Corrugated paperboard production line production corrugated paperboard is prone to warp phenomenon. The warped corrugated paperboard brings many difficulties to the production of the next process, such as printing slotting and walking rules. This course mainly explains the causes and principles of warping in the production process of corrugated cardboard. Through detailed analysis, the personnel involved in the operation of the tile line will understand the comprehensive solutions of horizontal warping, vertical warping, and S-curving.
Five factors affecting the bending of corrugated cardboard!
1. The correctness and proficiency of personnel operation technology
In the process of paperboard production, the most important factor is people first. If people's mental state is not good, the paperboard cannot be adjusted. Secondly, lack of knowledge, many people do not know the paperboard bending at all. The reason for the warp, so they do not understand how to adjust; the last is the problem of execution, for example, everyone knows the cause of the warpage of the cardboard, but no one comes forward to coordinate and execute, and this will also cause problems. Therefore, it is impossible for one person to adjust the warpage of cardboard. The warpage of cardboard needs the coordination of the entire production line.
2. The perfection of the function of machine equipment
(1) Downtime
The longer the corrugated production line stops, the greater the degree of cardboard warpage. If the corrugated production line is frequently shut down, the probability of cardboard warping will be greatly increased. The reason is that once the equipment is shut down, the cardboard will stay on the drying tunnel. The longer the shutdown time, the more the cardboard will warp.
When the paperboard stays on the drying tunnel, the bottom paperboard will dry quickly, the upper paperboard will dry slowly, and the moisture of the lower paperboard will be easily transferred to the top paperboard. As the moisture evaporates from the bottom up, the moisture of the upper cardboard becomes higher and higher, and the moisture of the cardboard below becomes less and less. When the moisture returns to equilibrium, the cardboard naturally bends upward. Therefore, it is particularly important to control the number of abnormal downtimes and abnormal downtime.
(2) Production speed
The production speed will directly affect the evaporation of moisture from the cardboard. Generally speaking, at a speed of 150 m / min, the moisture is reduced by 2%; at a speed of 45 m / min, the moisture is reduced by 4%. It can be concluded that the slower the vehicle speed, the more water will be transferred from the bottom up, and the greater the probability of the cardboard warping.
(3) Preheating cylinder
a. Running speed: the speed will affect how much heat the preheating cylinder transfers to the paper.
b. Coated area: the more coated, the more heat is transferred, and the more water is evaporated; the less coated, the less heat is transferred, and the less water is evaporated.
c. Tension of the base paper: The larger the wrap angle of the preheating cylinder means the tighter the wrap, the greater the frictional force. Conversely, the smaller the wrap angle, the looser the wrap.
d. Original paper contact surface: It has a certain relationship with the contact surface (backing paper or facial paper). As some people say, if the original paper is changed to another side, the cardboard will be flat, which is caused by the different tension of the inner paper.
Of course, in the process of adjusting the above points, the balance roller needs to be adjusted synchronously.
3. Control of the moisture uniformity of the base paper
Each 1% change in the moisture content of the base paper will change the size of the corrugated cardboard by 0.06% to 0.10%. Because the change of moisture content can reach 15% -20% during the passage of the corrugated board production line, it may cause a relative change of 0.9% -2% in the size of the board. If the moisture error reaches 3%, it is enough to cause the cardboard to warp.
And the moisture of the same paper roll also needs to be controlled within 3%, otherwise it will also cause different degrees of cardboard warpage. Whether it is different rolls of paper or the same roll of paper, if the moisture on both sides and the middle of the cardboard changes, it will cause different degrees of warping. Therefore, careful control of the moisture content of the base paper is essential for the production of flat cardboard.
Measurement of moisture content at normal speeds shows that the amount of moisture removed in the "loosened" area of ​​the paper web is a bit lower than in the "tight" area. The fluffiness of the paper roll is actually a change of moisture, and it has two effects: first, it affects the tension, that is, the tensile force; second, it affects the moisture of the cardboard, which is itself caused by moisture.
Another very important factor is the flyover. When the overpass is running normally, the paperboard produced is straight; when the overpass is empty, the trajectory of the cardboard warpage is shifted in the reverse direction; when the overpass has too much paper, the trajectory of the cardboard warpage is shifted in the positive direction, These are caused by how much water is dispersed.
In addition, the single-wafer section and the double-wafer section should be operated at the same speed. The continuous production of corrugated cardboard production line not only needs to be connected, but its constant production speed will minimize the problem of cardboard warpage.
4. Stability and reliability of heating and gas supply
The heat and gas supply needs to be stable, continuous and uniform. If the air supply is unstable and the vehicle speed is stable, it will cause the inconsistent heat of the cardboard to form a warp.
By the way, the amount of paste, we just need to remember that more glue is more water. Because the water-powder ratio is 3: 1, all the water going up will evaporate. If you have more glue on a certain part, it means that this part also has more water. Due to the different shrinkage at the time of moisture balance, the cardboard is warped.
There are three factors that affect the state of gluing: the gap between the cutting roller and the gluing roller will directly affect the amount of gluing; the gap between the gluing roller and the corrugated roller will directly affect the amount of gluing; the number of mesh lines of the gluing roller will also affect the Paste amount.
5. Natural climate of production environment
In the storage section of cardboard, there are also factors that affect the unevenness of the cardboard, such as the skewness of the cardboard stack, and the exposed cardboard due to the difference in the distribution area and the force, which causes the warping. In addition, the outdoor temperature and humidity will also cause the cardboard to warp. If the humidity is high, it will easily warp.
Four solutions for corrugated cardboard bending!
Equipment, paper selection, in-process control and post-stage processing are all factors that affect the warpage of the cardboard, and solving the warpage of the cardboard is controlled according to these factors. In terms of base paper, the moisture content is generally best at (8 ± 1)%, and the water distribution of the entire door width is uniform (the deviation is controlled within 1%), otherwise it is easy to form an "S" shape or diagonally warped cardboard. In terms of paper distribution, the gram weight of facial paper and backing paper should not be too different. Generally, it should not be more than 50 grams. The base paper with high moisture content and low moisture content should not be produced together.
1. Horizontal upward
The main reason for the horizontal upward warpage of the cardboard is uneven moisture, and the cardboard is bent toward the side with high moisture, that is, the moisture of the inner paper is too high. So how to reduce the moisture in the paper? .
The first method is to reduce the amount of paste on the single-sided machine, while increasing the amount of paste on the machine. Because the two correspond to each other, increase here, and decrease there.
The second method is to increase the moisture of the facial paper. Spray water on the facial paper to increase its humidity. It can also reduce the angle of the cardboard on the preheating cylinder. This can also increase the moisture of the facial paper.
The third method is to reduce the temperature of the hot plate, so that the moisture of the cardboard below is not easily transferred upwards, at the same time, it can increase the speed of the vehicle and solve the problem of the cardboard upwards.
There are two points for the measures on the inner paper. The first method is to reduce the amount of paper accumulated in the flyover, so that the probability of the moisture of the inner paper evaporating on it will be reduced; the second method is to increase the preheating of the inner paper. When the wrap angle of the preheating cylinder becomes larger, the moisture of the cardboard above is reduced. In fact, this is a principle of controlling moisture.
2. Horizontal downturn
The principle of horizontal downward warping is opposite to that of lateral upward warping, because the moisture of the facial paper is too high, which can increase the moisture of the inner paper, increase the amount of glue on the single-sided machine, or increase the amount of paper accumulated on the overpass, because the accumulated paper on the bridge Increase the amount of water will not be easily distributed.
In addition, we can reduce the preheating of the backing paper (backing paper) to make the backing paper more watery, and we can also spray water on the backing paper. We can also reduce the speed of the tile line, that is, increase the speed of the hot plate, these are all It is the opposite of horizontal upturning.
3. Longitudinal bending
Longitudinal bending is mainly caused by tension, and we mainly adjust the angle of the preheating cylinder wrap angle and the brake of the original paper holder. If the brake pulls down, it means that the pulling force of the tissue is too large, and the pulling force of the tissue is too large, then the wrap angle should be adjusted down, and the brakes should be relaxed. The angle between the wrap angle of the cylinder and the position of the large belt below is increased, thereby increasing the pulling force of the inner paper.
4. Equipment control
The equipment must have certain automatic control methods, such as the parallelism of the corrugated roller, pressure roller, paste roller, and the pressure need to be set, otherwise in the case of difficult loading, your adjustment is meaningless. The preheating cylinder and the temperature must be kept uniform. Only when the temperature is uniform can the real change be caused by the increase and decrease of the wrap angle.
In this process, there is also a water spray device. We know that the position of the hot plate, the position of the facial paper, and the amount of paper accumulated in the flyover are all achieved through automatic control, so we need to grasp the control value. Of course, we must also pay attention to the breathability of the conveyor belt. Generally, the better the breathability, the lower the error. All in all, the points mentioned above must have corresponding control values ​​and amplitudes.
Summarizing the above situations, it is summarized as follows:
Causes and solutions of lateral S-curve and diagonal warp
a. The base paper has uneven moisture and uneven paper strength. b. The arm support of the original paper holder is unbalanced, resulting in inconsistent heating of the paper at the wrap angle of the preheating cylinder. c. The installation level of the splicer.
Solution: It is most suitable to calibrate the arm level of the original paper holder or the level of the paper receiving machine, and at the same time add the balance roller.
Causes and solutions of horizontal upward warping
The temperature of the facial paper is too high, and the temperature difference with the base paper is too large, which causes the shrinking force of the base paper after cooling to be greater than that of the facial paper.
Solution: a. Increase the wrap angle of the bottom paper to shrink the bottom paper in advance. b. Increase the amount of facial tissue glue. c. Minimize low-speed operation. d. Properly reduce the steam pressure of the hot plate. e. Reduce the wrap angle of facial tissue. f. Spray the tissue paper properly.
The reason and solution of horizontal warp
The temperature of the backing paper is too high, and the temperature difference between the backing paper and the backing paper is too large, so that the shrinking force of the backing paper after cooling is greater than the backing paper. (The principle and solution are the opposite of Upturn)
Solution: a. Increase the wrap angle of facial tissue to shrink the facial tissue in advance. b. Increase the amount of base paper glue. c. Minimize high-speed operation. d. Increase the steam pressure of the hot plate appropriately. e. Reduce the bottom paper wrap angle. f. Spray the bottom properly.
Causes and solutions of longitudinal warpage
The tension of the tissue and the single tile in the paste machine are not consistent.
Solution: Adjust the brake tension of facial tissue or flyover.
Small link:
After the cardboard is warped, what are the measures?
The first method is to wipe the surface of the warped cardboard with water and then press forward and reverse.
The second method is to humidify the warped cardboard storage environment.
The third type is back pressure after steam injection. The newly produced cardboard has high temperature and high humidity, and the moisture is distributed from the middle to the surroundings. At this time, it should be stacked in a positive and negative direction, and pressed with a wooden board. After cooling, it is relatively smooth.
What aspects should be paid attention to when stacking freight?
First, the freight driver unloading cardboard should be stacked flat on the pallet, and it is not allowed to exceed the pallet. In principle, stacking upside down can easily cause the cardboard to warp, leading to customer complaints.
Secondly, if the customer's storage conditions are in a ventilated place, the cardboard needs to be wrapped around to prevent the large amount of water loss caused by bending.
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