Trouble shooting for the inaccurate overprint of front gauge line

Recently, we encountered a case where the image on both ends of the J2108 offset printing machine had vertical ghosting, that is, the front line overprinting was not allowed to malfunction. Rechecking and adjusting each handover relationship of the machines will not help. There are many reasons for the irregular overprinting at the two ends of the front gauge, including mechanical, printing process, paper, etc. After excluding the latter factors, the problem is still concentrated on mechanical factors.

After a period of search, it was found that after the paper was positioned on the delivery table, the delivery gripper fell and the preparation was just ready for gripping. The paper had to bounce back before being gripped by the delivery gripper and sent to the printing area. It always happens when the paper is positioned on the dental table. Is the paper pad with a small gap from the dental table and it is hit by the dental pad, or is it caused by other reasons? Use a feeler gauge to check the gap between each delivery tooth pad and dental table one by one, and the gap meets the requirements (that is, the gap is three or four times the printed paper), and the paper handover time is correct. Is the tooth pad surface too Oblique, which caused the hand-over tooth to touch the sheet, did the paper come out? We have also adjusted the delivery tooth pads, but the problem has not been solved.

After careful observation, it is found that the paper delivery tooth is not located at the lowest position of the paper delivery pad from the paper delivery table. Although the longitudinal position is held by the mountains on the inside of the two wallboards, the longitudinal paper gripping position is fixed, but the paper delivery tooth is fixed. The two eccentric magnets of the shaft have been moving at a constant speed. When the paper-handed tooth falls and wants to close the teeth, since it is not at the lowest point, the moving tooth slice touches the paper holding mouth before the teeth are completely closed, and the paper is bumped back a bit, causing The process of gripping paper is unstable, and in the movement, the teeth of the paper collide with the paper, so that the insulation is different to the same degree, that is, the paper is inconsistent, resulting in irregular overprinting at the two ends of the front line of the printed product. Shadow phenomenon.

According to the requirements, the paper delivery tooth is at the position of 76 degrees to 78 degrees. When the center of the eccentric central axis of the paper delivery tooth and the midpoint of the gripper mouth are in a straight line, the instantaneous speed of the gripper is zero. This is for gripping paper. The best moment. However, the correlation between the scale of the J2108 offset printing machine we used and the actual mechanical action, so the actual action relationship of the machine should be used when adjusting. We adjust the tooth closing time to 3 degrees to 5 degrees in the positive direction, that is, the tooth closing time is about 72 degrees, at this time it is just in the best gripping state, that is, the center of the eccentric central axis of the delivery tooth, the gripper mouth Point on a straight line. After adjustment, feed the paper again. Observe that the paper will not rebound on the tooth table. At the same time, the printed product is not ghosted in the longitudinal direction, and the overprint is accurate.

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