Bilateral irregular longitudinal overprint inaccuracy refers to the inaccurate overprint that occurs on the operation surface or the transmission surface at the same time. There is no rule for the distance between the cross line and the standard line on the same printed sheet. According to the past printing work experience, the causes and treatment methods are summarized as follows: 1. The two front gauges are not on the same straight line, and there are differences on both sides of the paper bite width, which is caused by improper operation. In the actual production work, the front gauge controls the bite width of the teeth, and it is best to maintain a bite distance of about 5mm on both sides. When adjusting the printing plate, the correct method is to use the pull plate to achieve the standard size of the graphic positioning. If you do not pull the plate and adjust the front gauge, there is a difference in the width of the bite on both sides, so that the paper contacts the front gauge The time is not a "line" but a "point". The paper's impulse is concentrated on two points. The paper edges cannot bear the forward impulse and produce different degrees of curl at these two points. At the same time, because the paper thickness is not First, the frontal impulse force is large or small, and the frontal impulse force at the two points of the front gauge is inconsistent and the irregular longitudinal overprint is not accurate. This situation is more common in monochrome machines. The general treatment method is to readjust the pre-regulation to make the bite reach the standard of 5mm, keep the balance consistent and present a line, and then pull the plate to solve it. 2. The stationary time of swinging teeth is too short. When swinging the paper bite, it should be carried out in a still state to ensure the accuracy of the bite. The rest time is controlled by the adjustment screw on the "backer". When the swinging bite block and the "backer" "When in contact, the roller on the connecting rod should be on the smallest surface of the cam with a gap of 0.03-0.05mm. If it is less than 0.03mm or there is no gap at all, it means that the rest time is too short or there is no rest time at all, and it will be unstable. In the state, it is easier to cause the failure of bilateral irregular overprinting. The general treatment method is to recalibrate the adjustment screw on the "backer" to keep the gap between the two at 0.03-0.05mm when the roller is on the smallest surface of the cam. When adjusting, two “backer†screws should be calibrated at the same time. First loosen the lock nut, then turn the adjusting screw clockwise, and insert a 0.05mm thick gauge between the cam and the roller until It can be inserted tightly. At the same time, in order to prevent the inconsistency of the weights of the two "backer" screws, the machine should be turned on and tested again. The kraft paper with the same thickness on both ends is placed on the "backer" screws, and the machine is slowly rotated. Consistent with the weight even if adjusted. 3. The distance between the swinging bite and the impression cylinder bite is too short. According to the design of the printing machine, the period of time that the high-speed machine swings the bite roller contacting the cam is very short. For the Beiren high-speed machine, according to the factory standard, the platen bite of the impression cylinder is 0 ° when the bite bite. When the paper teeth are opened, it is 359 °, and it only needs to be rotated by 1 °, which is calculated based on the circumference of the drum. It is about 2.62mm. With such a short distance, it is obviously very short to complete the paper bite transfer under high-speed operation. Of course, the transfer time can be adjusted to make it longer, but it should be based on the principle of not tearing the paper. If the transfer distance is reduced again, it may happen that the swinging bite begins to loosen, but the impression cylinder bite has not yet The phenomenon of starting to bite paper is also good at slow handover, but at high speeds due to vibration and other factors, the handover is not good and irregular overprinting is not accurate. Therefore, in the processing method, the opening time of the swinging teeth should be extended as long as possible based on the impression teeth of the impression cylinder, and the opening cam of the swinging teeth should be slowed down to make the impression after bilateral bite. The roller can rotate a distance of 3 ~ 5mm to ensure the accuracy and stability of the handover, but it should be based on the premise that the paper is not torn and the overprint is accurate after printing. 4. The bite force of paper bite is too light. There are many reasons for the bite force of the paper bite is too light or the disparity of the bite force of several paper bites. The common ones are (1) the spring. The tension spring is broken or the metal fatigue (all the bite force is too light). (2) The dental pad is lowered (all or part of the bite force is too light), (3) The fastening screw of the paper bite is loose (several few bite force is light), (4) The "backer" screw hits the "backer" (all bite) (The force is too light), (5) The rigid tooth pad is smooth (most of the bite force is too light), (6) The correction of the paper bite is poor (individual or most bite force is too light). Due to the above-mentioned reasons, the clenched teeth work abnormally, resulting in irregular longitudinal overprinting. The treatment methods for the paper teeth that are too light for the above (1). (2). (4) are some common-sense operation standards. The rigid tooth pads at (5) are too smooth and can be removed for overall polishing. Then re-do diamond stripes or replace a set of teeth. For (6) point, when correcting the bite force of paper bite, it should be dealt with separately in two cases. During the overall correction, first put a paper strip with a thickness of 0.3mm on the "backer" screw, then correct it from the middle, and separate it to both sides. The pressure of the latter should never exceed that of the previous one. For several corrections, you should first check whether the "backer" gap meets the above standards. If so, continue to correct from the middle to both sides. If there is an individual bite force in the middle of a bite If it is too heavy, it can be loosened and then corrected. 5. Crushing paper teeth hit the "backer". Before correcting the bite force of the platen of the impression cylinder, a paper strip or thickness gauge with a thickness of 0.3 mm should be placed on the "backer" first. When the bite teeth are leveled and the pressure is evened out, the paper pads at the "backer" are taken out. At this time, the screws at the "backer" and "backer" cannot be touched, but sometimes because the tooth pad is worn, Improper correction of the bite teeth, and illegal rotation during mechanical maintenance, causing the "backer" and "backer" screws to collide with each other, affecting the bite force of the bite and causing inaccurate overprinting. If you find this kind of situation, you need to find out whether it is the factor of the "backer" screw, or the factor of biting the paper, and then treat it separately. If the movement of the "backer" screw is not corrected when repairing the machine, readjust the "backer" screw to solve it. When the bite pads are less than 0.5mm, they should be raised or replaced with new ones. If it is a violation to calibrate the paper teeth, causing the "paper teeth" to collide with the "backer", the paper teeth should be corrected again. 6. The impression roller bite the shaft or sleeve worn. After the impression cylinder bites the paper shaft, the swinging paper shaft or the sleeve is worn, which makes the bite teeth in an unstable state during the paper bite process, so that bilateral irregular longitudinal overprinting is inaccurate. It is more likely to appear on low-speed machines, because the impact force of the tipping bucket of the low-speed machine is large, and the rotation range of the bite shaft is also relatively large. The high-speed machine adopts swing indirect paper delivery, and the opening of the bite teeth is also small. At the same time, due to the lubrication of the automatic circulation oil system, the bite shaft and sleeve are not easy to wear, but pay attention to the oil eye. The road is blocked and the oil is cut tight. The general treatment method is to remove the paper bite shaft or sleeve, re-machine the sleeve and install the correction. 7. The support spring of the impression roller bite is broken. The support spring of the paper bite shaft requires good toughness. The support force is sufficient, but it is often prone to fracture due to problems such as steel quality and quenching. The support spring is sleeved on the thin iron rod, even if it is broken, it will not fall, and it is not easy to be noticed by people and often overlooked. It was only discovered when more and more overprinting was not allowed, sometimes because the support spring was used for a long time, or the weight of the paper was often changed to print, so that the support spring lost the support force or the support force could not be restored for a while, and it would also cause bilateral failure. Regular overprinting is not allowed. Therefore, once such a situation is found, the brace spring should be inspected first and found to be broken or lack of bracing force; a new brace spring should be replaced. 8. The pins on the swing lever of the swing bite and impression cylinder bite shaft are loose or broken. The swing end of the swing bite cutter axis and the impression cylinder bite shaft is equipped with an open tooth swing lever, and the pin for swing lever and shaft Tighten, the force that this pin bears is relatively large, so it is easier to loosen or break and cause inaccurate overprinting. When checking this situation, you should first scrub it clean, and then use a small crowbar to pry the swing bar Check the condition of the pin at this place, and observe whether the paper teeth follow the movement. If you do not follow the movement when prying the swing lever, you can determine that the pin is broken and should be replaced with a new one.
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Reasons and treatment of irregular overprint in printing