Accelerated Drying of Lodgepole Pine and Western Larch Poles

This paper reports a study designed to evaluate the performance of a pole-dryer developed by the J. Neils Lumber Co. and to obtain information on: 1) the effect of high- temperature drying on pole strength, 2) the development of drying defects, and 3) the effect of accelerated drying on the depth of penetration and the retention of the preservative. The 154-foot pole dryer is composed of 2 chambers: the upper chamber, serving as an air duct, contains 4 baffles; the lower drying chamber has 8 bands of heating coils. The recorder-controller has dual dry bulbs and one wet bulb. Machine-peeled western larch and lodgepole pine were randomly selected and dried for either 70 or 40.5 hours at temperatures of 180? and 230?F. Surface checking of from 126.5 to 143.5 inches per foot was found to occur uniformly over the poles. Strength and toughness differences between the dried and green specimens were generally small and inconsistent. When preservative penetration and retention were studied, it was found that, except for three poles, penetration exceeded the minimum required in American Wood-Preservers Standard C4-60. Average retention was greater than the 6-lbs.-per-cubic-foot minimum, with a maximum measurement of 9.9 lbs. in one high- temperature run. These results indicate that lodgepole pine and western larch poles can be dried at relatively high temperatures in 2 to 3 days and be satisfactorily treated with preservative.

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