The aging of the equipment makes many printing faults also appear on the original high-precision Heidelberg offset press, especially after the domestic parts replace the imported parts, the fault phenomenon is particularly obvious. When using Heidelberg's 102V (started in 1986) and 102F (started in 1992) two offset presses to print 880mm × 540mm specifications, serious ink bar failure occurred, and the ink bar of each color group appeared at the mouth of the paper. At 540mm, and there is a particularly bright trace on the surface of the impression cylinder 540mm away from other surfaces, and the ink frame on the paper is exactly the same as the length and width of this trace. The operator took a lot of detours when troubleshooting this fault, but the problem was finally resolved. The troubleshooting process is described below for reference by colleagues.
Fault phenomenon
Heidelberg's two multicolor offset presses 102V and 102F have been printing paper of 780mm × 540mm size for many years. With the format of books and periodicals becoming more and more international, they have changed to printing paper of 880mm × 540mm size. When the operator used Heidelberg 102F to complete the overprint of magenta and yellow plates, he found that there was an ink bar about 80mm away from the trailing edge of the paper. At first, it was considered that there was a problem with the magenta group, so he checked the ink roller, ink roller and ink. Check the pressure between the roller and the printing plate, check whether the ink roller seat is worn and loose, and replace with a new blanket and liner according to the technical parameters. After the equipment is at the best speed, try printing again, and the ink frame still exists. . The operator changed the magenta version to another color set for printing, and the ink frame still exists. Due to the tight delivery time, the operator had to switch to Heidelberg 102V to print, unexpectedly whether the ink bar or the paper appeared in the same position. Therefore, the operator suspected that there was a problem with the film, so he changed the film in one direction and printed the test machine. As a result, the ink stick was still in the same position, so it was determined that the ink stick had nothing to do with the ink roller and the film.
Next, I started to check the mechanical aspects. When I put a printed paper with an ink bar on the front gauge and moved it into the printing color group for inspection, I accidentally found that the surface of the impression cylinder had a brighter trace than other surfaces. Exactly at the same position as the ink stick on the paper, the operator went to check other color groups and found that there was such a bright mark at the same position of each color group. In the past, these two Heidelberg presses mostly printed 780mm × 540mm paper. The impression cylinder had a certain degree of wear at a distance of 540mm from the gripper, which was determined to be an unsolvable "impression cylinder wear bar".
Troubleshooting
The two Heidelberg multicolor offset presses 102V and 102F have been used for more than 10 years, and the long-term three shifts and offset printing have increased the wear of the equipment. If the ink stick is caused by the impression cylinder, it means that the two devices can only print the prints below 780 × 540mm, so the operator decided to confirm again whether it is caused by the impression cylinder.
When visually and manually measuring the surface of the impression cylinder, the operator found that there were also bright marks on the left and right sides of the 780mm position of 780mm × 540mm, but when printing 880mm × 540mm specifications, there were circumferential marks on the paper. . Therefore, the operator first pressed the equipment and checked the roller pillow with a fuse. As a result, no abnormalities were found in the three rollers, and they all met the technical parameter requirements, and the gap was 0.05 ~ 0.06mm. Secondly, by using the plate cylinder, the relative position of the pattern is changed, but the ink bar is still at 540mm. Operators with the experience of using Heidelberg equipment know that the three-point floating type adopted by the pressure-combining mechanism has been adjusted before leaving the factory. The center distance between the three rollers has been adjusted and cannot be moved casually. The liner is not replaced every time a plate is installed like a domestic offset press, and the liner is not changed every time a plate is installed, but this time the operator decided to break the technical parameters specified in the Heidelberg manual. Peel off the liner tightly attached to the printing plate, wash off the glue on the surface of the printing plate cylinder, place the pressure gauge in the "0" position, and use a 4mm diameter fuse to compress the cylinder shell. Experimental results: The gap between the impression cylinder and the rubber cylinder is 3.2 mm, and the gap between the rubber cylinder and the plate cylinder is 3.65 mm. From the above data analysis, usually the blanket + pad thickness is 3.25mm, plus the printing paper thickness, the printing pressure is about 0.13mm, and the plate + pad thickness is 0.6mm, then the rubber cylinder and the plate cylinder The printing pressure between is 0.2mm, indicating that the printing pressure between the rubber cylinder and the plate cylinder is too large. Therefore, the operator reduced the thickness of the printing plate + pad to 0.5mm for trial printing, so that the printing pressure between the rubber cylinder and the plate cylinder was about 0.1mm. After the trial printing, the fault disappeared. The plate pads and rubber pads of the two Heidelberg presses are now used according to the above data, and the so-called "impression cylinder wear bar" of each color group has been eliminated.
Lessons Learned
The reason for the appearance of the circumferential 540mm ink stick is that for more than 10 years, most of these two offset presses have printed 780mm x 540mm offset paper textbooks from publishing houses. Due to the rough surface of the paper, the printing pressure used is relatively smooth with respect to the surface of the paper ( Such as coated paper, etc.) should be too large, so the gap between the plate cylinder and the rubber cylinder is small when the pressure is combined. For a long time, the cylinder gears of each color group will be subject to different degrees of wear at 540mm in the circumferential direction of the printing width. For 880mm paper, the same printing pressure will increase the gear vibration at 540mm, so the printing pressure needs to be readjusted.
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