The biggest disadvantage of silica bricks is poor thermal shock resistance (the number of water cooling cycles is generally 1 to 4 times). In addition, the thermal conductivity of silica bricks is low, only about 1/50 of the thermal conductivity of steel, and it is a poor conductor of heat. In addition, SiO2 has a variety of crystal transformations under different temperature conditions, and the crystal transformation is accompanied by volume changes. Therefore, the heating rate should not be too fast during kiln baking. When the inner surface temperature of the melting furnace brick reaches the crystal transformation temperature, the inner surface (inner end) of the brick body expands in volume, while the outer surface (outer end) of the brick body does not expand due to temperature lag, and stress will be formed inside the brick body. When the stress exceeds the strength of the brick body itself, the brick body will break. In order to maintain the strength of the brick body, when the kiln is heated, insulation is required during the crystal transformation temperature period to reduce the temperature difference between the inside and outside. However, the SiO2 crystal transformation temperature point measured above is measured in the laboratory, which is somewhat different from the actual situation of industrial production. First, the SiO2 crystal used in the laboratory has high purity, and the crystal transformation temperature point will change after the mineralizer is added to the silica bricks actually used; second, the temperature measuring instruments used in the laboratory have high precision, and industrial production does not have these conditions, so there must be a certain error between the two; in addition, silica bricks are poor conductors of heat, have thermal resistance, and slow heat transfer. To solve this contradiction, we will insulate the silica bricks at one temperature point to form a slow temperature rise with a large temperature range, so that the purity of the silica brick crystal and the accuracy of the temperature measuring instruments will be minimized. In order to reduce the temperature difference between the inside and outside of the brick body, we will insulate the furnace cover in a cold state, leaving only a 1m wide area in the middle of the furnace cover without insulation (insulation will be done after the kiln is baked), and cover it with aluminum silicate fiber felt, the purpose is to reduce the temperature difference as much as possible and facilitate inspection.
As the temperature continues to rise, the volume of the brick body continues to expand. It is necessary to adjust the top screw of the big arch or the tie rod of the column in time to prevent the brick body from climbing up too high and causing the brick body to crack. If the top screw of the furnace cover or the tie rod of the column is not loosened in time, cracks will occur between the arch bricks of the furnace cover, and the arch bricks will change from "curved" contact to "line contact". The weight of the entire brick body is concentrated on the contact point (line), and the pressure of the contact point (line) is particularly large, resulting in uneven force. In severe cases, the edges and corners will be crushed, thereby affecting the strength of the brick body. In this "line contact" condition, when individual arch bricks are small or the lower mud is not full or the adhesion of the mud is small, it will cause the arch brick to "pull out" and fall off. Therefore, special attention should be paid when baking the kiln, and the top screw of the big arch or the tie rod of the column should be adjusted in time.
After the kiln is baked, the normal furnace cover bricks are in "surface contact" with each other, the whole cover has good force effect and sealing effect, is not easily corroded by alkaline dust or alkaline vapor, and the flames cause less burning, erosion and scouring of brick joints.
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