Special process for refractory production - electrofusion

In refractory technology, material melting occupies a special place. Because electrofusion materials have special properties - high density and corrosion resistance. There are two ways to use molten material for fused chrome sand: casting the melt in the model to obtain the product and crushing the molten material and producing fused large crystalline products. Granular molten material is introduced into various refractory powders as refractory framework and used in powder form. Although smelting is energy-intensive, there are many occasions where the use of molten material is economically advantageous. Because the first is to improve the properties of the refractory material and increase its service life, and secondly, the melting of the material can be carried out very quickly, and the ceramic composite semi-finished product must have a relatively long interval. Even after prolonged calcination, the crystals of the synthetic phase tend to have nucleation properties. The products produced by melt casting are mainly closed pores, with a porosity of 4%-6%, and can produce products with large sizes up to 1000mm. The impurities are partially sublimated during smelting. Other impurities are transferred to the periphery, and it should be further excluded. Therefore, when smelting, the material itself undergoes some random enrichment. At the same time, molten refractories have their own unique shortcomings. However, its indisputable superiority has made the production of fused refractories continue to increase.

 The melt with a relatively low viscosity value can be directly poured into the model after smelting and releasing. Silicate melts with high silica content and some very viscous oxide melts are not allowed to be poured in the mold (immediate solidification). Such melts are cooled directly in the furnace (melting of ingots). In some cases a method of forming an article from a high viscosity melt is obtained. At the melting temperature, the viscosity values of so-called crystalline substances and vitreous substances are significantly different.

Fused chrome sand

 Production of fused crystals

 Most of the refractory materials are smelted in electric furnaces with arc system or resistance system. The arc column (voltage arc) is a plasma composed of neutral gas particles, cations and electrons. So the melting arc is called plasma arc. The plasma temperature of the arc reaches 5000 - 6000K. The key equipment for the production of cast refractories is the electric arc furnace. Whether its structure is reasonable and the level of automation directly affect the quality of cast refractories and the cost of products. Most of the melting equipment used in the melting and casting refractory industry in my country follows the steelmaking electric arc furnace in the metallurgical industry. In recent years, China National Building Materials Research Institute has developed a special electric arc furnace for external cooling cast refractory materials.

 The melt is poured into the mold, crystallizing from the mold wall, and then a skin is formed on it. The inside of the ingot is still liquid, it should be confinement in an airtight container and hardened with the substance. Before the skin is formed, the liquid state turns into a solid and precipitates into crystallization under atmospheric pressure. At the same time, the position of the evolved gas leaves pores and forms shrinkage cavities, and different crystallizations cause very unbalanced densities in the ingot volume. If crystallization can be achieved under negative pressure instead of pressure, and after melt vacuum treatment, the casting may eliminate shrinkage cavities.

 In some cases, opening the outer skin and filling the model with the melt can actually reduce the shrinkage cavity volume. It is also possible to heat the top of the ingot and try to keep the top of the ingot in a liquid state until the entire casting is almost uncrystallized, fill it with vibration of the model, slow down the heat withdrawal rate, ie artificially slow the crystal growth rate, and so on. There are a number of factors that influence crystallization, indicating the multivariate nature of running the crystallization process, showing that it is possible to alter the crystallization run by forcing methods.

 Reasonable heat treatment of fused refractory structure is a complex thermal and thermomechanical problem.