Method for insulating coating of ultrafine soft magnetic powder

Abstract

This invention discloses an insulating coating method for ultrafine soft magnetic powder. First, a water glass mixed solution is prepared using sodium silicate solution and deionized water. Then, metal raw materials are weighed, mixed, and smelted / atomized. Finally, nitrogen gas is introduced for pressure filtration, and the powder is dried and sieved. The modulus of the sodium silicate solution is 2.3 or 3.3, and the sodium silicate concentration in the water glass mixed solution is 0.5-10%. This invention uses the water glass mixed solution prepared from sodium silicate and deionized water as the atomizing water, directly forming an insulating coating on the powder surface during the smelting / atomization process. The coating is more uniform, and the powder exhibits better magnetic properties, eliminating the need for subsequent additional insulating coating and reducing the risk of flammability and explosion during operation. Simultaneously, the reduced surface tension of the atomizing water significantly reduces crushing energy consumption. The increased internal water viscosity prevents the powder from colliding and agglomerating again, retaining a finer particle size.

Description

Technical Field

[0001] This invention relates to the field of ultrafine soft magnetic powder production technology, and more specifically, to an insulating coating method for ultrafine soft magnetic powder. Background Technology

[0002] Fe 73.5 Cu1Nb3Si 13.5 B9 nanocrystalline (also known as Finement alloy) soft magnetic alloy material was first successfully developed in 1987 by Katsuhito Yoshizawa of Hitachi Development Corporation. He found a way to refine the grain size of iron-based alloys to 1–100 nm, while simultaneously bringing the saturation magnetostriction coefficient λs and the magnetocrystalline anisotropy constant K towards zero; and for the first time, he achieved a very high Bs (approximately 1.35 T) while maintaining an initial relative permeability μ. i The number exceeds 100,000. Nanocrystalline soft magnetic materials are currently developing towards high frequency and multifunctionality, and their applications will extend to many aspects of soft magnetic materials, such as power transformers, pulse transformers, high-frequency high-voltage transformers, saturable reactors, current transformers, magnetic shielding, magnetic heads, magnetic switches, and sensors. Ultrafine nanocrystalline soft magnetic powder is made by incorporating Fe... 73.5 Cu1Nb3Si 13.5 B9 nanocrystalline soft magnetic alloy strip is a magnetic powder with a particle size of less than 10 μm obtained by crushing. It is widely used in soft magnetic powder cores, magnetic coatings, magnetic composite materials, and electronic encapsulation adhesives.

[0003] For example, application number 201911219738.6 discloses a method for preparing metal or alloy powders by atomizing molten metal or alloy with ammonia water. First, ammonia water is prepared by passing ammonia gas into deionized water, with the ammonia water concentration ranging from 1% to 35% by mass, as needed. Second, molten metal is prepared and melted according to the requirements of the target product. Third, the entire atomization system is evacuated and protected with nitrogen gas. A high-pressure water pump pressurizes the ammonia water to 10MPa-150MPa, impacting the molten metal or alloy stream leaking from the tundish, resulting in a mixture of metal or alloy powder and ammonia water. Finally, after the mixture of metal or alloy powder and ammonia water settles, the ammonia water is recycled into a storage tank. The wet powder is then filtered, dried, sieved, or classified by airflow under nitrogen protection to obtain the metal or alloy powder.

[0004] However, this process of using ammonia water to atomize and produce metal alloy powder has several drawbacks. First, the cost of ammonia water is high, which affects the profit. Second, ammonia water is highly corrosive and harmful to people and the environment. Third, the subsequent insulation coating uses liquids such as acetone and alcohol, which are flammable and explosive, posing considerable safety hazards. Fourth, the soft magnetic powder is not crushed thoroughly enough, and the particles are generally too large, resulting in high pressure in the screening process. Fifth, most of the soft magnetic powder still needs to be insulated and coated afterward, which is not efficient. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an insulating coating method for ultrafine soft magnetic powder, thereby solving one or more of the above-mentioned problems.

[0006] To achieve the above objectives, the present invention provides the following technical solution: An insulating coating method for ultrafine soft magnetic powder, comprising the following steps: S1. Prepare a water glass mixed solution using a stirred tank; S2. Weigh and mix the metal raw materials, then add them to an induction furnace for melting. S3. Subsequently, in the atomization equipment, the molten liquid metal is atomized using a water glass mixed solution to produce atomized powder; S4. Dehydrate and dry the atomized powder, and then sieve it.

[0007] Further, in step S1, sodium silicate solution and deionized water are added to a stirring vessel and mixed evenly for 1-2 hours to obtain a water glass mixed solution.

[0008] Furthermore, the modulus of the sodium silicate solution is 2.3 or 3.3, and the concentration of sodium silicate in the water glass mixed solution is 0.5-10%.

[0009] Furthermore, the metal raw materials in step S2 include industrial silicon, pure chromium, and electrical pure iron weighed in a certain proportion.

[0010] Furthermore, the prepared metal raw materials contain 5-6% silicon and 5-6% chromium, with the remainder being iron.

[0011] Furthermore, in step S2, the final smelting temperature of the metal raw materials is 1630-1730℃.

[0012] Furthermore, in step S4, nitrogen gas is introduced for protection during the dehydration process, and the powder is dried under vacuum.

[0013] Furthermore, in step S3, the water glass mixture reduces the surface tension during atomization, requiring less energy to overcome the tension when spraying the molten metal, thus tearing the liquid metal into smaller metal droplets.

[0014] Furthermore, during the atomization process in step S3, the silica produced by the decomposition of water glass directly forms an insulating coating on the powder surface.

[0015] Furthermore, in step S3, atomization increases the viscosity of the water inside the device, preventing the broken-up micro-metal droplets from colliding and merging again, resulting in finer atomized powder particles.

[0016] In summary, this invention offers the following advantages: Using a water glass mixture solution prepared from sodium silicate and deionized water as the atomizing water directly forms an insulating coating on the powder surface during the smelting atomization process. This coating is more uniform, resulting in better magnetic properties of the powder. No additional insulating coating is required afterward, reducing the risk of flammability and explosion during operation. Simultaneously, the reduced surface tension of the atomizing water significantly decreases crushing energy consumption. Increased internal water viscosity prevents the powder from re-colliding and agglomerating, resulting in finer particle sizes. Detailed Implementation Example

[0017] S1. Using sodium silicate solution and deionized water, with the sodium silicate solution having a modulus of 2.3, add them to a stirring tank and mix thoroughly for 1.5 hours to obtain a water glass mixed solution. The sodium silicate concentration in the water glass mixed solution is 5%. The proportion of sodium silicate solution can be adjusted according to the customer's insulation requirements.

[0018] S2. Industrial silicon, pure chromium and electrical pure iron are weighed in a certain proportion and mixed together. The prepared metal raw materials contain 5.5% silicon and 5.5% chromium, with the remainder being iron. Then, they are added to an induction furnace for smelting. The final smelting temperature of the metal raw materials is 1680℃.

[0019] S3. Subsequently, in the atomization equipment, the molten liquid metal is atomized using a water glass mixed solution to produce atomized powder.

[0020] The water glass mixture, whose main component is silica, reduces the surface tension during atomization. When sprayed at high speed onto molten liquid metal for shearing and fragmentation, less energy is required to overcome the surface tension, and the liquid metal is torn into smaller droplets. Atomization increases the viscosity of the water inside the equipment, preventing the broken-up micro-droplets from colliding and merging again, resulting in finer atomized powder particles. During atomization, the silica produced by the decomposition of water glass directly forms an insulating silica coating on the powder surface.

[0021] S4. Nitrogen gas is introduced for protection and the atomized powder is filtered under pressure. The atomized powder is dehydrated and dried in a vacuum environment and then sieved in a sieving device. Example

[0022] S1. Using sodium silicate solution and deionized water, with a modulus of 2.3, add them to a stirring tank and mix thoroughly for 1 hour to obtain a water glass mixed solution. The sodium silicate concentration in the water glass mixed solution is 0.5%. The proportion of sodium silicate solution can be adjusted according to the customer's insulation requirements.

[0023] S2. Industrial silicon, pure chromium and electrical pure iron are weighed in a certain proportion and mixed together. The prepared metal raw materials contain 5% silicon and 5% chromium, with the remainder being iron. Then, they are added to an induction furnace for smelting. The final smelting temperature of the metal raw materials is 1630℃.

[0024] S3. Subsequently, in the atomization equipment, the molten liquid metal is atomized using a water glass mixed solution to produce atomized powder.

[0025] The water glass mixture, whose main component is silica, reduces the surface tension during atomization. When sprayed at high speed onto molten liquid metal for shearing and fragmentation, less energy is required to overcome the surface tension, and the liquid metal is torn into smaller droplets. Atomization increases the viscosity of the water inside the equipment, preventing the broken-up micro-droplets from colliding and merging again, resulting in finer atomized powder particles. During atomization, the silica produced by the decomposition of water glass directly forms an insulating silica coating on the powder surface.

[0026] S4. Nitrogen gas is introduced for protection and the atomized powder is filtered under pressure. The atomized powder is dehydrated and dried in a vacuum environment and then sieved in a sieving device. Example

[0027] S1. Using sodium silicate solution and deionized water, with the sodium silicate solution having a modulus of 3.3, add them to a stirring tank and mix thoroughly for 2 hours to obtain a water glass mixed solution. The sodium silicate concentration in the water glass mixed solution is 10%. The proportion of sodium silicate solution can be adjusted according to the customer's insulation requirements.

[0028] S2. Industrial silicon, pure chromium and electrical pure iron are weighed in a certain proportion and mixed together. The prepared metal raw materials contain 6% silicon and 6% chromium, with the remainder being iron. Then, they are added to an induction furnace for smelting. The final smelting temperature of the metal raw materials is 1730℃.

[0029] S3. Subsequently, in the atomization equipment, the molten liquid metal is atomized using a water glass mixed solution to produce atomized powder.

[0030] The water glass mixture, whose main component is silica, reduces the surface tension during atomization. When sprayed at high speed onto molten liquid metal for shearing and fragmentation, less energy is required to overcome the surface tension, and the liquid metal is torn into smaller droplets. Atomization increases the viscosity of the water inside the equipment, preventing the broken-up micro-droplets from colliding and merging again, resulting in finer atomized powder particles. During atomization, the silica produced by the decomposition of water glass directly forms an insulating silica coating on the powder surface.

[0031] S4. Nitrogen gas is introduced for protection and the atomized powder is filtered under pressure. The atomized powder is dehydrated and dried in a vacuum environment and then sieved in a sieving device. Example

[0032] The difference from Example 1 is that a calcium silicate solution is used instead of a sodium silicate solution. Similarly, the concentration of the calcium silicate solution is higher, and the oxygen content in the water atomization is reduced. However, the introduction of calcium silicate will damage the furnace lining. The oxygen content in the 316L atomization environment is 2388 ppm.

[0033] The oxygen content in all water atomization environments in Examples 1-4 was above 2000 ppm, but far below the 3000-4000 ppm range of traditional water atomization.

[0034] Examples 1-3 mainly involve different adjustments to the sodium silicate concentration. In a traditional 316L water atomization environment, the oxygen content is 3000-4000 ppm, which is costly and the pipeline is prone to clogging during atomization. Comparatively, the average oxygen content of Examples 1-3 is 2229 ppm, 2536 ppm, and 2178 ppm, respectively. Example 3 has the highest sodium silicate concentration, followed by Example 1, and Example 2 has the lowest. Correspondingly, Example 3 has the lowest oxygen content, Example 1 is second, and Example 2 has the highest oxygen content. It can be concluded that increasing the sodium silicate concentration inevitably leads to a decrease in oxygen content.

[0035] Traditional water atomization for preparing metal alloy powders uses deionized water or tap water as the atomizing medium. This results in low atomization energy, low yield of ultrafine powder, and subsequent insulating coating of soft magnetic powders, which must be performed after powder sieving using organic or inorganic coating methods in kneaders or new mixers. Of particular concern is the use of liquids such as acetone or alcohol in the coating process, which is lengthy, generates significant dust, is flammable and explosive, poses safety hazards, is costly, and makes it difficult to guarantee coating quality, often leading to uneven coating and poor magnetic properties of the powder. A solution using a water glass mixture of sodium silicate solution and deionized water as the atomizing water can effectively break up the liquid metal during atomization and simultaneously insulatingly coat the broken powder, eliminating the need for a separate subsequent insulating coating step.

[0036] It should be noted that this specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for insulating coating of ultrafine soft magnetic powder, characterized in that, Follow these steps: S1. Prepare a water glass mixed solution using a stirred tank; S2. Weigh and mix the metal raw materials, then add them to an induction furnace for melting. S3. Subsequently, in the atomization equipment, the molten liquid metal is atomized using a water glass mixed solution to produce atomized powder; S4. Dehydrate and dry the atomized powder, and then sieve it.

2. The insulating coating method for ultrafine soft magnetic powder according to claim 1, characterized in that, In step S1, sodium silicate solution and deionized water are added to a stirring vessel and mixed evenly for 1-2 hours to obtain a water glass mixed solution.

3. The insulating coating method for ultrafine soft magnetic powder according to claim 2, characterized in that, The modulus of sodium silicate solution is 2.3 or 3.3, and the concentration of sodium silicate in water glass mixed solution is 0.5-10%.

4. The insulating coating method for ultrafine soft magnetic powder according to claim 1, characterized in that, The metal raw materials in step S2 include industrial silicon, pure chromium, and electrical pure iron weighed in a certain proportion.

5. The insulating coating method for ultrafine soft magnetic powder according to claim 4, characterized in that, The prepared metal raw materials contain 5-6% silicon and 5-6% chromium, with the remainder being iron.

6. The insulating coating method for ultrafine soft magnetic powder according to claim 1, characterized in that, In step S2, the final smelting temperature of the metal raw materials is 1630-1730℃.

7. The insulating coating method for ultrafine soft magnetic powder according to claim 1, characterized in that, In step S4, nitrogen gas is introduced for protection during the dehydration process and the powder is filtered under pressure. The atomized powder is then dried in a vacuum environment.

8. The insulating coating method for ultrafine soft magnetic powder according to claim 1, characterized in that, In step S3, the water glass mixture reduces the surface tension during atomization, requiring less energy to overcome the tension when spraying the molten metal, thus tearing the liquid metal into smaller metal droplets.

9. The insulating coating method for ultrafine soft magnetic powder according to claim 1, characterized in that, During the atomization process in step S3, the silica produced by the decomposition of water glass directly forms an insulating coating on the powder surface.

10. The insulating coating method for ultrafine soft magnetic powder according to claim 1, characterized in that, In step S3, atomization increases the viscosity of the water inside the equipment, preventing the tiny metal droplets after breakage from colliding and merging again, resulting in finer atomized powder particles.