The grinding efficiency and the surface roughness of the workpiece are considered in the selection of abrasive granularity. We need to consider the below factors when we choose the granularity.

1.When the machining precision of the workpiece is high and the surface roughness is low, the abrasive tool with fine granularity should be selected. The smaller the abrasive and the more abrasive involved in cutting, the smaller the abrasive trace remaining on the workpiece surface and the lower the surface roughness value. However, the choice of abrasive size must be considered in combination with the grinding conditions used. If the selected grinding amount is small and the grinding wheel is fine, then the abrasive size can be coarser and the workpiece surface roughness can be lower.

2.Abrasive and workpiece surface contact area is larger, or grinding depth is larger, should choose coarse abrasive. Coarse-grained abrasive and workpiece surface friction less, less calorific value. Therefore, when grinding the end face of the grinding wheel, the abrasive size selected can be coarser than that of the periphery of the grinding wheel.

3.Usually the grinding wheel with granularity of 36#~46# is used for plain grinding. The surface roughness Ra of the workpiece can reach 0.8~0.4 m. If the grinding wheel speed vs is increased and the grinding depth AP is reduced, the surface roughness Ra of the workpiece can reach 0.4 m~0.2 m. In fine grinding, the abrasive of 150#~240# is used for grinding, and the surface roughness Ra of the workpiece can reach or lower. In the process of mirror grinding, graphite wheel with resin binder with particle size of W10~W7 is selected.

4.Coarse grinding, machining allowance and grinding depth are relatively large, abrasive granularity should be coarser than fine grinding, so as to improve production efficiency.

5.In cutting and ditching process, abrasive with coarse grain, loose structure and high hardness should be used.

6.When grinding ductile metal and soft metal, such as brass, copper, soft bronze, etc., the surface of the grinding tool is easy to be blocked by chips, so you should choose coarse abrasive.

7.For grinding materials with high hardness, such as quenched steel and alloy steel, coarse-grained abrasive should be selected. When grinding hard alloy, due to the poor thermal conductivity of the material, easy to burn, cracking, so should choose a coarser abrasive. For the grinding of thin and thin-walled workpieces, the abrasive with coarser particle size should be selected because of its easy deformation due to heating.

8.For the cutting margin is small, or the abrasive and workpiece contact surface is not big workpiece, you can choose a finer abrasive. The abrasive granularity of wet mill can be finer than that of dry mill.

9.In the rigid good grinding machine processing, you can choose a coarser abrasive.

10.During forming grinding, it is hoped that the shape of the working surface of the grinding wheel can be maintained well, so it is advisable to choose a fine abrasive. In high speed grinding, in order to improve the grinding efficiency, the abrasive granularity should be thinner than ordinary grinding 1~2 particle size. Because the fine particle size is more sharp, easy to cut into the workpiece. At the same time, the grinding wheel has more working grains per working area, and the bearing inside of each grinding grain is smaller, so it is not easy to be blunt. In addition, even if individual grinding particles fall off, the impact on the non-uniformity of grinding wheel wear is not as great as that of coarse grain, so it is beneficial to maintain the smoothness of grinding process. However, the grain size of the grinding wheel should not be too fine during high-speed grinding, otherwise the chip discharge condition will become worse, which is not conducive to improving grinding efficiency.

In general, medium – grained abrasives are most commonly used. Fine-grained abrasives are usually used only for fine grinding, grinding and polishing. In batch production, on the premise of meeting the roughness requirement of the workpiece, abrasive with coarser particle size should be selected as far as possible to improve production efficiency. And in small batch or single piece of production, generally focus on the processing quality of the workpiece, so choose some fine abrasive is more favorable.

The application range of abrasive of different granularity is shown in the table: