A slurry for high-power medium-frequency induction furnace coil and its preparation method

Abstract

The present application relates to the technical field of refractory materials, in particular to a slurry for high-power medium-frequency induction furnace coil and a preparation method thereof. The present application solves the problem of poor thermal shock resistance and high-temperature resistance of the slurry after pouring. The synthetic raw materials of the slurry in the present application include sintered tabular corundum, bauxite clinker, aluminate cement, high-purity low-sodium alpha-Al2O3 micro powder, industrial-grade aluminum lactate powder, polypropylene fiber, silicone resin, composite active agent and modified dispersant. The present application reduces the volume change rate and apparent porosity of the slurry by changing the amount of sintered tabular corundum and aluminate cement and the amount of bauxite clinker and alpha-Al2O3 micro powder; improves the explosion-proof capacity of the slurry by changing the amount of aluminum lactate powder, polypropylene fiber and silicone resin; reduces the burning loss rate of the slurry by introducing the composite active agent and controlling the ball milling time; and improves the strength of the slurry by synthesizing the modified dispersant and controlling the mixing time.

Description

Technical Field

[0001] The present invention relates to the technical field of refractory materials, specifically to a slurry for high-power medium-frequency induction furnace coils and a preparation method thereof. Background Art

[0002] Coil slurry is a material applied to the surface of the coils in medium-frequency coreless induction furnaces. Its primary function is to stabilize the coils and prevent deformation during operation and furnace lining removal. Coil slurry generally has good insulation properties, providing excellent insulation between coil turns. If molten metal penetrates the furnace lining, the slurry protects the coils from corrosion. Higher coil power increases static voltage, which reduces the distance between coil turns and degrades the insulation performance. Coils weighing more than 40 tons are generally considered high-power medium-frequency induction furnace coils, with the largest coils currently on the market weighing 90-100 tons.

[0003] At present, conventional coil slurry on the market is mainly composed of conventional cement combined with aluminum silicate and high-alumina refractory raw materials. After adding water on site, this type of slurry requires a long baking time due to its high cement content, complex hydration products, and high proportion of bound water. If you are not careful, the material may burst due to baking too quickly; this type of slurry is prone to shrinkage under long-term high temperature, causing the material to crack, which is particularly prominent in the coils of high-power medium-frequency induction furnaces. It cannot stabilize the coil well, easily causing instability in the furnace structure, and greatly reducing the service life of the furnace working lining.

[0004] In summary, today's coil slurry still has shortcomings such as poor explosion-proof ability, high shrinkage rate, and poor thermal stability, which leads to poor thermal shock resistance and high temperature resistance of the coil slurry after pouring, seriously affecting its application in industry.

[0005] Therefore, a slurry for a high-power medium-frequency induction furnace coil and a preparation method thereof are proposed. Summary of the Invention

[0006] The present invention aims to design a slurry for high-power medium-frequency induction furnace coils and a preparation method thereof. The raw materials for synthesizing the slurry for high-power medium-frequency induction furnace coils include sintered tabular corundum, bauxite clinker, aluminate cement, high-purity low-sodium α-Al2O3 micropowder, industrial-grade 99wt% aluminum lactate powder, polypropylene fiber, silicone resin, a composite active agent, and a modified dispersant. The present invention reduces the volume change rate of coil slurry by changing the amount and particle size of sintered plate-shaped corundum and aluminate cement; reduces the apparent porosity of the coil slurry and improves the volume density by changing the amount, component content and particle size of bauxite clinker and high-purity low-sodium α-Al2O3 fine powder; improves the explosion-proof capability of the coil slurry by changing the amount of industrial-grade 99wt% aluminum lactate powder, polypropylene fiber and organic silicon resin, as well as the length and diameter of the polypropylene fiber; reduces the burnout rate of the coil slurry by introducing a composite active agent and controlling the ball milling time and the particle size of the fine powder; and improves the flexural strength and compressive strength of the coil slurry by synthesizing a modified dispersant and controlling the mixing time.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] In one aspect, the present invention provides a slurry for a high-power medium-frequency induction furnace coil. The synthetic raw materials for the slurry for a high-power medium-frequency induction furnace coil include the following components in parts by weight:

[0009] Sintered tabular corundum: 65-70 parts;

[0010] Bauxite clinker: 8-14 parts;

[0011] Aluminate cement: 8.9-14.9 parts;

[0012] High-purity low-sodium α-Al2O3 powder: 7-10 parts;

[0013] Industrial grade 99wt% aluminum lactate powder: 1-2 parts;

[0014] Polypropylene fiber: 0.05-0.1 parts;

[0015] Silicone resin: 9-13 parts;

[0016] Composite active agent: 2-4 parts;

[0017] Modified dispersant: 6 to 9 parts.

[0018] Preferably, the sintered tabular corundum is obtained by ball-milling Al2O3 into balls and then calcining them, wherein the mass percentage of Al2O3 is 99.7% to 99.9%, and the rest is SiO2; the particle size of the sintered tabular corundum is 0.045 to 6 mm.

[0019] Preferably, the mass percentage of Al2O3 in the bauxite clinker is 87% to 91%, and the rest is SiO2; the particle size of the bauxite clinker is 0.075 to 3 mm.

[0020] Preferably, the particle size of the aluminate cement is 8 to 10 μm.

[0021] Preferably, the mass percentage of Al2O3 in the high-purity low-sodium α-Al2O3 micropowder is 99.7% to 99.9%, and the rest is Na2O; the particle size of the high-purity low-sodium α-Al2O3 micropowder is 1.8 to 2.4 μm.

[0022] Preferably, the polypropylene fiber has a length of 5 to 6 mm and a diameter of 4 to 6 μm.

[0023] Preferably, the silicone resin is liquid methyl polysiloxane resin.

[0024] Another aspect of the present invention provides a method for preparing a slurry for a high-power medium-frequency induction furnace coil, the method comprising the following steps:

[0025] S1: 8.9-14.9 parts of aluminate cement, 7-10 parts of high-purity low-sodium α-Al2O3 powder, 1-2 parts of industrial-grade 99wt% aluminum lactate powder, and 2-4 parts of a composite active agent are mixed and continuously ground for 4-8 hours to obtain a particle size of the ground powder of 2.4-3.0 μm to obtain a functional additive A;

[0026] S2: 65-70 parts of sintered plate-shaped corundum, 8-14 parts of bauxite clinker, and 0.05-0.1 parts of polypropylene fiber are placed in a mixer and mixed for 5-7 minutes to obtain a premix B;

[0027] S3: placing the functional additive A, the premix B, and 6 to 9 parts of the modified dispersant into a mixer and mixing for 14 to 18 minutes to obtain powder C;

[0028] S4: Before pouring, the powder C is mixed with 9 to 13 parts of silicone resin for 2 hours to obtain the slurry for the high-power medium-frequency induction furnace coil.

[0029] Preferably, the preparation method of the composite active agent in S1 is: ball-milling 8 to 10 parts of graphite and 3 to 5 parts of silicon powder with water as the medium for 3 hours, and drying to obtain the composite active agent.

[0030] Preferably, the preparation method of the modified dispersant in S3 is: dissolving 3 to 5 parts of sodium carboxymethyl cellulose in 10 parts of deionized water to obtain mixture one; adding 2 parts of melamine to the mixture one and stirring for 30 minutes to obtain mixture two; reacting the mixture two in a closed manner at 130 to 150° C. for 8 hours, cooling to room temperature after the reaction is completed, washing and drying to obtain the modified dispersant.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. This invention reduces the volume change rate of coil slurry by varying the dosage and particle size of sintered tabular corundum and aluminate cement. Compared to traditional corundum powder, the sintered tabular corundum used in this invention has advantages such as smaller open pores, lower apparent porosity, lower water absorption, more internally closed pores, and better thermal shock and spalling resistance. Sintered tabular corundum also exhibits excellent volume stability at high temperatures and minimal re-firing shrinkage. Aluminate cement has excellent high-temperature tolerance, and its high-temperature strength is generally higher than that of ordinary Portland cement. It can maintain high strength and stability at high temperatures. Therefore, the coil slurry of the present invention has good thermal shock stability and high-temperature resistance when used at high temperatures. The addition of sintered tabular corundum facilitates the sintering process of the aluminate cement. Especially at high temperatures, the CA / CA2 minerals formed by the hydration reaction of the aluminate cement have strong bonding ability, which can help the sintered tabular corundum to better bond together during the sintering process. The final volume change rate of the coil slurry after firing at 1050°C is -0.04%, and the volume change rate after firing at 1500°C is -0.14%.

[0033] 2. The present invention reduces the apparent porosity of the coil slurry and increases the bulk density by changing the amount of bauxite clinker and high-purity low-sodium α-Al2O3 micropowder, the content of the components therein, and the particle size. The high-purity low-sodium α-Al2O3 micropowder selected in the present invention easily reacts with SiO2 in the bauxite clinker at high temperatures to generate a large amount of rod-shaped or needle-shaped mullite. The formation of mullite can significantly reduce the porosity of the material and densify the material, thereby reducing the apparent porosity of the slurry and improving the thermal shock stability of the slurry. The final slurry has an apparent porosity of 10.3% after sintering at 1050°C and a bulk density of 2.86g / cm 3 After sintering at 1500℃, the apparent porosity is 10.2% and the bulk density is 2.82g / cm 3 .

[0034] 3. The present invention improves the explosion-proof capability of the coil slurry by varying the amounts of industrial-grade 99wt% aluminum lactate powder, polypropylene fiber, and silicone resin, as well as the length and diameter of the polypropylene fiber. The aluminum lactate selected in the present invention can significantly improve the coil slurry's explosion-proof properties. This is because the aluminum lactate dehydrates and gels with the free water in the liquid methylpolysiloxane resin, creating a network of microcracks in the matrix, thereby increasing the material's air permeability and preventing the slurry from bursting. The present invention also incorporates a certain amount of polypropylene fiber to address the problem of bursting caused by rapid baking of the coil slurry and improve the slurry's high-temperature resistance. Ultimately, the coil slurry does not burst at 1000°C.

[0035] 4. The present invention reduces the burnout rate of coil slurry by introducing a composite active agent and controlling the ball milling time and micropowder particle size. The introduction of the composite active agent promotes the formation and stabilization of minerals in the coil slurry, reducing the risk of cracking or breakage during the high-temperature cooling process. Controlling the milling time enhances the activity and filling properties of the α-Al2O3 micropowder, reducing the amount of liquid methylpolysiloxane resin required and filling the pores. After these pores are filled with the α-Al2O3 micropowder, only a very small amount of free water from the methylpolysiloxane resin remains, reducing the loss of the coil slurry during the rapid baking process, thereby improving the slurry's thermal shock stability and high-temperature resistance. The final coil slurry had a burnout rate of 0.32% after being fired at 1050°C for 2 hours and a burnout rate of 1.08% after being fired at 1500°C for 2 hours.

[0036] 5. The present invention improves the flexural strength and compressive strength of the coil slurry by synthesizing a modified dispersant and controlling the mixing time. The main function of the modified dispersant is to improve the dispersibility of the particles in the coil slurry, making the particles evenly distributed, reducing agglomeration caused by mutual attraction between particles, and improving the microstructure between the components. This can make the mixture more uniform and more fluid, thereby improving its flexural strength and compressive strength. Controlling the mixing time is conducive to the interaction between the components and ensures that the components are evenly mixed to achieve the best effect, ultimately improving the flexural strength and compressive strength of the coil slurry. The flexural strength of the coil slurry after being calcined at 1500°C for 2 hours is 27.9MPa, and the compressive strength after being calcined at 1500°C for 2 hours is 198.6MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a volume change rate diagram of Example 1, Example 3, Examples 6-8, Examples 10-11, Examples 13-16 and Comparative Examples 1-3 in the present invention after firing at different temperatures. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] Specific reference Figure 1 The present invention provides a slurry for high-power medium-frequency induction furnace coil and a preparation method thereof. The technical solution is as follows:

[0040] Example 1

[0041] Preparation of composite active agent:

[0042] 8 parts of graphite and 3 parts of silicon powder were ball-milled with water as a medium for 3 hours, and then dried to obtain the composite active agent.

[0043] Preparation of modified dispersant:

[0044] 3 parts of sodium carboxymethyl cellulose were dissolved in 10 parts of deionized water to obtain mixture 1; 2 parts of melamine were added to the mixture 1 and stirred for 30 minutes to obtain mixture 2; the mixture 2 was sealed and reacted at 130° C. for 8 hours. After the reaction was completed, it was cooled to room temperature, washed and dried to obtain the modified dispersant.

[0045] Preparation of slurry for high power medium frequency induction furnace coil:

[0046] S1: 8.9 parts of aluminate cement, 7 parts of high-purity low-sodium α-Al2O3 powder, 1 part of industrial-grade 99wt% aluminum lactate powder, and 2 parts of composite active agent were mixed and continuously ground for 4 hours to obtain a powder particle size of 2.4 μm to obtain functional additive A;

[0047] S2: 65 parts of sintered plate-shaped corundum, 10 parts of bauxite clinker, and 0.1 parts of polypropylene fiber were placed in a mixer and mixed for 5 minutes to obtain premix B;

[0048] S3: placing the functional additive A, the premix B, and 6 parts of the modified dispersant into a mixer and mixing for 14 minutes to obtain powder C;

[0049] S4: Before pouring, the powder C is mixed with 9 parts of silicone resin for 2 hours to obtain the slurry for the high-power medium-frequency induction furnace coil.

[0050] Example 2-16

[0051] Referring to the parameter conditions of the preparation method in Example 1, the specific differences are shown in Table 1.

[0052] Table 1 Parameter conditions of Examples 1-16

[0053]

[0054] Comparative Example 1 refers to the parameter conditions of the preparation method in Example 1, except that no aluminate cement is added.

[0055] Comparative Example 2 refers to the parameter conditions of the preparation method in Example 1, except that silicate cement is used instead of aluminate cement.

[0056] Comparative Example 3 refers to the parameters and conditions of the preparation method in Example 1, except that corundum powder is used instead of sintered plate-shaped corundum.

[0057] Example 17 Volume Change Rate Test

[0058] The coil slurry was cast into standard test blocks of 40×40×160 mm in size using a triple mold, and the volume change rates of Examples 1-16 and Comparative Examples 1-3 after firing at 1050°C and 1500°C were tested. "-" represents volume shrinkage after casting. The results are shown in Table 2. The volume change rates of Examples 1, 3, 6-8, 10-11, 13-16 and Comparative Examples 1-3 after firing at different temperatures are shown in Table 2. Figure 1 shown.

[0059] Table 2 Volume change rate test of Examples 1-16 and Comparative Examples 1-3

[0060] Example Volume change rate after sintering at 1050℃ / % Volume change rate after sintering at 1500℃ / % Example 1 -0.21 -0.32 Example 2 -0.17 -0.29 Example 3 -0.15 -0.26 Example 4 -0.18 -0.28 Example 5 -0.20 -0.31 Example 6 -0.23 -0.32 Example 7 -0.13 -0.23 Example 8 -0.16 -0.25 Example 9 -0.12 -0.22 Example 10 -0.09 -0.20 Example 11 -0.11 -0.23 Example 12 -0.07 -0.17 Example 13 -0.06 -0.15 Example 14 -0.08 -0.16 Example 15 -0.04 -0.14 Example 16 -0.06 -0.15 Comparative Example 1 -0.35 -0.48 Comparative Example 2 -0.28 -0.37 Comparative Example 3 -0.23 -0.35

[0061] From Table 2 and Figure 1 It can be found that in Comparative Example 1, aluminate cement was not added, and the volume change rate of the coil slurry was relatively high, indicating that the addition of aluminate cement can make the coil slurry have better high temperature resistance; in Comparative Example 2, silicate cement was used instead of aluminate cement, and the volume change rate of the coil slurry was significantly improved, because the high temperature resistance of aluminate cement is usually higher than that of ordinary silicate cement, and the high temperature resistance of the slurry can be improved by adding aluminate cement; in Comparative Example 3, corundum powder was used instead of sintered plate-shaped corundum, and the volume change rate of the coil slurry also increased. This is because the sintered plate-shaped corundum after ball milling and calcination has a lower apparent porosity than ordinary corundum powder and has stronger high temperature resistance. Figure 1In Examples 1-6, the amount of sintered plate-shaped corundum was changed. Finally, when the amount was 67 parts, the volume change rate of the coil slurry was the smallest. This is because the sintered plate-shaped corundum selected in the present invention has the advantages of small open pores, low apparent porosity, low water absorption, more internal closed pores, good thermal shock resistance and anti-stripping performance. The sintered plate-shaped corundum has excellent volume stability at high temperatures and relatively small re-firing shrinkage. In Examples 7-11, the content of Al2O3 in the sintered plate-shaped corundum was changed to The volume change rate is the smallest when the Al2O3 content is 99.8% and the particle size is 3.5mm. At this time, the volume change rate of Example 10 after sintering at 1050℃ is -0.09%, and the volume change rate after sintering at 1500℃ is -0.20%. In Examples 12-16, the amount and particle size of aluminate cement are changed. When the amount of aluminate cement is 12.9 parts and the particle size is 1.5μm, the volume change rate of the coil slurry is the smallest. Example 15 is at 10 The volume change rate after firing at 50°C is -0.04%, and the volume change rate after firing at 1500°C is -0.14%. This is because aluminate cement has excellent high-temperature tolerance, and the main mineral phase is CA / CA2. The main characteristic of CA is to ensure that the coil slurry has early demolding strength, and the main characteristic of CA2 is to ensure that the coil slurry has certain high-temperature resistance while promoting high-temperature sintering of the coil slurry, ensuring that the coil slurry has good medium and high temperature performance. Therefore, the coil slurry of the present invention has good high-temperature resistance and thermal shock stability when used at high temperatures, but the introduction of too much aluminate cement will form complex hydration products and a high proportion of bound water, which will lead to prolonged baking time; the addition of sintered plate-shaped corundum helps the sintering process of aluminate cement, especially at high temperatures, the CA / CA2 minerals formed by the hydration reaction of aluminate cement have strong bonding ability, which can help the sintered plate-shaped corundum to better combine together during the sintering process.

[0062] Examples 18-32

[0063] Referring to the parameter conditions of the preparation method in Example 15, the difference lies in the changes in the amount of bauxite clinker and high-purity low-sodium α-Al2O3 micropowder, the component content and the particle size thereof. The specific differences are shown in Table 3.

[0064] Table 3 Parameters and conditions of Example 15 and Examples 18-32

[0065]

[0066]

[0067] Comparative Example 4 refers to the parameter conditions of the preparation method in Example 15, except that no bauxite clinker is added.

[0068] Comparative Example 5 refers to the preparation method of Example 15, the difference is that high-purity low-sodium α-Al2O3 micro powder is not added.

[0069] Comparative Example 6 refers to the preparation method of Example 15, the difference is that high-purity low-sodium α-Al2O3 micro powder is replaced by ordinary α-Al2O3 micro powder.

[0070] Example 33 porosity, bulk density test

[0071] The coil slurry is poured into a 40x40x160mm standard test block by a triple mold, and the porosity and bulk density of the coil slurry of Example 15, Example 18-32 and Comparative Example 4-6 after being fired at 1050℃ and 1500℃ are tested, and the results are shown in Table 4.

[0072] Table 4 Porosity and bulk density test of Example 15, Example 18-32 and Comparative Example 4-6

[0073]

[0074]

[0075] From Table 4, it can be found that in Comparative Example 4, no bauxite clinker is added, the porosity of the coil slurry is significantly increased, and the bulk density is significantly decreased, because the presence of bauxite clinker can improve the high temperature strength of the coil slurry and help it form a dense structure; in Comparative Example 5, high-purity low-sodium α-Al2O3 micro powder is not added, the porosity of the coil slurry is also higher, and the bulk density also decreases significantly, because the presence of high-purity low-sodium α-Al2O3 micro powder can improve the thermal shock resistance of the coil slurry, reduce the porosity of the slurry, and make the material more dense and firm; in Comparative Example 6, ordinary α-Al2O3 micro powder is used instead of high-purity low-sodium α-Al2O3 micro powder, the porosity of the coil slurry is increased compared with the data of the comparative example, and the bulk density is decreased, because the sodium in α-Al2O3 micro powder can form a low-melting-point substance with other raw materials at high temperature, reducing the high-temperature performance of the material, and easily causing the material to shrink at high temperature, thereby causing the material to crack and damage, so the high-purity low-sodium α-Al2O3 micro powder used in the present application can avoid this situation. In Example 15 and Example 18-20, the amount of bauxite clinker is changed, the porosity of the coil slurry first decreases and then increases, and the bulk density first increases and then decreases, when the amount of bauxite clinker is 10 parts, the porosity of Example 18 after being fired at 1050℃ is 11.5%, and the bulk density is 2.71g / cm 3 , the porosity after being fired at 1500℃ is 11.4%, and the bulk density is 2.68g / cm 3In Examples 21-24, the content and particle size of Al2O3 in the bauxite clinker were changed. Example 23 showed the best performance, with an apparent porosity of 11.1% and a bulk density of 2.78 g / cm after firing at 1050 ° C. 3 The apparent porosity after sintering at 1500℃ is 11.2%, and the bulk density is 2.74g / cm 3 In Examples 25-27, the amount of high-purity low-sodium α-Al2O3 powder was changed. When the amount was 8 parts, the performance of Example 25 was the best. At this time, the apparent porosity after sintering at 1050°C was 10.8%, and the bulk density was 2.81g / cm 3 The apparent porosity after sintering at 1500℃ is 10.9% and the bulk density is 2.78g / cm 3 Because the α-Al2O3 micropowder has a small particle size, it has excellent specific surface area and sintering activity. It easily reacts with SiO2 in the bauxite clinker at high temperature to form rod-shaped or needle-shaped mullite. Mullite not only has excellent high-temperature volume stability, but also can densify the material, reduce the porosity of the coil slurry, and improve the high-temperature resistance and thermal shock stability of the coil slurry. In Examples 28-32, the Al2O3 content and particle size in the high-purity low-sodium α-Al2O3 micropowder are changed. Example 31 shows the best performance. The apparent porosity after sintering at 1050°C is 10.3 and the bulk density is 2.86g / cm 3 The apparent porosity after sintering at 1500℃ is 10.2% and the bulk density is 2.82g / cm 3 .

[0076] Examples 34-48

[0077] Referring to the parameter conditions of the preparation method in Example 31, the difference is that the amount of industrial-grade 99wt% aluminum lactate powder, polypropylene fiber and silicone resin, as well as the length and diameter of the polypropylene fiber are changed. The specific differences are shown in Table 5.

[0078] Table 5 Parameters and conditions of Example 31 and Examples 34-48

[0079]

[0080] Comparative Example 7 refers to the parameter conditions of the preparation method in Example 31, except that no polypropylene fiber is added.

[0081] Comparative Example 8 refers to the parameter conditions of the preparation method in Example 31, except that deionized water is used instead of the silicone resin.

[0082] Example 49 Explosion-proof Performance Test

[0083] The anti-explosion performance of the samples of Example 31, Examples 34-48 and Comparative Examples 7-8 were tested by making them into 115x115x115mm samples using a triple die. After the samples were demolded, they were placed into a re-fired furnace and heated from room temperature to 1000°C at a heating rate of 15°C / min. The temperature at which the slurry exploded was recorded as a basis for judging whether the material could be rapidly fired. V represents that the slurry passed the anti-explosion test at that temperature, and x represents that the slurry exploded at that temperature. The results are shown in Table 6.

[0084] Table 6 Anti-explosion performance test of Example 31, Examples 34-48 and Comparative Examples 7-8

[0085]

[0086] It can be seen from Table 6 that in Comparative Example 7, polypropylene fibers were not added, and the coil slurry burst at 500°C, at which time the coil slurry had poor explosion-proof performance; in Comparative Example 8, deionized water was used to replace the silicone resin, and the coil slurry also burst at 500°C, indicating that deionized water as a mixed liquid cannot improve the high-temperature resistance of the coil slurry. In Examples 31 and 34-35, the amount of industrial-grade 99wt% aluminum lactate powder was changed, and the coil slurry had the best explosion-proof performance when the amount was 1.5 parts, and Example 34 burst at 700°C, because industrial-grade 99wt% aluminum lactate powder is a new type of basic emulsion explosion-proof agent composed of a polynuclear complex of aluminum hydroxide ions, can be effectively dissolved in water, and does not produce toxic gases upon heating, and after heating becomes Al2O3, thus having strong high-temperature resistance. The introduction of aluminum lactate can improve the explosion-proof performance of the rapid baking coil slurry, because aluminum lactate can undergo a dehydration gelation reaction with free water in the liquid methyl polysiloxane resin, producing a network of microcracks in the matrix to increase the air permeability of the material, thereby preventing the slurry from bursting. In Examples 36-40, the amount of polypropylene fibers was changed, and Example 37 had better explosion-proof performance and burst at 700°C, because the fibers rapidly shrink, melt, or carbonize upon heating, forming fine pores in the coil slurry, which facilitates the rapid removal of water vapor generated by heating from the coil slurry, rather than the accumulation of water vapor in the coil slurry to form a large steam pressure, thereby improving the explosion-proof performance of the coil slurry. In Examples 41-44, the length and diameter of the polypropylene fibers were changed, and Example 43 had the best explosion-proof performance and burst at 700-1000°C. In Examples 45-48, the amount of silicone resin was changed, and the explosion-proof performance was best when the amount was 11 parts, and Example 46 did not burst at 1000°C, having very strong high-temperature resistance and thermal shock stability, because the use of resin instead of water in the coil slurry greatly improves the performance of the coil slurry, as the resin has a high solid content and little free water, which can prevent cracking after pouring and achieve the purpose of rapid baking without bursting. Liquid methyl polysiloxane resin is a bulk resin with a highly cross-linked structure, has high hardness after curing, is easily combined with inorganic materials, and has very high high-temperature resistance, and is combined in the slurry in the form of Si-O and Si-C bonds, thus the coil slurry combined with this resin has strong adhesion under high-temperature conditions, can tightly combine the aluminum lactate powder and the polypropylene fibers, and together improve the explosion-proof performance of the coil slurry, while also having excellent high-temperature resistance.

[0087] Examples 50-60

[0088] Referring to the preparation method in Example 46, the difference is that the preparation parameters of the composite active agent and the ball milling time and particle size of the micro powder are changed, as shown in Table 7.

[0089] Table 7 Parameters conditions for Example 46 and Examples 50-60

[0090]

[0091]

[0092] Comparative Example 9 refers to the parameters conditions of the preparation method in Example 46, except that no composite active agent is added.

[0093] Comparative Example 10 refers to the parameters conditions of the preparation method in Example 46, except that only graphite is used as the composite active agent.

[0094] Comparative Example 11 refers to the parameters conditions of the preparation method in Example 46, except that no ball milling is performed.

[0095] Example 61 Burn-off rate test

[0096] Examples 46, Examples 50-60 and Comparative Examples 9-11 are respectively cast into 40x40x160mm size standard test blocks using a triplex mold, and the burn-off rate after burning at 1050℃ and 1500℃ for 2h is tested, and the results are shown in Table 8.

[0097] Table 8 Burn-off rate test of Example 46, Examples 50-60 and Comparative Examples 9-11

[0098] Example Burning rate at 1050℃×2h / % Burning rate at 1500℃×2h / % Example 46 0.65 1.40 Example 50 0.58 1.33 Example 51 0.63 1.38 Example 52 0.51 1.27 Example 53 0.54 1.32 Example 54 0.46 1.22 Example 55 0.50 1.26 Example 56 0.40 1.17 Example 57 0.45 1.22 Example 58 0.36 1.13 Example 59 0.32 1.08 Example 60 0.35 1.11 Comparative Example 9 1.03 2.25 Comparative Example 10 0.72 1.54 Comparative Example 11 1.62 3.66

[0099] It can be found from Table 8 that in Comparative Example 9, no composite active agent is added, and the burning loss rate of the coil slurry is obviously higher than that of the examples, indicating that the presence of the composite active agent can reduce the burning loss rate of the coil slurry; in Comparative Example 10, the graphite in the composite active agent is removed, and the burning loss rate of the coil slurry increases, indicating that the presence of graphite can improve the overall performance of the composite active agent, thereby reducing the burning loss rate of the coil slurry; in Comparative Example 11, no ball milling is performed, and the burning loss rate of the coil slurry is very high, indicating that without ball milling, the particle size of the material is too large, which can easily cause damage during subsequent sintering, thereby increasing the burning loss rate. In Examples 46 and 50-53, the amounts of graphite and silicon powder are changed, and the burning loss rate of the coil slurry is the lowest when the amount of graphite is 9 parts and the amount of silicon powder is 4 parts; the burning loss rate of Example 52 after sintering at 1050°C for 2 hours is 0.51%, and the burning loss rate after sintering at 1500°C for 2 hours is 1.27%; in Examples 54-55, the amount of the composite active agent is changed, and the burning loss rate of Example 54 is the lowest, which is 0.46% after sintering at 1050°C for 2 hours and 1.22% after sintering at 1500°C for 2 hours; because the introduction of the composite active agent can promote the formation and stability of minerals in the coil slurry, it can reduce the risk of cracking or damage of the coil slurry during high-temperature cooling; in Examples 56-60, the ball milling time and the particle size of the micro powder are changed, and the burning loss rate of the coil slurry is the lowest when the ball milling time is 6h and the particle size of the micro powder is 2.8μm; at this time, the burning loss rate of Example 59 after sintering at 1050°C for 2 hours is 0.32%, and the burning loss rate after sintering at 1500°C for 2 hours is 1.08%; this is because controlling the milling time makes the α-Al2O3 micro powder have higher activity and be more easily filled, while reducing the amount of liquid methyl polysiloxane resin added, which has the advantage of filling the pores and gaps excellently; after the pores are filled with the α-Al2O3 micro powder, only a very small amount of free water in the methyl polysiloxane resin remains in the pores, which reduces the loss of the coil slurry during rapid baking, thereby improving the thermal shock stability and high-temperature resistance of the slurry.

[0100] Examples 62-72

[0101] Referring to the parameter conditions of the preparation method in Example 59, the difference is that the preparation parameters of the synthetic modified dispersant and the mixing time are changed, and the specific differences are shown in Table 9.

[0102] Table 9 Parameter conditions of Example 59 and Examples 62-72

[0103]

[0104]

[0105] Comparative Example 12 refers to the parameters of the preparation method in Example 59, except that no modified dispersant was added.

[0106] Comparative Example 13 refers to the parameters of the preparation method in Example 59, except that the temperature of the reaction in the synthesis of the modified dispersant was 200°C.

[0107] Comparative Example 14 refers to the parameters of the preparation method in Example 59, except that the temperature of the reaction in the synthesis of the modified dispersant was 80°C.

[0108] Example 73 Flexural and compressive strength test

[0109] The samples of Example 59, Examples 62-72 and Comparative Examples 12-14 were respectively cast into 40x40x160mm standard test blocks using a triplex mold, and the flexural and compressive strength of the test blocks at the corresponding temperature was tested, and the results are shown in Table 10.

[0110] Table 10 Flexural and compressive strength test of Example 59, Examples 62-72 and Comparative Examples 12-14

[0111]

[0112] It can be found from Table 10 that in Comparative Example 12, no modified dispersant is added, and the bending strength and compressive strength of the coil slurry are significantly reduced, indicating that the modified dispersant plays a certain auxiliary role in the slurry, helping to improve the high temperature resistance and thermal shock stability of the slurry; in Comparative Example 13, when the temperature for synthesizing the modified dispersant is changed to 200°C, the bending strength and compressive strength of the coil slurry decrease, because when the temperature is too high, the crosslinking between polymers is too tight, which makes the coil slurry brittle and reduces the high temperature resistance and thermal shock stability; in Comparative Example 14, when the temperature for synthesizing the modified dispersant is changed to 80°C, the bending strength and compressive strength of the coil slurry also decrease, because when the temperature is too low, the crosslinking reaction is not sufficient, and the modified dispersant is difficult to achieve the expected effect, thereby reducing the high temperature resistance of the coil slurry. In Examples 59 and 62-65, the preparation parameters of the modified dispersant are changed, and the effect of Example 64 is the best, with the highest bending strength and compressive strength; in Examples 66-68, the amount of modified dispersant is changed, and the bending strength and compressive strength are the highest when the amount of modified dispersant is 8 parts, and the bending strength after burning at 1500°C for 2 hours is 27.2 MPa, and the compressive strength after burning at 1500°C for 2 hours is 197.9 MPa. The main role of the modified dispersant is to improve the dispersibility of the particles in the coil slurry, make the particles uniformly distributed, reduce the agglomeration phenomenon caused by the mutual attraction between particles, and improve the microstructure between components, so that the mixture is more uniform and has better flowability, thereby improving the bending strength and compressive strength. In Examples 69-72, the mixing time is changed, and the bending strength and compressive strength of Example 71 are the highest, with a bending strength of 27.9 MPa after burning at 1500°C for 2 hours, and a compressive strength of 198.6 MPa after burning at 1500°C for 2 hours. Because controlling the mixing time is beneficial to the interaction between components and makes the components uniformly mixed to achieve the best effect, the bending strength and compressive strength of the coil slurry are ultimately improved.

[0113] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A slurry for high-power medium-frequency induction furnace coil, characterized by: The synthetic raw materials of the slurry for high-power medium-frequency induction furnace coil include the following components in parts by weight: Sintered tabular corundum: 65-70 parts; Bauxite clinker: 8-14 parts; Aluminate cement: 8.9-14.9 parts; High-purity low-sodium α-Al2O3 powder: 7-10 parts; Industrial grade 99wt% aluminum lactate powder: 1-2 parts; Polypropylene fiber: 0.05-0.1 parts; Silicone resin: 9-13 parts; Composite active agent: 2-4 parts; Modified dispersant: 6-9 parts; The composite active agent is obtained by ball-milling 8 to 10 parts of graphite and 3 to 5 parts of silicon powder using water as a medium for 3 hours and then drying. The modified dispersant is prepared by dissolving 3 to 5 parts of sodium carboxymethyl cellulose in 10 parts of deionized water to obtain a first mixture; adding 2 parts of melamine to the first mixture and stirring for 30 minutes to obtain a second mixture; and subjecting the second mixture to a closed reaction at 130 to 150° C. for 8 hours, cooling the mixture to room temperature after the reaction is completed, and washing and drying the mixture.

2. The slurry for high-power medium-frequency induction furnace coil according to claim 1, characterized in that: The sintered tabular corundum is obtained by calcining Al2O3 after ball milling, wherein the mass percentage of Al2O3 is 99.7% to 99.9% and the rest is SiO2; the particle size of the sintered tabular corundum is 0.045 to 6 mm.

3. The slurry for high-power medium-frequency induction furnace coil according to claim 1, characterized in that: The mass percentage of Al2O3 in the bauxite clinker is 87% to 91%, and the rest is SiO2; the particle size of the bauxite clinker is 0.075 to 3 mm.

4. The slurry for high-power medium-frequency induction furnace coil according to claim 1, characterized in that: The particle size of the aluminate cement is any one of 0.075 μm, 1.5 μm and 3 μm.

5. The slurry for high-power medium-frequency induction furnace coil according to claim 1, characterized in that: The mass percentage of Al2O3 in the high-purity low-sodium α-Al2O3 micropowder is 99.7% to 99.9%, and the rest is Na2O; the particle size of the high-purity low-sodium α-Al2O3 micropowder is 1.8 to 2.4 μm.

6. The slurry for high-power medium-frequency induction furnace coil according to claim 1, characterized in that: The polypropylene fiber has a length of 5 to 6 mm and a diameter of 4 to 6 μm.

7. The slurry for high-power medium-frequency induction furnace coil according to claim 1, characterized in that: The organic silicone resin is liquid methyl polysiloxane resin.

8. A method for preparing a slurry for a high-power medium-frequency induction furnace coil, characterized in that: The slurry for high-power medium-frequency induction furnace coil according to claim 1 is prepared by a preparation method comprising the following steps: S1: 8.9-14.9 parts of aluminate cement, 7-10 parts of high-purity low-sodium α-Al2O3 powder, 1-2 parts of industrial-grade 99wt% aluminum lactate powder, and 2-4 parts of a composite active agent are mixed and continuously ground for 4-8 hours until the ground powder has a particle size of 2.4-3.0 μm, thereby obtaining a functional additive A; S2: 65-70 parts of sintered plate-shaped corundum, 8-14 parts of bauxite clinker, and 0.05-0.1 parts of polypropylene fiber are placed in a mixer and mixed for 5-7 minutes to obtain a premix B; S3: placing the functional additive A, the premix B, and 6 to 9 parts of the modified dispersant into a mixer and mixing for 14 to 18 minutes to obtain powder C; S4: Before pouring, the powder C is mixed with 9 to 13 parts of silicone resin for 2 hours to obtain the slurry for the high-power medium-frequency induction furnace coil.

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