Peeling and sawing pruned E. fastigata for high-stiffness veneers: Part 2. Dry grade recovery and downstream testing
By Rosie Sargent, Steve Riley, November 2020.
Download SWP-T109 (pdf)
The feasibility of producing high stiffness veneers from E. fastigata has been investigated. Previous work found that the net veneer recovery was good (60% of peelable volume) and the Metriguard stiffness measurements were much higher than those typical of radiata pine (average of 14.3GPa, compared to 9.9GPa for radiata pine). Here the Metriguard measurements have been verified by separate density and time of flight measurements.
Logs that were not suitable for peeling (due to end splitting or log defects such as sweep and knots) were sawn into 100x25mm, or 100x50mm boards. This resulted in the logs being sawn having higher than average levels of growth stress, which will influence the results. The sawing pattern used led to a large volume of wood being trimmed from the board edges, which gave a low sawing recovery (35% net recovery) but should not have impacted the quality of the timber. The boards were air dried, and many of the boards exhibited collapse during drying. Once the boards were close to fibre saturation (20-30% MC) they were steamed to recover the collapse, then kiln dried. The boards showed no collapse following drying but did develop high levels of crook.
The major defects seen in the graded boards were crook (present in around 56% of boards), kino veins (present in 36% of boards) and knots (present in 26% of boards). 10% of boards achieved clears grade, 22% high feature grade and 22% cuttings grade. If crook was ignored (assuming it could be removed by improving the sawing process) 19% of boards achieved clears grade, 55% high feature grade and 8% cuttings grade. Overall, this shows that sawing and drying pruned E. fastigata is possible, but the sawing methods need to be improved to increase overall recovery and to mitigate the effects of crook.
A high level economic analysis showed that the value of products from these logs would need to be increased to make the process viable. Increasing the recovery of sawn timber would go some way towards addressing that, but finding higher value applications for the logs that were not suitable for this study would have a greater impact.
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