Permeability of fibre, particle and strand mats for gas

After an explanation of the importance of mat permeability during wood-base d panel manufacture the relevant literature is reviewed. Preparation of spe cimens and gas-permeability measurement methods are described. Darcy's law can be applied to describe the gas flow in wood-based panel mats under the influence of a pressure gradient during the hot pressing process. The perme ability parallel to the panel surface influences the rate of venting. The t ransverse permeability is important for the convective transfer of heat and moisture into the core layer. The permeability of fibre, particle and stra nd mats with densities varying from 200 to 1200 kg/m(3) was determined. At lower densities, the parallel and transverse permeability of fibre mats and the transverse permeability of OSB mats are distinctly lower than the perm eability of particle mats. Particle mats made from surface material are les s permeable than those made from core material. At higher densities, fibre mats reveal highest permeability followed by surface and core layer particl e mats and strand material. At higher densities, mat permeability decreases with increasing glue and moisture contents. The pressing temperature and t he accompanying plastizisation of the mats does not influence the permeabil ity.