In the offset printing process, due to the offset mechanism of the offset press, the front and back, left and right paper sorting baffles, the collection of teeth, improper adjustment of the paper brake, and poor flatness and uniformity of the paper, it is easy to cause uneven paper collection on the offset printing machine The problem even caused the paper to fold into corners to fold the printed matter out of the impression, which affected the quality of the product and caused trouble for the binding, sorting and statistics of the printed sheets.
The quality requirements of the paper collection table of the offset printing machine are: full penetration, full collection, flat stacking, no angle, broken loss and oily debris. Especially for printing semi-finished products, it is required that the trailing edge and the bite, the upper and lower positions cannot be reversed, and try to avoid the irregular and disorderly paper collection. There are several reasons for the irregular paper collection of the offset printing machine. The specific operation should be comprehensively inspected and analyzed comprehensively to solve them in a targeted manner.
1. The distance between the left and right or front and rear paper stoppers is too large, which is not suitable for the size of the printed paper, resulting in uneven paper collection. At this time, adjust the telescopic positions of the left and right or front and rear paper sorting flaps so that they are the same as or slightly larger than the printing paper size.
In addition, if the swing times of the paper sorting plates on the front, back, left, and right sides of the paper collection table are incorrect, the printing paper will be hindered during the falling process and cannot fall into the paper collection table smoothly, which will also cause uneven paper collection. The board controls the position of the cam, so that its swing time is coordinated with the time when the paper is collected and the teeth are placed to ensure that the paper is collected neatly.
2. The paper collection teeth in the chain paper conveyor are too early or too late to allow the printed paper to enter the paper collection table accurately, and the problem of uneven paper collection is also prone to occur. At this time, it is necessary to collect the teeth of the paper at a high speed, so that the paper can enter the paper collection table in a timely manner.
3. The printed paper moves upward when entering the receiving table, resulting in uneven paper collection. This is due to the poor stress of the printed paper itself, on the other hand, it is caused by the failure of the suction wheel of the printing sheet brake or the suction wheel suction is too small. The failure of the suction wheel is that the small hole on the wall of the suction wheel is blocked. The paper dust and dirt on the suction wheel can be cleaned and used. If the suction wheel is too small, the suction power can be adjusted appropriately.
4. The printing paper curls down when it enters the receiving table, causing uneven paper collection. This is mainly due to the excessive moisture of the printing plate, which causes the water content of the front and back of the printing paper to be too large, which causes the printing plate to be properly maintained. Water volume, master the balance of water and ink, and use the minimum amount of water under the premise of not dirty version to reduce the bending deformation of the paper. So as to avoid uneven receipt.
5. Due to paper quality reasons such as poor flatness and uniformity, the paper rolls down, curls up, bows, wrinkles, and ruffles when the paper enters the receiving table, which causes uneven paper collection. Before printing, the above-mentioned poor-quality paper should be carefully hung and humidified. After hanging, it should be stored in a warehouse or offset printing workshop for a period of time. The paper stack is placed on the cardboard and pressed on heavy objects (big stones, iron) Board, etc.) to make it flat, the paper on the machine should be knocked to increase the stress of the paper.
6. If the paper is too thin when printing, it is often prone to uneven delivery. Because the offset printing paper is usually large in size (more than four sheets of paper) and needs to be dampened with water, if the paper is too thin (such as 35 g / m2, 28 g / m2), from the impression cylinder to the rubber cylinder After one pass, the moisture is transferred to the paper through the blanket, the paper will be soft and no stress, and it is difficult to collect the paper, so it is best to keep the offset paper at 52 g / m2 or more to ensure that the paper collection table is tidy .
7 The relative humidity in the workshop is too low, and the moisture content of the paper is too low, which is easy to generate static electricity, which makes the paper suck each other and the paper is unevenly received. In this case, a static eliminator can be used to eliminate static electricity, or to increase the relative humidity of the workshop, especially in dry weather in winter. If conditions permit, a humidifier can be used to adjust the humidity of the workshop. In addition, the offset printing workshop should open fewer windows, the glass windows should be sealed, and some water can be sprinkled on the floor of the workshop to play the role of humidity control.
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