2.2 Impression cylinder The impression cylinder is the most important cylinder in the printing unit. Its functions are: ①Support the paper and form the pressure to complete the printing. Through the role of the impression cylinder, its important position can be seen. The accuracy of the surface of the impression cylinder directly determines the rolling amount of the dot. If the accuracy of its surface is low, the dots will become imaginary and deformed. The accuracy of the paper transfer by the impression cylinder directly determines the overprint accuracy of the printed product. Therefore, in the printing process, it must always run stably. The time and displacement of the impression cylinder directly affect the time and displacement of the other two cylinders. In summary, there are two requirements for the impression cylinder: (1) The surface has high processing accuracy and can be consistent in work. When the impression cylinder leaves the factory, it needs to be ground. Under certain conditions, the surface of the drum needs to be treated to prevent it from being corroded by acids and alkalis and destroying its accuracy. (2) The operation is accurate and stable. All the rollers are tested for static balance before leaving the factory, and dynamic balancing can be done if possible. The purpose is to eliminate their own unbalanced factors first. Select high-quality materials to make the drum have high rigidity and strength, resist impact and vibration, and optimize the design to minimize the stress. The accurate and smooth operation of the impression cylinder can create good conditions for the balanced operation of the other two cylinders. 2.2.1 Analysis of paper movement on the impression cylinder What is the movement of paper in this part? Does it depend on the pressure of the dental tablets? This concept is incorrect. The paper passes from the register cylinder to the impression cylinder. To ensure the accuracy of the register, the original positioning accuracy must be maintained on the cylinder. On the roller, as long as the front position of the paper is consistent, its positioning accuracy will not be damaged. The dental sheet and the dental pad clamp the paper so that the front opening of the paper does not appear wave-shaped, even if it is in a horizontal plane. Therefore, the pressure of the teeth is to make the positioning relationship of the paper in the radial direction of the roller unchanged. So how can we ensure that the position of the front and back of the paper remains unchanged? In order to keep the front-to-back positioning relationship unchanged, there must be a force that hinders the relative movement of the paper and the roller. The obvious pulling and pushing forces are not visible from the roller, and the only force that can hinder the relative movement of the paper is friction. There are two conditions for generating friction: pressure and friction coefficient. The pressure (n) of the dental pad is just one of the conditions. The friction coefficient (u) on the surface of the dental pad has an important influence on the formation of friction, that is, f = n · u is the maximum static friction that hinders the relative movement of the paper on the surface of the roller force. Above this value, the paper will slide relatively on the roller surface; below this value, the paper will remain relatively still with the roller surface. In normal operation, the friction that hinders the relative motion of the paper must be less than its critical value. The wear of dental pads in actual work is one of the most powerful demonstrations of friction transmission. There are two ways to prevent the relative movement of the paper and the roller, one is to increase the pressure of the dental tablets. Increasing the pressure of the dental disc can increase its critical value f, but the greater the pressure of the dental disc, the greater the impact of opening and closing the tooth. Therefore, it is limited to increase f by adjusting the pressure of the dental disc; second, increase the coefficient of friction , Increasing the friction coefficient to increase the critical value f is a very effective measure. At present, many manufacturers are making efforts to increase the friction coefficient. 2.2.2 Analysis of the role and requirements of the impression cylinder in paper transfer The accuracy of the transfer of the impression cylinder must be absolutely guaranteed, which requires that its critical value f can always maintain the relatively static state of the paper. Because the impression cylinder needs to "peel" the paper from the rubber cylinder, the magnitude of this force is related to the graphic distribution on the surface of the printing plate, but in design, it can only be calculated based on the full plate. This requires sufficient friction at any point in the direction of the drum axis. According to the above analysis, from the perspective of paper transfer, there are the following requirements for the impression cylinder: 1. All dental pads are at the same level. This is a prerequisite for the flat positioning of the paper on the roller. Therefore, the pads of the impression cylinder cannot be adjusted or replaced at will. Generally, the dental pad of the impression cylinder is made non-adjustable. At the same time, after the dental pad is installed, it needs to be leveled with a grinder in the horizontal direction. It is usually required that the level error is within 0.3mm. 2. The pressure of all dental pads is the same. This is one of the conditions to ensure that the paper does not slide relatively anywhere on the roller. At the same time, the pressure is consistent, which also prevents stress concentration. Otherwise, when the pressure is inconsistent, the force of the individual springs is too large, and it may pop out during the process of opening and closing the teeth, causing machine accidents. 3. The friction coefficient of all dental pads is the same. This is another prerequisite for ensuring that the paper does not slide relatively on the roller. To ensure this prerequisite, it is required that the surface of the dental pad is not damaged, but when grinding on a grinder, the grinding amount of all dental pads is different. Some wear more and some wear less, because the height of the dental pad is inconsistent and there is an error, so that the friction coefficient of the surface of the dental pad may be inconsistent. This is an essential condition to ensure that the printed product does not appear local ghosting, dot slipping or wrinkling. 4. The opening and closing movements of all dental pads are consistent. If the opening and closing movements of the dental disc are inconsistent, there may be friction between some of the teeth and the pad, and others may not, resulting in uneven force on the front of the paper and printing failure. In summary, to ensure that the paper is accurately transferred on the surface of the impression cylinder, these requirements should be basically met, so this part must be regularly checked. The way to check is: ①Check the level of the dental pad with a dial indicator to see if it is consistent. Grow With Child Chair,Baby Seat,Infant Rocking Chair,Children'S Dining Chair Zhejiang Lamon Technology Inc. , https://www.baby-chair.com
â‘¡ Pass the paper.
â‘¢It is the benchmark for printing unit installation and debugging.
â‘¡ Check the indentation of the dental pad on the surface by visual inspection or offset paper, and see if the indentation is even.
â‘¢ Visually observe the time of opening and closing teeth to see if their movements are consistent.