Causes and troubleshooting of ghosting failure in offset printing
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
Ghosting faults are common in offset printing for a variety of reasons. The operator can easily eliminate the fault according to different fault phenomena. In the printing process, the author has encountered a relatively special ghosting fault, which is described below, for peer reference only.
Trouble phenomenon: When the two-color machine starts printing after the school version is finished, or when the printing is stopped after the machine is stopped, the ink color of the first 20 sheets is deepened, and then the ink color gradually becomes stable, and the ink color deepening occurs irregularly during the normal printing process. . This phenomenon is not obvious when printing live parts; when the printing screen is live, the ink of the entire sheet is irregularly agglomerated, or occasionally one sheet of ink is particularly deep. Observed with a magnifying glass, there is a virtual point around the solid dot. This is a typical ghosting fault. This phenomenon occurs mostly in the previous color version. In order to verify whether there is a problem with the machine, we changed the upper and lower color sequence. Although the situation is slightly improved, there is still a phenomenon that the ink color of a certain sheet suddenly becomes deeper.
Troubleshooting
As usual, check pressure, lining and blankets, etc., all within the technical requirements. At first, it was suspected that the bearing of the impression cylinder was damaged, but the two color groups sharing one impression cylinder did not have a ghost phenomenon at the same time. In the case of unresolved problems, it is only necessary to continue to use the machine to focus on printing the field work, and to hand over the screen to other machines.
In the subsequent printing process, the machine suddenly made a "beep" noise. Emergency stop check, slowly move the machine at the position of the console, listen to the sound of the sound, and carefully observe the operation of the drum. It was found that the rubber cylinder of the upper color group had obvious axial turbulence, and the hub of the drum collided with the wall part, and an abnormal sound was emitted. Open the operating side cover and find that the shaft end thrust nut is loose. Position the roller in the center position, lock the thrust nut, turn it on again, the abnormal sound disappears, and the darkening phenomenon disappears when the printing is started, and the fault is eliminated.
Cause analysis
The axial sway of the rubber cylinder of the previous color group is the main cause of ghost failure. The plate transfers the print to the blanket. The paper can only transfer about 85% of the ink from the blanket, and a small amount of ink remains on the blanket. If the next impression is imprinted, the blanket will be axially twitched. Then, the imprint cannot overlap with the front, and thus a ghosting failure occurs. Since the two color groups share one impression cylinder, in the case of two color overprinting, the imprint of the first color group inevitably has a small amount of ink transferred to the second color group blanket cylinder through the paper, so even if the ink is changed, The color sequence of the lower color group, the ghosting fault still exists. When printing live parts, because the color of the ink itself is thick, even if a ghosting failure occurs, it is difficult to detect, basically does not affect the quality of the print, unless there is a reverse word on the layout.
In summary, the operator should regularly maintain and maintain the offset press, and try to avoid the machine running under problem, so as to improve the quality of the printed product and extend the service life of the machine.