At present, offset printing is the main printing method for printing companies, and lithographic offset printing due to the failure of the paper feeding system makes the printed products overprint, black unevenness, and even printing can not be carried out, delaying delivery. This is one of the most difficult problems encountered by printing workers. At present, offset presses used by printing companies all over China are basically overlapping paper feeding. Although the structure of the paper feeding system is different, the working principles are similar, and the generated faults have certain regularity. Generally, in the printing process, The most common occurrence is a double or multiple sheet feed failure. Now some analysis and discussion are made on the main reasons and countermeasures in this respect.
1. The paper is uneven and the edges are upturned. When the airflow from the loose paper blowing nozzle touches the edge of the paper, the airflow is divided into two parts because the edge of the paper curls up into a round and lone angle. One part of the airflow lifts the paper upward, while the other part of the airflow presses the paper downward, making the paper unable to separate, and the paper blocking brush is also useless, causing double or multiple sheets, or even a large stack to enter the cardboard. The general processing method is to flatten the paper and facilitate separation.
2. The paper loading height exceeds the allowable height of the paper stopper. According to the previous printing experience, the height of the general paper loading should be about 5mm lower than the paper stopper. If the adjustment is inappropriate and exceeds its allowable range, double or multiple sheets will be generated to enter the cardboard. The general processing method is to control the wedge to keep the paper on the same plane. If the model has an adjuster, you can use the adjuster to reduce the paper height.
3. Blowing presser foot and paper blocking brush extend too little into the paper edge. According to the previous operating experience, the general paper blocking brush extends into the paper edge of about 8mm, and the air pressure foot extends into the paper edge of about 10 ~ 15mm. If the adjustment is improper or the paper is not cut properly, double or more sheets will appear Zhang. Generally, the paper feeder is adjusted into the whole, so that the separation nozzle is about 5mm away from the edge of the paper, and the paper blocking brush and the air pressure foot are adjusted to solve the problem.
4. When the paper is too thin, the air volume is not adjusted properly. When printing 70g / m2 thin paper, if the air volume is not adjusted properly, it is also easy to produce double or multiple sheets. The general processing methods are as follows: â‘ Adjust the blowing foot downward to increase the distance between the stack and the paper suction nozzle; â‘¡ Adjust the air volume appropriately; â‘¢ Cut the rubber ring or the transparent glue on the paper suction nozzle Paper to reduce the wind force; â‘£press the paper blocking brush down a bit and increase its pressure to control.
5. The paper is not loose or sticky. Generally, when cutting the paper, the cutting edge is sticky, or when printing the full version of the semi-finished product, water stains and ink stains cause sticking, thus forming double or multiple sheets. Therefore, before printing, that is, when the paper is loaded into the unit, the paper must be shaken and stacked, the semi-finished products should be loosened one by one, and the package should be installed a little less to avoid sticking due to heavy pressure. Knot.
6. The blower presser foot wears out. When the blower 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 the direction, and the paper will move forward , Making the paper blocking brush useless, the paper suction nozzle will suck on the edge of the paper when it sucks down the paper, and forms double or multiple sheets. It is generally handled by replacing the new blower presser foot. If the wear is not serious, It can be solved by soldering copper sheet and then flattening it with a knife.
7. In general, the paper conveying system produces double or multiple sheets, which are generally the above situations. Before operating the machine, pay attention to the causes and treatment methods of the above faults, which can be completely avoided.
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