Analysis of the most popular sheet fed offset prin

2022-07-18
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After the sheet fed offset press has been running for a period of time, due to the wear of various parts, especially the tooth opening cam, bump, tooth pad and tooth seat, the paper handover cannot be carried out normally during printing. It is often easy to bite the bite paper edge, resulting in inaccurate overprint, inaccurate positioning of the bite paper edge in the front gauge, and the printing product quality is affected. 1. during the paper receiving process of the offset press, the biting edge of the paper shall be comprehensively analyzed and treated differently. Carefully check that the position between the receiving teeth and the roller teeth is too close, and the biting edge of the paper will be broken during the handover of the printing paper. The solution is to properly cross open

2. In general, the nip of the large and small press imprinting cylinder and the paper feeding tooth is about 12mm. Without experimental analysis, the nip distance between the cylinder and the paper feeding tooth is too large, so the nip distance of the paper receiving tooth is too large. If the continuity of the paper edge is bitten and the position remains unchanged. If such faults are found, find the causes on the paper feeding teeth and the roller teeth, slow down the offset press, and carefully check whether the paper transfer process between the paper feeding teeth and the roller teeth is accurate and in place. If the tooth opening time is too slow or the tooth opening angle is large, it is easy to cause the paper edge to bite and break. Check the wear of the paper tooth cam of the paper feeding teeth. If the cam is seriously worn, repair welding or replace it with a new part. When the paper feeding teeth are required to pass the paper to the big teeth of the embossing cylinder, the paper feeding teeth and the big teeth of the cylinder control the paper at the same time

3. The edge of the biting paper is bitten due to improper adjustment of the biting teeth of the biting row of the offset paper receiving part. The main reason is that the height of the tooth pad of each biting tooth is inconsistent, or the tooth pad is not straight, so that individual biting teeth are not stretched enough or not closed. Therefore, the paper edge is broken. Solution: readjust each tooth pad of the paper receiving toothing row to make it straight and consistent in height, and then carefully adjust its biting force. A piece of 80g/㎡ kraft paper can be used to adjust the biting force of each bite. It can be stretched into the bite and pulled out by hand to test the biting force for the unused user group

4. The position of the front gauge is not well adjusted, which causes too much paper biting distance between the roller teeth and the paper receiving teeth, so the paper biting edge is broken during the handover process. Solution: properly adjust the paper biting distance of the front gauge and control the paper biting distance at 3-5mm

5. The edge of the offset nip paper is bitten, and the paper is broken irregularly, and the break is wide at one time and narrow at another time. Generally, this phenomenon is due to the inconsistent tightness of the wire belt on the paper feeder of the offset press. In addition, turn on the paper feeder to see whether the pressing wheel of the paper feeder belt can rotate flexibly. Slow down the offset press to see if the time for the paper to reach the front gauge is appropriate. Generally, it is required that when the front gauge reaches the paper receiving position, the paper edge should be 8-10mm away from the front gauge. If it is not appropriate, it needs to be adjusted

6. The most important point is that the edge of the biting paper is bitten. The joint position between the paper receiving teeth and the roller teeth is not on the public law line, or the joint parallel time between the paper receiving teeth and the roller teeth is too long. Solution: first, adjust their handover position, move the machine with both hands during adjustment, carefully check and correct; The second is to shorten the parallel time between the paper receiving teeth and the roller teeth

7. The edge of the paper is broken due to paper problems. In the process of papermaking, the paper is formed only by interwoven fibers, which will cause uneven density, many sand holes and voids in the organization, and uneven paper surface. Therefore, a certain amount of fillers, adhesives, pigments, etc. should be added to improve the smoothness of the paper surface, reduce the transparency of the paper, reduce the ink absorption of the paper, and increase the whiteness, weight, water resistance, toughness, etc. If the paper is too dry, with poor fiber toughness, embrittlement, loose paper, poor flatness and other reasons, it is also easy to make the paper edge broken in the process of paper feeding, short sizing, and imprint receiving

in a word, there are three forms of biting at the paper edge during offset printing:

① the paper biting is continuously bitten and the damage position remains unchanged. The reason is that the paper feeding teeth and the roller teeth are improperly connected or the paper feeding teeth and the roller teeth are improperly adjusted

② not every piece of the paper edge is bitten, but the corresponding collet is locally inserted into the upper and lower jaws, and several pieces of uncut printing sheets are separated with regularity, which is mainly caused by the paper receiving tooth row of the paper receiving system. At this time, pay attention to adjusting the biting force of the paper receiving tooth row

③ the undercut edge of the paper is sometimes large, sometimes small, sometimes good, sometimes bad, and does not have regularity. This phenomenon is generally due to improper adjustment of the paper feeder of the offset press, or improper height adjustment of the front gauge. These two parts should be adjusted respectively

during daily work, all parts of offset printing from paper feeding, rules, embossing and paper receiving shall be adjusted properly. The paper edge at the nip is bitten and related to each part. The worn open tooth cam requires welding repair and replacement of new accessories. Do not move blindly after the fault occurs to avoid disordered adjustment and a series of process faults. Make reasonable adjustment according to the data required in the mobility table in the operation manual of offset printing machine, and deliver the paper teeth, The height of the three nip transfer parts of the drum big tooth and the paper receiving tooth pad must be adjusted to be consistent. The opening and closing time and size of the three parts of the paper receiving tooth, the drum big tooth and the paper receiving tooth pad must be consistent. The quick commutation and the accurate speed change are all the problems that should be paid special attention to in the adjustment process when the nip paper edge is broken

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