China Senbo Industry Co.,ltd , https://www.yuyilang.com
Due to the effects of roller dents, drums, blankets, printing pressure, and fountain solution, various conditions of paper deformation occur during the imprinting process.
As shown in Fig. 1, in the Heidelberg 102 series offset press, the impression cylinder row has only 14 teeth. When printing positively on the paper, there were only 10 gingiva crepe papers, and the distance between the two cavities was relatively large. The paper had 45 mm out of control positions at both front corners.
The position where the paper is deformed always starts from the two sides of the print mouth and the cavities, so that the image position of the print and the plate cannot be completely coincident or cannot be changed according to the same rule. Between printing units, there are differences in the locations and degree of deformation due to differences in printing conditions. Due to wet and wet printing, the deformation of the paper eventually translates into ghosting and throw-off failures of the printed product. The following factors in the imprinting process can cause roll-off failure of the printed product.
(1) The two front corners of the paper are dragged back by the release force of the blanket. When the impression cylinder is in contact with the first small transfer cylinder, the paper is not in a "one line" state.
(2) Due to the peeling force, the paper is deformed between the two phases of caries and is not a line state. Especially when printing longitudinal warp and paper, the front edge of the paper is more deformed due to the expansion of the paper fibers.
(3) The "dental teeth" appear on the tooth row and cannot exert sufficient force on the paper. Under the action of the peeling force, the paper is dragged backward at this position for a certain distance so that the front mouth cannot maintain the "one line" state.
(4) Use dental plaques and dental pads that do not meet the requirements. The contact form between the dental piece and the dental pad is line contact. Because there is not enough nip area, the paper cannot overcome the peeling force between the paper and the squeegee at the occlusal position, resulting in the deformation of the paper at the gargle.
(5) If the paper tension is not good, the blanket is too viscous or the printing pressure is too high, the paper will also be deformed in the mouth.
3. One line problem in the embossed area
If the impression cylinder is deformed, the quality of the blanket is not good or the blanket is uneven, the longitudinal section of the contact area between the impression cylinder and the blanket is not a straight line. When the deformation of the impression cylinder body is large, the printing product will wrinkle, causing partial overprinting or rejection.
4. “One Line†Problem During Paper Transfer (1) The ideal point of intersection between the intersection of the tooth row and the common delivery time is the tangent point of the two rollers. In order to ensure the stability of the transfer process, there must be a common transfer time of 1.0 to 1.6 degrees between the rows of drums (in the single-sided printing state, the common transfer time of the inverting cylinder to the impression cylinder is 1.0 to 1.8 degrees, and the roller is reversed to the storage roller. The common handover time is 1.0 to 2.0 degrees. The midpoint of the transfer time between all the roller rows is the tangential position of the two rollers.
When the outer surface of the drum tooth or the open tooth is worn, the transfer time between the teeth of the drum will become smaller or there will be no transfer time, and at this time, it should be readjusted. If the abrasion exceeds a certain limit, the common time for feeding the drum teeth will not be adjusted. At this time, the tooth chip and the open tooth must be replaced. When the tooth pad wears, the paper appears wavy on the tooth row. At this time, the tooth pad must be replaced. When the open teeth of the roller have obvious gaps, the wear of the copper shaft of the tooth shaft and the tooth base, and the damage of the bearing of the tooth shaft, the opening and closing teeth of the roller tooth or a certain tooth become indefinite and cannot be adjusted normally. At this time, the tooth should be changed. The worn parts in the row.
For large transfer drums and storage rollers, the open and close teeth of two rows of cavities should be strictly identical.
Compared with other models, the cylinder diameter of the Heidelberg 102 series offset press is small, and the common transfer time between the rows of teeth cannot be too long (the transfer length is 2.5 to 3.5 mm). Since the drum row has a slope of 2.5 degrees, the deformation of the paper at the junction point is increased, which limits the extension of the transfer time between the rows of drum teeth. Therefore, it is necessary to strictly follow the standard data when adjusting the hand-over time. Especially when adjusting the opening and closing time of the tumbler drum, careful operation is required.
(2) Pad gap The most reasonable gap between pads is the thickness of the paper. Pay attention to the adjustment of the height of the dental pad. When printing thin paper, it is recommended to adjust the gap between the rollers to 0.15 to 0.20 mm.
For small transfer drums, the operator can change the height of the pad to meet the printing needs of different thicknesses of paper. When the equipment is under full maintenance and overhaul, the height of the pad of the small transfer roller should be carefully adjusted. For the tumbler, the relative position of the tuck flap and the tumbler should be carefully adjusted.
When repairing the roll row, some maintenance personnel arbitrarily change the front-to-rear position of the tooth row (positioning pins on the tooth row seat is not installed) and the positioning positions of the gears at both ends of the row in order to increase the force of turning the row of teeth. At the point of intersection, the gap between the gasket of the flipping cylinder and the storage pad and the pad of the impression cylinder is seriously deviated from the standard data, and the front side of the paper will undergo severe deformation during the transfer process.
(3) In the process of the transfer of any two rows of teeth, the "one line" problem of arranging the cusps of the teeth row is mutually transmitted.
Because there is a slope on the surface of the tooth pad, the cusps of the tooth rows intersecting each other are in a straight line, which can reduce the deformation of the paper. Due to manufacturing, installation and other reasons, it is difficult to do this strictly.
(4) "One Line" Problem in the Transmission of Paper
Prevent deformation of the front edge of the paper during paper transport.
When "dental teeth" appear in the teeth row, the paper will be out of control in this area, and the two front corners of the paper are generally out of control (parts that are outside the tusks). When the paper encounters an external impact, the uncontrolled portion of the paper is dragged backwards, causing the position of the rear tooth row to be inaccurate, causing the paper to deform.
For the first small transfer drum, the end of the stack is still between the impression cylinder and the blanket cylinder when the row of teeth is creped. If a tooth decayed is "dead tooth," the paper will be deformed at this point.
(5) "One line" problem of rinsing teeth
Under normal circumstances, the crepe size of each unit drum tooth should be equal or no significant change. For some machines, the size of the first group of impression cylinders is 6mm. In the following group, the size of the jaws of the impression cylinder gradually decreases, and the last unit becomes 2mm. Department will be deformed.
This is due to the fact that the common time between drum teething is too long, the teeth of the pick-up drums are too early to make the mussels smaller; there is no common hand-off time between the rows, and the entire paper is in an out of control state (paper throw) at the time of hand-over; The pad gap is unreasonable.
Solving the problems of rejection with "one line"
In order to accurately print, every link in the paper must be in perfect condition. However, most maintenance personnel do not understand the equipment
Source: Qingdao Development Printing Machinery Co., Ltd. Ning Ronghua
The problem of rejection of printed goods and the view of "one line" (below)
2. The "line" problem of the front edge of the paper in the imprinting process