Before entering the high-temperature tunnel kiln for sintering, high-alumina bricks must be dried with moisture. The moisture content of the formed high-alumina bricks is generally above 3.5%. They cannot be sintered immediately and need to be dried to reduce moisture. The drying system of the green body varies with the different molding methods and unit weight of the green body. The green body formed by the semi-dry method should be dried in a tunnel dryer. The hot air temperature is 140~160℃, and the exhaust gas temperature is 60~90℃. The residual moisture of the green body should be less than 2%.

 

The green body formed by hand molding, air hammer ramming and vibration molding should be naturally dried first. The drying time varies with the unit weight. For the body with a unit weight of less than 10Kg, it can be naturally dried for 16~24h: for a body with a unit weight of 10~25Kg, it is naturally dried for 36~40h, and for a body with a unit weight of 25~40kg, it is naturally dried for 72~96h. The heavier the green body, the longer the natural drying time should be.

The dried high-alumina bricks can be loaded into the kiln car, and the kiln car is generally flat-packed. In order to avoid black cores during firing, side mounting can also be used. Firing in an inverted flame kiln requires high-alumina bricks to build a shelf. If it is fired in a tunnel kiln, high-alumina clinker sand can be used on the kiln car platform, and a layer of bricks should be laid between each layer of bricks. The brick height is generally 650~1000mm. Among them, the height of the three-level high alumina bricks can be higher, and the first-level and second-level high alumina bricks can be lower.

 

After the kiln car is installed, the high-alumina brick blanks can enter the high-temperature tunnel kiln for sintering. If an inverted flame kiln is used to burn the primary and secondary high-alumina bricks, the general sintering temperature is 1430~1450℃, and the heat preservation is 40h. When firing the third-grade high alumina brick, the firing temperature is 1390~1400℃, and the heat preservation is 24~32h. If the first and second high alumina bricks are fired in a tunnel kiln, the firing temperature is usually 1550~1560°C.

 

The rate of heating varies with different raw materials and products. In the low temperature stage before 600℃, the temperature should be raised slowly: 600~1200℃, the heating speed can be slightly faster: 1200℃ to the highest firing temperature, the heating speed should be controlled. The cooling rate should also be controlled during the cooling phase.