How are magnesia - chrome bricks manufactured?

The loose effect caused by the expansion when the oxides in the iron gunning mix react to form spinel can also be used to produce magnesia-chrome bricks with synthetic co-sintered materials. In addition, there are also unburned magnesia-chrome bricks. For example, unburned magnesia-chrome bricks bonded with inorganic magnesium salt solutions. The production process of unburned magnesia-chrome bricks is simple, the cost is low, and the thermal stability is also good, but the high-temperature strength is far inferior to that of fired bricks. At the end of the 1950s, a so-called "direct-bonded" magnesia-chrome brick was developed.

The characteristics of this type of brick are that the raw materials are pure, the firing temperature is high, and the high-temperature phases such as periclase and spinel are directly bonded, while the low-melting phases such as silicates are distributed in an isolated island-like manner. Therefore, the high-temperature strength and slag resistance of the brick are significantly improved. The production process of firing magnesia-chrome bricks is generally similar to that of magnesia bricks. In order to eliminate the loose effect during the firing process of the brick due to MgO and Cr2O3, Al2O3, or the method of using the fine powder obtained by co-grinding and pressing the chromite ore and magnesite and then calcining it to make bricks in combination with the coarse particles of magnesite is an effective measure to eliminate the loose effect.

Compared with ordinary magnesia-chrome bricks, the magnesia-chrome bricks made by this method have a lower porosity, and higher compressive strength, load softening temperature, and flexural strength. The magnesia-chrome bricks made from the synthetic magnesia-chrome sand obtained by pressing the chromite ore and magnesite powder and then calcining it at a high temperature have better slag resistance and high-temperature strength than other magnesia-chrome bricks.