The Selection Of Abrasive Materials For Abrasive Tools
There are many types of abrasives, and the selection principle is directly related to the physical and mechanical properties of the workpiece material.
In general, when grinding workpiece materials with higher tensile strength, it is better to choose corundum abrasives with higher toughness; for grinding workpiece materials with lower tensile strength, it is better to choose silicon carbide with greater brittleness and higher hardness. See Table 1 for the tensile strength and the selected abrasives materials.
When selecting the abrasive, the chemical properties between the workpiece material and the abrasive must be considered. The chemical reaction between the abrasive and the workpiece material is the main reason for the chemical wear of the abrasive. If silicon carbide abrasives are used to grind steel, strong chemical abrasion will occur. There is no such reaction when corundum abrasives are used, and no chemical wear occurs. In contrast, when corundum abrasives are used to grind glass, especially when cooled by water, a strong chemical reaction occurs, but when silicon carbide abrasives are used to grind glass, there is no such reaction. Therefore, corundum abrasives can be used to grind steel workpieces, which are not suitable for grinding glass, while silicon carbide abrasives are not suitable for grinding steel.
Attention must also be paid to the chemical affinity between abrasives and workpiece materials, especially the affinity between some difficult-to-machine materials and abrasives is obvious. For example, when silicon carbide abrasives are used to grind heat-resistant alloys, because silicon carbide can self-chemically react with iron and under the action of high temperature in the grinding zone, silicon carbide can decompose and interact with certain metal components (such as Co , Ni, Cr, W, etc.) to form compounds, which will cause serious wear of the silicon carbide grinding wheel, and when single-crystal corundum is used to grind heat-resistant alloys, a better grinding effect can be achieved. In addition, the red hardness of the abrasive must be considered when selecting the abrasive.
The performance and application range of the respective abrasives are described below.
Brown fused alumina has high toughness, high hardness, and 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 fused alumina is widely used and is considered as a universal abrasive. The second grade of brown fused alumina can be used for grinding wheels, abrasive tiles, abrasive cloths, abrasives for sandpaper and resin cutting wheels.
The hardness of white fused alumina is slightly higher than that of brown fused alumina, but it has less toughness. Hard abrasives are easy to cut into the workpiece, which can reduce workpiece deformation and grinding heat. White fused alumina is most suitable for precision grinding, tool sharpening, thread grinding and grinding of workpieces that are easily deformed and burned.
3. Single Crystal Alumina (SA)
Single crystal alumina has good polygonal cutting edges, and has high hardness and toughness. This kind of abrasive is not easy to break during grinding, has strong cutting ability and long life. It is suitable for processing harder metal materials, such as high-vanadium high-speed steel, heat-resistant alloy steel and cobalt-based, nickel-based alloy steel and stainless steel. In particular, high-vanadium steels containing 2% to 3% of vanadium have very poor grindability and are difficult to grind with ordinary abrasives, while single crystal alumina is applicable. Single crystal corundum alumina can achieve good grinding results when grinding hardened steel, tool steel and other alloy steels. The production of single crystal alumina is small, and it is only recommended for grinding heat-resistant alloys and difficult-to-grind metal materials.
4. Microcrystalline Alumina (MA)
Its appearance, color and chemical composition are similar to brown corundum, except 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 the grinding process. The abrasive tool made of it has low wear and is suitable for grinding of stainless steel, carbon steel, bearing steel, special nodular cast iron and other materials. It is also used for heavy-duty grinding and precision grinding.
The hardness of pink fused alumina is similar to that of white fused alumina, its toughness is slightly higher than that of white fused alumina, and its cutting performance is good with high strength and sufficient brittleness. Therefore, the surface of the abrasive workpiece is not easy to burn and crack, and can be improved productivity. Abrasive tools made with it are well-maintained and therefore suitable for forming grinding. Pink fused alumina has better grinding performance than white fused alumina, which can reduce the surface roughness value of the processed surface. Pink fused alumina is widely used in the grinding of hardened steel, alloy steel tools, threads, precision grinding of measuring tools and instrument parts.
6. Zirconia Fused Alumina (ZA)
Zirconium fused alumina is a composite oxide of Al2O3 and ZrO2, which has good toughness. It is suitable for heavy-duty grinding and heat-resistant alloy steel, titanium alloy, and austenitic stainless steel.
7. Black Fused Alumina (BA)
Black fused alumina is black in appearance, and has certain toughness, lower hardness than brown fused alumina, and is mostly used for free grinding, such as before electroplating, polishing or rough grinding, sandblasting, making coarse wheels, abrasive cloth, sandpaper, etc.
8. Black Silicon Carbide (C)
Black silicon carbide is harder than corundum abrasive, and its cutting edge is sharp, but brittle. It has good thermal conductivity, fast heat dissipation, self-sharpening performance, compared with corundum abrasive. It is suitable for processing materials with low tensile strength, such as gray cast iron, white cast iron, bronze, brass, ore, refractory, glass, ceramics, leather, rubber, etc., also suitable for grinding heat sensitive materials, can be used for dry grinding. Black silicon carbide can be used for free grinding, and are widely used for cutting and shaping jewelry, jade, and agate products.
9. Green Silicon Carbide (GC)
Green silicon carbide is harder and more brittle than black silicon carbide. It is sharper, with sharp cutting micro-edges, easy to cut into the workpiece, but the toughness is not high. In addition to the same use as black silicon carbide, green silicon carbide is mainly suitable for grinding of hard alloy tools and workpieces, thread grinding and fine grinding of tools. Cutting and free grinding of precious metals such as germanium. Its price is higher than black silicon carbide. Except for grinding hard alloy materials and some workpieces with high technical requirements, black silicon carbide abrasives should be used as much as possible.
10. Boron Carbide (BC)
Boron carbide is black, and the particles are more easily broken than diamond to form a new sharp cutting edge, which maintains good cutting performance. However, due to the small scale of industrial production, the particle size of boron carbide produced is only 100 # and finer. In addition, the boron carbide abrasive has poor thermal stability and cannot withstand high temperature effects, so it is often made into abrasive paste or mixed with oil. For free grinding, suitable for machining and polishing of hard alloys, precious stones, ceramics, molds, precision components.