When firing alkaline oxide-based refractory products, such as high-purity fused and re-bonded Mg0-Cr203 bricks, and special high-purity magnesia bricks with Si02 less than 1% directly bonded to MgO-Cr2O3, it is necessary to tunnel at ultra-high temperature (1800-2000 °C).
The lining of such ultra-high temperature tunnel furnaces needs to be comprehensively built with a variety of different types and grades of refractory products. Since the temperature requirements of each section are different, the physical and chemical indicators of the refractory products used are very different. For example, the ultra-high temperature tunnel furnace used by a company to produce 10,000tMgO-Cr203 bricks annually uses 18 different types and grades of refractory products. The higher firing temperature of the above-mentioned tunnel furnace is 1900°C, so the working lining of the firing zone is made of fused corundum bricks (recombined, BD=3.41g/cm3), and the working lining of the furnace wall is made of 80MgO-Cr203 bricks. The furnace roof of the tropical zone, the section immediately following the firing zone and the cooling zone is lined with 60MgO-Cr203 bricks (including the corresponding working lining of the furnace wall). The double-layer arch support wall of the fired belt is built with mullite bricks, and other parts are built with different types of high-alumina bricks, clay bricks and heat-insulating bricks according to the working conditions.
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