A method for producing an anisotropic injection molded magnet

Abstract

This invention discloses a method for preparing anisotropic injection-molded magnets, comprising: a secondary orientation process in which pulsed magnetic field orientation and continuous electromagnetic field orientation are sequentially applied to molten magnetic powder during injection molding, enabling the magnetic powder to achieve effective orientation during the molten stage, thereby obtaining anisotropic injection-molded magnets with significantly improved orientation degree and magnetic properties. Magnetic property optimization: Secondary orientation reduces the problem of localized insufficient orientation, optimizing the magnetic properties of the magnet and improving the consistency of the magnetic powder arrangement inside the magnet. Secondary orientation reduces dependence on a single high-intensity magnetic field, reduces equipment energy consumption, and improves system operational stability. The method of this invention is applicable to various bonded magnet systems and has good versatility and engineering feasibility.

Description

Technical Field

[0001] This invention belongs to the field of magnetic material preparation technology. More specifically, this invention relates to a method for preparing anisotropic injection-molded magnets, specifically a method for preparing anisotropic injection-molded magnets that achieves secondary orientation by combining a pulsed magnetic field with a continuous electromagnetic field. Background Technology

[0002] Bonded magnets possess advantages such as good performance consistency, precise dimensions, complex shapes, high material utilization, and easy integration with metal / plastic parts, holding an important position in the field of rare-earth permanent magnets. Among them, anisotropic injection-molded magnets exhibit superior magnetic properties and remanence (…). B r ) and maximum magnetic energy product (( BH ) max The final magnet thickness is significantly higher than that of isotropic injection-molded magnets; however, the magnet's final thickness... B r and( BH ) max Isomagnetic properties are determined by the orientation of the magnetic powder in the same direction during injection molding. Traditional methods for determining the magnetic powder orientation in bonded magnets have the following shortcomings: Limited orientation efficiency: Traditional processes involve a single magnetic field action stage, making it difficult for magnetic powder to achieve sufficient orientation in high-viscosity melts.

[0003] Poor orientation stability: Oriented magnetic powder is prone to disturbance and rebound during flow and cooling.

[0004] Limited material adaptability: The process parameter window is narrow, making it difficult to adapt to various magnetic powder and binder systems.

[0005] High energy consumption and equipment burden: Relying on a high-strength steady-state magnetic field to compensate for insufficient orientation, the system has prominent energy consumption and heat generation problems.

[0006] How to obtain magnetic powder with high orientation is an important issue in the study of high magnetic performance bonded magnets. Summary of the Invention

[0007] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0008] To achieve these and other advantages according to the present invention, the present invention provides a method for preparing an anisotropic injection-molded magnet, comprising: a secondary orientation process in which pulsed magnetic field orientation and continuous electromagnetic field orientation are sequentially applied to molten magnetic powder during the injection molding process, so that the magnetic powder obtains effective orientation in the melting stage, thereby obtaining an anisotropic injection-molded magnet with significantly improved orientation degree and magnetic properties.

[0009] Preferably, the process specifically includes the following steps: Step 1: Mix the magnetic powder and binder, feed the mixture into an extruder, and after melting, shearing and mixing, extrude it into a continuous strip melt and cool it; feed the cooled strip into a cutter and sieve it, and finally dry the granules. Step 2: Place the granules into the injection molding machine. Apply an instantaneous pulsed magnetic field to the molten magnetic powder through a pulse orientation coil set outside the first mold, thereby orienting the molten magnetic powder with a pulsed magnetic field. Step 3: The molten magnetic powder after the first orientation is introduced into the second mold through the nozzle. The electromagnetic orientation coil outside the second mold continuously applies a stable magnetic field to the molten magnetic powder to perform continuous electromagnetic field orientation. After the continuous electromagnetic field orientation is completed, it is cooled to obtain anisotropic injection-molded magnet.

[0010] Preferably, in step one, the magnetic powder is NdFeB doped with SmFeN, wherein the mass percentage of SmFeN is 0~40wt%.

[0011] Preferably, in step one, the adhesive is a thermoplastic resin.

[0012] Preferably, the adhesive comprises one or a combination of two or more of polyamide, nylon, polyphenylene sulfide, and polyetheretherketone.

[0013] The adhesive is replaced with modified nylon, and the preparation method of modified nylon includes the following steps: Step 1: Mix tris(2-aminoethyl)amine and dodecanolactam at a mass ratio of 1:6~30 and put them into a reaction vessel. Add NaH, the amount of NaH being 0.25wt%~2wt% of the total mass of tris(2-aminoethyl)amine and dodecanolactam. Under nitrogen protection, react at 180~200℃ for 2~4h to obtain the modified nylon precursor. Step 2: Mix the modified nylon precursor with p-acetoxybenzoic acid at a mass ratio of 10:1~2, add triphenyl phosphite and zinc acetate at a mass ratio of 1~2:1, and triphenyl phosphite accounts for 1wt%~2wt% of the modified nylon precursor. Under nitrogen protection, heat to 180~200℃ and stir for 1~2h. Then heat to 220~230℃, reduce pressure to 10~50Pa, and react for 1~3h. Finally, heat to 240~250℃ and react under a vacuum of 1~10Pa for 1~2h to obtain modified nylon.

[0014] Preferably, the binder accounts for 8 wt% to 20 wt% of the mass of the mixed raw materials.

[0015] Preferably, in step one, the melting temperature is 200℃~330℃.

[0016] Preferably, in step two, the pulse width of the pulse magnetic field is 1μs~1000ms, the pulse magnetic field strength is 1.2~2.2T, and the orientation voltage is 1000~4000V.

[0017] Preferably, in step two, the duration of the electromagnetic orientation coil on the molten magnetic powder is 1~1000s, the orientation direction is the same as the direction of the pulsed magnetic field, and the orientation voltage is 200~400V.

[0018] Preferably, the orientation device used for primary and secondary orientation of molten magnetic powder includes the following structure: The first mold has a nozzle at its front end and a pulse coil is sleeved on the outside of the first mold. The second mold has an electromagnetic orientation coil fitted on its outside.

[0019] This invention offers at least the following advantages: The invention employs a secondary orientation process during injection molding, sequentially applying a pulsed magnetic field and a continuous electromagnetic field to the molten magnetic powder. This process ensures effective orientation of the magnetic powder during the molten stage, resulting in anisotropic injection-molded magnets with significantly improved orientation and magnetic properties. Magnetic property optimization: Secondary orientation reduces localized inadequacy, optimizing the magnet's magnetic properties and improving the consistency of the magnetic powder arrangement within the magnet. Secondary orientation reduces dependence on a single high-intensity magnetic field, lowers equipment energy consumption, and improves system operational stability. The method of this invention is applicable to various bonded magnet systems, exhibiting good versatility and engineering feasibility.

[0020] Meanwhile, based on the secondary orientation of molten magnetic powder, this invention uses branched modified nylon to replace conventional nylon 12 as a binder, improving the filling rate and orientation degree of the magnetic powder, and further enhancing the magnetic properties of the injection-molded magnet. First, a precursor is obtained by reacting dodecyl lactam with tris(2-aminoethyl)amine and oxalic acid. Then, the precursor is copolymerized with p-acetoxybenzoic acid to prepare modified nylon. Compared with ordinary nylon 12, it has lower melt viscosity and better flowability, effectively improving the filling rate of magnetic powder. Simultaneously, the terminal amino groups in this modified nylon can form a good interfacial bond with the magnetic powder, improving the uniformity of magnetic powder dispersion. Combined with a high-vacuum polycondensation process, it can reduce small molecule and pore defects in the system, significantly improving the orientation degree of the magnetic powder and the density of the product under pulsed and continuous two-step magnetic fields. Ultimately, it significantly improves the remanence, coercivity, and maximum energy product of the injection-molded magnet, achieving overall optimization of magnetic properties.

[0021] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0022] Figure 1 A schematic diagram of the orientation device used in this invention for pulsed magnetic field orientation and continuous electromagnetic field orientation of molten magnetic powder. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0024] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof. The structure of the orientation device used in each embodiment is as follows: Figure 1 As shown, the structure of the orientation device includes: The first mold 1 has a nozzle 2 at its front end and a pulse coil 3 is sleeved on the outside of the first mold 1. The second mold 4 has an electromagnetic orientation coil 5 fitted on its outside.

[0025] The first mold 1 and the second mold 4 are used to contain the molten magnetic powder for molding and injection. The pulse coil 3 and the electromagnetic orientation coil 5 respectively perform pulsed magnetic field orientation and continuous electromagnetic field orientation on the molten magnetic powder.

[0026] Example 1 A method for preparing an anisotropic injection-molded magnet includes the following steps: Step 1: Mix magnetic powder with nylon 12 (12 wt% of the mixed raw material) to obtain a mixed raw material. The magnetic powder is NdFeB doped with SmFeN, and the mass ratio of SmFeN is 30 wt%. The mixed raw material is fed into an extruder, melted, sheared, and mixed at 250°C, and then extruded into a continuous strip melt, which is then cooled. The cooled strip is fed into a cutting machine and sieved, and finally the granules are dried. Step 2: Place the granules into the injection molding machine. Apply an instantaneous pulsed magnetic field to the molten magnetic powder through a pulse orientation coil set outside the first mold. The pulse voltage is 3000V, the pulse width is 20ms, and the pulse magnetic field strength is 2T, thereby orienting the molten magnetic powder with a pulsed magnetic field. Step 3: After the first orientation, the molten magnetic powder is introduced into the second mold through the nozzle. The electromagnetic orientation coil outside the second mold continuously applies a stable magnetic field to the molten magnetic powder. The orientation voltage is 400V and the orientation time is 15s. The molten magnetic powder is continuously oriented by the electromagnetic field. After the continuous electromagnetic field orientation is completed, it is cooled to obtain anisotropic injection-molded magnet.

[0027] Example 2 A method for preparing an anisotropic injection-molded magnet includes the following steps: Step 1: Mix magnetic powder with nylon 12 (12 wt% of the mixed raw material) to obtain a mixed raw material. The magnetic powder is NdFeB doped with SmFeN, and the mass ratio of SmFeN is 30 wt%. The mixed raw material is fed into an extruder, melted, sheared, and mixed at 250°C, and then extruded into a continuous strip melt, which is then cooled. The cooled strip is fed into a cutting machine and sieved, and finally the granules are dried. Step 2: Place the granules into the injection molding machine. Apply an instantaneous pulsed magnetic field to the molten magnetic powder through a pulse orientation coil set outside the first mold. The pulse voltage is 4000V, the pulse width is 20ms, and the pulse magnetic field strength is 2T, thereby orienting the molten magnetic powder with a pulsed magnetic field. Step 3: After the first orientation, the molten magnetic powder is introduced into the second mold through the nozzle. The electromagnetic orientation coil outside the second mold continuously applies a stable magnetic field to the molten magnetic powder. The orientation voltage is 400V and the orientation time is 15s. The molten magnetic powder is continuously oriented by the electromagnetic field. After the continuous electromagnetic field orientation is completed, it is cooled to obtain anisotropic injection-molded magnet.

[0028] Example 3 A method for preparing an anisotropic injection-molded magnet includes the following steps: Step 1: Mix magnetic powder with nylon 12 (10 wt% of the mixed raw material) to obtain a mixed raw material. The magnetic powder is NdFeB doped with SmFeN, and the mass ratio of SmFeN is 30 wt%. The mixed raw material is fed into an extruder. After melting, shearing, and mixing at 250°C, the mixed raw material is extruded into a continuous strip melt and cooled. The cooled strip is fed into a cutting machine and sieved. Finally, the granules are dried. Step 2: Place the granules into the injection molding machine. Apply an instantaneous pulsed magnetic field to the molten magnetic powder through a pulse orientation coil set outside the first mold. The pulse voltage is 4000V, the pulse width is 15ms, and the pulse magnetic field strength is 2T, thereby orienting the molten magnetic powder with a pulsed magnetic field. Step 3: After the first orientation, the molten magnetic powder is introduced into the second mold through the nozzle. The electromagnetic orientation coil outside the second mold continuously applies a stable magnetic field to the molten magnetic powder. The orientation voltage is 400V and the orientation time is 15s. The molten magnetic powder is continuously oriented by the electromagnetic field. After the continuous electromagnetic field orientation is completed, it is cooled to obtain anisotropic injection-molded magnet.

[0029] Example 4 A method for preparing an anisotropic injection-molded magnet includes the following steps: Step 1: Mix magnetic powder with modified nylon (modified nylon accounts for 10 wt% of the mass of the mixed raw materials) to obtain a mixed raw material, wherein the magnetic powder is NdFeB doped with SmFeN, and the mass ratio of SmFeN is 30 wt%. The mixed raw material is fed into an extruder, and after melting, shearing and mixing at 250℃, it is extruded into a continuous strip melt and cooled. The cooled strip is fed into a cutting machine and sieved, and finally the granules are dried. The preparation methods for modified nylon include: Step 1: Mix 5g of tris(2-aminoethyl)amine with 60g of dodecanoic acid, add 0.5g of NaH, and react at 180℃ for 4h under nitrogen protection to obtain the modified nylon precursor. Step 2: Mix 100g of modified nylon precursor with 15g of p-acetoxybenzoic acid, add 1g of triphenyl phosphite and 0.5g of zinc acetate, heat to 200℃ under nitrogen protection, stir and react for 2h, then heat to 220℃, reduce pressure to 50Pa, react for 3h, and finally heat to 240℃ and react under vacuum of 8Pa for 2h to obtain modified nylon.

[0030] Step 2: Place the granules into the injection molding machine. Apply an instantaneous pulsed magnetic field to the molten magnetic powder through a pulse orientation coil set outside the first mold. The pulse voltage is 4000V, the pulse width is 15ms, and the pulse magnetic field strength is 2T, thereby orienting the molten magnetic powder with a pulsed magnetic field. Step 3: After the first orientation, the molten magnetic powder is introduced into the second mold through the nozzle. The electromagnetic orientation coil outside the second mold continuously applies a stable magnetic field to the molten magnetic powder. The orientation voltage is 400V and the orientation time is 15s. The molten magnetic powder is continuously oriented by the electromagnetic field. After the continuous electromagnetic field orientation is completed, it is cooled to obtain anisotropic injection-molded magnet.

[0031] Example 5 A method for preparing an anisotropic injection-molded magnet includes the following steps: Step 1: Mix magnetic powder with modified nylon (modified nylon accounts for 10 wt% of the mass of the mixed raw materials) to obtain a mixed raw material, wherein the magnetic powder is NdFeB doped with SmFeN, and the mass ratio of SmFeN is 30 wt%. The mixed raw material is fed into an extruder, and after melting, shearing and mixing at 250℃, it is extruded into a continuous strip melt and cooled. The cooled strip is fed into a cutting machine and sieved, and finally the granules are dried. The preparation methods for modified nylon include: Step 1: Mix 5g of tris(2-aminoethyl)amine with 100g of dodecanoic acid, add 1g of NaH, and react at 180℃ for 4h under nitrogen protection to obtain the modified nylon precursor. Step 2: Mix 100g of modified nylon precursor with 20g of p-acetoxybenzoic acid, add 1g of triphenyl phosphite and 0.5g of zinc acetate, heat to 200℃ under nitrogen protection, stir and react for 2h, then heat to 220℃, reduce pressure to 50Pa, react for 3h, and finally heat to 250℃ and react under vacuum of 8Pa for 2h to obtain modified nylon.

[0032] Step 2: Place the granules into the injection molding machine. Apply an instantaneous pulsed magnetic field to the molten magnetic powder through a pulse orientation coil set outside the first mold. The pulse voltage is 4000V, the pulse width is 15ms, and the pulse magnetic field strength is 2T, thereby orienting the molten magnetic powder with a pulsed magnetic field. Step 3: After the first orientation, the molten magnetic powder is introduced into the second mold through the nozzle. The electromagnetic orientation coil outside the second mold continuously applies a stable magnetic field to the molten magnetic powder. The orientation voltage is 400V and the orientation time is 15s. The molten magnetic powder is continuously oriented by the electromagnetic field. After the continuous electromagnetic field orientation is completed, it is cooled to obtain anisotropic injection-molded magnet.

[0033] Comparative Example 1 A method for preparing an anisotropic injection-molded magnet includes the following steps: Step 1: Mix magnetic powder with thermoplastic resin nylon 12 (nylon 12 accounts for 12 wt% of the mixed raw material) to obtain a mixed raw material, wherein the magnetic powder is NdFeB doped with SmFeN, and the mass ratio of SmFeN is 30 wt%. The mixed raw material is fed into an extruder, and after melting, shearing and mixing at 250℃, it is extruded into a continuous strip melt and cooled. The cooled strip is fed into a cutting machine and sieved, and finally the granules are dried. Step 2: Place the granules into the injection molding machine. Apply a stable magnetic field to the molten magnetic powder through an electromagnetic orientation coil set outside the second mold to perform continuous electromagnetic field orientation on the molten magnetic powder. The orientation voltage is 300V and the orientation time is 10s. After the continuous electromagnetic field orientation is completed, cool to obtain anisotropic injection-molded magnets.

[0034] Comparative Example 2 A method for preparing an anisotropic injection-molded magnet includes the following steps: Step 1: Mix magnetic powder with thermoplastic resin nylon 12 (nylon 12 accounts for 12 wt% of the mixed raw material) to obtain a mixed raw material, wherein the magnetic powder is NdFeB doped with SmFeN, and the mass ratio of SmFeN is 30 wt%. The mixed raw material is fed into an extruder, and after melting, shearing and mixing, it is extruded into a continuous strip melt and cooled. The cooled strip is fed into a cutting machine and sieved, and finally the granules are dried. Step 2: Place the granules into the injection molding machine. Apply an instantaneous pulsed magnetic field to the molten magnetic powder through a pulse orientation coil set outside the first mold. The pulse voltage is 1000V, the pulse width is 20ms, and the pulse magnetic field strength is 2T, thereby orienting the molten magnetic powder with a pulsed magnetic field. After the pulsed magnetic field orientation is completed, apply a stable magnetic field to the molten magnetic powder again through an electromagnetic orientation coil 5 set outside the second mold to orient the molten magnetic powder with a continuous electromagnetic field. The orientation voltage is 300V and the orientation time is 10s. After the orientation is completed, cool to obtain an anisotropic injection-molded magnet.

[0035] The samples from Comparative Examples 1 and 2 without pulsed magnetic field orientation, and the samples without continuous electromagnetic field orientation, were compared with the samples from Examples 1-3 in terms of magnetic properties (e.g., ...). B r 、( BH ) max The following table is obtained through comparison: Table 1. Comparison of magnetic properties of anisotropic injection-molded magnets prepared in Examples 1-3 and Comparative Examples 1-2 The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0036] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing an anisotropic injection-molded magnet, characterized in that, include: A secondary orientation process, in which pulsed magnetic field orientation and continuous electromagnetic field orientation are applied sequentially to molten magnetic powder during injection molding, enables the magnetic powder to achieve effective orientation during the melting stage, thereby obtaining anisotropic injection-molded magnets with significantly improved orientation and magnetic properties.

2. The method for preparing anisotropic injection-molded magnets as described in claim 1, characterized in that, Specifically, the following steps are included: Step 1: Mix the magnetic powder and binder, feed the mixture into an extruder, and after melting, shearing and mixing, extrude it into a continuous strip melt and cool it; feed the cooled strip into a cutter and sieve it, and finally dry the granules. Step 2: Place the granules into the injection molding machine. Apply an instantaneous pulsed magnetic field to the molten magnetic powder through a pulse orientation coil set outside the first mold, thereby orienting the molten magnetic powder with a pulsed magnetic field. Step 3: The molten magnetic powder after the first orientation is introduced into the second mold through the nozzle. The electromagnetic orientation coil outside the second mold continuously applies a stable magnetic field to the molten magnetic powder to perform continuous electromagnetic field orientation. After the continuous electromagnetic field orientation is completed, it is cooled to obtain anisotropic injection-molded magnet.

3. The method for preparing anisotropic injection-molded magnets as described in claim 2, characterized in that, In step one, the magnetic powder is NdFeB doped with SmFeN, wherein the mass percentage of SmFeN is 0~40wt%.

4. The method for preparing anisotropic injection-molded magnets as described in claim 2, characterized in that, In step one, the adhesive is a thermoplastic resin.

5. The method for preparing anisotropic injection-molded magnets as described in claim 4, characterized in that, The adhesive includes one or a combination of two or more of polyamide, nylon, polyphenylene sulfide, and polyetheretherketone.

6. The method for preparing anisotropic injection-molded magnets as described in claim 2, characterized in that, The binder accounts for 8 wt% to 20 wt% of the mass of the mixed raw materials.

7. The method for preparing anisotropic injection-molded magnets as described in claim 2, characterized in that, In step one, the melting temperature is 200℃~330℃.

8. The method for preparing anisotropic injection-molded magnets as described in claim 2, characterized in that, In step two, the pulse width of the pulse magnetic field is 1μs~1000ms, the pulse magnetic field strength is 1.2~2.2T, and the orientation voltage is 1000~4000V.

9. The method for preparing anisotropic injection-molded magnets as described in claim 2, characterized in that, In step two, the duration of the electromagnetic orientation coil on the molten magnetic powder is 1~1000s, the orientation direction is the same as the direction of the pulsed magnetic field, and the orientation voltage is 200~400V.

10. The method for preparing anisotropic injection-molded magnets as described in claim 1, characterized in that, The structure of the orientation apparatus used for primary and secondary orientation of molten magnetic powder includes: The first mold has a nozzle at its front end and a pulse coil is sleeved on the outside of the first mold. The second mold has an electromagnetic orientation coil fitted on its outside.

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