1、Designation: A977/A977M 07 (Reapproved 2013)Standard Test Method forMagnetic Properties of High-Coercivity Permanent MagnetMaterials Using Hysteresigraphs1This standard is issued under the fixed designation A977/A977M; the number immediately following the designation indicates the yearof original ad
2、option or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers how to determine the magneticcharacteristics o
3、f magnetically hard materials (permanentmagnets), particularly their initial magnetization,demagnetization, and recoil curves, and such quantities as theresidual induction, coercive field strength, knee field, energyproduct, and recoil permeability. This test method is suitablefor all materials proc
4、essed into bulk magnets by any commonfabrication technique (casting, sintering, rolling, molding, andso forth), but not for thin films or for magnets that are verysmall or of unusual shape. Uniformity of composition,structure, and properties throughout the magnet volume isnecessary to obtain repeata
5、ble results. Particular attention ispaid to the problems posed by modern materials combiningvery high coercivity with high saturation induction, such as therare-earth magnets, for which older test methods (see TestMethod A341/A341M) are unsuitable. An applicable interna-tional standard is IEC Public
6、ation 60404-5.1.2 The 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 operatingtemperatur
7、e. This test method describes only how to measurethe properties of the permanent magnet material. The basic testmethod incorporates the magnetic specimen in a magneticcircuit with a closed flux path. Test methods using ring samplesor frames composed entirely of the magnetic material to becharacteriz
8、ed, as commonly used for magnetically softmaterials, are not applicable to permanent magnets.1.3 This test method shall be used in conjunction withPractice A34/A34M.1.4 The values and equations stated in customary (cgs-emuor inch-pound) or SI units are to be regarded separately asstandard. Within th
9、is test method, SI units are shown 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 value
10、s from the two systems may result 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 generallyaccepted by the industry.1.6 This test method is useful for magnet materials havingHcivalues between about 10
11、0 Oe and 35 kOe 8 kA/m and 2.8MA/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
12、 into the measuringyoke. Typical values of the magnetizing fields, Hmag, requiredfor saturating magnet materials are shown in Table A2.1.1.7 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 e
13、stablish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A34/A34M Practice for Sampling and Procurement Testingof Magnetic MaterialsA340 Terminology of Symbols and Definitions Relating toMagne
14、tic TestingA341/A341M Test Method for Direct Current MagneticProperties of Materials Using D-C Permeameters and theBallistic Test MethodsE177 Practice for Use of the Terms Precision and Bias inASTM Test Methods1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties an
15、d is the direct responsibility of Subcommittee A06.01 on TestMethods.Current edition approved May 1, 2013. Published July 2013. Originally approvedin 1997. Last previous edition approved in 2007 as A977/A977M07. DOI:10.1520/A0977_A0977M-07R13.2For referenced ASTM standards, visit the ASTM website, w
16、ww.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States12.2
17、Magnetic Materials Procedure Association Standard:3MMPA No. 010000 Standard Specifications for PermanentMagnet Materials2.3 International Electrotechnical Commission Document:4Publication 60404-5 Magnetic Materials Part 5: PermanentMagnet (Magnetically Hard) Materials Methods ofMeasurement of Magnet
18、ic Properties3. Terminology3.1 Basic magnetic units are defined in Terminology A340and MMPA No. 010000. Additional definitions with symbolsand units are given in Table 1 and Figs. 1-3 of this test method.4. Significance and Use4.1 This test method is suitable for magnet specification,acceptance, ser
19、vice evaluation, quality control in magnetproduction, research and development, and design.4.2 When a test specimen is 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.
20、In such instances, the testresults must be viewed in context of part performance history.4.3 Tests performed in general 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 betwee
21、n the different test systemsin the geometry of the region surrounding the sample, such as,size and shape of the electromagnet 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 correspondin
22、g flux values (Hall-effectprobes, inductive sensing coils). Also important is the methodof B calibration, for example, 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 repor
23、ts (see Section 9).5. Measuring Methods and Apparatus5.1 Measuring Flux and Induction (Flux Density):5.1.1 In the preferred 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
24、winding length should be no more than athird of the specimen length, preferably less than one fifth, andmust be centered 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 vo
25、ltage induced in this coil. This measurement is takenwith a fluxmeter. Modern hysteresigraphs use electronic inte-grating fluxmeters that allow convenient continuous integra-tion and direct graphic recording of magnetization curves. Ifthe signal is large enough, high-speed voltage sampling at thecoi
26、l and digital integration is also possible.5.1.2 The magnetic induction B is determined by dividingthe total flux by the area-turns product NA of the B-sensingcoil. For permanent magnets in general, and especially forhigh-coercivity materials, an air-flux correction is required (see5.1.5).5.1.3 The
27、total error of measuring B shall be not greater than62%.5.1.4 The change of magnetic induction, B = B2 B1,inthe time interval between the times t1and t2is given as follows: B 5 108/AN! *t1t2edtcustomary units! (1) B 5 1/AN! *t1t2edtSI units! (2)where:B = magnetic induction, G T;A = cross-sectional a
28、rea of the test specimen, cm2m2;N = number of turns on the B-sensing coil;e = voltage induced in the coil, V;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
29、 linked by the sensing coil. The corrected change, Bcorr,is given as follows: Bcorr5 108/AN! *t1t2edt2 H At2 A!/A customary units!(3)Bcorr5 1/AN! *t1t2edt2 0H At2 A!/A SI units! (4)where:A = average cross-sectional area of the sensing coil,cm2m2; H = change in field from t1until t2, Oe A/m; and3Avai
30、lable from Magnetic Materials Producers Association, 8 S. Michigan Ave.,Suite 1000, Chicago, IL 60603.4Available from International Electrotechnical Commission (IEC), 3 rue deVaremb, P.O. Box 131, CH-1211, Geneva 20, Switzerland.TABLE 1 Symbols, Quantities, and UnitsNOTE 1IEC nomenclature calls Br“r
31、emanence,” when Brrepresentsthe B at H = 0 of the outermost hysteresis loop, and it calls Br“remanentmagnetic induction” for B at H = 0 at smaller loops.Symbol Quantity SI UnitCustomarycgs-emuAtCross section of search coil m2cm2BdMagnetic induction at BHmaxT GBrecMagnetic induction at low point ofre
32、coil loopT GBrMagnetic induction at remanence T GdlDiameter of pole piece m cmd2Diameter of homogeneous field m cmHdMagnetic field strength at BHmaxA/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 c
33、oile Voltage induced in test coil V Vd Total air gap between testsample andpole facesm cm0A constant with value 0=410-7H/mrecRecoil permabilityA977/A977M 07 (2013)20= magnetic constant 4 10-7H/m.5.2 Determining Intrinsic Induction :5.2.1 For high-coercivity magnets, it is more convenient tosense dir
34、ectly 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. B then is obtained by mathematical or electronicaddition of H to B.5.2.2 The change of intrinsic induction in the
35、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 contained in onlyone of the coils (Coil 1). If each individual coil has the samearea-turns product, and if the windings are c
36、onnected electri-cally in opposition, the signal induced by the flux linking Coil2 (not containing the specimen) will compensate for the outputFIG. 1 Normal and Intrinsic Hysteresis Loops and Initial Magnetization Curves for Permanent Magnet Materials Illustrating Two Ex-tremes of Virgin Sample Beha
37、viorA977/A977M 07 (2013)3of Coil 1 except for Biwithin the test specimen. The change ofintrinsic induction in the specimen then is given as follows: Bi5 108/AN! *t1t2edtcustomary units! (5)Bi5 1/AN! *t1t2edt SI units! (6)where:Bi= intrinsic induction, G T;A = cross section of the test specimen, cm2m
38、2; andN = number of turns on Coil 1 containing the test specimen.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 then be measured with thesa
39、me 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 specimens of short pole-to-pole lengt
40、h.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).5.2.4 The total error of measur
41、ing 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 be measured. At the surface o
42、f 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 specimen is placed near the specimen
43、 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 surfacecoil, a tightly fitted annular
44、 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 of 5.3.2 are adequate for mea
45、sure-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 thin annular H-sensing coils of
46、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 also shall be a thin conform
47、ing 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 gapsbetween the flat ends of the test s
48、pecimen 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).FIG. 2 Normal and Intrinsic Demagnetization Curves with Sym-bols for Special Points of Interest and Definition of Salient Prop-erties. Illustration of Maximum Energy Product, Coerc
49、ive Fields,and Definition of Knee FieldFIG. 3 Normal and Intrinsic Demagnetization Curves with Sym-bols for Special Points of Interest and Definition of Salient Prop-erties. Illustration of Recoil Loop. Recoil Permeability is Definedas rec= B/HA977/A977M 07 (2013)45.3.6 The magnetic field strength measuring system shall becalibrated. Any temperature dependence of the measuringinstruments, (for example, Hall probes), must be taken intoaccount. The total error of measuring H shall be not greate
