The throwing angle refers to the phenomenon of inadequacy of fitting on the trailing edge of the printed paper. In recent years, most rollover failures have occurred in multi-color offset printing. The main reason is:

(1) The front rule is not on a straight line, causing the paper to reach the front gauge, while holding less paper.

(2) Big difference in paper thickness

(3) Pressure in each color group is increasing

(4) The blanket cylinder is uneven

(5) There are differences in the elasticity of the impression rolls on both sides of the cavities

(6) The impression pad is smooth or too low on both sides of the impression cylinder

(7) As the blank area on the two sides of the printing plate is larger on both sides, the amount of wetting fluid in this area is larger, resulting in more wetting liquid on the paper, causing the stretching and retracting of the dragging part to form a rejection angle.

(8) The amount of liquid in the blank area on both sides of the printing plate is different, and it will also cause one side to form a rejection angle.

Similar problems occur in monochrome offset presses.

[Case]

A factory uses a four-color off-set offset printing machine to print atlases and uses 80g/m2 offset printing paper to print. Some red and blue slips are often found on the tip, especially some special symbols. For example, some city symbols are blue circles. red. Most of this phenomenon occurs in the latter half of the printed web.

[case analysis]:

The above example is a noticeable phenomenon of sloshing. The main reason for this phenomenon is that the printing pressure is not reduced enough. Therefore, the printing pressure must be re-determined and adjusted. In addition, it is also related to the tightness of the paper and the elasticity of the grippers here.

[Case]:

In the process of commissioning the CP2000-CD102 machine, a certain factory carried out color printing tests after passing the inspection of various indicators, and added portraits to different locations of the 50% flat screens of black, cyan, magenta and yellow. The test results showed that the coated paper and board of 128g/m2 or more were normal, but when testing the book of 80g/m2 coated paper, the “swing angle” phenomenon occurred in the lower right corner of the printed matter, and the overprint of the corner rule was not allowed.

[case analysis]:

This kind of “swing angle” failure is generally not related to the pressure and blanket lining of the printing plate color groups. May be related to dental caries, but when checking the caries, the caries are normal, and then the double-diameter impression cylinder is observed. When grabbing the paper, the caries do not hold the paper in the range of about 4mm in the lower right corner. The paper is slightly deformed when pressed, causing "sweeping angles."

Approach:

Re-set the position of the paper side pull gauge, adjust the relevant parts, and then try to print the boot, troubleshooting.

[Expert Tips]:

Whether it is a multi-color offset press or a monochrome offset press, do not make any reckless changes to some key parts and pay more attention to the position and range of the gripper. For harder paper, such failures do not occur easily.

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