The main reason for the appearance of cross helix trace on the bearing surface is the poor flatness of the grinding wheel's bus and the presence of concave-convex phenomenon. During grinding, the grinding wheel only partially contacts the bearing workpiece. When the workpiece or the grinding wheel moves back and forth several times, the cross helix trace will appear in the workpiece performance and can be observed by the naked eye. The pitch of these helices is related to the speed of the workpiece and the speed of the workpiece, and is also related to the non-parallel of the grinding wheel axis and the table guide rail.
(I) Main causes of helix formation
1. Wheel dressing is not good, corners are not chamfered, and coolant is not used for dressing;
2. Excessive lubricating oil for the guide rail of the table causes the table to float;
3. Poor accuracy of the machine tool;
4. Excessive grinding pressure, etc.
(2) The cause of forming the spiral line on the bearing surface
1. V-shaped guide is not rigid. When grinding, the wheel is offset, only the edge of the wheel is in contact with the working surface;
2. When dressing the noisy wheel, the reversing speed of the table is not stable and the precision is not high, so that one edge of the grinding wheel is trimmed less;
3. Poor rigidity of the workpiece itself;
4. There are sand grains too broken and peeled on the grinding wheel and iron chip deposits under the grinding of the workpiece attached to the surface of the grinding wheel. For this reason, the dressing grinding wheel should be rinsed or cleaned with cooling water;
5. Bad dressing of grinding wheel, local bulge, etc.
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. At this time, the vibration is larger.
The specific reasons for the appearance of fish-scale marks on the workpiece surface are as follows:
1. Garbage and oil dirt on the grinding wheel surface;
2. Untrimmed grinding wheel;
The grinding wheel becomes blunt. Not sharp enough to trim;
4. The diamond fastening frame is not firm, the diamond is shaken or the diamond quality is not sharp;
5. Uneven hardness of grinding wheel.
The main reason for the appearance of the drawing marks on the surface of the working face is that the coarse particle is clamped between the workpiece and the grinding wheel after it falls off.
The specific reasons why the surface of the workpiece is pulled during grinding are as follows:
1. The marks left by rough grinding are not removed by fine grinding;
2. The coarse and micro abrasive particles in the coolant are not filtered cleanly;
3. When the coarse grit grinding wheel is just dressed, the grinding grains are easy to fall off;
4. Validity period of material toughness or too soft grinding wheel;
5. The toughness of abrasive particles is not compatible with the toughness of workpiece materials, etc.
The bearing workpiece surface has a straight waveform trace. We cross - section the vertical axis of the worn workpiece and enlarge it. Make its center along the axis without rotation translation, sinusoidal wave around the track is the wave cylinder, also known as the polygon. The cause of the straight waveform is the vibration caused by the movement of the grinding wheel relative to the workpiece or the periodic change of grinding pressure of the grinding wheel on the workpiece. This vibration may be either forced vibration or self-excited vibration, so there is often more than one direct wave frequency on the workpiece.
The specific reasons for the straight waveform trace are:
1. Large gap of grinding wheel spindle;
2. Grinding wheel is too hard;
3. Poor static balance of grinding wheel or dull grinding wheel;
4. The workpiece speed is too high;
5. The transverse feed is too large;
6. Grinding wheel spindle bearing wear, fit clearance is too large, resulting in radial runout;
7. Grinding wheel pressing mechanism or table "crawling", etc.
The surface of the workpiece is often burned during grinding. There are several types of burns. First, burns appear dark patches along the grinding wheel processing direction. The second is a line or intermittent line.
The surface of the workpiece is burned in the grinding process, which can be summarized as follows:
1. The grinding wheel is too hard or the grain size is too fine and the structure is too dense;
2. Too much feed, insufficient cutting fluid supply, poor heat dissipation conditions;
3. Too low workpiece speed and too fast grinding wheel speed;
4. The grinding wheel vibrates too much and burns because the grinding depth changes constantly;
5. Grinding wheel dressing is not timely or not well dressed;
6. Diamond is sharp and grinding wheel is not well dressed;
7. The burn is too deep during rough grinding, and the fine grinding reserve is too small to wear off;
8. The workpiece clamping force or suction is insufficient, under the action of grinding force, the workpiece stops.
Then how do you know whether the workpiece surface burns during grinding? This can be checked out by regular pickling.
After pickling the workpiece, when the surface is wet, it should be visually inspected under astigmatism lamp immediately. The normal surface should be uniformly dark gray. If the software point, it will appear cloud - like dark spots, and the boundary is indefinite; If decarburized, gray or dark spots appear; If the grinding process crack, the crack will be like a crack, if the burn, one is the surface along the grinding wheel processing direction appears dark patches, and the other is the line or intermittent line. If the above burn phenomenon occurs in the grinding process, the cause must be analyzed in time, and effective measures should be taken to solve the problem to prevent batch burn.
There are standard and technological requirements for the surface roughness of bearing parts, but in the process of grinding and superfinishing, the specified requirements are often not met for various reasons.
The main reasons for the workpiece surface roughness not meeting the requirements are as follows:
1. Too low grinding speed, too fast feed speed, too much feed, too short non-feed grinding time;
2. The workpiece speed is too high or the workpiece shaft and sand wheel shaft vibration is too large;
3. Grinding wheel particle size is too coarse or too soft;
4. Too fast dressing speed of grinding wheel or too large clearance of dressing mechanism;
5. The diamond of dressing grinding wheel is not sharp or of poor quality;
6. Ultra-fine whetstone is of poor quality and incorrect installation position;
7. The quality of ultra-fine kerosene fails to meet the requirements;
8. Ultra-fine time is too short, etc.
During the grinding process, the working surface of the bearing is ground by a high-speed grinding wheel. Therefore, if the equipment is not adjusted and operated according to the operating instructions, various defects will appear on the working surface of the bearing, which will affect the overall quality of the bearing.