Properties And Classification Of Corundum

Brown corundum is made from bauxite, anthracite and iron filings by smelting at high temperature in electric arc furnace. In the smelting process, the carbon in the anthracite bauxite in silicon oxide, iron oxide and titanium oxide impurities reduced to metal, for some metals combined together to become ferroalloy, due to its proportion is larger than corundum molten liquid and settling to the bottom of the furnace and corundum molten liquid separation. Only a small amount of impurities included in the corundum melt.The main mineral composition of brown corundum is physical corundum, trigonal crystal system, a small amount of mineral impurities are: calcium silicate, calcium plagioclase, aluminum-rich andalusite (also known as mullite) titanium, vitreous body and a small amount of iron alloy.Brown corundum has strong crushing resistance, oxidation resistance and corrosion resistance, and has good chemical stability. It is a widely used abrasive. It is suitable for grinding metal materials with high tensile strength, such as ordinary carbon steel, hard bronze, alloy steel fine grinding and fine grinding, grinding threads and gears, etc. White corundum can also be used for precision casting and high-grade refractory materials.

The smelting process of chrome corundum is the same as that of white corundum, except that a certain amount of chromium oxide is added in the smelting process, which is light purple or rose color.Chromium corundum due to the introduction of Cr3+ to improve the toughness of the abrasive toughness is higher than that of white corundum, and the hardness is similar to that of white corundum. When it is used for processing materials with greater toughness, its processing efficiency is higher than that of white corundum, and the surface finish of the workpiece is also better. Chromium corundum is suitable for processing the workpiece with high toughness, such as hardened steel, alloy steel, precision measuring tools and instrument parts.

The raw materials and smelting method of microcrystalline corundum are basically the same as that of brown corundum, and the molten liquid is poured into the branch mold rapidly cooling (generally within 30 minutes) immediately after the furnace is stopped.Microcrystalline corundum in the smelting process, the degree of reduction of impurities is poor, the content of A1203 is 94~96%, the crystal size is generally 80~300 microns, the crystal accounts for 57~85%, and the maximum crystal size does not exceed 400~600 microns. It has the characteristics of high strength and greater toughness. Suitable for heavy load grinding, can grind stainless steel, carbon steel, bearing steel and special ductile iron and other materials, because the abrasive particles in the grinding process is micro-edge broken state, is also used for precision grinding and even mirror grinding.

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