Printing part

(PRINTING UNIT) Printed parts are those devices in the printing press that are capable of printing on plates and rely on blankets to transfer images to print media (usually paper). In a monochrome printing press, printing is achieved by three printing cylinders, a plate cylinder, a blanket cylinder, and an impression cylinder. The correct contact between the three rollers is more important than the order. When printing, the three rollers must be pressed against each other to transfer ink. When not printing, the rollers should be able to separate. The line of contact between the rollers is called a nip line. The pressure at the contact surface is generally around 200 pounds per square inch (1,380 Pascals). In a multi-color printing press, several sets of such three-printed cylinders are required, and some paper feeding equipment is also provided between the rollers. Plate cylinder The plate cylinder is usually at the top of the three cylinders, with the plate loaded on it. Because the plate needs to be replaced frequently, the plate cylinder should be placed in a position where the operator can easily operate. There are four functions of the plate cylinder: * Fix the offset printing plate tightly; * Touch the printing plate fixed on it with the dampening roller and moisten the graphic part of the printing plate; * Make the printing plate fixed on it and The ink roller contacts and inscribes the graphic portion of the plate; * Transfers the graphics of the ink on the plate to the blanket. The plate cylinder has an approximately circular shape, and the material is mostly made of metal. On a sheet-fed press, the drum is not a closed circle. It has a groove that is approximately 20% of the circumference and is used to hold the plate clamp. Another function of the groove is also to facilitate the machine's ink supply system to stop refilling the new ink in preparation for the next print. In addition, it also functions as a print compensation. Because sheet-fed printing is different from continuous-fed printing, each sheet must be paused after printing, and then the second sheet must be printed, and the printing roller cannot stop. Therefore, by reducing the printing area of ​​the roller, The continuous and smooth operation of the entire printing process is maintained. The end of the plate cylinder is a relatively hard metal ring called a drum roll, which is connected with the plate cylinder or the drum journal to support the cylinder. In terms of structure, this ring of pillows should be in direct contact with the rollers of the blanket cylinder. Its diameter is the effective diameter of the plate cylinder and it is also the working diameter of the gear on the cylinder journal. The plate cylinder gear drives the plate cylinder to rotate on the one hand, and the other side of the plate cylinder gear engages with the rubber cylinder. The tooth profile of the roller gear can be either straight (old machine) or helical (new model). Each tooth of the spur gear is perpendicular to the edge of the gear plate, and the teeth of the helical gear have an included angle with the edge line. The rollers of a general spur gear are equipped with another very thin pull back gear to reduce the free drift between the gears. Printing machines that are not in contact with the plate cylinders and blanket cylinder metal rollers generally use helical gears (helical gears) to reduce gear drift and keep the machine driving smoothly. Some drill holes are left on the gear side of the plate cylinder, through which bolts can be inserted to fix the gears to the plate roller's bolster or drum journal flange, so that it can be tightly connected with the entire roller (the gear is mounted on the Outside the printing press, lubrication and cleaning are also very convenient). Elastic bolts can adjust the position of the plate cylinder, and it is extremely important to adjust the blank boundary of the printed sheet and the position of the plate. Many multicolor printers are equipped with a registration system that can adjust the lateral registration and circumferential positioning of the plate cylinder by remote control while the printer is in operation. The diameter of the cylinder of the plate cylinder is smaller than the diameter of the support roller. The gap between them is the sinking part of the roller to the surface of the cylinder and is called the drum sink groove. Its role is to provide space for the printing plate and pad, by changing the pad between the plate cylinder and plate, so that the plate to achieve the height requirements of the printing work, or can be used to adjust the circumference to meet the length of the print Printing requirements. Typically, the backing is paper or some other material. In general printing presses, the depth of the sinking groove of the plate cylinder is hit on a metal plate of a printing machine, so that even if the operator does not print the manual, he can do some basic processing on the pad. Some drums also engrave a horizontal line for marking the printing area, which is about one inch from the leading edge of the plate cylinder. From this line of printing to the leading edge of the cylinder, the radius gradually decreases, forming a bevel. The role of this ramp is to ensure that when the printing press is working at a high speed, there will be no detachment between the ink roller and the dampening roller and the plate cylinder. After the printing plate is installed on the roller, all printing and graphic parts should be behind the printing line. The plate clamp can serve to fix the plate and adhere to the cylinder body. Although the types of plate clamps are all different, their function is the same. Some plate clamps are quick-disconnect type, and a simple cam is used to hold the plate. Some are made up of several parts. Each part works independently and together plays a role in clamping. All plate holders have voids for use in lateral alignment and circumferential adjustments to produce qualified printed products. Some new types of printing equipment are more advanced, and the clamping of the plate clamps can be adjusted by means of a remote control device. Nowadays, more and more plate cylinders and plate clamps are equipped with positioning pin devices. As long as the positioning pins on the roller correspond to the holes in the plate, the plate can be fixed. This printing plate positioning system greatly reduces a large number of printing roller adjustment operations, and can obtain a good printing effect. Rubber Blanket The rubber blanket is covered with a rubber blanket. The main functions are as follows: * The blanket is brought into contact with the graphic part of the plate cylinder; * The paper that is used to transfer or print the ink on the impression cylinder (or other printing) Above material). Its structure is similar to that of a plate cylinder, and it also has gaps, grooves, gears, bearings, and so on. However, its fixing device is different from the plate roller plate clamp. One or two reels are used to fix the blanket. In some machines, there is a cross bar at the end of the blanket. When it is fixed, the cross bar can be placed directly on the reel. By adjusting the reel, the operator can tightly stretch the blanket on the blanket cylinder. Rotary adjustment of the reel is achieved by a worm or ratchet mechanism, and many presses can perform this function if a crossbar is to be added to the blanket. The relative position of the blanket cylinder and the other cylinders of the printing press must be adjustable for two reasons: it can be used to make contact with other cylinders or not, and secondly, thickness compensation is performed when using different printing materials and liners. When the blanket cylinder is not engaged with the other cylinder, it can be removed from the back. Note, however, that the gap between the rollers cannot be too large because the rollers' gears must also be meshed together. Of course, it is also necessary to leave gaps. It should not cause problems for the installation and cleaning of the printing plate, and it will not stain the blanket when cleaning the printing plate, and the cleaning solution will not be washed when the blanket is cleaned. Stained to the plate. The printer can also remain idle when it is not necessary to transfer the plate image to the blanket. The eccentric shaft is a device that plays this role. The distance between the blanket cylinder and the impression cylinder should also be adjustable so that compensation adjustments can be made for different printing materials. The distance adjustment can be achieved by another pair of eccentric shafts. When adjusting the distance between the blanket cylinder and the impression cylinder, the distance between the blanket cylinder and the plate cylinder will not be affected. In the monochrome printing machine, the gear of the blanket cylinder is also the drive gear of the other two cylinders, and it is controlled and driven by the central motor. The connection between the blanket cylinder gear and the cylinder is basically the same as that of the plate cylinder. Its position is adjustable, mainly used for printing time control, but the operator generally does not adjust it. The rubber body itself also sinks, providing space for installing blankets and pads. However, unlike the plate cylinder, it does not become an inclined surface when it reaches the edge, and its tube radius remains uniform throughout. Some printers, especially the ones in which the blanket cylinder and the plate cylinder are not in contact with each other, have deep depressions in the cylinder and can be installed with two blankets and gaskets. The rubber blankets sold in the United States are single-layered, while European countries are double-layered.