Three Ways to Easily Check and Troubleshoot Offsets

Editor's note: The greatest distress among offset press operators is the failure of the printing process to find the cause of the failure. Often for overprinting errors, bars, ghosts, paper baskets, inverted hairs and other faults, had to stop the school bus, each time spent two or three hours is a common occurrence, sometimes to solve a fault or even take a few days, serious time loss . It is estimated that the time taken for offset printing to eliminate malfunctions in daily production accounts for about 5-10% of the total man-hours, which is more than double that of lead printing. This is unfavorable for improving product quality, shortening the publishing cycle, and increasing economic efficiency. For this reason, every operator of an offset press can work hard to improve its technical level in solving problems, and can make greater contributions to factories and countries.

The offset press has a complex structure and high printing process requirements. In addition, the variable factors of paper and ink are large, so the operating technology must be improved. Generally speaking, new workers learn to operate easily, but it is more difficult to find out the cause and eliminate the trouble in time whenever there is a defect or malfunction.

There are many factors that produce offset printing faults, and sometimes there are dozens of possible reasons for the occurrence of a failure. To avoid losing or detouring and avoid wasting unnecessary effective hours, the following methods can be used.

First, analysis

After the offset printing fault occurs, there are multiple ways to find out the cause of the fault. Among various methods, analysis is the fastest way to find the cause of the fault.

The so-called analysis method is based on the analysis of the time, location, conditions, shape and other aspects of the failure. The subjective factors of the four aspects are listed one by one, and then a comprehensive analysis is performed. Many failures can be solved. In actual production, some operators lack comprehensive analysis of these four aspects after encountering faults, resulting in prolonged downtime and unnecessary man-hour losses.

An example is as follows: During the work process of an offset printing press, the operator finds that the paper is bowed and deformed. The product is a magazine cover, with two colors on the opposite side and four colors on the front. When the reverse side is printed first, the paper is normal, and in reverse, the front side is printed. When printing on the 25th order paper, it is found that there is a 50mm long bowing phenomenon in the paper. After the machine is shut down, an experienced person analyzes various possible factors by analysis. Analysis, preliminary conclusion:

1 The failure was just produced, indicating that there are new factors causing the bow.

The two parts in the paper drag, there may be a machine factor, it may also be paper factors.

3 From the point of view of the shape of the paper basket only 50mm, it cannot be caused by a mechanical failure.

4 From the analysis of paper conditions that produce 50 mm long bows, it is generally possible under the condition of “foliage”, but the intuitive paper is very smooth and it is impossible to produce bows.

After such an analysis, the machine factor and the paper factor were negated, and they focused on a "why just created" problem, prompting people to immediately think of the possibility that the backside imprinter sticks to the impression cylinder. Because the back of the printed two-color prints, often due to imprinting has not dried out and gradually accumulate in the surface of the impression cylinder, this ink deposits are both irregular and thicker, equal to gradually increase the rubber roller and irregularly The pressure between the impression cylinders causes the paper to be pressed on the rugged surface, thus causing a bow fault. After checking the impression cylinder, it was determined that the ink piled up. When cleaning and then printing this failure is gone, before and after spent more than 10 minutes.

Of course, some faults are more complex, and the analysis method alone cannot solve the problem. It must be used in conjunction with testing methods and test methods.

Second, the detection method

The so-called detection method is to use a magnifying glass, a micrometer card, an iron absorption dial indicator, a diameter detector, a vibration oscilloscope, a density meter, and other tools and testing instruments to observe the fault and check and measure the parts to find out The cause of the failure.

Often use the detection method to find failures such as bars, ghosts, and voids.

The time required for the detection method to resolve the fault is much longer than the analysis method. Generally, before the detection method is adopted, the analysis method is firstly used for analysis, and then the necessary detection is focused on one or two points to find the cause of the fault.

For example, the dots on the printed matter produce false defects. For the entire picture, the transmission side is empty and the control side is completely solid. Similar problems like this, how to solve?

After analysis, we can know that there are two main reasons for this type of failure: the first may be ink failure, the layout does not have enough ink, and the second may be pressure failure. The pressure regulator of a roller walks by itself. The pressure disappeared.

The factors of ink failure include: the end of the layout is too watery; the pressure of one end of the ink roller is light on the plate; the pressure between one end of the ink roller and the ink roller is too small; the surface of the ink roller is aged, cracked, etc.

The factors of pressure failure include: the pressure between the plate cylinder and the blanket cylinder disappears; the pressure between the blanket cylinder and the impression cylinder disappears.

The detection method should be carried out easily afterwards, because the layout is too watery. When the machine is running, it can be seen in the light. First, eliminate this factor. Then check the pressure between the ink roller and the layout roller and the ink roller. Meet the requirements of consistent pressure at both ends. If the surface of the ink roller is aged and cracked, replace with a new one. The ink roller part is normal, the fault is still not resolved, and then the pressure between the rollers is checked. The electric fuse (20 fuse) and the micrometric card can be used to test the roll gap without removing the printing plate and blanket. When the clearance between the rollers exceeds the value specified in the instruction manual, the pressure regulator is adjusted so that the gap between the two ends of the roller bearing meets the requirements in the manual, and the fault can be eliminated.

Third, the test method

The test method is commonly referred to as "try it." Some inexperienced new workers and those who do not have comprehensive analytical skills often use this method. The test method takes a long time, it is easy to take a detour, and it brings some loss to the production. However, once successful, operators not only accumulated experience, but also improved the technology.

The test method is generally more effective for the use of new papers, inks, plates, and the like. But sometimes the common failures that occur in the printing process are caused by the lack of experience of new workers, and it is also regarded as a new problem to be tested. This often complicates simple problems and wastes many man-hours.

For example: The overprint is not accurate when one end is not in place, and it is not allowed to be about 2mm. The reason for this failure is that the paper is skewed and the end of the paper is not in place, or the hard paper with 80g/m2 or more is ejected from the front gauge. . Some operators have spent a lot of time correcting the regulation, the pressure of the teeth, and the handover relationship. People have also been very fatigued and the failure has not been ruled out. Therefore, after the failure in the printing process is advocated, the reason for the failure is sought through consultation. New workers must especially discuss with higher-tech middle-aged and older workers in order to troubleshoot the problem faster and improve product quality. He also learned the techniques of troubleshooting and improved the operation level.

In short, for the failures encountered in offset printing production, it is advisable to use analytical and test methods to find out the cause of the failure. When complex faults are encountered, comprehensive analysis and inspection methods must be used to eliminate all kinds of faults quickly and well, so as to improve product quality and increase effective working hours.