Comparison between HT-dried and LT-dried spruce timber in terms of shape and dimensional stability

Abstract

Abstract The performance of timber studs from Norway spruce (Picea abies) in terms of shape and dimensional stability was evaluated. The shape stability studied included three modes of distortion, i.e. twist, bow and spring. The dimensional stability was assessed by measuring longitudinal shrinkage and swelling properties. The study comprised 96 studs measuring 45 mm×70 mm×2500 mm from 15 butt logs. Half the studs from each log were dried using a high-temperature method (HT) at 115°C, while the other half were dried using a conventional low-temperature method (LT) at 70°C. Distortion in the studs was measured at moisture contents of 14% and 9%. The HT-dried timber had significantly lower distortion values than the LT-dried timber. As a result, 80% of the high-temperature-dried studs were able to pass the limits for distortion, while only 60% of the low-temperature-dried studs passed the same limit. Studs cut close to the pith displayed the largest twist, independent of the drying method. A simple model for predicting twist that was used in previous studies was also valid for HT-dried timber. The most important parameters in this model for both HT- and LT-dried timber were grain angle, annual ring curvature and tangential shrinkage.