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Comparison of two methods for testing the magnetic properties of NdFeB (brand N42UH)
Release time:
2022-04-22
Source:
Www.fe2100.com Hunan Yongyi Technology Co., Ltd.
Recently, some enterprises have proposed to measure the magnetization curve of rare earth permanent magnet materials. As we all know, with reference to the existing international or national standards, there is no requirement to test the magnetization curve of permanent magnetic materials (soft magnetic materials need to test the magnetization curve). Most of the permanent magnetic materials use saturation magnetization, especially rare earth permanent magnets, which mostly use solenoid pulse magnetization. Comparison of the magnetic properties of NdFeB tested by two methods (grade N42UH) The original data obtained from the test are plotted as follows:
Recently encountered some enterprises proposed to rare earth permanent magnet materials.magnetization curveFor measurement, there have been some enterprises to test the magnetization curve of permanent ferrite before. As we all know, with reference to the existing international or national standards, there is no requirement to test the magnetization curve of permanent magnetic materials (soft magnetic materials need to test the magnetization curve). Most of the permanent magnetic materials use saturation magnetization, especially rare earth permanent magnets, which mostly use solenoid pulse magnetization.
Although personal feel not too much significance! Friends proposed to conduct a test of the magnetization curve. To obtain the magnetization curve of rare earth permanent magnet, the only thing I can do at present is to use our FE-2100HAB permanent magnet material magnetic measurement device. The test magnetization curve means that under the condition that the sample is not magnetized (thermal demagnetization treatment can be considered to test repeatability), it is not difficult to directly test the BH curve in one quadrant. At the same time, I also refer to the provisions of national standard GB/T3217-2008 and international standard IEC404-5 to test the performance of the sample after pre-saturation magnetization.Comparison of two methods for testing the magnetic properties of NdFeB (brand N42UH)The raw data obtained from the test are plotted as follows:
1. Comparison of BH curves of direct magnetization test (blue) and solenoid pre-saturation magnetization (8T) test (orange):
2. Comparison of JH curves of direct magnetization test (blue) and solenoid pre-saturation magnetization (8T) test (orange):
3. Graphical analysis:
3-1. You can see that no matter which method is used for testing, the magnetization curve and hysteresis loop collapse when the B value reaches about 2.3T;
3-2. The sample of this case is N42UH sample, and the location of the stay is marked with a blue arrow;
3-3. The electromagnet adopts Fe65Co35 iron-cobalt alloy pole head, and Bs reaches saturation of about 2.3T. The position indicated by the corresponding two arrows is the saturation of FeCo alloy pole head. Collapse occurs when one quadrant corresponds to H reaching 1000kA/m. When the three quadrants correspond to H reaching-1900kA/m (the value of B becomes smaller), the curve warps up. For rare earth permanent magnet materials with high intrinsic temperature, the Hcj obtained by the electromagnet method is larger than the actual Hcj of the material, and a reasonable explanation is obtained.
4. Data analysis:
Comparison of two ways to test BH (Hmax = 2390kA/m):
| Test mode | Br（T） | Hcb(kA/m) | IR(s/s) | BHmax（kJ/m³） |
| Direct magnetization measurement of electromagnet | 1.268 | 987 | 1955 | 313.4 |
| Solenoid pre-charge (8T) measurement | 1.297 | 1011 | 1960 | 328.2 |
4-1. Measurement by electromagnet methodmagnetization curveWhen H is lower than 1000kA/m, the magnetization curve obtained is basically true, and the magnetization curve under a larger magnetic field needs to be corrected in the later period. In this case, the BH curve is directly extended to a straight line, and the difference will be very small, so I think it is not very meaningful to test the magnetization curve;
4-2, using the electromagnet method testdemagnetization curveWhen Hcj is less than 1900kA/m, the obtained demagnetization curve is close to the actual curve of the material, but when testing materials with higher intrinsic coercivity, the obtained Hcj is larger than the actual value of the material. The pulse measurement correction method of high intrinsic permanent magnet open-circuit sample can be compared and verified with the electromagnet method test data (including demagnetization curve) when Hcj is less than 1900kA/m;
4-3. Test Reference of Two Methodsmaximum magnetic energy productBHmax analysis, direct use of electromagnet magnetization saturation: 95.5, the industry used in the so-called non-destructive measurement method (or direct blank measurement), need to consider the test sample Hcj can not be too high, the SH level of the material can be simple approximation, otherwise need to add a larger magnetic field;
4-4. The permanent magnet motor rotor uses a magnetizing fixture to magnetize, and the designed magnetic field is only a little more than 3T. The effect is not better than that of the electromagnet magnetic field to achieve the same magnetic field magnetization. It may be necessary to hit a friend who says that the whole magnetizing is good, but this is only for the saturation of a single magnet, and the whole multi-pole magnetizing situation will be more complicated, the working points of the whole multi-pole magnetizing magnetic steel and the single-chip saturated magnetic steel corresponding to the demagnetization curve are two different things, but the whole magnetizing is better than the single-chip magnetizing saturation, and the usable effect is better (I have not experimented specifically).
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