Four-color offset press failure detection and elimination

There was a Pz4880-01B type four-color offset printing press. During the offset printing operation, there was a problem of overprinting and ghosting in the third color group. When the fault first appeared, it was not obvious. After two shifts were run, the above-mentioned poor conditions became more pronounced, and the ghosting became even more serious in the case of speeding up.
The cause of the above failure is difficult to judge for a time. There are many reasons for the occurrence of ghosting or overprinting in the offset printing process of a multicolor offset printing press. The two have similarities and differences. For example: paper deformation, resulting in curl and flanks; imprinting cylinder grippers lack of force, in the imprinting process of paper shift; these will lead to prints produce ghosting or overprinting is not allowed. However, the operating time of the former rules and side rules is not accurate. Inadequate positioning in the paper feeding process and unstable paper movement will result in inaccurate overprinting. Axial pulsation and vibration of the drum, improper lining of the squeegee roller causes excessive slippage between the rollers, abrasion of journals and linings of the printing plate and squeegee, or matching of the outer surface of the watt sleeve and the hole of the machine wall Loosening, causing instability and vibration in the operation of the roller will cause ghosting of printed products (some local ghost, some irregular positions or intermittent ghosting).
Due to the different causes of failures, there are differences in the occurrence of ghosting or overprinting failures. We have experience in the field of production operations and quality monitoring control. Therefore, in response to the failures, in the troubleshooting, we carry out the following checks and commissioning of each of the following items: 1. Replace the paper test for comparative analysis; 2. Adjust the lining thickness; 3. Adjust the plate cylinder according to the specifications. The pressure between the blanket cylinders; 4. Uniform correction to adjust the pressure of the impression cylinder's teeth; Make the force of the teeth consistent; 5. The uniformity of the outer surface of the ink roller of this color group (external circle diameter) detection, deviation Big change.
Through the above-mentioned treatments and tests, there has been little success.
In order to solve the problem, we further conducted meticulous inspections and monitoring of the operating conditions, and found that during the operation of the machine, an abnormal noise was heard at the end of the driving surface of the plate cylinder, and then the bearing was disassembled and the oblique cylinder was found. The bearing (model 2007116) is normal, and another set of rolling bearings (outer set, model 116) has been severely worn. The outer ring raceway of the bearing has a section of worn out ball that has been damaged by a damaged ball. . This discovery, we thought that we should find the crux of the problem. We immediately replaced the new bearing and started the test. The ghosting still exists, but the bad situation is only slightly improved. So where exactly is the underlying reason?
After observing, it was found that the ghost images produced at different speeds are indistinguishable from those of overprinting. Therefore, the machine is gradually accelerated from a low speed, and the noise and vibration conditions are monitored in each position (the third color group in the fault) and found in a fast state. The vibration of the plate cylinder has been significantly increased, and the ghosting of the printed product has also increased. Described in the operating process of the printing plate cylinder "abnormal" situation, this metamorphosis has a serious consequence of ghosting, which shows that the operating state of the plate cylinder and the cause of the fault. After shutting down, we checked the horizontal and radial run-out capacity of the plate cylinder and found that there was a larger change than the one checked before the start of the machine. This resulted in an abnormal deviation. This is particularly evident at the end of the drive side of the plate cylinder. So he checked at this end and found that the four screws fastened with the gears were broken and removed, leaving only one, and the rotation of the plate cylinder relied on the transmission of the gears, and the three fastened The broken screw causes the connection of the two transmission parts to be loosely fastened. In the rapid rotation, the rotational inertia of the plate cylinder increases, and the fastening by a single screw is obviously not stable and firm, which makes the roller's At one end, the center shift occurs, the drum in operation loses its balance, the vibration increases, and the pressure at both ends is uneven. In this case, it is inevitable that the images and images transmitted in the printing process are ghosted and misprinted. When the fault just occurred, the ghosting was not too serious. It was probably broken only one screw. After that, it continued to run. It broke off two branches again, causing the roller to become more unbalanced and the vibration increased, causing the bearing to end. The damage. After the root cause of the problem was found, the problem was completely eliminated after processing.
Through this time of failure analysis and elimination, we feel that in the course of maintaining the offset printing press, we must pay attention to the fastening parts of those key components. If there is any looseness or wear, we will handle it in time to eliminate hidden dangers. Especially for those kinds of sudden vibrations, abnormal sounds, ghosts, and rejection angles during the running process, the first thing to do is to check the fastening of the bearing and the key tightening position, and then calm down. Analyze the causes of failures, eliminate them step by step, and do not blindly adjust them. As a result, new failures will occur more and more disorderly. (Chen Jintai) (Guangdong Packaging 2000)