Things to note during the kiln baking process of fused bricks
There are many domestic companies producing fused bricks for glass kilns, and the product quality levels and prices vary greatly. Many domestic manufacturers have great room for advancement in terms of appearance quality, composition design, casting technology and dimensional accuracy. The refractory materials 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 dense structure and low porosity, electrofused refractory materials have an extremely high Young's modulus at 800°C and are very brittle. The cold compressive strength is very high, greater than 350MPa, but the tensile strength is only about 20MPa. When subjected to thermal shock When heated unevenly, the tensile stress caused by the temperature difference is too large and the volume changes too quickly, there will be no pores to act as a buffer and it will easily burst.
2. Precautions when heating up
During the heating process of the electric fused corundum pool wall bricks in the kiln, when the temperature is between 0 and 1100°C, as the temperature rises, the bricks gradually expand linearly. During this process, the expansion amount is about 0.8%, and the temperature is between 1100 and 1200°C. At this time, the monoclinic Zr02 in the brick body transforms into the tetragonal Zr02 system. Along with the change in volume, the brick body shrinks, and the total expansion rate drops from about 0.8% to about 0.6%: when the temperature is higher than 1200 At ℃, as the temperature rises, the bricks begin to expand again: below 1600% ℃, the overall expansion characteristics of the pool wall bricks are not large, and the average expansion coefficient is about 7x10^-6/℃.
During the kiln baking process, the maximum tensile stress appears in the non-insulation area on the upper part of the pool wall brick, close to the cold side of the brick, and increases as the temperature rises until the temperature stabilizes. When the cooling wind starts to blow, the brick body The tensile stress has a short-term peak, so generally when the stress is small, that is, when the temperature of the baking sleeve is lower than 700°C, air is gradually added, and the number of cracks produced is relatively small. Due to the thermal insulation of the lower layer, the stress component in the longitudinal direction of the pool wall is larger than the component forces in the vertical and thickness directions of the pool wall, often exceeding the tensile strength limit of the bricks. Therefore, longitudinal cracks commonly occur in pool wall bricks during the kiln baking process. , generally appear after a period of time after the cooling air is turned on and when the baking temperature is 950~1200℃. The cracks develop towards the thickness and vertical direction of the brick. When the kiln temperature is 900~1200℃, the heating rate should not be too fast. Generally It is required not to exceed 15℃/h. When the internal temperature of the brick body is greater than 1000°C, the brick body becomes a plastic body, which can completely absorb the stress and cracks generated, and the cracks are also bridged. Cracks caused by the kiln will not spread to the hot side and insulation areas of the bricks.
Due to design and brick laying reasons, expansion joints are reserved between the pool wall bricks or the joints in some locations are not close to each other. During the kiln baking process, heat is dissipated at the straight joints, the temperature of the brick edges increases, and the tensile stress originates from the bricks. As the outer surface moves inward and changes stresses, there is a risk of horizontal cracks. Therefore, the pre-arrangement and precision processing of pool wall tiles are also very important.
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