The paper feed adjustment of sheet-fed offset printing press is an important preparation before printing. Improper adjustment will cause various paper feed failures. The adjustment of the feeder head includes the adjustment of the paper suction nozzle, the paper feeding nozzle, the paper pressure steel sheet, the paper pressure block, the presser foot, the loose paper blower, and the presser foot blower. It involves more aspects. This article only makes a brief analysis of the common paper feeding problems caused by paper feeding nozzles.
In the process of adjusting paper feed before printing on a sheet-fed offset press, due to improper adjustment or wear of machine parts, various paper feed faults are often caused, such as skewed sheets, double sheets, empty sheets, and so on. There are many occurrences. Once crooked sheets appear, they will be detected by the photoelectric eye at the prescribed position on the paperboard, which will stop the paper feeder and interrupt the paper feed.
There are many reasons for crookedness. According to my experience, the following are common:
â‘ The adjustment of the two sides of the pressure steel sheet is inconsistent. The inconsistent adjustment of the paper pressing steel sheets on both sides will cause uneven pressure on both sides of the paper, and the paper separation nozzle is likely to cause skew when sucking the paper.
â‘¡The loose paper blowing height adjustment is inconsistent. The wind force on the trailing edge of the paper stack is different, and the amount of paper on the two sides that can be blown off by the wind blowing is also different, which is easy to cause skew.
â‘¢The stack of paper is too low, and it is easy to be distorted by the blocking tongue.
â‘£ The paper blocking tongue is not in a line, which will cause the paper stack to be uneven and cause the paper to skew.
⑤ The adjustment on both sides of the paper receiving roller is inconsistent. After receiving the paper from the paper suction nozzle, if the two sides of the paper receiving wheel are adjusted inconsistently, the friction of the paper forward will be different, and the paper will easily skew on the paper feeding board.
â‘¥ The inconsistent position or pressure on both sides of the paper pressing roller and the brush roller cause the paper to be subjected to different sizes of friction during the forward process, which can also cause skew.
⑦The inconsistency of the belt tension will cause the rotation speed of the pressure roller and brush roller to be inconsistent, which will cause the paper to skew.
⑧ Improper adjustment of the side gauge. The positioning plate of the side gauge should be 3mm ~ 5mm away from the side of the paper. If the positioning plate of the side gauge is too close to the edge of the paper or even blocks the paper, it will make the paper unable to advance by the side, causing skew.
⑨The time to open the air pump is wrong. The time of opening the air pump should be controlled when the paper separation nozzle starts to inhale. The time too early or too late will cause the paper to skew.
â‘©The paper is not straightened. The paper is skewed when loading paper on the feeder, which will definitely cause a skewed sheet failure.
This article takes Guanghua PZ1650 as an example, and mainly makes a brief analysis on the misalignment of paper caused by the paper suction nozzle.
The role of the paper suction nozzle is to suck the paper separated by the separation nozzle, lift it slightly and deliver it forward, and hand it over to the paper receiving roller and the paper guide wheel. The paper delivery and reception are mechanically reciprocated by the corresponding mechanism The movement and the suction and deflation actions of the suction nozzle are matched to complete.
The skew failure caused by the paper suction nozzle usually has the following points.
1 The height of the paper nozzles on both sides is inconsistent
If the paper suction nozzle is low on one side and high on the other hand, when the suction head starts to suck and fall, the paper suction nozzle on the side higher than the paper surface will reduce the suction force of the paper due to the large gap, and the paper suction is unstable or leaks. The movement slowly lags during forwarding of the paper, causing the paper to skew.
Solution: Through the adjustment device, visually make the height of the paper suction nozzles on both sides consistent.
2 The paper feed nozzle on the transmission side is not horizontal
The paper suction nozzle on the transmission side is not horizontal and tilts backward. When the paper feeding nozzle delivers the previous sheet to the paper guide roller and the pickup roller and then retracts to suck the next sheet of paper, because the nozzle is not horizontally inclined to the rear side, the rear part of the nozzle returns to meet the paper first, and The closer to the paper surface, the greater the suction force. This will make the paper transfer speed on the transmission surface faster than the suction nozzle with a horizontal operation surface, and the paper will be delivered earlier, causing the paper to fall off the transmission surface faster, causing the paper to skew. The paper feed nozzle on the transmission side shown in b of Fig. 4 is not horizontal, and is inclined forward. When the paper feeding nozzle is retracted, although the rear end of the nozzle meets the paper first, it is farther away from the paper surface, and the suction force is smaller, while the front end of the nozzle is closer to the paper surface, and the suction force is greater, but the front end of the nozzle , The paper delivery speed on the transmission surface is slower than that on the suction nozzle with a horizontal operation surface, and the paper delivery lags, causing the paper under the transmission surface to be slow and the paper skewed.
Solution: Twist the adjustment handle to adjust the level of the suction nozzle with a non-level transmission surface. The angle of Guanghua PZ1650's operating surface paper feed nozzle is horizontal and cannot be adjusted. It is used as a reference for adjusting the angle of the paper feed nozzle of the transmission surface.
3 The paper feeding nozzle on one side does not suck the paper, causing continuous and large skew
The skewed sheet mentioned above, the skew degree of the paper is small, and sometimes it will not affect the normal paper feeding at low speed. However, there is another kind of crooked sheet failure, the paper is skewed to a large extent, and at this time, paper feeding becomes quite difficult. This kind of failure is mostly caused by the failure of one side paper feed nozzle, which can not work normally.
1) The suction air is too small, so that the suction head does not fall, so that the force on one side of the paper will definitely cause a large skew. Solution: Adjust the suction knob of the air pump to increase the suction volume.
2) The air path is not smooth and needs to be cleaned. After the printing machine has worked for a long time, the suction nozzle will draw a lot of paper wool, paper powder, and dust into the air path, causing the air path to be blocked or the air path blocked, causing the suction air to be too small, and the suction head not to fall. Solution: Use organic solvent to clean the gas line.
3) The parts of the nozzle mechanism are worn. The diameter of the bottom of the paper delivery nozzle is larger than that of the outer jacket. In addition to a large straight hole in the middle and 6 small oblique holes around it, there is a slightly convex edge on the side to protect the suction and prevent it from spreading and focusing the suction. However, the paper delivery nozzle will wear out after a long time. Not only will the protruding edges be worn away, but also the entire suction surface will be smooth and the edges will be sharp. As a result, the paper slipped when sucking the paper, and the paper could not be absorbed, causing the paper to be skewed and other undesirable phenomena, which brought disadvantages to the work.
The common treatment method is to either put a apron on the paper delivery nozzle, or use the sand suction surface of the nozzle to make it rough, increase the friction, and no longer slip. Although both methods can be effective, they have their own shortcomings. First, it is easy to suck the paper through the apron. If the paper is not flat, it is easy to make the paper skew; second, the use period of the sand buffalo is very short. Pass the paper nozzle.
In the pre-feed adjustment of sheet-fed offset printing machine, master the adjustment of the feeder, can deal with various problems calmly, debug the machine in the shortest time, and lay a good foundation for starting printing. Is what we all expect.
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