Modeling the continuous hot-pressing of MDF

Abstract

The continuous pressing became the most important press-drying process in the manufacture of wood-based panels and a great number of manufacturers have been substituting the conventional batch process by a continuous line. One of the most important and innovative aspects is the understanding of the combined effects of physical–chemical and mechanical phenomena involved. Due to the multiplicity and interdependency of these phenomena, the development of predictive models will permit the simulation of this operation and finally a better understanding, optimization and control of the press cycle. Based on a model previously developed for batch pressing, a three-dimensional model for medium density fiberboard (MDF) continuous pressing is presented by integrating all mechanisms involved in panel formation: heat and mass transfer, chemical reaction and mechanical behavior. In this case, the description of these phenomena corresponds to the modeling of a porous and heterogeneous media in movement. The main difficulty associated to this type of problems is the choice of the reference system for the numerical solution of the equations of conservation of mass, energy and momentum. This model was used to predict the evolution of the variables related with heat and mass transfer (temperature, moisture content, gas pressure and relative humidity), as well as the variables related with mechanical behavior (pressing pressure, strain, elasticity module and density). The model performance was analyzed using the typical operating conditions for the continuous pressing of MDF by comparison of its predictions with experimental data from the literature.