In the raw materials for the production of lightweight high-alumina bricks, if the content of Fe2O3, FeO, TiO2 and other impurities is high, and the temperature rises too fast during firing, the temperature and oxidation atmosphere in the back zone of the preheating zone and the front zone of the firing zone will be very high. Concentrated, the degree of "black heart" of high-alumina refractory bricks will increase. The firing temperature of high alumina refractory bricks above is relatively high, using an oxidizing atmosphere, such as AL2O3, the average firing temperature of high alumina refractory bricks with a content of greater than or equal to 60% is 1450 ℃, using a strong oxidizing atmosphere, the air excess coefficient α is not less than 1.15.

When high-alumina refractory bricks are fired in a high-temperature tunnel kiln, the temperature in the rear zone of the preheat zone must meet the basic temperature requirements. For a short high-temperature tunnel kiln (the length of the preheating zone is relatively short), any improper operation during the heating operation will cause the temperature to rise too fast, resulting in a large amount of oil sprayed by the oil gun in the front area of ​​the firing zone, and the flame will be damaged. In a thick state, after the circulating agitated air in the rear zone of the preheating zone, the flame becomes clear and the temperature rises, so the basic temperature of the preheating zone will increase significantly. Under this high temperature and the reducing atmosphere formed by the local thick flame, the Fe2O3 (pink) in the brick will decompose into FeO (dark brown).

Fe2O3 (pink) +CO at a temperature of 1000℃~1100℃→2FeO (dark brown) +CO2↑

After the "black core" of lightweight high-alumina bricks occurs, its refractoriness is 10~20℃ lower than that of normal products, its apparent porosity is 1~3% higher than that of normal products, its normal temperature compressive strength is about 10MPa lower than that of normal products, and its load softening temperature [ KD) is 40~70℃ lower than normal products, and the outer dimensions of the products change greatly during use. The product is highly brittle, that is, it has low bending resistance and is easy to break. It can be inferred from this that high-alumina "black-core" bricks have poor density and poor thermal stability. The use performance at high temperatures is poor, that is to say, the use effect of high-aluminum "black core" bricks is far less good than that of normal products. So what causes the "black heart" of high alumina refractory brick products in the production of high alumina refractory bricks?

Among them, the TiO2 in the lightweight high-alumina brick is partially converted into Ti2O3, and Ti2O3 synthesizes black FeO·Ti2O3 spinel with FeO at high temperature. The common result of the reaction of Fe2O3 and TiO2 is to deepen the coloring of the brick and increase the The degree to which the product produces a "black heart". Therefore, if the firing is too fast, the heating operation is improper, and the atmosphere formed is unreasonable, the "black heart" of high-alumina refractory bricks will be aggravated. In addition, practice has proven that the dry bricks are not completely dried and the moisture content of the dry bricks is relatively high. If the temperature rises too quickly after the kiln is encountered, the degree of "black heart" in the product will also be aggravated.