TECHNIQUES TO MONITOR DRYING STRESSES AND DIMENSIONAL CHANGES IN TIMBER FROM PLANTATION-GROWN EUCALYPTS FOR KILN SCHEDULE DEVELOPMENT AND KILN CONTROL

R Northway

Abstract


Drying tests were conducted with timber from 13 year-old plantation-grownEucalyptus nitens and E. globulus, to determine shrinkage and drying degrade of tangential- and radial-sawn boards. The eucalypt species investigated exhibited a high level of collapse which was difficult to distinguish from normal shrinkage and confounded the results. Nevertheless some useful conclusions about the potential for these techniques to indicate drying stress in plantation grown Eucalyptus were drawn from the qualitative work undertaken: Cup measurements on a half-thickness board, sealed on one face, provided a qualitative indication of stress reversal. This was confirmed with stress prongs. Width of an artificial check did not provide a useful indication of the development of stress. Transverse surface shrinkage measured across specimens and across a fixed core did not provide a useful indication of the development of stress. Cup measurements and stress prongs indicated transverse strains at the surface while surface moisture content was still above fibre-saturation. Non-contact measurement of shape change during drying showed some potential for indicating drying stress but needs higher resolution scanning and special image analysis techniques to be developed. Optical profiling and image analysis may be useful in the development of a kiln control system based on material behaviour

Key words : drying; shrinkage; drying degrade; drying stress; kiln drying; kiln controls; eucalyptus.


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