Basis weight, MD varying

Note: Check all wet end recorders for cycling as an initial indication of the source of weight variation.
1. Consistency too low in the chest on run-outs caused by low consistency saveall return.
— check basis weight on reel frequently and adjust basis weight regulator accordingly.
— mixed stock consistency may be varying (when there is a regulator on the machine).
2. Correct the level variation in the machine chest.
3. Dilution valve on consistency regulator not working properly allowing variation in dilution water flow to the regulator.
— check valve and, if necessary, have repaired.
— varying consistency at headbox is not tolerable.
4. Varying flow at the consistency regulator causing changes in head which result in an uneven flow to the machine.
— check stock pump for blockage’
— vent any air from stock loop.
— check pump packing, etc.
5. Basis weight valve or stuff box level may be varying.
— check level control and/or stock supply system.
— check basis weight valve for erratic movement.
6. Reset level control on vibrating screens.
— check shower water for uniform flow.
7. Varying delivery of stock from fan pump.
— bleed off any air in pump and if necessary, open fan pump for inspection.
— check fan pump drive.
— investigate double consistency regulation..
8. Level variation in vacuum rejects tank.
— check wire pit level.
— check secondary centrifugal cleaner pump pressure.
— check primary centrifugal cleaner tips for vacuum leaks.
— check primary centrifugal cleaner rejects tank shower water flow.
— if above are correct, switch rejects tank level controller to manual.
— vacuum in rejects tank should not be high enough to offset secondary pump suction condition.
9. Variation in white water shower to headbox, vibrating screen and centrifugal cleaning system.
— check white water shower pump pressure and white water chest level.
10. Check headbox level control.
11. Check operation of pressure screen.
12. Adjust headbox rectifier or distributor roll speed to eliminate surging.
13. Cut outs on forming fabric edge or slack forming fabric cause vacuum fluctuations.
— may need to trim forming fabric and push in heads on suction boxes.
14. Check suction boxes and be sure each one is operating properly.
15. Increase wire tension to eliminate slippage on couch.
— reduce vacuum on suction boxes to eliminate draw variation at couch.
16. Find cause of wire pit level variation and rectify.
17. Speed variation indicated by changes in vacuum, varying draws at presses, and sudden changes in dry line after dandy.
18. If belts are slipping, have belt dressing applied or tighten belt.
19. Correct headbox shower water temperature so it does not vary more than ± 2 F .
20. Eliminate headbox shower water pressure pulsations that disturb both MD and CD profiles.
21. Eliminate fluctuations in static head of fan pump arising from varying fines and filler in white water loop.
22. Check for partial plugging of screens.
23. Too much white water added.
— broke pulper or hydropulpers may be dumped at too light a consistency.
24. There may be restricted dilution in the white water at the machine, i.e., no overflow in the canal or white water box supplying the mixing pump.
25. The headbox level can be varying excessively (over 10 mm).
— the fan pump may be sucking air through impeller shaft seats.
26. A headbox operating beyond its capacity causes swirls and vortices.
27. The forming fabric may not be flat over the breast roll due to large temperature differences between the stock and the forming fabric.
28. The sheet may be set too far down the forming fabric causing too much uncontrolled flow on the table.
29. Too high a vacuum on suction boxes may be causing too many fines to be removed.
30. The couch pit may be overflowing.
31. Check for pulsations from:
— fan pump.
— pressure screens.
— system natural and harmonic frequencies.
32. There may be a variable flow of retention aid.
33. The headbox temperature may be varying.
See Consistency varying