Experience exchange: pre-printing of the offset printing machine is not allowed to be trouble-shooting
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Recently, we encountered a longitudinal ghosting of the image on both ends of the J2108 offset press, that is, the front gauge is not allowed to be overprinted. It is no help to re-examine and adjust the various handover relationships of the machines. There are many reasons for the irregular overprinting of the two ends of the front gauge, such as mechanical, printing process, paper, etc. After the elimination of the latter factors, the problem is still concentrated on the mechanical factors.
After a period of searching, it was found that when the paper was positioned on the transfer paper table, the paper was dropped and the paper was just ready to pick up the paper. The paper had to be bounced back to be picked up by the paper and sent to the printing area. It is always the case when the paper is positioned on the tooth table. Is the gap between the paper pad and the tooth surface small and is touched by the tooth pad, or is it caused by other reasons? Use the feeler gauge to check the gap between each transfer pad and the table. The clearance is in accordance with the requirements (that is, the gap is three or four times that of the printed paper), and the paper delivery time is also correct. Is it the tooth pad surface too? Oblique, causing the paper to touch the sheet and knock the paper out? We have also adjusted the transfer pad, and the problem has not been solved.
After careful observation, it is found that the paper-feeding teeth are not at the lowest position of the transfer paper pad from the top of the transfer paper table. Although the longitudinal direction is on the top of the two wall panels, the longitudinal crepe paper position is fixed, but the paper feed teeth are fixed. The two eccentric magnets of the shaft are always moving at a constant speed. When the paper tooth is intended to close the gums, since it is not at the lowest point, the tooth in motion is not completely closed, and it touches the paper mouth, and the paper is knocked out later, causing The process of creping paper is unstable, and the paper sheets collide with the paper during the movement, so that the degree of insulation is different, that is, the paper is inconsistent, resulting in irregular printing on both ends of the front line of the printed product. Shadow phenomenon.
According to the requirements, the paper feeding teeth are in the position of 76 degrees to 78 degrees. When the center of the eccentric center axis of the paper feeding paper and the midpoint of the crepe paper nipple are in a straight line, the instantaneous speed of the paper feeding dent is zero, which is for the crepe paper. The best moment. However, the scale of the J2108 offset press we use is related to the actual mechanical action. Therefore, the actual action relationship of the machine should be taken into account when adjusting. We adjust the closing time to 3 to 5 degrees in the positive direction, that is, the closing time is about 72 degrees. At this time, it is in the best state of crepe paper, that is, the center of the center axis of the paper eccentricity, the jaws of the paper. Point on a straight line. After the adjustment, the paper is fed again, and the paper does 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.