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.
Wet Web Crushing
Structural Rupture
Destruction of internal web structure takes place when hydraulic pressure forces in a press nip exceed the physical shear strength of the wet paper sheet. Machine operators identify wet web crushing as large structural defects or total web breakage in wet press sections. High internal fluid pressure displaces wet fibres horizontally, creating localized disruption and tearing in the wet mat.
The boundary of this press failure mode is restricted to wet press sections where moisture content exceeds forty percent by weight.
Hydrodynamic Displacement
Excessive water volume trapped in press nips creates hydro-dynamic forces that push wet fibres apart. Heavy wet web crushing destroys fiber-to-fiber contact, forming thin, transparent patches or irregular holes across the paper machine direction. High press felt moisture content reduces water reception capacity, forcing water sideways through the delicate wet web.
Lowering web speed or increasing vacuum dewatering before the press section prevents fluid pressure build-up. Press roll cover hardness and nip profile settings influence local peak hydraulic pressure, governing web rupture thresholds.
Press Defect
Over-wet sheet entering the press nip triggers immediate hydraulic disruption of the wet fibre network. Uncontrolled wet web crushing causes frequent machine breakages and lost production capacity in paper mills.