Printing Pressure Adjustment Principles and Analysis of Common Problems (3)

In addition, the need to change the thickness of the cylinder liner is:

1) When the blanket has been deformed for a long time, the cushion of the rubber bridge needs to be properly thickened (this type of thickening usually requires a little trial at a time to achieve the best effect).

2) When the overprinting occurs, the circumferential overprinting is inaccurate. When this overprinting is overprinted along the size of the circumferential printing plate. { Considering the problem of overprinting in multi-color printing, we usually reduce the total thickness of the third and fourth printing plates and their pads by 0.05 mm (compression) compared to the first group when setting the printing pressure. }

On more advanced printing machines, since changing the center distance of the drum is simple enough to only rotate the handle or push the button, and the pressure display device is generally more reliable, it is generally advisable to use the second method to complete the adjustment. The benefits of doing so are many:

1) The adjustment is simple and convenient, that is, when the thickness of the substrate changes, or the pressure of the impression cylinder and the blanket cylinder needs to be adjusted during the printing process, we only need to change the center distance between the two rollers. There is no need to simultaneously increase or decrease the pad of the plate cylinder and the blanket cylinder. Adjusting the center distance of the roller on the current printing press is a relatively simple task, and even remote control can be performed on the console (many printers nowadays, as long as the operator enters the printing paper thickness control system, the system will automatically adjust The default value of the pressure, and automatically adjust).

2) It can effectively avoid the change of roller circumference due to the use of pad, and the speed difference of roller surface in printing occurs. This speed difference often leads to distortion of dots in printing and even related defects such as overprinting and ghosting.

3) Due to the change of printing pressure using the pad method in the replacement plate, overprinting problems may occur (when the diameter of the surface of the plate cylinder is increased, a circumferential shortening of the image finally transferred to the substrate occurs).

The adjustment of the center distance of the drum applies to the following situations at the same time:

A. When printing rough, uneven thickness paper, in order to increase the printing pressure of the blanket and impression cylinder, it is necessary to reduce the center distance between the blanket cylinder and the impression cylinder to meet the printing needs.

B When the machine is used for a long time, the roller gear or roller bearing wears badly, and if the backlash of the gear is too large and “ink bars” (bar heads) or other problems occur, it must be solved by appropriately reducing the roller spacing.

Printing pressure test:

(1) Gradually increase the paper full-page version:

1. Place a 0.4mm (normal than normal) pad in the blanket.

2. Wash the plate and evenly fill the plate with ink (recommended to use yellow ink).

3. Compress and transfer the full version of ink on the plate to the blanket.

4. Then observe if the ink distribution on the blanket is even.

The above method is a rough detection method, it can only detect whether the blanket is flat, the printing pressure is in a reasonable range (this detection can only limit a relatively large range), and because the operation is more cumbersome, so in There is not much used in the operation of the machine. The methods described in (2)(3) are more often used and work efficiency and effectiveness are better.

(2) Use signal strips in combination with full-size cable detection:

The method is the same as (1) except that the ink transferred to the blanket is the network cable and signal bar on the printing plate, and then the size of the printing pressure can be determined based on the detection result. Usually, this detection is very accurate, especially 50 %% of outlets are very sensitive to printing pressure. When the printing pressure is a little abnormal, it can be very obvious.

(3) pressure strips

The pressure is checked by the drum contact width, which includes checking the parallelism between the rollers and the pressure of the print cylinder. The process is similar to the above two methods. First, the printing plate is full of ink, then the machine is set to the middle position of the plate cylinder and the blanket cylinder, and the pressure is manually pressed. Finally, it is checked whether the streak on the blanket meets the normal requirements. The same process is repeated between the blanket and the impression cylinder (when there is a substrate), and the pressure between the blanket cylinder and the impression cylinder can be detected. The following table gives a set of data for the reference of the more common models (the roller gear indexing circle diameter is between 270-300, and the impression roller is doubled):

Liner Type Compression (mm) Indent Width (mm)

Plates - Erasers - Embossing Plates - Erasers - Erasers

Soft lining 0.2~0.3 0.2~0.4 7~8 8~9

Hard lining 0.08 or less 0.08 3 to 4 4 to 5

Because of the large influence of the width of the impression and the diameter of the drum, and the degree of softness and hardness of the extreme pad of the blanket, it is for reference only.