Refractory castable for forming a gradient insulation of a furnace working layer and method of use

Abstract

A refractory castable for creating a gradient insulation layer in the lining of a furnace or kiln, comprising the following raw materials and their wt% contents: aggregate with a particle size ≥1mm: 50-70%; fine powder with a particle size ≤0.088mm: 20-35%; fiber: 1-3%; dispersant: 0.05-0.1%; accelerator: 0.01-0.02%; binder: 5-8%; alumina foam not exceeding 20%; and water of 6-8% of the total weight of the above raw materials. Application method: The working layer in an industrial furnace or high-temperature vessel is divided into three layers from the inside out according to its thickness: Working Layer 1, Working Layer 2, and Working Layer 3, which are then cast separately. Preparation of Working Layer 1 castable; Preparation of Working Layer 2 castable; Preparation of Working Layer 3 castable. This invention, while ensuring a compressive strength of not less than 40MPa at 1500℃ for 3h, improves the thermal insulation performance by casting the furnace working lining into three layers: working layer one, working layer two, and working layer three, and by creating a thermal insulation gradient through the density gradient structure design of each layer of castable material. This means that the furnace surface temperature can be reduced by at least 35℃, and the heat transfer can be reduced by about 800MJ.

Description

Technical Field

[0001] This invention relates to a refractory castable and its application method, specifically a refractory castable and its application method for creating a gradient insulation layer in the working layer of a furnace. Background Technology

[0002] The extensive use of refractory materials in furnace linings undoubtedly has a significant impact on energy conservation and cost reduction in steel enterprises. In the furnace structure, the working lining is in direct contact with high-temperature molten metal and slag, thus requiring excellent resistance to erosion and penetration. To meet these requirements, existing technologies mostly employ heavy refractory materials. However, the high density and low porosity of heavy refractory materials result in high thermal conductivity and large heat capacity in the furnace lining, leading to significant heat loss from the furnace body, high heat storage capacity in the lining itself, and low thermal efficiency. In contrast to heavy refractory materials, lightweight refractory materials are also used, offering better insulation due to their higher porosity and lower thermal conductivity. However, they suffer from relatively lower strength and insufficient erosion resistance, limiting their application in furnace working linings.

[0003] Currently, heavy refractories are mainly used for the working linings of industrial furnaces and high-temperature vessels. Heavy refractories have advantages such as high strength, low porosity, and strong resistance to erosion and penetration. However, their high thermal conductivity (3 to 10 times that of lightweight refractories) and large heat capacity lead to high external surface temperatures and significant heat loss in high-temperature equipment. While lightweight refractories have low thermal conductivity and good insulation, their low strength, high porosity, and poor erosion resistance make them unsuitable for furnace working linings. Some steel companies have attempted to reduce external surface temperatures and heat dissipation by increasing the furnace lining thickness. While this method reduces heat loss, it increases heat storage loss. The increased heat capacity of the thicker lining slows down heating and cooling rates, reducing thermal efficiency. Furthermore, the increased lining thickness reduces furnace volume, impacting output, and increases refractory material usage, thus raising costs.

[0004] Some steel companies also add insulation linings after the permanent lining of furnaces and kilns. Studies have shown that the insulation material has a better insulation effect the closer it is to the working surface. Therefore, adding an insulation lining after the permanent lining cannot achieve the best insulation effect.

[0005] Search results:

[0006] Chinese patent application CN200710071033.5 discloses a novel gradient composite insulation layer and its manufacturing method. The insulation layer consists of hollow alumina spheres, hollow corundum spheres, and a perlite layer, which are sequentially composited along a temperature gradient. The manufacturing method includes steps such as batching, forming an insulating cavity in a mold, feeding, vibration-pressurization molding, drying, and firing. This document only relates to the insulation layer, and the designed material has a low density, ranging from 0.6 to 1.6 g / cm³. 3 While other performance data are lacking, its density index indicates poor strength and erosion resistance, making it unsuitable for use in the working layer of high-temperature furnaces. Furthermore, as a shaped product—insulating brick—its on-site construction convenience and adaptability to furnace shapes are inferior to unshaped refractory castables.

[0007] Chinese patent application CN201611246344.6 relates to "A gradient material for castables and its preparation method." The gradient material has a core-shell structure, with a core of magnesia particles and a shell of Al2O3 material, with a transition layer between the core and shell. The preparation method involves coating the surface of the magnesia particles with an Al2O3 slurry and then firing it at high temperature. This document describes a raw material for castable production, where the so-called gradient refers to the phase change from the magnesia core to the aluminum-rich spinel shell. Strength data is provided, but no other indicators are available, and no advantages are demonstrated in terms of thermal insulation.

[0008] Chinese patent application CN201310477845.5 describes a "High-purity zirconia refractory product with gradient function and its preparation method." The product has an extremely high ZrO2 content and a non-uniform internal microstructure, with parameters such as porosity and bulk density exhibiting gradient changes along a specific direction. The finished product is cylindrical, limiting its practical application. While the gradient changes in porosity, bulk density, and thermal conductivity along a specific direction are described, specific testing data are not provided. The bulk density is greater than 4.3 g / cm³. 3 Therefore, it can be concluded that the thermal conductivity is good, but it is not conducive to heat preservation and energy saving.

[0009] Chinese patent application CN201410116753.9 discloses a graded-functional yttrium-stabilized zirconia refractory product for use as a lining material in sapphire crystal growth furnaces. The product, through specific raw material ratios and processes, exhibits a linear gradient change from the working surface to the non-working surface. This application is primarily for sapphire crystal growth furnaces and is not applicable to general industrial furnaces. It describes gradient changes in porosity and bulk density along a specific direction but does not provide specific testing data. The bulk density is greater than 4.3 g / cm³. 3 This is not conducive to the heat preservation and energy saving of the furnace.

[0010] Chinese patent application CN201020155049.1 discloses a ladle lining based on gradient insulation, comprising a permanent layer, an insulation layer, and a working layer. The insulation layer uses lightweight insulating material and has a concave joint groove, while the working layer is a castable refractory layer. This document describes the structural design of the ladle lining, placing the insulation layer between the permanent and working layers, but does not disclose the refractory material formulation for the furnace lining. The bulk density of the insulation layer material is between 0.7 and 1.0 g / cm³. 3 Between 5 and 10 MPa, its strength and corrosion resistance are poor, and it cannot be used in the working layer of high-temperature furnaces. Summary of the Invention

[0011] This invention aims to overcome the shortcomings of existing technologies and provide a refractory castable that, while ensuring a compressive strength of not less than 40 MPa at 1500℃ for 3 hours, creates a gradient insulation performance in the furnace lining by casting the furnace working lining into three layers (working layer one, working layer two, and working layer three) and forming an insulation gradient through a density gradient structure design of each layer of castable, thereby improving the thermal insulation performance and reducing the furnace surface temperature by approximately 40℃.

[0012] Measures to achieve the above objectives:

[0013] A refractory castable that creates a gradient insulation layer in the working layer of a furnace has the following raw material composition and weight percentage content: aggregate with a particle size ≥1mm: 50-70%; fine powder with a particle size ≤0.088mm: 20-35%; fiber: 1-3%; dispersant: 0.05-0.1%; accelerator: 0.01-0.02%; binder: 5-8%; alumina foam not exceeding 20%; plus 6-8% water by weight of the above raw materials.

[0014] Further: aggregates with a particle size ≥1mm: 50-60%; fine powders with a particle size ≤0.088mm: 20-25%; fine fiber powders: 1-2%; dispersant: 0.085-0.1%; accelerator: 0.01-0.015%; binder: 5-6.5%.

[0015] The aggregate is one or a mixture of two or more of the following in any proportion: white corundum, sub-white corundum, brown corundum, sintered corundum, premium bauxite, and spinel; and the weight percentage of Al2O3 in the corundum aggregate is required to be no less than 94%, the weight percentage of Al2O3 in the premium bauxite is required to be no less than 85%, and the weight percentage of Al2O3 in the spinel is required to be no less than 70%.

[0016] The fine powder is, in part, one or more of the following: sintered corundum powder, fused corundum powder, α-alumina micro powder, bauxite powder, spinel powder, magnesia powder, and silica micro powder, in any proportion; and requires that: the weight percentage of Al2O3 in the corundum powder is not less than 90%, the weight percentage of Al2O3 in the α-alumina micro powder is not less than 95%, the weight percentage of Al2O3 in the bauxite powder is not less than 85%, the weight percentage of Al2O3 in the spinel powder is not less than 70%, the weight percentage of MgO in the magnesia powder is not less than 90%, and the weight percentage of SiO2 in the silica micro powder is not less than 95%.

[0017] The fiber is aluminum silicate fiber or steel fiber or a mixture of both in any proportion.

[0018] The dispersant is sodium tripolyphosphate, sodium pyrophosphate, sodium tetrapolyphosphate, or a mixture of any two of these in any proportion.

[0019] The key difference is that the coagulant is lithium carbonate or sodium silicate.

[0020] The key feature is that the binder is calcium aluminate cement or barium aluminate cement, and the weight percentage of Al2O3 in the cement is required to be not less than 70%.

[0021] A method for using a refractory castable to create a gradient insulation layer in the working layer of a furnace, comprising the following steps:

[0022] The working layer in industrial furnaces or high-temperature containers is divided into three layers from the inside out according to its thickness: Working Layer 1, Working Layer 2, and Working Layer 3, which are then poured separately.

[0023] 1) Preparation of the working layer castable:

[0024] Add the following ingredients to a mixer according to the set quantities: aggregate with a particle size ≥1mm: 50-70%; fine powder with a particle size ≤0.088mm: 20-35%; fiber: 1-3%; dispersant: 0.05-0.1%; accelerator: 0.01-0.02%; binder: 5-8%; alumina foam: 15-20%. Mix these ingredients for 8-10 minutes. Then add water equal to 7% of the total weight of the above ingredients and continue mixing for 3-5 minutes. After placing the mold, pour and vibrate the uniformly mixed castable. Let it stand for at least 18 minutes. The working layer should be 25-40% of the total working layer thickness.

[0025] 2) Preparation of the second-layer castable refractory

[0026] Add the following ingredients to a mixer according to the set quantities: aggregate with a particle size ≥1mm: 50-70%; fine powder with a particle size ≤0.088mm: 20-35%; fiber: 1-3%; dispersant: 0.05-0.1%; coagulant: 0.01-0.02%; binder: 5-8%; alumina foam: 10-15%. Mix these ingredients for 8-10 minutes. Then add water equal to 7% of the total weight of the above ingredients and continue mixing for 3-5 minutes. After placing the mold, pour and vibrate the uniformly mixed castable. Let it stand for at least 18 minutes. The working layer should be 25-50% of the total thickness of the working layer.

[0027] 3) Preparation of the working layer three-layer castable refractory:

[0028] Aggregate with a particle size ≥1mm: 50-70%; fine powder with a particle size ≤0.088mm: 20-35%; fiber: 1-3%; dispersant: 0.05-0.1%; coagulant: 0.01-0.02%; binder: 5-8%; put them into a mixer according to the set amount and mix for 8-10 minutes; then add water equal to 7% of the total weight of the above raw materials; continue mixing for 3-5 minutes; after placing the mold, pour and vibrate the above-mixed casting material; after routine curing, demolding, and baking, it can be put into use; its thickness is the remainder.

[0029] The second working layer is poured in two stages, namely, the second working layer 1 and the second working layer 2, according to its insulation requirements. The thickness ratio of the two layers is 35-65% and 65-35% of the thickness of the second working layer, respectively.

[0030] The role and mechanism of each raw material and main process in this invention

[0031] The reason why the aggregate with a particle size ≥1mm accounts for 50-70% in this invention is that it plays a skeleton role in the castable, enhancing the strength, high-temperature resistance, and resistance to erosion and penetration. However, when its content is less than 50%, an effective skeleton structure cannot be formed, affecting the high-temperature performance of the castable, causing a decrease in strength, making it prone to deformation or collapse at high temperatures, and reducing its resistance to erosion. When its content is greater than 70%, it reduces the fluidity of the castable, affects the uniformity and density of the material, leading to an increase in the internal porosity of the castable, reducing the strength of the material, and increasing the cost of the aggregate.

[0032] The reason why this invention controls the fine powder with a particle size ≤0.088mm at 20-35% is to use it as a matrix material to improve the density of the material and provide high-temperature resistance, erosion resistance, and permeability resistance. However, when its content is less than 20%, it will lead to insufficient fluidity of the castable, making it difficult to fill the mold, affecting the molding quality, and reducing the strength of the castable at low temperatures. Too little powder will result in more unfilled voids between the aggregates, reducing the density and decreasing the material's erosion resistance. When its content is higher than 35%, it will not achieve a reasonable particle size distribution, forming a dense packing with the aggregate, leading to reduced strength, making the castable too viscous, affecting construction, and also prolonging the drying and sintering time of the castable, affecting production efficiency.

[0033] The reason why the fiber content is controlled at 1-3% in this invention is to enhance the toughness and strength of the castable and improve its thermal shock resistance. However, when its content is less than 1%, it will lead to a decrease in the strength and toughness of the castable, making it prone to cracking during use and reducing its thermal shock resistance. When its content is more than 3%, it will increase the cost of the material, make the castable too viscous, increase the difficulty of construction, increase the thermal conductivity of the castable, and affect its thermal insulation performance.

[0034] The reason why the dispersant content is controlled at 0.05% to 0.1% in this invention is to improve the fluidity of refractory castables and reduce the amount of water used. However, when its content is below 0.05%, it will lead to insufficient fluidity of the castable, increase construction difficulties, affect molding quality, increase porosity, and reduce the density and strength of the material. When its content is above 0.1%, it will increase the cost of the material and affect the final strength of the castable because the dispersant will not form a high-strength bond at high temperatures.

[0035] The reason for controlling the setting accelerator content to 0.01-0.02% in this invention is that setting accelerators can accelerate the hardening speed of castables, reduce waiting time caused by layered construction, and improve construction efficiency. However, excessive setting accelerators will cause the castables to harden too quickly, resulting in too short a working time and making it difficult to complete pouring and leveling before hardening.

[0036] The reason for controlling the binder content to 5-8% in this invention is that the binder content affects the workability of the castable, such as its fluidity and plasticity; too high or too low a content will lead to construction difficulties. The binder provides the refractory castable with initial room temperature strength, facilitating construction and molding. However, at high temperatures, it easily reacts with refractory raw materials to form low-melting-point compounds, affecting the refractoriness and high-temperature performance of the castable. Therefore, it is necessary to control the amount added.

[0037] The reason why the alumina foam content is controlled to be no more than 20% is that it is used to adjust the density of refractory castable, increase the closed porosity, realize the density gradient inside the material, and improve the thermal insulation performance. However, when its content is higher than 20%, the material density will be too low and the porosity will be too high, affecting the strength and erosion resistance of the castable, and it will no longer be suitable for the working layer of high-temperature furnaces.

[0038] Compared with the prior art, this invention, while ensuring a compressive strength of not less than 40MPa at 1500℃ for 3 hours, improves the thermal insulation performance by casting the furnace working lining in three layers (working layer one, working layer two, and working layer three) and creating a thermal insulation gradient through the density gradient structure of each layer of castable material. This results in a reduction of at least 35℃ in the furnace surface temperature and a reduction of approximately 800MJ in heat transfer. Furthermore, it combines the advantages of heavy refractory materials and lightweight insulating refractory materials, while avoiding the drawbacks of heavy refractory materials (high thermal conductivity and large heat loss) and lightweight refractory materials (low strength, high porosity, and poor erosion resistance). This effectively reduces heat transfer from the furnace lining, meeting the stringent operating conditions of the furnace working lining while resisting the scouring and erosion of high-temperature molten metal and slag, reducing the temperature drop of the molten metal, protecting the furnace shell, reducing thermal deformation, and extending service life. Detailed Implementation

[0039] The present invention will now be described in detail:

[0040] The values ​​of the castables in each embodiment are within the following range:

[0041] A refractory castable for creating a gradient insulation layer in the working layer of a furnace, comprising the following raw material composition and weight percentage: aggregate with a particle size ≥1mm: 50-70%; fine powder with a particle size ≤0.088mm: 20-35%; fiber: 1-3%; dispersant: 0.05-0.1%; accelerator: 0.01-0.02%; binder: 5-8%; alumina foam not exceeding 20%; plus 6-8% water by weight of the above raw materials.

[0042] How to use:

[0043] Example 1

[0044] The working layer in industrial furnaces or high-temperature containers is divided into three layers from the inside out according to its thickness: Working Layer 1, Working Layer 2, and Working Layer 3, which are then poured separately.

[0045] 1) Preparation of the working layer castable:

[0046] Aggregate with a particle size ≥1mm: 50% white corundum; fine powder with a particle size ≤0.088mm: 16% fused corundum powder, 6% magnesium oxide powder, 2.74% silica micro powder; fiber: 1.15% aluminum silicate fiber; dispersant: 0.1% sodium tripolyphosphate; accelerator: 0.01% lithium carbonate; binder: 6% calcium aluminate cement; alumina foam: 18%; put the above raw materials into a mixer and mix for 8.5 minutes; then add water equal to 7% of the total weight of the above raw materials; continue mixing for 4 minutes; after placing the mold, pour and vibrate the above uniformly mixed castable, controlling the first working layer to account for 28% of the total thickness of the working layer; after standing for 20 minutes, proceed with the construction of the second working layer;

[0047] 2) Preparation of the second-layer castable refractory

[0048] Aggregate with a particle size ≥1mm: 60% white corundum; fine powder with a particle size ≤0.088mm: 8% fused corundum powder, 7.25% magnesium oxide powder, 4.75% silica micro powder; fiber: 2% aluminum silicate fiber; dispersant: 0.185% sodium tripolyphosphate; accelerator: 0.015% lithium carbonate; binder: 6.5% calcium aluminate cement; alumina foam: 11.3%; put the above raw materials into a mixer and mix for 9 minutes; then add water equal to 8% of the total weight of the above raw materials; continue mixing for 4 minutes; after placing this layer in the mold, pour and vibrate the above uniformly mixed castable, controlling the second working layer to occupy 35% of the total thickness of the working layer; after standing for 20 minutes, construct the third working layer;

[0049] 3) Preparation of the working layer three-layer castable refractory:

[0050] Aggregate with a particle size ≥1mm: 70% white corundum; fine powder with a particle size ≤0.088mm: 10% fused alumina powder, 8% magnesium oxide powder, 4% silica micro powder; fiber: 1.8% aluminum silicate fiber; dispersant: 0.185% sodium tripolyphosphate; accelerator: 0.015% lithium carbonate; binder: 6% calcium aluminate cement; put them into a mixer according to the set amount and mix for 8 minutes; then add water equal to 7% of the total weight of the above raw materials; continue mixing for 3 minutes; after placing the mold, pour and vibrate the above uniformly mixed castable, the thickness of which is the remaining 37%; after routine curing, demolding, and baking, it can be put into use.

[0051] Test results:

[0052] Working layer performance: Bulk density 1.95 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 16.2 MPa, and the compressive strength at 1500℃ for 3 hours is 43.7 MPa. The thermal conductivity of the hot surface at 1000℃ is 0.63 W / mK.

[0053] Working layer 2 properties: Bulk density 2.36 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 21.7 MPa, and the compressive strength at 1500℃ for 3 hours is 57.0 MPa. The thermal conductivity of the hot surface at 1000℃ is 0.78 W / mK.

[0054] Three properties of the working layer: bulk density 2.79 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 28.0 MPa, and the compressive strength at 1500℃ for 3 hours is 71.2 MPa. The thermal conductivity of the hot surface at 1000℃ is 1.03 W / mK.

[0055] Example 2

[0056] The working layer in industrial furnaces or high-temperature containers is divided into three layers from the inside out according to its thickness: Working Layer 1, Working Layer 2, and Working Layer 3, which are then poured separately.

[0057] 1) Preparation of the working layer castable:

[0058] Aggregates with a particle size ≥1mm: 30% brown corundum aggregate, 9% spinel aggregate; fine powders with a particle size ≤0.088mm: 15% α-alumina micro powder, 5% spinel powder, 9.88% magnesium oxide powder, 5% silica micro powder; fiber: 1% aluminum silicate fiber; dispersant: 0.05% sodium tripolyphosphate, 0.05% sodium pyrophosphate; accelerator: 0.02% sodium silicate; binder: 5% barium aluminate cement; alumina foam: 20%; put the above raw materials into a mixer and mix for 8.5 minutes; then add water equal to 7% of the total weight of the above raw materials; continue mixing for 4 minutes; after placing the mold, pour and vibrate the above uniformly mixed castable, controlling the first working layer to account for 30% of the total thickness of the working layer; after standing for 20 minutes, proceed with the construction of the second working layer;

[0059] 2) Preparation of the second working layer castable: Aggregate with a particle size ≥1mm: 40% brown corundum aggregate, 9% spinel aggregate; fine powder with a particle size ≤0.088mm: 15% α-alumina micro powder, 5% spinel powder, 9.88% magnesium oxide powder, 5% silica micro powder; fiber: 1% aluminum silicate fiber; dispersant: 0.05% sodium tripolyphosphate, 0.05% sodium pyrophosphate; accelerator: 0.02% sodium silicate; binder: 5% barium aluminate cement; alumina foam: 10%; put the above raw materials into a mixer and mix for 9 minutes; then add water equal to 8% of the total weight of the above raw materials; continue mixing for 4 minutes; after placing the mold for this layer, pour and vibrate the uniformly mixed castable, controlling the second working layer to occupy 30% of the total thickness of the working layer; after standing for 20 minutes, construct the third working layer;

[0060] 3) Preparation of the working layer three-layer castable refractory:

[0061] Aggregates with a particle size ≥1mm: 50% brown corundum aggregate, 9% spinel aggregate; fine powders with a particle size ≤0.088mm: 15% α-alumina micro powder, 5% spinel powder, 9.88% magnesium oxide powder, 5% silica micro powder; fiber: 1% aluminum silicate fiber; dispersant: 0.05% sodium tripolyphosphate, 0.05% sodium pyrophosphate; accelerator: 0.02% sodium silicate; binder: 5% barium aluminate cement; add the above materials to a mixer according to the set amount and mix for 8 minutes; then add water equal to 7% of the total weight of the above materials; continue mixing for 3 minutes; after placing the mold, pour and vibrate the above uniformly mixed castable to a thickness of the remaining 40%; after routine curing, demolding, and baking, it can be put into use.

[0062] Test results:

[0063] Working layer 1 properties: Bulk density 2.01 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 14.9 MPa, and the compressive strength at 1500℃ for 3 hours is 41.7 MPa. The thermal conductivity of the hot surface at 1000℃ is 0.68 W / mK.

[0064] Working layer 2 properties: Bulk density 2.47 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 19.8 MPa, and the compressive strength at 1500℃ for 3 hours is 55.4 MPa. The thermal conductivity of the hot surface at 1000℃ is 0.81 W / mK.

[0065] Three properties of the working layer: bulk density 2.80 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 26.2 MPa, and the compressive strength at 1500℃ for 3 hours is 67.4 MPa. The thermal conductivity of the hot surface at 1000℃ is 1.06 W / mK.

[0066] Example 3

[0067] The working lining in industrial furnaces or high-temperature containers is divided into three layers from the inside out, based on its thickness: working layer one, working layer two, and working layer three, which are poured separately.

[0068] 1) Preparation of the working layer castable:

[0069] Aggregates with a particle size ≥1mm: 38% sintered corundum aggregate, 10% premium bauxite aggregate; fine powders with a particle size ≤0.088mm: 8% sintered corundum powder, 2% bauxite powder, 7.89% magnesium oxide powder, 4% silica micro powder; fibers: 1% steel fiber, 2% aluminosilicate fiber; dispersant: 0.05% sodium tripolyphosphate, 0.05% sodium tetrapolyphosphate; accelerator: 0.01% lithium carbonate; binder: 8% calcium aluminate cement; alumina foam: 19%; mix the above raw materials in a mixer for 8 minutes; then add water equal to 7% of the total weight of the above raw materials; continue mixing for 4 minutes; after placing the mold, pour and vibrate the uniformly mixed castable, controlling the first working layer to account for 27% of the total thickness of the working layer; after standing for 20 minutes, construct the second working layer;

[0070] 2) Preparation of the second-layer castable refractory

[0071] This second working layer is to be poured separately as working layer 21 and working layer 22;

[0072] Preparation of Castable Material for Working Layer 2

[0073] Aggregates with a particle size ≥1mm: 44% sintered corundum aggregate, 10% premium bauxite aggregate; fine powders with a particle size ≤0.088mm: 8% sintered corundum powder, 2% bauxite powder, 7.89% magnesia powder, 4% silica micro powder; fibers: 1% steel fiber, 2% aluminosilicate fiber; dispersant: 0.05% sodium tripolyphosphate, 0.05% sodium tetrapolyphosphate; accelerator: 0.01% lithium carbonate; binder: 8% calcium aluminate cement; alumina foam: 13%; mix the above raw materials in a mixer for 8 minutes; then add water equal to 8% of the total weight of the above raw materials; continue mixing for 4 minutes; after placing the mold for this layer, pour and vibrate the uniformly mixed castable, controlling the second working layer to occupy 20% of the total thickness of the working layer; after standing for 20 minutes, proceed with the second working layer...

[0074] 2. Masonry;

[0075] Preparation of Castable Material for Working Layer 2

[0076] Aggregates with a particle size ≥1mm: 50% sintered corundum aggregate, 10% premium bauxite aggregate; fine powders with a particle size ≤0.088mm: 8% sintered corundum powder, 2% bauxite powder, 7.89% magnesium oxide powder, 4% silica micro powder; fibers: 1% steel fiber, 2% aluminosilicate fiber; dispersant: 0.05% sodium tripolyphosphate, 0.05% sodium tetrapolyphosphate; accelerator: 0.01% lithium carbonate; binder: 8% calcium aluminate cement; alumina foam: 7%; mix the above raw materials in a mixer for 8 minutes; then add water equal to 8% of the total weight of the above raw materials; continue mixing for 4 minutes; after placing this layer in the mold, pour and vibrate the uniformly mixed castable, controlling the second working layer to account for 10% of the total thickness of the working layer; after standing for 20 minutes, construct the third working layer;

[0077] 3) Preparation of the working layer three-layer castable refractory:

[0078] Aggregates with a particle size ≥1mm: 57% sintered corundum aggregate and 10% premium bauxite aggregate; fine powders with a particle size ≤0.088mm: 8% sintered corundum powder, 2% bauxite powder, 7.89% magnesium oxide powder, and 4% silica micro powder; fibers: 1% steel fiber and 2% aluminum silicate fiber; dispersant: 0.05% sodium tripolyphosphate and 0.05% sodium tetrapolyphosphate; accelerator: 0.01% lithium carbonate; binder: 8% calcium aluminate cement; add the above materials to a mixer according to the set amount and mix for 9 minutes; then add water equal to 7% of the total weight of the above materials; continue mixing for 3 minutes; after placing the mold, pour and vibrate the uniformly mixed castable to a thickness of the remaining 43%; after routine curing, demolding, and baking, it can be put into use.

[0079] Test results:

[0080] Working layer performance: Bulk density 1.89 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 15.6 MPa, and the compressive strength at 1500℃ for 3 hours is 40.1 MPa. The thermal conductivity of the hot surface at 1000℃ is 0.65 W / mK.

[0081] Working layer 2.1 performance: Bulk density 2.20 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 21.3 MPa, and the compressive strength at 1500℃ for 3 hours is 53.3 MPa. The thermal conductivity of the hot surface at 1000℃ is 0.80 W / mK.

[0082] Working layer 2 properties: Bulk density 2.43 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 23.9 MPa, and the compressive strength at 1500℃ for 3 hours is 60.5 MPa. The thermal conductivity of the hot surface at 1000℃ is 0.92 W / mK.

[0083] Three properties of the working layer: bulk density 2.77 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 27.1 MPa, and the compressive strength at 1500℃ for 3 hours is 69.8 MPa. The thermal conductivity of the hot surface at 1000℃ is 1.10 W / mK.

[0084] Example 4

[0085] The working layer in industrial furnaces or high-temperature containers is divided into three layers from the inside out according to its thickness: Working Layer 1, Working Layer 2, and Working Layer 3, which are then poured separately.

[0086] 1) Preparation of the working layer castable:

[0087] Aggregates with a particle size ≥1mm: 25% sub-white corundum aggregate, 23% spinel aggregate; fine powders with a particle size ≤0.088mm: 5% fused corundum powder, 5% spinel powder, 7.94% magnesium oxide powder, 4% silica micro powder; 2% aluminum silicate fiber; dispersant: 0.05% sodium pyrophosphate; accelerator: 0.01% lithium carbonate; binder: 6% calcium aluminate cement; alumina foam: 22%; put the above raw materials into a mixer and mix for 8 minutes; then add water equal to 7% of the total weight of the above raw materials; continue mixing for 4 minutes; after placing the mold, pour and vibrate the above uniformly mixed castable, controlling the first working layer to account for 28% of the total thickness of the working layer; after standing for 20 minutes, proceed with the construction of the second working layer;

[0088] 2) Preparation of the second-layer castable refractory

[0089] Aggregates with a particle size ≥1mm: 30% sub-white corundum aggregate, 28% spinel aggregate; fine powders with a particle size ≤0.088mm: 5% fused corundum powder, 5% spinel powder, 7.94% magnesium oxide powder, 4% silica micro powder; fiber: 2% aluminum silicate fiber; dispersant: 0.05% sodium pyrophosphate; accelerator: 0.01% lithium carbonate; binder: 6% calcium aluminate cement; alumina foam: 12%; put the above raw materials into a mixer and mix for 9 minutes; then add water equal to 8% of the total weight of the above raw materials; continue mixing for 4 minutes; after placing this layer in the mold, pour and vibrate the above uniformly mixed castable, controlling the second working layer to occupy 25% of the total thickness of the working layer; after standing for 20 minutes, construct the third working layer;

[0090] 3) Preparation of the working layer three-layer castable refractory:

[0091] Aggregates with a particle size ≥1mm: 35% sub-white corundum aggregate and 35% spinel aggregate; fine powders with a particle size ≤0.088mm: 5% fused alumina powder, 5% spinel powder, 8% magnesium oxide powder, and 4% silica micro powder; fiber: 1.94% aluminum silicate fiber; dispersant: 0.05% sodium pyrophosphate; accelerator: 0.01% lithium carbonate; binder: 6% calcium aluminate cement; add the above materials to a mixer according to the set amount and mix for 8 minutes; then add water equal to 7% of the total weight of the above materials; continue mixing for 3 minutes; after placing the mold, pour and vibrate the above-mentioned uniformly mixed castable to a thickness of the remaining 47%; after routine curing, demolding, and baking, it can be put into use.

[0092] Test results:

[0093] Working layer 1 properties: Bulk density 2.03 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 18.1 MPa, and the compressive strength at 1500℃ for 3 hours is 47.8 MPa. The thermal conductivity of the hot surface at 1000℃ is 0.61 W / mK.

[0094] Working layer 2 properties: Bulk density 2.39 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 26.3 MPa, and the compressive strength at 1500℃ for 3 hours is 61.5 MPa. The thermal conductivity of the hot surface at 1000℃ is 0.86 W / mK.

[0095] Three properties of the working layer: bulk density 2.83 g / cm³ 3 The compressive strength at 110℃ for 24 hours is 30.2 MPa, and the compressive strength at 1500℃ for 3 hours is 75.1 MPa. The thermal conductivity of the hot surface at 1000℃ is 1.08 W / mK.

[0096] This specific embodiment is merely a best example and is not intended to limit the implementation of the technical solution of the present invention.

Claims

1. A method for using a refractory castable to create a gradient insulation layer in the working layer of a furnace, comprising the following steps: The working layer in industrial furnaces or high-temperature containers is divided into three layers from the inside out according to its thickness: Working Layer 1, Working Layer 2, and Working Layer 3, which are then poured separately. 1) Preparation of the working layer castable: The raw material composition and weight percentage are as follows: aggregate with a particle size ≥1mm: 50-70%; fine powder with a particle size ≤0.088mm: 20-35%; fiber: 1-3%. Dispersant: 0.05–0.1%; Accelerator: 0.01-0.02%; binder: 5-8%; alumina foam: 15-20%. Add these ingredients to a mixer according to the set amounts and mix for 8-10 minutes. Add water equal to 7% of the total weight of the above ingredients and continue mixing for 3-5 minutes. Place the mold in the mold, then pour and vibrate the uniformly mixed casting material. Let it stand for at least 18 minutes, ensuring the working layer accounts for 25-40% of the total working layer thickness. 2) Preparation of the second-layer castable refractory The raw material composition and weight percentage are as follows: aggregate with a particle size ≥1mm: 50-70%; fine powder with a particle size ≤0.088mm: 20-35%; fiber: 1-3%. Dispersant: 0.05–0.1%; Accelerator: 0.01-0.02%; binder: 5-8%; alumina foam: 10-15%; add to the mixer according to the set amount and mix for 8-10 minutes; then add water equal to 7% of the total weight of the above raw materials; continue mixing for 3-5 minutes; after placing the mold, pour and vibrate the uniformly mixed casting material; let stand for no less than 18 minutes; and control the working layer to account for 25-50% of the total thickness of the working layer. 3) Preparation of the working layer three-layer castable: The raw material composition and weight percentage are as follows: aggregate with a particle size ≥1mm: 50-70%; fine powder with a particle size ≤0.088mm: 20-35%; fiber: 1-3%. Dispersant: 0.05–0.1%; Accelerator: 0.01-0.02%; binder: 5-8%; add to the mixer according to the set amount and mix for 8-10 minutes; then add water equal to 7% of the total weight of the above raw materials; continue mixing for 3-5 minutes; after placing the mold, pour and vibrate the uniformly mixed casting material; after routine curing, demolding, and baking, it can be put into use; its thickness is the remainder; The aggregate of the castable in the first to third working layers is one or a mixture of two or more of the following in any proportion: white fused alumina, sub-white fused alumina, brown fused alumina, sintered fused alumina, premium bauxite, and spinel. The fine powder of the castable in the first to third working layers is one or a mixture of two or more of the following in any proportion: sintered corundum powder, fused corundum powder, α-alumina micro powder, bauxite powder, spinel powder, magnesium oxide powder, and silicon oxide micro powder.

2. The method of using a refractory castable to create a gradient insulation layer in the working layer of a furnace as described in claim 1, characterized in that: The second working layer is poured in two stages, namely the second working layer 1 and the second working layer 2, according to its insulation requirements. The thickness ratio of the two layers is 35-65% and 65-35% of the thickness of the second working layer, respectively.

3. The method of using a refractory castable to create a gradient insulation layer in the working layer of a furnace as described in claim 1, characterized in that: Requirements: The weight percentage of Al2O3 in corundum aggregate shall not be less than 94%, the weight percentage of Al2O3 in premium bauxite shall not be less than 85%, and the weight percentage of Al2O3 in spinel shall not be less than 70%.

4. The method of using a refractory castable for creating a gradient insulation layer in the working layer of a furnace as described in claim 1, characterized in that: the following requirements apply: the weight percentage of Al2O3 in corundum powder is not less than 90%, the weight percentage of Al2O3 in α-alumina micro powder is not less than 95%, the weight percentage of Al2O3 in bauxite powder is not less than 85%, the weight percentage of Al2O3 in spinel powder is not less than 70%, the weight percentage of MgO in magnesia powder is not less than 90%, and the weight percentage of SiO2 in silica micro powder is not less than 95%.

5. The method of using a refractory castable to create a gradient insulation layer in the working layer of a furnace as described in claim 1, characterized in that: The fibers in the first to third working layers are aluminum silicate fibers, steel fibers, or a mixture of both in any proportion.

6. The method of using a refractory castable to create a gradient insulation layer in the working layer of a furnace as described in claim 1, characterized in that: The dispersant in working layers one to three is sodium tripolyphosphate, sodium pyrophosphate, sodium tetrapolyphosphate, or a mixture of any two of these in any proportion.

7. The method of using a refractory castable to create a gradient insulation layer in the working layer of a furnace as described in claim 1, characterized in that: The coagulant in working layers one to three is lithium carbonate or sodium silicate.

8. The method of using a refractory castable to create a gradient insulation layer in the working layer of a furnace as described in claim 1, characterized in that: The binder in the first to third working layers is calcium aluminate cement or barium aluminate cement, and the weight percentage of Al2O3 in the cement is required to be not less than 70%.