Differences among the first, second and third grade high alumina bricks

November 28, 2018

Differences among the first, second and third grade high alumina bricks

(1) Different aluminum content, high temperature resistance and use temperature. For example, three grade high aluminum bricks’ refractoriness > 1750℃, use temperature is about 1400℃(can not exceed the refractoriness under load for a long time), special high-alumina bricks’ refractoriness > 1790℃, the use temperature is above 1550℃.

(2) The cold crushing strength and bulk density are different, and the raw materials grade of high bauxite clinker is different. The high alumina bauxite clinker is also divided into various grades according to the aluminum content, such as special grade, first grade, second grade, third grade, etc. Different aluminium content, different impurity content, and different service performance of high alumina brick are provided. The molding pressure and firing temperature of the production process are also different. The higher the aluminum content, the higher the bulk density, the lower the porosity, the higher the cold crushing strength and the stronger the friction resistance.

(3) Different thermal shock resistance. Due to the increased aluminum content, the higher the strength of the high alumina bricks, the long-term contact with the high temperature flame or solution, but it is not suitable for the parts with frequent temperature changes or intermittent operation, because the fluctuation of temperature will cause cracks on the brick surface of the high alumina brick under the action of cold and hot stress, which destroys the service life of high alumina bricks. Therefore, the lower the aluminum content, the higher the thermal shock resistance. Among the high-aluminum bricks, the third grade high-aluminum bricks have excellent thermal shock resistance.

(4) The main crystal phase at high temperature is different. With the increase of aluminum content, a series of chemical changes will take place in high-alumina bricks at high temperature, which will form glass phase or crystal structure. The high temperature main crystal phase of the special high alumina bricks is mainly corundum phase and a small amount of mullite phase. The high-alumina brick is mainly composed of mullite phase and a small amount of corundum phase. The second-grade high-aluminum brick is mainly composed of mullite phase and glass phase, and the third-grade high-aluminum transition is mainly composed of low mullite phase and a large amount of glass phase. It can be seen that the high temperature resistance of high alumina bricks varies greatly with the different of main crystal phase.