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Publication: Forest Products Journal
Authors: Kemp A E
Reference ID: 9(3):124-130
Publish Year: 1959
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Title: Factors Associated with the Development of Collapse in Aspen During Kiln Drying
Description:
Knowledge of the phenomenon of collapse is limited; yet it occurs commonly in several species including aspen, particularly in wet wood. This study relates to incidence, extent, and characteristics of collapse, and to the conditions under which it occurs; especially time-to-collapse as affected by temperature and relative humidity. A special instrument was developed to measure small changes (indicating collapse) in board profile while the board was undergoing simulated kiln conditions within the range of 140-170°F. and 40-70 percent R.H. Time-to-collapse was directly and linearly related to temperature while the relationship with relative humidity was third-degree (sigmoid). Collapse developed during the early part of the drying schedules (44-150 minutes after drying commenced), and usually started in the springwood. Wetwood zones were most likely to collapse, but these areas were not completely saturated as had been suggested before. However, collapse did occur while the entire specimen was above the fiber saturation point. Between about 40 and 70 percent, relative humidity appeared to affect time-to-collapse more than temperature did. Frequently, collapse was associated with a yellowish infiltration product.
Knowledge of the phenomenon of collapse is limited; yet it occurs commonly in several species including aspen, particularly in wet wood. This study relates to incidence, extent, and characteristics of collapse, and to the conditions under which it occurs; especially time-to-collapse as affected by temperature and relative humidity. A special instrument was developed to measure small changes (indicating collapse) in board profile while the board was undergoing simulated kiln conditions within the range of 140-170°F. and 40-70 percent R.H. Time-to-collapse was directly and linearly related to temperature while the relationship with relative humidity was third-degree (sigmoid). Collapse developed during the early part of the drying schedules (44-150 minutes after drying commenced), and usually started in the springwood. Wetwood zones were most likely to collapse, but these areas were not completely saturated as had been suggested before. However, collapse did occur while the entire specimen was above the fiber saturation point. Between about 40 and 70 percent, relative humidity appeared to affect time-to-collapse more than temperature did. Frequently, collapse was associated with a yellowish infiltration product.
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