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Analysis and Reflection on the cause of an offset printing failure

the author witnessed the constant tension requirement from empty to full plate. A factory imported a second-hand four-way four-color offset printing. After several days of debugging after the imported equipment was installed in the factory, the operators still couldn't print prints that met the quality requirements. There was a problem that the printing plate was easy to produce dirty plates and flower plates. The trial printing Chinese printing plate was very tolerant, and Chinalco Luoyang copper was easy to be scrapped due to market demand

the main reason why the printed matter does not meet the quality requirements is that it is easy to produce dirty plates and flower plates, which is easy to scrap the printing plates. If the sample failure occurs in the offset printing process of the domestic offset press, it is not difficult to analyze. Generally, it is caused by the excessive pressure between the water roller and the printing plate or by the excessive pressure between the ink roller and the printing plate

as we all know, in the transmission process of the offset press, due to the compression deformation of the water roller, there is a certain linear speed difference with the printing plate cylinder, so the water roller and the printing plate will produce surface friction. When the water roller and the ink layer without protection in the layout pattern department, it will promote the contact between the fountain solution and the worn surface, the printing plate sand mesh will be damaged, the specific surface area will be reduced, the stability of the inorganic salt layer will be destroyed, and the blank department will be prone to grease and produce dirty plates, The photosensitive adhesive layer of the pattern part is also worn, resulting in poor performance of the new ink and stencil

in the offset printing process, the number of times of friction by the plate inking roller is the most, and the surface ink, some ink pigment particles are relatively coarse, which will produce greater friction when the pressure is high, so that the sand eyes will be worn, and the inking part of the pattern will be significantly worn. Therefore, too much pressure between the plate inking roller and the printing plate will also make the blank part of the printing plate dirty, and the pattern part of the stencil

the machine captain in charge of the commissioning operation has operated the domestic machine for a long time. It was easy to analyze, judge and deal with this kind of offset printing fault. During this commissioning process, the pressure between the water roller and the printing plate, the ink roller and the printing plate was adjusted several times, but the effect was not achieved and the fault could not be eliminated

is it because the second-hand equipment itself has no accuracy or defects, and it is useless to adjust it again, or is it lack of practical experience in adjusting this equipment, and can't grasp it properly? Or is it wrong to judge the cause of the fault

for this reason, the operator of the seller's machine was invited to debug. After the master came, he slightly adjusted those pressures. The fault was eliminated, the printing quality met the requirements, and the equipment was in normal use. From the structural analysis of the offset press, the difference between this domestic machine and foreign equipment is that the domestic machine uses the liquid moistening version of the weeping version, the foreign equipment moistens the version with alcohol, the domestic machine uses the water roller to wrap the flannelette, and the foreign equipment does not use the flannelette, but uses the rubber roller. The existence of these differences is exactly the difference from the discretion of pressure value adjustment. If there is a lack of practical experience in this regard, insisting on applying these pressure values of high-speed foreign equipment by adjusting the pressure adjustment methods (and adjustment parameters) adopted by domestic machines, it is obvious that the variable angle shear attachment that cannot adjust the appropriate pressure value is designed and manufactured according to gb/t23561.11 ⑵ 010, and the existing faults cannot be eliminated. Where is the secret of master Qiu's adjustment? After introducing several pressure parameters for reference, the master said: it's also important to feel by hand. If you are familiar with it, you will be handy. What the master said by hand is the practical operation experience in the actual adjustment process. This is very important. If there is no practical operation, careful research and experience accumulation in the production operation, it cannot be felt by the feel of oilfield chemical production enterprises. This is the same experience for operators who operate foreign equipment or domestic machines. (Chen Jinru, Putian County printing factory, Fujian Province)