Fused Zirconia Corundum Bricks

Fused-cast zirconium corundum bricks are corundum-based refractory products made by the fusion casting method with corundum as the main crystal phase. They include corundum products composed of α-Al2O3, β-Al2O3 and α, β-Al2O3 three different crystal phases. Among them, β-Al2O3 fused-cast bricks, namely Na2O·(11~12)Al2O3, contain about 5% Na2O. α, β-Al2O3 fused-cast bricks are composed of α-Al2O3 and β-Al2O3 two crystal phases.

Performance Fused-cast zirconium corundum bricks have good high-temperature volume stability and corrosion resistance. α-Al2O3 fused-cast bricks have dense crystal structure and have certain resistance to glass melt corrosion and erosion resistance. β-Al2O3 fused-cast bricks contain almost no glass phase, basically no shrinkage cavities, good thermal shock resistance, and good high-temperature alkali vapor stability.

 

α, β-Al2O3 fused-cast bricks have the characteristics of α-Al2O3 and β-Al2O3 fused-cast bricks. Its main crystal phase is directly combined, and only a small amount of glass phase is contained in the composition. It has a dense crystal structure, low porosity, good high-temperature wear resistance, high mechanical strength, and good high-temperature alkali vapor stability.

Raw materials and batch materials preparation The product made by melting and pouring with a single industrial alumina powder as raw material is α-Al2O3 fused-cast corundum brick. Using industrial alumina powder as raw material is beneficial to reducing the cracking rate of fused-cast zirconium corundum bricks.

When manufacturing β-Al2O3 and α, β-Al2O3 fused-cast bricks, a certain amount of Na2O should be added. Soda ash, caustic soda or sodium peroxide can be used. Industrial soda ash with higher purity is mostly used in industry, and its Na2CO3 content is 95%~96%. The chemical composition of the raw materials used should be stable, and they should be accurately weighed strictly according to the proportion, and the batch with uniform composition should be prepared after sufficient mixing. Some mix the ingredients thoroughly and then granulate them, then melt them after roasting.

Melting Use a single-phase or three-phase electric arc furnace to melt the batch material. The furnace body is a water-cooled metal shell, and the molten material self-solidifies the furnace lining to ensure that the melt is not contaminated by the furnace lining material. When the batch material is melted in an electric arc furnace, the contact between the graphite electrode and the melt will increase the carbon content in the melt, reduce the porosity of the molten brick, and then increase the glass phase seepage temperature during use, improve its anti-glass erosion performance and reduce the pollution of the glass liquid, and extend the service life of the kiln.

The melt temperature should be moderate. If the temperature is low, a highly uniform melt cannot be obtained, and it is easy to form a porous body in the casting, so that the molten cast product will produce pores and cracks, and the shrinkage will also increase accordingly, so that the product will form a larger shrinkage cavity. The key to the melting process is to maintain a stable melting temperature system to obtain a melt with uniform chemical composition, low carbon content, a certain temperature and good casting performance.

Casting Pour the melt into the mold to make a fused-cast brick with a dense structure and good performance. The melt temperature, casting performance, pouring speed and casting method have a great influence on the structure and performance of the fused-cast brick, especially the melt temperature. When casting with a properly overheated melt, the shrinkage cavities of the fused-cast brick are concentrated, the thickness of the dense area increases, and the density of the entire product also increases. However, when the degree of overheating is too high, although the melt density increases, it is easy to cause cracks and large shrinkage cavities in the fused-cast zirconium corundum brick.

Using processes such as inclined casting, large riser casting or multiple supplementary casting, the melt is directly injected into the pre-made and installed mold at a certain pouring speed.

Different mold materials have different heat storage capacities and different effects on the crystallization process of castings. The mold material has a certain influence on the density and performance of the fused-cast brick. In the production of fused-cast corundum bricks, sand molds made of quartz sand, graphite molds or metal molds made of heat-resistant cast iron are usually used.

Heat treatment During the cooling and crystallization process of castings, excessive thermal stress caused by the temperature difference between the inside and outside is easy to cause cracks in the product. The greater the temperature gradient, the greater the thermal stress, and the greater the possibility of product cracking. If the temperature gradient exceeds the limit value, cracks will first appear inside and then expand to the outside. At the same time, when the melt is cast, the edge of the melt in contact with the mold cools the fastest, forming a dense edge zone with fine crystals and high density. Coarse crystals and shrinkage zones appear in the central area, with coarse crystals and loose texture. The volume effect caused by uneven structure also has a certain influence on the cracking of the product. Therefore, during the hardening stage of the casting, the temperature gradient inside and outside should be reduced as much as possible, so that the surface temperature drop rate is as close as possible to the temperature drop rate of the center. Use an incubator or provide heat to the casting to maintain its surface temperature for a certain period of time and heat the casting.

Usually, an insulation box filled with diatomite and other insulation materials is used for annealing with molds, or an adjustable temperature resistance furnace or tunnel kiln is used for annealing with molds or demolding according to a certain temperature system. The initial temperature of annealing and the insulation condition have a significant impact on the annealing effect.

Mechanical processing The annealed fused-cast zirconium corundum bricks are then mechanically processed to make products that meet the requirements. Mechanical processing is also a means to improve the quality of fused-cast zirconium corundum bricks and extend their service life. After the castings are mechanically processed such as cutting, grinding, drilling and assembly, they are finished fused-cast zirconium corundum bricks.

Uses β-Al2O3 fused-cast bricks are suitable for the upper structure of the working pool of the glass melting furnace and the burner at the rear of the melting zone and the breast wall, small furnace platform and other parts nearby.

The composition of β-Al2O3 fused-cast bricks contains only a small amount of glass phase, which will not seep out and pollute the glass melt when used. It is an ideal furnace building material for the pool wall, kiln bottom and float glass melting furnace launder of the cooling part of the glass melting furnace.

The use of fused-cast zirconium corundum bricks together with fused-cast zirconium corundum materials can extend the service life of the flat glass melting furnace to 5~7 years.

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