ANALYSIS AND OPTIMIZATION OF THE CONDITIONING PHASE IN TIMBER DRYING

摘要

The conditioning phase of the conventional timber drying process has been investigated.rnDue to wood shrinkage, tensile stress will develop in the surface layer of the boardrnduring drying. This stress combined with the change in MC causes mechano-sorptiverncreep. If the process is abruptly terminated when the target MC is reached, then therernwill be a considerable internal MC gradient and the creep deformation will cause distortionsrnin subsequent machining. A conditioning phase is often introduced at the end,rnin order to reduce these problems. The conditioning phase has been analyzed with arnwood drying simulation model. It is shown that traditional conditioning cannot completelyrnreverse the deformations, even at very long conditioning times.rnAn optimizing procedure has thus been used to create a new conditioning “schedule”rnwhich gives the best possible result within a given time. Features of such optimizedrnschedules are presented. As the surface layer is elongated during drying, there is a riskrnthat considerable stress develops as the moisture profile levels out. In some cases internalrnchecking will be the result. The optimization procedure is thus modified to avoidrnsuch situations and the impact on the conditioning schedule is discussed.