How to deal with the failure of paper tearing in printing
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In lithographic offset printing, the occurrence of tearing during paper printing can be said to be a relatively common fault. It is possible to judge the cause of the fault in time and to perform timely processing, which is undoubtedly beneficial to the work.
In fact, paper tearing is not a mysterious fault. The master of the heart does not immediately adjust the equipment or make some blind replacement of the parts. Instead, calm down and carefully consider the circumstances under which the tearing of the paper occurs. In general, the most common occurrences occur in three situations: after the equipment has just been overhauled (debug); after a long period of fixed printing is suddenly replaced; there is also an ever-increasing tear in the printing process. Why analyze these situations? Because the causes of problems are significantly different under different circumstances, this analysis can help us find the root cause of the fault quickly and accurately. Then deal with the fault in a targeted manner.
For the sake of discussion, the author divides the common tears into several cases:
1. The paper is uneven during the paper feeding process.
Features:
It is easy to appear in the printing process of relatively thin paper, and generally the tearing is relatively long, and often accompanied by overprinting.
analysis:
For thinner papers, be sure to pay attention when adjusting the machine, because it is easy to occur in either the feeder, the cardboard or the subsequent paper transfer.
The most common cause of such problems is that the pressure of the pressure roller on the cardboard is too large, causing the paper to be crushed out during the traveling process, so that in the subsequent imprinting and transmission, the problem of paper tearing is inevitable.
deal with:
For the thinner paper, during the adjustment process, the author suggests that the Feida's blowing and suction should be properly reduced until it can be properly fed. Excessive air volume will cause the paper to deform.
The pressure of the pressure roller on the cardboard should be properly adjusted and slightly offset outward (eight characters in the outer) to flatten the uneven paper.
2. Paper feeding and positioning are not coordinated
Features:
Such faults are often extreme. For example, the mouth of the whole paper is bitten by the teeth, or half of the row, which is often more serious, and the offset of the overprint is quite serious.
analysis:
This type of failure is often due to the timing of the delivery of Feida relative to the pickup roller or the timing of the delivery of Feida and the pre-regulation (commonly known as the lower paper). When the paper with the relative position advance reaches the positioning position, since the limit that can be compensated by the positioning has been exceeded, the cornice will be bent and deformed until the paper is bitten by the transfer paper. At this time, the paper mouth is not straight, and of course, it will not be able to be torn in the future.
deal with:
The handling of such faults is as long as the relative angular position of the paper feed is adjusted correctly.
3. The front position is too far behind (the transfer paper is too big)
Features:
The entire or half of the mouth is torn (the spacing is the pitch of the teeth), and the degree of tear depends on the size of the paper.
analysis:
The positioning position of the current gauge is too far behind, which will directly lead to an increase in the length of the transfer paper and all the gnawing papers at this time. At this time, the paper sputum may not be able to be smoothly transferred during the mutual transfer process (when the next row of gnashing teeth enters the paper feed) In the position, the open mouth can not avoid the oversized mouth, or the teeth after the paper is transferred outwards can not open enough space to open the paper), and the mouth is torn.
deal with:
In fact, the processing method is very simple, that is, the position of the front gauge can be changed accordingly.
However, such a simple fault often causes a big trouble for the operator due to a mistake in judgment. The author has seen a case of the same fault, and the operator immediately judged that it was caused by the abnormal handover of the teeth, and the result was to adjust the bite force of the teeth and adjust the handover position over and over again.
Suggest:
When a problem occurs, it is often more important than judgment. Of course, prevention is more important than judgment. This example is caused by the operator's abnormal adjustment of the front gauge (more than the range allowed by the previous gauge) (no one adjusts, the front gauge generally does not move its own position, of course, except for very special circumstances).
In addition, the author suggests that there is no machine that adjusts the front and rear positions of the front gauge. Under normal circumstances, try not to change the position of the front gauge to adjust the registration of the plate. Pay particular attention to the production of old-fashioned equipment (the scale is not obvious, or lost due to multiple repairs), or in shift production.
4. The edge of the paper just did not bite into the teeth.
Features:
The position of the tearing mouth is only about 2-3 cm at the edge, and the length of the tearing opening is not large. The entire overprint has no effect, but local overprinting problems often occur near the tear. Generally, it is not Zhang Zhang, and the frequency of occurrence is irregular.
analysis:
This type of problem usually occurs after the conversion of the printing, especially after the paper has changed. The root cause of the problem is that at least one of the teeth on the edge of the paper should be placed next to the embossed area, thus ensuring that it is always transmitted during control. When the paper corner of the edge is not bitten, the paper corner is easily hanged during the transfer.
deal with:
Properly align the side gauges to ensure that the edges of the paper are controlled by the paper. Adjust the axial position of the plate at the same time.
Sometimes you should also pay attention to the situation that the edge of the paper mouth is upturned or squatted. It is also prone to such a problem. The solution is to drop the paper (paper that cannot be dropped, or paper that has problems with the paper tail, can Paper is fed by paper or soft paper)
5. The tooth pad is too close or too far in the handover position
Features:
When the pad is very far away, the length of the tear is very short. Generally, when the fault occurs, it is just after replacing the paper that is "sensitive" to the machine (such as a relatively crisp or thin paper). When the pad is close, the tear is sometimes only the width of the pad, and the length is quite stable, and the tear is very smooth.
analysis:
When the distance between the dental pads is relatively long, if the paper with good flexibility is printed, there is no problem of tearing, but when the paper with poor mechanical strength is encountered, the problem is manifested. In the two rows of teeth at the handover position, the two rows of hooks are easily torn at the moment of biting the paper. The too close tooth pads are like a set of sickles, and the paper is easily cut under such a sickle. This often occurs when a long tooth pad is suddenly replaced with a new one.
deal with:
For general models, a 0.2 mm thick steel bar (approximately 1 cm wide and a long tooth row width) can be used to assist in adjusting the distance of the pad at the transfer position. Generally, in the transfer position, the two rows of teeth can straighten the steel strip (the tooth pad preferably has a slight distance, that is, the steel strip is slightly curved). Then readjust the bite force.
6. The teeth are too small to open
Features:
This is the most common cause of tearing of paper during printing. It is characterized by the fact that the length of the paper opening of the tearing mouth is not large, and it is often turned up to one side of the tooth piece (we also often use this phenomenon as an important basis for judging whether it is an odd row of teeth or an even row of teeth).
analysis:
When the opening size of the teeth does not meet the requirements (too small, generally too big, no problem), when entering the wiring, you can not avoid the paper mouth that enters the wiring at the same time, kick the paper at the corresponding position, often this is The action also causes the paper to be torn over and folded over.
There are two reasons why this bite is too low.
One is that the entire row of teeth is getting smaller. In this case, we must first consider whether the open bearing is damaged. (The machine that opens the teeth at a high point), the general opening of the teeth may not be damaged.
In another case, the single bite is too small, which may be caused by the baldness of the small top wire on the tooth. It may also be due to long-term wear between the braces and the floss. Caused. In the actual work, the above two situations are often occurred, sometimes due to the normal wear and tear of the machine, but more cases are caused by artificially increasing the bite force of the teeth, resulting in excessive force between the parts, resulting in abnormal wear. of. Therefore, the author has to remind the operator again that it is very important to adjust and maintain the equipment correctly, otherwise it will give you trouble.
Judging:
A sheetfed offset press has a lot of handovers, especially the four-color offset press. The number of rows of teeth is sometimes a headache. If you try one row or one row, it will be too much trouble, that is, labor and effect. Not necessarily obvious. Therefore, it is very important to quickly determine the faulty teeth.
In the long-term work, the author explored some tips for judging problems with teeth.
1 If it is a problem with the element, then the frequency of occurrence must be proportional to the number of rows of the chain. (If it is a 11-row chain machine, the gap between the paper and the paper that appears to be a tear must be a multiple of 11 or 11.) Conversely, if the interval between the tears is proportional to the number of rows of the chain, then we can almost certainly have problems with one or more rows of fasteners.
If it is determined that it is a problem with the element, it will cost a dozen sheets of paper (because the problem of the element does not affect the overprint, so it will not affect other prints without tearing), in one of the rows. Marking the eye-catching mark (such as white ink), visual inspection during the boot printing process, will quickly find the problematic chain.
2 If it is a problem with the drum biting, then the tearing will not be so regular, or there will be Zhang Zhang. However, we have found that the tearing caused by the insufficient height of the teeth is usually accompanied by the phenomenon of the socket. According to the direction of the socket, we can further narrow the scope of the fault. According to the experience, the direction of the nest is always in the direction of the tooth.
3 If it is a regular one, or two next, then we must first consider the double roller.
4 This kind of tearing due to the insufficient opening of the teeth is often accompanied by a very inconspicuous phenomenon of partial overprinting. When the color order is arranged as black and yellow, the black and yellow are separately registered, and there is a problem of inaccurate overprinting between them. Then we can further lock the faulty teeth on the roller between the green and the product.
In the whole process of judging the above judgment, in most cases, we can quickly find the position of the faulty tooth by judgment.
deal with:
When the judgment is over, the process is the simplest process. As long as the faulty tooth is found, the corresponding whole row can be re-adjusted (note that the whole row of adjustments must be made, otherwise the tearing is solved due to the change of the tooth force. It is very likely that the overall pressure will be exerted on other individual teeth, which will lead to new problems soon.)
7. The handover time is too long
Features:
Generally, this kind of situation is difficult to appear in the normal working process, but sometimes it will appear after overhaul or debugging. The characteristics of the tearing mouth are that there are tearing but there is usually no litter (because the paper is broken) of). But sometimes the shape of the tear is not easy to distinguish from the above. When judging, it is generally considered based on the possibility of occurrence.
analysis:
When the two rows of teeth are in the process of handing over, a common bite of paper is moved for a short period of time, so that the paper is smoothly transferred, and then the two rollers are separated into their respective circumferential directions, if the teeth of the paper are at the prescribed angular position. If you haven't opened your teeth yet, you will get a paper grab. Tear the paper.
deal with:
Adjust the open jaws of the corresponding teeth to the correct position.
8. The wiring is not in the correct position
Features:
The frequency of occurrence is not high, and it usually occurs after the replacement or adjustment of the corresponding teeth. If there is no large unloading machine, it will not appear on the roller teeth. This situation occurs in the chain of teeth, which is caused by The adjustment and installation of the element itself is determined (most of the teeth of the element can be rotated around the axis, and the position can often be buckled at different positions, which is not easy to detect). The place where the tearing occurs is similar to the case where the chain is not open, and the specific judgment is the same as above.
analysis:
The reason is very simple, the handover is not on the circumferential tangent line where the handover should be, and the paper will be damaged.
deal with:
Rotate the pad and re-align the teeth. Also ensure that the bite pads are on the same level.
Because the brand and model of the offset press are numerous, the author is only doing a review of the possible failure of the tearing, and in fact it is inseparable. No matter what type of machine, as long as the analysis and judgment according to the above ideas, it should be very helpful.
Above we have listed some of the reasons that are more likely to cause tearing during the printing process. There are some hard-to-find faults in the actual work, which are not listed here. But no matter what the cause of the tear, as long as we carefully observe the appearance of the tear, combined with the machine's consistent situation, comprehensive analysis and judgment, the problem can be solved.