Dirt in the sheet

Note: Further back in the integrated mill, broke chests, white water systems, screens, and cleaners should be constantly checked, washed, and changed as experience dictates.
1. Following a shutdown:
(a) all screens, wire pits or silos, seal pits, stuffboxes, etc., should be emptied and hosed out.
— pulpers, beaters and chests are to be thoroughly washed.
(b) the headbox must be carefully cleaned with a high-pressure hose, including the lower surface of the upper converging slice (clean via bleed holes at side).
— clean under slice apron.
— clean perforated rolls.
— foam cleaning can be used on hard to remove soils inside the headbox.
(c) hose off frames, deflectors, and ends of drainage elements.
(d) wash drop legs and suction box interiors during wire or fabric change.
(e) periodic boil-out of wire pit, headbox, and piping may be required on machines which develop build-ups in the headbox circuit.
— good wash-up after boil-out is also essential to prevent dirt coming through on start-up.
(f) ensure that baskets are sound in machine screens.
(g) scrape and clean presses.
(h) check instrument pods and all dead areas for accumulation.
2. During normal operation:
(a) check that glands sealing rotor of machine screens do not leak.
(b) reduce aeration to the minimum.
(c) avoid any protruding gaskets (they make fiber strings).
(d) ensure that centrifugal cleaners operate at proper pressures (the size of cleaners must be appropriate to the service).
— examine tertiary rejects.
— ensure that cones in cleaners are not worn or corroded.
(e) check that reject lines from machine screens are working.
— check secondary screen.
— examine rejects.
(f) keep dryer hoods clean inside and free of dust.
3. Is the dirt biological (nitrogenous)?
— check biocide addition.
— is biocide added far enough back in system?
— is biocide dosage correct?
— are breaks, holes, etc. related to addition time?
— check with biocide supplier.
— boil-out.
4. If dirt is not biological:
— check for foreign material or chemical lumps.
— check dispersion of chemicals and additives with fine screen.
— check dryers and ropes for deposits.
— check system for strings or stock lumps.
5. Material is pressed onto top side of sheet.
— check top press felt.
— check for stock build-up inside headbox.
— check doctors.
— look for sources of falling material.
— check headbox upper surface.
— check water handling in headbox.
— check wire cleaning system.
6. Material is pressed onto bottom side.
— check bottom press felts.
— inspect breast roll shower.
— check below apron.
— check wire cleaning system.
— check outside wire roll doctor.
— check high-pressure showers.
— check wire tension.
7. Material is part of the sheet.
— check headbox for cleanliness.
— check upper converging section.
— check perforated roll.
— check bearings.
— check edges.
— check presses for crown and crown curve.
— check presses for edge pinching.
For more information, see Deposit control.