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Summary

Two plywood mills processing the same species, Douglas fir and Spruce into plywood veneer but using different log conditioning systems made their weekly production records, digitally archived since 2010, available for analysis and comparison. Variation on the yearly, monthly and in some cases weekly basis was examined for possible signs of seasonal effects on conditioning and log dryness on veneer production. The main findings were: • Identifiable factors such as extreme log dryness and lower log conditioning temperatures in winter had strong effects on recovery, particularly in the case of Douglas fir. • While overall the mills were similar in weekly recovery, one was more variable and had experienced a few sustained periods of depressed weekly production associated with extreme log dryness (very low % heavy sap sheet counts) and high spinout rates. Average weekly net recovery is normally between about 600 to 700 sf (3/8’s basis) per m3, but during a 27 week period in mid-2015 it fell to below 600. A calculated green veneer recovery per volume fell to as low as 650 sf 3/8s/m3 when it should be around 780 sf 3/8s/m3. An estimate of plywood revenue losses associated with this April-September period of processing dry logs compared with the same time frame in other years was > $1 million. • After the backlog of very dry logs had been processed by the mill, average weekly net recovery increased to mostly between 650 and 700 sf 3/8’s per m3 during 2016, through a combination of significant improvements in stock handling and rotation times, conditioning practices and incremental optimisation of lathe operations. • Seasonal patterns in the production data suggest the existing water spray conditioning process is not as effective in winter as steam conditioning facilities at the other mill, even though the conditioning time is considerably longer. Even with the longer conditioning times used in December-January, average weekly block (core) temperatures were lower and much more variable than the summer months. • Higher spin-out rates and lower recovery were observed in the winter months at the mill using warm water conditioning. Over the 6 year data sample period average weekly net recovery for Douglas fir was 604 sf 3/8’s per m3 in December-January compared with an average of 645 sf 3/8’s per m3 during the May to September period. An estimated value of the reduced production was more than $0.5 million in today’s plywood prices. • Despite the differences in veneer temperature measurement between the two mills, average veneer temperatures and production indices at the mill using steam conditioning were far less variable, and there was no ‘winter’ effect observed on spinout rates and recovery. In fact average veneer temperatures were higher in winter than summer with the slightly longer steaming time given to blocks. • The historic veneer conversion rates between the two mills were only slightly different, likely reflecting background differences in diameters, taper and log dryness at peeling, as well as differences in lathe operating parameters. Spruce was estimated to have a slightly lower conversion efficiency than Douglas fir, especially at the mill with water conditioning.

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