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Method for Solving Moisture Control Problems in Corrugated Cardboard
During production, many manufacturers encounter problems with inaccurate moisture control of corrugated cardboard. Excessive moisture can cause cartons to collapse or develop surface condensation, while insufficient moisture can lead to cracking and breakage. Moisture control is therefore a critical factor in corrugated cardboard production.
Proper moisture control is essential throughout the processing of corrugated board. When moisture content is too high, the cardboard becomes soft and weak, and cartons may collapse or develop condensation after forming. When moisture content is too low, the board becomes hard and brittle and may crack during box forming. High-quality corrugated board and cartons can only be produced by strictly controlling moisture levels.
Moisture content is influenced by multiple factors. The moisture content of base paper entering the factory should comply with national standards and is generally maintained between 9% and 12%. The delivery condition and storage environment of the base paper are also critical.
Raw Material Control
The first step is to inspect raw materials and measure the moisture content of incoming base paper, ensuring suppliers provide qualified paper. Base paper should be stored in a dedicated warehouse with a temperature of 15–20°C and relative humidity of 30–40%. It should not be stored outdoors, as exposure can cause uneven moisture distribution, increasing processing difficulty.
Temperature Control
Temperature is one of the most important factors affecting corrugated board quality. Proper heating adjusts moisture content and provides the conditions necessary for adhesive curing. Corrugated board production lines are therefore equipped with preheaters and drying plates to regulate moisture and bond layers effectively.
Production speeds are typically above 100 m/min, and adhesive curing temperatures generally range from 160–180°C, requiring saturated steam pressure of approximately 0.9–1.4 MPa.
Single-Facer Moisture Adjustment
During single-faced board forming, the optimal moisture content of base paper is 9–12%. This is controlled by adjusting preheating rollers, preheaters, and spray devices before and after the single-facer.
- If moisture is too high and temperature is adequate, increase the wrap angle and preheating area to reduce moisture.
- If maximum preheating is insufficient, reduce machine speed.
- If temperature is insufficient, increase boiler steam pressure to achieve saturated steam.
- If moisture is too low, reduce preheating and use spray devices to add moisture, or increase line speed.
Moisture and temperature should be monitored using moisture meters, thermometers, or pressure gauges. As a practical method, properly adjusted single-faced board will lie flat on the conveyor. When thermometers are unavailable, saliva placed on the preheater evaporating immediately indicates a temperature above 150°C, suitable for production.
Dryer Section Control
The dryer significantly affects final moisture content. Dryers typically consist of multiple heating plate groups with adjustable steam pressure. Before entering the dryer, moisture changes may occur due to storage time on the bridge conveyor, especially when adhesive moisture is high. Preheating adjustments should be made accordingly.
Inside the dryer, ensure proper adhesive gelatinization, then adjust steam pressure to achieve suitable moisture levels. Cooling section length also affects moisture distribution. If cooling is insufficient, forced air may be used.
If moisture remains too high, reduce line speed; if too low, increase speed.
The dryer should not be stopped unless absolutely necessary. During paper roll changes, additional single-faced board should be accumulated on the bridge to prevent dryer stoppage, as stopping can cause excessive drying and scrap.
Steam System and Condensate Removal
Steam pressure and condensate removal directly affect heating efficiency. Condensed water must be discharged promptly to maintain preheater performance.
If temperature differences across the preheater exceed 5°C, inspect steam traps for damage or improper installation. Steam traps should have sufficient drainage capacity and be inspected weekly.
Adhesive Control
Adhesive quality, water ratio, and viscosity strongly influence board moisture. Excessive water increases moisture content, while insufficient water reduces it.
Adhesive preparation should strictly follow specified ratios and mixing times. Typical viscosity values:
- Single-facer: 50–60 seconds
- Double-backer: ~100 seconds
Fresh adhesive prepared on the same day should be used for best results.
Glue Application Amount
Glue quantity directly affects moisture content. Excess glue increases moisture; insufficient glue reduces it.
Roller gaps should be adjusted precisely using feeler gauges:
- Single-facer glue roller gaps: 0.2–0.25 mm
- Pressure roller gap: 0.1–0.2 mm
- Double-backer gaps adjusted according to board thickness
- Glue line width is generally 1.5–2 mm.
Damaged rollers or foreign matter can cause uneven glue application and uneven moisture. Rollers should be replaced if worn and cleaned daily.
Conveyor Belt and Storage Issues
Poor belt permeability or spraying water on belts increases moisture. Belts should be kept clean and replaced when worn. Water should not be sprayed on conveyor belts.
Excessive accumulation of single-faced board on bridge conveyors can cause moisture loss. Storage should be limited to 2/3–3/4 of conveyor length, and line speeds should be coordinated across stations.
Environmental Factors
Climate also affects moisture. During hot, humid seasons, adhesive performance changes and moisture control becomes more difficult.
Measures include increasing heating area, reducing spray water, lowering adhesive moisture, and fully utilizing preheaters.