Aspen Bibliography

High-temperature kiln-drying of northern Aspen 2- by 4-inch light framing lumber


J.F.G. Mackay

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Forest Products Journal





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A high-temperature schedule suitable for drying mixed trembling aspen (Populus tremuloides Michx.) and balsam poplar (P. balsamifera L.) studs, according to grade requirements for maximum moisture content (MC) and with acceptably low degrade, was developed in a small laboratory kiln and confirmed in a semi-commercial steam kiln. Laboratory runs indicated that a high-temperature schedule with no high-humidity equalization period, or one of less than 18 hours, resulted in an unacceptably high percentage of pieces failing to meet the 19 percent-MC. requirement. Wet pockets in kiln-dried pieces could be detected by a resistance meter, but not by a power-loss meter. Wet-core aspen lumber will collapse and check during subsequent storage as the moisture gradients equalize. Drying temperatures of 250°F dry bulb and 180°F wet bulb, with an 18-hour high-humidity period to give satisfactory dissipation of wet pockets, result in a total drying time of about 96 hours. Although the average green MC of balsam poplar was 135 percent and that of aspen was 90 percent, the apparent greater permeability of the balsam poplar allowed both to dry in approximately equal times. Predominant degrade in aspen was crook, while in balsam poplar ring shake was very common. Since a supply of saturated steam is required for the high-humidity period, the use of gas-fired kilns is not recommended.