Troubleshooting skills of the most popular offset

Troubleshooting skills for tearing paper in offset printing receipt

offset printing machines, whether sheet fed offset printing machines or two-color and four-color offset printing machines, after several years of operation, due to varying degrees of wear and tear of various parts, especially several open tooth cam bumps, tooth pads and tooth seats, paper receiving tooth row and other parts are easy to wear and tear, and their precision decreases, so that the paper handover cannot be carried out normally in the printing process. The manifestation of the failure is that the mouth edge of the paper is torn, so that the overprint of the second color cannot be carried out normally. The torn edge of the paper also affects the cleaning of the paper, and in serious cases, it causes the scrap loss of the printed product. In actual work, when the paper is torn when receiving, we should analyze comprehensively, treat differently, and correct the key points to eliminate the faults

1. Causes and elimination of tearing paper at its mouth in front of the paper

① the handover time between the teeth of the imprint drum and the paper receiving teeth is too long. Appropriately shorten the handover time of two sets of teeth

② the opening and closing teeth of the impression cylinder are different. Adjust the teeth of the imprint cylinder to be consistent in opening and closing

③ the impression cylinder and the paper receiving tooth row do not intersect on the tangent point or deviate greatly from the tangent point. Adjust to the tangent position handover

④ the opening and closing of the paper receiving teeth are different. Adjust the tooth row of makeup paper to be consistent in opening and closing

⑤ the edge of the receiving teeth is too close to the edge of the embossing cylinder, or collides with the edge of the embossing cylinder. Adjust the distance between the edge of the receiving tooth row and the edge of the embossing cylinder, which is generally about 1mm

⑥ the opening cam of the impression cylinder or the opening cam of the paper receiving tooth row is worn, resulting in small opening of the opening tooth and paper touching. Replace the embossing cylinder or the opening cam of the paper receiving teeth

⑦ the edge of the paper is torn when the paper in the tooth row touches the paper support rod or other obstacles during transmission. Check and deal with the above points

⑧ in addition to the reasons why the adjustment error of the offset press and the improper handover of the paper cause the paper to tear in its mouth, the quality of the paper itself is also prone to tear in its mouth. If the flexibility of paper is poor in the process of researching and exploring new materials, new processes, new technologies and new structures, the paper is stored for too long, exposed to sunlight, and the paper warehouse environment is dry, which will make the paper yellow and brittle. Such paper will also tear the paper in its mouth when it is printed on the machine

2. Causes and elimination of tearing at the mouth of the paper during normal printing

if you find tearing at the mouth of the paper during normal printing, you should first find the cause of the problem and carefully check the tearing of the paper. Generally speaking, there are no more than three phenomena of tearing at the mouth: first, the mouth edge of the paper is continuously torn and the position remains unchanged. Second, not every piece of paper is torn at its mouth, but several pieces of paper that have not been torn are separated in the middle, and they are regular. Third, the gap at the mouth of the paper is sometimes large and sometimes small, sometimes good and sometimes broken, and there is no regularity

now the causes and troubleshooting methods of the above three faults are analyzed as follows:

1 During offset printing, the paper is regularly torn at its mouth, and the number of sheets in the middle is just the number of receiving teeth

this situation is generally caused by improper adjustment of the paper receiving teeth

solution: drive the offset press slowly and carefully observe whether the tension of each tooth in the paper receiving tooth row is consistent, then adjust it, and then drive the machine to try to remove the paper to see if there is still paper tearing

2. The paper is continuously torn at its mouth edge, and the position remains unchanged

if this fault occurs, we need to find the cause on the paper feeding teeth and roller teeth

first, drive slowly and carefully observe the process of paper delivery between the paper delivery teeth and the roller teeth to see whether the paper edge is torn due to the slow opening time of the paper delivery teeth or the insufficient opening of the teeth

solution: check whether the tab of the paper feeding tooth is worn. If it is worn, repair welding or replace it with a new part, and make careful adjustment. The requirement is that when the paper feeding tooth passes the paper to the big tooth of the embossing cylinder, the distance between the paper feeding tooth and the big tooth of the cylinder shall not be greater than 3mm at the same time

second, because the roller tooth seat is jacked into a round pit by the jackscrew, the opening of the roller tooth is not enough. When the paper is handed over to the roller tooth, the paper edge touches the roller tooth and tears

solution: if only one or several tooth bases are damaged by the jacking wire, repair welding can be carried out on the machine. If there are many roof damages, it is necessary to remove them and replace them with new ones

third, the connection between the tooth seat shaft of the roller teeth and the pulley frame is loose, resulting in the slow opening time of the roller teeth or the insufficient opening of the teeth, which will tear the paper edge

solution: first check whether the pointer of the testing machine is aligned with the pin at the zero line connection of the dial, and whether it is loose or cut off. If it is only loose, the pin can be tightened again. If it is cut off, it needs to be replaced with a new pin

fourth, the distance between the tooth pad of the paper delivery tooth and the edge of the embossing cylinder is not adjusted properly. The distance is too close, so that the tooth pad of the paper delivery tooth rubs against the edge of the embossing cylinder, causing the edge of the paper to be torn. The distance is too far, so that the edge of the paper will be torn when the embossing cylinder picks up the paper

solution: carefully adjust the distance between the paper delivery tooth pad and the edge of the embossing cylinder. Generally, the distance between the two should be adjusted to 0.5mm. When printing card paper, it should be 2 ~ 3 times the thickness of the paper

fifth, the opening boss of the paper receiving teeth is worn, and the opening time of the paper receiving teeth slows down, causing the paper to tear due to the small opening distance

solution: remove the tooth opening boss and repair it with electric welding or replace it with a new one

3. The paper breaks irregularly at its mouth, and the gap is sometimes wide and sometimes narrow

this phenomenon is generally caused by improper adjustment of the paper conveyor or front gauge, and the cause should be found on the paper conveyor. ① Carefully observe whether the tightness of the cloth belt of the paper conveyor is consistent; ② Start the offset press and run it to see whether the belt pulley of the paper feeding line can rotate flexibly; ③ The offset press jogs at idle to see whether the time when the paper reaches the front gauge is appropriate. The general requirement is that when the current gauge reaches the paper receiving position, the distance between the paper edge and the front gauge is mm. If it is not appropriate, it needs to be adjusted; ④ Carefully check whether the height of the front gauge 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 into it, and it is appropriate to have a slight resistance when pulling

to sum up, when removing the problem of tearing paper at its mouth, it is necessary to pay attention to the paper delivery teeth, roller teeth, and paper receiving teeth. The handover between teeth must be reasonable, and must be adjusted according to the required data in the mobility relationship table on the machine operation manual. The height of the tooth pads of a row of teeth must be adjusted to be consistent. The opening and closing time of each tooth and the opening and closing size of the open tooth must be consistent. The deviation between the conditional stress measured with a piece of paper and the real stress on the sample is also larger; Try to balance the biting force after "necking down"