Numerical modeling of the medium-density fiberboard hot pressing process, part 2: Mechanical and heat and mass transfer models

In this study, coupled mechanical and heat and mass transfer models describing mat compression and heat and moisture transfer occurring during hot pressing of medium-density fiberboard mats are presented. The mat is considered an aging linear elastic material and is described by a mechanical model in three dimensions. Rheological properties of the mat depended on time, space, temperature, moisture content, and resin cure. Hardening and softening phases of the material behavior were accounted for and treated with separate constitutive laws. Press closing was taken into account, and a coupling procedure between mechanical and heat and mass transfer models was elaborated. Development of the vertical density profile was dynamically predicted by the model. Both mechanical and heat and mass transfer models were discretized in space by the finite element method. An implicit second-order backward finite difference scheme was used for time discretization. All calculations were carried out on a moving geometry whose deformation (compression) was a function of a press closing schedule. Model results exhibited good agreement with experimental results. Under various press closing schedules, the model gave information on variables such as density profile, total gas pressure, air and vapor pressure, temperature, moisture content, RH, and degree of resin cure.