Process for producing neodymium-iron-boron magnets which are easily injection moulded

Abstract

The application relates to the technical field of production and manufacturing of magnetic materials, in particular to a neodymium-iron-boron magnet production process easy to injection molding.The production process comprises the following steps: powder preparation: after neodymium, iron and boron are uniformly mixed, smelting, crushing are carried out, and neodymium-iron-boron alloy powder is obtained; material mixing: the neodymium-iron-boron alloy powder and wax-containing powder glue solution are uniformly mixed to obtain rheological mixture, and in the rheological mixture, the content of the wax-containing powder glue solution is 6-30 wt%; embryo injection: the rheological mixture is subjected to injection molding to obtain a mold embryo; embryo setting: the mold embryo is subjected to embryo setting treatment to obtain a magnet embryo; sintering: the magnet embryo is subjected to sintering to obtain a neodymium-iron-boron magnet.The wax-containing powder glue solution and the neodymium-iron-boron alloy powder are mixed, the rheological mixture has better rheological property, the injection and demolding are easy, the production efficiency and product quality are improved, and through embryo setting, sintering and other processes, the compactness of the neodymium-iron-boron magnet and the quality stability after batch production are improved.

Description

Technical Field

[0001] This application relates to the field of magnetic material manufacturing technology, and in particular to a manufacturing process for neodymium iron boron magnets that is easy to injection mold. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets, due to their strong magnetic properties, are widely used in aerospace, wind power generation, new energy vehicles, home appliances, smart consumer electronics, and motor equipment. With the rapid development of these industries, the demand for high-performance magnets is increasing, especially for magnet components with complex shapes and precise dimensions. Existing pressing methods are no longer sufficient to meet the demands for efficient and high-quality production. Therefore, developing new production processes to improve the production efficiency and product quality of NdFeB magnets has become an urgent problem to be solved.

[0003] In order to overcome the limitations of pressing methods in the existing NdFeB magnet production process, some companies have adopted injection molding technology. Common solutions include mixing different types of resins with powder and heating them to melt the resin and improve the flowability of the powder, enabling the production of NdFeB magnets through injection molding.

[0004] While the above-mentioned heated injection molding technology can improve production efficiency, the process requires heating the resin to melt before injection, resulting in high energy consumption and the need for cooling. Furthermore, in continuous production, irregularly shaped magnets are prone to defects such as defects, cracks, surface depressions, and deformation, reducing the yield rate of NdFeB magnets. In addition, injection molding cannot completely eliminate stress concentration points within the preform, reducing the density of the NdFeB magnets. Summary of the Invention

[0005] This application provides a manufacturing process for neodymium iron boron magnets that is easy to injection mold, in order to obtain neodymium iron boron magnets with high density and quality stability.

[0006] A manufacturing process for neodymium iron boron magnets that is easy to injection mold, the manufacturing process comprising the following steps:

[0007] Powdering: Neodymium, iron, and boron are mixed evenly, then smelted and pulverized to obtain neodymium-iron-boron alloy powder;

[0008] Mixing: Neodymium iron boron alloy powder and wax-containing adhesive are mixed evenly to obtain a rheology mixture; in the rheology mixture, the content of the wax-containing adhesive is 6-30 wt%;

[0009] Preform injection molding: The rheological mixture is injection molded to obtain a preform;

[0010] Preform setting: The preform is subjected to preform setting treatment to remove the wax-containing powder and glue liquid from the preform, resulting in a magnet preform;

[0011] Sintering: The magnet blank is sintered, and the resulting neodymium iron boron magnet is post-processed to obtain neodymium iron boron magnets.

[0012] By employing the above technical solution, the prepared NdFeB magnets exhibit high density and stable quality. The use of wax-containing adhesive promotes the uniform dispersion of the rheological mixture and improves flowability during injection molding, avoiding defects such as incompleteness and dents, thus increasing product yield and production efficiency. During sintering, the wax-containing adhesive in the preform is effectively removed, ensuring the structural stability and high density of the final NdFeB magnets. The entire production process is simple and efficient, suitable for large-scale industrial production.

[0013] This application has the following specific advantages:

[0014] This application utilizes a small amount of wax-containing adhesive and neodymium iron boron alloy powder mixed together, such as 6-30 wt% wax-containing adhesive, to give the rheological mixture better rheological properties. This makes it easier to inject and demold, avoiding blockages during the injection process and product defects after injection, thus improving quality. At the same time, the wax-containing adhesive also has better binding force, enabling the preform to form a stable preform structure after molding. The preform molding process can ensure the stability of the structure, avoiding defects, cracks, etc., thus improving the density of neodymium iron boron magnets and the stability of quality after mass production.

[0015] This application eliminates the need for heating and cooling during the injection molding process, thus offering advantages such as energy saving and ease of operation.

[0016] Preferably, the particle size of the neodymium iron boron alloy powder is 0.01-5 μm; and the content of the wax-containing adhesive in the rheological mixture is 13.8-20 wt%.

[0017] By adopting the above technical solution, the particle size of NdFeB alloy powder is controlled within the range of 0.01-5μm, making it easier for the NdFeB alloy powder to mix evenly with wax-containing adhesives. The resulting rheological mixture exhibits better rheological properties and dispersibility. This not only improves the flowability of materials during injection molding but also enhances the stability of the preform, reducing defects such as imperfections and dents, thereby improving the density of NdFeB magnets and the quality stability of mass production.

[0018] Preferably, the injection molding process conditions are: pressure of 50-80 MPa and holding time of 10-20 s.

[0019] By adopting the above technical solution, the amount of wax-containing adhesive is 6-30 wt%, which gives the rheological mixture better rheological properties, dispersibility, and adhesion. Therefore, it flows easily during injection molding, forming a stable preform and avoiding defects, dents, and other phenomena, thus improving the stability of the magnets in continuous production. Specifically, injection molding conditions of 50-80 MPa pressure and 10-20 s holding time make it easier for the wax-containing adhesive to be injection molded, and the preform structure formed by injection is dense and stable, further improving structural stability and quality, and ensuring the compactness of NdFeB magnets and the quality stability of mass production.

[0020] Preferably, the preform treatment process is as follows: in the first stage, the preform is heated to 80-120°C at a heating rate of 5-10°C / min under a pressure of 10-20 MPa; in the second stage, the preform is heated to 230-280°C at a heating rate of 3-5°C / min under a pressure of 25-35 MPa; and in the third stage, the preform is heated to 355-405°C at a heating rate of 5-8°C / min under a pressure of 20-30 MPa to obtain the preform.

[0021] By adopting the above technical solution, the precise control of pressure and heating rate at each stage of the gradual removal of wax-containing adhesive liquid ensures the gradual stabilization of the internal structure of the preform. Specifically:

[0022] The first stage involves heating the mold to 80-120°C at a pressure of 10-20 MPa and a heating rate of 5-10°C / min. This process initially removes some of the wax-containing adhesive, allowing the preform to begin forming a relatively stable core.

[0023] The second stage involves heating the mold to 230-280℃ at a rate of 3-5℃ / min under a pressure of 25-35MPa, which further removes more wax-containing adhesive and improves the overall density and strength of the mold.

[0024] The third stage: Under a pressure of 20-30 MPa, the temperature is heated to 355-405℃ at a heating rate of 5-8℃ / min, and the remaining wax-containing adhesive is completely removed, forming a magnet blank with a very stable structure and high density.

[0025] The entire preform-making process effectively avoids problems such as preform cracking and deformation caused by the one-time removal of wax-containing adhesive, ensuring that the final neodymium iron boron magnet has high density and stable quality.

[0026] Preferably, the specific sintering process is as follows: the magnet blank is sintered to obtain a neodymium iron boron magnet, and then the neodymium iron boron magnet is sequentially magnetized, tested for magnetic energy, processed, electroplated, and packaged to obtain a neodymium iron boron magnet.

[0027] By adopting the above technical solution, the specific sintering process ensures the high performance and stability of NdFeB magnets. Specifically:

[0028] Sintering process: By precisely controlling the sintering of the magnet blank, the magnet parts are fully densified at high temperature, which improves the density and mechanical strength of the magnet.

[0029] Post-processing steps: magnetization, magnetic energy testing, processing, electroplating, and packaging are carried out in sequence. The quality of each step is strictly controlled to ensure that the magnetic properties and appearance of the final product meet high standards, thereby enhancing the product's market competitiveness.

[0030] Consistent quality: The high degree of standardization in the entire sintering and post-processing process ensures that mass-produced NdFeB magnets maintain consistent performance, enhancing product reliability and user trust.

[0031] Preferably, the wax-containing adhesive solution is composed of the following raw materials by weight percentage:

[0032] Wax powder 2-8%

[0033] EVA emulsion 20-35%

[0034] Water-soluble resin 0.3-10%

[0035] Maleic anhydride copolymer 1-3%

[0036] Dispersant 0.5-1%

[0037] Accelerator 0.1-0.3%

[0038] The remainder is diluent.

[0039] By adopting the above technical solution, the combination of EVA emulsion and wax powder can adjust the rheological properties of the adhesive, making it easier to coat and handle. The initial tack-enhancing effect of the EVA emulsion allows the adhesive to quickly form adhesion upon contact with the substrate, while the lubricity of the wax powder helps reduce frictional resistance during coating. This synergistic adjustment of rheological properties allows the adhesive to be coated more evenly on the surface of the NdFeB alloy powder, thereby improving the agglomeration stability of the NdFeB alloy powder after injection molding. The combined action of water-soluble resin, EVA emulsion, and maleic anhydride copolymer can significantly enhance the bonding between the wax-containing adhesive and the NdFeB alloy powder. Combined with the wax powder, the rheological mixture is easily injection molded, resulting in a stable preform structure. Furthermore, the preform-setting process of this application ensures that the preform maintains excellent structural stability during the preform-setting process, resulting in NdFeB magnets with high density and stable quality.

[0040] Preferably, the water-soluble resin is a water-soluble rosin resin and / or a water-soluble alkyd resin.

[0041] By adopting the above technical solutions, water-soluble rosin resin and / or water-soluble alkyd resin can significantly enhance the overall properties of wax-containing adhesives, such as adhesion, durability, and flowability. Water-soluble rosin resin adjusts the flowability of the wax-containing adhesive, making it easier to coat and handle, while simultaneously enhancing adhesion and improving rheological properties. Water-soluble alkyd resin exhibits good compatibility with water-based components, maintaining the uniformity and stability of the adhesive, preventing stratification or sedimentation, and flexibly adjusting the viscosity of the wax-containing adhesive to adapt to different application scenarios. These improvements make the rheology mixture easier to injection mold, resulting in a stable preform structure, and ultimately producing neodymium iron boron magnets with high density and stable quality.

[0042] When water-soluble resins are water-soluble rosin resin and water-soluble alkyd resin in a weight ratio of 1:(0.1-0.5), they have a synergistic effect and enhance the effects of wax powder, maleic anhydride copolymer and EVA emulsion. This makes the rheological mixture easy to rheologically disperse, the material binding stable, and easy to injection mold, resulting in neodymium iron boron magnets with good density and stable quality.

[0043] Preferably, the wax powder is one or more of polyethylene oxide wax powder, palm wax powder, and AKD wax powder.

[0044] By adopting the above technical solution, the wax powder selected is one or more of polyethylene oxide wax powder, palm wax powder, and AKD wax powder. These wax powders have good lubricity and dispersibility, which can effectively reduce the internal frictional resistance of the rheological mixture during injection molding and improve the smoothness of injection molding. At the same time, the combination of different types of wax powder can further optimize the rheological properties of the adhesive, ensure the structural stability and uniformity of the preform during injection molding, thereby improving the density and quality stability of the final product.

[0045] When wax powder is composed of polyethylene oxide wax powder, palm wax powder, and AKD wax powder in a weight ratio of 1:(0.1-1):(0.1-1), it plays a synergistic rheological role. Combined with raw materials such as EVA emulsion, water-soluble resin, and maleic anhydride copolymer, the resulting wax powder-containing adhesive has better comprehensive performance, thereby improving the density and quality stability of the final product.

[0046] Preferably, the dispersant is isotretinoin polyoxyethylene ether phosphate and / or oleamidopropyl betaine.

[0047] By adopting the above technical solution and using isomeric tridecyl alcohol polyoxyethylene ether phosphate and / or oleamidopropyl betaine as dispersants, the dispersibility of wax-containing adhesives can be effectively improved, ensuring that the rheological mixture is evenly distributed during injection molding and preventing agglomeration. This improves the density and surface quality of NdFeB magnets and further enhances the stability and consistency of the product.

[0048] Preferably, the maleic anhydride copolymer is a methyl vinyl ether-maleic anhydride copolymer.

[0049] By adopting the above technical solution, the methyl vinyl ether-maleic anhydride copolymer exhibits excellent film-forming, dispersing, and emulsifying properties, effectively enhancing the bonding force between the wax-containing adhesive and the NdFeB alloy powder, and improving the stability of the rheological mixture and the injection molding effect. Specifically:

[0050] Film-forming properties: Methyl vinyl ether-maleic anhydride copolymer can form a protective film on the surface of the preform, increasing the mechanical strength and stability of the preform and reducing the risk of cracking and deformation.

[0051] Dispersibility: The methyl vinyl ether-maleic anhydride copolymer can be uniformly dispersed in the rheology mixture, preventing particle agglomeration, ensuring uniform distribution of each component, and improving the consistency of injection molding and the quality of finished products.

[0052] Emulsifying properties: Methyl vinyl ether-maleic anhydride copolymer can promote the emulsification of wax-containing adhesives and other components, making them easier to mix and handle, improving production efficiency and product density.

[0053] The production process described in this application is suitable for complex product shapes, saves raw materials and subsequent processes, and saves cutting, grinding and other processes compared with the existing die casting method, which is beneficial for the production of magnets with irregular structures.

[0054] This application involves heating during sintering to vaporize and degrease the solvent, removing wax-containing adhesive liquid. Sintering must be carried out under vacuum and inert gas protection. Simultaneously, the rheological mixture obtained in this application can be granulated before injection molding. Furthermore, this application magnetizes the injection process and demagnetizes it after injection is complete.

[0055] In summary, this application includes at least one of the following beneficial technical effects:

[0056] 1. This application utilizes a small amount of wax-containing adhesive liquid and neodymium iron boron alloy powder to make the rheological mixture have better rheological properties, making it easy to inject and demold, thereby improving production efficiency and product quality; at the same time, it can also form a stable preform structure, and the preform setting process can ensure the stability of the structure, avoid defects, cracks and other phenomena, and improve the density of neodymium iron boron magnets and the stability of quality after mass production;

[0057] 2. The special formulation and dosage of the wax-containing adhesive (6-30wt%, preferably 13.8-20wt%), when mixed with NdFeB alloy powder, effectively improves the rheological properties, dispersibility, and adhesion of the rheology mixture. In particular, the use of wax powder, EVA emulsion, water-soluble resin, and maleic anhydride copolymer further enhances the performance of the rheology mixture, making the injection molding process smoother, avoiding clogging and defects, and improving product quality and stability.

[0058] 3. The multi-stage heating and pressurization steps of the preform process effectively remove the wax-containing adhesive liquid from the preform, ensuring the structural stability and compactness of the magnet, solving the problem of stress concentration points in traditional methods, and improving the performance and reliability of the final product. Detailed Implementation

[0059] The present application will be further described in detail below with reference to the embodiments.

[0060] AKD wax powder is an alkyl ketene dimer, CAS number 144245-85-2;

[0061] EVA emulsion is also known as polyvinyl acetate emulsion, CAS number 24937-78-8; VA content is 91-95%;

[0062] Water-soluble rosin resin is an aqueous liquid rosin tackifying emulsion with a curing content of 45-55%, brand: Jufeng Chemical, model: F0302-X, pH value: 7.0-8.0;

[0063] Water-soluble alkyd resin, CAS number 63148-69-6;

[0064] The brand of polyethylene oxide wax powder is Honeywell, and the model is AC-316A.

[0065] The palm wax powder is Brazilian palm wax powder;

[0066] The brand name of isomeric tridecyl alcohol polyoxyethylene ether phosphate is Hai Shi Hua, and the model is PEG200DL.

[0067] Oleamidopropyl betaine CAS No. 25054-76-6;

[0068] CAS No. 9011-16-9 for methyl vinyl ether-maleic anhydride copolymer.

[0069] Preparation example of wax-containing adhesive liquid

[0070] Preparation Example 1

[0071] A wax-containing adhesive solution is prepared by the following method:

[0072] Weigh out 2% wax powder, 20% EVA emulsion, 10% water-soluble resin, 1% maleic anhydride copolymer, 1% dispersant, 0.3% accelerator, and diluent by weight percentage and place them in a stirring device. Stir at 200 r / min for 20 min to ensure thorough mixing and obtain a wax powder-containing adhesive solution.

[0073] The water-soluble resin is water-soluble rosin resin, the wax powder is polyethylene oxide wax powder; the diluent is water; the dispersant is isotridecyl alcohol polyoxyethylene ether phosphate; the maleic anhydride copolymer is methyl vinyl ether-maleic anhydride copolymer; and the accelerator is ammonium persulfate.

[0074] Preparation Examples 2-3

[0075] The difference between Preparation Example 2-3 and Preparation Example 1 is that the amount of raw materials used is different, as shown in Table 1.

[0076] Table 1. Raw material usage (%) for Preparation Examples 1-3

[0077] raw material Preparation Example 1 Preparation Example 2 Preparation Example 3 Wax powder 2 6.5 8 EVA emulsion 20 28 35 Water-soluble resin 10 2 0.3 Maleic anhydride copolymer 1 2.3 1 dispersant 1 0.5 0.5 Accelerator 0.3 0.2 0.1 diluent 65.7 60.5 55.1

[0078] Preparation Example 4

[0079] The difference between Preparation Example 4 and Preparation Example 2 is that the wax powder is palm wax powder.

[0080] Preparation Example 5

[0081] The difference between Preparation Example 5 and Preparation Example 2 is that the wax powder is AKD wax powder.

[0082] Preparation Example 6

[0083] The difference between Preparation Example 6 and Preparation Example 2 is that the wax powder is composed of polyethylene oxide wax powder and palm wax powder in a weight ratio of 1:1.

[0084] Preparation Example 7

[0085] The difference between Preparation Example 7 and Preparation Example 2 is that the wax powder is composed of polyethylene oxide wax powder, palm wax powder and AKD wax powder in a weight ratio of 1:0.3:0.2.

[0086] Preparation Example 8

[0087] The difference between Preparation Example 8 and Preparation Example 2 is that the water-soluble resin is a water-soluble alkyd resin.

[0088] Preparation Example 9

[0089] The difference between Preparation Example 9 and Preparation Example 2 is that the water-soluble resin is composed of water-soluble rosin resin and water-soluble alkyd resin in a weight ratio of 1:0.2.

[0090] Preparation Example 10

[0091] The difference between Preparation Example 10 and Preparation Example 7 is that the water-soluble resin is composed of water-soluble rosin resin and water-soluble alkyd resin in a weight ratio of 1:0.2.

[0092] Preparation of comparative examples

[0093] Preparation of Comparative Example 1

[0094] The difference between Comparative Example 1 and Preparation Example 2 is that the water-soluble resin was replaced with an equal amount of EVA emulsion.

[0095] Preparation of Comparative Example 2

[0096] The difference between Comparative Example 2 and Preparation Example 2 is that the maleic anhydride copolymer was replaced with an equal amount of EVA emulsion.

[0097] Preparation of Comparative Example 3

[0098] The difference between Comparative Example 3 and Preparation Example 2 is that the wax powder was replaced with an equal amount of maleic anhydride copolymer to obtain a wax powder-free adhesive.

[0099] Example

[0100] Example 1

[0101] A process for manufacturing neodymium iron boron magnets that is easy to injection mold includes the following steps:

[0102] Powdering: Neodymium, iron, and boron are placed in a stirring device, mixed evenly, smelted, and pulverized to obtain neodymium-iron-boron alloy powder; wherein, the content of metallic element iron (Fe) in neodymium-iron-boron alloy powder is about 64%; the content of rare earth metal neodymium (Nd) is about 32%; the content of non-metallic element boron (B) is about 1%, and the balance is impurities or rare metals.

[0103] Mixing: NdFeB alloy powder and wax-containing adhesive are mixed evenly to obtain a rheology mixture. In the rheology mixture, the content of wax-containing adhesive is 13.8 wt%, and the balance is NdFeB alloy powder.

[0104] Preform injection: The rheological mixture is injection molded in an injection molding machine to obtain a preform;

[0105] Preform setting: The preform is placed in a heating furnace for preform setting treatment, which removes the wax-containing adhesive liquid from the preform to obtain the magnet preform;

[0106] Sintering: The magnet blank is then placed in a sintering furnace for sintering to obtain neodymium iron boron magnets.

[0107] The particle size of the neodymium iron boron alloy powder is 0.01-5μm, and in this embodiment it is preferably 1μm; the injection molding process conditions are: pressure of 50MPa and holding time of 20s;

[0108] The preform treatment process is as follows: In the first stage, the preform is heated to 80°C at a heating rate of 10°C / min under a pressure of 20MPa; in the second stage, the preform is heated to 280°C at a heating rate of 5°C / min under a pressure of 25MPa; and in the third stage, the preform is heated to 355°C at a heating rate of 8°C / min under a pressure of 20MPa to obtain the preform.

[0109] The specific sintering process is as follows: The magnet blank is sintered under nitrogen protection. The sintering process is as follows: Under vacuum conditions, the vacuum gauge reads -0.1MPa. Nitrogen gas is introduced, and the temperature is first raised to 300℃ and sintered for 1 hour. Then the temperature is raised to 600℃ and sintered for 3 hours. Then the temperature is raised to 800℃ and sintered for 2 hours. Then the temperature is raised to 1200℃ and sintered for 2.5 hours. Then the temperature is cooled to 30℃ to obtain the neodymium iron boron magnet. The neodymium iron boron magnet is then magnetized, tested for magnetic properties, processed, electroplated, and packaged to obtain the neodymium iron boron magnet.

[0110] The neodymium iron boron magnet has a semi-circular structure with an inner radius of 3.8cm, an outer radius of 5.8cm, and a thickness of 2cm.

[0111] Example 2

[0112] The difference between Example 2 and Example 1 is that the process parameters are different;

[0113] The preform treatment process is as follows: In the first stage, the preform is heated to 100°C at a heating rate of 8°C / min under a pressure of 15MPa; in the second stage, the preform is heated to 255°C at a heating rate of 4°C / min under a pressure of 30MPa; and in the third stage, the preform is heated to 375°C at a heating rate of 6°C / min under a pressure of 25MPa to obtain the preform.

[0114] The injection molding process conditions are: pressure of 80MPa and holding time of 10s.

[0115] In the rheological mixture, the content of wax powder adhesive is 15.5 wt%, and the balance is neodymium iron boron alloy powder.

[0116] Example 3

[0117] The difference between Example 3 and Example 1 is that the process parameters are different;

[0118] The preform treatment process is as follows: In the first stage, the preform is heated to 80°C at a heating rate of 10°C / min under a pressure of 20MPa; in the second stage, the preform is heated to 280°C at a heating rate of 5°C / min under a pressure of 25MPa; and in the third stage, the preform is heated to 355°C at a heating rate of 8°C / min under a pressure of 20MPa to obtain the preform.

[0119] In the rheological mixture, the content of wax powder adhesive is 20 wt%, and the balance is neodymium iron boron alloy powder.

[0120] The injection molding process conditions are: pressure of 60MPa and holding time of 18s.

[0121] Example 4

[0122] The difference between Example 4 and Example 2 is that the specific process of embryo fixation is different, as follows: The embryo fixation process is as follows: Under a pressure of 30MPa, the temperature is heated to 375℃ at a heating rate of 8℃ / min to obtain the embryo.

[0123] Example 5

[0124] The difference between Example 5 and Example 2 is that the source of the wax powder-containing adhesive is different, as shown in Table 2.

[0125] Table 2. Sources of wax-containing adhesive solutions in Examples 2, 5-15

[0126] Example Sources of wax-containing adhesives Example 2 Preparation Example 1 Example 5 Preparation Example 2 Example 6 Preparation Example 3 Example 7 Preparation Example 4 Example 8 Preparation Example 5 Example 9 Preparation Example 6 Example 10 Preparation Example 7 Example 11 Preparation Example 8 Example 12 Preparation Example 9 Example 13 Preparation Example 10 Example 14 Preparation of Comparative Example 1 Example 15 Preparation of Comparative Example 2

[0127] Comparative Example

[0128] Comparative Example 1

[0129] The difference between Comparative Example 1 and Example 2 is that the content of wax powder in the rheology mixture is 35 wt%.

[0130] Comparative Example 2

[0131] The difference between Comparative Example 2 and Example 2 is that the amount of wax powder-containing adhesive in the rheological mixture is 5 wt%.

[0132] Comparative Example 3

[0133] The difference between Comparative Example 3 and Example 2 is that Comparative Example 3 does not include a preform-setting process, and the obtained preform is directly sintered.

[0134] Comparative Example 4

[0135] The difference between Comparative Example 4 and Example 2 is that the wax powder content of the adhesive solution is replaced with the wax powder-free adhesive solution obtained in Comparative Example 3.

[0136] Under the injection molding process conditions of this application, the wax-free adhesive liquid blocked the injection outlet of the injection equipment, resulting in the failure of neodymium iron boron magnet preparation.

[0137] Performance testing

[0138] Detection methods / test methods

[0139] 1. Density test

[0140] The densities of the neodymium iron boron alloy powder, the neodymium iron boron magnets obtained in Examples 1-15 and Comparative Examples 1-3 were measured using a densitometer. The density of the alloy powder was denoted as A, and the density of the neodymium iron boron magnet was denoted as B. The density ratio was calculated as A / B × 100%. A higher density ratio indicates better density of the magnet.

[0141] 2. Quality Inspection

[0142] The neodymium iron boron magnets obtained after mass production of Examples 1-15 and Comparative Examples 1-3 were observed for surface defects or other defects. If such defects were found, they were considered unqualified. At the same time, the dimensions were measured. If the measured dimensional value differed from the preset value by more than 0.2 mm, it was considered unqualified. Finally, the unqualified products were counted and the pass rate was calculated.

[0143] The specific experimental data are shown in Table 3.

[0144] Table 3 Data Analysis of Examples 1-15 and Comparative Examples 1-3

[0145] Test Items Density (%) Pass rate (%) Example 1 98.02 98.3 Example 2 98.16 98.5 Example 3 98.08 97.9 Example 4 98.11 96.8 Example 5 98.31 98.8 Example 6 98.10 98.2 Example 7 98.15 98.4 Example 8 98.13 98.5 Example 9 98.42 98.9 Example 10 99.31 100 Example 11 99.14 98.5 Example 12 98.89 99.0 Example 13 99.83 100 Example 14 95.63 93.5 Example 15 94 92.5 Comparative Example 1 89.66 83.6 Comparative Example 2 85.21 77.5 Comparative Example 3 80.7 73.3

[0146] Combining Example 2 and Comparative Examples 1-3 with Table 2, it can be seen that the density and pass rate of Comparative Examples 1-3 are both below 90%, while the density and pass rate of Example 2 are both above 98%. This indicates that the wax-containing adhesive solution of this application can better promote the injection molding of NdFeB alloy powder, and the resulting preform structure is stable. Furthermore, in the specific preform-setting process of this application, the magnet preform can obtain better stability. After sintering, a NdFeB magnet part with stable structure and good quality is formed.

[0147] Combining Examples 5 and 9 with Table 2, it can be seen that the density and pass rate of Example 9 are higher than those of Example 5. This indicates that the compounding of polyethylene oxidized wax powder, palm wax powder and AKD wax in this application has a synergistic effect, further improving the comprehensive performance of the wax powder-containing adhesive, making the rheological mixture easy to inject and forming a stable structure during the injection molding process, thus giving it better stability during the production process.

[0148] As can be seen from Examples 14-15 and Example 5 and the structure in Table 2, the density and pass rate of the qualified examples are higher than those of Example 5. This indicates that the wax powder, EVA emulsion, water-soluble resin, maleic anhydride copolymer, etc. are compounded in this application. The wax powder-containing adhesive can be better mixed evenly with NdFeB alloy powder, and the structure is stable after injection molding. Combined with the preform process of this application, the obtained NdFeB magnet has high density and quality stability.

[0149] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A manufacturing process for neodymium iron boron magnets that is easy to injection mold, characterized in that, The production process includes the following steps: Powdering: Neodymium, iron, and boron are mixed evenly, then smelted and pulverized to obtain neodymium-iron-boron alloy powder; Mixing: Neodymium iron boron alloy powder and wax-containing adhesive are mixed evenly to obtain a rheology modifier; in the rheology modifier, the content of the wax-containing adhesive is 6-30 wt%; Preform injection molding: The rheological mixture is injection molded to obtain a preform; Preform setting: The preform is subjected to preform setting treatment to remove the wax-containing powder and glue liquid from the preform, resulting in a magnet preform; Sintering: The magnet blank is sintered to obtain neodymium iron boron magnets; The preform treatment process is as follows: First stage, under a pressure of 10-20 MPa, heating to 80-120℃ at a heating rate of 5-10℃ / min; Second stage, under a pressure of 25-35 MPa, heating to 230-280℃ at a heating rate of 3-5℃ / min; Third stage, under a pressure of 20-30 MPa, heating to 355-405℃ at a heating rate of 5-8℃ / min to obtain the preform. The wax-containing adhesive solution is composed of the following raw materials by weight percentage: Wax powder 2-8% EVA emulsion 20-35% Water-soluble resin 0.3-10% Maleic anhydride copolymer 1-3% Dispersant 0.5-1% Accelerator 0.1-0.3% The remainder is diluent; The water-soluble resin is a water-soluble rosin resin and / or a water-soluble alkyd resin. The wax powder is one or more of polyethylene oxide wax powder, palm wax powder, and AKD wax powder.

2. The manufacturing process for easily injection-molded neodymium iron boron magnets according to claim 1, characterized in that: The particle size of the neodymium iron boron alloy powder is 0.01-5µm; in the rheological mixture, the content of the wax powder-containing adhesive is 13.8-20wt%.

3. The manufacturing process for easily injection-molded neodymium iron boron magnets according to claim 1, characterized in that, The injection molding process conditions are: pressure of 50-80MPa and holding time of 10-20s.

4. The manufacturing process for easily injection-molded neodymium iron boron magnets according to claim 1, characterized in that, The specific sintering process is as follows: the magnet blank is sintered to obtain a neodymium iron boron magnet, and then the neodymium iron boron magnet is magnetized, tested for magnetic energy, processed, electroplated and packaged in sequence to obtain a neodymium iron boron magnet.

5. The manufacturing process for easily injection-molded NdFeB magnets according to claim 1, characterized in that: The dispersant is isotridecyl polyoxyethylene ether phosphate and / or oleamidopropyl betaine.

6. The manufacturing process for easily injection-molded neodymium iron boron magnets according to claim 1, characterized in that: The maleic anhydride copolymer is a methyl vinyl ether-maleic anhydride copolymer.