Poor paper feed is one of the most common problems in the production process of sheet-fed offset presses, and it is also a problem that must be solved before the offset press starts normal production. The common cause of paper feed failure is that the paper separation mechanism and conveying mechanism cannot be adjusted according to the characteristics of the paper. The operation manuals and various professional books of various machines have a large and detailed introduction to this aspect, but generally use the commonly used paper as the main object to introduce the operation and adjustment methods. The companies I have served previously mainly produce packaging color boxes, which usually weigh more than 300 grams of cardboard. This kind of cardboard is much heavier than ordinary sheet paper. If the paper fails, it will not only affect the production efficiency, but also may affect the blanket and printing machine. Bring greater damage. This article is based on the author's experience in printing thick paperboard, taking Heidelberg SORSZ sheet-fed offset printing press as the main basis, discussing some of the different experiences of ordinary paper printing in the adjustment and troubleshooting of offset printing thick paperboard for peer reference and exchange.
1. Adjustment of paper separation mechanism
Generally speaking, the feeding adjustment of printing thick cardboard is easier than printing thin paper. Due to the heavy weight of the cardboard, more air is required for blowing the paper and sucking the paper, so pay attention to regular inspection and cleaning of the filter screen, blow nozzle and suction nozzle of the air pump to ensure that there is sufficient air volume. Generally speaking, when printing thick cardboard, the air volume of each blowing nozzle and suction nozzle should be opened to the maximum. The rubber ring of the paper feeding nozzle and the separating nozzle should be large and thick, and the cylindrical piece of loose paper blowing nozzle should be used. , Can concentrate the wind force, and can blow 3 to 5 sheets of cardboard on the top of the paper stack. The machine's standard paper blocking brush is suitable for printing on ordinary paper. When the standard metal separator is used for thick cardboard, we find that it is still soft and easy to break. If it is purchased for a long time, it will increase a certain cost burden. The method we use is to grind the metal strapping to a certain thickness and use it as a tablet, the effect is very good. Because the self-grinding tablet is harder, the thick cardboard is harder than ordinary paper, so the steel sheet cannot reach too much into the stack, generally not more than 3mm, otherwise the cardboard is blocked by the steel sheet, and even the first sheet of paper cannot be separated The nozzle sucked up.
Because the steel sheet does not extend into the paper stack less, the paper stack is required to be more tidy. If the length of the cut cardboard is too large, it may cause a paper feed failure due to too much pressing of the tablet or no scraping. In addition, because the cardboard is relatively hard, it is not like thin paper that is sucked up by the separation nozzle, and the paper edge of the trailing portion is slanted, so the paper pressing nozzle can not reach too much into the stack, otherwise it will step on The first cardboard sucked up. In short, the requirements of the thick cardboard for the separation mechanism are: sufficient air volume, harder and better elasticity of the tablet, and accurate cutting size of the cardboard.
2. Adjustment of double-sheet 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 printed board is easier to adjust the double-sheet controller. It is worth noting that the thickness accuracy of cardboard is often not as good as thin paper. When cutting, if the cutter is a little blunt, the fibers on the back of the cardboard are not smooth at the edge of the cut, which causes a certain error in the thickness of the cardboard passing through the double sheet controller. When adjusting the height of the double sheet controller, The error is taken into account.
3. Regulation of regulatory components
Heidelberg presses use pull gauge wheels and paper bars to form side pull gauges. When printing thick cardboard, in order to provide greater pulling force, the support spring of the tension gauge wheel needs to be replaced with a thicker one, and the pressure is greater. The thick cardboard is easy to sink under the pressure of the gauge wheel, and after the cardboard is cut, it is easy to have If the burrs, cardboard surface and pull gauge cover are in close contact, they will not be pulled in place due to friction, as shown in Figure 1. Therefore, when printing thick cardboard, pay attention to increase the height of the drawing cover, so that there is a gap of 0.2 ~ 0.3mm between the cardboard surface.
Because the machine prints thick cardboard for a long time, it uses thick supporting springs. The force required to lift the gauge wheel to overcome the spring supporting force is greater, which may cause serious wear at the contact point A. As shown in Figure 2, the surface wears After the pull gauge wheel is not raised high enough, when the pull gauge wheel is in a high position, it is not enough to let two thick cardboards pass under it. As a result, the bite portion of the previous cardboard has entered the delivery roller, but the trailing portion is still When it is under the paper pressing wheel, it will block another paper board that has been connected to pass through the front gauge under the pull gauge wheel, causing the paper board to skew and stop. Our machine had encountered this problem when printing thick and large cardboard, which made the paper feeding impossible. The remedy is to spot weld at the worn and concave A, so that the gauge wheel can be raised higher. In order to ensure that the paper pressing wheel is lifted off the paper pulling iron bar, the two cardboards can pass smoothly.
Most modern presses use a hem-type front rule, and there are usually 6 to 8 front rules for booting. Cardboard is a water-absorbent substance. After being deformed due to the change of water content, the paper corner may be lifted. If the corner where the bite edge of the cardboard intersects the side pull ruler is just inside the front ruler, as shown in Figure 3. At the dotted line, when the cardboard is conveyed forward, it can smoothly reach the front gauge. However, when the side gauge pulls the cardboard, the normal positioning position should be under the front gauge tongue, but the raised paper corner may be blocked by the inner side of the falling front gauge tongue, or the cardboard may not be pulled in place. Obliquely. Although this kind of fault is not easy to occur, once it occurs, it will lead to inaccurate positioning. The measures we take are: pay attention to certain specific sizes of cardboard before printing. If the width of the cardboard is approximately equal to the distance inside the two symmetrical front regulations, special attention is required. If necessary and allowed, try to move the side regulations The positioning position of the paperboard can avoid the awkward position of the cardboard, which is really unavoidable, and the paper corner does have a lifting phenomenon, and there is a risk that it may not be pulled in place. You can temporarily remove this front rule and wait for the printing Batch of products, and then put it back.
Due to the uneven moisture content, the wavy curved cardboard enters the front gauge. Due to the rigidity of the cardboard, the paper suction table can not suck the cardboard flat. The bite edge of the cardboard is easily blocked by the front regulation tongue. Enter the front position, for this reason, it may be necessary to press the arched or tilted cardboard bite edge with a harder paper pressing sheet, as shown in Figure 4. If the paper pressure plate is very close to the front gauge, when the bite edge of the cardboard is caught by the delivery roller and pulled into the machine, the front gauge has risen from the fallen position and is at the highest position. The trailing part is drawn from the top of the front gauge and the bottom of the paper sheet. Because the back of the cardboard is usually rough, and the upper surface of the front gauge tongue has been rubbed for a long time, the head becomes a little sharp. 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 printing press, so the tablet cannot be too hard or too tight. If you really need to use a hard tablet, it can not be pressed directly in front of the front rule or too close to it, it should be placed on the side of the front rule, at least 1cm apart. Of course, the ideal situation is that the cardboard is immediately printed after opening and cutting. The flat cardboard does not need to be pressed with steel tablets, and naturally there will be no problems in this regard.
4. Adjustment of paper delivery mechanism
The height of the dental pads of the paper delivery row of the offset printing machine can be adjusted. For the commonly used paper, the height of the dental pads can be set according to the factory setting, but if printing thick cardboard, the height of the dental pads must be adjusted, otherwise it will fall The distance between the dental pad and the paper table is too small, it may hit the cardboard, making it impossible to reach the front rule. The height of the dental pads should be taken into consideration of the thickness of the paper and the height of the front gauge tongue depressor. If the front gauge tongue depressor is low and the tooth cushion is high, the front gauge depressor tongue will control the height of the paper, and the phenomenon of clenching teeth will raise the paper As a result, wavy deformation appeared on the bite edge of the paper, resulting in inaccurate overprinting. If the front gauge and the height of the dental pad are strictly adjusted according to the thickness of the paper, it is too troublesome to print the cardboard with frequent thickness changes, so we only make two settings for the height of the dental pad: one is paper under 300 grams, The front gauge is adjusted according to the thickness of the paper, and the dental pad is set according to the machine benchmark; the other is cardboard with a weight of more than 300 grams. Considering the thick bite edge of the cardboard, it will not be bent by collision, so the height of the front gauge is raised to The highest, the dental pad is also adjusted to the highest position.
5. Paper guide mechanism adjustment
Due to the thicker cardboard, for the SORS series offset presses with equal diameter impression cylinder and paper transfer cylinder, the paper is forced to pass along the arc to produce a greater rebound force. Therefore, the paper transfer of the SORS series offset press The roller has three paper guide strips to protect the paper in an orderly direction along the rotation direction of the roller. As shown in Figure 6, we generally hope that the three paper guide strips are placed within the width of the cardboard. If the cardboard is small, you can use only one or two, but do not place it just on the edge of the cardboard, because the cardboard may be deformed during the printing process, or the iron bar will move a little, and the side of the cardboard will be affected. If the iron bar is scratched, the edge of the cardboard will be scratched or fall off from the teeth, and it will be rotten in the machine, causing damage to the rubber blanket. In serious cases, it may even damage the machine. For the same reason, there are many small wheels scattered on the take-up roller to prevent the back of the paper from getting dirty. These small wheels should not be placed just on the edge of the cardboard, otherwise the edge of the cardboard may be scratched or the cardboard may fall off.
6. Adjustment of delivery device
Since the cardboard is very stiff, no matter whether it is printed on the full plate or not, there is no need to open the flat paper to absorb the air. Otherwise, the effect of the flat paper will not be achieved, but the powder will be inhaled. The suction volume of the reduction wheel is generally opened to the maximum, and the suction port and filter screen of the reduction wheel must be cleaned frequently to prevent insufficient air volume. Nevertheless, due to the high mass and inertia of the cardboard, for the cardboard with a relatively short length in the rotation direction of the drum, because there is not enough deceleration time, it is necessary to carefully adjust the teeth according to the thickness, size, printing speed and other factors of the cardboard Opening time.
When printing thin paper, it is usually necessary to clamp the cardboard at the receiving part to make the printed paper as tidy as possible. But when printing thick cardboard, the distance between the symmetrical paper organizers on the delivery table should be slightly larger than the paper size. Otherwise, when the paper sorter moves inwards, due to the rigidity of the paperboard, it is easy to arch downwards when the two ends are pressed, as shown in Figure 7, which gives a large force to the ink layer of the next printed sheet, causing the back to rub dirty.
The above is that when we use Heidelberg SORSZ two-color offset printing machine to print thick cardboard, it is different from ordinary paper printing, what needs special attention, and some measures we have taken. Although the maximum printing thickness specified by the machine we use is 0.8mm, cardboards with a thickness of more than 0.8mm and even 1.2mm are often printed in production. After paying attention to the details of the above aspects, there is no paper transport. There are other problems.
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