Analysis of the factors influencing the overprint

2022-09-21
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Analysis of factors affecting the overprint quality of rotary offset press

domestic rotary offset press has a lot to do with the technical level of operators in overprint, point reproduction, field density and so on. As long as we master the machine performance, we can completely get satisfactory prints

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 manually controls the current on the primary tension to ensure that the tension of the paper tape is balanced and consistent. Under normal conditions, 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, and the tension of the paper tape is different, resulting in larger overprint error. Technicians use 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, and manually adjust the current to make the slider in the same position to ensure that the tension of the paper tape is balanced and consistent

(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 stepless transmission is particularly important, especially the tightness of the chain in the stepless transmission has a great impact on the overprint quality. The chain is too loose, and the paper feeding fluctuation is large. When the paper is fed, the paper will shake, the overprint changes greatly, and even the ghosting fault occurs

(3) the clamping rods on both sides of the blanket

half a year after the machine is installed, local overprint inaccuracies often appear on the printing products. At first, it was suspected that it was the problem of the machine. Check the roundness and straightness of the drum with a dial indicator, and the runout was within 0.02mm, which met the use requirements; Also 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 rubber blanket were bent by 8 When the pendulum is in the vertical position, it is wavy, and the maximum error of the parallelism of the clamping rod is 2mm

(4) bending machine

there is no diagonal plate drawing device on the plate cylinder of PJs machine, so it is very critical for the plate to be bent on the bending machine. If the parallelism of the bending machine is not enough, the diagonal overprint will exceed the standard, causing the bending skew. This kind of fault is difficult to adjust on the machine. PJs bending machine used for a period of time, some parts of the steel is often used, so one of the screws of the material is loose. After inspection, the parallelism error of the platform guide rail of the bending machine can reach 0.3mm at most, and the bent printing plate cannot be corrected on the machine

in order to ensure the bending accuracy, technicians specially made a special measurement and correction tool to correct the parallel accuracy of the guide rail analysis of the bending platform. When measuring and correcting, put 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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