Preparation and molding of high alumina bricks

1 Preparation of mud for high alumina bricks

First, prepare the clay mud. The clay mud is prepared in a mud mixer, the density of the mud is 1.50~1.65g/cm3, and the temperature is 50~70℃.

The mud is prepared in a wet mill. The preparation procedure is as follows: according to the ratio of ingredients, the cone material is first discharged into the wet mill, clay mud and sulfite pulp waste liquid are added, mixed for 2 to 3 minutes, then added to the drum mill, and then mixed for 10 to 20 minutes.

The moisture content of the mud should meet the following requirements:

Generally 5.5~6.5% of high alumina bricks; 5.3~5.8% of blast furnace high alumina bricks, 9.2~9.7% of hand-formed high alumina bricks with a unit weight of more than 60kg, and 9.7-10.2% of high alumina bricks with a unit weight of less than 60kg; the height of the air hammer is greater than 200mm 6.1~6.6% of high-alumina bricks; 6.8-7.3% of high-alumina bricks with a height of less than 200mm.

The mud should be trapped after mixing. Material trapping conditions: temperature 15~30℃, relative humidity above 80%, time not less than 20h. The wet sack should be covered during the trapping period to reduce water evaporation.

2 Forming of high alumina bricks

In order to reduce the porosity of high alumina bricks and improve the quality of high alumina bricks, the molding pressure must be increased. For ordinary high-alumina bricks, the molding pressure should reach 137MPa; the molding pressure of high-density high-alumina bricks should be in the range of 176~215MPa. In other words, this effect can only be achieved by using a friction brick press with a capacity of 250t or more. The porosity of high alumina bricks should meet the following requirements: [contour aluminum bricks <21%; Ⅱ contour alumina bricks <23%; Ⅲ contour alumina bricks <22%.

Before forming, check the size of the model. Ordinary high alumina brick model scale rate: upper 1.5%; middle and lower pressure surface 3.0%; non-compression surface 1.5%.

3 Drying of high alumina bricks

The moisture content of the formed bricks is generally above 3.5%, and it cannot be fired in the kiln immediately. It needs to be dried to reduce the 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℃, the exhaust gas temperature is 60~90℃, and the residual moisture of the green body should be less than 2%. The blanks formed by hand molding, air hammer ramming and vibration molding should be naturally dried first. The drying time varies depending on the unit weight. For a 10kg single weight body, it can be dried naturally for 16~24h; for a 10-25kg body, it can be dried naturally for 36*40h; for a body weight of 25*40kg, it can be dried naturally for 72-96h. If the body is overweight, the natural drying time should be longer. After natural drying, the body can enter the dryer for drying. The temperature of the hot air inlet of the dryer is 100~120℃; the temperature of the exhaust gas is 60~80℃.

4 The firing temperature of different grades of high alumina bricks

When using an inverted flame kiln to burn high alumina bricks such as Ⅰ and Ⅱ, the general firing temperature is 1430~1450℃ and the heat preservation is 40h. The firing temperature is 1390~1400℃ when firing high alumina bricks of grade Ⅰ. Keep warm for 24~32h. If high alumina bricks such as I and II are fired in a tunnel kiln, the firing temperature is usually 1550~1560℃.

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

The high-alumina brick kiln (or kiln loading car) generally adopts flat installation. To avoid black cores during firing, side installation can also be used. Firing in an inverted flame kiln requires high alumina bricks to build a shelf.

The surface can be leveled with high-alumina clinker sand, and a layer of rice husk is laid between each layer of bricks. In order to make the stack of bricks stable, a layer of pad bricks should be stretched flat at a certain height, and the height of bricks is generally 650~1000mm. Among them, the height of the Ⅰ grade aluminum bricks can be higher, and the Ⅰ, Ⅱ bricks can be lower.