Analysis of Off-pressing Mechanism of Offset Press(I)

2.5 away from the pressure mechanism

1. The role of clutch pressure mechanism

The clutch between the blanket cylinder and the plate cylinder and the impression cylinder is controlled, and the action of the pressure-compressing mechanism is such that the blanket cylinder is in contact with the impression cylinder and the plate cylinder to complete the transfer process from the ink to the paper; when no printing is performed, the pressure-releasing mechanism operates Keep the blanket cylinder away from the impression cylinder and the plate cylinder to prevent the ink from transferring to the back of the cylinder. When the machine malfunctions, the pressure-releasing mechanism works automatically, so that abnormally-entered paper or Other foreign matter enters between the rollers and damages the blanket.

2. The working principle of clutch pressure mechanism

There are two methods of clutch pressure, one is simultaneous clutch pressure; the other is sequential clutch pressure. According to the arrangement of the rollers, it can be seen that at the same time the clutch pressure, that is, the blanket cylinder is in contact with and separated from the impression cylinder and the plate cylinder simultaneously, the gap of the roller must be the same as the arrangement angle of the roller, so as to prevent the half of the first sheet from being printed on half Not printed. The arrangement angle of the drum generally accounts for more than one third of the drum, which greatly reduces the utilization of the drum surface. To complete large-format printing, the diameter of the roller must be increased. The larger the diameter of the roller, the more problems it brings. This is not described here. This structure has now been eliminated. Sequential pressure, that is, the blanket cylinder first presses with the plate cylinder, and then presses with the impression cylinder. When the pressure is released, the pressure plate is first separated from the impression cylinder, and then the pressure is released from the plate cylinder. In a word, no matter if the pressure is on or off, its actions are performed in sequence. For example, when the blanket cylinder and the plate cylinder are pressed together, the gap of the blanket cylinder is just opposite to the gap of the plate cylinder, as shown in Figure 2.6.

This pressure is also called the first time. After the first press, the blanket cylinder continues to rotate forward. When its notch is opposite to the notch of the impression cylinder, the blanket cylinder and the impression cylinder are pressed together. This combined pressure is usually also referred to as the second press. Contrary to the pressure separation process, the pressure of the blanket cylinder and the impression cylinder is called the first pressure, and the pressure of the blanket cylinder and the plate cylinder is called the second pressure. In this way, the notch on the drum has no relation with the arrangement angle of the drum, so the notch can be made as small as possible, so that the diameter of the drum can be reduced. Reducing the diameter of the roller brings many benefits, so almost all presses currently use sequential clutch pressure.

During clutch pressure, in order to enable the drum to quickly enter a stable state and begin printing, in general, there is an advance angle at the clutch pressure, and this angle is basically around 10°.

3. The type of clutch pressure mechanism

Separation pressure mechanism is generally divided into two types: one is three-point suspension type, the other is eccentric sleeve type.

(1) The three-point suspension clutch press adopts a three-point support roller, as shown in Fig. 2.7: 1 and 2 adopt an eccentric structure, 3 is a round wheel plus a spring, 4 is a convex sleeve, and 5 is a rubber roller The shaft, 6 is the connecting rod. 1, 2 in the clutch pressure is a fixed point, when the convex sleeve and 1, 2 contact position changes, the axis of the rubber roller shaft 5 and the distance between 1 and 2, will change to achieve the clutch pressure. The following analysis of the role and working principle of these three points.

One point is used to adjust the center distance of the drum, which is composed of an eccentric shaft and a bearing outer ring. When the position of the eccentric shaft changes, the position of the outer ring of the bearing also changes, and the axis of the roller also changes accordingly. The key to using the bearing outer ring is to change the sliding friction to rolling friction to reduce wear and power loss. The movement of this eccentric shaft is generally driven by a worm gear mechanism. In addition to this, there is also the role of supporting the drum and bearing part of the printing pressure. Therefore, of these three points, 1 point is the thickest, and even if it fails, it is not allowed to break.

The two points are used for positioning the convex sleeve 4, ie, each time the convex sleeve is in a new position, this point keeps the convex sleeve in the new position and does not continue to move to the right. Since this point only plays a positioning role, the required force is very small, so its axis is relatively small. Because of this, this point can also play a protective role. When the machine is subjected to a relatively large impact, this point is a weak link, and it is first broken to prevent further damage to other components. In addition to the above-mentioned effects, another important role of this point is the pressure regulating effect. The structure of this point is basically the same as that of the one-point structure. It is also an eccentric bearing and a bearing outer ring. When the position of the eccentric shaft is changed, the contact position between the convex sleeve 4 and the point is changed, thereby changing the position of the roller and realizing the pressure regulation.

The movement of the eccentric shaft is generally driven by a gear, that is, the eccentric shaft is assembled with the shaft of the sector gear, and a small gear is used to drive the sector gear to rotate. In normal operation, since the eccentric shaft itself is self-locking, that is, when the clutch is pressed, the gear will not rotate.