Magnesia Bricks’Specifications and Production Process
The refractoriness of magnesia bricks can reach more than 2000 ℃, and its load softening temperature varies greatly with the melting point of the cementitious phase and the number of liquid phases produced at high temperatures. Generally, the load softening temperature of magnesia bricks is between 1520 and 1600℃, while high-purity magnesia bricks can reach 1800℃. The load softening start temperature of the magnesia brick is not much different from the collapse temperature. The linear expansion rate of magnesia brick at 20~1000℃ is generally 1.2%~1.4%, and it is approximately linear. When a liquid phase appears in the brick at high temperatures, it shrinks suddenly. The thermal conductivity of magnesia bricks is relatively high, second only to carbon bricks and silicon carbide bricks in refractory products, and it decreases with the increase of temperature. The thermal shock resistance of magnesia bricks is poor. Increasing the purity of magnesia bricks can appropriately improve the thermal shock resistance. The ability of magnesia bricks to resist acid slag is very poor, and it cannot be directly contacted with silica bricks when in use. Generally, neutral bricks should be used to separate them. The conductivity of magnesia bricks at room temperature is very low, but it cannot be ignored at high temperatures (such as 1500°C). If used in the bottom of an electric furnace, attention should be paid.
The magnesia raw material is crushed into granular material and powder material, and after mixing according to a certain proportion, the binder is added and mixed to form a mud material, and then the magnesia brick is made into a fired magnesia brick through processes such as forming, drying and firing. The firing temperature of ordinary magnesia bricks is generally 1500~1650℃, and the firing temperature of high-purity magnesia bricks is as high as 1700~1900℃. The production process of chemically bonded magnesia bricks is basically the same, except that the chemical bonding agent is combined without high-temperature firing, and only proper low-temperature heat treatment is needed to make unburned magnesia bricks. The production process of magnesia bricks is shown in the figure below.