A method for preparing neodymium iron boron magnet

Abstract

The present disclosure relates to a method for spraying NdFeB magnets. The method comprises placing a NdFeB matrix in a rotating drum cavity and rotating the drum axially at a speed of 3 to 10 rpm. The drum comprises an opening formed by a bottom and a wall, the opening of the drum cavity being oriented obliquely upward, the axial direction of the drum being inclined relative to a horizontal plane, the angle α between the axial direction of the drum and the horizontal plane being 30° to 50°, the drum wall having a plurality of openings, and the volume of the deposit formed by the NdFeB matrix in the drum cavity accounting for 5 to 25% of the volume of the drum cavity. The method disclosed herein can effectively solve the problem of uneven slurry adhesion caused by magnet sticking during the spraying process. The NdFeB magnets prepared using this system have excellent magnetic property consistency.

Description

Technical Field

[0001] The present application relates to the technical field of NdFeB magnet processing, and in particular, to a method for preparing NdFeB magnets. Background Art

[0002] Neodymium iron boron magnets, with their excellent magnetic properties such as high remanence, high coercivity, and high magnetic energy product, are widely used in hybrid vehicles, wind power generation, servo motors, and energy-saving home appliances. To improve the coercivity and operating temperature of magnets and reduce production costs, grain boundary diffusion (GBD) technology has emerged and is widely used. GBD involves depositing a layer of heavy rare earth powder on the magnet surface through methods such as sputtering, evaporation, coating, and impregnation. Heat treatment then diffuses the heavy rare earth elements from the surface into the magnet, forming a magnetically hardened shell at the boundaries of the main phase grains, thereby increasing the coercivity. As devices become increasingly intelligent, miniaturized, and lightweight, the size of neodymium iron boron magnets is also decreasing. For small-sized NdFeB magnets, it is difficult to achieve the swinging and flipping actions of conventional sputtering, evaporation, coating and other methods. When the dipping method is used, the heavy rare earth coating on the surface of small-sized NdFeB magnets is uneven, resulting in poor performance consistency after grain boundary diffusion. Therefore, it is necessary to propose a grain boundary diffusion method that can achieve small-sized NdFeB magnets and obtain a heavy rare earth coating with uniform thickness and high bonding strength on the magnet surface.

[0003] Patent CN113963932 discloses a rotational spraying method for small-sized rare earth permanent magnets. This method involves immersing the lower portion of a rotating device containing stacked sintered magnets in a slurry, allowing the slurry to impregnate the sintered magnets. This rotational impregnation method fails to achieve uniform adhesion of heavy rare earth elements to the magnet surface, resulting in inconsistent magnetic performance improvements in the diffused magnets and poor stability in batch production. The patent also discloses spraying the slurry onto the rotating sintered magnets. However, small products are prone to sticking during the spraying process, leading to variations in the spraying amount for each product in batch production and inconsistent performance of the diffused magnets. Summary of the Invention

[0004] The purpose of the present disclosure is to provide a method for preparing NdFeB magnets, which can effectively solve the problem of uneven adhesion of heavy rare earth slurry caused by magnet sticking during the spraying process. The NdFeB magnets prepared by this method have better magnetic property consistency.

[0005] In order to achieve the above object, the present disclosure provides a method for preparing a neodymium iron boron magnet, the method comprising:

[0006] A NdFeB matrix having a unit weight of less than 1g is placed in a cavity of a rotating drum, and the rotating drum is rotated axially at a speed of 3 to 10 rpm. The rotating drum includes a cavity with an opening formed by a bottom and a wall. The opening of the cavity faces obliquely upward. The axial direction of the rotating drum is inclined relative to a horizontal plane. The angle α between the axial direction of the rotating drum and the horizontal plane is 30° to 50°. The wall of the drum has a plurality of openings. The volume of the accumulation of the NdFeB matrix in the cavity accounts for 5 to 25% of the volume of the cavity of the rotating drum.

[0007] An air supply device is used to supply hot air to the NdFeB substrate located in the cavity of the rotating drum through the opening, the air supply device is arranged outside the rotating drum and below the drum wall, and a heavy rare earth slurry with a viscosity of 50 to 2000 mPa·s is intermittently sprayed onto the NdFeB substrate using a spray gun to obtain a NdFeB substrate coated with the heavy rare earth slurry;

[0008] The spray gun is arranged on the axis of the drum, the spray direction of the spray gun is toward the drum cavity and inclined downward, the angle β between the spray direction of the spray gun and the axial direction of the drum is 45° to 65°, the single spray volume of the spray gun is 0.1 to 5 mL, and the spray air flow pressure is 0.1 to 0.4 MPa;

[0009] The NdFeB substrate coated with the heavy rare earth slurry is heat-treated to obtain the NdFeB magnet.

[0010] Optionally, based on the total area of ​​the stacked surface of the stacked body, the coating area of ​​the heavy rare earth slurry on the stacked surface is 10-20%; the coating area is 2000-30000mm 2 .

[0011] Optionally, the angle α is 30° to 40°, and the angle β is 50° to 60°; the distance between the nozzle of the spray gun and the plane where the bottom of the drum is located accounts for 60 to 95% of the axial height of the drum wall.

[0012] Optionally, the rotation speed of the drum is 4 to 5 rpm, the single spray volume of the spray gun is 0.1 to 1 mL, and the jet air flow pressure is 0.2 to 0.4 MPa; the spraying interval is 1 to 2 s, and the single spraying time is 3 to 10 s; the temperature of the hot air supplied by the air supply device is 60 to 90°C, and the air volume of the hot air is 3000 to 4500 L / min.

[0013] Optionally, before using the spray gun to intermittently spray a heavy rare earth slurry with a viscosity of 50 to 2000 mPa·s onto the NdFeB substrate, the method further includes: preheating the NdFeB substrate located in the cavity of the rotating drum through the air supply device, the preheating comprising supplying hot air with a temperature of 60 to 90°C for preheating, and the preheating time is 10 to 30 minutes.

[0014] Optionally, the heat treatment includes a diffusion process and a tempering process in sequence; the conditions of the diffusion process include: a temperature of 800 to 950°C, a time of 5 to 20 hours, a vacuum degree of 10 -4 ~10 -2 Pa; The tempering process conditions include: temperature of 450 ~ 550 ℃, time of 3 ~ 8h, vacuum degree of 10 -4 ~10 -2 Pa.

[0015] Optionally, the diameter of the bottom of the drum is 400-600 mm, the axial height of the drum wall is 200-350 mm; the total area of ​​the openings accounts for 10-40% of the total area of ​​the drum wall, and the aperture of the openings is 1-5 mm.

[0016] Optionally, the distance between the nozzle and the plane where the bottom of the drum is located is 120 to 332 mm.

[0017] Optionally, based on the total weight of the heavy rare earth slurry, the heavy rare earth slurry includes 5 to 25 weight percent of a compound containing a heavy rare earth element, 74 to 94 weight percent of an organic solvent, and 0.5 to 5 weight percent of a binder.

[0018] Optionally, the heavy rare earth element is selected from one or more of Dy, Tb and Ho, and the compound containing the heavy rare earth element is selected from one or more of heavy rare earth element hydrides, heavy rare earth element oxides, heavy rare earth element fluorides and heavy rare earth element alloys; the organic solvent is selected from ethanol and / or acetone, and the binder is selected from one or more of dammar resin, shellac and alkyd resin.

[0019] Through the above technical solution, the method disclosed in the present invention can quickly dry the NdFeB substrate with slurry attached, thereby effectively solving the problem of uneven slurry adhesion caused by the sticking of the NdFeB substrate during the slurry spraying process for the preparation of NdFeB magnets. The magnetic properties of the NdFeB magnets prepared by this method are more consistent.

[0020] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0022] Figure 1 It is a structural schematic diagram of a specific embodiment of the system for preparing NdFeB magnets disclosed in the present invention.

[0023] Figure 2 Schematic diagram of the drum arrangement of the system for preparing NdFeB magnets disclosed herein.

[0024] Figure 3 Schematic diagram of the spray gun arrangement of the system for preparing NdFeB magnets disclosed herein.

[0025] Figure 4 The figure shows the motion trajectory of the NdFeB substrate with heavy rare earth slurry attached after it is lifted off.

[0026] Figure 5 It shows the falling position of the NdFeB substrate with heavy rare earth slurry attached after it is lifted into the air. DETAILED DESCRIPTION

[0027] The following describes the specific embodiments of the present disclosure in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0028] In the present disclosure, unless otherwise specified, directional words such as "upper" and "lower" generally refer to the upper and lower parts of the system of the present disclosure when it can be used normally, and "inside" and "outside" refer to the inside and outside of the system of the present disclosure when it can be used normally.

[0029] like Figures 1 to 3 As shown, the present disclosure provides a method for preparing NdFeB magnets, the system adopted in the method includes a rotating drum, a spray gun and an air supply device, the rotating drum includes a rotating drum cavity with an opening surrounded by a drum bottom and a drum wall, the opening direction of the rotating drum cavity is inclined upward, the axial direction of the rotating drum is inclined relative to the horizontal plane, the angle α between the axial direction of the rotating drum and the horizontal plane is 30° to 50°, the drum wall has a plurality of openings, the volume of the accumulation formed by the NdFeB matrix in the rotating drum cavity accounts for 5 to 25% of the volume of the rotating drum cavity; the air supply device is arranged on the outside of the rotating drum and below the drum wall; the spray gun is arranged on the axis of the rotating drum, the spray direction of the spray gun is toward the rotating drum cavity and inclined downward, and the angle β between the spray direction of the spray gun and the axial direction of the rotating drum is 45° to 65°.

[0030] In the system disclosed herein, the opening of the rotating drum is tilted upward and the axis of the rotating drum has a specific angle. This allows the accumulation formed by the NdFeB matrix in the rotating drum to expose a more suitable accumulation surface. At the same time, the spray gun has a specific spray angle that matches it. The purpose is to make the spray gun have an inclined spray angle relative to the NdFeB matrix, that is, to achieve "oblique spraying". In the prior art, the spray angle of the spray gun relative to the NdFeB matrix is ​​close to vertical. During the spraying process, the near-vertical spray angle will be affected by the hot air of the air supply device, resulting in an unstable spraying process, which in turn causes uneven adhesion of the heavy rare earth slurry. The present disclosure adopts the "oblique spraying" method, which can minimize the influence of the hot air of the air supply device on the spraying process, making the spraying process more stable, the adhesion of the heavy rare earth slurry more uniform, and preventing the NdFeB matrix from sticking.

[0031] In a preferred embodiment of the present disclosure, the angle α between the axial direction of the rotating drum and the horizontal plane is 30° to 40°, the angle β between the spray direction of the spray gun and the axial direction of the rotating drum is 50° to 60°, and the bottom of the rotating drum has multiple openings.

[0032] According to the present disclosure, the apertures can vary within a wide range. In a preferred embodiment, the apertures are 1 to 5 mm in diameter, and the total area of ​​the apertures accounts for 10 to 40% of the total area of ​​the drum wall. Preferably, the apertures on the drum body are evenly distributed, forming a reticular structure. The present disclosure does not limit the material of the drum; it can be any heat-resistant material with a certain strength, such as stainless steel, copper, iron, etc.

[0033] In a specific embodiment of the present disclosure, the system also includes a slurry container, a pump and a pipe. The slurry container is used to hold the heavy rare earth slurry. The spray gun is connected to the slurry container through a pipe. The pump is cooperatively connected to the pipe and is configured to control the flow rate of the heavy rare earth slurry in the pipe.

[0034] The present disclosure provides a method for preparing an NdFeB magnet. The method comprises: S1, placing an NdFeB matrix having a unit weight of less than 1 g in a cavity of a rotating drum, wherein the volume of the NdFeB matrix formed in the cavity accounts for 5 to 25% of the volume of the rotating drum cavity; rotating the rotating drum axially at a speed of 3 to 10 rpm; supplying hot air to the NdFeB matrix in the rotating drum cavity through the opening using an air supply device; and intermittently spraying a heavy rare earth slurry having a viscosity of 50 to 2000 mPa·s onto the NdFeB matrix using a spray gun to obtain an NdFeB matrix coated with the heavy rare earth slurry, wherein the spray gun has a single spray volume of 0.1 to 5 mL and a spray air pressure of 0.1 to 0.4 MPa.; and S2, heat treating the NdFeB matrix coated with the heavy rare earth slurry to obtain the NdFeB magnet.

[0035] According to the present disclosure, the unit weight of the NdFeB matrix in step S1 refers to the weight of each NdFeB matrix. In a preferred embodiment, the unit weight of the NdFeB matrix is ​​0.05 to 0.5 g.

[0036] In a specific embodiment of the present disclosure, the distance between the nozzle of the spray gun and the plane of the bottom of the drum is 60-95% of the axial height of the drum wall, based on the axial height of the drum wall. According to the present disclosure, the diameter of the drum bottom and the axial height of the drum wall can vary within a wide range. In a specific embodiment, the diameter of the drum bottom is 400-600 mm, and the axial height of the drum wall is 200-350 mm.

[0037] Furthermore, the distance between the nozzle of the spray gun and the plane where the bottom of the drum is located is 120 to 332 mm; preferably, the distance between the nozzle and the plane where the bottom of the drum is located is 130 to 300 mm.

[0038] According to the present disclosure, in step S1, the viscosity of the heavy rare earth slurry is 50 to 2000 mPa·s, for example, it can be 50 mPa·s, 55 mPa·s, 60 mPa·s, 70 mPa·s, 120 mPa·s, 200 mPa·s, 400 mPa·s, 800 mPa·s, 1000 mPa·s or 1500 mPa·s, but is not limited to the listed values.

[0039] Figure 4 The dotted line in the figure shows the trajectory of the NdFeB substrate with heavy rare earth slurry attached after it is lifted off. Figure 5 The gray area in the figure shows the falling position of the NdFeB matrix with heavy rare earth slurry attached to it after it is lifted into the air. In the prior art, after the heavy rare earth slurry is sprayed on the NdFeB matrix, due to the rotation of the drum, the NdFeB matrix with heavy rare earth slurry attached to it is not completely dry and adheres to other NdFeB matrices, thus causing a sticking problem. According to the present disclosure, the nozzle of the spray gun is configured to be away from the bottom of the drum and tilted downward at a specific angle β, that is, it is configured to be close to the opening of the drum cavity. At this specific position, the spray gun can "obliquely spray" out an ideal spraying area. The ideal spraying area is a quasi-circular area, for example, it can include but is not limited to a circle, an ellipse, etc. In a specific embodiment, based on the total area of ​​the stacking surface of the stacking body, the coating area of ​​the heavy rare earth slurry on the stacking surface is 10 to 20%; preferably, the coating area is 2000 to 30000 mm 2In the above embodiment, the coating area of ​​the heavy rare earth slurry on the stacking surface is the spraying area of ​​the spray gun, that is, the ideal spraying area is 10-20% of the stacking surface of the stack formed by the NdFeB matrix.

[0040] The inventors of the present disclosure have found that when the deposited body formed by the NdFeB matrix exposes a suitable depositing surface, the spray gun has a better spray angle, and the nozzle position is adapted to the above, an ideal spray area can be formed under a specific spray gun spray volume and spray air flow pressure, that is, Figure 5 The white area in the spray area, and the NdFeB matrix with heavy rare earth slurry attached in the spray area can be completely dried when falling and the falling position is reasonable, so it is not easy to have bumping problems. Specifically, the NdFeB matrix in the spray area can be vacated instantly after the heavy rare earth slurry is attached under the impact of the slurry airflow, and fall after a short stay in the air. During the short stay in the air, since the air supply device continuously supplies hot air, the NdFeB matrix with heavy rare earth slurry attached can be completely dried when falling, thereby effectively preventing the NdFeB matrix from sticking. The present disclosure solves the NdFeB matrix sticking problem more effectively by controlling the NdFeB matrix in the spray area so that it can be "instantly vacated" during the spraying process. This is different from the technical solution in the prior art that maximizes the area of ​​the spray area to improve production efficiency and ensure economic benefits. Preferably, the single spray volume of the spray gun is 0.1~5mL and the spray air flow pressure is 0.1~0.4Mpa.

[0041] According to the present disclosure, when the viscosity of the heavy rare earth slurry is 50 to 2000 mPa·s, the air supply device is used to supply hot air to the NdFeB substrate in the cavity of the rotating drum through the opening. After the heavy rare earth slurry is sprayed on the NdFeB substrate, it can be dried in a short time under the action of the hot air, thereby preventing the NdFeB substrate coated with the heavy rare earth slurry from sticking. The viscosity of the heavy rare earth slurry is higher than 2000 mPa·s. Excessive viscosity makes it difficult to spray from the nozzle of the spray gun, easily clogging the nozzle, and it cannot be quickly dried under the action of hot air. The viscosity of the heavy rare earth slurry is lower than 50 mPa·s. Too low viscosity makes the heavy rare earth slurry too fluid, and it is easy to flow after being sprayed on the NdFeB substrate, thereby causing sticking problems.

[0042] In a specific embodiment, the rotation speed of the drum is 4 to 5 rpm, the single spray volume of the spray gun is 0.1 to 1 mL, the jet air flow pressure is 0.2 to 0.4 MPa, the spraying interval time is 1 to 2 s, the single spraying time is 3 to 10 s, the temperature of the hot air supplied by the air supply device is 60 to 90°C, and the air volume is 3000 to 4500 L / min.

[0043] According to the present disclosure, the NdFeB substrate can be preheated using hot air before the slurry is sprayed on it. The temperature of the hot air delivered by the air supply device can vary within a wide range. In a specific embodiment of the present disclosure, before using the spray gun to intermittently spray a heavy rare earth slurry with a viscosity of 50 to 2000 mPa·s onto the NdFeB substrate, the method further includes: preheating the NdFeB substrate located in the rotating drum cavity using the air supply device, wherein the preheating includes supplying hot air at a temperature of 60 to 90°C for preheating, and the preheating time is 10 to 30 minutes.

[0044] According to the present disclosure, in step S1, the air supply device continuously supplies hot air to the NdFeB substrate in the rotating drum. The temperature of the hot air can vary within a large range, for example, 60 to 90°C.

[0045] According to the present disclosure, the NdFeB substrate coated with heavy rare earth slurry needs to be heat treated for grain boundary diffusion. The present disclosure does not impose any specific restrictions on the device used for heat treatment. For example, it can be carried out in a vacuum sintering furnace. In one embodiment, the NdFeB substrate coated with heavy rare earth slurry is placed in a composite graphite box lined with a molybdenum plate and then heat treated. In a specific embodiment of the present disclosure, in step S2, the heat treatment includes a diffusion process and a tempering process in sequence; the conditions of the diffusion process include: a temperature of 800 to 950°C, a time of 5 to 20 hours, and a vacuum degree of 10 -4 ~10 -2 Pa; the tempering process conditions include: temperature of 450 ~ 550 ℃, time of 3 ~ 8h, vacuum degree of 10 -4 ~10 -2 Pa.

[0046] In a specific embodiment of the present disclosure, the present disclosure does not impose any specific limitation on the rotation direction of the drum, which may be clockwise, counterclockwise, or alternating clockwise and counterclockwise rotation.

[0047] In one embodiment of the present disclosure, the heavy rare earth slurry comprises 5 to 25 weight percent of a compound containing a heavy rare earth element, 74 to 94 weight percent of an organic solvent, and 0.5 to 5 weight percent of a binder. The present disclosure does not limit the specific form of the compound containing a heavy rare earth element; for example, the compound may be a powder.

[0048] In a specific embodiment of the present disclosure, the heavy rare earth element is selected from one or more of Dy, Tb and Ho, the compound containing the heavy rare earth element is selected from one or more of the hydride of the heavy rare earth element, the oxide of the heavy rare earth element, the fluoride of the heavy rare earth element and the alloy of the heavy rare earth element, the organic solvent is selected from ethanol and / or acetone; and the binder is selected from one or more of dammar resin, shellac and alkyd resin.

[0049] In a specific embodiment of the present disclosure, the auxiliary spheres and the NdFeB matrix are mixed and placed in the rotating drum. On the one hand, this prevents the NdFeB matrix from being bumped and chipped during the spraying process. On the other hand, it can make the NdFeB matrix more evenly dispersed, which is beneficial to further improve the consistency of the magnetic properties of the prepared NdFeB magnet. The present disclosure does not impose any specific restrictions on the material of the auxiliary spheres. For example, zirconium oxide and aluminum oxide can be used. The diameter of the auxiliary spheres is adaptively selected according to the size of the NdFeB matrix. For example, it can be 2 to 5 mm. The mass ratio of the sintered magnet to the auxiliary spheres can vary from a large range, preferably 2:1 to 5:1. When the auxiliary spheres and the NdFeB matrix are mixed and placed in the rotating drum, the stack is composed of the NdFeB matrix and the auxiliary spheres in the cavity of the rotating drum.

[0050] In some embodiments of the present invention, the NdFeB matrix includes 28wt% to 33wt% of R, 0.8wt% to 1.5wt% of B, 0 to 3wt% of M and the balance of Fe, wherein R is a rare earth element, and the rare earth element R is selected from any one or a combination of at least two of Nd, Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb or Lu; M is selected from any one or a combination of at least two of Cu, Al, Zr, Ga, Co, Nb, Mn, Mg, Si, Cr or Ti, wherein typical but non-limiting combinations can be, for example, a combination of Cu, Co, Al, and a combination of Zr and Ti.

[0051] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited thereby.

[0052] The NdFeB matrix in the following examples and comparative examples has a composition represented by (PrNd)29.5Co0.7B0.91Cu0.1Ga0.1Zr0.2Fe68.49, and is prepared by melting the raw materials according to the formula, and obtaining an alloy rapid solidification sheet with a thickness of 0.3 mm by a conventional rapid solidification method; then hydrogen cracking is performed, and then gas grinding is performed to a powder with an average particle size of 4.2 μm, wherein the gas composition includes conventional air, carbon-containing Solvent, lubricant and antioxidant; the powder is then oriented and formed in a 2T magnetic field, and sintered after static pressing, the sintering temperature is 1000℃, and the sintering time is 8h; after cooling to 900℃, primary aging is carried out for 3h, and then cooled to 500℃ for secondary aging for 5h to obtain a magnetic blank; after cutting the magnetic blank, a NdFeB matrix with a size of 4mm×8mm×1.2mm (except Comparative Example 4) is obtained, and the unit weight of the NdFeB matrix is ​​0.3g.

[0053] Example 1

[0054] This embodiment provides a method for preparing a neodymium iron boron magnet, the method comprising the following steps:

[0055] like Figure 1 As shown, the drum includes a drum cavity with an opening surrounded by a drum bottom and a drum wall. The drum wall has a plurality of openings with a diameter of 2 mm, and the total area of ​​the openings accounts for 30% of the total area of ​​the drum wall. A NdFeB matrix is ​​placed in a rotating drum cavity of a rotating drum, and the volume of the accumulation body formed by the NdFeB matrix in the cavity accounts for 15% of the volume of the rotating drum cavity. A blower device is used to supply hot air at a temperature of 80°C to the NdFeB matrix in the rotating drum through an opening for preheating for 10 minutes, and then hot air at a temperature of 80°C is continuously supplied and a heavy rare earth slurry is intermittently sprayed on the NdFeB matrix using a spray gun to obtain a NdFeB matrix coated with the heavy rare earth slurry; wherein the viscosity of the heavy rare earth slurry is 1000 mPa·s, the single injection volume of the spray gun is 1 mL, the injection air flow pressure is 0.35 MPa, and the air volume of the hot air is 4000 L / min; based on the total area of ​​the accumulation surface of the accumulation body, the coating area of ​​the heavy rare earth slurry on the accumulation surface is 15%, and the coating area is 22500 mm 2 The rotation speed of the drum is 5 rpm, the opening direction of the drum cavity is obliquely upward, the axial direction of the drum is inclined relative to the horizontal plane, the angle α between the axial direction of the drum and the horizontal plane is 35°, the angle β between the spray direction of the spray gun and the axial direction of the drum is 60°, the distance between the nozzle of the spray gun and the plane where the bottom of the drum is located is 90% of the axial height of the drum wall, the axial height of the drum wall is 350 mm, and the diameter of the bottom of the drum is 500 mm.

[0056] The NdFeB substrate coated with heavy rare earth slurry was placed in a composite graphite box lined with a molybdenum plate and heated to 10 -4 In a vacuum sintering furnace of Pa, a diffusion process at a temperature of 850°C is first carried out for 6 hours, and then a tempering process at a temperature of 500°C is carried out for 4 hours to obtain a NdFeB magnet.

[0057] Example 2

[0058] NdFeB magnets were prepared using the same method as in Example 1, except that in the system used, the angle α between the axis of the rotor and the horizontal line was 45°, the angle β between the spray direction of the spray gun and the axis of the rotor was 45°, and the distance between the nozzle of the spray gun and the plane of the bottom of the rotor was 80% of the axial height of the rotor wall.

[0059] Example 3

[0060] NdFeB magnets were prepared by the same method as in Example 1, except that the single injection volume of the spray gun was 2.5 mL, the injection air flow pressure was 0.1 MPa, and the rotating speed of the drum was 7 rpm.

[0061] Example 4

[0062] NdFeB magnets were prepared in the same manner as in Example 1, except that the volume of the accumulation of NdFeB matrix in the cavity accounted for 25% of the volume of the drum cavity, and the drum rotated at 10 rpm.

[0063] Example 5

[0064] NdFeB magnets were prepared using the same method as in Example 1, except that the NdFeB substrate in the drum cavity was not preheated before the heavy rare earth slurry was sprayed onto the NdFeB substrate using a spray gun.

[0065] Example 6

[0066] NdFeB magnets were prepared using the same method as in Example 1, except that the viscosity of the heavy rare earth slurry was 50 mPa·s.

[0067] Comparative Example 1

[0068] The NdFeB magnets were prepared by the same method as in Example 1, except that the angle α between the axial direction of the drum and the horizontal plane was 0°, that is, the drum was placed horizontally.

[0069] Comparative Example 2

[0070] NdFeB magnets were prepared using the same method as in Example 1, except that the angle β between the spray direction of the spray gun and the axial direction of the drum was 90°, that is, the spray gun sprayed the heavy rare earth slurry vertically onto the surface of the NdFeB substrate.

[0071] Comparative Example 3

[0072] NdFeB magnets were prepared by the same method as in Example 1, except that the single injection volume of the spray gun was 7 mL and the injection air flow pressure was 0.5 MPa.

[0073] Comparative Example 4

[0074] The NdFeB magnets were prepared by the same method as in Example 1, except that the weight of the cut NdFeB matrix was 2 g.

[0075] Comparative Example 5

[0076] NdFeB magnets were prepared using the same method as in Example 1, except that the viscosity of the heavy rare earth slurry was 30 mPa·s.

[0077] Comparative Example 6

[0078] NdFeB magnets were prepared using the same method as in Example 1, except that the viscosity of the heavy rare earth slurry was 3000 mPa·s.

[0079] Comparative Example 7

[0080] The NdFeB magnet was prepared by the same method as in Example 1, except that the spray gun continuously sprayed the heavy rare earth slurry onto the NdFeB substrate.

[0081] Comparative Example 8

[0082] The NdFeB matrix is ​​placed in the cavity of a rotating drum, the bottom of the rotating drum is placed in heavy rare earth slurry, and the NdFeB magnet is prepared by a rotary impregnation method.

[0083] Test Case

[0084] The NdFeB magnets prepared in Examples 1 to 6 and Comparative Examples 1 to 8 were tested for adhesion rate, coercive force and high-temperature magnetic loss fluctuation rate using the following methods. The test results are shown in Table 1.

[0085] (1) Coercive force after diffusion: Use a magnetic property measuring instrument to measure the coercive force of NdFeB magnets.

[0086] (2) Fluctuation rate of high-temperature magnetic loss: Measure the magnetic flux after the NdFeB magnet is saturated with magnetization. Measure the magnetic flux after keeping it at 120℃ for 2 hours under semi-open circuit conditions. Calculate the ratio of magnetic flux loss and record it as the fluctuation rate of high-temperature magnetic loss.

[0087] (3) Sticking rate: Before the NdFeB substrate coated with heavy rare earth slurry is heat-treated, 1,000 pieces of products from the same batch are randomly inspected, and the ratio of the number of pieces with sticking to the total number of pieces inspected is calculated to obtain the sticking rate.

[0088] Table 1

[0089]

[0090]

[0091] As can be seen from the above, when preparing NdFeB magnets using the disclosed method, the heavy rare earth slurry can be adhered to the NdFeB substrate and then dried instantly, eliminating the problem of sticking during the preparation process. The heavy rare earth slurry adheres more evenly to the surface of the NdFeB substrate. Compared with the existing technology, the coercive force of the prepared NdFeB magnets is significantly improved, and the fluctuation rate of high-temperature magnetic loss is reduced, indicating that the NdFeB magnets have excellent magnetic properties and are particularly suitable for industrial production.

[0092] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0093] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0094] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for spraying a neodymium iron boron magnet, characterized in that: The method includes: A NdFeB matrix having a unit weight of less than 1g is placed in a cavity of a rotating drum, and the rotating drum is rotated axially at a certain speed; the rotating drum includes a cavity with an opening formed by a bottom and a wall, the opening of the cavity facing obliquely upward, the axis of the rotating drum is inclined relative to a horizontal plane, and the angle α between the axis of the rotating drum and the horizontal plane is 30° to 50°; the wall of the drum has a plurality of openings, and the volume of the deposit formed by the NdFeB matrix in the cavity of the rotating drum accounts for 5% to 25% of the volume of the cavity of the rotating drum; An air supply device is used to supply hot air to the NdFeB substrate located in the cavity of the rotating drum through the opening. The air supply device is arranged outside the rotating drum and below the drum wall. A heavy rare earth slurry with a viscosity of 50 to 2000 mPa·s is intermittently sprayed onto the NdFeB substrate using a spray gun to obtain a NdFeB substrate coated with the heavy rare earth slurry. The NdFeB substrate in the spraying area can be lifted off the ground immediately after the heavy rare earth slurry is attached due to the impact of the slurry airflow. The spray gun is arranged on the axis of the drum, the spray direction of the spray gun is toward the drum cavity and inclined downward, and the angle β between the spray direction of the spray gun and the axial direction of the drum is 45° to 65°; The distance between the nozzle of the spray gun and the plane where the bottom of the rotating drum is located is 60-95% of the axial height of the drum wall; the temperature of the hot air supplied by the air supply device is 60-90°C, and the air volume of the hot air is 3000-4500L / min.

2. The method according to claim 1, wherein The rotation speed of the drum is 3-10 rpm; the single injection volume of the spray gun is 0.1-5 mL, and the injection air flow pressure is 0.1-0.4 MPa.

3. The method according to claim 1, wherein Based on the total area of ​​the stacked surface of the stacked body, the coating area of ​​the heavy rare earth slurry on the stacked surface is 10-20%; the coating area is 2000-30000mm 2 .

4. The method according to claim 1, wherein The angle α is 30° to 40°, and the angle β is 50° to 60°.

5. The method according to claim 1, wherein The rotation speed of the drum is 4-5 rpm, the single injection volume of the spray gun is 0.1-1 mL, and the injection air flow pressure is 0.2-0.4 MPa; The spraying interval is 1~2s, and the single spraying time is 3~10s.

6. The method according to claim 1, wherein Before using the spray gun to intermittently spray a heavy rare earth slurry with a viscosity of 50~2000mPa·s onto the NdFeB substrate, the method also includes: preheating the NdFeB substrate located in the cavity of the rotating drum by the air supply device, wherein the preheating includes supplying hot air with a temperature of 60~90°C for preheating, and the preheating time is 10~30 minutes.

7. The method according to claim 1, wherein The method further comprises heat-treating the NdFeB substrate coated with the heavy rare earth slurry to obtain the NdFeB magnet, wherein the heat-treating comprises a diffusion process and a tempering process in sequence; The diffusion process conditions include: temperature of 800-950°C, time of 5-20 hours, vacuum degree of 10 -4 ~10 -2 Pa; the tempering process conditions include: temperature of 450 ~ 550 ℃, time of 3 ~ 8h, vacuum degree of 10 -4 ~10 -2 Pa.

8. The method according to claim 1, wherein The diameter of the bottom of the drum is 400-600 mm, and the axial height of the drum wall is 200-350 mm; The total area of ​​the openings accounts for 10-40% of the total area of ​​the cylinder wall, and the aperture of the openings is 1-5 mm.

9. The method according to claim 1, wherein The distance between the nozzle and the plane where the bottom of the drum is located is 120-332 mm.

10. The method according to claim 1, wherein Based on the total weight of the heavy rare earth slurry, the heavy rare earth slurry includes 5-25 weight percent of a compound containing a heavy rare earth element, 74-94 weight percent of an organic solvent, and 0.5-5 weight percent of a binder.

Images