1.2 Paperboard The role of the cardboard is to accurately and smoothly transfer the paper delivered by Feida to the regulatory section. The paper does not allow relative sliding on the paperboard, which is the general guiding principle for adjusting the components on the paperboard. 1. Analysis of the movement of paper on the cardboard. The paper in the Feida part depends on the differential pressure transmission, so what kind of transmission does the paper rely on on the cardboard? When a paper feed failure occurs on the paper feed board, it is usually necessary to check the tightness of the cloth tape and the strength of the pressure roller. Why is this done? When you place an object on a smooth surface, you will find that it is much easier to move it than on a rough surface. Put a heavy object and a light object on the surface of the same object. It is found that heavy objects are more difficult to move than light objects. From this point of view, the pressure of the object and the smoothness of its contact surface determine the difficulty of moving the object. The force that obstructs the object is called friction. The transmission of paper on the cardboard is actually friction transmission. The friction force is equal to the product of the pressure on the surface of the object (n) and the smoothness of the contact surface (friction coefficient u), ie f = n · u In order to prevent the paper from sliding relatively on the paperboard, there must be sufficient friction, so the frictional conditions must be created on the paperboard. The driving force for paper forward transmission comes from the paper feeding belt, and at the same time, the paper drives the platen roller, so the platen roller generates a frictional force that prevents the paper from moving forward. Let the friction force of the paper feeding belt against the paper feeding board be f1 = n · u (n is the pressure of the paper pressing wheel). The frictional resistance of the platen roller to the paper is f2 = n · u2. The other forces on the paper can be ignored, so the force on the paper is f = f1-f2 = n · (u1-u2). Because the paper is moving at a constant speed on the paperboard, f = 0 means u1 = u2. Where u1 is the sliding friction coefficient and u2 is the rolling friction coefficient. In general, u1> u2, because the paper and the cloth belt are in the stage of static friction, that is, the maximum value f1 has not been reached, that is, it is always balanced with f2, so the paper will not be in an accelerated state on the cardboard. (1). The forward movement of the paper has nothing to do with the pressure of the pressure roller, that is, no matter how much the pressure is, the paper will not accelerate or decelerate. 2. The function and adjustment of various components on the cardboard. The components on the paperboard include the paper receiving roller, the guide plate, the double-sheet controller, the paper belt, the paper pressing wheel, the brush wheel, the paper board, the suction hole, and the paper pressing frame. The following is a detailed analysis of the role of each component. (1). Paper pick-up roller The function of the paper pick-up roller is to lead the paper passed by the paper suction nozzle into the paperboard. The horizontal lines on the paper pick-up roller play the role of increasing friction, so as to prevent the cloth tape and the paper receiving Relative slippage occurs between the rollers. There are two paper pressure rollers on the paper receiving roller, and their function is to make the paper and the paper receiving roller contact reliably. The paper pressing time should be consistent with the paper passing time of the paper feeding nozzle. (2) .Guide plate The role of the guide plate is to guide the paper from the paper receiving roller to the paper feeding board. The degree of flatness can be adjusted with screws. (3). Double sheet detector How much paper is there under the double sheet detector? This question is sometimes unclear. The key question is not knowing what the double-sheet detector does. The function of the double-sheet detector is to detect that two or more sheets of paper are input each time, regardless of how many sheets of paper there are below. Taking paper with a width of 540mm as an example, the paper feeding step of a general Heidelberg printing machine is 200mm (the distance between the two holding mouths of the paper feeding step). It can be seen that there are at most three sheets of paper under the double-sheet detector (under normal conditions) if the paper width is 720 mm. It is expressed as: There are up to four sheets of paper under the double-sheet detector. Therefore, the paper size changes, and the number of sheets under the double-sheet detector also changes. As shown in Figure 1.11, when the thickness of the paper increases, the lower roller gradually rises and contacts the upper roller. As soon as the two contact, the upper roller will rotate. After the roller rotates, the dial pin on the roller also rotates with it, thereby pushing the micro switch and sending out a double-sheet detection signal. The adjustment is as follows: After the machine works normally, the paper pressure roller has been pressed down, and at this time, the paper under the double-sheet detector is the most. At this time, adjust the screw on the double-sheet controller to make the light on, then put a piece of paper with the same thickness as the paper to be printed under the detection wheel, adjust the double-sheet controller so that the light is just off, and record the number of turns of the screw Invert half of its laps. (4). The function of the paper feeding belt is to transfer the paper from the feeder part to the regulation part. The paper transport belt is in contact with the paper receiving roller by friction, and the paper is transmitted by friction. Therefore, the conditions for friction of the paper transport belt must be ensured during normal operation. There are three points to note for the paper transport belt: a. The paper transport belt should be tightly wrapped on the drive roller, and it cannot be covered on top; b. The cloth belt should be in contact with the textured part of the drive roller, and should not be The smooth part is in contact; c. The surface of the paper belt should have a large friction coefficient. (5). The function of the paper pressing roller on the paper feeding roller is to make the paper reliably contact with the paper feeding belt, and generate enough friction to move the paper forward. The adjustment of the pressure roller is basically the same as the adjustment of the two pressure rollers on the receiving roller. There are two points that must be noted in the adjustment process of the paper pressing roller: one is the principle of symmetry; the second is the connection relationship between the papers, that is, the paper feeding step must be considered. The pressure roller on the paper pick-up roller leaves the paper conveying table, and the pressure roller on the paper conveying paper should be pressed against the paper. (6). Brush wheel The function of the brush wheel is to prevent the paper from rebounding after positioning, so it is generally placed at the tail (or the back half) of the paper. (7). Paper pressure frame The paper pressure frame mainly plays a role of supporting other paper pressure or paper blocking parts such as paper pressure wheel. The position of the paper pressing frame is generally designed and cannot be adjusted during use. (8). The function of conveying paperboard is to support the cloth to convey paper. The requirements of the paperboard must not have any factors that destroy the friction transmission on the surface, that is, the surface should be flat and smooth. The paper belt is in direct contact with the paperboard, so it is critical to the abrasion of the paper belt. The warpage of the paperboard directly affects the paper transport. If the surface is severely uneven, it will scratch the surface of the paper. Another function of conveying paperboard is that it can be used to eliminate static electricity. Foreign equipment generally chooses conveying paperboard made of steel material to have a certain relationship. (9). Suction hole There is a suction hole in the middle of the conveying board. The function of the suction hole is to suck the paper on the conveying board when the paper conveying part fails, to prevent it from sliding due to inertia.
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It can also be seen from the above analysis:
(2). The role of the paper pressure roller is to make reliable contact between the paper and the cloth belt, and generate sufficient static friction.
(3). If the surface of the tape becomes very smooth, that is, u1 <u2, the paper will slip on the tape.
(Figure 1.10a)
(Figure 1.10b)
The working principle of the double-sheet detector is to convert the thickness of the paper into an angle to enlarge.
(Figure 1.11)
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