TL;DR
Poor glue bond shows as low pin adhesion scores and delamination under flex. Check starch viscosity, gel temperature, and double backer heat before adjusting application rate.
What you might see
- pin adhesion test scores below specification
- board delaminating under flex or compression
- starch application visible but not gelled at the bond line
- bond failure concentrated on one face or at one liner grade
Likely causes
Starch viscosity out of specification, too thin for adequate coverage or too thick to gel
Double backer heat plates below the gel temperature for the starch formulation
Starch application rate insufficient for the liner surface porosity
Starch gel point temperature shifted from a formulation or water quality change
Required tools
- Stein Hall viscosity cup
- Pin adhesion tester
- IR thermometer for heat plate check
- Heated plate for gel point test
Safety first
- Starch kitchen equipment contains hot liquids. Use heat-resistant gloves and face shield when sampling from starch tanks.
- Double backer heat plates exceed 170 deg C. Keep hands clear of exposed heat plate surfaces.
Procedure
- 1
Run a pin adhesion test on board from the last 30 minutes of production. Record scores for top and bottom faces separately.[1]
- 2
Measure starch viscosity in the glue kitchen with a Stein Hall cup. Compare to the specification for the grade combination being run.
- 3
Check the starch gel temperature by running a small sample on a heated plate and confirming the gel point temperature. A shift in gel temperature requires formulation adjustment.[1]
- 4
Measure heat plate temperatures at multiple points along the double backer. Plates below gel temperature will not cure the starch.
- 5
Inspect the applicator roll and metering roll gap for uniform starch film. An uneven gap gives variable application across the board width.
- 6
If viscosity is in spec, gel temperature is confirmed, and heat plates are at temperature, increase starch application rate by 5-10% and retest pin adhesion.
- 7
Log all starch parameters and pin adhesion scores for the affected grade to establish a corrective baseline.
Sources
BHS Corrugated BHS Modular Corrugator general technical documentation, BHS Corrugated
Corrugator starch adhesive system and pin adhesion testing, general corrugating practice (general)
More guides for BHS Corrugated BHS Modular
How to reduce flute crush at the single facer on a BHS Modular Corrugator
Flute crush at the single facer is caused by excessive nip pressure or dull corrugating rolls. Check nip load settings, corrugating roll surface condition, and paper temperature before adjusting.
How to reduce warp in corrugated board from a BHS Modular Corrugator
Board warp is caused by a moisture differential between the two liner facings. Check the moisture profiles of both liners, the double backer heat setting, and starch gel point consistency.
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