Pre-drying of collapse prone wood free of surface and internal checking

Abstract

Collapse is an abnormal shrinkage which occurs in some species of wood during seasoning. It is due to physical collapse of the fibre cells, and is usually seen to occur in one or more discrete earlywood bands. Surface and internal checks can be induced by differential shrinkages arising from collapse in some parts of boards. It has already been established that the onset of collapse during seasoning is a temperature dependant process. To determine how this temperature sensitivity affects collapse induced checking in Australian eucalypts during seasoning, a stress and drying model was used to compare different drying strategies for avoiding collapse induced checking. The model demonstrated that the best way of avoiding collapse checking is to dry at temperatures below the “collapse threshold temperature” for the timber. It indicated that it may be possible to dry the timber at fully collapsing high temperatures and then recover the collapse by steam reconditioning, but this strategy requires more investigation.