Particle Composition of High Aluminum Brick
The particle composition of high aluminum brick is similar to that of producing multi-clinker clay products. In order to determine the composition of the particles, the expansion and loosening caused by the secondary mullite reaction must be considered in addition to the factors such as dense accumulation, which is beneficial to the sintering of the products during molding and sintering. High aluminum brick and other refractory materials, the use of coarse, medium, fine three-stage batching, three-stage batching should be in accordance with the basic principle of "two ends large, medium small". From the sintering point of view, the less the content of fine powder, the more difficult it is to sintering, and even the phenomenon of expansion. The increase of fine powder is beneficial to improve the sintering and density of billet, and can make the secondary mullite occur when the product is fired. The reaction is adjusted to fine powder to reduce the expansion and loosening of the billet caused by the reaction around the coarse particles. In practical production, the content of fine powder in mud is generally 45% ≤ 50% (including bonded clay).
The production experience shows that properly increasing the size of coarse particles of clinker (under the condition of enough fine powder) can reduce the porosity of the product, increase the load softening temperature, thermal shock resistance and structural strength of the product. However, attention must be paid to the phenomenon of particle segregation and the distribution uniformity and microstructure density of clinker mineral composition. The critical particle size of grade II bauxite clinker with rough structure should not be too large. For dense grade Ⅰ and III bauxite clinker, the particle size can be properly increased to improve some high temperature properties of the product.
Intermediate particles generally play an adverse role. Reducing the number of intermediate particles is beneficial to improving the bulk density of the mud and improving the density and thermal shock resistance of the product. According to the specific conditions of production, the number of intermediate particles is generally reduced to below 10%~20%.
The common fine grinding of clinker and bonded clay is an important technological measure in the production of high alumina brick. It plays an obvious role in improving the quality of products and controlling the range of secondary mullite reaction. Common fine grinding increases the activity of corundum lattice and improves the dispersion of clay in fine powder, which can be in close contact with clinker, so that mullite reaction can be carried out evenly in fine powder, and a large number of secondary mullite reactions can be reduced accordingly. In order to effectively control the secondary mullite reaction in fine powder, the ratio of clinker and clay should be suitable when grinding together, so that free Al2O3 and free SiO in mixture should be made. (2) to avoid the expansion of residual SiO2 and corundum in coarse particles. Therefore, the mass ratio of Al2O3/SiO2 in the mixture should be slightly greater than 2.55. Especially when grade II bauxite clinker is used to make brick, more attention should be paid to the suitable proportion of clinker and clay in mixed fine powder.
The firing temperature of the product mainly depends on the sintering property of bauxite clinker. When the microstructure of raw materials is uniform and dense and the content of impurity Fe2O3,TiO2 is high, the billet is easy to be sintered, the range of safe firing temperature is narrow, and it is easy to cause overfiring or underfiring of the products because of the uniform and dense microstructure of the raw materials and the high content of impurity Fe2O3,TiO2 in the brick made from special grade bauxite clinker and grade I bauxite clinker. When grade II bauxite clinker is used to make brick, the main problem in the firing process is the expansion and loosening effect caused by secondary mullite, which makes the billet difficult to be sintered, so the firing temperature is on the high side. The microstructure of grade III bauxite clinker is uniform and dense, the Al2O3 content is low, and its firing temperature is lower, which is generally slightly higher than that of multi-clinker clay. The firing temperature of the product is about 30 ℃ 50 ℃. According to the production experience of several factories, the firing system of high alumina brick is generally as follows:
Kiln loading: because the firing temperature of the product is close to its load softening temperature, it can not be palletized too high, and most of them use flat code. The palletizing height is 500 mm 700 mm and the maximum height is not more than 1000 mm. When fired with inverted flame kiln, silicon brick is needed to set up the frame.
In the low temperature stage of firing (below 600 ℃), the heating rate is slower to avoid cracking caused by excessive water excretion.
The heating rate in the middle temperature stage has no great effect on the quality of the product. In order to make the reaction in the product more complete, it is necessary to slow down the heating rate in the high temperature stage above 1300 ℃. In the high aluminum brick of equal temperature, because of the high TiO2 content, it is beneficial to the sintering of the product, so the firing temperature is lower.
When fired in inverted flame kiln, the firing temperature of high aluminum brick Ⅰ and II is 1430 ℃ 1450 ℃ and the holding time is about 40 h, and the holding time of III high aluminum brick is 1390 ℃ 1420 ℃ and 24 ℃ 32 h, respectively. the firing temperature of high aluminum brick is 1430 ℃ and 1450 ℃, the holding time is about 40 h, and the holding time is 1390 ℃ 1420 ℃. When fired in tunnel kiln, the firing temperature of Ⅰ and II high aluminum brick is 1500 ≤ 1600 ℃, and that of III equal high aluminum brick is about 1450 ≤ 1500 ℃.
In order to make the re-crystallization of corundum and mullite fully carry out and eliminate the black core, when fired in inverted flame kiln, reductive flame is generally used in high temperature stage, and then weak oxidizing flame is used in heat preservation and slow cooling stage to keep cooling to about 1200 ℃, which is beneficial to the growth of tiny grains in liquid phase. Or the weak oxidizing flame, which is close to neutral, is used in the high temperature stage, and the weak reductive flame is used in the heat preservation stage, which is beneficial to the uniform temperature and grain growth in the kiln. These two different firing methods have achieved good results in different factories. When firing in tunnel kiln, weak oxidizing flame is better in high temperature stage.