Effective non-destructive segregation of Eucalyptus grandis logs according to radial and tangential hardness

Abstract

SummaryBasic density and hardness strongly influence the quality of high—value end products, such as floor boards. Significant variations in wood properties have been identified both within and amongst logs of plantation-grown Eucalyptus grandis (flooded gum or rose gum), which typically feature an inner cylinder of corewood characterised by low wood density, hardness and strength. These and other defects near the core are not easily detected until the log is sawn open and thus committed to a particular end-use. Despite this, it is important that only logs with suitably dense and hard wood in the core are processed into high-quality flooring.This study assessed the utility of a non-destructive tool, the Pilodyn, for gauging the radial variation in density and hardness amongst plantation-grown E. grandis logs prior to sawing. Pilodyn readings were taken at intervals across the ends of 40 typical fresh flooded gum logs about 5 m long. A sub-sample of 15 logs, representative of the Pilodyn penetration (P-pen) spectrum, was selected for more intensive testing. Janka hardness tests on air-dried specimens indicated characteristically low hardness (<3 kN) in the inner zone of every log. However, Janka hardness in the outerwood was found to be highly variable amongst logs. The segregation of logs into classes of P-pen readings (low, medium and high) provided a useful basis for predicting Janka hardness values: the correlation between the weighted average P-pen reading and weighted average Janka hardness was 0.80 and 0.81 for hardness on the radial and tangential faces respectively. Within each of the Pilodyn classes, the bending stiffness and strength, and compression strength parallel to grain of the timber, increased in the radial direction.Pilodyn tests on the end face of logs may assist processors to identify those logs with particularly problematic proportions of corewood and/or quality.