During the operation of the offset press, failure of its positioning components will cause various problems in the printing of the product, and the most direct result will be inaccurate overprinting of the printed product. There are many situations of faults in positioning components, mainly in the following aspects.
1 Improper paper feed time
Improper paper feeding time refers to the problems that the paper arrives early or late, and the positioning time is incorrect and the positioning time is insufficient. This situation is actually caused by the paper machine and the host is not synchronized. But sometimes the paper feed time will change after the machine is adjusted and synchronized, then it is necessary to check whether the machine itself is faulty, such as whether the Feida bearing is damaged or the universal joint pin is broken, etc., because these parts are easier Worn. Solution: Check the time when the leading edge of the paper reaches the front gauge. Generally, when the current gauge arrives on the paperboard, the bite edge of the paper should be 4 to 6 mm away from the previous prescribed plane. Keep this distance to stabilize the front gauge in place; check the input Whether the elasticity of the paper tape is suitable, if it feels wrong, adjust the elasticity according to the situation; check whether the connecting pin of Feida and the universal shaft is damaged, and replace it if it is damaged; check whether there are selected objects on the paperboard that block the paper Conveying, especially the interface part of the paper belt.
2 Inaccurate horizontal overprint
The positioning component sometimes has a fault of inaccurate lateral overprinting. If the paper blocking tongue is adjusted too high, the pull rule can also cause curling, which can cause the paper to over-position. In addition, the non-parallel paper edge is also the cause of the inaccurate horizontal overprint. Treatment method: adjust the height of the paper stopper tongue to 3 to 4 times the thickness of the printed paper, pull the specified position to be parallel to the paper, and select the springs with different hardness according to the paper of different thickness.
3 Irregular printing is not allowed at both ends
Irregular overprint inaccuracy at both ends means that overprint inaccuracy occurs on the same printing sheet at the same time on the operation surface and the transmission surface, but the error between the two ends and the standard line is not the same. There are several reasons for this situation.
1) The transfer time between the transfer teeth and the impression cylinder gripping teeth is not enough. The transfer time between the transfer teeth and the impression cylinder gripping teeth is too long will tear the bite, too short will result in overprinting phenomenon, the faster the speed The more serious. Because when handing over the paper, due to insufficient handover time, the impression cylinder gripper has not completely closed the bite, and the delivery tooth has released the paper. In particular, in some machines, the paper delivery teeth are closed by the spring, rather than the high point of the cam, so it is more likely to cause such failures. Solution: On the premise of not tearing the paper, adjust the opening time of the delivery tooth a little later, and adjust the opening cam. In addition, it is also possible to tighten the gripping spring of the impression cylinder.
2) The pre-prescribed position plane is not parallel to the impression cylinder busbar. In order to make the position of the picture and text meet the requirements, it can be achieved by moving the pull plate, but it cannot be moved too much, and the previous regulations should be restored after the work is completed. If the two pre-positioning planes are not on the same line and the difference is too large, then there may be only two points when the front edge of the paper contacts the pre-positioning plane. The impact force of the paper is concentrated at two points, so that the force per unit area is too large, causing the edge of the paper to curl, resulting in irregular overprinting. In addition, both sides of the paper should be at right angles. If the positioning is not a right angle, it is difficult to stabilize the positioning requirements. Solution: Before restoration, stipulate that the plane is parallel to the generatrix of the impression cylinder, and reinstall the plate for correction.
3) The rest time of the delivery tooth is not enough. When the delivery tooth takes the positioned paper away from the paper feeding board, the delivery is carried out in a still state. It takes a certain stabilization time for the paper-feeding tooth to move from the motion state to completely stationary to ensure that the paper is picked at the same position. If this time is not enough or not enough, there will be an error in the position of the delivery tooth to take the paper again, resulting in the failure of overprinting. Solution: adjust the adjusting screw on the "positioning backer" to make the roller have a gap of 0.03mm on the smallest surface of the cam. When correcting, the "backer" on both sides should be corrected at the same time. The method is to insert a 0.03mm feeler gauge Between the roller and the cam, and then press the roller against the cam, adjust the "backer" screw to the position that meets the requirements, and tighten the screw. Adjust repeatedly until it is in the correct position.
4. Bilateral symmetric and consistent overprinting is not allowed
Bilateral consistent overprint inaccuracy means that both the operation surface and the transmission surface are inaccurate at the same time, and the crosshairs of the inaccurate overprint are basically the same distance as the standard line in the direction of bite or drag. The reasons for this phenomenon are various. If it is a second mobile phone, it may be caused by the wear of the roller surface of the hand or the bearing damage and the wobble tooth cam or the horizontal axis of the wobble hand. If it is a new machine, the adjustment of the large tension spring of the swing row is generally not good. Of course, it may not be a problem of positioning components. Solution: After the above problem occurs, first check the large tension spring of the swinging tooth row, adjust it or replace it with a new one. If the problem cannot be solved, check the degree of wear of the pivot pin of the swinging hand, check the gap or ellipse between the pivot pin and the sleeve, and replace or repair immediately if excessive wear is found. If it is a second mobile phone, the swinging tooth cam and the holding roller may also be worn. If this is the case, it should be replaced if there are accessories. If there are no accessories, it is best to use oil stone to repair the worn uneven parts. Sleek. Wrong paper release time of the front gauge will also cause inaccurate overprinting at both ends. This requires loosening the fastening screw of the control cam and changing the relative position of the cam to make it reach the correct time requirement.
5 One-sided overprint is not allowed
Sometimes the phenomenon of inaccurate overprinting only appears on one side of the paper, while the other side can register. There are two main situations: overprinting at one end with a pull gauge and overprinting at the end without a pull gauge.
1) Overprinting on one end of the pull gauge is not allowed. The most common cause of failure is the pull gauge itself. The analysis is as follows. When the paper that is normally conveyed has not reached the front gauge, the paper pulling roller has fallen and pressed the paper, causing the paper pulling end to go out of position. Treatment method: Adjust the side gauge cam so that the paper reaches the front gauge and after a certain stabilization time, the side gauge will fall and press the paper. The lifting time should be when the delivery teeth bite the paper and are ready to leave the front gauge. You can also adjust the speed of the paper to make it go a little faster.
When the paper gripper gripped the paper and started to transfer it forward, the side gauge pressure roller was not fully lifted and pressed against the edge of the paper, blocking the advancement of the paper, resulting in inaccurate overprinting at the end of the gauge. Treatment method: There are two cases, one is that the pull-down pressure roller is set at the correct time, but the lifting time is too late, that is, the work time of the pull rule is too long, which requires fine-tuning the control cam. During operation, the vehicle must be jogged forward and not reversed as much as possible. The cam can only move slightly, and the position should be determined according to the actual situation. The other is that the pull gauge pressure roller drops too slowly, and then it lifts slowly. This is because the working time is wrong. Adjust the pull gauge to make it fall faster.
The height of a single front rule is incorrect. The position of the front gauge paper tongue should be a gap of 3 times the thickness of the paper. Too low or too high adjustment will prevent the paper from entering the front gauge. Treatment method: adjust the height of the front gauge according to the thickness of the paper.
2) The overprint is not allowed on one end without the pull gauge. This means that the paper is unstable after entering the side gauge. After the lateral positioning of the side gauge, the positioned paper should not move anymore. Therefore, the brush wheel or the pressing wheel on the paper side of the paper without a side rule will play a great role in stabilizing the paper. The reasons for the above situation are as follows: â‘ The paper is sometimes not in place, which requires checking the speed of the paper and whether there are objects on the paper board that hinder the running of the paper; â‘¡ The paper is ejected; If the front regulation plane is not parallel to the roller generatrix, when the side gauge pulls the paper, the other end of the paper will be disconnected from the front regulation. Treatment method: Check the reason why the paper is not in place, and make corresponding treatment according to different situations. If the paper rebounds, increase the brush or move the pinch roller on the conveyor belt slightly forward. If the front plane is not parallel, adjust the front gauge before printing according to the size of the paper bite at both ends of the paper.
There are other malfunctions of the positioning component, such as paper skew, the front gauge tongue is too low, the paper feeding tooth bite force is insufficient, the side gauge is raised too slowly, etc., the processing methods are also various, but we all need us On the basis of being familiar with the components of the offset press, carefully find the root of the problem, and patiently adjust the repair or replacement parts.
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