Abrasive is the basic material for manufacturing all kinds of precision products. Many natural abrasives have been replaced by artificial abrasives. Except for diamond, the nature of natural abrasive is not stable, but it still has its use value. Diamond is the hardest abrasive, mainly produced in South Africa, accounting for 95% of the world's total output, and the rest are Brazil, Australia, Guyana and Venezuela. Industrial diamonds range from gray to black, and can be made into grinding wheels, abrasive belts, polishing wheels and grinding powder after grinding.
The chemical composition of natural corundum is alumina, which is mainly produced in South Africa. It is used to polish and grind glass. Emery is also a natural form of alumina. Generally speaking, it is not as pure as corundum. Mainly produced in Greece and Turkey, it is mostly used to make emery cloth or sandpaper. Garnet is used to make coated abrasives, mostly used in wood and leather industries. Flint is usually used to make sandpaper. Timely is the earliest material for making grinding wheels, and it is still used for making tools and processing glass. Pumice comes from volcanoes and is the raw material for making polishing powder. Silica is a component of polishing powder and oilstone. Other natural abrasives include talc, silica, feldspar, black silica and chalk.
Since the 1970s, a large number of artificial abrasives have been produced, among which silicon carbide and alumina are the most important. Silicon carbide, commonly known as emery, is made by mixing pure silicon sand with coke, adding a small amount of sawdust and putting it in an electric furnace at a temperature of 2200? 6? Calcined at 52480℃ for about 36 hours. Alumina, commonly known as corundum, is usually formed by heating and melting bauxite by electric arc furnace. White and transparent, used as an abrasive for heat-sensitive metals, and black is used for processing castings and steel. Synthetic diamond grinding wheel is the abrasive tool with the highest hardness, which is necessary for sharpening cemented carbide tools. Synthetic diamonds can also be made into tools of various shapes and sizes, which are suitable for cutting glass and ceramics. The hardness of boron carbide is higher than that of silicon carbide, so it is not suitable for grinding wheels. It can be used to replace expensive diamond to polish hard materials. The hardness of cubic boron carbide is twice that of silicon carbide and 2.5 times that of alumina, so it is very effective to grind some tool steels.
An important characteristic of abrasive is its hardness, which must be harder than the material being processed. Mohs scale of mineral hardness is often used to measure the hardness of various abrasives. Another important characteristic of abrasives is toughness or volume strength. This property can be controlled by changing the mixing amount, purity, particle size and crystal structure of raw materials, so it is suitable for various applications.
When manufacturing abrasive products, all raw materials except talcum powder and iron oxide need to be crushed and screened, and the screening particle size should be 4? 6? 5900, that is, the diameter is about 6 millimeters (mm) to 6 microns (one thousandth of 65438 +0 mm) or less. The grinding wheel is the most important abrasive product, which is made by mixing, molding and sintering abrasive and binder according to a certain proportion. Finally, it must be shaped, balanced and overspeed tested. Abrasive cloth and sandpaper are another kind of abrasive products with large output, which are made of abrasive particles bonded to basic materials (cloth or paper), dried and cut into different specifications. Others are powdery or granular abrasives. After screening, they need to undergo certain technological treatment, such as grinding or polishing abrasives, and usually mineral ointment or wax is added to meet the needs of different working conditions.
Abrasives are widely used in industry, especially when processing parts with high precision or low roughness or particularly hard parts, abrasives and abrasives are essential. In addition, the grinding wheel is also an essential tool for sharpening and cutting hard materials. In the automobile manufacturing industry, the close cooperation between piston ring and cylinder, valve and valve seat, the accuracy of transmission and gear, etc. , must be processed with abrasives and abrasives to ensure. Other related new products, such as media for plastic bonding roller grinding, save a lot of time for deburring parts and improve productivity.
Significant progress has been made in abrasive production technology. The efficiency of diamond grinding wheel is 4 times higher than that of 14 years ago. The total cost of zirconium-aluminum grinding wheel for rolling mill is only 25% of that of 1948, and the speed is increased by 7 times. The current problem is that the basic theory of grinding is not clear and needs to be studied; Product specifications are complex and changeable, and it is not easy to simplify.