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Summary – E. obliqua A summary of the results for the E. obliqua trials is provided in Table 60 where unacceptable results are highlighted. The total drying time for the MES1 vacuum drying trial was 36.3 days, 61% of reported conventional drying time from the green condition. Final cross–sectional MC variation, MC gradient, residual drying stress, distortion, and surface checking were within acceptable limits, for both the MES 1 conventional and vacuum drying trials. An unacceptable number of MES1 vacuum and conventionally dried boards contained internal checking. E. obliqua is particularly prone to this type of degrade. Unacceptable end–splitting resulted from the MES1 conventional trial which failed to make the lowest quality grade, but was minimal for the MES1 vacuum drying trial. We used a milder schedule for the second MES2 vacuum drying trial in an attempt to alleviate internal checking. The total drying time for the MES2 vacuum drying trial was 39 days, 63% of reported conventional drying time from the green condition. Final cross–sectional MC, MC gradient, residual drying stress, distortion, and surface checking were within acceptable limits for the MES2 vacuum drying trial. Internal checking results for the MES2 vacuum trial were still outside the acceptable limitations, but were an improvement on the first MES1 vacuum drying trial. For the MES2 conventional trial, all forms of degrade were within acceptable limits except for surface checking and end-splitting. As material provided for the MES3 trials were partially air-dried through exposure prior to testing the results are considered to be compromised and cannot be compared with previous trials. Although the results are presented in this report they are not discussed in this summary. Due to favourable dried quality resulting from the MES2 vacuum trial, we increased the DBT during the latter stages of the MES4 schedule, from 30% MC to final dry, to increase the drying rate and improve overall drying time. The total drying time for the MES4 vacuum drying trial was 36.7 days, 62% of reported conventional drying time. For the MES4 vacuum drying trial all forms of degrade were within acceptable limits. For the corresponding conventional trial, all forms of degrade were acceptable except for drying stress. Collapse was present for all vacuum dried boards before reconditioning. No noticeable collapse was present on the MES1 conventional trial boards as they had been reconditioned by the sawmill prior to analysis. Using MeshPore, we generated cross–section edge contours and calculated the surface area. The results show a significant increase in the average cross–sectional area between dry non– reconditioned and reconditioned samples and corresponding dry/green cross–sectional area ratios. Successful recovery of collapse after reconditioning was evident as 100% of reconditioned boards, when dressed to a thickness of 19 mm, were free of collapse-induced ‘miss’. Between 40 and 50% of non–reconditioned boards were free of collapse-induced ‘miss’ or ‘skip’ after dressing for all trials. The author proposes that the normalised ratio of dry/green surface area has potential to be used as a quantitative and comparative method (between/within species and treatments) to characterise collapse and the effectiveness of the reconditioning process. Overall, the results show vacuum drying E. obliqua was significantly faster producing the same or better dried quality than for conventional kiln drying. We recommend using the MES4 vacuum drying schedule for this species based on the dried quality outcomes and drying time. 91 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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