A thermal insulation castable composed of alumina hollow spheres and pure calcium aluminate cement and its preparation method.

Abstract

This invention discloses a thermal insulation castable combining hollow alumina spheres and pure calcium aluminate cement, and its preparation method. The thermal insulation castable mainly consists of 15-25% 5-3mm hollow alumina spheres, 17-28% 3-1mm hollow alumina spheres, 12-20% 1-0mm hollow alumina spheres, 15-30% tabular corundum powder, 0.5-3% chromium oxide, 8-15% alumina micropowder, 3-10% pure calcium aluminate cement, and 0-5% cenospheres; additionally, 0.05-0.15% explosion-proof fiber and 0.03-0.08% other additives are added. The hollow alumina spheres, tabular corundum powder, chromium oxide, and cenospheres are dry-mixed, then alumina micropowder, pure calcium aluminate cement, explosion-proof fiber, and other additives are added and stirred. Water is then added and stirred to form a slurry. The slurry is then subjected to vibration molding, curing, and baking to obtain the thermal insulation castable. This invention optimizes particle size distribution and component matching to achieve a synergistic improvement in the thermal insulation performance, mechanical strength and high-temperature stability of the material, thereby preparing a thermal insulation castable that meets the requirements of electric furnace lids.

Description

Technical Field

[0001] This invention belongs to the field of refractory and heat insulation materials technology, specifically relating to a heat insulation castable made of alumina hollow spheres and pure calcium aluminate cement, its preparation method and application. The heat insulation castable of this invention is mainly suitable for the heat insulation lining of electric furnace lids. Background Technology

[0002] As a core heating device in industries such as metallurgy and chemical engineering, the furnace lid of an electric furnace is constantly exposed to high temperatures and plays a crucial role in isolating heat loss and protecting the furnace structure. The performance of the thermal insulation material used for the furnace lid directly affects the thermal efficiency, energy consumption, and service life of the electric furnace. Currently, commonly used thermal insulation castables for electric furnace lids often suffer from a trade-off between thermal insulation performance and mechanical strength: some materials have high porosity and low thermal conductivity, but their strength decreases significantly after high-temperature firing, making them prone to peeling and breakage; other materials have excellent mechanical properties, but their high density results in poor thermal insulation, leading to increased heat loss from the furnace and higher energy consumption.

[0003] Alumina hollow spheres, as a lightweight, high-strength insulating aggregate, possess advantages such as high alumina content, high melting point, high porosity, and low thermal conductivity, and are widely used in high-temperature insulating refractory materials. Pure calcium aluminate cement, as a binder, exhibits rapid hardening, high strength, high temperature resistance, and good compatibility with refractory aggregates, making it an ideal binder for preparing high-temperature castables. However, existing alumina hollow sphere castables suffer from problems in their formulation design, such as unreasonable particle size distribution and insufficient high-temperature stability, making it difficult to fully utilize the synergistic effect of each component and failing to meet the comprehensive requirements of electric furnace lids for material insulation performance, mechanical strength, and high-temperature stability. Therefore, developing a formulation-optimized, high-performance alumina hollow sphere-pure calcium aluminate cement-bonded insulating castable has significant industrial application value. Summary of the Invention

[0004] The technical problem this invention aims to solve is to address the issues of imbalance between insulation and strength, and poor high-temperature stability, found in existing insulating castables for electric furnace covers. This invention provides an insulating castable combining alumina hollow spheres and pure calcium aluminate cement, along with its preparation method. By optimizing particle size distribution and component composition, this invention achieves a synergistic improvement in the material's insulation performance, mechanical strength, and high-temperature stability, thereby producing an insulating castable that meets the requirements for electric furnace covers.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a thermal insulation castable combining alumina hollow spheres and pure calcium aluminate cement. Expressed as a percentage by weight, the thermal insulation castable mainly consists of 15-25% 5-3mm alumina hollow spheres, 17-28% 3-1mm alumina hollow spheres, 12-20% 1-0mm alumina hollow spheres, 15-30% 325-mesh tabular corundum powder, 0.5-3% 200-mesh chromium oxide, 8-15% alumina micro powder, 3-10% pure calcium aluminate cement, and 0-5% cenospheres. Additionally, it contains 0.05-0.15% explosion-proof fiber and 0.03-0.08% other additives by weight of all raw materials.

[0007] According to the above-mentioned thermal insulation castable combining alumina hollow spheres and pure calcium aluminate cement, the thermal insulation castable is composed of 20% 5-3mm alumina hollow spheres, 20% 3-1mm alumina hollow spheres, 16% 1-0mm alumina hollow spheres, 23% 325-mesh tabular corundum powder, 1.5% 200-mesh chromium oxide, 10% alumina micro powder, 8% pure calcium aluminate cement, and 1.5% cenospheres; in addition, explosion-proof fiber and other additives accounting for 0.1% of the total weight of various raw materials are added.

[0008] According to the above-mentioned thermal insulation castable combining alumina hollow spheres and pure calcium aluminate cement, the alumina hollow spheres contain ≥98.5% alumina and have an apparent density ≤1.2g / cm³; the chromium oxide has a purity ≥99% and a 200-mesh passing rate ≥98%.

[0009] According to the above-mentioned heat-insulating castable material composed of hollow alumina spheres and pure calcium aluminate cement, the particle size of the alumina powder is ≤0.0015mm, and the alumina content in the alumina powder is ≥99.5%.

[0010] According to the above-mentioned heat-insulating castable material composed of hollow alumina spheres and pure calcium aluminate cement, the pure calcium aluminate cement contains ≥75% alumina and has a particle size ≤0.044mm.

[0011] According to the above-mentioned heat-insulating castable material composed of alumina hollow spheres and pure calcium aluminate cement, the explosion-proof fiber is polypropylene fiber with a length of 3-5 mm; the other additives are polycarboxylate dispersants.

[0012] In addition, a method for preparing a thermal insulation castable bonded to alumina hollow spheres and pure calcium aluminate cement is provided, the method comprising the following steps:

[0013] (1) Ingredients: Weigh each component according to the above-mentioned heat insulation castable ratio (measurement accuracy error ≤ ±0.1%).

[0014] (2) Dry mixing: The weighed hollow alumina spheres, plate-shaped corundum powder, chromium oxide and cenospheres are dry mixed (dry mixing time is 3 to 5 minutes).

[0015] (3) Wet mixing: Add alumina micro powder, pure calcium aluminate cement, explosion-proof fiber and other additives to the material obtained by dry mixing and stir (stirring time is 2-3 minutes), then add water and continue stirring (the amount of water added accounts for 4-6% of the total mass of raw materials, and the stirring time is 5-8 minutes) to make a slurry;

[0016] (4) Casting and molding: The slurry is poured into the mold and vibrated to form the shape;

[0017] (5) Curing: Curing the product obtained by vibration molding;

[0018] (6) Baking: The cured product is baked to obtain the finished heat insulation casting material.

[0019] According to the above preparation method of heat insulation castable of alumina hollow sphere-pure calcium aluminate cement, the curing in step (5) is to cure for 24-48 hours in an environment of room temperature 20-25℃ and relative humidity ≥60%.

[0020] According to the above preparation method of heat insulation castable with alumina hollow spheres and pure calcium aluminate cement, the baking in step (6) is to bake at 80-110℃ for 12 hours, and then bake at 110℃ for 24 hours.

[0021] According to the above preparation method of the heat-insulating castable of alumina hollow spheres-pure calcium aluminate cement, the resulting heat-insulating castable is used as the heat-insulating lining of the electric furnace cover.

[0022] In this invention, the hollow alumina spheres used have an alumina content ≥98.5% and an apparent density ≤1.2 g / cm³, ensuring excellent thermal insulation performance and high-temperature stability. The chromium oxide raw material has a purity ≥99% and a 200-mesh pass rate ≥98%, enabling it to form a stable composite phase with the matrix, improving the material's high-temperature strength and corrosion resistance. The alumina micropowder has a particle size ≤0.0015 mm and an alumina content ≥99.5%, filling matrix pores and promoting high-temperature sintering densification. The pure calcium aluminate cement raw material has an alumina content ≥75% and a particle size ≤0.044 mm, possessing good hydration bonding ability and high-temperature stability. The cenospheres have a bulk density ≤0.4 g / cm³. 3The SiO2+Al2O3 content is ≥90%, which further reduces the bulk density of the material and optimizes the heat insulation effect; the raw material, plate-shaped corundum powder (325 mesh), contains ≥99% alumina and has a complete plate-shaped crystal structure, which can improve the mechanical strength and wear resistance of the material; the explosion-proof fiber is polypropylene fiber with a length of 3-5mm, which can decompose and escape during baking to form micropores, relieve thermal stress, and prevent the material from cracking; the polycarboxylate dispersant used can optimize the slurry fluidity, reduce the amount of water used in construction, and improve the density of the material.

[0023] The positive and beneficial effects of this invention are as follows:

[0024] 1. Optimized particle size distribution and excellent thermal insulation performance: This invention uses three-graded alumina hollow spheres (5-3mm, 3-1mm, 1-0mm) combined with cenospheres to form a reasonable pore structure. Combined with the filling effect of alumina micro powder, the porosity of the material reaches 40% after baking at 110℃, and increases to 55% after firing at 1500℃. The thermal conductivity at 350℃ is only 0.5W / (m·K), which can effectively block heat loss from the electric furnace cover and reduce energy consumption.

[0025] 2. Synergistic improvement of mechanical strength and high-temperature stability: This invention uses pure calcium aluminate cement as a binder, combined with tabular corundum powder to enhance the matrix strength. Chromium oxide forms a stable composite phase with the matrix at high temperature, reducing the formation of low-melting-point liquid phase. This results in a flexural strength ≥3MPa and a compressive strength ≥10MPa after baking at 110℃, and a flexural strength ≥10MPa and a compressive strength ≥30MPa after firing at 1500℃. The high-temperature strength not only does not decrease but is significantly improved, thus enabling it to withstand the high-temperature impact and mechanical erosion of the electric furnace lid.

[0026] 3. Excellent explosion-proof performance and convenient construction: The explosion-proof fibers added in this invention can form micropores during the baking process, which can alleviate the concentration of thermal stress and effectively prevent the material from cracking; the slurry has good fluidity and can be formed by vibration to obtain a seamless overall structure, which can be adapted to the complex shape of the electric furnace cover, resulting in high construction efficiency and better overall sealing performance than traditional brick masonry.

[0027] 4. Highly targeted and long service life: The formula of the thermal insulation castable of this invention is specifically designed for the working conditions of electric furnace cover. The prepared material has the characteristics of low thermal conductivity, high strength, high temperature resistance and corrosion resistance. It can adapt to the thermal shock conditions and high temperature environment of frequent start-up and shutdown of electric furnace cover, which can significantly extend the service life of furnace cover lining and reduce equipment maintenance costs.

[0028] 5. The relevant performance data of the heat insulation castable prepared by the present invention are detailed in Table 1.

[0029] Table 1. Relevant performance data of the thermal insulation castable of the present invention.

[0030] . Detailed Implementation

[0031] The present invention will be further illustrated below with reference to the embodiments, but this does not limit the scope of protection of the technical solution of the present invention.

[0032] In the following examples, the alumina hollow spheres used have an alumina content ≥98.5% and an apparent density ≤1.2 g / cm³. 3 Chromium oxide purity ≥99%, 200 mesh passing rate ≥98%; alumina micro powder particle size ≤0.0015mm, alumina content ≥99.5%; pure calcium aluminate cement alumina content ≥75%, particle size ≤0.044mm; explosion-proof fiber is polypropylene fiber, length 3-5mm; other additives are polycarboxylate dispersants.

[0033] Example 1:

[0034] This invention relates to a thermal insulation castable combining alumina hollow spheres and pure calcium aluminate cement. Expressed by weight percentage, it comprises 20% 5-3mm alumina hollow spheres, 20% 3-1mm alumina hollow spheres, 16% 1-0mm alumina hollow spheres, 23% 325-mesh tabular corundum powder, 1.5% 200-mesh chromium oxide, 10% alumina micro powder, 8% pure calcium aluminate cement, and 1.5% cenospheres. Additionally, it includes 0.1% explosion-proof fiber and 0.05% polycarboxylate dispersant by weight of all raw materials.

[0035] Example 2:

[0036] The detailed steps of the preparation method of the thermal insulation castable of alumina hollow spheres-pure calcium aluminate cement bond in Embodiment 1 of the present invention are as follows:

[0037] (1) Ingredients: Weigh each component according to the proportion of the heat insulation castable described in Example 1 (measurement accuracy error ≤ ±0.1%).

[0038] (2) Dry mixing: The weighed hollow alumina spheres, tabular corundum powder, chromium oxide and cenospheres are dry mixed for 4 minutes;

[0039] (3) Wet mixing: Add alumina micro powder, pure calcium aluminate cement, explosion-proof fiber and polycarboxylate dispersant to the material obtained by dry mixing and stir for 3 minutes. Then add water accounting for 5% of the total weight of each raw material and continue stirring for 7 minutes to make a slurry.

[0040] (4) Casting and molding: The slurry is injected into the electric furnace cover mold and vibrated to form the mold;

[0041] (5) Curing: The product obtained by vibration molding is cured at room temperature and relative humidity ≥60% for 48 hours;

[0042] (6) Baking: The cured product is baked at a low temperature of 80℃ for 12 hours, and then baked at a constant temperature of 110℃ for 24 hours to obtain the finished heat insulation casting material.

[0043] The finished product obtained in this embodiment was tested for performance: after drying at 110℃ for 24 hours, the bulk density was 1.49 g / cm³. 3 Porosity 40%, flexural strength 3.5 MPa, compressive strength 13.5 MPa; density after firing at 1500℃ for 3 hours 1.45 g / cm³ 3 It has a porosity of 55%, a flexural strength of 13.3 MPa, and a compressive strength of 36.2 MPa; a thermal conductivity of 0.48 W / (m·K) at 350℃; and it can withstand 20 air-cooled thermal shocks at 1100℃ without damage, meeting the requirements for heat insulation of electric furnace lids.

[0044] Example 3:

[0045] This invention relates to a thermal insulation castable combining alumina hollow spheres and pure calcium aluminate cement. Expressed as a percentage by weight, it comprises 18% 5-3mm alumina hollow spheres, 22% 3-1mm alumina hollow spheres, 14% 1-0mm alumina hollow spheres, 25% 325-mesh tabular corundum powder, 1.0% 200-mesh chromium oxide, 12% alumina micro powder, 6% pure calcium aluminate cement, and 2.0% cenospheres. Additionally, it includes 0.12% explosion-proof fiber and 0.07% polycarboxylate dispersant by weight of all raw materials.

[0046] Example 4:

[0047] The preparation method of the thermal insulation castable of alumina hollow spheres-pure calcium aluminate cement in Example 3 of this invention is basically the same as that in Example 2, except that:

[0048] In step (3): the amount of water added accounts for 4.5% of the total mass of each raw material.

[0049] The finished product obtained in this embodiment was tested for performance: after drying at 110℃ for 24 hours, the bulk density was 1.48 g / cm³. 3 It has a porosity of 41%, a flexural strength of 3.5 MPa, and a compressive strength of 13.2 MPa; after firing at 1500℃ for 3 hours, the porosity is 56%, the flexural strength is 12.1 MPa, and the compressive strength is 34.2 MPa; the thermal conductivity at 350℃ is 0.49 W / (m・K), indicating the best thermal insulation performance.

Claims

1. A thermal insulation castable refractory bonded to alumina hollow spheres and pure calcium aluminate cement, characterized in that: Expressed as a percentage by weight, the thermal insulation castable mainly consists of 15-25% 5-3mm alumina hollow spheres, 17-28% 3-1mm alumina hollow spheres, 12-20% 1-0mm alumina hollow spheres, 15-30% 325-mesh tabular corundum powder, 0.5-3% 200-mesh chromium oxide, 8-15% alumina micro powder, 3-10% pure calcium aluminate cement, and 0-5% cenospheres; in addition, it contains 0.05-0.15% explosion-proof fiber and 0.03-0.08% other additives by weight of all raw materials.

2. The thermal insulation castable refractory combining alumina hollow spheres and pure calcium aluminate cement according to claim 1, characterized in that: The heat-insulating castable is composed of 20% 5-3mm hollow alumina spheres, 20% 3-1mm hollow alumina spheres, 16% 1-0mm hollow alumina spheres, 23% 325-mesh tabular corundum powder, 1.5% 200-mesh chromium oxide, 10% alumina micro powder, 8% pure calcium aluminate cement, and 1.5% cenospheres; in addition, explosion-proof fiber and other additives accounting for 0.1% of the total weight of various raw materials are added.

3. The thermal insulation castable refractory combining alumina hollow spheres and pure calcium aluminate cement according to claim 1, characterized in that: The alumina hollow spheres contain ≥98.5% alumina and have an apparent density ≤1.2g / cm³; the chromium oxide has a purity ≥99% and a 200-mesh pass rate ≥98%.

4. The thermal insulation castable refractory combining alumina hollow spheres and pure calcium aluminate cement according to claim 1, characterized in that: The alumina micro powder has a particle size ≤0.0015mm and an alumina content ≥99.5%.

5. The thermal insulation castable refractory combining alumina hollow spheres and pure calcium aluminate cement according to claim 1, characterized in that: The pure calcium aluminate cement has an alumina content of ≥75% and a particle size of ≤0.044mm.

6. The thermal insulation castable refractory combining alumina hollow spheres and pure calcium aluminate cement according to claim 1, characterized in that: The explosion-proof fiber is polypropylene fiber with a length of 3-5 mm; the other additives are polycarboxylate dispersants.

7. A method for preparing a thermal insulation castable refractory bonded to alumina hollow spheres and pure calcium aluminate cement, characterized in that, The preparation method includes the following steps: (1) Ingredients: Weigh each component according to the proportion of the heat insulation castable as described in claim 1; (2) Dry mixing: The weighed hollow alumina spheres, tabular corundum powder, chromium oxide and cenospheres are dry mixed; (3) Wet mixing: Add alumina micro powder, pure calcium aluminate cement, explosion-proof fiber and other additives to the material obtained by dry mixing and stir. Then add water and continue stirring to make a slurry. (4) Casting and molding: The slurry is poured into the mold and vibrated to form the shape; (5) Curing: Curing the product obtained by vibration molding; (6) Baking: The cured product is baked to obtain the finished heat insulation casting material.

8. The preparation method of the thermal insulation castable of alumina hollow spheres-pure calcium aluminate cement bonded according to claim 7, characterized in that: The curing described in step (5) is carried out for 24 to 48 hours at a room temperature of 20 to 25°C and a relative humidity of ≥60%.

9. The preparation method of the thermal insulation castable of alumina hollow spheres-pure calcium aluminate cement bonded according to claim 7, characterized in that: The baking in step (6) is to bake at 80-110℃ for 12 hours, and then bake at a constant temperature of 110℃ for 24 hours.

10. The preparation method of the thermal insulation castable of alumina hollow spheres-pure calcium aluminate cement according to claim 7, characterized in that: The resulting heat-insulating castable is used as the heat-insulating lining for the electric furnace cover.