Low thermal conductivity, high strength calcium hexaaluminate castable for walking beams in heating furnaces

Abstract

This invention discloses a low thermal conductivity, high strength calcium hexaaluminate castable for walking beams in heating furnaces, composed of a main castable material and appropriate additives. The main castable material is characterized by the following components by mass: 43-87 parts calcium hexaaluminate, 0-20 parts microporous corundum aggregate, 0.5-5 parts hollow alumina spheres, 6-10 parts calcined alumina powder, 4-9 parts activated alumina micropowder, 0-1 parts nano-alumina, and 2.5-12 parts calcium aluminate cement raw material, with the total mass of all components being 100 parts. The additives are a water-reducing agent and a composite sintering aid. This invention overcomes the problem of simultaneously achieving good thermal conductivity, strength, resistance to iron oxide scale and ferrous silicate corrosion in refractory castables for walking beams in heating furnaces. It improves the heat insulation performance of the castable, enhances its high-temperature mechanical strength, increases the service life of the castable for walking beams in steel rolling furnaces, and reduces water-cooled heat loss.

Description

Technical Field

[0001] This invention relates to the field of refractory materials for heating furnaces, specifically to a low thermal conductivity, high strength calcium hexaaluminate castable for walking beams in heating furnaces. Background Technology

[0002] With the continuous development of my country's iron and steel metallurgical industry, China has become a major steel producer. Heating furnaces, as crucial equipment for heating billets before rolling, have become key high-temperature equipment in the steel rolling process of iron and steel enterprises. Hot rolling accounts for 10-15% of the energy consumption in iron and steel metallurgy, with approximately 70-80% of this energy consumption used in billet heating furnaces. However, the thermal efficiency of heating furnaces is mostly only 50-60%, and improving the energy efficiency of heating furnaces has always been a key focus for researchers and engineers. The heat carried away by the cooling water in the walking beam column accounts for approximately 14-25% of the total heat loss. Therefore, improving the thermal insulation of the refractory material used for the walking beam wrapping in the heating furnace and improving its structural performance are crucial to reducing heat loss caused by cooling water. During high-temperature use, the refractory castable used for walking beam wrapping may crack and detach, leading to the failure of the insulation lining and direct exposure of the water-cooled steel pipes to the high-temperature environment. This significantly increases water cooling heat loss, reduces the thermal efficiency of the heating furnace, increases energy consumption, and also brings about production safety issues. In addition to insufficient material strength and thermal shock resistance, as well as large fluctuations in on-site construction quality, the damage to the refractory castable wrapped in the walking beam is caused by the reaction of iron oxide scale falling from the surface of the heated steel billet with the aluminosilicate castable to form a low-melting phase. This is especially significant when heating certain steel billets with high silicon content, resulting in iron oxide scale covering the entire surface of the longitudinal beam and even exceeding the high-temperature pad. This causes the pressure of the steel billet to be transferred to the refractory castable of the walking beam through the iron oxide scale, resulting in the damage to the refractory castable.

[0003] In China, heavy aluminosilicate castables are commonly used for wrapping refractory beams in heating furnaces. While they have high strength, they also have high thermal conductivity. The national standard "Refractory Castables for Steel Rolling Heating Furnaces" (GB / T22590-2021) does not specify requirements for the thermal conductivity of castables used in water-cooled pipes. While lightweight calcium hexaaluminate raw materials from abroad are extremely expensive, and although they offer good insulation, their low compressive strength cannot fully meet the practical requirements for high-temperature insulation and protection of heating furnace walking beams. The challenge in designing low-thermal-conductivity castables for heating furnace walking beams lies in balancing strength, insulation, corrosion resistance, and workability.

[0004] 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.

[0005] 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, and it is difficult to fully form the calcium hexaaluminate phase at the furnace temperature of 900-1300℃ in the steel rolling furnace, making it difficult to use for heat insulation of the walking beam of the heating furnace.

[0006] 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 comprises 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 based on the total weight of the above raw materials. This invention's lightweight insulating calcium hexaaluminate castable is used for the permanent lining insulation layer of steel ladles, with a low bulk density (0.22-0.35 g / cm³). 3It has good thermal insulation performance, but poor strength (2.9~6.2MPa), so it cannot be used as a hot working surface for a long time and cannot be used for thermal insulation of the hot surface of the walking beam in the heating furnace.

[0007] 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 thermal insulation performance and reducing 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 walking beam of the heating furnace.

[0008] 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.

[0009] The existing literature does not provide solutions to the problems of high thermal conductivity and poor resistance to iron oxide scale and ferrous silicate corrosion in the commonly used heavy aluminosilicate castables for walking beams in heating furnaces. It also fails to overcome the difficulty of simultaneously achieving good thermal conductivity, strength, and resistance to iron oxide scale and ferrous silicate corrosion in heavy aluminosilicate castables. Therefore, it is necessary to provide a low thermal conductivity, high-strength castable with high mechanical properties, good thermal insulation, and good corrosion resistance for walking beams in heating furnaces. Summary of the Invention

[0010] To overcome the shortcomings of the above-mentioned technologies, the present invention provides a low thermal conductivity, high strength calcium hexaaluminate castable for walking beams 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 walking beams of heating furnaces, thereby achieving the purpose of improving the service life of the walking beam castable, reducing water cooling heat loss, and increasing corrosion resistance.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A low thermal conductivity, high strength calcium hexaaluminate castable for a walking beam in a heating furnace is composed of a main castable material and appropriate additives. The main castable material consists of the following raw materials in parts by weight: 43-87 parts calcium hexaaluminate, 0-20 parts microporous corundum aggregate, 0.5-5 parts hollow alumina spheres, 6-10 parts calcined alumina powder, 4-9 parts activated alumina micro powder, 0-1 parts nano alumina, and 2.5-12 parts calcium aluminate cement raw material, with the sum of the parts by weight of each raw material being 100 parts. The additives are a water-reducing agent and a composite sintering aid. The water-reducing agent accounts for 0.05-0.25% of the total weight of the main castable material, and the composite sintering aid accounts for 0-0.5% of the total weight of the main castable material.

[0013] Preferably, the composite sintering aid accounts for 0.15%-0.35% of the total weight of the main material of the castable.

[0014] Preferably, the mass ratio of different particle sizes in the calcium hexaaluminate is as follows: 3-12 parts of calcium hexaaluminate aggregate with a particle size of 3mm < ≤ 5mm, 7-30 parts of calcium hexaaluminate aggregate with a particle size of 1mm < ≤ 3mm, and 33-45 parts of calcium hexaaluminate fine powder with a particle size of 0 < ≤ 1mm, wherein the calcium hexaaluminate fine powder with a particle size of < 0.074mm comprises 18-24 parts; 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 .

[0015] 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.

[0016] Preferably, the mass ratio of different particle sizes in the microporous corundum aggregate is: 0-3 parts of microporous corundum aggregate with a particle size of 3mm ≤ 5mm, and 0-17 parts of microporous corundum aggregate with a particle size of 1mm ≤ < 3mm; wherein, the purity of the microporous corundum raw material is ≥ 98.5%, and the bulk density is ≤ 3.4 g / cm³. 3Porosity ≥ 8%.

[0017] Preferably, the alumina hollow spheres have a purity of ≥99%, a particle size of 0.2-0.5 mm, and a bulk density of 0.8-0.9 g / cm³. 3 The calcined alumina powder has a purity ≥99% and a particle size d50 of 3-6 μm; the activated alumina micro powder has a purity ≥99% and a particle size d50 of 1-2.5 μm; the nano alumina has a purity ≥99% and a specific surface area BET of 100-150 m². 2 / g.

[0018] Preferably, the Al2O3 content in the raw material components of the calcium aluminate cement is 68.5-71%.

[0019] Preferably, the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

[0020] Preferably, the composite sintering aid is composed of 20-50 wt% titanium dioxide, 25-40 wt% yttrium oxide, and 25-40 wt% cerium oxide by weight; wherein the purity of titanium dioxide is ≥99% and the particle size d50 is 1-10 μm; the purity of yttrium oxide is ≥99% and the particle size d50 is 1-10 μm; and the purity of cerium oxide is ≥99% and the particle size d50 is 1-10 μm.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention provides a low thermal conductivity, high strength calcium hexaaluminate castable for walking beams in heating furnaces. It utilizes the intrinsic properties of calcium hexaaluminate and the micropores formed by its interwoven hexagonal lamellar structure to achieve a low high-temperature thermal conductivity. Furthermore, the thermal conductivity is further reduced through microporous corundum and hollow alumina spheres, significantly improving the heat insulation performance of the castable. 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 walking beam castable for steel rolling furnaces and reducing water-cooled heat loss. This invention solves the problems of high thermal conductivity, poor insulation performance, and insufficient resistance to iron oxide scale and ferrous silicate corrosion in existing heavy aluminosilicate refractory castables for walking beams in heating furnaces, achieving a balance between thermal conductivity, strength, and resistance to iron oxide scale and ferrous silicate corrosion.

[0023] This invention utilizes calcium hexaaluminate raw material 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 existing ultralight calcium hexaluminate aggregates (bulk density 0.4–0.5 g / cm³). 3Compared to other materials, although they share similar calcium hexaaluminate phases and chemical compositions, the mechanical and thermal properties of different aggregates vary significantly due to differences in their internal microstructure and porosity. This invention selects calcium hexaaluminate raw materials containing a certain amount of closed pores based on the actual high-temperature flue gas environment requirements of the hot-rolled furnace walking beam. 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.

[0024] Because the refractory insulation lining of the walking beam in the heating furnace 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 walking beam in the heating furnace. 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 not only acts as a filler but also facilitates the flow of the castable. Furthermore, the addition of hollow alumina spheres utilizes their spherical shape to increase the flowability of the castable, improving its workability. Simultaneously, their high strength and hollow, closed-pore characteristics compensate for the insufficient strength of the calcium hexaaluminate fine aggregate, improving the strength and insulation performance of the castable. Finally, the addition of polycarboxylate superplasticizers utilizes their anionic backbone to react with the Ca on the surface of cement particles. 2+ Al on the surface of ionic, activated alumina micro powder and nano alumina micro powder particles 3+ Ions undergo complexation reactions, adsorbing onto the surfaces of cement, activated alumina micropowder, and nano-alumina micropowder particles to form an adsorption layer of anionic backbone. The numerous branched chains create a steric hindrance effect, ensuring the presence of an appropriate amount of free water 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 micropowder particles and the flowability of the castable. By employing these measures, the flowability of low thermal conductivity, high-strength calcium hexaaluminate castables for walking beams in heating furnaces is improved, meeting the specific construction requirements of self-flowing molding. This significantly reduces water addition during construction, minimizes cracking defects caused by water 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.

[0025] To further improve the strength of the low thermal conductivity, high strength calcium hexaaluminate castable for the walking beam of the heating furnace, the addition of calcium hexaaluminate fine powder with a particle size of <0.074mm not only further serves as a filler, but also promotes the sintering of the matrix at high temperatures through the addition of calcined alumina powder, activated alumina micro powder, and nano alumina. 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, and the high chemical reactivity of nanoparticles in nano alumina accelerates the high-temperature sintering chemical reaction rate, thereby improving the high-temperature strength of the castable.

[0026] To improve the thermal insulation performance of low thermal conductivity, high-strength calcium hexaaluminate castables for walking beams in heating furnaces and reduce the material's thermal conductivity, in addition to selecting the aforementioned calcium hexaaluminate raw material main system of 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-aluminum self-flowing castables for walking beams in heating furnaces, which have high thermal conductivity and a significant increase in thermal conductivity with increasing temperature. Furthermore, this is achieved through the use of microporous corundum... The introduction of aggregates reduces the thermal conductivity of the material by utilizing its internal micron-sized pores, and the high hardness of corundum aggregates increases the strength of the castable. Secondly, the addition of hollow alumina spheres physically introduces certain pores, reducing the bulk density of the castable and thus improving its thermal insulation performance. Finally, the combined effect of the micropores formed by the high-temperature dehydration reaction of the hydration products of activated alumina powder and the coordinated refinement of pores by nano-alumina powder creates a large number of submicron and nano-sized micropores within the castable, further enhancing its thermal insulation performance.

[0027] Calcium aluminate cement is used as a binder to provide initial strength to the castable, and reacts with alumina powder at high temperature to generate calcium hexaaluminate in situ, thereby improving 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 around 1300℃, and the temperature at which a large amount of calcium hexaaluminate is generated is between 1550 and 1700℃, the above chemical reaction is difficult to occur under the conditions of furnace temperature of 900 to 1300℃. In order to solve the above problems, a composite sintering aid composed of titanium dioxide, yttrium oxide and cerium oxide is added to promote sintering and the in-situ reaction of calcium hexaaluminate. The titanium dioxide is dissolved into the aluminum oxide lattice, generating vacancies and defects, which lowers the activation energy of the chemical reaction between CaO and Al2O3, and accelerates the in-situ reaction of calcium hexaaluminate. Calcium hexaaluminate is continuously generated starting at 1100℃. The addition of rare earth oxides yttrium oxide and cerium oxide further accelerates the generation rate, so that CaO in calcium aluminate cement can be generated in large quantities with Al2O3 in the matrix at a relatively low temperature, thereby improving the high-temperature mechanical properties and thermal insulation properties of the castable.

[0028] Compared to Al2O3-SiO2-based castables, the low thermal conductivity, high strength calcium hexaaluminate castable for walking beams in heating furnaces involved in this invention has an extremely low or even zero SiO2 content. This avoids the reaction between iron oxide scale and SiO2 to form a low-melting-point 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 0.4-0.6 W / (m·K) at 800℃, and the room-temperature compressive strength after firing at 1300℃ for 3 hours is 50-90 MPa. This achieves both low thermal conductivity and high strength, as well as good corrosion resistance, meeting the high-performance thermal insulation requirements of walking beams in heating furnaces. In industrial applications in steel plants, it also achieves excellent energy-saving effects by significantly reducing water cooling heat loss. Attached Figure Description

[0029] Figure 1 This is the microstructure of the low thermal conductivity, high strength calcium hexaaluminate castable for the walking beam of the heating furnace in Embodiment 1 of the present invention. 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.

[0032] Example 1

[0033] A low thermal conductivity, high strength calcium hexaaluminate castable for a walking beam in a heating furnace is composed of a main castable material and appropriate additives. The main castable material consists of 76.5 parts by weight of calcium hexaaluminate, 1.5 parts by weight of hollow alumina spheres, 8 parts by weight of calcined alumina powder, 6.5 parts by weight of activated alumina micro powder, 0.5 parts by weight of nano alumina, and 7 parts by weight of calcium aluminate cement raw material. Among them, the contents of calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, 1 mm < ≤ 3 mm, and 3 mm < ≤ 5 mm are 40.5 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 fine calcium hexaaluminate powder with a particle size < 0.074 mm is 21 parts by weight. The additive is a water-reducing agent accounting for 0.2% of the total 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 3 The alumina hollow spheres have a purity of 99.5%, a particle size of 0.2-0.5 mm, and a bulk density of 0.9 g / cm³. 3 The purity of calcined alumina is 99.6%, and the particle size d50 is 3.48 μm. The purity of activated alumina micropowder is 99.5%, and the particle size d50 is 1.78 μm. The purity of nano-alumina is 99.5%, and the specific surface area BET is 145 m². 2 / g. The Al2O3 content in calcium aluminate cement is 69%.

[0035] 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 walking beam mold, and cast by gravity.

[0036] Example 2

[0037] A low thermal conductivity, high strength calcium hexaaluminate castable for a walking beam in a heating furnace is composed of a main castable material and appropriate additives. The main castable material consists of 81 parts by weight of calcium hexaaluminate, 0.5 parts by weight of hollow alumina spheres, 6 parts by weight of calcined alumina powder, 4 parts by weight of activated alumina micro powder, and 8.5 parts by weight of calcium aluminate cement raw material. The contents of calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, 1 mm < ≤ 3 mm, and 3 mm < ≤ 5 mm are 43 parts by weight, 26 parts by weight, and 12 parts by weight, respectively. Among the calcium hexaaluminate raw material with particle size 0 < ≤ 1 mm, 18 parts by weight are calcium hexaaluminate fine powder with a particle size < 0.074 mm. The additives are a water-reducing agent accounting for 0.1% of the total weight of the main castable material and a composite sintering aid accounting for 0.25%.

[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 alumina hollow spheres have a purity of 99.5%, a particle size of 0.2-0.5 mm, and a bulk density of 0.9 g / cm³. 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 composite sintering aid consists of 50 wt% titanium dioxide, 25 wt% yttrium oxide, and 25 wt% cerium oxide by weight, with the purity of titanium dioxide, yttrium oxide, and cerium oxide all greater than 99.5% and a particle size d50 of 10 μm.

[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 walking beam mold, and cast by gravity.

[0040] Example 3

[0041] A low thermal conductivity, high strength calcium hexaaluminate castable for a walking beam in a heating furnace is composed of a main castable material and appropriate additives. The main castable material consists of 69.5 parts by weight of calcium hexaaluminate, 0.5 parts by weight of hollow alumina spheres, 10 parts by weight of calcined alumina powder, 9 parts by weight of activated alumina micro powder, 1 part by weight of nano alumina, and 10 parts by weight of calcium aluminate cement raw material. The calcium hexaaluminate raw material has the following contents: 34 parts by weight for particles with a particle size of 0 < ≤ 1 mm, 30 parts by weight for particles with a particle size of 1 mm < ≤ 3 mm, and 5.5 parts by weight for particles with a particle size of 3 mm < ≤ 5 mm. Among the calcium hexaaluminate raw material with a particle size of 0 < ≤ 1 mm, 19 parts by weight are fine calcium hexaaluminate powder with a particle size < 0.074 mm. The additives are a water-reducing agent comprising 0.05% of the total weight of the main castable material and a composite sintering aid comprising 0.15% 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 alumina hollow spheres have a purity of 99.5%, a particle size of 0.2-0.5 mm, and a bulk density of 0.9 g / cm³. 3 The purity of calcined alumina is 99.6%, and the particle size d50 is 6 μm. The purity of activated alumina micropowder is 99.5%, and the particle size d50 is 2.5 μm. The purity of nano-alumina is 99.5%, and the specific surface area BET is 100 m². 2 / g. The Al2O3 content in calcium aluminate cement is 71%. The composite sintering aid consists of 50wt% titanium dioxide, 25wt% yttrium oxide, and 25wt% cerium oxide by weight, and the purity of titanium dioxide, yttrium oxide, and cerium oxide is greater than 99.5%, with a particle size d50 of 10μm.

[0043] When using, add water at a weight percentage of 10.8% of the total weight of the above raw materials, stir well, pour into the heating furnace walking beam mold, and cast by gravity.

[0044] Example 4

[0045] A low thermal conductivity, high strength calcium hexaaluminate castable for a walking beam in a heating furnace is composed of a main castable material and appropriate additives. The main castable material consists of 50 parts by weight of calcium hexaaluminate, 19 parts by weight of microporous corundum aggregate, 5 parts by weight of hollow alumina spheres, 9 parts by weight of calcined alumina powder, 8 parts by weight of activated alumina micro powder, 1 part by weight of nano-alumina, and 8 parts by weight of calcium aluminate cement raw material; wherein 0 < particle size ≤ 1 mm, 1 mm < particle size ≤ 3 mm, and... The contents of calcium hexaaluminate raw materials with particle size 3mm < ≤ 5mm are 37 parts by mass, 7 parts by mass, and 6 parts by mass, respectively; the contents of calcium hexaaluminate raw materials with particle size 0 < ≤ 1mm and fine calcium hexaaluminate powder with particle size < 0.074mm are 19 parts by mass; the contents of microporous corundum aggregate with particle size 1mm ≤ < 3mm and 3mm ≤ ≤ 5mm are 17 parts by mass and 2 parts by mass, respectively; the additives are water-reducing agent and composite sintering aid accounting for 0.15% of the total weight of the main material of the castable.

[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 purity of the microporous corundum is 99.0%, and its bulk density is 3.3 g / cm³. 3 The closed porosity is 8.5%. The purity of the alumina hollow spheres is 99.5%, the particle size is 0.2-0.5 mm, and the bulk density is 0.9 g / cm³. 3 The purity of calcined alumina is 99.6%, and the particle size d50 is 3 μm. The purity of activated alumina micropowder is 99.5%, and the particle size d50 is 1 μm. The purity of nano-alumina is 99.6%, and the specific surface area BET is 150 m². 2 / g. The Al2O3 content in calcium aluminate cement is 69.8%. The composite sintering aid consists of 20wt% titanium dioxide, 40wt% yttrium oxide, and 40wt% cerium oxide by weight, and the purity of titanium dioxide, yttrium oxide, and cerium oxide is greater than 99.5%, with a particle size d50 of 1μm.

[0047] When using, add water at a weight percentage of 10.3% of the total weight of the above raw materials, stir well, pour into the heating furnace walking beam mold, and cast by gravity.

[0048] Example 5

[0049] A low thermal conductivity, high strength calcium hexaaluminate castable for use in a walking beam of a heating furnace is composed of a main castable material and appropriate additives. The main castable material consists of 64 parts by weight of calcium hexaaluminate, 11 parts by weight of microporous corundum aggregate, 5 parts by weight of hollow alumina spheres, 6 parts by weight of calcined alumina powder, 4 parts by weight of activated alumina micro powder, 1 part by weight of nano-alumina, and 9 parts by weight of calcium aluminate cement raw material, wherein 0 < particle size ≤ 1 mm and 1 mm < particle size ≤ 3 mm. The contents of calcium hexaaluminate raw materials with particle size 3mm < ≤ 5mm are 39 parts by mass, 15 parts by mass, and 10 parts by mass, respectively. Among the calcium hexaaluminate raw materials with particle size 0 < ≤ 1mm, the fine calcium hexaaluminate powder with particle size < 0.074mm is 18 parts by mass. The microporous corundum aggregate with particle size 1mm ≤ < 3mm and 3mm ≤ ≤ 5mm is 9 parts by mass and 2 parts by mass, respectively. The additives are water-reducing agent accounting for 0.1% of the main material of the castable and composite sintering aid accounting for 0.35%.

[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 purity of the microporous corundum is 98.8%, and its bulk density is 3.4 g / cm³. 3 The closed porosity is 8.9%. The purity of the alumina hollow spheres is 99.6%, the particle size is 0.2-0.5 mm, and the bulk density is 0.8 g / cm³. 3 The purity of calcined alumina is 99.6%, and the particle size d50 is 3 μm. The purity of activated alumina micropowder is 99.5%, and the particle size d50 is 1 μm. The purity of nano-alumina is 99.6%, and the specific surface area BET is 150 m². 2 / g. The Al2O3 content in calcium aluminate cement is 69.8%. The composite sintering aid consists of 40wt% titanium dioxide, 30wt% yttrium oxide, and 30wt% cerium oxide by weight, and the purity of titanium dioxide, yttrium oxide, and cerium oxide is greater than 99.5%, with a particle size d50 of 5μm.

[0051] 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 walking beam mold, and cast by gravity.

[0052] Example 6

[0053] A low thermal conductivity, high strength calcium hexaaluminate castable for use in a walking beam of a heating furnace is composed of a main castable material and appropriate additives. The main castable material consists of 56 parts by weight of calcium hexaaluminate, 20 parts by weight of microporous corundum aggregate, 3.5 parts by weight of hollow alumina spheres, 7 parts by weight of calcined alumina powder, 5 parts by weight of activated alumina micro powder, 0.5 parts by weight of nano-alumina, and 8 parts by weight of calcium aluminate cement raw material, wherein 0 < particle size ≤ 1 mm and 1 mm < particle size ≤ 3 mm. The contents of calcium hexaaluminate raw materials with particle size m and 3mm < particle size ≤ 5mm are 40 parts by mass, 13 parts by mass, and 3 parts by mass, respectively. Among the calcium hexaaluminate raw materials with particle size 0 < particle size ≤ 1mm, the content of calcium hexaaluminate fine powder with particle size < 0.074mm is 24 parts by mass. The contents of microporous corundum aggregate with particle size 1mm ≤ particle size < 3mm and 3mm ≤ particle size ≤ 5mm are 17 parts by mass and 3 parts by mass, respectively. The additives are water-reducing agent accounting for 0.25% of the main material of the castable and composite sintering aid accounting for 0.5%.

[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 purity of the microporous corundum is 98.8%, and its bulk density is 3.4 g / cm³. 3 The closed porosity is 8.9%. The purity of the alumina hollow spheres is 99.6%, the particle size is 0.2-0.5 mm, and the bulk density is 0.8 g / cm³. 3 The purity of calcined alumina is 99.6%, and the particle size d50 is 3 μm. The purity of activated alumina micropowder is 99.5%, and the particle size d50 is 1 μm. The purity of nano-alumina is 99.6%, and the specific surface area BET is 150 m². 2 / g. The Al2O3 content in calcium aluminate cement is 68.5%. The composite sintering aid consists of 40wt% titanium dioxide, 30wt% yttrium oxide, and 30wt% cerium oxide by weight, and the purity of titanium dioxide, yttrium oxide, and cerium oxide is greater than 99.5%, with a particle size d50 of 5μm.

[0055] When using, add water accounting for 9.7% of the total weight of the above raw materials, stir evenly, pour into the heating furnace walking beam mold, and cast by gravity.

[0056] Comparative Example

[0057] The preparation methods and performance testing 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 beamfurnaces 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 low thermal conductivity calcium hexaaluminate castable refractory for the furnace walking beams prepared in the above embodiments was thoroughly mixed with a measured amount of water in a mixer, and then poured into a mold for molding. After curing at 25°C and 100% relative humidity for 24 hours, the refractory was demolded and then held at 110°C for 24 hours. The resulting samples were then 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] Table 1

[0061] As shown in Table 1, the calcium hexaaluminate castable prepared in this embodiment of the invention has a bulk density comparable to that of aluminosilicate castables, a significantly higher compressive strength than CA6 lightweight castables, and a thermal conductivity of less than 0.6 W / m·K at 800℃, only one-third that of aluminosilicate castables, thus providing thermal insulation. The stacked flake-like calcium hexaaluminate contributes to improving the strength of the castable, and its microstructure is as follows: Figure 1 As shown.

[0062] On the walking beam of a hot rolling heating furnace in a steel plant (the highest slab exit temperature is 1280℃, the highest temperature in the soaking zone is 1300℃, and the soaking zone temperature is 900℃), the above-mentioned Example 4 was tested and promoted for application. 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 28%, and the gas consumption of the heating furnace was reduced by 10%-15%, achieving good energy-saving and carbon reduction effects.

[0063] All other unspecified parts belong to the prior art.

Claims

1. A low thermal conductivity, high strength calcium hexaaluminate castable for a walking beam in 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: 43-87 parts calcium hexaaluminate, 0-20 parts microporous corundum aggregate, 0.5-5 parts hollow alumina spheres, 6-10 parts calcined alumina powder, 4-9 parts activated alumina micro powder, 0-1 parts nano alumina, and 2.5-12 parts calcium aluminate cement raw material, with the sum of the parts by weight of each raw material being 100 parts; the additives are a water-reducing agent and a composite sintering aid, with the water-reducing agent accounting for 0.05-0.25% of the total weight of the main component of the castable, and the composite sintering aid accounting for 0.15-0.5% of the total weight of the main component of the castable; the bulk density of the microporous corundum aggregate is ≤3.4 g / cm³. 3 The closed porosity is ≥8%; the composite sintering aid is composed of 20-50wt% titanium dioxide, 25-40wt% yttrium oxide and 25-40wt% cerium oxide by weight.

2. The low thermal conductivity, high strength calcium hexaaluminate castable for the walking beam of the heating furnace according to claim 1, characterized in that: The composite sintering aid accounts for 0.15%-0.35% of the total weight of the main material of the castable.

3. The low thermal conductivity, high strength calcium hexaaluminate castable for the walking beam of the heating furnace according to claim 1 or 2, characterized in that: The mass proportions of different particle sizes in the calcium hexaaluminate are as follows: 3-12 parts of calcium hexaaluminate aggregate with a particle size of 3mm < ≤ 5mm, 7-30 parts of calcium hexaaluminate aggregate with a particle size of 1mm < ≤ 3mm, and 33-45 parts of calcium hexaaluminate fine powder with a particle size of 0 < ≤ 1mm. Among the calcium hexaaluminate fine powder with a particle size of 0 < ≤ 1mm, 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 .

4. The low thermal conductivity, high strength calcium hexaaluminate castable for the walking beam of the heating furnace according to claim 3, 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.

5. The low thermal conductivity, high strength calcium hexaaluminate castable for the walking beam of the heating furnace according to claim 1 or 2, characterized in that: The mass ratio of different particle sizes in the microporous corundum aggregate is as follows: 0-3 parts of microporous corundum aggregate with particle size 3mm≤5mm and 0-17 parts of microporous corundum aggregate with particle size 1mm≤<3mm; wherein, the purity of the raw material of microporous corundum is ≥98.5%.

6. The low thermal conductivity, high strength calcium hexaaluminate castable for the walking beam of the heating furnace according to claim 1 or 2, characterized in that: The hollow alumina spheres have a purity of ≥99%, a particle size of 0.2-0.5 mm, and a bulk density of 0.8-0.9 g / cm³. 3 The calcined alumina powder has a purity ≥99% and a particle size d50 of 3-6µm; the activated alumina micro powder has a purity ≥99% and a particle size d50 of 1-2.5µm; the nano alumina has a purity ≥99% and a specific surface area BET of 100-150m². 2 / g.

7. The low thermal conductivity, high strength calcium hexaaluminate castable for the walking beam of the heating furnace according to claim 1 or 2, characterized in that: The raw material composition of the calcium aluminate cement contains 68.5-71% Al2O3.

8. The low thermal conductivity, high strength calcium hexaaluminate castable for the walking beam of the heating furnace according to claim 1 or 2, characterized in that: The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

9. The low thermal conductivity, high strength calcium hexaaluminate castable for the walking beam of the heating furnace according to claim 1 or 2, characterized in that: In the composite sintering aid, the purity of titanium dioxide is ≥99% and the particle size d50 is 1-10µm; the purity of yttrium oxide is ≥99% and the particle size d50 is 1-10µm; and the purity of cerium oxide is ≥99% and the particle size d50 is 1-10µm.

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