Corundum is a gem formed from the crystallization of aluminum oxide (Al2O3). Corundum doped with metallic chromium is bright red in color and is generally called ruby; while blue or colorless corundum is generally classified as sapphire.
Corundum ranks 9th on the Mohs hardness scale. The specific gravity is 4.00, and it has a lattice structure of hexagonal prisms. Because of its hardness and relatively lower price than diamond, corundum is a good material for sandpaper and grinding tools.
As a kind of abrasive, corundum is widely used in abrasives, among which there are many types of corundum, and different types of corundum are used for different purposes.
1. Black corundum
It is a derivative of brown corundum and has a black appearance. Low hardness but good toughness.
It is mostly used for free grinding, such as grinding or rough grinding before electroplating of products, and also used to make coated abrasives, resin cutting discs, polishing blocks, etc.
2. Sintered corundum
It is sintered with fine materials of bauxite or aluminum oxide powder. It is characterized by good toughness and can be made into abrasive grains of various special shapes and sizes.
Mainly used for heavy-duty grinding of steel ingots, suitable for grinding stainless steel ingots.
3. Zirconium corundum
It is characterized by slightly lower hardness, but larger toughness value, higher strength, usually smaller crystal size and good wear resistance.
The foreign zirconium corundum abrasive is mainly used for heavy-duty grinding, suitable for grinding heat-resistant alloy steel, titanium alloy and austenitic stainless steel.
4. Chrome Corundum
It is a derivative of white corundum, with rose-colored appearance, similar hardness to white corundum, slightly higher toughness than white corundum, high strength, good grinding performance and high grinding accuracy. Abrasives made of this abrasive have good shape retention.
The application range is similar to that of white corundum, especially suitable for fine grinding and forming grinding of various tools, measuring tools and instrument parts. Generally, chrome corundum has better grinding performance than white corundum.
5. Microcrystalline corundum
It is a derivative of brown corundum. Its appearance, color and chemical composition are similar to those of brown corundum. It is characterized by small crystal size (50-280 μm), good abrasive toughness, high strength and good self-sharpening.
It is suitable for grinding stainless steel, carbon steel, ductile cast iron, etc. The grinding method is suitable for profile grinding, plunge grinding, precision grinding and heavy-duty grinding.
6. Single crystal corundum
The particle of single crystal corundum abrasive is composed of a single crystal, and has a good multi-edge cutting edge, high hardness and toughness, strong grinding ability, and low grinding heat. The disadvantage is that the production cost is high and there is waste gas in production. , waste water is generated, and the output is low.
It can be used to grind hard and tough metal materials, such as stainless steel, high vanadium high speed steel, heat resistant alloy steel and workpieces that are easy to deform and burn. Considering that single crystal corundum abrasives are limited by production conditions, generally only Recommended for grinding of heat-resistant alloys and hard-to-grind metals.
7. White corundum
The hardness of white corundum is slightly higher than that of brown corundum, but the toughness is slightly worse than that of brown corundum.
It is suitable for grinding steel with higher hardness, such as high-speed steel, high-carbon steel, quenched steel, alloy steel, etc.
8. Brown corundum
The appearance of brown corundum is tan, and the content is 94.5%--97%. It has the characteristics of high hardness, high toughness, sharp particles and relatively low price. It is suitable for grinding metals with high tensile strength. In the absence of other abrasives, it can generally be replaced.
It is widely used for rough grinding of common steel, such as: carbon steel, general alloy steel, malleable cast iron, hard bronze, etc. The secondary abrasive of brown corundum is often used as rice grinding wheel and resin cutting wheel. Sand tile, emery cloth, sandpaper, etc.