Analysis of the impression cylinder and the force of the cylinder
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In sheetfed offset presses, the impression cylinder is one of the most important components. Among them, the force of the gripper is very critical. If the oars are damaged or maintained, or worn after long-term use, it may cause the force of the gripper to decrease or the force of the entire stack of grippers. Inconsistent, and caused printing failures such as overprinting and ghosting.
There are 15 grippers on the gripper shaft of the impression cylinder. The force of the gripper is mainly determined by the pressure of the springs at both ends of the rod. The greater the pressure of the spring, the greater the force of the gripper. The main factors that cause the change of the gripper force are as follows.
1. Long-term use causes the spring's spring force to decrease, reducing the force.
The force of the impression cylinder is greater than the peel force of the blanket cylinder, and the impression cylinder should be able to peel the paper off the blanket cylinder after the paper and blanket cylinder are imprinted. After a long time of use, the spring force of the springs at both ends of the rod is reduced, so that the force of the impression cylinder is reduced, the paper will be removed from the gripper, and the paper can not be printed normally on the blanket cylinder. Even if the force of the impression cylinder is slightly larger than the peeling force, the paper does not come out of the gripper, and it may be displaced in the gripper, causing the print to be misaligned, ghosted, and the like.
The ghosting fault that I have encountered in the past is caused by the too small force of the impression cylinder. When a white cardboard having a basis weight of 250 g/m2 is printed by a Beiren J2205 offset printing machine, the first color is printed separately (that is, in the case where the second color is not pressed), and the first color is not generated, and in the case of two-color printing, the first color is used. The picture is ghosted. Originally suspected to be caused by the second color of the blanket, after re-printing after replacing the new blanket, the ghosting fault still exists. After careful inspection, it was found that the root cause of the failure was that the force of the impression cylinder was not suitable. The area of the first color image is small, and the peeling force of the blanket cylinder is smaller than that of the gripper. Therefore, no ghost image is generated when the first color is printed separately; and the image area of the second color is larger, and the peeling force of the blanket cylinder is correspondingly It is slightly larger. When the first color and the second color are simultaneously printed, the paper is displaced in the second color group, causing the image of the first color to produce a ghost image on the second color blanket.
2. After long-term use, the dental pad wears out, causing the force of the gripper to decrease or the force to be inconsistent.
In the printing process, the long-term work of the mechanical external force causes the dental pad to wear, the degree of wear is different, the dental pad becomes uneven, or the tooth pattern is smoothed, which will inevitably affect the force of the gripper. In addition, if the offset printing press is often used to print small-format paper, the wear process of the dental pad will be different, that is, the middle dental pad wears more heavily, and the dental pads on both sides wear less. When printing large-format paper again, the force of the entire row of grippers will not be good, the force of the middle gripper is small, the grip of the grippers on both sides is large, and the flaps of the paper are wavy when the paper is picked up. Troubles such as pleating, cornering, and smashing may occur during printing.
3. Improper adjustment of the gripper, inconsistent opening and closing time, will also cause different degrees of wear of the pad, resulting in inconsistent force of the gripper.
If the gripper is improperly adjusted, the opening and closing time is early and late, and the gripper's gripper is first contacted, and the pressure is instantaneously received. Not only is the pad worn seriously, but the small compression spring that is in contact with the pad is also easily broken, resulting in Dead teeth cause tearing of paper during printing.
4. When printing, the paper is often stuck with foreign matter such as paper powder, dusting, ink, etc. If it is not cleaned in time, it will accelerate the wear of the gripper, causing the crease of the gripper to decrease and cause various malfunctions.
In short, the operator must be familiar with the structure of the impression cylinder gripper for proper adjustment and maintenance, and should pay attention to the following.
1. The height of the dental pad should be adjusted before and after.
2. The length of the teeth should be adjusted consistently.
3. The opening and closing time of the gripper should be adjusted consistently.
4. Regularly check the wear of the gripper and replace the worn gripper in time.