A method for preparing a Fe-Si soft magnetic powder core for improving the strength of green body and finished product

Abstract

The application discloses a preparation method of a Fe-Si soft magnetic powder core for improving green body and finished product magnetic core strength, and belongs to the technical field of Fe-Si soft magnetic powder core preparation. The Fe-Si soft magnetic powder core is prepared by the following steps: firstly, insulating coating is performed on the gas atomized Fe-Si magnetic powder by using a mixed ethanol solution of nano silicon oxide and nano aluminum oxide, and then the Fe-Si magnetic powder is pressed into a green body; secondly, the green body is soaked in a reaction strengthening liquid prepared from sodium borate, sodium hydroxide, glycerol, polyurethane dispersion liquid and water; thirdly, the green body is dried and subjected to high-temperature annealing treatment. The green body strength of the Fe-Si soft magnetic powder core is increased to 130-234 N, and the finished product tensile strength is increased to 638-762 N. The method has low cost and simple operation, can avoid the baking overflow problem of the conventional infiltration enhancement process, has remarkable strength improvement effect, can greatly improve the tensile strength of the Fe-Si ring-shaped soft magnetic powder core green body and finished product magnetic core and the cutting force of the block-shaped soft magnetic powder core green body and finished product magnetic core, and the magnetic performance does not obviously change compared with the magnetic core treated by the conventional infiltration enhancement process.

Description

Technical Field

[0001] This invention belongs to the field of iron-silicon soft magnetic powder core preparation technology, and more specifically, it relates to a method for preparing iron-silicon soft magnetic powder cores that improves the strength of green and finished magnetic cores. Background Technology

[0002] Gas-atomized iron-silicon soft magnetic powder cores are widely used in medium- and high-power power electronic equipment due to their high saturation magnetic induction, good DC superposition characteristics, and high resistivity. The manufacturing process of iron-silicon soft magnetic powder cores generally consists of three parts: insulation coating, pressing, and stress-relief annealing. Because gas-atomized iron-silicon powder has a high sphericity, it is difficult to form during the pressing process. Furthermore, the heat treatment of the soft magnetic powder core is not high-temperature sintering, but only stress-relief annealing at a relatively low temperature. This results in low strength in both the green blank and the finished magnetic core after annealing.

[0003] To effectively address the low strength issue of soft magnetic powder cores without affecting their magnetic properties, the powder core industry currently incorporates an impregnation process during soft magnetic powder core preparation. This involves immersing the annealed soft magnetic powder core in a resin solution of a specific concentration for a certain period, allowing the resin to penetrate into the air gaps within the powder core. The resin is then cured through low-temperature baking. While this process significantly improves the strength of the finished soft magnetic powder core, it also has some drawbacks: First, the impregnation solution used in this process is generally composed of organic resins, which have poor heat resistance and decompose at high temperatures, causing a significant reduction in core strength. Therefore, the impregnation process can currently only be implemented after the annealing process, thus only improving the strength of the finished soft magnetic powder core and failing to address the issue of poor strength in the green compact. Second, due to the high resin content in the impregnation solution, a large amount of resin overflows from the powder core surface during baking due to volume expansion, resulting in glue overflow and negatively impacting the appearance of the magnetic powder core. Therefore, it is of great significance to invent a method that can simultaneously improve the strength of soft magnetic powder core green blanks and the strength of finished magnetic cores without affecting product performance and appearance yield. Summary of the Invention

[0004] To address the issue of strength differences between green and finished iron-silicon soft magnetic powder cores, this invention provides a method for preparing iron-silicon soft magnetic powder cores that improves the strength of both the green and finished cores.

[0005] In this invention, atomized iron-silicon powder is placed in a mixed ethanol solution of nano-silicon oxide and nano-alumina for insulating coating. Then, the pressed iron-silicon soft magnetic powder core blank is immersed in a reaction strengthening liquid made of sodium borate, sodium hydroxide, water, glycerol and polyurethane dispersion, dried, and then subjected to high-temperature annealing treatment.

[0006] The preparation steps of an iron-silicon soft magnetic powder core that improves the strength of both green and finished magnetic cores are as follows:

[0007] (1) 1 kg of gas-atomized iron-silicon alloy powder and 405-714 g of mixed ethanol solution are mixed evenly and reacted to achieve insulating coating to obtain a mixture; the mixed ethanol solution is made by mixing 3-6 g of nano silicon oxide, 2-8 g of nano aluminum oxide and 400-700 g of ethanol evenly.

[0008] The mixture is dried, passed through an 80-mesh sieve, and pressed into annular green bodies under 1600-2000 MPa conditions; the tensile strength of the annular green bodies is 130-234 N.

[0009] (2) Immerse 5 kg of ring-shaped green body in 2000-3000 g of reaction strengthening solution for 30-70 min at a temperature of 60-90 °C to obtain a strengthened green body; the reaction strengthening solution is prepared by uniformly mixing 500-1000 g of sodium borate, 1500-2500 g of sodium hydroxide, 250-750 g of glycerol, 300-500 g of polyurethane dispersion and 250-2450 g of water.

[0010] (3) Anneal the reinforced green blank to obtain iron-silicon soft magnetic powder core; the tensile strength of the iron-silicon soft magnetic powder core is 638-762N.

[0011] Further technical solutions are as follows:

[0012] In step (1), the insulation coating reaction time is 30-90 min; the drying temperature of the mixture is 120-160℃.

[0013] In step (3), the annealing process is as follows: in a nitrogen atmosphere, the temperature is maintained at 200℃-300℃ for 30-60 minutes; the temperature is then raised to 700-900℃ and maintained for 40-90 minutes.

[0014] The beneficial technical effects of this invention are reflected in the following aspects:

[0015] 1. This invention does not employ the traditional method of solely using organic resin to improve the strength of the magnetic core. Instead, it simultaneously leverages the advantages of both the high viscosity and high thermal stability of the inorganic products generated by the reaction between the insulating layer on the surface of the magnetic powder particles and the reaction strengthening liquid, as well as the high viscosity of the organic resin in the reaction strengthening liquid, to address the problem of low strength in both the green and finished magnetic core blanks. Specifically, this invention first forms a uniform and dense nano-silica and nano-alumina insulating layer on the surface of the magnetic powder particles. Then, the nano-silica and nano-alumina react with sodium borate and sodium hydroxide in the reaction strengthening liquid, generating highly viscous inorganic reaction products, sodium silicate and sodium aluminate, on the surface of the magnetic powder. This enhances the bonding strength between the magnetic powder particles and improves the strength of the green magnetic core blank. Secondly, the polyurethane dispersion in the reaction strengthening liquid, along with glycerol and water as solvents, slows down the dissolution rate of sodium hydroxide and sodium borate, thereby reducing the reaction rate between the nano-oxides on the surface of the magnetic powder and the sodium borate and sodium hydroxide in the reaction strengthening liquid. This prevents the magnetic powder particles near the core surface from clogging the magnetic powder due to the violent reaction of the insulating layer, which would generate a large amount of highly viscous inorganic reaction products. The air gap prevents the reaction strengthening liquid from fully wetting the core, thus ensuring a uniform, highly viscous inorganic reaction product on the surface of the magnetic powder inside the core, effectively improving the overall strength of the core. Secondly, the two highly viscous inorganic reaction products are high-temperature resistant and will not decompose during high-temperature annealing, effectively avoiding the problem of reduced core strength after annealing. Finally, adding an appropriate amount of polyurethane dispersion to the reaction strengthening liquid can increase the strength of the iron-silicon soft magnetic powder core green body by utilizing the high viscosity of polyurethane. However, because the amount added is small and the polyurethane decomposes during subsequent high-temperature heat treatment, the problem of excess adhesive on the surface of the finished core during baking, which occurs in conventional organic resin impregnation processes, can be completely avoided while improving the strength of the green body.

[0016] Table 1

[0017]

[0018] 2. The iron-silicon soft magnetic powder core prepared by the method of the present invention has a significant strength improvement effect, and is low in cost and simple to operate. Table 1 shows the comparison data of the green strength and the strength and magnetic properties of the iron-silicon soft magnetic powder core prepared in Example 1 of the present invention and the iron-silicon soft magnetic powder core with the same magnetic permeability level (60±8%) prepared by conventional impregnation reinforcement process. Both the green core and the finished magnetic core are toroidal cores with an outer diameter of 27 mm, an inner diameter of 15 mm, and a height of 12 mm. It can be seen that the present invention can significantly improve the tensile strength of the green core and the finished magnetic core of the iron-silicon soft magnetic powder core, but does not affect the magnetoelectric properties of the iron-silicon powder core. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to specific embodiments.

[0020] Example 1

[0021] The preparation steps of an iron-silicon soft magnetic powder core that improves the strength of both green and finished magnetic cores are as follows:

[0022] (1) Take 1 kg of gas-atomized iron-silicon alloy powder and 405 g of mixed ethanol solution, mix them evenly, and react for 30 min to achieve insulation coating. The mixed ethanol solution is made by mixing 3 g of nano-silica, 2 g of nano-alumina and 400 g of ethanol evenly. Dry the mixture at 120℃. Then pass it through an 80-mesh sieve and press it into a ring-shaped green blank with an outer diameter of 27 mm, an inner diameter of 15 mm and a height of 12 mm under 1600 MPa. The tensile strength of the ring-shaped green blank is 130 N.

[0023] (2) Take 5 kg of ring-shaped green body and put it into 2000 g of reaction strengthening solution, soak for 30 min to obtain strengthened green body. The temperature of the reaction strengthening solution during the soaking process is 60℃. The reaction strengthening solution is made by mixing 500 g of sodium borate, 1500 g of sodium hydroxide, 250 g of glycerol, 300 g of polyurethane dispersion-80 and 2450 g of water evenly.

[0024] (3) The reinforced green blank is annealed. First, it is kept at 200℃ for 30 minutes, then the temperature is raised to 700℃ and kept for 90 minutes in a nitrogen atmosphere to obtain iron-silicon soft magnetic powder core.

[0025] The annular iron-silicon soft magnetic powder core prepared in Example 1 has an outer diameter of 27 mm, an inner diameter of 15 mm, and a height of 12 mm. The tensile strength of the finished annular iron-silicon soft magnetic powder core is 638 N.

[0026] Example 2

[0027] The preparation steps of an iron-silicon soft magnetic powder core that improves the strength of both green and finished magnetic cores are as follows:

[0028] (1) Take 1 kg of gas-atomized iron-silicon alloy powder and 500 g of mixed ethanol solution, mix them evenly, and react for 60 min to achieve insulation coating. The mixed ethanol solution is made by mixing 4 g of nano-silicon oxide, 6 g of nano-alumina, and 600 g of ethanol evenly. Dry the mixture at 140℃. Then pass it through an 80-mesh sieve and press it at 1700 MPa to form a block iron-silicon powder core green blank with an outer diameter of 50 mm, an inner diameter of 20 mm, and a height of 20 mm. The tensile strength of the ring green blank is 175 N.

[0029] (2) Take 5 kg of block green body and put it into 2500 g of reaction strengthening solution and soak for 50 min to obtain strengthened green body. The temperature of the reaction strengthening solution during the soaking process is 70℃. The reaction strengthening solution is made by mixing 750 g of sodium borate, 2000 g of sodium hydroxide, 500 g of glycerol, 400 g of polyurethane dispersion-80 and 1350 g of water evenly.

[0030] (3) The reinforced green blank is annealed. First, it is kept at 200℃ for 50 minutes, then the temperature is raised to 800℃ and kept for 50 minutes in a nitrogen atmosphere to obtain iron-silicon soft magnetic powder core.

[0031] The annular iron-silicon soft magnetic powder core prepared in Example 2 has an outer diameter of 27 mm, an inner diameter of 15 mm, and a height of 12 mm. The tensile strength of the finished annular iron-silicon soft magnetic powder core is 689 N.

[0032] Example 3

[0033] The preparation steps of an iron-silicon soft magnetic powder core that improves the strength of both green and finished magnetic cores are as follows:

[0034] (1) Take 1 kg of gas-atomized iron-silicon alloy powder and 714 g of mixed solution, mix them evenly, and react for 90 min to achieve insulation coating. The mixed ethanol solution is prepared by mixing 6 g of nano-silica, 8 g of nano-alumina and 700 g of ethanol evenly. Dry the mixture at 160℃. Then pass it through an 80-mesh sieve and press it into a ring-shaped green blank with an outer diameter of 27 mm, an inner diameter of 15 mm and a height of 12 mm under 2000 MPa. The tensile strength of the ring-shaped green blank is 234 N.

[0035] (2) Take 5 kg of ring-shaped green body and put it into 3000 g of reaction strengthening solution and soak for 70 min to obtain strengthened green body. The temperature of the reaction strengthening solution during the soaking process is 90℃. The reaction strengthening solution is made by mixing 1000 g of sodium borate, 2500 g of sodium hydroxide, 750 g of glycerol, 500 g of polyurethane dispersion-80 and 250 g of water evenly.

[0036] (3) The reinforced green blank is annealed. First, it is kept at 300℃ for 60 min, then the temperature is raised to 900℃ and kept for 40 min in a nitrogen atmosphere to obtain an annular iron-silicon soft magnetic powder core.

[0037] The annular iron-silicon soft magnetic powder core prepared in Example 3 has an outer diameter of 27 mm, an inner diameter of 15 mm, and a height of 12 mm. The tensile strength of the annular iron-silicon soft magnetic powder core is 762 N.

Claims

1. A method for preparing iron-silicon soft magnetic powder cores that enhance the strength of green and finished magnetic cores, characterized in that... The preparation steps are as follows: (1) Mix 1 kg of gas-atomized iron-silicon alloy powder and 405-714 g of mixed ethanol solution evenly, and react to achieve insulating coating to obtain a mixture; the mixed ethanol solution is made by mixing 3-6 g of nano silicon oxide, 2-8 g of nano aluminum oxide and 400-700 g of ethanol evenly. The mixture is dried, passed through an 80-mesh sieve, and pressed into annular green bodies under 1600-2000 MPa conditions; the tensile strength of the annular green bodies is 130-234 N. (2) Immerse 5 kg of ring-shaped green body in 2000-3000 g of reaction strengthening solution for 30-70 min at a temperature of 60-90 °C to obtain a strengthened green body; the reaction strengthening solution is prepared by uniformly mixing 500-1000 g of sodium borate, 1500-2500 g of sodium hydroxide, 250-750 g of glycerol, 300-500 g of polyurethane dispersion and 250-2450 g of water. (3) Anneal the reinforced green blank to obtain iron-silicon soft magnetic powder core; the tensile strength of the iron-silicon soft magnetic powder core is 638-762N.

2. A method for preparing an iron-silicon soft magnetic powder core with improved strength in both green and finished magnetic cores as described in claim 1, characterized in that: In step (1), the insulation coating reaction time is 30-90 min; the drying temperature of the mixture is 120-160℃.

3. A method for preparing an iron-silicon soft magnetic powder core with improved strength of green and finished magnetic cores as described in claim 1, characterized in that: In step (3), the annealing process is as follows: in a nitrogen atmosphere, the temperature is maintained at 200℃-300℃ for 30-60 minutes; the temperature is then raised to 700-900℃ and maintained for 40-90 minutes.

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