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Process and requirements for processing joint bearings
2025-04-25
Joint bearings www.guan-Jie.comIn fine grinding, due to the high roughness requirements, the grinding marks on the surface of the task can often be seen with the naked eye. The following types of grinding marks are secondary:
The appearance of the bearing shows traces of interlaced spiral lines, which are mainly due to the poor flatness of the grinding wheel's generatrix and the presence of concave and convex phenomena. During grinding, the grinding wheel only makes partial contact with the bearing workpiece. When the workpiece or grinding wheel moves back and forth several times, interlaced spiral lines will appear again on the workpiece and can be observed by the naked eye. The pitch of these spiral lines is related to the speed and rotational speed of the workpiece table, as well as the non parallelism between the axis of the grinding wheel and the guide rail of the task table.
（1） The secondary reason for the formation of spiral lines
1. Poor grinding wheel dressing, corners not chamfered, and no coolant used to stop dressing;
2. The smooth guide rail of the task platform has too much oil, causing the task platform to float;
3. Poor precision of the machine tool;
4. Excessive grinding pressure, etc.
（2） The reason for the formation of spiral lines on the outer surface of bearings
The rigidity of the V-shaped guide rail is poor, causing the grinding wheel to shift during grinding,
Spherical Plain BearingJust the edge of the grinding wheel is in contact with the surface of the task;
When repairing noisy wheels, the task table's reversing speed does not fluctuate and the accuracy is not high, resulting in slightly less trimming of one edge of the grinding wheel;
3. Poor rigidity of the workpiece itself;
4. If there are broken and peeling sand particles and iron filings from the workpiece grinding on the surface of the grinding wheel, the repaired grinding wheel should be rinsed or brushed clean with cooling water;
5. The grinding wheel is not well trimmed, with some dents, etc.
The secondary reason for the appearance of fish scale like marks on the surface is that the cutting edge of the grinding wheel is not sharp enough, causing a "gnawing" phenomenon during grinding, which results in significant vibration.
The detailed reason for the formation of fish scale like marks on the surface of the workpiece is:
1. There are slag and oil stains on the surface of the grinding wheel;
2. The grinding wheel has not been rounded;
3. The grinding wheel becomes dull. The trimming is not sharp enough;
4. The diamond fastening frame is not sturdy,
Spherical Plain BearingDiamond shaking or diamond quality is not sharp enough;
5. Uneven hardness of grinding wheel, etc.
The secondary reason for the appearance of the task surface to reproduce the scratch marks is due to the coarse-grained abrasive particles falling off and being sandwiched between the workpiece and the grinding wheel.
The detailed reason why the surface of the workpiece is roughened during grinding is:
1. The marks left during rough grinding were not removed during fine grinding;
2. The filtration of coarse and large abrasive particles in the coolant is not clean;
3. When the coarse-grained grinding wheel is just finished, the abrasive particles are prone to falling off;
4. The data toughness is invalid or the grinding wheel is too soft;
5. Improper combination of abrasive toughness and workpiece material toughness.
There are straight waveform marks on the surface of the bearing workpiece. We cut a cross-section of the vertical axis of the ground workpiece and reduced it, and we can see that its periphery is approximately a sine wave. When the center of the sine wave moves along the axis without rotation or translation, the trajectory around the sine wave becomes a cylindrical waveform, also known as a polygon. The reason for the occurrence of a straight waveform is the absolute movement of the grinding wheel on the workpiece, or perhaps the periodic change in pressure exerted by the grinding wheel on the workpiece, which causes vibration. This type of vibration can be forced or self-excited, so there are often more than one direct wave frequency on the workpiece.
The detailed reason for the occurrence of straight waveform traces is:
1. The clearance between the grinding wheel spindle is too large;
2. The hardness of the grinding wheel is too high;
3. Poor static balance of the grinding wheel or dull grinding wheel;
4. The workpiece speed is too high;
5. The horizontal feed is too large;
6. Wear of grinding wheel spindle bearings,www.guan-jie.comExcessive clearance during cooperation leads to radial jumping;
7. Grinding wheel pressing mechanism or task table "creeping", etc.
The appearance of the workpiece often shows burn marks during the grinding process. There are several types of burns, one of which is a dark black patch along the direction of the grinding wheel; The second is in the form of lines or intermittent lines.
The surface of the workpiece is burned during the grinding process, which can be attributed to the following reasons:
1. The grinding wheel is too hard or the grain size is too fine, and the structure is too dense;
2. Excessive feed rate, lack of cutting fluid supply, and poor heat dissipation conditions;
3. The workpiece speed is too low and the grinding wheel speed is too fast;
4. Excessive vibration of the grinding wheel can cause burns due to occasional changes in grinding depth;
5. The grinding wheel is not adjusted in a timely manner or is not properly adjusted;
6. The diamond is sharp and the grinding wheel is not well trimmed;
7. The workpiece was burned too deeply during rough grinding, and the amount left for fine grinding was too small, resulting in no wear off;
8. Lack of clamping force or suction force on the workpiece, and the workpiece may experience stalling under the action of grinding force.
So how do we know if the surface of the workpiece can be burned during the grinding process? This can be reflected upon through regular acid washing.
After pickling, if the surface of the workpiece is damp, it should be visually inspected immediately under a diffuse light, and the normal appearance should be average dark gray. If it is a software point, cloud like dark black spots appear, and the perimeter is not fixed; If decarburization occurs, gray white or dark black spots will appear; If there is a crack during grinding, it will appear as a crack. If it is burned, there will be dark spots on the surface along the direction of the grinding wheel, and there will be lines or intermittent lines. If the above-mentioned burn phenomenon occurs during the grinding process, it is necessary to analyze the cause in a timely manner, take ineffective measures to deal with it, and eradicate mass burns.
The surface roughness of bearing parts does not meet the required standards and process requirements, but in grinding and ultra precision processes, due to various reasons, it often fails to meet the regular requirements.
The secondary reason for the surface roughness of the workpiece not meeting the requirements is:
1. The grinding speed is too low, the feed rate is too fast, the feed amount is too large, and the grinding time without feed is too short;
2. The workpiece speed is too high or there is excessive vibration between the workpiece shaft and the grinding wheel shaft;
3. The grain size of the grinding wheel is too coarse or too soft;
4. The grinding wheel dressing speed is too fast or the clearance between the repaired parts is too large;
5. The diamond used to repair the grinding wheel is not sharp or of poor quality;
6. Poor quality of ultra precision oilstone and incorrect device status;
7. The quality of ultra refined kerosene does not meet the requirements;
8. Insufficient precision time, etc.
During the grinding process of bearings, the surface of the task is stopped by a high-speed rotating grinding wheel. Therefore, if the operation and equipment adjustment are not stopped according to the operation instructions during grinding, various defects will appear on the surface of the bearing task, which will affect the overall quality of the bearing.
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