When the author deals with a case of paper wrinkle failure, he checks the roller pressure and the time of tooth decay, and no abnormalities are found. The paper is also very smooth on the paperboard, and there is no phenomenon of "foil" or "tight edge". Replacing the roller pad, school leveling, uniform tooth strength, test machine printing, fold failure is still hidden. After many times of starting up, shutting down, and repeatedly debugging the squeaking force, it was found that most of the roller cavities were in a state of full clenching, but some were in a state of falsification, that is, unilateral cicadas were not tight. It seems that the cause of the malfunction is here. Sure enough, there is a slight gap between the worn shaft and the dental mouthpiece (it must be used to try it out). As a result, the copper bushings and stand-off bushings of the shaft were replaced, and the teeth and retest machines were evenly mixed. The failure was completely eliminated. Inspired by this, our company overhauled all the equipment that had this fault, effectively eliminated the wrinkle fault and ensured normal production.
Paper wrinkle faults are commonly referred to as wrinkle, crepe paper, and squeeze paper. When the grippers pinch the paper and roll between the rollers, airflow is generated on the paper. If the paper is evenly pressed by the rolling moment and the paper is pressed flatly, no wrinkles will be produced. If the paper displacement or the amount of deformation occurs momentarily, wrinkles will occur. Causes include uneven paper. Roller pressure is inconsistent or too large, loose teeth, etc.
Paper affected by the environment temperature and humidity, water content changes, easy to appear "foliage", "tight edge" and so on. If the paper is not printed in the direction of the taper, the folds are characterized by fine tapering on both sides. The general rule is that the pleats are similar. In order to avoid wrinkles, it is recommended that the paper be printed on the spot and printed before it is printed to increase the flatness of the paper or to cover it with a plastic cloth.
Caused by the equipment due to wrinkle failure, which is characterized by the direction from the mouth to the tip of the paper, there are pleats on both sides of the paper or in the middle, there are large and small, sometimes regular, and sometimes there is no law to follow.
Due to the wrinkle failure caused by the equipment, the author summarizes the solution to the following three aspects.
1. Check the roller pressure
Roller pressure should be adjusted according to the standard lining and standard pressure of the equipment. To ensure its accuracy, multiple measurements, multiple calculations, and repeated adjustments should be made. School "flat" drum is a necessary condition for the normal operation of the equipment, to eliminate excessive pressure between the drum and pressure inconsistencies in order to prevent excessive paper deformation and unilateral rolling. To ensure that the pressure between the impression cylinder and the blanket cylinder is less than the pressure between the plate cylinder and the blanket cylinder, the general contact width should be less than 2mm. Special attention should be paid to the fact that the rubber liner is prone to oil, water, and swell, which affects the pressure. At this time, it needs to be handled to ensure that the embossed ink stick is uniform. Replace the blanket in time to prevent it from losing its elasticity and causing it to wrinkle.
2. Check drum teeth
The basic requirement for roller cavities is that the dental pads are flat, the teeth are flush, and the force is uniform. The amount of stacking paper is controlled at 4 to 6mm, and the best is 5mm, and the amount of paper pick-up on both sides is the same. Should focus on checking roller shaft, braces fit clearance is excessive. If the gap is large, the crepe paper is unstable and the paper is easily displaced and wrinkles occur. This is the most important and direct cause of wrinkle failure. Therefore, it is the key to solve the wrinkle faults by ensuring that the tamping of the cavities is not caused by peristaltic deformation of the paper. Secondly, check whether the buckling brace spring is broken or elastic fatigue phenomenon, to prevent the blunt force is not enough, because the pimple is not tight and wrinkles. The force should be greater than the sum of the roller pressure and the paper peel force. Then check the paper transfer time, to avoid tooth decay and pull rules, point paper needles to fight paper, let paper, so that the paper out of control. In addition, if you use the upper swing delivery mechanism, you should carefully adjust to ensure a smooth transfer of paper.
3. Check other details
The printing area is often changed. It is easy for the roller to accumulate dirt and affect its flatness. It is necessary to clean up the dirt on the surface of the drum and the roller. To check whether the rules plate is bent, the paper is flat and natural on the paperboard. When the printing speed is too high, the unstable factors increase, and it is easy to cause the paper to wrinkle, so the printing speed should be adjusted properly. If the local area of ​​the printed product is too large or the ink is too thick and has a large viscosity, the local paper may be subjected to excessive force and wrinkle failure. The printing ink may be thinned or the printing process may be adjusted. Also check that the relevant screws or pins on the device are loose or broken.
The accuracy of the equipment must be kept under control. Under the combined pressure condition, whether the roller gear meshing clearance or the roller bushing allowance is within the standard of use, the wear status of the drum surface, etc., are all related to the paper wrinkle fault, which needs timely adjustment and overhaul.
To quickly solve the problem of paper folding, we must first be familiar with the principles of offset printing technology and mechanical principles, we must not only comprehensive analysis, but also to break the shackles of conventional experience and dare to innovate. For example, some offset printers use electric heaters to blow paper edge printing (using a small offset press); some improve the mechanical structure in order to better stabilize the delivery of paper and the transfer of paper. Finding the direct or indirect cause of paper wrinkles, adjusting or repairing them in time, and effectively controlling the static, dynamic, and static processes of equipment and printed paper can quickly resolve paper wrinkle failures.
Source: Shandong Wenshang Xinhua Printing Co., Ltd. (Hu Yongmin)
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