Clay, siliceous, high alumina, corundum and other heat-insulating refractory bricks can be produced by the foam method. Among them, high-alumina and corundum heat-insulating refractory bricks are mostly produced by this method, which are briefly described as follows:
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(1) High-alumina heat-insulating refractory bricks, the finely crushed bonded clay, bauxite clinker and sieved sawdust are prepared in proportion, and mixed with water to form a slurry, and then mixed with the prepared foam in proportion Mix in a blender to make a foamy slurry. The ratio of foam to mud depends on the bulk density of the product. Foamed mud with bulk density of 0.51-1.26g/cm3 can be made into products with bulk density of 0.4-1.0g/cm3.
Using wood mold or metal mold, casting molding. The brick mold is placed on a drying board with padding paper, and the working surface of the brick mold should be lubricated. In order to prevent the product from producing large air bubbles and affecting the organizational structure, the foam slurry should be slowly injected, and the slurry should be stirred or shaken in the mold to exhaust, and the remaining slurry should be scraped off with a wooden board.
The cast bricks are dried for 18 to 20 hours at a temperature of about 40 °C. When the 3-5 mm gap is opened around the brick mold, the mold is released. After demoulding, continue drying. If a tunnel dryer is used, the inlet temperature should not exceed 40 °C. °C, the outlet temperature does not exceed 150 °C. The residual moisture of the bricks is not more than 3%, and the large bricks are not more than 1% can be installed in the kiln. The drying process is very important. If it is not dried properly, there will be cracks, concave cores, falling edges and corners, sticking molds and other waste products.
Generally, it is fired in an inverted flame kiln, and it can also be fired in a tunnel kiln. Generally, silica bricks are used to set up the kiln, and the bricks are stacked in the frame, and the height of the frame is generally not more than 1.6m. According to the bulk density and Al2O3 content, determine the location of the kiln and the fire stop temperature. Generally, bricks with low bulk density and low Al2O3 content are installed in the upper part, while those with lower content of the two are installed in the lower part. Generally, the firing temperature is 1320-1380 °C, and the temperature is kept for 5-8 hours. Products with higher Al2O3 content have higher fire-stopping temperature, even as high as 1580-1620℃.
Because the shape of the cast molding products after burning is generally irregular, it needs to be ground or cut to make the shape meet the requirements of use, and its physical and chemical indicators meet the indicators specified in the national standards.
High-alumina thermal insulation bricks have high refractoriness and good thermal shock resistance, and are often used as high-temperature thermal insulation layers for furnaces. When slag directly corrodes. Due to the good chemical stability of lightweight high-alumina bricks in a reducing atmosphere, high-alumina thermal insulation linings are generally used in furnaces with hydrogen, CO and other gases as protective atmosphere. Lightweight high-alumina bricks are used at a temperature of 1350 to 1500 °C.
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(2) Corundum heat-insulating refractory bricks can be made of various grades of industrial alumina, pre-fired at 1550-1600 °C to completely transform into α-Al2O3, and then ground by a vibration mill to make the particle size of alumina Less than 30μm, the requirement is less than 3μm to reach 70% to 80%. The particles should not be too coarse or they will seriously destroy the foam. As well as layering the mud. Add appropriate amount of clay, alum and water to the alumina powder to form a slurry, and then add the prepared foam into the slurry and stir evenly. The total water content in the mixture is about %, and then the mud with a lot of foam is poured into the mold. The formed green body together with the mold is dried in a drying room at 60-70 ° C for about 4d and demoulded, and then dried after demoulding. The residual moisture of the dried brick body is below 3% and can be fired in a kiln.
The method of loading the kiln is the same as that of the lightweight high-alumina brick, and finally it is fired at a temperature of 1300-1600 °C, and the total firing time is 50-60 hours. The products after leaving the kiln do not have accurate external dimensions. They must be mechanically or manually processed to obtain a density of 0.8~1.3g/cm3, a compressive strength of 4MPa, a porosity of 70% to 80%, and a thermal conductivity of 0.17W/ (m·K), corundum heat-insulating refractory bricks with a temperature of 1500-1700°C are used.
(3) Silica thermal insulation refractory bricks, a factory uses the foam method to produce lightweight silica bricks, grinding 65% quartz stone and 35% waste silica bricks into fine powder less than 0.088mm, plus 14% lime milk, 1.5% iron scale, 0.5% bone glue, 3% calcium lignosulfonate and 45% to 48% water are wet-milled in a ball mill equipped with pebble balls for more than 10 hours, and all the mud passes through a 0.048mm screen. The foaming agent is saponified with rosin and alkali, and foamed in a foaming machine.
Put the ground mud into the beating drum, add 0.1% to 0.15% alum by weight of the mud, stir for 2 minutes, and then add the foaming agent, the amount of which is 1% of the weight of the mud, and the bulk density of the foam mud is 0.65g /cm3. Put a bottomless wooden mold on the perforated aluminum slats or the ground, put waste newspapers between the aluminum slats or the ground and the wooden mold, and then pour the mud into the mold to make the surface convex, and dry the mold with the drying temperature. It is 30～45 ℃. After drying for 24 hours, demould, and after 48 hours, the bricks are turned over and placed on the side. After 96 hours, the moisture content of the bricks is less than 3%. After 96 hours, the bricks are put into the inverted flame kiln and fired together with ordinary silica bricks. 32h. After burning, the products must be cut and ground to meet the requirements of use.
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