Characterization of Heat and Mass Transfer in the Mat during the Hot Pressing of MDF Panels
Keywords:Medium density fiberboard, heat and mass transfer, gas permeability, hot pressing
AbstractThe two objectives of this project were to determine gas permeability of the mat as a function of density, and to characterize panel properties and temperature and gas pressure evolution in the mat during hot pressing as a function of press closing strategy, panel density, and mat moisture content. Panels of 560 X 460 X 16 mm were made in a 600- X 600-mm laboratory press. The manufacturing parameters were the following: press closing strategy of 145, 155, and 165% of the target panel thickness after 30 s of pressing; initial mat moisture content of 10, 12, and 14%; and panel density of 650, 725, and 800 kg m-3. Temperature and gas pressure were measured at the surface and core of the mat. The gas permeability of the panel was measured for panels of uniform densities of 400, 650, 900, and 1150 kg m-3. Gas permeability decreased by a factor of 1000 when panel density increased from 400 to 1150 kg m-3. The flexural properties increased with an increase in mat moisture content and panel density, and a decrease in press closing strategy. The internal bond increased with an increase in mat moisture content and panel density. Thickness swell decreased with an increase of panel density, and increased with an increase in press closing strategy. The time required to reach 100°C in the mat core decreased with a decrease in press closing strategy. The maximum gas pressure in the mat core was proportional to panel density. It also increased with mat moisture content for a press closing strategy of 165% and a panel density of 800 kg m-3.
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