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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 cup of trial BBT2 and spring and bow of trial BBT3. All other comparisons exhibited significant differences. All other comparisons exhibited significant differences. Total distortion results were unacceptable (< 90%) after drying for BBT1 vacuum trial but was acceptable for all other trials. A significant reduction in distortion to within acceptable limits between vacuum trial BBT1 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 37. Distortion results after drying – E. pilularis Trial BBT1 BBT2 BBT3 BBT4 Table 38. Distortion grade results – E.pilularis Trial Distortion - % In grade Spring Bow NA NA 100 100 NA NA 100 100 NA NA 100 100 Distortion (mm) Spring 3.5 Conventional Twist Cup Total NA NA NA 96 92 96 NA NA NA 93 99 93 NA NA NA 91 90 91 Conventional Bow Twist Cup 2.8 2.1 0.4 9.0 17.0 4.0 0.0 0.0 0.0 2.2 2.6 0.8 NA NA NA 4.2 3.6 0.3 15.0 25.0 4.0 1.0 0.0 0.0 2.7 3.7 0.6 NA NA NA 2.2 2.9 0.5 8.0 23.0 4.0 0.0 0.0 0.0 2.0 3.4 0.8 NA NA NA Vacuum Spring Bow Twist Cup Total Before drying 100 100 100 100 100 After drying 100 98 78 90 78 Before drying 100 98 100 100 98 After drying 100 100 93 80 93 Before drying 100 85 98 100 83 After drying 100 99 93 77 92 Before drying 100 100 99 100 99 After drying 100 100 96 77 96 Vacuum Spring Average 2.7 Maximum 10.0 Minimum 0.0 Standard deviation 2.1 Significance (p) 0.011 Bow Twist Cup 1.9 3.5 0.3 15.0 15.0 4.0 0.0 0.0 0.0 2.9 3.8 0.8 0.001 0.004 0.011 Average 2.4 Maximum 12.0 Minimum 0.0 Standard deviation 2.2 Significance (p) 0.0001 3.3 2.3 0.6 9.0 12.0 5.0 0.0 0.0 0.0 2.1 2.4 1.2 0.008 0.004 0.130 Average 2.5 Maximum 9.0 Minimum 0.0 Standard deviation 2.1 Significance (p) 0.529 2.2 1.9 0.8 17.0 9.0 5.0 0.0 0.0 0.0 2.2 2.1 1.1 0.925 0.003 0.029 Average 2.3 Maximum 11.0 Minimum 0.0 Standard deviation 2.3 Significance (p) NA 2.0 1.7 1.1 11.0 10.0 9.0 0.0 0.0 0.0 1.9 2.0 1.6 NA NA NA 11.0 0.0 2.4 NA 3.7 11.0 0.0 2.6 NA 2.7 10.0 BBT3 0.0 2.3 NA BBT4 Surface and internal checking BBT1 BBT2 Significant differences exist between the surface checking population means of the BBT1 and BBT3conventional and vacuum end-matched trials (Table 39). This was not the case for the BBT2 trial indicating comparable results. Unacceptable surface checking grade quality resulted for all trials. The BBT3 vacuum trial produced the best grade quality results (82% select, 70% check free) compared with all other trials. This can be attributed to schedule 72 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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