Continuous densification of wood with a belt press: how knot features impact the densification outcome

Abstract

ABSTRACT Densification, i.e. the transverse compression of sawn timber has been studied and commercialised for well over 100 years but remains an expensive niche product with low annual production volumes. One reason for this is the reliance on time-consuming batch processes in a hot press. To solve this, a continuous densification process using a belt press, capable of densifying full-sized sideboards was developed. However, there is insufficient knowledge about the effect of knots on the densification outcome. The objective of this study was to assess how different knot parameters affect the densified wood in terms of damage and deformation to the knot itself and the surrounding wood material. Multivariate data analysis methods were applied to a dataset of 171 knots, described by 23 variables. The data showed that it is possible to densify knots in a continuous process without causing damage. Especially sound knots are often unproblematic, even at relatively large sizes, while densifying dead knots often resulted in unacceptable damage to the knot or the surrounding wood. From a material selection standpoint, any knots bleeding into the board edge and dead knots greater than 20 mm in diameter should be avoided altogether.