Analysis of wear failure of roller bearings
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Roller bearings are one of the most critical parts of a press, and are directly related to the quality of the printing surface and the accuracy of the printing press. At present, the printing centers of major newspapers across the country have basically introduced internationally advanced newspaper web offset presses. Because of its high precision and high speed, the service personnel of the equipment manufacturers have replaced and repaired the roller bearings. With the improvement of the technical level of domestic equipment maintenance personnel, the printing centers of many newspapers in the country have begun to rely on their own technical strength to diagnose the roller bearings. Since 1995, the technicians of the factory have started exploratory work on the failure of the roller bearing of the rotary machine. Up to now, the roller bearings of the UNIMAN, UNISET and GEOMAN newspaper rotary offset printing machines of Manroland have been used. I have exchanged and repaired and accumulated a certain amount of experience. I would like to talk about a few points here.
In the high-speed printing process of the paper roller offset press, in addition to the high-speed rotation to ensure the completion of the printing task, the roller bearing needs to bear the heavy load and the mechanical impact caused by the printing pressure. High-speed operation, so the bearing material is prone to fatigue and malfunction. The roller bearings of the three models of the factory can be roughly divided into two types: one is the tapered roller bearing used by UNIMAN, and the other is the so-called three-ring bearing.
Wear type
Based on years of maintenance experience, the author found that there are three main types of roller bearing wear.
1. Stripping pitting
Due to the contact fatigue of the bearing bearing, fish scale-like peeling damage will occur on the raceway, and even the groove will be ground. This phenomenon is called peeling pitting. Figure 1 shows the wear photos of the GEOMN newspaper web offset roller bearings, where the deepest position of the groove can be above 0.2 mm.
2. Indentation bruise
In the high-speed rotation of the printing roller of the newspaper web offset press, the continuous impact of the plate mouth causes the roller bearing to bear a very strong radial impact force, so the roller of the bearing continuously and the rolling surface generate mutual impact for a long time. The pits are formed on the rolling surface, and the needle roller portion of the outer ring of the three-ring bearing is particularly noticeable. Figure 2 shows a photograph of the indentation and bruise on the three-ring bearing of the UNISET newspaper web offset press.
3. burn
When the roller bearing is short of oil or the internal clearance is too small, the bearing heat will cause the bearing material temperature to be too high and burns. When the burn phenomenon is serious, the bearing will be worn or bitten quickly, especially when the bearing is bitten, and the bearing will go away and the roller journal will also wear. This failure has occurred many times on our UNIMAN newspaper web offset press.
Inspection Method
After the roller bearing produces a certain amount of wear, it will be reflected in various aspects, and there are several common phenomena.
1. Generate ink stick
In the newspaper's layout, a certain color appears a light-colored ink bar that is light or even completely absent. In the case of severe wear and tear, the photo text may be blurred or not printed on the entire layout. When such a failure occurs, it is doubtful whether there is a problem with the roller bearing, but first of all, the factor of the rubber roller needs to be excluded.
2. Grinding
In the printing process of newspapers, when the printing durability of the PS plate is lower and lower than before, the grinding phenomenon is serious, and even when there is a cracking phenomenon, it is also suspected whether there is a problem with the roller bearing. In this case, it is first necessary to queue up the pressure of the rubber roller.
3. Increased machine vibration
When the roller bearing is in the normal state, the machine will emit a soft and uniform vibration sound; when the roller bearing wears, the vibration of the machine will increase. Especially in the roller where the wear occurs, if one end of one metal rod is placed on the journal of the operation side and the other end is attached to the ear, a strong impact sound is clearly heard.
4. Printing roller gap changes
If the roller bearing is worn, it is found that the printing pressure has changed by measuring the gap between the rollers with a standard feeler gauge. In particular, when the difference between the measured gap value and the standard value is 0.05 mm or more, it is particularly important to detect the working condition of the roller bearing. Of course, not all of the print cylinder gap changes are caused by the wear of the roller bearings, and sometimes it is possible that the eccentricity is offset. Pay special attention to this.
5. The circle on the surface of the drum is larger
When the roller bearing wears severely, the circular runout of the drum surface is usually above 0.04 mm, so the surface of the drum can be measured with a magnetic watch and a dial gauge to determine whether there is a problem.
6. Analysis with bearing fault detector
Now many testing instrument manufacturers have developed and produced bearing fault detectors. These instruments generally use the shock pulse technology or the method of detecting the oil film condition and lubrication state to monitor the roller bearing. Conditional manufacturers can apply this method for testing.
In addition, problems can be found by measuring the temperature of the outer surface of the metal at the roller bearing installation. In special cases, you can also find problems based on the different structural characteristics of the machine. For example, when the axial registration plate system of the GEOMAN newspaper web offset press cannot be smoothly adjusted, it is possible to indicate that the bearing of the plate cylinder is worn because the mechanical structure of the plate cylinder transmission surface determines the plate cylinder. When the bearing is worn out, it will affect the adjustment of the axial plate registration system.
In short, when judging whether the roller bearing is worn or not, it should be replaced by the above several conditions.
Cause of wear
Combined with the characteristics of newspaper printing, the wear of roller bearings mainly has the following reasons.
1. Normal fatigue wear
Any bearing will produce fatigue and wear, and it has a certain service life. Therefore, the wear of the roller bearing is also a normal phenomenon. Since the printing machine runs for a long time every day, after 5 years of operation, the roller bearing appears. Wear beyond the normal allowable range.
2. Long-term excessive printing pressure
During the printing process, some operators want to use a thicker liner paper in order to make the ink on the printed layout thicker. This invisibly increases the printing pressure and increases the bearing capacity of the roller bearing. Force accelerates wear.
3. Poor lubrication
Abnormal wear of the bearings is largely related to poor lubrication. The main purpose of lubrication is to allow the lubricant to form a dense protective film between the mutually rubbed metal surfaces, reducing the friction between them and delaying the wear progress. Therefore, when the lubrication line is not smooth or improper lubrication and poor lubricant are used, the bearing wear will be directly accelerated.
4. Machine tilted horizontally
It is easy to ignore the level of regular inspection of the press during the maintenance of the equipment. When the equipment is installed and operated for a period of time, it may cause the original adjusted machine to deviate in the horizontal direction due to vibration or foundation. If the deviation is too large, the roller bearing will be in the inclined working position, which will increase the axial force of the bearing and accelerate its wear.
Disputes and normal maintenance
When the roller bearing wears out, the printing quality of the newspaper can be maintained at the beginning by thickening the liner paper. However, when the wear is severe, the best solution is to replace the bearing in time to avoid further affecting the printing quality and other parts of the newspaper. Before replacing the roller bearing, it is necessary to carefully analyze the cause of the wear to determine whether there is abnormal wear. For example, the roller bearing of the UNISET newspaper rotary offset printing machine of our factory has a phenomenon that the needle roller of the three-ring bearing is rusted and the impression is hit on the raceway. After checking the structure of the roller bearing, it was found that the three-ring bearing was not provided with a sealing ring on the inner side of the wall panel. When the operator scrubs the blanket cylinder every day, the cleaning solution is often splashed on the wall panel, and then the cleaning solution slowly penetrates into the needle roller of the three-ring bearing to cause the rust to fail. Then, the sealing ring in the three-ring bearing is exchanged and installed on the inner side of the wall plate to prevent the penetration of the cleaning liquid. Practice has proved that this method works well, and basically no similar faults appear again.
After analyzing the cause of the roller bearing wear, it is necessary to pay attention to the regular inspection of the roller bearing during daily maintenance work. First, you can determine the working condition of the machine by checking whether the machine is level. Under normal circumstances, the system can be checked once a year. As long as the fitter level is placed on the reference drum, the drum is rotated, and several points are measured. The horizontal level of the integrated measurement should not exceed 0.06 mm/m, and the longitudinal level on the longitudinal reference surface should not exceed 0.1 mm/m. Second, check for lubrication problems. Check that the lubricant meets the requirements of the machine and that a lubricant containing extreme pressure and anti-wear additives should be used. In normal times, the oil should be regularly replenished in strict accordance with the requirements of the “machine operating instructions”. Pay attention to the preservation of the lubricant and do not cause it to be contaminated. For roller bearings that are lubricated with grease, if a centralized automatic grease supply method is not used, a special person is required to periodically add grease to the grease nipple. But pay attention not to add too much at a time, just use a common oil gun to spray 3~4. Lubricating oil in the gearbox of the transmission surface should be regularly taken to the oil supplier for inspection of its active ingredients and impurities. If it does not meet the requirements, it should be replaced immediately. Finally, adjust the printing pressure. Too small printing pressure will make the layout of the layout unrealistic, and too much printing pressure will also affect the layout, but the most important will increase the radial force of the roller bearing, thus speeding up the roller bearing wear. The speed reduces its normal service life. Therefore, proper printing pressure is an important part of balancing the relationship between print quality and roller bearing life.