Shoe Press Dewatering Profiles and Secondary Fiber Internal Cohesion Limits
Shoe press peak hydraulic pressure must remain below wet web z-tensile limits to prevent core delamination in secondary fiber containerboard manufacturing.
Press Exit Dryness
Water Removal
Dewatering performance in the mechanical press section of a paper machine determines the percentage of solid fiber in the wet web as it enters the thermal drying section. Achieving high press exit dryness reduces the amount of steam required to evaporate the remaining water from the sheet. This parameter is essential because mechanical dewatering is significantly more energy-efficient than thermal drying.
Elevating this dry content improves the wet web strength, which reduces the frequency of sheet breaks at the transfer points.
Energy Impact
Mechanical compression in the press nip forces water out of the paper sheet and into the pressing felts. Factors affecting press exit dryness include nip pressure, machine speed, roll hardness, and sheet temperature. Heated press rolls or steam boxes are often employed to lower the viscosity of the water, allowing it to flow more freely from the fiber network.
Monitoring this property helps operators optimize felt washing schedules and press roll maintenance to avoid unexpected drops in productivity.
Web Handling
Felt age and compaction limit the maximum achievable dewatering capacity over time. As press felts lose their void volume, the exit dryness of the sheet decreases, necessitating higher steam consumption in the dryer section.