The Role of Glue Rollers in the Formation of Corrugated Cardboard
To ensure the strength and good adhesion of corrugated cardboard, adjustments should be made according to the configuration of the corrugated cardboard production line.
1. The ideal moisture content of the corrugated base paper entering the single facer should be controlled between 9% and 12%. If the moisture content exceeds this range, increasing the preheating area or reducing the speed can help. Conversely, if the moisture content is below this range, spraying can be used to address the issue. It is believed that when single-face corrugated cardboard is transported in a consistent and orderly manner on the bridge conveyor, with the base paper and corrugated medium having adjusted moisture content, the accumulation of single-face corrugated cardboard on the bridge should not be excessive. However, to ensure that the double facer does not stop during paper changes, the accumulation can be slightly increased during the paper change of the single facer.
2. The temperature of the dryer significantly affects the moisture content of the corrugated cardboard. The heating section of the corrugated cardboard production line typically consists of three (or sometimes four) groups, with the number of heating plates determined by their size and the speed of the production line, and each group equipped with independent control valves. To ensure that the moisture content of single-face corrugated cardboard entering the dryer is relatively uniform, adjustments can be made to the preheating area on the triple preheater. If the moisture content is too high, increase the preheating area; if too low, decrease it.
3. During the production of corrugated cardboard, a large amount of heat is removed, and some saturated steam in the preheater and corrugating rollers condenses into water. This can typically be drained through a condensate trap. To ensure proper drainage of the condensate, it is suggested to open the bypass valve of the condensate trap for 3 to 5 minutes every 4 hours to maintain relative temperature stability.
Controlling the glue application is essential; the adhesive commonly used for corrugated cardboard production is corn starch-based, primarily composed of corn starch, water, sodium hydroxide, and borax. Due to different configurations and speeds of the production lines, the viscosity, concentration, and gelatinization temperature of the adhesive will vary. The moisture content of the corrugated cardboard changes with the amount of glue applied: a higher glue application leads to higher moisture content and vice versa. For the glue rollers and glue limit rollers of the single and double facers, the gaps are generally between 0.2mm and 0.25mm; for the single facer, the gap between the lower corrugating roller and the glue roller is typically between 0.1mm and 0.2mm; for the double facer, the gap between the pressure roller (pressure rod) and the glue roller should be slightly lower than the height of the single-face corrugated cardboard by 0.05mm to 0.1mm. These gaps can be measured using feeler gauges, but it is important to ensure that the rollers are parallel.
With changes in temperature and relative humidity (summer and winter), the amount of glue applied may decrease. In summer, the viscosity of the adhesive becomes thinner, which can be adjusted by increasing the solid content and using corrugated base paper with a high ring crush index and low moisture absorption. In winter, the fluidity of the adhesive is poor; increasing the temperature of the adhesive can help maintain its good flow. Besides the factors mentioned that affect the strength of corrugated cardboard, strengthening the responsibility of operators and improving their skill levels are crucial. Each operator should be able to observe carefully, make precise adjustments, and strictly follow the process requirements to produce high-quality corrugated cardboard.
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