Because the top of an electric arc furnace is subject to rapid temperature changes, slag spraying, flue gas erosion and thermal radiation, the refractory materials used for the top must have good thermal shock stability, corrosion resistance and high refractoriness. The refractory bricks used for the furnace cover are an evolutionary process from silica bricks to high alumina bricks to alkaline bricks to amorphous refractory materials (large prefabricated blocks).
Due to the poor thermal shock resistance of silica refractory bricks, the furnace top is only used about 60 times. In China, silica firebricks were no longer used for the top of electric furnaces as early as 20 years ago. Alkaline refractory bricks also have some shortcomings of their own. They cannot resist the extremely cold and hot changes in temperature under ultra-high power. Silica bricks and alkaline bricks have been replaced by first-class high alumina bricks, corundum bricks, high alumina prefabricated blocks, and castables.
Especially for the fully water-cooled furnace cover, refractory materials are only used in the central part of the furnace cover. It is time-consuming and labor-intensive to use molded bricks to build the furnace, and the mortar joints between bricks are not tight, which will cause uneven stress distribution and reduce the service life of the top guard. In recent years, large prefabricated blocks made of high-strength castables have been used to build furnace roofs for more than 1,000 times. In China, high-aluminum is generally used for top bricks, and the number of furnaces used is between 300-400. It is 5-6 times the service life of silica bricks, but small furnace roofs are suitable for high-aluminum bricks and corundum castables. At present, the amount of large prefabricated blocks used in domestic electric furnace roofs has increased, because according to the shape of the furnace roof, electrode holes are reserved for the integral furnace cover, which greatly reduces the cumbersomeness of the construction process. And the service life is more than twice that of the first-class high-aluminum brick. However, the price of prefabricated integral furnace roofs is relatively high. Some small furnace roofs use high-quality high-aluminum bricks as furnace roofs because of funding considerations.
With the development of amorphous refractory castables, ultra-low cement castables have been successfully used in electric furnace roofs. Ultra-low cement castables are used in the triangle area, and the service life is greatly improved. The entire furnace roof is prefabricated as a whole, and the life of the furnace roof has reached 600 times, and the small furnace cover has reached more than 1,000 times.
Generally, electric furnaces are intermittently produced, with frequent rapid cooling and heating. Using silica fire bricks on the furnace roof will increase the number of replacements and production costs. Therefore, silica bricks are not suitable for electric furnace roofs.
