Gradient permanent magnet and manufacturing method and application thereof

Abstract

The invention discloses a gradient permanent magnet and a manufacturing method and application thereof, and relates to the technical field of permanent magnet steel, and the method comprises the following steps: S1, obtaining the operation temperature distribution condition of the permanent magnet by using finite element analysis software; s2, determining a working temperature boundary line of the permanent magnet according to the step S1, and dividing the permanent magnet into different areas; s3, when the permanent magnet is manufactured, an isolation plate is arranged in a mold, the shape and the position of the isolation plate are determined according to the working temperature boundary line of the permanent magnet in the step S2, corresponding magnetic steel raw materials are added into all the areas in the mold according to the different isolated areas, preliminary pressing is conducted, then the isolation plate is taken out, pressing forming is conducted, and the permanent magnet is manufactured. Carrying out high-temperature sintering and tempering treatment on the obtained magnetic steel pressed blank; or, the gradient permanent magnet is manufactured by adopting a local grain boundary infiltration method, the obtained gradient permanent magnet can be used for preparing a semi-direct-driven wind driven generator, and the cost can be remarkably reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of permanent magnet steels, and particularly relates to a gradient permanent magnet, a manufacturing method thereof, and an application thereof. Background Art

[0002] When asynchronous high-speed wind turbines and low-speed permanent magnet direct-drive generators are developing, the market share of medium-speed permanent magnet semi-direct-drive wind turbines, which combine the characteristics of high-speed wind turbines and low-speed permanent magnet direct-drive generators, is also increasing. Semi-direct drive is generated due to problems encountered in the development of direct-drive and high-speed generator sets towards large-scale and cost-effective development. It takes into account the characteristics of both and has obvious advantages in mechanical structure, cost, and overall machine structure load. However, with the continuous intensification of market price competition, each motor manufacturer is constantly exploring the manufacturing cost of motors to create more market-competitive products.

[0003] The main raw materials for manufacturing semi-direct-drive wind turbines are neodymium iron boron, silicon steel sheets, copper, etc. Among them, the permanent magnet material neodymium iron boron is mainly used to manufacture rotor permanent magnets, and its cost composition is about 30%. Due to the addition of various rare earth elements during the manufacturing process of permanent magnets, especially permanent magnets with high temperature resistance and high intrinsic coercivity, the proportion and types of added rare earth elements have increased to varying degrees, resulting in continuous cost increases.

[0004] In the prior art, people in the industry have continuously studied permanent magnets and optimized their manufacturing processes in order to improve the properties such as the temperature resistance of permanent magnets and reduce their production costs. For example, the invention patent application with the publication number "CN115620978A" and the name "A Rare Earth Permanent Magnet Steel and Its Preparation Method and Application", which was published on January 17, 2023, discloses that the rare earth permanent magnet steel includes a first rare earth layer, a central rare earth layer, and a second rare earth layer. By laminating and pressing neodymium iron boron rare earth layers with limited heavy rare earth element content and mass ratio, a rare earth permanent magnet steel with a gradient distribution is formed after isostatic pressing and sintering, which can give full play to the eddy current effect during the operation of the magnet steel, making the surface performance of the magnet steel sufficient to resist the demagnetizing field and the core part meet the working requirements of the wind turbine; and the central rare earth layer uses low-cost and low-performance magnet steel powder with a low rare earth content, and uses less or no heavy rare earth elements, thus saving a large amount of rare earth resources and reducing the production cost. This method uses a lamination and pressing method from the inside to the outside, reducing the use of rare earth elements and forming an internal and external gradient magnetic material performance. Although the use of rare earth elements is reduced, there is a large difference in the actual operating magnetic material temperature distribution of the semi-direct-drive wind turbine. The temperature distribution during the operation of the permanent magnet is not high in the center and low around. There is still a high-temperature environment in the core of the magnet steel. This permanent magnet with internal and external performance gradients still has a demagnetization risk during the actual operation of the motor, and this rare earth permanent magnet steel is not suitable for semi-direct-drive wind turbines.

[0005] For another example, the invention patent application with the publication number "CN112562952A" and the title "A neodymium-iron-boron permanent magnet material and its preparation method", which was published on March 26, 2021, improves the temperature resistance of the permanent magnet material through the material ratio of the neodymium-iron-boron permanent magnet material. However, the use of rare earth elements has not been significantly reduced, and the cost remains relatively high. Moreover, this solution is considered from the perspective of manufacturing single-type permanent magnets, and its relevance to the actual operating conditions of the permanent magnets in a semi-direct drive wind turbine is not close enough.

[0006] When designing a semi-direct drive wind turbine, in addition to selecting the magnetic steel according to the excitation requirements, it is also necessary to select the temperature resistance of the magnetic steel according to the operating temperature of the motor. For example, the main difference between the magnetic steels N42H and N42SH is the temperature resistance of the magnetic steel, and the price difference between the two is 10% - 15%. In other words, for permanent magnets with the same intrinsic coercivity, the change in the magnetic steel grade caused by the difference in the operating environment temperature will increase the cost. In the process of the in-depth promotion of the parity of the wind power market, how to reduce the material cost has become an important factor considered in the design process of wind turbines.

[0007] When simulating and calculating the wind turbine rotor, it is found that during the operation of the semi-direct drive salient pole rotor, the temperature difference in different regions of the rotor magnetic pole is relatively large, and the temperature difference reaches 30°C - 40°C. Refer to the appendix Figure 1 ; Cut the magnetic pole along different cross-sections to view the temperature rise distribution of different cross-sections of the permanent magnet, as shown in the appendix Figure 2 ; It can be clearly seen that the internal temperature distribution of the permanent magnet is such that the temperature on one side close to the surface of the magnetic pole is relatively high, and the temperature in the remaining regions is generally low. To ensure the operating conditions in the high-temperature region, usually only a higher grade of magnetic steel can be selected, which means an increase in cost for the permanent magnets in the regions with lower operating temperatures. Summary of the Invention

[0008] To solve the foregoing problems, the present invention proposes a gradient permanent magnet, its manufacturing method, and application, and the prepared permanent magnet matches the operating temperature conditions of the motor rotor, improving the utilization rate and economy of the permanent magnet material for the rotor of a semi-direct drive wind turbine.

[0009] The object of the present invention is achieved through the following technical solutions: A manufacturing method of a gradient permanent magnet, comprising the following steps: S1. Use finite element analysis software to obtain the temperature distribution of the permanent magnet during operation; S2. According to step S1, determine the working temperature boundary of the permanent magnet and divide the permanent magnet into different regions; S3. When manufacturing the permanent magnet, A separator plate is set in the mold. The shape and position of the separator plate are determined according to the working temperature boundary of the permanent magnet in step S2. Then, according to the separated different regions, the corresponding magnetic steel raw materials are added to each region in the mold respectively, and then preliminary pressing is carried out. Then the separator plate is taken out, and it is pressed into shape. The obtained magnetic steel green compact is then subjected to high-temperature sintering and tempering treatment; Alternatively, a gradient permanent magnet is manufactured by the local grain boundary penetration method.

[0010] Further, in step S2, according to the working temperature boundaries of permanent magnets of different grades, the magnets are divided into several temperature regions.

[0011] Further, the magnetic steel grades include N, M, H, SH, UH, EH, TH, and the corresponding working temperature boundaries are 80°C, 100°C, 120°C, 150°C, 180°C, 200°C, 230°C in sequence.

[0012] Further, in step S2, after zoning, the magnetic material ratios suitable for different temperature working conditions are selected in each temperature region. For the high-temperature region of the magnetic steel, permanent magnet raw materials with higher temperature resistance are used; for the relatively low-temperature region, permanent magnet raw materials with the same intrinsic coercivity but lower temperature resistance are used.

[0013] Further, in step S3, when preparing a permanent magnet by the separator plate method, after determining the magnetic steel raw materials according to the separated different regions, they are respectively weighed, melted at high temperature, hydrogenated and crushed into coarse particles, and then the coarse particles are pulverized into powder by a jet mill.

[0014] Further, in step S3, during preliminary pressing, a green compact is obtained by die pressing under vacuum conditions. After taking out the separator plate, die pressing and cold pressing are carried out again to compact the green compact; after sintering treatment, the sintered material needs to be subjected to primary tempering and secondary tempering treatments in sequence.

[0015] Further, in step S3, when the green compact is sintered, the treatment temperature is 1050 - 1100°C, and the treatment time is 4 - 6 h; during the primary tempering process, the treatment temperature is 850 - 900°C, and the treatment time is 2 - 4 h; during the secondary tempering process, the treatment temperature is 480 - 530°C, and the treatment time is 3 - 5 h.

[0016] Further, in step S3, when manufacturing a gradient permanent magnet by the local grain boundary penetration method, according to the zoning in step S2, after the permanent magnet blank is processed into a semi-finished product and cleaned, dysprosium or terbium, which are heavy rare earth substances, are attached to the high-temperature working condition region of the semi-finished product, and the workpiece with the attached heavy rare earth substances is subjected to grain boundary diffusion under vacuum, so that dysprosium or terbium elements penetrate to the grain boundary to obtain a gradient permanent magnet.

[0017] A gradient permanent magnet prepared by the preparation method described in any one of the foregoing.

[0018] Application of the gradient permanent magnet as described in any of the foregoing items in the preparation of a semi-direct drive wind turbine generator.

[0019] The beneficial effects of this technical solution are as follows: First, in the present invention, by using this manufacturing method, without changing the traditional raw material ratio, the permanent magnet materials can be partitioned according to the actual operating condition temperature of the magnetic materials, rather than according to the magnetic material structure. Then, different grades of existing permanent magnet raw materials are selected for each partition to achieve a temperature resistance performance gradient of the permanent magnet, which is more matched with the actual operating conditions, reducing the investment in high-temperature-resistant magnetic materials and lowering the cost of magnetic materials.

[0020] Second, in the present invention, a tooling magnetic material isolation plate matching the operating condition temperature is provided. When initially pressing the permanent magnet, it is used to distinguish different performance magnetic material raw materials. After the initial pressing is completed, the tooling isolation plate is taken out to complete the final pressing of the magnetic materials.

[0021] Third, in the present invention, without changing the existing manufacturing equipment, according to the actual operating condition temperature of the permanent magnet and the partition, a local grain boundary penetration process is adopted for the high-temperature part to achieve a temperature resistance gradient performance of the permanent magnet, which can also effectively reduce the investment in rare earth heavy elements and lower the cost of magnetic materials. Description of the Drawings

[0022] Figure 1 It is a diagram showing the analysis results of the temperature rise of the salient pole rotor magnetic poles of a permanent magnet semi-direct drive wind turbine generator.

[0023] Figure 2 It is a distribution diagram of the temperature rise of the permanent magnets at different cross-sections of the salient pole rotor magnetic poles.

[0024] Figure 3 It is a schematic diagram of the rectangular structure of the gradient permanent magnet.

[0025] Figure 4 It is a schematic diagram of the arc-shaped isolation plate structure of the gradient permanent magnet.

[0026] Figure 5 It is a structural diagram of the permanent magnet manufactured by the grain boundary penetration process method. Detailed Embodiments

[0027] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0028] In order to improve the utilization rate and economy of the permanent magnet material of the rotor of a semi-direct drive wind turbine generator, the present invention provides a gradient permanent magnet and its manufacturing method, and the obtained permanent magnet is matched with the operating condition temperature of the motor rotor and has excellent temperature resistance performance.

[0029] The manufacturing method of the gradient permanent magnet specifically includes the following steps: Step 1: When designing the permanent magnet, use finite element analysis software to calculate the operating temperature of the permanent magnet.

[0030] Step 2: According to Step S1, determine the working temperature boundary of the permanent magnet and divide the permanent magnet into different regions.

[0031] Based on the differences in the working conditions calculated by simulation, the magnet is divided into a low-temperature area and a high-temperature area with the working temperature boundaries (80°C, 100°C, 120°C, 150°C, 180°C, 200°C) of different grades of permanent magnets. For example, if the working condition temperature is 90°C to 120°C, then the high-grade permanent magnet of variety H is selected for the highest working condition temperature. Taking the working temperatures of varieties M and H as the boundary, that is, setting the temperature field of 100°C as the setting point of the tooling isolation plate. The low-temperature area selects the magnet steel of variety M, and the magnet steel is designed as a magnet with a temperature-resistant performance gradient. The temperatures set for the tooling isolation plate are shown in the following table: Step 3: When manufacturing the permanent magnet, Method 1 is to manufacture a stepped permanent magnet by setting an isolation plate method.

[0032] Set an isolation plate in the mold. The shape and position of the isolation plate are determined according to the working temperature boundary of the permanent magnet in Step 2. Then, according to the different isolated regions, add the corresponding magnet steel raw materials to each region in the mold and perform preliminary pressing. Then take out the isolation plate and press it into shape. The obtained magnet steel green compact is then subjected to high-temperature sintering and tempering treatments.

[0033] Specifically, in this solution, without changing the existing magnetic material ratio, taking a certain specific temperature as the boundary, different magnetic material ratios suitable for different temperature working conditions are selected in different regions. Refer to Figure 3 Or 4, use the permanent magnet raw materials with higher temperature resistance for the high-temperature area of the magnet steel, and use the permanent magnet raw materials with the same intrinsic coercivity but lower temperature resistance for the low-temperature area, so as to reduce the input of rare earth elements, improve the utilization rate of magnetic materials, and reduce costs.

[0034] During the manufacturing process of permanent magnets, according to the actual operating temperature distribution of the permanent magnets, a certain temperature field is selected as the boundary, and a tooling isolation plate is used to isolate the low-temperature area and the high-temperature area of the permanent magnets. Permanent magnet raw materials with corresponding temperatures and intrinsic coercivities are selected according to the highest temperature in each area. For example, when the operating temperature is 90°C to 120°C, a tooling isolation plate is set at the temperature boundary of 100°C for M and H grade magnetic materials. H grade magnetic steel raw materials are added to the high-temperature area, and M grade magnetic steel raw materials are added to the low-temperature area. They are weighed separately, melted at high temperature, hydrogenated and crushed into coarse particles, and then the coarse particles are crushed into powder form using a jet mill. Subsequently, the alloy powder is filled into the predetermined area in a mold with an isolation device under vacuum and subjected to preliminary pressing. During preliminary pressing, a green compact is obtained by means of die pressing under vacuum conditions. Then, the tooling isolation plate is removed, and the green compact is compacted again by die pressing and cold isostatic pressing; Preferably, the green compact is sintered at a treatment temperature of 1050 - 1100°C for a treatment time of 4 - 6h; Preferably, after the sintering, the preparation method further includes the steps of performing primary tempering and secondary tempering treatments on the sintered material in sequence; Preferably, during the primary tempering process, the treatment temperature is 850 - 900°C and the treatment time is 2 - 4h; Preferably, during the secondary tempering process, the treatment temperature is 480 - 530°C and the treatment time is 3 - 5h.

[0035] The manufactured permanent magnets can match the operating temperature conditions of semi-direct drive wind turbines, reducing the use of high-temperature resistant magnetic materials, thereby reducing the raw material cost.

[0036] The selection of the tooling isolation plate matches the operating conditions of the permanent magnets, and the shape matches the set temperature field boundary. Refer to Figure 3 Or 4, the shape and installation position of the isolation plate are determined by its operating conditions. The isolation plate can be in the shape of an arc plate, a rectangular plate, etc.

[0037] For the magnetic material selection in each area of the permanent magnets, in addition to selecting raw materials of magnetic materials with the same intrinsic coercivity and different temperature-resistant grades, such as N45H and N45SH, the second method can also be selected: manufacturing permanent magnets by the local grain boundary penetration process.

[0038] The method of the local grain boundary penetration process is as follows: A blank is made using the same process as the traditional process. Heavy rare earth elements dysprosium or terbium are not added in the first step (i.e., after vacuum melting of raw materials and alloying into ingots or thin strips), but after the blank is processed into a semi-finished product (to be attached with a workpiece) and cleaned, then the heavy rare earth substances dysprosium or terbium are attached to the high-temperature operating area part of the semi-finished product. The workpiece with the attached heavy rare earth substance is subjected to grain boundary diffusion under vacuum, so that the dysprosium or terbium element penetrates into the grain boundary, achieving the performance target of preparing permanent magnets with different temperature-resistant gradients.

[0039] In the process of magnetic material manufacturing, this solution does not use a separator. Only in the stage of adding heavy rare earth elements, according to the operating conditions of the magnetic material, the grain boundary penetration treatment process is carried out in the areas with higher temperature resistance requirements, which also reduces the use of heavy rare earth elements and lowers the manufacturing cost. Refer to Figure 5 .

[0040] The permanent magnet obtained by using the preparation method of the present invention has magnetic steel performance meeting the requirements of the actual operating conditions of a semi-direct drive wind turbine generator. For a single piece of magnetic steel, due to the reduction of the addition of heavy rare earth substances, the cost is saved by about 5%. Taking a 6MW semi-direct drive wind turbine generator as an example, the weight of the magnetic steel of a single unit is 1.4 tons, and the cost can be saved by about 23,000 yuan.

[0041] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A manufacturing method of a gradient permanent magnet, characterized in that, It includes the following steps: S1. Use finite element analysis software to obtain the operating temperature distribution of the permanent magnet; S2. According to step S1, determine the working temperature boundary of the permanent magnet and divide the permanent magnet into different regions; S3. When manufacturing the permanent magnet, set a separator in the mold. The shape and position of the separator are determined according to the working temperature boundary of the permanent magnet in step S2. Then, according to the isolated different regions, add the corresponding magnetic steel raw materials to each region in the mold and conduct preliminary pressing. Then take out the separator, press and form it. The obtained magnetic steel green compact is then subjected to high-temperature sintering and tempering treatment; or, use the local grain boundary penetration method to manufacture the gradient permanent magnet.

2. The manufacturing method of a gradient permanent magnet according to claim 1, characterized in that In step S2, the magnet is divided into several temperature regions according to the working temperature boundary of permanent magnets of different grades.

3. The manufacturing method of a gradient permanent magnet according to claim 2, characterized in that, The grades of the magnetic steel include N, M, H, SH, UH, EH, TH, and the corresponding working temperature boundaries are 80°C, 100°C, 120°C, 150°C, 180°C, 200°C, 230°C in sequence.

4. The manufacturing method of a gradient permanent magnet according to claim 3, characterized in that, In step S2, after zoning, select the magnetic material ratios applicable to different temperature conditions in each temperature region. Use permanent magnet raw materials with higher temperature resistance in the high-temperature region of the magnetic steel; use permanent magnet raw materials with the same intrinsic coercivity but lower temperature resistance in the relatively low-temperature region.

5. The manufacturing method of a gradient permanent magnet according to claim 4, characterized in that: In step S3, when using the separator method to prepare the permanent magnet, after determining the magnetic steel raw materials according to the isolated different regions, weigh them respectively, conduct high-temperature melting, hydrogen break them into coarse particles, and then use a jet mill to crush the coarse particles into powder form.

6. The manufacturing method of a gradient permanent magnet according to claim 5, characterized in that: In step S3, during preliminary pressing, a green compact needs to be obtained by die pressing under vacuum conditions. After taking out the separator, die pressing and cold pressing are carried out again to compact the green compact; after sintering treatment, the sintered material needs to be subjected to primary tempering and secondary tempering treatments in sequence.

7. The manufacturing method of a gradient permanent magnet according to claim 6, characterized in that: In step S3, when the green compact is sintered, the treatment temperature is 1050 - 1100°C and the treatment time is 4 - 6h; during the primary tempering process, the treatment temperature is 850 - 900°C and the treatment time is 2 - 4h; during the secondary tempering process, the treatment temperature is 480 - 530°C and the treatment time is 3 - 5h.

8. A manufacturing method of a gradient permanent magnet according to claim 1, characterized in that: In step S3, when using the local grain boundary penetration method to manufacture the gradient permanent magnet, according to the zoning in step S2, after processing the permanent magnet blank into a semi-finished product and cleaning it, attach the heavy rare earth substances dysprosium or terbium to the high-temperature working condition region of the semi-finished product, and conduct grain boundary diffusion on the workpiece with the attached heavy rare earth substances under vacuum to make the dysprosium or terbium element penetrate to the grain boundary to obtain the gradient permanent magnet.

9. A gradient permanent magnet prepared by the preparation method according to any one of claims 1 - 8.

10. Application of the gradient permanent magnet according to any one of claims 1 - 9 in the preparation of a semi-direct drive wind turbine.

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