Printing pressure adjustment principle and analysis of common problems (1)

Printing is the process of transferring ink to the surface of a substrate. Offset printing is certainly not an exception. The entire printing process is an ink transfer process. First, the ink in the ink fountain is transferred by the ink roller to the surface of the printing plate under a certain pressure and friction, and then the surface of the printing plate. The ink is transferred to the surface of the blanket under a certain pressure, and finally the ink on the surface of the blanket is transferred to the surface of the paper under the action of a certain pressure (discussed mainly on paper). We will find that the entire process is carried out under the premise of pressure. It is not difficult to imagine that without pressure, ink cannot complete this series of transmission. This directly shows how important the role of pressure in printing is. It can be said that it is able to grasp the reasonable adjustment of pressure and is a prerequisite for good printing.

There are several common pressure adjustments that we commonly use in our work: ink pressure regulation, water pressure regulation, and inter-drum pressure regulation. This article will discuss the principle of adjusting the pressure between rollers (also called the printing pressure directly) and the printing problems caused by pressure.

For the adjustment of printing pressure, I believe that the following steps should be followed:

First, data preparation. There are three main sources of data:

1. Actual measurement. The actual measurement is mainly the measurement of printing plates and blankets. When using a micrometer for measurement, it should be noted that several points should be measured at the same time on different parts of the printing plate or blanket, and then averaged; in addition to taking into account the deformation of the blanket after stretching on the machine, The thickness of the blanket measured under the machine should be slightly larger than the calculated thickness. Generally, the thickness of the blanket is controlled to be 0.1mm larger than that of the ordinary blanket, and about 0.15mm larger than that of the air-cushion blanket. After the liner and the blanket are tightened into the roller, it is just The correct thickness.

2. The data on the random description of the printing press. There are two kinds of data about the printing pressure on the random description of the offset printing press. One is to mark the absolute size of the cylinder and the pillow, including the plate cylinder, the blanket cylinder, the diameter of the impression cylinder, and the three-roller pillow. Diameter, also marked with the machine's roll gap when printing certain paper (many machines marked with 0.1mm as standard), plus the total thickness of the plate and blanket and its liner; there is a Directly given the roller diameter reduction (relative height of the surface of the roller bearing and the roller body surface), excessive roller (the amount of lining higher than the surface of the roller bearing), the gap between the rollers; the concept of convenient operation of the printing press operator has become a The trend of machine design is, of course, also in the use of equipment. It has become more and more fool-like in the provision of data, and more and more calculations of printing pressure and roller clearance have been less and less used in the past. Arrived;

3. Determine the printing pressure by setting the printing process and the condition of the machine. At the same time, we have a more ideal setting for the roller lining (we will have a focused discussion in this article). This step mainly depends on the combination of computation and actual experience.

2. Measure and adjust the center distance of the roller according to the reference value of the roll gap specified in the instruction of the printing machine . Modern printing presses can generally be automated. However, for the older domestic models, such as the J2108 and J2205 models, this step is often very cumbersome. First of all, the surface of the cylinder should be removed (or it will affect the measurement results), and then clean the roller, and finally use the method of pressing the wire (in the state of pressure, put the fine wire into the gap between the pillow, and then press the printing press Flatten it.) Measure and then adjust. Then measure and adjust. Repeat this process until the roll gap reaches the standard value. The reason why such a complicated process to adjust the printing pressure is that the data of the roll gap of the old-fashioned domestic printing machine is often displayed on the outside of the machine by mechanical means (such as a screw dial), especially for a machine with a relatively long service life, from The data read on the dial is often not trustworthy.

The center distance of the pillow is not fixed. When the machine is old and the wear of the roller gear is serious, sometimes the “gear roller” caused by the improper meshing of the gears will be reduced as needed. Roller clearance (adjustment of the roll clearance is actually the adjustment of the center distance of the roll).

Third, according to the data given in the instructions for use ( in the more traditional printing press instructions, the total thickness of the plate and blanket and their respective lining are given) on the measurement of the printing plate and blanket to be used Calculate the lining thickness, and reasonably lining the plate and blanket.

Plate lining thickness = total thickness of printing plate and pad - plate thickness

Thickness of rubber blanket lining = Overall thickness of rubber blanket and lining - Rubber blanket thickness

4. After the lining is completed, press the printing press to check if there is any mechanical problem. Then move the long car and touch the surface of the printing plate or the blanket to check if there is uneven surface, if any, it may be due to The liner is lining with foreign objects or wrinkled. Need to be eliminated immediately.

The above four steps are a relatively complete pressure adjustment process. Actually, only the old-fashioned home-made printing presses must follow the above steps. This process has become quite simple on modern, more advanced printing presses. Many times, only the control window is required. The input printing paper thickness and the desired printing pressure (usually the compression of the blanket cylinder) are sufficient, and the remaining computers can be automatically completed.

The above-mentioned procedure is to adjust the machine according to the instructions for use. The gap between the pillow and the pad thickness is used. When the thickness of the substrate is assumed, the printing process is generally set. So some simple calculations are used when the thickness of the substrate changes:

Plate and blanket cylinder pressure (compression) = (plate cylinder diameter + blanket cylinder diameter) / 2+ plate thickness + plate pad thickness + blanket thickness + blanket pad thickness - [(Roller Plate Roller Diameter + Blanket Roller Diameter) / 2+ Roller Clearance]

The pressure between the blanket cylinder and the impression cylinder (compression) = (the diameter of the blanket cylinder + the diameter of the impression cylinder) / 2 + the thickness of the blanket + the thickness of the blanket + the thickness of the substrate - [(the blanket cylinder roll) Pillow Diameter + Roller Diameter of Imprinted Roller/2+ Roller Clearance]

The pressure of the plate cylinder and the blanket cylinder (compression) = the thickness of the printing plate and its pad + the thickness of the blanket and its pad - the reduction of the plate cylinder + the reduction of the blanket cylinder + plate cylinder and blanket Roller clearance

The pressure between the blanket cylinder and the impression cylinder (compression amount) = the thickness of the blanket and its pad + the thickness of the substrate - the contraction amount of the blanket cylinder + the reduction of the impression cylinder + the rollers of the blanket cylinder and the impression cylinder gap

Under normal circumstances, we set the printing pressure mainly based on the instructions for printing equipment. The print pressure values ​​given in the instructions for use that we can generally see are based on the assumption that the print paper has a thickness of 0.1 mm. However, in the setting of printing pressure, the standards given by equipment often have some changes due to the actual situation.

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