Improve the accuracy of paper transfer to ensure the quality of printed products
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
In order to meet the market demand for high-quality, high-efficiency printing, the construction of offset printing machines at home and abroad has almost no exception to the development of the unit. The unit printing unit of the unit type offset printing machine has the same structure, strong color group expansion, uniform parts between units, high level of manufacturing standardization, and is convenient for controlling quality and reducing cost in the production organization process. Consistent operating modes and high degree of automation facilitate machine maintenance and troubleshooting during use. Four-color machine, six-color machine, double-sided four-color machine, etc., complete the whole road printing work in one pass, the machine high efficiency and the small proportion of printing per color, has become the main driving force for printing enterprises.
The unit offset printing machine represents the development direction of today's printing machine technology. Compared with single unit and satellite and BB offset printing machines, it features a sequential and continuous printing process with a long paper path. To the delivery, the paper needs to be handed over several times, and it is in the wet-wet printing form, that is, in the case that the previous color ink is not dry, the subsequent color printing is performed, and in the process of multiple delivery, the paper has a relative particle point. No error is allowed in the position of each plate at any position. Otherwise, the ink of the previous color on the paper is printed on the back color eraser or impression cylinder, and does not coincide with the cross line or dot at the correct position. The residual shadows are left and right, and the normal and virtual imprints enlarge the actual area of the dots, which is equivalent to changing the number of dots, which changes the height and low of the printing color. This kind of enamel is crucial for multi-color printing. The concept of precision, with the popularization of unit-type offset printing presses, has gradually been valued and paid attention by printers.
First, the impact of paper transfer error on the quality of printed products
The paper passing error is evaluated by the precision of the paper passing in the national standard. Under the condition that the paper passing precision is up to standard, the relative position of the front color and the rear color cross line is fixed. If there is a distance between the two, pull the pull. The version of the agency, the former color and the next color cross line overlap. When the accuracy of paper transfer does not meet the requirements of the standard, the quality of the printed product will be affected first because the registration error is large, and the horizontal and vertical cross lines cannot be set. This error cannot be eliminated by the drawing mechanism because of the accuracy of the paper. Non-standard overprinting is not allowed to change each of the front and rear crosshairs, and the size of the distance is not fixed. More serious is wet-wet printing, which results in an increase in the ink area of the dots caused by the unwound, non-coincident prints, resulting in a change in hue, the so-called discoloration. Moreover, the change in hue varies with the error of the accuracy of the transfer, so that the printing cannot achieve the purpose of copying the original.
Second, the factors affecting the accuracy of paper transfer
There are many factors that cause the accuracy of the paper to pass the standard. In the past, because of the large number of monochrome machines used, the satellite two-color machine and the BB double-sided machine were used in a large amount. The paper-making route was extremely short, the contradiction was not prominent, and the paper-feeding precision did not cause enough people. The emphasis on the analysis is also superficial, and the countermeasures are naturally less, and the effect is not obvious. It is often difficult and troublesome to troubleshoot. The factors that cause the low precision of paper transfer mainly include paper problems, such as the manufacture of equipment such as dental shafts and roller gears, as well as the problems of machine debugging and maintenance and process operation.
1. Paper problem
In the printing process, the paper is separated by sheets by the paper feeder, sent to the rule system for positioning, and the printing is completed by the transfer mechanism of the transfer mechanism and a series of imprint transfer rollers. The paper participates in the whole process of printing, and its flatness directly affects the accuracy of the bite of the tooth. When the paper produces a wavy ruffle, the dots on the edge of the paper are arranged in a straight line, which cannot form an exact one-to-one correspondence with the point of the pick tooth. The point of the gripper does not guarantee that the front and rear positions are fixed. When the tooth piece bites the paper into the tooth pad, the wavy paper edge returns to a straight line, and the paper will be displaced microscopically. With the pressing of the rubber and the embossing, the displacement of the paper dot gradually expands, and the tail print does not overlap. In severe cases, the paper may even wrinkle and the printing cannot proceed. For a single unit, because it is not wet-wet printing, only the position change of the first color cross line will be irregular, which will bring difficulties to the back color registration, but it will not be dry, not coincident like the unit color. The blot was reverse printed on the back color set rubber, leaving a ghost phenomenon next to the normal print. There is no change in the number of dots, that is, the printing tone is basically unchanged, so the contradiction is not prominent.
2. Machine equipment problems
Because the paper path is long and there is an error accumulation amplification effect, the accuracy of the machine must be made very high. The unit-type multi-color machine must not be regarded as a simple superposition of a single unit. The influence of machine precision on the accuracy of paper transfer is multi-faceted. The factors affecting the roller assembly from the perspective of design and manufacture are that the axial clearance of the drum is too large, the axial clearance of the dental shaft is too large, and the longitudinal clearance and axial clearance of the tooth pass. Great. The influencing factors of the gear assembly are that the gear transmission precision is not enough, the gear tooth shape and tooth tooth error are large, the gear common normal length variation error is large, the ring gear radial runout error is large, and the gear pair intersection point side gap is large. The influencing factors of the open and closed dental cam system are the contact area of the paper tooth, the tooth piece and the tooth pad, the tooth of the tooth piece is not sharp, the positive pressure of the biting paper is small, the force of the closing tooth spring is small, the rigidity of the tooth shaft is torsion and bending resistance. Insufficient, the spacing of the teeth is not properly arranged, the synchronization time of the roller transfer is short, and so on.
3. Commissioning and maintenance of the printing process
The factors affecting product quality are nothing but the five factors of people, machine, material, law and ring. Paper problems and equipment problems are the main aspects of the two major factors of machine and material. In addition to the design and manufacturing process, printing process, machine debugging, maintenance and other aspects of use, the five factors can not be ignored, only these contradictions and problems are completed. Solved, the performance of the machine can be maximized, in order to truly achieve the unity of heaven and man, to achieve the highest quality printing. Poor maintenance of equipment such as lack of oil in the shaft bearing, accumulation of dust in the tooth cuff, occlusion of the jaw, movement of the jaw, insufficient bite or even dead teeth; teeth, teeth wear or depression, contact surface is reduced, In addition, the teeth of the teeth are filled with paper gray paper, and the friction between the teeth and the pad is small; the fatigue of the small spring is invalid, the paper is not solid, the paper will slip in the printing, the teeth are worn, the cam Wear and tear, the synchronization time will be reduced; the bearing of the dental shaft and the roller end face will wear, the axial clearance will increase, and the roller shaft will produce excessive axial turbulence when rotating at high speed; the raw and auxiliary materials are improperly selected, and the viscosity of the ink is too large. The calculation of the lining of the operation process is incorrect, and the relative sliding amount between the rollers in the printing is large, which adversely affects the accuracy of the paper.
Third, improve the countermeasures for the accuracy of paper transfer
According to the analysis of factors affecting the precision of paper transfer, the fundamental path to improve the precision of paper transfer is to improve the quality of processing and assembly of the paper-passing system parts, eliminate unreasonable gaps, increase the bite force, and pay attention to maintenance. Specifically, the following measures can be taken:
1. Strictly machined fine assembly
The processing and assembly of precision parts in the paper-passing system must be strictly controlled. The roller, especially the double-diameter impression cylinder, must strictly control its radial runout, because the radial runout is the most fundamental cause of AB ghosting. The transmission gear movement accuracy such as the cumulative error of the weekly section, the variation of the length of the common normal line, the ring diameter jump, the gear side clearance of the junction point, the gear tooth profile, the tooth direction, and the non-conformity requirements shall not be assembled. At the junction point, the cam profile, roughness, hardness and surface of the ball are super-finely processed, and the runout deviation is strictly controlled to ensure that there is no vibration during the operation of the roller, no looseness, wear resistance, no biting force, and the paper is opposite to the roller. No displacement occurs.
2. Eliminate the gap to roll
The shaft seat is axially supported radially, supported by a roller, and replaced by a rolling bearing. Sliding bearings have gaps no matter how precise they are made. If there is a gap, the stiffness will decrease and there will be elastic clearance. As the position of the contact line changes, the motion has uncertainty. The rolling bearing can be made without pre-tightening, rigid foot, less deformation and movement determination.
3. Ensure the bite force
In the printing to ensure that the paper does not move, the key is tangential biting force. The printing speed is increased, the printing format is increased, and the wet pressing wet printing peeling force requires a strong paper-feeding force of the crepe paper. The contact area of the paper tooth decay, the contact form of the tooth decay, the elastic deformation of the tooth decay, etc. are crucial to the impact of the bite force. It can be said that the quality of the tooth decay is the core of ensuring the accuracy of the paper transfer. In the past, because of the less production of unit-type machines, the study of tooth decay is also a weak link. The reason why the accuracy of paper transfer is not high is mostly due to this. The unit type tooth decay must ensure sufficient contact area. In theory, the tangential bite force F=fn seems to be independent of the contact area, but the paper is a flexible body. When the tooth piece compacts the paper, the tangential bite force is no longer Simply calculate the frictional force calculation formula above, especially when the tooth piece is made into a sharp tooth, with the soft tooth pad, the tangential bite force is the paper shearing force, which is related to the size of the shearing surface and is the contact area. Positive proportional function. The hard and soft combination mode is adopted, that is, the tooth piece is hard, and the tooth pad is soft, so that a good contact area is better ensured, and the shear coefficient is large, and the paper is not easily displaced by the printing force. In the past, in the assembly and debugging, only the positive pressure of the tooth piece was checked and the tangential force of the working state was neglected, which was the main reason for the low accuracy of the paper transfer. If the positive pressure of the tooth piece is increased blindly, the open tooth ball and the cam working face are easily worn, and the precision is easily lost. Under the premise of ensuring the contact area of the tooth piece and ensuring the bite depth of the tooth, on the contrary, we should appropriately reduce the positive pressure of the closed tooth, so that the precision of the paper transfer precision can be long.
4. Pay attention to the daily maintenance of the dental shaft
The dental shaft, including the drum, should be regularly inspected, filled with grease, and cleaned and cleaned. Ensure that there is no gap in the axial direction of the dental shaft and the roller, the tooth opening and closing is flexible, there is no jamming phenomenon, no dead teeth, the spring does not fail, and the cavities are closed. The tooth surface of the tooth has no dust and no dust, and the teeth are sharp. When the machine is used for a long time, the ball should be inspected, and the cam wear condition. When the cam and the open ball are worn, the common paper feeding time will be slightly shortened when the hand is transferred. This is because the high point closed cam or the ball is worn. It is equivalent to shifting the high point of the paper-feeding cam, the timing of opening the teeth is advanced, and the paper-taking cam is relatively moved forward, and the time of closing the teeth is delayed. The reduction of the handover time has a great influence on the accuracy of the paper transfer, especially in the high-speed operation state, and the necessary synchronous handover time should be ensured. When adjusting, the method of reducing the radius of the teeth of the adjustment tool can be adopted, because the reduction of the tool ball is equivalent to the increase of the work ball, thereby compensating for the wear of the cam and increasing the common handover time. When the tooth piece is worn and the "front teeth" are lost, the tooth piece must be replaced to ensure sufficient tangential bite force.
5. The printed materials are not qualified and are not on the machine.
Firstly, the paper is not flat and needs to be processed first. For example, to eliminate the paper flanging measures, an infrared drying lamp can be added to the paper stacker of the paper machine to properly remove the moisture absorption deformation at the edge of the paper, and mechanical paper is added at the front feed. The film should be as flat as possible to enter the rule system and the transfer paper. For static electricity, the static eliminator can be added, so that the paper can enter the printing unit in a better controlled state, and the precision of the paper transfer can be ensured from the source.