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Summary – E. marginata A summary of the results for the E. marginata trials is provided in Table 31where unacceptable results are highlighted. The total drying time for the JAR1 vacuum drying trial was 25.6 days, 42% of the conventional drying time from the green condition. For both vacuum and conventional JAR1 trials, we recorded unacceptable levels of twist distortion and drying stress. For both JAR1 trials, collapse internal checking and final MC gradient were within permissible limits. The final cross–sectional MC variation for the JAR1 vacuum trial was outside the permissible limits due to five under–dried ‘wet’ outlying boards, possibly caused by case-hardening. Unacceptable surface checking results were recorded for the JAR1 vacuum drying trial. Unacceptable end–splitting resulted from the JAR1 conventional trial. Due to results from the first trial, we implemented a milder schedule for the JAR2 vacuum drying trial. The total drying time for the JAR2 vacuum drying trial 19.5 days 32% of the conventional kiln drying time from the green condition. Schedule refinements resulted in acceptable final cross– sectional MC variation. Due to under-drying, the final cross-sectional MC results for the JAR2 conventional trial were unacceptable. Residual drying stress was improved between vacuum drying trials; but although still unacceptable, it was comparable to the conventional trial. We greatly reduced twist distortion to within acceptable limits for the JAR2 vacuum drying trial by doubling the concrete stack weighting between trials. For the JAR2 vacuum drying trial, surface checking results were still unacceptable but were acceptable for the JAR2 conventional trial. Similar to the previous trial, the JAR3 vacuum schedule was adjusted to give milder conditions. The total drying time for the JAR3 vacuum drying trial was 27.9 days, 41% of the conventional kiln drying time from the green condition. Apart from unacceptable drying stress (a problematic form of degrade even when conventionally dried) all other dried quality results were acceptable for the JAR3 vacuum trial. All dried quality results were acceptable for the JAR3 conventional trial. For the JAR4 vacuum trial we chose the same schedule used for the JAR3 trial except the equalisation time was increased from 48 to 72 hours in an attempt to alleviate drying stress. Unfortunately, a PLC circuit board malfunction cut short the JAR4 trial; consequently, we cannot directly compare the results with the other trials. Thus, the results of this trial are highlighted grey in Table 31. Overall, the results show vacuum drying E. marginata was significantly faster producing the same dried quality as for conventional kiln drying. We recommend using the JAR4 vacuum drying schedule for this species based on the dried quality outcomes of trial JAR3 that used the same schedule but with a shorter equalisation period. We believe an extended equalisation period for this species should improve drying stress grade quality results. Results show that drying stress seems to be an endemic form of degrade for this species independent of drying method. 66 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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