The types of abrasives are numerous with their classification generally based on their hardness. The hardest is diamond, with two kinds - synthetic diamond and natural diamond; followed by carbides, such as black silicon carbide, green silicon carbide, boron carbide, and silicon boron carbide, etc. Next are the higher hardness corundum, such as brown corundum, white corundum, single crystal corundum, chromium corundum, microcrystalline corundum, black corundum, zirconia corundum, and sintered corundum, etc.; and the lowest hardness oxide include chromic oxide, iron oxide, magnesium oxide, and cerium oxide, etc. The above is a general classification method, but there is also a classification based on natural and synthetic abrasives. However, because natural abrasives have limitations such as impurities, uneven grains, high price, and lack of high-quality abrasive resources, almost all of them currently use synthetic abrasives.
Synthetic diamond is a highly hard abrasive raw material. Its color indicates the composition of impurities, with various colors such as gray, light pink, and yellowish white, etc. It has good thermal conductivity and little thermal expansion. Synthetic diamond abrasive is mainly used for grinding hard alloy workpieces. Its price is relatively expensive but using a grinding wheel embedded with synthetic diamond powder, it can process two hard alloy gauge surfaces continuously for more than ten years, so overall, it is still suitable. The way to add synthetic diamond powder is generally by coating, to make the abrasive grains uniform and appropriate, it is often used a grinding paste made of synthetic diamond powder with a grain size of W0.5~W14 for rough grinding and precision machining by coating on the surface of the grinding tool.
Boron carbide is a compound that is obtained by melting a mixture of industrial boric acid and low-ash carbon raw materials (petroleum coke). Boron carbide's hardness is second only to diamond, and its shattered abrasive grains are almost all of equal size and with sharp edges and corners. In cutting ability, it is similar to diamond and is often used as a substitute abrasive material for diamond because it is cheaper. Boron carbide is mainly used for grinding hard alloys, quenched steels, optical glass, and gems, etc., and it is particularly suitable for rough grinding work with large machining allowances.
White corundum abrasive powder is commonly known as emery, also known as alumina abrasive powder. It is obtained by melting alumina powder in an electric furnace to form white corundum crystals, which are then crushed and sorted according to particle size standards. White corundum and brown corundum belong to the same corundum abrasive category, the difference is in the amount of alumina crystal content. Generally, they can be distinguished by their color, such as deep brown with alumina crystal content about 92%, light brown with alumina crystal content about 96%, pink with alumina crystal content about 98%, and white with alumina crystal content of more than 98.5%. White corundum has the highest alumina crystal content, fewer harmful impurities, and pure color, which is conducive to improving cutting performance. Furthermore, white corundum has a low cost and high hardness, making it particularly suitable for processing quenched steels, cast iron, soft steels, and non-metallic materials, etc. Therefore, white corundum abrasive raw materials are the most widely used in coarse grinding, precision grinding, and polishing operations.
Carbon silicon carbide is divided into two types: black carbon silicon carbide and green carbon silicon carbide, which are obtained by heating silica and carbon in a resistance furnace. Carbon silicon carbide has good thermal conductivity and a low thermal expansion coefficient. Compared to green carbon silicon carbide, black carbon silicon carbide has higher hardness but lower toughness. In addition, they can also be distinguished based on their colors. For example, carbon silicon carbide with a carbon content of 96-99% is black, and carbon silicon carbide with a carbon content of more than 99% is green. Black carbon silicon carbide is mainly used for grinding brass castings, bronze castings, aluminum castings, marble, granite, ceramics, and glass, etc., while green carbon silicon carbide is mainly used for grinding hard alloys, quenched steels, etc.
This abrasive material has the lowest hardness, with soft and fine abrasive grains, and is generally coated on a grinding tool or elastic felt wheel for precision grinding or polishing of workpiece surfaces. Chromium oxide is made by roasting potassium chromate and sulfur. It is mainly used for the final processing of precision surfaces, especially for the final precision grinding and polishing of quenched steel parts, such as the precision grinding and polishing of the calibration column for micrometers and the Moerse cone taper gauge. In practice, to improve the cutting ability of chromium oxide and achieve the best process effect, a grinding paste made of blended alumina powder and an appropriate amount of stearic acid is often used for processing. Iron oxide is an extremely fine polishing agent that is often used to polish hard and brittle workpieces, such as polishing optical flats and optical glass lenses. Magnesium oxide and cerium oxide are good polishing agents used mainly for polishing hard and brittle materials such as glass, monocrystalline silicon wafers, etc.