The Reasons and Treatments of the Unacceptable Longitudinal Overprint in the Printing

Longitudinal misalignment with bilateral irregularity means that overprinting at the same time on the operating surface or the transmission surface is not allowed. There is no rule to follow on the wrong distance between the reticle and the standard line on the same printed sheet. Based on past printing experience, the causes and treatment methods are summarized as follows:

1. The two front gauges are not on the same line. There are differences between the two sides of the paper. This is due to improper operation. In the actual production work, the front gauge controls the bite rate of the bite teeth, and it is best to maintain a bite distance of about 5 mm on both sides. When adjusting the printing plate, the correct method is to use the pull plate to achieve the standard size of the document and positioning. If you do not pull the printing plate and adjust the front rule, the width of the two sides of the bite paper is different, making the paper contact the front rule. When it is not "line" but "point", the paper's impact is concentrated on two points. On these two points, the paper edge can not withstand the impact of the forward momentum and generate different degrees of curl, and at the same time, the paper thickness is not First, the frontal impact has caused a large or small, leading to the inconsistency of the frontal impact of the two points of the former regulations, resulting in vertical irregular registration is not allowed, this situation is more common in monochrome machines. The general treatment method is to re-adjust the standard of the pre-regulation jaw bite to 5mm, maintain a balance line, and then re-pull the plate.

2, swing teeth bite is too short. Swing bite teeth should be carried out in the static state when biting paper, so as to ensure the accuracy of biting paper, the rest time is controlled by the adjustment screw on the "backing", when the swinging bite teeth pendulum bar with "backing" "When in contact, the rollers on the connecting rod should be on the smallest face of the cam. The clearance is

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, it will be in an unstable state, and it is more likely to cause faults with no bilateral overprint. The general approach is to recalibrate the adjustment screws on the "back-up" so that the rollers maintain a clearance of 0.03-0.05 mm on the smallest face of the cam. When adjusting, two "backing" screws should be calibrated at the same time. First, loosen the lock nut, then turn the adjusting screw clockwise. Use a 0.05mm thick gauge to insert the test between the cam and the roller. Until it can be inserted tightly. At the same time, in order to prevent the inconsistency of the two "backing" screws, the machine should be re-introduced once. Two kraft papers of the same thickness are placed on the "backing" screw, allowing the machine to slowly turn until it leaves the kraft paper at the same time. Conformity is even better.

3. The distance between the swinging bite teeth and the embossing cylinder bite paper tooth is too short. According to the design of printing machinery, the period during which the high-speed machine swings and engages the paper-contacting roller contacts the cam is very short. In the case of the North High-speed Machine, according to the factory standard, the embossing roller bites the paper teeth when they bite, and the swing bites. When the paper teeth are open, it is 359°. It only needs to rotate by 1°. It is calculated based on the circumference of the drum, which is about 2.62mm. With such a short distance, the paper-bearing transfer operation is completed at high speed, which is obviously very short. 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 further reduced, it may happen that the swinging gripper teeth start to release, and the impression cylinder does not bite the paper teeth yet. The phenomenon of starting to bite the paper is also good at the slow transfer, but the high speed operation due to vibration and other factors caused by poor transfer caused by irregular overprint situation. Therefore, in terms of processing methods, based on the embossing cylinder bite paper teeth, the opening time of the swinging bite teeth should be extended as much as possible, and the opening teeth of the swinging bite teeth should be slowed down, so that after bilateral bite, the stamping will be imprinted. The roller can rotate 3~5mm distance to ensure the accuracy and stability of the transfer, but it should be based on the premise that after printing, it does not tear the paper and overprint accurately.

4, bite paper teeth bite too light. There are many reasons why the bite force of the bite paper teeth is too light or the bite force of the bite paper teeth is very large. Commonly, there are (1) the brace spring, the tensile spring or the metal fatigue (all the bite force is too light). (2) The gum pads go down (total or partial bite force is too light), (3) Loosen the fastening screws of the paper teeth (individual bite bite force is light), (4) "Backing the mountain" screw hits "backing" (all bite The force is too light), (5) The rigid tooth pad is smooth (most of the bite force is too light), and (6) The bite teeth are badly corrected (individual or most of the bite force is too light). Due to the above-mentioned various reasons, the bite-cutting teeth work abnormally, resulting in inaccurate longitudinal overprinting. The processing methods for the paper teeth produced by the above (1), (2) and (4) are all common sense operating standards. The (5) rigid tooth pads are too smooth and can be removed and polished. Afterwards, re-do the diamond strips or replace the teeth again. For (6) points, when correcting the bite force of the bite teeth, separate the two cases. When the overall correction is performed, first lay a 0.3mm thick piece of paper on the "backing" screw, and correct it from the center to the two sides. Separately, the latter pressure must not exceed the previous one. Individual calibrations should also check whether the “backing” gap meets the above criteria. If yes, continue to correct from the middle to both sides. If there is any bite in the middle of a biting tooth, Too heavy, can be adjusted before loosening.

5, bite paper teeth collision "backing." Before correcting the bite-paper force of the impression cylinder, it is first necessary to pad the "back-up" with a paper strip or thickness gauge with a thickness of 0.3 mm. When the teeth are leveled and the pressure is evenly distributed, remove the paper from the "backing" pad. At this time, the screws at the "backing" and "backing" are not touched, but sometimes the pads are worn out. Improper correction of biting paper teeth and irregular rotation during mechanical maintenance cause the "backing" and "backing" screws to collide with each other and affect the bite force of the bite teeth, resulting in inaccurate overprinting. Found that this situation should be identified as a "backing" screw factor, or a factor in paper teeth, and then treated separately. If the "backing" screw is not properly calibrated when repairing the machine, the "backing" screw should be readjusted. When the bite tooth pad below 0.5mm, should be raised or replaced with a new tooth pad to solve. If it is a violation of correcting the teeth, causing "bite teeth" collision "backing" should be re-correction teeth.

6, the embossing roller bite paper shaft or sleeve wear. After the embossing roller bites the paper shaft and the pendulum bite shaft or sleeve wears, the bite teeth are in an unstable state during the bite paper process, so that a bilaterally irregular longitudinal overprint is not allowed. This is the case. The low-speed machine is relatively easy to appear, because the impact force of the low-speed machine tipping bucket is large, and the rotation amplitude of the bite paper shaft is also relatively large. The high-speed machine adopts indirect delivery of the swing, and the width of the bite opening is also small. At the same time, due to the lubrication of the automatic cycle oil system, the bite shaft and the sleeve are not easy to wear, but pay attention to oil and oil. Blocked roads cause oil cut-off. The general approach is to remove the bite shaft or sleeve, re-machin the sleeve and install the correction.

7, the impression roller bite paper spring brace rupture. The springs that bite paper shafts require good toughness and sufficient supporting force, but they are prone to breakage due to problems such as steel quality and quenching. The retainer spring is placed on a thin iron, and even if it breaks, it does not fall. It is not easily noticeable and often overlooked. When more and more overprints are not discovered, they are sometimes used because the springs are used for a long time. Or they often change the weight printing of the papers. As a result, the stay springs lose their support or their forces cannot be restored for a moment. Regular overprint is not allowed. Therefore, once such a situation is found, the brace spring should be checked first to find that there is a lack of breakage or support; a new brace spring should be replaced.

8. Loosing or breaking of pins on pendulum shaft pendulum swinging bite teeth and embossing roller and embossing roller, swinging bite teeth shaft and indentation roller biting paper shaft ends with open teeth pendulum rods, pendulum rods and shaft pins Fastening, this pin is subjected to a relatively large force, so it is relatively easy to produce loose or broken and overprinting is not allowed. When checking this kind of situation, it should be scrubbed clean, then use a small crowbar to shake the swing rod to Check the situation of the pin at the same time, and observe whether the teeth of the paper catcher follow the movement. If the lever does not follow the movement, it can be determined that the pin is broken and it should be replaced with a new one. (author Liu Tiefu)