Press dewatering of thin substrates: The volume under load model

Wet pressing is a critical dewatering stage in the production of thin substrates such as paper and microcellulose films, as it directly influences drying energy consumption and product performance. This study introduces and validates the volume under load (VUL) model, a quantitative approach to describe and predict press dewatering efficiency in the load-distribution-limited regime. A combined experimental–computational method was developed to determine the VUL from three-dimensional press felt surface topographies under load, simulated felt–paper contact areas (via a rolling-ball algorithm), and substrate thickness. Six industrial press felts with distinct base weave structures and batt fiber diameters were characterized. Wet pressing trials using a high-speed MTS press simulator reproduced industrial press impulses (1–2 MPa, 10 ms) on papers of varying grammages (70–110 g/m 2 ). The results demonstrate that dewatering efficiency increases linearly with the paper volume under load and correlates strongly with the felt–paper contact area. Finer felts with smaller batt fibers and more uniform base weaves yielded higher contact areas and solids content after pressing. The volume under load is independent of the technique used to determine the substrate–felt contact area; methods such as pressure-sensitive films or finite element modeling can equally provide the necessary input for VUL calculation. The findings confirm the validity of the VUL model for predicting and optimizing press dewatering in thin substrates, offering a practical framework for designing high-performance press felts and energy-efficient wet pressing processes.