1. The characteristics of fused zirconia corundum bricks
There are many domestic manufacturers of fused refractory materials for glass kilns, and the product quality level and price vary greatly. Many domestic manufacturers have great room for improvement in appearance quality, composition design, casting process and dimensional accuracy. The quality directly affects the life of the pool wall, especially the crystal phase structure, glass phase content and processing accuracy of the bricks.
Due to its compact structure and low porosity, fused refractories have extremely high Young's modulus and brittleness below 800°C. The cold compressive strength is greater than 350MPa, but the tensile strength is only about 20MPa. During impact and uneven heating, when the tensile stress caused by the temperature difference is too large and the volume changes too fast, there is no pore as a buffer, and it is easy to burst.
2. Precautions when heating up
During the heating up process of the kiln, the fused zirconia corundum pool wall bricks gradually expand linearly when the temperature is between 0--1100°C. As the temperature rises, the expansion amount is about 0.8%, and the temperature is at 1100--1200℃, the monoclinic ZrO2 in the brick body will transform into the tetragonal ZrO2, and with the volume change, the brick body will shrink, and the bus expansion rate will drop from about 0.8% to about 0.6%; when the temperature is higher than 1200℃, as the temperature rises, the bricks start to expand again; below 1600℃, the overall expansion characteristics of the pool wall bricks are not great, and the average expansion coefficient is about 7×10^-6/℃.
During the baking process, larger tensile stress appears in the non-insulation area on the upper part of the pool wall brick, close to the cold surface of the brick, and increases as the temperature rises until the temperature stabilizes. When the cooling air is blown, the tensile stress of the brick body has a short peak. Therefore, when the stress is small, that is, when the kiln temperature is lower than 700 ℃, the air is added step by step, and the number of cracks generated is relatively small. Because of the insulation of the lower layer, the stress component in the longitudinal direction of the pool wall is larger than the component force in the vertical and thickness directions of the pool wall, and often exceeds the tensile strength limit of the bricks. Therefore, the pool wall bricks generally appear longitudinal cracks during the baking process. Generally, it appears after the cooling air is turned on for a period of time and the kiln temperature is 950--1200℃. The cracks develop in the thickness and vertical direction of the brick. When the kiln temperature is 900--1200℃, the heating speed should not be too fast. , Generally requires no more than 15℃/h. When the internal temperature of the brick body is greater than 1000 ℃, the brick body becomes plastic body, which can fully absorb the generated stress and cracks, and the cracks are also bridged. The cracks produced by the kiln will not spread to the hot surface and insulation area of the brick.
Due to design and bricklaying reasons, expansion joints are reserved between the pool wall bricks or some joints are not close to each other. The heat is dissipated at the straight joints during the baking process, the temperature of the brick edges rises, and the tensile stress is removed from the bricks. The outer surface moves to the inside, and the stress changes, that is, there is a danger of horizontal cracks. Therefore, the pre-arrangement and precision machining of pool wall tiles are also very important.