A sintering process for neodymium-iron-boron with shortened sintering time

Abstract

The application discloses a sintering neodymium-iron-boron process for shortening sintering time, relates to the technical field of neodymium-iron-boron magnets, and comprises a rough vacuum extraction step, a variable-speed exhaust and temperature rising step, a high-temperature holding step and a cooling step, wherein the variable-speed exhaust and temperature rising step is a core process step, the whole process is carried out in a vacuum environment, and the variable-speed exhaust and temperature rising step adopts a temperature rising mode of alternating multi-section rapid temperature rising and multi-section slow temperature rising to realize sufficient escape of gas in a neodymium-iron-boron magnetic powder blank. The neodymium-iron-boron blank after sintering is subjected to detection of various performance indexes, and meanwhile, data such as time consumption and energy consumption of each process stage are recorded, the detection equipment is a magnetic property tester, a carbon-oxygen analyzer and a density tester, all of which are calibrated by measurement, and detection data is kept to three significant figures.

Description

Technical Field

[0001] This invention relates to the field of neodymium iron boron magnet technology, and in particular to a sintering process for neodymium iron boron magnets that shortens the sintering time. Background Technology

[0002] With Nd2Fe 14 Re-Fe-B type rare earth sintered NdFeB magnets, with B-type compounds as the main phase, have become the best-performing permanent magnet materials in the field of magnetic materials due to their excellent magnetic energy product and coercivity. They are widely used in high-end equipment manufacturing fields such as new energy vehicle drive motors, industrial servo motors, variable frequency air conditioning compressors, and wind turbines, and are one of the core basic materials for the development of high-end intelligent manufacturing industries. The preparation process of sintered NdFeB magnets has matured. The core processes include melting and ingot making, hydrogen crushing and powder making, air jet milling, orientation pressing, vacuum sintering, and subsequent tempering. Among them, the vacuum sintering process is the key to achieving densification of the magnetic powder blank and forming a stable crystal phase structure, which directly determines the density, carbon and oxygen content, and final magnetic properties of the magnet. Existing vacuum sintering processes are generally divided into four continuous stages: rough vacuuming, exhaust heating, high-temperature holding, and cooling. The exhaust heating stage, as the core pre-sintering stage, mainly functions to promote the full escape of adsorbed gases, residual hydrogen, and additive decomposition products from the magnetic powder blank through the heating process, laying the foundation for subsequent high-temperature densification sintering. This stage typically adopts a step-by-step heating process combined with a long-term holding period in the low-temperature stage. By controlling the heating rate, the gas escape is ensured, and this process has been widely used and practiced in the industry.

[0003] In existing sintering NdFeB magnet processes, to ensure sufficient gas escape from the billet, the process design employs low-rate heating throughout or long-duration holding periods in multiple temperature ranges. While this approach guarantees gas release to some extent, it significantly extends the process cycle of the venting and heating phase, thereby increasing the overall sintering production time for a single furnace of magnets. Due to these process characteristics, the utilization rate of equipment per unit time is difficult to improve, significantly restricting capacity release. Furthermore, the prolonged heating and holding processes increase energy consumption. Moreover, to meet the venting requirements of this process, some production scenarios require extending the holding time to compensate for insufficient venting efficiency, further exacerbating the long production cycle. This design feature of the existing process is a choice made under the premise of ensuring basic product performance, but its limitations in improving production efficiency are no longer sufficient to meet the current market demand for large-scale, high-efficiency production of sintered NdFeB magnets. The industry urgently needs a technical solution to optimize the venting and heating process to shorten sintering time without changing the configuration of existing mainstream production equipment or reducing product performance. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a sintering NdFeB process for shortening the sintering time, which solves the problems that in the existing process, in order to ensure the degassing effect, a low-rate heating throughout the process or long-time heat preservation in multiple temperature ranges is adopted, resulting in a long process cycle in the exhaust gas heating section, a long overall sintering production time, and further, low equipment utilization rate, limited production capacity and increased energy consumption.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: In a first aspect, the present invention provides a sintering NdFeB process for shortening the sintering time, which includes a rough vacuum pumping step, a variable-speed exhaust gas heating step, a high-temperature heat preservation step and a cooling step. The variable-speed exhaust gas heating step is the core process step, which is carried out in a vacuum environment throughout the process, and the variable-speed exhaust gas heating step adopts a heating method of alternating multi-stage rapid heating and multi-stage slow heating to achieve the full escape of gas in the NdFeB magnetic powder blank.

[0007] As a preferred scheme of the sintering NdFeB process for shortening the sintering time according to the present invention, wherein: in the rough vacuum pumping step, after the tooling containing the NdFeB magnetic powder blank is placed in the sintering furnace and the furnace door is closed, the vacuum pumping system is started to pump the vacuum degree in the furnace chamber to ≤5×10 - ²Pa, and the pumping system continues to operate in the subsequent variable-speed exhaust gas heating and high-temperature heat preservation steps.

[0008] Furthermore, the rough vacuum pumping step is a precondition step for the sintering process. During operation, first, the NdFeB magnetic powder blank after orientation pressing is regularly placed in a high-temperature resistant graphite tooling, and then the tooling containing the blank is smoothly placed at the designated position in the furnace chamber of the sintering furnace, and the furnace door of the sintering furnace is closed and locked to ensure the airtightness of the furnace chamber; subsequently, the vacuum pumping system supporting the sintering furnace is started, and the rough pumping operation is first completed by a mechanical pump, and the vacuum degree in the furnace chamber is accurately pumped to ≤5×10 - ²Pa, the required value of the process, and the vacuum pumping system remains in a continuous operation state throughout the subsequent variable-speed exhaust gas heating and high-temperature heat preservation processes, timely pumping out the gas in the furnace chamber and the gas escaped from the blank, and always maintaining the vacuum environment in the furnace chamber to provide a basic vacuum condition for subsequent degassing and sintering.

[0009] As a preferred scheme of the sintering NdFeB process for shortening the sintering time according to the present invention, wherein: the starting temperature range of the variable-speed exhaust gas heating step is 0-50°C, the ending temperature is 950-1120°C, and the heating rate in the slow heating section is controlled to be 0.1-2°C / min, and the heating rate in the rapid heating section is adaptively adjusted according to different temperature ranges.

[0010] Furthermore, the variable-speed exhaust heating step, as a core process step, has an initial temperature range of 0-50℃, which corresponds to the initial ambient temperature range of the sintering furnace chamber. The final temperature is set at 950-1120℃ to match the process requirements for sintering NdFeB, ensuring seamless connection with the sintering temperature of the subsequent high-temperature holding step. In this step, the heating rate of all slow heating sections is uniformly controlled within the process range of 0.1-2℃ / min to ensure sufficient gas escape from the billet at different temperature nodes. The rapid heating section, on the other hand, is adaptively adjusted according to the characteristics of different temperature ranges. This minimizes the ineffective heating time while avoiding thermal stress caused by sudden temperature changes in the billet, achieving a process balance between rapid heating and sufficient gas release.

[0011] As a preferred embodiment of the sintering NdFeB process for shortening sintering time described in this invention, the variable-speed exhaust heating step specifically includes a first heating stage: heating from the initial temperature to 320-370℃ at a rapid heating rate of 5-10℃ / min, and then heating to 420-470℃ at a slow heating rate of 0.1-2℃ / min.

[0012] Furthermore, the variable-speed exhaust heating step specifically includes a first heating stage, which is a low-temperature basic heating and gas release stage. First, the temperature is rapidly increased from the initial temperature of 0-50℃ to the initial temperature of 320-370℃ for low-order gas escape at a rapid heating rate of 5-10℃ / min, so as to quickly complete the basic heating while avoiding excessive time consumption in the low-temperature stage. Then, the heating rate is switched to a slow heating rate of 0.1-2℃ / min, and the temperature is gradually increased from 320-370℃ to 420-470℃, so as to provide sufficient time for the air, moisture and a small amount of residual hydrogen adsorbed on the surface of the NdFeB magnetic powder blank to escape, thereby achieving the initial and sufficient discharge of the gas on the surface of the blank.

[0013] As a preferred embodiment of the sintering NdFeB process for shortening sintering time described in this invention, the variable-speed exhaust heating step further includes a second heating stage: heating from 420-470℃ to 520-570℃ at a rapid heating rate of 2-7℃ / min, and then heating to 620-670℃ at a slow heating rate of 0.1-2℃ / min.

[0014] Furthermore, the variable-speed exhaust heating step also includes a second heating stage, which is a medium-temperature deep venting stage. After completing the first stage of heating and venting, the temperature is rapidly increased from 420-470℃ to 520-570℃ at a rate of 2-7℃ / min, which is suitable for the internal temperature conduction characteristics of the billet, thus avoiding excessively rapid heating that would prevent the internal gas from escaping in time. Subsequently, the temperature is switched to a slow heating rate of 0.1-2℃ / min, increasing from 520-570℃ to 620-670℃. This temperature range is the main venting range for residual hydrogen and additive decomposition products in the billet. The slow heating ensures that these gases can escape smoothly from the inside of the billet, effectively reducing gas retention.

[0015] As a preferred embodiment of the sintering NdFeB process for shortening sintering time described in this invention, the variable-speed exhaust heating step further includes a third heating stage: heating from 620-670℃ to 820-890℃ at a rapid heating rate of 5-10℃ / min, and then heating to 920-950℃ at a slow heating rate of 0.1-2℃ / min.

[0016] Furthermore, the variable-speed exhaust heating step also includes a third heating stage, which is a high-temperature pre-sintering venting stage. After completing the second stage of medium-temperature venting, the temperature is rapidly increased from 620-670℃ to 820-890℃ at a rate of 5-10℃ / min, quickly approaching the sintering temperature range and shortening the heating cycle. Then, the temperature is increased from 820-890℃ to 920-950℃ at a slow rate of 0.1-2℃ / min. In this temperature range, trace amounts of deeply adsorbed gases and hydrocarbon decomposition products still escape from the billet. The low-speed heating can fully exhaust these trace gases and preheat the billet for entering the liquid phase sintering stage, avoiding temperature shocks during subsequent high-temperature sintering. In addition, the continuous vacuum pumping system in this stage can promptly remove the escaped gases from the furnace.

[0017] As a preferred embodiment of the sintering NdFeB process for shortening sintering time as described in this invention, the variable-speed exhaust heating step further includes a fourth heating stage: heating from 920-950℃ to 950-1120℃ at a rapid heating rate of 5-10℃ / min, completing the variable-speed exhaust heating and entering the high-temperature holding stage.

[0018] Furthermore, the variable-speed exhaust heating step also includes a fourth heating stage, which is a sintering temperature transition stage. After completing the third stage of high-temperature pre-sintering venting, the temperature is rapidly increased from 920-950℃ to the sintering endpoint temperature of 950-1120℃ at a rapid heating rate of 5-10℃ / min. This rate ensures uniform temperature conduction of the billet while quickly completing the process requirement of heating to the sintering temperature without additional heat preservation and venting steps, effectively shortening the overall exhaust heating cycle. When the furnace temperature reaches the set value of 950-1120℃, the variable-speed exhaust heating step is officially completed, and the sintering process directly and seamlessly enters the subsequent high-temperature heat preservation step, realizing the continuous connection of process steps.

[0019] As a preferred embodiment of the sintering NdFeB process for shortening sintering time described in this invention, the high-temperature holding step involves stabilizing the furnace temperature at the sintering endpoint temperature of 950-1120℃, with temperature fluctuations controlled within ±1℃. The holding time is adjusted according to the thickness of the NdFeB magnetic powder blank: 2-3 hours for blank thickness ≤20mm, 3-4 hours for thickness 20-50mm, and 4-5 hours for thickness >50mm.

[0020] Furthermore, the high-temperature holding step is the core sintering step for achieving densification of the NdFeB magnetic powder blanks. After the variable-speed exhaust heating step, the furnace temperature is precisely stabilized at the sintering endpoint temperature of 950-1120℃ through the sintering furnace temperature control system, with temperature fluctuations strictly controlled within ±1℃ to ensure uniform temperature in all areas of the furnace and avoid uneven sintering of the blanks due to temperature deviations. The holding time in this step is adjusted in stages according to the thickness of the NdFeB magnetic powder blanks. For small blanks with a thickness ≤20mm, the holding time is 2-3 hours to ensure sufficient densification; for medium-sized blanks with a thickness of 20-50mm, the holding time is 3-4 hours to adapt to the internal temperature conduction and liquid phase sintering rate of the blank; for blanks with a thickness >50mm, the holding time is 3-4 hours. Large-sized billets are held at heat for 4-5 hours to ensure that the billets can achieve full liquid phase sintering from the surface to the inside, forming a stable crystal phase structure. During the heat holding process, the vacuum pumping system runs continuously to remove a small amount of residual gas in time.

[0021] As a preferred embodiment of the sintering NdFeB process for shortening sintering time as described in this invention, the cooling step adopts a gradient cooling method, which is divided into high-temperature cooling, medium-temperature cooling and low-temperature cooling in sequence, and the sintering furnace is kept in a sealed state throughout the cooling process until the furnace temperature drops to room temperature.

[0022] Furthermore, the cooling step is the final shaping step of the sintering process. It adopts a gradient cooling process, which is divided into three consecutive stages: high-temperature cooling, medium-temperature cooling, and low-temperature cooling. This avoids the billet from developing thermal stress due to rapid cooling, which could lead to cracks, deformation, or distortion of the crystal structure. Throughout the cooling process, the sintering furnace is kept sealed, with the furnace door closed and no outside air allowed in. This effectively prevents the high-temperature billet from oxidizing upon contact with air until the temperature inside the furnace naturally drops to room temperature. Only then is the billet removed, ensuring the integrity of the appearance and performance of the sintered NdFeB billet.

[0023] As a preferred embodiment of the sintering NdFeB process for shortening sintering time described in this invention, the high-temperature cooling section involves cooling from the sintering endpoint temperature to 600°C using natural cooling within the furnace, with a cooling rate controlled at 3-5°C / min; the medium-temperature cooling section involves cooling from 600°C to 200°C using natural cooling or low-speed water cooling, with a cooling rate controlled at 5-8°C / min; and the low-temperature cooling section involves naturally cooling from 200°C to ≤50°C, followed by filling the furnace with dry inert gas to restore atmospheric pressure to complete the cooling process.

[0024] Furthermore, the high-temperature cooling stage involves reducing the temperature from the sintering endpoint of 950-1120℃ to 600℃. During this stage, the billet is in the high-temperature crystal phase stabilization period. Natural cooling within the furnace is adopted, with the sintering furnace heating system shut down. Cooling is achieved through the furnace's own thermal radiation and conduction, with the cooling rate precisely controlled at 3-5℃ / min to ensure stable crystal phase structure formation of the billet. The medium-temperature cooling stage involves reducing the temperature from 600℃ to 200℃. At this stage, the billet temperature has been significantly reduced. Natural cooling or low-speed water cooling can be selected based on the production equipment configuration, with the cooling rate controlled at 5-8℃ / min. The cooling efficiency is appropriately increased while ensuring no thermal stress on the billet. The low-temperature cooling stage involves continuing natural cooling from 200℃ to ≤50℃. After the temperature drops to this range, the vacuum pumping system is shut down, and dry inert protective gas is slowly introduced into the furnace to gradually restore the furnace pressure to atmospheric pressure. At this point, all cooling steps are completed, and the furnace door can be opened to remove the sintered NdFeB billet.

[0025] The beneficial effects of this invention are as follows: The coarse vacuuming step establishes a stable vacuum environment for the entire sintering process and maintains continuous operation of the evacuation system, promptly removing various gases escaping from the furnace. This provides the basic vacuum conditions for gas release and densification sintering of the billets, preventing gas stagnation in the furnace from affecting the release effect. Simultaneously, it ensures the stability of the sintering environment in subsequent steps. Through the core step of variable-speed exhaust heating, a multi-stage alternating rapid and slow heating method is used, adapting and adjusting the heating rate in different temperature ranges. This allows the billets to obtain sufficient gas release time in the corresponding temperature range, achieving full release of various gases from the surface to the depths of the billets. Simultaneously, the rapid heating stage effectively shortens the time spent on ineffective heating, significantly reducing the overall exhaust heating cycle and shortening the sintering time from the core. Furthermore, the temperature range design of this step seamlessly connects with the subsequent high-temperature holding step, ensuring the continuity of the sintering process. The high-temperature holding step adjusts the holding time and precisely controls the temperature according to the billet specifications, allowing NdFeB magnetic powder billets of different specifications to achieve full sintering. Liquid-phase sintering forms a stable and uniform crystalline structure, ensuring the densification effect and core magnetic properties of the magnet. Simultaneously, a continuous vacuum environment further removes any residual gas, preventing it from affecting the sintering quality of the blank. The cooling process employs a gradient cooling method while maintaining a sealed furnace throughout. The cooling rate is adjusted in stages to prevent defects such as cracks and deformation caused by thermal stress in the blank. It also prevents oxidation of the high-temperature blank upon contact with air, ensuring the integrity of the appearance and performance of the sintered blank. The coordinated operation of these steps effectively shortens the overall production time of sintered NdFeB magnets without adding new equipment or changing existing configurations, improving equipment utilization and capacity. It also ensures sufficient gas release from the blank, reducing carbon and oxygen residue in the sintered blank, optimizing grain boundary phase distribution, and improving the finished product performance and batch consistency of NdFeB magnets. Furthermore, it reduces energy consumption caused by prolonged heating and holding, balancing production efficiency and product quality. This method is suitable for the large-scale, efficient production of NdFeB magnets required in fields such as new energy vehicles and servo motors. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A flowchart of the sintering process for NdFeB to shorten sintering time. Detailed Implementation

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0030] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0031] Reference Figure 1 This is one embodiment of the present invention, which provides a sintering process for NdFeB magnets that shortens the sintering time, comprising the following steps: In this experiment, N45 grade NdFeB magnetic powder blanks were used as the test substrate. The blanks were uniformly prepared as 30mm thick cubic structures, free from defects such as cracks, missing corners, and deformation. The blanks were randomly divided into two groups: the experimental group used the shortened sintering time NdFeB sintering process described in this invention, while the control group used the existing conventional NdFeB sintering process. Both groups used the same model of vacuum sintering furnace with a furnace volume of 2m³ and identical graphite fixtures. Before the experiment, the vacuum system, temperature control system, and heating system of the sintering furnace were fully calibrated. The vacuum gauge accuracy was ±0.01Pa, and the thermocouple temperature control accuracy was ±1℃ to ensure consistent equipment parameters and eliminate the influence of equipment differences on the test results. Before the experiment, the two groups of blanks were neatly placed in the graphite fixtures, with an 8mm gap between the blanks to ensure gas escape channels. The fixtures were then placed in the designated positions within the sintering furnace chamber.

[0032] The specific process of implementing the process of this invention in the experimental group is as follows: The first step is to perform a rough vacuuming step, close and lock the sintering furnace door, start the vacuum pumping system, and use a mechanical pump to roughly pump the air until the vacuum degree inside the furnace reaches 4.5 × 10⁻⁶. -²Pa, the exhaust system remains continuously operational throughout all subsequent steps. The second step is the variable-speed exhaust heating step, a core process. The starting temperature is 25℃, and the ending temperature is 1080℃, specifically divided into four stages: the first stage heats up to 350℃ at a rate of 8℃ / min, then to 450℃ at a rate of 1℃ / min; the second stage heats up to 550℃ at a rate of 5℃ / min, then to 650℃ at a rate of 1℃ / min; the third stage heats up to 850℃ at a rate of 8℃ / min, then to 930℃ at a rate of 1℃ / min; the fourth stage heats up to 1080℃ at a rate of 8℃ / min. After completing the variable-speed exhaust heating, the process directly proceeds to the high-temperature holding step. The third step involves high-temperature heat preservation, stabilizing the furnace temperature at 1080℃ with temperature fluctuations controlled within ±1℃. Based on a billet thickness of 30mm, the heat preservation time is set at 3.5 hours. During this process, continuous vacuuming is maintained to ensure a stable vacuum level within the furnace. The fourth step is cooling, employing a gradient cooling method while keeping the furnace sealed throughout: the high-temperature section cools naturally from 1080℃ to 600℃ at a rate of 4℃ / min; the medium-temperature section cools from 600℃ to 200℃ using low-speed water cooling at a rate of 6℃ / min; and the low-temperature section cools naturally from 200℃ to 45℃. Dry argon gas is then slowly introduced into the furnace to restore the pressure to 0.1MPa, completing the cooling step.

[0033] The control group underwent the existing conventional sintering NdFeB process, specifically: rough vacuuming to 4.5 × 10⁻⁶. - After reaching 2Pa, the exhaust heating section employs a low-rate heating method throughout, uniformly raising the temperature from 25℃ to 1080℃ at a rate of 1℃ / min, without segmented variable-speed heating design. The high-temperature holding step also stabilizes the temperature at 1080℃, with a holding time set to 5 hours to ensure sufficient exhaust. The cooling step utilizes a completely natural cooling method, cooling from 1080℃ to room temperature without gradient temperature control design. After both sets of experiments, various performance indicators of the sintered NdFeB blanks were tested, and data such as time consumption and energy consumption at each process stage were recorded. The testing equipment included a magnetic property tester, a carbon-oxygen analyzer, and a density tester, all of which were calibrated, and the test data retained three significant figures.

[0034] In summary, this invention establishes a stable vacuum environment throughout the sintering process through a preliminary vacuuming step, ensuring continuous operation of the extraction system and timely removal of various gases escaping from the furnace. This provides the basic vacuum conditions for billet venting and densification sintering, preventing gas stagnation in the furnace from affecting the venting effect. Simultaneously, it coordinates with subsequent steps to ensure the stability of the sintering environment. Through the core step of variable-speed exhaust heating, a multi-stage alternating rapid and slow heating method is employed, adapting and adjusting the heating rate within different temperature ranges. This allows the billet sufficient venting time at each temperature range, enabling the full escape of various gases from the surface to the deeper layers of the billet. Simultaneously, the rapid heating stage effectively shortens the time spent on ineffective heating, significantly reducing the overall exhaust heating cycle and shortening the sintering time from this core aspect. Furthermore, the temperature range design of this step seamlessly connects with the subsequent high-temperature holding step, ensuring the continuity of the sintering process. The high-temperature holding step adjusts the holding time and precisely controls the temperature according to the billet specifications, allowing NdFeB magnetic powder billets of different specifications to achieve sufficient liquid cooling. Phase sintering forms a stable and uniform crystal phase structure, ensuring the densification effect and core magnetic properties of the magnet. Simultaneously, a continuous vacuum environment further removes any residual gas, preventing it from affecting the sintering quality of the blank. The cooling process employs a gradient cooling method while maintaining a sealed furnace throughout. The cooling rate is adjusted in stages to prevent defects such as cracks and deformation caused by thermal stress in the blank. It also prevents oxidation of the high-temperature blank upon contact with air, ensuring the integrity of the appearance and performance of the sintered blank. These steps work in synergy, effectively shortening the overall production time of sintered NdFeB magnets without adding new equipment or changing existing configurations, improving equipment utilization and capacity. It also ensures sufficient gas release from the blank, reducing carbon and oxygen residue in the sintered blank, optimizing grain boundary phase distribution, and improving the finished product performance and batch consistency of NdFeB magnets. Furthermore, it reduces energy consumption caused by prolonged heating and holding, balancing production efficiency and product quality. This method is suitable for the large-scale, efficient production of NdFeB magnets required in fields such as new energy vehicles and servo motors.

[0035] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A sintering process for NdFeB magnets that shortens sintering time, characterized in that: The process includes a rough vacuuming step, a variable-speed exhaust heating step, a high-temperature holding step, and a cooling step. The variable-speed exhaust heating step is the core process step, which is carried out in a vacuum environment throughout. The variable-speed exhaust heating step adopts a heating method that alternates between multiple rapid heating stages and multiple slow heating stages to achieve full escape of gas from the NdFeB magnetic powder blank.

2. The sintering NdFeB process for shortening sintering time as described in claim 1, characterized in that: The rough vacuuming step involves placing the tooling containing the NdFeB magnetic powder blank into the sintering furnace, closing the furnace door, and then starting the vacuum pumping system to evacuate the vacuum level inside the furnace to ≤5×10⁻⁶. - ²Pa, and the extraction system continues to operate in the subsequent variable speed exhaust heating and high temperature insulation steps.

3. The sintering NdFeB process for shortening sintering time as described in claim 2, characterized in that: The starting temperature range of the variable-speed exhaust heating step is 0-50℃, and the ending temperature is 950-1120℃. The heating rate of the slow heating section is controlled at 0.1-2℃ / min, and the heating rate of the rapid heating section is adjusted according to different temperature ranges.

4. The sintering NdFeB process for shortening sintering time as described in claim 3, characterized in that: The variable-speed exhaust heating step specifically includes a first heating stage: heating from the initial temperature to 320-370℃ at a rapid heating rate of 5-10℃ / min, and then heating to 420-470℃ at a slow heating rate of 0.1-2℃ / min.

5. The sintering NdFeB process for shortening sintering time as described in claim 4, characterized in that: The variable-speed exhaust heating step also includes a second heating stage: heating from 420-470℃ to 520-570℃ at a rapid heating rate of 2-7℃ / min, and then heating to 620-670℃ at a slow heating rate of 0.1-2℃ / min.

6. The sintering NdFeB process for shortening sintering time as described in claim 5, characterized in that: The variable-speed exhaust heating step also includes a third heating stage: heating from 620-670℃ to 820-890℃ at a rapid heating rate of 5-10℃ / min, and then heating to 920-950℃ at a slow heating rate of 0.1-2℃ / min.

7. The sintering NdFeB process for shortening sintering time as described in claim 6, characterized in that: The variable-speed exhaust heating step also includes a fourth heating stage: heating from 920-950℃ to 950-1120℃ at a rapid heating rate of 5-10℃ / min, completing the variable-speed exhaust heating and entering the high-temperature heat preservation step.

8. The sintering NdFeB process for shortening sintering time as described in claim 7, characterized in that: The high-temperature heat preservation step involves stabilizing the furnace temperature at the sintering endpoint temperature of 950-1120℃, with temperature fluctuations controlled within ±1℃. The heat preservation time is adjusted according to the thickness of the NdFeB magnetic powder blank: 2-3 hours for blank thickness ≤20mm, 3-4 hours for thickness 20-50mm, and 4-5 hours for thickness >50mm.

9. The sintering NdFeB process for shortening sintering time as described in claim 8, characterized in that: The cooling process employs a gradient cooling method, consisting of high-temperature cooling, medium-temperature cooling, and low-temperature cooling, while maintaining the sintering furnace chamber in a sealed state throughout the cooling process until the furnace temperature drops to room temperature.

10. The sintering NdFeB process for shortening sintering time as described in claim 9, characterized in that: The high-temperature cooling section involves cooling from the sintering endpoint temperature to 600℃ using natural cooling within the furnace, with a cooling rate controlled at 3-5℃ / min. The medium-temperature cooling section involves cooling from 600℃ to 200℃ using natural cooling or low-speed water cooling, with a cooling rate controlled at 5-8℃ / min. The low-temperature cooling section involves naturally cooling from 200℃ to ≤50℃, followed by filling the furnace with dry inert gas to restore atmospheric pressure to complete the cooling process.

Images