In the grinding process of bearing, its working surface is ground by high-speed rotating grinding wheel, so if the grinding does not follow the operation instructions and adjust the equipment, there will be a variety of defects on the bearing working surface, so as to affect the overall quality of bearing.Bearing in the precision grinding, due to the high roughness requirements, the work surface of the grinding marks often can be observed by the naked eye surface grinding marks are mainly the following.
The appearance of cross helix traces
The main reason for the appearance of such trace is that the bus bar of the grinding wheel is of poor flatness and concavity. During grinding, the grinding wheel is only partially in contact with the workpiece. When the workpiece or the grinding wheel moves back and forth several times, the cross helix will be reproduced in the performance of the workpiece and can be observed by the naked eye.The pitch of these spirals is related to the speed of the workpiece, the speed of the workpiece, and the axis of the grinding wheel and the guide rail of the table are not parallel.
(1) the main reason for the formation of spiral
1. Poor dressing of the grinding wheel, unchamfered edges and corners, and dressing without coolant;
2. Too much lubricating oil in the guide rail of the workbench causes the workbench to float;
3. Poor precision of machine tool;
4. Excessive grinding pressure, etc.
There are causes for the formation of spiral lines
1. The rigidity of v-shaped guide is not good. When grinding, the grinding wheel produces deviation, and only the edge of the grinding wheel contacts with the working surface;
2. When dressing the noise wheel, the reversing speed of the table is not stable and the precision is not high, so that the dressing of one edge of the grinding wheel is slightly less;
3. The rigidity of the workpiece itself is poor;
4. There are sand particles on the grinding wheel that are too broken and peeled off and iron scraps from the grinding part are deposited on the surface of the grinding wheel. For this reason, the dressed grinding wheel should be washed or cleaned with cooling water;
5. The dressing of grinding wheel is not good, and there are local protrusions, etc.
Fish scales appear on the surface
The main reason for the appearance of fish scale marks 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.The specific reasons for the appearance of fish scale marks on the workpiece surface are as follows:
1. There are garbage and oil stains on the surface of the grinding wheel;
2. The grinding wheel is not trimmed;
3. Grinding wheel becomes blunt.The trimming is not sharp enough;
4. The diamond fastening frame is not firm, the diamond shakes or the diamond quality is not good and not sharp;
5. Uneven hardness of grinding wheel, etc.Working face hair
The main reason for reappearance of the scratch marks on the surface is that the abrasive particles are sandwiched between the workpiece and the grinding wheel after the coarse-grained abrasive particles fall off.The specific reasons for the surface of the workpiece to be pulled during grinding are as follows:
1. The traces left over from rough grinding are not worn off during fine grinding;
2. Coarse abrasive particles and small abrasive particles in the cooling fluid are not filtered cleanly;
3. The abrasive grains are easy to fall off when the coarse-grained grinding wheel is just dressed;
4. The expiry date of material toughness or the grinding wheel is too soft;
5. Improper coordination between abrasive toughness and workpiece material toughness, etc
The workpiece surface has straight waveform trace
We cut a cross section of the vertical axis line of the worn workpiece and magnify it.If the center is not rotated along the axis line, the track around the sine wave is the waveform cylinder, also known as polygon.The direct waveform is caused by the movement of the grinding wheel relative to the workpiece or the vibration caused by the periodic change of grinding pressure of the grinding wheel on the workpiece.This vibration may be forced or self-excited, so there is often more than one direct wave frequency on the workpiece.The specific reasons for the direct waveform trace are as follows:
1. Excessive clearance of grinding wheel spindle;
2. The hardness of grinding wheel is too high;
3. The static balance of the grinding wheel is not good or the grinding wheel becomes blunt;
4. The workpiece speed is too high;
5. Horizontal qi knife is too large;
6. The main shaft bearing of the grinding wheel is worn, and the clearance is too large, resulting in radial run-out;
7. Grinding wheel pressing mechanism or working table "crawling", etc.
Burn marks appear on the surface of the workpiece
The surface of the workpiece is often burned in the grinding process. There are several types of burns.The second is a line or intermittent line shape.The workpiece surface was burned in the grinding process, which can be summarized as the following reasons:
1. The grinding wheel is too hard or the granularity is too fine and the structure is too dense;
2. Too much feed, insufficient cutting fluid supply and poor heat dissipation conditions;
3. The workpiece speed is too low and the grinding wheel speed is too fast;
4. The vibration pendulum of the grinding wheel is too large and burns due to the constant change of grinding depth;
5. The dressing of grinding wheel is late or not good;
6. Sharp diamond and poor dressing of grinding wheel;
7. The workpiece burns too deeply during rough grinding, and the fine grinding retention is too small, so it does not wear off;
8. The clamping force or suction of the workpiece is not enough. Under the action of grinding force, the workpiece will stop.
Then how do you know if the workpiece surface is burning during grinding?This can be detected by regular pickling.After pickling the workpiece, when the surface is wet, it should be visually inspected under astigmatism lamp immediately. The normal surface is uniformly dark gray.If the software point, it appears as a cloud dark spot, and the boundary is variable;If it is decarbonized, it will show gray or dark colored spots.If the grinding process crack, the crack is like a crack, if burns, one is the surface along the direction of grinding wheel processing appears dark spots, the other is the appearance of lines or intermittent lines.Such as in the grinding process of the occurrence of the burn phenomenon, we must promptly analyze the cause, take effective measures to solve, to eliminate the batch burn.
The surface roughness is not up to the requirement
The surface roughness of bearing parts has the standard and technical requirements, but in the grinding and superfine process, because of a variety of reasons, often can not meet the requirements.The main reasons for the failure of the surface roughness of the workpiece are as follows:
1. Grinding speed is too low, feed speed is too fast, feed amount is too large, no feed grinding time is too short;
2. The workpiece speed is too high or the vibration of the workpiece shaft and the abrasive wheel shaft is too large;
3. Grinding wheel size is too thick or too soft;
4. Dressing speed of grinding wheel is too fast or clearance of dressing mechanism is too large;
5. The diamond for dressing the grinding wheel is not sharp or of poor quality;
6. The quality of ultra-fine stone is not good, and the installation position is not correct;
7. The quality of super-fine kerosene cannot meet the requirements;
8. Ultra-fine time is too short;