Ladle building method for improving heat preservation effect of pouring ladle

Abstract

The invention relates to the field of iron and steel smelting, in particular to a ladle building method for improving the heat preservation effect of a pouring ladle, and aims at solving the problems that in the prior art, a pouring ladle is large in overall heat dissipation loss and high in energy consumption, the following scheme is provided, the ladle building method comprises the following steps that S1, a steel ladle shell is pretreated, specifically, the inner wall of the steel ladle shell of the pouring ladle is cleaned, and the inner wall of the steel ladle shell is cleaned; surface dirt is removed, and it is ensured that the inner wall is flat and dry; s2, a heat insulation layer is laid, specifically, ceramic fiber paper is cut into the size matched with the inner wall of the steel cladding, the ceramic fiber paper is tightly attached to the inner wall of the steel cladding to be laid, and the heat insulation layer is formed; and S3, a second heat preservation layer is installed, specifically, a nanometer heat preservation plate is laid on the outer side of the heat insulation layer, and the heat insulation layer is completely covered with the nanometer heat preservation plate. The heat preservation performance of the pouring ladle can be remarkably improved, the heat energy loss can be effectively reduced, the molten metal temperature preservation time can be prolonged, the process is stable and controllable, and the method is suitable for building pouring ladles with different capacities.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting, and in particular to a method for improving the insulation effect of a casting ladle. Background Technology

[0002] The casting ladle is a crucial piece of equipment used in casting and steelmaking processes for holding, transporting, and pouring molten metal at high temperatures. Its insulation performance directly affects the temperature stability of the molten metal, energy consumption, and the quality of the final casting. Poor insulation not only leads to significant waste of heat energy and increased production costs but may also cause casting defects such as cold shuts and incomplete pouring due to a rapid drop in molten metal temperature.

[0003] Currently, the common lining structure of casting ladles typically consists of, from the inside out: a working layer in direct contact with the molten metal (usually composed of refractory castable), a layer of insulation board (such as aluminum silicate fiberboard), and an outermost layer of ceramic fiber paper. This traditional structure provides some insulation; however, traditional insulation materials have relatively high thermal conductivity at high temperatures, and the overall insulation layer is thin with limited thermal resistance, resulting in significant overall heat loss from the casting ladle. Therefore, this paper proposes a method for constructing casting ladles to improve their insulation performance. Summary of the Invention

[0004] The present invention proposes a method for improving the heat insulation effect of casting ladles, which solves the problems of large overall heat loss and high energy consumption of casting ladles in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for improving the thermal insulation effect of a casting ladle includes the following steps:

[0007] S1. Pre-treatment of steel cladding: Clean the inner wall of the steel cladding of the casting ladle to remove surface dirt and ensure that the inner wall is flat and dry.

[0008] S2. Laying the insulation layer: Cut the ceramic fiber paper to a size that fits the inner wall of the steel shell and lay it tightly against the inner wall of the steel shell to form an insulation layer.

[0009] S3. Install the second insulation layer: Lay a nano insulation board on the outside of the insulation layer and make the nano insulation board completely cover the insulation layer;

[0010] S4. Constructing the first insulation layer: Insulation bricks are laid on the outside of the second insulation layer using a staggered construction method. During the construction process, refractory mortar is used to fill the brick joints to ensure that the bricks are tightly bonded to form the first insulation layer. The inner side of the first insulation layer is in complete contact with the second insulation layer, with no suspended areas.

[0011] S5. Casting working layer: Refractory castable is cast on the outside of the first insulation layer. Vibration molding is used to ensure that the refractory castable is dense. After casting, it is cured in accordance with the curing process of refractory castable.

[0012] The above technical solution, through a multi-layer composite insulation structure, effectively reduces heat loss from the casting ladle, improves insulation performance, and ensures the stability and durability of the structure.

[0013] As a further improvement to the above solution, in step S1, the cleaning process includes sandblasting to remove rust, alkaline degreasing, and rinsing with clean water in sequence to remove rust, oil stains and impurities from the inner wall surface of the steel cladding. After rinsing, hot air drying is used to ensure that the moisture content of the inner wall of the steel cladding is less than 0.5%.

[0014] The above technical solution thoroughly cleans the inner wall of the steel cladding, avoiding the impact of impurities and moisture on the bonding performance of the insulation layer, and providing a good foundation for the subsequent layer laying.

[0015] As a further improvement to the above scheme, in step S2, the ceramic fiber paper is 610mm wide and 3mm thick. During the laying process, it is ensured that the ceramic fiber paper is seamlessly spliced ​​together. The splice is sealed with a high-temperature resistant adhesive. The high-temperature resistant adhesive is a ceramic fiber adhesive with a working temperature range of not less than 1000℃ and a bonding strength of not less than 0.8MPa.

[0016] Through the above technical solution, ceramic fiber paper, as a heat insulation layer, has good flexibility and high temperature resistance. Seamless splicing ensures effective heat insulation and reduces the thermal bridging effect.

[0017] As a further improvement to the above solution, in step S3, the nano-insulation board has a length of 600mm, a width of 100mm, and a thickness of 10mm. It is made of nano-sized silica powder, and adjacent nano-insulation boards are fixed with a high-temperature resistant adhesive to ensure that there are no gaps between the layers.

[0018] Through the above technical solutions, the nano-insulation board has an extremely low thermal conductivity, and the gapless design between layers maximizes the insulation effect, forming a highly efficient thermal barrier.

[0019] As a further improvement to the above solution, the porosity of the nano-insulation board is not less than 90%, the pore size is smaller than the mean free path of air molecules, and the thermal conductivity is not greater than 0.03 W / (m·K) in a high-temperature environment above 600℃.

[0020] Through the above technical solutions, high porosity and nanoscale pore size suppress air convection and conduction, enabling the nano-insulation board to maintain ultra-low thermal conductivity at high temperatures, thus significantly improving insulation performance.

[0021] As a further improvement to the above scheme, in step S4, the insulation brick has the following specifications: length 230mm, width 113mm, and thickness 30mm. The refractoriness of the insulation brick is not less than 1500℃, the compressive strength at room temperature is not less than 15MPa, and the thermal conductivity (800℃) is not greater than 0.6W / (m・K).

[0022] Through the above technical solutions, the insulating bricks not only provide structural support, but also have a certain heat insulation capacity. The staggered joint construction ensures the tightness between layers, further reducing heat loss.

[0023] As a further improvement to the above scheme, the refractory castable is a high-alumina refractory castable with an Al2O3 content of not less than 60%, a room temperature compressive strength (after curing) of not less than 30 MPa, and a service temperature of not less than 1600℃.

[0024] Through the above technical solutions, high-alumina refractory castables have high refractoriness and strength, and can directly withstand the high-temperature impact of molten metal, ensuring the stability and service life of the working layer.

[0025] As a further improvement to the above scheme, the curing process in step S5 is as follows: after pouring, let it stand for 24 hours, then keep it moist at 50-60℃ for 3 days, then heat it up to 110℃ to dry for 24 hours, and finally let it cool naturally to room temperature.

[0026] Through the above technical solutions, the scientific curing process ensures the strength development and durability of refractory castables, and avoids cracking and spalling.

[0027] A casting ladle includes a steel shell and an inner lining structure disposed inside the shell. The inner lining structure includes, from the inside out, a working layer, a first insulation layer, a second insulation layer, and a heat insulation layer.

[0028] As a further improvement to the above scheme, the working layer is a refractory castable layer, the first insulation layer is an insulation brick layer and is disposed on the outside of the working layer, the second insulation layer is a nano insulation board layer and is disposed on the outside of the first insulation layer, and the heat insulation layer is a ceramic fiber paper layer and is disposed in close contact with the inner wall of the steel shell.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. By introducing nanoporous insulation board as the core insulation layer, the thermal conductivity of this material in the high temperature zone (above 600℃) is much lower than that of traditional insulation materials, which greatly increases the thermal resistance of the inner lining structure and effectively reduces heat loss through the wall.

[0031] 2. Gradient Insulation and Structural Stability: An innovative composite insulation structure of "nanoboard + insulating brick" is employed. The inner insulating brick layer possesses a certain heat storage capacity and can withstand some of the mechanical stress from the castable layer, protecting the relatively fragile nanoboard layer. The nanoboard layer, with its ultra-low thermal conductivity, forms a strong thermal barrier. This gradient design balances structural strength with ultimate insulation.

[0032] 3. Significant Energy Saving and Economic Benefits: Compared to the traditional "ceramic fiber paper + insulation board + castable" structure, this invention can significantly reduce the outer wall temperature of the casting ladle (by more than 30°C), and improve the heat preservation effect of the molten iron inside the ladle by 45% to 60%. This means that at the same tapping temperature, the molten metal cools down more slowly inside the casting ladle, allowing for longer transportation and waiting times for casting, while reducing energy consumption and resulting in significant economic benefits.

[0033] 4. Extend equipment life: Due to the improved overall insulation effect, the working temperature of the steel shell of the casting ladle is reduced, which reduces steel fatigue and deformation caused by thermal stress and helps to extend the overall service life of the casting ladle. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of the present invention;

[0035] Figure 2 This is a top view of the present invention.

[0036] Explanation of key symbols:

[0037] 1. Steel casing; 2. Insulation layer; 3. Second insulation layer; 4. First insulation layer; 5. Working layer. Detailed Implementation

[0038] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0039] Example 1:

[0040] Please combine Figures 1-2 This embodiment describes a method for improving the insulation effect of a casting ladle, comprising five key steps: pre-treatment of the steel cladding shell, laying of an insulation layer, installation of a second insulation layer, construction of the first insulation layer, and pouring of the working layer. The final result is a multi-layered composite structure consisting of a working layer, a first insulation layer, a second insulation layer, an insulation layer, and a steel cladding shell, arranged from the inside out. The construction method includes the following steps:

[0041] S1. Pretreatment of the steel cladding: As the outer support structure of the casting ladle, the condition of the inner wall of the steel cladding directly affects the adhesion and stability of the subsequent inner lining. In this step, the inner wall of the steel cladding is first sandblasted to remove surface oxide scale and rust; then, a 5%-8% sodium hydroxide solution is used for alkaline degreasing to remove oil and impurities; finally, it is rinsed clean with water and dried with hot air (hot air temperature 80-100℃) to reduce the moisture content of the inner wall to below 0.5% to prevent the subsequent inner lining from cracking or falling off due to moisture.

[0042] S2. Laying the insulation layer: The insulation layer uses ceramic fiber paper with a width of 610mm and a thickness of 3mm. Its function is to achieve initial insulation and buffering, and reduce the transfer of heat to the steel shell.

[0043] During installation, the ceramic fiber paper is cut according to the dimensions of the inner wall of the steel casing to ensure that each sheet of ceramic fiber paper is completely adhered to the inner wall. The joints between adjacent sheets are sealed with ceramic fiber adhesive (operating temperature ≥1000℃, bonding strength ≥0.8MPa) to prevent heat loss from the joints. The ceramic fiber paper is lightweight and flexible, and can adapt to the curvature of the inner wall of the steel casing to ensure no gaps between layers.

[0044] S3. Install the second insulation layer: The second insulation layer is the core insulation layer, using a nano-insulation board that is 600mm long, 100mm wide, and 10mm thick. This insulation board is formed from nano-sized silica powder using a special process.

[0045] It has extremely high porosity (≥90%) and pore size smaller than the mean free path of air molecules (70nm), which can suppress convective heat transfer and gas conduction heat transfer to the maximum extent. At the same time, it has excellent high temperature stability. Even at temperatures above 600℃, its thermal conductivity can still be maintained below 0.03W / (m・K), which is far lower than that of traditional aluminum silicate fiberboard (0.1-0.2W / (m・K)).

[0046] During installation, the nano insulation board is completely covered on the outside of the insulation layer, and adjacent insulation boards are fixed with high-temperature resistant adhesive to ensure tight contact between layers without air gaps, giving full play to its ultra-low thermal conductivity and forming a strong thermal barrier.

[0047] S4. Constructing the first insulation layer: The first insulation layer uses insulation bricks that are 230mm long, 113mm wide, and 30mm thick. They are mainly used to bear part of the mechanical stress from the working layer, protect the fragile nano-insulation board layer, and prevent the nano-insulation board from being damaged by impact and compression. At the same time, they use their own heat storage capacity to help regulate temperature fluctuations and improve the overall insulation stability.

[0048] During construction, a staggered joint method is adopted (the joints of bricks in the same layer are staggered by ≥1 / 3 of the brick length), the width of the joints is controlled at 2-3mm, and refractory mortar (Al2O3 content ≥40%) is used to fill the joints, ensuring that the bricks are tightly bonded together to form a structurally stable support layer, while further blocking heat transfer.

[0049] S5. Casting the Working Layer: The working layer is in direct contact with the high-temperature molten metal. This step uses high-alumina refractory castable with an Al2O3 content ≥60%. The casting thickness is determined based on the ladle capacity (usually 100-200mm). During casting, an immersion vibrator (vibration frequency 2800-3000r / min) is used for compaction to ensure the castable is dense and to avoid defects such as internal porosity and looseness.

[0050] After pouring, follow the curing process:

[0051] Settling stage: After pouring, let stand for 24 hours to allow the castable to initially solidify;

[0052] Moisturizing and maintenance: In an environment of 50-60℃, use a spray method to moisturize and maintain for 3 days to promote strength development;

[0053] Drying stage: Heat to 110℃ and dry for 24 hours to remove internal moisture;

[0054] Cooling stage: Naturally cool to room temperature to form a dense and high-strength working layer.

[0055] Example 2:

[0056] Combination Figures 1-2 This embodiment, based on Embodiment 1, further improves upon the following: For a 10-ton capacity cast iron ladle, the method of this invention is used for ladle construction, with the specific steps as follows:

[0057] S1. Pre-treatment of steel cladding: The inner wall of the steel cladding has a diameter of 1.2m and a height of 1.5m. First, rust is removed by sandblasting (sand particle size 0.5-1mm, air pressure 0.6MPa). Then, it is sprayed with 6% sodium hydroxide solution to remove oil (soaked for 30 minutes). After rinsing with clean water, it is dried with hot air at 90℃ for 4 hours. The moisture content of the inner wall is measured to be 0.3%.

[0058] S2. Laying the insulation layer: Select ceramic fiber paper (Al2O3 content 45%) with a width of 610mm and a thickness of 3mm. Cut it according to the curvature of the inner wall of the shell and lay 3 layers along the circumference (overlap width 50mm). Seal the splice with ceramic fiber adhesive (use temperature 1200℃, bonding strength 1.0MPa) to form a continuous insulation layer.

[0059] S3. Install the second insulation layer: Use a nano insulation board with a length of 600mm, a width of 100mm, and a thickness of 10mm (nano silica content of 92%, porosity of 93%, thermal conductivity of 0.028W / (m・K) at 600℃), and lay it along the outside of the insulation layer with staggered joints (longitudinal overlap length of 100mm). Adjacent boards are bonded with high-temperature resistant adhesive (temperature resistance of 1100℃) to ensure no gaps, with a total thickness of 10mm.

[0060] S4. Constructing the first insulation layer: Select high-alumina insulating bricks with a length of 230mm, a width of 113mm, and a thickness of 30mm (Al2O3 content 55%, refractoriness 1600℃, thermal conductivity 0.55W / (m・K) at 800℃), and use staggered joint construction (the brick joints in the same layer are staggered by 100mm). Fill the brick joints with refractory mortar with an Al2O3 content of 45% (joint width 2mm). The construction height is flush with the shell, forming a first insulation layer with a thickness of 30mm.

[0061] S5. Casting working layer: Use high alumina refractory castable with Al2O3 content of 65% (compressive strength at room temperature 35MPa, service temperature 1700℃), cast to a thickness of 150mm, vibrate with an immersion vibrator (3000r / min) until the surface is covered with slurry, let stand for 24 hours, then keep moist at 55℃ for 3 days, heat to 110℃ and dry for 24 hours, and then cool naturally to room temperature.

[0062] Performance Test: After the ladle was filled with molten iron at 1450℃, under an ambient temperature of 25℃, the temperature of the molten iron dropped to 1410℃ (a temperature drop of 40℃) after standing for 2 hours, and the highest temperature on the outer wall of the ladle was 68℃. Under the same conditions, a ladle of the same specifications using traditional casting methods showed a temperature drop of 85℃ and a highest outer wall temperature of 102℃. This embodiment demonstrates a 53% improvement in heat preservation and a 34℃ reduction in outer wall temperature.

[0063] Example 3:

[0064] Combination Figures 1-2 This embodiment, based on Embodiments 1 and 2, further improves upon the following: For a 5-ton capacity cast steel ladle, the method of this invention is used for ladle construction, with the specific steps as follows:

[0065] S1. Pre-treatment of steel cladding: The inner wall of the cladding is 0.8m in diameter and 1.2m in height. After sandblasting to remove rust (air pressure 0.5MPa), it is ultrasonically degreased with 5% sodium hydroxide solution (power 500W, time 20 minutes). After rinsing with clean water, it is dried with hot air at 80℃ for 3 hours, and the moisture content of the inner wall is 0.4%.

[0066] S2. Laying the insulation layer: Use ceramic fiber paper (Al2O3 content 40%) with a width of 610mm and a thickness of 3mm. Cut it according to the shell size and lay it longitudinally. Seal the joints with ceramic fiber adhesive (temperature resistance 1100℃, bonding strength 0.9MPa) to ensure no gaps.

[0067] S3. Install the second insulation layer: Select a nano insulation board with a length of 600mm, a width of 100mm, and a thickness of 10mm (nano silica content of 90%, porosity of 91%, thermal conductivity of 0.03W / (m・K) at 600℃), and fully lay it along the outside of the insulation layer. Use high-temperature resistant adhesive to fix adjacent boards, with a total thickness of 10mm.

[0068] S4. Constructing the first insulation layer: Use clay insulation bricks with a length of 230mm, a width of 113mm, and a thickness of 30mm (30% Al2O3 content, refractoriness of 1500℃, and thermal conductivity of 0.58W / (m・K) at 800℃), and lay them in a staggered manner (the brick joints in the same layer are staggered by 80mm). Fill the brick joints with refractory mortar with an Al2O3 content of 40% (joint width 2.5mm) to form a first insulation layer with a thickness of 30mm.

[0069] S5. Casting working layer: Use high alumina refractory castable with 60% Al2O3 content (compressive strength at room temperature 32MPa, service temperature 1650℃), cast to a thickness of 120mm, vibrate to compact, let stand for 24h, keep moist at 50℃ for 3d, dry at 110℃ for 24h, and cool naturally.

[0070] Performance Test: After the ladle was filled with molten steel at 1550℃, under an ambient temperature of 25℃, the steel temperature dropped to 1515℃ (a temperature drop of 35℃) after standing for 2 hours, with the highest temperature on the outer wall of the ladle reaching 72℃. Under the same conditions, a ladle of the same specifications constructed using traditional methods showed a 75℃ temperature drop in molten steel and a highest outer wall temperature of 105℃. This embodiment demonstrates a 53% improvement in insulation performance and a 33℃ reduction in outer wall temperature.

[0071] Example 4

[0072] Combination Figures 1-2 This embodiment is further improved on the basis of embodiments 1-3 in that:

[0073] A casting ladle includes a steel shell 1 and an inner lining structure disposed inside the shell. The inner lining structure includes, from the inside to the outside, a working layer 5, a first insulation layer 4, a second insulation layer 3 and a heat insulation layer 2. The working layer is a refractory castable layer, which is in direct contact with molten metal and is subjected to high-temperature erosion and scouring.

[0074] The first insulation layer is an insulation brick layer located on the outside of the working layer. The insulation brick has a length of 230mm, a width of 113mm, and a thickness of 30mm. It has high fire resistance and strength and can effectively block heat from being transferred to the outside.

[0075] The second insulation layer is a nano-insulation board layer and is set on the outside of the first insulation layer. The nano-insulation board has a length of 600 mm, a width of 100 mm, and a thickness of 10 mm. The nano-insulation board is composed of nano-sized silica powder, which has extremely high porosity and a pore size smaller than the mean free path of air molecules. It can suppress convective heat transfer and gas conduction heat transfer to the maximum extent, so that it can maintain an extremely low thermal conductivity at high temperatures.

[0076] The insulation layer is a ceramic fiber paper layer that is tightly attached to the inner wall of the steel shell, serving as initial insulation and buffering. The insulation layer is 610mm wide and 3mm thick.

[0077] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A ladling method for improving the heat retention effect of a ladle, characterized by, The method comprises the following steps: S1, pretreating the steel shell: cleaning the inner wall of the steel shell of the pouring ladle to remove surface dirt and ensure that the inner wall is smooth and dry; S2, laying the thermal insulation layer: cutting the ceramic fiber paper to a size suitable for the inner wall of the steel shell and laying it tightly against the inner wall of the steel shell to form a thermal insulation layer; S3, installing the second thermal insulation layer: laying nano thermal insulation boards outside the thermal insulation layer so that the nano thermal insulation boards completely cover the thermal insulation layer; S4, building the first thermal insulation layer: building thermal insulation bricks outside the second thermal insulation layer using a staggered building method, filling the brick joints with refractory mortar during the building process to ensure that the bricks are tightly fitted together, forming the first thermal insulation layer, and the inner side of the first thermal insulation layer is in complete contact with the second thermal insulation layer without any suspended areas; S5, pouring the working layer: pouring refractory castable outside the first thermal insulation layer and using vibration forming to ensure that the refractory castable is dense, and after pouring is completed, the refractory castable is cured according to the curing process.

2. A method of building a ladle according to claim 1, characterized in that, In the S1 step, the cleaning process includes sandblasting, alkali solution degreasing, and water rinsing in sequence to remove rust, oil stains, and impurities on the surface of the inner wall of the steel shell, and hot air drying is used after rinsing to ensure that the water content of the inner wall of the steel shell is less than 0.5%.

3. A method of building a ladle according to claim 1, characterized in that, In the S2 step, the ceramic fiber paper has a size of 610 mm in width and 3 mm in thickness, and during laying, the ceramic fiber paper is seamlessly spliced together, and the joints are sealed with a high-temperature resistant adhesive, which is a ceramic fiber adhesive with a use temperature range of not less than 1000℃ and a bonding strength of not less than 0.8MPa.

4. A method of building a ladle according to claim 3, characterized in that, In the S3 step, the nano thermal insulation board has a size of 600 mm in length, 100 mm in width, and 10 mm in thickness, is composed of nano-sized silicon dioxide powder, and is fixed between adjacent nano thermal insulation boards by a high-temperature resistant adhesive to ensure that there are no gaps between the layers.

5. A method of building a ladle according to claim 4, characterized in that, The porosity of the nano thermal insulation board is not less than 90%, the pore size is less than the average free path of air molecules, and the thermal conductivity in a high temperature environment above 600℃ is not greater than 0.03W / (m・K).

6. A method of building a ladle according to claim 1, wherein In the S4 step, the thermal insulation brick has a size of 230 mm in length, 113 mm in width, and 30 mm in thickness, the refractoriness of the thermal insulation brick is not less than 1500℃, the compressive strength at room temperature is not less than 15MPa, and the thermal conductivity (800℃) is not greater than 0.6W / (m・K).

7. A method of building a ladle according to claim 1, wherein The refractory castable is a high-alumina refractory castable with an Al2O3 content of not less than 60%, a compressive strength at room temperature (after curing) of not less than 30MPa, and a use temperature of not less than 1600℃.

8. A method of building a ladle according to claim 1, wherein In the S5 step, the curing process is as follows: after pouring is completed, the workpiece is left to stand for 24h, then it is kept moist at 50-60℃ for 3d, then it is heated to 110℃ for 24h, and finally it is naturally cooled to room temperature.

9. A ladle prepared by the ladle construction method of claim 1 to 8, characterized in that, The method comprises a steel shell and an inner lining structure arranged inside the shell, and the inner lining structure comprises, from the inside out, a working layer, a first thermal insulation layer, a second thermal insulation layer, and a thermal insulation layer.

10. A ladle according to claim 9, characterised in that The working layer is a refractory castable layer, the first heat-insulating layer is a heat-insulating brick layer and is arranged outside the working layer, the second heat-insulating layer is a nano heat-insulating plate layer and is arranged outside the first heat-insulating layer, and the heat-insulating layer is a ceramic fiber paper layer and is arranged in close contact with the inner wall of the steel shell.

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