Reasons and elimination of uneven delivery in offset press

In the offset printing process, due to the offset mechanism of the offset printing press, the front and rear sides of the offset press, the improper handling of the paper baffle, the improperly adjusted paper brakes, and the flatness and flatness of the paper, etc., may easily cause the offset of the offset press delivery table. The problem is that even the corners of the paper appear to fold the prints out of the prints, affecting the quality of the products, and causing troubles for binding, sorting, and statistics of printed sheets.

The quality requirements for the delivery press of the offset printing press are: looseness, good balance, flat stacking, no angling, crushing, loss and oil debris, especially semi-finished printing products, requiring dragging and nipping, top and bottom The position cannot be reversed. Try to avoid irregularities and chaos. There are several reasons why offset presses do not neatly receive paper. When performing specific operations, they must be comprehensively inspected and comprehensively analyzed and targetedly addressed.

1, left and right or before and after the rational paper baffle distance is too large, not suitable for printing paper format size, resulting in uneven delivery. In this case, adjust the stretching position of the left and right or front and back paper stoppers so that they are the same or slightly larger than the print paper size.

In addition, if the swinging time of the right and left flaps of the paper damper is not correct, the printing paper will be hindered during the falling process, and it will not be able to fall into the receiving position smoothly, which may also result in the delivery being uneven. The position of the control flapper control cam should be adjusted so that its swinging time is coordinated with the timing of the delivery of the gripper to ensure that the delivery is neat.

2. The delivery of teeth in the chain-type paper feeder is too early or too late to allow the printed paper to accurately enter the delivery table, and it is also prone to the problem of uneven delivery. At this time, it is necessary to adjust the time for the teeth to reach the receiving end so that the paper can enter the delivery table at a proper time.

3. The printed paper moves upwards when it enters the delivery table, resulting in uneven delivery. This is due to the poor stress of the printed paper itself, and on the other hand due to the failure of the suction wheel of the print brake or the suction of the suction wheel being too small. The failure of the suction wheel is the obstruction of the hole in the suction wheel wall. The paper dust and dirt on the suction wheel can be cleaned and used. If the suction wheel is too small, the suction force can be adjusted appropriately.

4. When the printed paper enters the delivery table, it curls downwards and causes the delivery to be uneven. This is mainly due to the fact that the water in the printing plate is too much and the water content on the front and back of the printing paper is too large. When printing, it is necessary to appropriately reduce the amount of water in the plate layout, grasp the balance of water and ink, and use the least amount of water in the premise of not compromising the plate to reduce the paper's bending deformation. In order to avoid paper delivery.

5, due to paper quality reasons such as flatness, poor uniformity, often lead to the paper into the delivery table when the next roll, upturned, bow, wrinkle, lotus leaf and other phenomena, resulting in uneven delivery. Before the printing, the above-mentioned poor-quality papers should be carefully treated with hanging and drying humidity, stored in a warehouse after being hanged, or stacked and stored in the offset printing shop for a certain period of time. The cardboard box should be put on cardboard and the heavy objects (large stones, iron) should be pressed. Plates, etc.) to make it flat, the paper on the machine to knock processing to increase the paper's stress.

6, if the paper is too thin when printing, it is often prone to paper delivery. Since the offset printing paper web is usually large (above four sheets of paper), at the same time the need for water dampening, the paper is too thin (Figure: 35g/m2, 28g/m2), from between the impression cylinder and the blanket cylinder After one pass, the water is transferred to the paper via the blanket, and the paper will appear fluffy and weak. It will be difficult to close the delivery. Therefore, it is best to keep the offset paper at 52 g/m2 or more in order to ensure that the delivery table receives the paper neatly.

7, the relative humidity of the workshop is too low, the water content of the paper is too small, it is easy to produce static electricity, so that the paper sucks each other and the paper is not received. In this case, static electricity can be used to eliminate static electricity, or to increase the relative humidity of the workshop, especially when the weather is dry in winter. If conditions permit, humidifiers can be used to humidify the workshop. In addition, the offset printing shop should have fewer windows, the glass windows should be sealed, and some water can be sprinkled on the floor of the workshop to control the humidity.