Fused mullite bricks are commonly called iron bricks, which are weakly acidic refractory materials. The manufacturing method is the same as the production process of fused zirconia corundum bricks, that is, the carefully selected and pretreated raw materials are put into the electric furnace to melt, and after a period of time, they are injected into the model to form. The main component is Al203, the content of which can reach more than 75%, and the content of SiO2 is about 15%. In addition to the corundum crystals, it is mainly mullite crystals. The glass phase is filled between the crystal phases. Its density is not as high as that of fused zirconia corundum bricks, but the density also reaches 2.7~3.2g/cm3. The refractoriness is 1730~1800℃. The load softening temperature is 1700°C or higher.

Due to its compactness and low porosity, fused refractories have no pores for buffer adjustment when subjected to thermal shock and uneven heating, so they are very easy to burst.

When it is cast, the contact part of the brick body and the mold is first cooled to form a shell, and then gradually cooled and solidified from the outside to the inside. Since the shell is first solidified and shaped, the shell cannot shrink when the inside is solidified, so a cavity is formed near the sprue and shrinkage. According to the keyhole, fused bricks can be pided into non-shrinkage fused bricks, semi-shrinkable fused bricks, and ordinary fused bricks. Shrinkage is the biggest factor affecting quality.

Mainly used in industrial furnaces such as glass melting furnaces. Its corrosion resistance is stronger than that of sintered refractory materials such as clay bricks, and its service life in the kiln of a glass melting furnace is 2-2.5 times that of clay bricks.

Fused mullite brick is the oldest fused refractory material. Although various fused refractory materials with good corrosion resistance (such as fused zirconia corundum bricks) have appeared. But it is still in use. The main reason is that although it is inferior to other fused refractory materials, it is better than sintered refractories. Therefore, it is used as a lower pool wall brick in a glass melting furnace, which can make the upper and lower pool walls last longer. Balance to reduce the cost.

The composition of mullite is 3Al2O3-2SiO2, the melting point is 1910°C, and the hardness is high.

Fused mullite products usually use high alumina bauxite, iron bauxite, industrial alumina and refractory clay as raw materials. The correct selection of ingredients is an important process condition for preparing fused bricks with high mullite content and low corundum and glass phases. The aluminum oxygen coefficient of the ingredients represents the relative content of Al203 and SiO2 in the ingredients, and indirectly reflects the amount of mullite produced in the fused brick. Add a small amount of reducing agent (charcoal or fine-grained coke) to the ingredients. In order to make the gas generated during the melting process easy to escape, a small amount of wood chips should be added to the ingredients, and the melting should be carried out at a temperature of 900-2200°C.

The molten liquid is injected into a model of a certain shape and size, and after cooling, it becomes an electric fusion brick with a certain shape and size with a dense structure and a uniform structure. The product is also heat-treated, the purpose is to make an ingot containing a large amount of a given crystal phase and a minimum amount of glass phase. The ingot after heat treatment should have sufficient mechanical strength without excessive internal stress. The heat treatment is also the same as the fused zirconia corundum brick, which is pided into two stages: crystallization and annealing.

The crystallization makes the chrysophane crystals in the fused mullite bricks become fibrous, with fine grains and uniform distribution. The corundum grains have enough time to interact with the melt to form mullite, so that the mullite content in the fused brick is the largest.

Annealing is the cooling of the casting. During the cooling process of the casting, due to the uneven heat dissipation of each part, there is a temperature gradient inside the casting, which generates a large internal stress, which will cause cracks and missing edges. In order to avoid excessive stress, the casting must be cooled slowly. There are two annealing methods, self annealing and external heating annealing.

Finally, mechanical processing is performed. Due to the incorrect shape of the model, the inconsistency of the up and down shrinkage during casting, the existence of the nozzle and the wrinkle defects on the surface of the casting caused by the addition of cooling materials, fused bricks should generally be used after surface treatment. However, the hardness of fused bricks is very large and processing is difficult. Usually, coarse-grained (16-20mm) emery wheels combined with phenolic plastic can be used for cutting.