Lightweight refractory bricks for glass kilns
Lightweight refractory bricks are shaped block-shaped insulation refractory products with porous internal structures and insulation properties, also known as lightweight insulation refractory bricks. According to the raw materials used, lightweight refractory bricks can be divided into clay, siliceous, high-alumina, magnesium and other lightweight bricks.
Lightweight bricks have low compressive strength, poor slag resistance, poor wear resistance, poor thermal shock resistance, and cannot be in direct contact with glass liquid or flames.
01 Lightweight clay bricks
Lightweight clay bricks are often added with sawdust and formed by plastic method. The blank is composed of clay (30%~40%), clinker (15%~25%), hardwood chips (30%~45%), etc., and a certain amount of syrup and sulfite pulp waste liquid are added. After mixing, trapped, and forming, it is dried (the residual moisture should be less than 10%), and then fired (firing temperature 1250~1350℃) and kept warm for 4h. Lightweight bricks can also be made by mixing clay with porous or hollow materials (such as fly ash beads and diatomaceous earth). Bricks deform greatly during drying and firing, and the fired products need to be reshaped. The volume density of lightweight clay bricks is 0.4~1.3g/cm3.
02 Lightweight silica bricks
The manufacturing method of lightweight silica bricks is similar to that of lightweight clay bricks. Grind ordinary silica to less than 1mm, add anthracite with an ash content of less than 10% (particle size less than 0.2~1mm) or 30%~45% coal coke, and then add a small amount of lime or gypsum and pulp waste liquid. After forming and drying, it is fired at 1270~1300℃. The volume density of lightweight silica bricks is 0.9~1.1g/cm3. The thermal conductivity is only half of that of ordinary silica bricks. The thermal shock resistance is also good. Its load softening start temperature can reach 1600℃, which is much higher than lightweight clay bricks. Therefore, the maximum use temperature of lightweight silica bricks can reach 1550℃. It does not shrink at high temperatures, and even expands a little.
03 Lightweight high-alumina bricks
Lightweight high-alumina bricks are often produced by the foam method. Use high-alumina clinker, clay, and a small amount of sawdust (to thicken the blank) to make mud, and add a certain amount of dielectric [such as Al2(SO4)3] to stabilize the mud. Add a foaming agent with low surface tension (such as rosin soap) to the mud in proportion to make it foam. Make foam mud in a mixer and pour it into the mold. The molded green body is first dried at low temperature (about 40°C), and then dried at 80~95°C after demolding. The residual moisture after drying should be 3%~5%. Then it is fired at 1300~1350°C and kept warm for 4~6h. The volume density of lightweight high-alumina bricks is 0.4~1.0g/cm3, and the porosity is 66%~67%.
Lightweight brick production method
The reason why lightweight bricks can insulate is that there are a large number of pores (closed pores and open pores) in the brick body. Methods for creating pores, that is, methods for producing lightweight bricks include:
① Adding combustibles. Add an appropriate amount of burnt additives to the mud, such as sawdust, charcoal powder, lignite or peat coke powder, petroleum coke powder, walnut shells, etc. The additives are burned when the bricks are fired to form pores. The ash content should be low when the additives are burned.
② Foaming method. Add a foaming agent to the mud to make bubbles in the mud. And add a fixative to stabilize the bubbles that have been formed.
③ Chemical method. Add carbonates and acids, caustic alkalis and aluminum or metals and acids to the mud. Gas is generated by chemical reactions to make the product have pores.
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