Formation, streaky

1. Narrow, fixed streaks are due to nicks, dried fibers, pitch or dirt behind slice lip; also may be due to dirt build-up in headbox.
— if necessary, shut down machine and wash headbox.
— for nicks, burrs, worn or corroded slice, report and have repaired at first opportunity.
2. Large, stable streaks can be caused by deformation in the slice lip, wire ridges, or excessive play in adjusting mechanisms.
— if wire is ridged, find reason for ridge and correct.
3. Unstable streaks are usually due to hydrodynamic instability behind the immediate slice area.
— adjust speed of perforated roll.
4. Unstable, narrow streaks that move around are due to wake effects, often seen with hydraulic headboxes.
5. Large, slow moving, flow instability indicates problems with the distribution system or headbox proper.
— check for plugged manifold tubes or holes, air, or flow vortices through the box.
6. Unstable profiles can result from pulsations from rotating elements such as pumps, etc.
7. Retention agent distribution across headbox manifold may not be uniform.
— adjust or change location of addition.
8. When head is correct, too high a slice opening with too much water in sheet will result in playing or loss of control on the forming fabric.
9. Ensure even setting of the slice lip.
— adjust slice to alter water removal at breast roll.
— level forming board and/or deflectors.
10. Uneven tension on forming fabric is indicated by a crooked seam, especially when forming fabric is old.
— have rolls checked for alignment.
11. Check for unevenly worn suction boxes.
— remove one suction box at a time for resurfacing.
12. Check for stock build-up on suction boxes.
— remove one box at a time and clean.
— check for worn suction boxes.
13. Streaky formation can also be caused by dirty rectifiers (where still used) or a dirty slice.
14. A common cause of streaky formation is wear at the patch bolts securing the slice screws.
See Formation improvement.