(This article is an original article from Bisheng. It is forbidden to reprint, and reprinting must be corrected)
In lithographic offset printing, tearing during paper printing can be said to be a relatively common failure. Being able to determine the cause of the failure in a timely manner and handle it in a timely manner is undoubtedly quite beneficial to the work.
In fact, the tearing of the paper is not a mysterious fault, and the intentional master generally does not immediately adjust the equipment or perform some blind replacements on the parts. Instead, calm down and carefully consider the circumstances under which the paper tear occurs. In general, the most common occurrences are in three situations: after the equipment has just been overhauled (commissioned); after a long-term fixed printing job is suddenly replaced; and there are constantly increasing tears during the printing process. Why analyze these situations? Because the cause of the problem is obviously different in different situations, this analysis can help us quickly and accurately find the source of the failure. Then deal with the fault in a targeted manner.
For the convenience of discussion, the author divides common tears into several situations:
1. The paper is uneven during feeding.
Features:
It is easy to appear in the printing process of relatively thin paper, and the tear is generally longer, and it is often accompanied by overprinting.
analysis:
For thinner paper, you must pay attention when adjusting the machine, because no matter it is Feida, paperboard or in the subsequent paper transfer, such problems are prone to occur.
The most common reason for this type of problem is that the pressure of the pressure roller on the paperboard is too high, which causes the paper to be crushed out of the arch during the travel process. In this way, the paper tearing problem will inevitably occur during the subsequent stamping and transmission.
deal with:
For thinner paper, during the adjustment process, the author recommends that Feida's blowing and suction should be properly reduced until the paper can be fed normally. Excessive air flow will deform the paper.
The pressure of the pressure roller on the paperboard should be lightened appropriately, and slightly shifted outward (into the outer eight characters) to smooth the uneven paper.
2. Paper feeding and positioning are not coordinated
Features:
Such failures often go to extremes. For example, the mouth of a whole piece of paper is completely gritted or half-rowed, and it is often more serious, and the deviation of the rule line of the overprint is quite serious.
analysis:
Such failures are often due to the relatively fast delivery time of Feida relative to the pick-up wheel or the delivery time of Feida and the front gauge (commonly referred to as the fast delivery). When the paper whose relative position is ahead reaches the positioning position, since the limit that the positioning can compensate is exceeded, the gripper will be bent and deformed until it is bitten by the feeding tooth. At this time, the paper mouth is not straight, so of course in the subsequent transfer process can not avoid tearing.
deal with:
To deal with this kind of fault, just adjust the relative angular position of the paper feeding correctly.
3. The front specified position is too far behind (the feeding teeth are too large)
Features:
The whole or half of the mouth tearing (spacing is the distance between the teeth), the degree of tearing depends on the size of the gripping paper.
analysis:
If the positioning position of the current gauge is too far back, it will directly lead to the increase of the length of the paper gripper and all the next bite grippers. At this time, the paper gripper may not be successfully transferred during the mutual transfer process (when the next row of bite teeth enters the pickup In the position, the opened teeth can not avoid the excessively large mouth, or the teeth after transferring the paper can not open enough space to open the paper), which will tear the mouth.
deal with:
In fact, the processing method is very simple, just change the position of the front gauge accordingly.
However, this simple failure often causes great trouble for the operator due to the wrong judgment. The author has seen a case of the same failure, and the operator immediately found that it was caused by the abnormal handing of the teeth. As a result, the force of the teeth was adjusted again and again, and the position of the handover was adjusted.
Suggest:
When problems occur, judgment is often more important than treatment, and of course prevention is more important than judgment. This example is caused by the operator's abnormal adjustment of the front gauge (beyond the allowable adjustment range of the front gauge) (no one adjusts, the front gauge generally does not move its position, of course, except for very special circumstances).
In addition, the author recommends that there is no machine that electrically adjusts the front and back positions of the front gauge. In general, try not to adjust the plate registration by changing the position of the front gauge. Special attention should be paid to the production of old-fashioned equipment (the scale is not obvious, or it has failed due to multiple repairs), or in the production of shifts.
4. The edge of the paper just does not bite
Features:
The location of the tear is only about 2-3 cm from the edge, and the length of the tear is not large. The overprint of the whole sheet has no effect, but local overprint problems often occur near the tear. Generally not all Zhang Zhang, the frequency of occurrence is irregularly distributed.
analysis:
This type of problem generally occurs after printing and live conversion, especially when the paper format changes. The root cause of the problem is that there should be at least one bite (paper feeding tooth) gripping the edge of the paper into the embossing area, so as to ensure that it is always transferred in control. When the paper corner of the edge is not clenched, the paper corner can easily be broken during the transfer process.
deal with:
The side gauges are properly connected to ensure that the edges of the paper are controlled by the paper feeding teeth as much as possible. At the same time adjust the axial position of the printing plate.
Sometimes you should also pay attention to the fact that the edge of the paper's gripper is up or down, and this problem is also prone to occur. The solution is to drop the paper (paper that cannot be dropped, or paper with a problem at the end of the paper, you can Make paper flat by knocking or soft paper operation)
5. Tooth pads are too close or too far in the handover position
Features:
When the dental pads are far away, the length of the tear is very short. Generally, when the failure occurs, it is mostly just after replacing the paper that is more "sensitive" to the machine (such as relatively brittle or thin paper). When the dental pad is close, the tear is sometimes only the width of the dental pad, and the length is quite stable, and the tear is very smooth.
analysis:
When the pads are far away, if the paper with better flexibility is printed, there will be no tearing problem, but when the paper with poor mechanical strength is encountered, the problem will manifest itself. The two rows of clenching teeth at the handover position are directed to the two rows of hooks, and it is easy to tear the paper at the moment of biting the paper at the same time. Tooth pads that are too close are like a set of smashing knives, and the paper will be cut easily under such a guillotine. This situation often occurs when a long-used dental pad is suddenly replaced with a new one.
deal with:
General models can use 0.2 mm thick steel bars (approximately 1 cm wide and length is the width of the tooth row) to assist in adjusting the distance between the dental pads at the handover position. Generally, in the handover position, two rows of teeth can straighten the steel bar (the tooth pad is preferably at a slight distance, that is, the steel bar is slightly bent). Then readjust the bite force.
6. Caused by too small open teeth
Features:
This is the most common reason for tearing in paper during printing. Its characteristic is that the length of the teared paper is not long, and it often flips to the side of the tooth (we often use this phenomenon as an important basis for judging whether the odd-numbered or even-numbered teeth).
analysis:
When the opening size of the gritted teeth does not meet the requirements (too small, generally too large, there is no problem), when entering the crossover line, you can not avoid the paper gripper that enters the crossover line at the same time, kick the paper at the corresponding position, often this is the case The action also caused the paper torn and turned over.
There are two reasons that can cause this kind of underbite.
One is that the entire row of teeth opening becomes smaller. In this case, the first thing we need to consider is whether the bearing is damaged? (High-point teeth-opening machine), generally, the teeth-opening spit block may not be damaged.
Another situation is that the single teeth are too small. This situation is likely to be caused by the abrasion of the small top wire on the tooth body. In addition, the gap between the brace and the dental shaft may become larger due to long-term wear. Cause. In the actual work, the above two situations often occur, sometimes caused by the normal wear of the machine, but more often due to artificially increased teeth bite force caused by excessive force between the parts, caused by abnormal wear of. Therefore, the author also reminds the operator again that correct adjustment and maintenance of the equipment is very important, otherwise it will cause trouble to myself.
Judgment:
A sheet-fed offset printing machine has many handovers, especially the four-color offset printing machine. The number of rows of teeth is sometimes a headache. If you try row by row, it will be too troublesome. 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 problematic teeth.
â‘ If it is a chain tooth problem, the frequency of occurrence must be proportional to the number of chain rows. (If it is a machine with 11 rows of chains, the gap between the paper where the tear occurs and the paper must be 11 or a multiple of 11). Conversely, if the gap between the tears is proportional to the number of chain rows, then we can almost certainly have a row or several rows of chain teeth.
If it is determined that it is the problem of the chain element, just spend a dozen papers (because the problem of the chain element will not affect the overprint, so it will not affect other printing activities that have not been ripped), on one of the rows The eye-catching mark (such as white ink) on the mark, visual inspection during the printing process, will quickly find the problematic fastener.
â‘¡ If it is a problem of roller teeth, the tear will not be so regular, or Zhang Zhang. However, we found that the tear caused by the insufficient opening of the teeth is generally accompanied by the phenomenon of the edge of the nest. According to the direction of the edge of the nest, we can also further reduce the scope of the fault. According to experience, the direction of the socket is always towards the direction of the dental slice.
â‘¢If there is a regular interval or two intervals, then we must first consider the double-diameter roller.
â‘£ This kind of tear that appears due to insufficient opening of the teeth is often accompanied by a very insignificant phenomenon of partial overprinting. For example, when the color sequence is arranged as black cyan and magenta, black cyan and magenta are registered separately, and there is a problem of inaccurate registration between them. Then we can further lock the faulty teeth on the roller between Qinghe Pin.
Combining the entire judgment process above, in fact, in most cases, we can quickly find the location of the faulty tooth by judgment.
deal with:
When the judgment is over, the processing is the simplest process, as long as the faulty tooth found is readjusted to the corresponding entire row (note that the entire row must be adjusted, otherwise the tear is solved, due to the change in tooth strength It is likely that the overall pressure will be placed on other individual teeth, resulting in new problems soon).
7. The transfer time is too long
Features:
In general, this kind of situation is difficult to appear during normal work, but sometimes it will appear after overhaul or debugging. The characteristic of the tear is that there is a tear, but there is generally no edge (because the paper is broken by the hook) of). But sometimes the shape of the tear is not easy to distinguish from the above. When judging, the final consideration is generally based on the possibility of occurrence.
analysis:
When the two rows of teeth are in the process of handing over, a small bit of paper biting movement is required. This is for the smooth handover of the paper. Then the two rollers will be separated in their respective circumferential directions. If you haven't opened your teeth, then there will be a paper grab. Torn the paper.
deal with:
Adjust the corresponding tooth-opening protrusion to the correct position.
8. The cross-connect line is not in the correct position
Features:
The frequency of occurrence is not high, usually after replacing or adjusting the corresponding teeth, and if there is no large unloading machine, it will not appear on the roller teeth. This situation occurs more frequently on the chain row teeth. The adjustment and installation of the chain element itself is determined (most of the chain elements of the chain element can be rotated around the axis, and the teeth can often be "buckled" in different positions, which is not easy to detect). The place where the tear occurs is similar to the situation where the fastener element does not open, the specific judgment is the same as above.
analysis:
The reason is simple. If the handover is not on the tangent line where the handover should be, the paper will be damaged.
deal with:
Rotate the dental pad and realign the teeth. At the same time, ensure that the teeth pad is on the same level.
Due to the numerous brands and models of offset presses, the author here is only a summary of possible tearing faults, but in fact they are inseparable. No matter what type of machine, as long as it is analyzed and judged according to the above ideas, it should be of great help.
We have listed some of the reasons that are more likely to cause tearing in the paper printing process. There are still some difficulties that are difficult to encounter in actual work. I will not list them here. But no matter what kind of reason is the tear, as long as we carefully observe the appearance of the tear and combine the consistent situation of the machine to carry out comprehensive analysis and judgment, the problem can be solved.
Sichuan Soper Science & Technilogy Co., Ltd , https://www.Soper.com.cn