The author had relocated a Czech ADAST 745P/A four-color four-color offset printing press. After the machine was moved to a new factory, the customer requested that all the ink rollers and the uniform ink roller and the gears on the magenta and cyan color groups should be changed. Become new, start testing after installation.
The prototype of the test machine is a monochromatic flat screen. The flat screens printed by the yellow, black and blue color groups are all normal. The screens are neat and full, but the proofs of the magenta group have an obvious ink bar at 270 mm from the mouth. And the location is fixed.
According to past maintenance experience, the first judgment is the gear bar, which may be caused by deformation of the gear teeth of a certain transmission gear. As a result, the gears on the plate cylinder, the blanket cylinder, the impression cylinder, and the adjacent transfer cylinders were carefully examined and all gears were found to be intact. Will it be caused by just a dozen or so small gears? Because if the pinion caused by the pinch, it should be a few evenly spaced fine ink, rather than a fixed position of the coarse ink.
As a result, attention was shifted to the printing roller. This type of machine has two water rollers. When the plate roller falls, it should always rest on the plate cylinder. However, at the roller gap, the position of the water roller will be slightly close to the cylinder body. If the pressure is too great, then Can cause the water roller to jump. Will this ink stick be caused by the runout of the plate roller? We have reduced the pressure of the two water rollers, but the ink stick is still there after the printer is turned on again.
Since adjusting the pressure of the reversing water roller is invalid, only the reprinting roller can be tried again. Each set of this machine has four print rollers, which may also result if the pressure is too high. Thus, the pressure of the four relies on the edition of the ink roller was reduced and the test was printed. The failure was still not eliminated. Later, only three of them were unloaded, leaving only one to be printed on the printing roller. The printed product still had an obvious ink bar and there was no change in position.
Is it caused by excessive pressure between the plate cylinder and the blanket cylinder? Because the plate cylinder and the blanket cylinder of this machine roll the rollers, the standard gap between the two cylinder bodies is 2.45mm, under normal conditions. The thickness of the plate is 0.3mm, the thickness of the plate cylinder liner is 0.15mm, the thickness of the blanket is 1.95mm, and the thickness of the blanket cylinder liner is also 0.15mm, so that the total thickness is 2.55mm, all the linings are printed The compression is 0.1mm, just to meet the transfer requirements. Then, is this color group padded according to the standard? Remove the plate and blanket, measure the liner of both, and find that the thickness is 0.2mm, so that the total lining thickness reaches 2.65mm. The total amount of compression is 0.2mm, which is very likely to result in the production of this ink stick. So the two cylinder liners were replaced with 0.15mm thick, and the printer was turned on again. The ink stick was really gone.
The elimination of this failure led the writer to realize that any problems encountered in the future must be broadened, and should not be limited to one-sided reasons. Only in this way can the problems be solved.
Source: Printing Talent Community