Modeling Pressure Distribution in a Belt Press During Manufacture of Fiberboards

Authors

  • Patrick Pettersson
  • T. Staffan Lundström
  • Elianne Wassvik

Keywords:

Modeling, fiberboard manufacturing, pressure distribution, belt press

Abstract

When forming fiberboards, a large amount of air is evacuated from the dry fiber mat and the fibers are subjected to forces generated by the flow. If the forces become too strong, the fiber mat bursts and the process stops with financial loss as a result. A simplified model for the pressure field during the pressing has been derived, by starting from first principles. This model indicates that the velocity of the belt can be increased as long as the length of the press is increased, or the viscosity of the penetrating fluid is decreased in a prescribed manner. The model furthermore suggests that the pressure distribution will be unaffected by variations in the basis weight of the fiber mat as long as the basis weight is matched with an equal change in the density of the fibers. Furthermore, by numerically deriving the pressure field as a function of boundary conditions, it is shown that minor variations in the pressure at the nip may result in huge differences in the pressure at the entrance of the press. In a validating procedure, it is shown that model parameters can be adjusted in a physically reasonable way to obtain acceptable agreement with experimental data, but also that the model must be considerably improved in order to obtain quantitative conformity.

References

Asklöf, C. A., K. O. Larsson, J. Linderoth, and P. B. Wahlström 1964. Flow conditions in a felt in a plain press nip. Pulp Paper Mag. Canada: 246-250.nBear, J. 1972. Dynamics of fluids in porous media. Dover Publications Inc, New York, NY.nEl-Hosseiny, F. 1991. Mathematical modeling of wet pressing of paper. Nordic Pulp Paper Res. J.1:30-34.nErgun, S. 1952. Fluid flow through packed columns. Chemical Engineering Progress48(2):89-94.nKataja, M., K. Hiltunen, and J. Timonen 1992. Flow of water and air in a compressible porous medium. A model of wet pressing of paper. J. Phys. D.25:1053-1063.nKershaw, T. N. 1972. The three dimensions of water flow in press felts. Tappi J.55(6):880-887.nKincaid, D., and W. Cheney 2002. Numerical Analysis: Mathematics of Scientific Computing. Brooks/Cole, 804nLobosco, V., B. Norman, and S. Östlund 2005. Modelling of forming and densification of fibre mats in twin-wire formers. Nordic Pulp Paper Res. J.20(1):16-23.nPeriera, C., M. Louisa, H. Carvalho, A. Carlos, and V. Costa 2006. Modeling the continuous hot pressing of MDF. Wood Sci. Technol.40:308-326.nPettersson, P., T. S. Lundström, and T. Wikström 2006. A method to measure the permeability of dry fiber mat. Wood Fiber Sci.38(3):10.nThoemen, H., Heiko 2006. Modeling the physical processes relevant during hot pressing of wood-based composites. Part I. Heat and mass transfer. Holz Roh-Werkst.64(1):1-10.nWahlström, P. B. 1960. A long term study of water removal and moisture distribution on a newsprint machine press section part 2. Pulp Paper Mag. Canada: 418-451.nZahrai, S., F. H. Bark, and D. M. Martinez (1997). On the fluid mechanics of Twin-Wire Formers. Department of Mechanics, Stockholm, Royal Institute of Technology: 32.nZhu, S., R. H. Pelton, and K. Collver 1995. Mechanistic modelling of fluid permeation through compressible fiber beds. Chem. Eng. Sci.50:3557-3572.n

Published

2007-09-27

Issue

Section

Research Contributions