In order to meet the market's requirements for high-quality, high-efficiency printing, the construction of offset presses at home and abroad is almost without exception developing in the direction of unit. The printing units of the unit-type offset press have the same structure, strong color group expandability, uniform parts between the units, and high standardization of manufacturing, which is convenient for quality control and cost reduction in the production organization process. The operation mode is consistent and the degree of automation is high, which is conducive to machine maintenance and troubleshooting during use. Four-color machine, six-color machine, double-sided four-color machine, etc., complete the printing process in one pass. The high efficiency of the machine and the small proportion of labor per color have become the main motivation for printing companies to purchase machines.

Unit-type offset presses represent the development direction of today's printing press technology. Compared with single-unit and satellite-type and BB-type offset presses, they are characterized by a sequential and continuous printing process with a long paper transfer path. When the paper is received, the paper needs to be handed over multiple times, and it is in the form of wet press wet printing, that is, the printing of the latter color is carried out immediately after the ink of the previous color is not dry. There is no slight position error at each printing plate position, otherwise the ink of the previous color on the paper will be printed back to the rubber or impression cylinder of the next color, and it will not overlap with the crosshairs or dots in the correct position. The ghost image remains on the front, back, left, and right sides. The normal and virtual printing marks expand the actual area of ​​the dots, which is equivalent to changing the number of dots, which also changes the high and low key of the printing color. This kind of defect is crucial for multi-color printing. The concept of precision is gradually paid attention and attention by printers with the popularization of unit-type offset presses.

1. The impact of paper transfer errors on the quality of printed products

The paper transfer error is evaluated by the paper transfer precision in the national standard. When the paper transfer precision reaches the standard, the relative position of the cross color of the previous color and the latter color is fixed. If there is a distance between the two, pass the pull The version of the institution, the cross color of the previous color and the second color overlap. When the paper transfer accuracy 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 cross lines cannot be fitted. This error cannot be eliminated by the plate pulling mechanism because of the paper transfer accuracy The overprint that does not meet the standard is not correct because the position of the two-color crosshairs at the front and back changes each time, and the distance is not fixed. What is more serious is wet press wet printing. The dotted ink area increases due to the wet and non-overlapping prints, resulting in a change in hue, the so-called discoloration. And the change of color tone changes with the error of paper transfer accuracy, so that the printing can not achieve the purpose of copying the original.

Second, the factors affecting the accuracy of paper transfer

There are many factors that cause the paper transfer accuracy to fail to meet the standard, but in the past, because of the large number of monochrome machines, satellite two-color machines and BB double-sided machines, the paper transfer route is extremely short, and the contradiction exposure is not prominent. The corresponding attention is also superficial, and the corresponding analysis and research are superficial, and the countermeasures are naturally few, and the effect is not obvious. Troubleshooting is often difficult and tricky. The factors that cause the low paper transfer accuracy are mainly paper problems, there are problems in the manufacture of equipment such as dental shafts and roller gears, and there are also three major categories of machine debugging and maintenance and process operation problems.

1. Paper problems

In the printing process, the paper is separated one by one by the paper feeder, sent to the rule system for positioning, and passed through the paper transfer mechanism and a series of embossed transfer cylinder gripper transfer transfer to complete the printing. Paper participates in the entire printing process, and its flatness directly affects the accuracy of gripping the paper. When the paper produces wavy ruffles, the dots on the edge of the paper are arranged linearly, and there is no accurate one-to-one correspondence with the gripping teeth. The point of gripping the paper teeth cannot guarantee that the positions of the front and back are fixed. When the dental tablet bites the paper on the tooth pad, the wavy edge of the paper returns to a straight line, and the paper will have a microscopic displacement. As the rubber and the imprint are pressed, the displacement of the paper particles gradually expands, and the degree of misalignment of the tail marks expands. In severe cases, the paper may even wrinkle, and the printing cannot be continued. For a single unit, because it is not wet press wet printing, only the position of the crosshairs of the first color will change irregularly, which will cause difficulty in the registration of the back color, but it will not be dry and not overlapping like the unit machine. The imprint is reverse printed on the rubber of the back color group, leaving a ghost phenomenon next to the normal imprint. There is no change in the number of dots, that is, the printing tone is basically unchanged, so the contradiction is not prominent accordingly.

2. Machine and equipment problems

Because the paper transfer path is long and there is an error accumulation and amplification effect, the accuracy of the machine must be very high. The unit-type multicolor machine must not be regarded as a simple superimposed continuation of a single unit. The influence of machine precision on paper transfer accuracy is various. From the perspective of design and manufacturing, the influencing factors of the roller assembly are analyzed. The axial gap of the roller is too large, the axial gap of the tooth shaft is too large, and the warp and axial gaps of the tooth body are too large. Great. The influencing factors of the gear assembly include insufficient gear transmission accuracy, large tooth shape and tooth direction errors, large gear common normal length variation errors, large gear ring runout errors, and large gear backlash. The influencing factors of the open and close tooth cam system are the gripping area of ​​the gripper, the dental disc and the dental pad, the tooth of the dental disc is not sharp, the positive force of the paper biting force is small, the force of the closing tooth spring is small, the rigidity of the tooth shaft torsion and bending resistance Insufficient, improperly arranged spacing of teeth, short and inaccurate synchronization time of roller handover, etc.

3. Commissioning and maintenance of printing operation process

The factors that affect product quality are nothing more than five factors: human, machine, material, method, and environment. 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 links, printing process, machine debugging, and maintenance, these five factors can not be ignored. Only these contradictions and problems are completed. Solved, the efficiency of the machinery and equipment can be maximized, and the unity of nature and man can be truly achieved, and the highest quality of printing can be achieved. Poor maintenance of equipment such as lack of oil on the gripper shaft bearing, dust and ink on the dental braces, blockage of the movement of the gripper's opening and closing, insufficient force to bite or even dead teeth; dental tablets, dental pads are worn or low, the contact surface is reduced, In addition, the tooth gap between the teeth is filled with paper gray paper hair, and the friction rate between the teeth and the pad is small; the small spring of the gripping teeth is fatigued, the gripping paper of the gripping teeth is not real, the paper will slip during printing, the opening ball wears, the cam Wear and tear, the transfer synchronization time will be reduced; the tooth shaft and the roller end bearing wear, the axial gap increases, the roller tooth shaft will produce excessive axial movement when rotating at high speed; the choice of raw and auxiliary materials, the ink viscosity is too large In the operation process, the calculation of the liner is wrong, and the relative sliding amount between the cylinders during printing is large, which has an adverse effect on the accuracy of the paper transfer.

3. Measures to improve paper transfer accuracy

According to the analysis of the factors that affect the precision of paper transfer, the fundamental path to improve the precision of paper transfer is to improve the quality of the processing and assembly of parts in the paper transfer system, eliminate unreasonable gaps, increase the bite force, and pay attention to maintenance.

1. Strict processing and fine assembly

The processing and assembly of precision parts in the paper transfer system must be strictly controlled. The cylinder, especially the double-diameter impression cylinder, must strictly control its radial runout, because radial runout is the most fundamental cause of AB ghosting. The accuracy of the transmission gear such as the cumulative error of the circumferential joint, the variation of the length of the common normal, the jump of the ring gear, the backlash of the gear at the junction, the tooth shape and direction of the gear, do not assemble if they do not meet the requirements of the drawing. The profile, roughness, hardness, and ball surface of the closed-cam of the junction are super-finely processed, and the run-out deviation is strictly controlled to ensure that the roller gripper has no vibration, looseness, wear resistance, no change in bite force, and the paper is relative to the roller No displacement occurs.

2. Eliminate the gap and roll instead of sliding

The axial support of the arbor seat and the roller support, and the sliding bearing is replaced by a rolling bearing. No matter how precise the sliding bearing is manufactured, there is a gap. If there is a gap, the stiffness drops, and there is elastic yield. As the position of the contact line changes, the motion has uncertainty. Rolling bearings can be pre-tightened without gaps, rigid feet, less deformation, and determined movement.

3. Make sure your teeth bite

The key to ensuring that the paper does not move during printing is the tangential force of teeth. The printing speed is increased, the printing format is increased, and the wet press wet printing peeling force requires a strong gripping force. The contact area of ​​the paper gripper, the contact form of the gripper, the elastic deformation of the gripper, etc. are critical to the impact of the bite force. It can be said that the quality of the gripper is the core of ensuring the accuracy of the paper transfer. In the past, because the machine-type machines produced less, the research on gripping teeth was also a weak link. Most of the reasons for the low paper transfer accuracy are also for this reason. Unit-type grippers must ensure sufficient contact area. Theoretically, the tangential biting force F = fn does not seem to be related to the contact area, but the paper is a flexible body. When the teeth are compacted, the tangential biting force is no longer Simply calculate according to the above friction calculation formula, especially when the teeth are made into sharp teeth, with a soft tooth pad, the tangential bite force is the paper shear force, which is related to the size of the shear surface and is the contact area. Proportional function. The hard-soft combination mode is adopted, that is, the dental disc is hard, and the dental pad is soft, so as to better ensure a good contact area, and at the same time, the shear coefficient is large, and the paper is not easy to be displaced under the action of printing force. In the past, during assembly and debugging, only the positive pressure of the dental discs was checked and the tangential force of the working state was ignored, which was the main reason for the low accuracy of the paper transfer. If the positive pressure of the teeth is increased blindly, the open tooth rolling ball and cam working surface are easy to wear and the accuracy is easy to be lost. On the premise of ensuring the contact area of ​​the dental slices and the depth of tooth bite, on the contrary, we should appropriately reduce the positive pressure of the closed teeth, so that the machine can maintain the accuracy of paper transmission for a long time.

4. Pay attention to the daily maintenance of dental dentition

The dental shaft including the roller should be regularly maintained and inspected, filled with grease, and cleaned and cleaned. Ensure that there is no gap between the axis of the tooth and the roller, flexible opening and closing of the tooth body, no jamming, no dead teeth, no failure of the spring, and strong closing of the gripper. There is no dust or dust on the tooth surface, and the teeth are sharp. When the machine is used for a long time, you should also check the opening of the teeth and the wear of the cam. When the cam and the opening of the teeth are worn, the common paper feeding time will be slightly shortened during the handover. It is equivalent to that the high point of the delivery cam moves backward, and the opening time of the teeth is advanced, while the receiving cam moves relatively forward, and the closing time of the teeth is delayed. The reduction of the transfer time has a great influence on the accuracy of the paper transfer, especially in the high-speed operation state, it should ensure that the necessary transfer time is synchronized. When adjusting, you can take the method of reducing the radius of the adjustment tooling ball, because the reduction of the tooling ball is equivalent to the increase of the working ball, which can compensate for the wear of the cam and achieve the purpose of increasing the common handover time. When the teeth are worn and the "sharp teeth" are lost, the teeth must be replaced to ensure sufficient tangential bite force.

5. The printed material is not qualified and not on the machine

First of all, the paper unevenness needs to be treated first. For example, to eliminate the paper ruffles, you can add an infrared drying lamp to the paper stacker of the paper conveyor to properly remove the moisture absorption and deformation of the paper edge. Sheet, try to make the paper flat into the rule system and paper delivery teeth. If the static electricity is serious, you can add a static eliminator, so that the paper can enter the printing unit in a better controlled state and ensure the precision of paper transfer from the source.

We are a manufaturer of Bath Cleaning Products in JiangMen City, GuangDong Province.  We have 40 sets machines and a good team.The products that we made are Memory Foam Sponge,quick dry sponge and Packaging Sponge. Any items that u are interested in, welcome to contact us! We will be at your service at all time. 

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