Refractory Bricks

What are the fused refractory bricks used in glass melting furnaces? Which one is suitable?

Apr 19,2024

Fused refractory bricks for glass melting furnace

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 bricks, fused zirconium corundum bricks, fused chromium zirconium corundum bricks, fused quartz bricks, fused corundum bricks, etc.

01Fused Mullite Brick

Mullite bricks are aluminum-silicon system refractory products with mullite as the main crystal phase. The refractory temperature is around 1850℃, the load softening temperature is high, the high temperature creep rate is low, and the thermal shock resistance is good.

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.

02Fused zirconium corundum brick

Fused zirconium corundum bricks belong to the Al2O3-ZrO2-SiO2 system (AZS bricks for short). 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).

Fused zirconium corundum bricks use zircon stone and industrial alumina as the main raw materials, and then add a small amount of zircon-rich sand (in order to increase the content of ZrO2), soda ash and borax.

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.

The following aspects should be paid attention to when using fused zirconium corundum bricks.

①Irregular changes in thermal expansion

The characteristics of fused zirconium corundum bricks are stable and dense structure and strong resistance to glass liquid erosion.

②Electrical insulation

The electrical insulation of fused zirconium corundum bricks is good and decreases with the increase of temperature. It can be seen that fused zirconium corundum bricks can be used as electrode bricks in the production of soda-lime glass furnaces.

③Thermal conductivity

The thermal conductivity of fused zirconium corundum bricks is twice that of clay bricks. Therefore, when making pool wall bricks, the cooling air volume required near the liquid surface should be twice as large as when clay bricks are used as pool walls.

03Fused 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 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.

04Fused 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 bricks (abbreviated as AZCS bricks, French brand name is ER2161). 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.

05Fused silica brick

The production process of fused silica bricks is the same as that of quartz glass. Use high-purity silica 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.

06Zircon 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 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 are refractory products fired with zircon as the main raw material. Zircon is the only compound in the ZrO2-SiO2 system, and its chemical formula is ZrSiO4. The theoretical chemical composition of zircon is: ZrO2 67.2%, SiO2 32.8%. Zircon bricks have excellent properties such as high temperature resistance, good thermal shock resistance and resistance to glass liquid erosion.

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