Caliper, variation

1. Improve headbox flows for uniform stock distribution across the machine.
2. Check condition of calender stack.
— calender maintenance is critical to maintaining uniform caliper profile.
— use calender cooling air jets to reduce localized calender stack heating.
3. Overheated calender roll bearing can cause low caliper edges.
— make repairs or replace bearing on calender stack.
— use calender cooling air jets to reduce heating.
— use calender stack wedges to open nips on either side of overheating bearing.
4. Often due to non-uniform moisture across sheet.
5. If calender rolls are damaged due to improperly fitted doctor or use of wrappings on calender roll, initiate corrective action.
6. For worn or improperly crowned king roll, fix situation as soon as possible.
7. Check suction and plain presses for crown, crown curve and loading.
8. Adjust crown on variable crown roll.
9. Should have scanning devices with profiling capability for caliper, basis weight, and moisture.
— these units provide operator with immediate data for corrective action and controlling operation.
10. Check Yankee coating for uniformity.
— adjust crepe coarseness if possible.
11. Check moisture profile.
— moisture variations will cause caliper variations.
12. Check calender roll temperature profile.