Production method of sintered neodymium-iron-boron spliced magnet

Abstract

The invention discloses a production method of a sintered neodymium-iron-boron spliced magnet. The method comprises the following steps: processing a magnet to a predetermined size, cleaning and drying; dissolving solid epoxy resin, a solid latent curing agent and an accelerant by using an organic solvent to prepare an impregnating adhesive; gluing the two sides of the glass fiber cloth, and fully volatilizing a solvent to obtain pre-impregnated glass fiber cloth; after being cut, the magnetic blocks are inserted between the to-be-spliced magnets; and after being clamped by a clamp, the insulating adhesive layer is heated and cured to form a compact and pore-free insulating adhesive layer. According to the invention, air holes of the adhesive layer are thoroughly eliminated through a prepreg process, the formed insulating adhesive layer has excellent dielectric strength and insulativity, adjacent magnets can be effectively isolated, an eddy current channel can be effectively cut off, the eddy current heating problem in high-frequency application is remarkably reduced, and meanwhile, high strength and high reliability of the spliced magnet are ensured. The method is particularly suitable for the fields of motors and the like needing to reduce eddy-current loss.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rare earth permanent magnet manufacturing, in particular to a production method of large-size, high-insulation, high-strength sintered Nd-Fe-B spliced magnet. BACKGROUND

[0002] Sintered Nd-Fe-B magnets are widely used in high-end fields such as wind power, new energy vehicles, medical devices, etc. due to their extremely high magnetic energy product and coercivity. In these application scenarios, the magnets are often in a high-frequency alternating magnetic field environment. Since sintered Nd-Fe-B is a conductive metal material, it will generate significant eddy current effect in a changing magnetic field, resulting in heating of the magnet, reduction of efficiency, and even irreversible demagnetization of the magnet in severe cases.

[0003] To reduce eddy current loss, the industry adopts a scheme of dividing a large magnet into multiple small pieces and then splicing them, using an insulating adhesive layer to cut off the eddy current path. However, the existing adhesive splicing method has obvious drawbacks: 1) when using liquid epoxy adhesive, the diluent added to obtain low viscosity is prone to volatilization and residue during the curing process, forming micro pores that reduce the adhesive strength and, more importantly, the poor insulation reliability, which can easily be broken down under high pressure, failing to effectively block the eddy current; 2) liquid adhesive has strong flowability during operation and curing, which easily contaminates the non-adhesive surface of the magnet, and the thickness of the adhesive layer is difficult to control, resulting in uneven splicing gaps and affecting the precision of the magnetic circuit; 3) the heat resistance and strength of ordinary adhesives are limited, affecting the reliability of the spliced magnet in high-temperature and high-stress environments. Therefore, there is an urgent need for a sintered Nd-Fe-B magnet splicing method that can achieve excellent insulation performance, high strength, high precision, and high reliability. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art and provide a production method of sintered Nd-Fe-B spliced magnet. This method uses pre-impregnated glass fiber cloth as the adhesive material, achieving a dense adhesive layer with excellent insulation performance that can effectively block the eddy current path and significantly reduce eddy current. It also has the advantages of uniform and controllable adhesive layer thickness, high precision, high adhesive strength, good heat resistance, and effective prevention of adhesive contamination, making it particularly suitable for precise splicing of sintered Nd-Fe-B magnets.

[0005] To achieve the above-mentioned purposes, the present application adopts the following technical solutions: A production method of sintered Nd-Fe-B spliced magnet, comprising the following steps: S1. Magnet preparation: process the sintered Nd-Fe-B magnet block into the required precise size before splicing by wire cutting or grinding; then clean the processed magnet to remove oil stains and impurities and perform drying treatment; S2. Preparation of impregnating glue: mix the solid epoxy resin, latent curing agent and accelerator in proportion, add volatile organic solvent, stir until completely dissolved, and form a low-viscosity impregnating glue solution; S3. Preparation of pre-impregnated glass fiber cloth: immerse or use a doctor blade to apply the prepared impregnating glue solution on both sides of the glass fiber cloth; then, under ventilation, allow the organic solvent to fully and completely volatilize, obtaining a dry solid pre-impregnated glass fiber cloth without solvent residue; S4. Cutting of pre-impregnated material: according to the shape and size of the magnet splicing surface, accurately cut the pre-impregnated glass fiber cloth obtained in step S3; S5. Assembly: assemble the plurality of magnet blocks to be spliced and the pre-impregnated glass fiber cloth cut in step S4, ensuring that a layer of the pre-impregnated glass fiber cloth is inserted between every two adjacent magnets; S6. Curing and forming: clamp the assembled magnet group with a special clamp under uniform pressure, and then put the whole into a curing oven for heating and curing according to the set temperature rising program. Under the action of pressure, the resin in the pre-impregnated material softens and fills, and finally solidifies to form a dense epoxy resin / glass fiber composite insulating adhesive layer.

[0006] Excellent high insulation and low eddy current loss: the pre-impregnated material prepared by the present application has completely volatilized the solvent after coating, and there is no low molecular volatilization in the subsequent hot pressing and curing process, so that a dense and pore-free cured glue layer can be formed. The glue layer cooperates with the glass fiber cloth to have extremely high insulation strength and volume resistivity, which can effectively isolate adjacent magnet pieces and completely cut off the eddy current path, greatly reducing the eddy current heating problem of spliced magnets in high frequency applications.

[0007] Uniform and dense glue layer, thickness controllable: the glass fiber cloth as the framework ensures the uniform thickness of the insulating adhesive layer, improving the magnetic circuit precision. At the same time, pressure curing ensures the full infiltration of the resin to the surface of the magnet, eliminating interface defects and forming a high-strength and high-reliability adhesive interface.

[0008] High strength and high reliability: the reinforcing effect of the glass fiber cloth makes the adhesive layer have excellent shear and peel strength, which can withstand greater mechanical stress and thermal stress, ensuring the structural integrity of the spliced magnet under harsh working conditions such as high speed rotation or temperature change.

[0009] No pollution, simple operation: the pre-impregnated glass fiber cloth is in a dry state, which is clean and efficient, and facilitates precise positioning and automated production. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 The process flowchart of the method of the present application.

[0011] Figure 2 The schematic diagram of the spliced magnet structure prepared by the method of the present application. In the figure: 1 - sintered neodymium-iron-boron magnet block; 2 - dense pore-free epoxy resin / glass fiber composite insulation adhesive layer. DETAILED DESCRIPTION

[0012] The present application is further described in detail by specific examples, but the scope of protection of the present application is not limited thereto. EXAMPLE

[0013] S1. Several sintered neodymium-iron-boron magnets (N52 grade) were processed into square blocks with a size of 50mm × 50mm × 3mm by a surface grinder to ensure that the splicing surface is smooth and flat. Then they were cleaned in an ultrasonic cleaner with anhydrous ethanol for 10 minutes, and then dried in an oven at 80℃ for 1 hour.

[0014] S2. Prepare the impregnated glue: weigh 100 parts by weight of solid bisphenol A type epoxy resin (epoxy equivalent weight 600-700), 3 parts by weight of dicyandiamide (solid latent curing agent) and 0.2 parts by weight of high-efficiency urea accelerator UR500 (solid accelerator), and add them together into an appropriate amount of acetone solvent (the weight of the solvent is about 1.67 times the total weight of the solid components), mechanically stir for 4 hours until all are dissolved, forming a low-viscosity transparent glue solution.

[0015] S3. Select a plain glass fiber cloth with a thickness of 0.1mm, pass it through a container containing the impregnated glue, and use a scraper to control the glue coating on both sides to be uniform. The glass fiber cloth coated with glue is hung at room temperature for 30 minutes to allow the acetone solvent to evaporate completely, and the pre-impregnated glass fiber cloth is obtained.

[0016] S4. Use a precision knife mold to cut the pre-impregnated material into 50mm × 50mm square sheets.

[0017] S5. Assemble the dried magnet N piece and the cut pre-impregnated material N-1 piece, with the pre-impregnated material between the magnets.

[0018] S6. Place the assembled piece into a special fixture and apply a pressure of about 0.4MPa (100kg) to clamp and fix it. Then put the whole fixture into a circulating hot air oven and cure according to the following program: increase the temperature from room temperature to 180℃ at a rate of 10℃ / min, and keep the temperature for 0.75 hours; after curing is completed, cool down to below 60℃ with the oven and take out, disassemble the fixture, and the final high-strength spliced magnet is obtained.

[0019] The shear strength of the bonding layer of the spliced magnet is greater than 15 MPa after testing. Crucially, the structure of the insulating bonding layer is compact and free of visible micro pores under 100 times microscopic observation. The breakdown voltage strength of the spliced magnet is more than 15 kV / mm measured by a voltage-withstanding tester. When the spliced magnet is placed in a high-frequency alternating magnetic field, the temperature rise is reduced by more than 30% compared with a similar magnet bonded by traditional liquid glue, which significantly proves the excellent insulation and anti-eddy current capability of the spliced magnet.

Claims

1. A method for producing a sintered NdFeB spliced ​​magnet, characterized in that, Includes the following steps: a) Magnet preparation: The sintered NdFeB magnets are machined to the predetermined size and then cleaned and dried; b) Preparation of impregnation adhesive: Dissolve solid epoxy resin, solid latent curing agent and solid accelerator in volatile organic solvent to prepare a low viscosity impregnation adhesive solution; c) Preparation of pre-impregnated glass fiber cloth: The glass fiber cloth is coated on both sides with the impregnation adhesive prepared in step b). After the organic solvent has completely evaporated, a dry solid pre-impregnated glass fiber cloth with no solvent residue is obtained. d) Cutting: Cut the pre-impregnated fiberglass cloth according to the dimensions of the splicing surface; e) Assembly: Insert the pre-impregnated fiberglass cloth cut in step d) between the multiple magnets to be assembled; f) Curing: The assembled magnet assembly is clamped with a fixture and then placed in an oven for heating and pressure curing to form a dense insulating adhesive layer. According to the production method described in claim 1, the complete evaporation of the organic solvent in step c) ensures that the pre-impregnated glass fiber cloth is in a dry state for easy cutting and assembly, and forms a dense cured adhesive layer after curing.

2. The production method according to claim 1, characterized in that, The insulating adhesive layer formed in step f) is used to electrically isolate adjacent sintered NdFeB magnets to suppress eddy currents.

3. The production method according to claim 1, characterized in that, In step b), the solid epoxy resin is one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, or dicyclopentadiene type phenolic epoxy resin; the solid latent curing agent is one of dicyandiamide or adipic dihydrazide; and the solid accelerator is one of high urea accelerator, 2-methylimidazole, or 2-ethyl-4-methylimidazole.

4. The production method according to claim 1, characterized in that, In step b), the volatile organic solvent is one or more of acetone, butanone, methyl acetate, and ethyl acetate.

5. The production method according to claim 1, characterized in that, In step c), the thickness of the glass fiber cloth is 0.05mm to 0.2mm.

6. The production method according to claim 1, characterized in that, In step f), the curing process adopts programmed temperature rise, the curing temperature is 150℃ ~ 190℃, and the curing time is 0.5 ~ 4 hours; the pressure applied by the fixture is 0.2MPa ~ 1.0MPa.

7. A sintered NdFeB spliced ​​magnet prepared by the method according to any one of claims 1-7, characterized in that, The spliced ​​magnet is composed of at least two sintered NdFeB magnets joined together by a dense, non-porous epoxy resin / glass fiber composite insulating adhesive layer in the middle layer, with adjacent magnets being electrically insulated from each other.

8. The sintered NdFeB spliced ​​magnet according to claim 8, characterized in that, The breakdown voltage of the insulating adhesive layer is not less than 10kV / mm.

9. The sintered NdFeB spliced ​​magnet according to claim 8, characterized in that, The spliced ​​magnet is used in motors or generators that generate alternating magnetic fields to reduce eddy current losses.

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