2.4 Plate cylinder
1. The role of plate cylinder.
(1) Make the graphic part in ink, and the non-graphic part in water, and make it stable, that is, the water-ink balance, which is the key to ensuring the quality of the print (about the water-ink balance later).
(2) It can make up for the error of the plate and the previous version. The plate and the upper version sometimes cannot guarantee that the positioning relationship between the graphic part and the regulatory part is the same. Therefore, a plate adjustment mechanism must be installed on the printing plate. When the printing plate is skewed or more When the position of the color printing plate is inconsistent, it can be corrected, that is, front and rear adjustment, and left and right adjustment.
(3) Can change the front and back position of the picture and text. When the picture and text lead or lag on the paper and need to be adjusted, it can be achieved by changing the front and back position of the plate cylinder. This is commonly referred to as borrowing the cylinder. It is better not to use the roller in general. If you use it, you must return to the original position after use.
(4) The length of the print can be changed. The change of the print length is also often required in the printing process, mainly because the paper is stretched back and forth. For multi-color printing, subsequent overprinting often needs to lengthen the length of the blot. The solution to this problem is to reduce the thickness of the liner under the plate cylinder, thereby lengthening the transferred blot. The amount of print deformation caused by a piece of 0.1mm thick paper is 0.1 × 2 × 3.14 = 0.628 (mm), which is approximately 6 times the thickness of the paper. This number is the maximum deformation value at the end of the paper, from the mouth to the end of the paper, The length of the imprint is gradually increased from 0 to 0.628mm.
(5) It can make up for the paper's flicking and closing angle. When the paper is flicking and closing, it will cause overprinting of the back corner of the paper. The printing plate stretching and compression mechanism is installed on the rear plate clamp of the plate cylinder. Make the rear corner of the printing plate consistent with the flick angle of the paper, so that the rear corner overprint is accurate.
(6) Change the printing pressure, when the thickness of the pad under the printing plate changes, the printing pressure will change, so that the purpose of adjusting the printing pressure can be achieved by changing the thickness of the pad.
2. The composition of the plate cylinder and the role of each part.
The printing plate cylinder is generally composed of a printing plate, a pad, a plate clamping mechanism, a plate connection mechanism and a cylinder body. The role of the above-mentioned plate cylinder is shown through these parts.
(1) The first role in printing plate 1 is actually the role of printing plate. There are two reasons to keep a mouth when printing, there are two reasons: â‘ There is a part of the front opening of the printing plate that needs to be installed in the plate clip, and it does not make any sense to print graphics in this part. â‘¡The front opening of the printing plate has a large impact at the moment of contact with the water roller and the ink roller, which is extremely unstable. Therefore, the water roller and the ink roller must have a buffer area, and the image and text can not be transferred well in this place. Combining these two factors, there must be a place in the front of the printing plate that does not produce graphics, that is, a mouth. From the point of view of the printing plate, the smaller the mouth of the printing plate, the better. Therefore, products with low requirements can have smaller mouth openings (such as lines and text). Color printing). There are five points to pay attention to when printing plates: â‘ The size of the gripper should be consistent, the same printing plate should be the same, and the set of printing plates should be consistent; Exposure; â‘¢ Whether there are dirty spots on the surface of the printing plate, whether there are any false or pasted areas on the graphics; â‘£ Are the outlets complete?
(2) The padding of the pad printing plate is higher than the padding in the rubber cylinder, that is, the surface needs a higher flatness. General equipment is equipped with special pad paper, such as no special pad paper It can be replaced by other papers, but you should also consider preventing them from sliding relatively when choosing pad paper. Generally, offset paper, kraft paper or cloth paper can be used. Choosing these backing papers also has the function of making up for the machining errors on the back of the printing plate and the surface of the printing plate cylinder. But this is not the main role. Some devices now use standard plates without pad paper, which greatly improves the speed of the plate. In order to compensate for the deformation of the print during printing, the thickness of the liner needs to be changed, and paper must be added or reduced, but it must be carefully calculated. The change in the length of the general print is also approximately 6 times the thickness of the added paper (tip) . The paper mark is shortened, and the paper mark is shortened.
(3) The role of Article 2 in the clamp mechanism 1 is the role of the clamp mechanism. The printing plate needs to be installed in the clamping mechanism, so that the printing plate and the surface of the cylinder are in a relatively static state. When the printing plate is installed incorrectly or slanted, it can be adjusted by the adjustment mechanism in the clip. This adjustment is generally for correcting the plate. There are two methods: one is the front and back version, and the other is the left and right top version. No matter which method is used, the corresponding surface needs to be released.
When pulling the plate back and forth, if you pull in the direction of the gripper, you need to loosen the top plate screw at the tip, and vice versa. When the amount of plate pulling is relatively large, it is necessary to pay attention to make all screws be evenly stressed, so as to prevent the local stress concentration of the edge of the plate, causing cracking at this place.
When the left and right top plates are used, a top screw must be selected as the shaft, and the remaining screws are loosened. The left and right top plates can sometimes be replaced by front and rear pull plates.
When installing the printing plate, you must ensure that the position of the printing plate gripper is flush, because at present many devices are equipped with positioning devices, there are special positioning pegs on the plate clip, and special positioning marks on the roller The former should be based on the latter, because the positioning marks on the drum are not adjustable, but the position of the plate clamp relative to the drum is not always consistent. The printing plate needs to be punched with a special punching device, and the printing plate needs to be dried with a special hanging nail. If you can ensure that all positioning relationships are accurate, you can basically meet the requirements of overprinting without any adjustment during printing. Even if the difference is very small, the general adjustment is not more than 0.10mm. Another important function of the plate clamping mechanism is to compensate for the flicking or closing angle of the paper (this device is generally installed on the lower plate clamp). The top screws on both sides must be borrowed during use.
If the left corner of the paper is compensated, tighten the right screw to make it tight against the roller, and then adjust the special mechanism in the middle. However, it should be noted that the amount of compensation is very small.
(4) When the plate-drawing mechanism is printing, if the cross-hairs of the printing plate are already parallel (front, back, left, and right), but do not overlap, it is inconvenient to adjust the adjustment mechanism on the plate clamp at this time, and it is very fast to use the plate-drawing mechanism. And accurate. The plate-pulling mechanism can also slightly change the front, back, left and right positions of the picture and text on the paper. The plate pulling mechanism includes two sets of mechanisms in the axial direction (horizontal or left and right) and in the circumferential direction (vertical or front and back). The axial pull plate must make the roller move axially, that is, there must be a device to drive the roller to move axially. The circumferential pull plate must move the periphery of the cylinder. Changing the relative position of the plate cylinder and the rubber cylinder can only be achieved by changing the meshing relationship of the gears. Therefore, there must be a mechanism to drive the gear movement of the cylinder. Summarizing the above analysis, the axial pull is the shaft of the drum, and the circumferential pull is the shaft of the gear. Putting aside the rollers and gears, the working principles of the two sets of plate-drawing mechanisms should be exactly the same. It should be noted in use: after the machine is running, you can use the plate-drawing mechanism, especially the circumferential plate-drawing mechanism. Pulling during operation allows continuous movement of the drum or gear, which prevents sudden impact. The limit device of the plate pulling mechanism must be absolutely reliable, otherwise it is easy to pull out the gear and cause machine accidents.
There are currently two types of pull mechanism used, manual and electric. Manual is generally used for two-color machines, and four-color machines are generally electric (individually there are manual). The structure of the pull-up mechanism of different equipment is different.
(5) Drum body. The requirements of the printing plate cylinder are basically the same as those of other cylinder bodies, and will not be described in detail here.
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