TL;DR
Glue skips cause box failures at the glue joint. Check glue pump pressure, nozzle cleanliness, and glue temperature before adjusting the application timing.
What you might see
- visible gaps in the glue bead on boxes
- box glue joint failing under compression test
- glue nozzle clogging intermittently
- glue bead width varying along the box flap
Likely causes
Glue nozzle partially clogged with hardened adhesive
Glue temperature below the minimum application viscosity for the adhesive grade
Glue pump pressure fluctuating, causing intermittent delivery to the nozzle
Application timing offset causing the nozzle to open late or close early relative to the box flap
Required tools
- Heat-resistant gloves
- Glue temperature meter
- Nozzle cleaning tools and approved hot melt solvent
- Compression tester for box quality check
Safety first
- Hot melt adhesive is above 150 deg C. Use heat-resistant gloves and face shield near the glue head. Molten glue causes severe burns.
- Never point a glue nozzle at personnel during purging. Always discharge onto a waste board.
Procedure
- 1
Examine a sample of failing boxes. Measure the gap length and note whether skips are periodic or random.[1]
- 2
Check the glue temperature display at the glue pot and application head. Temperature below the minimum for the adhesive grade reduces flow and causes skipping.
Warning: Hot melt adhesive systems operate above 150 deg C. Use heat-resistant gloves near the glue head and nozzle. Molten glue causes severe burns. - 3
Purge the glue nozzle with a short triggered burst to clear any partial clog. Catch the purged glue on a waste board.[1]
- 4
If clogging recurs, remove and clean the nozzle with the approved hot melt solvent or by soaking in the adhesive manufacturer's recommended cleaner.
- 5
Check the glue pump pressure gauge. Pressure below the setpoint indicates pump wear or a filter blockage. Clean or replace the pump inlet filter.
- 6
Verify the application timing setting against the setup sheet for the box size being run.
- 7
Run 20 boxes after each correction and compression test 5 boxes before releasing to production.
Sources
Bobst Bobst Mastercut / Expertfold / Vision Fold Die Cutter / Folder-Gluer general technical documentation, Bobst
Hot melt adhesive system maintenance and folder-gluer glue application, general packaging machinery practice (general)
More guides for Bobst Bobst Mastercut / Expertfold / Vision Fold
How to fix die cut quality and register on a Bobst Mastercut Die Cutter
Die cut registration errors produce off-center cuts and wasted material. Check sheet feed timing, die lock-up, and impression pressure before adjusting register settings.
How to fix folding angle variation on a Bobst Vision Fold Folder-Gluer
Folding angle variation produces boxes that do not close square. Check folding rail alignment, folding belt tension, and the squareness of the incoming blanks.
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