The improvement of the printing speed of the most

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The improvement of the printing speed of the sheet fed offset press has brought about the continuous development of the paper transfer mechanism

what kind of paper transfer mechanism is used in the sheet fed offset press has a great relationship with the printing speed, registration accuracy and print quality of the offset press

after the paper is positioned by the front gauge and the side gauge, it stops still on the paperboard and waits to enter the printing unit. The next thing to do is to accelerate the stationary paper to the linear speed equivalent to the rotation speed of the surface of the embossing cylinder, and the paper teeth of the embossing cylinder bite the paper and rotate it for printing. This process of accelerating the paper from the static state to the linear speed on the surface of the embossing cylinder is called the paper acceleration process. This set of mechanism is called the paper acceleration mechanism, which is commonly referred to as the paper delivery mechanism

many low-speed machines, such as 0l machine (J2101 split monochrome machine), which is very familiar to insiders, adopt the method of directly accelerating the delivery of paper. The paper advancing on the paper board is blocked by the front stop gauge. After being positioned by the front gauge and side gauge, it stops on the paper board. The paper teeth on the embossing cylinder turn over an angle of about 130 degrees at the moment of passing through the junction point, bite the paper, and bring the paper to the printing unit. The disadvantage of this paper delivery method is that when the paper stops on the paperboard, the speed is zero, and suddenly accelerates to the same speed as the embossing cylinder in an instant, and its acceleration is infinite. From the theoretical analysis and the reflection in the actual effect, this paper delivery method has a great impact on the paper, which is very detrimental to the quality of prints. For example, this is like putting a piece of goods on the side of the road, and then driving a car close to the roadside, and asking the people on the car to take away the goods placed on the side of the road without slowing down, and putting the goods in the same position every time. The reason why the speed of machine 01 cannot be improved is that in addition to the influence of many factors such as large drum diameter and thin wallboard, the bottleneck is actually the direct paper delivery method

this situation has changed a lot since the advent of the indirect accelerated paper delivery mechanism. In China, the more widely used and familiar indirect paper transfer mechanism is the eccentric up swing paper transfer mechanism. For example, machine 08 (J2108 split monochrome machine), which dominated the domestic printing industry for a long time in history, adopts the eccentric up swing paper transfer mechanism. The intermediate paper transfer mechanism has essentially changed from the direct paper transfer mechanism of the low-speed machine

it adds a "coordinator" - a paper delivery tooth between the paperboard and the embossing cylinder. When the paper feeding teeth "stop" on the cardboard, bite the paper in a basically static state, then accelerate, and then deliver the paper to the embossing cylinder at a constant speed. This has greatly improved the printing speed and registration accuracy. It is equivalent to adding a "Shenxing Taibao" that can change the speed as needed between the fast-moving car and the stationary goods on the roadside. It uses a pendulum pick-up to push the pendulum out of the car. Before it arrives, it picks up the goods, and then starts in front of the car, moving forward in the same direction. When it advances at the same speed as the car and ouyangming expresses his shoulder, it hands over the goods to the people sitting in the car while running. This method ensures the relative stability of paper taking and delivery, and greatly improves the speed and registration quality of the offset press

however, this eccentric up swing paper also has its own insurmountable defects

first of all, in order to make the paper delivery teeth move away from the surface of the high-speed imprinting drum when returning, so as to avoid damaging the drum and scraping the paper, the movement track of the paper delivery teeth must be designed into a typical "water drop" shape. To achieve this goal, the rotation center of the paper transfer tooth shaft must be offset. The diameter of the feeding tooth shaft of the 08 machine is 60-70 mm, and the eccentric diameter of its rotation center is 40 mm. This fact itself determines that the machine will vibrate greatly at high speed. We have all seen frog rammers on construction sites. Frog rammer uses the principle of center of gravity offset to drive the rammer to tamp the ground like a frog by inertia. Everyone has experienced the shock it caused. Of course, the tamping effect of eccentric up swinging paper teeth is far from so strong, but the principle is the same

besides, in order to ensure that the paper delivery teeth are in the correct position at all times, or to ensure that the rolling ball always rests on the paper delivery cam, there is a long and thick constant force spring on both sides of the paper delivery tooth shaft (in fact, there are three tension springs in total, and one side is a large spring with a small spring inside). Because it is "constant force", as the name suggests, these springs are in working state at any time. When the machine is running at high speed, this is also a vibration source that cannot be ignored

the disadvantages of eccentric up swing paper teeth are more than that. Because the axis of the paper feeding tooth shaft is constantly rotating around an eccentric, the paper feeding tooth is inevitably in motion all the time. In this way, the so-called "taking paper in a static state in front of the paper feeding table" is actually impossible. In other words, when taking paper in front of the paper feeding table, no matter how the paper feeding cam is designed, the eccentric up swing paper feeding teeth will always be in a "creeping" state before the paper feeding. This "creep" state will eventually have a certain impact on the accuracy of registration. This effect will increase with the increase of the printing speed of the offset press. Therefore, experienced printers know that although the 08 machine is known as 10000 prints per hour, it has never dared to drive the speed of the 08 machine to 10000, and in fact, its best printing speed can only be around 6000 prints per hour. When the speed increases to 7500 steering, the machine will have obvious tremor and noise, and the performance indicators of the machine will decline significantly, which will accelerate the wear of the machine and seriously affect the service life of the machine

after long-term use and research, people have designed better centering pendulum paper delivery teeth

its performance index coefficients are significantly better than the eccentric up swing paper transfer teeth. This form of paper delivery mechanism is currently the most representative of the high-speed offset press series produced by Jiangsu Chang (Risheng) group in China. In order to cancel the offset of the rotation center of the paper transfer tooth shaft, another drum is added in front of the imprint drum, which is called the paper transfer drum; Then put the paper delivery teeth under the cardboard conveyor. Since this roller only plays the role of transferring paper, it does not need to have a surface like the embossing roller, so the paper transfer teeth do not have to avoid the roller when returning. On the contrary, the paper transfer roller should avoid the paper transfer teeth, and the balance of the paper transfer roller itself is solved by the counterweight. After canceling the eccentricity of the rotation center of the paper feeding tooth shaft, the tamping effect of the eccentric up swing paper feeding tooth and the creep problem when taking paper in front of the paper feeding table are solved in one fell swoop, so that the paper feeding tooth is in an absolute static state when taking paper, which minimizes the vibration of the machine during high-speed operation and ensures the accuracy of registration. Accordingly, the actual use speed and service life of the machine have been greatly improved

in order to further ensure the smooth operation of the machine and eliminate the vibration source, the constant force device in the centering lower swing paper transfer mechanism and the constant force mechanism in the eccentric upper swing paper transfer mechanism have been fundamentally changed. It consists of two conjugate cams, a master and a pair, which firmly control the rocker arms driving the lower paper delivery teeth, while the tightness between the roller ball and the cam is solved by a short pressure spring supporting the two rocker arms. In this way, it is certainly not true to say that the machine does not move at high speed, but it has indeed reduced the vibration of the machine to a very low level. The quality inspection team of the National Printing Press Association conducted an on-site test in Jiangsu Chang (Risheng) group. During the test, a dime was jokingly placed vertically on the top of the ypiale type split monochrome Offset printing machine, which was running at 10000 revolutions per hour. The coin did not fall down or roll. "I stood still", which attracted applause from the crowd. In this case, it is a matter of course that the printing crystal index and actual printing speed of the centering lower swing paper transfer mechanism are higher than those of the eccentric upper swing paper transfer mechanism

eccentric up swing and centering hem belong to swing paper delivery mechanism. Due to the inertia of the swing arm and the fact that the rocker mechanism drives its motion, the inertia of the whole mechanism is larger, which limits the further improvement of the speed of the printing machine

people consider using a rotary paper transfer mechanism to continue to improve the speed and performance of the printing machine

this paper delivery tooth also forms a roller, which rotates in one direction like other rollers. In this way, its moment of inertia is much smaller than that of the swing paper delivery, so the impact vibration is smaller, which can better meet the requirements of the zigzag printing accuracy of the sleeve (6) toothed rod, and is conducive to further improving the printing speed. However, due to the corresponding improvement of its manufacturing accuracy and the level of supporting facilities, at present, the rotary paper transfer mechanism is mostly used in imported machines. Among the domestic sheet fed printing machines, the rotary paper transfer mechanism is rare. It is only heard that Jiangsu Chang (Risheng) group has produced intermittent rotary paper teeth with grooved wheel mechanism, which are used in the new product ypslaie double-sided high-speed offset printing machine in 2001, The product has passed the acceptance, and the effect is quite good. At present, it is forming a batch

although the indirect acceleration paper transfer mechanism has the characteristics of relatively stable paper transfer, small vibration and impact, and can meet the requirements of high-speed printing, these paper transfer methods all need to transfer the positioned paper once or twice to reach the paper biting teeth of the embossing cylinder. Due to the unavoidable errors in parts processing and machine assembly, as well as the vibration during machine operation, it is always inevitable to have a certain impact on the overprint accuracy

recently, a paper delivery method called "transcendental accelerated paper delivery" has appeared on some high-speed sheet fed offset printing machines abroad

this paper delivery method places the final positioning of the paper on the embossing cylinder, that is, the final registration rule is to set, and the experimental report can also be programmed and printed according to the format required by the user; On the embossing cylinder, rather than on the cardboard conveyor. The principle is as follows: first, the paper is pre positioned at the front gauge and side gauge on the paperboard, and then, the friction roller or vacuum belt and other mechanisms are used to accelerate the paper, so that the speed of the paper is higher than the surface linear speed of the embossing cylinder, push the paper to the front gauge on the embossing cylinder for the second time, that is, formal positioning, and then the paper is bitten by the paper biting teeth on the embossing cylinder, and then printing. In this way, the possibility that the positioning accuracy of the paper is damaged in the process of several times of paper transfer is ruled out. Because this paper delivery method has no reciprocating parts, which eliminates the vibration caused by the machine itself, and is finally directly positioned on the imprint cylinder, the transcendental accelerated paper delivery obviously has great advantages over other paper delivery methods. This will be the direction of our industry

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