Production technology characteristics of high - alumina brick

The production process flow of high alumina products is similar to that of clay products with multi-clinker. The production process should be determined according to the actual production conditions, raw material characteristics, product requirements and production conditions. Before crushing, clinker blocks are strictly graded, granule materials are stored and removed by grading, and clinker and clay are mixed and finely ground.

(1) Classification of bauxite clinker

Alumina clinker in use should be strictly graded to avoid doping and mixing, which is conducive to the quality of stable products and production process. When the clinker mixed grade is used, the chemical and mineral composition of the product will fluctuate, which will easily lead to the non-uniformity and expansion and loose effect of the secondary Mullitization in the brick making process, making the product difficult to be sintered, and difficult to obtain the product with qualified physical and chemical indexes and external dimensions.

(2) Quality requirements of clinker

The quality of clinker depends on the calcination temperature. Generally, the calcining temperature reaches or slightly higher than the sintering temperature of bauxite to ensure the clinker fully sintered and as high density as possible, and to make the secondary mullite and sintering shrinkage all or most of the process in the calcining process. If the calcination temperature of clinker is low, the water absorption rate is high, which not only affects the forming operation and product density, but also makes the product shrink greatly, dimension tolerance and deformation increase when it is fired at a higher temperature.

The secondary Mullite reaction is generally not completed in the underfired materials, so the secondary mullite reaction continues to occur in the granulated clinker when the products are fired, which increases the non-uniform volume expansion effect inside the products, and in severe cases, the cracking of the products increases. When the underfired material is crushed, the intermediate particles in the powder will be increased, which will make the composition of the billet fluctuate greatly and affect the reasonable particle gradation.

(3) Selection of formula

Binder. Soft clay or semi-soft clay is usually used as binder, and a small amount of pulp waste liquid is also added to improve the forming performance and increase the strength of the billet. The expansion of the billet caused by the secondary Mullite reaction is the primary problem to consider the amount of binding clay used. In the manufacture of high alumina bricks such as I and II, due to the large unevenness of corundum content of alumina clinker or its mineral composition, in order to reduce the formation of secondary mullite, it is generally not appropriate to add more clay in the ingredients. For the manufacture of high alumina brick with grade III alumina clinker, the amount of clay added can be determined according to the processing conditions such as the formation of clay and the firing of the product, without considering the secondary mullite problem. In actual production, the amount of clay used fluctuates between 5% and 10%.

(2) Mixed use of clinker of different grades. High alumina bricks can be produced using a mixture of different grades of raw materials to adjust the product's Al2O3 content and improve the matrix composition. When mixing ingredients, it is appropriate to mix adjacent grades, and the clinker with high Al2O3 content is added in the form of fine powder, so that the clay can fully act, and the secondary Mollification reaction occurs uniformly in the matrix, and the matrix components are mollified. When it is necessary to adjust the Al2O3 content in the ingredients, it is generally not appropriate to use the method of adjusting the amount of clay, while the clinker with Al2O3 content is used to adjust by mixing.

(4) Particle composition

The particle composition of high alumina brick is similar to that of clay products with multi - clinker. In the determination of particle composition, the expansion and looseness effect caused by the secondary Mullite reaction must be taken into account in addition to the factors such as obtaining compact accumulation, facilitating the sintering and sintering of the finished products. High aluminum brick and other refractory materials, the use of coarse, medium, fine three ingredients, three ingredients should be in line with the "two big, small in the middle" the basic principle. From the sintering situation, the less fine powder content, the more difficult to sintering, and even expansion phenomenon. The increase of fine powder quantity is beneficial to the improvement of sintering and densification of the billet, and to the adjustment of the secondary Mullite reaction to fine powder during sintering, and to the reduction of the expansion and looseness of the billet caused by the reaction around coarse particles. In the actual production, the fine powder content in the mud is generally about 45%~50% (including the binding clay).

The production experience shows that increasing the size of clinker coarse particle appropriately (in the case of enough fine powder) will reduce the porosity of the product, improve the softening temperature under load, thermal shock resistance and structural strength of the product. However, attention must be paid to particle segregation and mineral composition distribution uniformity and tissue density of clinker. For grade II bauxite clinkers with rough texture, the critical particle size should not be too large. For grade I and III aluminous clinker with dense tissue, the particle size can be appropriately increased to improve some high temperature properties of the product.

Intermediate particles generally act badly. Reducing the number of intermediate particles is beneficial to improving the accumulation density of mud, increasing the density and thermal shock resistance of the product. According to the specific conditions of production, the quantity of intermediate particles is generally reduced to less than 10%~20%.

The fine grinding of clinker and bonded clay is an important technological measure in the production of high alumina brick. It plays an important role in improving the product quality and controlling the range of secondary Mullite reaction. Joint fine grinding increases the activity of the corundum lattice, improves the dispersion of the clay in the fine powder, and makes the clay uniformly in close contact with the clinker, so that the mullite reaction can be uniformly carried out in the fine powder and a large number of secondary mullite reactions can be reduced correspondingly on the surface of the coarse particles. In order to effectively control the secondary Mullite reaction in fine powder, the ratio of clinker and clay should be appropriate when grinding together, so that free Al2O3 and free SiO2 in the mixture can fully act, and the remaining SiO2 can be prevented from reacting with corundum in coarse particles to generate expansion. Therefore, the Al2O3/SiO2 mass ratio in the mixture should be slightly greater than 2.55. Especially when grade II alumina clinker is used to make bricks, more attention should be paid to the appropriate proportion of clinker and clay in the mixed fine powder.