Cupola furnaces using hot air technology have become a new direction for cupola furnaces in recent years towards "large-scale, hot air water-cooling without lining, and continuous iron tapping". The erosion of the internal refractory materials of hot air technology cupola furnaces is far more serious than that of cold air furnaces. At the same time, we want to To achieve continuous tapping, that is, to increase the age of the cupola furnace, it is particularly important to select appropriate refractory materials. According to the temperature and usage requirements of different parts of the cupola, selecting refractory materials with excellent performance can effectively reduce corrosion and extend service life, which is of great significance to achieving a long furnace life and stable melting conditions of the cupola.
01Cupola furnace structure
EC&S cupola furnace body structure: The furnace body consists of the furnace shell (divided into two parts: melting zone and preheating zone), furnace hearth, taphole, slag separator, launder, draft ring, etc. The melting zone furnace shell adopts a lining-less design. The furnace shell is made of AIXI The corrosion rate of the material will be very fast, which cannot guarantee the long furnace life design of the cupola. At the same time, the furnace diameter of the melting zone will become larger with the extension of the melting time, causing the melting state to be unstable.
Except for the melting zone furnace shell, the rest of the EC&S cupola furnace body is filled with refractory materials. Table 1 shows the operating temperatures and requirements for refractory materials in the main parts of the EC&S cupola. According to the working temperature and requirements of each part, selecting appropriate refractory materials can effectively increase the service life and reduce costs.
02Air induction ring refractory materials
The draft ring is an annular pipe surrounding the furnace body in the upper part of the cupola. Its function is to lead the cupola furnace gas out and guide it to the combustion chamber. Its structure is shown in Figure 2. The refractory materials in the draft ring should have the function of heat insulation and at the same time protect the furnace body from damage. Spray coatings for hot blast cupolas often use refractory materials with clay clinker or high alumina bauxite clinker as aggregate and water glass as a binder.
GUN CAST 28LI spray paint is used inside the EC&S cupola air induction ring. This material has the characteristics of small rebound rate and excellent gunning performance. Its composition is Al2O3: 48.0%; SiO2: 41.4%; CaO: 6.0%; Fe2O3: 1.8%; Na2O+K2O: 1.8%. Among them, Na2O+K2O exists in the form of R2O, nSiO2·mH2O (R2O represents an alkali metal), commonly known as water glass. When water glass dissolves in water, it will hydrolyze to form a sol. The sol has good cementing properties. The spray paint is constructed using mechanical spraying. Adding an appropriate amount of water glass will help improve the construction performance of the material.
03 Preheat zone refractory materials
The preheating zone is located above the melting zone and below the draft ring. The operating temperature range is wide, between 650 and 1100°C. The preheating belt has to withstand the mechanical impact caused by the iron material falling from the furnace top and the wear caused by the falling charge during the melting process. At the same time, due to the wide operating temperature range of the preheating belt, it also needs to be able to withstand hot and cold shocks.
The preheating zone uses low-cement mullite castable, whose main component is SiO2: 27.2%. Mullite has good high-temperature mechanical properties. Refractory materials based on mullite have high density and purity, as well as excellent high-temperature strength and thermal shock resistance, and low thermal expansion rate. Natural mullite is relatively rare, and the mullite currently used in industry is basically artificial mullite, which is produced by sintering or electrofusion.
The cement content of low-cement mullite matrix castable is 3% to 8%, and the CaO content is only 2%. It has a higher service temperature than ordinary castables of the same material, and the maximum service temperature can reach 1700°C.
04Hearth refractory materials
The furnace area is located below the tuyere, and the working temperature is between 1350 and 1650°C. The inside of the furnace is eroded and eroded by molten iron and slag, and the working environment is relatively harsh. The hearth is composed of a variety of refractory materials, and its structure is shown in Figure 3. As can be seen from Figure 3, the furnace bottom material is two layers of ramming material, and the furnace wall is ceramic fiber paper, high alumina bricks, castables and spray coatings from the outside to the inside.
The lower layer of the furnace bottom uses refractory ramming material. Its composition is Al2O3: 59.8%; SiO2: 37.8%. It is an alumina-based refractory material. It is used in the bottom layer of the furnace bottom to effectively resist the molten iron at the furnace bottom. penetration. The upper layer of the furnace bottom uses refractory ramming material. Its composition is Al2O3: 52%; SiO2: 10%; (SiC+C): 32%. It is a mixture of Al2O3 and (SiC+C) with a resin binder added. Ramming refractory material has high strength, stable chemical properties, and larger particle size than the underlying material. At the same time, due to the addition of SiC+C, it can effectively resist the erosion and erosion of molten iron.
The outermost refractory material of the furnace wall is a layer of 1.6mm thick Al2O3/SiO2-based ceramic fiber paper, which has the functions of thermal insulation and sealing. The inside of the ceramic fiber paper is a layer of high-alumina bricks, and the gaps between the bricks are filled with air-hardening refractory mortar. The inside of the high-alumina brick is mullite castable with ultra-low moisture and cement. After construction is completed, the moisture inside the brick can be quickly discharged in the form of gas. It has high strength, low porosity and good volume stability. The innermost side of the furnace wall is a layer of KARBSHIELDGUN spray paint with a SiC+C content of up to 45% and added antioxidants. It has good construction performance and can effectively resist the erosion of molten iron and slag. After the furnace is built, it can be continuously melted for 35 days.
05 Taphole refractory materials
The taphole is located at the bottom of the furnace and connects the furnace and the slag separator. Its location is shown in Figure 3. The cross-sectional area of the taphole is small and the flow rate of the molten iron is fast. Therefore, the taphole is severely corroded by the molten iron, and its service life often determines the age of the furnace. The refractory material of the tap hole is CW368 plastic material, which is a corundum-based material containing 25% (SiC+C). It is especially suitable for parts with harsh corrosion resistance conditions. It has good construction performance, dense structure and low porosity.
06Slag separator refractory materials
The slag separator is located outside the taphole. Its function is to separate the molten iron and the furnace flood by utilizing the different densities. Its structure is shown in Figure 4. The molten iron is skimmed off by the slag baffle and then flows out of the slag separator, while the slag remains on the left side of the slag baffle and is discharged from the slag discharge port, thus achieving iron and slag separation.
The slag separator is made of corundum-based tide-beaten refractory material containing 28% (SiC+C). The material has a dense structure, low porosity, and excellent resistance to slag erosion and oxidation.
07 Launder refractory materials
The launder is the part that connects the slag separator and the insulation electric furnace. The refractory material uses high aluminum-based castables containing MgO4.5%. This material has strong resistance to molten iron erosion, high hot and cold strength and resistance to slag erosion. Al2O3-MgO-based refractory materials will produce spinel at 1400°C, causing volume expansion and densification of the structure, which can effectively resist the penetration of molten iron and slag.
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