Several offset failures
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
The faults caused by offset printing are mainly the inaccurate printing of printed products, uneven color of ink, etc. In the previous article, the causes and solutions of inaccurate overprinting have been mentioned, and will not be discussed here. The following describes the failure of the paper feeding system and uneven ink color.
Double or multiple failures in the paper feeding system
1. The paper is not flat and the edges are upturned. When the airflow blown by the bulk paper blowing nozzle contacts the edge of the paper, the edge of the printed sheet is curled into an arc angle, and the airflow is blown out into two parts: one part of the airflow lifts the paper, and the other part of the airflow causes the paper to go down. Pressing, the two parts of the airflow make the paper unable to separate, and the paper stopper brush also loses its effect, causing double or multiple sheets, or even a large stack to enter the paperboard. The general treatment method is to remove the paper for anti-tapping, so that the paper is flat and facilitate separation.
2. The paper loading height exceeds the allowable height of the paper teeth. According to past printing experience, the height of general paper loading should be lower than about 5mm of the paper. If the adjustment is not appropriate and exceeds its allowable range, two or more sheets will be produced. The general treatment is to use a cork wedge to control the paper on the same plane. If you have a regulator model, you can use a regulator to reduce the paper height.
3. the blowing presser foot and the paper stopper brush into the paper become too little. According to the previous operating experience, the general paper stopper brush protrudes into the paper edge by about 8 mm, and the blowing pressure foot extends into the paper edge by about 10-15 mm. If the adjustment is not correct or the paper is cut, double or multiple sheets will appear. Generally, the paper feeder is adjusted into a whole, so that the paper separation nozzle is about 5 mm away from the edge of the paper, and the paper stopper brush and the blowing pressure foot are adjusted to solve the problem.
4. When the paper is too thin, the air volume is not adjusted properly. When printing 70 g/m2 of thin paper, if the air volume is improperly adjusted, it is easy to produce double or multiple sheets. The general treatment method has the following points: (1) adjust the blowing foot downwards, increase the distance between the paper pile and the paper separation nozzle; (2) adjust the small air volume appropriately; (3) reduce the separation on the paper separation nozzle Rubber band or clear plastic to reduce wind; (4) Press the paper brush down and increase its pressure to control.
5. The paper is not loose or sticky. Generally, when the paper is cut, when the cutting edge is bonded, or when the full version of the semi-finished product is printed on the ground, the water stain and the ink stain cause adhesion, 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. For the semi-finished product, a small stack of small pieces should be loosened. When loading the machine, it should be installed less, avoiding heavy pressure and causing bonding. .
6. the blower 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 be angled, the force will change direction, and the paper will move forward, causing the paper stop brush to be lost. The paper is sucked into the edge of the paper when it is sucked down, and forms two or more sheets. Generally, it is replaced by a new blowing presser foot. If the wear is not serious, it can be solved by welding copper pieces and then using a trowel to flatten.
Product color unevenness failure
Reasons for uneven ink color: (1) The cylindricity wear of each rubber roller of water transfer, ink transfer, uniform ink and offset ink is poor, the shaft head of the bearing is worn, the skin of the rubber roller is aging, and the ink transfer capacity is decreased; (2) The water-separating roller layer peels off, the cylindricity wears out, the surface has a thin ink layer, and the two ends grow with ink-collecting strips, causing the roller to jump unevenly; (3) supporting the plate water and ink The lock of the roller and the swing bracket are severely worn, causing the rubber roller to jump against the plate, causing the pressure of the plate to be unstable, resulting in unbalanced ink, uneven ink, dry plate, ink bar, and old version (by the pressure of the rubber roller) (4) the phenomenon that the water roller pile is aged or poor in quality, resulting in a decrease in water transfer capacity; (5) the pressure of each of the ink roller and the plate cylinder and the offset ink roller is not regularly checked; (6) if the roller drive gear The wear is out of tolerance and there is a regular "gear ink bar" with the same spacing as the gear spacing.