Causes and analysis of defects in bearing surface grinding
During the grinding process, the working surface of the bearing is ground by a grinding wheel that rotates at a high speed. Therefore, if the equipment is not operated and adjusted according to the operation instructions during grinding, various defects will occur on the working surface of the bearing, thus affecting The overall quality of the bearing. When the bearing is in precision grinding, the roughening requirements are very high, and the grinding marks appearing on the working surface can be observed by the naked eye.
Performance showing cross spiral traces
The reason for this kind of trace is mainly due to the poor straightness of the busbar of the grinding wheel and the unevenness. When grinding, the grinding wheel is only partially in contact with the workpiece. When the workpiece or the grinding wheel reciprocates several times, the performance of the workpiece will reappear. The spiral is visible to the naked eye. The pitch of these spirals is related to the workpiece table speed and the workpiece rotation speed, and is also related to the grinding wheel axis and the table rail.
(1) The main reason for the formation of spirals
1. The grinding wheel is poorly trimmed, the corners are not chamfered, and the coolant is not used for trimming;
2. The guide rail guides too much lubricating oil, causing the workbench to float;
3. The machine tool accuracy is not good;
4. Grinding pressure is too large.
(2) The cause of the formation of the spiral
1. The V-shaped guide rail is not rigid, and the grinding wheel is offset when grinding, but the edge of the grinding wheel is in contact with the working surface;
2. When the quarrel is repaired, the commutation speed of the worktable is unstable, and the precision is not high, so that the edge of the grinding wheel is slightly trimmed;
3. The workpiece itself is poorly rigid;
4. There are crushed and spalled sand on the grinding wheel and iron scraps from the workpiece grinding on the surface of the grinding wheel. For this purpose, the finished grinding wheel should be rinsed or brushed with cooling water;
5. The grinding wheel is not well trimmed, and there are local bulges.
Fish scales appear on the surface
The main reason for the surface scale of the fish scale is that the cutting edge of the grinding wheel is not sharp enough, and the phenomenon of "clamping" occurs during grinding, and the vibration is large at this time. The specific reasons for the appearance of scales on the surface of the workpiece are:
1. There are garbage and oil on the surface of the grinding wheel;
2. The grinding wheel is not trimmed;
3. The grinding wheel becomes dull. The dressing is not sharp enough;
4. The diamond fastening frame is not strong, the diamond is rocking or the diamond quality is not good and not sharp;
5. The hardness of the grinding wheel is not uniform.
Working face
The main reason for the surface reappearing of the fluff marks is that the abrasive grains are sandwiched between the workpiece and the grinding wheel after the coarse-grained abrasive grains are detached.
The specific reasons for the surface of the workpiece being roughened during grinding are:
1. Traces left over from rough grinding, not worn away during fine grinding;
2. The coarse abrasive grains and the fine abrasive grains in the coolant are not cleaned;
3. When the coarse-grained grinding wheel is just finished, the abrasive particles are easy to fall off;
4. The material toughness is valid or the grinding wheel is too soft;
5. Improper matching of abrasive grain toughness and workpiece material toughness.
Straight wave marks on the surface of the workpiece
We cut the cross-section of the milled vertical axis of the workpiece and zoom in to see that its periphery is similar to a sine wave. The center of the sine wave is not rotated, and the trajectory around the sine wave is the waveform cylinder, which is also called polygon.
The reason for generating a straight waveform is the movement of the grinding wheel relative to the workpiece or the periodic variation of the grinding wheel's pressure on the workpiece to cause vibration. This vibration may be forced vibration or self-excited vibration, so there is often more than one direct wave frequency on the workpiece.
The specific reasons for producing straight waveform traces are:
1. The grinding wheel spindle clearance is too large;
2. The hardness of the grinding wheel is too high;
3. The static balance of the grinding wheel is not good or the grinding wheel becomes dull;
4. The workpiece speed is too high;
5. The lateral file is too large
6. The grinding wheel spindle bearing wears, and the matching clearance is too large, resulting in radial runout;
7. Grinding wheel pressing mechanism or work table "crawling" and so on.
Reproduce burn marks on the surface of the workpiece
The surface of the workpiece tends to burn during the grinding process. There are several types of burns. One is that the burn is in the direction of the grinding wheel, and it is dark black plaque; the second is a line or intermittent line.
The surface of the workpiece is burned during the grinding process and can be summarized for the following reasons:
1. The grinding wheel is too hard or the grain size is too fine and the structure is too dense;
2. The feed rate is too large, the supply of cutting fluid is insufficient, and the heat dissipation condition is poor;
3. The workpiece speed is too low, and the grinding wheel speed is too fast;
4. The grinding wheel is too large, and the grinding depth changes continuously and burns;
5. The dressing of the grinding wheel is not timely or the repair is not good;
6. The diamond is sharp and the grinding wheel is not well trimmed;
7. The burn is too deep when the workpiece is coarsely ground, and the amount of fine grinding is too small to be worn off;
8. The workpiece clamping force or suction is insufficient, and the workpiece has a stall phenomenon due to the grinding force.
Then how does the surface of the workpiece know whether it is burned during the grinding process? This can be checked by regular pickling.
After the workpiece is pickled, when the surface is wet, it should be visually inspected immediately under the astigmatism lamp. The normal surface is evenly dark gray. If it is a software point, it will appear dark black spots in the cloud, and the perimeter is not fixed; if it is decarburized, it will show gray or dark black spots; if the crack is ground, the crack will be cracked, such as burn, first surface The direction of the grinding wheel is dark black plaque, and the second is a line or intermittent line.
If the above-mentioned burn phenomenon occurs during the grinding process, the cause must be analyzed in time, effective measures should be taken to solve the problem, and mass burns should be eliminated.
Surface roughness does not meet the requirements
The surface roughness of bearing parts has standard and process requirements, but in the process of grinding and super-finishing, for various reasons, it often fails to meet the specified requirements. The main reasons for the surface roughness of the workpiece are not met:
1. The grinding speed is too low, the feed speed is too fast, the feed amount is too large, and the feedless grinding time is too short;
2. The workpiece rotation speed is too high or the workpiece shaft and the grinding wheel shaft are excessively vibrated;
3. The grinding wheel is too thick or too soft;
4. The dressing speed of the grinding wheel is too fast or the clearance of the dressing mechanism is too large;
5. The diamond of the dressing wheel is not sharp or of poor quality;
6. The quality of superfine oil stone is not good, and the installation position is not correct;
7. The quality of superfine kerosene does not meet the requirements;
8. Super fine time is too short;
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