Veneer Grade Analysis of Early to Mid-rotation Plantation Eucalyptus Species in Australia

Abstract

aProcessing Australian hardwood plantations into rotary veneer can produce more acceptable marketable product recoveries compared to traditional processing techniques (e.g. sawmilling). Veneers resulting from processing trials from six commercially important Australian hardwood species were dominated by D-grade veneer. Defects such as encased knots, gum pockets, gum veins, surface roughness, splits, bark pockets, and decay impacted the final assigned grade. Four grading scenarios were adopted. The first included a change to the grade limitations for gum pockets and gum veins, while the second investigated the potential impact of effective pruning on grade recovery. Although both scenarios individually had a positive impact on achieving higher face grade veneer qualities, the third and fourth scenarios, which combined both, had a substantial impact, with relative veneer values increasing up to 18.2% using conservative calculations (scenario three) or up to 22.6% (scenario four) where some of the upgraded veneers were further upgraded to A-grade, which attracts superior value. The total change in veneer value was found to depend on the average billet diameter unless defects other than those relating to the scenarios (gum or knots) restricted the benefit of pruning and gum upgrading. This was the case for species prone to high levels of growth stress and related defects.

Variation in Rotary Veneer Recovery from Australian Plantation Eucalyptus globulus and Eucalyptus nitens

“…The same grade scenario reported by McGavin et al (2014b) simulating effective pruning for E. nitens produced a change in grade recovery percentage of −33% for Dgrade, +16% for C-grade, and +19% for B-grade grade (difference between measured and simulated). This is close to what was observed in the present study, with D-grade recoveries for both the thinned and pruned sites having between 28% and 41% less than the unthinned and unpruned site, while C-grade recoveries for the thinned and pruned sites were between 13% and 16% higher than the unthinned and unpruned Florentine site.…”

“…Gum pockets ranked highly for the E. globulus sites. As suggested by McGavin et al (2014b), the size of this defect was often small and concentrated, and while it would influence the appearance of the veneer, it would be expected to have a negligible effect on mechanical properties or on the panel manufacturing process. The characteristics of this defect in the veneer are such that it may be unnecessarily severe to downgrade such quantities of veneer to D-grade, especially when compared with other appearanceaffecting defects, which are permissible in higher grades.…”

“…This was supported by the fact that surface roughness has more impact on E. globulus veneers, which also reported a higher severity of encased knots when compared with E. nitens. McGavin et al (2014b) reported a significant (p<0.001) and positive, although relatively weak correlation between sound or encased knot rank and veneer surface roughness rank.…”

“…Compression had less impact on the grade recovery of E. nitens veneer. McGavin et al (2014b) reported a grade scenario based on the improvement of veneer grade made possible with the implementation of effective pruning. For E. globulus, the simulated improvement included changes in veneer grade recovery percentage of −9% for D-grade, +11% for C-grade, and +5% for B-grade (difference between measured and simulated).…”

“…Defects such as bark and decay, encased knots, gum pockets, veneer splits, veneer roughness, and veneer compression were reported by McGavin et al (2014b) as the main contributing defects that cause high proportions of E. globulus and E. nitens veneer to be restricted to D-grade, the lowest grade described within AS/NZS 2269.0:2012 (Standards Australia 2012).…”