Reasons and Analysis of Double or Multiple Sheet Feeding

Offset printing is the main printing method for printing companies. The lithographic offset caused by the failure of the paper-transporting system made the overprinting of printing products inaccurate, uneven black, and even printing could not be carried out, which delayed the delivery time. This is one of the more thorny issues that printers most often encounter. Offset presses used by printing companies throughout China are basically overlapping paper feeders. Although the structure of the paper feeding system is different but the working principles are similar, the resulting failures also have certain regularities.
In the printing process, the most frequently encountered is a double-sheet or multiple-sheet process, and the most frequently encountered is a double-sheet or multiple-sheet feed failure. Now we analyze and discuss the main reasons and countermeasures in this area.
1, the paper is not smooth, the edge is upturned. When the airflow blown by the paper blowing nozzle comes into contact with the edge of the paper, the paper stream is blown out in two parts as the edge of the paper is twisted into a circular arc angle. A portion of the airflow lifts the paper upwards, while the other portion of the airflow pushes the paper down so that the paper cannot be separated and the blocking brush also loses its effect, resulting in double or multiple sheets, or even a large stack 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 the stopper. According to previous printing experience, the height of general paper loading should be less than 5 mm. If the adjustment is not appropriate and exceeds the allowable range, two or more sheets of incoming cardboard will be produced. The general approach is to control the wood wedge to keep the paper in 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 too little into the paper edge. According to previous operating experience, generally the paper bristle brush extends into the paper edge approximately 8 mm, and the air blowing foot extends into the paper edge approximately 10-15 mm. If the adjustment is improper or the paper is cut out, it will blow out two or more sheets. Generally, the entire paper feeder is adjusted in such a manner that the paper suction nozzle is approximately 5 mm away from the edge of the paper, and the paper baffle 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 70g/m2 thin paper, it is easy to produce double or multiple sheets if the air volume is improperly adjusted. The general processing method has the following points:
1 Adjust the blowing foot downwards to increase the distance between the paper stack and the paper suction nozzle;
2Adjust the air volume appropriately;
3 Cut the rubber band or transparent adhesive tape on the small paper suction nozzle to reduce the wind force;
4 Press down on the paper bristle brush to increase its pressure.
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. Generally, new hair pressure presser foot is used to deal with it. If the wear is not serious, it can be used to weld copper sheets, and then it can be solved by means of flattening.
In general, the paper-transporting system produces two or more sheets, usually in the above situations. Before operating the machine, it is completely avoidable to pay attention to the causes of the above-mentioned failures and the processing methods.

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