Felt damage

1. Major cause is due to wad burns.
— be extra careful while threading up the machine.
— maintain roll doctors to prevent build-up of stock that forms wads.
— provide devices that either deflect the sheet or instantaneously reduce the press loading when sheet breaks in the nip.
2. If damaged part of felt touches sheet, then felt should be changed immediately.
3. If damage is outside the paper, a change may not be needed and repair rather than replacement may be justified.
— with today’s machine speeds and clothing prices, felt repair is often not economically viable.
4. Mechanical causes of felt wear:
— improper roll crown or roll dubbing.
— bad press roll bearing.
— scissored (misaligned) press rolls.
— worn or rough suction box covers.
— worn or rough press rolls.
— improper high-pressure shower oscillation.
— excessive shower pressure.
— sand or abrasives in system.
— drag on the saveall.
5. Hydraulic causes for felt wear:
— reductive agents in system.
— oxidative damage (0.05 ppm chlorine can damage a nylon felt).
6. Variations in press nip loading damage felts due to uneven wear and subsequent irregular water removal.
7. Ensure that “take-up” mechanisms are free to move as they can prevent damage should a wad of paper go through the press.
— check guiding mechanisms on a regular basis.
8. Keep felts wet over a prolonged shut.
— occasional rotation will reduce possibility of roping the felt at startup.
9. Over-stretching a felt can result in a loss of its functional capabilities.