High alumina bricks are divided into light and heavy ones. Generally, heavy ones are used more and in large quantities.
The use temperature of high-alumina bricks is determined according to different chemical and physical indicators and different levels. High-alumina bricks are usually divided into one, two and three grades, with Al2O3 content between 55% and 75%. The aluminum content of the first-grade high-alumina brick is 75%; the aluminum content of the second-grade is 65%, and the aluminum content of the third-grade is 55%. This is also the standard for defining different grades of high-alumina bricks in the production process.
The high aluminum bricks produced under the current circumstances are usually high in strength and low under-load softening temperature. If a manufacturer needs to use bricks with high under-load softening temperature, sillimanite, kyanite or andalusite must be added to the high-alumina bricks to increase the load temperature of the high-alumina bricks. Otherwise, with the current situation of raw material resources, the load softening temperature required by the national standard by grade cannot be reached at all.
The use temperature of high alumina bricks of different grades is different. But the overall use temperature is determined according to the actual use of the kiln. Generally between 1200-1400℃, usually the third-grade high-alumina bricks are used for furnace linings at 1200-1250℃. The second-grade high-alumina bricks are used between 1250-1350℃, and the first-grade bricks are used for furnace linings at 1300-1400℃. However, there are also furnace linings above 1400℃, because high-alumina bricks are made of composite bricks made of corundum or mullite. The price of composite bricks is high, and the production cost is relatively high. However, for the case of severe erosion of the furnace lining, products with the same atmosphere should be selected.
High-alumina bricks have higher refractoriness than clay bricks and semi-silica bricks, but they must not be used in kilns with temperatures above 1600℃. Corundum bricks with an aluminum content of more than 90% can be used in furnace linings above 1600℃.
Although high-alumina bricks have high strength, stress concentration occurs due to differences in expansion when the temperature changes. The thermal shock stability will be poor, and even not as high as that of clay bricks. However, the wear resistance and load softening temperature are higher than clay bricks, and it has a certain resistance to weak acid and alkali furnace linings. However, it is better to choose products of the same nature in strong alkali and strong acid conditions.
High alumina bricks have a high firing temperature and sufficient firing time, so the volume is stable and the re-firing line changes little; the use effect is better than clay bricks, clay castables and high alumina castables.
