The so-called "fused" refers to a manufacturing process of refractory bricks, which heats and melts the batch material in an electric arc furnace, pours it into a mold in liquid state, and solidifies it to achieve ceramic bonding. Compared with sintered bricks, it has the characteristics of dense structure, very low porosity, high volume density, high mechanical strength and high-temperature structural strength, and strong resistance to glass liquid erosion.
The main varieties on the market at present are: fused mullite bricks, fused zirconium corundum bricks, fused chromium zirconium corundum bricks, fused quartz bricks, fused corundum bricks, etc.
Which of these fused refractory materials is more suitable for glass melting furnaces?
1. Fused mullite bricks
Fused mullite bricks use high-alumina bauxite as raw material, and mix different bauxites into the composition of mullite (3Al2O3·2SiO2, with mass fractions of Al2O372%, SiO228%). It melts at about 2300℃, is poured into a sand mold at 1850℃, 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 of zirconium dioxide (7%8.5%) can make the mullite crystals smaller and the brick structure denser, and the amount of mullite increases to 60%70%, which relatively reduces the content of glass phase and reduces the cracks of the product. Fused mullite bricks are gradually replaced by fused zircon bricks.
2. Fused zirconium corundum bricks
Fused zirconium corundum bricks are divided into three grades according to the content of ZrO2, and the corresponding grades are: AZS-33 (containing ZrO233%), AZS-36 (containing ZrO236%), and AZS-41 (containing ZrO241%).
Fused zirconium corundum bricks are made of zircon and industrial alumina as the main raw materials, and a small amount of zircon-rich sand (to increase the content of ZrO2), soda ash and borax are added. According to the different atmospheres during melting, there are two methods: reduction melting method and oxidation melting method. At present, the oxidation method is mainly used. The oxidation melting method can eliminate the pollution caused by graphite electrodes in the molten liquid, and the carbon content is low (0.005%0.02%), which can reduce the bubble content in the glass and improve the quality of the glass liquid.
There are several aspects to pay attention to when using fused zirconium corundum bricks.
① Irregular changes in thermal expansion
The characteristics of fused zirconium corundum bricks are stable and dense organization, and strong resistance to glass liquid corrosion. The thermal expansion curve of bricks containing 31%33% ZrO2 is shown in Figure 1. It can be seen from the figure that there is abnormal expansion between 9001200℃.
②Electrical insulation
Fused zirconium corundum bricks have good electrical insulation and decrease with increasing temperature. Its electrical insulation is shown in Figure 2. It can be seen that fused zirconium corundum bricks can be used as electrode bricks in the production of soda-lime glass melting furnaces.
③Thermal conductivity
The thermal conductivity of fused zirconium corundum bricks is more than twice that of clay bricks. Therefore, when used as pool wall bricks, the cooling air volume required near the liquid surface should be 1 times larger than when clay bricks are used as pool walls.
3. Fused corundum bricks
Fused corundum bricks are made of high-purity alumina as raw materials, and a small amount of soda ash is introduced, and melted at 20002200℃. The production process is similar to that of high-alumina products. There are fused α-corundum bricks, fused α, β-corundum bricks, fused β-corundum bricks, etc. Fused α-corundum bricks are mainly suitable for melting borosilicate glass, opalescent glass and melts containing sulfates. The composition of fused α, β-corundum bricks contains only a small amount of glass phase, which will not seep out during use, and has little pollution to the glass liquid. Direct contact with the glass liquid will not color the glass liquid, and it has good corrosion resistance. It is an ideal material for the cooling pool wall, kiln bottom and float glass melting furnace launder of the glass melting furnace. Fused corundum bricks are suitable for the upper structure of the working pool of the melting furnace and the burner at the rear of the melting zone and the breast wall and small furnace flat 瑄 nearby.
4. Fused chromium-zirconium corundum bricks
10%30% Cr2O3 is introduced into AZS-33 bricks, and fused chromium-zirconium corundum bricks (abbreviated as AZCS bricks, French brand ER2161) are produced by non-shrinkage cavity casting method. The surface and interior of the brick are dark green. The brick contains 4.5% shrinkage pores 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 bricks is the same as that of quartz glass. High-purity quartz sand (SiO2 content above 99.5%) is used as raw material, a small amount of Na20 is added as a mineralizer, and melted in a graphite resistance furnace (17501800℃). After melting, the whole 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. It has strong resistance to boron glass liquid erosion, but is not resistant to the erosion of sodium-lime-silicon glass liquid.
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