How to go to offset difficult problem (middle)

2. question

Questioning is a valuable quality of thinking. It is the basis for analyzing failures. When some failures occur, do not rush to make conclusions. It is necessary to carefully analyze whether these failures belong to the prepress or the printing process. They are process failures or machinery. Faults, whether it is a common fault or a faulty fault, and why it occurs, are questions that every print operator should have.

3. judgment

Observing can inspire thinking, judgment is the determination of thinking, and there are only two possible conclusions. If it is not affirmative, it is negative. In the course of offset printing, this or that difficult problem may occur. After observation, questioning and judgment, it is very important. First, the judgement must be true. Only on a real basis, the judgement is meaningful. Second, the judgement must be timely and accurate so as to reduce unnecessary auxiliary hours. Of course, these are based on observations and related knowledge and operating experience. .

4. exclude

Troubleshooting is a very meticulous task. It requires not only strong basic skills, but also meticulousness and patience. It must not be sloppy. If it is a mechanical failure, it must be performed in accordance with the order of disassembly and assembly of the machine. If it is a process failure, it must be done in accordance with the screening method. If it is a failure caused by raw materials, It should be decisively changed raw materials.

Third, difficult troubleshooting examples

In the printing process, there are many kinds of difficult faults. There are many very typical and difficult faults. It looks very simple, but it is not easy to handle. The following examples illustrate how to solve difficult faults through ghosting faults.

1. Common ghost failure categories

The so-called ghosting, that is, a kind of phantom appearing in the continuous printing, is a straight stripe or graphic that is perpendicular to the axis of the drum, with different shades of ink, and most of them occur on the spot screen printing products in the field. The performance of the graphics is divided into two types: positive and negative. Like the ghosts, they are divided according to their causes. They are ghosts affected by the process and ghosts caused by the machine. From this point of view, the positive and negative ghost images are the representations on the prints. The reason for this appearance is the technical or mechanical problems. It is in accordance with the general law of offset printing faults.

2. Ghosting fault identification

The use of observations, queries, and judgments for the identification of failures requires high technical skills and operating skills. For example, after taking a print and observing it, it is found that the positive image of the print itself is at the rear of its circumference, forming a negative shadow with a relatively shallow circumference. This is just like a ghost; for example, the pattern of the print itself is on its circumference. The formation of a shadowy image that is deeper than its surroundings is a negative image.

Ghosting is mainly caused by the lower series of ink rollers. The lower series of ink rollers in the offset printing machine is mainly used to rapidly even and refill the uneven ink layer remaining on the surface of the ink roller, but in fact this kind of uniform ink refill ability It is limited, but the human eye can not usually recognize the slight unevenness of the ink layer. If the layout design or the process is improperly adjusted, and the ink string roller cannot make up the uneven ink layer on the ink roller, ghosting may occur.

Just as the ghost is caused by the inking roller giving ink to the bar-shaped block, the ink layer in this area is not sufficiently replenished and evenly blended, so it appears on the following graphics that require a large amount of ink, and the negative ghost The shadow is because when the ink roller applies ink to the printing plate, the blank part is not filled with ink, so that the ink amount of the corresponding part on the ink roller is increased, and the ink roller does not evenly distribute the ink amount to other areas. The relatively thick ink layer on the roller is transferred to the plate during the next inking roller cycle, causing the printing plate to have an excessive amount of ink, resulting in a negative ghost image. (to be continued)