Blistering or cockling

1. Increase long fiber content.

2. Check presses for crowns and press roll loading.

3. Check moisture profile.
— cockle is more likely where paper is wetter into dryers.

4. Check that wet end dryers and/or Yankee dryer are not too hot.

5. Maintain sufficient felt tension.
— ensure that the stretchers are free.
— check that felt rolls are not deflecting.
— use heavier dryer felts.

6. Dirty or plugged felts.
— check felts and wash or change as needed.

7. Check all felt conditioning devices and shower nozzles.

8. Check felt caliper and permeability.
— replace worn felts.

9. Sheet moisture may be too high.
— check moisture and if possible, refine the stock less.

10. Reduce basis weight variation and wet streaks.

11. Put sheet through a size press with water to relieve dried-in stresses.

12. Use needled dryer felts to reduce localized moisture concentration.

13. Use dryer screens wherever they are practical.

14. Check Yankee coating and dryer profile.

15. Check Yankee surface for dirt.
— clean if needed.

16. May have problem with Yankee adhesion.
— check sheet moisture, stock freeness, white water pH, adhesive agent dosage, and coating uniformity.

17. Typically an edge problem.
— ensure that suction roll suction box is not plugged at edges.

Related information can be found at Blistering and Cockles.