The paper feeding method of the web offset printing machine is completely different from the paper feeding method of the sheet-fed offset printing machine. The former is carried out by the machine continuously pulling the paper tape. In the process of paper feeding, the force that makes the paper strip tensioned is called tension. Taking the rubber roller embossing line as the boundary, the tension can be divided into two parts: the paper feeding force before the embossing line and the paper receiving force after the embossing line. The size of the tape tension is directly related to whether the web offset press can work normally. If the size is not suitable, it will cause a series of process failures, such as paper tape drift. Wrinkles, tears or tears, inaccurate overprinting, inaccurate folding of the head, etc., thus causing paper waste, affecting machine operation efficiency, increasing labor intensity, and ultimately affecting print quality.
In order to ensure the normal operation of the machine, JJ204 web offset printing machine is equipped with many devices for controlling and adjusting the tension to meet the different requirements for tension at different positions.
Magnetic particle controller
The magnetic particle controller can directly control the paper roll, prevent the paper roll from being in a free state during paper unloading, avoid paper breakage and paper jamming during machine acceleration and deceleration, and ensure that the paper roll is discharged at a stable speed and pass Floating mechanism and tension detection circuit can eliminate or reduce tension fluctuations caused by the paper roll being not round, eccentric, loose end, tight end, etc., and can automatically adjust the tension change caused by the continuous reduction of the paper roll during the printing process .
Use adjustment method: install the whole roll of paper, press the manual key switch, and adjust the knob to change the braking current, while pushing the paper roll with both hands, it is appropriate to be able to push the paper roll. At this time, the value displayed on the table is the standard value of the current controlled by the magnetic particle controller, and this value determines the amount of tension during paper discharge. If the tension is too high, the paper roll will rotate unevenly; if the tension is too low, paper jams will occur during shutdown.
Paper feed roller and continuously variable transmission
The paper feed roller of JJ204 web offset press is composed of 2 metal rollers and 1 rubber roller. The paper feed speed of the paper belt is mainly generated by the paper feed roller and its stepless speed changer. Therefore, the quality of the adjustment here will directly affect the printing quality and folding quality.
1. Adjustment of paper feed roller pressure
Before adjustment, the paper feed roller should be cleaned, and the residues such as latex, double-sided adhesive or crayon marks should be removed to avoid affecting the adjustment work. There are two requirements for the adjustment of the pressure of the paper feed roller: first, the pressure at both ends must be the same; second, the pressure should be appropriate.
In order to ensure the same pressure on both ends, it is not recommended to adjust the inconsistent pressure on both ends to solve the problem of inconsistency between the ends of the paper roll. It is recommended to turn the paper roll toward the outside. To make the tension on both sides of the machine exactly the same, it is not easy to achieve. Turning the paper roll is to use uneven machine tension to make up for the shortcomings. If it doesn't work, it means that the tension of the two ends of the paper roll is too different. Even if the paper feeding force is adjusted by adjusting the machine, it can barely be printed. After the operation, it will become very troublesome to adjust the parts of the machine to the original state.
Appropriate pressure means that the pressure can neither be too small nor too large. If the pressure is too low, there will be a slip phenomenon between the paper belt and the feed roller, which cannot truly reflect the surface linear speed provided by the continuously variable transmission; the pressure is too high, which increases the machine load. When checking whether the pressure is appropriate, a paper strip with a width of about 2mm can be used to pull the paper strip out forcefully and continuously. In short, when adjusting the pressure, rather than light.
2. Adjustment of continuously variable transmission
Continuously variable transmission is the most important source of paper feeding force of JJ204 web offset press. Considering that the size of the paper feeding force will affect the size of the paper receiving force in the future, therefore, the adjustment of the continuously variable transmission is very important for the entire paper feeding process. The causes of 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, we must be careful and ensure accurate adjustment.
The so-called cautiousness means that when the machine fails, if the paper brand and basis weight have not changed, the folding machine or the post-printing part are generally the main reasons. Although it is very convenient to adjust, just move it with one hand, but if it is not adjusted properly, the problem can not only be solved, but may also bring new problems. The so-called precision means that when adjusting, don't be afraid of trouble, but work hard and strive to adjust to the best point.
The CVT is improperly adjusted, and there are two extreme states: too slow, the paper belt breaks; too fast, the paper belt pulls down and stretches. In order to be fast or slow, the author's approach is divided into three steps: adjustment of the pressure-off state; adjustment of the pressure-on state; fine-tuning of the two groups together. In order to adjust accurately, the first two steps first use a single paper path, individually adjusted in groups. The direction of adjustment is from loose to tight. If it is too tight at the beginning, the paper tape is easy to break and the adjustment cannot be continued. If you want to avoid the influence of the last adjustment on this adjustment, you can cut off the paper tape and re-thread the paper before the test machine.
Take-up flower roller and pressure rubber wheel
The printed paper tape is sent to the folding machine for folding. This action is completed by the cooperation of the take-up flower roller and the pressure rubber wheel. There is a maximum traction force between the take-up flower roller and the pressure rubber wheel on the paper belt. There are two sources for this maximum value: one is the tension at the take-up roller, which is determined by the theoretical error in the design and manufacture of the machine; the second is whether the paper belt slides on the take-up roller, that is, the rubber The wheel is not tight.
The rubber cylinder diameter of JJ204 web offset printing machine is 175mm, the diameter of the take-up roller is 153.3mm, the transmission ratio between the transmission gear of the rubber cylinder and the transmission gear of the take-up roller is 27:31. The 27-turn take-up roller turns 31 times. The distance traveled by any embossing line after 27 revolutions of the rubber roller is 27 × 175 = 4725mm, and the distance traveled by the take-up roller 31 revolutions is 31 × 153.3 = 4752.3mm. , The take-up roller is 1.01mm more than the rubber roller (<4752.3-4725> ÷ 27). This creates tension. From the above analysis, it can be seen that if the pressure of the pressure rubber wheel on the take-up roller is small, then the paper belt will slide on the take-up roller and the take-up force will become smaller.
In addition, the wear and aging of the pressure rubber wheel and the accumulation of ink skin on the surface of the paper collection flower will also affect the size of the paper collection force. It must be timely resolved in the work. In short, there are two requirements for the pressure of the paper pressing rubber wheel on the take-up roller: one must be consistent, and the other must be suitable. In general, it can be properly tightened.
Set square and paper guide roller
The main function of the triangle board and the paper guide roller is to longitudinally fold the paper tape. The adjustment of the take-up flower roller, the pressure rubber wheel and the continuously variable transmission only lay a good foundation for smooth folding. Specific to the quality of folding, in terms of vertical folding, the adjustment of the triangular plate and the paper guide roller is very important; in terms of horizontal folding, the adjustment of the three-roller folding machine is very important.
The triangle plate and the paper guide roller have two prerequisites for the influence of tension: one is that the paper belt does not slide between the take-up roller and the pinch roller; the other is that the paper belt does not slide between the two knurling rollers.
1. Set square adjustment
The upper and lower nose tips of the set square have an effect on the tension. The influence from the top is small. When adjusting, the plane of the triangular plate should be in the tangent direction of the circle of the feed roller section. The effect underneath is greater. A slight adjustment of the nose tip's advance and retreat changes the pitch of the set square and the tension at the mid-seam. This method is usually used in conjunction with the paper guide roller to adjust the position of the seam of the paper tape or solve the problem of tearing.
2. Paper guide roller adjustment
The adjustment of the paper guide roller is divided into two places: one is the middle seam and the other is the paper edge.
The main function of the mid-seam adjustment is to maintain a proper gap with the tip of the triangular plate to ensure that the paper tape smoothly enters the folding machine. 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-page sticker is appropriate. This gap is neither too large nor too small, it is not easy to cause a break, it is also very 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 crease of the paper tape, and at the same time, it also changes the magnitude of the tension between the seam of the paper tape and the paper edge. The narrower the gap between the paper guide rollers, the greater the tension on the edge of the paper and the smaller the tension on the middle seam; If the adjustment is not good here, it will cause the paper tape to be broken or torn, so when adjusting, pay attention to whether the middle seam is aligned, and carefully listen to the sound of the paper with no "pit" broken Comprehensive adjustment of the forward and backward movement of the set square.
Paper roller
The main function of the paper tightening roller is to pull the paper belt and feed the longitudinally folded paper belt into the three-roller folding machine in a balanced manner. In order to increase the friction of the traction paper belt, the tight paper roller is equipped with rolling wreaths at both ends. The adjustment content of the pinch roller includes axial adjustment and radial adjustment.
The axial adjustment is mainly to adjust the relative position of the roll wreath on the shaft to adapt to the change of the width of the paper tape or the position of the printed image and text, so that the roll wreath is pressed on the empty part that does not affect the quality of the print.
The radial adjustment is mainly to adjust the pressure of the two tight paper rollers on the paper belt. The quality of the radial adjustment will affect the change of the tension of the paper tape. If it is too tight, it is easy to break; if it is too loose, the longitudinal position of the paper tape is unstable. During the measurement, the thickness of the paper belt passing between the two tight paper rollers should be taken as the standard, that is, the thickness of 2 sheets of paper is used as the measurement standard when the single paper path; the thickness of 4 sheets of paper is used as the measurement standard when the double paper path is used. The magnitude of the pressure is better to be able to see slight knurling.
The paper tightening roller is a pair of steel rings that roll against each other, so the wear is faster. When a paper folding knife is used to plug the paper, there is a position that suddenly tightens the paper tape. Therefore, the wear on the roll wreath is uneven. Replace in time.
Common causes 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 mechanism components.
1. Paper tape drift
Cause: The tension is too low, the feed speed is too fast, the take-up speed is too slow or the tension roller is too loose.
2. Double paper path paper tape drift
Cause: The tension of the two paper belts is inconsistent, one fast and one slow. When entering the take-up roller at the same time, the tension will drift back and forth.
3. Tear or tear
Cause of failure: too much tension, too slow paper feed speed, too tight roller or too high folding knife.
4. Overprint is not allowed
Cause: The tension is too small or too large, which results in unstable paper feed.
5. The discount is not allowed to go up and down, like a stock chart
The cause of the failure: too much tension, resulting in unstable pages.
6. Change the hanging needle frequently
Cause of failure: high tension.
7. Replace rubber knife pads (commonly known as rubber strips) frequently
The cause of the failure: the tension is small, the paper is not tight or the cutting force is too large, resulting in serious wear.
Everything is connected with each other, and the tension of the paper tape is no exception. If the paper feed speed is too fast and the paper feed force is too small, it will affect the printing, receiving, and folding parts. Therefore, this point should be noted when analyzing the fault. When adjusting the tension control components, pay attention to the adjustment sequence. First adjust the components that have little impact on other aspects and those that can be adjusted in the shutdown state. Specifically, it is to adjust the tension roller, take-up roller and magnetic powder brake first, then adjust the paper guide roller and triangle plate, and finally adjust the continuously variable transmission. As long as we think more and continue to summarize in our work, the tension problem is not difficult to solve.
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