Knowledge collection of the hottest offset press m

2022-08-16
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Knowledge collection of offset press mechanism

the front mouth of the printing sheet is flush (reducer)

the printing sheet cannot be stopped on the receiving pile after it is transferred from the impression cylinder to the receiving cylinder without any reducer. The working principle of the reducer is analyzed in detail below

1. Chain deceleration. When an object is placed on a transmission belt (no relative sliding is allowed) and moves between two wheels (as shown in Figure 4.5), the speed of the object is the same as that of the transmission belt, because they are in translation. When it runs to the surface of the wheel, the transmission belt is close to the surface of the wheel, and its speed is the same as the original, while the speed of each point on the object is different. The farther away from the wheel center, the higher its speed; The closer to the wheel center, the lower the speed. It can also be seen from the above figure that the arc length of A2 is obviously greater than that of B2, that is, the speed of A2 is greater than that of B2. When the object reaches the middle of the two wheels below, it keeps the same speed with the conveyor belt. The speed of A3 is equal to the speed of B3. Replace the conveyor belt with a chain, and replace the object with a chain, then the mechanism becomes the paper receiving chain row of the paper receiving part

Point

a1 is equivalent to the position of the tooth pad. When the tooth row is connected with the impression cylinder, the speed of the tooth pad is the same as that of the tooth pad on the surface of the impression cylinder. Because the mutual connection can only be carried out on the arc, that is, the speed of the tooth pad is A2. When the tooth row runs to A3 after the handover, the speed of the tooth pad is the same as that of A3. Since the speed of A3 is less than that of A2, the speed of the tooth pad is reduced, and the paper moving with the tooth pad is also decelerated. This is the first stage of paper deceleration. Since the dental pad can decelerate, it must also have a process of acceleration. It can be seen from the figure that A1 and A2 are the acceleration stage of the dental pad. Therefore, the process of tooth pad running from the upper chain to the lower chain is actually the acceleration and deceleration process of tooth pad

from the point of view of paper deceleration, the larger the speed difference between A2 and A3, the better. But from the point of view of paper speed, the smaller the speed difference between A2 and A3, the better. Therefore, in the design, we must coordinate the relationship between them with less cooling water

2. Brake roll decelerates. When the paper passes through the brake roller, the brake roller begins to suck the air under the paper, causing the paper to produce a downward pressure, thereby increasing the friction resistance between the paper and the air. When the teeth are kept for a period of time after discharging the paper, the resistance plays a role of deceleration

this is the second stage of paper deceleration. Another function of the brake roll suction is to form a pressure difference to make the paper lean against the surface of the receiving stack to prevent the paper from drifting. The suction volume of the brake roll can be adjusted. When the speed is high, the suction volume is larger; When the speed is low, the inspiratory capacity is smaller. Different models have different adjustment methods. Some equipment is installed on the transmission system of the paper receiving part, that is, it changes with the speed of the transmission system; Some machines are equipped with a special speed regulating motor to control its speed, which is convenient to adjust. Its position can be adjusted back and forth according to the width of the paper

3. Fan decelerates. When the paper passes under the fan, the fan blows air, which increases the friction between the paper and the air. When the teeth discharge the paper, this friction resistance will slow down the paper. This is the third stage of paper deceleration. Another function of the fan is to blow air, and you will find a pressure difference, so that the paper is close to the surface of the stack, which is convenient for the speed of paper receiving. The blowing volume of fans can also be adjusted. The number of fans is different on different machines, but their distribution is symmetrical. In essence, the function of the fan is exactly the same as that of the brake roll

4. Open the die plate to slow down. The change of the position of the tooth opening plate can change the position of the tooth discharging paper. When the paper speed is too fast, the position of the tooth opening plate can be adjusted to discharge paper in advance, so as to achieve the purpose of deceleration. This is the fourth stage of paper deceleration

5. Slow down the front paper board. After the teeth are arranged, the paper is already in an unconstrained state. Due to the influence of various factors, the position of each piece of paper on the receiving stack cannot be exactly the same, but finally, it is hoped that they will be in the same position at the receiving stack as far as possible. This process is realized by the front flush board. When the paper is about to fall on the receiving pile, the front flush paperboard swings back. After it is stable, the front flush paperboard swings back and collides with the mouth of the paper, pushing the paper to make its front mouth flush. When the second paper comes, it begins to swing back. This action is repeated, and finally all the front edges of the paper can be flush. To some extent, it can be said that the front flush board has the function of positioning, but the positioning requirements are much lower than those of the regular part. Since the front flush board has the function of positioning, all the flush board strips on it should be on the same plane, but this is actually difficult to do. Generally, two of them are selected for positioning, and the rest are used for auxiliary positioning

Author: Cai Jifei

source: offset collar machine must read

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