The printing machine is designed and manufactured to achieve certain printing process requirements. Different printing plate types have different requirements for printing presses. If the printing plate used is a lithographic (PS version), it should be printed with a lithographic offset printing machine, and the printing device of the lithographic offset printing machine is significantly different from that of a letterpress or gravure printing machine; if the printing plate used is a gravure, then gravure printing The imprinting mechanism of the machine must be able to ensure the process requirements for achieving a strong printing pressure, because the printing pressure required for gravure printing is much greater than that of letterpress printing machines, especially offset printing machines. Therefore, the printing process characteristics are the main basis for designing and manufacturing printing machines.
The suitability of printing also has a great influence on the design, manufacture and use of printing machines. The so-called printability refers to the overall performance of the substrate, printing ink and other materials that match the printing conditions and are suitable for the printing job. In addition to the printability of the above printing materials, in order to obtain good printability during printing, the structure of the printing machine should also be continuously improved. For example, in order to maintain continuous and stable ink supply, an ink stirrer is specially installed in the inking system to keep the printing ink stable in fluidity to achieve the normal transfer of ink.
As another example, the dampening device of a lithographic offset press must ensure that an appropriate amount of water can be supplied. Excessive water supply will cause emulsification of ink; too small water supply will easily cause dirty failure. The principle of controlling the amount of water supply is to reduce the water supply as much as possible under the premise of ensuring the printing quality, thereby prompting people to continuously improve the wetting device to meet the basic requirements of printability. In addition, in order to improve the transfer rate of ink, in addition to using different printing methods, printing speeds, printing inks and printing materials, improving the imprint mechanism is also an important measure. It can be seen that the specific structure and quality of the printing press are closely related to the printability.
In order to evaluate the printing press correctly, the printing press manufacturers and printing press users put forward the following three requirements for the printing press.
Working performance
The working performance of the printing press mainly includes three indicators: overprint accuracy, ink color leveling and productivity.
â‘ Overprint accuracy
In the process of chromatic printing, the accuracy of the overlapping of prints is one of the main technical indicators of the working performance of the printing press. In the process of register printing, the conveyance, handover and printing of paper, etc., whether at low speed or high speed, should be able to ensure that they are in the specified position. For fine prints and color printing, this is even more important. This requires that the transmission system of the printing press, the position and time of the paper transfer and handover, and the transmission accuracy of the printing plate and the imprinting mechanism should meet certain requirements. Therefore, when we analyze the printing press, we must focus on understanding the various links related to overprint accuracy, mastering its characteristics and the role it plays.
â‘¡The ink color is solid
Uniform ink color refers to the consistency of the ink layer thickness of the printed product and the clarity of the ink mark. This is another indicator to measure the quality of the print, and is also an important content to evaluate the working performance of the printing press. Regardless of which printing method is used, to print a clear and solid ink, not only the ink color is uniform, but also sufficient printing pressure is required, which requires the printing device, including the inking system, to have higher accuracy and performance .
â‘¢Productivity
The productivity of the printing press is generally expressed in terms of printing speed. The method of expressing the printing speed is expressed in sheets / hour for a sheet-fed printing press; in m / min for a web press. The structure and characteristics of the printing machine and the technical level of the automatic control system are the main factors that determine the productivity. For example, the flattening press uses an impression cylinder, which has a significantly higher printing speed than the flattening press, but the reciprocating motion of its platen limits the further increase in productivity. Therefore, it is gradually printed by round presses. Replaced by machine. At present, printing presses are developing in the direction of large-scale, high-speed, and linkage, in order to maximize productivity. [next]
Use performance
The performance of the printing press mainly includes operating performance, safety and reliability and durability.
â‘ Operating performance
While improving the printing speed and the degree of automation of the printing press, it is also necessary to ensure good operating performance. Printing machines generally occupy a large area, and several sets of control panels should be installed to ensure that operators can operate at each main working position. Each operation vertical plate should conform to human movement habits, the working position is easy to observe, the adjustment position is intuitive and easy to contact, etc.
â‘¡Safe and reliable performance
In order to ensure the safety of the operator's personal and equipment, in addition to the absence of safety protection devices, there are also safety protection devices and safety insurance devices on the printing press, which can automatically shut down once the machine fails.
â‘¢Durability
It is required that the printing machine can maintain its original accuracy after long-term use, that is, the machine has a long service life, which has important economic significance for the country and enterprises. To achieve this, the parts materials and heat treatment process should be selected reasonably to ensure the wear resistance of the parts; in order to improve the motion accuracy of the transmission system, each matching surface should have a reasonable shape accuracy of several bodies and a good matching gap and lubrication device Wait.
Process performance
On the premise of satisfying the main working performance of the printing press, it should strive for its structure to be simple and compact, to have good processing technology, reduce manufacturing cost, and facilitate assembly and maintenance.
It should be pointed out that the above requirements are often mutually restrictive and contradictory. For example, to improve the accuracy of overprinting, it is not easy to achieve under high-speed operation. Because the printing speed is further improved, it will bring some new problems: the rapid and accurate handover and transmission of paper, the quick drying of ink and the stability of moving parts will be greatly affected, making it difficult to ensure the accuracy of overprinting. If a control device is added, the manufacturing cost of the machine will increase. As another example, there is a certain contradiction between simple structure and improved automation, printing speed and service life. Therefore, we can only use the above requirements as the starting point for analyzing the problem. According to the requirements of the printing process on the machine, we should grasp the main contradictions and weak links, weigh the weight from the whole, and properly resolve the secondary contradictions on the premise of meeting the main requirements. This is also the thought method that should be followed when researching and designing printing presses.
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