What is fused cast refractory material?

What is fused cast refractory material?

Electric fused refractory materials are made by melting a precisely prepared mixture in an electric arc furnace and then casting it in a sand mold. The ingot is then heat treated and then machined. The smelting process can obtain complete coarse crystals and dense structure. Compared with sintered refractory materials, it has the characteristics of dense structure, low porosity, high volume density, high mechanical strength and high temperature structural strength, and strong resistance to glass liquid erosion. Important indicators for evaluating the performance of electrofused refractory materials include: chemical and crystal phase composition, volume density, glass phase exudation temperature, glass phase exudation amount and foaming rate. The meaning of foaming is that when 02 diffuses into the brick, it reacts with the contained carbon or carbide, sulfide and nitride to release SO2, N2 and other gases. These gases squeeze the molten phase out of the brick and form visible bubbles on the surface. . The main varieties currently produced include: fused mullite bricks, fused zirconium corundum bricks, fused chromium zirconium corundum bricks, fused quartz bricks, fused corundum bricks, etc.

Fused refractory is a type of artificial rock. Its manufacturing methods include reduction method and oxidation method.

The reduction method is to put the selected and pretreated raw materials into an electric furnace, melt them with graphite electrodes, and then cast them into a mold after a certain period of time. The melting temperature is about 2000°C. In this method, since the graphite electrode is directly inserted into the molten liquid, the solution will be carburized. Moreover, the working space is in a reducing atmosphere, which reduces the iron and titanium oxide impurities in the batch materials into low-priced oxides, lowering the precipitation temperature of the glass phase.

The oxidation melting method is to melt the batch materials of a predetermined composition in an electric arc furnace, using a long arc. The electrodes are not in contact with the melt, so carbon will not penetrate into the melt, and the working space is in an oxidizing atmosphere. The electrofused refractory materials produced by this method have low carbon content and the glass phase precipitation temperature is more than 1000°C higher than that of the reduction method, which greatly improves the performance. Nowadays, the oxidation melting method is widely used in production.

Electric fused refractory materials are different from sintered refractory materials. Sintered refractory materials mainly undergo solid phase reactions during firing, while fused refractory materials are completely liquid phase reactions between various raw materials. The melt in the electric furnace is completely liquid and solidifies. The final phase is completely determined by the composition. This is something that sintered refractory materials cannot do. For example, sintered high alumina bricks are composed of cristobalite and corundum. Since both exist in granular form, mullite is only generated at the junction of the two during firing. Therefore, the brick body is easily eroded from the height of Si02 composition during use. It is very difficult to obtain complete mullite crystallization for this kind of brick. This problem does not exist for electrofused refractory materials. In the liquid phase, the various chemical components are fully mixed in molecular units and finally recrystallized. The crystals are well developed and the crystal form can be seen with the naked eye. The crystals of sintered refractory materials are very small and generally invisible to the naked eye. In this way, the crystal surface area of the fused refractory material is small among crystals of the same weight, so it has good resistance to corrosive agents. Since the fused refractory material is solidified in a liquid phase, its structure is very dense. This is also difficult to achieve with sintered refractory materials. In addition to the casting cavities caused by shrinkage, the porosity of the fused refractory material is very small, which can theoretically reach the following. Moreover, the pores are closed, so the corrosive agent is not easy to penetrate.

When raw materials with the same chemical composition are used for sintered refractory materials, the crystal quality will vary greatly due to different crystal phases. Therefore, the selection of raw materials for sintered refractory materials is very important. Fused refractory materials do not have this problem. As long as the raw materials have the same chemical composition, the final product can have the same crystal phase, which makes quality control much simpler. However, the production of fused refractory materials requires high power consumption and complex production technology.