During precision grinding of bearings, due to the high requirements for roughness, the grinding marks on the working surface can often be observed with the naked eye. The surface grinding marks mainly include the following:
The cross helix trace appears on the bearing surface. The reason for this trace is mainly due to the poor flatness of the bus of the grinding wheel and the concave convex phenomenon. During grinding, the grinding wheel is only in partial contact with the bearing workpiece. When the workpiece or grinding wheel moves back and forth several times, the cross helix will appear again in the workpiece and can be observed by the naked eye. The pitch of these spiral lines is related to the speed of the worktable and the rotating speed of the worktable. At the same time, it is also related to the non parallelism of the axis line of the grinding wheel and the guide rail of the worktable.
（1） Main causes of spiral formation
1. The grinding wheel is poorly trimmed, the edges and corners are not chamfered, and the coolant is not used for trimming;
2. There is too much lubricating oil in the guide rail of the workbench, causing the workbench to float;
3. Poor accuracy of machine tool;
4. Excessive grinding pressure, etc.
（2） There are reasons for the formation of helix on bearing surface
1. The rigidity of V-shaped guide rail is not good. When grinding, the grinding wheel is offset, but the edge of the grinding wheel is in contact with the working surface;
2. When trimming noisy wheels, the reversing speed of the worktable is unstable and the precision is not high, so that the trimming of one edge of the grinding wheel is slightly less;
3. The rigidity of the workpiece itself is poor;
4. There are broken and peeling sand particles on the grinding wheel and iron filings under the grinding of the workpiece accumulated on the surface of the grinding wheel. Therefore, the trimmed grinding wheel should be washed or brushed with cooling water;
5. The grinding wheel is not well trimmed, with local bulges, etc.
The main reason for the fish scale like trace on the surface is that the cutting edge of the grinding wheel is not sharp enough, and the phenomenon of “gnawing” occurs during grinding, and the vibration is large at this time.
The specific causes of fish scale marks on the surface of the workpiece are:
1. There are garbage and oil dirt on the surface of the grinding wheel;
2. The grinding wheel is not rounded;
3. The grinding wheel becomes blunt. Trimming is not sharp enough;
4. The diamond fastening frame is not firm, the diamond shakes or the diamond quality is not sharp;
5. Uneven hardness of grinding wheel, etc.
The main reason for the reproduction of galling marks on the galling surface of the working face is that the coarse-grained abrasive particles fall off and are sandwiched between the workpiece and the grinding wheel.
Post time: Aug-23-2022