Analysis of paper feeding failure in offset printing
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One, double, multiple failures
For the pneumatic continuous overlap type paper feeding which is widely used at present, when two or more failures occur, the work time is lost or the blanket is damaged, and the machine parts are damaged, causing the drum to jump. We need to prevent such failures as much as possible. . The causes and solutions are as follows:
1. improper adjustment of the separation head
The suction of the 1 minute paper nozzle is too large, adjust the air volume adjustment knob or the regulating valve on the air pump to reduce the air intake; or replace the small nozzle rubber ring. The position of the separation nozzle is too low to raise the position of the nozzle.
2 The loose paper blowing mouth is too large, adjust the air volume adjusting knob or the regulating valve on the air pump to reduce the blowing amount, so that it can blow 5-10 sheets of paper, less thick paper and more thin paper. The position of the loose paper mouthpiece is too low to raise the position of the loose paper mouthpiece.
3 The pressure of the paper blowing nozzle is too small to increase the amount of blowing. The amount of paper pressed by the platen nozzle is too small to increase the amount of paper.
4 The paper feed nozzle has too much air intake, reduce the air intake or replace the small nozzle rubber ring.
The position of the 5 paper stop brush is too high, and the paper stop function can not be achieved, and the position is lowered. The position of the paper stopper brush into the paper cassette is insufficient, and the amount of penetration is increased.
2. The reason for the paper
1 Paper has static electricity, which makes paper feeding difficult. The solution is to install static eliminator, increase indoor humidity or use antistatic agent.
A. Install the static eliminator. The static eliminator used on the printing machine has an inductive static eliminator, a high frequency high voltage static eliminator, a power frequency high voltage static eliminator, etc., and should be placed near the drum during installation.
B. Increase indoor humidity. The generation of static electricity is related to the relative humidity of the operating environment. When the relative humidity of the workshop is lower than 40%, static electricity is prone to occur. Therefore, when printing, sprinkle some water around the paper pile and the machine, or use an air humidifier to adjust the printing workshop. Relative humidity to avoid static electricity (generally, the humidity should be kept at 55%-65% at 20 °C).
C. Condition the paper. When the water content of the paper is low, the paper is easily electrostatically charged. When the paper is heavily static, it is necessary to hang the paper or place the paper in a relatively humid environment for a period of time, but care should be taken to prevent the paper from flanging.
2 The ink on the paper is not dry, the upper and lower papers are stuck, and the ink is dried before being printed on the machine.
3 If the paper is not loaded, reload the paper. The paper cutting error is too large to re-cut the paper.
Second, the empty failure
In the event of a blank failure, if the machine fails to detect, the ink that should have been transferred to the paper is transferred to the impression cylinder, which will cause the next ten sheets of paper to appear on the back side, causing waste. The reasons for the empty sheet are:
The suction of the 1 minute paper nozzle is too small, increase the inhalation volume or replace the large rubber band. In addition, it may be blocked by the airway and the airway is repaired. The position of the separation nozzle is too high, the paper cannot be sucked, and the separation nozzle is lowered. The separation nozzle is not parallel to the surface of the stack, adjust the angle of the nozzle or use a wooden wedge to lift the stack.
2 The looseness of the loose paper mouthpiece is too small to increase the amount of blowing. If the position of the loose paper mouth is too high or too low, adjust the position of the paper mouth.
3 Press the paper brush or press paper into the stack and adjust it to the proper position.
4 Pressing the paper nozzle to press too much paper, reducing the amount of paper.
Third, arbitrage failure
歪 是 means that the paper is skewed, and the skew of the paper will cause the rules to stop the paper from being properly positioned and waste work hours. When the paper is skewed, we can see that the edges of the running paper are jagged from the paperboard. The reasons for the arrogance are:
The inspiratory volume of the 1 minute paper nozzle is inconsistent, which is usually caused by the blockage of the gas path, and the gas path can be cleaned. The separation nozzle has different heights and adjusts its position. The left and right rubber bands of the separation nozzle are different in size, and the same size rubber band is used. The separation nozzle moves up and down inflexibly and takes off the inspection.
2 The position of the paper brush is not consistent, and it is adjusted to the same position.
3 The left and right loose paper mouthpieces are inconsistent in position and adjust to the same position.
4 The movement of the paper feed nozzle is not flexible, and the maintenance is taken off.
5 The paper stopper is not in the same plane or the working time is wrong. Adjust the paper stopper or paper stopper cam.
6 The two oscillating platen papers have different paper pressing times, and the control cams are adjusted to make the paper pressing time consistent.
7 The paper feeding belts are different in tension, and the tensioning pulleys are adjusted to make the paper feeding belts have the same tension.
8 The paper feeder itself is skewed to adjust the position of the feeder.
9 If the paper-pressing roller is placed improperly or the paper is skewed due to inflexible rotation, adjust it to a suitable position and regularly add a small amount of lubricating oil.
Fourth, the paper is unstable
Unstable paper feeding means that the paper feeding speed is not uniform, and it is fast and slow. When the paper is fed fast, the paper will break under the front bezel, the paper will be slow, and the paper will not go out. In both cases, the overprinting is not allowed, and the product will be scrapped. To this end, the paper feed speed must be adjusted for a while, and it will be slowed down for a while, making it unreasonable. Many machines have not been solved for a long time because of this problem, which affects both quality and production. The causes and solutions are as follows:
1 After the paper feed nozzle feeds the paper, there is still a residual suction, so that the paper that has entered the paper feed shaft is blocked due to the backward pulling force of the suction nozzle, causing a pause. Since the paper is superimposed, the previous sheets of paper are affected at the same time and slow down. In the middle of the stop, if the paper is stopped after the air pump is first turned off, the last few sheets of paper on the paper will be slightly faster due to the suction of the nozzle, resulting in unstable paper feeding. There are two solutions:
A. Adjust the front and rear movement cams of the paper feed nozzle so that when the nozzle feed distance to the limit position is about 10mm, the paper should be placed during manual inspection, and no residual suction will occur.
B. Block the air duct of the suction piston. For example, the "Beiren" SZ201 paper feeder adopts a method of blocking the wind trough, and the effect is good. The practice is as follows: Remove the piston and fill the tail of the air duct with a copper block of 3 to 5 mm. The copper block should be welded firmly to prevent the accident from falling off.
The paper feeding caused by the 2-wire belt is unstable.
A. The belt is too loose, the belt is tightened, and the tension of each belt should be as uniform as possible.
B. The belt tensioner is not working well, and it is cleaned with kerosene and lubricated.
C. The paperboard creates resistance to the belt and removes the dirt on the steel sheet support on the upper belt of the cardboard to eliminate the resistance.
D. Use double-layer tape to avoid jitter caused by uneven thickness of the tape.
3 The paper feed roller jumps (not round) and replaces the new paper feed roller.
4 The gap between the running parts of the paper feeding parts is too large, check the parts, and carry out the necessary repair or replacement.
5 Clutches accumulate paper wool and excessive oil, causing the clutching action to be inflexible. The clutch is not attached to the position of the hanging clutch, causing the paper feed to be slow and fast, and cleaning the clutch can solve the problem.
6 The bearing inside the passive roller of the paper feeding belt is damaged, and does not turn when it occurs. It is also the cause of the instability of the paper feeding. When checking, you can lift the paperboard, loosen the belt, and turn the belt by hand to find the problem. Replace the bearing to solve the problem.
Fifth, the paper arrives early or late
When the paper is not positioned before the side gauge starts to be positioned, the specified bit line is called the paper arrives late, and when the paper arrives early, the paper feeding time of the paper feeder and the front gauge falling time are improperly matched, so that the paper arrives ahead of the previous specified time. Pre-defined bit line. Whether the paper arrives early or late, the rules will not be able to achieve normal positioning of the paper, causing misregistration. The causes and solutions are as follows:
1 The paper feeding time of the paper feeder and the falling time of the front gauge are not properly matched. The correct mating time should be 5~8mm of the specified bit line before the current edge of the paper falls to the positioning position. For the chain drive J4105, you can loosen the three fastening screws on the sprocket, then turn the paper feed wheel to adjust the paper to the appropriate position, then tighten the three screws; Heidelberg Speed-Master The series can also adjust the mating time by changing the gear meshing relationship in the gearbox of the paper feeder.
2 The stack height is lower than the allowable height of the front sheet, and the delivered paper is blocked, causing the paper to arrive late. The height of the paper stack should not be lower than the axis of the swinging axis of the front paper block. Generally, it should be 5 to 10 mm lower than the top of the front paper block. When this happens, the feeder can be raised appropriately; if the stack is too high, even above the top of the front stop, the paper arrives early. At this time, the height of the feeder can be lowered or the wedge can be inserted to lower the stack height, and the adjustment requirements are the same as described above.
3 The swinging platen roller has a late fall or severe wear. The oscillating platen should be fed out of the paper at the paper feed nozzle. It will stop the suction and stop the suction just when the suction is stopped. The pressure can be felt when the machine stops. When the wear is serious, it should be replaced in time.
4Feida's paper feeding time is too late (relative to the swinging paper roller). Under the premise that the swinging platen hem time is correct, the transmission time of the feeder is adjusted according to the hem time (the PZ4880-01 of Beiren and the Speed-Master of Heidelberg have a relative position in the transmission gearbox of the feeder. Sprocket.
The 5-wire belt has a small tension, or the pressure of the paper feed roller is too light, causing the paper to arrive late. On the contrary, it causes the paper to arrive early. The solution is to tension the belt to a suitable level or to properly adjust the pressure of the paper feed roller.
In the offset printing process, there are many factors that affect the paper feeding. If a paper feed failure occurs during the operation, it can be eliminated as described above to ensure smooth production.