With the development of modern kiln technology, the large-scale and efficient high-temperature kiln equipment and other technological innovations have put forward higher requirements on the performance and life of refractory materials in the furnace. In particular, the requirements for refractory materials on the kiln roof are getting higher and higher. At present, the top structure of the kiln adopts two masonry methods, one is to use wedge-shaped refractory bricks for arch masonry, and the other is to use refractory castables for overall prefabrication. The furnace roof of the integral castable is limited by the nature of the castable, and the lining material is easy to peel off or even collapse in large pieces, affecting the overall life of the refractory material.At the same time, the construction conditions of the cast lining material are high, and it needs to be baked to demould. The relatively long construction time will also affect the overall masonry construction progress. The structure using refractory firebricks is often prone to unreasonable masonry structure, uneven stress on the overall arch, and local brick falling or collapse. For example, some problems exist in the common shuttle kiln arch top.
1: Stress changes of shuttle kiln arched roof refractory bricks
As an intermittent kiln, shuttle kiln has the characteristics of flexible production and convenient operation, and is widely used; the shuttle kiln generally has a maximum operating temperature of 1650℃-1750℃. When the temperature rises, the arched roof bricks expand toward the two ends of the kiln body side wall due to heat. The center bricks of the arched roof will be squeezed from the arched roof bricks on the left and right sides, forming extrusion stress, and the center bricks will be lifted into the upper insulation layer; when the kiln is stopped and cooled, the arched roof bricks shrink toward the two ends of the kiln body, and the center bricks of the arched roof fall due to gravity. At the same time, they will be pulled by the arched roof bricks on the left and right sides, forming tensile stress; the shuttle kiln is frequently operated intermittently, and the center bricks of the arched roof are in a state of thermal expansion and contraction for a long time. The compressive stress and tensile stress act repeatedly, and the center bricks are repeatedly lifted and dropped. When the stress accumulates to a certain extent, cracks appear until they break, causing the arched roof bricks to fall off, so the center bricks of the arched roof must have higher compressive and tensile properties.
2. Defects of shuttle kiln plane structure vault bricks
At present, shuttle kilns generally use alumina hollow ball bricks to build vaults, which are lightweight and high-strength. However, the current vault structure consists of two parts: arch foot bricks and vault bricks. The arch foot bricks have an inclined support surface as an integral structural brick, which is directly built on the kiln body and the walls on both sides as a support for the vault bricks. The vault bricks are built into a bridge arch shape by multiple wedge-shaped flat bricks, and the two ends of the arch are supported on the inclined support surface of the arch foot bricks. This type of masonry with an arched top surface has a great risk of the arch sliding down, because the arch foot bricks are integral structural bricks, which are directly masoned on the wall brick surface. There is no external force in the horizontal direction to limit their anti-slip. They tend to be pushed outward under the horizontal component of the arch top. In addition, the arch bricks will expand due to heat under high temperature conditions, which intensifies the squeezing of the arch bricks on the arch foot bricks, greatly increasing the horizontal thrust of the arch foot bricks. When the horizontal thrust is greater than the static friction resistance inherent in the arch foot bricks, the arch foot bricks will slide along the wall brick surface, causing the arch to sink and crack. In this way, not only will a large amount of heat in the kiln be lost, resulting in greater heat loss and lower thermal efficiency, but also when the side slip of the arch foot bricks is too large, the arch bricks will fall, and in severe cases, the arch will collapse, seriously affecting the service life of the kiln and the normal production. Therefore, the plane structure of this arch brick is obviously defective and does not have the ability to resist horizontal thrust to prevent it from sliding.
3: Solutions to the side sliding and collapse of refractory bricks in the vaulted roof
①Solve the damage caused by high temperature stress. The center bricks of the vault are replaced by heavy bricks instead of alumina hollow ball bricks, and the body density is increased to more than 2.9kg/cm3, and the compressive strength at room temperature is increased from 10MPa to more than 100MPa. The high temperature performance is greatly improved, which greatly improves the compressive and tensile resistance of the center bricks of the vault, and reduces the fracture of the center bricks of the vault due to stress.The heavy bricks are also wedge-shaped bricks with a larger upper end and a smaller lower end. The thickness difference between the large end and the small end is not less than 10mm. When laying, the heavy bricks are dry-laid between the vaulted bricks on the adjacent side; the large heads of the two bricks are locked to ensure that they do not fall due to gravity; a gap is left between the lower parts of the two bricks, and the gap width is 1-2mm, forming a dry seam belt running vertically through the center of the vault. ②The solution to the side sliding of the vault bricks is to change the plane structure of the vault wedge bricks to a mortise and tenon connection method. The lining bricks are all engaged together through semicircular protrusions and semicircular grooves. It can ensure good connection and sealing of the vault, and the structure is stable and has a long service life.
