During the grinding process, the working surface of the bearing is ground by a high-speed rotating grinding wheel. Therefore, if the equipment is not operated and adjusted according to the operating instructions during grinding, various roughness defects will appear on the working surface of the bearing, thus affecting the overall quality of the bearing.
When bearings are precision ground, due to the high requirements for surface roughness, the grinding marks on the working surface can often be observed with the naked eye. The main types of surface grinding marks are as follows. (To detect the roughness, it is recommended to use: Roughness Tester)
Crossed spiral traces appear on the surface
The main reason for this trace is that the grinding wheel has poor straightness and unevenness. During grinding, the grinding wheel and the workpiece are only partially in contact. After the workpiece or the grinding wheel moves back and forth several times, cross spirals will reappear on the workpiece surface and can be observed with the naked eye. The pitch of these spirals is related to the workpiece table speed and workpiece rotation speed, and is also related to the non-parallelism of the grinding wheel axis and the worktable guide rail.
The main reasons for the formation of spiral lines:
1. The grinding wheel is poorly dressed, the edges and corners are not chamfered, and coolant is not used for dressing;
2. There is too much lubricating oil in the guide rail of the workbench, causing the workbench to float;
3. The machine tool accuracy is poor;
4. The grinding pressure is too high, etc.
Specific reasons for the formation of spiral lines:
1.The rigidity of the V-shaped guide rail is not good. When grinding, the grinding wheel is offset, and only the edge of the grinding wheel contacts the work surface;
2.When dressing the grinding wheel, the workbench reversing speed is unstable and the accuracy is not high, so that one edge of the grinding wheel is slightly less dressed;
3. The rigidity of the workpiece itself is poor;
4. There are broken and peeled sand particles and iron filings from the grinding of the workpiece on the grinding wheel. For this reason, the dressed grinding wheel should be rinsed or brushed with cooling water;
5. The grinding wheel is not well dressed, and there are local bulges, etc.
Fish scales appear on the surface.
The main reason for the reappearance of fish scales on the surface is that the cutting edge of the grinding wheel is not sharp enough, and the "biting" phenomenon occurs during grinding, and the vibration is large at this time, causing the workpiece.
The specific reasons for the appearance of fish scales on the surface are:
1.There is garbage and oil on the surface of the grinding wheel;
2.The grinding wheel is not rounded;
3. The grinding wheel becomes blunt and the dressing is not sharp enough;
4. The diamond fastening frame is not firm, the diamond shakes or the diamond quality is poor and not sharp;
5. The hardness of the grinding wheel is uneven, and the working surface is roughened.
The main reason for the reappearance of roughening marks on the surface is that after the coarse-grained abrasive particles fall off, the abrasive particles are sandwiched between the workpiece and the grinding wheel.
The specific reasons why the workpiece surface is roughened during grinding are:
1.The traces left over from rough grinding are not removed during fine grinding;
2.The coarse and fine abrasive particles in the coolant are not filtered cleanly;
3. The abrasive particles are easy to fall off when the coarse-grained grinding wheel is just trimmed;
4. The material toughness expires or the grinding wheel is too soft;
5.The toughness of the abrasive particles and the toughness of the workpiece material are not properly matched, etc.
