A method for preparing nanocrystalline magnetic core

Abstract

A preparation method for a nanocrystalline magnetic core belongs to the field of magnetic core material technology. The preparation method comprises the following steps: winding an amorphous strip into a toroidal magnetic core; performing a two-step heat treatment on the toroidal magnetic core, including a high-temperature heat treatment of 500-600°C and a magnetic field heat treatment of 400-450°C, wherein the direction of application of the magnetic field is consistent with the axial direction of the toroidal magnetic core; impregnating and curing the magnetic core with a curing glue, wherein the curing glue comprises bisphenol A epoxy resin, epoxidized hydroxyl-terminated polybutadiene, methyltetrahydrophthalic anhydride, and polypropylene glycol diglycidyl ether; and bonding the magnetic core to a protective box with an organic silica gel, wherein the organic silica gel comprises vinyl-terminated polydimethylsiloxane, dimethyl silicone oil, a catalyst, and aluminum hydroxide. The present invention adopts a two-step heat treatment of high-temperature heat treatment and magnetic field heat treatment, and impregnates and cures the magnetic core with the curing glue, thereby improving the stability of the magnetic core in high and low temperature environments.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic core materials, and particularly relates to a method for preparing a nanocrystalline magnetic core. Background Art

[0002] Iron-based amorphous nanocrystalline alloys have excellent soft magnetic properties. Heat treatment of amorphous nanocrystalline alloys can obtain a dual-phase structure of amorphous and crystalline phases (i.e., nanocrystalline magnetic core). During the process of improving magnetic properties, the brittleness and magnetocrystalline anisotropy of the material also increase. In order to reduce the generation of debris and the influence of external stress on the magnetic properties of the alloy after heat treatment, it needs to be protected during actual use.

[0003] Conventional technology uses epoxy resin to cure and bond the magnetic core to protect it. However, during the curing process or after changes in ambient temperature, epoxy resin undergoes volume changes, which can generate stress within the core and affect its soft magnetic properties. This high volume change rate can also affect bonding performance. Therefore, to minimize the impact of epoxy resin curing on the core's soft magnetic properties, it is necessary to reduce the volume change caused by the epoxy resin. Summary of the Invention

[0004] In view of the above situation, in order to overcome at least part of the defects of the above-mentioned prior art, the present invention provides a method for preparing a nanocrystalline magnetic core.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A first aspect of the present invention provides a method for preparing a nanocrystalline magnetic core, wherein an amorphous strip is wound into a toroidal magnetic core;

[0007] The annular magnetic core is subjected to a two-step heat treatment, including a high-temperature heat treatment at 500-600° C. and a magnetic field heat treatment at 400-450° C., wherein the direction of application of the magnetic field is consistent with the axial direction of the annular magnetic core;

[0008] The magnetic core is impregnated and cured using a curing adhesive, wherein the curing adhesive comprises bisphenol A epoxy resin, epoxidized hydroxyl-terminated polybutadiene, methyltetrahydrophthalic anhydride, and polypropylene glycol diglycidyl ether;

[0009] The magnetic core is bonded to the protective box by using organic silicone, wherein the organic silicone comprises vinyl-terminated polydimethylsiloxane, dimethyl silicone oil, a catalyst and aluminum hydroxide.

[0010] In some embodiments of the present invention, in the curing adhesive, the mass ratio of bisphenol A epoxy resin, epoxidized hydroxyl-terminated polybutadiene, methyltetrahydrophthalic anhydride and polypropylene glycol diglycidyl ether is 10:(2-3):(8-10):(1-2).

[0011] In some embodiments of the present invention, the viscosity of the curing adhesive at 25° C. is 300-1000 mPa·s.

[0012] In some embodiments of the present invention, in the organic silica gel, the mass ratio of vinyl-terminated polydimethylsiloxane, dimethyl silicone oil, catalyst and aluminum hydroxide is 10:(1-3):(0.001-0.01):(3-6).

[0013] In some embodiments of the present invention, the viscosity of the organic silica gel at 25° C. is 5000-10000 mPa·s.

[0014] In some embodiments of the present invention, the specific steps of the two-step heat treatment are:

[0015] Place the toroidal core in a heat treatment furnace, under nitrogen protection, heat it to 500-600℃ at 5℃ / min, and keep it at this temperature for 60-80min;

[0016] Apply a 50-60 mT magnetic field in a heat treatment furnace, cool the sample to 400-450°C at a rate of 3°C / min, and keep the temperature for 60-80 minutes.

[0017] In some embodiments of the present invention, the dimensions of the annular magnetic core are an outer diameter of 30-40 mm, an inner diameter of 20-25 mm, a height of 10-15 mm, and a gap between winding layers of ≤0.1 mm.

[0018] In some embodiments of the present invention, the impregnation curing conditions of the curing adhesive include:

[0019] Vacuum impregnation pressure ≤ 0.1MPa;

[0020] The curing temperature is 80-120℃ and the curing time is ≥4h.

[0021] In some embodiments of the present invention, the organic silicone is dispensed in a manner of evenly distributing 3-6 dispensing locations along the circumference of the magnetic core, with a single dispensing amount of 0.1-0.3 g.

[0022] In some embodiments of the present invention, the material of the protection box is polyphenylene sulfide or liquid crystal polymer with a temperature resistance of -60°C to 200°C.

[0023] The beneficial effects achieved by the present invention are as follows:

[0024] The present invention employs a two-step heat treatment process involving high-temperature heat treatment and magnetic field heat treatment to reduce the remanence of the magnetic core and simultaneously adjust its coercive force, making the core more stable in high and low temperature environments. This makes it suitable for high-frequency transformers or inductors. Furthermore, the core is impregnated and cured with a curing adhesive comprising bisphenol A epoxy resin, epoxidized hydroxyl-terminated polybutadiene, methyltetrahydrophthalic anhydride, and polypropylene glycol diglycidyl ether. This reduces the internal stress of the epoxy resin after curing and the effect of ambient temperature on its volume, further improving the core's stability in high and low temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure is a flow chart of a method for preparing a nanocrystalline magnetic core according to an embodiment of the present invention.

[0026] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods and materials similar or equivalent to those described herein can be applied to the present invention. The preferred embodiments and materials described herein are for illustrative purposes only and are not intended to limit the scope of this application.

[0029] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0030] Reference Figure 1In response to the deficiencies in the prior art mentioned in the background technology, an embodiment of the present invention provides a method for preparing a nanocrystalline magnetic core, comprising the following steps: winding an amorphous strip into a toroidal magnetic core; subjecting the toroidal magnetic core to a two-step heat treatment, comprising a high-temperature heat treatment at 500-600°C and a magnetic field heat treatment at 400-450°C, wherein the direction of application of the magnetic field is consistent with the axial direction of the toroidal magnetic core; impregnating and curing the magnetic core with a curing glue comprising bisphenol A epoxy resin, epoxidized hydroxy-terminated polybutadiene, methyltetrahydrophthalic anhydride and polypropylene glycol diglycidyl ether; and bonding the magnetic core to a protective box with an organic silicone gel comprising vinyl-terminated polydimethylsiloxane, dimethyl silicone oil, a catalyst and aluminum hydroxide.

[0031] First, the closed magnetic circuit of the ring core makes the magnetic field lines evenly distributed along the circumference. By spirally winding the amorphous strip into a ring, the edge magnetic leakage problem of the open magnetic circuit structure can be avoided, thereby reducing the magnetic leakage rate of the core. Among them, the amorphous strip can be made of iron-based nanocrystalline alloy strip with a composition range of Fe 73.5-75 Cu 1-1.5 Nb 2-3 Si 14-16 B 6-8 , strip thickness t = 16-18μm, surface roughness Ra ≤ 0.2μm. In addition, the outer strip ends can be fixed by laser welding.

[0032] Secondly, the primary goal of high-temperature heat treatment is to optimize the microstructure of the core material. During processing (winding, welding, etc.), the core material generates internal stresses that hinder the free movement of magnetic domains, leading to increased hysteresis losses. High-temperature heat treatment releases these stresses through atomic diffusion at high temperatures. Simultaneously, at high temperatures, the core material's grains rearrange and grow, resulting in a more uniform grain size and orientation, thereby reducing the core's coercivity and increasing its permeability. The primary goal of magnetic field heat treatment is to induce directional alignment of magnetic domains. When a magnetic field is applied during the cooling process, the magnetic domains align along the magnetic field, forming uniaxial magnetic anisotropy. This directional alignment significantly reduces hysteresis and eddy current losses. Furthermore, the magnetic field reduces remanence and adjusts the coercivity, making the core more stable in high and low temperature environments, making it suitable for high-frequency transformers or inductors.

[0033] Then, the impregnation and curing in the step can fill the pores of the magnetic core and reduce magnetic leakage. In the curing glue, bisphenol A epoxy resin as the matrix resin mainly provides adhesion, mechanical strength and heat resistance. Its bisphenol A structure gives the resin rigidity, ensuring the dimensional stability and high-temperature performance of the cured material. The polybutadiene main chain of the epoxidized hydroxy-terminated polybutadiene is a flexible long-chain structure. Through the epoxy group and the epoxy resin co-curing, a rigid-flexible interpenetrating network can be formed, reducing the volume shrinkage of the epoxy resin during the curing process. The anhydride group of methyltetrahydrophthalic anhydride and the epoxy group undergo nucleophilic addition reaction under heating conditions to generate ester bonds and hydroxyl groups to form a three-dimensional cross-linked structure. More importantly, methyltetrahydrophthalic anhydride is a liquid anhydride. After mixing with the epoxy resin, it has good fluidity and is easy to impregnate and penetrate. At the same time, the curing process of methyltetrahydrophthalic anhydride is exothermic, thereby reducing the internal stress of the epoxy resin after curing. The addition of polypropylene glycol diglycidyl ether can reduce the viscosity of the cured adhesive and improve the impregnation permeability. In addition, its long-chain polypropylene glycol structure provides flexibility, and the epoxy groups in the molecule can react with the resin and curing agent, making the long-chain polypropylene glycol structure a part of the cross-linked network, thereby reducing the impact of ambient temperature on the volume of epoxy resin.

[0034] Finally, the protective box secures the magnetic core by bonding, providing stable mechanical support and preventing displacement. In the silicone rubber, vinyl-terminated polydimethylsiloxane serves as the main component, providing bonding strength, flexibility, and high-temperature resistance. The addition of dimethyl silicone oil adjusts the colloid viscosity, improving fluidity and facilitating filling the gap between the magnetic core and the protective box. Furthermore, dimethyl silicone oil enhances the flexibility of the cured adhesive layer and reduces the stress generated by the silicone rubber after bonding and curing. Nano-sized aluminum hydroxide particles fill the colloid micropores, enhancing the tear resistance and hardness of the silicone rubber. A catalyst is used to trigger and accelerate the hydrosilylation reaction, completing the cross-linking and curing process. Preferably, the catalyst is a platinum catalyst or a peroxide initiator.

[0035] In some embodiments, in the curing glue, the mass ratio of bisphenol A epoxy resin, epoxidized hydroxyl-terminated polybutadiene, methyltetrahydrophthalic anhydride and polypropylene glycol diglycidyl ether is 10: (2-3): (8-10): (1-2). Among them, if the amount of epoxidized hydroxyl-terminated polybutadiene added is too much, the phase separation risk of the curing glue increases, the mechanical strength decreases, the crosslinking density decreases, and the heat resistance and solvent resistance deteriorate. If the amount of epoxidized hydroxyl-terminated polybutadiene added is too little, the effect of reducing the volume shrinkage of the epoxy resin is insufficient. If the amount of methyltetrahydrophthalic anhydride added is too much, unreacted acid anhydride remains, resulting in increased hygroscopicity of the magnetic core material and decreased electrical insulation. If the amount of methyltetrahydrophthalic anhydride added is too little, the curing is incomplete, and the cured magnetic core material has low hardness and poor heat resistance. If the amount of polypropylene glycol diglycidyl ether added is too much, the cross-linking density will be insufficient, and the mechanical strength and heat resistance of the magnetic core material will be significantly reduced. If the amount of polypropylene glycol diglycidyl ether added is too little, the viscosity of the cured glue will be too high and the fluidity will be poor, making it difficult to fill the micropores of the magnetic core, resulting in incomplete impregnation.

[0036] In some embodiments, the viscosity of the curing glue at 25°C is 300-1000mPa·s. In the magnetic core impregnation process, the viscosity of the curing glue is a key parameter that determines its process adaptability and final performance. Controlling the viscosity within the range of 300-1000mPa·s (25°C) can balance permeability, process efficiency and curing effect. If the viscosity of the curing glue is less than 300, the low-viscosity glue may quickly penetrate into the pores of the magnetic core, but due to excessive fluidity, the surface glue layer is too thin or even unable to form an effective protective layer, resulting in poor performance of the magnetic core; if the viscosity of the curing glue is greater than 1000, the high viscosity restricts molecular motion, resulting in local cross-linking density differences, increasing the internal stress of the magnetic core material after curing, and also causing the magnetic properties of the magnetic core to decline.

[0037] In some embodiments, the mass ratio of vinyl-terminated polydimethylsiloxane, dimethyl silicone oil, catalyst, and aluminum hydroxide in the organic silica gel is 10:(1-3):(0.001-0.01):(3-6). Excessive addition of dimethyl silicone oil will result in insufficient crosslinking density, making the organic silica gel colloid prone to creep; while insufficient addition of dimethyl silicone oil will result in poor fluidity of the organic silica gel, making it difficult to fill the gap between the magnetic core and the protective box; excessive addition of the catalyst will trigger side reactions, while insufficient addition will result in slow curing; excessive addition of aluminum hydroxide will reduce the fluidity of the organic silica gel, while insufficient addition of aluminum hydroxide will prevent the colloid micropores from being fully filled, resulting in decreased performance of the organic silica gel.

[0038] In some embodiments, the viscosity of organic silicone at 25°C is 5,000-10,000 mPa·s. During the organic silicone dispensing process, the assembly gap between the magnetic core and the protective box is typically 0.1-0.5 mm. If the viscosity of the organic silicone is too low, it will easily flow downward during vertical coating, resulting in uneven adhesive layer thickness. If the viscosity of the organic silicone is too high, the organic silicone colloid will have difficulty penetrating the microscopic roughness of the protective box surface, resulting in a reduced actual bonding area and a decrease in interfacial bonding strength.

[0039] In some embodiments, the two-step heat treatment process involves placing the toroidal core in a heat treatment furnace and, under nitrogen protection, heating the core at a rate of 5°C / min to 500-600°C and holding for 60-80 minutes. A magnetic field of 50-60 mT is then applied to the furnace, followed by cooling the core at a rate of 3°C / min to 400-450°C and holding for 60-80 minutes. The high-temperature (500-600°C) heat treatment is primarily used for structural optimization. However, at high temperatures, magnetic domains are too active to effectively orient the magnetic field (thermal disturbances can disrupt the domain alignment). By applying the magnetic field at a lower temperature (400-450°C), the core material retains sufficient atomic mobility to respond to the magnetic field while minimizing thermal disturbances, resulting in more stable magnetic properties. The high-temperature heat treatment prioritizes addressing structural defects, while the magnetic field heat treatment optimizes magnetic properties. The two steps are synergistic but not interchangeable.

[0040] In some embodiments, a magnetic field is applied by arranging permanent magnetic materials on the upper and lower sides of a heat treatment furnace, wherein the opposite magnetic poles of the permanent magnetic materials are opposite (e.g., the upper side is the N pole and the lower side is the S pole), and the magnetic field lines pass vertically from the upper N pole through the heat treatment furnace to the lower S pole, forming a magnetic field in the upper and lower directions, and during the heat treatment process, the axial direction of the annular magnetic core is consistent with the direction of the magnetic field.

[0041] In some embodiments, the toroidal core has an outer diameter of 30-40 mm, an inner diameter of 20-25 mm, a height of 10-15 mm, and a gap of 0.1 mm or less between winding layers. The difference between the outer and inner diameters (5-15 mm) creates a moderate toroidal cross-sectional area, ensuring uniform distribution of magnetic flux density at high frequencies and avoiding local saturation. Tight winding to a gap of 0.1 mm or less between layers can suppress magnetic leakage and reduce eddy current losses.

[0042] In some embodiments, the curing conditions for the curing adhesive include: a vacuum impregnation pressure ≤ 0.1 MPa; a curing temperature of 80-120°C; and a curing time of ≥ 4 hours. The vacuum pressure draws out air and volatile substances from the pores of the magnetic core, preventing residual bubbles after curing and improving the magnetic properties of the cured core. A curing temperature of 80-120°C and a curing time of ≥ 4 hours ensures that the magnetic core is fully impregnated and cured.

[0043] In some embodiments, the silicone adhesive is dispensed in 3-6 locations evenly distributed around the circumference of the magnetic core, with a single dispense volume of 0.1-0.3g. This even distribution of adhesive dots reduces the air gap between the core and the housing, minimizing losses and interference in electromagnetic signal transmission. For example, in high-frequency electronic devices, this design can effectively improve magnetic field uniformity and reduce parasitic capacitance between the core and coil, thereby ensuring stable electrical performance.

[0044] In some embodiments, the protective box is made of polyphenylene sulfide or liquid crystal polymer, which is temperature-resistant from -60°C to 200°C. Using polyphenylene sulfide or liquid crystal polymer can improve the stability of the magnetic core in extreme high and low temperature conditions, adapting to the needs of extreme environments such as automotive engine compartments and aerospace equipment.

[0045] The present invention will be further described below by way of specific embodiments.

[0046] The experimental methods in the following examples are conventional methods unless otherwise specified; the experimental materials used in the following examples are purchased from commercial channels unless otherwise specified.

[0047] Example 1: An amorphous ribbon is wound into a toroidal magnetic core using an automatic amorphous ribbon winding machine.

[0048] The annular magnetic core was placed in a heat treatment furnace. Under nitrogen protection, the temperature was raised to 600°C at a rate of 5°C / min and kept at that temperature for 60 minutes. A 50mT magnetic field was applied in the heat treatment furnace. The direction of the applied magnetic field was consistent with the axial direction of the annular magnetic core. The temperature was lowered to 400°C at a rate of 3°C / min and kept at that temperature for 60 minutes.

[0049] The magnetic core is impregnated and cured with curing glue. In the curing glue, the mass ratio of bisphenol A epoxy resin, epoxidized terminal hydroxyl polybutadiene, methyl tetrahydrophthalic anhydride and polypropylene glycol diglycidyl ether is 10:2:8:1. The curing adopts vacuum impregnation pressure ≤0.1MPa, curing temperature is 80-120℃, and curing time is ≥4h.

[0050] Use organic silicone to bond the magnetic core to the protective box. The mass ratio of vinyl-terminated polydimethylsiloxane, dimethyl silicone oil, catalyst and aluminum hydroxide in the organic silicone is 10:3:0.01:6. The glue is dispensed in 6 locations evenly distributed along the circumference of the magnetic core, with a single glue dispense amount of 0.3g.

[0051] Example 2: An amorphous ribbon is wound into a toroidal magnetic core using an automatic amorphous ribbon winding machine.

[0052] The annular magnetic core was placed in a heat treatment furnace. Under nitrogen protection, the temperature was raised to 500°C at a rate of 5°C / min and kept at that temperature for 80 minutes. A 60mT magnetic field was applied in the heat treatment furnace. The direction of the magnetic field was consistent with the axial direction of the annular magnetic core. The temperature was lowered to 450°C at a rate of 3°C / min and kept at that temperature for 80 minutes.

[0053] The magnetic core is impregnated and cured with curing glue. In the curing glue, the mass ratio of bisphenol A epoxy resin, epoxidized terminal hydroxyl polybutadiene, methyl tetrahydrophthalic anhydride and polypropylene glycol diglycidyl ether is 10:3:10:2. The curing adopts vacuum impregnation pressure ≤0.1MPa, curing temperature is 120℃, and curing time is ≥4h.

[0054] Use organic silicone to bond the magnetic core to the protective box. The mass ratio of vinyl-terminated polydimethylsiloxane, dimethyl silicone oil, catalyst, and aluminum hydroxide in the organic silicone is 10:1:0.001:3. The glue is dispensed at three locations evenly distributed along the circumference of the magnetic core, with a single glue dispense amount of 0.1g.

[0055] Example 3:

[0056] The same as Example 1, except that, in the curing glue, the mass ratio of bisphenol A epoxy resin, epoxidized hydroxyl-terminated polybutadiene, methyltetrahydrophthalic anhydride and polypropylene glycol diglycidyl ether is 10:2.5:9:1.5.

[0057] Example 4:

[0058] The same as Example 1, except that, in the curing glue, the mass ratio of bisphenol A epoxy resin, epoxidized hydroxyl-terminated polybutadiene, methyltetrahydrophthalic anhydride and polypropylene glycol diglycidyl ether is 10:3:10:1.

[0059] Example 5:

[0060] The same as Example 1, except that, in the curing glue, the mass ratio of bisphenol A epoxy resin, epoxidized hydroxyl-terminated polybutadiene, methyltetrahydrophthalic anhydride and polypropylene glycol diglycidyl ether is 10:2:8:3.

[0061] Comparative Example 1:

[0062] The method is consistent with Example 1, except that no magnetic field is introduced in the heat treatment step, that is, the annular magnetic core is placed in a heat treatment furnace, and under nitrogen protection, the temperature is raised to 500° C. at 5° C. / min and kept warm for 120 minutes.

[0063] Comparative Example 2:

[0064] The same as Example 1, except that a commercially available curing adhesive is used, the main components of which are epoxy resin and polyamide, and the mass ratio of epoxy resin to polyamide is about 10:3.

[0065] Examples 1-5 and Comparative Examples 1 and 2 were tested, and the test contents are as follows:

[0066] Viscosity test of curing glue and organic silicone: Use a rotational viscometer. First, place the curing glue or organic silicone in a vacuum degassing machine and degas at -0.08MPa for 5 minutes to eliminate internal bubbles. Transfer the sample to a constant temperature water bath and let it stand for 30 minutes until the temperature is uniform (25±0.5℃). Slowly immerse the rotor in the sample to the marked line, start the viscometer, select a speed of 20rpm, and record three consecutive measurement values after stabilization. The average value is taken as the final result.

[0067] Core performance testing: The single-turn inductance and impedance of the core were measured using an impedance analyzer at a test frequency of 100kHz. A two-slot thermal shock chamber was used to provide high and low temperature shock conditions. The test chamber was stored at 130°C for 30 minutes, then at -40°C for 30 minutes, with the transition time no longer than 2 minutes. This constituted one cycle. This cycle was repeated 500 times, with the sample removed after every 100 cycles, returned to room temperature, and allowed to rest for 8 hours before testing.

[0068] The test results are shown in Table 1.

[0069] Table 1

[0070]

[0071] Referring to the viscosity test results in Table 1, the viscosity of the curing agents of Examples 1-5 is between 300 and 1000 mPa·s, and the viscosity of the organic silica gel is between 5000 and 10000 mPa·s. The viscosity of the curing agent of Comparative Example 2 is much greater than that of the curing agents of Examples 1-5.

[0072] Referring to the performance test results of the magnetic core in Table 1, the inductance change rate of Examples 1-5 is small, indicating that the performance consistency of Examples 1-5 is good and they perform well under high and low temperature shock conditions. The inductance change rate of Comparative Example 1 is -5.21%, which is a significant decrease compared to Example 1, indicating that the introduction of a magnetic field during the heat treatment step can improve the performance of the magnetic core under high and low temperature shock conditions. The inductance change rate of Comparative Example 2 is -7.68%, which is an even greater decrease compared to Example 1, indicating that the use of the curing agent of the present invention can improve the performance of the magnetic core under high and low temperature shock conditions.

[0073] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, and all of these should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a nanocrystalline magnetic core, characterized in that: The following steps are involved: Winding the amorphous strip into a toroidal magnetic core; The annular magnetic core is subjected to a two-step heat treatment, including a high-temperature heat treatment at 500-600° C. and a magnetic field heat treatment at 400-450° C., wherein the direction of application of the magnetic field is consistent with the axial direction of the annular magnetic core; The magnetic core is impregnated and cured using a curing adhesive, wherein the curing adhesive comprises bisphenol A epoxy resin, epoxidized hydroxyl-terminated polybutadiene, methyltetrahydrophthalic anhydride, and polypropylene glycol diglycidyl ether, wherein the mass ratio of the bisphenol A epoxy resin, epoxidized hydroxyl-terminated polybutadiene, methyltetrahydrophthalic anhydride, and polypropylene glycol diglycidyl ether is 10:(2-3):(8-10):(1-2), and the viscosity of the curing adhesive at 25° C. is 300-1000 mPa·s; The magnetic core is bonded to the protective box by using organic silicone, wherein the organic silicone comprises vinyl-terminated polydimethylsiloxane, dimethyl silicone oil, a catalyst and aluminum hydroxide.

2. The preparation method according to claim 1, characterized in that In the organic silica gel, the mass ratio of vinyl-terminated polydimethylsiloxane, dimethyl silicone oil, catalyst and aluminum hydroxide is 10:(1-3):(0.001-0.01):(3-6).

3. The preparation method according to claim 2, characterized in that The viscosity of the organic silica gel at 25° C. is 5000-10000 mPa·s.

4. The preparation method according to claim 1, characterized in that The two-step heat treatment is specifically as follows: Place the toroidal core in a heat treatment furnace, under nitrogen protection, heat it to 500-600℃ at 5℃ / min, and keep it at this temperature for 60-80min; Apply a 50-60 mT magnetic field in a heat treatment furnace, cool the sample to 400-450°C at a rate of 3°C / min, and keep the temperature for 60-80 minutes.

5. The preparation method according to claim 1, characterized in that The dimensions of the annular magnetic core are an outer diameter of 30-40 mm, an inner diameter of 20-25 mm, a height of 10-15 mm, and a gap between winding layers of ≤0.1 mm.

6. The preparation method according to claim 1, characterized in that The impregnation and curing conditions of the curing adhesive include: Vacuum impregnation pressure ≤ 0.1MPa; The curing temperature is 80-120℃ and the curing time is ≥4h.

7. The preparation method according to claim 1, characterized in that The dispensing method of the organic silica gel is to evenly distribute 3-6 dispensing positions along the circumference of the magnetic core, and the amount of each dispensing position is 0.1-0.3g.

8. The preparation method according to claim 1, characterized in that The material of the protection box is polyphenylene sulfide or liquid crystal polymer which is temperature-resistant from -60°C to 200°C.

Images