Thermal deformation magnet preparation method and preheating device

Abstract

The invention discloses a thermal deformation magnet preparation method and a preheating device. The preparation method of the thermally-deformed magnet comprises the following steps: performing cold pressing on magnetic powder to obtain a cold-pressed blank with the density of 4.5-5.5 g / cm < 3 >, performing hot pressing on the cold-pressed blank in a hot-pressing female die at 600-800 DEG C to obtain a pre-pressed blank, and preheating the pre-pressed blank with the temperature of 850-950 DEG C after preheating; the preheated pre-pressed blank is transferred into a thermal deformation female die, and the temperature of the thermal deformation female die ranges from 750 DEG C to 800 DEG C; and keeping the temperature of the upper punch at 600-700 DEG C, and enabling the upper punch to enter a thermal deformation female die to perform thermal deformation on the pre-pressed blank to obtain the magnet. In the thermal deformation process of the magnet, the temperature of the pre-pressed blank is higher than that of the female die, and the temperature of the female die is higher than that of the upper punch, so that precipitation of a rare earth-rich phase in the pre-pressed blank is reduced, loss of the female die is reduced, and the service life of the die is prolonged.

Description

Technical Field

[0001] The present application relates to the field of magnet preparation, and in particular to a method for preparing a heat-deformed magnet and a preheating device. Background Art

[0002] Rare earth permanent magnet materials have been widely used in many fields such as motors, computers, automobiles, instruments, meters, household appliances, aerospace, etc. Compared with the traditional powder metallurgy sintering magnet process, the hot deformation process prepares magnets by thermal deformation to obtain a deformation texture inside the magnet, and anisotropic magnets can be obtained without magnetic field orientation. In addition, compared with the micron-sized grains of sintered magnets, hot deformation magnets have a nano-grained organizational structure and have better corrosion resistance and high temperature resistance.

[0003] However, the output of NdFeB magnets produced by thermal deformation process accounts for a very low proportion in the entire rare earth permanent magnet industry. One of the reasons is that the thermal deformation process causes serious loss of mold materials. The mold needs to be replaced after producing about 1,000 magnets. The mold cost is high, and the replacement of molds causes frequent downtime, resulting in low production efficiency.

[0004] The inventors have found that the pre-pressed blank is heated by the die during thermal deformation. In order to meet the temperature requirements of the magnet thermal deformation, the temperature of the die is relatively high, for example, the temperature of the die is 850-900°C. The pre-pressed blank of the magnet contains a rare earth-rich phase with a low melting point. During thermal deformation, the rare earth-rich phase in the pre-pressed blank has been liquefied. The hot extrusion process causes a large amount of rare earth-rich phase to precipitate. The rare earth-rich phase is in contact with the cemented carbide inner wall of the die at high temperature for a long time, which will cause corrosion to the inner wall of the die, thereby causing the loss of mold material and affecting the service life of the mold. Summary of the invention

[0005] Based on the above problems, the present application provides a method for preparing a hot-deformed magnet and a preheating device to reduce the precipitation of rare earth-rich phase in the pre-pressed blank during hot deformation and improve the life of the mold.

[0006] In order to achieve the above effects, the technical solutions adopted in this application are as follows:

[0007] A method for preparing a thermally deformed magnet, comprising:

[0008] The magnetic powder is cold pressed to obtain a cold pressed blank, wherein the density of the cold pressed blank is 4.5 to 5.5 g / cm 3 ,

[0009] Hot pressing the cold pressed blank in a hot pressing concave die at 600-800° C. to obtain a pre-pressed blank;

[0010] Preheating the pre-pressed green sheet, wherein the temperature of the pre-pressed green sheet after preheating is 850-950° C.;

[0011] Transferring the pre-pressed blank after preheating to a hot deformation die, wherein the temperature of the hot deformation die is 750-800°C;

[0012] The temperature of the upper punch is maintained at 600-700° C., and the upper punch is made to enter the thermal deformation concave die to thermally deform the pre-pressed blank after preheating to obtain a magnet.

[0013] According to some embodiments of the present application, the preheating of the pre-pressed blank includes: heating the pre-pressed blank at 850-950° C. for 1-10 min.

[0014] According to some embodiments of the present application, the preheated pre-pressed blank is transferred to the hot deformation die within 5 seconds.

[0015] According to some embodiments of the present application, during the process of transferring the preheated pre-pressed blank to the hot deformation die, the temperature of the pre-pressed blank drops by ≤15°C.

[0016] According to some embodiments of the present application, the step of thermally deforming the pre-pressed blank adopts floating pressing.

[0017] According to some embodiments of the present application, the upward movement rate V 1 is 0.2-1.0 mm / s, and the moving speed of the thermal deformation die is:

[0018]

[0019] Wherein, K is 0.8-1.2, D is the inner diameter of the heat deformation die, d is the outer diameter of the upper punch, V 1 is the moving speed of the upward punch.

[0020] An embodiment of the present application provides a preheating device, comprising:

[0021] A heater is provided with a heating chamber with openings at both ends;

[0022] A first push rod is slidably disposed at one end of the heater, and the first push rod can close an opening at one end of the heater;

[0023] A second push rod is slidably disposed at the other end of the heater, and the second push rod can close the other end opening of the heater;

[0024] A hopper for storing pre-pressed blanks, wherein the first push rod can push the pre-pressed blanks on the hopper into the heating chamber;

[0025] The turning wheel is arranged below the second push rod, and the pre-pressed blank rotates when passing through the turning wheel.

[0026] The present application adopts a thermal deformation process to prepare magnets. During the thermal deformation process, the temperature of the pre-pressed billet is greater than the temperature of the thermal deformation die, and the temperature of the thermal deformation die is greater than the temperature of the upper punch, so as to reduce the precipitation of rare earth-rich phase in the pre-pressed billet, reduce the loss of the thermal deformation die, and increase the life of the mold. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without exceeding the scope of protection required by the present application.

[0028] Figure 1 is a micrograph of a magnet according to an embodiment of the present application;

[0029] Figure 2 is a schematic diagram of a method for preparing a thermally deformed magnet according to an embodiment of the present application;

[0030] Figure 3 is a schematic diagram of the thermal deformation process of an embodiment of the present application;

[0031] Figure 4 is a schematic diagram of a preheating device according to an embodiment of the present application;

[0032] Figure 5 is a side view of a preheating device according to an embodiment of the present application;

[0033] Figure 6 This is the working process of the preheating device in the embodiment of the present application Figure 1 ;

[0034] Figure 7 This is the working process of the preheating device in the embodiment of the present application Figure 2 ;

[0035] Figure 8 This is the working process of the preheating device in the embodiment of the present application Figure 3 . DETAILED DESCRIPTION

[0036] The following is a clear and complete description of the technical solution of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0037] The traditional thermal deformation process for preparing thermally deformed magnets includes:

[0038] 1. Cold press the magnetic powder to obtain a cold pressed blank;

[0039] 2. Hot-press the cold-pressed blank to obtain a pre-pressed blank;

[0040] 3. The pre-pressed blank is thermally deformed in a die at 850-900°C to obtain a cup-shaped magnet.

[0041] During thermal deformation, the pre-pressed blank is heated by the die, and the temperature of the die is 850-900°C. The die is made of cemented carbide, and the high temperature causes the strength and hardness of the cemented carbide to decay rapidly. During the thermal deformation process, the rare earth-rich phase in the pre-pressed blank melts and is squeezed out. The precipitated rare earth-rich phase corrodes the inner wall of the die, affecting the service life of the die.

[0042] like Figure 1 As shown in the microtexture of the magnet, the main phase grain area that does not melt at the hot deformation process temperature accounts for a higher proportion, and the rare earth-rich phase area that causes corrosion on the inner wall of the die accounts for a smaller proportion. Figure 1 The black part in the middle is the lath-shaped main phase, the white part is the rare earth-rich phase, and the c-axis is the easy magnetization direction.

[0043] The inventors discovered that when the temperature of the die is appropriately lower than the temperature of the pre-pressed billet, the main phase grains on the surface of the pre-pressed billet can cool the rare earth-rich phase around the main phase by contacting the inner wall of the die, making the cooled rare earth-rich phase viscous or even returning to a solid state, thereby forming a diaphragm to prevent the liquid rare earth-rich phase inside the pre-pressed billet from precipitating.

[0044] like Figure 2 As shown, the embodiment of the present application provides a method for preparing a thermally deformed magnet, comprising:

[0045] S1. Cold press the magnetic powder under room temperature and atmosphere to obtain a cold pressed blank. The density of the cold pressed blank is 4.5-5.5 g / cm 3 .

[0046] S2. In an argon atmosphere, the cold pressed blank is hot pressed in a hot pressing die at 600-800°C to obtain a pre-pressed blank. Optionally, the density of the pre-pressed blank is 7.5-7.6 g / cm 3 .

[0047] S3, preheating the pre-pressed blank, wherein the temperature of the pre-pressed blank after preheating is 850-950°C.

[0048] S4. Transfer the preheated pre-pressed blank to a hot deformation die, wherein the temperature of the hot deformation die is 750-800°C.

[0049] like Figure 3As shown, the thermal deformation device can be an existing thermal deformation device, which can heat the thermal deformation die 30 and the upper punch 10 to keep the thermal deformation die 30 and the upper punch 10 at a preset temperature. The preheated pre-pressed blank 40 is transferred to the lower punch 20, and the lower punch 20 and the pre-pressed blank 40 are synchronously lowered, and the pre-pressed blank 40 enters the thermal deformation die 30.

[0050] In the process of transferring the preheated pre-pressed billet to the hot deformation die, the temperature of the pre-pressed billet will drop slightly. When the pre-pressed billet enters the hot deformation die, the temperature of the hot deformation die should be lower than that of the pre-pressed billet. The temperature difference between the pre-pressed billet and the hot deformation die is in the range of 50 to 200°C.

[0051] The temperature of the pre-pressed billet after preheating is coordinated with the temperature of the hot deformation die so that the pre-pressed billet in the hot deformation die meets the temperature required for hot deformation. At the same time, since the temperature of the hot deformation die is lower than the temperature of the pre-pressed billet after preheating, the rare earth-rich phase precipitated from the pre-pressed billet is reduced during hot deformation, thereby reducing corrosion to the hot deformation die.

[0052] S5 , maintaining the temperature of the upper punch at 600-700° C., the upper punch 10 enters the hot deformation die 30 to hot deform the pre-pressed blank 40 after preheating, and obtains the magnet 50 .

[0053] Keeping the temperature of the upper punch at 600-700°C can prevent cracks from occurring in the pre-pressed blank during thermal deformation.

[0054] During the process of preparing magnets by the hot deformation process of this embodiment, the temperature is arranged as follows: the temperature of the pre-pressed billet after preheating > the temperature of the hot deformation die > the punching temperature. Since the temperature of the hot deformation die is relatively low, a small amount of rare earth-rich phase precipitated from the pre-pressed billet solidifies after contacting the inner wall of the hot deformation die, thereby preventing the precipitation of more rare earth-rich phases inside the pre-pressed billet, reducing corrosion to the hot deformation die, increasing the life of the hot deformation die, and improving production efficiency.

[0055] Optionally, as required, the bottom of the cup-shaped magnet is cut off to obtain a magnetic ring.

[0056] In some embodiments, preheating the prepress includes heating the prepress at 850-950° C. for 1-10 minutes. The preheating time of the prepress is determined according to the size of the prepress, so that the prepress is fully heated to facilitate subsequent thermal deformation.

[0057] In some embodiments, the preheated pre-pressed green compact is transferred to the hot deformation die within 5 seconds. If the preheated pre-pressed green compact is transferred to the hot deformation die, the temperature of the pre-pressed green compact will drop too much, thus affecting the subsequent hot deformation.

[0058] In some embodiments, the temperature of the pre-pressed blank decreases by ≤15°C during the process of transferring the pre-heated pre-pressed blank to the heat deformation die, so as to ensure that the temperature difference between the pre-pressed blank and the heat deformation die when the pre-pressed blank enters the heat deformation die is in the range of 50 to 200°C.

[0059] In some embodiments, floating pressing is used for thermal deformation of the pre-pressed green body. When only the pressing method of moving the upper punch downward is used, the friction between the inner wall of the thermal deformation die and the pre-pressed green body will increase the pressing force of the upper punch and may cause cracks in the magnet. When the thermal deformation die is used for floating pressing, the thermal deformation die moves upward together with the part of the pre-pressed green body that contacts the thermal deformation die to avoid the influence of the friction between the inner wall of the thermal deformation die and the pre-pressed green body on the pressing.

[0060] In some embodiments, the downward movement rate V of the upward stroke 1 The moving speed of the hot deformation die upward is 0.2-1.0 mm / s.

[0061]

[0062] Among them, K is 1.0~1.2, D is the inner diameter of the hot deformation die, and d is the outer diameter of the upper punch.

[0063] Downward movement rate V of the upward impulse 1 It can be determined based on the size of the magnet after thermal deformation, for example,

[0064] The outer diameter of the magnet is 40-50 mm, the thickness of the single side wall is 4-6 mm, and the downward movement rate of the upper punch is V 1 0.2~0.4mm / s;

[0065] The outer diameter of the magnet is 30-40 mm, the thickness of the single side wall is 3-4 mm, and the downward movement rate of the upper punch is V 1 0.5~0.6mm / s;

[0066] The outer diameter of the magnet is 20-30 mm, the thickness of the single side wall is 2-3 mm, and the downward movement rate of the upper punch is V 1 0.9~1.0mm / s.

[0067] When the coefficient K is determined by experiment, K can be selected as 0.8, 0.9, 1.0, 1.1 and 1.2. When preparing the thermal deformation sample, select K = 1. If there is no crack on the surface of the experimental sample, then use this value. If cracks appear on the surface of the sample, then adjust K to 0.8, 0.9, 1.1 or 1.2 to ensure that there is no crack on the surface of the sample.

[0068] During the pressing process, the downward movement rate V of the upper punch 1 and the upward movement rate V of the thermal deformation die 2The cooperation makes the deformation rate of the inside of the ring wall (the part not in contact with the die) and the deformation rate of the edge of the ring wall (the part in contact with the die) during the thermal deformation of the pre-pressed billet the same, avoiding cracks in the pre-pressed billet due to the different deformation rates between the inside and the edge.

[0069] Optionally, the thermal deformation of the pre-pressed blank is completed within 30 seconds, ensuring that the pre-pressed blank maintains an optimal process temperature during the thermal deformation process.

[0070] like Figure 4 As shown, the embodiment of the present application provides a preheating device 100, which is used for preheating pre-pressed blanks. The preheating device 100 includes a heater 1, a first ejector rod 2, a second ejector rod 3, a hopper 4 and a turning wheel 5.

[0071] The heater 1 is provided with a heating chamber with openings at both ends, and optionally, the axis of the heater 1 is parallel to the horizontal direction. The heater 1 is provided with a temperature sensor 11 to detect the temperature in the heating chamber. The pre-pressed blank 40 enters the heating chamber for preheating.

[0072] The first push rod 2 is slidably disposed at one end of the heater 1, and the first push rod 2 can close the opening at one end of the heater 1. The second push rod 3 is slidably disposed at the other end of the heater 1, and the second push rod 3 can close the opening at the other end of the heater 1. The opening of the heater 1 closed by the first push rod 2 is the feed port, and the opening of the heater 1 closed by the second push rod 3 is the discharge port.

[0073] like Figure 5 As shown, a plurality of pre-pressed blanks are sequentially arranged in the hopper 4, the hopper 4 is tilted, and the first push rod 2 can push the pre-pressed blanks 40 at the bottom end of the hopper 4 into the heating chamber.

[0074] The turning wheel 5 is arranged below the second push rod 3 , and the pre-pressed blank 40 rotates when passing through the turning wheel 5 .

[0075] like Figure 6 As shown, after the pre-pressed blank 40 in the heater 1 is heated, the second push rod 3 slides away from the first push rod 2, the discharge port of the heater 1 is opened, and the first push rod 2 slides toward the second push rod 3, pushing a pre-pressed blank in the heating chamber out, and the pre-heated pre-pressed blank rotates through the turning wheel 5, and the axis of the pre-pressed blank 40 changes from the horizontal direction to the vertical direction, and the pre-pressed blank 40 slides onto the support plate 6. The pre-pressed blank 40 on the support plate 6 is quickly transferred to the hot deformation die.

[0076] like Figure 7 As shown, the second push rod 3 slides toward the direction approaching the first push rod 2 to close the discharge port of the heater 1, and the first push rod 2 slides toward the direction away from the second push rod 3. The first push rod 2 slides to the side of the accumulator 4 away from the heater 1, the feed port of the heater 1 is opened, and the pre-pressed billet at the bottom end of the accumulator 4 slides to the feed position.

[0077] like Figure 8 As shown, the first push rod 2 slides toward the direction close to the second push rod 3, pushes the pre-pressed blank on the feeding position into the heating chamber, and closes the feeding port of the heater 1.

[0078] Optionally, the hopper 4 is provided with a displacement sensor 41 and a baffle plate 42. The displacement sensor 41 is used to detect whether the first push rod 2 moves to the side of the hopper 4 away from the heater 1. The baffle plate 42 is slidably arranged on the bottom plate of the hopper 4. When the displacement sensor 41 detects that the first push rod 2 moves to the side of the hopper 4 away from the heater 1, the baffle plate 42 moves down, the pre-pressed blanks at the bottom of the hopper 4 slide to the feeding position, and the baffle plate 42 moves up to block the movement of the remaining pre-pressed blanks in the hopper 4.

[0079] In the hot deformation process of this embodiment, the temperature arrangement is: the temperature of the pre-pressed billet after preheating > the temperature of the hot deformation die > the upper punch temperature. By coordinating the upper punch movement rate and the hot deformation die movement rate, the amount of rare earth-rich phase precipitation of the pre-pressed billet during the hot deformation process is reduced, thereby increasing the service life of the hot deformation die.

[0080] Example 1

[0081] Select MQU-F magnetic powder (Nd 30.2 Fe bal B 0.92 Co 4.1 Ga 0.44 , wt%).

[0082] 1. Weigh 50g of magnetic powder at room temperature and pressure, pour the magnetic powder into a cold pressing die sprayed with lubricant for cold pressing at a pressure of 300MPa. After the pressing is completed, take out a columnar cold pressing blank with an outer diameter of 21.0mm and a height of 27.9mm. The lubricant is graphite.

[0083] 2. Under argon atmosphere, the cold pressed blank with lubricant sprayed on the surface is transferred to the hot pressing die at 700℃. At this time, the upper punch of the press is heated to 600℃ and hot pressed at a pressure of 400MPa. After hot pressing, a columnar pre-pressed blank with an outer diameter of 22.1mm and a height of 17.3mm is taken out. The lubricant is graphite.

[0084] 3. Preheat the preform in a heater at 900°C and keep it warm for 2 minutes. Transfer the preform to the lower punch within 5 seconds. Keep the temperature of the hot deformation die at 800°C and the upper punch at 650°C for floating pressing. The upper punch moving rate is 0.90 mm / s, and the hot deformation die floating rate is 2.23 mm / s (hot deformation die inner diameter D = 25.00 mm, upper punch outer diameter d = 20.80 mm, k value is 1.1). The pressing is completed within 30 seconds to prepare a cup-shaped magnet of 24.8 (Φ outside) × 21 (Φ inside) × 43 mm (H). The lubricant is graphite.

[0085] 4. Cut off the bottom of the magnet to obtain a magnetic ring with a height of 38 mm.

[0086] 5. Cut the magnetic ring to obtain the magnetic properties measurement sample and measure the magnetic properties.

[0087] Example 2

[0088] Select MQU-F magnetic powder (Nd 30.2 Fe bal B 0.92 Co 4.1 Ga 0.44 , wt%).

[0089] 1. Weigh 150g of magnetic powder at room temperature and pressure, pour the magnetic powder into a cold pressing die sprayed with lubricant for cold pressing at a pressure of 300MPa. After the pressing is completed, take out a columnar cold pressing blank with an outer diameter of 36.0mm and a height of 29.2mm. The lubricant is molybdenum disulfide.

[0090] 2. Under argon atmosphere, the cold pressed blank with lubricant sprayed on the surface is transferred to the hot pressing die at a temperature of 700°C. At this time, the upper punch of the press is heated to 600°C for hot pressing at a pressure of 400MPa. After hot pressing, a columnar pre-pressed blank with an outer diameter of 37.5mm and a height of 18.1mm is taken out. The lubricant is molybdenum disulfide.

[0091] 3. Preheat the prepressed blank in a heater at 950°C and keep it warm for 4 minutes. Transfer the prepressed blank to the lower punch within 5 seconds. Keep the temperature of the hot deformation die at 750°C and the upper punch at 650°C for floating pressing. The upper punch moving rate is 0.30 mm / s, and the hot deformation die floating rate is 0.88 mm / s (hot deformation die inner diameter D = 42.70 mm, upper punch outer diameter d = 36.40 mm, k value 1.1). Complete the pressing within 30 seconds to prepare a cup-shaped magnet of 42.5 (Φ outside) × 36.7 (Φ inside) × 33 mm (H). The lubricant is molybdenum disulfide.

[0092] 4. Cut off the bottom of the magnet to obtain a magnetic ring with a height of 28 mm.

[0093] 5. Cut the magnetic ring to obtain the magnetic properties measurement sample and measure the magnetic properties.

[0094] Example 3

[0095] Select MQU-G magnetic powder (Nd 11.2 Pr 16.8 Dy 1.92 Fe bal .B 0.91 Co 4.0 Ga 0.49 , wt%).

[0096] 1. Weigh 50g of magnetic powder at room temperature and pressure, pour the magnetic powder into a cold pressing die sprayed with lubricant for cold pressing at a pressure of 300MPa. After the pressing is completed, take out a columnar cold pressing blank with an outer diameter of 21.0mm and a height of 29.9mm. The lubricant is one of graphite, molybdenum disulfide and BN.

[0097] 2. Under argon atmosphere, the cold pressed blank with lubricant sprayed on the surface is transferred to the hot pressing die at 700℃. At this time, the upper punch of the press is heated to 600℃ and hot pressed at a pressure of 400MPa. After hot pressing, a columnar pre-pressed blank with an outer diameter of 22.1mm and a height of 17.5mm is taken out. The lubricant is BN.

[0098] 3. Preheat the prepressed blank in a heater at 900°C and keep it warm for 2 minutes. Transfer the prepressed blank to the lower punch within 5 seconds. Keep the temperature of the hot deformation die at 800°C and the upper punch at 650°C for floating pressing. The upper punch moving rate is 1.00 mm / s, and the hot deformation die floating rate is 2.70 mm / s (hot deformation die inner diameter D = 25.00 mm, upper punch outer diameter d = 20.80 mm, k value is 1.2). The pressing is completed within 30 seconds to prepare a cup-shaped magnet of 24.8 (Φ outside) × 21 (Φ inside) × 41 mm (H). The lubricant is BN.

[0099] 4. Cut off the bottom of the magnet to obtain a magnetic ring with a height of 35 mm.

[0100] 5. Cut the magnetic ring to obtain the magnetic properties measurement sample and measure the magnetic properties.

[0101] Comparative Example 1

[0102] Select MQU-F magnetic powder (Nd 30.2 Fe bal B 0.92 Co 4.1 Ga 0.44 , wt%).

[0103] 1. Weigh 50g of magnetic powder at room temperature and pressure, pour the magnetic powder into a cold pressing die sprayed with lubricant for cold pressing at a pressure of 300MPa. After the pressing is completed, take out a columnar cold pressing blank with an outer diameter of 21.0mm and a height of 27.9mm. The lubricant is graphite.

[0104] 2. Under argon atmosphere, the cold pressed blank with lubricant sprayed on the surface is transferred to the hot pressing die at 700℃. At this time, the upper punch of the press is heated to 600℃ and hot pressed at a pressure of 400MPa. After hot pressing, a columnar pre-pressed blank with an outer diameter of 22.1mm and a height of 17.3mm is taken out. The lubricant is graphite.

[0105] 3. The pre-pressed blank was transferred to the lower punch, the temperature of the hot deformation die was maintained at 850°C, the upper punch was maintained at 650°C, and floating pressing was performed. The upper punch moving rate was 0.90 mm / s, and the floating rate of the hot deformation die was 2.23 mm / s (the inner diameter of the hot deformation die D = 25.00 mm, the outer diameter of the upper punch d = 20.80 mm, and k was 1.1). The pressing was completed within 30 seconds to prepare a cup-shaped magnet of 24.8 (Φ outside) × 21 (Φ inside) × 41 mm (H). The lubricant was graphite.

[0106] 4. Cut off the bottom of the magnet to obtain a magnetic ring with a height of 35 mm.

[0107] 5. Cut the magnetic ring to obtain the magnetic properties measurement sample and measure the magnetic properties.

[0108] Comparative Example 2

[0109] Select MQU-F magnetic powder (Nd 30.2 Fe bal B 0.92 Co 4.1 Ga 0.44 , wt%).

[0110] 1. Weigh 50g of magnetic powder at room temperature and pressure, pour the magnetic powder into a cold pressing die sprayed with lubricant for cold pressing at a pressure of 300MPa. After the pressing is completed, take out a columnar cold pressing blank with an outer diameter of 21.0mm and a height of 27.9mm. The lubricant is graphite.

[0111] 2. Under argon atmosphere, the cold pressed blank with lubricant sprayed on the surface is transferred to the hot pressing die at 700℃. At this time, the upper punch of the press is heated to 600℃ and hot pressed at a pressure of 400MPa. After hot pressing, a columnar pre-pressed blank with an outer diameter of 22.1mm and a height of 17.3mm is taken out. The lubricant is graphite.

[0112] 3. The pre-pressed blank was transferred to the lower punch, the temperature of the hot deformation die was maintained at 850°C, the upper punch was maintained at 650°C, and non-floating pressing was performed. The upper punch moving rate was 0.90 mm / s, and the floating rate of the hot deformation die was 0 mm / s (the inner diameter of the hot deformation die D = 25.00 mm, the outer diameter of the upper punch d = 20.80 mm, and k was 0). The pressing was completed within 30 seconds to prepare a cup-shaped magnet of 24.8 (Φ outside) × 21 (Φ inside) × 39 mm (H). The lubricant was graphite.

[0113] 4. Cut off the bottom of the magnet to obtain a magnetic ring with a height of 32 mm.

[0114] 5. Cut the magnetic ring to obtain the magnetic properties measurement sample and measure the magnetic properties.

[0115] Comparative Example 3

[0116] Select MQU-F magnetic powder (Nd 30.2 Fe bal B 0.92 Co 4.1 Ga 0.44 , wt%).

[0117] 1. Weigh 50g of magnetic powder at room temperature and pressure, pour the magnetic powder into a cold pressing die sprayed with lubricant for cold pressing at a pressure of 300MPa. After the pressing is completed, take out a columnar cold pressing blank with an outer diameter of 21.0mm and a height of 27.9mm. The lubricant is graphite.

[0118] 2. Under argon atmosphere, the cold pressed blank with lubricant sprayed on the surface is transferred to the hot pressing die at 700℃. At this time, the upper punch of the press is heated to 600℃ and hot pressed at a pressure of 400MPa. After hot pressing, a columnar pre-pressed blank with an outer diameter of 22.1mm and a height of 17.3mm is taken out. The lubricant is graphite.

[0119] 3. Preheat the prepressed blank in a heater at 900°C and keep it warm for 2 minutes. Transfer the prepressed blank to the lower punch within 5 seconds. Keep the temperature of the hot deformation die at 800°C and the upper punch at 650°C for floating pressing. The upper punch moving rate is 0.90 mm / s, and the hot deformation die floating rate is 1.01 mm / s (hot deformation die inner diameter D = 25.00 mm, upper punch outer diameter d = 20.80 mm, k value is 0.5). The pressing is completed within 30 seconds to prepare a cup-shaped magnet of 24.8 (Φ outside) × 21 (Φ inside) × 40 mm (H). The lubricant is graphite.

[0120] 4. Cut off the bottom of the magnet to obtain a magnetic ring with a height of 33 mm.

[0121] 5. Cut the magnetic ring to obtain the magnetic properties measurement sample and measure the magnetic properties.

[0122] Comparative Example 4

[0123] Select MQU-F magnetic powder (Nd 30.2 Fe bal B 0.92 Co 4.1 Ga 0.44 , wt%).

[0124] 1. Weigh 50g of magnetic powder at room temperature and pressure, pour the magnetic powder into a cold pressing die sprayed with lubricant, and cold press at a pressure of 300MPa. After the pressing is completed, take out a columnar cold pressing blank with an outer diameter of 21.0mm and a height of 27.9mm. The lubricant is graphite.

[0125] 2. Under argon atmosphere, the cold pressed blank with lubricant sprayed on the surface is transferred to the hot pressing die at 700℃. At this time, the upper punch of the press is heated to 600℃ and hot pressed at a pressure of 400MPa. After hot pressing, a columnar pre-pressed blank with an outer diameter of 22.1mm and a height of 17.3mm is taken out. The lubricant is graphite.

[0126] 3. Preheat the pre-pressed blank in a heater at 900°C and keep it warm for 2 minutes. Transfer the pre-pressed blank to the lower punch within 5 seconds. Keep the temperature of the hot deformation die at 800°C and the upper punch at 650°C for floating pressing. The upper punch moving rate is 0.90 mm / s, and the hot deformation die floating rate is 2.84 mm / s (hot deformation die inner diameter D = 25.00 mm, upper punch outer diameter d = 20.80 mm, k value is 1.4). The pressing is completed within 30 seconds to prepare a cup-shaped magnet of 24.8 (Φ outside) × 21 (Φ inside) × 44 mm (H). The lubricant is graphite.

[0127] 4. Cut off the bottom of the magnet to obtain a magnetic ring with a height of 36 mm.

[0128] 5. Cut the magnetic ring to obtain the magnetic properties measurement sample and measure the magnetic properties.

[0129] Table 1 Magnetic properties of magnetic rings

[0130]

[0131]

[0132] Table 2 Maximum pit size of the inner wall corrosion of the hot deformation die after preparing multiple magnets

[0133]

[0134] Table 3 Punch down pressure rate and hot deformation die floating rate in the embodiment

[0135]

[0136] From the data in Table 1 and Table 2, all embodiments and all comparative examples can obtain good magnetic properties. The corrosion pits on the inner wall of the heat-deformed die in Table 2 are formed by corrosion of the rare earth-rich phase precipitated from the magnet. After pressing multiple magnets, the maximum pit size of the corrosion on the inner wall of the heat-deformed die is measured. Compared with Comparative Examples 1 and 2, the maximum pit size of the corrosion on the inner wall of the heat-deformed die in Embodiments 1-3 is smaller, that is, the temperature arrangement method of the present application can greatly reduce the loss of the heat-deformed die and increase the service life of the die.

[0137] Comparison between Example 1 and Example 3 shows that when G magnetic powder and F magnetic powder are used for hot deformation, the cold-pressed blank prepared by using G magnetic powder is higher under the same pressure, so G magnetic powder is a little "harder", so the pressing rate and hot deformation die floating rate are different from those of F magnetic powder. In addition, since G magnetic powder contains heavy rare earth Dy, its magnetic properties are higher than those of hot-deformed magnets prepared by F magnetic powder.

[0138] Comparison between Example 1 and Example 2 shows that when the same magnetic powder F is used to prepare the hot deformation magnetic ring, the preheating temperature and the holding time are longer because the weight and volume of the magnet prepared in Example 2 are larger, so that the pre-pressed blank can be transferred to the hot deformation die for smooth hot deformation forming. Due to the higher preheating temperature, the magnetic properties of the magnet in Example 2 are lower than those in Example 1. In addition, the pressing rate V1 of the upper punch and the floating rate V2 of the hot deformation die in Example 2 are both smaller, so as to facilitate the smooth hot deformation forming of the magnet.

[0139] By comparing Example 2 (k = 0), Example 3 (k = 0.5), Example 1 (k = 1.1) and Example 4 (k = 1.4), it is found that the value of k has almost no effect on the magnetic properties, but has a significant impact on the maximum pit size on the inner wall of the hot deformation die. When K = 0 (when the hot deformation die is not floating), after pressing about 1000 pieces of hot deformation magnets, the hot deformation die is greatly damaged, and the lower punch and the hot deformation die will be stuck under the obstruction of the magnet, resulting in the inability to continue pressing. When there is preheating and floating pressing, when pressing to 4000 pieces, the lower punch and the hot deformation die can continue to work, indicating that the situation of the precipitated rare earth-rich material has been improved.

[0140] The embodiments of the present application are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solution and core ideas of the present application. Therefore, changes or deformations made by those skilled in the art based on the ideas of the present application, the specific implementation methods and the scope of application of the present application, all belong to the scope of protection of the present application. In summary, the contents of this specification should not be construed as limiting the present application.

Claims

1. A method for preparing a heat-deformed magnet, characterized in that: include: The magnetic powder is cold pressed to obtain a cold pressed blank, wherein the density of the cold pressed blank is 4.5 to 5.5 g / cm 3 , Hot pressing the cold pressed blank in a hot pressing concave die at 600-800° C. to obtain a pre-pressed blank; Preheating the pre-pressed green sheet, wherein the temperature of the pre-pressed green sheet after preheating is 850-950° C.; Transferring the pre-pressed blank after preheating to a hot deformation die, wherein the temperature of the hot deformation die is 750-800°C; The temperature of the upper punch is maintained at 600-700° C., and the upper punch is made to enter the thermal deformation concave die to thermally deform the pre-pressed blank after preheating to obtain a magnet.

2. The method for preparing a thermally deformed magnet according to claim 1, characterized in that: The preheating of the pre-pressed blank comprises: heating the pre-pressed blank at 850-950° C. for 1-10 minutes.

3. The method for preparing a thermally deformed magnet according to claim 1, characterized in that: The preheated pre-compact is transferred to the hot deformation die within 5 seconds.

4. The method for preparing a thermally deformed magnet according to claim 1, characterized in that: During the process of transferring the preheated pre-pressed green body to the hot deformation die, the temperature of the pre-pressed green body drops by ≤15°C.

5. The method for preparing a thermally deformed magnet according to claim 1, characterized in that: The step of thermally deforming the pre-pressed blank adopts floating pressing.

6. The method for preparing a thermally deformed magnet according to claim 5, characterized in that: The moving speed V1 of the upper punch is 0.2-1.0 mm / s, and the moving speed of the thermal deformation die is: Among them, K is 0.8-1.2, D is the inner diameter of the thermal deformation die, and d is the outer diameter of the upper punch.

7. A preheating device, characterized in that: include: A heater is provided with a heating chamber with openings at both ends; A first push rod is slidably disposed at one end of the heater, and the first push rod can close an opening at one end of the heater; A second push rod is slidably disposed at the other end of the heater, and the second push rod can close the other end opening of the heater; A hopper for storing pre-pressed blanks, wherein the first push rod can push the pre-pressed blanks on the hopper into the heating chamber; The turning wheel is arranged below the second push rod, and the pre-pressed blank rotates when passing through the turning wheel.

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