Print Overprinting Failure Analysis (2)

The following analysis of these problems is based on the operation of the paper in the machine. And provide some solutions.

1. Misprints may occur due to problems that may occur during the feeding process of the feeder

The smooth and correct feeding of paper is the first step to ensure the accuracy of the overprinting of printed products, especially in the printing of multi-color prints on single and double-color printing presses.

(1) Usually the phenomenon that the paper has not reached the front defined bit line when the side rule is positioned is called “slow paper”, and there are many reasons for the slow paper. Here are some of the most common problems in actual production. analysis.
Cause 1: The suction force of the paper suction nozzle and the delivery nozzle is insufficient, resulting in the paper being unable to be properly conveyed by the feeder.
Solution: Increase the inspiratory volume or reduce the air pressure properly; regularly clean the air circuit (the suction chamber and the trachea are most likely to be blocked), and ensure the air path is smooth: regular maintenance of the air pump.

Reason 2: The rubber band of the suction nozzle is too small or too thin.

Solution: Replace the rubber band that separates the paper nozzles.

Cause 3: The presser foot and the nozzle of the paper separation nozzle (press the foot to the separated paper).

Solution: If the amount of undercut is too large, this is easy to happen, because once the foot is pressed to the depression, the distance between the paper nozzle and the paper stack is shortened, and the tail cannot be leveled. It will cause the presser foot to fall to the end of the paper.

Use a wedge or paper pad to flatten the paper. Then adjust feeder height.

Cause 4: The relative height of the presser foot and the suction nozzle is too small.

Solution: Reduce the height of the presser foot or increase the height of the paper nozzle.

Cause 5: The stack height is too low for the front block, and the transported paper is blocked, causing slow down.

Solution: The stack height should not be lower than the axis of the swing block axis of the front block, generally lower than the top block of the front block, 5~10mm. Feida is properly raised, and the actual increase is the detection device.

Cause 6: The pressure roller has fallen late.

Solution: Adjust the position of the pinch roller so that it will just fall down and press the paper when the paper is ejected by the delivery nozzle to stop suctioning but has not stopped inhaling. When the pressure stops, you can feel a certain tension. In fact, it is more reasonable to adjust the machine according to the angular position of the machine. Because feeder's paper feeding time should be adjusted based on the pressure roller, the other parts of the roller should be accurately adjusted, and the machine mechanism is different. It will also be different.

Cause 7: The roller has worn out.

Solution: Replace the pressure roller in time.

Reason 8: Feeder feeds too late with respect to the platen roller.

Solution: Under the premise of correct paper press time, adjust feeder's paper feed time according to the drop time of the paper roll. Refer to Cause 6 solution for specific time cooperation relationship. Beiren PZ4880-01 and Heidelberg SM series presses have installed a sprocket with adjustable relative position in the transmission box of Feida.

Cause 9: The tension on the tape is too small or the pressure on the platen is too light.

Solution: Tighten the straps or increase the pressure on the rollers. Machines that use vacuum conveyor belts will exhibit high air pressure, so it is important to increase the platen pressure appropriately.

Reason 10: The paper-feeding pad is too low, the height of the upper swing-type front gauge is too low, or the gauge of the hem-type front gauge is too close to the paper-transport board.

Solution: Adjust its position correctly, hand paper pad. The distance between the cover gauge on the front of the pendulum or the front sway of the hem shall be the thickness of the three sheets of paper or the thickness of the thick paper plus 0.2 mm.