Whether it is a sheet-fed offset press or a two-color or four-color offset press, after running for several years, all parts will have different degrees of wear, especially several cams, tooth pads and teeth The parts such as the seat and the take-up tooth row are easy to wear, and their precision is reduced, so that the paper transfer cannot be carried out normally during the printing process. The manifestation of the failure is that the edge of the paper is torn, which makes the overprinting of the second color not normal. The tearing of the edge of the paper also affects the cleanliness of the paper and causes the loss of the printed product in serious cases. In the actual work, when the paper is torn when it is received, it should be analyzed comprehensively, treated differently, and the main points should be eliminated to eliminate the fault.
1. The reason and elimination of tearing the paper in front of the paper
â‘ The transfer time between the gripping teeth of the impression cylinder and the delivery teeth is too long. Properly shorten the transfer time of two sets of grippers.
â‘¡ The opening and closing teeth of the impression cylinder are different. Adjust the gripper of the impression cylinder to open and close.
â‘¢ The impression cylinder and the delivery line are not connected at the cut point or deviated from the cut point. Adjust to the handover of the tangent point.
â‘£The opening and closing of the paper-collecting teeth row and gripper teeth are different. Adjust the makeup paper row to be consistent with opening and closing.
(5) The edge of the gripper of the delivery roller is too close to the edge of the impression cylinder, or it collides with the edge of the impression cylinder. Adjust the distance between the edge of the gripper and the edge of the impression cylinder, generally about 1mm.
â‘¥ The opening cam of the impression cylinder or the opening cam of the paper-collecting teeth are worn out, which causes the opening of the teeth to be small and the paper is hit. Replace the impression cylinder or take-up teeth to displace the tooth cam.
⑦The tooth row gripper paper touches the paper support rod or other obstacles during the transmission and tears the edge of the paper. Check the above points.
⑧In addition to the adjustment errors of the offset press and the improper handover of the paper, which causes the tearing of the gripper of the receiving paper, the quality of the paper itself is also prone to tearing the paper. If the paper has poor flexibility, the paper is stored for too long, the sunlight is irradiated, the paper warehouse environment is dry, and other reasons make the paper yellow and brittle, such paper printing on the machine will also make the paper tear the paper.
2. The reason and elimination of the tearing of the paper edge during the normal printing process
In the normal printing process, if you find that the paper tearing edge, you should first find the cause of the problem, carefully check the paper tearing. Generally speaking, there are only three phenomena of tearing the edge of the mouth: First, the edge of the paper is continuously torn and the position is unchanged. Second, not every sheet of paper is torn, but a few sheets of paper that are not torn apart in the middle are regular. Third, the tears at the edge of the paper are large and small, and sometimes broken, without regularity.
Now the causes of the above three faults and the methods of elimination are analyzed as follows:
1. During the offset printing process, the edge of the paper is regularly torn, and the number of sheets in the middle is exactly the number of the rows of paper-receiving teeth.
This situation is generally caused by improper adjustment of the delivery line.
Solution: Drive the offset press slowly and carefully observe whether the tension of each tooth of the delivery row is the same, then adjust it, and then drive to try the paper to see if there is still a phenomenon of tearing the paper.
2. The edge of the paper is continuously torn, and the position has not changed.
If this failure occurs, we have to find the reason on the delivery tooth and roller tooth. First, take a slow car and carefully observe the process of handing over the paper between the delivery teeth and the roller teeth to see if the paper delivery time of the delivery teeth is slow or the opening of the teeth is not enough, causing the paper torn.
Solution: Check whether the protruding bumps of the delivery teeth are worn. If they are worn, they need to be repaired or replaced with new ones, and be carefully adjusted. The requirement is that when the delivery teeth hand the paper to the large teeth of the impression cylinder, the delivery teeth The distance to control the paper at the same time as the roller teeth should not exceed 3mm.
Secondly, the roller tooth base is formed into a circular pit by the jacking wire, resulting in insufficient opening of the roller teeth. When the delivery tooth and the roller tooth transfer the paper, the paper edge touches the roller tooth and tears.
Solution: If only one or several tooth holders are damaged by the jacking wire, repair welding can be carried out on the machine. If the jacking is more damaged, it needs to be removed and replaced with a new one.
Thirdly, the connection between the roller shaft of the roller teeth and the pulley frame is loose, which causes the roller teeth to open slowly or the opening of the teeth is not enough to tear the paper edge.
Solution: First check whether the pin at the connection is loose or cut. If it is only loose, it can be re-tightened. If it is cut, you need to replace it with a new pin.
Fourth, the distance between the tooth pad of the delivery tooth and the impression cylinder is improperly adjusted. If the distance is too close, the tooth pad of the delivery tooth rubs against the edge of the impression cylinder, causing the edge of the paper to tear, and the distance is too far to hold the impression cylinder. Torn the edge of the paper.
Solution: Carefully adjust the distance between the delivery tooth pad and the impression cylinder. Generally, the distance between the two should be adjusted to 0.5mm. Cardboard printing should be 2 to 3 times the thickness of the paper.
Fifth, the open tooth protrusion of the paper collecting tooth is worn, and the tooth opening time of the paper collecting tooth is slowed down, and the paper is torn due to the too small tooth opening distance.
Solution: Remove the open tooth bumps and repair by welding or replace with new ones.
3. The edge of the paper is broken irregularly at the edge of the paper, and the width of the paper is narrow when it is broken.
This phenomenon is generally caused by improper adjustment of the paper feeder or the front gauge, and the cause should be found on the paper feeder. â‘ Carefully observe whether the belt tension of the paper conveyor is consistent; â‘¡Start the offset printing machine to see whether the conveyor belt pulleys can rotate flexibly; â‘¢The jog of the offset printing machine to see whether the time for the paper to reach the pre-regulation is appropriate, general requirements When the current rule reaches the paper receiving position, the distance between the paper edge and the front rule is 8-10mm. If it is not suitable, it needs to be adjusted; â‘£ carefully check whether the height of the front rule meets the requirements. The general requirement is that when the current gauge reaches the paper receiving position, just three sheets of printed paper can be put in, and there is a slight resistance when pulling.
In summary, when troubleshooting the tear paper tearing problem, we must pay attention to the delivery tooth, roller tooth, and tooth pad. The hand-to-tooth connection must be reasonable and must be in accordance with the motor relationship table in the machine instruction manual To adjust the required data, the height of the pads of a row of teeth must be adjusted uniformly. The opening and closing time of each tooth and the opening and closing size of the open tooth must be the same. The bite force of each tooth was tested with a paper strip to determine its bite force balance.
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