Comprehensive discussion on the technology of the

2022-09-22
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Comprehensive discussion of web offset press technology structure part II

2 traditional mechanical transmission

1) transmission characteristics and requirements

① strict speed ratio requirements: web offset press is composed of paper feeding, printing, folding and other main parts. In the form of web paper unfolded as a paper belt, it is printed and folded (or cut into a single sheet of paper) in turn by the paper feeding system. Unlike the single sheet offset press, which uses its teeth to firmly hold and stably drive the paper for printing, the smooth movement of the web offset press's paper belt completely depends on the strict tension control of the paper belt. In order to ensure the stable and reliable tension of the paper tape, the speed ratio of the tight spot resources of traders in each department of the web offset press is required to be very strict. Mechanical design should not only ensure strict speed ratio, but also have many adjustable links. For example, the tension control feedback system of the paper feeding system, the stepless speed regulation of the paper feeding roller, the stepless speed regulation of the cold B, C, D, e and f-level counter rollers, the stepless speed regulation of the triangle pattern roller, the stepless speed regulation of the relevant parts of the folding part, etc. The setting of the specific stepless speed regulation position and the determination of the control mode (manual and automatic) are mainly different according to the grade, purpose, accuracy and printing quality requirements of the web offset press

② large speed regulation range: how to choose the well cover pressure tester for web offset press? The normal printing speed of is very high. When wiping the printing plate, rubberized cloth and threading paper, it is required to use a lower speed. Therefore, the speed regulation range of web offset press is very large, and the maximum and minimum speeds often differ by tens of times to hundreds of times. In order to meet the requirements of a wide range of speed regulation, many web offset presses are designed with separate low-speed motors. Low speed motor is used for plate wiping, and main motor is used for normal printing. Due to the progress of technology, there are many AC motors with variable frequency speed regulation, so only one motor is enough

③ high requirements for transmission accuracy: in order to ensure the quality of web offset press in high-speed printing, high requirements are put forward for the transmission system, especially for commercial web offset press. In the traditional mechanical transmission, helical cylindrical gear and spiral bevel gear are more used in web offset press, which also puts forward high requirements for the accuracy of the gear to improve the transmission accuracy and running stability. In shaftless transmission, better control elements are often used to ensure the special requirements of web offset press for transmission

④ stepless speed regulation is adopted for speed adjustment: in order to ensure the paper belt tension, printing quality and folding accuracy, the web offset press is equipped with many local micro speed adjustment mechanisms, and these micro speed adjustments must be stable and stepless. At the same time, in order to ensure the stability of paper tape tension and the requirements of printing quality and folding accuracy, the speed change must also be stable and stepless in the process of machine speed increase and decrease. If the smooth stepless speed regulation cannot be guaranteed, the tension will change. In serious cases, the paper tape may be broken or relaxed. Therefore, normal printing cannot be guaranteed

⑤ effective braking: the printing speed of the web offset press is very high. In the process of printing the most accurate brush, due to some fault, it may need to stop urgently. In order to ensure safety and prevent damage to the machine, the web offset press is required to have a sensitive, effective and reliable braking mechanism. And the relevant parts are required to have sufficient strength. Generally, in addition to braking on the main motor, each printing unit and folding machine is also equipped with a separate braking mechanism

⑥ reliable safety device: due to the complex structure and high speed of the web offset press, in case of overload and failure, in order to ensure the safety of personnel and equipment, the web offset press is required to have an effective and reliable safety device. The general electrical system is equipped with multiple overcurrent protection, and the mechanical structure is equipped with a safety device. The commonly used safety device is safety pin or safety key. Generally, the main drive of the web offset press is designed with an overload safety device separately. When the folding machine is overloaded or fails, the safety device is cut off and the folding machine stops working

⑦ the clutch relationship should be correct: the structure of web offset press is complex, and some parts often do not work according to the requirements of printed matter. For example, when the multi-color machine is printing monochrome and two colors, some printing units need to stop working; The folding machine stops working when cutting sheets of paper; When it is not folded by 32, the double folding drum needs to stop working; When folding is not needed, the folding mechanism needs to stop working; When the 16 opening is not folded, the 16 opening machete mechanism and folding conveying mechanism stop working. When relevant institutions need to work, they are required to enter the working state quickly. This requires relevant institutions to have clutch institutions. Due to the cooperation relationship between the action of each mechanism of web offset press and time, position, etc., it is required that the clutch mechanism must be in a fixed position when combined. Therefore, the joint position of the clutch mechanism of relevant parts is required to be fixed. The commonly used clutch mechanism is a single tooth clutch or similar mechanism. It should be pointed out here that the transmission ratio between the main drive shaft and the printing cylinder (when the development length is a cutting size) and the folding cylinder (when the development length is a cutting size) of the domestic web offset press is generally 2:1, and its clutch mechanism is often designed on the main drive shaft. Therefore, when the printing unit and the folding machine are combined, half a sheet of paper may appear. This is because when the main drive shaft rotates for two revolutions, the printing cylinder and folding cylinder rotate for one revolution. Therefore, when combining, only one of the two revolutions of the main drive shaft is closed, and the position is correct. If there is half a sheet of paper, you can disconnect the printing unit or folding unit, let the main drive shaft rotate again, and then connect the clutch. (to be continued)

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