A uniform heat treatment process for NdFeB permanent magnet materials

Abstract

The present invention relates to the technical field of heat treatment of NdFeB permanent magnet materials, specifically a uniform heat treatment process for NdFeB permanent magnet materials. A uniform heat treatment process for NdFeB permanent magnet materials comprises the following steps: preparation of fluorinated carbon nanotubes; preparation of permanent magnet powder containing fluorinated carbon nanotubes; ultrasonic preheating of the permanent magnet powder; and uniform heat treatment of the permanent magnet. In the process of tempering the sintered magnetic blocks, the present invention allows plasma with good thermal conductivity to fill the tempering furnace, and uses a magnetic field generating device to offset the magnetic field generated by the magnetic blocks, preventing the magnetic field from affecting the distribution of the plasma, thereby making the plasma uniformly distributed in the tempering furnace. When some heating burners are started to perform low-temperature tempering treatment on the magnetic blocks, heat can also be evenly distributed in the tempering furnace through the plasma, so that the magnetic blocks are evenly heated, thereby better improving the coercive force of the NdFeB permanent magnet material.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of NdFeB permanent magnet materials, in particular to a uniform heat treatment process of NdFeB permanent magnet materials. Background Art

[0002] NdFeB is a tetragonal crystal formed by neodymium, iron and boron. Due to its extremely high magnetism and high coercivity, it is widely used in motors, human magnetic resonance imaging devices, communications and other fields. It is the most commonly used rare earth magnet today.

[0003] NdFeB is divided into sintered NdFeB and bonded NdFeB. Sintered NdFeB is prepared through batching, smelting, powder making, pressing, sintering and tempering heat treatment and subsequent processing. Sintering and tempering heat treatment is the most critical step in the process of preparing sintered NdFeB. Tempering heat treatment of sintered NdFeB magnets can greatly improve their coercive force.

[0004] The existing NdFeB magnet tempering heat treatment process usually places the sintered NdFeB magnet in a tempering furnace and directly heats it through the burners in the tempering furnace, which can adjust the furnace temperature faster and more conveniently. However, when the tempering furnace is heated at a low temperature, only a part of the burners are started to heat the furnace, and the gaps between the opened burners become larger. In addition, since the burners are installed on the furnace wall, the local temperature of the steel plate is too high, resulting in uneven temperature in the furnace, which makes the NdFeB magnet heated unevenly during the heat treatment process, affecting the heat treatment effect of the NdFeB magnet.

[0005] In order to solve the above process difficulties, the present invention studies a uniform heat treatment process for NdFeB permanent magnet materials, which can make NdFeB magnets be heated uniformly during the heat treatment process, thereby better improving the coercive force of the magnets. Summary of the Invention

[0006] In order to solve the above technical defects, the present invention studies a uniform heat treatment process for NdFeB permanent magnet materials, which can make NdFeB magnets be heated uniformly during the heat treatment process, thereby better improving the coercive force of the magnets.

[0007] A uniform heat treatment process for NdFeB permanent magnet material comprises the following steps:

[0008] S1: Preparation of fluorinated carbon nanotubes

[0009] A funnel is installed at the top of the container to control the falling speed of the powder in the funnel. Carbon nanotubes are placed in the funnel, and carbon tetrafluoride gas is introduced into the container. The container is then closed and heated at high temperature for a period of time. The funnel is opened to allow the carbon nanotubes to fall slowly. The resulting solid powder is cooled to obtain fluorinated carbon nanotubes.

[0010] S2: Preparation of permanent magnet powder

[0011] Nd, Fe, Dy, Cu and B are uniformly mixed and then smelted to obtain an alloy melt, the alloy melt is cast to obtain a permanent magnet ingot, the permanent magnet ingot is subjected to microwave heating and then hydrogen-crushed together with a catalyst, the crushed ingot is taken out after standing to obtain permanent magnet particles, the permanent magnet particles and fluorinated carbon nanotubes are placed in a jet mill for jet milling to obtain permanent magnet powder;

[0012] S3: Ultrasonic preheating of permanent magnet powder

[0013] Permanent magnetic powder, a solvent, and a surfactant are mixed and added to a container to obtain a mixture, the mixture in the container is heated and stirred to obtain a homogeneous solution, the container containing the homogeneous solution is placed in an ultrasonic generator, and the homogeneous solution is ultrasonically heated. The homogeneous solution is heated under ultrasonic treatment, and the solvent evaporates until only solid powder remains in the homogeneous solution, and the preheated permanent magnetic powder is collected;

[0014] S4: Uniform heat treatment of permanent magnets

[0015] The preheated permanent magnetic powder is placed in a mold, and a strong magnetic field is applied to directionally press it between the plates to obtain a material block. The material block is isostatically pressed to obtain a compact. The compact is sintered at high temperature and then placed in a tempering furnace for high temperature tempering to obtain a high temperature tempered magnetic block. A plasma generator is started to introduce plasma into the tempering furnace. When the plasma content reaches a certain value, the tempering furnace is closed. A magnetic field generating device is placed near the tempering furnace. After eliminating the magnetic field of the magnetic block, the magnetic block is low-temperature heated and cooled to obtain a neodymium iron boron permanent magnetic material.

[0016] Furthermore, the preparation of fluorinated carbon nanotubes in step S1 includes the following steps:

[0017] S1.1: Install a funnel at the top of a container to control the falling speed of the powder in the funnel. Place 5-6 portions of carbon nanotubes in the funnel and introduce carbon tetrafluoride gas to a concentration of 90-95% of the total gas content in the container. Seal the container to obtain a closed container.

[0018] S1.2: Place the sealed container in a muffle furnace and heat it at 600-650°C for 20-25 minutes. At the same time, open the funnel to allow the carbon nanotubes to fall to the bottom of the container within 20-25 minutes. Remove the resulting solid powder and cool it naturally for 1.5-2 hours to obtain fluorinated carbon nanotubes.

[0019] Furthermore, step S2 of preparing a permanent magnetic powder containing fluorinated carbon nanotubes comprises the following steps:

[0020] S2.1: 25-27 parts of Nd, 60-62 parts of Fe, 1.3-1.5 parts of Dy, 0.9-1.1 parts of Cu, and 1-1.2 parts of B are mixed and smelted in a vacuum suspension furnace to obtain an alloy melt, which is then poured into a water-cooled copper mold to obtain a permanent magnet ingot;

[0021] S2.2: Place the permanent magnet ingot in an industrial microfurnace and microwave-heat it at 200-220°C for 15-20 minutes. Place the microwave-heated permanent magnet ingot and 6-7 parts of catalyst in a hydrogen crushing furnace. Add hydrogen to the furnace to keep the pressure at 10-12 MPa. Adjust the temperature to 350-400°C and hydrogen-crush the ingot for 20-25 minutes. Then stop heating and let it stand for 2-3 hours. Remove the crushed ingot to obtain permanent magnet particles.

[0022] S2.3: Place the permanent magnetic particles and 5-7 parts of fluorinated carbon nanotubes into a jet mill, adjust the jet mill power to 200-250kw, and the gas consumption to 30-35m 3 / min, the gas pressure is 0.7-0.8Mpa, and the permanent magnetic particles and fluorinated carbon nanotubes are mixed and jet milled for 25-30 minutes to obtain permanent magnetic powder.

[0023] Furthermore, step S3 of ultrasonic preheating of the permanent magnet powder comprises the following steps:

[0024] S3.1: Mix the permanent magnet powder, 200-220 parts of solvent, and 15-20 parts of surfactant in a container to obtain a mixture. Adjust the temperature to 40-45°C and the rotation speed to 200-220 rpm to stir the mixture in the container for 40-45 minutes to obtain a homogeneous solution.

[0025] S3.2: Place the container containing the homogeneous solution into an ultrasonic generator, adjust the ultrasonic frequency to 25-28KHz, and ultrasonically heat the homogeneous solution. The homogeneous solution heats up under ultrasonic treatment and the solvent evaporates until only solid powder remains in the homogeneous solution. The preheated permanent magnetic powder is collected.

[0026] Furthermore, step S4, uniform heat treatment of the permanent magnet, comprises the following steps:

[0027] S4.1: Place the preheated permanent magnetic powder in a mold, apply a strong magnetic field, and directionally press the preheated permanent magnetic powder between the plates to obtain a material block. Immerse the material block in a cold isostatic press under great pressure for isostatic pressing to obtain a briquette;

[0028] S4.2: Place the compact in a vacuum sintering furnace and sinter at a temperature of 1100-1200°C for 3-3.5 hours to obtain a sintered magnetic block. Place the sintered magnetic block in a tempering furnace, start the heating burner, and heat the furnace at a temperature of 850-900°C for 55-60 minutes to obtain a high-temperature tempered magnetic block.

[0029] S4.3: Start the plasma generator, adjust the power to 0.5-0.6MW, and introduce plasma into the tempering furnace until the plasma content in the tempering furnace reaches 90-95%. Close the tempering furnace, place a magnetic field generating device near the tempering furnace, adjust the direction of the magnetic field to be opposite to the magnetic field generated by the high-temperature tempered magnetic block, and adjust the magnetic field strength until the compass is observed to point accurately to the south, eliminate the magnetic field of the magnetic block, start the heating burner, and heat at a temperature of 475-500℃ for 1-1.5 hours. Then, water quench the obtained low-temperature tempered magnetic block to room temperature to obtain NdFeB permanent magnet material.

[0030] Furthermore, the catalyst in step S2.2 is aluminum oxide.

[0031] Furthermore, the gas used for jet milling in step S2.3 is nitrogen.

[0032] Furthermore, the surfactant in step S3.1 is sodium dodecylbenzenesulfonate.

[0033] Furthermore, in step S3.1, the material of the container is ceramic.

[0034] Furthermore, the solvent in step S3.1 is acetone.

[0035] The beneficial effects are: 1. In the process of tempering heat treatment of the sintered magnetic blocks, the present invention first performs normal high-temperature tempering treatment on the magnetic blocks, then fills the tempering furnace with plasma with good thermal conductivity, and offsets the magnetic field generated by the magnetic blocks through a magnetic field generating device to prevent the magnetic field from affecting the distribution of the plasma, thereby making the plasma evenly distributed in the tempering furnace. When some heating burners are started to perform low-temperature tempering treatment on the magnetic blocks, the heat can also be evenly distributed in the tempering furnace through the plasma, so that the magnetic blocks are evenly heated, thereby better improving the coercive force of the NdFeB permanent magnet material.

[0036] 2. The present invention fluorinates carbon nanotubes to obtain fluorinated carbon nanotubes, and adds fluorinated carbon nanotubes during the air flow milling process of permanent magnetic particles to fully mix the two and obtain permanent magnetic powder with smaller particle size. C and F elements are introduced into the subsequently prepared magnetic blocks to enhance the thermal conductivity of the magnetic blocks, so that the magnetic blocks can be heated more evenly during the heat treatment process, thereby improving the coercive force of the NdFeB permanent magnet material.

[0037] 3. The present invention controls the falling speed of carbon nanotube powder through a funnel, causing it to slowly fall from the top in a container filled with carbon tetrafluoride, and applies high temperature to allow the carbon nanotube powder to fully contact and react with carbon tetrafluoride gas, thereby increasing the output rate of fluorinated carbon nanotubes.

[0038] 4. The present invention disperses the permanent magnetic powder evenly in a solvent and then ultrasonically heats the homogeneous solution until the solvent evaporates. This significantly reduces the inhomogeneous phase α-Fe in the obtained permanent magnetic powder, reduces the stress between the components in the powder, and makes the distribution of the components in the powder more uniform. In the subsequent heat treatment, the magnetic blocks are heated more evenly, thereby improving the coercive force of the NdFeB permanent magnetic material.

[0039] 5. The present invention first performs microwave heating treatment on the permanent magnet ingot to make the molecules of the permanent magnet ingot more active and enhance its surface activity, and adds a catalyst during the hydrogen crushing process to improve the subsequent binding ability of hydrogen and the permanent magnet ingot, thereby improving the effect of hydrogen crushing and obtaining permanent magnet particles with smaller particle size. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a process flow chart for uniform heat treatment of NdFeB permanent magnet material used in an embodiment of the present invention.

[0041] Figure 2 This is a table comparing the coercive forces of the NdFeB permanent magnet material prepared in the embodiment of Comparative Example 1 of the present invention and the NdFeB permanent magnet material prepared by the traditional process for preparing NdFeB magnets.

[0042] Figure 3 This is a table comparing the coercive forces of the NdFeB permanent magnet material prepared in Example 2 of the present invention and the NdFeB permanent magnet material prepared without adding fluorinated carbon nanotubes.

[0043] Figure 4 This is a table comparing the coercive forces of the NdFeB permanent magnet material prepared in Example 1 of the present invention and the NdFeB permanent magnet material prepared in Example 3 without the operation of introducing plasma into the tempering furnace and eliminating the magnetic field.

[0044] Figure 5 This is a table comparing the coercive forces of the NdFeB permanent magnet material prepared in the embodiment of Comparative Example 2 of the present invention and the NdFeB permanent magnet material prepared by removing step S3.

[0045] Figure 6 This is a table comparing the quality of the permanent magnet particles obtained by hydrogen crushing the permanent magnet ingots in Example 5 of the present invention and Comparative Example 5, which are sieved through a 100-mesh screen.

[0046] Figure 7This is a table comparing the fluorine atom content after the reaction of carbon nanotubes and carbon tetrafluoride when a funnel is provided and when no funnel is provided in Comparative Example 6 of the present invention. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] Example 1

[0049] A uniform heat treatment process for NdFeB permanent magnet materials, such as Figure 1 As shown, the following steps are included:

[0050] S1: Preparation of fluorinated carbon nanotubes

[0051] S1.1: Install a funnel at the top of a container to control the falling speed of the powder in the funnel. Place 5 portions of carbon nanotubes in the funnel and introduce carbon tetrafluoride gas to a concentration of 90% of the total gas content in the container. Seal the container to obtain a closed container.

[0052] S1.2: Place the closed container in a muffle furnace and heat it at 600°C for 20 minutes. At the same time, open the funnel to allow the carbon nanotubes to fall to the bottom of the container within 20 minutes. Take out the obtained solid powder and cool it naturally for 1.5 hours to obtain fluorinated carbon nanotubes. Introduce C and F elements into the magnetic block to enhance the thermal conductivity of the magnetic block, so that the magnetic block can be better and more evenly heated during the heat treatment process, thereby improving the coercive force of the NdFeB permanent magnet material.

[0053] S2: Preparation of permanent magnetic powder containing fluorinated carbon nanotubes

[0054] S2.1: 25 parts of Nd, 60 parts of Fe, 1.3 parts of Dy, 0.9 parts of Cu, and 1 part of B are mixed and smelted in a vacuum suspension furnace to obtain an alloy melt, which is then poured into a water-cooled copper mold to obtain a permanent magnet ingot;

[0055] S2.2: The permanent magnet ingot is placed in an industrial micro furnace and microwave-heated at 200°C for 15 minutes to improve the subsequent hydrogen-to-ingot bonding ability and the hydrogen crushing efficiency. The microwave-heated permanent magnet ingot and 6 parts of alumina are placed in a hydrogen crushing furnace. The alumina further improves the hydrogen crushing efficiency. Hydrogen is introduced to keep the furnace pressure at 10 MPa and the temperature at 350°C. The ingot is hydrogen-crushed for 20 minutes. The heating is then stopped and the mixture is allowed to stand for 2 hours. The crushed ingot is then removed to obtain permanent magnet particles.

[0056] S2.3: Place the permanent magnetic particles and 5 parts of fluorinated carbon nanotubes into the air flow mill, adjust the power of the air flow mill to 200 kW, blow in nitrogen, and the gas consumption is 30 m3 / s. 3 / min, the gas pressure is 0.7 MPa, and the permanent magnetic particles and fluorinated carbon nanotubes are jet milled for 25 minutes to obtain permanent magnetic powder.

[0057] S3: Ultrasonic preheating of permanent magnet powder

[0058] S3.1: Mix the permanent magnet powder, 200 parts of acetone, and 15 parts of sodium dodecylbenzenesulfonate in a ceramic container to obtain a mixture. Stir the mixture in the ceramic container at a temperature of 40°C and a speed of 200 rpm for 40 minutes to obtain a homogeneous solution.

[0059] S3.2: Place the ceramic container containing the homogeneous solution into the ultrasonic generator, adjust the ultrasonic frequency to 25KHz, and perform ultrasonic heating on the homogeneous solution. The homogeneous solution heats up under ultrasonic treatment, and the acetone evaporates until only solid powder remains in the homogeneous solution, which greatly reduces the inhomogeneous phase α-Fe in the permanent magnetic powder, reduces the stress between the components in the powder, makes the distribution of the components in the powder more uniform, and makes the magnetic block better heated evenly in the subsequent heat treatment.

[0060] S4: Uniform heat treatment of permanent magnets

[0061] S4.1: Place the preheated permanent magnetic powder in a mold, apply a strong magnetic field, and directionally press the preheated permanent magnetic powder between the plates to obtain a material block. Immerse the material block in a cold isostatic press under great pressure for isostatic pressing to obtain a briquette;

[0062] S4.2: Place the compact in a vacuum sintering furnace and sinter at 1100°C for 3 hours. Place the resulting sintered magnetic block in a tempering furnace, start the heating burner, and heat the furnace at 850°C for 55 minutes to obtain a high-temperature tempered magnetic block.

[0063] S4.3: Start the plasma generator, adjust the power to 0.5MW, and introduce plasma into the tempering furnace until the plasma content in the tempering furnace reaches 90%. Close the tempering furnace, place a magnetic field generating device near the tempering furnace, adjust the direction of the magnetic field to be opposite to the magnetic field generated by the high-temperature tempered magnetic block, and adjust the magnetic field strength until the compass is observed to point accurately to the south, eliminate the magnetic field of the magnetic block, and prevent the magnetic field from affecting the distribution of plasma, so that the plasma is evenly distributed in the tempering furnace. When some heating burners are started to perform low-temperature tempering treatment on the magnetic block, heat can also be evenly distributed in the tempering furnace through the plasma, so that the magnetic block is evenly heated, and the coercive force of the NdFeB permanent magnet material is better improved. Start the heating burner and heat at 475℃ for 1 hour. Then the obtained low-temperature tempered magnetic block is water quenched and cooled to room temperature to obtain NdFeB permanent magnet material.

[0064] Example 2

[0065] A uniform heat treatment process for NdFeB permanent magnet materials, such as Figure 1 As shown, the following steps are included:

[0066] S1: Preparation of fluorinated carbon nanotubes

[0067] S1.1: Install a funnel at the top of a container to control the falling speed of the powder in the funnel. Place 6 portions of carbon nanotubes in the funnel and introduce carbon tetrafluoride gas to a concentration of 90% of the total gas content in the container. Seal the container to obtain a closed container.

[0068] S1.2: Place the closed container in a muffle furnace and heat it at 600°C for 20 minutes. At the same time, open the funnel to allow the carbon nanotubes to fall to the bottom of the container within 20 minutes. Take out the obtained solid powder and cool it naturally for 1.5 hours to obtain fluorinated carbon nanotubes. Introduce C and F elements into the magnetic block to enhance the thermal conductivity of the magnetic block, so that the magnetic block can be heated more evenly during the heat treatment process, thereby improving the coercive force of the NdFeB permanent magnet material.

[0069] S2: Preparation of permanent magnetic powder containing fluorinated carbon nanotubes

[0070] S2.1: 27 parts of Nd, 62 parts of Fe, 1.5 parts of Dy, 1.1 parts of Cu, and 1.2 parts of B are mixed and smelted in a vacuum suspension furnace to obtain an alloy melt, which is then poured into a water-cooled copper mold to obtain a permanent magnet ingot;

[0071] S2.2: The permanent magnet ingot is placed in an industrial micro furnace and microwave-heated at 200°C for 15 minutes to improve the subsequent hydrogen-to-ingot bonding ability and the hydrogen crushing efficiency. The microwave-heated permanent magnet ingot and 6 parts of alumina are placed in a hydrogen crushing furnace. The alumina further improves the hydrogen crushing efficiency. Hydrogen is introduced to keep the furnace pressure at 10 MPa and the temperature at 350°C. The ingot is hydrogen-crushed for 20 minutes. The heating is then stopped and the mixture is allowed to stand for 2 hours. The crushed ingot is then removed to obtain permanent magnet particles.

[0072] S2.3: Place the permanent magnetic particles and 7 parts of fluorinated carbon nanotubes into a jet mill. Adjust the jet mill power to 200 kW and blow nitrogen gas into the mill. The gas consumption is 30 m3 / min. 3 / min, the gas pressure is 0.7 MPa, and the permanent magnetic particles and fluorinated carbon nanotubes are jet milled for 25 minutes to obtain permanent magnetic powder.

[0073] S3: Ultrasonic preheating of permanent magnet powder

[0074] S3.1: Mix the permanent magnet powder, 220 parts of acetone, and 20 parts of sodium dodecylbenzenesulfonate in a ceramic container to obtain a mixture. Stir the mixture in the ceramic container at a temperature of 40°C and a speed of 200 rpm for 40 minutes to obtain a homogeneous solution.

[0075] S3.2: Place the ceramic container containing the homogeneous solution into the ultrasonic generator, adjust the ultrasonic frequency to 25KHz, and perform ultrasonic heating on the homogeneous solution. The homogeneous solution heats up under ultrasonic treatment, and the acetone evaporates until only solid powder remains in the homogeneous solution, which greatly reduces the inhomogeneous phase α-Fe in the permanent magnetic powder, reduces the stress between the components in the powder, makes the distribution of the components in the powder more uniform, and makes the magnetic block better heated evenly in the subsequent heat treatment.

[0076] S4: Uniform heat treatment of permanent magnets

[0077] S4.1: Place the preheated permanent magnetic powder in a mold, apply a strong magnetic field, and directionally press the preheated permanent magnetic powder between the plates to obtain a material block. Immerse the material block in a cold isostatic press under great pressure for isostatic pressing to obtain a briquette;

[0078] S4.2: Place the compact in a vacuum sintering furnace and sinter at 1100°C for 3 hours. Place the resulting sintered magnetic block in a tempering furnace, start the heating burner, and heat the furnace at 850°C for 55 minutes to obtain a high-temperature tempered magnetic block.

[0079] S4.3: Start the plasma generator, adjust the power to 0.5MW, and introduce plasma into the tempering furnace until the plasma content in the tempering furnace reaches 90%. Close the tempering furnace, place a magnetic field generating device near the tempering furnace, adjust the direction of the magnetic field to be opposite to the magnetic field generated by the high-temperature tempered magnetic block, and adjust the magnetic field strength until the compass is observed to point accurately to the south, eliminate the magnetic field of the magnetic block, and prevent the magnetic field from affecting the distribution of plasma, so that the plasma is evenly distributed in the tempering furnace. When some heating burners are started to perform low-temperature tempering treatment on the magnetic block, heat can also be evenly distributed in the tempering furnace through the plasma, so that the magnetic block is evenly heated, and the coercive force of the NdFeB permanent magnet material is better improved. Start the heating burner and heat at 475℃ for 1 hour. Then the obtained low-temperature tempered magnetic block is water quenched and cooled to room temperature to obtain NdFeB permanent magnet material.

[0080] Example 3

[0081] A uniform heat treatment process for NdFeB permanent magnet materials, such as Figure 1 As shown, the following steps are included:

[0082] S1: Preparation of fluorinated carbon nanotubes

[0083] S1.1: Install a funnel at the top of a container to control the falling speed of the powder in the funnel. Place 5 parts of carbon nanotubes in the funnel and introduce carbon tetrafluoride gas to a concentration of 95% of the total gas content in the container. Seal the container to obtain a closed container.

[0084] S1.2: Place the closed container in a muffle furnace and heat it at 650°C for 25 minutes. At the same time, open the funnel to allow the carbon nanotubes to fall to the bottom of the container within 25 minutes. Take out the obtained solid powder and cool it naturally for 2 hours to obtain fluorinated carbon nanotubes. Introduce C and F elements into the magnetic block to enhance the thermal conductivity of the magnetic block, so that the magnetic block can be heated more evenly during the heat treatment process, thereby improving the coercive force of the NdFeB permanent magnet material.

[0085] S2: Preparation of permanent magnetic powder containing fluorinated carbon nanotubes

[0086] S2.1: 25 parts of Nd, 60 parts of Fe, 1.3 parts of Dy, 0.9 parts of Cu, and 1 part of B are mixed and smelted in a vacuum suspension furnace to obtain an alloy melt, which is then poured into a water-cooled copper mold to obtain a permanent magnet ingot;

[0087] S2.2: The permanent magnet ingot is placed in an industrial micro furnace and microwave-heated at 220°C for 20 minutes to improve the subsequent hydrogen-to-ingot bonding ability and the hydrogen crushing efficiency. The microwave-heated permanent magnet ingot and 6 parts of alumina are placed in a hydrogen crushing furnace. The alumina further improves the hydrogen crushing efficiency. Hydrogen is introduced to keep the furnace pressure at 12 MPa and the temperature at 400°C. The ingot is hydrogen-crushed for 25 minutes. The heating is then stopped and the mixture is allowed to stand for 3 hours. The crushed ingot is then removed to obtain permanent magnet particles.

[0088] S2.3: Place the permanent magnetic particles and 5 parts of fluorinated carbon nanotubes into the air flow mill. Adjust the power of the air flow mill to 250 kW and blow in nitrogen gas with a gas consumption of 35 m3 / min. 3 / min, the gas pressure is 0.8 MPa, and the permanent magnetic particles and fluorinated carbon nanotubes are jet milled for 30 minutes to obtain permanent magnetic powder.

[0089] S3: Ultrasonic preheating of permanent magnet powder

[0090] S3.1: Mix the permanent magnet powder, 200 parts of acetone, and 15 parts of sodium dodecylbenzenesulfonate in a ceramic container to obtain a mixture. Stir the mixture in the ceramic container at a temperature of 45°C and a speed of 220 rpm for 45 minutes to obtain a homogeneous solution.

[0091] S3.2: Place the ceramic container containing the homogeneous solution into the ultrasonic generator, adjust the ultrasonic frequency to 28KHz, and perform ultrasonic heating on the homogeneous solution. The homogeneous solution heats up under ultrasonic treatment, and the acetone evaporates until only solid powder remains in the homogeneous solution, which greatly reduces the inhomogeneous phase α-Fe in the permanent magnetic powder, reduces the stress between the components in the powder, makes the distribution of the components in the powder more uniform, and makes the magnetic block more evenly heated in the subsequent heat treatment.

[0092] S4: Uniform heat treatment of permanent magnets

[0093] S4.1: Place the preheated permanent magnetic powder in a mold, apply a strong magnetic field, and directionally press the preheated permanent magnetic powder between the plates to obtain a material block. Immerse the material block in a cold isostatic press under great pressure for isostatic pressing to obtain a briquette;

[0094] S4.2: Place the compact in a vacuum sintering furnace and sinter at 1200°C for 3.5 hours. Place the resulting sintered magnetic block in a tempering furnace, start the heating burner, and heat the furnace at 900°C for 60 minutes to obtain a high-temperature tempered magnetic block.

[0095] S4.3: Start the plasma generator, adjust the power to 0.6MW, and introduce plasma into the tempering furnace until the plasma content in the tempering furnace reaches 95%. Close the tempering furnace, place a magnetic field generating device near the tempering furnace, adjust the direction of the magnetic field to be opposite to the magnetic field generated by the high-temperature tempering magnetic block, and adjust the magnetic field strength until the compass is observed to point accurately to the south, eliminate the magnetic field of the magnetic block, and prevent the magnetic field from affecting the distribution of plasma, so that the plasma is evenly distributed in the tempering furnace. When some heating burners are started to perform low-temperature tempering on the magnetic block, heat can also be evenly distributed in the tempering furnace through the plasma, so that the magnetic block is evenly heated, and the coercive force of the NdFeB permanent magnet material is better improved. Start the heating burner and heat at a temperature of 500°C for 1.5 hours. Then the obtained low-temperature tempered magnetic block is water quenched and cooled to room temperature to obtain NdFeB permanent magnet material.

[0096] Comparative Example 1

[0097] Compared with Example 1, the difference of Comparative Example 1 is that Comparative Example 1 is a traditional process flow for preparing NdFeB magnets, specifically including batching, smelting, powder making, pressing, sintering and tempering heat treatment, wherein the tempering heat treatment is to place the NdFeB magnet in a tempering furnace for tempering heat treatment.

[0098] Nd, Fe, Dy, Cu, and B were prepared using the processes of Example 1, Example 2, Example 3, and Comparative Example 1, respectively, with the same mass ratio of Nd, Fe, Dy, Cu, and B. Three portions of each were prepared. The coercive force of the obtained NdFeB permanent magnet materials was measured using the method of "Measurement of the coercive force of magnetic materials in an open magnetic circuit" in GBT13888-2009. The data were recorded and tabulated. Figure 2 It can be seen that the coercive force of the NdFeB permanent magnet materials prepared in Example 1, Example 2, and Example 3 is higher than that of the NdFeB permanent magnet material prepared in Comparative Example 1. This proves that the process in the embodiment can make the NdFeB magnet uniformly heated during the heat treatment process, thereby better improving the coercive force of the magnet.

[0099] Comparative Example 2

[0100] Compared with Example 1, the difference of Comparative Example 2 is that the permanent magnetic particles and the fluorinated carbon nanotubes are not jet milled together in Comparative Example 2. The rest of the process for preparing the NdFeB permanent magnetic material is the same as that in Example 1. The preparation is repeated three times. The NdFeB permanent magnetic materials prepared in Example 1, Example 2, Example 3 and Comparative Example 2 are measured for their coercive force using the method of "GBT13888-2009 Measurement of coercive force of magnetic materials in an open magnetic circuit". The data are recorded and tabulated. Figure 3It can be seen that the coercive force of the NdFeB permanent magnet materials prepared in Example 1, Example 2, and Example 3 is higher than that of the NdFeB permanent magnet material prepared in Comparative Example 2. This proves that adding fluorinated carbon nanotubes during the casting of permanent magnet ingots can enable the magnetic blocks to be heated more evenly during the heat treatment process, thereby improving the coercive force of the NdFeB permanent magnet material.

[0101] Comparative Example 3

[0102] Compared with Example 1, the difference of Comparative Example 3 is that the operation of introducing plasma into the tempering furnace and eliminating the magnetic field in step S4.3 of Comparative Example 3 is removed, and low-temperature tempering is directly performed. The remaining processes for preparing the NdFeB permanent magnet material are the same as those in Example 1. The process of Comparative Example 3 is repeated three times, and the NdFeB permanent magnet material prepared in Comparative Example 3 is measured for its coercive force using the method of "GBT13888-2009 Measurement of Coercive Force of Magnetic Materials in Open Magnetic Circuit". The data are recorded and tabulated together with the data of Examples 1, 2, and 3 in Comparative Example 1, as shown in FIG. Figure 4 It can be seen that the coercive force of the NdFeB permanent magnet materials prepared in Example 1, Example 2, and Example 3 is higher than that of the NdFeB permanent magnet material prepared in Comparative Example 3. This proves that introducing plasma into the tempering furnace and eliminating the magnetic field can make the heat evenly distributed in the tempering furnace through the plasma, thereby making the magnetic block evenly heated, and better improving the coercive force of the NdFeB permanent magnet material.

[0103] Comparative Example 4

[0104] Compared with Example 1, the difference of Comparative Example 4 is that step S3 is removed in Comparative Example 4, and the remaining processes for preparing the NdFeB permanent magnet material are the same as those in Example 1. The process of Comparative Example 4 is repeated three times, and the NdFeB permanent magnet material prepared in Comparative Example 3 is measured for its coercive force using the method of "GBT13888-2009 Measurement of coercive force of magnetic materials in an open magnetic circuit", and the data are recorded and tabulated together with the data of Example 1, Example 2 and Example 3 in Comparative Example 2, as shown in FIG. Figure 5 It can be seen that the coercive force of the NdFeB permanent magnet materials prepared in Example 1, Example 2, and Example 3 is higher than that of the NdFeB permanent magnet material prepared in Comparative Example 4. This proves that ultrasonic preheating of the permanent magnet powder can make the distribution of the various components in the powder more uniform, so that the magnetic block is better heated evenly in the subsequent heat treatment, thereby improving the coercive force of the NdFeB permanent magnet material.

[0105] Comparative Example 5

[0106] Compared with Example 1, the difference of Comparative Example 5 is that the microwave heating of the permanent magnet ingot and the added aluminum oxide in step S2.1 are removed in Comparative Example 5. The rest of the process for preparing the NdFeB permanent magnet material is the same as that in Example 1. Six portions of 500g of the permanent magnet ingot obtained by Example 1 are taken and subjected to hydrogen crushing three times in Example 1 and three times in Comparative Example 5, respectively. The obtained permanent magnet particles are passed through a 100-mesh sieve to screen out permanent magnet particles with smaller particle size. The larger the mass, the better the hydrogen crushing effect. The permanent magnet particles passing through the sieve are weighed and the data are recorded to make a table, as shown in FIG. Figure 6 It can be seen that the content of permanent magnetic particles passing through the 100-mesh sieve obtained in the three examples 1 is more than that in the comparative example 5. This proves that microwave heating treatment of the permanent magnetic ingot and addition of a catalyst during the hydrogen crushing process can improve the subsequent binding ability of hydrogen and the permanent magnetic ingot, thereby improving the effect of hydrogen crushing.

[0107] Comparative Example 6

[0108] Compared with Example 1, Comparative Example 6 is different in that the funnel device is removed in Comparative Example 6, and the carbon nanotubes are directly placed in a container to react with carbon tetrafluoride at high temperature. The other conditions for preparing fluorinated carbon nanotubes are the same as those in Example 1. Fluorinated carbon nanotubes are prepared five times using the processes of Example 1 and Comparative Example 6 respectively. The fluorine atom content in the fluorinated carbon nanotubes is measured by atomic absorption spectrometry and the percentage is calculated. The data are recorded and tabulated, as shown in FIG. Figure 7 It can be seen that the fluorine atom content of the fluorinated carbon nanotubes prepared in Example 1 is higher than that of the fluorinated carbon nanotubes prepared in Comparative Example 6, which proves that the output rate of fluorinated carbon nanotubes can be increased by dropping the carbon nanotube powder from the top of the container through a funnel.

[0109] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A uniform heat treatment process for NdFeB permanent magnet materials, characterized in that: The following steps are involved: S1: Preparation of fluorinated carbon nanotubes A funnel is installed at the top of the container to control the falling speed of the powder in the funnel. Carbon nanotubes are placed in the funnel, and carbon tetrafluoride gas is introduced into the container. The container is then closed and heated at high temperature for a period of time. The funnel is opened to allow the carbon nanotubes to fall slowly. The resulting solid powder is cooled to obtain fluorinated carbon nanotubes. S2: Preparation of permanent magnetic powder containing fluorinated carbon nanotubes Nd, Fe, Dy, Cu and B are uniformly mixed and then smelted to obtain an alloy melt, the alloy melt is cast to obtain a permanent magnet ingot, the permanent magnet ingot is subjected to microwave heating and then hydrogen-crushed together with a catalyst, the crushed ingot is taken out after standing to obtain permanent magnet particles, the permanent magnet particles and fluorinated carbon nanotubes are placed in a jet mill for jet milling to obtain permanent magnet powder; S3: Ultrasonic preheating of permanent magnet powder Permanent magnetic powder, a solvent, and a surfactant are mixed and added to a container to obtain a mixture, the mixture in the container is heated and stirred to obtain a homogeneous solution, the container containing the homogeneous solution is placed in an ultrasonic generator, and the homogeneous solution is ultrasonically heated. The homogeneous solution is heated under ultrasonic treatment, and the solvent evaporates until only solid powder remains in the homogeneous solution, and the preheated permanent magnetic powder is collected; S4: Uniform heat treatment of permanent magnets The preheated permanent magnetic powder is placed in a mold, and a strong magnetic field is applied to directionally press it between the plates to obtain a material block. The material block is isostatically pressed to obtain a compact, and the compact is sintered at high temperature. The obtained sintered magnetic block is placed in a tempering furnace for high-temperature tempering treatment to obtain a high-temperature tempered magnetic block. The plasma generator is started to introduce plasma into the tempering furnace. When the plasma content reaches a certain value, the tempering furnace is closed. A magnetic field generating device is placed near the tempering furnace. After eliminating the magnetic field of the magnetic block, the magnetic block is low-temperature heated and cooled to obtain a neodymium iron boron permanent magnetic material.

2. The uniform heat treatment process for NdFeB permanent magnet material according to claim 1, characterized in that: Step S1: Preparation of fluorinated carbon nanotubes, comprising the following steps: S1.1: Install a funnel at the top of a container to control the falling speed of the powder in the funnel. Place 5-6 portions of carbon nanotubes in the funnel and introduce carbon tetrafluoride gas to a concentration of 90-95% of the total gas content in the container. Seal the container to obtain a closed container. S1.2: Place the sealed container in a muffle furnace and heat it at 600-650°C for 20-25 minutes. At the same time, open the funnel to allow the carbon nanotubes to fall to the bottom of the container within 20-25 minutes. Remove the resulting solid powder and cool it naturally for 1.5-2 hours to obtain fluorinated carbon nanotubes.

3. The uniform heat treatment process for NdFeB permanent magnet material according to claim 1, characterized in that: Step S2 prepares a permanent magnetic powder containing fluorinated carbon nanotubes, comprising the following steps: S2.1: 25-27 parts of Nd, 60-62 parts of Fe, 1.3-1.5 parts of Dy, 0.9-1.1 parts of Cu, and 1-1.2 parts of B are mixed and smelted in a vacuum suspension furnace to obtain an alloy melt, which is then poured into a water-cooled copper mold to obtain a permanent magnet ingot; S2.2: Place the permanent magnet ingot in an industrial microfurnace and microwave-heat it at 200-220°C for 15-20 minutes. Place the microwave-heated permanent magnet ingot and 6-7 parts of catalyst in a hydrogen crushing furnace. Add hydrogen to the furnace to keep the pressure at 10-12 MPa. Adjust the temperature to 350-400°C and hydrogen-crush the ingot for 20-25 minutes. Then stop heating and let it stand for 2-3 hours. Remove the crushed ingot to obtain permanent magnet particles. S2.3: Place the permanent magnetic particles and 5-7 parts of fluorinated carbon nanotubes into a jet mill, adjust the jet mill power to 200-250kw, and the gas consumption to 30-35m 3 / min, the gas pressure is 0.7-0.8Mpa, and the permanent magnetic particles and fluorinated carbon nanotubes are mixed and jet milled for 25-30 minutes to obtain permanent magnetic powder.

4. The uniform heat treatment process for NdFeB permanent magnet material according to claim 1, characterized in that: Step S3: ultrasonic preheating of the permanent magnet powder, comprising the following steps: S3.1: Mix the permanent magnet powder, 200-220 parts of solvent, and 15-20 parts of surfactant in a container to obtain a mixture. Adjust the temperature to 40-45°C and the rotation speed to 200-220 rpm to stir the mixture in the container for 40-45 minutes to obtain a homogeneous solution. S3.2: Place the container containing the homogeneous solution into an ultrasonic generator, adjust the ultrasonic frequency to 25-28KHz, and ultrasonically heat the homogeneous solution. The homogeneous solution heats up under ultrasonic treatment and the solvent evaporates until only solid powder remains in the homogeneous solution. The preheated permanent magnetic powder is collected.

5. The uniform heat treatment process for NdFeB permanent magnet material according to claim 1, characterized in that: Step S4 is a uniform heat treatment of the permanent magnet, comprising the following steps: S4.1: Place the preheated permanent magnetic powder in a mold, apply a strong magnetic field, and directionally press the preheated permanent magnetic powder between the plates to obtain a material block. Immerse the material block in a cold isostatic press under great pressure for isostatic pressing to obtain a briquette; S4.2: Place the compact in a vacuum sintering furnace and sinter at a temperature of 1100-1200°C for 3-3.5 hours. Place the resulting sintered magnetic block in a tempering furnace, start the heating burner, and heat the furnace at a temperature of 850-900°C for 55-60 minutes to obtain a high-temperature tempered magnetic block. S4.3: Start the plasma generator, adjust the power to 0.5-0.6MW, and introduce plasma into the tempering furnace until the plasma content in the tempering furnace reaches 90-95%. Close the tempering furnace, place a magnetic field generating device near the tempering furnace, adjust the direction of the magnetic field to be opposite to the magnetic field generated by the high-temperature tempered magnetic block, and adjust the magnetic field strength until the compass is observed to point accurately to the south, eliminate the magnetic field of the magnetic block, start the heating burner, and heat at a temperature of 475-500℃ for 1-1.5 hours. Then, water quench the obtained low-temperature tempered magnetic block to room temperature to obtain NdFeB permanent magnet material.

6. The uniform heat treatment process for NdFeB permanent magnet material according to claim 3, characterized in that: The catalyst in step S2.2 is alumina.

7. The uniform heat treatment process for NdFeB permanent magnet material according to claim 3, characterized in that: The gas used for jet milling in step S2.3 is nitrogen.

8. The uniform heat treatment process for NdFeB permanent magnet material according to claim 4, characterized in that: The surfactant in step S3.1 is sodium dodecylbenzenesulfonate.

9. The uniform heat treatment process for NdFeB permanent magnet material according to claim 4, characterized in that: The material of the container in step S3.1 is ceramic.

10. The uniform heat treatment process for NdFeB permanent magnet material according to claim 4, characterized in that: The solvent in step S3.1 is acetone.

Images