Наукові праці Лісівничої академії наук України (Oct 2018)
Mathematical model of the pressing process of lightweight particleboards with the expanded polystyrene in content
Abstract
Assuming that the chip-polymer package overlaid by rotary-cut veneer has the form of a plate located between the press plates heated to a certain temperature, and applying the known laws of Fourier thermal conductivity and the equation of heat quantity which is used to heat the material to the appropriate depth, a mathematical model of the pressing process of lightweight particleboards with different contents of expanded polystyrene was proposed. The model combines the physical properties of the constituent components of the chip-polymer package of the overlaid by rotary-cut veneer lightweight particleboard containing expanded polystyrene and the parameters of the pressing regime. Duration of heating of chip-polymer package up to 100°С depending on the pressing temperature, the density of the boards and the content of expanded polystyrene based on the mathematical model was calculated. It was found that the duration of heating of the chip-polymer package up to 100°C increases by 10% with an increase in the density of the boards from 350 kg/m3 to 550 kg/m3 for the same values of the contents of the expanded polystyrene and the pressing temperatures. This increase in the duration of heating the middle of the chip-polymer package up to 100°C is due to the increase in the mass of its components at a constant heat flux transmitted from the press plates. The presence of expanded polystyrene leads to an increase in the duration of heating of the chip-polymer package up to 100°C. This growth was 3, 7 and 9% with the content of expanded polystyrene in the boards 4, 7 and 10%, respectively, compared to the boards without the expanded polystyrene. The reason for this is the lower thermal conductivity of polystyrene foam compared to wood particles. An increase in the pressing temperature from 180°C to 200°C reduces by 12% the heating time of the chip-polymer package to 100°C at the same densities of the boards and the values of the expanded polystyrene content. As the pressing temperature increases, the temperature gradient increases, which is inversely proportional to the heating time of the chip-polymer package. Calculated by the model, the value of the duration of heating the middle of the package without expanded polystyrene to a temperature of 100°C coincides with the values of the duration of heating of the particleboards recommended in the literature. For the chip-polymer package with expanded polystyrene, the resulting model was tested experimentally. The values of theoretical and experimental dependencies are close, which confirms the adequacy of the developed model. Minor discrepancies in the experimental and theoretical values of the temperatures in the middle of the package are due to the heat losses into the environment, which are not taken into account in the developed model.
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