Sheet blowing, press nips

Note: Sheet blowing results from localized accumulation of air from stock to felt that creates an air pocket between the felt and the sheet; can occur at ingoing nips and is more often a problem with new felts.
1. If blowing is on the edges, adjust heads in suction box.
—watch for a frozen box in a cold climate.
2. Use a blow box or suction pipe on the inside of the felt ahead of the nip to prevent blowing.
3. When sheet and felt travel together for some distance ahead of the nip there is a greater tendency toward blowing.
— use a paper roll to hold sheet down on felt to reduce air carried into nip.
4. Alternatively, run sheet into press so that it does not contact felt until it is in nip and most blowing will be eliminated.
5. Keep felt open, clean and at proper tension.
— it may be advantageous to use a more porous felt, e.g., a needled felt.
— ensure that felt is not too dirty, too thin, or too hard for application.
— check and modify felt cleaning methods if needed.
6. Adjust tension to prevent air blowing through the felt in the wedge created by the felt and grooved roll.
7. The felt void volume must be controlled to prevent air from being carried internally and being compressed out in the nip.