Analysis and Elimination of the Causes of "Belts" Produced by Offset Printing Machines (I)

Ink roller with string ink roller pressure is too large. Since the ink roller is rotated by the friction of the plate cylinder and the ink roller, the pressure between the ink roller and the ink roller is too large, so that the ink roller depends on the ink roller too much, and the friction on both sides of the ink roller is not equal. There may be frictional slippage on the surface of the printing plate, which produces a bar.
In the same way, when the pressure between the water roller and the plate roller and the water roller is too heavy, it will affect the uniform transfer of the water film and cause white bars.
(2) Roller lining excessive. As the pressure on the upper or lower pressure is too small, increase the drum lining, so that the drum lining over, increase the roller in the rolling of the micro-speed difference and trace friction. From the microscopic point of view, the linear speed of the drum is not absolutely equal due to the influence of various factors. It is only a relative balance, and a certain degree of micro speed difference is always present. Overfilling the blanket results in excessive friction under the effect of the blanket, and there is intermittent wear and imprinting of the plate layout, resulting in a clubbing.
(3) The blanket and impression cylinders are under too much pressure. The offset press is printed by three rollers and the working face of the roller has a certain pressing force. When the drum runs to neutral, the load changes: When point B comes out of neutral, an impact occurs at point A.
Because there are tiny gaps in the roller bearing and the elastic deformation of the roller and bearing, the roller will produce slight displacement and cause vibration. The pressure between the blanket roller and the impression roller is too large, it will aggravate the vibration, and it will not roll. In the case of pillow presses, this kind of vibration is not eliminated and produces a bar.
(4) The blanket is loose. When the blanket is too loose, due to the rolling action, the blanket slides back and forth on the surface of the drum. This relative movement produces one or more bars.
(5) The layout is too watery. In the printing process of the offset printing press, too much water on the plate will affect the uniform transfer of the ink film, making the printing density too low and aggravating the appearance of the bar. Therefore, for offset printing, under the premise of ensuring that the layout is not dirty, the amount of water supply should be controlled within the smallest possible range, and the amount of water supply and ink supply should be in a relatively stable state. A well-controlled ink balance is an important part of improving print quality.
2. Mechanical problems (1) The roller gear is worn and the precision is reduced.
The accuracy of offset roller gears is very high, and it is almost close to the aircraft's aviation gear. In order to make the center distance can be adjusted in a small amount (to accommodate a certain range, printing different thickness of paper), to minimize the increase of the backlash To ensure smooth operation, most offset presses use involute gears and toothed pressure angles of 14.5° to 15°.
In general, due to the slight periodic speed change between the gears caused by the gear transmission, it is not sufficient to display the bars. However, when the gear tooth surface is excessively worn or the individual tooth is damaged, and there is foreign matter in the tooth groove, the gear cannot roll at a uniform speed according to the meshing line. Shaking occurs during operation, which can cause the roller speeds to be mutually inconsistent, resulting in relative slippage between the transfer surfaces. Cyclic gears.
Gears are characterized by the spacing between the bars T = π Ms (Ms is the face of the gear module), the shape of the board is covered by the entire layout, if it is a few teeth or foreign objects in the tooth groove, then produce a few correspondence The position of the tap.
(2) The bushing sleeve wears badly or the skewer gear wears excessively. The sleeve clearance is enlarged, and the vibration generated by the gear mesh is transmitted to the ink string roller, which affects the normal transmission of the ink film and causes the emergence of the lever. Due to wear of the shaft head mating surface or debris, the three ink fountain rollers are installed with different concentricity, which causes the pulsation of the ink string to affect the transfer of the ink film and generate a lever.
(3) Roller bearing wear. Roller bearing wear causes various bars, depending on the bearing position. When the load is not normal, poor lubrication or debris immersed into the bearing wear caused by improper bearing clearance, the drum load changes, resulting in vibration caused by the lever.
(4) Ink roller bouncing and end play. Ink roller outer aging, uneven, mandrel bending, shaft seat lock wear and other factors will cause ink roller beat, resulting in the emergence of bars. Abrasion of the ink roller shaft seat and excessive error in the length of the bearing step produce end play. The ink roller will generate excessive axial movement under the action of the ink roller, affecting the transfer of the ink film and causing the lever. (to be continued)