The conditioning regime in industrial drying of Scots pine sawn timber studied by X-ray computed tomography: a case-study

Abstract

Industrial drying of sawn timber is a process driven by a difference in moisture content (MC) between the core and the surface as moisture moves from the wet inner region towards the drier surface. After drying, the timber surface is always drier than its core, and stresses have developed within the wood volume. If the timber is to be further processed, these stresses and the moisture gradient need to be reduced to avoid unwanted distortion, i.e. the timber needs to be conditioned. Conditioning is usually accomplished by exposing the timber to a hot and humid climate after the drying regime. The conditioning regime is essential for timber quality, and it is energy and time consuming; therefore of interest for optimisation. This research was a case study where for the first time the MC during conditioning was studied in an X-ray computed tomography (CT) scanner. The aim was to test a previously developed algorithm and investigate the influence of MC and heartwood-sapwood proportion on the effectivity of the moisture equalisation in 30 mm thick Scots pine boards. The MC was estimated from CT data acquired during the drying and conditioning of the boards in a lab-scale kiln adapted to a medical CT scanner. Results show that the algorithm can provide relevant data of internal MC distribution of sawn timber at the pixel level. Furthermore, for the drying schedules studied, the conditioning at low MC (8%) does not need to be longer than 3 h, while higher MC (18%) requires a longer conditioning.

Investigating the drying characteristics of Anthocephalus chinensis (Lam.) A. Rich ex Walp wood

“…The proportion of collapse occurred for 7.3% of the total dried boards. Drying defects depend on the initial moisture content [ 5 , 23 , 24 , 25 , 26 ] and pith content [ 2 , 27 ] of the samples. From this study, it was noticed that 38.1% of the wood pieces consist of knots (dead and alive), and 25.82% consist of pith.…”

Macroscopic X-ray computed tomography aided numerical modelling of moisture flow in sawn timber

“…1. It consists of (a) an experiment to image the kiln drying of timber using macro X-ray CT (Couceiro et al 2020), (b) an image processing step to determine the MC of timber from CT data (Hansson and Cherepanova 2012), (c) a numerical step to develop a CT-aided FE model to simulate moisture flow within timber during kiln drying, and (d) an experimental validation of the numerical simulations based on the outcomes of steps b and c. The figure also illustrates the required input and output for each step. The experiment is described in subsect.…”

“…A medical Siemens Somatom Emotion Duo CT-scanner (Siemens, Munich, Germany) was used in combination with a custom-made integrated kiln (Hansson and Cherepanova 2012) to obtain cross-sectional density images of the specimen during drying. A detailed description of the experimental setup has been reported earlier by Couceiro et al (2020).…”