In the production process, many people have encountered the problem that the moisture control of corrugated cardboard is inaccurate, and the problem is too large (carton collapse, corrugated) or too small (cardboard breakage), and this problem is precisely very important. .
In the process of manufacturing corrugated cardboard, the control of the moisture content of the cardboard is very critical. When the water content is too high, the processed corrugated cardboard will appear soft and not stiff, and will cause collapsed and exposed corrugated boxes after being formed into boxes. When the water content is low, the processed corrugated cardboard becomes hard and brittle, and easily breaks after being boxed. Therefore, only by strictly controlling the moisture content of corrugated cardboard, high-quality cardboard and carton can be produced. Of course, the control of the moisture content of the cardboard is a very complicated matter. It is determined by many factors, mainly including: the moisture content of the base paper entering the factory must be strictly controlled in accordance with the provisions of national standards, the delivery status of the base paper The water content is generally 9% to 12%.
To meet this requirement, the solution is to first check the quality, inspect the moisture content of the base paper entering the factory, and require the supplier to supply qualified base paper. In addition, a separate warehouse must be set up for the storage of raw paper. The temperature is generally 15 ° C to 20 ° C, and the relative humidity is generally 30% to 40%. Do not put it in the open air, otherwise it will easily cause the moisture content of the base paper to change, and make the moisture content at both ends and the middle part inconsistent, which will bring greater difficulty to the subsequent processing.
Temperature is one of the determinants of corrugated board quality.
The temperature can not only adjust the moisture content of the base paper, but also make the base paper have a certain temperature, which is an important condition for curing the paste. Therefore, in a corrugated cardboard production line, many preheaters and drying boards are installed, which are used to adjust the moisture content of the base paper and single-sided cardboard, and make the paste solidify and adhere the corrugated cardboard layers. Generally, the vehicle speed is above 100m / min, and the curing temperature of the paste is usually 160 ° C to 180 ° C. In other words, the pressure of the boiler saturated water vapor should reach 0.9MPa to 7.4MPa.
Because to produce qualified corrugated cardboard, it is necessary to go through different equipment, and different equipment has different effects on the moisture content during the formation of corrugated cardboard, which are described below:
According to the analysis of the tension in the forming process of the single-sided corrugated cardboard by the single-sided machine, we know that in the corrugated forming, the moisture content of the raw paper entering the single-sided machine is 9% to 12%. According to this principle, we must make full use of the preheating roller on the single-sided machine and the preheating machine and spray device before and after the single-sided machine to adjust the moisture content of the base paper.
The method is: when the temperature of the preheating roller reaches the requirement and the moisture content of the base paper is too high, adjust the movable paper guide roller of the preheating roller, increase the preheating wrap angle, increase the preheating area, and reduce the moisture content of the base paper , Meet the standard requirements. If the preheating area of ​​the preheating roller is adjusted to the maximum, the moisture content of the base paper is still too high, and it can be solved by reducing the vehicle speed.
If the water content is too high and the temperature of the preheating roller does not meet the requirements, the steam supply pressure of the boiler must be increased so that the steam it supplies reaches saturated water vapor, and the pressure reaches 0.9MPa to 1.4MPa.
If the moisture content is too low, it is necessary to adjust the movable paper guide roller to reduce the preheating area. At the same time, the spray device on the preheating roller and the single-sided machine is used to spray the base paper to increase the moisture content of the base paper to meet the standard requirements. At the same time, the method of increasing vehicle speed can also be used to solve the problem of low water content.
For the moisture content and temperature of the base paper, you can measure it at any time with a moisture meter and a thermometer or look at a pressure gauge, and adjust it at any time according to the measurement results. Of course, in addition to instrument measurement, the "soil" method can also be used. According to our experience, if the single-sided corrugated cardboard on the flyover conveyor belt is in the shape of positive ∞, it means that the moisture adjustment of the base paper and the tile paper is better, and the moisture content is also more appropriate. When there is no thermometer, as long as you spit a saliva on the preheater, the saliva can rise on the preheater, which means that the temperature has exceeded 150 ℃, and production can be carried out.
The temperature of the dryer greatly affects the moisture content of the corrugated cardboard formed. Since the heating plates of the dryer are generally divided into three groups, each group consists of four, five and six heating plates. Each group of heating plates is equipped with a pressure regulating valve, which is used to adjust the pressure of steam entering the heating plate, thereby changing the temperature of the heating plate, so as to produce high-quality corrugated cardboard.
The treatment method is: before the single-sided corrugated cardboard enters the dryer, the moisture content of the single-sided cardboard is stored on the flyover for different lengths, and the moisture content has changed. On the triple preheater, preheat the single-sided machine board. During the preheating process, it is also necessary to properly adjust the movable paper guide roller according to the size of the water content, and change the preheating area so that it reaches the appropriate water content.
After entering the dryer, we must first ensure that the paste is gelatinized, and then adjust the pressure-reducing valve according to the water content to make it get the right temperature, so as to get the right water content. Of course, the length of the cooling section of the dryer also affects the moisture content of the cardboard. When the cooling section is too short, if the moisture cannot be distributed in a timely manner, you can blow it with a blower.
When the temperature adjustment does not meet the ideal requirements, you can use the method of changing the speed to adjust. If the water content is too high, the speed can be slowed down; when the water content is too low, the speed can be increased.
When the dryer is working, it is less than a last resort and cannot be stopped. When the front single-sided machine needs to replace the paper roll, the single-sided machine can speed up the sports car before the roll change, accumulate a part of single-sided cardboard on the flyover, and the dryer can run at a reduced speed after receiving the paper change notification. When the dryer is stopped, the moisture of the cardboard on the dryer is completely evaporated, causing all the cardboard to be scrapped.
Influencing the temperature of the cardboard production line, in addition to whether the saturated steam supplied by the boiler reaches the specified pressure, the drainage device of the steam piping system is also very important. Because the base paper and single-sided cardboard pass through each preheater, a large amount of heat needs to be taken away, and part of the saturated steam becomes condensate. This part of the condensate must be discharged in time, otherwise it will affect the preheating effect of the preheater.
Solution: If the preheating roller of the rotary head is used, the temperature paper or the temperature difference between the two ends is more than 5 ℃, it means that the suction pipe is damaged or the installation position is wrong, and it needs to be disassembled for maintenance.
The drain capacity of the trap is 2 to 3 times that of the condensate. If the drain capacity is not enough, the trap should be replaced.
Check the drain outlet of the steam trap every week, and clean it if it is blocked.
The quality of the paste, the amount of water and the thickness of the paste have a great influence on the moisture content of the cardboard.
If the amount of water in the paste is large, the paste is thin, the penetration is fast, and the moisture content of the cardboard is high. Conversely, the water content is small.
The solution is to make the paste strictly in accordance with the amount of water and the ratio of the paste and the mixing time, and master the viscosity of the paste. Generally, the viscosity of the single-sided machine is 50 to 60 seconds, and the double-sided glue machine is about 100 seconds, and the double-sided glue machine should use the new paste made on the same day. Only when a good paste is produced can a qualified cardboard be produced.
The amount of paste affects the moisture content of the cardboard.
When the paste is the largest, the moisture content of the cardboard is large, and the moisture content is small when the paste is small.
The processing method is: for a single-sided machine, adjust the gap between the top roller and the rubber roller, the top roller and the main corrugated roller. In general, the gap between the glue roller and the rubber scraper roller is 0.2 to 0.25 mm, and the gap between the glue roller and the main corrugated roller is generally 0.1 to 0.2 mm. The measurement method is the same as that of feeler gauge, and both ends must be consistent.
The gap between the squeegee roller and gluing roller of the double-sided gluing machine is 0.2 to 0.25 mm. The gap between the pressure roller and the top roller should be 0.05 to 0.1 mm lower than the height of the corrugated cardboard of the single-sided machine passing through. The measurement method is to use a feeler gauge, and the data at both ends should be consistent. Whether it is a single-sided machine or a double-sided glue machine, the width of the corrugated cardboard glue line produced is generally 1.5 to 2 mm.
If the surface of the glue roller is damaged or there is foreign matter, the uneven glue application will affect the uneven moisture content of the cardboard.
The solution is: if the roller surface is worn or damaged, replace the rubber roller as soon as possible. If there is any foreign object, stop and remove it immediately. All top rollers should be cleaned every day after work, and any foreign objects should be removed with a soft brush.
If the conveyor belt of the dryer has poor air permeability, or sprays water on the conveyor belt at will, it can cause a large moisture content of the cardboard. The solution is to analyze the reasons for the poor air permeability of the conveyor belt. If any waste paper sticks, stop it immediately If the large belt is used for a long time, it must be replaced with a new belt. Do not spray water on the conveyor belt casually during use.
If there is too much single-sided cardboard stacked on the conveyor belts of each single-sided machine on the flyover, the time is long, and the moisture is distributed more, it is easy to cause the moisture content of the cardboard to be less
The solution is: the operation stations of the whole line should be in constant contact, take care of each other, and the operation speed should generally be unified. The storage capacity of the single machine board on the conveyor belt of each single-sided machine on the flyover can best account for 2/3 or 3/4 of the length of the conveyor belt.
Climate and environment will also affect the moisture content of the cardboard.
In the high-temperature and rainy season, the relative humidity is high, and the fluidity of the paste in winter is poor, and the amount of paste is small, which will affect the moisture content of the cardboard.
The solution is: in the season with high temperature, increase the heat area, reduce spraying, reduce the water content of the paste, increase the temperature, and make full use of the preheating roller to adjust the water content.
In short, there are many factors that affect the moisture content of the cardboard, which requires the operator to strengthen his sense of responsibility, carefully observe, and carefully adjust to produce qualified corrugated cardboard.
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