An oriented silicon steel large-tension coating material and its preparation method

Abstract

This application relates to the technical field of metal material surface coating, and specifically discloses an oriented silicon steel large-tension coating material and a preparation method thereof. The coating material of the large-tension coating is prepared by mixing the following raw materials in parts by mass: 70-80 parts of acidic silica sol, 15-20 parts of mixed slurry, 3-5 parts of nano magnesium oxide, and 1.5-2 parts of nano zinc oxide; the preparation steps are as follows: Take the acidic silica sol, add nano magnesium oxide and zinc oxide, adjust the stirring speed to 150-200 rpm, stir for 10-30 min, then add the mixed slurry, stir intermittently at a low speed for 25-30 min, and then obtain the coating material after evacuating and exhausting at 0.01-0.03 Mpa. The oriented silicon steel large-tension coating material prepared in this application has excellent anti-cracking performance, and the coefficient of thermal expansion is lower than 3.86×10-6 / K under the test temperature condition of 200 °C; the iron loss < 0.92 W / kg, and the magnetic induction intensity > 1.71 T.

Description

Technical Field

[0001] The present application relates to the technical field of metal material surface coating, and more specifically, to an oriented silicon steel large-tension coating material and a preparation method thereof. Background Art

[0002] Oriented silicon steel is known as the art of steel, and is a soft magnetic alloy with high magnetic flux density, mainly used for making the iron cores of motors and transformers. At present, in addition to adjusting the composition of oriented silicon steel to improve its magnetic properties, an insulating coating can also be applied on the surface of oriented silicon steel, and the contact stress generated by the difference in the thermal expansion coefficients of the coating and the silicon steel itself is used to refine the magnetic domains and improve the magnetic properties. Due to the difference in thermal expansion coefficients, a certain tension is formed between the insulating coating and the oriented silicon steel. Based on this characteristic, this kind of coating is also called a tension coating. In addition to providing a certain tension, the tension coating also requires excellent insulation performance and adhesion performance on the magnesium silicate bottom layer. To meet these requirements and reduce production costs, usually, phosphates, silica sols, chromic anhydride, water, and other additive components are mixed and heat-treated to prepare the tension coating.

[0003] The Chinese patent application document with the publication number CN104530782A discloses a phosphate coating solution and a preparation method thereof. This application provides a formulation of an insulating coating solution. In the application, aluminum dihydrogen phosphate, magnesium dihydrogen phosphate, chromic anhydride, and silica sol are used as raw materials, and 0.5 - 1.5 wt% of polyether-modified silicone oil is added to improve the leveling property. After baking and high-temperature sintering processes, the coating is finally obtained. In the application solution, the oriented silicon steel needs to be stress-relieved annealed at a high temperature before use to reduce the iron loss, while the organic part in this coating is easily decomposed at a high temperature, volatilizing harmful gases, resulting in a decrease in the heat resistance and weldability of the coating.

[0004] Nippon Steel Corporation of Japan is based on an insulating layer solution mainly composed of iron oxide or iron hydroxide. After an oxidation reaction, a tension coating mainly composed of SiO2 is also formed on the surface of the oriented silicon steel strip. And the company has also developed an insulating treatment agent mainly composed of phosphates and colloidal silica. The insulating coating prepared by it has excellent adhesion and corrosion resistance, and the coating tension is also improved, thereby significantly improving the magnetic properties of the oriented silicon steel.

[0005] After the above coatings are modified, although the obtained coating materials have a great improvement in the tension property, the processes adopted in the solutions have high requirements for production equipment and technical control means. And due to the limitation of the poor anti-cracking performance of silica sol, one of the main components of the tension coating, the prepared tension coating often has a short service life. Therefore, there is still a need to find a tension coating that can effectively refine the magnetic domains, reduce the iron loss, and improve the anti-cracking property of the coating. Summary of the Invention

[0006] In order to further effectively refine magnetic domains and reduce iron loss, and at the same time enhance the anti-cracking property of the tension coating, the present application provides an oriented silicon steel large-tension coating material and a preparation method thereof.

[0007] First, the present application provides a preparation method of an oriented silicon steel large-tension coating material. The coating of the large-tension coating material is prepared by mixing raw materials including the following parts by mass: 70-80 parts of acidic silica sol, 15-20 parts of mixed slurry, 3-5 parts of nano magnesium oxide, and 1.5-2 parts of nano zinc oxide; the preparation steps include the following:

[0008] Take the acidic silica sol, add nano magnesium oxide and zinc oxide, mix, and then add the mixed slurry, stir intermittently at a low speed for 25-30 min, and then evacuate and exhaust under 0.01-0.03 Mpa to obtain the coating;

[0009] The preparation steps of the mixed slurry include the following:

[0010] [S01] Take zirconium nitrate, dissolve it in water to obtain solution A;

[0011] [S02] Take ammonium tungstate, add it to ammonia water with a mass fraction of 5%-9%, dissolve it to obtain solution B;

[0012] [S03] Add dilute nitric acid with a mass fraction of 20%-25% and a crystal growth promoter to water, disperse, then adjust the temperature to 65-70 °C, and at the same time drop solution A and solution B into the system, adjust the magnetic stirring speed to 100-150 rpm, process for 3-4 h, then filter to obtain flocculent precipitate, add a mixed dispersant to disperse, and then add water to make up, adjust the magnetic stirring speed to 300-500 rpm, and disperse and process for 10-30 min to obtain the mixed slurry.

[0013] By adopting the above technical solution, after the above steps of treatment, a mixed solution in which acidic silica sol and zirconium tungstate precursor are isolated and dispersed can be obtained. During the subsequent film coating and calcination treatment, the molten zirconium tungstate diffuses at the boundary formed between it and the acidic silica sol component, and continuously eliminates the isolation boundary. Finally, after cooling, a zirconium tungstate coating part with a patchy distribution is obtained.

[0014] Preferably, in the steps [S01] and [S02], the mass-volume ratio of zirconium nitrate, water, ammonium tungstate, and ammonia water is (7-7.2) g: (100-110) mL: (5.4-5.7) g: (65-75) mL.

[0015] By adopting the above technical solution, the ratio of the reactant raw materials is regulated to ensure that during the subsequent mixing process of solution A and solution B, zirconium and tungsten elements react according to a molar ratio close to 1:2, and by adjusting the reaction conditions, a zirconium tungstate (ZrW2O8) precursor is finally obtained.

[0016] Preferably, in the step [S03], the crystal growth promoter is nano-silica with an average particle size of 100 nm.

[0017] By adopting the above technical solution, nano-silica can serve as the crystal nucleus for the growth of zirconium tungstate crystals in the subsequent heat treatment annealing stage, promoting the growth of zirconium tungstate grains to obtain a more regular crystal structure.

[0018] Preferably, in the step [S03], the mixed dispersant is prepared by mixing sodium alkylbenzene sulfonate, hydroxyethyl cellulose, and dichloromethane in a mass-to-volume ratio of (0.3 - 0.5) g : (1.2 - 1.5) g : (50 - 55) mL.

[0019] By adopting the above technical solution, the used mixed dispersant can reduce the flocculation degree of the zirconium tungstate precursor, avoiding the over-flocculation that affects the homogeneity during the subsequent blending with acidic silica sol. At the same time, the mixed dispersant is hydrophobic and can form an oil-water isolation film at the contact surface between the mixed slurry and the acidic silica sol during blending, promoting the distribution behavior of the mixed slurry dispersed in small liquid clusters in the acidic silica sol system. In the subsequent heat treatment baking stage, the dichloromethane in the mixed dispersant escapes, and the molten zirconium tungstate diffuses at the isolation film during calcination, continuously eliminating the isolation boundary, and finally obtaining a patchy distribution of the zirconium tungstate coating part.

[0020] Preferably, in the step [S03], the volume ratio of the added water to the mixed solvent is (4 - 5) : (1 - 1.5).

[0021] By adopting the above technical solution, deionized water incompatible with the mixed dispersant is used to pre-disperse the zirconium tungstate precursor. Utilizing the property of poor compatibility between the two solvents, the zirconium tungstate precursor droplets can be fully dispersed, and the best effect is achieved with the raw materials in this volume ratio.

[0022] Preferably, the intermittent stirring is as follows: stirring at a speed of 50 - 75 rpm for 2 - 3 min, then standing for 1 - 2 min, and repeating the above operations.

[0023] By adopting the above technical solution, a metastable mixed homogeneous slurry of acidic silica sol and the mixed slurry can be obtained. The mixed slurry exists in the form of droplets that are immiscible with other components and are dispersed in the acidic silica sol. After subsequent heat treatment and cooling, patchy distributed zirconium tungstate crystals are obtained.

[0024] In a second aspect, the present application provides an oriented silicon steel large-tension coating material, which is obtained by the following steps:

[0025] [Ⅰ] Silicon steel pretreatment: Take the original silicon steel sheet, polish it with sandpaper, immerse it in acid solution, wash it, dry it in an airtight environment, then coat it with magnesium oxide coating solution, dry it in a protective gas atmosphere, and then heat-burn it at 1100 - 1175 °C. After cooling to room temperature, the pretreated silicon steel is obtained;

[0026] [Ⅱ] Coating spraying and heat treatment: Take the pretreated silicon steel, preheat it and then coat it with the coating material to obtain the coated silicon steel, and then perform heat treatment in an argon atmosphere. After cooling, it is obtained.

[0027] Preferably, in the step [Ⅰ], the magnesium oxide coating solution is prepared by mixing nano-magnesium oxide (30 nm) and deionized water according to a mass-volume ratio of 1 g : (5 - 7) mL; the protective gas is composed of nitrogen with a volume fraction of 25% and hydrogen with a volume fraction of 75% mixed.

[0028] By adopting the above technical solution, nano-magnesium oxide can be used as an isolation agent for the high-temperature treatment of silicon steel, improving the ability of silicon steel to resist external erosion. The nano-magnesium oxide evenly dispersed on the surface layer of silicon steel can increase the coating hardness and reduce the wear of the coating. During the subsequent high-temperature heat-burning process in a protective gas atmosphere, nano-magnesium oxide reacts with the silicon element on the surface layer of silicon steel to form magnesium silicate, further improving the magnetic properties of silicon steel.

[0029] Preferably, in the step [Ⅱ], the heat treatment includes baking, calcining, and annealing, and the steps are as follows:

[0030] Baking: Fix the coated silicon steel with a metal bracket, suspend it in the oven, bake it with hot air at 55 - 60 °C for 20 - 30 min, and then bake it at 220 - 240 °C for 30 - 40 s;

[0031] Calcining: Transfer the baked coated silicon steel to an atmosphere furnace and treat it at 850 - 920 °C for 1 - 2 min;

[0032] Annealing: Gradually cool down at a cooling rate of 5 - 7 °C / min;

[0033] In the annealing step, after gradually cooling down to a furnace temperature of 45 - 50 °C, keep it at a constant temperature for 1 - 2 h.

[0034] By adopting the above technical solutions, in the heat treatment and baking operation, hot air baking can fully remove the interfacial separation solvent dichloromethane in the coating, eliminating the boundary between the zirconium tungstate precursor and acidic silica sol in the previous coating; raising the temperature and baking again can fully remove the moisture in the coating, avoiding the influence of residual moisture on the coating during subsequent calcination. In the second-stage calcination stage, during the short-time high-temperature heat treatment process, the solid part of the coating rapidly melts, and the components of the molten coating diffuse into each other, forming a diffusion crystal phase region. At this time, due to the influence of instantaneous phase changes in the molten coating, there is a relatively high stress inside. During the third-stage annealing operation, the slow cooling operation can eliminate the hardened region and residual stress, and finally obtain a uniform coating film. In the zirconium tungstate part, the nano-silica dispersed therein serves as the crystal nucleus for the annealing crystallization of molten zirconium tungstate, promoting the crystallization behavior of zirconium tungstate.

[0035] In summary, the present application has the following beneficial effects:

[0036] 1. The present application uses the zirconium tungstate precursor obtained by the reaction of zirconium nitrate and ammonium tungstate as a component of the mixed slurry. The obtained zirconium tungstate precursor is a material with excellent negative thermal expansion coefficient, which can be used to enhance the negative expansion coefficient of the coating and improve the tension property of the coating. During the preparation process of the mixed slurry, by constructing a solvent system in which water and dichloromethane are immiscible, the dispersion effect of the subsequent zirconium tungstate precursor in acidic silica sol is enhanced; at the same time, during the heat treatment process, the solvent evaporates, and the coating melt diffuses to eliminate the dispersion boundary, and finally the coating material is obtained.

[0037] 2. In the present application, preferably through heat treatment and dispersion treatment, the cracking reinforcement effect of zirconium tungstate on the coating is enhanced. After heat treatment and dispersion treatment, zirconium tungstate crystals are distributed in patches in the coating material among the cured films of acidic silica sol. When the external environment changes, the difference in thermal expansion coefficient between the silicon steel and the coating acts on the coating, applying an outward expanding tension force to the coating, promoting the thermal deformation behavior of the cured film of acidic silica sol. At this time, the dispersed zirconium tungstate shrinks due to heat, providing a tension buffer area for the cured film of silica sol and restraining the thermal deformation behavior of the surrounding cured films of acidic silica sol. Zirconium tungstate plays a role similar to a "patch" in the tension coating, inhibiting the overall cracking of the coating.

[0038] 3. The large-tension coating material of silicon steel prepared by using the coating of the present application has excellent anti-cracking performance. The thermal expansion coefficient is lower than 3.86×10 -6 / K under the test temperature condition of 200°C; the iron loss < 0.92 W / kg, and the magnetic induction intensity > 1.71 T. Description of the Drawings

[0039] Figure 1 It is the thermal expansion coefficient of the large-tension coating materials of silicon steel in Examples 1-3 and Comparative Examples 1-2 of the present application.

[0040] Figure 2 For the magnetic properties and iron losses of the large-tension coating materials of silicon steel in Examples 1-3 and Comparative Examples 1-2 of the present application. Specific Embodiments

[0041] The raw material compositions of the original silicon steel sheets used in Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0042] Table 1 Raw Material Compositions of Original Silicon Steel Sheets

[0043]

[0044] Example 1

[0045] In this example, the coating material for the large-tension coating is prepared by mixing the following raw materials by weight: 70 g of acidic silica sol, 15 g of mixed slurry, 3 g of nano-magnesium oxide, and 1.5 g of nano-zinc oxide; the preparation steps are as follows:

[0046] Take the acidic silica sol, add nano-magnesium oxide (30 nm) and nano-zinc oxide (50 nm), adjust the magnetic stirring speed to 150 rpm, stir for 10 min, then add the mixed slurry, stir at a magnetic stirring speed of 50 rpm for 2 min, and then intermittently stir and process for 25 min at a frequency of standing for 1 min, and finally evacuate under 0.01 Mpa and stand for degassing for 0.5 h to obtain the coating material.

[0047] In this example, the preparation steps of the mixed slurry are as follows:

[0048] [S01] Take 7 g of zirconium nitrate, dissolve it in 100 mL of deionized water to obtain Solution A;

[0049] [S02] Take 5.4 g of ammonium tungstate, dissolve it in 65 mL of ammonia water with a mass fraction of 5% to obtain Solution B;

[0050] [S03] Take 150 mL of deionized water, add 30 mL of dilute nitric acid with a mass fraction of 20% and 0.2 g of nano-silica (100 nm), adjust the magnetic stirring speed to 200 rpm, disperse for 1 min, then raise the system temperature to 65 °C, control the magnetic stirring speed to 100 rpm, and drop Solution A and Solution B into the system at a dropping rate of 5 mL / min respectively. Under constant temperature conditions, process for 3 h. Then filter to obtain the flocculent precipitate, add 45 mL of mixed dispersant and disperse for 20 min, then add 10 mL of deionized water, increase the magnetic stirring speed to 300 rpm, and continuously stir for 10 min to obtain the mixed slurry.

[0051] In this example, the preparation steps of the grain-oriented silicon steel large-tension coating material are as follows:

[0052] [Ⅰ] Silicon steel pretreatment: Take a silicon steel original sheet of 250mm×70mm×2mm. After polishing the surface with 800-mesh sandpaper, immerse it in a dilute sulfuric acid solution with a mass concentration of 5% for 0.5h. Wash it twice with absolute ethanol and then dry it in an airtight environment. Then, use a coating roller to coat a layer of magnesium oxide coating solution on the silicon steel with a coating amount of 1.62g / m 2 . After the coating is completed, place it in an oven and bake it at 70℃ for 1h. Then transfer the silicon steel to an atmosphere furnace. Under the atmosphere of the protective gas, raise the furnace temperature to 1100℃ at a heating rate of 50℃ / h. After keeping it at a constant temperature for 1h, transfer it to the room temperature environment and let it cool naturally to obtain the pretreated silicon steel.

[0053] [Ⅱ] Coating spraying and heat treatment: Preheat the pretreated silicon steel in an oven at 30℃. Then use a coating roller to coat the coating on the pretreated silicon steel with a coating amount of 3.24g / m 2 to obtain the coated silicon steel. Then fix the coated silicon steel with a metal bracket and suspend it in an oven. Bake it in a gentle flowing hot air of argon atmosphere at 55℃ for 20min, and then bake it at 220℃ for 30s. After the baking is completed, transfer the coated silicon steel to an atmosphere furnace, maintain the argon atmosphere, and treat it at 850℃ for 1min. Finally, lower the furnace temperature to 45℃ at a cooling rate of 5℃ / min and keep it at a constant temperature for 1h to complete the heat treatment. After cooling, the large-tension coating material of the grain-oriented silicon steel is obtained.

[0054] Among them, the acidic silica sol (model SW-20, SiO2%wt: 30%) is provided by Dongying Yiming New Materials Co., Ltd. Zirconium nitrate (purity 99.5%) is provided by Jining Huicheng New Materials Co., Ltd. Ammonium tungstate (purity 99.9%) is provided by Shanghai Linghao Metal Materials Co., Ltd. The mixed dispersant is prepared by mixing sodium alkylbenzene sulfonate, hydroxyethyl cellulose, and dichloromethane according to the mass-volume ratio of 0.3g:1.2g:50mL. The magnesium oxide coating solution is prepared by mixing nano-magnesium oxide (30nm) and deionized water according to the mass-volume ratio of 1g:5mL. The protective gas is composed of nitrogen with a volume fraction of 25% and hydrogen with a volume fraction of 75% mixed.

[0055] Example 2

[0056] In this example, the coating material of the large-tension coating is prepared by mixing the following raw materials by weight: 75g of acidic silica sol, 16g of mixed slurry, 4g of nano-magnesium oxide, and 1.75g of nano-zinc oxide; the specific preparation steps are as follows:

[0057] Take acidic silica sol, add nano magnesium oxide (30 nm) and nano zinc oxide (50 nm), adjust the magnetic stirring speed to 150 rpm, stir for 20 min, then add the mixed slurry, stir at a magnetic stirring speed of 60 rpm for 2 min, and then intermittently stir and process for 30 min at a frequency of standing for 1 min. Finally, evacuate under 0.02 Mpa, and after standing and exhausting for 0.5 h, a coating material is obtained.

[0058] In this embodiment, the preparation steps of the mixed slurry are specifically as follows:

[0059] [S01] Take 7.1 g of zirconium nitrate, dissolve it in 105 mL of deionized water to obtain solution A;

[0060] [S02] Take 5.5 g of ammonium tungstate, dissolve it in 70 mL of ammonia water with a mass fraction of 8% to obtain solution B;

[0061] [S03] Take 150 mL of deionized water, add 30 mL of dilute nitric acid with a mass fraction of 25% and 0.3 g of nano silica (100 nm), adjust the magnetic stirring speed to 225 rpm, disperse for 1 min, then raise the system temperature to 70 °C, control the magnetic stirring speed to 150 rpm, and drop solutions A and B into the system at a dropping rate of 7 mL / min. Under constant temperature conditions, process for 4 h. Then filter to obtain the flocculent precipitate, add 50 mL of the mixed dispersant and disperse for 30 min, then add 15 mL of deionized water, increase the magnetic stirring speed to 500 rpm, and continuously stir for 15 min to obtain the mixed slurry.

[0062] In this embodiment, the preparation steps of the grain-oriented electrical steel large-tension coating material are specifically as follows:

[0063] [Ⅰ] Silicon steel pretreatment: Take a silicon steel original sheet of 250 mm × 70 mm × 2 mm, polish the surface layer with 800-mesh sandpaper, then immerse it in a dilute sulfuric acid solution with a mass concentration of 7.5% for 1 h, wash it 3 times with absolute ethanol, dry it in an airtight manner, and then use a coating roller to coat a layer of magnesium oxide coating solution on the silicon steel at a coating amount of 1.67 g / m 2 After the coating is completed, place it in an oven and bake at 75 °C for 2 h. Then transfer the silicon steel to an atmosphere furnace, and under a protective gas atmosphere, raise the furnace temperature to 1150 °C at a heating rate of 65 °C / h, keep it at a constant temperature for 2 h, then transfer it to a room temperature environment and cool naturally to obtain the pretreated silicon steel.

[0064] [Ⅱ] Coating spraying and heat treatment: Place the pretreated silicon steel in an oven and preheat it at 35 °C, and then use a coating roller to coat at 3.35 g / m 2Coat the pre-treated silicon steel with the coating amount to obtain coated silicon steel. Then fix the coated silicon steel with a metal bracket and suspend it in an oven. Bake it in a gentle flowing hot air at 60 °C for 30 min under an argon atmosphere, then bake it at 230 °C for 35 s. After baking, transfer the coated silicon steel to an atmosphere furnace, maintain the argon atmosphere, and treat it at 900 °C for 1.5 min. Finally, lower the furnace temperature to 50 °C at a cooling rate of 6 °C / min and perform isothermal treatment for 1.5 h to complete the heat treatment. After cooling, the high-tension coating material of grain-oriented silicon steel is obtained.

[0065] Among them, the acidic silica sol (model SW-20, SiO2%wt: 30%) is provided by Dongying Yiming New Materials Co., Ltd. Zirconium nitrate (purity 99.5%) is provided by Jining Huicheng New Materials Co., Ltd. Ammonium tungstate (purity 99.9%) is provided by Shanghai Linghao Metal Materials Co., Ltd. The mixed dispersant is prepared by mixing sodium alkylbenzene sulfonate, hydroxyethyl cellulose, and dichloromethane according to a mass-volume ratio of 0.4 g: 1.5 g: 50 mL. The magnesium oxide coating solution is prepared by mixing nano-magnesium oxide (30 nm) and deionized water according to a mass-volume ratio of 1 g: 6 mL. The protective gas is composed of nitrogen with a volume fraction of 25% and hydrogen with a volume fraction of 75%.

[0066] Example 3

[0067] In this example, the coating material for the high-tension coating is prepared by mixing raw materials with the following weights: 80 g of acidic silica sol, 20 g of mixed slurry, 5 g of nano-magnesium oxide, and 2 g of nano-zinc oxide; the specific preparation steps are as follows:

[0068] Take the acidic silica sol, add nano-magnesium oxide (30 nm) and nano-zinc oxide (50 nm), adjust the magnetic stirring speed to 200 rpm, stir for 30 min, then add the mixed slurry, stir at a magnetic stirring speed of 75 rpm for 3 min, and then intermittently stir at a frequency of standing for 2 min for 30 min. Finally, evacuate the vacuum at 0.03 Mpa and stand for 1 h to exhaust gas to obtain the coating material.

[0069] In this example, the specific preparation steps of the mixed slurry are as follows:

[0070] [S01] Take 7.2 g of zirconium nitrate and dissolve it in 110 mL of deionized water to obtain solution A;

[0071] [S02] Take 5.7 g of ammonium tungstate and dissolve it in 75 mL of ammonia water with a mass fraction of 9% to obtain solution B;

[0072] [S03] Take 175 mL of deionized water, add 35 mL of dilute nitric acid with a mass fraction of 25% and 0.3 g of nano-silica (100 nm), adjust the magnetic stirring speed to 250 rpm, disperse for 2 min, then raise the system temperature to 70 °C, control the magnetic stirring speed at 150 rpm, and dropwise add liquid A and liquid B into the system at a dropping rate of 8 mL / min. Under the condition of constant temperature, treat for 4 h. Then filter to obtain the flocculent precipitate, add 50 mL of mixed dispersant and disperse for 30 min, then supplement 15 mL of deionized water, increase the magnetic stirring speed to 500 rpm, and continuously stir for 30 min to obtain the mixed slurry.

[0073] In this example, the preparation steps of the grain-oriented electrical steel large-tension coating material are specifically as follows:

[0074] [Ⅰ] Pretreatment of electrical steel: Take a 250 mm × 70 mm × 2 mm original electrical steel sheet, polish the surface layer with 800-mesh sandpaper, then immerse it in a dilute sulfuric acid solution with a mass concentration of 7.5% for 1 h, wash it 3 times with absolute ethanol, dry it in an airtight manner, and then use a coating roller to coat a layer of magnesium oxide coating solution on the electrical steel with a coating amount of 1.72 g / m 2 . After the coating is completed, place it in an oven at 75 °C for baking for 2 h, then transfer the electrical steel to an atmosphere furnace, and raise the furnace temperature to 1175 °C at a heating rate of 75 °C / h under the atmosphere of protective gas. After maintaining the temperature for 2 h, transfer it to the room temperature environment and let it cool naturally to obtain the pretreated electrical steel.

[0075] [Ⅱ] Coating spraying and heat treatment: Place the pretreated electrical steel in an oven for preheating at 35 °C, and then use a coating roller to coat the coating on the pretreated electrical steel with a coating amount of 3.62 g / m 2 to obtain the coated electrical steel. Then fix the coated electrical steel with a metal bracket and suspend it in the oven. Bake it in a gentle flowing hot air of 60 °C in an argon atmosphere for 30 min, then bake it at 240 °C for 40 s. After the baking is completed, transfer the coated electrical steel to an atmosphere furnace, maintain the argon atmosphere, treat it at 920 °C for 2 min, and finally lower the furnace temperature to 50 °C at a cooling rate of 7 °C / min, and maintain the temperature for 2 h to complete the heat treatment. After cooling, the grain-oriented electrical steel large-tension coating material is obtained.

[0076] Among them, the acidic silica sol (model SW-20, SiO2%wt: 30%) was provided by Dongying Yiming New Materials Co., Ltd. Zirconium nitrate (purity 99.5%) was provided by Jining Huicheng New Materials Co., Ltd. Ammonium tungstate (purity 99.9%) was provided by Shanghai Linghao Metal Materials Co., Ltd. The mixed dispersant was prepared by mixing sodium alkylbenzene sulfonate, hydroxyethyl cellulose, and dichloromethane in a mass-volume ratio of 0.5 g: 1.5 g: 55 mL. The magnesium oxide coating solution was prepared by mixing nano-magnesium oxide (30 nm) and deionized water in a mass-volume ratio of 1 g: 7 mL. The protective gas was composed of a mixture of nitrogen with a volume fraction of 25% and hydrogen with a volume fraction of 75%.

[0077] Comparative Example

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is that an equal amount of combined liquid was used to replace the mixed slurry.

[0080] Among them, the combined liquid was obtained by uniformly mixing aluminum dihydrogen phosphate, deionized water, and boric acid in a mass-volume ratio of 15 g: 25 mL: 1.5 g.

[0081] All other steps were the same as those in Example 1.

[0082] Comparative Example 2

[0083] The difference between this comparative example and Example 1 is that the coating material for the large-tension coating was prepared by mixing the following raw materials by weight: 90 g of acidic silica sol, 5 g of mixed slurry, 3 g of nano-magnesium oxide, and 1.5 g of nano-zinc oxide.

[0084] All other steps were the same as those in Example 1.

[0085] Performance Detection Test

[0086] Coefficient of Thermal Expansion Test

[0087] Referring to the national standard GB / T44536-2024 "Test Methods for Coefficient of Thermal Expansion and Residual Stress of CVD Ceramic Coatings", the coefficient of thermal expansion of the coatings of Examples 1-3 and Comparative Examples 1-2 was tested and analyzed at 200 °C, 400 °C, and 600 °C respectively, and the test results are as Figure 1 shown.

[0088] Magnetic Properties and Iron Loss Test

[0089] Referring to the national standard GB / T 3655-2022 "Method for Measuring Magnetic Properties of Electrical Steel Strips (Sheets) Using Epstein Square Coils", the magnetic field strength was adjusted to 800 A / m, and the magnetic properties of the large-tension coating materials of silicon steel in each group of Examples 1-3 and Comparative Examples 1-2 were tested. The magnetic induction intensity was controlled at 1.6 T and the frequency was 45 Hz. The iron loss of each group was tested, and the test results are as Figure 2 shown.

[0090] Coating Property Test

[0091] 1.1 Surface Quality

[0092] It was evaluated from the coating leveling property, the appearance of the coating, and whether the surface was sticky after coating and drying.

[0093] 1.2 Corrosion Resistance

[0094] The corrosion resistance test was carried out in a cyclic corrosion chamber. Corrosion conditions: continuously spray with 5% brine solution at 35 °C for 5 h, and observe the surface of the specimen after taking it out. The corrosion resistance evaluation standard is: the rust area < 5% is excellent; the rust area of 5% - 29% is good; the rust area of 30% - 59% is average; the rust area > 60% is poor.

[0095] 1.3 Temperature Change Cracking Test

[0096] The large-tension coating materials of silicon steel in Examples 1-3 and Comparative Examples 1-2 were placed in an atmosphere furnace at 450 °C for 2 h, then immediately taken out and inserted into water, maintained for 10 - 15 s, taken out and left to stand at room temperature for 0.5 h, observe the number of cracks and measure the maximum crack length on the surface, and grade according to the length. The grading standard is shown in Table 2.

[0097] Table 2 Grading Standard for Temperature Change Cracking Test of Large-Tension Coating Materials of Silicon Steel in Examples 1-3 and Comparative Examples 1-2

[0098]

[0099] The coating property test results are shown in Table 3.

[0100] Table 3 Coating Property Test Results of Examples 1-3 and Comparative Examples 1-2

[0101]

[0102] Analyze Examples 1-3 and Comparative Examples 1-2 and combine with Figure 1It can be seen that as the test temperature increases, the coefficient of thermal expansion of the coating materials in the examples and comparative examples gradually increases. Among the five schemes, the starting point and the change rate of the coefficient of thermal expansion of Comparative Example 2 are at relatively high levels in the test schemes. This is because in the scheme of Comparative Example 2, only the mixed slurry accounting for 5.6% of the percentage of silica sol is added, and the mixed slurry only plays a very weak role in reducing the coefficient of thermal expansion in the coating. Therefore, the scheme of Comparative Example 2 performs the worst among the five test schemes.

[0103] Analysis of Examples 1-3 and Comparative Examples 1-2 and in combination with Figure 2 It can be seen that the iron loss and magnetic properties of the silicon steel coating material are approximately inversely correlated, which is consistent with the objective properties of the material. Among the five test schemes, the coating materials of the schemes of Example 2 and Example 3 have relatively excellent performances in both properties, showing relatively excellent effects in reducing iron loss and optimizing magnetic domains.

[0104] Analysis of Examples 1-3 and Comparative Examples 1-2 and in combination with Table 3 shows that in terms of the comprehensive properties of the coating, the test results of the example schemes are better than those of the comparative examples. In Comparative Example 2, due to the selection of the scheme with a low ratio of acidic silica sol and mixed slurry, the coating properties slightly decline. Among the five schemes, the test effect of Comparative Example 1 is the worst.

[0105] This specific embodiment is only an interpretation of the present application, and it does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A preparation method of a large-tension coating material for oriented silicon steel, characterized in that Specifically: [Ⅰ] Take the original silicon steel sheet, polish it with sandpaper, immerse it in acid solution, wash it, dry it in an airtight environment, then coat it with magnesium oxide coating solution, dry it in a protective gas atmosphere, and then heat it at 1100 - 1175 °C, and cool it to room temperature to obtain pretreated silicon steel; [Ⅱ] Take the pretreated silicon steel, preheat it and then coat it with the coating to obtain coated silicon steel, and then heat-treat it in an argon atmosphere and cool it to obtain; The heat treatment steps are as follows: Baking: Fix the coated silicon steel with a metal bracket and suspend it in the oven, bake it with hot air at 55 - 60 °C for 20 - 30 min, and then bake it at 220 - 240 °C for 30 - 40 s; Calcination: Transfer the baked coated silicon steel to a muffle furnace and treat it at 850 - 920 °C for 1 - 2 min; Annealing: Gradually cool it at a temperature reduction rate of 5 - 7 °C / min; The steps for preparing the coating are as follows: Take 70 - 80 parts of acidic silica sol, add 3 - 5 parts of nano magnesium oxide and 1.5 - 2 parts of nano zinc oxide, mix them, then add 15 - 20 parts of mixed slurry, stir intermittently at a low speed for 25 - 30 min, and then evacuate and exhaust under 0.01 - 0.03 Mpa to obtain; The steps for preparing the mixed slurry are as follows: [S01] Take zirconium nitrate, dissolve it in water to obtain solution A; [S02] Take ammonium tungstate, add it to ammonia water with a mass fraction of 5% - 9%, dissolve it to obtain solution B; [S03] Add dilute nitric acid with a mass fraction of 20% - 25% and a crystal growth promoter to water, disperse them, then adjust the temperature to 65 - 70 °C, and at the same time drop solution A and solution B into the system, adjust the magnetic stirring speed to 100 - 150 rpm, treat for 3 - 4 h, then filter to obtain flocculent precipitate, add a mixed dispersant to disperse it, and then add water to make up, adjust the magnetic stirring speed to 300 - 500 rpm, and disperse and treat for 10 - 30 min to obtain; The mixed dispersant is prepared by mixing sodium alkylbenzene sulfonate, hydroxyethyl cellulose, and dichloromethane.

2. The preparation method of a large-tension coating material for grain-oriented silicon steel according to claim 1, characterized in that, The stirring speed during mixing is 150 - 200 rpm and lasts for 10 - 30 min.

3. The preparation method of a large-tension coating material for grain-oriented silicon steel according to claim 1, characterized in that, In the steps [S01] and [S02], the mass - volume ratio of zirconium nitrate, water, ammonium tungstate, and ammonia water is (7 - 7.2) g : (100 - 110) mL : (5.4 - 5.7) g : (65 - 75) mL.

4. The preparation method of a large-tension coating material for grain-oriented silicon steel according to claim 1, characterized in that, In the step [S03], the crystal growth promoter is nano - silica with an average particle size of 100 nm.

5. The preparation method of an oriented silicon steel large-tension coating material according to claim 1, wherein, The mass - volume ratio of sodium alkylbenzene sulfonate, hydroxyethyl cellulose, and dichloromethane is (0.3 - 0.5) g : (1.2 - 1.5) g : (50 - 55) mL.

6. The preparation method of a large-tension coating material for grain-oriented silicon steel according to claim 1, wherein, The intermittent stirring is: stir at a speed of 50 - 75 rpm for 2 - 3 min, then let it stand for 1 - 2 min, and repeat the above operations.

7. The preparation method of a large-tension coating material for grain-oriented silicon steel according to claim 1, wherein In the step [Ⅰ], the magnesium oxide coating solution is prepared by mixing nano magnesium oxide (30 nm) and deionized water according to a mass - volume ratio of 1 g : (5 - 7) mL; the protective gas is composed of 25% nitrogen by volume fraction and 75% hydrogen by volume fraction.

8. The preparation method of a large-tension coating material for grain-oriented silicon steel according to claim 1, wherein, In the annealing step, after gradually cooling to a furnace temperature of 45 - 50 °C, keep it at a constant temperature for 1 - 2 h.

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