Production of Clay Bricks
Clay brick is a refractory with Al2O3 content of 30% ≤ 48% made from clay clinker as aggregate and refractory clay (soft clay or semi-soft clay) as binder. It is a kind of refractory product with wide use and the largest output.
The properties of clay products fluctuate in a wide range, which is due to the difference of chemical composition and production process of the products. Clay products generally have the following properties:
Chemistry, mineral composition. The content of Al _ 2O _ 3 is 30% ≤ 48%, the content of Sio _ 2 is 50% ≤ 65%, and a small amount of alkali metal, alkali earth metal oxide TiO2,Fe2O3, etc. Mineral composition is generally mullite, cristobalite and quartz, glass phase.
The refractory degree is generally 1580 ≤ 1750 ℃, which increases with the increase of Al2O3/SiO2. When the impurity content of low melt is more, the refractory degree of the product decreases significantly.
The load softening temperature is about 1250 ℃ ~ 1450 ℃, and the variation range is wide. The initial deformation temperature is low, and the difference between the initial deformation temperature and the 40% deformation temperature is about 200 ℃ 250 ℃.
The linear expansion coefficient is low, and the average linear expansion coefficient is 4.5 ≤ 6 ≤ 10 × 6 / ℃. The thermal conductivity is also low.
The thermal shock resistance is good and the fluctuation range is wide. The water cooling cycle at 1100 ℃ is generally more than 10 times. This is related to the low linear expansion coefficient of clay products, the lack of crystal transformation effect and the plasticity at high temperature.
Chemical corrosion resistance: because it is weak acid, it has strong resistance to acid slag erosion, and has weak resistance to alkaline material erosion.
Clay products belong to acid refractory products, and the acidity increases with the increase of SiO2 content. It has certain corrosion resistance to acid slag, but poor resistance to alkaline slag erosion, so clay products should be used as lining of acid kiln. It is also used in blast furnace, hot blast furnace, glass kiln, carbon calciner and other high temperature kilns.
Clay clinker is a barren material that acts as a skeleton in refractory bricks. Clay clinker is made of hard clay calcined in rotary kiln, or soft clay is pre-made into ball, block, and then calcined. The requirement of clay products for clinker is that the chemical composition is stable, the impurity content is not exceeding the standard, the sintering is good, the water absorption is 2% ≤ 4%, and the true density is above 2.7g/cm3.
Clay brick usually adopts secondary or third grade batching, the grain size is 1~3mm and less than 1.0 mm.
The basic requirements of bonded clay should be high plasticity, low sintering property and high fire resistance. According to the characteristics and technological process of raw materials in China, semi-soft clay and soft clay are usually mixed, and semi-soft clay is the main compound ingredient. The particle size of the combined clay is finer, and the crushing particle size is generally required to be less than 0.5 mm. In production practice, a certain amount of organic binder, such as sulfite pulp waste liquor, is often added in the range of 1% ≤ 2%.
The ratio of clinker to bonded clay should be determined by many factors, such as the quality requirement of the product, the shape size and the forming method of the brick billet. If the quality requirement is high, the clinker accounts for more than 80%, or even 90%. It is characterized by the correct shape and size, high density, high strength of high quality refractory products. For some special-shaped products, the molding performance is good, the amount of bonded clay is 25% ≤ 30%, sometimes up to 40%. For some large refractory products, in order to reduce firing compression, keep the shape and size good, the amount of clinker should be increased appropriately.
The particle composition of clay products is generally more thick and fine particles, but also less medium particles, which not only ensures the density and strength of refractory products, but also improves the thermal shock resistance of refractory products. At the same time, the particle size should be adjusted and modified according to the size and surface quality requirements.
When the material is mixed, the coarse particles of clinker are added first, then raw slurry is added, and finally clinker fine powder and bonded clay are added.