Reasons for the misregistration of offset printing machine and its elimination
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In the offset printing process, due to the paper-cutting mechanism of the offset printing machine, the paper-retaining baffle, the improper adjustment of the paper-carrying teeth, the paper brake, and the flatness and poor uniformity of the paper, it is easy to cause the paper-receiving machine of the offset press to receive the paper. The problem is that even the paper has a folding angle to fold the printed matter out of the print mark, which affects the quality of the product and brings trouble to the binding, finishing and counting of the printed sheet.
The quality requirements for the delivery of the offset paper receiving table are: transparent, flat, and flat, without folding angle, crushing loss and oily debris. Especially for the printing of semi-finished products, it is required that the tip and the bite, the upper and lower positions cannot be reversed, and the unrecognized and disordered phenomenon should be avoided as much as possible. There are several reasons for the improper delivery of the offset printing machine. The specific operation should be comprehensively checked and comprehensively analyzed to solve the problem.
1. The distance between the left and right or the front and back of the paper is too large, which is not suitable for printing the size of the paper, resulting in uneven delivery. At this time, adjust the telescopic position of the left and right or front and back paper baffles so that they are the same size or slightly larger than the size of the printed paper.
In addition, if the paper-cutting baffle of the front and rear of the paper-receiving table is not in the correct time, the printing paper will be hindered during the falling process, and it will not fall smoothly into the paper-receiving table, which will result in uneven paper delivery. The position of the plate control cam is such that the pendulum time is coordinated with the time of receiving the paper to ensure that the delivery is neat.
2. In the chain-type paper conveyor, the paper-feeding teeth are too early or too late, and the printed paper cannot be accurately entered into the paper-receiving table, and the problem of paper-receiving is also likely to occur. At this time, it is necessary to have a high-speed pick-up time for picking up the paper, so that the paper can enter the delivery table at the right time.
3. When the printed paper enters the delivery table, it will move upwards, resulting in uneven delivery. This is due to the stress difference of the printing paper itself, and on the other hand, due to the failure of the suction wheel of the printing brake or the suction of the suction wheel is too small. The failure of the suction wheel is the obstruction of the small hole in the wall of the suction wheel. The paper ash and dirt on the suction wheel can be cleaned and used. The suction of the suction wheel is too small to increase its suction force.
4. When the printing paper enters the delivery table, it will curl down and cause the paper to be picked up. This is mainly because the printing plate has too much moisture to make the front and back water content of the printing paper too large and cause printing. The amount of water, master the balance of ink and water, use the minimum amount of water without the dirty version to reduce the bending deformation of the paper. Thereby avoiding misfeeds.
5. Due to the quality of the paper, such as flatness and poor uniformity, the paper may cause the roll, the upturn, the bow, the wrinkles, the ruffles, etc. when the paper enters the delivery table, causing the paper to be misaligned. Before printing, the above-mentioned poor quality paper should be carefully hanged and conditioned. After hanging, it should be placed in the warehouse or offset printing workshop for storage for a period of time. The paperboard is covered with cardboard and pressed with heavy objects (large 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 during printing, it is often easy to pick up the paper. Since the offset printing paper is usually large (above four sheets of paper) and requires water to be used, the paper is too thin (eg 35 g/m2, 28 g/m2) from between the impression cylinder and the blanket cylinder. After one pass, the water is transferred to the paper through the blanket, the paper will be soft and stress-free, and it will be difficult to finish the delivery. Therefore, the offset paper should be kept at 52 g/m2 or more to ensure that the delivery paper is neatly received. .
7. The relative humidity of the workshop is too low, the water content of the paper is too small, and it is easy to generate static electricity, so that the papers are sucked together and the paper is not aligned. In this case, the static eliminator can be used to eliminate static electricity, or to increase the relative humidity of the workshop, especially in the winter when the weather is dry. If necessary, the humidifier can be used to adjust the humidity of the workshop. Moreover, the offset printing workshop should open the window less, the glass window should be sealed, and the water can be sprinkled on the floor of the workshop to adjust the humidity.