In the grinding process of the bearing, its working surface is ground by the high-speed rotating grinding wheel, so if the grinding does not follow the operating instructions and adjust the equipment, there will be a variety of defects on the bearing working surface, which will affect the overall quality of the bearing.Bearing in precision grinding, due to high rough requirements, the grinding surface grinding marks can often be observed by the naked eye its surface grinding marks are mainly the following.

There are cross helix marks

The main reason for the appearance of such marks is that the bus bar of the grinding wheel has poor flatness and concavity. During grinding, the grinding wheel only partially contacts 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 and the rotational speed of the workpiece. It is also related to the fact that the axis of the grinding wheel and the guide rail of the table are not parallel.

(1) the main reason for the formation of the spiral

1. The grinding wheel is not properly dressed, the edges and corners are not chamfered, and coolant is not used for dressing;

2. Too much lubricating oil for table guide rail causes the table to float;

3. Poor accuracy of machine tools;

4. Excessive grinding pressure, etc.

(2) there are reasons for the formation of the spiral

1. The rigidity of v-shaped guide is not good. When grinding, the grinding wheel has deviation, and only the edge of the grinding 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, which makes the dressing of a certain edge of the grinding wheel slightly less;

3. Poor rigidity of the workpiece itself;

4. There are too broken and peeled sand particles on the grinding wheel and iron filings from the workpiece grinding 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 the grinding wheel is not good and there are some local bumps.

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, so the vibration is large.The specific reasons for the appearance of fish scale marks on the surface of the workpiece 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 is shaken or the quality of the diamond is not good or sharp;

5. Uneven hardness of grinding wheel.

Face drawing

The main reason for the appearance of the scratch marks on the surface is that the coarse particle is sandwiched between the workpiece and the grinding wheel after the coarse particle falls off. 

The specific reasons why the workpiece surface is pulled during grinding are as follows:

1. Traces left over from rough grinding are not worn off during fine grinding;

2. Coarse abrasive particles and small abrasive particles in the coolant are not filtered cleanly;

3. The abrasive grains are easy to fall off when the coarse-grained grinding wheel is first dressed;

4. The validity of material toughness or the grinding wheel is too soft;

5. Improper combination of 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. We can see that its periphery is similar to sine wave.Make its center along the axis line without rotation and translation, the track around the sine wave is the waveform cylinder, also known as polygon.

The cause of the straight waveform is 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. Too high hardness of grinding wheel;

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 is too big

6. The main shaft bearing of the grinding wheel is worn, and the clearance is too large, resulting in radial runout;

7. "crawling" of grinding wheel pressing mechanism or working table, etc.

Burn marks appear on the surface of the workpiece

Workpiece surface in the grinding process is often burned, there are several types of burns, one is the burn along the grinding wheel processing direction, dark spots;The second is the line or intermittent line shape.

The workpiece surface was burned in the grinding process, which can be summarized into the following reasons:

1. The grinding wheel is too hard or the particle size 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 constantly changing grinding depth; 

5. The dressing of the grinding wheel is delayed or not done properly;

6. Sharp diamond, poor dressing of grinding wheel;

7. The workpiece was burned too deeply during rough grinding, and the fine grinding capacity was too small to be worn off;

8. Workpiece clamping force or suction is not enough, under the effect of grinding force, the workpiece has stopped phenomenon.

How do you know if the workpiece surface is burned during grinding?This can be detected by regular pickling.

After pickling the workpiece, when the surface is wet, it should be visually examined under astigmatism lamp immediately. The normal surface is uniformly dark gray.If the software point, the cloud will appear dark spots, and the boundary is not round;If it is decarbonized, it will appear gray or dark colored.If the grinding process cracks, the cracks are in the form of cracks, such as burns, one is the surface along the direction of grinding wheel processing 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 standard and technological requirements, but in the grinding and superfinishing process, due to a variety of reasons, often can not reach the specified requirements.The main reasons why the surface roughness of the workpiece fails to meet the requirements 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 sand wheel shaft is too big;

3. The particle size of grinding wheel is too thick or too soft;

4. The dressing speed of grinding wheel is too fast or the clearance of dressing mechanism is too large;

5. The diamond used 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 refined kerosene is not up to the requirements;

8. Super precision time is too short;