In order to reduce the porosity of high alumina bricks and improve the quality of high-alumina bricks, the forming pressure must be increased. For ordinary high-alumina bricks, the forming pressure should reach 137MPa; the forming pressure of high-density high-alumina bricks should be in the range of 176~215MPa. That is to say, such an effect can only be achieved by using a friction brick press of more than 250t.
The porosity of high alumina fire bricks should meet the following requirements: I-class high alumina bricks <21%; II-class high-alumina bricks <23% II-class high alumina bricks <22%.
Before molding, check the model size. Ordinary high alumina brick model placement rate: 1.5% for the upper part, 3.0% for the middle and lower parts of the pressure surface; 15% for the non-pressure surface
How to dry high alumina bricks?
The moisture content of the formed bricks is generally above 3.5%. The drying system of the green body varies with the molding method and the single weight of the green body. The green body formed by the semi-dry method should be dried in a tunnel dryer. The temperature of the hot air is 140~160℃, the temperature of the exhaust gas is 60~90℃, and the residual moisture of the green body should be less than 2%.
The green body formed by hand, ramming and vibration forming should be dried naturally. The drying time varies with the unit weight. For the green body with a unit weight of less than 10Kg, it can be naturally dried for 16~24h; for the green body of 10~25kg, it can be naturally dried for 36~40h, and for the green body with a single weight of 25~40kg, it can be naturally dried for 72~96h. The heavier the green body, the longer the natural drying time should be.
After natural drying, the green body can enter the dryer for drying. The inlet temperature of the hot air of the dryer is 100-120°C; the temperature of the exhaust gas is 60-80°C.
What is the difference in firing temperature of different grades of high alumina bricks?
When firing high-alumina bricks I, II and other high-alumina bricks with an inverted flame, the general firing temperature is 1430~1450 ° C, and the heat preservation is 40 hours. When firing grade I high alumina bricks, the firing temperature is 1390~1400C, and the heat preservation is 24~32h. If a tunnel kiln is used to fire high alumina bricks such as Ⅰ and Ⅱ, the firing temperature is usually 1550~1560℃.
The heating rate varies with raw materials and products. In the low temperature stage before 600 °C, the temperature should be raised slowly: 600-1200 °C heating rate can be slightly faster: 1200 °C to the highest firing temperature should control the heating rate. The cooling rate should also be controlled during the cooling phase.
High alumina bricks are generally installed in plain packaging. In order to avoid black hearts during firing, side mounting can also be used. It is fired in an inverted flame kiln, and high-alumina bricks are required to build a shelf.
If it is fired in a tunnel kiln, the table top of the kiln car can be leveled with high-alumina clinker sand, and a layer of rice paddy is laid between each layer of bricks. In order to make the brick stack stable, a whole layer of bricks should be pulled flat at a certain height.
The height of the bricks is generally 650~1000mm. Among them, the height of high-alumina refractory bricks of class I can be high, and the bricks of class I and II can be low.