Curl control

General:
(a) dry side away from curl last and hardest.
(b) high density aggravates curl.
— reduce refining and wet pressing
(c) increase hardwood or filler content.
(d) alter fiber alignment.
— square the sheet with slight drag.
(e) reduce draw tensions.
(f) keep moisture uniform across web.
(g) reduce hydration refining.
(h) maintain proper moisture at reel in line with end use
(i) run slower or with increased shake.
(j) consider fiber or filler changes.
(k) increase size press solids and clay.
(l) control moisture pick-up on each side of sheet at size press or calenders.
(m) deliver moisture in line with end use requirements.
(n) reduce wet pressing and use spreader rolls.
(o) avoid over drying or drying too fast.
To top side:
1. Decrease temperatures or pressures of top dryers after size press.
— dry bottom side last.
2. Increase temperatures or pressures of bottom dryers after size press.
3. Run cooling water in spring roll.
4. A high density sheet aggravates curl.
— free-up stock as other tests permit.
5. Control the fiber orientation on the forming fabric.
6. Alter the moisture pick-up on each side of sheet at size press or calender stack.
7. With size press:
— lower temperatures in top after-dryers.
— raise temperatures in bottom after-dryers.
8. Without size press:
— raise temperatures in top after-dryers.
— lower temperatures in bottom after-dryers.
To wire side:
1. Dry top side last.
2. With size press:
— raise temperatures in top after-dryers.
— lower temperatures in bottom after-dryers.
3. Without size press:
— lower temperatures in top after-dryers.
— raise temperatures in bottom after-dryers.
4. Reduce temperature of sweat dryer.
5. High density sheets aggravate curl so free-up the stock.
6. Control fiber orientation on forming fabric.
7. Alter the moisture pick-up on each side of sheet at size press or calender stack.
See Dimensional stability.