The production technology of clay brick

Clay bricks are made of clay clinker as aggregate and refractory clay (soft clay or semi-soft clay) as binder to make refractory materials with Al2O3 content of 30%~48%. It is a kind of refractory products with a wide range of uses and the largest output.

Clay clinker is a fine material which acts as a skeleton in refractory bricks. Clay clinker is made of hard clay calcined in rotary kiln, or soft clay is made into material ball and material block in advance and then calcined. The requirements of clay products for clinker are stable chemical composition, non-exceeding impurity content, good sintering, water absorption of 2%~4%, true density of above 2.7g/cm.

Clay bricks generally use secondary or tertiary ingredients, the size of 1~3mm and less than 1.0mm.

The basic requirements for the binding clay are high plasticity, low sintering and high fire resistance. According to the characteristics of raw materials and technological process in China, semi-soft clay and soft clay are usually used to mix, and semi-soft clay is the main compound ingredients. The particle size of the combined clay after crushing should be smaller than 0.5mm. In the production practice, often add a certain amount of organic binder, such as sulfurous acid pulp waste liquid, add between 1%~2%.

The ratio of clinker to bonded clay is determined by the quality requirements, shape and size of the product and the forming method of the brick. High quality requirements for clinker accounted for more than 80%, even 90%. It is characterized by the ability to produce high quality refractory products with correct dimensions, high density and high strength. For some special-shaped products, the molding performance is required to be good, the general amount of clay combined with 25%~30%, sometimes up to 40%. For some large refractory products, in order to reduce firing shrinkage and maintain good dimensions, the amount of clinker should be increased appropriately in the ingredients.

The composition of clay particles, generally more fine and thick particles, less particles, not only to ensure the density and strength of refractory products, but also improve the thermal shock resistance of refractory products. At the same time, the particle size should be adjusted and corrected according to the size and surface quality requirements.

When mixing materials, it is generally the first to add skilled coarse particles, then add raw mud, finally add clinker fine powder and combined clay.

In China, clay products are generally formed by semi-dry method, so the blank has low water content. If the kiln has a dry section, it can be fired directly into the kiln without pre-drying. For special shape and large and hand shaped brick, due to the difficulty of water discharge, in order to prevent drying too quickly and cracking, according to the general single weight and shape of the brick complex degree, the use of drying in the air for a week or so, and then into the dryer.

During the firing process of clay products, a series of physical and chemical changes take place in the brick under high temperature and suitable atmosphere. The heating characteristics of clay directly affect the determination of sintering system. Physical and chemical reactions occur during clay heating to promote brick sintering. The larger the amount of clay used, the lower the content of Al2O3 and the higher the content of impurities in clay, the more violent the reaction, uneven volume shrinkage and heating, and the greater the internal stress, which is easy to lead to brick cracking in the firing stage.

The firing of clay products can be divided into four stages:

(1) Room temperature to 200℃ : The temperature should not rise too fast at this time, in order to prevent cracking. When burning in the tunnel kiln, the front no. 4 parking space should not exceed 200℃;

(2) Medium temperature stage (200~900℃) : The temperature rise in this stage should be accelerated to facilitate the chemical reaction of organic matters and impurities in the brick. During the period of 600~900℃, a strong oxidizing atmosphere should be maintained in the kiln to avoid "black heart" waste products.

(3) 900℃ to the maximum firing temperature: the temperature rise in the high temperature stage should be stable, continue to maintain the oxidation atmosphere, so that the body is evenly heated, but also to prevent the brick cracking. Since sintering shrinkage is very strong at 1100℃ and the shrinkage rate is up to 5%, it is very important to maintain a gentle temperature gradient and eliminate internal stress.

Clay products check the fire temperature is higher than general sintering temperature of 100 ~ 150 ℃, if use a combination of narrow sintering temperature range of clay, is to stop the fire temperature is higher than the clay sintering temperature 50 ~ 100 ℃, clay products sintering temperature shall ensure that the combination of clay softening adequately, make its and clinker powder and the reaction of the coarse particle surface, bond clinker particles, make products to obtain the necessary strength and volume stability. The firing temperature is generally 1250~1350℃.