The faults caused by offset printing are mainly inaccurate overprinting, uneven ink color, etc. In the previous article, the causes and solutions of inaccurate overprinting have been discussed, and will not be discussed here. The following introduces the faults of the paper feeding system and the uneven ink color.
Double or multiple faults in the paper feeding system 1. The paper is not flat and the edges are upturned. When the air flow from the loose paper blowing nozzle touches the edge of the paper, the edge of the printed sheet is raised to an arc angle, and the air flow is divided into two parts: one part of the air flow lifts the paper upward, and the other part of the air flow makes the paper downward Pressure, the two parts of the air flow make 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 remove the paper for knocking paper processing, so that the paper is smooth and easy to separate.
2. The paper loading height exceeds the allowable height of the paper holder. According to the previous printing experience, the height of the general paper loading should be about 5mm lower than the tooth paper. If the adjustment is inappropriate and exceeds its allowable range, double or multiple sheets will be produced to enter the cardboard. The general processing method is to use a stopper wedge to control and 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 into the paper too little. According to the previous operation experience, the general paper blocking brush extends into the paper edge about 8mm, and the air blowing pressure foot extends into the paper edge about 10-15mm. Double or multiple sheets will appear if the adjustment is incorrect or the paper is not cut properly. 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 treatment methods are as follows: (1) Adjust the blowing foot downward to increase the distance between the stack and the separation nozzle; (2) Adjust the air volume appropriately; (3) Decrease the separation nozzle Use rubber bands or transparent glue to reduce the wind force; (4) Press the paper brush down and increase its pressure to control.
5. The paper is not loose or sticky. Generally, when cutting paper, there is adhesion at the cutting edge, or when printing the full version of the semi-finished product, water stains and ink stains cause adhesion, thereby forming double or multiple sheets. Therefore, before printing, that is, when the paper is loaded into the unit, it must be shaken hard and stacked, and 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. .
6. The air pressure foot is worn. 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, the paper will move forward, and the paper blocking brush will be lost Function, when the paper separation nozzle sucks the paper down, it will suck on the edge of the paper and form double or multiple sheets. Generally, it is replaced by a new blower presser foot. If the wear is not too serious, it can be solved by welding copper pieces and then flattening it with a file.
Product ink unevenness Reasons for product ink unevenness: (1) The cylindricity wear of each rubber roller of water transfer, ink transfer, ink distribution and plate-based ink is too poor, the shaft head of the bearing is worn, the surface of the rubber roller is aging, Decreased ink capacity, etc .; (2) Peeling of the water roller layer, excessive wear on cylindricity, thin ink deposit on the surface, and ink deposits on the two ends, which cause uneven roller jump and ink cross; (3) support The lock of the water and ink rollers and the swinging bracket are heavily worn, which causes the rubber roller to jump when it is against the plate, which causes the pressure of the plate to become unstable, resulting in unbalanced ink and ink, uneven ink color, dry plate, ink bar, old version (reliable Plate rubber roller pressure is too heavy) and other phenomena; (4) Water roller velvet sleeve aging or poor quality causes the water transmission capacity to decrease; (5) The pressure of each ink roller, plate cylinder and plate ink roller is not regularly checked; (6 ) If the roller drive gear wears out of tolerance, a regular "gear ink bar" appears at the same pitch as the gear pitch.
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