What types of high alumina bricks are commonly used in industrial kilns?
High alumina brick refers to a sintered product containing more than 348% Al2O aluminosilicate or pure alumina. Generally, high alumina bricks contain less than 80% Al2O3, and those containing more than 80% Al2O3 are called corundum bricks. Compared with clay bricks, high alumina bricks have the outstanding advantages of high refractoriness and high softening temperature under load. In the use of industrial kilns, common high alumina bricks fall into the following five categories.
(1) Ordinary high alumina brick
The main mineral composition of the brick is mullite, corundum and glass phase. As the content of Al2O3 in the product increases, mullite and corundum also increase, the glass phase will decrease accordingly, and the refractoriness and high temperature performance of the product will increase accordingly. Ordinary high-alumina bricks have a series of better fire resistance properties than clay products, and are a material with good application effects and a wide range of uses. It is widely used in various thermal kilns. Compared with clay products, the service life of the kiln can be improved.
(2) High load soft high alumina brick
Compared with ordinary high alumina bricks, high-load soft high-alumina bricks are different in the matrix part and the binder part: the matrix part is added with three-stone concentrate, and the chemical composition after firing is close to the theoretical composition of mullite, which is reasonably introduced Use high-aluminum materials, such as corundum powder, high-aluminum corundum powder, etc.; select high-quality spherical clay as the bonding agent, and use different clay composite bonding agents or mullite bonding agents depending on the variety. Through the above method, the load softening temperature of high alumina bricks can be increased by about 50 to 70°C.
(3) Low creep high alumina brick
Improve the creep resistance of high alumina bricks by adopting the so-called unbalanced reaction. That is, according to the use temperature of the kiln, add three-stone minerals, activated alumina, etc. to the matrix to make the composition of the matrix close to or completely mullite, because the mulliteization of the matrix will definitely increase the mullite content of the material , Reduce the glass phase content, and the excellent mechanical and thermal properties of mullite are conducive to the improvement of the high temperature performance of the material. In order to make the matrix completely mullite, controlling Al2O3/SiO2 is the key. Low creep high alumina bricks are widely used in hot blast furnaces, blast furnaces and other thermal kilns.
(4) Phosphate bonded high alumina brick
Phosphate-bonded high alumina bricks are made of compact super-grade or first-grade high-alumina bauxite clinker as the main raw material, phosphate solution or aluminum phosphate solution as the binder, after semi-dry press molding, heat treatment at 400~600℃ Manufactured chemically bonded refractory products. It is a non-fired brick. In order to avoid large shrinkage of the product during use, it is generally necessary to introduce heat-expandable raw materials, such as kyanite, silica, etc., into the ingredients. Compared with ceramic bonded fired high alumina bricks, its anti-stripping performance is better, but its load softening temperature is lower, and its corrosion resistance is poor. Therefore, a small amount of fused corundum, mullite, etc. needs to be added to strengthen the matrix . Phosphate bonded high alumina bricks are widely used in cement rotary kilns, electric furnace roofs and other kiln parts.
(5) Micro-expansion high alumina brick
The brick is mainly made of high-alumina bauxite as the main raw material, added with three stone concentrates, and made according to the production process of high-alumina bricks. In order to properly expand the high alumina bricks during use, the key is to select the three-stone concentrate and its particle size, and control the firing temperature, so that part of the selected three-stone minerals are mullite and some of the three-stone minerals remain. The remaining three-stone minerals are further mulliteized (primary or secondary mulliteized) during use, accompanied by volume expansion. The selected three-stone minerals are preferably composite materials. Because the decomposition temperature of the three stone minerals is different, the expansion caused by the mullite petrochemical is also different. Utilizing this feature, high alumina bricks have a corresponding expansion effect due to different working temperatures. The squeezing of the brick joints improves the overall compactness of the lining body, thereby improving the resistance of the bricks to slag penetration.