The correct evaluation of the printing press should start from three aspects
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The printing press is designed and manufactured to meet certain printing process requirements. Different plate types have different requirements for the press. If the plate used is a lithographic plate (PS plate), it should be printed with a lithographic offset press, and the printing device of the lithographic offset press is significantly different from the letterpress or gravure press; if the plate used is a gravure, gravure printing The embossing mechanism of the machine must be able to guarantee the process requirements of a strong printing pressure, because the printing pressure required for gravure printing is much greater than that of a letterpress printing machine, especially a lithographic offset printing press. Therefore, the printing process is the main basis for designing and manufacturing the printing machine.
The wetting device of the lithographic offset press must be able to supply the proper amount of water. The water supply is too large to produce emulsification of the ink; if the water supply is too small, it may cause a dirty malfunction. The principle of controlling the amount of water supply is to reduce the amount of water supply as much as possible while ensuring the quality of the printing, thereby urging people to continuously improve the wetting device to meet the basic requirements of printing suitability. In addition, in order to improve the transfer rate of ink, in addition to using different printing methods, printing speed, printing ink and printing materials, improving the imprinting mechanism is also an important measure. It can be seen that the specific structure of the printing press and the quality of the printed products are all closely related to the printability.
In order to correctly evaluate the printing press, the printing machine manufacturer and the printing machine user put forward the following three requirements for the printing machine.
Work performance
The working performance of the printing machine mainly includes three indicators: overprinting accuracy, ink color uniformity and productivity.
1 set of printing accuracy
In the process of color printing, the accuracy of the overlap of the print is one of the main technical indicators of the working performance of the printing press. In the process of color printing, the conveyance, transfer and printing of paper, etc., should be guaranteed to be in the specified position at low speed or high speed. This is even more important for fine prints and color printing. This requires that the transmission system of the printing press, the position and time of paper transfer 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 the various aspects related to the accuracy of overprinting, and master its characteristics and its role.
2 ink color
The uniformity of the ink color refers to the consistency of the thickness of the printed ink layer and the clarity of the ink. This is another indicator for measuring the quality of the printed product, and is also an important content for evaluating the working performance of the printing press. Regardless of the printing method used, it is necessary to print a clear and solid ink, which not only requires uniform ink color, but also requires sufficient printing pressure, which requires high precision and performance of printing equipment, including inking systems. .
3 productivity
The productivity of a 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 machine and m/min for a web-printing machine. The structural formation and characteristics of the printing press and the technical level of the automatic control system are the main factors determining the level of productivity. For example, the flat-pressing press uses an impression cylinder, which significantly improves the printing speed of the flat-pressing press, but the reciprocating motion of the plate limits the further improvement of productivity, so it is gradually rounded and printed. Replaced by the machine. At present, the printing press is developing in the direction of large-scale, high-speed, linkage, etc., in order to maximize productivity.
Performance
The performance of the press mainly includes operational performance, safety and reliability and durability.
1 operating performance
While improving the printing speed and automation of the printing press, it also ensures good operating performance. The printing press generally has a large footprint, and several sets of control panels should be provided to ensure that the operator can operate in every major working position. Each operation of the vertical plate should conform to the human movement habits, the working position is easy to observe, the adjustment position is intuitive and easy to contact.
2 safety and reliability
In order to ensure the safety of the operator's personal and equipment, in addition to the safety protection device on the printing machine, there must be a safety protection device, and a safety safety device is also provided. Once the machine malfunctions, it can automatically stop.
3 durable performance
It is required to maintain its original precision after long-term use, that is, the machine has a long service life, which is of great economic significance to the country and the enterprise. In order to do this, the parts materials and heat treatment process should be reasonably selected to ensure the wear resistance of the parts; in order to improve the motion accuracy of the transmission system, each mating surface should have reasonable shape accuracy and good matching clearance and lubrication device. Wait.
Process performance
Under the premise of the main working performance of the printing machine, the structure is simple and compact, with good processing technology, reduced manufacturing cost, and easy assembly and maintenance.
It should be pointed out that the above requirements are often mutually restrictive and contradictory. For example, to improve overprint accuracy, it is not easy to achieve at high speeds. Because the printing speed is further improved, it will bring some new problems: the rapid and accurate transfer and transfer of the paper, the quick drying of the ink and the smoothness of the moving parts will be greatly affected, making the overprinting accuracy difficult to guarantee. If a control device is added, the manufacturing cost of the machine will increase. For another example, there is a certain contradiction between the simple structure and the improvement of the degree of automation, and between the printing speed and the service life. Therefore, we can only use the above requirements as the starting point for the analysis of the problem, according to the requirements of the printing process for the machine, grasp the main contradictions and weak links, balance the weight from the overall situation, and properly resolve the secondary contradictions on the premise of meeting the main requirements. This is also the way to think about the design of printing presses.