Ghosting analysis and solution of the most popular

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Ghosting analysis and solutions for offset printing products editor's note: ghosting of offset printing products is easier to identify. If the product is in the form of text, the strokes become thicker in the slight case, and double strokes appear in the serious case. If the image is blurred, its hue and level will change, resulting in the decline of product quality. In addition, ghosting makes it difficult for readers to read. This phenomenon is common in the printing process. There are many reasons for ghosting, which should be faced by the industry to solve the problem of ghosting in printing

a folio four-color offset press was overhauled due to the wear of the embossing cylinder (double diameter). After the cylinder was sprayed and repaired, the whole machine was assembled and debugged. During the trial printing process, it was found that the first color group appeared ghosting. The more the ghosting characteristics were close to the trailing tip, the more serious the ghosting characteristics were, and the side close to the transmission was more serious than the other side, which belonged to circumferential ghosting. If only this color group was used to print monochrome, no ghosting would occur. 4. Relevant parameters of the impactor of the device

according to this symptom, it is preliminarily determined that there are two reasons: one is the paper handover time, and the other is that the pressure of each paper gripper in each paper gripper row is not adjusted properly

re adjust the handover angle for these two reasons, adjust the pressure of each paper gripper, the position of each tooth piece and tooth pad one by one, and replace the suspected tooth pad to make the height and position of the whole row of tooth pads consistent. Results the problem of double image could not be solved. There were changes in the position of double image in the process of adjusting the paper teeth. The final conclusion was that the reason was that the dental film and dental pad should be replaced completely; In order to be cautious, the maintenance personnel were asked to diagnose again. The dial indicator was used to check the surface of the imprinting cylinder, and no excessive machining error was found. If there was any looseness problem, the tooth row and tooth were adjusted again, but the problem was still not solved; The maintenance personnel re measured and adjusted the pressure of the ink stick, rubber cylinder liner, printing plate cylinder, rubber cylinder and embossing cylinder, re cleaned the tooth piece, tooth pad and adjusted the pressure of the paper teeth, but still failed to remove the ghost, and then directly transmitted the ink to the surface of the embossing cylinder. After observing the ink receiving on the surface of the embossing cylinder, it was found that the ink receiving was uneven. The conclusion was that the surface processing of the cylinder was not good, one end was larger and the other end was smaller (taper); Finally, the engineering and technical personnel were invited to make a diagnosis. After carefully listening to the efforts made by the previous personnel, the four groups of embossed rollers with a mass of about 25% smaller were measured again, and the meshing and assembly of the transmission helical gear were measured, and the handling suggestions were put forward:

1. The problem of paper teeth was basically eliminated. Therefore, there was no ghosting fault before the overhaul of the machine, and the previous adjustment by many people had no effect

2. After measuring the roller surface with a dial indicator, the data shows that the error (≤ 0.02mm) is not enough to cause such serious ghosting, and the factors of the imprinting roller itself can be basically eliminated

3. Through the side measurement of the dial indicator and other instruments, it is found that the gear assembly error is up to 0.6mm (because the helical gear is connected with the drum through six bolts). Theoretically, the transmission can be stable only when the two gears mesh their pitch circles for pure rolling. However, the fundamental reason for the ghosting is that the gear assembly error causes the runout of the imprint drum during operation. Why is it not found when measuring the drum surface error? In fact, it is a question of static and dynamic. Adopt the above treatment opinions, and finally correct the assembly errors of all gears, and adjust the clearance of conical bearing on the imprint cylinder shaft, and the ghosting is basically eliminated

to sum up, it shows that there are many reasons for ghosting in printing. It is very important to see the essence through the phenomenon, analyze the causes of the failure, and shorten the maintenance time. Otherwise, the production will be affected, and the loss caused by the delay in delivery will be immeasurable. Taking the sheet fed multi-color printing machine as an example, the reason for ghosting is that the transfer process of imprint (point) has a sliding, and the second is that there is a displacement in the process of paper handover. For this reason, it is required that all rollers (plate cylinder, rubber cylinder, embossing cylinder and paper passing cylinder) shall rotate smoothly without ghosting, and the geometric shape and size shall meet the requirements; The entire path of paper from the paper delivery roller to the final paper receiving tooth row has accurate and stable handover time and position, and the linear speed is constant. If a part changes during this process, ghosting will occur

the elimination of ghosting can be roughly identified as follows:

① a printing machine with a short service life is an adjustable ghosting. Generally, the mechanical parts of this kind of printing machine are not seriously worn, and the ghosting is often caused by the uneven gripping force of the paper feeding tooth row and the embossing cylinder tooth row due to the change of the gripping force of individual paper taking teeth during use. Generally, the pressure of the paper taking teeth can be adjusted through cleaning

② the printing press with long service life belongs to abrasive ghosting, which occurs in a process from small to large. Generally, there are tooth pads and tooth pieces worn, resulting in the change and size of paper holding force; The tooth shaft bearing is worn and the clearance becomes larger; The open tooth ball, cam and roller bearing are worn, causing displacement, etc; If local ghosting occurs, it is often caused by the wear of some dental splints, dental pads or some "dead teeth"; If the whole plate is ghosted, mainly check the wear of the tooth ball or each roller bearing, whether it is caused by the increase and displacement of the clearance and the radial or axial runout. Often determine the group, and then find out which roller it is from by observing the impression of the rubber roller

③ sudden type of ghosting, which is usually caused by the damage or failure of a bearing or a part. At the same time, the position of each part of the printer changes after replacement and maintenance. For example, the example of the above printing factory is this type, which should be analyzed according to the specific situation

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