There are two kinds of cracking in the firing process of the alumina ceramic plate kiln, one is hot frying, cracking formed in Ceramic Core Immersion Heaters the pretropics, and the other is cold frying, which is cracked in the acute cold zone.
Cracks produced in the pretropics (hot frying)
It is characterized by the irregular development of cracks from edges to centers, which are easily mistaken for transport collision cracking. Its cracks are generally smaller than those of mechanical cracks, and are mainly edge cracks, which occur on the outside. It generally appears in the pretropical anterior segment. The main reason for this defect is that the moisture and kiln temperature of the billet into the kiln are too high, the temperature rise rate of the kiln head is too fast, or the free quartz and dryness index of the blank are too high.
Pre-tropical cracks can be resolved by reducing the moisture entering the billet, the kiln head temperature, and the rate of pre-tropical warming. Generally, the moisture in the kiln is less than 0.5%, and the temperature of the kiln head is lower than 200 °C. In the operation of the kiln, the opening of the smoke extraction gate can be adjusted, and the small regulator and two pairs of burners can be solved. Some areas of the temperature difference between day and night changes large, the temperature plummets, out will produce cracks, because the cold billet into the kiln, the internal and surface temperature to reach the same time, if the kiln head temperature is too high, so that the difference between the inside and surface temperature of the billet is too large, resulting in the surface of the billet water exclusion is too urgent, the surface shrinkage is too fast, so that the internal moisture of the billet is not easy 2
Cold blasting is also called wind cracking or wind skimming. The section after cracking steatite c221 is smooth, the crack is sharp, and the crack is free of flow glaze. It generally appears in cooling belts because the cooling rate is too fast. Mainly in the cooling phase, the cooling is too fast during the quartz crystal form transformation at 573 °C.
The ultimate heating rate of porcelain bricks is twice the cooling rate, and the heating and cooling rate of porcelain tiles is proportional to the strength, temperature and conductivity coefficient of porcelain tiles in different shapes at different temperatures, and inversely proportional to the square and thermal expansion coefficients of elastic molds and product thicknesses. A reasonable temperature rise and cooling rate should be determined according to the actual process. It is mainly to control the cooling rate during the transformation of the 573 °C quartz crystal form.
(1) When the free quartz in the blank is high, the change of the quartz crystal form at 573 °C causes the coefficient of thermal expansion to increase, and the heating temperature and cooling rate should be reduced.
(2) When the temperature of the brick blank drops below 700 ° C, the glass phase begins to solidify, the modulus of elasticity increases, and the cooling rate should be mastered. However, at the same time, the temperature of the kiln should cordierite c520 be avoided to be too high, and the cold air volume of the kiln tail or the cold air volume of the cold air curtain can be increased to solve the cracking, and if it does not work, the speed of the roller rod can be reduced.
(3) Reduce the free quartz content in the formula of the alumina ceramic slab to reduce the expansion coefficient of the billet.