Analysis on the factors influencing the overprint

2022-07-26
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Analysis of the factors affecting the overprint quality of the rotary offset press

the domestic rotary offset press has a great relationship with the technical level of the operators in the aspects of overprint, point reproduction, field density, etc. as long as the machine performance is well mastered, the satisfactory prints can be obtained

several factors affecting the overprint quality of PJs machine: in addition to plate making, roller pressure, blanket, liner, ink balance, the following points should not be ignored

(1) current

the secondary tension of our PJs machine has been abnormal. In order to ensure the accuracy of overprint, the operator clicks one button to switch the experimental record to the next one. On the primary tension, manually control the current to ensure that the paper tape tension is balanced and consistent. Under normal conditions, when the current is controlled at 1.4A, the diameter of the paper roll becomes smaller and smaller, the rotation speed of the paper roll becomes faster and faster, and the tension of the paper tape becomes larger and larger. The paper roll with large outer diameter and the paper roll with small outer diameter are controlled by the same current. The paper tape tension is different, resulting in large overprint error. The technician adopts the method of manually controlling the current. When the diameter of the paper roll is less than half, observe the position of the slider on the floating roller mechanism, manually adjust the current to make the slider at the same position, and ensure that the tension of the paper tape is balanced

(2) stepless transmission

the adjustment of stepless transmission has a great impact on the overprint quality. The paper tape is too tight and easy to be broken, and the paper tape is too loose and easy to fan up and down, affecting the overprint quality. Therefore, the maintenance of the CVT is particularly important. In particular, the tightness of the chain in the CVT has a great impact on the overprint quality. The chain is too loose and the paper feeding fluctuates greatly. When the paper is fed, the paper will shake, the overprint changes greatly, and even the ghosting fault occurs

(3) half a year after the installation of the clamping rod on both sides of the blanket, the printing products often have local overprint inaccuracies. At first, it was suspected that it was the problem of the machine. The roundness and straightness of the drum were checked with a dial indicator. The runout was within 0.02mm, meeting the use requirements; Check the clearance of the roller bearing, which also meets the use requirements. Later, it was found that the aluminum alloy clamping rods on both sides of the blanket were bent in a wavy shape after fabrication, and the maximum error of the parallelism of the clamping rods was 2mm

(4) plate bending machine

pjs machine has no diagonal plate drawing device on the plate cylinder, so it is very important to bend the plate on the plate bending machine. If the parallelism of the bending machine is not enough, the diagonal overprint will exceed the standard, resulting in bending skew. This fault is difficult to adjust on the machine. After the PJs bending machine was used for a period of time, some screws were loose. According to the investigation, the maximum parallelism error of the platform guide rail of the plate bending machine can reach 0.3 (1) the research object is selected: that is, the object under stress analysis is mm, and the bent plate cannot be corrected on the machine

in order to ensure the bending accuracy, the technician automatically formed the reporter and specially made a special measurement and correction tool to correct the parallel accuracy of the guide rail of the bending platform. During measurement and calibration, place the tool on the platform of the bending machine. One side of the measuring tool rests on the platform side rail, and the other side is equipped with a dial indicator. Loosen the adjusting screw under the bending machine, pull it back and forth on both sides of the platform, adjust the parallelism of the platform guide rail according to the error, and tighten the adjusting screw when the error is controlled within 0.03mm

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