Structure and characteristics of offset printing press cylinder
I. Overview No matter what kind of offset press, the imprinting device follows the principle of three cylinders: mainly including plate cylinder, blanket cylinder and impression cylinder. The plate cylinder, blanket cylinder and impression cylinder of the offset printing machine have their own structural features. However, the basic structure of each roller body is the same, that is, it is composed of a journal, a roller pillow (shoulder iron) and a cylinder, as shown in Figure 6-1. 1. journal The journal is the document bearing part of the cylinder, which plays an important role in ensuring the uniform operation of the cylinder and the printing quality. 2. Rolling pillow The rolling pillow is also called shoulder iron. Modern offset press rollers have very precise roller pillows on both ends. There are two types of models: contact rolling pillow (such as CD102 machine) and non-contact rolling pillow (such as domestic J2108 machine). (1) Contact roller pillow mode, that is, in the cylinder pressure printing, the rollers at both ends of the plate cylinder and the blanket cylinder are printed in contact with each other. Therefore, it can partially absorb and eliminate vibration, ensure the smooth operation of the cylinder, and help improve the printing quality. In addition, the roller pillow is in contact with light pressure, and the roller gear is in the meshing position of the standard center distance, which is more beneficial to the work of the roller gear. Contact roller pillow requires that the center distance of the roller is fixed and is generally only used between the plate cylinder and the blanket cylinder. (2) The non-contact roller pillow means that the rollers of the two cylinders do not touch each other during the combined printing. The roller pillow of this type of offset press is the part that measures the gap between the cylinders. By measuring the gap between the rollers at both ends of the two rollers, the center distance and tooth gap of the two rollers can be calculated. Roller clearance is also an important basis for determining whether the centerline of the roller shaft is parallel and determining the size of the roller lining. Generally speaking, the plate cylinder and blanket cylinder roller pillow may or may not be in contact, but the blanket cylinder and the impression cylinder roller pillow are not in contact. This is because when increasing the thickness of the paper, in order to ensure that the printing pressure is consistent with the graphics, some pads need to be removed from the blanket cylinder and added under the printing plate, and only their adjustment between the blanket cylinder and the impression cylinder The center distance, so there is a gap between the blanket cylinder and the impression cylinder roller pillow, so that it can be adjusted when the paper thickness is changed. 3. Barrel The drum is surrounded by a liner which is the working part of direct transfer printing. The cylinder is composed of two parts: effective printing area and gap (notch). The effective area is used for printing or transferring graphics. The gap (notch) part is mainly used for installing grippers, blanket tensioning mechanism, and printing plates. Clamping and adjusting mechanism. There is a distance h between the drum body and the roller pillow, which is called the depression amount of the drum. The depression amounts of the three kinds of drums are inconsistent. The amount of depression can be used to calculate the thickness of the drum. [next] Two plate cylinder Generally, the cylinder diameter of the plate cylinder is between the cylinder diameter of the impression cylinder and the blanket cylinder. Its main functions are: (1) Install the printing plate and adjust the position of the printing plate. The printing plate fixed on the surface of the cylinder body makes the blank part of the printing plate get moisture first, and then contacts the ink roller, the graphic part receives ink, and finally contacts the blanket cylinder The ink on the printing plate is transferred to the surface of the blanket. The blank part of the printing plate cylinder body is provided with a printing plate clamping and plate position adjusting mechanism. The plate clamping mechanism commonly used in modern offset presses includes fixed and quick clamping mechanisms. Through the printing plate adjustment mechanism, the position of the printing plate that has been clamped on the cylinder is corrected to achieve the purpose of accurate registration. This entire process of correcting a printing plate is called plate pulling. Pulling is the main method that is often used in proofreading. In the pulling operation, it is necessary to prevent the deformation of the printing plate or the side of the printing plate being torn. Taking the J2108 model as an example, the steps of the pulling operation method are as follows: (1) If you want to pull the version, you must install it. When installing the plate, the plate clamp should be straight and flat, the position of the up and down screws and the upper and lower screws should be correct, and the pad should be suitable. [Case 6-1] An operator of an offset printing machine at a factory forgot to tighten the plate clamp screw when installing the J2101 machine. After about half an hour after the plate was put on the machine, the plate clamp screw fell between the impression and the blanket cylinder to print the impression cylinder The surface is crushed, causing serious economic losses. [Expert Tips] Loading, unloading, and pulling plates are one of the most basic methods of operation for offset press operators. They require agile movements, clean lines, accurate judgments, and a clear mind. The practice of this basic skill should attract attention from the moment you just learn the offset printing technique. If the plate making is not handled properly, the position of the picture and text on the printing plate is wrong, resulting in the mouth being too large or too small. At this time, the method of pulling the plate can not be used for adjustment, then the method of borrowing the roller is used. It is still commonly used in the operation of paper offset presses (for example, this method is also used in Heidelberg 6 = LX machines). The principle of the cylinder is to change the relative working position of the plate cylinder and its transmission gear. Borrowing roller operation process: If you want to increase the size of the gripper, loosen the fixing screw of the plate cylinder drive gear, so that the gear rotates in the direction of the printing work transmission, and the plate and the plate cylinder do not move, and the blanket cylinder is opposite to the plate cylinder. A certain distance was moved forward, and the printing plate moved a corresponding distance backward relative to the blanket cylinder. Then, the graphic imprint on the paper also moves back the same distance. On the contrary, if the transmission gear of the printing plate cylinder is moved by a certain distance in the direction opposite to the printing working direction, the picture and text on the printing plate will inevitably move in the direction of the gripper, which reduces the size of the gripper. Some machines have a special hole in the middle of the plate cylinder gap. Insert the dial roller into the hole to pull the roller, which can also change the relative working position of the cylinder body and the gear. Either way, we must pay attention to the screws of the transmission gear. [Expert Tips] In the plate-mounting operation, the plate cylinder needs to be lined. Most modern high-speed offset presses are wrapped on the plate cylinder with a plastic film base, but some models still use liner paper. It is recommended that when using liner paper, apply a little engine oil to both sides of the liner paper to prevent the penetration of wetting fluid Both sides of the drum corrode the drum body. This method can also be used in blankets of blanket rollers. [next] Three blanket rollers The blanket cylinder is lined with a thick, elastic blanket on the outer surface of the cylinder to transfer the imprints obtained from the printing plate (see Figure 6-3). (1) Transfer ink; [Related Links] During normal operation, the surface of the drum is subjected to a lot of forces, and the magnitude of the force is constantly changing, which means that the blanket roller is always in a complex vibration state, that is, the pressure of the lining at each place where the surface of the blanket roller contacts It can't be consistent, so that the pressure changes caused by machine vibration and machine processing and installation errors can be transformed into the elastic properties of the blanket. When contacting, elastic energy is generated; when it is out of contact, the elastic energy is released; when it is in contact again, new elastic energy is generated, and when it is out of contact, it is released again. This process is repeated repeatedly, but the damage caused by the impact and vibration of the machine is minimized by the blanket roller. Therefore, in addition to transferring ink, the blanket cylinder also compensates for the machine's overall error and absorbs vibration. Removing and installing the blanket is a very delicate operation. The blanket and liner must be trimmed. Before installing the blanket, clean the blanket roller with pure alcohol. If necessary, apply a non-corrosive oil to the surface. [Expert Tips] If there is a small-sized print with a large number of prints, the backing paper should be cut to be slightly smaller than the printed sheet, so as to avoid stacking ink and depositing paper hair on the blanket. If paper blankets appear on the blanket cylinder or ink skin appears on the plate cylinder. When the machine is running at high speed, do not pull it by hand to avoid personal accidents. The blank part of the blanket cylinder has a clamping and tensioning mechanism. One end of the blanket is fixed, and the other end is mounted on a shaft that can be tensioned, and then tensioned with a ratchet mechanism or a worm mechanism (Figure 6-4). [Case 6-2] A factory newly installed an offset printing press. When installing the blanket, the screws of the blanket clamp were not aligned with the mortise of the tensioning shaft. As a result, after the blanket was installed, the blanket clamp was thrown out soon after starting up, causing a mechanical accident. [Case 6-3] A factory has an M600 commercial rotary offset press. When the operator tensioned the blanket, the force on the tensioning rod caused the pin on the tensioning shaft to break, causing serious economic losses. [Expert Tips] The above two cases are illegal operations, leading to mechanical failure. In addition, if it is a new blanket, after installing it, press the hundreds of seals to consider the reply of the blanket. The height of the cushion. The blanket is often crushed or the surface is damaged due to foreign objects such as paper feeding in the middle of printing. If you want to partially cushion the blanket, you should pay attention to the following points: (1) Carefully remove the blanket and cushion. Four impression cylinder The impression cylinder is the most important cylinder in the offset press (Figure 6-10). Its surface has high processing accuracy, acid and alkali resistance, corrosion resistance, and its cylinder has high rigidity and strength to resist impact. And vibration, the gripper mechanism is installed at the idle position of the drum. The main function of the impression cylinder: (1) Support the paper and complete printing. When the paper enters the impression cylinder for printing, under the action of its printing pressure, it will inevitably be affected by the friction and will have a tendency to shift. In order to ensure the accuracy of the overprint, it is necessary to strictly prevent any changes in the position of the paper. The impression cylinder grips the teeth It is the component that accomplishes this task, and its structure is basically similar to the paper gripper. The function and structure of the gripper of the transfer roller and the gripper of the impression cylinder are the same. The procedure for adjusting the gripping force of the impression cylinder gripper is the same as the transfer gripper. Since the gripping force of the roller gripper is greater than that of the transfer paper gripper, the pad paper between the limit screw and the stopper is slightly thicker. The gripping force adjustment is usually carried out after one batch of products is printed and the other batch is printed. A factory has a J2204 machine. During the printing process, the half circle of the tooth cylinder of the impression cylinder fell off and fell between the blanket cylinder and the impression cylinder, which hurt the surface of the impression cylinder. [case study] Similar to the above situation, one is that the clamping screw of the impression cylinder gripper is loose, and the second is that the gripper on the brace has been working for a long time, and the lubrication is not in place, and the strong opening and closing causes the brace and the surface of the dental shaft to wear and loose. [Expert Tips] It is recommended that the operator conduct comprehensive inspections during the off-season printing to prevent similar accidents. The gripping force of the gripper of the impression cylinder depends on the support spring. Because the support spring is easy to shake in motion and has poor stability, the gripping force of the gripper often changes, which directly affects the accuracy of the overprint. In order to overcome this shortcoming, many offset printing The machine has made great improvements here, that is, using the cam to control the opening and closing of the gripper, according to the situation that the cam controls the opening or closing of the gripper, it is divided into high-point closed teeth and low-point closed teeth. High-point closed teeth means that when the roller of the swing shaft of the gripper shaft contacts the high-point part of the cam, the gripper teeth close and grip the paper. Low-point closed teeth means that when the roller on the swing shaft of the dental axis moves at the high point of the cam, the gripper is in an open state. After the roller enters the low point of the cam, the gripper is closed. Using the cam to control the opening and closing of the gripper, the impact is small and the movement is relatively stable. The adjustment method is simple and reliable, and the gripping force is consistent. [next] Features of the roller components of the five-roll offset press The basic structure of the cylinder of the web offset press and the sheet-fed offset press is the same, but the device is BB type. In addition, the cylinder of the web offset press has the following characteristics: (1) There is no paper transfer device, roller gripper and other paper transfer mechanisms. The accuracy of the color registration depends on the accuracy of the plate clamping and the stability of the tape tension. In addition, the plate cylinders of color presses are increasingly using double-width multi-diameter cylinders. It can increase the printing speed and the total number of newspaper editions, but this will easily affect the accuracy of registration. Now the new-style color newspaper printing machine has begun to use sleeve technology, that is, seamless rubber blanket, eliminating the roller gap necessary for installing the blanket, to a certain extent, reducing the plate cylinder and blanket cylinder at high speed The impact and vibration generated during operation reduces mechanical wear, effectively uses printing plates and paper, and ensures printing accuracy. On the basis of improving the printing quality, the printing speed is also increased. Outdoor Plant Container,Stainless Steel Planter,Durable Plant Vessel,Stylish Outdoor Plant Pot,High-Quality Gardening Container Jiangmen Xinweijie Stainless Steel Products Co., Ltd. , https://www.xxdkitchenware.com
Figure 6-1 Composition of the drum body
(2) The length of the blot can be changed.
(3) Change the contact pressure between the plate cylinder and the blanket cylinder.
Figure 6-2 Plate cylinder
(2) Before pulling the version, the amount of movement of the printing plate should be analyzed to be aware of it and taboo blindness.
(3) If you move the printing plate up or down, you must loosen the four fastening screws and turn one fastening screw (note that the upper or lower plate will affect the movement of the printing plate).
(4) Pull the plate up or down or move the plate around, you must loosen the four fastening screws, and pull the plate on both sides at the same time (when adjusting the plate, you must twist the screws on the left and right of the plate clamp) Evenly.
(5) The process of pulling the plate is best done by one person. After the operation, you must check whether the screws are tight.
Figure 6-3 Blanket roller
Figure 6-4 Blanket clamping and tensioning structure
The role of blanket roller:
(2) Make up the comprehensive error of the machine;
(3) Buffer vibration absorption.
(2) Use a ballpoint pen or pencil to trace the crushed area on the back of the blanket.
(3) Use the tail of a ballpoint pen or pencil to lift the damaged back and apply lubricant to the front.
(4) Use thin sulfuric acid paper as a cushion. If the pressure injury is serious, you can use two layers of sulfuric acid paper. [next]
(2) Pass the paper.
(3) In modern offset presses, the impression cylinder is the adjustment reference for the motor relationship of other machine parts.
Figure 6-5 Impression cylinder
The precision of the surface of the cylinder of the imprinting cylinder, the matching precision of the cylinder gear and the sleeve are very high, and the cylinder has good wear resistance and corrosion resistance.
Figure 6-6 Impression cylinder gripper structure
[Case 6-4]
(2) There are very few blanks left between the layouts on the paper tape. The size is determined by the size of the head and the cut. Therefore, the gap of the cylinder is very small, and the gap between the blanket cylinder of the color press printing machine for installing the blanket is only 10mm, and the gap between the plate cylinder and the printing plate is only 2mm, so the clamping mechanism of the printing plate and the blanket is very compact.
(3) The circumference of the cylinder should be equal to the width of the printed paper. If the diameter of the cylinder is 175cm, the circumference is 175 × = 550mm, which is the width of the folio.
(4) The printing plate cylinder has no plate pulling mechanism. When the printing plate is installed in the clamping mechanism of the cylinder, the printing plate can no longer be adjusted relative to the printing plate cylinder. However, the registration of the first and second colors, front and back, requires that the printing plate must be adjusted relative to the paper. Therefore, each color printing plate cylinder is provided with a fine adjustment mechanism in the axial direction and the circumferential direction.
(5) Some models have eccentric sleeves in addition to the upper plate cylinder in the four cylinders to change the center distance of the cylinder and meet the needs of separation and closing pressure adjustment.