Analysis of tension control and adjustment device of JJ204 offset printing machine
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The paper feeding method of the web offset printing machine is completely different from the paper feeding mode of the sheet-fed offset printing machine. The former is carried out by continuously pulling the paper tape by the machine. The force that causes the paper strip to be tensioned during the paper feeding process is called tension. With the blanket cylinder embossed line as the boundary, the tension can be divided into two parts: the front of the nip line is called the paper-feeding force, and the embossed line is called the paper-receiving force. The tension of the tape is directly related to whether the web offset press can work normally. If it is not the right size, it will cause a series of process failures, such as tape drift. Wrinkles, rips or tears, inaccurate overprinting, and inaccurate signage of the sky, resulting in waste of paper, affecting machine operation efficiency, increasing labor intensity, and ultimately affecting the quality of printed products.
JJ204 web offset presses are equipped with a number of devices for controlling and adjusting the tension to ensure the normal operation of the machine to meet the different tension requirements of different positions.
Magnetic powder controller
The magnetic powder controller can directly control the paper roll to prevent the paper roll from being free during the paper feeding process, avoiding paper breakage and paper jam when the machine is increasing or decelerating, ensuring that the paper roll is discharged at a smooth speed and passed. The floating mechanism and the tension detecting circuit eliminate or reduce the tension fluctuation caused by the paper roll not being rounded, eccentric, loose, tight, etc., and can automatically adjust the tension change caused by the paper roll becoming smaller during the printing process. .
Use the adjustment method: install the whole roll of paper, press the manual key switch, adjust the knob, change the brake current, and push the paper roll with both hands to promote the paper roll. The value displayed on the table at this time is the standard value of the control current of the magnetic powder controller, which determines the tension at the time of paper feeding. Too much tension will cause the paper roll to rotate unevenly; the tension is too small, and paper jam will occur when the machine is stopped.
Paper feed roller and continuously variable transmission
The paper feed roller of the JJ204 web offset press consists of two metal rollers and one rubber roller. The paper feed speed of the paper tape is mainly generated by the paper feed roller and its control adjustment device. Therefore, the adjustment here will directly affect the printing quality and folding quality.
1. Feed roller pressure adjustment
Before adjusting, the paper feed roller should be cleaned, and the residue such as latex, double-sided tape or crayon mark should be removed to avoid the impact on the adjustment work. There are two requirements for the adjustment of the paper feed roller pressure: first, the pressure at both ends should be the same, and second, the pressure should be appropriate.
In order to ensure the consistency of the pressure between the two ends, it is not recommended to adjust the inconsistency of the two ends of the paper roll to solve the problem of inconsistency between the two ends of the paper roll. It is recommended to turn the paper roll to the outside. To make the tension on both sides of the machine exactly the same, it is not easy to do. Turning the paper roll is to use the uneven machine tension to make up for the short. If it doesn't work, it means that the tightness of the two ends of the paper roll is too different. Even if the paper is adjusted by the adjustment mechanism, it can barely print, and it will inevitably cause wrinkles, blotting and other problems, and it is used in paper rolls. After that, the operation of returning the various parts of the machine to the original state becomes very troublesome.
Proper pressure means that the pressure is neither too small nor too large. The pressure is too small, there will be a slip between the paper belt and the paper feed roller, and the surface speed of the surface provided by the continuously variable transmission cannot be truly reflected; the pressure is too large, which increases the machine load. When verifying that the pressure is appropriate, a strip of about 2 mm wide can be used to pull the strip out of force and it is desirable. In short, when adjusting the pressure, it should be lighter.
2. Adjustment of continuously variable transmission
The continuously variable transmission is the most important source of paper output for the JJ204 web offset press. Considering that the force of the paper feed affects the amount of paper feed in the future, the adjustment of the continuously variable transmission is very important for the entire paper feed process. The several common process faults mentioned above are more or less related to the regulator of the continuously variable transmission. Therefore, when adjusting the continuously variable transmission, be careful and ensure accurate adjustment.
The so-called prudence means that when the machine fails, if the brand and the quantity of the paper have not changed, the reason is usually that the folding machine or the printing part is mostly used. Do not adjust the continuously variable transmission easily and easily. Although it is very convenient to adjust, the hand can move, but if it is not properly adjusted, the problem can not only be solved, but also may bring new problems. The so-called precision means that when adjusting, don't be afraid of trouble, you have to work hard and try to get to the best point.
The CVT has been improperly adjusted and has two extreme states: too slow, the tape is broken; too fast, the tape is pulled down and not stretched. In order to be unhappy or not slow, the author's approach is divided into three steps: the pressure state adjustment; the pressure state adjustment; the two groups together to fine-tune the state. In order to adjust the accuracy, the first two steps are first to use a single paper path, and the groups are individually adjusted. The direction of adjustment is from loose to tight. If it is too tight at the beginning, the tape will break easily and you will not be able to continue adjusting. If you want to avoid the impact of the last adjustment on this adjustment, you can break the paper tape and re-feed the paper before the test machine.
Cloth roll and paper press rubber wheel
The printed paper tape is fed to the folding machine for folding, and this action is performed by the cooperation of the paper take-up roller and the paper-pressing rubber wheel. There is a maximum value of the pulling tension of the paper take-up roller and the paper-pressing rubber wheel to the paper tape. There are two sources of this maximum value: one is the tension at the take-up roll, which is determined by the theoretical error in the design and manufacture of the machine; the second is whether the paper strip slides on the take-up roll, ie the paper-press rubber The wheel pressure is not tight.
The rubber roller of JJ204 web offset press has a diameter of 175mm, the diameter of the delivery roller is 153.3mm, the transmission ratio between the rubber roller drive gear and the delivery roller drive gear is 27:31, and the rubber roller rotates in a good unit time. The 27-ring delivery paper roller turns 31 turns. The distance traveled by any embossing line after 27 turns of the blanket cylinder is 27×175=4725mm, and the distance taken by the take-up flower roll to 31 turns is 31×153.3=4752.3mm, so every turn of the machine The delivery paper roller is 1.01mm more than the rubber roller (<4752.3-4725>÷27). Tension is also produced. It can be seen from the above analysis that if the pressure of the paper-feeding rubber wheel to the take-up flower roll is small, the paper tape will slide on the paper take-up roll, and the paper-receiving force will become small.
In addition, the wear and tear of the rubber roller of the paper-pressing paper, the accumulation of ink on the surface of the paper-receiving surface, etc., also affect the size of the paper-receiving force, and the work should be timely and timely solved. In short, the pressure of the rubber roller on the paper-feeding roller has two requirements: one must be consistent, the second should be suitable, under normal circumstances, it can be properly tight.
Triangle plate and paper guide roller
The main function of the set square and the paper guide roller is to longitudinally fold the paper strip. The adjustment of the delivery roller and the pressure rubber roller and the continuously variable transmission is only a good basis for smooth folding. Specific to the quality of the folding, vertical folding, the adjustment of the triangular plate and the paper guide roller is very important; horizontal folding, the adjustment of the three-roller folding machine is very important.
There are two preconditions for the influence of the triangular plate and the paper guide roller on the tension: one is that the paper tape does not slide between the paper take-up roller and the platen roller; the other is that the paper tape does not slide between the two knurled paper rollers.
1. Adjustment of the triangular plate
Tension at the top and bottom of the triangular plate affects the tension. The influence on the upper side is small. When adjusting, try to make the plane of the triangular plate in the tangential direction of the cross section of the paper feed roller. The influence underneath is large. Adjusting the advance and retreat of the tip of the nose slightly changes the pitch of the plane of the triangle, and the tension at the middle seam can be changed. This method is often used in conjunction with a paper guide roller to adjust the position of the seam in the tape or to solve the problem of breakage.
2. Adjustment of the paper guide roller
The adjustment of the paper guide roller is divided into two parts: one is the middle seam and the other is the paper edge.
The main function of the middle seam adjustment is to maintain a proper gap with the triangular counter to ensure that the paper strip enters the folding machine smoothly. For the size of the gap, there is a saying that the thickness of the paper plus 0.2mm, but the author believes that regardless of the double paper path or the single paper path, the thickness of a 16-open book sticker is appropriate. Such a gap is neither too large nor too small, it is not easy to cause a break, and it is convenient to wear paper, and it is easy to grasp.
The main function of the paper edge adjustment is to adjust the position of the paper tape crease, and at the same time change the tension between the paper tape and the paper edge. When the pitch of the paper guide roller is reduced, the tension at the paper edge becomes larger, and the tension of the middle slit becomes smaller; on the contrary, the tension at the paper edge becomes smaller, and the tension of the middle slit becomes larger. If the adjustment is not good here, it will cause the paper to break, tear, etc., so when adjusting, pay attention to observe whether the middle seam is aligned, and carefully listen to the paper with the sound of no "beep" break, combined The comprehensive adjustment of the advance and retreat of the triangle board.
Paper roll
The main function of the paper feed roller is to pull the paper tape and feed the longitudinally folded paper tape into the three-roller folding machine in a balanced manner. In order to enhance the friction of the traction paper strip, a roll wreath is attached to both ends of the paper feed roller. The adjustment of the paper feed roller includes both axial adjustment and radial adjustment.
The axial adjustment mainly adjusts the relative position of the rolling wreath on the shaft to adapt to the width of the paper strip or the change of the position of the printed image, so that the rolling wreath is pressed against the empty portion which does not affect the quality of the printed product.
Radial adjustment is mainly to adjust the pressure of the two paper rollers on the paper tape. The quality of the radial adjustment will affect the tension change of the paper tape, too tight, and easy to break; too loose, the longitudinal position of the paper tape is unstable. The thickness of the paper tape passing between the two paper rollers should be taken as the standard when measuring, that is, when the paper is single, the thickness of the two papers is used as the measurement standard; when the double paper is used, the thickness of the four papers is used as the measurement standard. The size of the pressure is preferably such that a slight knurling can be seen.
Since the paper-holding roller is a pair of steel rings that roll against each other, the wear is faster, and when a folding knife is used, there is a position where the paper tape is suddenly tightened. Therefore, the wear on the rolling wreath is uneven, so pay attention to Replace it in time.
Common cause of failure
After understanding the above, it is not difficult to understand the causes of a series of process failures caused by improper adjustment of these mechanical components.
1. Paper tape drift
Cause of the problem: The tension is too small, the paper feed speed is too fast, the delivery speed is too slow, or the paper feed roller is too loose.
2. Double paper tape drift
The cause of the failure: the tension of the two paper strips is inconsistent, one fast and one slow, and when entering the take-up flower roll, the tension is small and drifts back and forth.
3. Broken or tape tear
Cause: The tension is too high, the paper feed speed is too slow, the paper feed roller is too tight or the folding knife is too high.
4. Imprinting is not allowed
Cause of the malfunction: The tension is too small or too large, resulting in unstable paper feed.
5. The label is not up and down, like the stock K-line chart
The cause of the malfunction: The tension is too large, causing the page to be unstable.
6. Change needles frequently
The cause of the malfunction: the tension is large.
7. Change the rubber knife pad frequently (commonly known as rubber band)
The cause of the malfunction: the tension is small, the paper is not tight or the cutting force is too large, resulting in serious wear.
Everything is connected to each other, and the tension of the paper tape is no exception. The paper feeding speed is too fast, and the paper feeding force is too small, which will affect the printing, delivery, and folding. So, be aware of this when analyzing faults. When adjusting the tension control unit, pay attention to the adjustment order. First adjust the parts that have other influences on the other side and the parts that can be adjusted in the stop state. Specifically, it is first to adjust the paper feed roller, the delivery paper, the magnetic powder brake, and then adjust the paper guide roller and the triangular plate, and finally adjust the continuously variable transmission. As long as we think and summarize in our work, the tension problem is not difficult to solve.