Quantity SI UnitCustomarycgs-emuAtCross section of search coil m2cm2BdMagnetic induction at BHmaxT GBrecMagnetic induction at low point ofrecoil loopT GBrMagnetic induction at remanence T GdlDiameter of pole piece m cmd2Diameter of homogeneous field m cmHdMagnetic field strength at BH
32、maxA/m OeHpMagnetic field strength at lowpoint ofrecoil loopA/m Oel Distance between pole faces m cmlrLength of test sample m cmN Number of turns of test coile Voltage induced in test coil V Vd Total air gap between testsample andpole facesm cm0A constant with value 0=4p10-7H/mrecRecoil permabilityA
33、 977/A 977M 0225.2.1 For high-coercivity magnets, it is more convenient tosense directly an electrical signal proportional to the intrinsicinduction, derive the average Biby dividing this flux by thearea-turns product of the surrounding B coil, and to plot Biversus H as the primary demagnetization c
34、urve. B then isobtained by mathematical or electronic addition of H to B.5.2.2 The change of intrinsic induction in the test specimencan be determined by integrating the voltage induced in adevice comprising two sensing coils, both subject to the sameapplied field H, where the test specimen is conta
35、ined in onlyone of the coils (Coil 1). If each individual coil has the samearea-turns product, and if the windings are connected electri-cally in opposition, the signal induced by the flux linking Coil2 (not containing the specimen) will compensate for the outputof Coil 1 except for Biwithin the tes
36、t specimen. The change ofintrinsic induction in the specimen then is given as follows:D Bi5108/AN!*t1t2edtcustomary units! (5)FIG. 1 Normal and Intrinsic Hysteresis Loops and Initial Magnetization Curves for Permanent Magnet Materials Illustrating TwoExtremes of Virgin Sample BehaviorFIG. 2 Normal a
37、nd Intrinsic Demagnetization Curves withSymbols for Special Points of Interest and Definition of SalientProperties. Illustration of Maximum Energy Product, CoerciveFields, and Definition of Knee FieldA 977/A 977M 023DBi5 1/AN!*t1t2edt SI units! (6)where:Bi= intrinsic induction, G T;A = cross section
38、 of the test specimen, cm2m2; andN = number of turns on Coil 1 containing the test speci-men.5.2.3 The two-sensing-coil device shall lie totally within thehomogeneous field defined by Eq A1.1 and Eq A1.2. Testspecimens of lower-coercivity magnets having a range ofcross-sectional areas and shapes can
39、 then be measured with thesame coil device. An arrangement of side-by-side coils of equalsize is useful. Serious errors, however, are incurred whenmeasuring Bithis way on high-Bror high/coercivity magnets,or both, at applied fields of about 10 kOe or more. The errorsare most severe for test specimen
40、s of short pole-to-pole length.Local pole-piece saturation causes strong field inhomogene-ities. The specimen then must fill the cross section of Coil 1,and Coil 2 must be a thin and flat coil, or a coaxial annular coil,either centered on the specimen or in close proximity to itssurface (see 5.3).5.
41、2.4 The total error of measuring Bishall be not greaterthan 62%.5.3 Measuring the Magnetic Field Strength:5.3.1 For correct magnetization curves, one should knowthe magnetic field strength, H, inside the test specimen,averaged over the specimen volume if H is not uniform. Butthis inner field cannot
42、be measured. At the surface of the testspecimen, H is equal to the local field strength just inside thespecimen in those locations (and only there) where the Hvector is parallel to the side surface of the specimen. Therefore,a magnetic field strength sensor of small dimensions relative tothe specime
43、n is placed near the specimen surface and sym-metrical with respect to the end faces, covering the shortestpossible center portion of the specimen length. It shall be sooriented that it correctly measures the tangential field compo-nent.5.3.2 To determine the magnetic field strength, a flat surfacec
44、oil, a tightly fitted annular coil, a magnetic potentiometer, ora Hall probe is used together with suitable instruments. Thedimensions of the magnetic field sensor and its location shallbe such that it is within an area of limited diameter around thetest specimen (see Annex A1).5.3.3 The provisions
45、of 5.3.2 are adequate for measure-ments on magnets having low-to-moderate intrinsic coercivity,such as Alnico and bonded ferrites. For high-coercivity, denseferrites and especially for most rare earth-transition metalmaterials, it is essential for accurate measurement to use thinflat or radially thi
46、n annular H-sensing coils of short length(1/5 to 1/3 of the specimen length), centered on the specimenand placed as close as possible to the specimen surface.5.3.4 The same considerations apply to the H-flux compen-sation coil used in Bimeasurements (see 5.2.3.) When polesaturation can occur, Coil 2
47、 also shall be a thin conforming flatsurface coil for rectangular specimen shapes or a thin annularcoil closely surrounding a cyclindrical specimen, and thespecimen essentially shall fill the open cross-sectional area ofthe Bsensing Coil 1.5.3.5 To reduce other measurement errors, the air gapsbetwee
48、n the flat ends of the test specimen and the pole piecesshall be kept small, typically in the range 0.001 to 0.002 in.0.025 to 0.050 mm (see Fig. 4).5.3.6 The magnetic field strength measuring system shall becalibrated. Any temperature dependence of the measuringinstruments, (for example, Hall probe
49、s), must be taken intoaccount. The total error of measuring H shall be not greaterthan 62%.NOTE 1The end faces of the test specimen should be in intimatecontact with the pole faces. There are always unavoidable small air gapsas a result of surface roughness, poor parallelism of sample or pole faces,or intentional shimming to protect delicate specimens from deformation orcrushing. These cause additional errors in the magnetic field strengthmeasurement and indirectly in the Bimeasurements through air fluxcompe
