Heating furnace water beams and columns use calcium hexaaluminate porous insulating castable.

Abstract

This invention discloses a porous thermal insulation castable made of calcium hexaaluminate for use in heating furnace water beams and columns. It is composed of a main castable material and appropriate additives. The main castable material is composed of the following raw materials in parts by mass: 63-90 parts of calcium hexaaluminate, 3-10 parts of calcined alumina powder, 3-9 parts of activated alumina micro powder, and 4-18 parts of calcium aluminate cement raw material, and the sum of the parts by mass of each raw material is 100 parts. The additives are water-reducing agent, mineralizer, air-entraining agent and foam stabilizer. This invention utilizes the inherent low thermal conductivity of calcium hexaaluminate and the micropores formed by its interwoven hexagonal lamellar structure, and further reduces the thermal conductivity of the castable by creating pores with an air-entraining agent. This overcomes the problems of high thermal conductivity, poor thermal insulation performance, and insufficient resistance to iron oxide scale and ferrous silicate corrosion in existing heavy aluminosilicate refractory castables used for heating furnace water beams and columns. It improves the thermal insulation performance of the castable, increases its high-temperature mechanical strength, extends its service life, and reduces water cooling heat loss.

Description

Technical Field

[0001] This invention relates to the field of refractory materials for heating furnaces, specifically to a porous calcium hexaaluminate insulating castable for water beams and columns of heating furnaces. Background Technology

[0002] Calcium hexaaluminate (CaO·6Al₂O₃, CA6, mineral name: Hibonite) is the calcium aluminate phase with the highest Al₂O₃ content in the CaO-Al₂O₃ system, with a melting point as high as 1875℃. Calcium hexaaluminate exhibits excellent properties such as high refractoriness, low solubility in iron-containing slag, high stability in reducing atmospheres, good stability in alkaline environments, and low wettability to molten metals and slags. Due to the large number of micron-sized pores in CA6, its thermal conductivity remains low even at high temperatures, making it a unique new type of thermally insulating refractory material. Combined with its excellent thermal shock resistance and slag resistance, calcium hexaaluminate refractories have broad application prospects in high-temperature industries such as steel, ceramics, glass, and petrochemicals.

[0003] Currently, the insulation linings for water beams and columns in steel rolling mill heating furnaces mostly employ a double-layer composite structure. The inner layer is a 20mm thick refractory fiber blanket, and the outer layer is a 60mm thick heavy aluminosilicate castable. While this structure offers high strength, it also has high thermal conductivity, resulting in a service life of only 2-3 years. Sometimes, localized repairs are required after a very short period. Furthermore, the high thermal conductivity (1.2-1.66 W / m·K, hot surface temperature 1000℃) and poor insulation performance of heavy aluminosilicate castable are major contributing factors to the high heat loss from water cooling in water beams and columns. The national standard "Refractory Castables for Steel Rolling Mill Heating Furnaces" (GB / T22590-2021) does not specify requirements for the thermal conductivity of castables used in water-cooled pipes. While lightweight calcium hexaluminate raw materials from abroad offer good insulation, their low compressive strength cannot fully meet the practical requirements for high-temperature insulation and protection of heating furnace water beams and columns.

[0004] The invention patent with publication number CN107500747A discloses a dense calcium hexaaluminate castable, comprising the following raw materials by weight percentage: 15-45% calcium hexaaluminate raw material with a particle size of 3-5 mm, 10-30% calcium hexaaluminate raw material with a particle size of 1-3 mm, 0-20% calcium hexaaluminate raw material with a particle size of 0.088-1 mm, 0-20% corundum raw material with a particle size of 0.088-1 mm, 0-30% calcium hexaaluminate raw material with a particle size of less than 88 μm, 0-30% sintered corundum powder with a particle size of less than 88 μm, 0-10% α-Al2O3 micro powder, 5-15% pure aluminate cement, and 0-20% spinel. This invention is used for the production of working liners for steel ladles. It comes into direct contact with molten steel at 1530-1620℃. The mineral phases generated by the reaction at high temperatures are all high-melting-point phases, which have high strength and refractoriness, good resistance to erosion and spalling, and a purifying effect on molten steel. However, the material has a high density and relatively high thermal conductivity. It is also difficult to fully form the calcium hexaaluminate phase at the furnace temperature of 900-1300℃ in the steel rolling heating furnace, making it difficult to use for heat insulation of water beams and columns in the heating furnace.

[0005] Chinese patent application CN104086192A discloses a lightweight thermal insulation calcium hexaaluminate castable, comprising the following raw materials by weight percentage: ultra-lightweight calcium hexaaluminate with a particle size of 3-6 mm (bulk density 0.4-0.5 g / cm³). 3 The composition consists of 25-35% ultra-lightweight calcium hexaaluminate with a particle size of 1-3 mm, 10-15% ultra-lightweight calcium hexaaluminate with a particle size of 0.088-1 mm, 0-25% ultra-lightweight calcium hexaaluminate with a particle size <88 μm, 0-25% corundum fine powder with a particle size <88 μm, 0-10% α-Al2O3 micro powder, and 5-20% pure calcium aluminate cement; 0.12-0.18% water-reducing agent is added according to the total weight of the above raw materials. This invention's lightweight insulating calcium hexaaluminate castable is used for permanent lining insulation layers of steel ladles. It has a low bulk density (0.22-0.35 g / cm3) and good thermal insulation performance, but its strength is relatively poor (2.9-6.2 MPa), making it unsuitable for long-term use as a hot working surface and unsuitable for thermal insulation of water beams and columns in heating furnaces.

[0006] The invention patent with publication number CN114874003A discloses a low thermal conductivity steel ladle permanent layer castable containing calcium hexaaluminate. Its raw material composition and wt% are as follows: microporous mullite aggregate with a particle size ≥5mm to <20mm: 25-30%; calcium hexaaluminate aggregate with a particle size ≥1mm to <5mm: 15-35%; fine calcium hexaaluminate aggregate with a particle size <1mm: 5-15%; fine mullite powder with a particle size ≤0.074mm: 20-35%; α-Al2O3 micro powder with a particle size ≤20μm: 3-7%; SiO2 micro powder with a particle size ≤50μm: 1-4%; calcium aluminate cement with a particle size ≤0.074mm: 2-5%; organic fiber: 0.1-0.5%; and polycarboxylate water-reducing agent: 0.05-0.3%. This invention reduces the thermal conductivity of the ladle permanent layer castable from 0.9–1.2 W / (m·K) to below 0.75 W / (m·K), and maintains a compressive strength of no less than 60 MPa after high-temperature firing at 1500℃ for 3 hours. It also reduces the number of open and closed pores, significantly improving insulation performance and lowering the ladle outer surface temperature by no less than 50℃. However, the extensive use of microporous mullite aggregate, fine mullite powder, and SiO2 powder in this patent results in poor resistance to iron oxide scale and ferrous silicate corrosion, making it difficult to directly apply from the ladle permanent layer to the heating furnace water beams and columns.

[0007] Chinese patent CN102211945A discloses a calcium hexaaluminate-based lining castable that, although in contact with molten high-purity aluminum during the refining, melting, and heat preservation processes, does not contaminate the composition of the high-purity aluminum. The raw materials used to prepare this castable consist of: synthetic calcium hexaaluminate material, auxiliary materials, micro-powder, cement, and additives. This patent primarily utilizes the anti-aluminum corrosion and wetting capabilities of calcium hexaaluminate material to solve the problem of furnace lining material contaminating molten high-purity aluminum during the refining, melting, and heat preservation processes. However, its thermal insulation performance remains relatively insufficient.

[0008] Currently used heavy aluminosilicate castables for heating furnace water beams and columns suffer from high thermal conductivity, short service life, and poor insulation, leading to high heat loss. Existing technologies have not provided corresponding solutions, nor have they overcome the difficulty of simultaneously achieving good thermal conductivity, strength, and resistance to iron oxide scale and ferrous silicate corrosion in refractory castables for heating furnace water beams and columns. Therefore, it is necessary to provide a low-thermal-conductivity, high-strength castable for heating furnace water beams and columns that offers high compressive strength, good insulation, and excellent corrosion resistance. Summary of the Invention

[0009] To overcome the shortcomings of the above-mentioned technologies, the present invention provides a porous calcium hexaaluminate insulating castable for water beams and columns of heating furnaces, which solves the problems of high thermal conductivity, poor heat insulation performance, and insufficient resistance to iron oxide scale and ferrous silicate corrosion of refractory castables for water beams and columns of heating furnaces, thereby achieving the purpose of improving the service life of water beams and columns of heating furnaces, reducing water cooling heat loss, and increasing corrosion resistance.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A porous thermal insulation castable made of calcium hexaaluminate for use in heating furnace water beams and columns is composed of a main castable material and appropriate additives. The main castable material is composed of the following raw materials in parts by weight: 63-90 parts of calcium hexaaluminate, 3-10 parts of calcined alumina powder, 3-9 parts of activated alumina micro powder, and 4-18 parts of calcium aluminate cement raw material, with the sum of the parts by weight of each raw material being 100 parts. The additives are water-reducing agent (0.05-0.25% by weight), mineralizer (0-0.5% by weight), air-entraining agent (0.01-0.08% by weight), and foam stabilizer (0.01-0.03% by weight) of the main castable material.

[0012] Preferably, the mass ratio of different particle sizes in the calcium hexaaluminate is as follows: 6-12 parts of calcium hexaaluminate aggregate with a particle size of 3mm < ≤ 5mm, 24-30 parts of calcium hexaaluminate aggregate with a particle size of 1mm < ≤ 3mm, and 33-48 parts of calcium hexaaluminate fine powder with a particle size of 0 < ≤ 1mm, wherein 18-24 parts of the calcium hexaaluminate fine powder with a particle size < 0.074mm are included in the 0 < ≤ 1mm particle size fine powder; the bulk density of the calcium hexaaluminate aggregate with a particle size of 3mm < ≤ 5mm and 1mm < ≤ 3mm is 2.60-3.05 g / cm³. 3 The bulk density of all of them is 1.45-1.60 g / cm³. 3 .

[0013] Preferably, the raw material composition and mass percentage content of the calcium hexaaluminate are: Al2O3 88-92%, CaO 7-11%, SiO2 < 0.5%, Fe2O3 < 0.3%, with the balance being unavoidable impurities.

[0014] Preferably, the calcined alumina powder has a purity of ≥99% and a particle size d50 of 3-6μm; the activated alumina micro powder has a purity of ≥99% and a particle size d50 of 1-2.5μm.

[0015] Preferably, the Al2O3 content in the raw material components of the calcium aluminate cement is 68.5-71%.

[0016] Preferably, the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

[0017] Preferably, the mineralizing agent is titanium dioxide with a purity ≥99% and a particle size d50 of 1-10 μm.

[0018] Preferably, the air-entraining agent is a sulfosuccinate-based air-entraining agent.

[0019] Preferably, the foam stabilizer is a mixture of 2-hydroxyethyl methyl ether cellulose and sodium chloride, wherein the mass percentage of 2-hydroxyethyl methyl ether cellulose in the mixture is ≥85%, and the viscosity of a 2% aqueous solution of the foam stabilizer is 300-500 mPa·s at a shear rate of 2.55 / s.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This invention relates to a porous thermal insulation castable made of calcium hexaaluminate for heating furnace water beams and columns. Utilizing the inherent low thermal conductivity of calcium hexaaluminate and the micropores formed by its interwoven hexagonal lamellar structure, and further reducing the thermal conductivity of the castable by using an air-entraining agent to create pores, the thermal insulation performance of the castable is significantly improved. Simultaneously, the formation of the calcium hexaaluminate phase in the matrix enhances the high-temperature mechanical strength of the castable, thereby increasing the service life of the water beam castable for steel rolling heating furnaces, reducing water cooling heat loss, and increasing corrosion resistance.

[0022] By selecting calcium hexaaluminate raw materials containing a certain amount of closed pores (bulk density 2.60-3.05 g / cm³), 3 Bulk density 1.45-1.60 g / cm³ 3 As an aggregate, it has good thermal insulation properties and also plays a supporting role in the skeleton. This is in contrast to the ultra-lightweight calcium hexaaluminate aggregate (bulk density 0.4–0.5 g / cm³) in existing lightweight insulating calcium hexaaluminate castables. 3 Compared to other materials, although they share similar calcium hexaaluminate phases and chemical compositions, the mechanical and thermal properties of calcium hexaaluminate vary significantly due to differences in internal microstructure and porosity. This invention selects calcium hexaaluminate raw materials containing a certain amount of closed pores based on the material performance requirements under the actual high-temperature flue gas environment of hot-rolled heating furnace water beams and columns. This significantly improves the strength and resistance to flue gas erosion of the aggregate, avoiding problems such as decreased aggregate strength, large quality fluctuations, and performance degradation caused by the easy breakage of ultra-light calcium hexaaluminate aggregates during manufacturing and transportation.

[0023] Because the refractory insulation lining of the heating furnace water beams and columns is relatively thin (60mm thick) and has a large number of Y-shaped anchors around its perimeter, the castable cannot be constructed using conventional vibration molding methods. Therefore, it is necessary to improve the flowability of the castable to meet the self-flowing molding requirements of the heating furnace water beams and columns. In this invention, the calcium hexaaluminate fine powder with a particle size of 0 < ≤ 1mm includes not only calcium hexaaluminate fine powder with a particle size < 0.074mm, but also calcium hexaaluminate fine aggregate with a particle size of 0.074 ≤ ≤ 1mm. The addition of the calcium hexaaluminate fine aggregate serves a filling function while also facilitating the flow of the castable. Furthermore, the addition of polycarboxylate superplasticizers allows their anionic backbones to bind with the CaO on the surface of cement particles. 2+ ionic and activated alumina microparticle surface Al 3+ Ions undergo complexation reactions, adsorbing onto the surface of cement and activated alumina microparticles to form an adsorption layer of anionic backbone. The numerous branched chains create a steric hindrance effect, ensuring a suitable amount of free water is present during castable construction. Simultaneously, the abundant carboxyl, sulfonic acid, and hydroxyl groups in the polycarboxylate superplasticizer effectively form a hydration film on the particle surface, producing a lubricating effect. This reduces water addition while improving the dispersion of microparticles and the flowability of the castable. By employing these measures, the flowability of calcium hexaaluminate porous insulating castables for heating furnace beams and columns is improved, meeting the specific construction requirements of self-flowing molding. This significantly reduces water addition during construction, minimizes cracking defects caused by moisture evaporation during casting, curing, and high-temperature use, reduces high-temperature volume shrinkage, maintains good volume stability, and improves the mechanical strength of the castable.

[0024] To further improve the strength of the porous thermal insulation castable made of calcium hexaaluminate for the water beams and columns of the heating furnace, the addition of calcium hexaaluminate fine powder with a particle size of <0.074mm not only further fills the gaps, but also promotes the sintering of the matrix at high temperatures through the addition of calcined alumina powder and activated alumina micro powder. At the same time, the synergistic effect of activated alumina micro powder and aluminate cement is utilized to improve the room temperature strength of the castable.

[0025] To improve the thermal insulation performance and reduce the thermal conductivity of porous calcium hexaaluminate insulating castables used for water beams and columns of heating furnaces, in addition to selecting the aforementioned calcium hexaaluminate raw material main system aggregates and fine powders, this method fully utilizes the inherent characteristics of calcium hexaaluminate material, such as a slight decrease in thermal conductivity with increasing temperature and its own low thermal conductivity. This improves the thermal insulation performance of the castable under high-temperature operating conditions, overcoming the shortcomings of conventional silicon-aluminate self-flowing castables used for water beams and columns of heating furnaces, which have high thermal conductivity and a significant increase in thermal conductivity with increasing temperature. Furthermore, the method utilizes the dehydration reaction of the hydration products of activated alumina micropowder at high temperatures to form a large number of submicron-sized micropores inside the castable, thereby improving the thermal insulation performance of the material. Furthermore, the addition of an air-entraining agent creates more fine pores within the aluminum-calcium castable, further reducing its thermal conductivity. The use of a foam stabilizer made from a mixture of 2-hydroxyethyl methyl ether cellulose and sodium chloride reduces bubble breakage, ensuring the foaming effect of the air-entraining agent. Simultaneously, by controlling the amount and viscosity of the foam stabilizer, a composite porous structure of pores within pores is formed in the castable, further improving its thermal insulation performance.

[0026] Using calcium aluminate cement as a binder provides initial strength to the castable and allows it to react in situ with alumina powder at high temperatures to generate calcium hexaaluminate, ensuring the volume stability and high-temperature strength of the castable. Since the theoretical starting temperature for the chemical reaction between pure CaO and Al₂O₃ is 1300℃, and the temperature for the large-scale formation of calcium hexaaluminate is between 1550 and 1700℃, this chemical reaction is difficult to occur under furnace temperatures of 900–1300℃. To solve this problem, titanium dioxide mineralizer is added to promote sintering and the in-situ reaction of calcium hexaaluminate. Titanium dioxide dissolves into the alumina lattice, creating vacancies and defects, which lowers the activation energy of the CaO-Al₂O₃ chemical reaction, accelerating the in-situ reaction of calcium hexaaluminate. Calcium hexaaluminate is continuously generated starting at 1100℃, allowing CaO in the calcium aluminate cement to react with Al₂O₃ in the matrix to form a large amount at relatively lower temperatures, thus improving the high-temperature mechanical properties and thermal insulation performance of the castable.

[0027] Compared to Al2O3-SiO2-based castables, the calcium hexaaluminate porous insulating castable for heating furnace water beams and columns involved in this invention has a very low or even zero SiO2 content. This avoids the reaction between iron oxide scale and SiO2 to form a low-melting phase. Furthermore, by utilizing the excellent resistance of CA6 material to ferrous silicate corrosion, the problem of corrosion by ferrous silicate and iron oxide scale is solved. Through the use of the above measures, the thermal conductivity of the calcium hexaaluminate castable reaches 0.35-0.5 W / (m·K) at 800℃, and the room temperature compressive strength after firing at 1300℃ for 3 hours is 35-55 MPa. This achieves both low thermal conductivity and high strength, meeting the high-performance insulation requirements of heating furnace water-cooled beams and realizing excellent energy-saving effects by significantly reducing water cooling heat loss in industrial applications in steel plants. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the microstructure of the calcium hexaaluminate porous heat-insulating castable used for the heating furnace water beams and columns in Embodiment 1 of the present invention.

[0029] Figure 2 for Figure 1 A schematic diagram of the microstructure of micropores on the wall of a medium-circular pore. Detailed Implementation

[0030] To better explain the present invention, the main contents of the present invention are further illustrated below with reference to specific embodiments, but the contents of the present invention are not limited to the following embodiments.

[0031] The water-reducing agent used in the embodiments of the present invention is the WSM-M type new generation polycarboxylate high-efficiency water-reducing agent produced by Hubei Siman New Material Co., Ltd.; the air-entraining agent is the AEA2066 type produced by Dongguan Xianchuang.

[0032] Example 1

[0033] A porous thermal insulation castable made of calcium hexaaluminate for use in heating furnace water beams and columns is composed of a main castable material and appropriate additives. The main castable material consists of 78 parts by weight of calcium hexaaluminate, 8 parts by weight of calcined alumina powder, 7 parts by weight of activated alumina micro powder, and 7 parts by weight of calcium aluminate cement raw material. Among them, the contents of 0 < particle size ≤ 1 mm, 1 mm < particle size ≤ 3 mm, and 3 mm < particle size ≤ 5 mm in the calcium hexaaluminate raw material are 42 parts by weight, 27 parts by weight, and 9 parts by weight, respectively. Among the calcium hexaaluminate raw material with 0 < particle size ≤ 1 mm, the content of calcium hexaaluminate fine powder with a particle size < 0.074 mm is 21 parts by weight. The additives are water-reducing agent (0.15% by weight), air-entraining agent (0.06% by weight), and foam stabilizer (0.02% by weight) of the main castable material.

[0034] The raw material for calcium hexaaluminate used contains 90.32% Al₂O₃, 7.31% CaO, 0.44% SiO₂, and 0.1% Fe₂O₃. The bulk density of calcium hexaaluminate aggregate with particle sizes of 3mm < ≤ 5mm and 1mm < ≤ 3mm is 2.62 g / cm³. 3 The bulk density is 1.45 g / cm³. 3 and 1.50g / cm 3The calcined alumina has a purity of 99.6% and a particle size d50 of 3.48 μm. The activated alumina micropowder has a purity of 99.5% and a particle size d50 of 1.78 μm. The calcium aluminate cement contains 69% Al2O3. The foam stabilizer is a mixture of 2-hydroxyethyl methyl ether cellulose and sodium chloride produced by Dow Chemical, wherein the content of 2-hydroxyethyl methyl ether cellulose is 85% and the content of sodium chloride is 15%, and the viscosity of a 2% foam stabilizer aqueous solution is 300 mPa·s at a shear rate of 2.55 / s.

[0035] When using, add water at a weight percentage of 10.2% of the total weight of the above raw materials, stir well, pour into the heating furnace water beam and column mold, and cast by gravity.

[0036] Example 2

[0037] A porous thermal insulation castable made of calcium hexaaluminate for use in heating furnace water beams and columns is composed of a main castable material and appropriate additives. The main castable material consists of 78 parts by weight of calcium hexaaluminate, 8 parts by weight of calcined alumina powder, 7 parts by weight of activated alumina micro powder, and 7 parts by weight of calcium aluminate cement raw material. Among them, the contents of the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, 1 mm < ≤ 3 mm, and 3 mm < ≤ 5 mm are 42 parts by weight, 27 parts by weight, and 9 parts by weight, respectively. Among the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, the content of calcium hexaaluminate fine powder with a particle size < 0.074 mm is 21 parts by weight. The additives are water-reducing agent (0.1% by weight), mineralizer (0.25% by weight), air-entraining agent (0.01% by weight), and foam stabilizer (0.01% by weight) of the main castable material.

[0038] The raw material for calcium hexaaluminate used contains 90.32% Al₂O₃, 7.31% CaO, 0.44% SiO₂, and 0.1% Fe₂O₃. The bulk density of calcium hexaaluminate aggregate with particle sizes of 3mm < ≤ 5mm and 1mm < ≤ 3mm is 2.62 g / cm³. 3 The bulk density is 1.45 g / cm³. 3 and 1.50g / cm 3 The calcined alumina has a purity of 99.6% and a particle size d50 of 3.48 μm. The activated alumina micropowder has a purity of 99.5% and a particle size d50 of 1.78 μm. The calcium aluminate cement contains 69% Al2O3. The mineralizer is titanium dioxide with a purity of 99.5% and a particle size d50 of 10 μm. The foam stabilizer is a mixture of 2-hydroxyethyl methyl ether cellulose and sodium chloride produced by Dow Chemical, wherein the content of 2-hydroxyethyl methyl ether cellulose is 85% and the content of sodium chloride is 15%, and the viscosity of a 2% foam stabilizer aqueous solution is 300 mPa·s at a shear rate of 2.55 / s.

[0039] When using, add water at a weight percentage of 10.4% of the total weight of the above raw materials, stir well, pour into the heating furnace water beam and column mold, and cast by gravity.

[0040] Example 3

[0041] A porous thermal insulation castable made of calcium hexaaluminate for use in heating furnace water beams and columns is composed of a main castable material and appropriate additives. The main castable material consists of 79 parts by weight of calcium hexaaluminate, 6 parts by weight of calcined alumina powder, 5 parts by weight of activated alumina micro powder, and 10 parts by weight of calcium aluminate cement raw material. Among them, the contents of the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, 1 mm < ≤ 3 mm, and 3 mm < ≤ 5 mm are 38 parts by weight, 29 parts by weight, and 12 parts by weight, respectively. Among the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, the content of calcium hexaaluminate fine powder with a particle size < 0.074 mm is 23 parts by weight. The additives are water-reducing agent (0.25% by weight), mineralizer (0.5% by weight), air-entraining agent (0.04% by weight), and foam stabilizer (0.02% by weight) accounting for 0.25% of the total weight of the main castable material.

[0042] The raw material for calcium hexaaluminate used contains 91.85% Al₂O₃, 7.01% CaO, 0.28% SiO₂, and 0.05% Fe₂O₃. The bulk density of calcium hexaaluminate aggregate with particle sizes of 3mm < ≤ 5mm and 1mm < ≤ 3mm is 3.05 g / cm³. 3 The bulk density is 1.53 g / cm³. 3 and 1.60 g / cm 3 The calcined alumina has a purity of 99.6% and a particle size d50 of 6 μm. The activated alumina micropowder has a purity of 99.5% and a particle size d50 of 2.5 μm. The calcium aluminate cement contains 71% Al2O3. The mineralizer is titanium dioxide with a purity of 99.5% and a particle size d50 of 10 μm. The foam stabilizer is a mixture of 2-hydroxyethyl methyl ether cellulose and sodium chloride produced by Dow Chemical, wherein the content of 2-hydroxyethyl methyl ether cellulose is 90% and the content of sodium chloride is 10%, and the viscosity of a 2% foam stabilizer aqueous solution is 400 mPa·s at a shear rate of 2.55 / s.

[0043] When using, add water at a weight percentage of 9.5% of the total weight of the above raw materials, stir well, pour into the heating furnace water beam and column mold, and cast by gravity.

[0044] Example 4

[0045] A porous thermal insulation castable made of calcium hexaaluminate for use in heating furnace water beams and columns is composed of a main castable material and appropriate additives. The main castable material consists of 81 parts by weight of calcium hexaaluminate, 6 parts by weight of calcined alumina powder, 5 parts by weight of activated alumina micro powder, and 8 parts by weight of calcium aluminate cement raw material. Among them, the contents of the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, 1 mm < ≤ 3 mm, and 3 mm < ≤ 5 mm are 40 parts by weight, 29 parts by weight, and 12 parts by weight, respectively. Among the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, the content of calcium hexaaluminate fine powder with a particle size < 0.074 mm is 23 parts by weight. The additives are water-reducing agent (0.2% by weight), mineralizer (0.35% by weight), air-entraining agent (0.06% by weight), and foam stabilizer (0.02% by weight) accounting for 0.2% of the total weight of the main castable material.

[0046] The raw material for calcium hexaaluminate used contains 88.2% Al₂O₃, 8.65% CaO, 0.36% SiO₂, and 0.15% Fe₂O₃. The bulk density of calcium hexaaluminate aggregate with particle sizes of 3mm < ≤ 5mm and 1mm < ≤ 3mm is 2.6 g / cm³. 3 The bulk density is 1.45 g / cm³. 3 and 1.48 g / cm 3 The calcined alumina has a purity of 99.6% and a particle size d50 of 3 μm. The activated alumina micropowder has a purity of 99.5% and a particle size d50 of 1 μm. The calcium aluminate cement contains 69.8% Al2O3. The mineralizer is titanium dioxide with a purity of 99.5% and a particle size d50 of 1 μm. The foam stabilizer is a mixture of 2-hydroxyethyl methyl ether cellulose and sodium chloride produced by Dow Chemical, wherein the content of 2-hydroxyethyl methyl ether cellulose is 90% and the content of sodium chloride is 10%, and the viscosity of a 2% foam stabilizer aqueous solution is 400 mPa·s at a shear rate of 2.55 / s.

[0047] When using, add water accounting for 9.7% of the total weight of the above raw materials, stir evenly, pour into the heating furnace water beam and column mold, and cast by gravity.

[0048] Example 5

[0049] A porous thermal insulation castable made of calcium hexaaluminate for use in heating furnace water beams and columns is composed of a main castable material and appropriate additives. The main castable material consists of 78 parts by weight of calcium hexaaluminate, 7 parts by weight of calcined alumina powder, 6 parts by weight of activated alumina micro powder, and 9 parts by weight of calcium aluminate cement raw material. Among them, the contents of the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, 1 mm < ≤ 3 mm, and 3 mm < ≤ 5 mm are 48 parts by weight, 24 parts by weight, and 6 parts by weight, respectively. Among the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, the content of calcium hexaaluminate fine powder with a particle size < 0.074 mm is 24 parts by weight. The additives are water-reducing agent (0.15% by weight), mineralizer (0.3% by weight), air-entraining agent (0.03% by weight), and foam stabilizer (0.02% by weight) accounting for 0.15% of the total weight of the main castable material.

[0050] The raw material for calcium hexaaluminate used contains 88.2% Al₂O₃, 8.65% CaO, 0.36% SiO₂, and 0.15% Fe₂O₃. The bulk density of calcium hexaaluminate aggregate with particle sizes of 3mm < ≤ 5mm and 1mm < ≤ 3mm is 2.6 g / cm³. 3 The bulk density is 1.45 g / cm³. 3 and 1.48 g / cm 3 The calcined alumina has a purity of 99.6% and a particle size d50 of 3 μm. The activated alumina micropowder has a purity of 99.5% and a particle size d50 of 1 μm. The calcium aluminate cement contains 69.8% Al2O3. The mineralizer is titanium dioxide with a purity of 99.5% and a particle size d50 of 5 μm. The foam stabilizer is a mixture of 2-hydroxyethyl methyl ether cellulose and sodium chloride produced by Dow Chemical, wherein the content of 2-hydroxyethyl methyl ether cellulose is 95% and the content of sodium chloride is 5%, and the viscosity of a 2% foam stabilizer aqueous solution is 500 mPa·s at a shear rate of 2.55 / s.

[0051] When using, add water at a weight percentage of 10.1% of the total weight of the above raw materials, stir well, pour into the heating furnace water beam and column mold, and cast by gravity.

[0052] Example 6

[0053] A porous thermal insulation castable made of calcium hexaaluminate for use in heating furnace water beams and columns is composed of a main castable material and appropriate additives. The main castable material consists of 70 parts by weight of calcium hexaaluminate, 10 parts by weight of calcined alumina powder, 9 parts by weight of activated alumina micro powder, and 11 parts by weight of calcium aluminate cement raw material. Among them, the contents of the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, 1 mm < ≤ 3 mm, and 3 mm < ≤ 5 mm are 34 parts by weight, 30 parts by weight, and 6 parts by weight, respectively. Among the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, the content of calcium hexaaluminate fine powder with a particle size < 0.074 mm is 18 parts by weight. The additives are water-reducing agent (0.05% by weight), mineralizer (0.15% by weight), air-entraining agent (0.08% by weight), and foam stabilizer (0.03% by weight) of the main castable material.

[0054] The raw material for calcium hexaaluminate used contains 88.1% Al₂O₃, 10.7% CaO, 0.36% SiO₂, and 0.06% Fe₂O₃. The bulk density of calcium hexaaluminate aggregate with particle sizes of 3mm < ≤ 5mm and 1mm < ≤ 3mm is 2.6 g / cm³. 3 The bulk density is 1.45 g / cm³. 3 and 1.48 g / cm 3 The calcined alumina has a purity of 99.6% and a particle size d50 of 3 μm. The activated alumina micropowder has a purity of 99.5% and a particle size d50 of 1 μm. The calcium aluminate cement contains 68.5% Al2O3. The mineralizer is titanium dioxide with a purity of 99.5% and a particle size d50 of 5 μm. The foam stabilizer is a mixture of 2-hydroxyethyl methyl ether cellulose and sodium chloride produced by Dow Chemical, wherein the content of 2-hydroxyethyl methyl ether cellulose is 95% and the content of sodium chloride is 5%, and the viscosity of a 2% foam stabilizer aqueous solution is 500 mPa·s at a shear rate of 2.55 / s.

[0055] When using, add water at a weight percentage of 10.6% of the total weight of the above raw materials, stir well, pour into the heating furnace water beam and column mold, and cast by gravity.

[0056] Comparative Example

[0057] The preparation methods of the aluminum-silica castable and CA6 lightweight castable in the comparative examples of this invention are derived from the literature: J. Heinlein, H. Siefkes, M. Springer, et al. Energy saving in walking beam furnaces at ArcelorMittal (Bremen, Germany) by a new concept for skid pipeinsulation. Proceedings of the Unified International Technical Conference on Refractories (UNITECR 2013), 2014:367-372.

[0058] Performance testing:

[0059] The heating furnace water beams and columns prepared in the above embodiments were made of calcium hexaaluminate porous insulating castable. A measured amount of water was added to a mixer, and the mixture was thoroughly stirred before being poured into a mold for molding. After curing at 25°C and 100% relative humidity for 24 hours, the molded samples were demolded and then held at 110°C for 24 hours. The resulting samples were held at 1300°C for 3 hours, and their bulk density, room temperature compressive strength, and thermal conductivity were tested. The results are shown in Table 1.

[0060] As shown in Table 1, the calcium hexaaluminate castable prepared in this embodiment of the invention has a slightly lower bulk density than aluminosilicate castables, significantly higher compressive strength than CA6 lightweight castables, and a thermal conductivity of less than 0.5 W / m·K at 800℃, only 30% of that of aluminosilicate castables, exhibiting excellent thermal insulation properties. Small pores, i.e., "pore-within-pore" phenomena, also appeared on the inner walls of the pores in the castable, such as... Figure 1 and Figure 2 As shown. This structure, with its very small and densely distributed pores, increases the resistance to heat transfer, thereby further reducing the thermal conductivity of the material.

[0061] Table 1

[0062]

[0063] Industrial trials and widespread application of the above-mentioned Example 3 were conducted on the water beams and columns of a hot-rolling heating furnace in a steel plant (the highest slab tapping temperature is 1280℃, the highest temperature in the soaking zone is 1300℃, and the temperature in the preheating zone is 900℃). The results showed that compared with conventional aluminum-silicon self-flowing castables, the water cooling heat loss of the heating furnace was reduced by more than 32%, and the gas consumption of the heating furnace was reduced by 12%-16%, achieving good energy-saving and carbon reduction effects.

[0064] All other unspecified parts belong to the prior art.

Claims

1. A porous thermal insulation castable made of calcium hexaaluminate for water beams and columns of a heating furnace, comprising a main castable material and appropriate additives, characterized in that: The main component of the castable is composed of the following raw materials in parts by weight: 63-90 parts calcium hexaaluminate, 3-10 parts calcined alumina powder, 3-9 parts activated alumina micro powder, and 4-18 parts calcium aluminate cement raw material, with the sum of the parts by weight of each raw material being 100 parts; the additives are 0.05-0.25% water-reducing agent, 0.25-0.5% mineralizer, 0.01-0.08% air-entraining agent, and 0.01-0.03% foam stabilizer, accounting for 0.05-0.25% of the total weight of the main component of the castable; the mineralizer is titanium dioxide; the castable is used for self-flowing casting molding; The mass proportions of different particle sizes in the calcium hexaaluminate are as follows: 6-12 parts of calcium hexaaluminate aggregate with a particle size of 3mm < ≤ 5mm, 24-30 parts of calcium hexaaluminate aggregate with a particle size of 1mm < ≤ 3mm, and 33-48 parts of calcium hexaaluminate fine powder with a particle size of 0 < ≤ 1mm, of which 18-24 parts are calcium hexaaluminate fine powder with a particle size < 0.074mm; the bulk density of both the calcium hexaaluminate aggregates with a particle size of 3mm < ≤ 5mm and 1mm < ≤ 3mm is 2.60-3.05 g / cm³. 3 The bulk density of all of them is 1.45-1.60 g / cm³. 3 ; The foam stabilizer is a mixture of 2-hydroxyethyl methyl ether cellulose and sodium chloride, wherein the mass percentage of 2-hydroxyethyl methyl ether cellulose in the mixture is ≥85%, and the viscosity of a 2% aqueous solution of the foam stabilizer is 300-500 mPa·s at a shear rate of 2.55 / s.

2. The porous thermal insulation castable made of calcium hexaaluminate for heating furnace water beams and columns according to claim 1, characterized in that: The raw material composition and mass percentage content of the calcium hexaaluminate are as follows: Al2O3 88-92%, CaO 7-11%, SiO2 < 0.5%, Fe2O3 < 0.3%, with the balance being unavoidable impurities.

3. The porous thermal insulation castable made of calcium hexaaluminate for heating furnace water beams and columns according to any one of claims 1 to 2, characterized in that: The calcined alumina powder has a purity of ≥99% and a particle size d50 of 3-6µm; the activated alumina micro powder has a purity of ≥99% and a particle size d50 of 1-2.5µm.

4. The porous thermal insulation castable made of calcium hexaaluminate for heating furnace water beams and columns according to any one of claims 1 to 2, characterized in that: The raw material composition of the calcium aluminate cement contains 68.5-71% Al2O3.

5. The porous thermal insulation castable made of calcium hexaaluminate for heating furnace water beams and columns according to any one of claims 1 to 2, characterized in that: The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

6. The porous thermal insulation castable made of calcium hexaaluminate for heating furnace water beams and columns according to any one of claims 1 to 2, characterized in that: The titanium dioxide has a purity of ≥99% and a particle size d50 of 1-10µm.

7. The porous thermal insulation castable made of calcium hexaaluminate for heating furnace water beams and columns according to any one of claims 1 to 2, characterized in that: The air-entraining agent is a sulfosuccinate-based air-entraining agent.

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