Hydrogen decrepitation method and coarse powder of r-t-b rare earth permanent magnet

Abstract

This invention discloses a method for hydrogen decomposition of R-T-B rare earth permanent magnets. The method involves placing NdFeB alloy castings and metal balls into a reaction vessel and performing hydrogen absorption treatment under vacuum to obtain powder. The hydrogen absorption treatment includes an initial hydrogen absorption stage, a vigorous hydrogen absorption stage, and a saturated hydrogen absorption stage. In the initial hydrogen absorption stage, the rotation speed is adjusted so that the metal balls slide to point A1 within the reaction vessel. In the vigorous hydrogen absorption stage, the rotation speed is adjusted again so that the metal balls slide to point A2 within the reaction vessel. In the saturated hydrogen absorption stage, the rotation speed is adjusted again so that the metal balls slide to point A1 within the reaction vessel. The powder obtained in step S2 is then subjected to dehydrogenation treatment, cooling, separation, and transfer to obtain coarse powder. This method can produce coarse powder with a relatively uniform particle size distribution and low oxygen content. This invention also provides coarse powder obtained using this method.

Description

Technical Field

[0001] This invention belongs to the field of rare earth magnets, and specifically relates to a method for hydrogen fragmentation of RTB rare earth permanent magnets. Background Technology

[0002] In the fabrication of sintered NdFeB magnets, hydrogen breakage (HD) is a crucial pre-powdering process that determines the final magnet performance. This technology utilizes the reaction of rare earth phases with hydrogen to generate hydrides, inducing lattice volume expansion and enormous internal stress, causing the alloy casting to burst and break along the grain boundaries, providing coarse powder for subsequent air jet milling. Compared with traditional mechanical breakage methods, hydrogen breakage has advantages such as low energy consumption, high efficiency, and no pollution.

[0003] Patent application CN101051544A discloses a method for preparing high-performance sintered NdFeB magnets using an air jet mill with hydrogenation. The steps are as follows: 1) NdFeB alloy is cast into ingots using a casting process or rapidly solidified into flakes using a rapid solidification process; 2) The ingot alloy or rapidly solidified flakes is crushed into coarse powder using a hydrogen explosion process or a crusher; 3) The coarse powder is crushed into fine powder using an air jet mill, which employs a mixed compressed gas of nitrogen and hydrogen; 4) The fine powder, gasoline, and antioxidant are uniformly mixed in a mixer to obtain a mixed powder; 5) The mixed powder is pressed into a blank in a magnetic field of 1.2-2.0T; 6) The blank is placed in a high-vacuum sintering furnace and sintered at 1050-1120℃ for 2-4 hours, followed by heat treatment and tempering at 500-650℃ for 2-4 hours to obtain a sintered magnet. The magnet produced by this invention has a higher coercivity than that produced by traditional methods, and the fine powder produced by this process has a high powder yield, making it suitable for mass production of sintered NdFeB magnets.

[0004] Patent application CN108122654A discloses a grain boundary diffusion heavy rare earth neodymium iron boron magnet and its preparation method, including smelting and casting. A mixed powder is fed into a vacuum induction melting furnace and smelted under vacuum at 1000-1450℃ to form molten steel. Electromagnetic stirring is used to enhance the convection, heat transfer, and mass transfer processes of the molten steel. The electromagnetically stirred molten steel is then cast onto a copper roller with cooling water. By adjusting the rotation speed of the copper roller, the thickness of the solidified casting is made approximately 0.25 mm. Hydrogen crushing is then performed by placing the casting into a hydrogen crushing furnace to break it into mixed particles B.

[0005] However, the method disclosed in the aforementioned patent application suffers from low hydrogen absorption efficiency and poor dimensional uniformity of the powder due to the dense oxide layer on the surface of the cast billet hindering hydrogen permeation. It is evident that traditional hydrogen crushing processes have long faced two major technical bottlenecks: First, the dense oxide layer on the surface of the cast billet severely hinders initial hydrogen permeation, leading to a prolonged hydrogen absorption induction period and reduced efficiency; second, the unevenness of the hydrogenation reaction progressing from the surface to the interior results in a wide particle size distribution, a mixture of fine and coarse powder, and the presence of "uncrushed nuclei" in thick sections or dense oxide zones. These insufficiently crushed hard particles are difficult to eliminate in subsequent processes, ultimately becoming structural defects in the magnet, strongly pinning magnetic domain movement, leading to a significant decrease in coercivity, and severely affecting product consistency and reliability.

[0006] To address these issues, existing improvements such as optimizing hydrogen pressure, employing multi-stage heating, or extending holding time have failed to fundamentally break down the oxide layer barrier, resulting in limited effectiveness and often sacrificing production efficiency. While fabricating thinner cast sheets can partially improve the situation, it significantly increases process complexity and cost.

[0007] Therefore, developing a new hydrogen crushing technology that can actively break down the surface oxide layer, accelerate hydrogen diffusion, ensure uniform crushing, and be compatible with existing production lines has become an urgent need for the industry. Summary of the Invention

[0008] This invention provides a hydrogen-based crushing method for RTB rare earth permanent magnets, which can produce coarse powder with relatively uniform particle size distribution and low oxygen content.

[0009] This invention provides a method for hydrogen decomposition of RTB rare-earth permanent magnets, comprising: S1. Place the neodymium iron boron alloy casting sheet and metal balls into the reactor, wherein the ball-to-material ratio k is: 1:3 < k < 1:15, and the diameter d of the metal balls is: 1 mm < d < 7 mm. S2. Hydrogen absorption treatment is performed in a vacuum environment to obtain powder. The hydrogen absorption treatment includes an initial hydrogen absorption stage, a vigorous hydrogen absorption stage, and a saturated hydrogen absorption stage. In the initial hydrogen absorption stage, the rotation speed is adjusted so that the metal ball slides to point A1 in the reactor. In the vigorous hydrogen absorption stage, the rotation speed is adjusted again so that the metal ball slides to point A2 in the reactor. In the saturated hydrogen absorption stage, the rotation speed is adjusted again so that the metal ball slides to point A1 in the reactor. The angle between the straight line connecting point A1 and the center of the reactor and the vertical direction is between 10-20°, and the angle between the straight line connecting point A2 and the center of the reactor and the vertical direction is between 21-30°. S3. The powder obtained in step S2 is subjected to dehydrogenation treatment, cooling, separation and transfer to obtain coarse powder.

[0010] In the initial hydrogen absorption stage, the invention operates at a low sliding angle, limiting the height the metal ball moves along the inner wall of the reactor. This results in relatively mild impact kinetic energy, controlling the kinetic energy to break the oxide film on the SC sheet surface without violently shattering the SC sheet. In the intense hydrogen absorption stage, the reactor rotation speed is increased, causing the metal ball to move along the inner wall of the reactor at a higher angle, thus significantly enhancing the kinetic energy of the metal ball. At this point, the impact force of the metal ball on the casting increases, opening deeper channels for hydrogen gas and forcing it to diffuse into the material more rapidly, achieving deep hydrogen fragmentation and further reducing the particle size of the coarse powder. In the saturated hydrogen absorption stage, where the hydrogen fragmentation process is nearing its end, the reactor rotation speed and the kinetic energy of the metal ball are reduced to ensure that the final coarse powder has a relatively uniform particle size.

[0011] This invention controls the ball-to-material ratio to ensure that the metal balls have a minimum mechanical impact energy while also increasing the frequency and coverage of impacts on the SC sheets, thus facilitating more uniform crushing. If the ball-to-material ratio is too high, there will be excessive mechanical energy, resulting in overly crushed SC sheets with uneven particle size distribution and excessive oxygen content. If the ball-to-material ratio is too low, there will be insufficient mechanical energy, making it impossible to break the dense oxide film in the initial hydrogen absorption stage and to open deeper channels for hydrogen in the intense hydrogen absorption stage.

[0012] This invention controls the diameter and mass of the metal spheres to ensure sufficient kinetic energy during rotation in the reactor, effectively breaking the oxide layer on the surface of NdFeB cast sheets. Simultaneously, the appropriate volume of the metal spheres facilitates efficient movement within the SC sheet, increasing the probability of collisions. If the metal sphere diameter is too large, the few impact points result in uneven fragmentation, often with incomplete core breaking and inconsistent coarse particle size. Conversely, if the diameter is too small, the impact momentum of a single sphere is insufficient to effectively break the oxide layer, and the excessive total surface area of ​​the spheres exacerbates wear, generally leading to excessive fine powder and excessive oxygen content.

[0013] Preferably, the ball-to-material ratio k is 1:5≤k≤1:10, the diameter d of the metal ball is 3mm≤d≤5mm, and the weight of the metal ball is 10-20kg.

[0014] This invention further controls the ball-to-material ratio, the diameter of the metal balls, and the weight of the metal balls, so that the metal balls can have suitable kinetic energy and coverage area, thereby obtaining coarse powder of suitable size with low oxygen content.

[0015] Preferably, during the hydrogen absorption process, in the initial hydrogen absorption stage, the number of hydrogen absorptions is ≤0.1X; in the vigorous hydrogen absorption stage, the number of hydrogen absorptions is 0.1X-0.9X, excluding 0.1X; in the saturated hydrogen absorption stage, the number of hydrogen absorptions is ≤0.1X, where X is the saturated hydrogen absorption count, which is obtained by testing as follows: SC sheets of equal weight and specifications are placed in a reactor, and after evacuation, hydrogen gas with a positive pressure of 0.1 MPa is introduced. The positive pressure refers to the difference between the absolute pressure and the standard atmospheric pressure. The hydrogen absorption of the SC sheets causes the hydrogen pressure in the reactor to decrease, and the positive pressure in the reactor decreases to 0.05~0.06 MPa. Hydrogen gas is then introduced into the reactor again until the positive pressure is 0.1 MPa. Each hydrogen introduction action is counted as one hydrogen absorption count. After multiple hydrogen absorptions, if the pressure change is less than 0.5% within 10 minutes after a certain hydrogen introduction, it indicates that the SC sheet is saturated with hydrogen absorption. The total number of hydrogen introductions at this time is the saturated hydrogen absorption count X.

[0016] More preferably, in the initial hydrogen absorption stage, the number of hydrogen absorption cycles is 10-20; in the vigorous hydrogen absorption stage, the number of hydrogen absorption cycles is 90-120; and in the saturated hydrogen absorption stage, the number of hydrogen absorption cycles is 10-20.

[0017] Preferably, the diameter of the reactor is 2500-3500 mm, the rotation speed is 0.38-1 r / min in the initial hydrogen absorption stage, the rotation speed is 1-1.5 r / min in the vigorous hydrogen absorption stage, and the rotation speed is 0.38-1 r / min in the saturated hydrogen absorption stage.

[0018] This invention controls the size of the reactor and the rotation speed at each stage, so that the metal ball slides to a set point A1 or A2 within the reactor at different stages.

[0019] Preferably, the metal sphere is made of stainless steel, tungsten steel, nickel-based alloy, maraging steel, or quenched-tempered maraging steel. The material of the metal sphere provided by this invention is stable in a hydrogen atmosphere, does not react with hydrogen, and does not hydrogenate itself. Simultaneously, this material possesses excellent mechanical properties, has high density, and can provide sufficient mass and impact momentum to effectively impact the casting during hydrogen crushing. Furthermore, the material has high hardness, which can effectively resist wear generated during impact, thereby avoiding secondary contamination of the raw materials.

[0020] Preferably, the mass percentage of each component in the NdFeB alloy casting includes: Pr 0-10%, Nd 20-30%, B 0.9-1.1%, and Fe-Co 60-70%.

[0021] Further, the mass percentage of each component in the NdFeB alloy casting also includes: Al 0-0.5%, Cu 0-0.2%, and Ga 0.1-0.2%.

[0022] Preferably, the vacuum in the reactor is controlled below 2 Pa, and the hydrogen absorption pressure is 50-90 kPa. This invention controls the vacuum level to prevent rare earth elements from contacting residual moisture and oxygen within the reactor. By controlling the hydrogen absorption pressure, this invention provides sufficient reaction driving force for the SC wafers, ensuring sufficient and uniform hydrogen fragmentation.

[0023] Preferably, the dehydrogenation temperature is 500-580℃, the dehydrogenation time is 2-6 hours, and the highest sliding point of the metal ball in the reactor is maintained at point A1. This invention achieves efficient dehydrogenation of hydrides by controlling the dehydrogenation temperature and time, and by activating a vacuum pump, while minimizing the reflection disproportionation reaction of the NdFeB phase. During the dehydrogenation process, the metal ball can open a channel for hydrogen escape, accelerating the process.

[0024] Preferably, the cooling process involves first air cooling of the reactor, followed by water cooling. By controlling the cooling method, the cooling rate of the coarse powder is kept low, thereby obtaining coarse powder with excellent performance.

[0025] Preferably, separation and transfer are carried out under an inert gas atmosphere and a vacuum degree below 50 Pa. By controlling the vacuum degree, this invention ensures that a small amount of residual hydrogen remains in the coarse powder, effectively reducing oxidation during subsequent transfer.

[0026] This invention accelerates the separation of coarse powder and metal balls using a vibrating screen. Finally, the separated coarse powder is transferred to a stainless steel storage tank, through which inert gas is introduced to prepare for the next process.

[0027] More preferably, the inert gas is argon or nitrogen.

[0028] On the other hand, the present invention also provides a coarse powder, which is prepared by the hydrogen crushing method of an RTB rare earth permanent magnet.

[0029] Preferably, the particle size D50 of the coarse powder is 90-420 μm, and the oxygen content of the coarse powder is 800-1200 ppm.

[0030] Preferably, the coarse powder is subsequently milled by air jet milling, shaped, and sintered, and the remanence is 14.2-14.5 kGs, and the coercivity is 17.5-19 kOe.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention controls the ball-to-material ratio—the mass ratio of metal balls to NdFeB alloy cast sheets (SC sheets)—and the diameter of the metal balls. During the initial hydrogen absorption stage, the sliding position of the metal balls ensures sufficient yet gentle mechanical energy to break up the dense oxide film on the surface of the NdFeB alloy cast sheets. This facilitates hydrogen penetration, improves hydrogen absorption efficiency, and minimizes the violent fragmentation of the SC sheets, achieving better particle size uniformity. Furthermore, during the intense hydrogen absorption stage, the higher sliding position of the metal balls enhances the impact force on the cast sheets, opening deeper channels for hydrogen and forcing it to diffuse more rapidly into the material, achieving deep hydrogen fragmentation and resulting in a more uniform particle size distribution of the coarse powder. Finally, during the saturation hydrogen absorption stage, the sliding position of the metal balls, nearing the end of the hydrogen fragmentation process, reduces the impact force while maintaining a certain level of mechanical energy, ensuring relatively uniform particle size and low oxygen content in the obtained coarse powder. Attached Figure Description

[0032] Figure 1 A schematic diagram of the highest sliding point of the metal ball during the initial hydrogen absorption stage provided in Example 1; Figure 2 This is a schematic diagram of the highest sliding point of the metal ball during the intense hydrogen absorption phase provided in Example 1.

[0033] Figure 3 This is a rough physical image of the object obtained in Example 1. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0035] Example 1 This embodiment provides a method for hydrogen fragmentation of RTB rare earth permanent magnets, including: S1, with Nd as the component 29.5 Pr 2.5 B 1.03 Al 0.25 Cu 0.1 Nb 0.4 Ga 0.15 Co 0.5 Fe 65.57 Neodymium iron boron alloy castings and metal balls (by mass ratio) are placed in a reactor with a diameter of 3100 mm. The metal balls are made of 304 stainless steel with a diameter of 4 mm. The mass ratio of the metal balls to the SC castings is 1:8, and the mass of the SC castings is 800 kg.

[0036] S2. Under vacuum conditions, with a vacuum level below 2 Pa, during the initial hydrogen absorption stage (20 hydrogen absorption cycles), the rotation speed is controlled at 0.72 r / min so that the angle between the line connecting the highest sliding point of the steel ball and the center of the reactor and the vertical direction is 15°. Figure 1 As shown; during the intense hydrogen absorption phase (hydrogen absorption count 100, controlling the rotation speed to 1.1 r / min so that the angle between the line connecting the highest sliding point of the steel ball and the center of the reactor and the vertical direction is 25°, as shown)... Figure 2 As shown; during the saturation stage (20 hydrogen absorption cycles, controlling the rotation speed to 0.72 r / min so that the angle between the line connecting the highest sliding point of the steel ball and the center of the reactor and the vertical direction is 15°).

[0037] In step S3, a dehydrogenation treatment is performed at a temperature of 550°C for 3 hours. This is because without dehydrogenation treatment, the coarse powder consists entirely of hydrides. At 550°C, turning on the vacuum pump can achieve the dehydrogenation effect, allowing the metal balls to open channels for hydrogen escape during the dehydrogenation process, thus accelerating the process.

[0038] In step S4, after the dehydrogenation is completed, the reactor is cooled, and under the protection of an inert gas, the coarse powder is separated from the metal balls by a vibrating screen. The coarse powder is then transferred to a stainless steel storage tank. During the cooling process, the temperature is first lowered by air cooling, and then the reactor is cooled more quickly by water cooling. This method aims to reduce the cooling rate of the coarse powder and obtain coarse powder with excellent performance, such as… Figure 3 As shown. Simultaneously, the vacuum level must be maintained below 50 Pa to ensure a small amount of residual hydrogen in the coarse powder, effectively reducing oxidation during subsequent transfer. Argon or nitrogen is used as the inert gas, and a vibrating screen accelerates the separation of the coarse powder and metal balls. Finally, the separated coarse powder is transferred to a stainless steel storage tank, and inert gas is introduced to prepare for the next process.

[0039] Comparative Example 1 (1) Neodymium iron boron is generally made into rapidly solidified thin sheets using the traditional vacuum rapid solidification casting process; (2) Place the quick-setting sheet into the hydrogen crushing furnace, evacuate to <1Pa, and introduce hydrogen gas at about 80Pa to allow the casting sheet to fully react with the hydrogen gas. After hydrogen absorption saturation, dehydrogenation is performed to obtain coarse powder of about 100-200μm. (3) Mix the fine powder evenly in a mixer to obtain mixed powder, add it to an air jet mill and introduce nitrogen gas, so that the coarse powder particles collide with each other in a high-speed air jet to obtain fine powder with an average particle size of about 2-4 μm. (4) The mixed powder is pressed into shape in a magnetic field of 1.2-2.0T. (5) Place the blank into a high vacuum sintering furnace and sinter at 1050-1120℃ for 5-7 hours. Then, heat-treat at 800-1000℃ for 2-4 hours, and then temper at 400-600℃ for 4-5 hours to obtain the sintered magnet.

[0040] The final powder output rate was calculated by recording time and powder output quality. The powder particle size distribution was measured using a laser particle size analyzer, and the magnetic properties of the magnet were measured using a NIM magnetic property testing device. Under the condition of the same powder particle size, the results are shown in Table 1.

[0041] Table 1 shows the powder output rate and magnetic properties of the coarse powders obtained in Example 1 and Comparative Example 1. Table 1 shows that, under the premise of obtaining the same powder particle size, the method proposed in this invention exhibits several advantages over traditional methods. Specifically, the powder output rate is increased from 120 kg / h to 150 kg / h, proving that mechanical activation effectively breaks down the oxide layer and accelerates hydrogen diffusion; ultimately, the magnetic properties are simultaneously improved, with remanence (Br) increasing from 14.17 kGs to 14.25 kGs and coercivity (Hcj) significantly increasing from 16.3 kOe to 17.5 kOe. This is attributed to the significant improvement in the uniformity of the coarse powder and the optimization of its microstructure during the powder preparation process. This demonstrates that the process in Example 1 of this invention successfully achieves a synergistic breakthrough in production efficiency and magnet performance.

[0042] Examples 2-5, Comparative Examples 2-13 Compared with Example 1, the differences are that the ball-to-material ratio and the diameter of the metal balls provided in Examples 2-5 and Comparative Examples 2-5 are detailed in Table 2.

[0043] A traditional hydrogen dehydrogenation process was used to process 100 kg of neodymium iron boron alloy castings (average thickness 0.3 mm) intended for manufacturing 52M grade magnets. The process was as follows: the castings were loaded into a reactor with the ball-to-material ratio as shown in Table 2. After evacuating to 2 Pa, hydrogen gas at 90 kPa was introduced. The rolling of the steel balls and the increased surface area of ​​the castings for hydrogen absorption accelerated dehydrogenation. The entire process took approximately 5 hours, with final dehydrogenation at 560℃ for 3 hours. Table 2. Metal ball diameter, ball-to-material ratio, coarse powder particle size, and oxygen content for Examples 2-5 and Comparative Examples 2-13. In a specific embodiment of the present invention, a laser particle size analyzer is used to measure the particle size distribution and span of the powder, and an oxygen analyzer is used to measure the oxygen content of the powder. The oxygen content is based on 1200 ppm, and <1200 ppm is considered qualified, while ≥1200 ppm is considered unqualified. Analysis of Comparative Examples 2-13 and Examples 2-5 reveals that both the diameter of the metal spheres and the sphere-to-particle ratio significantly influence the particle size distribution and oxygen content of the final coarse powder. When the sphere diameter is too small (1 mm), insufficient impact momentum of a single sphere prevents effective breaking of the oxide layer. Simultaneously, the excessively large total surface area of ​​the spheres exacerbates wear, generally resulting in excessive fine powder and excessive oxygen content. When the sphere diameter is too large (7 mm), the scarcity of impact points leads to uneven crushing. Although the oxygen content decreases somewhat, the presence of unbroken cores is prevalent, and the median coarse powder particle size (D50) often exceeds 232 μm. The optimal sphere diameter range is identified as 3-5 mm, which provides moderate impact energy and good coverage area.

[0044] Regarding the ball-to-material ratio, a high ratio results in excessive total mechanical energy, invariably leading to over-fragmentation and increased oxygen content; while a low ratio, due to insufficient activation, fails to address the "unfragmented core" problem. Comprehensive evaluation shows that a ball-to-material ratio within the range of 1:5 to 1:10 ensures the best overall activation effect. Therefore, determining the parameter range provided in this invention facilitates the efficient synergy between mechanical energy and the hydrogenation reaction.

[0045] Comparative Example 14 Compared with Example 1, the difference is that in the initial hydrogen absorption stage provided by Comparative Example 14, the rotation speed is controlled at 0.36 r / min so that the angle between the line connecting the highest sliding point of the steel ball and the center of the reactor and the vertical direction is 7°.

[0046] Comparative Example 15 Compared with Example 1, the difference is that in the initial hydrogen absorption stage provided by Comparative Example 15, the rotation speed is controlled at 1.3 r / min so that the angle between the line connecting the highest sliding point of the steel ball and the center of the reactor and the vertical direction is 30°.

[0047] Comparative Example 16 Compared to Example 1, the difference is that in the intense hydrogen absorption stage provided by Comparative Example 16, the rotation speed is controlled at 0.98 r / min so that the angle between the line connecting the highest sliding point of the steel ball and the center of the reactor and the vertical direction is 18°.

[0048] Comparative Example 17 Compared to Example 1, the difference is that in the intense hydrogen absorption stage provided by Comparative Example 17, the rotation speed is controlled at 1.53 r / min so that the angle between the line connecting the highest sliding point of the steel ball and the center of the reactor and the vertical direction is 35°.

[0049] Comparative Example 18 Compared with Example 1, the difference is that in the saturated hydrogen absorption stage provided by Comparative Example 18, the rotation speed is controlled at 0.22 r / min so that the angle between the line connecting the highest sliding point of the steel ball and the center of the reactor and the vertical direction is 5°.

[0050] Comparative Example 19 Compared with Example 1, the difference is that in the saturated hydrogen absorption stage provided by Comparative Example 17, the rotation speed is controlled at 1.25 r / min so that the angle between the line connecting the highest sliding point of the steel ball and the center of the reactor and the vertical direction is 28°.

[0051] Table 3. Particle size, span, and oxygen content of the coarse powder provided by Comparative Examples 14-15 Compared with Example 1, analysis of Comparative Examples 14-19 reveals that in the initial stage, adjusting the reactor rotation speed controls the angle of the steel balls. Too fast or too slow a rotation speed results in varying degrees of collision between the cast iron and the steel balls during hydrogen crushing, leading to either excessively coarse or excessively fine coarse particles. Coarse particles do not meet size requirements, affecting subsequent powdering, while fine particles have a high oxygen content. During the intense hydrogen absorption stage, too slow a rotation speed results in a low maximum sliding point of the metal balls within the reactor, leading to excessively coarse particles and a high oxygen content; too fast a rotation speed results in a high maximum sliding point of the metal balls within the reactor, leading to excessively fine coarse particles and a similarly high oxygen content. In the saturated hydrogen absorption stage, too slow a rotation speed results in a low maximum sliding point of the metal balls within the reactor, leading to excessively coarse particles; too fast a rotation speed results in a high maximum sliding point of the metal balls within the reactor, leading to excessively fine coarse particles and an excessively high oxygen content.

[0052] Comparative Example 20 This example will have a composition of Nd. 29.5 Pr 2.5 B 1.03 Al 0.25 Cu 0.1 Nb 0.4 Ga 0.15 Co 0.5 Fe 65.57 (by mass) NdFeB alloy castings were placed in the same reactor as in Example 1. The reactor was 3100 mm in size and the SC castings weighed 800 kg. The dehydrogenation was carried out using the conventional method without the addition of steel balls. The dehydrogenation time was 4 h. The results are shown in Table 4.

[0053] Table 4 shows the dehydrogenation time and hydrogen content provided for Example 1 and Comparative Example 20. During the hydrogen crushing process, five points were randomly sampled in chronological order to detect the hydrogen content, and the average hydrogen content of the five samples was calculated.

[0054] Based on the comparative experimental data from Example 1 and Comparative Example 20, under the same dehydrogenation temperature conditions, the traditional dehydrogenation method requires 4 hours to reduce the hydrogen content to 900 ppm, while the method of the present invention only requires 3 hours to achieve the same hydrogen content level. This indicates that the present invention, by introducing mechanical activation assistance, can open the hydrogen escape channel during the dehydrogenation process, accelerate the dehydrogenation process, and significantly improve the dehydrogenation efficiency. While maintaining comparable product quality, the dehydrogenation time is shortened by 25%, effectively improving production efficiency and reducing energy consumption.

Claims

1. A method for hydrogen fragmentation of RTB rare earth permanent magnets, characterized in that, include: S1. Place the neodymium iron boron alloy casting sheet and metal balls into the reactor, wherein the ball-to-material ratio k is: 1:3 < k < 1:15, and the diameter d of the metal balls is: 1 mm < d < 7 mm. S2. Hydrogen absorption treatment is performed in a vacuum environment to obtain powder. The hydrogen absorption treatment includes an initial hydrogen absorption stage, a vigorous hydrogen absorption stage, and a saturated hydrogen absorption stage. In the initial hydrogen absorption stage, the rotation speed is adjusted so that the metal ball slides to point A1 in the reactor. In the vigorous hydrogen absorption stage, the rotation speed is adjusted again so that the metal ball slides to point A2 in the reactor. In the saturated hydrogen absorption stage, the rotation speed is adjusted again so that the metal ball slides to point A1 in the reactor. The angle between the straight line connecting point A1 and the center of the reactor and the vertical direction is between 10-20°, and the angle between the straight line connecting point A2 and the center of the reactor and the vertical direction is between 21-30°. S3. The powder obtained in step S2 is subjected to dehydrogenation treatment, cooling, separation and transfer to obtain coarse powder.

2. The hydrogen fragmentation method for RTB rare earth permanent magnets according to claim 1, characterized in that, The ball-to-material ratio k is 1:5≤k≤1:10, the diameter d of the metal ball is 3mm≤d≤5mm, and the weight of the metal ball is 10-20kg.

3. The hydrogen fragmentation method for RTB rare earth permanent magnets according to claim 1, characterized in that, During the hydrogen absorption process, in the initial hydrogen absorption stage, the number of hydrogen absorptions is ≤0.1X; in the vigorous hydrogen absorption stage, the number of hydrogen absorptions is 0.1X-0.9X, excluding 0.1X; in the saturated hydrogen absorption stage, the number of hydrogen absorptions is ≤0.1X, where X is the number of saturated hydrogen absorptions.

4. The hydrogen fragmentation method for RTB rare earth permanent magnets according to claim 1, characterized in that, The reactor has a diameter of 2500-3500 mm. During the initial hydrogen absorption stage, the rotation speed is 0.38-1 r / min; during the vigorous hydrogen absorption stage, the rotation speed is 1-1.5 r / min; and during the saturated hydrogen absorption stage, the rotation speed is 0.38-1 r / min.

5. The hydrogen fragmentation method for RTB rare earth permanent magnets according to claim 1, characterized in that, The metal sphere is made of stainless steel, tungsten steel, nickel-based alloy, maraging steel, or quenched-tempered maraging steel.

6. The hydrogen fragmentation method for RTB rare earth permanent magnets according to claim 1, characterized in that, In the reactor, the vacuum is controlled below 2 Pa, and the hydrogen absorption pressure is 50-90 kPa.

7. The hydrogen fragmentation method for RTB rare earth permanent magnets according to claim 1, characterized in that, The dehydrogenation temperature of the dehydrogenation treatment is 500-580℃, the dehydrogenation time is 2-6h, and the highest sliding point of the metal ball in the reactor is maintained at point A1.

8. The hydrogen fragmentation method for RTB rare earth permanent magnets according to claim 1, characterized in that, The cooling process involves first air cooling the reactor, followed by water cooling.

9. A coarse powder, prepared by the hydrogen crushing method for RTB rare earth permanent magnets according to any one of claims 1-8.

10. The coarse powder according to claim 9, characterized in that, The average coarse powder particle size D50 is 90-420μm, and the oxygen content of the coarse powder is 400-1200ppm.

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