Printing paper adjustment experience of offset printing cardboard
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The lack of smooth paper feeding is one of the most common problems in the production process of sheetfed offset presses, and it is also a problem that must be solved before the offset press starts normal production. A common cause of paper feed failure is that the paper separation mechanism and the transport mechanism are not adjusted according to the characteristics of the paper. The operating instructions and various professional books of various types of machines have a large number of detailed introductions in this respect, but generally use the commonly used paper as the main object to introduce the operation and adjustment methods. The company that I used to serve mainly produces packaging color boxes. Usually, the paperboard is more than 300 grams. This type of paperboard is much thicker than ordinary single sheets. If the paper fails, it will not only affect the production efficiency, but also the blanket or even the printing machine. Brings more damage. Based on the author's experience in printing thick cardboard, the Heidelberg SORSZ sheetfed offset press is the main basis. Discussing the experience of offset printing and thickening in some paper printing and troubleshooting, for peer reference and communication.
1. Adjustment of the paper separation mechanism
In general, the paper feed adjustment of printed cardboard is easier than printing thin paper. Due to the heavy weight of the cardboard, more wind is required to blow the paper and suck the paper. Therefore, it is necessary to check and clean the filter and nozzle of the air pump and the nozzle regularly to ensure sufficient air volume. Generally speaking, the printing of thick cardboard should maximize the air volume of each nozzle and nozzle, and the rubber ring of the paper feeding nozzle and the paper separating nozzle should be large and thick, and the cylindrical paper blowing nozzle should use a cylindrical member. It can concentrate the wind and can blow 3 to 5 sheets of paperboard in the upper part of the paper pile. The machine's standard paper stopper brush is suitable for printing on ordinary paper. When the standard metal separation sheet is used for thick cardboard, we find it is soft and easy to break. If it is purchased for a long time, it will increase the cost burden. The method we use is to grind the metal packing tape to a certain thickness for use as a tablet, which works well. Since the self-grinding tablet is harder and the cardboard is harder than ordinary paper, the steel sheet cannot protrude into the paper pile too much, generally no more than 3mm, otherwise the cardboard is blocked by the steel sheet, and even the first paper cannot be separated. The nozzle is sucked up.
Since the steel sheet protrudes into the paper pile less, the paper pile is required to be more tidy. If the length of the cut cardboard is too large, the paper may be damaged due to too much pressure on the sheet or scratching. In addition, since the cardboard is relatively hard, it is not like the thin paper is sucked up by the separation nozzle, and the edge of the paper is inclined downward, so the paper blowing nozzle can not reach into the paper pile too much, otherwise it will slam The first piece of cardboard sucked up. In short, the requirements of the cardboard for the separation mechanism are: the air volume should be sufficient, the tableting should be hard and have good elasticity, and the cutting size of the cardboard should be accurate.
2. Adjustment of double control mechanism
The mechanical double-sheet controller detects double sheets by controlling the thickness of the paper between the two wheels. It should be said that the paperboard is easier to adjust the double-sheet controller. It is worth noting that the thickness accuracy of the cardboard is often not as good as that of thin paper. When cutting, if the paper cutter is slightly blunt, the fibers on the back of the cardboard are not neat on the side of the cut, which causes a certain error in the thickness of the cardboard passing through the double controller. When adjusting the height of the double controller, The error is taken into account.
3. Adjustment of the rule parts
Heidelberg presses use pull gauge wheels and pull-iron bars to form side pull gauges. When printing thick cardboard, in order to provide greater pulling force, the tension spring of the tension wheel needs to be replaced with thick, the pressure is large, the thick cardboard is easy to sink under the pressure of the pulling wheel, and it is easy to have the cardboard after cutting. The burrs, cardboard surface and pull gauge cover will not be pulled by friction if they are in close contact, as shown in Figure 1. Therefore, when printing thick cardboard, pay attention to increase the height of the pull gauge cover so that there is a gap of 0.2 to 0.3 mm between the cardboard and the surface of the cardboard.
Because the machine prints thick cardboard for a long time, it uses thick springs. The force required to raise the tension wheel by the spring force is greater, which may cause the wear of the contact point A to be more serious. As shown in Figure 2, the surface wears. After that, the pull gauge wheel is not raised enough. When the pull gauge wheel is at a high position, it is not enough for the two thick cardboards to pass underneath. As a result, the bite portion of the current cardboard has entered the transfer cylinder, but the tip portion is still When the paper roller is under the pressure roller, another cardboard that has been blocked is passed from the pull gauge wheel to the forward gauge, causing the cardboard to be skewed and stopped. Our machine encountered this problem when printing thick and large cardboard, which made the paper feeding impossible. The remedy was to spot weld the worn and recessed A, so that the puller wheel could be lifted higher. In order to ensure that the two paperboards pass smoothly after the platen roller is lifted off the paper iron bar.
Most modern printing presses use a hem-style front gauge, which usually has 6 to 8 front gauges. Cardboard is a water-absorbent substance. After deformation due to changes in water content, the paper angle may be lifted. If the corner between the edge of the cardboard and the side of the side gauge is just near the inside of a front gauge, as shown in Figure 3. At the dotted line, the front gauge can be reached smoothly when the cardboard is transported forward. However, when the side gauge pulls the cardboard, the normal positioning position should be below the front gauge tongue, but the curled paper corner may be blocked by the falling inner side of the front gauge tongue, or the cardboard may be pulled. Slanted off. Although this kind of failure is not easy to occur, once it occurs, the positioning will be inaccurate. The measures we take are: pay attention to certain specific sizes of cardboard before printing. If the width of the cardboard is about equal to the distance between the two symmetrical front sides, special care should be taken. If necessary and permitted, move the side gauges as much as possible. The positioning position allows the cardboard to avoid this squatting position, which can't be avoided, and the paper corner does have a lifting phenomenon. There is a risk of being pulled out, and this front gauge can be temporarily removed. Batch the product and put it back.
The cardboard which is undulated due to uneven water content enters the front gauge. Since the cardboard is hard, the suction of the paper feeding table cannot absorb the cardboard, and the edge of the cardboard is easily blocked by the front of the front gauge tongue. To enter the pre-defined position, it may be necessary to press the hardened sheet to press the edge of the arched or raised cardboard, as shown in Figure 4. If the paper sheet is close to the front gauge, when the edge of the cardboard is bitten into the machine by the transfer cylinder, the front gauge has been raised from the lowered position and is in the highest position, then the cardboard The tip of the tip is pulled out from the top of the front gauge and the bottom of the platen. Since the back of the cardboard is usually rough, and the upper surface of the front gauge tongue is rubbed for a long time, the head becomes a bit sharp, and the tongue of the front gauge is The back of the cardboard may be scratched, as shown in Figure 5. The scraped paper is randomly attached to the back of the cardboard and enters the machine, which will crush the blanket of the press, so the tablet should not be too hard or too tight. If you really need to use hard compression, you can't press it in front of the front gauge or too close to it. It should be placed on the side of the front gauge, at least 1cm apart. Of course, the most ideal situation is that the cardboard will be put into printing immediately after the cutting is cut, and the flat cardboard does not need to be pressed by steel, and naturally there will be no such problems.
4. Adjustment of the transfer mechanism
The height of the dental pad of the offset printing machine can be adjusted. For the common paper, the height of the dental pad can be set at the factory, but if the cardboard is printed, the height of the dental pad must be adjusted, otherwise it will fall. The spacing between the dental pads and the paper table is too small and may hit the cardboard so that it cannot reach the front gauge. The height of the dental pad should be set in consideration of the thickness of the paper and the height of the front gauge tongue. If the front gauge tongue is low and the dental pad is high, the height of the paper will be controlled by the front gauge tongue, and the paper will be raised by the teeth. As a result, wavy deformation occurred at the edge of the paper, which caused the overprint to be inaccurate. If the height of the front gauge and the pad is adjusted strictly according to the thickness of the paper, it is too much trouble for the paperboard with frequent printing thickness, so we only make two settings for the height of the dental pad: one is paper of less than 300 grams. The front gauge is adjusted according to the thickness of the paper, and the dental pad is set according to the machine standard; the other is a cardboard of more than 300 grams. Considering that the edge of the cardboard is thicker and does not bend due to collision, the height of the front gauge is raised to The highest, the dental pad is also adjusted to the highest position.
5. Adjustment of the paper guide mechanism paper guide
Due to the thicker cardboard, the SORS series offset press for the equal-diameter impression cylinder and the transfer cylinder, the paper is forced to generate a large rebound force along the circular arc transfer process. Therefore, the SORS series offset printing machine The drum has three paper guides that protect the paper in an orderly direction along the direction of rotation of the drum. As shown in Figure 6, we generally want the three paper strips to be placed within the width of the cardboard. If the cardboard is small, you can use only one or two, but don't just place it on the edge of the cardboard. This may be caused by the deformation of the cardboard during printing or the small amount of movement of the iron. The iron strip is scraped, causing the edge of the cardboard to be scraped or detached from the teeth, damaging the machine, causing damage to the blanket and, in severe cases, even damaging the machine. By the same token, there are many small wheels on the delivery roller that are used to prevent the back of the paper from being dirty. This small wheel can't just be placed on the edge of the cardboard. Otherwise, the edge of the cardboard may be scraped or the cardboard may fall off.
6. Adjustment of the delivery device
Since the cardboard is very hard, it is not necessary to open the flat paper to absorb the air, whether it is printed or not. Otherwise, the effect of the flat paper will not be obtained, but the dust will be sucked in. The suction air volume of the reduction wheel is generally opened to the maximum, and the suction port and the filter net of the reduction wheel must be cleaned frequently to prevent the air volume from being insufficient. However, due to the large mass of the cardboard and the large inertia, for the paperboard which is relatively short in the direction of rotation of the drum, because there is not enough deceleration time, it is necessary to carefully adjust the teeth of the tooth according to the thickness, size and printing speed of the cardboard. The time of opening the teeth.
When printing thin paper, it is usually necessary to clamp the cardboard of the delivery position so that the printed paper is as neat as possible. However, when printing thick cardboard, the distance between the symmetrical paper organizers on the delivery table should be slightly larger than the size of the paper. Otherwise, when the paper organizer is strung inward, since the cardboard is hard and the two ends are pressed, it is easy to arch downward, as shown in Figure 7, giving the next printed ink layer a large force, resulting in back dirty.
The above is what we need to pay special attention to when printing thick cardboard with Heidelberg SORSZ two-color offset printing press, and some measures we have taken. Although the maximum printing thickness specified by the machine we use is 0.8mm, paperboard with a thickness of more than 0.8mm or even 1.2mm is often printed in production. After paying attention to the above details, there is no paper feeding. There are other problems.