Minimizing Press Time for Radio Frequency-Cured Flakeboard

Minimizing press time is critical to economical flakeboard production. One possible method of minimizing press time is to incorporate radiofrequency heating in the pressing operation. This study was undertaken to compare radiofrequency heating-assisted hot pressed panels with steam-heated platen cured panels made in earlier studies. The processing variables evaluated were press temperature (107? to 163?C), press closing time (15 to 120 sec.), mat MC (8 percent to 12 percent), density (0.48 to 0.96 g/cm3), panel thickness (6.4 to 19.1 mm), resin type (urea- and phenol-formaldehyde), and wood species (Douglas-fir, aspen, southern pine). For each combination of variables, minimum press time was determined by sequentially reducing press times within each set of panels until delamination occurred. Radiofrequency-cured panels had more uniform vertical SG gradients (radio of face to core SG of 1.13 vs. 1.29), 4 percent more springback out of the press, and 9.6 percent lower average SG than panels cured with steam-heated platens. Minimum press times ranged from as little as 2.5 minutes to as much as 11 minutes over the range of variables evaluated, and were controlled by the combined effects of energy input (positive relation), average panel density (negative relation) and panel thickness (negative relation). Vertical SG gradients were not strongly affected by most processing variables. As a result, panel properties were not significantly correlated to most processing variables over the levels evaluated.

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