Impact of steam pressing variables on the dimensional stabilization of flakeboard

초록

The objective of this study was to determine if an unsealed steam-injection system affects flakeboard dimensional stability. Two steam pressures (690 and 1370 kPa) and two steam times (10 and 30 sec.) were investigated. Core temperatures in isocyanatebonded, steam-injected pressed flakeboards were well above those recorded in conventionally pressed boards. Closing board pressures were considerably less than needed for conventionally pressed boards. Thickness swell of the steam-injected pressed flakeboard, following exposure to either relative humidity conditioning or a vacuum pressure soak treatment, was less than experienced in a conventional pressed board. Thickness swell, as well as linear expansion properties, improved as steam pressure and steam exposure time increased. The increase in board thickness during a 24-hour soak was similar in all specimens. Rapid moisture movement in the steam-injected press (SIP) boards is attributed to a reduction in the vertical density gradient and increased permeability as a result of the steam treatment. An analysis of variance test based on the board-to-board variance indicated no statistical difference in bending properties. Differences in shear properties are attributed in part to changes in the vertical density gradient.