Production technology of high aluminium brick

High alumina refractory is aluminosilicate refractory with Al2O3 content above 48%. Generally divided into three categories, I et al. : Al2O3 content greater than 75%; II et al. : 60%~75% Al2O3 content; III et al. : Al2O3 content 48%~60%. It can also be classified according to its mineral composition, generally divided into: low Mullite, Mullite, Mullite - rigid jade, corundum - mullite and rigid jade five categories. Its mineral composition is mainly corundum mullite and glass phase. The proportion of each mineral phase depends on the Al2O3/SiO2 of the product, the type and amount of impurities contained in the product, and also depends on the production process conditions.

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.

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.

The sintering temperature of the products mainly depends on the sintering property of alumina clinker. The brick made of super grade and Grade I alumina clinker is easy to be sintered and the range of safe firing temperature is narrow due to the uniform and dense structure of raw materials and the high content of impurities Fe2O3 and TiO2. When grade II alumina clinker is used to make bricks, the main problem in the firing process is the expansion and looseness effect caused by secondary mullite, which makes the billet difficult to be sintered, so its firing temperature is high. The microstructure of grade III alumina clinker is uniform and dense, the Al2O3 content is low, and its firing temperature is low, which is generally slightly higher than the firing temperature of multi-clinker clay products about 30~50℃.

According to the production experience, the firing system of high alumina brick is roughly as follows:

(1) Loading kiln: As the firing temperature of the products is close to the softening temperature of load, stacking should not be too high when loading kiln, and flat code is mostly used. Stacking height is 500-700mm, and the maximum is not more than 1000mm. When fired in an inverted flame kiln, you need to build a brick of silicon.

(2) At the low temperature stage of firing (below 600℃), the heating rate should be slower to avoid cracking caused by too fast water discharge.

(3) The temperature rise rate in the medium temperature stage has no great influence on the quality of the product. In order to make the reaction in the product can be relatively complete, it is necessary to slow down the temperature rise rate in the high temperature stage above 1300℃. In high alumina bricks such as I, the sintering temperature is lower due to the high TiO2 content, which is conducive to the sintering of the products.

When the bricks are fired in an inverted kiln, the firing temperature of I and II high alumina bricks is 1430~1450℃, and the holding time is 40h. Grade III high aluminum brick is 1390~1420℃, heat preservation for 24~32h. When the bricks are fired in tunnel kiln, the firing temperature of I and II equi-aluminum bricks is 1500~1600℃, and that of III equi-aluminum bricks is about 1450~1500℃.

In order to fully carry out recrystallization of corundum and Mullite and eliminate the black core, reducing flame is generally used in the high temperature stage when the corundum and Mullite are burned in the inverted flame stage, and then weak oxidizing flame is used in the heat preservation and slow cooling stage to keep the cooling to about 1200℃, which is conducive to the growth of tiny grains in the liquid phase. Or a weak oxidizing flame close to neutral is used in the high temperature stage, and a weak reducing flame is used for heating in the heat preservation stage, which is conducive to temperature balance and grain growth in the kiln. These two different firing methods have achieved good results in different factories. In the tunnel kiln firing, the high temperature stage weak oxidation flame is good.

The characteristics of high alumina bricks are as follows:

(1) Softening temperature under load. Common refractoriness under load of high aluminum refractory products for more than 1420 ~ 1550 ℃, higher than the clayey refractory products, and increase with the increase of Al2O3 content, when Al2O3 < 70%, the refractoriness under load with mullite phase and higher than the increase of the number of glass phase, liquid phase and the number of properties have obvious effects on refractoriness under load, thus reduce the impurity content in the raw material, is beneficial to improve the refractoriness under load and high temperature creep; When Al2O3 > is 70%, the load softening temperature does not increase significantly with the increase of Al2O3 content.

(2) Thermal shock resistance. The thermal shock resistance of ordinary high alumina refractory products mainly depends on the composition of chemical minerals and microstructure. Generally worse than clay products,

(3) Chemical erosion resistance. High alumina refractory products are resistant to corrosion and oxidation of acidic or alkaline slag and liquid metal. The reduction reactivity is good, and increases with the increase of Al2O3 content and the decrease of harmful impurity content.

High aluminum products are generally used in blast furnace, hot air furnace, electric furnace and other industrial kilns.