1. The dilemma of chemical erosion
In the high temperature operating environment of the kiln, magnesia chrome bricks are often threatened by chemical erosion from inside and outside. From the inside, its own chemical composition may decompose or phase change under certain high temperature conditions. Externally, the various process materials and atmospheres in the kiln constitute a complex source of chemical erosion. In the glass kiln, the glass liquid is rich in a variety of oxides, among which the acidic oxides such as silicon dioxide, etc., will chemically react with the basic magnesium oxide components in the magnesia chrome brick to generate low-melting silicate substances. This reaction not only directly consumes the effective composition of magnesia chrome brick, but also the formed low-melting phase is liquid at high temperature, which will further penetrate into the interior of the brick, destroy the integrity of its microstructure, make the originally tightly integrated crystal structure become loose, and greatly reduce the strength and erosion resistance of magnesia chrome brick. In some metal smelting kilns, impurities such as metal oxides and sulfides in the furnace and special smelting atmospheres, such as strong oxidizing or reducing atmospheres, will also have complex chemical reactions with magnesia chrome bricks.
2. The challenge of thermal shock stability
The kiln will inevitably experience frequent temperature fluctuations during operation, which puts forward a severe test to the thermal shock stability of magnesia chrome brick. Magnesia chrome brick has a certain coefficient of thermal expansion, when the temperature of the kiln rises rapidly, the brick body is heated and expanded. If this expansion is limited by the surrounding brick or kiln structure, compressive stress will occur within the brick. When the temperature drops sharply, the brick will shrink again, and then tensile stress will occur. The stress alternations caused by the repeated process of thermal expansion and cold contraction make the internal microstructure of magnesia chrome brick gradually damaged. At first, there may only be tiny cracks inside the brick, and these cracks will continue to expand and extend during the subsequent thermal cycle. With the increase of cracks, the integrity of magnesia chrome brick is destroyed and its strength decreases rapidly. Finally, under the combined action of the impact, vibration and its own gravity of the materials in the kiln, the brick body may flake off or even break, which seriously affects the normal use and life of the kiln lining.
3. The effect of mechanical stress
The interior of the kiln is a complex environment full of various mechanical stresses, in which magnesia chrome bricks are subjected to multiple mechanical forces, which have a significant impact on their service life. First of all, during the loading and unloading of materials, magnesia-chrome bricks will be impacted and worn by materials. Secondly, the vibration of the kiln itself during operation and the centrifugal force generated by the rotating parts will also be transmitted to the magnesia-chromium brick, so that it is in a dynamic state of stress. Under the repeated action of the dynamic stress, the small defects and cracks in the magnesia-chrome brick are easy to expand, resulting in the destruction of the integrity of the brick. Moreover, because magnesia chrome bricks need to be laid together into a whole structure in the kiln lining, extrusion stress will occur between adjacent bricks. If the masonry process is not reasonable, the size of the brick seam is not uniform or the fit between the bricks is not tight, when the kiln is heated and expanded or subjected to other external forces, the local extrusion stress will be too large, which is easy to cause the fracture or displacement of the brick, thus affecting the stability and sealing of the entire kiln lining and reducing the service life of the magnesia chrome brick.
In summary, magnesia chrome brick in the kiln application is faced with chemical erosion, thermal shock stability and mechanical stress and other problems, these problems interweave and influence each other, jointly restrict the service life and performance of magnesia chrome brick. Therefore, in the process of kiln design, material selection and operation management, it is necessary to fully consider these factors and take appropriate measures to reduce or avoid the damage of these problems on magnesia chrome bricks to ensure the efficient, stable and long-term operation of the kiln.
