Mullite brick

Description

Mullite brick is a high-alumina aluminosilicate refractory whose main phase is mullite, a compound of aluminium and silicon oxides. It contains more than 62 % alumina, and mullite-corundum brick more than 72 %. For rotary kilns the grades are set by GOST 21436-2004: MLTs (mullite) and MKTs (mullite-corundum), in Russian МЛЦ and МКЦ. Mullite forms when high-alumina raw materials are fired and gives the brick a strong framework of needle-shaped crystals.

Compared with fireclay, mullite brick is denser, stronger and withstands higher temperatures: the onset of softening under load is at least 1450–1500 °C. Mullite expands little on heating, so the brick copes well with the thermal shocks that occur when coating falls off further up the kiln. Its dense structure lets fewer alkalis and sulphates from the raw materials and fuel through. This is why mullite brick lasts noticeably longer than ordinary fireclay in alkali-rich zones.

In a cement kiln, mullite brick is installed in the safety (calcining) zone, between the fireclay preheating zone and the magnesia hot section. On small-diameter kilns, MKTs mullite-corundum products are also used in the upper transition zone instead of magnesia brick. High-alumina brick is also used in the burning zone of shaft lime kilns and in boiler burners. Zone boundaries along the kiln depend on the burner, fuel and diameter, so we determine the length of the mullite section from shell scanner data and the replacement history.

We supply end and side wedges for the kiln diameter and straight brick; the working lining thickness and shapes are selected from the kiln drawing. The brick is laid with mullite mortar (MML grade to GOST 6137-97) or according to the lining design. Store it on pallets under a canopy and protect it from getting wet. We will supply mullite brick together with fireclay and magnesia products for the whole kiln. On request we supply wedges to ISO 5417 and VDZ for kilns of foreign design.

Technical data