Curl, moisture and reel handling: stopping liner defects before the board line
Most 'paper quality' complaints on a gypsum line are storage and conditioning problems. Moisture gradients, reel age and warehouse RH explain more defects than the mill does.
Paper is hygroscopic. A liner reel leaves the mill at 6–8 % moisture, wrapped and in equilibrium with itself. What happens between that moment and the unwind stand determines whether it runs flat or fights the line.
The three curl mechanisms
- Moisture curl: one side gains or loses water faster, usually after the wrap is opened in a warehouse that is drier or damper than the mill.
- Structural curl: built into the sheet by two-sidedness of the furnish or unequal drying at the mill. It does not relax with conditioning.
- Reel-set curl: the memory of tight winding, worst on the last 10 % of a reel and on small-diameter cores.
Conditioning rules that remove most complaints
| Control point | Recommendation |
|---|---|
| Warehouse RH | 45–60 % RH, 15–25 °C, stable. Avoid external walls and dock doors. |
| Acclimatisation | 24–48 h in the production hall, wrap intact, before unwrapping. |
| Wrap policy | Open only at the unwind stand; never store part-used reels unwrapped. |
| Stock rotation | FIFO with a 6-month ceiling; older reels go to back liner positions. |
| Handling | Reel clamps on the body, never on the edges; edge damage propagates as web breaks. |
Diagnosing: is it the mill or the warehouse?
Cut a 200 mm square from the reel, condition it 24 h at 23 °C / 50 % RH per ISO 187 and lay it flat. If the curl disappears, it is moisture and the fix is in your warehouse. If it persists, it is structural and the mill position needs to change. Doing this test before opening a claim saves weeks — and it is the first thing any mill quality department will ask for.
WeePaper reels ship with moisture recorded on the reel COA, so a conditioning dispute can be settled against the as-delivered figure rather than an argument.
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