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Summary – C. citriodora A summary of the results for the C. citriodora trials is provided in Table 17, where unacceptable results are highlighted. The total drying time for the SPG1 vacuum drying trial was 14 days, 66% of the conventional kiln drying time from the green condition (21 days). The average final cross–sectional MC, MC gradient, drying stress, distortion, collapse, surface check, and end split results were all within permissible grade limits for the SPG1 vacuum trial. Similar results for the SPG1 conventional trial were obtained, with the exception of the final cross–sectional MC variation. The unacceptable final cross–sectional MC results for the SPG1 conventional trial were due to under–drying. Due to a fan failure during the SPG1 vacuum drying trial, we repeated the same vacuum drying schedule for the SPG2 vacuum drying trial. The total drying time for the SPG2 vacuum drying trial was 17.2 days (82% of the SPG1 conventional drying from green trial) and was longer than the previous trial due to over–drying. The total SPG2 conventional air-drying time was 144 days. Over– drying resulted in both vacuum and conventionally dried SPG2 boards achieving unacceptable final cross-sectional MC limits in accordance with AS 2796:1999; however the acceptable grade quality B was achieved for both SPG2 runs in accordance with the more recent AS/NZS 4787:2001. This seems to highlight a discrepancy between the standards. All other wood and dried quality properties were within permissible limits for the SPG2 vacuum drying trial, however only 8% of SPG2 conventionally dried boards achieved select grade for surface checking and unacceptable grade quality resulted for drying stress. Due to favourable dried quality resulting from the first two vacuum trials, we increased the DBT throughout the schedule for the SPG3 vacuum trial, with the aim of reducing the drying time. Also, the final equalisation EMC was increased to bring the final MC closer to the target (11%) and reduce drying stresses. The total drying time for the SPG3 vacuum trial was 12 days, 57% of the conventional kiln drying time from the green condition. Dried quality results for the SPG3 vacuum trial were all acceptable except for drying stress. However, the end-matched conventionally dried boards also achieved unacceptable drying stress quality results, suggesting this batch of C. citriodora was particularly prone to this form of drying defect. Additionally, under-drying resulted in unacceptable final cross-sectional MC grade quality for the conventional SPG3 trial. For the SPG4 vacuum trial, we chose the same schedule used for the SPG3 trial except we increased the equalisation time from 48 to 72 hours in an attempt to alleviate unacceptable drying stress recorded in the previous two trials. The total drying time for this trial was 13.6 days, 66% of the conventional drying time. For the vacuum trial all grade quality results were within acceptable limits. For the end-matched conventionally dried boards unacceptable twist and surface checking were recorded. Overall, the results show vacuum drying C.citriodora was significantly faster, producing better dried quality, than for conventional kiln drying. We recommend using the SPG4 vacuum drying schedule for this species based on the dried quality outcomes. 55 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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