Four steps of printing pressure adjustment principle
Printing is a process that transfers ink to the surface of the substrate. Offset printing is of course not an exception. The entire printing process is an ink transfer process. First, the ink in the ink fountain is transferred to the surface of the printing plate by the ink roller under a certain pressure and friction, and then the surface of the printing plate. The ink of the ink transfers to the surface of the blanket under a certain pressure, and finally the ink on the surface of the blanket passes to the surface of the paper (this paper mainly discusses this paper) under the influence of a certain pressure. We will find that the whole process is carried out under the precondition of pressure. It is not difficult to imagine that without pressure in it, the ink cannot complete this series of transmission. This directly shows how important the role of pressure in printing is. It can be said that being able to master the reasonable adjustment of pressure is a prerequisite for good printing.
There are generally several types of pressure adjustments that are more common in our work: ink pressure adjustment, water pressure adjustment, and pressure adjustment between rollers. This article will discuss the adjustment principle of the pressure between the cylinders (which can also be directly called the printing pressure) and the printing problems caused by the pressure.
To adjust the printing pressure, I believe that the following steps should be followed:
1. Data preparation. There are three main sources of data:
1. Actual measurement. The actual measurement is mainly for the printing plate and blanket. Use a micrometer in the measurement. It should be noted that during the measurement, several points should be measured on different parts of the printing plate or the blanket at the same time, and then the average value is taken; in addition, considering the deformation of the blanket after stretching on the machine, in The thickness of the blanket measured under the machine should be slightly larger than the calculated thickness, and it is generally controlled to be: 0.1mm larger for ordinary blankets and 0.15mm larger for air cushion blankets, so that when the liner and blanket are loaded into the roller, it is just The correct thickness.
2. The data marked on the random description of the printing machine. The offset presses are marked on the random description. There are two main types of data on printing pressure: one is the absolute size of the cylinder and the roller pillow, including the diameter of the plate cylinder, blanket cylinder, impression cylinder, and three cylinder roller pillow The diameter is also marked with the roller pillow clearance of the machine when printing a specific paper (many machines are marked with 0.1? As the standard), and the total thickness of the printing plate and the blanket and its pad; there is also Directly give the amount of cylinder diameter reduction (the relative height of the surface of the roller pillow and the surface of the roller body), the excess of the roller (the amount of lining higher than the surface of the roller pillow), and the gap of the roller pillow; the concept of facilitating the operation of the printing press operator has become a The trend of machine design, of course, is also the same in the use of equipment. In the given data, it has become more and more a fool. For the previous calculation of printing pressure and cylinder gap, it has become less and less used. Arrived;
3. The printing pressure is determined by the setting of the printing process and the condition of the machine. At the same time, there is a more ideal setting for the roller lining (we will focus on the discussion in this article). This step relies mainly on the combination of calculation and practical experience.
2. Measure and adjust the center distance of the cylinder according to the reference value of the roller gap given on the printing machine instruction manual.
This step can be done automatically in modern printing machines. However, this step is often very cumbersome for the older domestic-made printers, such as J2108 and J2205. First, the pad on the surface of the roller should be removed (otherwise it will affect the measurement results), then the roller pillow is cleaned, and finally the method of pressing the lead wire (in the closed state, the fine lead wire is placed into the gap between the roller pillows, and then the printer is jogged) Flatten it) First measure and then adjust; then measure and adjust again, repeat this process until the roller pillow clearance reaches the standard value. The reason for such a complicated process to adjust the printing pressure is that the data of the roller pillow clearance of the old-fashioned domestic printing machine are often displayed on the outside of the machine by mechanical means (such as the screw dial), especially for machines with a long service life, from The data read on the dial is often untrustworthy.
The center distance of the roller pillow is not fixed. When the machine is old and the roller gear wears seriously, sometimes the "gear ink bar" due to the abnormal gear meshing occurs. At this time, it should be appropriately reduced according to the needs. Roller pillow clearance (the adjustment process of roller pillow clearance is actually the adjustment of the center distance of the roller).
3. According to the data given in the instructions (in the more traditional printing machine instructions, the total thickness of the printing plate and the blanket and their respective linings are given), the measurement of the printing plate and the blanket to be used is Calculate the thickness of the liner, and properly line the printing plate and blanket.
Thickness of printing plate package = total thickness of printing plate and liner—thickness of printing plate
Blanket blanket thickness = total thickness of blanket and blanket-blanket thickness
4. After the lining is completed, jog the printing machine to check whether there is any mechanical improperness, and then jog the carriage and rub the surface of the printing plate or the blanket with your hand to check whether there are uneven surfaces. If there are any, it may be due to The liner is covered with foreign objects or caused by wrinkling. Need to be eliminated immediately.
The above four steps are a relatively complete pressure adjustment process. In fact, only the old-fashioned domestic printing presses must follow the above steps. On modern more advanced printing presses, this process has become quite simple. Enter the printing paper thickness and the desired printing pressure (usually the amount of compression of the blanket cylinder), and the remaining computer can be automatically completed.
The procedure mentioned above is to adjust the machine according to the instructions. Among them, whether it is the roller gap or the pad thickness, the printing process is generally set when the thickness of the substrate is the assumed value. So when the thickness of the substrate changes, some simple calculations are used:
Pressure of plate cylinder and blanket cylinder (compression amount) = (plate cylinder body diameter + blanket cylinder body diameter) / 2 + plate thickness + plate pad thickness + blanket thickness + blanket pad thickness— [(Diameter roller roller pillow diameter + blanket roller roller pillow diameter) / 2 + roller pillow gap]
The pressure (compression amount) between the blanket cylinder and the impression cylinder = (the diameter of the blanket cylinder body + the diameter of the impression cylinder body) / 2 + the thickness of the blanket + the thickness of the blanket pad + the thickness of the substrate — [(blanket blanket roll Pillow diameter + embossing roller rolling pillow diameter) / 2 + Roller pillow clearance]
Pressure (compression amount) of plate cylinder and blanket cylinder = thickness of plate and pad + thickness of blanket and pad—diameter reduction of plate cylinder + diameter reduction of blanket cylinder + plate cylinder and blanket Roller pillow clearance
The pressure (compression amount) between the blanket cylinder and the impression cylinder = the thickness of the blanket and its pad + the thickness of the substrate-the reduction of the blanket cylinder diameter + the reduction of the impression cylinder + the roller pillow of the blanket cylinder and the impression cylinder gap
In general, when we set the printing pressure, we mainly set it according to the instructions of the printing equipment. The printing pressure values ​​given in the operating instructions we can generally see are given on the assumption that the thickness of the printed paper is 0.1 mm. However, in the setting of printing pressure, the standard given by the equipment will often have some changes due to the actual situation.
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