Sintering cooling method for sintered magnetic materials

Abstract

The present invention provides a sintering cooling method for sintered magnetic materials. Specifically, the method comprises: (1) heating a magnet blank to 1000-1150°C in a vacuum sintering furnace and keeping the temperature for 2-8 hours; (2) charging an inert gas, adjusting the pressure in the furnace to 5kPa-20kPa, and turning on a blower for cooling; (3) when the temperature drops to 1000°C, adjusting the pressure in the furnace to 20kPa-40kPa, and continuing to cool with a blower; (4) when the temperature drops to 700°C, adjusting the pressure in the furnace to within the range of 40kPa-60kPa, and continuing to cool with a blower; (5) when the temperature drops to 400°C, adjusting the pressure in the furnace to 60kPa-90kPa, and continuing to cool with a blower; and (6) when the temperature drops below 65°C, completing cooling to obtain a sintered body blank. The method according to the present invention can achieve rapid and uniform cooling of sintered magnetic materials, improve product cooling speed, shorten the cooling cycle, and the obtained sintered body blank product has a good appearance without cracks and peeling.

Description

Technical Field

[0001] The present 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, particularly sintered neodymium iron boron (NdFeB), are high-performance rare earth permanent magnets widely used in motors, speakers, hard disk drives, and other applications. The sintering and cooling process during the production of sintered magnetic materials significantly impacts the magnetic and physical properties of the final product. Traditional sintering and cooling processes suffer from long cycle times, high energy consumption, and the tendency for cracking and peeling in the product, all of which severely impact production efficiency and quality.

[0003] Existing technologies, such as Chinese patent application publication number CN 112728948A, propose a cooling method that uses air volume sensors to achieve consistent air volume across multiple ducts and a variable-frequency fan to adjust the air volume. However, this technology does not detail the corresponding adjustment relationship between air volume and NdFeB temperature, making it difficult to ensure cooling efficiency and product consistency.

[0004] Another existing technology, such as Chinese patent application publication number CN 108242306A, discloses a process that uses variable-frequency fans to automatically control the cooling process. Starting at a high temperature, the fan frequency is gradually increased to increase air volume and accelerate cooling. However, this technology also lacks a clear relationship between inflation pressure, different temperature stages, and variable frequency, making precise control and optimization of the cooling process difficult.

[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 the product cooling rate, shorten the cooling cycle, and the resulting sintered body blank product has a 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 to a sintering temperature of 1000-1150°C in a vacuum sintering furnace and keeping the temperature for 2-8 hours to complete sintering;

[0009] (2) filling the vacuum sintering furnace 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 to 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 in 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 drops 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 drops 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 in 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 aging treatment.

[0022] According to certain 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 R2Fe as the main phase. l4 B-type compound grains.

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

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

[0028] 1. Dynamic control of furnace pressure:

[0029] While existing technologies (such as Patent No. CN 112728948A) utilize air volume sensors and variable-frequency fans, the relationship between air volume and furnace pressure is unclear. The present invention dynamically controls furnace pressure by injecting inert gas, gradually increasing pressure based on changes in furnace temperature to improve heat exchange efficiency.

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

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

[0032] 3. Cooling speed optimization:

[0033] While existing technologies (such as Patent No. CN 108242306A) automatically control cooling using a variable frequency fan, they fail to explain the relationship between inflation pressure and different temperature stages. The present invention achieves rapid and uniform cooling of the material by precisely controlling the furnace pressure and the specific heat capacity of the gas, effectively shortening the cooling cycle.

[0034] 4. Product quality improvement:

[0035] Test results show that the cooling method of the present invention effectively reduces cracking and peeling rates to nearly 0%, while the cracking and peeling rates in the prior art are relatively high. This demonstrates that the present invention significantly improves the product's appearance quality while maintaining or enhancing its magnetic properties.

[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 inside the furnace and the fan frequency, thereby reducing overall energy consumption. This 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, demonstrating the adjustment of the cooling process under different conditions, showing the flexibility and adaptability of the process. This flexibility enables the present invention to adapt to different production needs and conditions.

[0042] 8. Technological innovation:

[0043] The invention combines the principles of thermodynamics and heat transfer to propose a new cooling process that is not seen in the prior art. This innovation not only improves cooling efficiency but also provides new ideas for the production of sintered magnetic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 FIG. 4 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 with reference to 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 present specification and claims to indicate feature sizes, quantities, and physicochemical properties should be understood as being modified in all cases by the term "about". Therefore, unless otherwise indicated, the numerical parameters listed in the above description and the appended claims are approximate values, and those skilled in the art will be able to appropriately change these approximate values ​​by utilizing the teachings disclosed herein to seek to obtain the desired properties. 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 an important rare earth permanent magnet material and are widely used in modern industry. However, there are some limitations in the sintering cooling process during its production process, such as long cooling cycle, high energy consumption, and the product is prone to cracking and peeling. These problems not only affect production efficiency, but also limit the improvement of product quality. In the existing technology, although equipment such as 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 the 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 product cooling rate, shorten the cooling cycle, and the obtained sintered body blank product has a good appearance without cracks and peeling.

[0049] Specifically, the inventors found in a systematic study that by making improvements in the following aspects, rapid and uniform cooling of sintered magnetic materials can be achieved to obtain sintered magnetic materials with good appearance (no cracks and peeling): by filling inert gas (for example, argon or nitrogen) to control the pressure in the furnace, and using the relationship between the pressure in the furnace and the heat exchange efficiency to improve the cooling efficiency; according to the temperature change of NdFeB, cooling gases with different specific heat capacities (argon and nitrogen) are selected to optimize the cooling process; as the temperature in the furnace decreases, the pressure in the furnace is gradually increased to compensate for the attenuation of heat exchange efficiency caused by the decrease in temperature difference; gas replacement is performed at specific temperature stages (such as 200°C-600°C, most 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 throughout the cooling process to ensure uniform flow of 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 to a sintering temperature of 1000-1150°C in a vacuum sintering furnace and keeping the temperature for 2-8 hours to complete sintering;

[0052] (2) filling the vacuum sintering furnace 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 to 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 includes 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 cooling is continued by the fan;

[0061] S4: When the temperature in the furnace drops to 700°C, the pressure in the furnace is adjusted to a range of 40kPa-60kPa, 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 green body.

[0064] Preferably, the furnace pressure used in the above steps (2) to (5) is increased in sequence. 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 thermal stress difference 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 drops 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 drops, nitrogen with a higher specific heat capacity is used to more effectively maintain the heat exchange efficiency. By precisely controlling the pressure in the furnace and the 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 traditional cooling processes. 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 traditional cooling processes and is considered 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 drops to 450°C, the argon is replaced by nitrogen. When the temperature in the vacuum sintering furnace is lowered to 450° C., gas replacement is 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 their research 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 resulting 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, using a lower furnace pressure can quickly absorb the heat of the sintered body because the gas flow rate is faster and the heat exchange area is larger at a 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, using a lower initial pressure can reduce the consumption of cooling gas, thereby reducing production costs. In addition, using a lower initial pressure can reduce the consumption of cooling gas, thereby reducing production costs. In actual operation, the present invention achieves near-zero crack and peel rates by precisely controlling the initial furnace pressure. This exceptionally low defect rate was unforeseen during the initial design phase. Despite the low initial pressure, the overall cooling time is shortened because the overall cooling process efficiency is enhanced by the present invention's integrated strategy.

[0068] According to certain preferred embodiments of the present invention, the fan operates at a power of 5-50 Hz. More preferably, the fan operates at a power of 50 Hz. By precisely controlling the pressure within the furnace and the fan frequency, the present invention achieves a more efficient cooling process, thereby reducing overall energy consumption. This is of great significance in terms of production cost control and environmental protection. Preferably, the fan frequency is maintained 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 adjustments inside the material, such as grain boundary improvement, etc. These changes can improve the magnetic properties of the material, such as increasing intrinsic coercivity (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 transformation 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 generally divided into different performance grades according to their magnetic properties, such as the N series (N35, N42, N50, N52, etc.) and the 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 an 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 an NdFeB magnet blank. According to certain preferred embodiments of the present invention, the NdFeB magnet blank contains R2Fe as the main phase. 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 for small-batch or large-scale production, the cooling method according to the present invention can be adjusted and applied according to production requirements to achieve optimal cooling effects and production efficiency. Because 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 will be described in more detail below with reference to the examples. It should be noted that these descriptions and examples are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The scope of protection of the present invention shall be subject to the appended claims.

[0075] Example

[0076] In the present invention, unless otherwise noted, the reagents employed are commercial products and are used directly without further purification. In addition, the "%", "wt%" mentioned are "percentages 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 64 mm × 54 mm × 36 mm) 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 and 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 is continuously injected 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 is continued to be injected.

[0082] When the temperature in the furnace drops to 450℃, 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.

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

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

[0085] 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 1 is obtained.

[0086] Example 2

[0087] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64 mm × 54 mm × 36 mm) 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 and 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 is continuously injected 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 is continued to be injected.

[0091] When the temperature in the furnace drops to 450℃, 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.

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

[0093] When the temperature inside 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 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 64 mm × 54 mm × 36 mm) 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 and heat exchange.

[0098] When the temperature in the furnace dropped to 900°C, the pressure in the furnace was gradually increased to 20 kPa, while argon was continuously injected 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 continued to be 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 80kPa, and the fan frequency is maintained at 50Hz.

[0102] When the temperature inside 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 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 64 mm × 54 mm × 36 mm) 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 and 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 is continuously injected 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 is continued to be injected.

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

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

[0111] 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 4 is obtained.

[0112] Example 5

[0113] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64 mm × 54 mm × 36 mm) 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 and 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 is continuously injected 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 is continued to be injected.

[0117] When the temperature in the furnace drops to 600℃, 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.

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

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

[0120] 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 and mechanical properties of the material, and finally a sintered NdFeB blank product 5 was obtained.

[0121] Comparative Example 1

[0122] The magnet blank (a square sintered NdFeB with a performance grade of N52 and a size of 64 mm × 54 mm × 36 mm) 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 80kPa. Then the fan is started and the frequency is set to 50Hz to ensure uniform gas flow in the furnace and heat exchange.

[0124] When the temperature inside 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 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 64 mm × 54 mm × 36 mm) 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 80kPa. Then the fan is started and the frequency is set to 50Hz to ensure uniform gas flow in the furnace and heat exchange.

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

[0130] After cooling, the sintered 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 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 64 mm × 54 mm × 36 mm) 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 50kPa. Then, the fan is started and the frequency is set to 50Hz to ensure uniform gas flow in the furnace and heat exchange.

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

[0135] After cooling, the sintered 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 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 were 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, as well as 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 properties of the sintered magnetic material using this 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 methods 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 scope of protection 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 to a sintering temperature of 1000-1150°C in a vacuum sintering furnace and keeping the temperature for 2-8 hours to complete sintering; (2) filling the vacuum sintering furnace 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 to 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 for sintered magnetic materials 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 for sintered magnetic materials 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 for sintered magnetic materials according to claim 1, wherein in step (2), the inert gas is filled, the pressure in the vacuum sintering furnace is adjusted to a range of 5kPa-15kPa, and a fan is turned on for cooling. 7 . The sintering cooling method for sintered magnetic materials 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 operates at a power of 50 Hz.

9. The sintering and cooling method of a sintered magnetic material according to claim 1, wherein after step (6), the obtained sintered body blank 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 as a main phase. 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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