How to choose abrasive?

There are many kinds of abrasives, and the selection principle is directly related to the physical and mechanical properties of the workpiece material to be processed.

Generally speaking, when grinding workpiece materials with high tensile strength, it is appropriate to choose corundum abrades with greater toughness; When grinding the workpiece material with low tensile strength, it is appropriate to choose the silicon carbide abrasives with greater brittleness and higher hardness. The tensile strength of some materials and the selected abrasives are shown in Table 1.

When selecting abrasives, the chemical properties between the workpiece material and the abrasives should be considered. The chemical reaction between abrasives and workpiece materials is the main cause of chemical wear. If the silicon carbide abrasive is used to grind steel, it will produce strong chemical wear. There is no such reaction when corundum abrasives are grinding, and chemical wear will not occur. On the contrary, when corundum abrasive grinding glass, especially when there is water cooling, there is a strong chemical reaction, and when silicon carbide abrasive grinding glass, there is no such reaction. Therefore, corundum abrasives can be used to grind steel workpieces, and are not suitable for grinding glass, and silicon carbide abrasives are not suitable for grinding steel.

The chemical affinity between abrasives and workpiece materials should also be paid attention to, especially the affinity between some difficult materials and abrasives is obvious. For example, when silicon carbide abrasive grinding heat resistant alloy, due to the chemical reaction of silicon carbide with iron and under the action of high temperature in the grinding zone, silicon carbide can decompose, and form compounds with some metal components in the workpiece material (such as Co, Ni, Cr, W, etc.), so that the silicon carbide grinding wheel has more serious wear, and the use of single crystal corundum grinding heat resistant alloy, Better grinding effect can be obtained. In addition, when selecting abrasives, the red hardness of abrasives should also be considered.

The following describes the performance and scope of use of the respective abrasives.

① Brown corundum (A) abrasive toughness, high hardness, sharp particles. Therefore, it is suitable for grinding materials with high tensile strength, such as carbon steel, ordinary alloy steel, malleable cast steel, hard bronze and so on. Brown corundum is cheap and widely used, and is regarded as a general abrasive. The second grade of brown corundum can be used as abrasive for grinding wheel, sand tile, emery cloth, sandpaper and resin cutting wheel.

② The hardness of white corundum (WA) abrasive is slightly higher than that of brown corundum, but its toughness is poor. Hard abrasives are easy to cut into the workpiece, which can reduce the deformation of the workpiece and grinding heat. White corundum abrasive is suitable for fine grinding, tool sharpening, thread grinding and grinding easily deformed and burned workpieces, but the price is higher than brown corundum.

③ Single crystal corundum (SA) abrasive has good multi-edge cutting edge, and has high hardness and toughness. This abrasive is not easy to break when grinding, cutting ability is strong, long life, suitable for processing harder metal materials, such as high vanadium high-speed steel, heat-resistant alloy steel and cobalt, nickel alloy steel and stainless steel and other materials. In particular, high-vanadium steel containing 2% to 3% vanadium has poor grinding performance, which is difficult to grind with general abrasives, while single-crystal corundum abrasives can be applied. When grinding quenched steel, tool steel and other alloy steel, the single crystal corundum abrasive can obtain good grinding effect. Single crystal corundum abrasive production is small, only recommended for heat resistant alloys and hard to grind metal materials grinding.

(4) microcrystalline corundum (MA) appearance, color, chemical composition are similar to brown corundum, the difference is that its particles are composed of many tiny crystals. It has the characteristics of high strength, high toughness and good self-sharpness, and it is not easy to fall off into large particles during grinding. The abrasive tool made of it has low wear, suitable for the grinding of stainless steel, carbon steel, bearing steel, special ductile iron and other materials, and is also used for heavy load grinding and precision grinding.

⑤ The hardness of chromium corundum (PA) abrasive is similar to that of white corundum, the toughness is slightly higher than that of white corundum, the cutting performance is better and has higher strength and enough brittleness, so the surface of the grinding workpiece is not easy to burn and crack, and can improve productivity. The abrasive tool made with it has good status quo retention, so it is suitable for form grinding. Chrome corundum has better grinding performance than white corundum, which can reduce the surface roughness value of the machined surface. Chrome corundum is widely used in the grinding of hardened steel, alloy steel tools, threads, precision grinding of measuring tools and instrument parts.

Zirconium corundum (ZA) is a composite oxide of Al2O3 and ZrO2, good toughness, suitable for heavy load grinding and heat resistant alloy steel, titanium alloy, austenitic stainless steel grinding.

⑦ Black corundum (BA) abrasive appearance is black, has a certain toughness, hardness is lower than brown corundum, more used for free grinding, such as before electroplating, polishing grinding or rough grinding, for sandblasting, making rough grinding wheel, emery cloth, sandpaper, etc.

Black silicon carbide (C) hardness is higher than corundum abrasive, cutting edge sharp, but brittle. Good thermal conductivity, fast heat dissipation, self-sharpening performance due to corundum abrasive. Suitable for processing materials with low tensile strength, such as gray cast iron, white cast iron, bronze, brass, ore, refractory, enamel, glass, ceramics, leather, rubber, etc., but also suitable for grinding heat sensitive materials, can be used for dry grinding. Black silicon carbide abrasive can be used for free grinding, widely used in jewelry, jade, agate products cutting and shaping operations.

⑨ Green silicon carbide (GC) abrasive properties than black silicon carbide hard and brittle, sharp, with sharp cutting micro edge, it is easy to cut into the workpiece to be processed, but the toughness is not high. In addition to having the same use as black silicon carbide, green silicon carbide is mainly suitable for carbide cutting tools and workpiece grinding, thread grinding and grinding of its tools, but also can grind agate, clock gem bearings, jewelry jade, precious metals (such as germanium) cutting and free grinding. Its price is higher than black silicon carbide, in addition to grinding cemented carbide materials and some workpiece processing with higher technical requirements, black silicon carbide abrasive should be selected as far as possible.

⑩ Cubic silicon carbide (SC) brittle and sharp. The whetstone and the small grinding wheel made of it have strong grinding ability for ultra-fine grinding and channel grinding of micro-bearing, and can reduce the surface roughness value of micro-bearing.

The boron carbide (BC) abrasive is black, and the particles are more easily broken than diamond to form a new sharp cutting edge, and the cutting performance is better maintained. However, due to the small scale of industrial production, the particle size of boron carbide produced is only 100# and finer particle size, coupled with the poor thermal stability of boron carbide abrasive, can not withstand high temperature, so it is made into grinding paste or mixed into oil agent for free grinding, suitable for carbide, gems, ceramics, molds, precision components processing and polishing.