Fused α-β corundum bricks are made of high-purity sintered alumina (above) and a small amount of additives. After mixing, they are put into a three-phase electric arc furnace, smelted at a high temperature of more than 2300℃, and then cast into a special mold. After insulation annealing, the taken out blank bricks are precisely cold processed, pre-assembled, and inspected to become fused bricks that meet customer needs. The following introduces how to solve the problem of insufficient bulk density of non-shrinkage fused bricks.
Non-shrinkage products are one of the varieties of fused α-β corundum bricks. They are large in shape and are mostly used in key parts such as pool walls. Bulk density is an important quality indicator. Insufficient bulk density means that the product is unqualified. In the early stage of production, the scrap rate caused by insufficient bulk density was almost less than 50% of similar products. In order to solve this problem, we looked at the overall situation and started from the details. We conducted a large number of experiments in mold design, electric furnace melting, insulation, chemical composition, etc., and finally solved the problem.
1. Improvement of casting design method
Through experiments, it was found that there were imperfections in the casting design method. It is mainly manifested in that the electric fused corundum brick did not form a reasonable temperature gradient when cooling, resulting in the product's internal crystallization being not dense. Therefore, a new casting design method was adopted, with the focus on forming a reasonable temperature gradient so that the product can be cooled layer by layer in sequence during rapid cooling.
2. Improvement of electric furnace melting
Melting is the key to electric fused refractory materials. Improving the melting quality plays a very important role in improving the intrinsic quality of the product. By referring to the melting of AZS brick products, the melting method was improved, so that the melting quality of the electric furnace was greatly improved compared with the past, and the intrinsic quality of the product was significantly improved. According to statistics, the bulk density of the product increased by more than 10% after the improvement of electric furnace melting.
3. Selection of insulation materials
Due to the natural annealing method in the insulation box, the insulation material plays an important role in the cooling speed of the product. The purity of the insulation material used at the beginning was not enough, and the thermal conductivity was too high. The temperature difference caused during the insulation process was large, which was fatal to the cooling of the product. It not only caused cracks in the product, but also loose internal tissue, which had an adverse effect on the bulk density. To solve this problem, a new type of insulation material with excellent performance imported from Japan was selected, which not only greatly reduced the cracks of the product, but also greatly improved the density of the internal organization.
4. Control of chemical composition
Since the chemical composition of fused α-β corundum bricks is relatively simple, namely alumina and sodium oxide, the content of sodium oxide has a significant impact on the ratio of α-Al2O3 and β-Al2O3 in the product, and the specific gravity of α-Al2O3 and β-Al2O3 is different. Therefore, controlling the content of sodium oxide can increase the ratio of α-Al2O3 in the product and increase the bulk density of the product.
Through the above four improvements, the problem of insufficient bulk density was finally solved, and the scrap rate caused by insufficient bulk density was reduced to below 5%.
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