CT-SCANNING DURING HEAT TREATMENT OF WOOD

Earlier experiences from industrial heattreatment of wood with the ThermoWood processshow that more or less extensive internal crackingmay occur for thicker dimensions. This type of timberdamage is particularly troublesome because thesecracks do not reach the surface and are thus notvisible on unprocessed timber. After resawing orplaning the boards, cracks can appear, resulting incostly downgrading of the material. TheThermoWood heat treatment process can bedivided into six periods. The first period, the heatingperiod, is when saturated steam is injected into thekiln, the second period is the drying step, which canbe either high or low temperature drying, the thirdperiod is when the final heating and drying takeplace, the fourth period is when the temperature iskept constant for about 2–4 hours, the fifth period isthe cooling regime, the sixth period is theconditioning regime for remoistening the material,and the last period is the cooling one. At the Divisionof Wood Physics at Lule University of Technologyin Skellefte a climate chamber has recently beeninstalled. This climate chamber together with a CTscannermakes it possible to study wood densitychanges in different climates. As the maximumtemperature that can be reached in the climatechamber is 220 °C, it is also possible to study theheat treatment process, besides conventional aircirculation drying. The aim of this study was to usethe CT-scanning (CT) technique during heattreatment of wood in order to investigate whether it ispossible to detect internal checking in situ during thetreatment.