Personal analysis: ghosting failure in printing

Editor's note: The ghosting phenomenon in newspaper pages is a very common printing problem. There are many reasons for this printing quality problem, such as printing roller bearing problems, blanket problems, paper ink problems, printing pressure and paper tension problems, and even There are problems with fountain solution, they are likely to make the newspaper layout appear ghosting phenomenon. Now let's analyze the shadow failure together:
Symptoms: When the machine is printing normally, it will often give off an unusual crash sound, and then the printing layout will appear as a serious ghost phenomenon. When the crash sound disappears, the printed layout will return to normal. Due to this failure, a large number of waste reports are generated every day, resulting in no small economic losses.
According to the phenomenon that ghosting always accompanies the impact sound, it is possible to eliminate the possibility of layout ghosting due to problems with blankets, paper, ink, fountain solution, and paper tension, starting with the search for an unusual percussion sound. After several on-site inspections, it was only confirmed that the percussion sound was emitted by the printing tower, but its specific location could not be determined. As the UNISET main gearbox had gear breakage in the past, the main gearbox of the lower unit was opened first, and the gears were inspected and the cone gear was found to be intact. Then turn on the gear box of the upper unit and check everything is normal. Finally, the cover plates of the upper and lower unit transmission surfaces are opened one by one, and the working conditions of the drum transmission gear and the ink roller transmission gear are carefully checked. The result is also normal and no gear breakage occurs. The problem of the gear was eliminated, and the printing roller bearing and the printing pressure were checked. By checking the gap between the rollers and monitoring the sound emitted by each pair of roller bearings during printing, it can be judged that the printing roller bearing and the printing pressure are under normal conditions. Keep looking for this source of percussion.
In the ordinary maintenance, it is often found that a certain bearing in the ink roller system snaps and a printing abnormality occurs. Turn to check the working conditions of all the water rollers and ink rollers, and check whether the pressure between the roller and the roller meets the requirements. , And to check whether the bearings of all the rollers are damaged, no special abnormalities have been found.
Exclude the direct damage to all mechanical moving parts, consider whether it is because the instability of the electrical control elements leads to the instant loss of speed in the printing process, and the possibility of abnormal sounding of the mechanical parts. On the one hand, on the one hand, the speed display on the console is monitored for a long time, and on the other hand, the voltage and current changes on the main motor are detected. It was found that the speed of the machine and the voltage and current on the main motor basically all changed within a reasonable range and did not cause a crash sound. As a result, the carbon brush and the tachometer generator of the main motor continued to be tested. As a result, the carbon brush was almost normal, but it was found that there was a problem with the coupling between the tachometer and the main motor, and the spindle, keyway, and coupling of the tachometer generator. The inner hole keyway has more serious wear. Due to the existence of gaps, the feedback signal of the tachogenerator cannot accurately stabilize the speed of the main motor, thereby causing the speed of the printing unit to be unstable, causing the mechanical components to emit a crash sound, and eventually causing ghosting on the printing plate. Since there is no spare part, the tachogenerator and the coupling are temporarily fixed with fastening screws, eliminating the gap between them due to wear. After the printer was restarted, the sound of the impact was gone and the ghosting on the layout was eliminated.
Through the investigation of this example of failure, the cause of the printing screen ghosting was felt to be various, and the relative stability of the printing speed also played a key role in the quality of the printing layout.