There are many kinds of abrasives, which are generally classified according to their hardness. The material of the highest hardness is diamond, including natural diamond pellets and synthetic diamond grits
; the second material is carbides, such as black silicon carbide, green silicon carbide, boron carbide and carbon silicon boron; the third material is the kind of corundum with higher hardness, such as brown corundum, white corundum, single crystal corundum, chromium corundum, microcrystalline corundum, black silicon carbide, zirconium corundum, sintered corundum and so on; The material with the lowest hardness is the oxides (also known as high-quality chemical abrasives), such as chromium oxide, iron oxide, magnesium oxide and cerium oxide. The above methods are general classification methods, but there are also classifications based on natural and artificial abrasives. However, due to the limitations of natural abrasives, such as many impurities, uneven abrasives, high price and lack of high-quality abrasive resources, so artificial abrasives are almost used at present.
1 Synthetic Diamond Grit
Synthetic diamond grits are abrasives with high hardness. Its color indicates that it contains impurities, having the color of gray, light pink and yellow-white. It has good thermal conductivity and little thermal expansion. Synthetic diamond grinding powder is mainly used for grinding cemented carbide workpieces. Its price is relatively expensive, but it can be used continuously for more than ten years if we use a grinding wheel inlaid with synthetic diamond powder to process two cemented carbide measuring surfaces of micrometer, so it is suitable in general. Synthetic diamond powder is usually added by coating. In order to make its abrasive particles uniform and suitable to be applied on the surface of abrasive tools, it commonly adopts the synthetic diamond grit with the particle size of W0.5~W14 to prepare abrasive paste to finish rough and fine grinding.
2 Boron Carbide
Boron carbide is a compound obtained by melting it from a mixture of industrial boric acid and low ash carbon raw material (petroleum coke). The hardness of boron carbide is only second to diamond. After grinding, almost all the abrasives become the shape of equal area and sharp edge. The cutting ability of boron carbide is similar to that of diamond. Because it is cheaper than diamond, it is often used as a substitute abrasive for diamond. Boron carbide is mainly used for grinding workpieces made from cemented carbide, hardened steel, optical glass and gemstone materials, especially for rough grinding with large margin.
3 White Corundum
White corundum grinding powder, commonly known as diamond, was also called alumina grinding powder. It is a white corundum crystalline block obtained by smelting aluminium oxide powder in an electric furnace, which is crushed and sorted according to particle size standards. White corundum and brown corundum both belong to corundum abrasives, and the difference between them lies in the content of alumina crystals. Generally speaking, they can be distinguished by their colors, such as dark brown alumina, accounting for 92%, light brown alumina, accounting for 96%, pink alumina, accounting for 98% and white alumina, accounting for 98.5%. Aluminum oxide of white corundum has the most crystalline content and less harmful impurities, that is. pure color, which is beneficial to improving cutting performance. In addition, white corundum has low price and high hardness, which is especially suitable for processing hardened steel, cast iron, soft steel and non-metallic materials. Therefore, white corundum abrasives are widely used in rough grinding, fine grinding and polishing.