Application of Fused Corundum Brick in Float Glass Melting Furnace

Fused corundum bricks are melted alumina in an electric arc furnace and cast into a specified model of a specific shape, annealed and heat-preserved, and then processed to obtain the desired product. The general production process is to use high-purity calcined alumina (above 95%) and a small amount of additives, put the ingredients into the electric arc furnace, and cast them into prefabricated molds after being melted at a high temperature above 2300 ° C, and then keep them warm After annealing, it is taken out, and the taken-out blank becomes a finished product that meets the requirements after precise cold working, pre-assembly and inspection.

Fused corundum bricks are divided into three types according to the different crystal forms and quantities of alumina: the first is α-Al2O3 as the main crystal phase, called α-corundum bricks; the second is α-Al2 The O 3 and β-Al2O3 crystal phases are mainly in the same content, which is called αβ corundum bricks; the third type is mainly β-Al2O3 crystal phases, called β corundum bricks. Fused corundum bricks commonly used in float glass melting furnaces are the second and third types, namely fused αβ corundum bricks and β corundum bricks. This article will focus on the physical and chemical properties of fused αβ corundum bricks and β corundum bricks and their application in float glass melting furnaces.

1. Performance analysis of fused corundum bricks

1. 1 Fused αβ corundum brick

 

Fused αβ corundum bricks are composed of about 50% α-Al2 O 3 and β-Al 2 O 3 , and the two crystals are interlaced to form a very dense structure, which has excellent strong alkali corrosion resistance. The corrosion resistance at high temperature (above 1350°C) is slightly worse than that of fused AZS bricks, but at temperatures below 1350°C, its corrosion resistance to molten glass is equivalent to that of fused AZS bricks. Because it does not contain Fe2 O 3 , TiO 2 and other impurities, the matrix glass phase is very small, and foreign matter such as bubbles is less likely to occur when it contacts with molten glass, so that the matrix glass will not be polluted.

Fused αβ corundum bricks are dense in crystallization and have excellent corrosion resistance to molten glass below 1350°C, so they are widely used in the working pool and beyond of glass melting furnaces, usually in launders, lip bricks, gate bricks, etc. . Fused corundum bricks in the world are best made by Japan's Toshiba.

1.2 Fused β corundum brick

 

Fused β-corundum bricks are composed of nearly 100% β-Al2 O 3 , and have a large plate-like β-Al 2 O 3 crystalline structure. Larger and less powerful. But on the other hand, it has good spalling resistance, especially it shows extremely high corrosion resistance to strong alkali vapor, so it is used in the upper structure of glass melting furnace. However, when it is heated in an atmosphere with low alkali content, it will react with SiO 2 , and β-Al 2 O 3 will easily decompose and cause volume shrinkage to cause cracks and cracks, so it is used in places far away from the scattering of glass raw materials.

1.3 Physical and chemical properties of fused αβ and β corundum bricks

 

The chemical composition of fused α-β and β corundum bricks is mainly Al 2 O 3 , the difference is mainly in the crystal phase composition, and the difference in microstructure leads to the difference in physical and chemical properties such as bulk density, thermal expansion coefficient, and compressive strength.

2. Application of fused corundum bricks in glass melting furnaces

Both the bottom and the wall of the pool are in direct contact with the glass liquid. For all parts directly contacting the glass liquid, the most important property of the refractory material is the corrosion resistance, that is, no chemical reaction occurs between the refractory material and the glass liquid.

In recent years, when assessing the quality indicators of fused refractory materials in direct contact with molten glass, in addition to chemical composition, physical and chemical indicators, and mineral composition, the following three indicators must also be assessed: glass erosion resistance index, precipitated bubble index and precipitated crystallization index.

With the higher requirements for glass quality and the greater the production capacity of the furnace, the use of fused electric bricks will be wider. Fused bricks commonly used in glass melting furnaces are AZS series (Al 2 O 3 -ZrO 2 -SiO 2 ) fused bricks. When the temperature of AZS brick is above 1350℃, its corrosion resistance is 2~5 times that of α β -Al 2 O 3 brick. Fused αβ corundum bricks are composed of closely staggered α-alumina (53%) and β-alumina (45%) fine particles, containing a small amount of glass phase (about 2%), filling the pores between crystals, with high purity, and can be used as cooling part pool wall bricks and cooling part bottom pavement Bricks and seam bricks etc.

The mineral composition of fused αβ corundum bricks only contains a small amount of glass phase, which will not seep out and pollute the glass liquid during use, and has good corrosion resistance and excellent high-temperature wear resistance below 1350 ° C. It is the cooling part of the glass melting furnace. It is an ideal refractory material for tank walls, tank bottoms and launders of float glass melting furnaces. In the float glass melting furnace engineering project, the fused αβ corundum brick is used as the pool wall brick of the cooling part of the glass melting furnace. In addition, fused αβ corundum bricks are also used for pavement bricks and cover joint bricks in the cooling section.

Fused β corundum brick is a white product composed of β -Al2 O 3 coarse crystals, containing 92%~95% Al 2 O 3 , only less than 1% glass phase, and its structural strength is relatively weak due to the loose crystal lattice. Low, the apparent porosity is less than 15%. Since Al2O3 itself is saturated with sodium above 2000°C, it is very stable against alkali vapor at high temperatures, and its thermal stability is also excellent. However, when in contact with SiO 2 , the Na 2 O contained in β-Al 2 O 3 decomposes and reacts with SiO2 , and β-Al 2 O 3 is easily transformed into α-Al 2 O 3 , resulting in a large volume shrinkage , causing cracks and damage. Therefore, it is only suitable for superstructures away from SiO2 flying dust, such as the superstructure of the working pool of a glass melting furnace, the spout at the rear of the melting zone and its nearby parapet, small furnace leveling and other parts.

Because it does not react with volatile alkali metal oxides, there will be no molten material oozing from the brick surface to contaminate the glass. In the float glass melting furnace, due to the sudden narrowing of the inlet of the flow channel of the cooling part, it is easy to cause the condensation of alkaline vapor here, so the flow channel here is made of fused β bricks that are resistant to corrosion by alkaline steam.

3. Conclusion

 

Based on the excellent properties of fused corundum bricks in terms of glass erosion resistance, foam resistance, and stone resistance, especially its unique crystal structure, it hardly pollutes molten glass. There are important applications in clarification belt, cooling section, runner, small furnace and other parts.