Sintering cooling method of sintered magnetic material

Abstract

The invention provides a sintering cooling method of a sintered magnetic material. Specifically, the method comprises the following steps: (1) heating a magnet blank to 1000-1150 DEG C in a vacuum sintering furnace, and keeping the temperature for 2-8 hours; (2) inert gas is filled, the pressure in the furnace is adjusted to 5 kPa to 20 kPa, and a draught fan is started for cooling; (3) when the temperature is reduced to 1000 DEG C, the pressure in the furnace is adjusted to 20 kPa to 40 kPa, and a fan is used for continuous cooling; (4) when the temperature is reduced to 700 DEG C, the pressure in the furnace is adjusted to be within the range of 40 kPa to 60 kPa, and a draught fan is used for continuous cooling; (5) when the temperature is reduced to 400 DEG C, the pressure in the furnace is adjusted to 60 kPa to 90 kPa, and a fan is used for continuous cooling; and (6) when the temperature is reduced to 65 DEG C or below, cooling is completed to obtain a sintered body blank. According to the method, rapid and uniform cooling of the sintered magnetic material can be achieved, the product cooling speed is increased, the cooling period is shortened, and the obtained sintered body blank product has good appearance and is free of cracks and peeling phenomena.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic materials, and in particular to a sintering cooling method for sintered magnetic materials. Background Art

[0002] Sintered magnetic materials, especially sintered neodymium iron boron (NdFeB) materials, as a high-performance rare earth permanent magnet material, are widely used in motors, speakers, hard disk drives and other fields. The sintering cooling process in the production process of sintered magnetic materials has an important influence on the magnetic properties and physical properties of the final product. The traditional sintering cooling process has problems such as long cycle, high energy consumption, and easy cracking and peeling of the product, which seriously affect the production efficiency and product quality.

[0003] In the prior art, for example, Chinese patent application publication number CN 112728948 A provides a cooling method that uses an air volume sensor to achieve consistent air volume in multiple pipes and adjusts the air volume through a variable frequency fan. However, the technology does not explain in detail the corresponding adjustment relationship between the air volume and the temperature of the NdFeB magnet, making it difficult to ensure cooling efficiency and product consistency.

[0004] Another prior art, such as Chinese patent application publication number CN 108242306 A, discloses a process of automatically controlling the cooling process using a variable frequency fan, wherein the fan frequency is gradually increased from high temperature to increase the air volume and speed up the cooling speed. However, this technology also does not clarify the specific relationship between the inflation pressure, different temperature stages and the variable frequency, making it difficult to accurately control and optimize the cooling process.

[0005] Therefore, it is of great significance to develop a sintering cooling method for sintered magnetic materials that can quickly and evenly cool the product, increase the cooling rate of the product, and shorten the cooling cycle. Summary of the invention

[0006] Based on the technical problems described above, one of the objects of the present invention is to provide a sintering cooling method for sintered magnetic materials, which can achieve rapid and uniform cooling of sintered magnetic materials, increase product cooling speed, shorten cooling cycle, and the obtained sintered body blank product has good appearance without cracks and peeling.

[0007] Specifically, the present invention provides a sintering cooling method for sintered magnetic materials, the method comprising the following steps:

[0008] (1) heating the magnet blank in a vacuum sintering furnace to a sintering temperature of 1000-1150°C and keeping the temperature for 2-8 hours to complete sintering;

[0009] (2) filling with inert gas, adjusting the pressure in the vacuum sintering furnace to a range of 5 kPa-20 kPa, and turning on the fan for cooling;

[0010] (3) When the temperature in the vacuum sintering furnace drops to 1000° C., the pressure in the vacuum sintering furnace is adjusted to a range of 20 kPa-40 kPa, and cooling is continued by the fan;

[0011] (4) When the temperature in the vacuum sintering furnace drops to 700° C., the pressure in the vacuum sintering furnace is adjusted to a range of 40 kPa-60 kPa, and cooling is continued by the fan;

[0012] (5) when the temperature in the vacuum sintering furnace drops to 400° C., adjusting the pressure in the vacuum sintering furnace to a range of 60 kPa to 90 kPa, and continuing cooling with the fan; and

[0013] (6) When the temperature in the vacuum sintering furnace drops to below 65° C., cooling is completed to obtain a sintered body blank.

[0014] According to certain preferred embodiments of the present invention, the pressure inside the furnace used in the above steps (2) to (5) is increased sequentially.

[0015] According to certain preferred embodiments of the present invention, the inert gas is argon, nitrogen or a mixture thereof.

[0016] According to certain preferred embodiments of the present invention, the inert gas filled in the above step (2) is argon, and when the temperature in the vacuum sintering furnace is reduced to 200° C.-600° C., the argon is replaced by nitrogen.

[0017] According to certain preferred embodiments of the present invention, the inert gas filled in the above step (2) is argon, and when the temperature in the vacuum sintering furnace is reduced to 450° C., the argon is replaced by nitrogen.

[0018] According to certain preferred embodiments of the present invention, in the above step (2), inert gas is filled, the pressure inside the vacuum sintering furnace is adjusted to a range of 5 kPa-15 kPa, and a fan is turned on for cooling.

[0019] According to certain preferred embodiments of the present invention, the fan operates at a power of 5-50 Hz.

[0020] According to certain preferred embodiments of the present invention, the fan operates at a power of 50 Hz.

[0021] According to certain preferred embodiments of the present invention, after the above step (6), the obtained sintered body is subjected to an aging treatment.

[0022] According to some preferred embodiments of the present invention, the magnet blank is an RTB-based rare earth sintered magnet blank, wherein R is one or more rare earth elements, and T is one or more Fe and Co.

[0023] According to certain preferred embodiments of the present invention, the R contains a light rare earth element RL and an optional heavy rare earth element RH, wherein RL includes at least one of Nd and Pr, and RH includes at least one of Dy and Tb.

[0024] According to certain preferred embodiments of the present invention, the magnet blank is a neodymium iron boron magnet blank.

[0025] According to certain preferred embodiments of the present invention, the NdFeB magnet blank contains R as the main phase. 2 Fe 14 B-type compound grains.

[0026] According to some preferred embodiments of the present invention, the sintered magnetic material is a sintered NdFeB magnetic material.

[0027] Compared with the sintering cooling method of the sintered magnetic material in the prior art, the sintering cooling method of the sintered magnetic material according to the present invention has the following advantages:

[0028] 1. Dynamic control of furnace pressure:

[0029] In the prior art (such as patent number CN 112728948 A), although air volume sensors and variable frequency fans are used, the adjustment relationship between air volume and furnace pressure is not clear. The present invention controls the furnace pressure dynamically by filling inert gas, and gradually increases the pressure according to the change of furnace temperature to improve the heat exchange efficiency.

[0030] 2. Selection and replacement of cooling gas:

[0031] The present invention uses cooling gases (argon and nitrogen) with different specific heat capacities at different temperature stages and performs gas replacement at 200° C.-600° C. This strategy utilizes the physical properties of different gases and optimizes the cooling process, while the prior art does not mention this gas replacement strategy.

[0032] 3. Cooling speed optimization:

[0033] In the prior art (such as patent number CN 108242306 A), although the cooling is automatically controlled by the variable frequency fan, the relationship between the inflation pressure and the different temperature stages is not explained. The present invention achieves rapid and uniform cooling of the material by accurately controlling the pressure in the furnace and the specific heat capacity of the gas, effectively shortening the cooling cycle.

[0034] 4. Product quality improvement:

[0035] The test results show that the cooling method of the present invention effectively reduces the crack rate and peeling rate to nearly 0%, while the crack rate and peeling rate in the prior art are relatively high. This shows that the present invention significantly improves the appearance quality of the product while maintaining or improving the magnetic properties of the product.

[0036] 5. Improvement of production efficiency:

[0037] By optimizing the cooling process, the present invention reduces the cooling time, which not only improves production efficiency but also reduces energy consumption.

[0038] 6. Energy consumption reduction:

[0039] The present invention achieves a more efficient cooling process by precisely controlling the pressure in the furnace and the frequency of the fan, thereby reducing the overall energy consumption, which is of great significance in terms of production cost control and environmental protection.

[0040] 7. Flexibility and adaptability of the process:

[0041] The present invention provides multiple embodiments, showing the adjustment of the cooling process under different conditions, and showing the flexibility and adaptability of the process. This flexibility enables the present invention to adapt to different production requirements and conditions.

[0042] 8.Technological innovation:

[0043] The invention combines the principles of thermodynamics and heat transfer and proposes a new cooling process, which has not been seen in the prior art. This innovation not only improves the cooling efficiency, but also provides a new idea for the production of sintered magnetic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The figure is a process flow chart of the sintering cooling method of the sintered magnetic material according to the present invention. DETAILED DESCRIPTION

[0045] The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. It will be appreciated that other embodiments are contemplated and may be implemented without departing from the scope or spirit of the present invention. Therefore, the following detailed description is non-restrictive.

[0046] Unless otherwise indicated, all numbers used in the specification and claims to represent feature sizes, quantities and physicochemical properties should be understood as being modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters listed in the above specification and the attached claims are approximate values, and those skilled in the art can use the teachings disclosed herein to seek to obtain the desired properties and appropriately change these approximate values. The use of numerical ranges expressed as endpoints includes all numbers within the range and any range within the range, for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4 and 5, etc.

[0047] As mentioned above, sintered magnetic materials such as sintered NdFeB materials are widely used in modern industry as an important rare earth permanent magnet material. However, there are some limitations in the sintering cooling process in its production process, such as long cooling cycle, high energy consumption, and easy cracking and peeling of products. These problems not only affect production efficiency, but also limit the improvement of product quality. In the prior art, although air volume sensors and variable frequency fans are used to control the cooling process, there is still a lack of in-depth research and optimization of furnace pressure, gas specific heat capacity, and cooling efficiency at different temperature stages.

[0048] The present invention aims to provide a sintering cooling method for sintered magnetic materials, which can achieve rapid and uniform cooling of the sintered magnetic materials, increase the cooling speed of the products, shorten the cooling cycle, and the obtained sintered body blank products have good appearance without cracks and peeling.

[0049] Specifically, the inventors of the present invention have found in a systematic study that rapid and uniform cooling of sintered magnetic materials can be achieved to obtain sintered magnetic materials with good appearance (without cracks and peeling) by making improvements in the following aspects: controlling the pressure in the furnace by filling with inert gas (for example, argon or nitrogen), and improving the cooling efficiency by utilizing the relationship between the pressure in the furnace and the heat exchange efficiency; selecting cooling gases (argon and nitrogen) with different specific heat capacities according to the temperature change of NdFeB to optimize the cooling process; gradually increasing the pressure in the furnace as the temperature in the furnace decreases to compensate for the attenuation of heat exchange efficiency caused by the decrease in temperature difference; performing gas replacement at a specific temperature stage (such as 200°C-600°C, preferably 450°C), replacing argon with low specific heat capacity with nitrogen with high specific heat capacity to further improve the cooling efficiency; keeping the fan frequency constant during the entire cooling process to ensure uniform flow of the cooling gas and efficient heat exchange.

[0050] Specifically, the present invention provides a sintering cooling method for a sintered magnetic material, the method comprising the following steps:

[0051] (1) heating the magnet blank in a vacuum sintering furnace to a sintering temperature of 1000-1150°C and keeping the temperature for 2-8 hours to complete sintering;

[0052] (2) filling with inert gas, adjusting the pressure in the vacuum sintering furnace to a range of 5 kPa-20 kPa, and turning on the fan for cooling;

[0053] (3) When the temperature in the vacuum sintering furnace drops to 1000° C., the pressure in the vacuum sintering furnace is adjusted to a range of 20 kPa-40 kPa, and cooling is continued by the fan;

[0054] (4) When the temperature in the vacuum sintering furnace drops to 700° C., the pressure in the vacuum sintering furnace is adjusted to a range of 40 kPa-60 kPa, and cooling is continued by the fan;

[0055] (5) when the temperature in the vacuum sintering furnace drops to 400° C., adjusting the pressure in the vacuum sintering furnace to a range of 60 kPa to 90 kPa, and continuing cooling with the fan; and

[0056] (6) When the temperature in the vacuum sintering furnace drops to below 65° C., cooling is completed to obtain a sintered body blank.

[0057] Figure 1 The process flow chart of the sintering cooling method of the sintered magnetic material according to the present invention is shown. Specifically, the sintering cooling method comprises the following steps:

[0058] S1: heating the magnet blank to a sintering temperature of 1000-1150°C and keeping the temperature for 2-8 hours;

[0059] S2: Fill with inert gas, adjust the pressure in the furnace to the range of 5kPa-20kPa, and turn on the fan for cooling;

[0060] S3: When the temperature in the furnace drops to 1000°C, the pressure in the furnace is adjusted to a range of 20 kPa-40 kPa, and the fan is used to continue cooling;

[0061] S4: When the temperature in the furnace drops to 700°C, the pressure in the furnace is adjusted to a range of 40 kPa-60 kPa, and the fan is used to continue cooling;

[0062] S5: when the temperature in the furnace drops to 400° C., adjusting the pressure in the furnace to within the range of 60 kPa-90 kPa, and continuing cooling with the fan; and

[0063] S6: When the temperature in the furnace drops below 65°C, cooling is completed to obtain a sintered body blank.

[0064] Preferably, the furnace pressure used in the above steps (2)-step (5) is increased successively. Without being bound by theory, it is speculated that the increase in furnace pressure can increase the density of gas molecules, thereby increasing the contact frequency and heat exchange area between the gas and the sintered NdFeB material, and further improving the heat exchange efficiency. By gradually increasing the furnace pressure, the heat exchange efficiency can be maintained or improved, and the rapid and uniform cooling of the sintered NdFeB can be achieved. Uniform cooling helps to reduce the difference in thermal stress inside the product and improve the consistency of the product magnetic properties and appearance. In addition, improving the heat exchange efficiency directly leads to a shortening of the cooling time, thereby improving production efficiency.

[0065] Preferably, the inert gas is argon, nitrogen or a mixture thereof.

[0066] Preferably, the inert gas filled in the above step (2) is argon, and when the temperature in the vacuum sintering furnace is reduced to 200°C-600°C, the argon is replaced by nitrogen. According to the technical solution of the present invention, when the temperature in the furnace is high, argon with a lower specific heat capacity is used to quickly absorb heat; and after the temperature is reduced, nitrogen with a higher specific heat capacity is used to more effectively maintain the heat exchange efficiency. By accurately controlling the pressure in the furnace and gas replacement, it is possible to achieve a comprehensive improvement in the magnetic properties of the product without sacrificing the production speed, which is difficult to predict in the traditional cooling process. The technical solution of the present invention achieves a crack rate and peeling rate close to 0%. This extremely low defect rate is difficult to achieve in the traditional cooling process and is regarded as an unexpected effect. More preferably, in order to achieve the technical effect of the present invention, the inert gas filled in the above step (2) is argon, and when the temperature in the vacuum sintering furnace is reduced to 450°C, the argon is replaced by nitrogen. When the temperature in the vacuum sintering furnace is reduced to 450° C., gas replacement can be performed to obtain a sintered body green product with a crack rate and a peeling rate of 0%.

[0067] Preferably, in the above step (2), an inert gas is filled, the furnace pressure in the vacuum sintering furnace is adjusted to a range of 5kPa-15kPa, and the fan is turned on for cooling. The inventors found in the study that in the above step (2), if the furnace pressure in the vacuum sintering furnace is adjusted to a pressure higher than 15kPa, the appearance of the obtained sintered body blank product deteriorates, and a product with a crack rate and a peeling rate of 0% cannot be obtained. Without being bound by theory, it is believed that in the initial cooling stage, the temperature of the sintered NdFeB is very high. At this time, the use of a lower furnace pressure can quickly absorb the heat of the sintered body, because the gas flows faster and the heat exchange area is larger under lower pressure. If the initial cooling pressure is too high, it may cause thermal shock to the high-temperature sintered body, increasing the risk of product cracking. A lower initial pressure helps to start the cooling process gently. In addition, the use of a lower initial pressure can reduce the consumption of cooling gas, thereby reducing production costs. In addition, the use of a lower initial pressure can reduce the consumption of cooling gas, thereby reducing production costs. In the actual operation of the present invention, by accurately controlling the initial furnace pressure, a crack rate and peeling rate close to 0% were achieved, and this extremely low defect rate was unforeseen in the initial design. Although the initial pressure is low, the overall cooling time can still be shortened because the overall strategy according to the present invention improves the efficiency of the entire cooling process.

[0068] According to certain preferred embodiments of the present invention, the fan is operated at a power of 5-50 Hz. More preferably, the fan is operated at a power of 50 Hz. The present invention achieves a more efficient cooling process by accurately controlling the pressure in the furnace and the fan frequency, thereby reducing the overall energy consumption. This is of great significance in terms of production cost control and environmental protection. Preferably, the fan frequency is kept constant throughout the cooling process to ensure uniform flow of cooling gas and efficient heat exchange.

[0069] According to certain preferred embodiments of the present invention, after the above step (6), the obtained sintered body blank is subjected to aging treatment. During the sintering process, residual stress may be generated inside the material. Aging treatment helps to release these stresses by maintaining the material under certain temperature and time conditions, thereby reducing the risk of deformation and cracking of the product. In addition, aging treatment can promote microstructural adjustment inside the material, such as grain boundary improvement, etc. These changes can improve the magnetic properties of the material, such as increasing intrinsic coercive force (Hcj) and squareness. In addition, through aging treatment, the internal heterogeneity of the material, such as defects such as pores and microcracks, can be reduced, thereby improving magnetic stability and the long-term reliability of the product. Aging treatment can promote phase changes inside the material, such as forming a more favorable magnetic phase, thereby optimizing the microstructure of the material. In addition, aging treatment can also improve the surface state and chemical composition of the material, improve its corrosion resistance, and extend the service life of the product. Preferably, the aging treatment includes primary aging and secondary aging. The primary aging treatment keeps the obtained sintered body blank at 800-950° C. for 2-6 hours, and the secondary aging treatment keeps the obtained sintered body blank at 400-700° C. for 2-6 hours.

[0070] There is no particular restriction on the specific type of the magnet blank that can be used in the present invention. NdFeB materials are usually divided into different performance grades according to their different magnetic properties, such as N series (N35, N42, N50, N52, etc.) and M series (M40, M45, etc.). The embodiments described in the present invention are directed to NdFeB materials with a performance grade of N52, but in principle, the cooling method can also be applied to other NdFeB materials with similar magnetic properties. The composition of NdFeB materials may vary depending on the manufacturer and application requirements, however, the cooling method of the present invention mainly focuses on the cooling process after sintering, so in theory it can be applied to NdFeB materials of different compositions, as long as these materials have undergone a similar sintering process.

[0071] Preferably, the magnet blank is a RTB-based rare earth sintered magnet blank, wherein R is one or more rare earth elements, and T is one or more of Fe and Co. More preferably, the R contains a light rare earth element RL and an optional heavy rare earth element RH, wherein RL includes at least one of Nd and Pr, and RH includes at least one of Dy and Tb. Most preferably, the magnet blank is a NdFeB magnet blank. According to certain preferred embodiments of the present invention, the NdFeB magnet blank contains R as the main phase. 2 Fe 14 B-type compound grains.

[0072] There is no particular limitation on the specific type of the sintered magnetic material that can be mentioned in the present invention. Preferably, the sintered magnetic material is a sintered NdFeB magnetic material.

[0073] Whether it is small batch production or large-scale production, the cooling method according to the present invention can be adjusted and applied according to production requirements to achieve the best cooling effect and production efficiency. Since the method of the present invention involves gas charging and pressure control, it is suitable for production environments that can meet these environmental requirements, including but not limited to factories with appropriate gas supply and pressure control systems.

[0074] The present invention is described in more detail below in conjunction with the examples. It should be noted that these descriptions and examples are intended to facilitate the understanding of the present invention, rather than to limit the present invention. The protection scope of the present invention shall be subject to the attached claims.

[0075] Example

[0076] In the present invention, unless otherwise indicated, the reagents used are commercial products and are used directly without further purification. In addition, the "%", "wt%" mentioned are "percentage by weight", and the "parts" mentioned are "parts by weight".

[0077] Example 1

[0078] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64mm×54mm×36mm) was heated to a sintering temperature of 1090°C in a vacuum sintering furnace and kept at this temperature for 5 hours to complete the sintering.

[0079] After sintering is completed in the vacuum sintering furnace, argon is filled into the furnace and the pressure in the furnace is adjusted to 5kPa. Then the fan is started and the frequency is set to 50Hz to ensure uniform gas flow in the furnace for heat exchange.

[0080] When the temperature in the furnace drops to 1000°C, the pressure in the furnace is gradually increased to 20 kPa, while argon gas is continuously introduced to maintain this pressure.

[0081] When the temperature in the furnace drops to 700°C, the pressure in the furnace is further increased to 40 kPa and argon gas is continuously injected.

[0082] When the temperature in the furnace drops to 450°C, stop the fan, use the vacuum pump group to extract the argon in the furnace until the pressure is lower than 5kPa, then turn off the pump group and fill with nitrogen.

[0083] When the temperature in the furnace drops to 400°C, the pressure in the furnace is further increased to 80 kPa, and the fan frequency is maintained at 50 Hz.

[0084] When the temperature in the furnace drops below 65°C, the cooling process is completed.

[0085] After cooling, the sintered body blank is subjected to primary aging and secondary aging treatment (primary aging is heated to 900°C and kept warm for 4 hours, and secondary aging is heated to 500°C and kept warm for 4 hours) to further optimize the magnetic properties and mechanical properties of the material, and finally a sintered NdFeB blank product 1 is obtained.

[0086] Example 2

[0087] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64mm×54mm×36mm) was heated to a sintering temperature of 1090°C in a vacuum sintering furnace and kept at this temperature for 5 hours to complete the sintering.

[0088] After sintering is completed in the vacuum sintering furnace, argon is filled into the furnace and the pressure in the furnace is adjusted to 20kPa. Then the fan is started and the frequency is set to 50Hz to ensure uniform gas flow in the furnace for heat exchange.

[0089] When the temperature in the furnace drops to 1000°C, the pressure in the furnace is gradually increased to 40 kPa, while argon gas is continuously introduced to maintain this pressure.

[0090] When the temperature in the furnace drops to 700°C, the pressure in the furnace is further increased to 60 kPa and argon gas is continuously injected.

[0091] When the temperature in the furnace drops to 450°C, stop the fan, use the vacuum pump group to extract the argon in the furnace until the pressure is lower than 5kPa, then turn off the pump group and fill with nitrogen.

[0092] When the temperature in the furnace drops to 400°C, the pressure in the furnace is further increased to 80 kPa, and the fan frequency is maintained at 50 Hz.

[0093] When the temperature in the furnace drops below 65°C, the cooling process is completed.

[0094] After cooling is completed, the sintered body blank is subjected to primary aging and secondary aging treatment (primary aging is heated to 900°C and kept warm for 4 hours, and secondary aging is heated to 500°C and kept warm for 4 hours) to further optimize the magnetic properties and mechanical properties of the material, and finally a sintered NdFeB blank product 2 is obtained.

[0095] Example 3

[0096] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64mm×54mm×36mm) was heated to a sintering temperature of 1090°C in a vacuum sintering furnace and kept at this temperature for 5 hours to complete the sintering.

[0097] After sintering is completed in the vacuum sintering furnace, argon is filled into the furnace and the pressure in the furnace is adjusted to 5kPa. Then the fan is started and the frequency is set to 50Hz to ensure uniform gas flow in the furnace for heat exchange.

[0098] When the temperature in the furnace drops to 900°C, the pressure in the furnace is gradually increased to 20 kPa, while argon gas is continuously introduced to maintain this pressure.

[0099] When the temperature in the furnace drops to 500°C, the pressure in the furnace is further increased to 40 kPa and argon is continuously injected.

[0100] When the temperature in the furnace drops to 300°C, stop the fan and use the vacuum pump group to extract the argon in the furnace until the pressure is lower than 5kPa, then turn off the pump group and fill it with nitrogen.

[0101] When the temperature in the furnace drops to 200°C, the pressure in the furnace is further increased to 80 kPa, and the fan frequency is maintained at 50 Hz.

[0102] When the temperature in the furnace drops below 65°C, the cooling process is completed.

[0103] After cooling, the sintered body blank was subjected to primary aging and secondary aging treatment (primary aging was heated to 900°C and kept warm for 4 hours, and secondary aging was heated to 500°C and kept warm for 4 hours) to further optimize the magnetic properties and mechanical properties of the material, and finally a sintered NdFeB blank product 3 was obtained.

[0104] Example 4

[0105] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64mm×54mm×36mm) was heated to a sintering temperature of 1090°C in a vacuum sintering furnace and kept at this temperature for 5 hours to complete the sintering.

[0106] After sintering is completed in the vacuum sintering furnace, argon is filled into the furnace and the pressure in the furnace is adjusted to 5kPa. Then the fan is started and the frequency is set to 50Hz to ensure uniform gas flow in the furnace for heat exchange.

[0107] When the temperature in the furnace drops to 1000°C, the pressure in the furnace is gradually increased to 20 kPa, while argon gas is continuously introduced to maintain this pressure.

[0108] When the temperature in the furnace drops to 700°C, the pressure in the furnace is further increased to 40 kPa and argon gas is continuously injected.

[0109] When the temperature in the furnace drops to 400°C, the pressure in the furnace is further increased to 80 kPa, and the fan frequency is maintained at 50 Hz.

[0110] When the temperature in the furnace drops below 65°C, the cooling process is completed.

[0111] After cooling, the sintered body blank is subjected to primary aging and secondary aging treatment (primary aging is heated to 900°C and kept warm for 4 hours, and secondary aging is heated to 500°C and kept warm for 4 hours) to further optimize the magnetic properties and mechanical properties of the material, and finally a sintered NdFeB blank product 4 is obtained.

[0112] Example 5

[0113] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64mm×54mm×36mm) was heated to a sintering temperature of 1090°C in a vacuum sintering furnace and kept at this temperature for 5 hours to complete the sintering.

[0114] After sintering is completed in the vacuum sintering furnace, argon is filled into the furnace and the pressure in the furnace is adjusted to 5kPa. Then the fan is started and the frequency is set to 50Hz to ensure uniform gas flow in the furnace for heat exchange.

[0115] When the temperature in the furnace drops to 1000°C, the pressure in the furnace is gradually increased to 20 kPa, while argon gas is continuously introduced to maintain this pressure.

[0116] When the temperature in the furnace drops to 700°C, the pressure in the furnace is further increased to 40 kPa and argon gas is continuously injected.

[0117] When the temperature in the furnace drops to 600°C, stop the fan, use the vacuum pump group to extract the argon in the furnace until the pressure is lower than 5kPa, then turn off the pump group and fill with nitrogen.

[0118] When the temperature in the furnace drops to 400°C, continue to fill the furnace with nitrogen to further increase the pressure in the furnace to 80kPa, and maintain the fan frequency of 50Hz.

[0119] When the temperature in the furnace drops below 65°C, the cooling process is completed.

[0120] After cooling, the sintered body blank is subjected to primary aging and secondary aging treatment (primary aging is heated to 900°C and kept warm for 4 hours, and secondary aging is heated to 500°C and kept warm for 4 hours) to further optimize the magnetic properties and mechanical properties of the material, and finally a sintered NdFeB blank product 5 is obtained.

[0121] Comparative Example 1

[0122] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64mm×54mm×36mm) was heated to a sintering temperature of 1090°C in a vacuum sintering furnace and kept at this temperature for 5 hours to complete the sintering.

[0123] After sintering is completed in the vacuum sintering furnace, argon is filled into the furnace and the pressure in the furnace is adjusted to 80 kPa. Then the fan is started and the frequency is set to 50 Hz to ensure uniform gas flow in the furnace for heat exchange.

[0124] When the temperature in the furnace drops below 65°C, the cooling process is completed.

[0125] After cooling, the sintered body blank was subjected to primary aging and secondary aging treatment (primary aging was heated to 900°C and kept warm for 4 hours, and secondary aging was heated to 500°C and kept warm for 4 hours) to further optimize the magnetic properties and mechanical properties of the material, and finally a comparative sintered NdFeB blank product 1 was obtained.

[0126] Comparative Example 2

[0127] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64mm×54mm×36mm) was heated to a sintering temperature of 1090°C in a vacuum sintering furnace and kept at this temperature for 5 hours to complete the sintering.

[0128] After sintering is completed in the vacuum sintering furnace, nitrogen is filled into the furnace and the pressure in the furnace is adjusted to 80 kPa. Thereafter, the fan is started and the frequency is set to 50 Hz to ensure uniform gas flow in the furnace for heat exchange.

[0129] When the temperature in the furnace drops below 65°C, the cooling process is completed.

[0130] After cooling, the sintered body blank was subjected to primary aging and secondary aging treatment (primary aging was heated to 900°C and kept warm for 4 hours, and secondary aging was heated to 500°C and kept warm for 4 hours) to further optimize the magnetic properties and mechanical properties of the material, and finally a comparative sintered NdFeB blank product 2 was obtained.

[0131] Comparative Example 3

[0132] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64mm×54mm×36mm) was heated to a sintering temperature of 1090°C in a vacuum sintering furnace and kept at this temperature for 5 hours to complete the sintering.

[0133] After sintering is completed in the vacuum sintering furnace, argon is filled into the furnace and the pressure in the furnace is adjusted to 50 kPa. Thereafter, the fan is started and the frequency is set to 50 Hz to ensure uniform gas flow in the furnace for heat exchange.

[0134] When the temperature in the furnace drops below 65°C, the cooling process is completed.

[0135] After cooling, the sintered body blank was subjected to primary aging and secondary aging treatment (primary aging was heated to 900°C and kept warm for 4 hours, and secondary aging was heated to 500°C and kept warm for 4 hours) to further optimize the magnetic properties and mechanical properties of the material, and finally a comparative sintered NdFeB blank product 3 was obtained.

[0136] The magnetic properties (including remanence Br, coercive force Hcj and magnetic energy product / coercive force (HK / Hcj)) of the sintered NdFeB blank products obtained in each of Examples 1-5 and Comparative Examples 1-3 were measured, and the results are shown in Table 1 below. In addition, the appearance (including crack rate and peeling rate) of the sintered NdFeB blank products obtained in each of Examples 1-5 and Comparative Examples 1-3 was also evaluated. The "crack rate" is determined by counting the percentage (%) of the crack area on the surface of the product to the total surface area of ​​the product. The "peeling rate" is determined by counting the percentage (%) of the peeling area on the surface of the product to the total surface area of ​​the product. The crack rate and peeling rate are shown in Table 1 below. In addition, the cooling time required in each of Examples 1-5 and Comparative Examples 1-3 is also shown in Table 1 below.

[0137] Table 1 Magnetic properties and appearance properties of the sintered NdFeB blank products obtained in Examples 1-5 and Comparative Examples 1-3, and the cooling time required for Examples 1-5 and Comparative Examples 1-3

[0138]

[0139] It can be seen from the results shown in Table 1 that the magnetic performance parameters of the sintered magnetic material using the present technical solution are excellent. In addition, the crack rate and peeling rate are effectively reduced, and the cooling time after sintering is shortened, thereby improving production efficiency and reducing production energy consumption.

[0140] The embodiments described in the present invention are merely descriptions of the preferred implementation modes of the present invention, and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by engineers and technicians in this field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have all been recorded in the claims.

Claims

1. A sintering cooling method for a sintered magnetic material, the method comprising the following steps: (1) heating the magnet blank in a vacuum sintering furnace to a sintering temperature of 1000-1150°C and keeping the temperature for 2-8 hours to complete sintering; (2) filling with inert gas, adjusting the pressure in the vacuum sintering furnace to a range of 5 kPa-20 kPa, and turning on the fan for cooling; (3) When the temperature in the vacuum sintering furnace drops to 1000° C., the pressure in the vacuum sintering furnace is adjusted to a range of 20 kPa-40 kPa, and cooling is continued by the fan; (4) When the temperature in the vacuum sintering furnace drops to 700° C., the pressure in the vacuum sintering furnace is adjusted to a range of 40 kPa-60 kPa, and cooling is continued by the fan; (5) when the temperature in the vacuum sintering furnace drops to 400° C., adjusting the pressure in the vacuum sintering furnace to a range of 60 kPa to 90 kPa, and continuing cooling with the fan; and (6) When the temperature in the vacuum sintering furnace drops to below 65° C., cooling is completed to obtain a sintered body blank.

2. The sintering cooling method for sintered magnetic materials according to claim 1, wherein the pressure in the furnace used in steps (2) to (5) is increased sequentially. 3 . The sintering cooling method of a sintered magnetic material according to claim 1 , wherein the inert gas is argon, nitrogen or a mixture thereof.

4. The sintering cooling method of sintered magnetic material according to claim 1, wherein the inert gas filled in step (2) is argon, and when the temperature in the vacuum sintering furnace drops to 200°C-600°C, the argon is replaced by nitrogen.

5. The sintering cooling method of sintered magnetic material according to claim 1, wherein the inert gas filled in step (2) is argon, and when the temperature in the vacuum sintering furnace drops to 450°C, the argon is replaced by nitrogen.

6. The sintering cooling method of sintered magnetic material according to claim 1, wherein in step (2), the inert gas is filled, the furnace pressure in the vacuum sintering furnace is adjusted to the range of 5kPa-15kPa, and the fan is turned on for cooling.

7. The sintering cooling method of a sintered magnetic material according to claim 1, wherein the fan operates at a power of 5-50 Hz.

8. The sintering cooling method of a sintered magnetic material according to claim 1, wherein the fan is operated at a power of 50 Hz.

9. The sintering cooling method of a sintered magnetic material according to claim 1, wherein after step (6), the obtained sintered body is subjected to an aging treatment. 10 . The sintering cooling method of a sintered magnetic material according to claim 1 , wherein the magnet blank is an RTB-based rare earth sintered magnet blank, wherein R is one or more rare earth elements, and T is one or more Fe and Co.

11. The sintering cooling method of a sintered magnetic material according to claim 10, wherein the R contains a light rare earth element RL and an optional heavy rare earth element RH, wherein RL includes at least one of Nd and Pr, and RH includes at least one of Dy and Tb. 12 . The sintering cooling method of a sintered magnetic material according to claim 1 , wherein the magnet blank is a neodymium iron boron magnet blank.

13. The sintering cooling method of a sintered magnetic material according to claim 12, wherein the NdFeB magnet blank contains R2Fe 14 B-type compound grains. 14 . The sintering cooling method of a sintered magnetic material according to claim 1 , wherein the sintered magnetic material is a sintered NdFeB magnetic material.

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