Method for manufacturing neodymium iron boron permanent magnet part with complex shape

Abstract

The method for manufacturing the neodymium-iron-boron permanent magnet part in the complex shape comprises the steps of mixed material preparation, internal mixing and granulation, injection molding, degreasing, sintering, aftertreatment, final magnetizing and the like, a material pipe formed through injection molding is made of non-magnetic die steel, an annular magnetic field is additionally arranged at the front end of the material pipe, a magnetic field is additionally arranged on a die formed through injection molding, and therefore the neodymium-iron-boron permanent magnet part in the complex shape can be manufactured. According to the method, neodymium iron boron powder before injection molding can be magnetized, neodymium iron boron powder in the injection molding process can also be magnetized, meanwhile, only part of the macromolecule adhesive is removed in the degreasing process, and degreasing comprises high-temperature degreasing in which a green body is heated to 160-170 DEG C; in addition, the remaining high-molecular adhesive can be melted and wrap the neodymium iron boron powder under the action of capillary force, oxidation is avoided, the neodymium iron boron powder can be bound, displacement of the neodymium iron boron powder due to magnetic repulsive force is avoided, the neodymium iron boron permanent magnet part is good in shape retention, good in magnetic property and good in magnetic uniformity, and the requirement of the market for high-end products can be met.

Description

Technical Field

[0001] The invention relates to the technical field of permanent magnet parts processing, and in particular to a method for manufacturing NdFeB permanent magnet parts with complex shapes. Background Art

[0002] Neodymium iron boron (Nd2Fe14B) is one of the most powerful magnetic materials to date. It has the advantages of high magnetic energy product, high coercive force, high energy density, high cost performance, stable mechanical properties, etc. It is widely used in aerospace, automotive industry, electronics, medical equipment, energy-saving motors, new energy, wind power generation and other fields. It is the fastest growing permanent magnet material with the best market prospects in the world today.

[0003] At present, the production methods of NdFeB permanent magnet parts are roughly divided into two categories: non-sintering and sintering. Non-sintering is mainly achieved through injection molding, which can form a more complex shape, but because it contains binders, its magnetic properties are relatively poor. At present, sintering is mainly achieved through dry pressing, which can obtain high-density NdFeB products, so its magnetic properties are better than non-sintering, but it is limited by the dry pressing method and can only achieve a relatively simple appearance shape. When making complex-shaped special-shaped NdFeB permanent magnet parts, it is necessary to carry out processing processes such as stripping, cutting, drilling, and wire cutting. Due to the high brittleness of NdFeB products, they are easy to break and produce defects during this type of processing, and the production efficiency is also low. At the same time, when the existing NdFeB permanent magnet parts are produced, magnetization and polarization guidance are only carried out after the final molding. Its surface magnetism is strong but the internal magnetism is relatively weak, and the magnetic uniformity is poor, which makes it difficult to meet the market demand for high-end products. Summary of the invention

[0004] The purpose of the present invention is to solve one or more shortcomings in the prior art and provide a method for manufacturing NdFeB permanent magnet parts with complex shapes.

[0005] To achieve the above object, the technical solution adopted by the present invention is a method for manufacturing a complex-shaped NdFeB permanent magnet part, comprising the following steps:

[0006] a) preparing a mixture, mixing NdFeB powder and a polymer binder in a weight ratio of 65-95wt%:35-5wt% to obtain a mixture;

[0007] b) Mixing and granulation: the mixed material is put into a mixer and mixed under pressure and heating, and granulated into mixed particles with a diameter of 3 to 5 mm;

[0008] c) Injection molding, feeding the kneaded granules into a material pipe, and injecting the molten kneaded granules into a mold by injection molding, and after cooling, opening the mold to obtain a green embryo;

[0009] d) defatting, defatting the raw embryos by a defatting system to obtain brown embryos;

[0010] e) Sintering: placing the brown embryo into a vacuum furnace for sintering, and forming a rough embryo with metallic luster after being taken out of the furnace;

[0011] f) Post-processing: grinding the size and appearance of the rough blank to obtain a product with mechanical parameters that meet the design requirements;

[0012] The material tube set in step c) is made of non-magnetic mold steel, and a circular magnetic field is added to the side of the material tube to achieve primary magnetization polarization guidance; the mold in step c) is also added with a magnetic field to achieve secondary magnetization polarization guidance, and after step f), the step of performing final magnetization polarization guidance on the product part to make it a NdFeB permanent magnet part is also included;

[0013] The degreasing in step d) only removes part of the polymer binder. During degreasing, low-temperature degreasing is performed first and then high-temperature degreasing. High-temperature degreasing refers to heating the green embryo to 150-170°C under a protective atmosphere (argon and / or nitrogen) to melt the remaining polymer binder and cover the NdFeB powder through capillary force, which can isolate oxygen in the air and prevent oxidation of the NdFeB powder, and can also bind the NdFeB powder and increase the strength of the brown embryo.

[0014] Preferably, the NdFeB powder in step a) is any one of N series NdFeB powder, M series NdFeB powder, H series NdFeB powder, SH series NdFeB powder, UH series NdFeB powder, EH series NdFeB powder, TH series NdFeB powder or a mixture thereof.

[0015] Preferably, in step a), the D50 average particle size of the NdFeB powder is 2 to 10 um.

[0016] Preferably, the polymer binder in step a) comprises a main polymer, a backbone auxiliary material, a heat stabilizer, a plasticizer and a surfactant.

[0017] Further preferably, the weight ratio of the main polymer, backbone auxiliary materials, heat stabilizer, plasticizer and surfactant is 80-90wt%: 5-15wt%: 0.5-5wt%: 0.5-5wt%, and the rest is surfactant, which can be anionic surfactant (such as α-sulfonic fatty acid ester), cationic surfactant (such as dialkyl dimethyl ammonium salt), zwitterionic surfactant (such as alkyl betaine), non-ionic surfactant (such as polyoxyethylene alkyl ether).

[0018] More preferably, the weight ratio of the surfactant is 0.1-1 wt %.

[0019] Preferably, the internal mixing and granulation in step b) is carried out under a protective atmosphere, which means that the internal mixing furnace is filled with argon and / or nitrogen.

[0020] Preferably, the material pipe in step c) is provided with an electric heating coil to keep the temperature of the material pipe at 160-210°C.

[0021] Preferably, the degreasing in step d) removes 70-90% of the polymer binder.

[0022] Preferably, the degreasing method in step d) includes thermal degreasing, solvent degreasing and catalytic degreasing.

[0023] Preferably, the sintering in step e) refers to placing the brown embryo in a vacuum furnace with a protective atmosphere (argon and / or nitrogen) and sintering it at a temperature of 850 to 1250° C. for 60 to 180 minutes.

[0024] More preferably, the sintering temperature is 1050-1150°C.

[0025] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0026] By making the injection molding material tube of non-magnetic mold steel, and adding a circular magnetic field to the side of the material tube, and also adding a magnetic field in the injection molding mold according to product needs, the NdFeB powder before injection molding can be magnetized and polarized and guided, and the NdFeB powder during the injection molding process can be magnetized and polarized and guided. At the same time, by removing only part of the polymer binder during degreasing, the degreasing includes high-temperature degreasing to heat the green embryo to 150-170°C, and the remaining polymer binder can be melted and coated with the NdFeB powder through capillary force, which can avoid oxidation and bind the NdFeB powder, increase the strength of the brown embryo, and make the NdFeB permanent magnet parts have good shape retention, good magnetic properties, small difference in magnetism between the surface and the inside, good magnetic uniformity, and can meet the market demand for high-end products with high yield and high production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0028] like Figure 1 As shown, the method for manufacturing a complex-shaped NdFeB permanent magnet part provided by the present invention comprises the following steps:

[0029] a) preparing a mixture, mixing NdFeB powder and a polymer binder in a weight ratio of 65-95wt%:35-5wt% to obtain a mixture;

[0030] b) Mixing and granulation: the mixed material is put into a mixer and mixed under pressure and heating, and granulated into mixed particles with a diameter of 3 to 5 mm;

[0031] c) Injection molding, feeding the kneaded granules into a material pipe, and injecting the molten kneaded granules into a mold by injection molding, and after cooling, opening the mold to obtain a green embryo;

[0032] d) defatting, defatting the raw embryos by a defatting system to obtain brown embryos;

[0033] e) Sintering: placing the brown embryo into a vacuum furnace for sintering, and forming a rough embryo with metallic luster after being taken out of the furnace;

[0034] f) Post-processing: grinding the size and appearance of the rough blank to obtain a product with mechanical parameters that meet the design requirements;

[0035] The material tube set in step c) is made of non-magnetic mold steel, and a circular magnetic field is added to the side of the material tube to achieve primary magnetization polarization guidance; the mold in step c) is also added with a magnetic field to achieve secondary magnetization polarization guidance, and after step f), the step of performing final magnetization polarization guidance on the product part to make it a NdFeB permanent magnet part is also included;

[0036] The degreasing in step d) only removes part of the polymer binder. During degreasing, low-temperature degreasing is performed first and then high-temperature degreasing. High-temperature degreasing refers to heating the green embryo to 150-170°C under a protective atmosphere (argon and / or nitrogen) to melt the remaining polymer binder and cover the NdFeB powder through capillary force, which can isolate oxygen in the air and prevent oxidation of the NdFeB powder, and can also bind the NdFeB powder and increase the strength of the brown embryo.

[0037] By making the injection molding material tube of non-magnetic mold steel, and adding a circular magnetic field to the side of the material tube, and also adding a magnetic field in the injection molding mold according to product needs, the NdFeB powder before injection molding can be magnetized and polarized and guided, and the NdFeB powder during the injection molding process can be magnetized and polarized and guided. At the same time, by removing only part of the polymer binder during degreasing, the degreasing includes high-temperature degreasing to heat the green embryo to 150-170°C, and the remaining polymer binder can be melted and coated with the NdFeB powder through capillary force, which can avoid oxidation and bind the NdFeB powder, increase the strength of the brown embryo, and make the NdFeB permanent magnet parts have good shape retention, good magnetic properties, small difference in magnetism between the surface and the inside, good magnetic uniformity, and can meet the market demand for high-end products with high yield and high production efficiency.

[0038] Preferably, the NdFeB powder in step a) is any one of N series NdFeB powder, M series NdFeB powder, H series NdFeB powder, SH series NdFeB powder, UH series NdFeB powder, EH series NdFeB powder, TH series NdFeB powder or a mixture thereof.

[0039] Preferably, in step a), the D50 average particle size of the NdFeB powder is 2 to 10 um.

[0040] Preferably, the polymer binder in step a) comprises a main polymer, a backbone auxiliary material, a heat stabilizer, a plasticizer and a surfactant.

[0041] Further preferably, the weight ratio of the main polymer, backbone auxiliary materials, heat stabilizer and plasticizer is 80-90wt%: 5-15wt%: 0.5-5wt%: 0.5-5wt%, and the rest is a surfactant, which can be an anionic surfactant (such as α-sulfonic fatty acid ester), a cationic surfactant (such as dialkyl dimethyl ammonium salt), a zwitterionic surfactant (such as alkyl betaine), or a non-ionic surfactant (such as polyoxyethylene alkyl ether).

[0042] More preferably, the weight ratio of the surfactant is 0.1-1 wt %.

[0043] Preferably, the internal mixing and granulation in step b) is carried out under a protective atmosphere, which means that the internal mixing furnace is filled with argon and / or nitrogen.

[0044] Preferably, the material pipe in step c) is provided with an electric heating coil to keep the temperature of the material pipe at 160-210°C.

[0045] Preferably, the degreasing in step d) removes 70-90% of the polymer binder.

[0046] Preferably, the degreasing method in step d) includes thermal degreasing, solvent degreasing and catalytic degreasing.

[0047] Preferably, the sintering in step e) refers to placing the brown embryo in a vacuum furnace with a protective atmosphere (argon and / or nitrogen) and sintering it at a temperature of 850 to 1250° C. for 60 to 180 minutes.

[0048] More preferably, the sintering temperature is 1050-1150°C.

[0049] The following is described with specific embodiments:

[0050] Embodiment 1

[0051] In the catalytic degreasing system, oxalic acid or nitric acid vapor reacts with polyoxymethylene (POM) to form CH2 (benzene ring) which is then separated from the NdFeB product to achieve the purpose of removing a large amount of polymers from the product.

[0052] (1) Material preparation:

[0053] (a) NdFeB powder as raw material powder: N35 NdFeB powder is selected, with an average particle size (D50) of 2um to 10um, a weight of 4370g, and a total amount of binder of 630g. (Weight ratio = 87.4:12.6)

[0054] (b) Binder: Prepare a binder according to the weight ratio of polyoxymethylene, polypropylene, compatibilizer, plasticizer, and surfactant: 86%: 4.5%: 4%: 5%: 0.5%. After preparation, weigh 630 g (approximately 12.6% of the total weight) of the binder.

[0055] (2) Internal mixing and granulation:

[0056] In an environment with protective gas, the mixed materials of (1) are sequentially added into the chamber of a heated and pressurized internal mixer and kneaded into a mass. The temperature of the internal mixer chamber is set to 180°C. After the powder and the binder are completely combined and agglomerated, the chamber temperature is lowered to 160°C and the feed is pushed to the pelletizing section via a screw to produce small cylindrical pellets with a diameter of 3*5 mm.

[0057] (3) Injection molding:

[0058] First, the material pipe and the material barrel are vented by introducing protective gas, and the prepared feed material (2) is added to the storage barrel of the injection machine, and a protective gas atmosphere is introduced at the male and female molds, and a strong magnetic field is applied to the outer periphery of the barrel. Injection molding is performed according to the preset parameters to form a green embryo.

[0059] (4) Degreasing and sintering:

[0060] The molded green embryo is degreased in a two-stage degreasing method in a dedicated oxalic acid catalytic degreasing furnace. After oxalic acid degreasing treatment in an environment of 120℃ for 8 hours, the cavity is heated to 160℃ after the acid is stopped to form a thin layer of polymer protective film on the surface of the brown embryo to prevent the brown embryo from contacting with oxygen in the air. The degreased parts are then transferred to a dedicated vacuum sintering furnace, the furnace temperature is set to 1050℃, and this temperature is maintained for 2 hours. During the sintering process, argon protective gas is injected into the furnace. N35 NdFeB rough embryos with a sintering density of 7.51g / cm3 can be obtained.

[0061] (5) Post-processing:

[0062] Through grinding, the rough blank is made to meet the requirements in size and appearance, and the product parts with mechanical parameters meeting the design requirements are obtained. The product parts are then subjected to final magnetization and polarization guidance to turn them into NdFeB permanent magnet parts.

[0063] Embodiment 2

[0064] It is a solvent degreasing system, which uses alkane solvents to react with paraffin (CnH2n+2), dissolving the paraffin in the solvent and then separating it from the NdFeB product, so as to achieve the purpose of removing a large amount of polymers in the product.

[0065] (1) Material preparation:

[0066] (a) NdFeB powder as raw material powder: N35 NdFeB powder is selected, with an average particle size (D50) of 2um to 10um, a weight of 4370g, and a total amount of binder of 630g. (Weight ratio = 87.4:12.6)

[0067] (b) Binder: Prepare a binder according to the weight ratio of microcrystalline wax, polypropylene, compatibilizer, plasticizer, and surfactant: 86%: 4.5%: 4%: 5%: 0.5%. After preparation, weigh 630 g (approximately 12.6% of the total weight) of the binder.

[0068] (2) Internal mixing and granulation:

[0069] In an environment with protective gas, the mixed material of (1) is added into the chamber of a heated and pressurized internal mixer and kneaded into a mass. The chamber temperature is set to 175°C. After the powder and the binder are completely combined and agglomerated, the chamber temperature is lowered to 150°C and the material is fed to the pelletizing section via a screw to produce small cylindrical pellets with a diameter of 3*5 mm.

[0070] (3) Injection molding:

[0071] First, the material pipe and the material barrel are vented by introducing protective gas, and the prepared feed material (2) is added to the storage barrel of the injection machine, and a protective gas atmosphere is introduced at the male and female molds, and a strong magnetic field is applied to the outer periphery of the barrel. Injection molding is performed according to the preset parameters to form a green embryo.

[0072] (4) Degreasing and sintering:

[0073] The molded green embryo is degreased in a two-stage degreasing method in a special solvent degreasing furnace. After the n-heptane solvent degreasing treatment is carried out in an environment of 60℃ for 24 hours, the cavity is heated to 160℃ after the residual solvent is removed to form a thin layer of high-electron protective film on the surface of the brown embryo to avoid contact with oxygen in the air. The degreased parts are then transferred to a professional sintering furnace, the furnace temperature is set to 1050℃, and this temperature is maintained for 2 hours. During the sintering process, argon protective gas is injected into the furnace. N35 NdFeB rough embryos with a sintering density of 7.52g / cm3 can be obtained.

[0074] (5) Post-processing:

[0075] Through grinding, the rough blank is made to meet the requirements in size and appearance, and the product parts with mechanical parameters meeting the design requirements are obtained. The product parts are then subjected to final magnetization and polarization guidance to turn them into NdFeB permanent magnet parts.

[0076] Embodiment 3

[0077] It is a thermal debinding system. It melts more than a dozen polymer materials with different melting points at different temperatures, and slowly removes the polymers with different melting points from the NdFeB product within its melting point temperature range, so as to achieve the purpose of removing a large amount of polymers in the product.

[0078] (1) Material preparation:

[0079] (c) NdFeB powder as raw material powder: N35 NdFeB powder is selected, with an average particle size (D50) of 2um to 10um, a weight of 4370g, and a total amount of binder of 630g. (Weight ratio = 87.4:12.6)

[0080] (d) Binder: Prepare the binder according to the weight ratio of wax system (microcrystalline wax, paraffin (52°, 54°, 56°, 58°, 60°, 62°, 64°), high-temperature plastic wax), polypropylene (HDPE, LDPE, LLDPE), polyethylene (PE), compatibilizer, plasticizer, and surfactant: 45%: 30%: 19%: 5%: 1%. After preparation, weigh 630 g (approximately 12.6% of the total weight) of the binder.

[0081] (2) Internal mixing and granulation:

[0082] In an environment with protective gas, the mixed material of (1) is added into the chamber of a heated and pressurized internal mixer and kneaded into a mass. The temperature of the internal mixer chamber is set to 180°C. After the powder and the binder are completely combined and agglomerated, the chamber temperature is lowered to 160°C and the material is fed to the pelletizing section via a screw to produce small cylindrical pellets with a diameter of 3*5 mm.

[0083] (3) Injection molding:

[0084] First, the material pipe and the material barrel are vented by introducing protective gas, and the prepared feed material (2) is added to the storage barrel of the injection machine, and a protective gas atmosphere is introduced at the male and female molds, and a strong magnetic field is applied to the outer periphery of the barrel. Injection molding is performed according to the preset parameters to form a green embryo.

[0085] (4) Degreasing and sintering:

[0086] The molded green embryo is directly placed in a vacuum sintering furnace. The polymers with different melting points are removed from the NdFeB green embryo in batches at a slow heating rate and holding time. The degreasing time (650℃) is as long as 48 hours, and the furnace temperature is set to 1050℃ and maintained at this temperature for 2 hours. During the sintering process, argon protective gas is injected into the furnace. The N35 NdFeB rough embryo with a sintering density of 7.48g / cm3 can be obtained.

[0087] (5) Post-processing:

[0088] Through grinding, the rough blank is made to meet the requirements in size and appearance, and the product parts with mechanical parameters meeting the design requirements are obtained. The product parts are then subjected to final magnetization and polarization guidance to turn them into NdFeB permanent magnet parts.

[0089] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for manufacturing complex-shaped NdFeB permanent magnet parts, comprising the following steps: a) preparing a mixture, mixing NdFeB powder and a polymer binder in a weight ratio of 65-95wt%:35-5wt% to obtain a mixture; b) Mixing and granulation: the mixed material is put into a mixer and mixed under pressure and heating, and granulated into mixed particles with a diameter of 3 to 5 mm; c) Injection molding, feeding the kneaded granules into a material pipe, and injecting the molten kneaded granules into a mold by injection molding, and after cooling, opening the mold to obtain a green embryo; d) defatting, defatting the raw embryos by a defatting system to obtain brown embryos; e) Sintering: placing the brown embryo into a vacuum furnace for sintering, and forming a rough embryo with metallic luster after being taken out of the furnace; f) Post-processing: processing the size and appearance of the rough blank to obtain a product with mechanical parameters that meet the design requirements; Features: The material tube set in step c) is made of non-magnetic mold steel, and a circular magnetic field is installed on the side of the material tube to achieve primary magnetization polarization guidance; a magnetic field is also installed in the mold in step c) according to product requirements to achieve secondary magnetization polarization guidance, and after step f), the step of performing final magnetization polarization on the product part to make it a NdFeB permanent magnet part is also included; The degreasing in step d) only removes part of the polymer binder. During degreasing, low-temperature degreasing is performed first and then high-temperature degreasing. High-temperature degreasing means heating the green embryo to 150-170°C to melt the remaining polymer binder and coat the NdFeB powder through capillary force, which can isolate oxygen in the air and prevent oxidation of the NdFeB powder, and can also bind the NdFeB powder and increase the strength of the brown embryo.

2. The method for manufacturing complex-shaped NdFeB permanent magnet parts according to claim 1, characterized in that: The NdFeB powder in step a) is any one of N series NdFeB powder, M series NdFeB powder, H series NdFeB powder, SH series NdFeB powder, UH series NdFeB powder, EH series NdFeB powder, TH series NdFeB powder or a mixture thereof.

3. The method for manufacturing complex-shaped NdFeB permanent magnet parts according to claim 1, characterized in that: The D50 average particle size of the NdFeB powder in step a) is 2 to 10 μm.

4. The method for manufacturing complex-shaped NdFeB permanent magnet parts according to claim 1, characterized in that: The polymer binder in step a) includes a main polymer, a backbone auxiliary material, a heat stabilizer, a plasticizer and a surfactant.

5. The method for manufacturing complex-shaped NdFeB permanent magnet parts according to claim 4, characterized in that: The weight ratio of the main polymer, the backbone auxiliary material, the heat stabilizer and the plasticizer is 80-90wt%: 5-15wt%: 0.5-5wt%: 0.5-5wt%, and the rest is the surfactant.

6. The method for manufacturing complex-shaped NdFeB permanent magnet parts according to claim 1, characterized in that: The internal mixing and granulation in step b) is carried out under a protective atmosphere, which means that the internal mixing furnace is filled with argon and / or nitrogen.

7. The method for manufacturing complex-shaped NdFeB permanent magnet parts according to claim 1, characterized in that: The material pipe in step c) is provided with an electric heating coil to keep the temperature of the material pipe at 160-210°C.

8. The method for manufacturing complex-shaped NdFeB permanent magnet parts according to claim 1, characterized in that: The degreasing in step d) removes 70-90% of the polymer binder.

9. The method for manufacturing complex-shaped NdFeB permanent magnet parts according to claim 1, characterized in that: The degreasing methods in step d) include thermal degreasing, solvent degreasing and catalytic degreasing.

10. The method for manufacturing complex-shaped NdFeB permanent magnet parts according to claim 1, characterized in that: The sintering in step e) refers to placing the brown embryo in a vacuum furnace with a protective atmosphere and sintering it at a temperature of 850 to 1250° C. for 60 to 180 minutes.

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