Air Bubbles & Positioning Drift on Automatic Rigid Box Lines (157gsm Art Paper)

[Kylin machinery]

Hi everyone,

I wanted to share a technical case we recently solved regarding air bubbling and registration drift during a high-speed run on an automatic rigid box line. Hopefully, this helps anyone facing similar issues with coated paper stocks.

The Scenario:

• Machine Type: Fully Automatic Rigid Box Machine (Visual Positioning System).
• Material: 157gsm C1S Art Paper (Gloss Lamination) + 2.0mm Greyboard.
• Glue: Hot Jelly Glue (Animal glue).
• Speed: Running at 25-30 pcs/min.

The Problems:

1. Bubbling: After the box was formed, small air bubbles appeared on the large side panels after about 30 minutes of drying.
2. Drift: The positioning accuracy started to drift (offset > 0.5mm) after running continuously for 2 hours, requiring frequent recalibration of the cameras.

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The Solution & Root Cause Analysis​

After troubleshooting the entire line, here is how we fixed it:

1. Fixing the Bubbling Issue (Glue Viscosity vs. Open Time)The root cause was the "Open Time" of the glue being too short for the conveyor speed.

• Diagnosis: The glue was cooling down too quickly on the conveyor belt before the greyboard was spotted (placed) onto it. The gloss lamination on the paper also reduced the absorption rate, causing the paper to push back against the board, trapping air.
• Fix:
  
  • Viscosity Adjustment: We added 5% warm water to dilute the glue slightly. A lower viscosity allows for better spread and faster tack.
  • Temperature: Increased the glue tank temperature from 60°C to 65°C and, crucially, heated the conveyor belt (if your machine has a heated belt feature) to keep the glue "open" longer.
  • Pressing: We increased the pressure on the side-wrapping station's brushes to force air out more aggressively before the bond set.

2. Fixing the Positioning Drift (Camera & Belt Hygiene)The drift wasn't a software error, but a physical maintenance issue often overlooked.

• Diagnosis: Static electricity from the high-speed running was attracting paper dust onto the conveyor belt (suction belt). This dust covered the black/white contrast reference points, confusing the visual positioning cameras (Yamaha/Epson robot arms).
• Fix:
  
  • Cleaning Routine: We implemented a "wipe down" of the camera lens and the conveyor belt every 4 hours using an anti-static cleaner.
  • Suction Power: We checked the vacuum pump. It turned out the suction was slightly weak due to a clogged filter. Cleaning the vacuum filter ensured the paper stayed perfectly flat for the camera to capture the coordinates accurately.

Result:After these adjustments, we ran the machine at 35 pcs/min stably with <0.1mm error and zero bubbling over a 10,000 piece run.

If anyone else is struggling with lamination paper bubbling, check your glue viscosity first—it's usually the culprit!

Jacob | Tech Support at Kylin Machinery | Expert in Rigid Box Automation & V-Grooving Solutions