2.1 Type of printing machine and cylinder arrangement
2.1.1 Several typical printing machines
1. Satellite printing machine.
The characteristic of the all-satellite printing machine is that there is only one impression cylinder, and there are four plate cylinders and rubber cylinders, as shown in Figure 2.1a:
(Figure 2.1a)
The printing cylinder can complete four-color printing after one revolution, which is fast and convenient, and it takes up little space. But its shortcomings are mainly: when printing large format, the impression cylinder needs to be very large, and the plate cylinder and the rubber cylinder are closely arranged, which causes great difficulty in installing and removing the printing plate and the rubber; The distance between them is too short, and the ink is completely wet and wet, which is not good for the transfer of ink. Because of these shortcomings, the large-format multicolor printing presses no longer use this cylinder arrangement. ?
The semi-satellite printing machine is characterized by one impression cylinder, two plate rollers and two rubber cylinders. As shown in FIG. The printing plate cylinder can make two-color printing with one revolution. Due to the small color set, it can make full use of space for arrangement and occupy a small space, so this model was once accepted by many printing machine manufacturers in the world. The representative ones are Beijing Renmin Machine Factory and German Roland Printing Machinery. Two-color machine produced by the factory. The disadvantage of this model is that the distance between the two colors is too short, and the ink is in a wet state. When four-color printing is performed, the interval between the second color and the third color is too long. Therefore, the current multi-color printing machine has not used this arrangement of cylinders.
2. To roll printing machine.
Roll-to-roll printing machine, also known as BB type printing machine, as shown in Figure 2.1b. There is no special impression cylinder for this type of printing machine, but the upper and lower rubber sheets are used as impression cylinders for each other. That is, each printing color group formed by the upper printing plate cylinder and the upper rubber cylinder; the lower printing plate cylinder and the lower rubber cylinder and the upper rubber cylinder constitute another printing color group. It can complete double-sided printing in one turn, so this model is very suitable for printing books and magazines. The disadvantage is that the position is too high, which brings great inconvenience to the operation and adjustment of the machine. Now other drum arrangements are also used to replace this model.
(Figure 2.1b)
3. Unit printing.
The simplest unit type printing machine is composed of a printing color group. This type of printing machine is suitable for monochrome printing. If multi-color printing is to be performed, it must be completed by overprinting. In this way, color printing is time-consuming and labor-intensive, and the level of the master of offset printing is also very high, so multi-color printing machines have appeared. At present, almost all multi-color printing presses adopt a unit-type cylinder arrangement structure. The characteristics of the unit type structure are: â‘ easy to operate. Because from the perspective of a unit, the arrangement is the simplest and the most available space. â‘¡Because the distance between each unit is much longer than the satellite type, this creates good conditions for the transfer of ink. â‘¢ The unit type printing machine is short and has a low center of gravity, which is conducive to the stable operation of the machine. â‘£According to the requirements, the number of units can be changed, so the units can be serialized, with strong interchangeability, and also provide convenient conditions for the subsequent requirements of other auxiliary printing equipment (such as glazing devices). Therefore, the unit type printing press has become the main direction of the development of printing presses.
(Figure 2.1c Double unit printing machine)
2.1.2 Arrangement of rollers
The arrangement of the cylinder is one of the most critical parts of the design of the offset press, and it is also the most studied place. At present, almost all the printing machine arrangement angles on the market are different. Which one is more reasonable is currently inconclusive, because there are many factors that affect the arrangement of the cylinder. However, no matter how many influencing factors, the final requirements for its working state are always the same, that is, â‘ when the drum is running, the force it receives is the smallest, and it can always be stable in a working state. â‘¡ The clutch of the roller is accurate, stable and the impact is minimum. â‘¢It is easy and convenient to carry out various operations on the drum.
From the perspective of the arrangement of the drum, the drum takes up the smallest space in a vertical plane, and the force of the drum is better, but from the perspective of the clutch pressure, the arrangement angle of the drum is preferably less than 90 ° (less than 180 ° The angle of the drum is called the arrangement angle of the drum), but this time the force of the drum shaft is the worst. Therefore, the arrangement angle of the general drum is between 90 ° and 180 °. This angle is currently around 130 °. As shown in Figure 2.2, there are two typical roller arrangements: one is the rubber roller on the left, and the other is the rubber roller on the right, each with its own advantages and disadvantages.
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