Heat flow in particle mat and properties of particleboard under steam-injection pressing

1) The temperature behavior of the particle mat during hot-pressing and steam-injection pressing was investigated under various conditions. With an increase of moisture content, the time necessary for the middle layer to reach 100 degrees C tended to shorten, whereas the time to maintain a constant temperature was prolonged in the case of hotpressing. The temperature in the middle layer of a mat with a higher moisture content in the face layers increased more than that of a mat with a uniform distribution of moisture content. In the case of steam-injection pressing, the temperature in the middle layer of the mats immediately increased to a specific degree decided by injection pressure and the characteristics of mats at the moment of steam-injection, and maintained a constant level during steam-injection. After stopping steam-injection, the temperature decreased a little, and then started to rise again. The rates of temperature increase in the middle layers of mats were independent of thickness, moisture content and density in the range of the experimental conditions. 2) Each of seven types of Japanese red pine particles with different dimensions, strictly controlled for length, width, and thickness, was prepared in order to investigate the temperature behavior in the mat, and the air permeability of the boards with specific gravities of 0.30-0.60. The variables influencing the temperature behavior in the mat by steam-injection press is directly related to the air permeability of mats. The air permeability of the boards in the horizontal direction to the heat platen is always higher than in the vertical direction. A functional equation with a higher coefficient of determination that explains the air permeability is obtained by a multiple regression analysis. It is inferred that the temperature increase in the mat result from the repetition of the steam diffusion among particles in two dimensions