Dimensional stability

1. General:
— maintain uniform retention of fines and fillers.
— operate with slack draws at wet end and at dryers.
— maintain dryer felt tension.
— maintain moisture at dry end at desired level by automatic control.
— relieve the paper of dried-in stresses in a size press.
— relieve dried-in stress in an after-dryer humidifier.
2. High density (low porosity):
— reduce refining to keep sheet open, if conditions permit.
— keep refining uniform.
— decrease press loading to keep sheet porous.
— consider possible changes to furnish.
— lower size press solids.
— run drier to calenders.
— decrease refining consistency.
3. High stretch (high CD shrinkage):
— decrease refining, free up stock.
— reduce refining consistency.
— relieve couch and press draws.
— increase dryer felt tensions.
— use more hardwood or filler in furnish.
— use variable bow and spreader rolls.
— slight lead will give squarest and most stable sheet.
4. Sheet too dry:
— run to proper moisture at reel.
— graduate dryers, do not dry too fast.
— improve formation.
— check for wet streaks or dirty felts.
— check dryer profiles and dryer ventilation.
5. Change furnish if other tests permit.
— increasing hardwood content usually improves dimensional stability.
See Curl control.