Paper trouble troubleshooting
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The stable and accurate paper feeding of the paper feeder is an important condition for ensuring the quality of the printed matter. Since the printing paper often changes, the structure and movement of the paper feeding part are complicated, and many causes of paper feeding failure are difficult to judge correctly, which makes it difficult for the operator to handle. The following examples of analysis and elimination of paper feeding failures are for peer reference.
Double or multiple sheets
Feida has to separate and transport the paper, and there must be a pressure difference. The mouthpiece and the presser foot blow air under the paper, and the mouthpiece inhales on the paper, so that the air under the paper is continuously increased, the air pressure is continuously increased, the air above the paper is continuously reduced, the air pressure is continuously reduced, and the pressure difference is formed up and down, sucking The mouth can pick up the paper. In order to make the paper on the stack pile up and down one by one to form a complete pressure difference and smoothly transfer it to the paper feeding table (ie no double or multiple sheets), the parts of Feida must coordinate and the paper must be in a free state. (The surface of the paper is flat, there is no resistance between the upper and lower sheets).
1. Printing thin paper
When printing thin paper, especially paper of 60g/m2 or less, due to its poor strength and light weight, the paper edge has a fluffy wave shape when the loose paper mouth blows the paper edge. When the separation nozzle sucks up the first sheet of paper, the mouthpiece stops blowing, and when the presser foot is ready to be pressed, the edge of the paper that is blown into a fluffy shape is difficult to quickly return to a straight free state. When the presser foot is pressed down, it is easy to insert under the second or multiple sheets, resulting in two or more sheets. Even if the presser foot is accurately pressed under the sheet of paper picked up by the separation nozzle, the paper along the edge of the presser foot is still convex and fluffy, preventing the presser foot from blowing on the four sides of the paper, which affects the formation of the pressure difference between the upper and lower sides of the paper. If the paper is not completely separated, the transfer nozzle may pick up and send out two or more sheets.
In view of the above situation, the following adjustments should be made to each adjustment part of Feida: (1) appropriately reduce the air volume of the loose paper mouthpiece, increase the stack height, increase the sensitivity of the detection switch, increase the paper raising frequency, and reduce the paper pile every time. The extent of the rise ensures that the loose paper mouthpiece only blows down the top sheets of paper at a time. (2) The separation nozzle should not be too low from the paper surface. Otherwise, when it moves down the suction paper, the air between the upper and lower papers will be squeezed out, and the two papers will be sucked together. (3) Adjust the angle of the separation nozzle so that the paper between the two nozzles is in a tight state when the paper is sucked, so that the presser foot has the largest amount of paper. (4) The presser foot should be pressed more without touching the paper edge, and the amount of air blow should be increased to make the air blow to the four corners of the paper to form a complete air cushion layer. (5) The tablet and the brush should be pressed down as far as possible without affecting the separation of the separation nozzle, so that the edge of the loosened paper is restored in time after the blown nozzle stops blowing.
2. The effect of paper with static electricity
In the dry season, the air humidity is low, the paper has poor electrical conductivity, and it is easy to generate static electricity. Paper with static electricity attracts each other and the faster it separates, the greater the suction. Not only is it difficult to blow loose, but also the paper that is delivered by the paper nozzle, after the presser foot stops blowing, the tail of the paper will re-suck the paper under the paper pile, and the neat paper will be pulled toward the bottom. The front is staggered, and when the separation nozzle sucks the paper again, it is easy to pick up two or more sheets. Therefore, the paper should be treated to eliminate static electricity, such as hanging and adjusting humidity or increasing air humidity.
Paper skew
The neat delivery of the paper must follow the symmetry principle of the paper feeder. Pairs of brushes, tablets, clamps, mouthpieces, nozzles, and paper-feeding rollers on the paper feeder should be symmetrical about the top, bottom, front, and left. The amount of blowing of the left and right mouthpieces and the amount of inhalation of the left and right nozzles should be the same, and the amount of blowing of the presser foot to the middle and both sides should be uniform. It is worth noting that the symmetry of the paper can not be ignored. The ideal state is that the surface of the paper is flat, the front and side sides are flush, and there is no resistance between the papers. When the paper feed nozzle feeds the paper to the paper feed roller, the paper front The mouth should be parallel to the axis of the pickup roller. However, in actual production, this ideal state is often difficult to achieve. First, due to the electrostatic attraction between the paper, the adhesion of the ink, and the uneven local resistance formed by the surface of the paper, the paper is easily skewed; the second is because the bending of the left and right sides of the paper front is different. When the paper is between the paper feed roller and the paper feed roller, it may be smoothly fed forward in parallel, and the other side and the paper take-up roller axis are crossed and collide with the surface of the paper feed roller, causing the paper to be skewed. In addition, Feida has more parts and complicated movements. It is inevitable that the jitter is unstable during the paper separation and transfer process. These factors can easily cause the paper to be skewed and difficult to overcome. Therefore, some modern offset printing machines correct the skew of the paper by changing the paper path of the two ends at the transfer link of the transfer nozzle. For example, the Heidelberg CD 102 offset press has an adjustment knob above the feeder's transfer nozzle to correct the skew of the paper.
Paper flickering or flickering
In the case of abnormal changes in the paper feed speed, sometimes even if the paper feed time is changed several times, or the paper is shaken during conveyance, especially the first few sheets just output, except that the gears or other parts are worn out because the pins are broken. As well as paper static and other reasons, improper adjustment of the paper feed wheel and unobstructed air path will seriously affect the smoothness of the paper feed speed.
1. Pickup wheel fall time or pressure adjustment is not suitable
(1) The correct paper roll falling time is that the front mouth of the paper fed by the paper feed nozzle crosses the contact point of the paper picking roller and the paper picking roller by about 5 mm. At this time, the paper feed nozzle is ready to put paper, and the paper picking wheel should be Press the paper in time, and the handover should be completed in the shortest possible time, but it cannot be out of control. If the falling time of the pickup roller is too early, the paper feed roller has pressed the paper and the paper feed nozzle has not been released, and both control the paper. Because the transmission speed of the paper feed roller does not coincide with the paper feed speed of the paper feed nozzle, the paper feed speed in this case is not the paper feed speed of the paper feed roller, but the paper feed roller and the paper feed nozzle are simultaneously controlled. Paper feeding speed. When the nozzle releases the paper, the paper feed speed suddenly becomes the paper feed speed of the paper feed roller, which may cause the paper to be unstable or shake. If the paper pick-up time falls too late, the paper will not be controlled in time when the paper feed nozzle releases the paper, and the paper will have a noticeable pause during transport.
(2) There must be proper contact pressure between the pickup roller and the pickup roller. If the pressure is too small and the friction is insufficient, the paper between the paper feed roller and the paper feed roller will slide relative to each other. Especially when the paper has static electricity or the paper feed nozzle has residual suction, the paper feed speed will be obvious. Variety.
(3) Adjustment procedure of the paper take-up roller: When the paper pick-up roller falls and presses the paper and walks through half of the total length of the drop-down time, adjust the adjusting screw on the paper-taking roller so that there is a slight gap between the screw and the pick-up wheel Generally, it is 0.3mm. At this time, there should be a certain gap between the minimum radius of the cam that controls the upper and lower swing of the paper feed roller and the roller, which is about 1.5mm, so as to ensure that the paper picking wheel has enough pressing time. The paper feeding is more stable, and it also ensures that the pulling force of the large spring acts on the paper picking wheel and becomes the pressure of the docking paper roller. If the pressure is not enough, you can adjust the top wire at the small spring on the pickup roller to increase the pressure. The final adjustment is the take-off time of the pickup roller, which can be changed by changing the cam position. Although adjusting the adjusting screw on the paper feed roller can also change the lifting time, when the screw is adjusted, the length of the falling time and the pressure will also change, so the adjusting screw can only be adjusted slightly.
2. The gas path is not smooth
After a period of work, a lot of dust impurities will accumulate in the ventilation duct, especially in the air pipe joint of the suction pipe, the gas distribution valve groove, the gas volume adjustment knob hole and the air supply hole.
(1) The blockage of the suction pipe will inevitably cause the suction volume to decrease and the suction time to be shortened, so that the standard action and working time of the paper separation nozzle and the paper feed nozzle are mutated, and the two control the transfer paper is not stable and is sent out. The distance and speed of the paper will change.
(2) Generally, there will be a vent hole next to the separation and transfer suction adjustment knob. For example, the left side of the separation and suction adjustment knob of the Beiren J2108 offset printing machine has 2 air holes, and the paper suction adjustment knob There are 3 air holes on the right side of the suction valve housing. The function of these air vents is: when the suction slot in the air separation valve rotates through the suction adjustment knob hole to block the air pump suction, from the suction nozzle of the paper suction to the suction adjustment knob, the air pressure ratio in the pipeline The outside air pressure is small, so it must be connected to the outside through the air supply hole, let the outside air flow into the pipe, balance the internal and external air pressure, and let the nozzle completely relax the paper. Once the air supply passage is not smooth, the suction nozzle will have a residual suction phenomenon, that is, the paper separation nozzle still sucks the paper when the paper feed nozzle advances the paper, and the paper feed nozzle sucks the paper back on the way back. Causes the paper feed speed to slow down or have a pause. At this time, if the air volume of the nozzle is adjusted, the paper feed speed will also change. In particular, the residual suction of the paper feed nozzle will make the first paper of the fresh air pump counter the residual suction force of the paper feed nozzle when the air pump is just opened, and the front gauge is particularly slow, and after the wind pump is closed The last piece of paper, because there is no suction of the nozzle, will go over because of the speed.
(3) Cleaning of the air circuit: the position of the air blowing pipe and the air suction pipe on the air pump are changed, the air pump is turned on and the fly motor is activated, and the dust in the air suction pipe is blown out. For the inside of the gas volume adjustment knob and the gas distribution valve groove where the dust accumulation is serious, the adjustment knob fixing screw can be loosened, and the adjustment knob can be taken out to remove the dust in the knob hole and the valve groove.