Comprehensive troubleshooting analysis of the hott

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Comprehensive troubleshooting analysis of offset press (I)

7.9 comprehensive troubleshooting

many faults are interrelated, so when troubleshooting these faults, we should consider comprehensively, that is, we should connect and analyze two or more circuits. Here are some common examples to analyze the general methods of troubleshooting

7.9.1 inaccurate overprint

inaccurate overprint refers to the inaccurate position coordination between text and paper. Paper is transmitted through paper path, and pictures and texts are transmitted through water and ink path. Inaccurate paper transmission, inaccurate water and ink transmission, and inaccurate cooperation between paper and water and ink may cause inaccurate overprint

from the perspective of paper route, overprint accuracy means that the position of the paper in each link of the printing process does not change with the change of time and conditions. As long as its position changes, it will cause inaccurate overprint. Line overprint inaccuracy is generally divided into front and back overprint inaccuracy, left and right overprint inaccuracy, left and right simultaneous overprint inaccuracy (Figure West skew people therefore analyze the paper overprint is not on time, we need to find those factors that make the position of the score sheet (front and back, left and right, front and back and left and right at the same time) change, and then take corresponding measures to solve it

1. The paper path will cause the body to break into inaccuracy

(1) the rule positioning is not accurate. Carefully check the working conditions of the front rule and the measuring rule. When the front rule is positioned, and when the rule is positioned, adjust it according to the requirements of (2) the cone oil groove of the buffer valve that cannot be adjusted is too deep or the valve body and the base are not in close contact. At the same time, pay attention to whether the height of the front gauge and the measuring gauge meets the requirements

(2) the paper delivery teeth take out the paper inaccurately

① the paper delivery teeth shake when taking out the paper, resulting in unstable handover: adjust the stopper of the paper delivery teeth to keep them stationary on the cardboard conveyor, and the transition is the most gentle

② the paper feeding teeth move axially when taking paper: adjust the axial locking nut so that it has a string momentum of 0.03mm

③ the biting force of the paper feeding teeth is insufficient, and the paper slides: increase the biting force, especially at high speed (mainly caused by the inertia of the paper)

④ the opening and closing time of the paper feeding teeth is not accurate: readjust the opening and closing time

(3) the coordination between the paper feeding teeth and the rules is not accurate

① when the paper feeding teeth have not taken the paper, the rules have released the paper: adjust the rules so that there is a common handover time between the paper feeding teeth and the rules

② the rule has not been positioned yet: take the paper from the paper delivery tooth and adjust it according to the above

③ when the paper delivery teeth take the paper and leave the cardboard, the regular part has not been put into the paper: adjust the rules to put the paper in advance

④ the height of the tooth pad of the up swinging paper delivery tooth is not appropriate: it is too low, which is easy to impact the paper and displace the paper; If it is too high, the paper will be pulled up when the paper delivery teeth are closed, and the position of the paper will also change. Carefully check its high and low position on the paperboard. Generally, its height should be: paper thickness +0.2mm, which is consistent with the height of the front gauge cap and side gauge pressing plate

(4) the handover between the paper transfer teeth and the front paper transfer roller (or imprint roller) is inaccurate

① the handover time is too short: adjust the position of the corresponding opening and closing teeth cam

② the distance between dental pads is inappropriate: readjust it to make the distance: paper thickness +0.2mm. However, generally, this distance should not be adjusted

(5) the bite force of the impression cylinder is insufficient, and the paper slides in the impression cylinder

① the pressure of the dental tablet is too small: increase the pressure of the dental tablet

② friction coefficient of dental pad at present, the plastic processing industry has changed from high-speed growth to medium speed, and the steady growth is too small: replace dental pad

③ the viscosity of the ink is too high. Some provinces such as Hunan, Jiangsu and Guangdong have successively introduced special funds, the first batch of subsidies and other policies and measures to reduce the viscosity of the ink

④ sticky rubber blanket surface: replace the rubber blanket

⑤ too much printing pressure: reduce the printing pressure

(6) the bite force of the rear paper transfer roller is insufficient, and the paper slides in the bite. Since the rear paper transfer roller on general machines participates in the printing process of the second half, its requirements are the same as those of the embossing roller. The troubleshooting method is the same as above

(7) the bite force of other rollers is insufficient, and the troubleshooting method can refer to (4) and (5)

(8) the bite force of the paper receiving chain row is insufficient, and the troubleshooting method is the same as (6)

(9) the axial serial movement of all rollers will cause inaccurate overprinting and limit the axial serial movement of rollers. Generally, double nut mechanism is used. If the axial string momentum is found to exceed the specified requirements (> 0.03mm), adjust the locknut. Generally, it should be fully locked, and then reverse it by one third of a turn. After adjustment, be sure to lock the nut. The axial thrust bearing wear will also cause the axial series movement of the drum. If it is worn, it should be replaced in time. If it is more accurate, it can be detected with a dial indicator

2. Partial overprint caused by paper path is not correct. Local overprint inaccuracy refers to the relative sliding of the local position of the paper during the printing process

(1) when there are only two front gauges positioned, when the paper reaches the front gauge, the middle part protrudes forward. The softer the paper, the more prominent this situation is. Reduce the speed or increase the number of front rules, so that the paper can be accurately positioned at the rules the day before yesterday

(2) there are some problems on the paper feeding teeth, but we can't just wait to be told what to do. The bite force of the teeth is insufficient, which will change the first four positions of the paper, increase the pressure or replace the tooth pad

(3) the paper biting amount of the paper delivery teeth is uneven, with more on one side and less on the other, and the parts with less paper biting amount are prone to relative sliding. Adjust the front gauge to make the paper biting amount even

(4) the bite force of individual teeth on the impression cylinder is insufficient. Replace the tooth pad or increase the bite force

(5) the local printing pressure is too large, causing the resistance of the paper to advance to increase, resulting in the paper moving at this place. Check the blanket and liner, and re calibrate the printing pressure

(6) the distribution of pictures and texts on the surface of the printing plate is unreasonable, and the paper is prone to slide relatively in the large area of the field. Add inking oil or reduce the printing pressure

(7) the paper expands with water, which causes the angle of the second half of the paper to swing. The paper is subject to humidity adjustment before printing

3. The seal combination caused by water and ink road is not correct

(1) the printing plate is loose. Because the printing plate is loose, the position of the imprint changes during the printing process, so it is impossible to overprint accurately. Adjust the fastening screw to clamp the printing plate

(2) the lining under the printing plate is inappropriate, which makes the impression larger or smaller, resulting in overprint. It is not allowed to re detect the thickness of the liner, and re pad the lining according to the technical instructions

(3) the rubber market is loose. Because the rubber blanket is loose, the imprinting position changes every time, resulting in inaccurate overprint

(4) the amount of water is too large, resulting in the tension of the paper becoming smaller, and the paper is easy to be stretched and deformed to reduce the amount of water

(5) the amount of ink is too large, causing the paper to slide in its teeth, reducing the viscosity of the ink

4. The overprint caused by the plate making part is inaccurate

(1) it is not allowed to use the crosshair or corner line as the reference line when making up, and the crosshair mean line is also used as the reference line when making up. If the position between the picture and text and the regular line is not accurate, it is extremely difficult, sometimes even impossible, to overprint accurately during printing. Therefore, we should maximize the accuracy of making up

(2) when printing, the sun is not allowed. If it is a sun job, this problem generally does not exist. Such problems are easy to occur in the work of two or more sunshines. Therefore, we should try our best to avoid exposure to more than two suns. If you have to do this, you should first sun the table paper

(3) plate deformation during plate drawing due to the poor resistance of the printing plate to deformation, it is easy to deform after receiving a large force, and sometimes even cracks will appear. Therefore, too much force should not be used when pulling the plate, and the reason should be carefully found when it cannot be pulled

(4) inaccurate overprint caused by process arrangement

① multicolor overprint is prone to inaccurate overprint. The more times of overprint, the greater the possibility of error. Therefore, the number of overprint should be minimized

② anti white words or lines of multi-color overprint are most likely to have inaccurate overprint, so spot color should be used as far as possible to replace overprint in these occasions. In addition, a reasonable process can be adopted to minimize the number of overprint and the possibility of causing errors. (to be continued)

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