The positioning mechanism on the offset press is the main mechanism for controlling the positioning of the paper. It occupies a very important position in the entire machine and is known as the throat of the offset press. The structure, performance of the components, and the quality of the regulation are not only decisive for the quality of the product, but also have a close relationship with the production efficiency. Many offset press manufacturers are striving to shorten the preparation time and improve the efficiency of the tuning machine. Therefore, the rules of offset presses are constantly improving and developing.

Although the models vary, their structure is much the same, and there are many common exceptions in the use of adjustments and guarantees of accuracy. The non-litigation is what kind of rules are used, and adjustment work is mainly carried out around its accuracy so that it can achieve the purpose of accurate overprinting. The following takes the positioning rules of the J2180 Offset Press as an example to discuss several aspects that are easily overlooked during adjustment.

First, side pull paper time

During the printing process, it is necessary to ensure that the overprinting of the printed sheets is accurate in both vertical and horizontal directions, and the drawing time of the side gauge pressing roller cannot be ignored. Because the machine uses a roller continuous side gauge, the machine will complete a pull paper positioning job once a week.
Its completion of a printing drawing time is:
t=a/v
The time for lifting the side profile is: t'=(ZD-a)/v
In the formula: t-pulling time a- arc length when the paper-drawing cam contacts at the end D-pulling cam diameter V-rotating speed It can be seen from the above company that when a is large, t and t' are small. In other words, during the process of the machine running for a week, if the side profile pulls the paper for a long time, the lifting time will be short. If the time for lifting the side gage is fixed, the time for pulling down the paper will be early, which is bound to result in The positioning time of the paper at the front gauge is reduced.

As the paper feeder cannot guarantee the absolute accuracy of the paper transport and the positioning time at the front gauge is short, the paper conveyance will advance or lag slightly, which will affect the stability of the front defined position and make the paper not yet stable at the front gauge. , Lateral regulations have dropped down paper, papermaking before the regulations are not accurate, but also affect the accuracy of the side regulations. If the drawing time is too long, after the paper is pulled into place, the pickup roller continues to pick up the paper, which also easily reduces the paper stress and curls the edge of the paper slightly. This causes overprinting failure (thinking is more obvious when the paper is thin); If the paper time is too short, paper that is farther away from the side gauge will not be pulled in place, which will also affect overprinting.

Side platen roller lift time

In the printing process, the side gauges and the front gauges always complement each other and cooperate with each other to complete the overprinting process. If one party does not pull the rules, it will affect the other party. When the printing paper is conveyed to the front gauge through the paper conveying board, the paper is positioned by the front regulation plate, then the paper is pulled down by the side profile, and then the paper is sent to the impression cylinder for printing by the transfer paper.

If the side pressure roller is lifted too early at this time, because the pull time is relatively constant, that is, the time of falling down the paper is also too early, it is easy to cause the paper to be positioned at the front gauge and is not yet stable. The wheel has already been pressed down and the paper is pressed. After the paper is pulled up, the paper is pulled up too early. As a result, the gripper has not completely closed the gummed paper. The side gauge is lifted. The paper is not controlled at this time and the paper runs out of control. , resulting in inaccurate overprinting. If the platen roller is lifted too late, after the gripper is closed, the paper may not be pulled into place or the gripper is already holding the paper. When the paper is ready to be sent to the platen roller, the side profile has not been lifted yet. This affects overprinting.

When the platen roller is lifted and the gripper is closed, the paper passes through the front gauge and the side set position, enters the instant that the gripper teeth are closed, the side gauge platen roller is also lifted, and the paper will not be transferred due to the two parts. Out of control, the overlay error is small.

This transfer is not ideal, only to ensure accurate overprinting at low speed, once the high speed sleeve printing gripper teeth and pick-up transfer of the time is very short, grippers close the moment the pressure roller lift, the completion of the handover time is very short In addition, the vibration of the machine at high speeds, and the effects of various forces, can easily affect its handover. At this time, the paper will also appear intermittently out of control.

Normally, when the adjustment is done, the side-look up time should be slightly later than the gripper time 0.5-1.5°. At this time, the paper will not be out of control due to the premature lift of the side gauges, nor will it be pulled up too late. Paper phenomenon.