A method to improve the efficiency of high-temperature irreversible flux loss test of NdFeB

Abstract

The invention discloses a method for improving the efficiency of a high-temperature irreversible magnetic flux loss test of NdFeB, relates to the technical field of sintered NdFeB magnetic materials, and aims to solve the problem that the long time of the high-temperature irreversible magnetic flux loss test affects production efficiency. The invention comprises the following steps: performing a high-temperature irreversible magnetic flux loss test on a sample to obtain a magnetic flux loss rate; applying a reverse magnetic field of a magnetizing magnetic field to samples treated in the same manner to obtain a magnetic flux loss rate; changing the voltage of the magnetizer to perform multiple tests until the two magnetic flux loss rates are similar, and recording the voltage; performing the above steps on different NdFeB samples to obtain voltage values corresponding to various samples; and when it is necessary to measure the high-temperature irreversible magnetic flux loss, applying a reverse magnetic field of a corresponding voltage value to replace the high-temperature irreversible magnetic flux loss test of the corresponding sample. The method of the invention is simple and easy to operate, can greatly shorten the test time, and improve production efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of sintered NdFeB magnetic materials, in particular to a method for improving the efficiency of a high-temperature irreversible magnetic flux loss test of NdFeB. Background Art

[0002] In recent years, with the rapid development of new energy vehicles, the NdFeB industry has not only been provided with very good development prospects, but also faced unprecedented challenges. As we all know, a new energy vehicle uses a large amount of NdFeB magnetic materials, which is related to the safety of new energy vehicles during operation. It is also the first consideration for customers when choosing new energy vehicles. Therefore, the qualification rate of NdFeB magnetic materials is also of paramount importance for a new energy vehicle.

[0003] At present, when new energy vehicle manufacturers purchase NdFeB magnetic materials, they are particularly concerned about the performance of NdFeB magnetic materials, which is directly related to whether a new energy vehicle is qualified or not. Among them, high-temperature irreversible loss rate, magnetic flux value, remanence, coercive force, magnetic energy product, etc. are all key indicators. The high-temperature irreversible loss rate of NdFeB magnetic materials refers to the magnetic flux value A1 measured at room temperature of a NdFeB magnet of a certain size magnetized to saturation. After the magnet is kept at 90℃-200℃ for 2-3 hours, the magnetic flux value A2 is measured when it is cooled to room temperature. (A1-A2) / A1 is the high-temperature irreversible magnetic flux loss rate of the magnet. The high-temperature irreversible magnetic flux loss rate is also an important indicator of the performance of NdFeB magnetic materials. For details, please refer to GB / T40794-2021 "Test Method for High-Temperature Magnetic Flux Irreversible Loss of Rare Earth Permanent Magnet Materials". In practical work, the high-temperature irreversible flux loss of NdFeB magnetic materials from semi-finished products to finished products must undergo multiple experiments. The test temperature requirements are numerous and the experimental requirements are different. It takes a lot of time to conduct the tests. The long test time affects product circulation and delivery efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for improving the efficiency of high-temperature irreversible flux loss testing of NdFeB, so as to solve the problem that the high-temperature irreversible flux loss testing takes a long time and affects production efficiency.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for improving the efficiency of high-temperature irreversible flux loss testing of NdFeB, comprising the following specific steps:

[0006] S1 takes the magnetized NdFeB samples with the same treatment and divides them into n groups;

[0007] After measuring the initial magnetic flux of the first group of S2 samples, a high-temperature irreversible magnetic flux loss test was performed, and the magnetic flux after the test was measured to calculate the magnetic flux loss rate;

[0008] After measuring the initial magnetic flux of any group from the 2nd to the nth group of S3 samples, use a magnetizer to apply a magnetic field opposite to the magnetizing magnetic field to the group of samples, measure the magnetic flux of each sample after the reverse magnetic field is applied, and calculate the magnetic flux loss rate;

[0009] S4: If the deviation between the result of step S3 and the result of step S2 exceeds the threshold range, then repeat step S3 for any other group of samples from groups 2 to n, and the reverse magnetic field magnetizer voltages of different groups of samples are different, until the deviation between the result of step S3 and the result of step S2 is within the threshold range, and record the magnetizer voltage of this test;

[0010] S5 repeats steps S1 to S4 for different NdFeB samples to obtain voltage values corresponding to various samples;

[0011] S6 When the sample to be tested needs to undergo a high-temperature irreversible magnetic flux loss test, after measuring the initial magnetic flux, find the voltage value corresponding to the sample to be tested from the voltage values corresponding to the various samples obtained in step S5, apply a reverse magnetic field of the corresponding voltage to the sample to be tested, and then measure the magnetic flux to calculate the magnetic flux loss rate.

[0012] Preferably, in step S4, the deviation is the difference between the magnetic flux loss rate in step S3 and the magnetic flux loss rate in step S2 divided by the magnetic flux loss rate in step S2, and the threshold is ±5%.

[0013] Preferably, in step S1, the NdFeB sample processing includes cutting, surface treatment, cleaning, drying and cooling the NdFeB blank, and finally magnetizing the product to a saturated state.

[0014] Preferably, the conditions for measuring the magnetic flux are a temperature of 20±2° C., a humidity of ≤60%, and the sample is cooled to ambient temperature.

[0015] Preferably, in steps S3 and S6, the method of applying the reverse magnetic field is to place the sample or the sample to be tested in the magnetizer in a direction opposite to that during magnetization.

[0016] Preferably, in steps S2 and S3, the magnetic flux loss rate is an average value of samples in the same group.

[0017] Preferably, the voltage values corresponding to the various samples obtained in step S5 are tabulated and used in production to apply a reverse magnetic field with a corresponding voltage value to replace the high-temperature irreversible flux loss test of the corresponding sample.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The method for improving the efficiency of the high-temperature irreversible flux loss test of NdFeB has simple steps and is easy to operate. It only requires applying a reverse magnetic field by changing the voltage value of the magnetizer and comparing the results with those of the high-temperature irreversible flux loss test. When the results are similar, the method can replace the high-temperature irreversible flux loss test of the corresponding product. In this way, the original single test time of 2-4 hours can be shortened to within 0.5-1 hour, greatly improving production efficiency. DETAILED DESCRIPTION

[0020] A method for improving the efficiency of a high-temperature irreversible flux loss test of NdFeB magnets comprises the following specific steps:

[0021] S1 takes the magnetized NdFeB samples with the same treatment and divides them into n groups;

[0022] After measuring the initial magnetic flux of the first group of S2 samples, a high-temperature irreversible magnetic flux loss test was performed, and the magnetic flux after the test was measured to calculate the magnetic flux loss rate;

[0023] After measuring the initial magnetic flux of any group from the 2nd to the nth group of S3 samples, use a magnetizer to apply a magnetic field opposite to the magnetizing magnetic field to the group of samples, measure the magnetic flux of each sample after the reverse magnetic field is applied, and calculate the magnetic flux loss rate;

[0024] S4: If the deviation between the result of step S3 and the result of step S2 exceeds the threshold range, then repeat step S3 for any other group of samples from groups 2 to n, and the reverse magnetic field magnetizer voltages of different groups of samples are different, until the deviation between the result of step S3 and the result of step S2 is within the threshold range, and record the magnetizer voltage of this test;

[0025] S5 repeats steps S1 to S4 for different NdFeB samples to obtain voltage values corresponding to various samples;

[0026] S6 When the sample to be tested needs to undergo a high-temperature irreversible magnetic flux loss test, after measuring the initial magnetic flux, find the voltage value corresponding to the sample to be tested from the voltage values corresponding to the various samples obtained in step S5, apply a reverse magnetic field of the corresponding voltage to the sample to be tested, and then measure the magnetic flux to calculate the magnetic flux loss rate.

[0027] In a preferred embodiment, in step S4, the deviation is the difference between the magnetic flux loss rate in step S3 and the magnetic flux loss rate in step S2 divided by the magnetic flux loss rate in step S2, and the threshold is preferably ±5%. In steps S2 and S3, the magnetic flux loss rate can be the average value of each sample in the same group; of course, the deviation calculation method and threshold can also be set in other ways. For example, by comparing the median values of the magnetic flux loss rates of multiple samples in each group, the threshold can be that the difference between the two is within ±0.1%. Other statistical methods can also be used as long as they can compare the degree of closeness of the two groups of results.

[0028] The conditions for measuring magnetic flux are all temperature 20±2℃, humidity ≤60%, and the sample is cooled to ambient temperature. Specifically, the sample can be adsorbed in a special sample frame for high-temperature irreversible magnetic flux loss test, placed at ambient temperature for 30 minutes, and then the initial magnetic flux value is measured. After the high-temperature irreversible magnetic flux loss test is completed in step S2, due to the high temperature, it needs to be placed in the magnetic flux value measurement room to naturally cool to ambient temperature before measurement. In steps S3 and S6, there is no high temperature and the cooling time is short. Of course, for the accuracy of the experiment, the same measurement method as step S2 can also be used for comparison.

[0029] In steps S3 and S6, the method for applying the reverse magnetic field is to place the sample or the sample to be tested in the magnetizer in the opposite direction to that during magnetization, that is, the N pole is upward during magnetization, and the S pole is upward when the reverse magnetic field is applied. In this way, there is no need to change other conditions of the magnetizer, only voltage adjustment is required.

[0030] By adopting the method of the present invention, the voltage values corresponding to various samples obtained in step S5 can be made into a table, which can be used in production to apply a reverse magnetic field with a corresponding voltage value to replace the high-temperature irreversible flux loss test of the corresponding samples. The original single test time of 2-4 hours can be shortened to within 0.5-1 hour, greatly improving production efficiency.

[0031] Example 1:

[0032] N45SH brand NdFeB blanks were selected and processed into products of 45mm×9mm×2mm. After manual chamfering of R0.2-R0.4mm, vibration chamfering was performed for 5 hours, and the surface was phosphating treated. Finally, the product was cleaned and discharged, and the surface moisture of the product was manually blown dry. After cooling, the voltage of the magnetizer was adjusted to 1800-2000V, and the sample was magnetized to saturation.

[0033] Take 5 samples from the first group and place them in a special sample frame for high-temperature irreversible magnetic flux loss test. Place them in an environment with a temperature of 20±2℃ and a humidity of ≤60% for 30 minutes. Measure the initial magnetic flux value. Then conduct an open-circuit high-temperature irreversible magnetic flux loss test at 130℃ for 2 hours. After the test, place them in a magnetic flux measurement room and cool them naturally to ambient temperature. The magnetic flux loss rate after aging is measured as follows:

[0034] Initial magnetic flux 4950 4932 4988 4962 4942 Magnetic flux after aging 4899 4880 4938 4909 4888 Loss rate 1.03％ 1.05％ 1.00％ 1.07％ 1.09％

[0035] Take five samples from the second group (this isn't actually the second group, but the redundant steps can be omitted; this group is used as an example to represent the results of the second group). Place the samples in a dedicated sample frame for the high-temperature irreversible flux loss test and place them in an environment with a temperature of 20±2°C and a humidity of ≤60% for 30 minutes. Measure the initial magnetic flux. Then adjust the magnetizer voltage to 604V, apply a reverse magnetic field with the sample's S pole facing upward, and measure its magnetic flux. The magnetic flux loss rate data is as follows:

[0036] Initial magnetic flux 4930 4922 4952 4988 4962 Magnetic flux after aging 4901 4899 4922 4950 4931 Loss rate 0.59％ 0.47％ 0.61％ 0.76％ 0.66％

[0037] Take five samples from the third group (again, this is not the actual third group, but this group is used as an example to represent the third group's results). Place the samples in a special sample frame for high-temperature irreversible magnetic flux loss testing and place them in an environment with a temperature of 20±2°C and a humidity of ≤60% for 30 minutes. Measure the initial magnetic flux value. Then adjust the magnetizer voltage to 830V, apply a reverse magnetic field with the sample's S pole facing upward, and measure its magnetic flux value. The magnetic flux loss rate data is as follows:

[0038] Initial magnetic flux 4942 4930 4973 4950 4960 Magnetic flux after aging 4890 4877 4919 4896 4902 Loss rate 1.05％ 1.08％ 1.09％ 1.09％ 1.17％

[0039] The above (average loss rate of the third group - average loss rate of the first group) / average loss rate of the first group = 4.58%, which is less than 5%. The corresponding voltage of the sample of this embodiment can be recorded as 830V.

[0040] Example 2:

[0041] N30SH brand NdFeB blanks were processed into 50mm×20mm×3.5mm products. After manual chamfering of R0.3-R0.4mm, the product was vibrated for 3 hours and then nickel-copper-nickel plated. Finally, the product was cleaned, discharged, and the surface moisture was manually dried. After cooling, the magnetizer voltage was adjusted to 1950-2050V and the sample was magnetized to saturation.

[0042] Take five samples from the first group and place them in a dedicated sample frame for the high-temperature irreversible magnetic flux loss test. Place them in an environment with a temperature of 20±2°C and a humidity of ≤60% for 30 minutes, and measure the initial magnetic flux value. Then, conduct a semi-open circuit high-temperature irreversible magnetic flux loss test at 100°C for 3 hours. After the test, place them in a magnetic flux measurement chamber and allow them to cool naturally to ambient temperature. The magnetic flux loss rate after aging is measured as follows:

[0043] Initial magnetic flux 7895 7880 7903 7899 7910 Magnetic flux after aging 7840 7824 7851 7844 7858 Loss rate 0.70％ 0.71％ 0.66％ 0.70％ 0.66％

[0044] Take five samples from the second group (not actually the second group, but the redundant process can be omitted, and this group is used as an example to represent the results of the second group). Place the samples in a special sample frame for high-temperature irreversible magnetic flux loss testing and place them in an environment with a temperature of 20±2°C and a humidity of ≤60% for 30 minutes. Measure the initial magnetic flux value. Then adjust the magnetizer voltage to 880V, place the samples with the S pole facing up, apply a reverse magnetic field, and measure their magnetic flux value. The magnetic flux loss rate data is as follows:

[0045] Initial magnetic flux 7900 7895 7880 7905 7902 Magnetic flux after aging 7875 7872 7852 7875 7881 Loss rate 0.32％ 0.29％ 0.36％ 0.38％ 0.27％

[0046] Take five samples from the third group (again, this is not the actual third group, but this group is used as an example to represent the third group's results). Place the samples in a special sample frame for high-temperature irreversible magnetic flux loss testing and place them in an environment with a temperature of 20±2°C and a humidity of ≤60% for 30 minutes. Measure the initial magnetic flux value. Then adjust the magnetizer voltage to 980V, place the samples with the S pole facing up, apply a reverse magnetic field, and measure their magnetic flux value. The magnetic flux loss rate data is as follows:

[0047] Initial magnetic flux 7880 7899 7903 7903 7900 Magnetic flux after aging 7827 7840 7842 7852 7844 Loss rate 0.67％ 0.75％ 0.77％ 0.65％ 0.71％

[0048] The above (average loss rate of the third group - average loss rate of the first group) / average loss rate of the first group = 3.50%, which is less than 5%. The corresponding voltage of the sample of this embodiment can be recorded as 980V.

[0049] Example 3:

[0050] N40UH NdFeB blanks were selected and processed into 43mm×20mm×6mm products. After manual chamfering to R0.2-R0.4mm, the surface was galvanized, cleaned, discharged, and the surface moisture was manually dried. After cooling, the magnetizer voltage was adjusted to 2080-2220V and the sample was magnetized to saturation.

[0051] Take five samples from the first group and place them in a dedicated sample frame for the high-temperature irreversible magnetic flux loss test. Place them in an environment with a temperature of 20±2°C and a humidity of ≤60% for 30 minutes, and measure the initial magnetic flux value. Then, conduct a semi-open circuit high-temperature irreversible magnetic flux loss test at 150°C for 3 hours. After the test, place them in the magnetic flux measurement room and allow them to cool naturally to ambient temperature. The magnetic flux loss rate after aging is measured as follows:

[0052] Initial magnetic flux 9868 9855 9878 9888 9890 Magnetic flux after aging 9848 9837 9861 9872 9869 Loss rate 0.20％ 0.18％ 0.18％ 0.17％ 0.21％

[0053] Take five samples from the second group (not actually the second group, but the redundant process can be omitted, and this group is used as an example to represent the results of the second group). Place the samples in a special sample frame for high-temperature irreversible magnetic flux loss testing and place them in an environment with a temperature of 20±2°C and a humidity of ≤60% for 30 minutes. Measure the initial magnetic flux value. Then adjust the magnetizer voltage to 1000V, place the samples with the S pole facing up, apply a reverse magnetic field, and measure their magnetic flux value. The magnetic flux loss rate data is as follows:

[0054] Initial magnetic flux 9875 9886 9890 9900 9877 Magnetic flux after aging 9866 9876 9879 9892 9869 Loss rate 0.09％ 0.10％ 0.11％ 0.08％ 0.08％

[0055] Take five samples from the third group (again, this is not the actual third group, but this group is used as an example to represent the third group's results). Place the samples in a special sample frame for high-temperature irreversible magnetic flux loss testing and place them in an environment with a temperature of 20±2°C and a humidity of ≤60% for 30 minutes. Measure the initial magnetic flux value. Then adjust the magnetizer voltage to 1405V, place the samples with the S pole facing up, apply a reverse magnetic field, and measure their magnetic flux value. The magnetic flux loss rate data is as follows:

[0056] Initial magnetic flux 9875 9887 9877 9901 9891 Magnetic flux after aging 9853 9867 9860 9883 9871 Loss rate 0.22％ 0.20％ 0.17％ 0.18％ 0.20％

[0057] The above (average loss rate of the third group - average value of the first group) / average value of the first group = 3.20%, which is less than 5%. It can be recorded that the corresponding voltage of the sample of this embodiment is 1405V.

[0058] Example 4:

[0059] According to production requirements, N40UH brand NdFeB blanks were used as raw materials to prepare products with a size of 43mm×20mm×6mm. The blanks were manually chamfered to R0.2-R0.4mm, then galvanized, cleaned, discharged, and the surface moisture of the products was blown dry. After cooling, the magnetizer voltage was adjusted to 2080-2220V, and the sample was magnetized to saturation. When measuring the high-temperature irreversible magnetic flux loss, reverse magnetization was used instead: one sample to be tested was taken and placed in an environment with a temperature of 20±2°C and a humidity of ≤60%. After the sample cooled to ambient temperature, the initial magnetic flux value was measured to be 9871. Since this product was the same as that in Example 3, the voltage of the magnetizer was adjusted to 1405V, compared with that in Example 3. The sample was placed with the S pole facing upward and a reverse magnetic field was applied. The magnetic flux value was measured to be 9850, and the magnetic flux loss rate was calculated to be 0.21%.

[0060] The present invention achieves the purpose of irreversible magnetic flux loss by applying a reverse magnetic field to the NdFeB sample after magnetization saturation. It can be seen from the comparison of the data in the examples that the results obtained by this invention are similar to the results of the high-temperature irreversible magnetic flux loss test. The voltage values of the reverse applied magnetic field to samples of different sizes can be statistically analyzed and made into a table, which can greatly shorten the high-temperature irreversible magnetic flux loss test time and improve the test efficiency. In addition, since the products produced by the factory are usually fixed in several types, it is extremely convenient in actual application. There is no need to obtain lengthy tables. Only the tables of several fixed products can guide the production test, which helps to save time and cost.

[0061] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims.

[0062] Any matters not described in detail in the present invention are well-known technologies to those skilled in the art.

Claims

1. A method for improving the efficiency of high-temperature irreversible flux loss testing of NdFeB, characterized in that: The specific steps include: S1 takes the magnetized NdFeB samples with the same treatment and divides them into n groups; After measuring the initial magnetic flux of the first group of S2 samples, a high-temperature irreversible magnetic flux loss test was performed, and the magnetic flux after the test was measured to calculate the magnetic flux loss rate; After measuring the initial magnetic flux of any group from the 2nd to the nth group of S3 samples, use a magnetizer to apply a magnetic field opposite to the magnetizing magnetic field to the group of samples, measure the magnetic flux of each sample after the reverse magnetic field is applied, and calculate the magnetic flux loss rate; S4: If the deviation between the result of step S3 and the result of step S2 exceeds the threshold range, then repeat step S3 for any other group of samples from groups 2 to n, and the reverse magnetic field magnetizer voltages of different groups of samples are different, until the deviation between the result of step S3 and the result of step S2 is within the threshold range, and record the magnetizer voltage of this test; S5 repeats steps S1 to S4 for different NdFeB samples to obtain voltage values corresponding to various samples; In step S6, when the sample to be tested needs to undergo a high-temperature irreversible magnetic flux loss test, after measuring the initial magnetic flux, the voltage value corresponding to the sample to be tested is found from the voltage values corresponding to the various samples obtained in step S5, a reverse magnetic field with the corresponding voltage is applied to the sample to be tested, and the magnetic flux is measured again to calculate the magnetic flux loss rate; In the steps S3 and S6, the method of applying the reverse magnetic field is to place the sample or the sample to be tested in the magnetizer in the opposite direction to that during magnetization.

2. The method for improving the efficiency of high-temperature irreversible flux loss testing of NdFeB according to claim 1, characterized in that: In step S4, the deviation is the difference between the magnetic flux loss rate in step S3 and the magnetic flux loss rate in step S2 divided by the magnetic flux loss rate in step S2, and the threshold is ±5%.

3. The method for improving the efficiency of high-temperature irreversible flux loss testing of NdFeB according to claim 1, characterized in that: In step S1, the NdFeB sample processing includes cutting, surface treatment, cleaning, drying and cooling the NdFeB blank, and finally magnetizing it to a saturated state.

4. The method for improving the efficiency of high-temperature irreversible flux loss testing of NdFeB according to claim 1, characterized in that: The conditions for measuring magnetic flux are as follows: ambient temperature 20±2℃, humidity ≤60%, and the sample is cooled to ambient temperature.

5. The method for improving the efficiency of high-temperature irreversible flux loss testing of NdFeB according to claim 1, characterized in that: In steps S2 and S3, the magnetic flux loss rate is the average value of each sample in the same group.

6. A method for improving the efficiency of a high-temperature irreversible flux loss test of NdFeB according to any one of claims 1 to 5, characterized in that: The voltage values corresponding to the various samples obtained in step S5 are tabulated and used in production to apply a reverse magnetic field with a corresponding voltage value to replace the high-temperature irreversible flux loss test of the corresponding sample.