Analysis and solution of ghosting fault of Hardcover Books
Mar 03, 2022
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Analysis and solution of ghosting fault of Hardcover Books
The harm of ghosting failure to Hardcover Books is well known, it will cause the entire picture of Hardcover Books to be blurred and distorted. Therefore, in the production of offset printing, measures should be taken to avoid the occurrence of ghosting failures. According to the different ghosting directions, ghosting can be divided into three types: horizontal ghosting, vertical ghosting and AB ghosting. The dots of horizontal ghosting are on the left and right sides of the original dots, and their positions are basically fixed. Longitudinal ghosting is also called up and down ghosting. The virtual shadow of the dot is at the upper and lower ends of the original dot, and the position is fixed in the direction perpendicular to the axis of the drum. AB ghosting, some of the virtual shadows of the dots are on the upper and lower sides of the original dot, and some are on the left and right sides of the original dot, and the position is not fixed. AB ghosting is sometimes present on every printed sheet, and sometimes appears only after one or several sheets.
(1) Causes and adjustment methods of horizontal ghosting
①The gripper shaft moves in series in the axial direction, resulting in inaccurate paper transfer and displacement of the paper, resulting in ghosting. Adjustment method: Adjust the gap between the two ends of the roller gripper shaft and the end face of the shaft sleeve to overcome the ghosting caused by the axial movement of the gripper.
②The loosening of the roller thrust bearing screw, wear or the loosening of the nut tightening the thrust bearing may cause the roller to undergo relative axial displacement during high{{0}}speed operation, resulting in ghosting. Adjustment method: If the thrust bearing is found to be worn, it should be replaced immediately; find the roller with large axial momentum (generally, the axial momentum of the machine is required to be 0.03-0.05mm), and tighten the thrust bearing nut to eliminate this problem. ghosting.
③The printing paper is not stable, and the local force of the paper is unbalanced during the printing process, which causes the paper to deform and cause horizontal ghosting. Adjustment method: According to the requirements of the machine manual, adjust the parameters of each component in the paper feeding system correctly; check the air suction and blowing environment inside the machine, and solve any problems in time. How to troubleshoot printing ghosting faults?
(2) Causes and adjustment methods of vertical ghosting
①The accuracy of the cylinder journal and the shaft sleeve, the eccentric sleeve and the wall plate hole is poor, and the matching gap is too large, especially the large matching gap of the printing plate cylinder. Most of these ghosts occur at the mouth of the printed product. Adjustment method: When the gap between the roller shaft diameter and the shaft sleeve is too large after long{{0}}term use, it should be replaced in time. In addition, it is necessary to adjust the matching gap of the roller bushing, and the matching gap of the roller bushing is preferably 0.01 to 0.02 mm.
②The printing pressure is too large. This is usually related to improper lining of the drum. If the pressure is too large, the blanket cannot be restored to its original state in time during high{{0}}speed printing, resulting in longitudinal ghosting. At the same time, if the pressure is large, the peeling force will be large, and the gripping force will be less than the peeling force of the paper from the blanket, causing the longitudinal displacement of the paper. Produces vertical ghosting. Adjustment method: According to the requirements of the manual, select a reasonable lining to avoid longitudinal ghosting caused by improper lining of the cylinder; at the same time, adjust the printing pressure reasonably. Generally speaking, the pressure between the printing plate and the blanket is 0.100.15mm, The printing pressure between the blanket and the impression cylinder is 0.15-0.20mm.
③The reasons such as low machining precision of drum gears, serious wear, large gear backlash and large radial runout may cause each drum to fail to operate normally, and instantaneous relative displacement occurs between the drums, resulting in longitudinal ghosting. Adjustment method: choose gears with high machining accuracy, and replace gears with serious wear; adjust the printing pressure by adjusting the thickness of the lining; use liner paper to pad the grip of the blanket into a trapezoid to reduce the gripping Vibration caused by hitting, etc.
④The various units of the multi-color offset printing machine are inaccurately handed over to each other, which leads to the displacement of the ink marks that are printed first, and the imprints of each color transfer cannot be overlapped, causing ghosting. Adjustment method: Check and adjust the wear degree, installation accuracy and position of the paper positioning and handover components to ensure accurate paper handover.
⑤When the vertical fine-tuning mechanism of the multi-color machine is loose and the bearing is seriously worn, the printing plate cylinder has an impulse from the empty to the mouth under the action of printing pressure, which causes the printing plate cylinder to move circumferentially and cause longitudinal ghosting. Adjustment method:
Adjust the gap of the fine-tuning mechanism so that it will not affect the rotation of the printing plate cylinder, but also play its role in fixing the printing plate cylinder.
(3) Causes and adjustment methods of AB ghosting
AB ghosting generally occurs on printing presses that use double-diameter or multi-diameter cylinders. The possible reasons for the failure and the adjustment methods are as follows.
①The manufacturing and installation accuracy of the gripper device is not enough or the wear is serious, which reduces the working accuracy and causes ghosting. Adjustment method: Check the wear degree of the gripper device and replace it in time; check the gripper force, and correct the gripper pad and gripper force according to the installation and adjustment instructions in the manual; check the working condition of the gripper and adjust it to normal , so that the gripper can move flexibly to ensure the accuracy of paper transfer.
②The viscosity of the ink is too large, which increases the peeling tension of the paper. For paper with high tensile strength and high elongation ratio, different elongation degrees during peeling may also cause AB ghosting. Adjustment method: According to the requirements of printing suitability, adjust the viscosity of the ink appropriately to make it meet the printing requirements.
The above briefly introduces the possible causes and adjustment methods of common faults in offset printing. There are many reasons for the failure. There are both machine reasons and human errors. It cannot be generalized, and there is no fixed routine to follow. This requires printing operators to work hard to master the printing process and mechanical properties of various machines. and other relevant knowledge, conscientiously summarize the practical experience of production, and better prevent and eliminate various printing failures, thereby reducing the occurrence of defects in printed products and improving the quality of printed products.