Study On The Heat-transfer Properties Of Flakeboard During Hot-pressing

The relationship between mat structural performance and inner heat and mass transfer in the hot pressing process of the particleboard plays a significant role in improving the efficiency of productivity and establishing the appropriate hot pressing technique. This paper adopted the continuous temperature and pressure on-line testing method, and studied the influence of inner temperature field and pressure field based on resin content, moisture content of mat and the target density of flakeboard when resin is carried out, this paper provided the theoretic basis to establish the relationship between the structural performance of mat and the changes of temperature and pressure, moreover, and it also assists to set and optimize the hot-pressing process. The main results and innovation in this paper are shown as following:1. Through the analyses of experiment and theory, the author obtains the change regulation of the temperature and pressure of the surface and central layers in the hot-pressing process. (1) the curve of the central layer temperature can be divided into 4 stages: the short constant temperature stage in which the temperature is constant or increases very slowly, the fast temperature rising stage in which the moisture in the mat is not vaporizing, the constant temperature stage in which the moisture is vaporizing, and the slow temperature rising stage in which the moisture vaporizing process is near to the end. (2) The temperature curve of surface layer can be divided into 2 stages: rapid temperature rising stage and slow temperature rising stage. (3) the pressure curve of the central layer can be divided into short balance stage, pressure rising stage and pressure falling stage.2. The influence of the resin content on temperature and pressure in the hot-pressing process of flakeboard is illustrated for first time based on the experiment results: (1) consuming adhesive is favorable to the heat transfer process on the direction of thickness. (2) the resin content is between 8% and 13%. when the resin content reaches 11%, the central layer of the poplar flakeboard obtains a relatively faster temperature rising speed at the fast temperature rising stage, however, the resin content more than 11% will lead to a decreasing temperature rising speed. The resin content put little influence on the temperature changes in central layer of the acacia flakeboard.(3) To poplar flakeboard, a large resin content will lead to a high pressure in the hot-pressing process. However, to the acacia flakeboard with the same density, whether the resin content is high or not, the pressure of the central layer of mat is fluctuating, but always keeps it in the horizontal direction, the 3 pressing phase is not emerged. But the 3 pressing phase curve will emerge in the mat central layer when the density is high (0.75 g/cm~3 and 0.85 g/cm~3), this result reveals that the density and the tree species will put influence on the pressure of thecentral layer.3. The analyses of experiment and theory show the influence of the target density of the flakeboard on the heat and mass transfer process in the flakeboard: (1) With the increase of density, the temperature rise speed of facial and central layers, which is in the fast temperature rising stage, is slowing down, but the degree of the speed decrease is different. The higher the density of the flakeboard, the wider the time gap between the surface and central when the temperature reach 100℃, (2) The higher the density of the flakeboard is, the higher the maximum pressure of the surface and central layers of the flakeboard is, similarly, the higher the vaporizing temperature is.(3) The low density is favorable to the even distribution of the temperature in the center plane, whether the density is high or not, In the fast temperature rising stage, before the center point reach the vaporizing point, the highest temperature will not emerge at the center point of the center plane, but emerge at the areas around the center point in the center plane, the higher the density is, the wider the tempera...