Analysis of the impression cylinder of the hottest

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Analysis of the embossing cylinder of the offset press

2.2 embossing cylinder

the embossing cylinder is the most important cylinder in the printing unit. Its functions are:

① supporting the paper to form pressure to complete printing

② transfer paper

③ is the benchmark for the installation and commissioning of the printing unit

its important position can be seen through the function of the embossing cylinder. The surface accuracy of the embossing cylinder directly determines the "quantity" of the point. If the accuracy of its surface is low, the points will be virtual, deformed, etc. The accuracy of the paper transfer of the imprint cylinder directly determines the overprint accuracy of the printed matter. Therefore, it must always operate stably in the printing process. The time and displacement of the impression cylinder directly affect the time and displacement of the other two cylinders. Generally speaking, there are two requirements for the imprint cylinder:

(1) the surface has high machining accuracy and can be consistent in work. When the embossing cylinder leaves the factory, its surface needs to be ground. If possible, the surface of the drum needs to be treated to prevent acid and alkali corrosion and damage its accuracy

(2) the operation is accurate and stable. All rollers are tested for static balance before leaving the factory, and dynamic balance can be carried out if conditions permit. The purpose is to eliminate its own imbalance factors first. Select high-quality materials to make the drum have high stiffness and strength, resist impact and vibration, and optimize the design to minimize the stress. The accurate and stable operation of the embossing cylinder can create good conditions for the balanced operation of the other two cylinders

2.2.1 analysis of the movement of the paper on the impression cylinder

what is the movement of the paper in this part? Is it the pressure of dental tablets? This concept is incorrect. The paper is transferred from the registration cylinder to the imprint cylinder. In order to ensure the overprint accuracy, 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 tooth slice and tooth pad clamp the paper, mainly so that the front mouth of the paper does not appear wavy, even if it is in a horizontal plane. Therefore, the pressure of the dental film is to keep the positioning relationship of the paper in the radial direction of the drum unchanged. So how can we ensure that the position of the front and back of the paper remains the same? In order to keep its front and rear positioning relationship unchanged, there must be a force that prevents the relative movement of the paper and the drum. There is no obvious tension and thrust from the drum, and the only force that can hinder the relative movement of the paper is friction. There are two conditions for friction: pressure and friction coefficient. The pressure (n) of the dental pad is only one of the conditions. The friction system on the surface of the dental pad is cellene particles, which do not contain silica gel, latex, phthalates or halogens. The formula number (U) 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 paper on the surface of the drum. Beyond this value, the paper will slide relatively on the surface of the drum; Below this value, the paper will remain relatively stationary with the surface of the drum. In normal operation, the friction that prevents the relative movement of the paper must be less than its critical value. As the core component of electro-hydraulic servo control, tooth pad wear in practical work is the most powerful demonstration of friction transmission

there are two ways to prevent the relative movement between the paper and the roller. One is to increase the pressure of the dental film. Increasing the pressure of dental slices can increase its critical value f, but the greater the pressure of dental slices, the greater the impact of opening and closing teeth, so it is limited to increase f by adjusting the pressure of dental slices; The second is to increase the friction coefficient. Increasing the friction coefficient to improve the critical value f is a very effective measure. At present, many manufacturers are making an issue of increasing the friction coefficient

2.2.2 analysis of the role and requirements of the imprint cylinder in paper transfer

the accuracy of the paper transfer of the imprint cylinder must be absolutely guaranteed, which requires that its critical value f can always maintain the relative static state of the paper. Because the embossing cylinder needs to peel the paper off the rubber cylinder, the magnitude of this force is related to the graphic distribution on the surface of the printing plate, but in the design, it can only be calculated according to the full plate. This requires that there must be sufficient friction at any place in the direction of the drum axis. According to the above analysis, from the perspective of paper transfer, popularizing the knowledge of green packaging and recycling has the following requirements for the imprint cylinder:

1 All dental pads are level. This is a prerequisite for the plane positioning of the paper on the drum. Therefore, the tooth pad of the impression cylinder cannot be adjusted or replaced at will. Generally, the tooth pad of the impression cylinder is made into an adjustable one. At the same time, after the tooth pad is installed, the horizontal direction needs to be leveled with a grinder. Generally, the levelness error is required to be 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 drum. At the same time, the same pressure can also prevent stress concentration. Otherwise, when the pressure is inconsistent, the force of individual springs is too large, which may pop up in the process of opening and closing teeth, causing machine accidents

3. The friction coefficients of all dental pads are the same. This is another prerequisite to ensure that the paper does not slide relatively on the drum. To ensure this prerequisite, the surface of the tooth pad is required not to be damaged, but when grinding on the grinder, the grinding amount of all tooth pads is different. Some grind more and some grind less, because the height of the dental pad is inconsistent, there is an error, which may make the friction coefficient of the surface of the dental pad inconsistent. This is an essential condition to ensure that prints do not appear local ghosting, dot slippage or pleating

4. All dental pads have the same action of opening and closing teeth. If the opening and closing actions of dental slices are inconsistent, there may be friction between some teeth and dental pads, while others do not, resulting in uneven stress on the front mouth of the paper and printing failure. To sum up, these requirements should be basically met to ensure the accurate transmission of paper on the surface of the embossing cylinder, so this part must be checked regularly. The inspection method is:

① check the level of the dental pad with a dial indicator to see whether its level is consistent

② check the indentation of the dental pad on its surface by visual inspection or with offset paper to see whether the indentation is uniform

③ visually check the time of opening and closing teeth to see whether their actions are consistent

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