The aluminum-magnesium castables are made of bauxite clinker and sintered magnesia, together with an appropriate amount of activated silica fume and water reducer. When using, add water directly to mix and shake.

① crack

The aluminum-magnesium castable exhibits cracks in the application and reduces the service life. The phenomenon is: when the ladle is used for 5 times, the crack at the beginning of the inner wall of the bag presents a full wall, followed by the application of the number of times, and the crack becomes deeper. Wide, when used in more than 20 furnaces, had to be forced to stop. In order to deal with the problem of casting cracks, the following methods have been tested:

(1) Replace the bauxite clinker calcined in the shaft kiln with the bauxite calcined by the downdraft kiln, so that the sinterability and bulk density of the bauxite are added, so that it can be reduced because the bauxite is not completely burned. The volume formed by de novo sintering in the process is shortened, but it is not successful;

(2) It is thought that the crack is related to the total amount of fine powder in the castable. Try to reduce the fine powder in the castable to less than 30% (mass fraction), and the lowest to 25%, and fail to deal with the problem;

(3) Handling cracks from chemical reactions. Because Al2O3 and MgO can form aluminum-magnesium spinel under high temperature, and with a large volume expansion, after a series of experiments, Al2O3/MgO is adjusted, and the satisfactory effect is not achieved, even when the MgO content is too high. On the contrary, it has fallen off.

In the end, the following method was used to deal with this problem:

(1) The upper limit of the aggregate size is adjusted from the original 15mm to 25 mm, and the 20-25mm portion accounts for 7.2% (mass fraction) of the total. This is because the presence of super-large particles not only acts as a skeleton, but also can change the direction of long cracks, which helps to hinder the expansion of internal cracks;

(2) Participate in zircon powder in the matrix. This zircon powder is produced in Australia, with a ZrO2 content of around 66%. Because ZrO2 itself has a high melting point, it can absorb CaO in the slag during use, and it can form CaZrO3 with high melting point and high corrosion resistance, close the pores and cracks, and strengthen the matrix. Together with the presence of zircon, it can also form a microcrack structure in the castable, improving the high temperature performance of the castable;

(3) Decrease the amount of active silica fume as much as possible. Because the quality of silica fume powder is unstable and the amount of participation is large, the amount of impurities introduced is large, and helium gas is used. Controlling the amount of silica ash in the castable below 1.5% (mass fraction), the effect is better;

(4) When pouring, it is also very important to strictly control the amount of water added and ensure uniform oscillation.