Inter-Ply Bond Strength Development in Recycled Fiber Formations under Variable Dewatering Pressures
Optimizing shoe press peak pressure and wet-end couch solids maximizes inter-ply bond strength in multi-ply recycled fiber formations.
Dewatering Pressures
Drainage Force
Mechanical extraction of water from a wet fiber web occurs through the application of controlled forces in the press section of a paper machine. Optimizing dewatering pressures allows mills to increase the dry content of the sheet before it enters the energy-intensive thermal dryer section. This mechanical step balances water removal with the preservation of sheet bulk.
Nip Mechanics
Press rolls apply a graduated load that increases as the web moves through the press nip to prevent structural crushing of the delicate wet sheet. The application of dewatering pressures must be carefully coordinated with the design of the press felts, which receive and transport the expressed water away from the paper. If the load rises too quickly, the hydraulic force within the sheet exceeds the strength of the wet web, causing localized ruptures and defects.
Conversely, insufficient pressure leaves excessive moisture in the web, which forces the dryer section to run at slower speeds.
Sheet Consolidation
Consolidation of the fiber network improves the tensile strength and surface smoothness of the finished board. Wet pressing brings the fibers into closer contact, promoting the hydrogen bonding that gives paperboard its structural integrity. Refining the press sequence ensures that the board retains its stiffness while achieving the target caliper and density.