Veneer incising at the peeling lathe, a new technology developed at Forintek, has been increasingly applied in Canadian softwood plywood mills. Significant benefits include reducing veneer curl-up and spin-outs and increasing veneer recovery. However, a comprehensive study of the effect of veneer incising on the conventional hot-pressing process has not been undertaken so far. As part of the work on optimization of LVL/plywood hot pressing process, this report investigated the effect of veneer incising on the strength properties of Douglas-fir LVL/Plywood products. Lightly-incised Douglas-fir veneer peeled with a Forintek mini-lathe was used in comparison to non-incised Douglas-fir veneer. The three veneer moisture levels considered were 0%, 3% and 6%. The number of plies for plywood and LVL panels were 5 and 13, respectively. A mixed-level experimental design was employed. Using a statistical software program, JMP, the importance of factors affecting Douglas-fir LVL/plywood hot-pressing and strength properties were identified. Also the t-test was used to test the significance of the difference in panel mean strength. The results showed that:
1. For Douglas-fir species, the lightly-incised veneer (similar to that now used at mills) does not significantly affect the conventional hot pressing times for 1) 5-ply plywood panels if the target core temperature is 115 0C and 2) 13-ply LVL if the target core temperature is 105 0C, compared to non-incised veneer. The hot-pressing time increases with increase in veneer moisture content ranging from 0 to 6% for 5-ply plywood.
2. For Douglas-fir veneer, no occurrences of blows were observed after unloading the press even with 5-ply plywood panels at 6% veneer moisture content. Under the same conditions, the compression ratios of 5-ply plywood and 13-ply LVL using the lightly-incised veneer are slightly larger compared to non-incised veneer. Also higher moisture veneer results in higher panel compression ratio.
3. For 5-ply Douglas-fir plywood, there are no significant differences in plywood bending MOE and shear strength (lap-shear) between non-incised and lightly-incised veneer at either 0% or 3% veneer moisture content. However, at 6% veneer moisture content, the differences in mean plywood bending MOE and shear strength between non-incised veneer and lightly-incised veneer were identified significant; the mean bending MOE of 5-ply plywood using the lightly-incised veneer is about 10% higher compared to the non-incised veneer; on the contrary, the shear strength (lap-shear) of 5-ply plywood using the lightly-incised veneer is about 20% lower compared to the non-incised veneer. On a statistical basis, there is no significant difference in plywood mean bending MOR between non-incised veneer and lightly-incised veneer at each of the three moisture content levels.
4. For 13-ply Douglas-fir LVL, there is no statistical difference in edgewise bending MOE and MOR between the incised veneer and non-incised veneer at 3% veneer moisture content. Based on the limited number of replicates, the block shear strength through-the-thickness using the lightly-incised veneer is found to be approximately 10% higher compared to the non-incised veneer and this difference is found to be significant on a statistical basis. But the difference in block shear strengths parallel to grain between the incised veneer and non-incised veneer is not significantly different.
The study objective was to determine if differences in the quality of Douglas-fir in the B.C. Interior could be assessed on the basis of characteristics visible in standing trees so as to provide site-specific measures of stand value. Six sawmill studies, with a final sample of 1,862 trees are described. Sample trees were selected and their quality characteristics recorded. These trees were felled and their logs processed into finished lumber from which individual tree values were calculated. An index shows the effect of tree quality and tree size on average lumber value per unit volume. A description of each mill study allows comparison of average sound lumber recovery factors.