Three reasons for the generation of bars in lithographic offset printing
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Since the empty space of the plate cylinder and the impression cylinder collides and impacts during the process of switching with the working surface, the cam, the connecting rod and the like vibrate under the action of inertia, and the outer circular surface of the drum is no longer uniformly rolled at a constant speed. Therefore, between the ink roller and the printing plate, between the plate cylinder and the blanket cylinder, between the blanket cylinder and the impression cylinder, a slight slip occurs, which breaks the balance of the ink and ink, and the ink layer is affected by the break of the ink layer. The thickness causes the dots to increase or decrease, and the bars appear in a direction parallel to the axis of the drum. The higher the speed of the machine, the more serious the bar phenomenon.
1. Design aspect
The arrangement position of the rollers is unreasonable, and the reversing of the squeezing rollers is not performed when the rollers are empty and the rolling, the wall panels and the rollers are deformed due to insufficient strength and rigidity.
2. Precision
The assembly accuracy of gears, eccentric sleeves and rollers is not high, which affects the smoothness of mechanical movement.
3. Dynamic load
The effect of the dynamic load on the ink stick is that the rotating parts are unbalanced in rotation, and the reciprocating motion of the mechanism generates vibration and the acceleration of the cam mechanism causes an impact. Related to the factors that cause the bars, there are embossing, leveling, wetting parts of the drum, bearings, drum gears, main drive gears, roller rollers, ink rollers, rubber rollers, water rollers, transfer paper cams, Assembly and adjustment of the rack and machine chassis. The accuracy error of these components during printing is directly expressed in the form of a bar, so the severity of the bar is also an overall evaluation of the accuracy of the offset press.