How cracks in coal gangue brick products are produced | Brick and tile technology

11-10

The surface crack of coal gangue porous brick products is one of the important factors affecting product quality. The crack defect is manifested on the product after baking, but the cause of the product crack is not only related to the baking process operation, but also related to the molding, mud and raw materials.

1. Dry crack

During the drying process of the brick, with the dehydration, the volume of the green body decreases, that is, drying shrinkage. In the drying shrinkage process, when the drying shrinkage is not uniform, stress will be formed inside the green body. If this stress exceeds the structural strength of the brick blank, cracks or cracks occur.

The size of the brick drying shrinkage depends on the nature of the clay and the molding moisture of the green body. Generally speaking, the clay with high plasticity shrinks more; the same kind of clay, with the increase of molding moisture, the shrinkage will also increase. Products with large shrinkage are prone to crack defects during the drying process. The difficulty of the brick drying crack can be judged by the drying sensitivity coefficient K of the clay. Low sensitivity: K <1; medium sensitivity: K = 1~2; high sensitivity: K>2. Reducing the plasticity of the clay can reduce drying cracks. As far as the roasting process is concerned, it should be strictly operated according to the drying process, that is, to extend the drying cycle of the brick, to slowly heat up, to slowly dehydrate, and to control the kiln temperature.

2. Forming crack

A considerable part of the waste products are caused by improper molding, such as spiral brick, S type crack, four corner crack, surface crack, etc.

The common forming crack has four corner crack and surface crack. The causes of these two kinds of cracks are: the mud moisture is too low and the lubrication of the machine mouth is not good.

3. Burning crack

The firing cracks are produced in the two firing stages of the pre-heating zone and the cooling zone of the roasting kiln, and the cause is the technical problem of the roasting process.

Cracks formed in the preheating zone of 3.1 brick blanks

The roasting process requires that the moisture content of the baked brick is less than 6℉. Therefore, the brick should be heated slowly and dehydrated slowly in the preheating zone. At a temperature of 105 ℃ ~ 220 ℃, the brick can only remove the adsorbed water, and only when the temperature is above 200 ℃, the brick can remove the structural water. Therefore, in the process of preheating and drying of the brick blank, if the heating rate is too fast, a large amount of superheated steam will inevitably be generated in the blank body. When the superheated steam pressure increases to greater than the structural strength of the blank body, the blank body will be cracked. In addition, during preheating, drying and dehydration, if the flue gas with a large amount of water vapor cannot be eliminated in time, the surface of the brick is prone to cracks due to water vapor condensation.

Cracks formed in the cooling zone of 3.2 products

The function of the cooling belt is to gradually cool the fired product. If the sharp cooling, will cause the product shrinkage crack. After the product enters the cooling zone from the baking zone, the kiln temperature of the cooling zone drops rapidly due to the hot air and the cold air at the end of the kiln. At this time, if the operation is careless, it is easy to cause cracks in the product. In particular, the windward side, top surface and ventilation on both sides of the brick pile on each kiln car are the most prone to cold cracking.

Identification of 3.3 firing cracks

Firing crack is divided into fry, net crack and hair three kinds.

Frying is an irregular burst produced on the surface of the product. The reason for the frying is that the brick with high moisture content heats up too fast in the preheating zone.

The net crack is caused by condensation, moisture regain or rapid heating and dehydration of the brick blank in the preheating zone.

Hair lines are very long and almost straight cracks on the surface of the product. The reason is that the product is cooled too quickly in the cooling zone.

For products appear crack quality problems, only careful analysis, correctly identify the causes of the formation of cracks in order to take effective measures to solve.

Sintered porous brick

Common faults and treatment of tunnel kiln | brick and tile technology

Sintered porous brick

Common faults and treatment of tunnel kiln | brick and tile technology