High alumina bricks are mainly divided into ordinary high alumina bricks and modified high alumina bricks. Ordinary high alumina brick refers to the commonly used standard fired brick, while modified high alumina brick mainly refers to four kinds: high load soft high alumina brick, micro expansion high alumina brick, low creep high alumina brick and phosphate bonded high alumina brick.
1、 Ordinary high alumina brick.
The main mineral composition of high alumina brick is mullite, corundum and glass phase. Ordinary high alumina bricks are mainly used for lining blast furnace, hot blast furnace, electric furnace top, blast furnace, reflection furnace and rotary kiln. In addition, high alumina bricks are also widely used in open hearth regenerative lattice bricks, plugs for gating systems, nozzle bricks, etc.
2、 High load soft high alumina brick.
Compared with ordinary high alumina brick, the difference between high load soft high alumina brick is matrix part and binder part.
(1) In addition to adding three stone concentrate, high alumina materials (ground high alumina bauxite, industrial alumina or a-Al2O3 micro powder, corundum powder and high alumina corundum powder) are reasonably introduced according to the theoretical composition of mullite after combustion.
(2) High quality spherical clay shall be selected as the binder, and clay composite binder or mullite binder shall be used according to different varieties. By adopting the above methods, the load softening temperature of high alumina brick is increased by 50-70 ℃.
3、 Micro expansion high alumina brick
Micro expansion high alumina brick is made with high alumina bauxite as the main raw material and three stone concentrate added according to the production process of high alumina brick. In order to make the high alumina brick expand properly in the use process, the key is to select the three stone minerals and their particle size, control the firing temperature, so that some of the selected stone minerals are mullitized and some of the three stone minerals remain. The residual three stone minerals are further mullitized (primary or secondary Mullitization) during use, accompanied by expansion reaction. The three stone minerals selected are better than composites. Because the decomposition temperatures of the three stone minerals are different. The expansion produced by Mullitization is also different. Using this feature, high alumina brick has corresponding expansion effect due to different working temperature. Squeeze the brick joint and improve the overall compactness of the brick, so as to improve the anti slag permeability of the brick.
4、 Low creep high alumina brick
The assessment index of clay brick and high alumina brick used in hot blast stove for a long time in China is mainly the load softening temperature, and the index requirement of butterfly rate is not put forward. After years of use, there are problems such as brick deformation, cracking and sinking. If the air temperature of the hot blast stove increases, such problems will become more prominent. With the development of large volume, high air temperature technology and longevity of iron making blast furnace, higher requirements are put forward for refractory materials for hot blast furnace, which are required to withstand the effects of long-term thermal stress and high air temperature without easy damage. Therefore, high alumina bricks for hot blast stove are required to have low creep rate. This plays an important role in the longevity of hot blast stove. The physical and chemical indexes of low creep high alumina brick are as follows: in order to solve the creep resistance of high alumina brick, the method of adding beneficial minerals is adopted and the so-called unbalanced reaction is used. When the creep temperature is 1550 ℃ and 1500 ℃, the additives are quartz and three stone minerals; When the creep temperature is 1450 ℃, 1400 ℃ and 1350 ℃, the additives are three stone minerals, and corundum and a-Al2O3 are introduced accordingly; When the creep temperature is 1300 ℃, 1270 ℃ and 1250 ℃, the additive is three stone mineral. Among them, three stone minerals and activated alumina are mainly added in the form of matrix, and the complete or near complete Mullitization of matrix is the key. Because the Mullitization of the matrix will increase the mullite content and reduce the glass phase content of the material, and the excellent mechanical and thermal properties of mullite are conducive to the improvement or improvement of the high-temperature properties of the material. The research shows that high load soft and low creep high alumina bricks for blast furnace hot blast stove with creep temperature of 1400-1450 ℃ can be prepared by adding 15% - 35% sillimanite concentrate in the production of high alumina bricks. For low creep high alumina bricks with creep temperature of 1500 ~ - 1550 ℃, in addition to adding an appropriate amount of sillimanite, a certain amount of mullite should be added; Or use some fused corundum and silica raw materials.
5、 Phosphate bonded high alumina brick
Phosphate bonded high alumina brick is a chemically bonded refractory product made of dense super grade or grade I high alumina bauxite clinker as the main raw material, phosphoric acid solution or aluminum phosphate solution as the binder, formed by semi dry machine and heat treated at 400-600 ℃. It belongs to unburned brick. In order to avoid large shrinkage of products during high-temperature use, it is necessary to introduce heating expansive raw materials, such as kyanite, sillimanite, pyrophyllite, silica, etc. Compared with ceramic bonded sintered high alumina, it has better spalling resistance, but its load softening temperature is low and its corrosion resistance is poor. Therefore, a small amount of fused corundum mullite should be added to strengthen the matrix. Phosphate bonded high alumina brick is suitable for cement kiln, electric furnace top and ladle.