[China Packaging Network News] It is another year that the rainy season is coming and there is a lot of wetness. There is nothing more painful than this in the production and printing of corrugated cardboard. The soft cardboard not only reduces the pressure resistance of the carton by half, but also easily causes creases and pits, and causes the printed bottom.
In order to solve the problem of softness of corrugated board, besides replacing the most direct and effective method of high-strength corrugated paper whose surface water absorption is less than 40 g/m2 (60S), the control of temperature during the production of corrugated board is also strengthened. Result. By controlling the temperature, the moisture content of the corrugated base paper can be adjusted, and the curing time of the paste liquid can also be controlled, thereby achieving the purpose of controlling the bonding speed and the firmness of the corrugated paper. Therefore, the control of temperature is a very important part of the production process of corrugated paper.
1. Temperature control of one-side unit
According to the analysis of the tension in the forming process of corrugated cardboard, the best moisture content of the raw paper entering the single-sided machine is 9% to 12% during the forming of the corrugated cardboard. According to this principle, it is necessary to make full use of the preheating roll on the single-sided machine and the preheater and sprayer before and after the single-faced machine to adjust the moisture content of the base paper.
If the water content of the base paper is too high, after the temperature of the preheating roller reaches the requirement, the movable guide roller of the preheating roller may be properly adjusted to increase the preheating wrap angle of the base paper and increase the preheating area. It plays a role in reducing the moisture content of the raw paper. If the warm-up area of ​​the preheating roller is adjusted to the maximum and the moisture content of the original paper is still too high, the method of reducing the speed of the vehicle should be adopted.
When the moisture content of the base paper is too high, the pre-adjusted preheat roll temperature may sometimes be lowered so that the preheating requirement cannot be achieved. At this time, under the premise of the conditions permitting, the boiler steam supply pressure should be appropriately increased to achieve the purpose of increasing the preheating roll temperature.
If the moisture content of the base paper is too low, it is necessary to adjust the movable paper guide roller accordingly to reduce the preheating area. At the same time, the base paper is sprayed using the preheating roller and the spray device on the single-sided machine to increase the moisture content of the base paper to meet the standard requirements. In addition, by properly increasing the speed of the vehicle, the contact time between the base paper and the preheating roller can be reduced in phase, and the problem of low water content can be solved to a certain extent.
The moisture content and temperature of the base paper should be measured at any time using a moisture meter, thermometer, or pressure gauge, and adjusted according to the results of the measurement. Some materials mentioned some “earth†methods, such as observing the single-sided corrugated cardboard on the overpass conveyor belt. If it is a positive ∞ font, it can be considered that the moisture content of the base paper is better and the water content is more appropriate; When the thermometer is on, spit saliva on the preheater. If the saliva can be picked up on the preheater, it means that the temperature has exceeded 150°C and can be produced. However, for the purpose of scientifically managing production and ensuring product quality, these methods are less suitable. As a regular company, it is necessary to reduce the influence of human factors, comply with scientific and accurate data, and manage production.
2. Dryer temperature control
The temperature of the dryer directly affects the moisture content of the final molded corrugated board. The heating plate of the dryer is generally three groups, each group is composed of four, five, six heating plates. Each set of heating plates of a steam-heated dryer is provided with a pressure regulating valve for adjusting the steam pressure entering the heating plate to change the temperature of the heating plate to ensure that a high-quality corrugated paperboard is produced. Among these, you need to pay attention to the following details.
Before entering the dryer, the moisture content will change due to the different lengths of time the single-faced corrugated cardboard is stored on the flyover. In addition, after a period of time, the moisture content of a single-sided machine paste will change, which will in turn cause a change in the moisture content of the single-faced corrugated cardboard. Therefore, prior to the final recombination, the single-sided corrugated board needs to be preheated twice. This preheating process also needs to be properly adjusted according to the amount of water content, that is, the purpose of adjusting the water content of the corrugated board by adjusting the movable paper guide roller and changing the preheating area.
The purpose of drying, first of all, is to ensure that the paste liquid curing, while the adjustment of the water content of corrugated board, the two can not be neglected. Therefore, the pressure reducing valve should be adjusted at any time according to the moisture content of the single-faced corrugated board so that the dryer can reach a suitable temperature, which not only ensures the solidification of the paste, but also ensures that the final formed corrugated board has a moderate moisture content. In addition, the length of the dryer cooling section also has a certain influence on the water content of the board. When the cooling section is too short, moisture cannot be volatilized in time. At this time, it is necessary to increase the amount of local air supply to achieve the purpose of drying.
If you can't reach the ideal situation through the conventional temperature adjustment, you can try to use the method of changing the speed of the adjustment. That is, if the water content is too high, the speed will be slowed down, and if the water content is too low, the speed will increase.
When the dryer is working, there is no last resort to stop. If the single-sided machine needs to replace the paper roll, the speed of the sports car can be faster before changing the roll and accumulating part of the single-sided cardboard on the flyover. After the dryer receives the paper change notification, it can run at a reduced speed. If the dryer shuts down, the board moisture on the dryer will evaporate completely, causing the board to be scrapped.
3. Influence of hydrophobic device on temperature
For the temperature of the corrugated board production line, in addition to the pressure of steam supplied by the boiler, the hydrophobic device of the steam piping system is also very important. This is because when raw paper and single-sided paperboard pass through each preheater, it will take a lot of heat, so that partially saturated water vapor condenses into liquid water. This part of the condensate must be discharged in time, otherwise it will affect the heating effect of the preheater.
In the daily work, for the preheating roller with rotary steamer, if the temperature is low or the temperature difference between the two ends is more than 5°C, it means that the suction pipe is damaged or the installation position is wrong, and it must be opened for maintenance. In general, the flow index of the trap should be 2 to 3 times that of the condensate. If the amount of water trap is not enough, the trap should be changed. In addition, in the daily operation and production, we should develop good habits. Check the trap outlet of the trap every week and find that the plug must be cleaned in time.
During the start-up operation of the corrugated paper production line, the above sections should be inspected and adjusted at any time. Only in this way can we guarantee the production of qualified products.