Drying schedule structure and subsequent post-drying equalisation effect on hemlock timber quality

Abstract

Western hemlock (Tsuga heterophylla), was dried using two different schedules with optional conditioning and seven day post-drying equalisation in a covered and climate controlled space that emulates outdoor conditions in south-central Japan from October to May. Timber quality was evaluated pre- and post-drying, and/or post-equilibration. Drying times, moisture content variation between and within timbers and internal stresses were also assessed. Data analysis revealed that conditioning and aggressive drying reduced casehardening, while milder drying resulted in less twist and diamonding. Although the control run seemed to develop less shape distortions than the treatments, it required longer drying times. With aggressive drying the kiln turnover will be quicker and the dried timber might be stored in a covered area for post-drying equalisation that will level out moisture gradients and alleviate casehardening. As a subsequent step, the timber might be planed to reduce twist, diamonding and superficial checks.