High alumina bricks are made of bauxite that is broken into particles, ground into powder of more than 180 mesh, mixed with binder and water in different proportions, and then shaped by a friction press, dried to drain out the moisture, and finally processed through high temperature Made by sintering.
However, the quality of bauxite is different, and the quality of the high alumina bricks produced is also different. Generally divided into first-grade, second-grade, third-grade high-alumina bricks, and special-grade high-alumina bricks. Different grades, different quality of raw materials, and different firing temperatures.
After high alumina bricks are formed, they have a moisture content of 3-10%. Generally, machine-made high aluminum bricks have a moisture content of 3-4%. Handmade bricks have a moisture content of about 10%. They must be dried before firing to reduce the moisture content by 2%. The high-temperature sintering can only be carried out if the temperature is below 100%, otherwise bursting will occur.
Under normal circumstances, bricks formed by hand and vibrated by hydraulic press must be naturally dried first. The green body of 10Kg needs to be naturally dried for 16~24 hours; the green body of 10~25Kg needs to be naturally dried for 36-40h; the green body with a unit weight of 25~40kg needs to be naturally dried for 72~96h. After natural drying, it must enter the drying kiln for low-temperature drying, and finally enter the tunnel kiln for sintering.
However, the dry high alumina bricks must be properly stacked on the kiln car and then transported into the tunnel kiln. When loading the kiln car, they must be packed flat. Uneven areas should be smoothed with bricks and sand, and fire channel gaps should be left between brick layers. The height of the kiln car should not exceed 1 meter. In principle, the middle is higher and the sides are lower. The brick stack must be stable. Prevent bricks from falling out when pulling back and forth.
The high-alumina bricks installed on the kiln car enter the drying kiln to dry for 24 hours, and then enter the high-temperature tunnel kiln for sintering. Generally, the sintering temperature of the third-level high-alumina bricks is 1390-1410°C. The firing temperature of secondary high alumina bricks is around 1430-1450℃, and the firing temperature of primary high alumina fire bricks is around 1450-1480℃. Special grade high alumina refractory bricks are around 1480-1500℃.
Regardless of the grade of high alumina bricks, the temperature cannot rise too fast. Generally, the temperature before 600°C is the low temperature stage and the temperature must be raised slowly. The heating rate can be slightly faster from 600 to 1200°C: the heating rate must also be controlled from 1200°C to the firing temperature, and the temperature cannot be raised for less than 2 hours. After high-temperature sintering, the temperature must be gradually lowered when reaching the cooling zone. Don't cool down too quickly.
The high alumina bricks sintered strictly according to the reasonable heating and cooling system have stable indicators and small errors in appearance and size.
