Several common offset faults

Offset printing is currently the main printing method for printing companies. The failure of lithographic offset printing due to the paper-transporting system is that the overprinting of printing products is not allowed, the black color is uneven, and even printing cannot be carried out, which delays the delivery period. This is one of the more thorny issues that printers most often encounter.
First, the number of straight double or multiple fault 1, the paper is not flat, the edge of upturned. When the airflow blown by the paper blowing nozzle comes into contact with the edge of the paper, the edge of the printed sheet is turned upwards into a circular arc angle, and the air blowing is divided into two parts. A portion of the air flow lifts the paper upward while the other portion of the air flow presses the paper down so that the paper cannot be separated and the baffle brush loses its effect, resulting in double or multiple sheets, or even large stacks entering the paper feed. The general approach is to remove the paper and perform an anti-knock paper process to make the paper flat and conducive to separation.
2. The loading height exceeds the allowable height of paper teeth. According to previous printing experience, the height of the general loading paper should be less than about 5mm. If the adjustment is not appropriate and exceeds the allowable range, two or more sheets of incoming cardboard will be produced. The usual method of handling is to use a cork wedge to control so that the paper stays on the same plane. If there is a regulator model, you can use the regulator to reduce the height of the paper.
3, hair pressure and stop paper brush into the paper too little. According to the previous operating experience, the general blocking paper brush extends into the paper edge approximately 8mm, and the air blowing foot extends into the paper edge approximately 10-15mm. If you do not adjust properly or the paper is miscut, you will see double or multiple sheets. Generally, the entire paper feeding machine is adjusted in such a way that the paper suction nozzle is approximately 5 mm away from the edge of the paper, and the paper bristles and the presser foot are adjusted to solve the problem.
4. When the paper is too thin, the air volume is adjusted improperly. When printing thin paper of 70 g/m^2, two or more sheets may easily be produced if the air volume is improperly adjusted. The general processing method has the following points: (1) Adjust the blowing foot downwards, increase the distance between the paper stack and the paper suction nozzle; (2) Adjust the air volume appropriately; (3) Reduce the number of paper nozzles Either use a rubber band or transparent glue to reduce the wind force; (4) Press down the block brush and increase its pressure to control it.
5. The paper is not loose or sticky. Generally when the paper is cut, the cutting edge is bonded, or when the full version of the semi-finished product is printed on the ground, water stains and ink stains cause sticking, thereby forming two or more sheets. Therefore, before the paper is printed, that is, when the paper is loaded into the unit, it must be shaken and shuffled, and the semi-finished products must be stacked and fluffed loosely. When the machine is on the machine, it should be installed less to avoid adhesion due to heavy pressure. .
6, blow pressure foot wear. When the presser foot is used for a period of time, it will wear out. When it presses down on the paper, the paper will make an oblique angle, the force will change direction, the paper will move forward, and the paper brush will lose. The role of the paper suction nozzle down when the suction paper suction on the edge of the paper, and the formation of double or multiple. It is generally used to replace the new hair pressure foot to deal with, if the wear is not too serious, you can use welded copper, and then use the file to flatten the way to solve.
Second, the uneven ink product failure product causes uneven ink: (1) pass water, transfer ink, even ink and by the ink version of the cylindricity of the rubber roller wear is poor, wear bearing shaft wear, rubber roller aging (2) The water roll layer is peeled off, the cylindricity wear is poor, the surface has a thin ink deposit layer, and the two heads have an accumulative ink ribbon, causing the roller to beat unevenly; (3) ) Supported by the printing water, ink roller lock, swinging bracket, serious wear and tear, causing the roller to run when the plate caused by the pressure instability, resulting in ink and ink imbalance, uneven ink, dry version, ink bar, the old version (Rely on the pressure of the printing roller, etc.), etc.; (4) The ageing or poor quality of the water roller pile causes the water transfer ability to decline; (5) There is no regular check of the pressure of each ink roller and the platen roller and the reel-ink roller; (6) If the roller drive gear is worn out badly, a regular “gear roller” with the same pitch as the gear spacing appears.
Third, overprint failure 1, the impact of printing plate deformation on overprint. The metal sheet has certain extensibility. Under the action of tensile force, it will produce tensile deformation, and the zinc plate will have more pronounced tensile deformation. Under normal circumstances, we found that overprinting was not allowed during printing, and most of them were adjusted by stretching the printing plate. The greater the tensile force, the greater the tensile deformation of the layout, and the uneven distribution of the tensile deformation, the greatest force is exerted on the crotch edge and the crest side of the plate. The tensile deformation is also large, the internal force is small, and the tensile deformation is also small. small. Therefore try to use as little as possible to solve the overprint problem.
2. The effect of the increase or decrease of cylinder liner on overprint. In the printing process, since overprinting of the paper can not be punctual, a method of increasing or decreasing the thickness of the drum liner can be used to solve the problem of misalignment between the radial paths. The increase or decrease of the printing plate liner affects the plate's tensile deformation. The thicker the plate pad, the greater the dimensional elongation of the pattern. When the pad of the printing plate is reduced and the pad of the rubber roller is increased, the tensile deformation of the looming gray fabric increases, and the radial deformation of the pattern increases. Another is to reduce the thickness of the blanket cylinder, while increasing the thickness of the printing plate liner, the deformation of the blanket extrusion deformation is reduced, the latter commonly used.
3, the effect of blanket elongation on the pattern overlay. The blanket is stretchable, and the tighter the blanket is stretched on the drum, the smaller the elongation is, and the pattern change is small. (1) Choose a blanket with a small elongation. (2) In the process of overprinting, try to keep the tightness of the blanket unchanged.
Imprinting is not allowed. In addition to the above-mentioned reasons, attention should also be paid to mechanical, adjustment, and paper issues. In short, overprinting is not always done at the instant of high-speed printing, but is caused by a slight accumulation of changes. It is difficult to observe directly. Therefore, as long as we pay full attention to printing, analyze the reasons, and take the most appropriate measures, we can avoid or reduce the occurrence of fitting errors.