A method for preparing an amorphous nanocrystalline magnetic core with stable performance

Abstract

The application provides a preparation method of an amorphous nanocrystalline magnetic core with stable performance, and relates to the technical field of magnetic core preparation, and comprises the following steps: winding an amorphous nanocrystalline strip into a magnetic core; placing the magnetic core into a heat treatment furnace for heat treatment and then cooling to room temperature to obtain a heat-treated magnetic core; preheating the heat-treated magnetic core; immersing the preheated magnetic core into a previously prepared and heat-preserved paint for vacuum immersion and then baking and curing to obtain an amorphous nanocrystalline magnetic core with stable performance; and the preparation method of the paint comprises the following steps: mixing and preparing a paint by using a resin, an ester compound and an organic solvent, and then heat-preservation of the paint. The magnetic core prepared has excellent high-frequency performance, the magnetic core inductance attenuation is small, and the attenuation rate is lower than 5%, so that the inductance prepared by using the amorphous nanocrystalline magnetic core with stable performance has excellent DC bias resistance, the application range of the magnetic core is expanded, the stability of the magnetic core in operation is ensured, and the design of the magnetic device and the function realization are facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic core preparation, in particular to a preparation method of amorphous nanocrystalline magnetic core with stable performance. BACKGROUND

[0002] With the increasing popularity of electronic devices and the development towards high frequency, small size, light weight and integration, as an important supporting component of electronic information industry, the application field of magnetic cores is gradually expanding. The expansion of various emerging fields puts forward higher performance requirements for magnetic elements such as magnetic cores. The performance of electronic devices is closely related to the internal components such as magnetic cores, in order to realize the high efficiency and miniaturization of power electronic devices, more and higher requirements are put forward for soft magnetic materials. At present, power electronic devices inevitably exist in electronic circuits due to leakage current and capacitive coupling, therefore, it is necessary to design EMI common mode inductance in the circuit with certain anti-saturation ability and anti-DC-bias (anti-direct current bias) characteristics, which also puts forward higher requirements for the performance of magnetic cores.

[0003] Although the existing nanocrystalline magnetic core has good high permeability and low loss, it has insufficient anti-saturation ability and anti-DC-bias characteristics, and will quickly saturate in a circuit with a direct current component, which easily causes poor EMI filtering effect, hindering the development and application of magnetic cores; in addition, although the magnetic core prepared by the traditional magnetic core preparation method can meet the magnetic performance, once the winding and boxing are formed into a common mode inductance, the magnetic core inductance decays seriously, which is not conducive to the design and function realization of magnetic devices. SUMMARY

[0004] In view of the problems in the prior art, the present application provides a preparation method of amorphous nanocrystalline magnetic core with stable performance, comprising:

[0005] Step S1, winding: winding the amorphous nanocrystalline strip into a magnetic core;

[0006] Step S2, heat treatment: placing the magnetic core in a heat treatment furnace for heat treatment and cooling to room temperature to obtain a heat-treated magnetic core;

[0007] Step S3, pretreatment: preheating the heat-treated magnetic core;

[0008] Step S4, varnish immersion and curing: immersing the preheated magnetic core in a pre-prepared and temperature-maintained varnish for vacuum immersion and baking curing to obtain an amorphous nanocrystalline magnetic core with stable performance;

[0009] The preparation method of the varnish comprises:

[0010] Mixing and configuring the resin, ester compound and organic solvent to prepare the varnish, and then temperature-maintaining the varnish.

[0011] Preferably, the step S2 comprises:

[0012] Step S21, placing the magnetic core into the heat treatment furnace, and increasing the heat treatment temperature of the heat treatment furnace from room temperature to a first temperature increasing temperature within a first temperature increasing time, and then holding for a first holding time;

[0013] Step S22, increasing the heat treatment temperature from the first temperature increasing temperature to a second temperature increasing temperature within a second temperature increasing time, and then holding for a second holding time;

[0014] Step S23, increasing the heat treatment temperature from the second temperature increasing temperature to a third temperature increasing temperature within a third temperature increasing time, and then holding for a third holding time;

[0015] Step S24, decreasing the heat treatment temperature from the third temperature increasing temperature to a first temperature decreasing temperature within a first temperature decreasing time, then holding for a fourth holding time, and applying a transverse magnetic field within the fourth holding time;

[0016] Step S25, decreasing the heat treatment temperature from the first temperature decreasing temperature to a second temperature decreasing temperature, and then furnace cooling to room temperature.

[0017] Preferably, the first temperature increasing time is 50-120 min, the first temperature increasing temperature is 300-370℃, and the first holding time is 20-60 min;

[0018] The second temperature increasing time is 30-80 min, the second temperature increasing temperature is 370-490℃, and the second holding time is 60-120 min;

[0019] The third temperature increasing time is 60-100 min, the third temperature increasing temperature is 520-580℃, and the third holding time is 100-150 min;

[0020] The first temperature decreasing time is 30-60 min, the first temperature decreasing temperature is 500-530℃, the fourth holding time is 100-300 min, and the current of the transverse magnetic field is 50-65 A;

[0021] The second temperature decreasing temperature is below 120℃.

[0022] Preferably, in the step S3, the pretreatment is to preheat the heat-treated magnetic core at 75-85℃ for 30-50 min.

[0023] Preferably, in the preparation of the glue paint, the glue paint is prepared by mixing the resin in a mass ratio of 10%-20%, the ester compound in a mass ratio of 40%-60%, and the organic solvent, and then the glue paint is incubated at 71-80°C for 20-40 min.

[0024] Preferably, the resin is at least one of epoxy resin, polyurethane, silicone resin, organosilicon resin, polyimide, cyanate ester, and acrylic resin.

[0025] Preferably, the ester compound is at least one of propylene glycol monoether acetate, polyacrylate, and aromatic isocyanate.

[0026] Preferably, the organic solvent is one of ethanol, diethyl ether, ethyl acetate, acetone, dimethylbenzene, toluene, and cyclohexane.

[0027] Preferably, in the step S4, the vacuum impregnation time is 10-30 s.

[0028] Preferably, in the step S4, the baking curing temperature is 120-180°C, and the baking time is 1-2 h.

[0029] The above technical solution has the following advantages or beneficial effects:

[0030] 1) The amorphous nanocrystalline magnetic core prepared by the technical solution has excellent high-frequency performance, the magnetic core inductance decay is small, and the decay rate is less than 5%, so that the inductance prepared by using the amorphous nanocrystalline magnetic core has excellent DC bias resistance, expands the application range of the magnetic core, ensures the stability of the magnetic core in work, and is beneficial to the design of the magnetic device and the realization of its function.

[0031] 2) The preparation method is simple in process and convenient to operate, the prepared amorphous nanocrystalline magnetic core is stable in performance and good in consistency, low in cost, and can be mass-produced. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 In a preferred embodiment of the present application, a flowchart of a preparation method of an amorphous nanocrystalline magnetic core with stable performance is shown.

[0033] Figure 2 In a preferred embodiment of the present application, a sub-flowchart of step S2 is shown.

[0034] Figure 3 A comparison chart of DC biasing capacity of the magnetic cores prepared in each embodiment and the comparative example is shown. DETAILED DESCRIPTION

[0035] The application will be described in detail below with reference to the drawings and specific embodiments. The application is not limited to this embodiment, and other embodiments can also fall within the scope of the application as long as they meet the main idea of the application.

[0036] In a preferred embodiment of the application, based on the above problems existing in the prior art, a preparation method of an amorphous nanocrystalline magnetic core with stable performance is provided, as shown in the formula: Figure 1 The preparation method comprises the following steps:

[0037] Step S1, winding: winding the amorphous nanocrystalline strip into a magnetic core;

[0038] Step S2, heat treatment: placing the magnetic core in a heat treatment furnace for heat treatment, and then cooling to room temperature to obtain a heat-treated magnetic core;

[0039] Step S3, pretreatment: preheating the heat-treated magnetic core;

[0040] Step S4, varnish immersion and curing: immersing the preheated magnetic core in a pre-prepared and temperature-maintained varnish for vacuum immersion, and then baking and curing to obtain an amorphous nanocrystalline magnetic core with stable performance;

[0041] The preparation method of the varnish comprises the following steps:

[0042] Mixing and configuring the varnish by mixing the resin, the ester compound and the organic solvent, and then temperature-maintaining the varnish.

[0043] Specifically, in this embodiment, the amorphous nanocrystalline strip is wound into a magnetic core by a winding machine, and then the magnetic core is heat-treated. The heat treatment preferably comprises three heating stages, one temperature-maintaining stage is performed for each heating stage, one cooling stage is performed after the completion of the third temperature-maintaining stage, and then one temperature-maintaining stage is performed. After the temperature-maintaining stage is completed, the heat treatment furnace is discharged for air cooling to room temperature to obtain a heat-treated magnetic core. Further, a transverse magnetic field is applied synchronously during the temperature-maintaining stage after the first cooling stage, as shown in the formula: Figure 2 The step S2 comprises the following steps:

[0044] Step S21, placing the magnetic core in a heat treatment furnace, and increasing the heat treatment temperature of the heat treatment furnace from room temperature to a first heating temperature within a first heating time, and then temperature-maintaining for a first temperature-maintaining time;

[0045] Step S22, increasing the heat treatment temperature from the first heating temperature to a second heating temperature within a second heating time, and then temperature-maintaining for a second temperature-maintaining time;

[0046] Step S23, increasing the heat treatment temperature from the second heating temperature to a third heating temperature within a third heating time, and then temperature-maintaining for a third temperature-maintaining time;

[0047] Step S24, the heat treatment temperature is decreased from the third temperature increasing temperature to the first temperature decreasing temperature in the first temperature decreasing time, then kept for the fourth holding time, and a transverse magnetic field is applied in the fourth holding time;

[0048] Step S25, the heat treatment temperature is decreased from the first temperature decreasing temperature to the second temperature decreasing temperature, then out of the furnace and cooled to room temperature.

[0049] In the preferred embodiment of the present application, the first temperature increasing time is 50-120 min, the first temperature increasing temperature is 300-370℃, and the first holding time is 20-60 min;

[0050] The second temperature increasing time is 30-80 min, the second temperature increasing temperature is 370-490℃, and the second holding time is 60-120 min;

[0051] The third temperature increasing time is 60-100 min, the third temperature increasing temperature is 520-580℃, and the third holding time is 100-150 min;

[0052] The first temperature decreasing time is 30-60 min, the first temperature decreasing temperature is 500-530℃, the fourth holding time is 100-300 min, and the current of the transverse magnetic field is 50-65 A;

[0053] The second temperature decreasing temperature is below 120℃.

[0054] After the heat treatment, the prepared heat-treated magnetic core is preheated at 75-85℃ for 30-50 min in step S3 to ensure the impregnation effect. At the same time, the prepared paint is kept warm, so that the paint has strong activity and low viscosity. Then, when the preheated magnetic core is placed in the vacuum impregnation of the kept warm paint, the paint can enter the inside of the magnetic core through its own gravity, ensuring the surface of the magnetic core is clean, which is beneficial to the subsequent cutting of the magnetic core. After vacuum impregnation and baking and curing, the paint can quickly form a sealing film on the surface of the magnetic core at high temperature, ensuring that the paint stays inside the magnetic core, solving the problems of paint leakage and low strength in the conventional method. At the same time, the high strength and low stress of the paint protect the DC bias resistance of the magnetic core. Finally, the inductance decay rate of the prepared magnetic core is reduced from 12.23% to 4.09% at 100 kHz / 0.3 V under the condition of applying a 1.5 A DC current, the inductance decay is low, and the DC bias resistance is strong.

[0055] In the preferable embodiment of the present application, in the preparation method of the glue paint, the glue paint is prepared according to the mixing ratio of 10%-20% of the mass ratio of the resin, 40%-60% of the mass ratio of the ester compound, and the rest of the organic solvent, and then the glue paint is kept at 71-80°C for 20-40 min.

[0056] In the preferable embodiment of the present application, the resin is at least one of epoxy resin, polyurethane, silicone resin, organosilicon resin, polyimide, cyanate resin and acrylic resin.

[0057] In the preferable embodiment of the present application, the ester compound is at least one of propylene glycol monoether acetate, polyacrylate and aromatic isocyanate.

[0058] In the preferable embodiment of the present application, the organic solvent is one of ethanol, diethyl ether, ethyl acetate, acetone, dimethylbenzene, toluene and cyclohexane.

[0059] In the preferable embodiment of the present application, in step S4, the vacuum impregnation time is 10-30 s.

[0060] In the preferable embodiment of the present application, in step S4, the baking curing temperature is 120-180°C, and the baking time is 1-2 h.

[0061] Embodiment 1

[0062] Fe-Si-B-Nb-Cu iron-based nanocrystalline soft magnetic alloy strips with an average thickness of 20±2 μm are selected, and the performance-stable amorphous nanocrystalline magnetic core is prepared by using the preparation method of the present application. In order to test the performance, the iron core is prepared into a circular ring in this embodiment, and the specific steps are as follows:

[0063] Winding: according to the size requirements of the magnetic core, the nanocrystalline strip is wound into multiple magnetic cores with a size of 50*35*20 mm by an automatic winding machine;

[0064] Heat treatment: the magnetic core is placed in a magnetic field heat treatment furnace, and is first heated to 350°C for 100 min and kept for 30 min, then heated to 400°C for 50 min, kept for 100 min, finally heated to 550°C for 80 min, kept for 120 min, then cooled, cooled to 520°C for 40 min, and kept for 200 min, and a transverse magnetic field with a current of 55 A is applied during the keeping stage, after the keeping stage, the temperature is reduced to below 120°C, and then cooled to room temperature;

[0065] Pre-treatment: the magnetic core after the heat treatment is preheated at 75°C for 40 min;

[0066] The glue paint is prepared by mixing and stirring epoxy resin, propylene glycol monoether acetate and acetone in a mass ratio of 3:9:8;

[0067] The prepared glue paint in the vacuum paint dipping equipment is preheated at 75°C for 30 min, then the preheated magnetic core is dipped in the glue paint, vacuum impregnated for 20 s, and then taken out and placed in an oven at 150°C for baking for 90 min to obtain the cured nanocrystalline magnetic core.

[0068] Ten magnetic cores prepared in Example 1 are selected, and the selected magnetic cores are tested for performance. The test method is as follows: a single-turn enameled copper wire is wound on each magnetic core, and an impedance analyzer is used to test the average single-turn inductance of the magnetic cores under the conditions of 100 kHz / 0.3 V, which is 26.9 μH, and the average single-turn inductance under the conditions of 100 kHz / 0.3 V / 1.5 A DC bias, which is 25.8 μH; the inductance decay rate is 4.09%.

[0069] Example 2

[0070] Fe-Si-B-Nb-Cu iron-based nanocrystalline soft magnetic alloy strips with an average thickness of 20±2 μm are selected, epoxy resin is selected as the resin, propylene glycol monoether acetate is selected as the ester compound, and acetone is selected as the organic solvent. The mass ratio of epoxy resin, propylene glycol monoether acetate and acetone is 1:4:5, and the mixture is stirred to obtain the glue paint. The other preparation methods and related parameters are the same as those of Example 1.

[0071] The same test method as in Example 1 is used to test the performance of the magnetic cores prepared by the preparation method in Example 2. The specific test results are shown in Table 1.

[0072] Comparative Example 1

[0073] The same soft magnetic alloy strip as in Example 1 is selected, i.e. Fe-Si-B-Nb-Cu iron-based nanocrystalline soft magnetic alloy strips with an average thickness of 20±2 μm. In order to test the performance conveniently, all the magnetic cores in this comparative example are prepared into circular cores, and the specific steps are as follows:

[0074] Winding: according to the size requirements of the magnetic cores, the nanocrystalline strips are wound into multiple magnetic cores with a size of 50*35*20 mm by an automatic winding machine;

[0075] Heat treatment: the magnetic ring is placed in a heat treatment furnace for heat treatment, and then cooled to room temperature after being kept at 550°C for 120 min to obtain the target magnetic core.

[0076] The comparative example selects 10 magnetic cores in the above-mentioned comparative example 1, and the performance of the selected magnetic cores is tested. The test method is as follows: a single-turn enameled copper wire is wound on each magnetic core, and an impedance analyzer is used to test the average value of the single-turn inductance under the condition of 100 kHz / 0.3 V, which is 27.8 μH, and the average value of the inductance under the condition of 100 kHz / 0.3 V / 1.5 A direct current bias is 24.4 μH; the inductance attenuation rate is 12.23%.

[0077] Comparative example 2

[0078] In the comparative example, the same soft magnetic alloy strip as in example 1 is selected, and the average thickness of the Fe-Si-B-Nb-Cu iron-based nanocrystalline soft magnetic alloy strip is 20±2 μm. In order to test the performance, the comparative example is prepared into a circular ring-shaped core, and the specific steps are as follows:

[0079] Winding: according to the size requirements of the magnetic core, the nanocrystalline strip is wound into multiple magnetic cores with a size of 50*35*20 mm by an automatic winding machine;

[0080] Heat treatment: the magnetic ring is placed in a heat treatment furnace for heat treatment, and is kept at 550℃ for 120 min, and then cooled to room temperature to obtain the target magnetic core.

[0081] Pre-treatment: the heat-treated magnetic core is preheated at 75℃ for 40 min;

[0082] Preparation of varnish: epoxy resin is selected as the resin, propylene glycol monoether acetate is selected as the ester compound, and acetone is selected as the organic solvent. The epoxy resin, propylene glycol monoether acetate and acetone are mixed and stirred in a mass ratio of 3:9:8 to obtain the varnish.

[0083] Varnish dipping and curing: the prepared varnish in the vacuum varnish dipping equipment is preheated at 75℃ for 30 min, then the preheated magnetic core is dipped in the varnish, vacuum impregnated for 20 s, and then taken out and placed in a 150℃ oven for baking for 90 min to obtain the cured nanocrystalline magnetic core.

[0084] The same test method as in example 1 is used to test the performance of the magnetic core prepared by the preparation method in comparative example 2, and the specific test results are shown in table 1.

[0085] Comparative example 3

[0086] In the comparative example, the average thickness of the Fe-Si-B-Nb-Cu iron-based nanocrystalline soft magnetic alloy strip is 20±2 μm, the resin is selected as epoxy resin, the organic solvent is selected as acetone, and the mass ratio of epoxy resin to acetone is 1:1 for mixing and stirring to obtain the varnish. The other preparation methods and related parameters are the same as in example 1.

[0087] The same test method as in Example 1 was used to test the performance of the magnetic core prepared by the preparation method in Comparative Example 3. The specific test results are shown in Table 1.

[0088] Table 1. Magnetic property parameters of the magnetic cores before and after solidification in Examples 1-2 and Comparative Examples 1-3.

[0089] AL (100 kHz / 0.3 V) AL (100 kHz / 0.3 V / 1.5 A) Inductive attenuation rate Example 1 26.9 25.8 4.09％ Example 2 26.7 25.4 4.87％ Comparative Example 1 27.8 24.4 12.23％ Comparative Example 2 27.5 24.3 11.63％ Comparative Example 3 24.1 15.6 35.26％

[0090] It can be seen that both Example 1 and Example 2 were prepared using the preparation method of the present invention. The only difference is the ratio of resin, ester compound, and organic solvent in the varnish. The DC-resistant magnetic cores prepared in both examples have excellent high-frequency performance, and their magnetic core inductance attenuation is small, with an attenuation rate of less than 5%. This makes the inductors prepared using the amorphous nanocrystalline magnetic core have excellent DC bias resistance, expands the application range of the magnetic core, ensures the stability of the magnetic core during operation, and is beneficial to the design and functional realization of magnetic devices.

[0091] In Comparative Example 1, a conventional heat treatment process was used, and the heat-treated magnetic core was not impregnated. The target magnetic core prepared under the same test method had an inductance attenuation rate of 12.23%, which was much higher than that of Example 1 and Example 2.

[0092] In Comparative Example 2, after heat treatment using conventional heat treatment processes, the heat-treated magnetic core was impregnated using the impregnation process of this technical solution. The nanocrystalline magnetic core prepared had an inductance attenuation rate of 11.63% under the same test method. Compared with the process without impregnation treatment in Comparative Example 1, its inductance attenuation rate was improved, but it was still much higher than that of Example 1 and Example 2.

[0093] In Comparative Example 3, the magnetic core was prepared using the preparation method of this technical solution, but the composition and ratio of the adhesive were different from those of this technical solution. The magnetic core prepared under the same test method had an inductance attenuation rate of 35.26%, which was much higher than that of Example 1 and Example 2.

[0094] like Figure 3 As shown, the DC bias capability of the magnetic cores prepared using each embodiment and comparative example is compared. It can be seen that the DC bias capability of the magnetic cores prepared in Embodiment 1 and Embodiment 2 is significantly better than that of Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0095] In summary, it can be seen that the excellent performance of Embodiments 1 and 2 of the present invention is mainly due to the use of the varnish prepared in this invention for impregnation and curing processes during heat treatment and magnetic core preparation. Figure 3It can be known that the DC bias resistance of the magnetic core obtained by the improved composite heat treatment process of the embodiment 1 and the embodiment 2 is significantly better than that of the magnetic core of the comparative example 1, the miniaturization, high efficiency and high frequency requirements can be realized, the application range is widened, and the product application of the magnetic core back end is facilitated. The magnetic core and the glue paint are preheated before solidification, and are kept at 71-80 DEG C. At this temperature, the glue paint is active and has low viscosity, so that the glue paint can enter the nanocrystalline magnetic core inside by its own gravity, the surface of the magnetic core is kept clean, the subsequent magnetic core cutting is facilitated, and in order to further improve the viscosity and fluidity of the glue paint, the organic solvent is used as a diluent, and the vacuum immersion and high-temperature baking methods are used to dry the magnetic core. The glue paint can rapidly form a sealing film on the surface of the magnetic core at high temperature, so that the glue paint is kept inside the magnetic core, the problems of paint leakage and low strength in the conventional method are solved, the high strength and low stress of the glue paint play a protective role on the DC bias resistance of the magnetic core, and finally the inductance decay rate of the obtained magnetic core is reduced from 12.23% to 4.09% under the condition of 1.5A DC current at 100kHz / 0.3V, the inductance decay is low, and the anti-saturation ability is strong.

[0096] The above description is only the preferred embodiments of the present application, and does not limit the implementation and protection scope of the present application. It should be realized by those skilled in the art that any equivalent replacement and obvious change made according to the content of the specification and drawings should be included in the protection scope of the present application.

Claims

1. A method for preparing a performance-stable amorphous nanocrystalline magnetic core, characterized in that, include: Step S1, winding: winding the amorphous nanocrystalline ribbon into a magnetic core; Step S2, heat treatment: The magnetic core is placed in a heat treatment furnace for heat treatment and then cooled to room temperature to obtain a heat-treated magnetic core; Step S3, Pre-treatment: Preheat the heat-treated magnetic core; Step S4, Impregnation and curing: The preheated magnetic core is impregnated in a pre-prepared and heat-insulated varnish under vacuum and then baked and cured to obtain a stable amorphous nanocrystalline magnetic core. The method of preparing the adhesive includes: Epoxy resin, propylene glycol monoether acetate, and acetone are mixed and stirred in a mass ratio of 3:9:8 or 1:4:5 to prepare a varnish, which is then heat-insulated; step S2 includes: Step S21: Place the magnetic core in the heat treatment furnace, and raise the heat treatment temperature of the heat treatment furnace from room temperature to a first heating temperature within a first heating time, and then hold it at the temperature for a first holding time. Step S22: The heat treatment temperature is increased from the first heating temperature to the second heating temperature within the second heating time, and then held at the temperature for a second holding time. Step S23: The heat treatment temperature is increased from the second heating temperature to the third heating temperature within a third heating time, and then held at the temperature for a third holding time. Step S24: The heat treatment temperature is reduced from the third heating temperature to the first cooling temperature within the first cooling time, and then held for a fourth holding time, during which a transverse magnetic field is applied. Step S25: The heat treatment temperature is reduced from the first cooling temperature to the second cooling temperature, and then the furnace is removed and allowed to cool to room temperature. The first heating time is 50 min-120 min, the first heating temperature is 300℃-370℃, and the first holding time is 20 min-60 min; The second heating time is 30-80 minutes, the second heating temperature is 370℃-490℃, and the second holding time is 60-120 minutes. The third heating time is 60min-100min, the third heating temperature is 520℃-580℃, and the third holding time is 100min-150min; The first cooling time is 30-60 minutes, the first cooling temperature is 500℃-530℃, the fourth heat preservation time is 100-300 minutes, and the current of the transverse magnetic field is 50A-65A. The second cooling temperature is below 120°C.

2. The production method according to claim 1, characterized by, In step S3, the pretreatment involves preheating the heat-treated magnetic core at 75°C-85°C for 30-50 minutes.

3. The preparation method according to claim 1, characterized in that, In the preparation of the adhesive, the adhesive is kept at 71℃-80℃ for 20min-40min.

4. The preparation method according to claim 1, characterized in that, In step S4, the impregnation time of the vacuum impregnation is 10s-30s.

5. The method of claim 1, wherein, In step S4, the baking and curing temperature is 120℃-180℃, and the baking time is 1h-2h.

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