Fused-cast refractory bricks are the most common refractory bricks purchased in glass kilns. Its main technical index assessment items include chemical composition, bulk density, glass phase infiltration temperature and quantity, and foaming rate. The inspection items of other general refractory materials, such as porosity, refractory degree and load softening point, etc., are of little significance to the actual use conditions. Due to the temperature gradient during the condensation process of the ingot, chemical phase composition segregation will be formed along the cross section. This is a rule for melting and casting AZS products. The higher the ZrO2 content and the larger the size of the ingot, the greater the degree of segregation. Generally, the ingot is divided into three parts:
① The surface rapid cooling zone has a small composition deviation from the original design, and the crystals are small and uniform.
② Zr02 is enriched in the middle dense area, and primary Zr02 crystals appear.
③ There is more liquid phase in the internal shrinkage cavity area, which can precipitate larger sizes and stacked directions (C+Z).
According to their chemical composition, fused zirconium products are divided into: fused AZS, AZS resintered fused bricks, fused zirconium mullite bricks, etc.
(2)AZS resintered fused bricks
AZS resintered fused bricks are mainly used for building thermal equipment such as the bottom and walls of glass tank kilns and checker bricks in regenerators.
(3)Zirconium mullite fused cast bricks
The main mineral phases of this brick are mullite, baddeleyite, corundum and glass phases. Its chemical composition is within the triangular area where stable compounds are generated in the A1203-Si02-ZrO2 ternary phase diagram (approximately A1203: 63%, Si02: 21%, ZrO2: 21%). The melting point of mullite solid solution in this area is 1830 ~1870℃.
The main raw materials for preparing zircon-mullite fused-cast bricks are: industrial alumina, natural zircon stone and a small amount of Na20 introduced (in the form of soda ash); some use raw alumina, soft clay and zircon stone to press into blanks. After firing, it is crushed to a suitable particle size, and the mineralizing agent MgO is added during casting. It is appropriate to select an AI203/Si02 ratio of 2.2-3.2 in the ingredients.
The characteristics of this kind of brick are dense crystal structure, high softening temperature under load, good thermal shock resistance, high mechanical strength at normal and high temperatures, good wear resistance, good thermal conductivity, and excellent ability to resist slag erosion. It is used for glass melt cooling part pool wall, etc., and the effect is very good.
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