High-alumina bricks are divided into light and heavy ones. In general, heavy ones are used more and in large quantities.
Standards for different grades of high-alumina bricks
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 the different grades of high-alumina bricks in the production process.
The high-alumina bricks produced under the current situation 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.
Different grades of high-alumina bricks have different use temperatures
Different grades of high-alumina bricks have different use temperatures. 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 lining. However, it is better to choose products of the same nature in the case of strong alkali and strong acid.
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.
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