The electric furnace cover is subject to high temperature and often to rapid cooling and heating, which requires high refractory materials. The refractory materials used in the electric furnace cover in my country have evolved from the large-scale specific siliceous composite bricks initially used to the unfired high-alumina bricks prepared by adding various binders (water glass, phosphoric acid, aluminum dihydrogen phosphate, etc.), or the introduction of sillimanite mineral raw materials in the ingredients, adding micropowder, spinel, silicon carbide, etc. In recent years, various types of refractory castables have been developed to meet the needs of the development of ultra-high power electric furnaces. The refractory materials used in the electric furnace cover are as follows:
01 High-alumina brick cover
my country's high-alumina bauxite resources are rich and complete in variety, which provides favorable conditions for the development of advanced aluminum refractory materials. The fired high-alumina bricks with the main crystal phase of corundum can be used for ultra-high power electric furnace covers, and the service life is about 150 furnaces. Preventing spalling and improving erosion resistance are the key to delaying the damage of refractory bricks.
02 Furnace cover bricks containing "three stones"
"Three stones" include sillimanite, kyanite, andalusite, which belong to the sillimanite family of minerals. They are allomorphs with a theoretical composition of Al2O3: 53.1%, SiO2: 36.9. The three mineral raw materials are all high-aluminum minerals with the properties of high-aluminum minerals. "Three stones" are heated to a certain temperature and irreversibly transformed into mullite crystals (short columnar, needle-shaped network structure).
The expansion rate of "three stones" is related to the purity, particle size, impurity composition and content of each mineral. Andalusite and sillimanite have small volume expansion and good volume stability when transformed into mullite, so they can be directly made into bricks without pre-burning or partially introduced for use. Kyanite can be used as an expansion agent for amorphous refractory materials or partially introduced into brick making due to its large volume expansion.
03 Unfired furnace cover bricks
Unfired furnace cover bricks are a new variety developed this year. Their advantages are simplified production process, energy saving, good thermal shock resistance and corrosion resistance, but slightly poor structural strength, performance and storage period are greatly affected by packaging methods and environment. The use of additives SiC, Mg0, Al203, C and other additives for high-aluminum unfired bricks through light oiling is an effective measure to improve the high-temperature performance of furnace cover bricks. Chemical combination bricks with SiC have good thermal shock resistance and corrosion resistance.
04 Integrally cast furnace cover
Refractory brick prefabricated blocks are used in the triangle area of the electric furnace cover. The main materials are corundum, chrome corundum, high alumina, mullite, etc. Refractory brick prefabricated blocks have good integrity and corrosion resistance, simple masonry construction, and relatively guaranteed construction quality, which greatly improves the overall quality of the electric furnace cover.
Generally, the triangle area of the ultra-high power electric furnace cover uses corundum (chrome corundum) prefabricated parts. High alumina and mullite prefabricated blocks are widely used in the triangle area of high-power electric furnace covers.
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