Common Issues with Corrugated Board Produced on Corrugator Line

 1. Board Warping

Problem Description: After leaving the corrugated cardboard production line, the board is not flat but curves upward, downward, or to one side.

Cause Analysis:

Uneven moisture content: This is the core cause. Different parts of the cardboard (face paper, liner paper, core paper) have inconsistent moisture levels, leading to varying drying shrinkage rates.

Upward Warping: Typically caused by excessively high moisture content in the face paper or overly dry liner paper. The face paper has a higher shrinkage rate than the liner paper.

Downward Warping: Opposite of upward warping, caused by excessively high moisture content in the liner paper or overly dry face paper. The liner paper has a higher shrinkage rate than the face paper.

S-curve warping: Lateral warping usually caused by uneven cross-directional temperature on the production line or inherent paper defects.

Inappropriate base paper combination: Significant disparities in physical properties (basis weight, sizing degree, compactness, etc.) between face and liner papers result in mismatched internal stresses.

Improper preheater adjustment: Preheaters regulate base paper moisture content and temperature. Mismatched preheating levels for face and liner papers result in differing moisture levels upon entering the paste machine.

Inadequate temperature control: Excessively high or low drying board temperatures, coupled with mismatched machine speeds, cause paper to become over-dried or under-dried.

Solutions:

Adjust preheating area: For upward curling, increase the preheating area for the face paper or reduce it for the liner paper; for downward curling, do the opposite.

Use spray devices (sprayers): Apply a light mist to the dry paper's reverse side (the side contacting the corrugating rollers) to increase its moisture content and balance shrinkage stress. This feature is installed on machines like single facer corrugators.

Adjust base paper configuration: Use face and liner papers with similar physical properties whenever possible.

Optimize production parameters: Set drying plate temperature and production line speed appropriately to ensure even and stable drying of the board.

Use a web guide (guide rollers): Correct boards that have developed slight warping or curling.

2. Cardboard pseudo-bonding (delamination)

Problem Description: The cardboard appears bonded, but applying slight pressure causes the liner/cover paper to separate from the corrugated medium, with visible separation at the adhesive line.

Cause Analysis:

Adhesive Issues: Improper starch paste formulation (ratio of main paste/carrier, borax dosage), excessive or insufficient gelatinization temperature, or inappropriate viscosity.

Improper Glue Application: Insufficient glue volume fails to form a complete glue line; excessive glue volume causes premature gelatinization, loss of tack, and “slurrying” phenomenon.

Insufficient Temperature: Inadequate temperature of the corrugating rollers or hot plates fails to provide sufficient heat for complete starch gelatinization. Gelatinization is the critical chemical process enabling starch to develop adhesive properties.

Insufficient pressure: Inadequate pressure from the pressure roller or hot plate prevents the liner/cover paper from making good contact with the flute peaks and maintaining sufficient contact time to complete bonding.

Base paper issues: Excessive moisture content or overly strong surface sizing in the base paper impedes adhesive penetration and adhesion.

Solutions:

Optimize adhesive formulation: Regularly test and adjust the adhesive formula to ensure its gelation temperature and viscosity suit the current production speed and base paper.

Adjust adhesive application: Inspect and adjust the gap between the adhesive roller and metering roller to ensure moderate and uniform adhesive application.

Check and Increase Temperature: Ensure sufficient steam pressure, inspect steam lines and condensate drainage for blockages, and maintain optimal operating temperatures for corrugating rolls and hot plates (typically 170-185°C).

Adjust Pressure: Inspect and appropriately increase pressure on pressure rolls and hot plates.

Control Base Paper Moisture: For base paper with excessively high moisture content, increase preheating area via the preheater to reduce moisture levels.

3. Washing-board effect

Problem Description: On the linerboard surface, a series of horizontal indentations appear between the flute peaks, resembling a washboard.

Cause Analysis:

Core Cause: The fibers in the liner paper contract due to the drying shrinkage of the adhesive and the pulling force from the corrugated peaks.

Excessive Glue Application: Excessive adhesive creates significant shrinkage stress during drying, pulling the liner paper down between the corrugated peaks.

Excessively high glue gelation temperature: The glue requires higher temperatures to gel, delaying gelation time. This may cause excessive glue penetration into the liner paper, exacerbating shrinkage.

Low-grammage or poor-quality linerboard: Linerboard with low grammage or loose fibers has low strength and is more susceptible to deformation from adhesive shrinkage stress.

Excessive bonding strength between linerboard and corrugated medium: If the linerboard adheres too firmly to the corrugated medium, shrinkage stress is concentrated on the relatively free linerboard.

Solutions:

Reduce adhesive application: This is the most direct and effective method. Minimize adhesive application while ensuring sufficient bonding strength.

Lower adhesive viscosity: Using adhesive with slightly lower viscosity can reduce penetration and shrinkage.

Switch to higher-grammage or higher-quality cover paper: Higher-grammage paper offers greater tensile strength, effectively resisting shrinkage stress.

Adjust adhesive formulation: Appropriately lower the adhesive's gelation temperature.

Fine-tune pressure: Ensure uniform bonding pressure to prevent localized overpressure causing excessive adhesive penetration.

4. Moisture Control in Corrugated Board and Issues of Excessive Softness and Box Collapse

Problem Description: Excessive overall moisture content in the cardboard causes it to become soft and lack rigidity. This results in poor load-bearing capacity of the finished cartons, making them prone to deformation and collapse.

Cause Analysis:

High moisture content in the base paper: The moisture level of the purchased base paper exceeded standards upon arrival.

Excessive sizing agent application: Excessive glue increases the total moisture content of the cardboard.

Insufficient drying capacity of the production line:

Low steam pressure: Results in insufficient temperatures of the corrugating rollers and heating plates.

Excessive production line speed: The cardboard spends too little time in the heating plate zone, preventing sufficient moisture evaporation.

Foreign objects or damage on the drying plates: Impairs heat transfer efficiency.

High ambient humidity: Particularly during humid rainy seasons, produced cardboard readily absorbs moisture from the air, causing re-moisture.

Poor cooling section performance: Cardboard exiting the drying section at high temperatures fails to cool and set adequately. When stacked, trapped internal water vapor cannot escape, leading to condensation and re-moisture.

Solutions:

Strictly control incoming base paper moisture: Establish inspection standards and reject base paper exceeding moisture limits.

Optimize sizing quantity: Reduce sizing while ensuring adequate bonding.

Enhance drying efficiency:

Ensure sufficient and stable boiler steam supply.

Set machine speed based on steam temperature, avoiding unnecessary acceleration.

Maintain clean, flat, and unobstructed heating plates.

Maximize preheater utilization: Evaporate excess moisture from base paper before entering the sizing machine.

Strengthen cooling processes:

Ensure cooling plates operate normally. Allow sufficient cooling transport distance to fully cool and set the board before stacking.

Control environmental humidity:

Dehumidify warehouses, especially during humid seasons.

Balance production:

Produced board requires a certain moisture content (typically 8-12%) to maintain stiffness and optimal die-cutting performance. The key lies in achieving “uniformity” and “moderation,” not solely pursuing low moisture.

Summary

These issues are often interrelated (e.g., moisture control directly impacts warping and adhesion), making corrugated board production a systematic engineering process requiring comprehensive regulation. Addressing any problem should begin with meticulous analysis and adjustment of the five core elements: base paper, adhesive, temperature, pressure, and speed (time). Establishing standardized operating procedures and continuously monitoring critical parameters are key to achieving stable, high-quality board production.

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