Specialty Timbers New ZealandPeeling pruned E. fastigata for high-stiffness veneers: Part 1. Green grade recoveries
By Rosie Sargent, John Lee, Doug Gaunt, March 2020.
Executive summary
New approaches are being sought to produce high stiffness veneers from New Zealand grown trees. Here the feasibility of producing high stiffness veneers from pruned Eucalyptus fastigata has been investigated.
42m3 of pruned 23 year old E. fastigata trees were harvested and 26 m3 of logs were delivered to JNL Masterton. Of these 13m3 were peeled into veneer and 11.5m3 were sawn. 1.5m3 of the logs delivered were deemed to be not suitable for peeling or for sawing. The primary reason for logs being unsuitable for peeling was end splitting, although some logs were too large (LED >600mm) to be peeled easily. The logs that were not peeled or sawn tended to be knotty and not very straight.
The logs to be peeled were divided into three stiffness classes. Peeling was straightforward, with good quality veneer being produced without needing to preheat the logs. The veneers were slower to dry than radiata pine, and even after slowing the drier down, or redrying the veneers, many were still above the moisture content limits.
All log stiffness classes produced veneers that had an average stiffness above that of the standard radiata pine veneers produced at the mill. Overall the E. fastigata veneers had an average stiffness of 14MPa, compared to 9.9MPa for radiata pine. This is a significant result, as improved veneer stiffness was the key outcome that was sought from this study. Net veneer recovery was 60% of the peelable volume (or 43% of the total volume of logs peeled).
End splitting was noted by mill staff as being an issue, based on their observations during production, but it was not possible to collect visual grading data for the veneers, so the severity of end splitting hasn’t be quantified. Future studies will need to quantify end splitting, to determine if this is likely to impact on the feasibility of producing E. fastigata veneer.
Sawing grade recoveries were relatively low (35% green recovery). The sawing pattern used (quarter sawing and cutting all boards to the same width) is likely to have reduced the recovery. Movement of boards off the saw, caused by growth stresses will also have reduced green recovery.
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