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Summary – E. pilularis A summary of the results for the E. pilularis trials are provided in Table 45 where unacceptable results are highlighted. The total drying time for the BBT1 vacuum drying was 25 days, 43% of reported (Pearn, 2007) conventional drying time from the green condition. The combined air/kiln drying time for the conventional trial was 144 days. Final cross–sectional MC, MC gradient, and collapse were within acceptable limits, according to the appropriate standards, for both the BBT1 vacuum and conventional drying trials. However, personal communications with Hurford Hardwood management (Engwirda, 2009), reveal tougher limitations are imposed on final cross-sectional MC variation for E. pilularis than those specified by AS 2796:1999 (Standards Australia 1999) and AS/NZS 4787:2001 (Standards Australia 1999). This is particularly true for strip flooring where a final cross–sectional variation of ± 1% is imposed for a target final MC of 10.5%. Therefore, the variation of final cross–sectional MC for the BBT1 vacuum trial is considered unacceptable by Hurford Hardwood. Using the same limitations, the BBT1 conventional trial final MC variation was acceptable. Drying stress results for the BBT1 vacuum trial were outside the acceptable limitations Surface checking results were not within acceptable limits for either the vacuum or conventional drying trials. Only 33% of the conventionally dried boards made select grade for surface checking compared with 78% for the vacuum drying trial. Internal checking was not within permissible limits for the BBT1 vacuum drying .Unacceptable end–splitting resulted from the BBT1 conventional trial Unacceptable twist distortion was recorded for the BBT1 vacuum drying trial. Unacceptable end splitting resulted from the BBT1 conventional trial. For the second BBT2 vacuum drying trial the drying schedule was adjusted to provide milder humidity conditions The total drying time for the BBT2 vacuum drying trial was 21.5 days, 37% of the conventional drying time (58 days) from the green condition. Final cross–sectional MC, MC gradient, collapse, and internal checking were within acceptable limits, according to the appropriate standards, for the BBT2 vacuum drying trial. Drying stress results for the BBT2 vacuum trial were still outside the acceptable limitations indicating again, surface checking results were not within acceptable limits for the vacuum trial Surface checking was also outside acceptable limits for the conventional BBT2 trial, so the results are comparable. Comparable results were also obtained for internal checking where unacceptable results were obtained for both trials. Twist distortion was greatly reduced to within acceptable limits for the BBT2 vacuum drying trial by doubling the concrete stack weighting between trials. An even milder schedule was used for the BBT3 vacuum where the total drying time for the BBT3 vacuum drying trial was 27.9 days, 48% of the conventional drying time (58 days) from the green condition. At the stage of writing this report the BBT3 conventional trial was still drying. Drying stress and internal check dried quality were improved to within acceptable limits for the BBT3 vacuum trial compared to previous trials due to careful schedule manipulation. All other BBT3 vacuum trial dried quality parameters were within acceptable limits except surface checking where 82% of boards made select grade. However, this is higher than any previous BBT vacuum or conventional drying trial to date. For the BBT4 vacuum trial we increased the EMC further during the early stages of drying up to 30% MC due to undesirable checking resulting from the BBT3 vacuum trial. Due to time constraints, conventional trial BBT4 did not occur. The total drying time for the BBT4 vacuum drying trial was 24.8 days, 43% of the previous conventional drying time (58 days) from the green 77 Evaluation of super–heated steam vacuum drying viability and development of a predictive drying model for Australian hardwood species – Final reportPDF Image | Evaluation of super-heated steam vacuum drying
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