Sintering method of sintered NdFeB magnet green body

Abstract

The present invention provides a sintering method for sintered NdFeB magnet green compacts. The sintering method comprises: sequentially coating the NdFeB magnet green compact with a first coating material and a second coating material to form a first coating layer and a second coating layer, wherein the first coating material has water vapor and air barrier properties, and the second coating material has buffering properties; sequentially vacuum sealing and isostatically pressing the NdFeB magnet green compact containing the first coating layer and the second coating layer; removing the second coating layer, and then sequentially vacuum sintering and vacuum tempering the NdFeB magnet green compact containing the first coating layer to obtain a sintered NdFeB blank. Using the above sintering method to process the NdFeB magnet green compact significantly reduces defects in the sintered NdFeB magnet blank and reduces its scrap rate.

Description

Technical Field

[0001] The present invention relates to the field of sintered NdFeB magnet preparation, and in particular to a sintering method for a sintered NdFeB magnet green compact. Background Art

[0002] Sintered NdFeB magnets, with their excellent comprehensive magnetic properties, are widely used in aerospace, microwave communications, automotive, instrumentation, and medical devices. In recent years, the promotion and application of sintered NdFeB magnets in high-end sectors such as wind power, variable-frequency compressors, and hybrid power have rapidly expanded. Large-sized wind turbine magnets (with a single piece weighing over 1kg) account for approximately 10% of global NdFeB production capacity, generating significant demand.

[0003] The manufacturing process for sintered NdFeB magnets varies depending on the product size. For small-sized products, a large blank is typically prepared first, then mechanically cut to the target size. Large-sized products, on the other hand, typically directly produce a blank close to the product size, followed by surface grinding to complete the finished product. Therefore, when manufacturing large-sized products, if a blank has defects such as chipping or oxidation in a localized area, the entire blank will be scrapped. In contrast, localized defects in small-sized blanks only affect the blank's utilization rate. Therefore, the pressing and sintering processes for large-sized blanks are more demanding.

[0004] NdFeB powder is highly reactive, making green billets susceptible to oxidation when exposed to air. Furthermore, green billets have not undergone densification, resulting in poor mechanical strength. Existing large-scale billet production typically involves pressing the NdFeB powder into green billets, wrapping them in a plastic film, then placing them in a plastic bag and vacuum packaging. After initial densification by isostatic pressing, the plastic bag and film are removed in a low-oxygen environment within a glove box, and the billets are then loaded into a furnace for vacuum sintering. This process protects the green billets from oxidation through vacuum packaging and unpacking in a low-oxygen environment. However, in actual production, due to the airflow within the glove box during operation, the green billets are exposed to moisture or air between unpacking and vacuum sintering in the furnace. Furthermore, collisions can occur during circulation and handling, resulting in defects such as oxidation and chipping after sintering, rendering the billets scrapped.

[0005] In view of the above problems, it is necessary to provide a method for firing large-size sintered NdFeB green bodies with fewer blank defects and low scrap rate. Summary of the Invention

[0006] The main purpose of the present invention is to provide a sintering method for sintered NdFeB magnet green compacts to solve the problem that more blank defects and a high scrap rate are caused when sintering large-sized NdFeB magnet green compacts using existing sintering methods.

[0007] In order to achieve the above-mentioned purpose, the present invention provides a sintering method for sintered NdFeB magnet green billets, and the sintering method for sintered NdFeB magnet green billets comprises: using a first coating material and a second coating material to coat the NdFeB magnet green billet in sequence to form a first coating layer and a second coating layer, the first coating material has water vapor and air barrier properties, and the second coating material has buffering properties; vacuum sealing and isostatic pressing the NdFeB magnet green billet containing the first coating layer and the second coating layer in sequence; removing the second coating layer, and then vacuum sintering and vacuum tempering the NdFeB magnet green billet containing the first coating layer in sequence to obtain a sintered NdFeB blank.

[0008] Furthermore, the first coating material is selected from polyethylene film, polypropylene film, polyisobutylene film or polystyrene film.

[0009] Furthermore, the thickness of the first coating material is ≤20 μm.

[0010] Furthermore, the thickness of the first coating material is 10-15 μm.

[0011] Furthermore, the second coating material is selected from pearl cotton and / or sponge sheet.

[0012] Furthermore, the thickness of the second coating material is 0.2 to 2 mm.

[0013] Furthermore, after the isostatic pressing step and before the step of removing the second coating layer, the sintering method also includes: placing the isostatically pressed NdFeB magnet green body in a glove box and filling the glove box with nitrogen to expel oxygen; preferably, the second coating layer is removed after the oxygen content in the glove box is less than 1000 ppm.

[0014] Furthermore, the sintering temperature of the vacuum sintering process is 1050-1100° C., and the sintering time is 3-8 hours.

[0015] Furthermore, the vacuum tempering treatment process includes a primary tempering treatment and a secondary tempering treatment, wherein the temperature of the primary tempering treatment is 850-950° C., and the tempering time is 1-4 hours; the temperature of the secondary tempering treatment is 480-520° C., and the tempering time is 3-6 hours.

[0016] Furthermore, the pressure during the isostatic pressing process is 180-220 MPa.

[0017] By applying the technical solution of the present invention, the surface of the NdFeB green body is wrapped with the first coating material and the second coating material before vacuum packaging. This can reduce the risk of collision or air leakage of the NdFeB green body in the subsequent isostatic pressing step, thereby reducing defects such as oxidation, chipping, and cracking of the NdFeB green body after sintering. During the isostatic pressing process, the pressure on each surface of the NdFeB green body is the same, which can reduce the distance between molecules without changing the appearance and shape, thereby increasing the density of the NdFeB green body and reducing the risk of cracking and deformation. At the same time, the packaging bag and the second coating material are removed before the sintering process, and the first coating material is retained during sintering. This ensures that the NdFeB green body is wrapped with the first coating material during the entire circulation operation, thereby greatly reducing the risk of oxidation before sintering. Finally, the desired NdFeB blank is obtained through vacuum sintering and vacuum tempering. On this basis, using the above sintering method to process the NdFeB magnet green body is beneficial to greatly reduce the defects of the sintered NdFeB magnet green body and reduce its scrap rate. DETAILED DESCRIPTION

[0018] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0019] As described in the background technology, when using existing sintering methods to sinter large-sized sintered NdFeB magnet green compacts, more blank defects and a high scrap rate will be caused. In order to solve the above technical problems, the present application provides a sintering method for sintered NdFeB magnet green compacts, which comprises: using a first coating material and a second coating material to coat the NdFeB magnet green compact in sequence to form a first coating layer and a second coating layer, wherein the first coating material has a water vapor barrier property and can be decomposed at the sintering temperature, and the second coating material has a buffering property; vacuum sealing and isostatic pressing are sequentially performed on the NdFeB magnet green compact containing the first coating layer and the second coating layer; the second coating layer is removed, and then the NdFeB magnet green compact containing the first coating layer is vacuum sintered and vacuum tempered in sequence to obtain a sintered NdFeB blank.

[0020] After the surface of the NdFeB green body is coated with the first and second coating materials, vacuum packaging is performed. This can reduce the risk of collision or air leakage of the NdFeB green body during the subsequent isostatic pressing step, thereby reducing defects such as oxidation, chipping, and cracking of the NdFeB green body after sintering. During the isostatic pressing process, the pressure on each surface of the NdFeB green body is the same, which can reduce the distance between molecules without changing its appearance, thereby increasing the density of the NdFeB green body and reducing its risk of cracking and deformation. At the same time, the packaging bag and the second coating material are removed before the sintering process, and the first coating material is retained during sintering. This ensures that the NdFeB green body is coated with the first coating material throughout the entire circulation operation, thereby greatly reducing its risk of oxidation before sintering. Finally, the desired NdFeB green body is obtained through vacuum sintering and vacuum tempering. On this basis, using the above sintering method to process the NdFeB magnet green body is beneficial to greatly reduce the defects of the sintered NdFeB magnet green body and reduce its scrap rate.

[0021] The first coating material is preferably an organic film formed from a low-carbon chain polymer. In a preferred embodiment, the first coating material includes, but is not limited to, polyethylene film, polypropylene film, polyisobutylene film, or polystyrene film. These coating materials exhibit excellent water vapor barrier properties and, during sintering, decompose at relatively low temperatures without residual carbon, thus not affecting the performance of the sintered NdFeB magnet green compact. Therefore, the use of these materials as the first coating material provides excellent water vapor barrier and antioxidant properties for the NdFeB green compact.

[0022] The first coating material has water vapor barrier properties and can decompose during the sintering process. Therefore, using the first coating material to coat the sintered NdFeB green body is beneficial to greatly reduce the probability of its oxidation while not affecting its sintering process. Preferably, the thickness of the first coating material is ≤20μm. Limiting the thickness of the plastic film to the above range can well wrap large-sized NdFeB green bodies, while reducing the risk of local extrusion during isostatic pressing due to excessive thickness, causing appearance defects. More preferably, the thickness of the first coating material is 10 to 15μm.

[0023] In a preferred embodiment, the second coating material includes, but is not limited to, pearl cotton and / or sponge sheets. The aforementioned second coating materials have good flexibility, water resistance, and shockproof properties. Therefore, the selection of the aforementioned second coating materials allows the second coating material to better fit the NdFeB green compact, while also further improving its shockproof properties, thereby further reducing defects and scrap rates in the sintered NdFeB magnet blanks.

[0024] During the sintering process, if the thickness of the second coating material is too large, it will affect the isostatic pressing effect, resulting in insufficient density of the magnet and an increased rate of chipping. If the thickness of the second coating material is too small, it will not provide a cushioning and shockproof effect. Preferably, the thickness of the second coating material is 0.2 to 2 mm. Limiting the thickness of the second coating material to this range can further reduce defects such as chipping and cracking caused by collisions during the transportation and handling of the NdFeB green billets, without affecting the isostatic pressing effect.

[0025] In a preferred embodiment, after the isostatic pressing step and before the second coating step, the sintering method further comprises: placing the isostatically pressed NdFeB magnet green compact in a glove box and filling the glove box with nitrogen to expel oxygen. Filling the glove box with nitrogen after the isostatic pressing step and before the second coating step to expel oxygen helps reduce the risk of oxidation of the NdFeB green compact. More preferably, the second coating is removed after the oxygen content is less than 1000 ppm.

[0026] The sintering process can cause the neodymium-rich phase to flow into the magnet and disperse around the main phase of the magnet, thereby giving the NdFeB blank a higher coercive force. In a preferred embodiment, the sintering temperature of the vacuum sintering process is 1050-1100°C, and the sintering time is 3-8 hours. The sintering temperature and sintering time of the vacuum sintering process include but are not limited to the above ranges, and limiting them to the above ranges is conducive to making the NdFeB magnet blank more compact, thereby further improving the magnetic properties such as magnetic energy density and coercive force of the subsequently produced sintered NdFeB blank.

[0027] The vacuum tempering process can eliminate stress, refine grains, and more evenly distribute the neodymium-rich phase around the main phase, thereby further improving its coercivity, maximum magnetic properties, and magnetic strength. In a preferred embodiment, the vacuum tempering process includes a primary tempering treatment and a secondary tempering treatment, wherein the primary tempering treatment temperature is 850-950°C and the tempering time is 1-4 hours; the secondary tempering treatment temperature is 480-520°C and the tempering time is 3-6 hours. Tempering the NdFeB green body twice within the above temperature range can slow the rate of decrease of internal stress in the sintered NdFeB green body, reduce its brittleness, and increase its hardness, thereby further improving the overall performance of the sintered NdFeB blank.

[0028] The green body has a low density and a large shrinkage ratio, which can lead to cracking, deformation, and even oxidation. Therefore, it is subjected to isostatic pressing to increase the density of the green body. In a preferred embodiment, the pressure during the isostatic pressing process is 180-220 MPa. Limiting the isostatic pressing pressure within this range helps further increase the magnet density of the NdFeB blank, thereby further improving its magnetic properties.

[0029] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0030] Example 1

[0031] A method for sintering a large-sized sintered NdFeB green compact comprises the following steps:

[0032] (1) After removing the residual powder on the surface of the NdFeB green body with a size of 154×64×27.5 mm in the glove box of the press, wrap it with a layer of polyethylene 18D plastic film with a thickness of 12 μm, wrap a layer of pearl cotton with a thickness of 0.5 mm on the outside of the plastic film, put it into a packaging bag and seal it with a vacuum packaging machine;

[0033] (2) Place the packaged NdFeB green body into an isostatic press and perform isostatic oil pressing at 200 MPa, then place it into a glove box supporting the sintering furnace and fill it with nitrogen to exhaust oxygen until the oxygen content is less than 1000 ppm;

[0034] (3) Remove the packaging bag in the glove box, remove the pearl cotton, put the large-sized green body wrapped with polyethylene 18D plastic film into the graphite box, and transfer it to the VS-300RPA vacuum sintering furnace at a vacuum degree of 5×10 -2 In the environment of pa, sintering treatment at 1080℃×6h, primary tempering treatment at 900℃×3h, and secondary tempering treatment at 500℃×5h were carried out to produce large-sized sintered NdFeB blanks.

[0035] After the above treatment, a blank is obtained, the material of which is N46H. A permanent magnetic material BH meter is used to perform a magnetic property test and an oxygen content test on the blank of this embodiment.

[0036] Example 2

[0037] A method for sintering a large-sized sintered NdFeB green compact comprises the following steps:

[0038] (1) After removing the residual powder on the surface of the NdFeB green body with a size of 154×64×27.5 mm in the glove box of the press, wrap it with a layer of 10 μm thick polypropylene (CPP) plastic film, wrap a layer of 0.5 mm thick pearl cotton on the outside of the plastic film, put it into a packaging bag and seal it with a vacuum packaging machine;

[0039] (2) Place the packaged NdFeB green body into an isostatic press and perform isostatic oil pressing at 200 MPa, then place it into a glove box supporting the sintering furnace and fill it with nitrogen to exhaust oxygen until the oxygen content is less than 1000 ppm;

[0040] (3) Remove the packaging bag in the glove box, remove the pearl cotton, put the large-sized green body wrapped with polypropylene CPP plastic film into the graphite box, and transfer it to the VS-300RPA vacuum sintering furnace at a vacuum degree of 5×10 -2 In the environment of pa, sintering treatment at 1080℃×6h, primary tempering treatment at 900℃×3h, and secondary tempering treatment at 500℃×5h were carried out to produce large-sized sintered NdFeB blanks.

[0041] After the above treatment, a blank is obtained, the material of which is N46H. A permanent magnetic material BH meter is used to perform a magnetic property test and an oxygen content test on the blank of this embodiment.

[0042] Example 3

[0043] The difference from Example 1 is that the thickness of the first coating layer is 10 μm.

[0044] A method for sintering a large-sized sintered NdFeB green compact comprises the following steps:

[0045] (1) After removing the residual powder on the surface of the NdFeB green body with a size of 154×64×27.5 mm in the glove box of the press, wrap it with a layer of polyethylene 18D plastic film with a thickness of 10 μm, wrap a layer of pearl cotton with a thickness of 0.5 mm on the outside of the plastic film, put it into a packaging bag and seal it with a vacuum packaging machine;

[0046] (2) Place the packaged NdFeB green body into an isostatic press and perform isostatic oil pressing at 200 MPa, then place it into a glove box supporting the sintering furnace and fill it with nitrogen to exhaust oxygen until the oxygen content is less than 1000 ppm;

[0047] (3) Remove the packaging bag in the glove box, remove the pearl cotton, put the large-sized green body wrapped with polyethylene 18D plastic film into the graphite box, and transfer it to the VS-300RPA vacuum sintering furnace at a vacuum degree of 5×10 -2 In the environment of pa, sintering treatment at 1080℃×6h, primary tempering treatment at 900℃×3h, and secondary tempering treatment at 500℃×5h were carried out to produce large-sized sintered NdFeB blanks.

[0048] After the above treatment, a blank is obtained, the material of which is N46H. A permanent magnetic material BH meter is used to perform a magnetic property test and an oxygen content test on the blank of this embodiment.

[0049] Example 4

[0050] The difference from Example 1 is that the thickness of the first coating layer is 15 μm.

[0051] A method for sintering a large-sized sintered NdFeB green compact comprises the following steps:

[0052] (1) After removing the residual powder on the surface of the pressed NdFeB green body with a size of 154×64×27.5 mm in the glove box of the press, wrap it with a layer of polyethylene 18D plastic film with a thickness of 1 μm, wrap a layer of pearl cotton with a thickness of 0.5 mm on the outside of the plastic film, put it into a packaging bag and seal it with a vacuum packaging machine;

[0053] (2) Place the packaged NdFeB green body into an isostatic press and perform isostatic oil pressing at 200 MPa, then place it into a glove box supporting the sintering furnace and fill it with nitrogen to exhaust oxygen until the oxygen content is less than 1000 ppm;

[0054] (3) Remove the packaging bag in the glove box, remove the pearl cotton, put the large-sized green body wrapped with polyethylene 18D plastic film into the graphite box, and transfer it to the VS-300RPA vacuum sintering furnace at a vacuum degree of 5×10 -2 In the environment of pa, sintering treatment at 1080℃×6h, primary tempering treatment at 900℃×3h, and secondary tempering treatment at 500℃×5h were carried out to produce large-sized sintered NdFeB blanks.

[0055] After the above treatment, a blank is obtained, the material of which is N46H. A permanent magnetic material BH meter is used to perform a magnetic property test and an oxygen content test on the blank of this embodiment.

[0056] Example 5

[0057] The difference from Example 1 is that the thickness of the first coating layer is 25 μm.

[0058] A method for sintering a large-sized sintered NdFeB green compact comprises the following steps:

[0059] (1) After removing the residual powder on the surface of the NdFeB green body with a size of 154×64×27.5 mm in the glove box of the press, wrap it with a layer of polyethylene 18D plastic film with a thickness of 25 μm, wrap a layer of pearl cotton with a thickness of 0.5 mm on the outside of the plastic film, put it into a packaging bag and seal it with a vacuum packaging machine;

[0060] (2) Place the packaged NdFeB green body into an isostatic press and perform isostatic oil pressing at 200 MPa, then place it into a glove box supporting the sintering furnace and fill it with nitrogen to exhaust oxygen until the oxygen content is less than 1000 ppm;

[0061] (3) Remove the packaging bag in the glove box, remove the pearl cotton, put the large-sized green body wrapped with polyethylene 18D plastic film into the graphite box, and transfer it to the VS-300RPA vacuum sintering furnace at a vacuum degree of 5×10 -2 In the environment of pa, sintering treatment at 1080℃×6h, primary tempering treatment at 900℃×3h, and secondary tempering treatment at 500℃×5h were carried out to produce large-sized sintered NdFeB blanks.

[0062] After the above treatment, a blank is obtained, the material of which is N46H. A permanent magnetic material BH meter is used to perform a magnetic property test and an oxygen content test on the blank of this embodiment.

[0063] Example 6

[0064] The difference from Example 1 is that the thickness of the second coating layer is 2 mm.

[0065] A method for sintering a large-sized sintered NdFeB green compact comprises the following steps:

[0066] (1) After removing the residual powder on the surface of the pressed NdFeB green body with a size of 154×64×27.5 mm in the glove box of the press, wrap it with a layer of polyethylene 18D plastic film with a thickness of 12 μm, wrap a layer of pearl cotton with a thickness of 2 mm on the outside of the plastic film, put it into a packaging bag and seal it with a vacuum packaging machine;

[0067] (2) Place the packaged NdFeB green body into an isostatic press and perform isostatic oil pressing at 200 MPa, then place it into a glove box supporting the sintering furnace and fill it with nitrogen to exhaust oxygen until the oxygen content is less than 1000 ppm;

[0068] (3) Remove the packaging bag in the glove box, remove the pearl cotton, put the large-sized green body wrapped with polyethylene 18D plastic film into the graphite box, and transfer it to the VS-300RPA vacuum sintering furnace at a vacuum degree of 5×10 -2 In the environment of pa, sintering treatment at 1080℃×6h, primary tempering treatment at 900℃×3h, and secondary tempering treatment at 500℃×5h were carried out to produce large-sized sintered NdFeB blanks.

[0069] After the above treatment, a blank is obtained, the material of which is N46H. A permanent magnetic material BH meter is used to perform a magnetic property test and an oxygen content test on the blank of this embodiment.

[0070] Example 7

[0071] The difference from Example 1 is that the thickness of the second coating layer is 3 mm.

[0072] A method for sintering a large-sized sintered NdFeB green compact comprises the following steps:

[0073] (1) After removing the residual powder on the surface of the NdFeB green body with a size of 154×64×27.5 mm in the glove box of the press, wrap it with a layer of polyethylene 18D plastic film with a thickness of 12 μm, wrap a layer of pearl cotton with a thickness of 3 mm on the outside of the plastic film, put it into a packaging bag and seal it with a vacuum packaging machine;

[0074] (2) Place the packaged NdFeB green body into an isostatic press and perform isostatic oil pressing at 200 MPa, then place it into a glove box supporting the sintering furnace and fill it with nitrogen to exhaust oxygen until the oxygen content is less than 1000 ppm;

[0075] (3) Remove the packaging bag in the glove box, remove the pearl cotton, put the large-sized green body wrapped with polyethylene 18D plastic film into the graphite box, and transfer it to the VS-300RPA vacuum sintering furnace at a vacuum degree of 5×10 -2 In the environment of pa, sintering treatment at 1080℃×6h, primary tempering treatment at 900℃×3h, and secondary tempering treatment at 500℃×5h were carried out to produce large-sized sintered NdFeB blanks.

[0076] After the above treatment, a blank is obtained, the material of which is N46H. A permanent magnetic material BH meter is used to perform a magnetic property test and an oxygen content test on the blank of this embodiment.

[0077] Example 8

[0078] The difference from Example 1 is that the thickness of the second coating layer is 0.1 mm.

[0079] A method for sintering a large-sized sintered NdFeB green compact comprises the following steps:

[0080] (1) After removing the residual powder on the surface of the NdFeB green body with a size of 154×64×27.5 mm in the glove box of the press, wrap it with a layer of polyethylene 18D plastic film with a thickness of 12 μm, wrap a layer of pearl cotton with a thickness of 3 mm on the outside of the plastic film, put it into a packaging bag and seal it with a vacuum packaging machine;

[0081] (2) Place the packaged NdFeB green body into an isostatic press and perform isostatic oil pressing at 200 MPa, then place it into a glove box supporting the sintering furnace and fill it with nitrogen to exhaust oxygen until the oxygen content is less than 1000 ppm;

[0082] (3) In the glove box, the packaging bag was removed, the pearl cotton was removed, and the large-sized green billet wrapped with polyethylene 18D plastic film was placed in a graphite box. It was then transferred to a VS-300RPA vacuum sintering furnace and sintered at 1080℃×6h, 900℃×3h for primary tempering, and 500℃×5h for secondary tempering under a vacuum degree of 5×10-2Pa to obtain a large-sized sintered NdFeB blank.

[0083] After the above treatment, a blank is obtained, the material of which is N46H. A permanent magnetic material BH meter is used to perform a magnetic property test and an oxygen content test on the blank of this embodiment.

[0084] Comparative Example 1

[0085] A method for sintering a large-sized sintered NdFeB green compact comprises the following steps:

[0086] (1) After removing the residual powder on the surface of the pressed NdFeB green body with a size of 154×64×27.5 mm in the glove box of the press, the green body is placed in a packaging bag and sealed with a vacuum packaging machine;

[0087] (2) Place the packaged NdFeB green body into an isostatic press and perform isostatic oil pressing at 200 MPa, then place it into a glove box supporting the sintering furnace and fill it with nitrogen to exhaust oxygen until the oxygen content is less than 1000 ppm;

[0088] (3) The packaging bag was removed in the glove box, and the large-sized green billet was placed in a graphite box. The green billet was then transferred to a VS-300RPA vacuum sintering furnace and sintered at 1080°C for 6 h, followed by a primary tempering treatment at 900°C for 3 h, and a secondary tempering treatment at 500°C for 5 h under a vacuum degree of 5×10-2 Pa to obtain a large-sized sintered NdFeB blank.

[0089] After the above treatment, a blank is obtained, the material of which is N46H. A permanent magnetic material BH meter is used to perform a magnetic property test and an oxygen content test on the blank of this embodiment.

[0090] Comparative Example 2

[0091] The difference from Example 1 is that no second coating layer is provided.

[0092] A method for sintering a large-sized sintered NdFeB green compact comprises the following steps:

[0093] (1) After removing the residual powder on the surface of the NdFeB green body with a size of 154×64×27.5 mm in the glove box of the press, wrap it with a layer of 12 μm thick polyethylene 18D plastic film, put it into a packaging bag and seal it with a vacuum packaging machine;

[0094] (2) Place the packaged NdFeB green body into an isostatic press and perform isostatic oil pressing at 200 MPa, then place it into a glove box supporting the sintering furnace and fill it with nitrogen to exhaust oxygen until the oxygen content is less than 1000 ppm;

[0095] (3) In the glove box, the packaging bag was removed, the pearl cotton was removed, and the large-sized green billet wrapped with polyethylene 18D plastic film was placed in a graphite box. It was then transferred to a VS-300RPA vacuum sintering furnace and sintered at 1080℃×6h, 900℃×3h for primary tempering, and 500℃×5h for secondary tempering under a vacuum degree of 5×10-2Pa to obtain a large-sized sintered NdFeB blank.

[0096] After the above treatment, a blank is obtained, the material of which is N46H. A permanent magnetic material BH meter is used to perform a magnetic property test and an oxygen content test on the blank of this embodiment.

[0097] Table 1

[0098]

[0099] It can be seen from the data in Table 1 that if the first and second coating materials are too thick, it will affect the transmission of isostatic pressing pressure, resulting in lower density of the blank and a higher proportion of corner chipping and cracking; while if the second coating material is too thin, the impact protection effect is poor.

[0100] From the above description, it can be seen that the above-mentioned embodiment of the present invention achieves the following technical effects: after the surface of the NdFeB green body is wrapped with the first coating material and the second coating material, vacuum packaging is performed, which can reduce the risk of collision or air leakage of the NdFeB green body in the subsequent isostatic pressing step, thereby reducing defects such as oxidation, chipping, and cracking of the NdFeB green body after sintering. During the isostatic pressing process, the pressure on each surface of the NdFeB green body is the same, which can reduce the distance between molecules without changing the appearance and shape, thereby increasing the density of the NdFeB green body and reducing the risk of cracking and deformation. At the same time, the packaging bag and the second coating material are removed before the sintering process, and the first coating material is retained during sintering. This ensures that the NdFeB green body is wrapped by the first coating material during the entire circulation operation, thereby greatly reducing the risk of oxidation before sintering. Finally, the desired NdFeB blank is obtained through vacuum sintering and vacuum tempering. On this basis, using the above sintering method to process the NdFeB magnet green body is beneficial to greatly reduce the defects of the sintered NdFeB magnet green body and reduce its scrap rate.

[0101] It should be noted that the terms "first," "second," and the like in the specification and claims of this application are used to distinguish similar objects, and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the application described herein can, for example, be implemented in an order other than that described herein.

[0102] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A sintering method for sintering NdFeB magnet green body, characterized in that: The sintering method of the sintered NdFeB magnet green body comprises: The NdFeB magnet green body is coated with a first coating material and a second coating material in sequence to form a first coating layer and a second coating layer, wherein the first coating material has water vapor and air barrier properties, and the second coating material has a buffering property; The NdFeB magnet green body containing the first coating layer and the second coating layer is placed in a packaging bag and subjected to vacuum sealing and isostatic pressing treatment in sequence; The packaging bag is removed, the second coating layer is removed, and then the NdFeB magnet green body containing the first coating layer is subjected to vacuum sintering and vacuum tempering treatment in sequence to obtain a sintered NdFeB blank; The second coating material is selected from pearl cotton and / or sponge sheet; The thickness of the second coating material is 0.2 to 2 mm; The thickness of the first coating material is ≤20 μm.

2. The sintering method of sintered NdFeB magnet green body according to claim 1, characterized in that: The first covering material is selected from polyethylene film, polypropylene film, polyisobutylene film or polystyrene film.

3. The sintering method of sintered NdFeB magnet green body according to claim 1, characterized in that: The thickness of the first coating material is 10-15 μm.

4. The sintering method of sintered NdFeB magnet green body according to claim 1, characterized in that: After the isostatic pressing step and before the step of removing the second coating layer, the sintering method further includes: placing the isostatically pressed NdFeB magnet green body in a glove box, and filling the glove box with nitrogen to expel oxygen.

5. The sintering method of sintered NdFeB magnet green body according to claim 4, characterized in that: After the oxygen content in the glove box is less than 1000 ppm, the second coating layer is removed.

6. The sintering method of a sintered NdFeB magnet green compact according to any one of claims 1 to 3, characterized in that: The sintering temperature of the vacuum sintering process is 1050-1100° C., and the sintering time is 3-8 hours.

7. The sintering method of sintered NdFeB magnet green body according to claim 6, characterized in that: The vacuum tempering process includes a primary tempering treatment and a secondary tempering treatment, wherein the temperature of the primary tempering treatment is 850-950° C. and the tempering time is 1-4 hours; the temperature of the secondary tempering treatment is 480-520° C. and the tempering time is 3-6 hours.

8. The sintering method of sintered NdFeB magnet green body according to claim 7, characterized in that: The pressure during the isostatic pressing process is 180-220 MPa.

Images