Soft spots

1. If soft spot is associated with a low basis weight, raise slice at this point.
— composite caliper and basis weight profiles will indicate whether wet end or dry end adjustments are needed.
2. Use calender air to cool the rolls and thus reduce roll diameter at this point.
— the calender air must be cool enough all year around; this usually means refrigeration in regions where summers are hot.
3. Use an adjustable spreader bar and ensure that the bar has no protuberances; for example, pitch that will bulge the sheet and cause a soft spot.
4. Eliminate calender doctors except on bottom and intermediate rolls (dragging doctors may cause soft spots).
5. If soft spots are due to moisture streaks:
(a) check at the presses.
(b) eliminate non-condensables.
(c) improve dryer ventilation.
(d) determine method to improve moisture profile.
6. Check that calender has been ground with correct crown curve.
— for example, a 180 curve may give two hard spots at the quarter points.