Annual ring orientation effect and slope of grain in hemlock timber drying
2004
Hao, B. | Avramidis, S.
This research was designed to evaluate the effect of annual ring orientation and slope of grain on the drying characteristic of 115-mm-square Pacific Coast hemlock timbers in a heat-and-vent kiln in an effort to reduce degradation and shorten drying time. The results suggested that the horizontal annual ring orientation pile arrangement shortened the drying time by 11.2 percent (2 days shorter) whereas the vertical one lengthened the drying time by 38 percent (7 days longer), compared to the control. Both vertical and horizontal orientations resulted in higher yield by at least 4.1 percent compared to the control. In each run, twist, bow, and diamonding changed significantly after the timbers were kiln dried when compared to their measured green deformations. After drying, the vertical ring orientation showed significantly greater bow change and shrinkage compared to the control and to other runs. The measured apparent slope of grain occurrence on the 800 specimens dried was not important as expected, resulting in a mean value of 1.2 degrees with a standard deviation of 0.34 degrees. Slope of grain effects on drying rates and shape distortions were inconclusive, probably due to the low value. Twist, bow, and diamonding after planing were significantly reduced for each run compared to their measured values before planing, but there were still 8.5 percent of timbers with bow and 7.8 percent of timbers with twist more than 3 mm.
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