Offset bar is a common quality problem in offset printing. There are many reasons for the emergence of the bar, and the analysis and processing are complicated and intractable. This article combines some of the problems of the ink bars encountered by the J4103 four-ply offset press in the production process of the factory, and proposes troubleshooting methods, together with the peers. To explore.
First, the cause of the ink bar
We know that the bars refer to irregular changes in the dot shape or the thickness of the ink film during printing, and streak marks of different shades of ink are formed in the direction of the axis of the parallel printing roller. It is influenced by certain factors, causing slight slip between the blankets, between the blanket and the printing cylinders, between the printing cylinders, and between the printing cylinders and the paper, thereby changing the thickness of the ink film or the shape of the dots And the size, the formation of a strip of ink changes, that is, the ink sticks, from the appearance of the characteristics, the occurrence of ink bars in the local network of irregular expansion, deformation elongated, ink color increase.
Second, J4103 offset press common analysis and troubleshooting
In the process of production, ink bars have emerged suddenly and gradually. However, all kinds of ink sticks have their causes. The following analysis is conducted.
1. The ink roller caused by the ink roller's improper adjustment of the plate cylinder's pressure. If the pressure of the ink roller against the plate cylinder is too large, when the plate cylinder shifts from neutral to the edge of the nip and hits the ink roller, the ink roller frame will be lifted and then dropped, changing the distribution of the ink film on the plate. In the vicinity of the print port, there is a light and heavy ink bar, which is also called an ink roller impact bar. This kind of ink bar will not exceed 150mm. If the pressure of the ink roller against the plate cylinder is only too large, this impact will only change the distribution of the ink film on the ink roller, resulting in a regular distribution of the ink bars. The distance between the ink bar and the print bite should be Equal to the circumference of the ink roller that produced the ink stick. The four ink roller diameters of the J4103 Four-Way Offset Press are Ф49.5mm, Ф50.5mm, Ф59mm and Ф69mm respectively, and the corresponding positions of the ink bars are respectively 155mm, 158.5mm, 185mm and 216.6mm from the print bite.
In this class, the ink bars produced by the improper pressure adjustment between the ink roller and the plate cylinder can be eliminated through proper adjustment. Generally, the indentation width of the ink roller on the printing plate should be 4-6mm, and two The end width is the same. Of course, in actual operation, we can also judge by removing one of the ink rollers that is thought to be the production of ink bars. If the ink bars disappear after removing the ink roller, the ink bars must be caused by the ink roller. If there is no change, then the ink stick has nothing to do with the ink roller, but continue to look for the reason.
2. Indentation caused by reduced roller gear accuracy. The precision of offset roller gears is very high. When the machine is used for a long time or improper use and maintenance, the accuracy will be reduced due to serious gear wear, which will lead to the production of ink bars. The characteristics of this type of ink bar are: the full plate is a equidistant and thicker ink bar with a fixed position and regular distribution, and the distance between the ink bars is 9.2 mm (equal to the pitch of the roller gear). This kind of ink bar is easier to distinguish, but there are four gears that cause this kind of ink bar. They are on the three printing cylinders and the delivery roller, which can be determined by the gears on the printing roller. . If the position of the ink stick changes after turning the gear on a certain printing roller, the gear must not be replaced by the gear; if the gear on the printing roller is turned, the positions of the ink sticks do not change, and the ink bar is pressed by the impression roller or Caused by the gear on the paper roller. In addition, for such an ink stick, the degree of ink stick can be reduced by appropriately retracting the center distance of the drum or changing the pad lining, but there is no way to reduce the accuracy of the gear on the delivery drum.
3. The main drive gear reduce the accuracy caused by the ink bar. This type of ink stick, like the roller gear, is caused by a reduction in accuracy due to long-term wear or improper use of the transmission gear. The feature is that the full version is a fixed-length and equidistantly-distributed white ink bar. The distance between the ink sticks is 10.1mm. The only solution to this problem is to replace gears with low precision.
4. Ink roller gear bars. When the gear portion of the ink supply portion is seriously worn or the precision is not high, a finer ink bar with an equal distance (a pitch of 8.6 mm) is also generated on the printed sheet. For this kind of ink stick, we can find out the bad gear and replace it. In addition, this kind of gear bar is also produced when there is no meshing gap between the roller gears.
5. The rubber roller sleeve wears heavily and the gap increases. The reason for this kind of ink stick is that when the impression cylinder is in contact with the blanket cylinder, the blanket cylinder is pushed against the plate cylinder due to the large clearance between the sleeves and collides with it, thereby changing the distribution of the ink film to form the ink bars. This kind of ink stick is formed due to the impact between the blanket cylinder and the plate cylinder. It is also called the impact ink stick. Its characteristics are: the position of the ink stick is 248mm away from the print seam, and the width is wider. The processing method is to replace the sleeve and reduce it. Clearance, and under the conditions that ensure the rotation of the sleeve, the smaller the gap, the better.
6. The printing plate sleeve wears badly and the gap increases. If the plate cylinder sleeve gap is large, the plate cylinder is contacted with the blanket cylinder when the plate cylinder is in contact with the blanket cylinder. This type of ink stick generally has only a few at the mouth of the printed sheet and a few are distributed at equal distances. Its approach is to replace the sleeve, reduce the gap.
7. Indentation produced by hard objects embedded in the gear tooth gap. When a hard object is embedded in the backlash of the gear, the movement of the gear is affected and an impact is generated, thereby forming an ink stick. There are two cases of this type of ink stick: the position of one kind of ink stick is fixed, and the position of another kind of ink stick is moving. If the position of the ink stick is fixed, it can be surely caused by a hard object in the backlash of the large gears on the three printing cylinders or delivery rollers. The speed of these large gears is the printing speed. However, it is determined by which gear causes the gear turning method described above to be used. If the position of the ink stick moves, it is mainly caused by the ink roller gear or the drive pinion gear. Because of these pinions and gears meshing position is changed. For these two types of ink sticks, it is only necessary to solve the hard objects in the gears. From this point of view, it is very important to pay attention to the maintenance of the machine.
8. The take-up roller launches the large gear on the outside of the side, which is the ink stick that occurs when the key is loosened. When the machine is used for a long time or the flat key fits loosely, an impact will be generated during printing to form the ink stick. This kind of ink stick is generally 160mm away from the mouth of the printed sheet and reaches the end. We can only solve this by reassembling the flat keys.
9. The ink roller does not round the ink roller. This type of ink stick is less than the head, but it is caused by the ink roller. We can judge it by removing one of the ink rollers at a time.
Third, the conclusion
Through the above analysis, we can know that the production of ink sticks in the offset printing process has certain rules and leads. As long as we calmly analyze when the ink bars appear, and gradually narrow the scope of investigations, we will certainly be able to solve the problem of ink bars.
The ink stick problem discussed in this paper also applies to the J4105 and J4103D models produced by Hunan Printing Machinery Co., Ltd.