GB/T 40794-2021 (GB/T40794-2021, GBT 40794-2021, GBT40794-2021)
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Measurement method of irreversible magnetic flux loss due to high temperature of rare earth permanent magnet
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GB/T 40794-2021
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| Standard ID | GB/T 40794-2021 (GB/T40794-2021) | | Description (Translated English) | Measurement method of irreversible magnetic flux loss due to high temperature of rare earth permanent magnet | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | H14 | | Classification of International Standard | 77.120.99 | | Word Count Estimation | 10,139 | | Date of Issue | 2021-10-11 | | Date of Implementation | 2022-05-01 | | Drafting Organization | Ningbo Ketian Magnetic Industry Co., Ltd., Beijing Zhongke Sanhuan High-tech Co., Ltd., Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Anhui Dadixiong New Materials Co., Ltd., Ningbo Yunsheng Co., Ltd., Fujian Changting Jinlong Rare Earth Co., Ltd., Ganzhou Fuerte Electronics Co., Ltd., Baotou Rare Earth Research Institute, Ningbo Keningda Industry Co., Ltd. | | Administrative Organization | National Rare Earth Standardization Technical Committee (SAC/TC 229) | | Proposing organization | National Rare Earth Standardization Technical Committee (SAC/TC 229) | | Issuing agency(ies) | State Administration for Market Regulation, National Standardization Administration |
GB/T 40794-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.120.99
CCS H 14
Measurement method of irreversible magnetic flux loss due
to high temperature of rare earth permanent magnet
ISSUED ON: OCTOBER 11, 2021
IMPLEMENTED ON: MAY 01, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Method principle ... 5
5 Test conditions ... 5
6 Instruments and equipment ... 5
7 Sample ... 6
8 Test steps ... 6
9 Test data processing ... 7
10 Uncertainty ... 8
11 Test report ... 9
Annex A (informative) Law and reason of irreversible magnetic flux loss due to high
temperature of rare earth permanent magnets changing with temperature ... 10
Measurement method of irreversible magnetic flux loss due
to high temperature of rare earth permanent magnet
1 Scope
This document specifies the measurement method of irreversible magnetic flux loss due
to high temperature of rare earth permanent magnet.
This document applies to the measurement of irreversible magnetic flux loss due to
high temperature of NdFeB permanent magnet.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 6379.2, Measurement methods and results - Accuracy (trueness and precision)
- Part 2: Determine the standard methods of measurement repeatability and
reproducibility of the basic method
GB/T 8170, Rules of rounding off for numerical values and expression and
judgement of limiting values
GB/T 9637, Electrotechnical terminology - Magnetic materials and components
GB/T 38437, Methods of measurement of the magnetic dipole moment of a
ferromagnetic material specimen by the withdrawal or rotation method
3 Terms and definitions
For the purposes of this document, the terms and definitions defined in GB/T 9637 as
well as the followings apply.
3.1 irreversible magnetic flux loss due to high temperature
The part where the magnetic flux cannot be restored when the magnet is heated from
normal temperature to high temperature and then returned to normal temperature.
NOTE: It is measured in percentage (%).
3.2 load line
The locus of the operating point of a permanent magnet forming part of a given
magnetic circuit when the magnitude of its magnetization varies.
NOTE: The operating point of a permanent magnet is a point on the demagnetization curve or return
line of a permanent magnet forming part of a given magnetic circuit. Its coordinates are the working
magnetic flux density and magnetic field strength.
[Source: GB/T 9637-2001, 221-04-11]
3.3 high temperature aging
The test that the permanent magnet is kept at a certain temperature in the high
temperature test box for a period of time, and the high temperature environment is
simulated to test the thermal stability.
4 Method principle
Use Helmholtz coils and fluxmeters, at the same room temperature, to measure the
irreversible loss of magnetic flux (magnetic dipole moment) of a magnet with saturated
magnetization before and after high temperature aging test. It is expressed in percent.
5 Test conditions
5.1 Normal temperature magnetic flux test: the ambient temperature is 23℃±3℃.
5.2 Optional temperatures for high temperature aging of NdFeB permanent magnets:
65°C, 85°C, 100°C, 120°C, 150°C, 180°C, 200°C, 250°C. If the customer has special
needs, it shall be determined through negotiation between the two parties.
6 Instruments and equipment
6.1 Magnetic flux measurement device: mainly composed of a fluxmeter and a
Helmholtz coil. The maximum display deviation of the fluxmeter shall be less than 1%.
6.2 High temperature test chamber: the inner wall and interlayer of the test chamber
shall be made of non-ferromagnetic materials. The high temperature test chamber shall
be able to adjust the heating rate and holding time. The maximum temperature deviation
of the working space of the test chamber shall be less than 1°C. During the constant
temperature period, the temperature fluctuation shall not exceed 1°C.
7 Sample
7.1 The samples are finished or machined semi-finished permanent magnets.
7.2 The sample shall be saturated and magnetized along the direction of easy
magnetization.
8 Test steps
8.1 Initial flux test
Place the sample at room temperature for no less than 2 h after magnetization and
saturation. Make sure that the specimen temperature is consistent with room
temperature. The sample is placed in the homogeneous space of the Helmholtz coil. The
easy magnetization direction of the sample is parallel to the axis of the Helmholtz coil.
Then measure the magnetic flux according to the provisions of GB/T 38437. Repeatedly
measure each sample for 3 times. Take the average value of the displayed values of
magnetic flux (magnetic dipole moment) as the measured value before the test.
8.2 High temperature aging test method and sample placement
8.2.1 Open-circuit mode
The test sample needs to be placed in a non-ferromagnetic sample frame. During the
test, avoid the sample close to the magnetic material. In order to avoid the mutual
adsorption of the samples during the test operation, causing damage to the samples and
injuring the test personnel, it is necessary to customize a special sample frame or a
fixing scheme with the same effect. If the aluminum alloy plate is fixed with high-
temperature-resistant adhesive tape, the distance between the specimens shall not be
less than 8 times the maximum side length of the specimen.
8.2.2 Semi-open-circuit mode
8.2.2.1 The sample is absorbed on a pure iron plate with a thickness of 1.0mm±0.1mm.
The easy magnetization direction of the specimen shall be perpendicular to the surface
of the iron plate. The distance between specimens shall not be less than 4 times the side
length of the same direction of the specimen. The direction of the N poles of the samples
shall be the same.
8.2.2.2 The inner arc of the tile-shaped magnet is adsorbed on the iron plate downward.
For samples that are inconvenient to be placed by magnetic pole surface adsorption or
samples with special shapes, place them on the principle of safety and convenience.
Indicate in the test report.
8.3 Determination of high temperature aging heating and heat preservation
Keys:
1 - Semi-open-circuit magnetic flux mode which the sample is placed on a 1mm thick iron plate;
2 - Open-circuit magnetic flux mode in which the sample is placed on a glass plate.
Figure A.1 -- The law of irreversible magnetic flux loss due to high temperature
of the same rare earth permanent magnet specimen in the open-circuit and semi-
open-circuit magnetic flux aging modes changing with temperature (sintered
NdFeB magnet, ϕ10.055mm×2.017mm 40SH, constant temperature for 2 h at
each temperature point)
A.2 Variation law of operating point of rare earth permanent magnet and position
of inflection point of B-H curve
A.2.1 The reason for the irreversible loss of magnetic flux is the relative change of the
operating point of the permanent magnet relative to the position of the inflection point
of the B-H curve of the magnetic material. Since the temperature coefficient of
remanence and intrinsic coercive force of rare earth permanent magnets above room
temperature is negative, and the absolute value of the temperature coefficient of
coercive force H is larger than the absolute value of the temperature coefficient of
magnetic flux density B, the higher the temperature, the higher the corresponding B-H
curve inflection point. See Figure A.2.
Example 1: In Figure A.2, when the temperature rises from 100°C to 120°C, the inflection point of
the B-H curve rises from point C1 to point C3.
A.2.2 In a static magnetic circuit, the permanent magnet operating load line is a straight
line. The operating point of the permanent magnet goes down along the load line with
increasing temperature.
Example 2: In Figure A.2, the 40SH ϕ10.055mm×2.017mm sintered NdFeB magnet is in the open-
circuit state. When the temperature rises from 100°C to 120°C, its operating point moves downward
from point A1 to point A3. That is, move down from above the inflection point C1 of the B-H curve
to below the inflection point C3 of the B-H curve.
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