Printing pressure adjustment principle and analysis of common problems (below)

Above we discussed how to determine a suitable printing pressure and how to adjust the printing pressure. Its purpose is nothing more than to ensure the printing pressure within a reasonable range when printing. In the actual production, whether the printing pressure is large or small will cause this or that problem.

    Printing pressure is too small will lead to ink can not be transferred normally, printed Internet points are empty, and other printing defects. We are accustomed to think that printing pressure is high, then the amount of ink transfer will be larger, but in the production of printing pressure and ink transfer is not proportional to the relationship. When the printing pressure is greater than a certain range, the amount of ink transferred will not only become larger with the increase of the printing pressure, but will become smaller. At the same time, the printing pressure is too large to cause the printed matter to increase or even spread. Excessive printing pressure can also cause damage to the mechanical structure of the printing press. A more direct manifestation is the wear of the printing plate and the damage to the surface of the printing material. From the above we can see that the printing pressure is too small and too large to be in printing, and accurate guarantee of reasonable printing pressure is very necessary.

Other analysis of common problems caused by printing pressure (pressure expressions mentioned below are all blanket compressions) . The following discussion will be mainly based on mechanical compression.

1.      Stick

cause:

( 1) The ink bars that are seriously worn by the roller gears.

1. Adjust the center distance too large;

2.. Or the roller gear is seriously worn. The backlash of the gear is more than 1.0mm. When the drum is pressurized, the gears vibrate, resulting in frictional sliding on the surface of the contacted roller. This eventually results in deformation of the dots during the transfer process.

Solution:

1. Replace new gears;

2 properly reduce the center distance of the roller, the gear meshing tightly, so that the backlash is less than 0.1 mm;

3. Use a soft lining. The compression between the plate cylinder and the blanket cylinder should not exceed 0.1 to 0.15 mm; the pressure between the blanket cylinder and the impression cylinder should not exceed 0.15 to 0.2 mm plus the thickness of a piece of paper.

( 2) The roller bars are worn out due to the wear of the roller bearings. When the shaft head and bush wear seriously, the squeezing mouth immediately yields after being pressed, causing sliding friction and deep dark bars. Solution: 1 replace the new sleeve; 2 if the old low-speed offset press can tighten the rigid band on the plate head.

( 3) The pressure between the plate cylinder and blanket cylinder is too high. The ink stick feature is a fixed area of ​​the ink bar. The pressure between the printing plate and the blanket cylinder is too large, and the blanket generates a large frictional slip under the effect of the extrusion, thereby causing the dot to be deformed to form the ink stick. To discriminate whether the pressure between the two rollers is too large, the obvious feature is the "click" sound when the pressure is turned on, and the surface of the plate is generally bright after printing 5,000 sheets.

Solution: Pads of plates and blankets should be digitized. The thickness of the plate liner must be within ± 0.03 mm of the standard , and the thickness of the liner in the blanket should be such that the pressure is as good as possible.

2. Longitudinal ghosting

cause:

( 1) Improper drum pressure. The ghosting feature is the appearance of several longitudinal ghosts at the start of printing. This is because the drum pressure can not be combined at one time. When it takes several times to complete, its various pressures are different. The compressive deformation of the blanket is also different. When the dots on the printing plate are transferred to the blanket, each time Imprints cannot overlap and produce ghosting. The reason for this is that the roller clutch mechanism is worn or loose, or the pressure between the rollers is too great.

Solution: Check the roller clutch mechanism. The loose screws should be tightened and the worn ones should be replaced. If it is a pneumatically combined machine model, be aware of whether the air path leaks or if there is any problem with the compressor air pressure. When the pressure between the rollers is excessive, the pressure of the rollers must be properly reduced.

( 2) The blanket is too loose. Ghost features are full or partial longitudinal ghosting. There are two situations in which the blanket is stretched too loose: one is that the entire blanket is stretched too loosely, causing the blanket not to be reset in time after being pressed, resulting in a large area of ​​ghost image. Second, the blanket is cut and skewed or clamped. Inaccurate, resulting in partial stretch too loose and cause partial ghosting.

( 3) The pressure between the rollers is too large. Ghost features are large area longitudinal ghosts. The pressure between the rollers is too large, especially when the combined pressure of the blanket cylinder and the impression cylinder is too large, the displacement of the blanket is large, and it cannot be completely reset after each transfer, resulting in a large-area longitudinal ghost.

Solution: When large vertical ghosting occurs, check for excessive pressure between the rollers. If it is too large, the pressure between the plate cylinder and the blanket cylinder should be adjusted to 0.1-0.15 mm, and the pressure between the blanket cylinder and the impression cylinder should be adjusted to 0.2-0.25 mm.

3. Paste, flower version

The reason is that the pressure between the rollers is too high. Sometimes the pressure between the impression cylinder and the blanket cylinder is insufficient, and the pressure between the plate cylinder and the blanket cylinder is just right. The operator then cushions the blanket, resulting in a plate cylinder. The pressure between the blanket cylinders is too great and increases friction.

Solution: When the above drawbacks occur, check whether the roller pressure is too large.

1 Recalculate and view the rollers of the rollers