Electric fused refractory materials are made by melting a precisely prepared mixture in an electric arc furnace and then pouring it into a sand mold. The ingot is then heat treated and then processed mechanically. The smelting process can obtain complete coarse crystals and dense structure. Compared with sintered refractory materials, it has the characteristics of dense structure, low porosity, high volume density, high mechanical strength and high temperature structural strength, and strong resistance to glass liquid erosion. The main varieties currently produced include: fused mullite refractory bricks, fused zirconium corundum bricks, fused chromium zirconium corundum bricks, fused quartz bricks, fused corundum bricks, etc.
1. Fused mullite bricks
Fused mullite bricks use high-alumina bauxite as raw material, and different bauxites are formulated into the composition of mullite (3Al2O3·2SiO2, the mass fractions are: Al2O3 72%, SiO2 28%). It is melted at about 2300°C, poured into a sand mold at 1850°C, and then annealed to eliminate stress. The main crystal phases are mullite and corundum, and the glass phase is filled between the crystal phases. Its resistance to glass liquid erosion is stronger than that of sintered refractory materials, but not as good as other fused refractory materials. Adding a small amount (7%~8.5%) of zirconium dioxide can make the mullite crystals smaller and the brick structure denser. The amount of mullite increases to 60%~70%, which relatively reduces the content of the glass phase and reduces the Cracks in the product. Fused mullite bricks have been basically replaced by fused zirconium bricks.
2. Fused zirconium corundum brick
Fused zirconium corundum refractory bricks are referred to as AZS bricks. According to the content of ZrO2, it is divided into three levels. The corresponding grades are: AZS-33 (containing 33% ZrO2), AZS~36 (containing 36% ZrO2), and AZS-41 (containing 41% ZrO2).
According to the different atmospheres during melting, there are two types: reduction melting method and oxidation melting method. At present, the oxidation method is mainly used. The oxidative melting method can eliminate the pollution caused by graphite electrodes in the molten liquid. It has low carbon content (0.005%~0.02%), can reduce the bubble content in the glass, and improve the quality of the glass liquid.
3. Fused corundum brick
Fused corundum bricks are made of high-purity alumina as raw material, introduced with a small amount of soda ash, and melted at 2000~2200°C. The production process is similar to that of high-aluminum products. There are fused α-corundum bricks, fused α, β-corundum refractory bricks, fused β-corundum bricks, etc. Fused α-corundum bricks are mainly suitable for melting borosilicate glass, opal glass and sulfate-containing melts. The composition of fused α, β-corundum bricks only contains a small amount of glass phase, which will not leak out when used, and will pollute the glass liquid less. Direct contact with the glass liquid will not color the glass liquid, and has good corrosion resistance. It is the ideal choice for glass melting. Ideal material for the walls of the kiln cooling section, the kiln bottom, and launders of float glass melting furnaces. Fused corundum bricks are suitable for the upper structure of the furnace working pool and the combustion port at the rear of the melting zone and its nearby breast walls, small furnace flats and other parts.
4. Fused chromium zirconium corundum brick
Introduce 10% to 30% Cr2O3 into AZS-33 bricks and use the non-shrinkage cavity casting method to produce fused chromium zirconium corundum refractory bricks. The skin and interior of the brick are dark green. The brick contains 4.5% shrinkage cavities and no connected pores. Due to the formation of aluminum chromium spinel solid solution, the viscosity of the glass phase is increased, and the resistance to glass liquid erosion is greatly improved. It is 3.4 times that of fused AZS-33 bricks and 2.6 times that of fused AZS-41 bricks.
5. Fused quartz bricks
The production process of fused quartz refractory bricks is the same as that of quartz glass. Use high-purity quartz sand (SiO2 content above 99.5%) as raw material, add a small amount of Na20 as mineralizing agent, and melt it in a graphite resistance furnace (1750~1800℃). After melting, the entire molten material is quickly taken out, rolled into bricks, and then mechanically processed after cooling in the air. The thermal expansion coefficient is extremely small and the thermal shock resistance is good. Boron glass liquid resistance is highly corrosive, but it is not resistant to soda-lime-silica glass liquid.
6. Zircon bricks
The main component of zircon stone products is ZrO2·SiO2. Zircon decomposes into ZrO2 and SiO2 when heated at 1680°C. Zircon product liquid glass has good corrosion resistance, and aluminum zirconium silicon series (AZS) fused cast refractory bricks and fired bricks have good resistance to glass liquid erosion and can be used for the tank wall and upper structure of glass melting furnaces. Zircon bricks have excellent properties such as high temperature resistance, good thermal shock resistance and resistance to glass liquid erosion.
