Among ordinary and special refractory materials, the commonly used varieties are mainly as follows: Regenerative bricks
Silica bricks and clay bricks are used in a larger amount. Silica bricks are siliceous products containing more than 93% SiO2. The raw materials used are silica, waste silica bricks, etc. The magnesia-chrome brick and silica brick have strong resistance to acid slag erosion, but are easily eroded by alkaline slag. Its load softening temperature is very high, which is close to its refractoriness. After repeated calcination, the volume does not shrink or even expands slightly, but it resists
Poor thermal shock resistance. Silica bricks are mainly used in thermal equipment such as coke ovens, glass melting furnaces, and acid steelmaking furnaces. Clay bricks contain 30% to 46% alumina. They use refractory clay as the main raw material, with a refractoriness of 1580 to 1770 °C and good thermal shock resistance. It is a kind of refractory with the largest production volume.
The main crystal phases in high-alumina products are mullite and corundum. The content of corundum increases with the increase of alumina content. Corundum products containing more than 95% of alumina are high-quality refractory materials with a wide range of uses. Chrome bricks are mainly made of chrome ore, and the main crystal phase is chromite. It has good corrosion resistance to steel slag, but poor thermal shock resistance and low deformation temperature under high temperature load. The chrome-magnesia bricks made of chrome ore and magnesia in different proportions have good thermal shock resistance and are mainly used as basic open-hearth furnace roof bricks.
heat storage brick
Carbonaceous products are another type of neutral refractory materials. According to the composition of carbon-containing raw materials and the mineral composition of the products, they are divided into three categories: carbon bricks, graphite products and silicon carbide products. Carbon bricks are made of high-grade petroleum coke as raw materials, and tar and asphalt are added as binders, and are fired at 1300 ℃ isolated from air. Graphite products (except natural graphite) are obtained by graphitizing carbonaceous materials in an electric furnace at 2500-2800°C. Silicon carbide products use silicon carbide as raw material, add clay, silicon oxide and other binders and sinter at 1350-1400 ° C. Silicon carbide and silicon powder can also be made into silicon nitride-silicon carbide products in an electric furnace under nitrogen atmosphere.
Carbon products have low thermal expansion coefficient, high thermal conductivity, good thermal shock resistance and high high temperature strength. It will not soften after long-term use at high temperature, is not subject to any acid and alkali erosion, has good salt resistance, and is not wetted by metal and slag. It is light in weight and is a high-quality high-temperature resistant material. The disadvantage is that it is easily oxidized at high temperature and should not be used in an oxidizing atmosphere. Carbonaceous products are widely used in high temperature furnace lining (furnace bottom, hearth, lower part of furnace shaft, etc.), lining of smelting non-ferrous metal furnaces. Graphite products can be used as linings for reaction tanks and petrochemical autoclaves. Silicon carbide and graphite products can also be made into crucibles for melting copper, gold and light alloys.
Represented by magnesium products. It contains more than 80% to 85% of magnesium oxide, with periclase as the main crystal phase. The main raw materials for the production of magnesia bricks are magnesite and seawater magnesia, which are calcined at high temperature from magnesium hydroxide extracted from seawater). Good resistance to alkaline slag and iron slag. The melting point of pure magnesia is as high as 2800 ℃, so the refractoriness of magnesia brick is higher than that of clay brick and silica brick. Since the mid-1950s, the production of basic refractories has gradually increased due to the use of oxygen-blown converter steelmaking and the use of basic open-hearth furnace tops, while the production of clay bricks and silica bricks has decreased. Basic refractory materials are mainly used in open hearth furnaces, oxygen-blown converters, electric furnaces, non-ferrous metal smelting and some high-temperature thermal equipment.