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The group offset press represents the development direction of today's printing press technology. Compared with the single-unit and satellite-type and BB offset presses, the group-type offset press is characterized by a sequential, continuous, long pass path from the printing process. By the time the paper is delivered, the paper needs to be transferred several times and printed in a wet and wet manner. That is, under the condition that the ink of the previous color is not dried completely, the latter color printing is performed immediately. During the multiple hand-over process of the paper, a certain point of the paper is relatively No slightest position error is allowed at each plate position, otherwise the previous ink color on the paper is reverse printed on the latter color eraser or impression cylinder, and does not coincide with the correct position of the crosshairs or dots. Left and right and left and right residual imaginary images, normal and imaginary imprinting make the actual area of ​​the dot network expand, which is equivalent to changing the number of dots, which also changes the high and low tone of the printing color. This kind of blemishes is crucial for multi-color printing. The concept of precision has gradually been paid attention by the printing people with the popularity and promotion of the group offset press.
First, the impact of paper transfer error on the quality of printed products
The paper transfer error is assessed by the national standard in the accuracy of paper transfer, in the case of the accuracy of the transfer of the paper, the relative position of the former and the latter color crosshair is fixed, if there is a distance between the two, through the pull The edition agency will align the former color with the latter one. When the accuracy of the transfer does not meet the requirements of the standard, the quality of the printed product is first affected by the large registration error, and the horizontal and vertical crosshairs cannot be set. This error cannot be eliminated by the pull plate mechanism because of the accuracy of the transfer. Non-compliance of overprinting is not allowed for each position of the front and rear crosshairs, and the distance is not fixed. More serious is wet-wet printing. The dot area of ​​the dot caused by the non-overlapping and non-coincided blots increases, resulting in a change in color tone, so-called color cast. And the change of hue changes with the error of the accuracy of the paper, so that printing can not achieve the purpose of copying the original.
Second, the factors affecting the accuracy of the transfer
There are many factors that cause poor accuracy of paper transfer. In the past, because of the large number of monochrome machines used, a large number of satellite-based dual-color machines and BB-type double-sided machines were used, the transfer routes were extremely short, the contradictions were not exposed, and the accuracy of the transfer did not cause enough people. The importance attached to it is that the corresponding analysis and research are superficial, and the countermeasures are naturally less, and the effect is not obvious. Troubleshooting is often difficult and tricky. The factors that cause poor paper transfer accuracy mainly include paper problems, such as the manufacturing problems of tooth shafts, roller gears, etc., as well as the three major categories of machine debugging and maintenance.
1, paper problems
The printing process is that the paper is separated by a sheet feeder, fed into the positioning system, and transferred by the transfer mechanism and a series of embossing transfer rollers to complete the printing. The paper participates in the printing process. Its flatness directly affects the accuracy of chewing teeth. When the paper produces wavy flounces, the edges of the paper are aligned linearly and do not form an accurate one-to-one relationship with the gripping cavities. The gripper's point does not guarantee that the two positions are fixed. When the tooth chip bites the paper on the gum pad, the wavy paper edge recovers into a linear shape, and the paper microscopically produces a displacement. With the pressing of the rubber and the embossing, the displacement of the paper particle point gradually expands, and the degree of misprinting of the tail edge print does not increase. In severe cases, it can even cause paper wrinkles and printing cannot be continued. For a single unit because it is not wet and wet printing, then there will only be a change in the position of the first color of the crosshair, which will bring difficulty to the subsequent color registration, but it will not be as dry and non-overlapping as the color of the former. The imprinting was reversed to the eraser of the post-coloring group, leaving a ghosting phenomenon beside the normal imprinting. There is no change in the number of outlets, that is, printing tone is basically the same, so the contradiction does not stand out.
2, machine equipment problems
Because the paper path is long, there is an error accumulation amplification effect, so the accuracy of the machine must be done very high. The unit multicolor machine must not be regarded as a simple superposition and extension of a single unit. The influence of machine precision on the accuracy of paper transfer is manifold. The factors influencing the drum assembly from the design and manufacturing perspective include the axial clearance of the drum is too large, the axial clearance of the tooth shaft is too large, and the meridional and axial clearance of the tooth Great. The influencing factors of the gear assembly include the inaccuracy of the gear transmission, the error of the tooth profile and teeth of the gear teeth, the large variation of the length of the gear normal line, the large radial runout error of the ring gear, and the large backlash of the gear joints. The factors that affect the opening and closing of the dental cam system include the small contact area of ​​the gripper, the denture, and the denture, the teeth of the dental implant are not sharp, the positive pressure of the paper is small, the strength of the closed spring is small, and the torsion rigidity and bending rigidity of the dental shaft are reduced. Inadequate, improper spacing of the teeth arranged in the density, the drum transfer time is not accurate, and so on.
3, debugging and maintenance of printing operation process
The factors affecting product quality are nothing but human, machine, material, law, and ring. Paper problems and equipment problems are the main aspects of the machine and material factors in the five major factors. Apart from the design and manufacturing processes, printing processes, machine commissioning, and maintenance, these five factors cannot be ignored. Only these issues and problems are satisfactory. Solve the problem, to maximize the effectiveness of the machine and equipment in order to truly achieve harmony between man and nature, to achieve the highest quality printing. Poorly maintained equipment such as lack of oil on the shaft bearing, dust accumulated in the teeth of the teeth, jamming in the closing movements of the teeth, insufficient teeth or even dead teeth, tooth wear and depression in the teeth, and reduced contact surface. In addition, the tooth gap is filled with paper gray paper, and the friction between the teeth and the pad is small; the tooth decay and failure of the small spring, false teeth bite the paper is not true, the paper will slip in the printing, open the ball wear, cam Wear, the transfer synchronization time will be reduced; tooth shaft and drum end bearing wear, axial clearance increases, drum shaft will produce excessive axial rotation at high speed rotation; raw and auxiliary materials are not properly selected, ink viscosity is too large The lining calculation error in the operation process, the large amount of relative sliding between the rollers in the printing, all have an adverse effect on the accuracy of the transfer.
Third, to improve the accuracy of the transfer measures
According to the factors affecting the paper-passing precision, it can be seen that the fundamental path to improve the precision of paper-passing is to improve the quality of the parts and components of the paper-passing system, eliminate irrational gaps, increase the paper-biting force, and pay attention to maintenance. Specifically, the following measures can be taken:
1, strict processing of fine assembly
The precision parts processing and assembly in the transfer system must be strictly controlled. The rollers, especially the double-diameter impression cylinders, must strictly control the radial runout because radial runout is the most fundamental cause of AB ghosting. Accuracy of the transmission gear, such as the cumulative error of the week, the variation of the length of the common normal, the radial displacement of the ring gear, the backlash of the gear at the transfer point, the tooth profile of the gear, and the direction of the teeth, cannot be assembled without meeting the pattern requirements. Closed-point cam profile, roughness, hardness, ball surface are all ultra-fine processing, strictly control the runout deviation, ensure that the drum teeth running without vibration, no looseness, wear resistance, no change in bite force, paper relative roller No displacement occurs.
2, eliminate the gap to roll on behalf of the slip
The shaft seat is axially radially supported and supported by a roller, and the rolling bearing replaces the sliding bearing. Sliding bearings, no matter how precise they are manufactured, there are gaps. When there are gaps, the stiffness decreases, and there is elastic resignation. As the position of the contact line changes, there is uncertainty in the movement. The rolling bearing can achieve no clearance through pre-tightening, rigid enough, less deformation, and movement determined.
3, to ensure the teeth force
The key to ensure that the paper does not take place during printing is the tangential teething force. The printing speed is increased, the printing format is increased, and the strong peeling force of the wet-press printing requires a strong paper-gripping force of the gripper. The contact area of ​​the cavities, the contact form of the cavities, and the elastic deformation of the cavities are important for the impact of the occlusal force. It can be said that the quality of cavities is the core of the accuracy of the transfer. In the past, the research on tooth decay was the weak link because of the relatively low production of machine-type machines. The reasons for the low transfer accuracy are also mostly due to this. Group-type dental caries must ensure sufficient contact area. Theoretically, the tangential force F=fn does not seem to be related to the contact area, but the paper is a flexible body. When the dental teeth compress the paper, the tangential bite force is no longer According to the above calculation formula of friction force, especially when the tooth chip is made into sharp teeth, with the soft tooth pad, the tangential force is the paper shear force, which is related to the size of the shear surface and is the contact area. Positive proportional function. Hard and soft bonding mode is adopted, that is, the dental chip is hard and the dental pad is soft, so that a good contact area is better ensured, and at the same time, the shear coefficient is large, and the paper is not easily displaced under the effect of the printing force. In the past, only checking the positive pressure of the dental piece during assembly and debugging and ignoring the tangential force of the working state was the main reason for the low accuracy of the transfer. If you blindly increase the positive pressure of the tooth chip, the open teeth ball and the cam work surface are easy to wear and the accuracy is easily lost. In the premise of guaranteeing the contact area of ​​the dental piece and ensuring the depth of biting of the teeth, we should appropriately reduce the positive pressure of the closed teeth, so that the machine can maintain long-term precision.
4, pay attention to the daily maintenance of dental shaft tooth
The dental shaft includes a roller for regular maintenance inspections, filling with grease, and cleaning the jaw face. To ensure that the shaft, roller axial gap-free, tooth opening and closing flexibility, no jamming phenomenon, no dead teeth, the spring does not fail, strong teeth closing. The tooth surface of the tooth chip has no accumulated dust and paperless hair, and the teeth are sharp. When the machine is used for a long time, it should also check the open ball, cam wear, when the cam and the open ball wear, the transfer time will be slightly shorter when the transfer, because the high point of closed teeth cam or ball after wear It is equivalent to the shift of the high point of the paper-feeding cam, the opening time is advanced, and the take-up cam is relatively moved forward and the closing time is delayed. The reduction of the transfer time has a great influence on the accuracy of the transfer. In particular, under high-speed operating conditions, it is also necessary to ensure the necessary transfer time. Adjustment can be taken to reduce the radius of the teething tooling method, because the work of the ball is reduced to increase the work ball, which can make up for the wear of the cam, to increase the common handover time purposes. When the dental chip wears and loses the teeth, the dental chip must be replaced to ensure sufficient tangential force.
5, the printed material is not qualified not on the machine
First, the paper needs to be treated first. For example, to eliminate paper flrush, an infrared drying lamp can be added to the paper stacker of the feeder to properly remove the moisture absorption and deformation of the edge of the paper. At the same time, mechanical pressing is added to the front gauge. Sheets, as far as possible to make the paper level into the system of rules and delivery of paper teeth, serious static electricity can increase the static elimination device, so that paper can enter the printing unit in a better controlled state, from the source to ensure the accuracy of the transfer. 
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