High alumina bricks can be said to be one of the most widely used refractory bricks in the refractory industry. There are hundreds of specifications and sizes of high alumina bricks, which can be used in a variety of thermal kilns such as the steel industry, building materials industry, and power industry.
Generally speaking, aluminum silicate refractories with Al₂O₃ content greater than 48% are collectively referred to as high-alumina refractories. The finalized products are commonly used high-alumina bricks, which are generally divided into three grades: Class I: Al₂O₃>75%; Class II: Al₂O₃ 60%~75%; Class III: Al₂O₃ 48%~60%.
Fire a high-alumina refractory brick, usually at a firing temperature of 1700 to 1800°C;
Firing secondary high-alumina refractory bricks, usually at a firing temperature of 1600 to 1700°C;
Fire three-level high-alumina refractory bricks, usually at a firing temperature of 1500 to 1600°C;
The production process of high alumina bricks and multi-clinker clay bricks are similar. The main refractory raw materials are: high alumina bauxite mainly composed of hydrated bauxite (monohydrate, gibbsite, etc.); sillimanite group minerals (Including kyanite, andalusite, sillimanite, etc.); synthetic raw materials, such as industrial alumina, synthetic mullite, fused corundum, etc. The difference is that the proportion of clinker in the ingredients is relatively high, which can be as high as 90%~95%. The clinker needs to be sorted and sieved to remove iron before crushing. The firing temperature is relatively high, such as tunnels for high alumina bricks such as I and II. It is generally 1500~1600°C during kiln firing.
The refractoriness of high alumina bricks fluctuates in a wide range, generally 1770~2000℃, which is mainly affected by the content of Al₂O₃, and increases with the increase of the content of Al₂O₃ in the product. At the same time, the refractoriness is also affected by the content and type of impurities, and is related to the mineral phase structure of the product.
The starting deformation temperature of high-alumina bricks under load is greater than 1400℃, and it increases with the increase of Al₂O₃ content. For products with Al₂O₃ content less than 71.8%, the load softening temperature depends on the quantity ratio of mullite and glass phase, and it increases as the quantity of mullite increases. The quantity and nature of the glass phase have a significant effect on the softening point under load. When the content of Al₂O₃ is 71.8%~90%, it is mullite and corundum products. With the increase of Al₂O₃ content, the glass phasor is basically unchanged. Although corundum increases, mullite decreases; therefore, the softening temperature of load does not increase. Significantly. After the content of Al₂O₃ exceeds 90%, as the content of Al₂O₃ increases, the amount of glass phase decreases, and the softening temperature under load increases significantly, from 1630℃ at 90% of Al₂O₃ to 1900℃ at 100% of Al₂O₃, and the softening temperature under load increases with the increase of Al₂O₃ content. improve.
The thermal conductivity of high alumina bricks decreases with increasing temperature. When the Al₂O₃ content in the high alumina brick is higher, the more mullite and corundum crystals there are, the more obvious the tendency of thermal conductivity to decrease with the increase of temperature. But above 1000°C, the drop rate decreases.
