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.
Out-Press Dry Solids
Dryness Ratio
Papermaking measurement protocols determine the percentage of dry solid matter present in a continuous fibrous web immediately upon exiting the mechanical press section. Out-press dry solids quantifies the ratio of bone-dry fibre and filler mass to total web mass before the sheet contacts the first steam-heated drying cylinder. This operational metric reflects the efficiency of mechanical dewatering operations, establishing the baseline evaporation load imposed on the downstream thermal drying section.
The measurement applies exclusively at the physical transfer point between the final press nip and the dryer section entry.
Thermal Burden
Mechanical water extraction consumes significantly less energy than thermal evaporation using pressurized steam cylinders. Raising out-press dry solids from forty percent to forty-two percent reduces the thermal drying burden by approximately eight percent, yielding substantial steam and energy savings. Modern shoe presses achieve dry solids levels between forty-five and fifty-four percent on heavy packaging grades, depending on furnish composition, basis weight and web temperature.
Virgin bleached kraft pulps dewater more readily than secondary recycled fibers containing high concentrations of hornified fines and gelatinized starch. Mill operators increase press nip dwell time and apply steam showers before the nip to heat the water, which reduces fluid viscosity and accelerates extraction through the press felts.
Runnability Control
Wet web tensile strength correlates directly with solid content during open sheet transfers. Insufficient out-press dry solids leaves excess water in the cellulose network, lowering sheet cohesion and increasing the likelihood of web breaks at high machine speeds. High moisture levels entering the dryer section can also induce cockling, surface blistering and internal delamination if surface fibres dry rapidly while internal layers remain saturated.
Continuous online gamma gauges or infrared sensors measure moisture content across the web width to detect wet streaks, allowing press roll crown adjustments and felt cleaning to restore uniform dewatering. Sustained dry solids stability maintains high machine efficiency and consistent board density.