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Distortion We measured distortion on undressed boards before and after drying. For all trials, cupping was not included in the total percentage of boards within acceptable limits as all cupping was removed after dressing. Significant differences do not exist between conventional and vacuum end-matched trials for spring and bow of trial JAR1, cup of trial JAR2, spring, twist and cup of trial JAR3, and bow, twist and cup of trial JAR4. All other comparisons exhibited significant differences. Total distortion results were unacceptable (< 90%) after drying for JAR1 conventional and vacuum trials but was acceptable for all other trials. A significant reduction in distortion to within acceptable limits between vacuum trial JAR1 and subsequent vacuum trials can be attributed to doubling the stack weighting from 500 kg to 1000 kg between trials. For all trials, twist was the predominant type of distortion for boards failing to meet the standard. Table 23. Distortion results after drying – E. marginata Trial JAR1 JAR2 JAR3 JAR4 Table 24. Distortion grade results – E.marginata Trial JAR1 Distortion - % In grade Spring Bow NA NA 99 100 NA NA 100 100 NA NA 100 100 NA NA 100 100 Distortion (mm) Spring 3.6 17.0 0.0 2.6 Conventional Twist Cup Vacuum Spring Bow Twist Cup Total Before drying 100 100 100 100 100 After drying 98 98 61 79 61 Before drying 100 100 100 100 100 After drying 0 0 96 81 96 Before drying 100 99 96 100 95 After drying 100 99 97 82 96 Before drying 100 100 100 100 100 After drying 100 100 94 97 94 Total NA NA NA 79 94 79 NA NA NA 92 81 92 NA NA NA 91 78 91 NA NA NA 94 97 94 Conventional Vacuum Spring Average 3.7 Maximum 15.0 Minimum 0.0 Standard deviation 2.9 Significance (p) 0.826 Bow Twist Cup 3.4 6.3 0.6 16.0 28.0 5.5 0.0 0.0 0.0 3.2 5.8 1.2 0.121 0.002 0.0002 Average 3.6 Maximum 11.0 Minimum 0.0 Standard deviation 2.2 Significance (p) 0.0004 2.9 8.0 0.0 1.7 < 0.0001 2.2 0.9 10.0 5.5 0.0 0.0 1.9 1.1 < 0.0001 0.325 Average 3.5 Maximum 10.0 Minimum 0.0 Standard deviation 2.2 Significance (p) 0.286 2.8 2.4 0.6 12.0 28.0 5.0 0.0 0.0 0.0 2.0 3.1 1.0 0.002 0.074 0.028 Average 1.7 Maximum 11.0 Minimum 0.0 Standard deviation 2.0 Significance (p) < 0.0001 1.5 2.0 0.2 9.0 32.0 2.0 0.0 0.0 0.0 1.7 3.6 0.4 0.688 0.274 0.243 4.8 15.0 JAR2 0.0 2.8 4.0 13.0 JAR3 0.0 2.9 3.0 11.0 JAR4 0.0 2.4 Surface and internal checking Bow 2.6 9.0 0.0 2.1 4.3 19.0 0.0 2.7 3.9 14.0 0.0 3.0 1.7 10.0 0.0 2.1 Twist Cup 4.0 0.2 22.0 4.0 0.0 0.0 4.0 0.7 3.6 0.7 24.0 3.0 0.0 0.0 3.6 0.8 3.1 0.9 16.0 3.0 0.0 0.0 3.1 0.9 2.1 0.2 12.0 5.0 0.0 0.0 2.4 0.6 Significant differences exist between the surface checking population means of all conventional and vacuum end-matched trials (Table 25). Unacceptable surface checking grade qualities resulted for the first two vacuum trials, JAR1 and JAR2 (Table 26). For the JAR3 and JAR4 vacuum trials acceptable surface checking grade quality resulted. We can attribute the improvement of surface check results for these vacuum these trials to reducing the DBT and increasing the WBD during the early stages of drying compared with previous trials. 61 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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