Experience of Paper Transfer Adjustment for Offset Printing Thick Cardboard

Inadequate paper feeding is one of the most common problems in the production process of a sheet-fed offset press, and it is also a good problem that must be solved before the offset press starts normal production. A common cause of paper failures is due to the fact that the paper separation mechanism and the conveying mechanism have not been adjusted according to the characteristics of the paper. Various types of machine operating instructions and various types of professional books have a lot of detailed introduction in this regard, but generally use the commonly used paper as the main object to introduce the operation and adjustment methods. The company that the author served previously mainly produces packaging boxes, usually with a cardboard weight of 300 grams or more. Such cardboard is much heavier than ordinary sheets. If the sheet fails, it will not only affect the production efficiency, but also may cause blankets or even printing machines. Bring more harm. Based on my experience in printing thick cardboard, this paper takes the SORSZ sheet-fed offset press in Heidelberg as the main basis. It discusses some paper printing experience in the adjustment and troubleshooting of offset printing and printing on thick paperboard for peer reference and communication.

1. Adjustment of paper separation mechanism

In general, it is easier to control the transport of printed cardboard than printed tissue. Because the cardboard is heavy, blowing air and sucking the paper need more wind, so pay attention to regularly check and clean the air filter and blow nozzles and nozzles to ensure that there is enough air volume. In general, printing thick paperboard to maximize the air volume of the mouthpiece and nozzle, feeding the paper nozzle and the paper suction nozzle rubber ring to use large, thick, loose paper mouthpiece to use a cylindrical member The wind can be concentrated, and it can blow up 3 to 5 pieces of cardboard on the upper part of the pile. The machine is equipped with a standard paper-blocking brush, suitable for ordinary paper printing. When the standard metal paper-sheeting is used for cardboard, we find that it is still soft and easy to break. If the long-term purchase will increase the cost burden, The method we use is to grind a certain thickness of the metal strap for use as a tablet, which works well. Because the hard pressed pieces are harder, and the cardboard is harder than ordinary paper, so the steel plate cannot reach into the paper stack too much, generally no more than 3mm, otherwise the cardboard is blocked by the steel sheet, and even the first sheet cannot be separated. The suction nozzle sucks up.

Because the steel sheet is less in the paper stack, the paper stack is required to be more neat. If the length of the cut paper board is too large, the paper sheet may be pressed too much or may not be scraped. In addition, because the cardboard is relatively hard, unlike the thin paper being sucked by the paper suction nozzle, the paper edge of the dragging part is inclined downwardly, so the paper blowing nozzle cannot reach too much into the paper stack. Suction the first cardboard. In short, the requirements for the separation mechanism of cardboard are: sufficient air flow, tablet compression and good elasticity, and the cardboard cutting size must be accurate.

2. Adjustment of double-sheet control mechanism

The mechanical double-sheet controller detects double sheets by controlling the thickness of the paper between two wheels. It should be said that the printing paperboard can easily adjust the double-sheet controller. It is worth noting that the thickness accuracy of the cardboard is not as good as that of the thin paper. During cutting, if the cutter is slightly blunt, the fibers on the back of the cardboard are not neat at the cut edges. This causes a certain error in the thickness of the cardboard through the double-sheet controller. When adjusting the height of the double-sheet controller, The error is taken into account.

3. Regulation of adjustment of parts

Heidelberg presses use pull gauge wheels and pull bars to form side pull gauges. When printing thick cardboard, in order to provide greater tension, the tension spring of the pull gauge wheel pressure needs to be replaced with a thick one, and the pressure is relatively large. The cardboard is easy to sink under the pressure of the gauge wheel, and after the cardboard is cut, it is easy to have The burrs, the cardboard surface and the pull-tab cover can not be pulled by friction if they are in close contact. Therefore, when printing thick cardboard, it is necessary to pay attention to increase the height of the pull gauge cover so that there is a clearance of 0.2 to 0.3 mm between the surface of the cardboard and the cardboard.

As the machine is printing thick cardboard for a long time, it is used to use thick-bracing springs. The force required to lift the gauge wheel to overcome the spring support force is greater, which may result in more serious wear of the contact point A, as shown in Fig. 2, the surface wear. Later, the pull gauge wheel was not raised sufficiently high. When the pull gauge wheel was at a high position, it was not enough to allow two cardboards to pass underneath. As a result, the position of the mouthpiece of a current cardboard sheet had already entered the transfer cylinder, but the position of Under the pressure roller, it will block another board from passing under the gauge wheel to the front gauge, causing the board to be skewed and shut down. Our machine had encountered this problem when printing thick and large cardboard, which made it impossible to carry paper. The remedy was to spot weld A at the point of wear and depression so that the gauge wheel could be lifted higher. In order to ensure that the platen roller lifts off the pull-out bar, the two boards can be passed smoothly.

Most modern printing presses use a hem-type front gauge, and usually have 6 to 8 front gauges for starting. Cardboard is a water-absorption substance. After being deformed due to changes in water content, the corners of the paper may warp. If the angle between the edge of the cardboard bite and the edge of the side pull tab is just near the inside of a certain front gauge, then when the cardboard is The front gauge can be smoothly reached in the front conveyor. However, when the side panel pulls the cardboard, the normal positioning position should be the underside of the front tongue, but the tilted paper corner may be blocked by the inner surface of the front tongue that is falling down and not pulled, or pull the cardboard Oblique off. Although this kind of failure is not easy to occur, once it occurs, it will result in 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 between the two symmetrical front gauges, special attention is required. If necessary and permitted, try to move the side gauges. Positioning position, so that the cardboard to avoid this position, it can not avoid, and the paper corner does exist tilt phenomenon, there is the risk of not pull the position, you can temporarily remove the former rule, to be printed after this Batch product, and then install it back.

Cardboard with wavy bending due to non-uniform moisture content enters the front gauge. Because the cardboard is hard, the suction on the paper feeding table does not suck up the cardboard. The edge of the paperboard is easily blocked by the front of the tongue and cannot be blocked by the front tongue. To enter the pre-positioned position, for this purpose may need to use a relatively hard pressure piece pressed against the arched or tilted cardboard edge, as shown in Figure 4. If the platen is close to the front gauge, when the edge of the cardboard is caught by the delivery cylinder and pulled into the machine, the front gauge has risen from the fallen position and is in the highest position. The tip part is drawn from the top of the front gauge and the underside of the platen. Since the back of the cardboard is usually rough, the front surface of the front gauge tongue is rubbed for a long time and the head becomes somewhat sharp. As a result, the tongue of the front gauge has The back of the cardboard may be scratched, as shown in Figure 5. The scratched paper is randomly stacked on the back of the cardboard and enters the machine, which will squash the blanket of the press. Therefore, the tablet cannot be too hard or too tight. If you really need to use a hard tablet, can not press in front of the front gauge or too close to place, should be placed on the side of the front gauge, separated by at least 1cm. Of course, the ideal situation is that the cardboard will be put into printing immediately after unsealing and cutting, and the flat cardboard will not need to be pressed with steel. Naturally, this problem will not arise.

4. Adjustment of paper delivery mechanism

The height of the dental pad of the offset press of the offset press can be adjusted. For the commonly used paper, the height of the dental pad can be set according to the factory setting. However, if a thick cardboard is printed, the height of the dental pad must be adjusted, or the height of the dental pad drops. The gap between the pad and the pad is too small and may hit the cardboard so that it cannot reach the front gauge. The height setting of the dental pad must take into account the thickness of the paper and the height of the front tongue. If the front tongue is low and the pad is high, the height of the paper will be controlled by the front tongue and the height of the paper will be raised by the teeth. As a result, wavy deformation occurred on the edge of the paper, resulting in inaccurate overprinting. If we strictly adjust the height of the front gauge and the pad according to the thickness of the paper, it is too much trouble for the paperboard with frequent changes in printing thickness, so we only set two kinds of settings for the height of the pad: one is a paper of 300 grams or less, The front gauge is adjusted according to the thickness of the paper, and the tooth pad is set according to the machine reference; the other is a paperboard of 300 grams or more. Considering that the paperboard has a relatively thick mouth and does not bend due to collision, raise the height of the front gauge to At the highest, the pad is also at its highest position.

5. Adjustment of the paper guide mechanism

Due to the thicker paperboard, the SORS series offset presses with equal diameter embossing cylinders and transfer cylinders, the paper is forced to produce a large rebound force along the circular transmission process, so the SORS series offset press The roller has three guide strips that are used to protect the paper in order to advance in the direction of rotation of the drum. Generally speaking, we hope that the three 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 just place it on the edge of the cardboard. This may be due to the deformation of the cardboard during the printing process, or the small amount of movement of the iron bar. The scraping of the iron bar causes the edge of the cardboard to be scratched or detached from the teeth, and is rotted in the machine, causing damage to the blanket. In severe cases, it can even damage the machine. By the same token, there are many small wheels on the take-up roller that are used to prevent the back of the paper from picking up the dirt. This small wheel can't be placed just on the edge of the paperboard. Otherwise, the edge of the paperboard may be scratched or the paperboard may fall off.

6. Adjustment of the delivery device

Because the cardboard is very hard, regardless of whether the full version of the printing field, do not need to open the paper suction device, otherwise, will not achieve the effect of plain paper, but will inhale powder. The suction volume of the deceleration wheel is generally open to the maximum, and the suction opening and the filter screen of the deceleration wheel must be cleaned frequently to prevent insufficient air flow. In spite of this, due to the large mass and inertia of the paperboard, for paperboards with relatively short lengths along the direction of rotation of the drum, or because there is not enough deceleration time, it is necessary to carefully adjust the tooth cavities according to the thickness, size, printing speed and other factors of the paperboard. The open time.

When printing thin paper, it is usually necessary to clamp the paper in the delivery area so that the printed paper is as tidy as possible. However, when printing cardboard, the distance between the symmetrical paper guides on the delivery table should be slightly larger than the paper size. Otherwise, when the paper guides are twisted inwards, since the paperboard is hard and the two ends are pressed, it is easy to bow downwards, giving a greater force to the ink layer of the next print, resulting in dirty backs.

These are the places we need to pay special attention to when printing thick cardboard with the SORSZ 2-color offset press from Heidelberg, as well as some of the measures we have taken. Although the maximum printing thickness specified by the machine we use is 0.8mm, we often print cardboard with a thickness exceeding 0.8mm and even reaching 1.2mm in production. After noticing the details of the above aspects, there is no paper feeding. There are other problems.