The Impact of Harvesting Age/Tree Size on Sawing, Drying and Solid Wood Properties of Key Regrowth Eucalypt Species

Transcription

1 Manufacturing & Products The Impact of Harvesting Age/Tree Size on Sawing, Drying and Solid Wood Properties of Key Regrowth Eucalypt Species Project No. PN

2 2005 Forest & Wood Products Research & Development Corporation All rights reserved. Publication: The Impact of Harvesting Age/Tree Size on Sawing, Drying and Solid Wood Properties of Key Regrowth Eucalypt Species The Forest and Wood Products Research and Development Corporation ( FWPRDC ) makes no warranties or assurances with respect to this publication including merchantability, fitness for purpose or otherwise. FWPRDC and all persons associated with it exclude all liability (including liability for negligence) in relation to any opinion, advice or information contained in this publication or for any consequences arising from the use of such opinion, advice or information. This work is copyright and protected under the Copyright Act 1968 (Cth). All material except the FWPRDC logo may be reproduced in whole or in part, provided that it is not sold or used for commercial benefit and its source (Forest and Wood Products Research and Development Corporation) is acknowledged. Reproduction or copying for other purposes, which is strictly reserved only for the owner or licensee of copyright under the Copyright Act, is prohibited without the prior written consent of the Forest and Wood Products Research and Development Corporation. Project no: PN Researchers: T. Innes Timber Research Unit University of Tasmania Locked Bag 1324, Launceston TAS 7250 M Armstrong Horticulture and Forestry Sciences Department of Primary Industries and Fisheries PO Box 631, Indooroopilly QLD 4068 G Siemon Forest Products Commission Locked Bag 888, Perth Business Centre, WA 6849 Final report received by the FWPRDC in December 2005 Forest and Wood Products Research and Development Corporation PO Box 69, World Trade Centre, Victoria 8005 Phone: Fax: info@fwprdc.org.au Web:

3 The Impact of Harvesting Age/Tree Size on Sawing, Drying and Solid Wood Properties of Key Regrowth Eucalypt Species Prepared for the Forest & Wood Products Research & Development Corporation by T. Innes, M. Armstrong and G. Siemon

4 Summary Younger and faster grown regrowth eucalypt forests are an increasingly important source of hardwood in Australia. The wood quality of this resource is largely unknown. This work quantifies the effect of age (or tree size) on sawing, drying and solid wood quality properties of regrowth Tasmanian messmate, Western Australian jarrah, Queensland spotted gum and Victorian silvertop ash. Three batches of jarrah, spotted gum and silvertop ash logs and four batches of messmate logs were each processed together following best commercial practice in sawing, drying and milling for each species. They were evaluated during and after processing. Processing was carried out in the source state except for silvertop ash, which was sent to Tasmania for drying and further processing following sawing in Victoria. Jarrah was batched by size class as jarrah is selectively logged, so determination of age is not possible. Spotted gum was also selected by size, but assessment of crown vigour indicated that the batches were also of distinct age. Younger messmate logs had lower heartwood proportion than older logs. There was no trend with age of basic density, initial moisture content, drying rate, strength or hardness. Boards cut from younger material shrank less than older but yield of select grade was substantially lower due to gum vein. It appears that the oldest logs had the highest growth stress, as those logs had the most end splitting and boards cut from them the most spring. The youngest messmate (1967 regrowth) underwent significant internal checking and its properties were generally more variable. Regrowth messmate had substantially lower differences between radial and tangential unconfined shrinkage than published figures. Strength properties measured were equivalent to those published for mature timber, while hardness was lower. Heartwood proportion in larger jarrah logs was higher than in smaller logs. Larger logs had lower initial moisture content and higher basic density. However, there was no significant difference between groups when comparing endsplit, stiffness, strength, grade, distortion or hardness. Strength properties measured were superior to those published for mature timber, while hardness was equivalent. Recovery of select grade boards was lower from smaller logs of spotted gum. There was no trend with log diameter of basic density, end splitting, surface checking, stiffness, strength, or hardness. Strength and hardness properties measured were superior to those published for mature timber. Younger logs of silvertop ash had lower heartwood proportion and produced timber of lower basic density and higher initial moisture content than that from older logs. There was no trend with tree age of unconfined shrinkage, drying rate, dried quality, strength or hardness. The oldest age batch produced timber of very poor quality, with large amounts of surface checking, end splitting, kino, insect attack, stain and decay. Despite being the oldest, this age batch produced logs of medium size only, indicating that the site was probably poor. Over 90% of boards from all batches suffered internal checking despite mild drying conditions. This work demonstrates that for regrowth messmate, there was a decrease in select grade recovery from younger logs along with higher variability in some properties and significant internal checking. Smaller spotted gum logs produced a lower yield of select grade boards. There were no substantial differences between timber cut from the three log sizes of jarrah. The youngest trees of silvertop ash had significantly higher heartwood proportion and produced timber with higher initial moisture content and lower basic density than that from trees ten years older. Dried quality of silvertop ash was very poor, particularly that cut from the oldest age class. i

5 Sawing volume recovery and wide board recovery will generally be lower from smaller logs given a similar sawing pattern (due to simple geometry), recovery of higher grades may be lower in some species due to natural defect such as gum vein and batching technologies may be required to reduce variability. It was not possible to specify an optimum age or range of ages for harvest of the species studied. ii

6 Contents INTRODUCTION TASMANIAN REGROWTH MESSMATE (EUCALYPTUS OBLIQUA) METHODOLOGY RESULTS ANALYSIS WESTERN AUSTRALIAN REGROWTH JARRAH (EUCALYPTUS MARGINATA) METHODS RESULTS AND DISCUSSION BOARD EVALUATION STRENGTH AND HARDNESS TESTING ANALYSIS QUEENSLAND REGROWTH SPOTTED GUM (CORYMBIA CITRIODORA) METHODOLOGY RESULTS VICTORIAN REGROWTH SILVERTOP ASH (EUCALYPTUS SIEBERI) METHODOLOGY RESULTS ANALYSIS RECOMMENDATIONS AND FURTHER WORK REFERENCES APPENDIX 1. REPORT ON RING COUNTS FROM SELECTED SPECIMENS OF TASMANIAN EUCALYPTUS OBLIQUA APPENDIX 2. REPORT ON RING COUNTS FROM SELECTED SPECIMENS OF EUCALYPTUS SIEBERI FROM VICTORIA iii

7 Introduction Under the Regional Forest Agreements, younger and faster grown regrowth eucalypt forests will be an increasingly important source of commercial hardwood in Australia. The wood quality of this resource is largely unknown but is expected to be different from that of currently harvested mature native forests. Knowledge of the wood quality of this resource is of interest for its efficient utilisation and will affect the economic viability of the timber industry. Processing and utilisation of this comparatively new resource may present problems typically associated with reduced log diameter, higher levels of growth stresses and a larger proportion of juvenile wood. Growth stresses result in end splitting of logs following tree harvesting and distortion of boards following sawing of logs. As end splits in logs and distortion of boards requires trimming they reduce sawn timber recovery and also the average dimensions of sawn boards. Sawn timber yield losses resulting from growth stresses are reported to exceed 10% in some Australian and South African sawmills. Seasoned regrowth timber is used for a range of applications including flooring, decking, structural, panelling, mouldings and furniture. Wood quality requirements for these applications include: (1) strength properties such as stiffness and hardness; (2) dimensional stability such as low distortion, shrinkage, collapse; (3) biological performance such as durability and consistent colour; and (4) manufacturing performance such as good machining. These wood quality requirements are important traits for evaluating the sawing properties and wood quality of a resource for solid timber utilisation. Strength, dimensional stability and biological performance are wood quality requirements thought to increase with tree age and it has also been suggested that extending harvesting age may reduce the effects of growth stresses. An understanding of the influence of age on these wood quality properties is therefore critical in maximising recovery and determining the suitability of the timber for particular applications and hence the harvesting age. This work quantifies the impact of age (or tree size) on sawing, drying and solid wood quality properties of regrowth Tasmanian messmate (Eucalyptus obliqua), Queensland spotted gum (Corymbia citriodora), Western Australian jarrah (Eucalyptus marginata) and Victorian silvertop ash (Eucalyptus sieberi). Work in Tasmania (on messmate and silvertop ash) was performed by the Timber Research Unit, University of Tasmania; that in WA by the Forest Products Commission and that in Queensland by the Department of Primary Industries and Fisheries. 1

8 1. Tasmanian regrowth messmate (Eucalyptus obliqua) Trevor Innes Timber Research Unit, University of Tasmania Note that all work on the 1901 batch described below was funded separately by the Tasmanian industry (through the Forests and Forest Industry Council, FFIC) as a control group, additional to the FWPRDC funded study on the other three age classes Methodology Sample Material Four different age classes were sampled; see Table 1.1. A minimum of 100 sample boards for each experimental group was required, with no more than ten boards cut from any log. The 1949 age group required eleven logs, with ten sampled for each of the other age classes. The butt log only was sampled for each tree. Trees were either co-dominant or dominant and not edge trees. Coupes were selected with the assistance of Forestry Tasmania as being representative of the resource of that age, with coupes consisting of trees of uniform age resulting from wildfires. Trees were selected as being generally representative of the stand, without limits on size or sweep etc. Age of trees was taken from the fire history for each coupe. Each log was identified by a colour (from Table 1.1) and a number Pre-felling Prior to felling, breast height diameter over bark was measured for each tree Post-felling For each tree: date of felling was recorded; total height, height to 30cm under bark small end diameter and height to 20cm under bark small end diameter were measured; a 3.1 m butt log (clear of butt swell) was cut for 1967 logs; other logs were delivered full length and cut to length at the sawmill; both ends of logs were painted with appropriate colour from Table 1.1; each log was marked with an identification label of tree number; large and small end diameters of log were measured; and length of longest endsplit up log on both small and large ends was measured. Logs were then transported to the appropriate mill and stored separately from general mill stock under waterspray, until sawing logs were cut in a thinning operation and delivered to Clennetts sawmill, Dover, in short lengths via tip truck, see Plates 1.1 and and 1934 logs were delivered as part of commercial loads to McKay Timber, Glenorchy (Plate 1.3), generally in long lengths logs were delivered to Kelly Timbers, Dunalley, in mixed lengths. 2

9 Log processing endsplit of both ends of each log was re-measured prior to sawing; 50 mm thick discs were cut from the butt end of each log, labelled and transported to the laboratory (these discs were all taken from approximately similar heights in the tree; over-length logs were docked to 3.0 m by removing the top end; logs were re-end coated and colour coded with a different colour on the freshly cut end so that individual logs could be tracked through the sawmill; and logs were quartersawn at the three locations described above (see Plates ) during normal commercial operation, with all boards cut clear of sapwood. Boards were cut to 25 mm thickness, width from 125 mm down to 75 mm (all dimensions are nominal dry). Where possible, boards were selected from throughout each log, rather than from one or two flitches. Experimental groups were kept separate. Sawn recovery was not recorded since the logs were sawn at three different mills. Useful comparisons of recovery could only have been made if each mill was set up to produce optimal recovery from the logs processed there. Boards were block stacked, tightly wrapped on all sides with plastic (Plate 1.7) and transported to the Neville Smith Tasmania (NST) site at Mowbray (Launceston) Drying for each board the following measurements were made: Length, Width, Thickness, Endsplit (numbered end), Endsplit (other end), Spring (if greater than 10mm), Length degraded by surface check. Endsplit was measured as the length of board affected by the longest end split at each end of the board. This is the length of board that would have to be docked to remove all endsplitting; racks were hand built on site at NST by TRU staff, see Plate 1.8; racks were end-coated; six 300 mm long sample boards were used per rack of approximately 100 boards. MC, width and thickness were monitored throughout the trial; an additional 100 mm long sample was cut adjacent to each MC sample board for determination of unconfined shrinkage, initial MC and basic density; and another 14 boards were randomly selected from each pack for determination of unconfined shrinkage (four boards only), initial MC and basic density. Boards were dried in a 10 m 3 kiln belonging to the FFIC, located at on the NST site at Mowbray see Plate 1.9. The kiln was constructed specifically for experimental predrying of Tasmanian eucalypts and so generally controls very well at low temperatures (typically within 0.5 C).The predrying schedule used is shown in Table 1.6. When sample boards indicated that MC had fallen to approximately 20%, timber was reconditioned and final dried to the schedules shown in Table Dry measurements sample boards were measured, oven dried and weighed; 3

10 following removal of samples for strength and hardness testing, boards were machined to 19 mm thickness, Plate 1.10, by removing 2 mm from the bottom surface and the rest from the top; boards were measured for: Endsplit (numbered end), Endsplit (other end), Spring (if greater than 10mm), Length degraded by surface check on each face, Length degraded by skip on each face, Grade to Australian Standard AS 2796 (Standards Australia 1999) and Moisture content (by resistance meter); and a 100 mm long section was then cut from the end of the board or clear of endsplit (whenever present) and the freshly cut end evaluated for internal check and sawing orientation. End split was measured using the same methodology as when green; the length of the longest end split at each end of the board. Australian Standard AS 2796 (Standards Australia 1999) describes four grades based on features and desired aesthetic appearance. The three grades commonly used are select, Medium Feature Standard and High Feature Grade. Grading was performed by a qualified commercial grader, who assigned the full length of each wide face a single grade, ignoring length affected by end splits and ignoring machining skip. Note that AS 2796 is generally applied on all four faces. For this study, the edges were not graded as they were not machined since boards were of varying width. The two wide faces were graded separately as many products expose only one face, for example flooring or architraves. Amount of spring (edgewise distortion) allowable in various products is also specified by AS 2796 (Standards Australia 1999) as a function of board width and length. A minimum of 10 mm over a board length of 2.4 m was recorded, as this is acceptable for the widths of boards studied for all products except joinery and dressed boards. Boards were only dressed on wide faces, so spring on the same boards dressed to width would have been lower than the figures recorded. Boards were scored with either no internal check, or internal check present, without attempting to categorise severity. Backsawn orientation was defined as all growth rings making an angle of less than 45 with the wide surfaces; quartersawn was defined as this angle being less than 45 ; transitional sawn was defined as having a mixture of backsawn and quartersawn parts Disc measurements A dendrochronologist performed a count of growth rings on several discs to verify that the age classes were indeed distinct and that tree age was consistent with recorded fire history; and pith, heartwood and sapwood width were measured on each disc across two diameters at right angles Green measurements initial MC and basic density were measured on twenty randomly selected board samples per group (see Drying section above); and unconfined shrinkage in the radial and tangential directions were measured for ten of the twenty samples from each group. 4

11 Unconfined shrinkage is the shrinkage undergone by a thin slice of wood (approximately 0.8 mm thick) allowed to dry naturally in the laboratory, unaffected by drying gradients and stresses. Board shrinkage is lower than unconfined shrinkage due to the restraining effect resulting from moisture gradients due to drying; early in drying, the surface of boards is under tension, while later in drying the middle parts are under tension. This tension induces a set in the board, reducing overall shrinkage. From each curve of shrinkage versus moisture content, three points were selected for reporting: green MC (zero shrinkage), and shrinkage and moisture content at both FSP and EMC Strength and hardness measurements 10 dry samples per experimental group were used for hardness and strength testing. They were cut from the same boards as the MC sample boards, plus another four taken randomly from the 14 boards initially sampled for shrinkage, initial MC and basic density. They were cut prior to machining as 20 mm thickness was required for strength testing; 400 mm long samples were cut 100 mm clear of endsplit, at least 200 mm from the board end. They were then machined to give a 100 mm long hardness sample and a mm MOE/MOR sample; strength and stiffness testing was carried out as described by (Mack 1979), in the section Static bending, centre point loading, as specified in Australian Standard 2878:2000. Samples were loaded in the radial direction; and hardness was measured using the Janka hardness test as described by Mack (1979). Two points were tested for each sample. Samples rejected because of defect were replaced with other samples cut from the same board if possible, otherwise replacement samples were cut from boards from the same log. Strength testing was performed on a calibrated Instron tensile testing machine located at FurnTech, Launceston; see Plates 1.13 and Modulus of elasticity (MOE) was calculated by fitting a straight line by eye to the first part of the load-deflection trace. Modulus of rupture (MOR) was also calculated. These were corrected to values at 12% MC based on the oven-dry MC (Standards Australia 1997) of each sample by adjusting bending strength by 4% for each 1% difference in MC and MOE by 1.5% for each 1% difference in MC. Adjustments were negative for MC below 12% and positive for MC above 12%. This complies with the rules of Australian Standard AS 2878 (Standards Australia 2000). A strength group was calculated for each sample and experimental group using the rules of AS Janka hardness testing was also conducted using FurnTech s Instron; see Plates 1.15 and Oven dry MC was measured for each sample, as was sawing orientation, that is, whether the test face was a radial or tangential surface Results Logs Coupe and log details for the four batches are shown in Table 1.1. The varying log lengths may have affected end splitting results, but were forced by practical constraints. No measurements could be made on 1949 logs prior to delivery to the sawmill due to practical constraints. 5

12 It was not possible to remove confounding effects from any site or silvicultural factors. Single-aged regrowth forests are not common. They generally arise in Tasmania as a result of fire, but fires sufficiently intense to kill all trees in a forest are unusual. Locating forests of different uniform ages on similar sites with similar silvicultural histories proved impossible. A dendrochronologist (Dr K. Allen; see report in Appendix 1) examined nine discs in an attempt to verify tree age. Note that dating of eucalypts by ring counting is generally not highly accurate; uncertainty in this case was approximately ±15-20 years. Dating was performed in this instance to ensure that the ages of each group were distinct and consistent with the fire history Disc measurements Disc measurement results, averaged over the four radii, are presented in Table 1.2. Heartwood proportion is calculated as a percentage of the disc surface area Sawing Summary sawing data is shown in Table Green timber properties Basic density and initial moisture content results are shown in Table 1.3. Fit points to the measured unconfined shrinkage curves are shown in Table Drying Unfortunately some kiln control problems were experienced for this trial. The humidification sprays had become partially blocked and the tuning parameters altered to suit. Replacement of the sprays was necessary to achieve the desired humidity level; unfortunately the humidity then remained well above setpoint until the control system was retuned. This slowed the drying significantly in the early stages (see hump at around 37 days drying in Figure 1.1 and following decreased drying rate). The kiln is situated on a commercial site that does not have steam on weekends or public holidays. The kiln was shut down for these periods. Moisture content samples in each experimental rack were regularly monitored. Drying progress of the samples is plotted in Figure 1.1. Thickness of the sample boards is plotted in Figure 1.2 to give an indication of shrinkage in thickness and recovery from reconditioning. Dry width and thickness of all boards is shown in Table Machining and dry grading Unfortunately, removal of 2 mm from the bottom surface was insufficient, and led to significantly greater machining skip on that surface. Grading results are shown in Table 1.8. Boards were assessed in the laboratory for total length degraded by endsplit (Table 1.9), machining skip or surface check on each side, Plate 1.12 and Table Spring (if greater than 10mm) was measured over a 2.4 m length of each board (Table 1.11). There was no significant twist or cup in any of the boards. A 100 mm length was then removed from the end of each board and the freshly cut end evaluated for internal check (Table 1.10) and sawing orientation (Table 1.5). 6

13 Strength testing Strength test results are shown in Table Hardness testing Janka hardness test results are shown in Table

14 3m Log Prior to sawing Log details Log Breast Height to Height to Small Large Endsplit Endsplit no. height dia 200 SED 300 SED end end length length over bark underbark underbark diameter diameter small end large end (mm) (m) (m) (mm) (mm) (mm) (mm) Coupe: Franklin 23b * 450 End-colour: Pink * 650 Sawmill: McKay Timber, Glenorchy * 700 GPS: 55G UTM: (Tree # 1) * 610 Average overall height: 48m * 660 Logs not end-coated at all Logs felled: 13/5/ * 1470 Logs sawn: 3/6/ Packs delivered: 5/6/ Mean Coupe: Arve 27c * 450 End-colour: Green * 170 Sawmill: McKay Timber, Glenorchy * 880 GPS: 55G * 1140 UTM: (Tree # 4) * 480 Average overall height: 47m * 0 Logs not end-coated at all Logs felled: 14/5/ * 130 Logs sawn: 3/6/ * 290 Packs delivered: 5/6/ * 1140 Mean Coupe: Taranna 5d * 580 End-colour: Orange * 0 Sawmill: Kelly Timbers, Dunalley * 0 GPS: 55G * 390 UTM: (General area only) * 0 Average overall height 42m * 850 Logs not end-coated at all * 0 Logs felled: Late May, Early June * 0 Logs sawn: 12/6/ * 0 Packs delivered: 12/6/ * * 600 Mean Coupe: Esperance 1f End-colour: Red Sawmill: Clennetts, Dover GPS: 55G UTM: (Tree # 6) Average overall height: 33m Logs end-coated at mill Logs felled: 28/5/ Logs sawn: 4/6/ Packs delivered: 5/6/ Mean Notes: *Delivered to mill as logs >3m length, small end docked down to get 3m log Average overall height includes stump. No measurements possible on 1949 logs prior to sawmill. Logs with no height to 200 or 300 SED did not taper down as far as that diameter Table 1.1. Summary log data for Tasmania 8

15 Log No. Mean Pith Radius Mean Heart Width Mean Sap Width Heart Prop. (%) Mean Pith Radius Mean Heart Width Mean Sap Width Heart Prop. (%) Mean Pith Radius Mean Heart Width Mean Sap Width Heart Prop. (%) Mean Pith Radius Mean Heart Width Mean Sap Width Mean Dimensions in mm. Heartwood proportion is a percentage of log volume. Table 1.2. Disc measurements. Heart Prop. (%) Board No IMC (%) BD (kg/m 3 ) Board No IMC (%) BD (kg/m 3 ) Board No IMC (%) BD (kg/m 3 ) Board No IMC (%) BD (kg/m 3 ) Mean Mean Mean Mean Std Dev Std Dev Std Dev Std Dev Table 1.3. Basic density and initial moisture content results 9

16 Radial shrinkage slices Tangential shrinkage slices Green FSP EMC Green FSP EMC Batch Board no. MC % MC % Sr % MC % Sr % MC % MC % St % MC % St % *44 *1.9 *10 * Broken Broken Broken Mean Broken Broken *34 *1.2 *10 * Mean *30 *1.9 *12 * *36 *1.5 *11 * *42 *1.1 *10 * *36 *2.9 *11 * *37 *1.5 *10 * *35 *1.6 *10 * *30 *2 *8 *9.3 Mean *38 *1.6 *13 * *29 *4 *10 * Broken 94 *29 *3.5 *10 * *39 *3.8 *8 * *31 *1 *8 * Mean Broken means slice was physically broken; no measurement possible *These slices underwent collapse shrinkage; measurements not used in calculation of means. Table 1.4. Shrinkage measurements 10

17 Batch Thickness mm Nominal board widths for trial. % of boards Orientation. % of boards Min Max Mean StdDev 75mm 100mm 125mm Backsawn Quartersawn Transitional Table 1.5. Summary green sawing data for Tasmania Time (days) Dry bulb temperature (deg C) Wet bulb temperature (deg C) Air speed (m/s) Predrying schedule Time (hours) Temperature (deg C) Comments 0-2 Ambient-98 Weights fitted, heat up Doors opened, charge allowed to cool for 14 hours Reconditioning schedule Time (hours) Dry bulb temperature (deg C) Wet bulb temperature (deg C) Air speed (m/s) Final drying schedule Table 1.6. Drying schedule 11

18 Green (mm) Dry (mm) Shrinkage (%) Thickness Width Thickness Width Thickness Width 1901 Min Max Mean StdDev Min Max Mean StdDev Min Max Mean StdDev Min Max Mean StdDev Table 1.7. Summary of dry dimensional recovery of all boards. Grade Top surface Bottom surface Both sides 1901 select Standard 8 8 High Feature select Standard High Feature select Standard High Feature select Standard High Feature 5 5 Table 1.8. Percentage of boards in each grade (to AS 2796, disregarding skip) on each face and percentage of boards with both faces select. Green Dry Loss to endsplit Loss to endsplit Total length length % of overall Total length length % of overall m m length m m length Table 1.9. Total length of board processed and length lost to endsplit. 12

19 Top surface Bottom surface Surface check Skip Surface check Skip Internal check Table Percentage of overall board length (disregarding endsplit) degraded by surface check or machining skip on both surfaces and percentage of boards affected by internal check. Green Dry % boards outside AS 2796 Spring>10mm % of boards Mean spring mm Spring>10mm % of boards Mean spring mm Flooring Lining Table Percentage of boards with spring greater than 10mm over 2.8m length, mean spring for those boards, and percentage of boards exceeding the AS 2796 allowance for spring in flooring and in lining. 13

20 No. 1st test (kn) 2nd test (kn) Mean (kn) MC % Orientation Radial Radial Radial Radial Radial Radial Radial Radial Radial Radial Mean 5.5 Std Dev Radial Radial Tangential Radial Radial Radial Radial Radial Radial Radial Mean 6.0 Std Dev Radial Radial Radial Radial Radial Radial Radial Radial Radial Radial Mean 7.2 Std Dev Radial Tangential Radial Radial 47(2) Radial Radial Radial Radial 71(2) Radial Radial Radial Radial Mean 5.8 Std Dev Overall Mean 6.1 Std Dev 1.5 Table Hardness testing results 14

21 Properties adjusted to 12%MC* No. Max load (kn) Width (mm) Depth (mm) Load/Deflection to PL (kn/mm) MOE (GPa) MOR (MPa) MC (%) MOE (GPa) MOR (MPa) SD (MOE) SD (MOR) SD Density** (kg/m 3 ) Comment*** (2) Replacement 47(3) Extra replacement Mean SD Mean SD Table Strength test results for mm clear sections of messmate loaded in the radial direction continued below 15

22 (3) Mean SD (2) (3) (3) Mean SD Overall Mean *MOE adjusted to 12% MC at 1.5% per 1%MC; MOR at 4% per 1%MC SD **Exceptionally low density is defined in AS 2082 as 578kg/m3 at 12% MC for E. obliqua. Specimens of lower density are unacceptable for the existing strength rating of SD3 ***AS 2878 specifies that samples are to be rejected if slope of grain is greater than 1 in 10 Table Strength test results for mm clear sections of messmate loaded in the radial direction continued from above. 16

23 175 Moisture content (%) Reconditioning Time (days) Figure 1.1. Progress of drying 17

24 Thickness (mm) Reconditioning Time (days) Figure 1.2. Sample board thickness during drying 18

25 Plate 1.1. Handling of 1967 logs Plate 1.5. Breaking down, Clennett s Plate 1.2. Trucking of 1967 logs Plate 1.6. Re-saw, Clennett Timber Plate logs, McKay Timber Plate 1.7. Pack wrapped for transport Plate 1.4. Break down, Kelly Timber Plate 1.8. Racking, Neville Smith Tas. 19

26 Plate 1.9. FFIC kiln, Mowbray. Plate Strength testing Plate Machining, NST, Mowbray Plate Strength test detail Plate Grading, NST, Mowbray Plate Hardness testing Plate Board measurement Plate Hardness test detail 20

27 Plate Typical 1901 regrowth Eucalyptus obliqua boards 21

28 Plate Typical 1934 regrowth Eucalyptus obliqua boards 22

29 Plate Typical 1949 regrowth Eucalyptus obliqua boards 23

30 Plate Typical 1967 regrowth Eucalyptus obliqua boards 24

31 1.3. Analysis Logs and discs There was a significant difference (ANOVA) between heartwood proportion for the four groups, except when comparing 1949 and 1967 discs, and 1901 and 1934 discs. There was significantly more endsplit in 1901 logs than in 1949 or 1967 logs (comparing the butt end only since logs were delivered in non-uniform lengths) with more than three times the log length subjected to splitting. This difference is not apparent in green board endsplit figures; this is most likely due to the skill of the sawyer in sawing around the log endsplits Green timber properties There was no consistent variation between initial moisture content of the four groups; 2 of the 6 pairwise comparisons showed a difference based on ranks (unequal variances). There was a significant difference (ANOVA) in three of the six pairwise comparisons of basic density measurements but not between the oldest and youngest groups. There was no significant difference in radial shrinkage between groups. There were insufficient samples for comparison of tangential shrinkage as several were discarded due to collapse or breakage. Summary results corrected to 12% by assuming linear shrinkage between FSP and EMC, and comparison with published data are shown in Table The tangential:radial shrinkage ratio is generally taken to be close to 2 for this timber; results measured here suggest a ratio closer to 1.5. Radial shrinkage (%) Tangential shrinkage (%) Mean SD Mean SD N/A mature regrowth yr Table Radial and tangential unconfined shrinkage and comparison with published values for mature timber and young regrowth (Kingston and Risdon 1961) Drying Figure 1.1 shows no noticeable difference in drying rate between the four groups. Moisture content variation decreased as drying progressed. There was a poor correlation between moisture meter reading and oven dry moisture content from the final dried sample boards and from hardness samples Dry evaluation There was a significant difference between shrinkage in thickness for all pairwise comparisons except for 1901 and 1934 groups. Mean shrinkage in thickness was lowest in 1967 material. Shrinkage in width was significantly lower in 1967 material than in all other groups (analysis based on ranks; data failed normality test) with a mean of 7.1% as compared to 8.1 to 8.6%. There was no significant difference in dry endsplit figures, although the nature of this data makes analysis problematic (most boards have no endsplit, so distribution is non-normal). 25

32 Percentage of overall length of board lost to endsplit from the 1967 boards was 5.0% as compared to 7.3% from the 1901 boards. The proportion of select grade material was strongly related to age, with proportion of select increasing from 20% in 1967 boards to 92% in 1901 boards. Downgrade was almost exclusively as a result of gum vein Strength There was no significant difference between groups for either MOE or MOR. Summary results and comparison with published figures for mature timber are shown in Table MOE and MOR correlated closely with both density at 12% moisture content (MC) and basic density. The strongest relationship was between density at 12% and MOE with an R 2 value of Properties adjusted to 12%MC* MC (%) MOE (GPa) MOR (MPa) Group (MOE) Group (MOR) Group Density (kg/m 3 ) 1901 Mean SD Mean SD Mean SD Mean SD Overall Mean SD : mature Table Summary strength properties, comparison with published data for mature timber (Bolza and Kloot 1963) Hardness There was a significant difference (P=0.017) between two of the groups (1901 and 1949), but only based on ranks (unequal variances). It cannot be concluded that there was a significant affect of age on hardness. Summary results and comparison with published data for mature timber are shown in Table There were strong relationships between hardness and basic density (R 2 = 0.597), and hardness and density at 12% MC (R 2 =0.719). Janka hardness (kn) MC % Mean Std Dev Overall mature: 7.3 Table Summary hardness properties, comparison with published figures for mature timber (Bolza and Kloot 1963). 26

33 2. Western Australian regrowth jarrah (Eucalyptus marginata) G.R. Siemon Forest Products Commission, Western Australia Methods Selection of area With changes in Government policy over recent years, a large proportion of the 1.4 Mha jarrah (Eucalyptus marginata) forest is in conservation areas and National Parks. The areas available for timber harvesting were assessed to find a suitable area for providing logs for this trial, but it was essential that it was representative of the resource. Various areas were considered. The area selected was Willowdale, situated about 100 km south of Perth and east of Waroona, which is part of the zone available to Alcoa World Alumina Australia for bauxite mining. Forest Products Commission s production staff gave the opinion that it was a good example of the northern jarrah forest, which produces high quality timber on lateritic soils. There was little variation in the site and factors such as variations in silvicultural treatment and fire history were not an issue. The major understorey species is WA sheoak (Allocasuarina fraseriana) Tree selection Log size batches were used rather than age class batches, because selective felling procedures result in the development of dominant naturally regenerated seedlings, while jarrah growth rings are difficult to identify. The project required a sample of ten trees from each of an average 25 cm, 40 cm and 55 cm when measured at diameter breast height over bark (dbhob). The dbhob and height of each of the sample trees were measured to the nearest centimetre and metre respectively. The shape of the crowns with often several spreading branches at the apex made this level of accuracy appropriate when assessing height. Each tree was marked so that identification could be maintained during processing. The three size classes were identified by a specific colour, and trees were numbered 1 to 10. Estimates of the number of stems/ha (sph) in the three different size classes were made in two separate assessments of the area Harvesting Following new standard practices, the trees were harvested as whole bole lengths on 3 rd September. The boles were then transported to the sawmill where logs were docked to the required lengths, with the butt log to be used in the trial. Jarrah is a stable species, and industry practice in the field is to leave log ends untreated Sawmilling The 2.4 m log taken from the butt of each bole log was milled at the Inglewood Products Group s sawmill at Mundijong, about 35 km south of Perth. The 2.4 m log length (rather than 3 m) was approved by the University of Tasmania as project manager because the batch kilns at Timber Technology could take this length while ensuring better control over drying than can be achieved in other kilns at the centre. 27

34 While ash-type eucalypt species can have growth rings counted to assess age, this is not possible with jarrah. Measurements of total diameter under bark and heartwood were made across the major and minor axes. It was not necessary to cut a 25 mm thick disc from each end, which would normally be used for estimates of age based on growth rings. Length of any end splits was then measured. Log volumes were estimated from the large and small end diameter measurements and log length, using Smalian s formula (i.e. the mean of the large and small end cross-sectional areas under bark is multiplied by log length). Percentage heartwood was estimated similarly. Each log was backsawn into 100 x 28 mm boards, with the smaller dimensions of 80 x 28 mm or 60 x 28 mm sawn when the major dimension could not be achieved. The boards were tallied and volume calculated to estimate green sawn recoveries Wood properties assessment (shrinkage and density) Each of the ten boards randomly selected for preparation of the sample boards also had a 100 mm long section docked for assessment of shrinkage and wood density, taken from beside the sample board location. Briefly, a 25 mm cube was cut from a strip cut 25 mm from the end of the 100 mm section. The residual 50 mm section was used for moisture content and basic density assessment. Density was estimated using mass from weighing to 0.01 g, and volume estimated from water displacement. The 25 mm cube had a tangential slice and a radial slice (approximately 1 mm thick) taken from it to measure unconfined shrinkage, i.e. the shrinkage from green to equilibrium moisture content. The slice was restrained in a wire frame and measurements made using a microscope and vernier calipers. The mean values and standard deviations of each variable from green to equilibrium moisture content were calculated Kiln drying and board evaluation As stated above, ten boards were randomly selected from the timber milled from each log for drying. The boards were end-painted with the appropriate colour for each log diameter class, and each board numbered for identification. Three packs of 100 boards each were prepared (i.e. one pack for each log diameter class). Obviously all boards milled from the smallest diameter class were needed for the trial. Ten sample boards were prepared from each pack according to the University of Tasmania specification, with one from each tree in the sample. The dimension cut was 300 mm length, with both ends of the board sealed. The kiln drying schedule supplied by the University of Tasmania is given in Table 2.1. Jarrah timber is very stable, and it was anticipated that preand post-treatments would not be required. However, delays in drying a previous charge and electrical equipment problems with batch kilns caused the delay in drying the jarrah. 28

35 Time (days) Dry bulb temperature (º C) Wet bulb temperature (º C) EMC (%) Air speed (m/s) Table 2.1. Kiln drying schedule used for drying jarrah regrowth boards Drying was not commenced until December 2003, and was done in two batch kilns, each designed to take 1 m3 of timber. However, in the high ambient temperatures of the Western Australian summer it was not possible to use the Schedule in Table 2.1, and after the first weeks the schedule was modified to use higher temperatures, while using the same equilibrium moisture content levels for each step in drying (Table 2.2). Time (days) Dry bulb temperature (º C) Wet bulb temperature (º C) EMC (%) Air speed (m/s) Finish Table 2.2. Kiln drying schedule actually used for drying jarrah regrowth boards in batch kilns The predominantly 110 x 28 mm boards were assessed for defect before drying, measuring end splits at the numbered and other end, spring greater than 10 mm, surface checks and grade. It was necessary to keep the timber in temporary wet storage before drying following kiln problems due to extended drying of other timber and electrical equipment faults. After drying and dressing by straightening planer to 90 x 20 mm, a standard size recommended by FIFWA (1992), the drying behaviour of each board was assessed by measuring end splits at each end, spring greater than 10 mm, surface checks (splits resulting from heart were noted here), skip, grade and percentage moisture content. Moisture content was measured using a capacitance type moisture meter to avoid the probe damage to the timber that occurs with resistance type meters and insertion of prongs. Thirty sample boards were used, with fifteen in each batch kiln. Jarrah is a high density species, and therefore drying times were expected to be significantly greater than for mountain ash. The drying times were further extended due to failure of solenoids in both batch kilns, but fortunately this occurred when the moisture contents were below fibre saturation point and timber quality was not disadvantaged. 29

36 2.2. Results and Discussion Tree dimensions The mean values and standard deviations of dbhob and height of the sample trees in each of the three size classes are given in Table 2.3. Tree No. DBHOB (cm) Height (m) 25/ / / / / / / / / / Mean 29.0 (2.3) 19.5 (1.6) 40/ / / / / / / / / / Mean 40.3 (3.8) 21.1 (2.5) 55/ / / / / / / / / / Mean 54.9 (4.0) 25.0 (2.2) Table 2.3. Dimensions of trees sampled from Willowdale mine site for jarrah sawmilling and drying study (means and standard deviation) Stems per hectare (sph) Two estimates of the number of jarrah stems per hectare (sph) above 25 cm dbhob, in each of the three size classes nominated, were made over quarter hectare selections. The results indicated that overall stocking varied from 45 sph to 50 sph. The mean percentage of trees in different size classes were as follows: 25 ( cm) 45 per cent 40 ( cm) 30 per cent 55 (>48 cm) 25 per cent. 30

37 Harvesting The trees were harvested as whole bole lengths to the standard 200 mm small end diameter under bark on 3 rd September The logs were identified to maintain identity, and then transported to the sawmill where logs were docked to the required lengths. The butt log was retained for the trial. Jarrah is a stable species, and standard industry practice is to leave log ends untreated Sawmilling The log volumes required for the trial were estimated from the large and small end diameter measurements and log length, using Smalian s formula. The logs in each size class were backsawn to standard dimensions of 100 x 28 mm, with 80 x 28 mm or 60 x 28 mm as recovery sizes. The combined log volumes and board volumes, mean percentage heartwood and green sawn recoveries from logs in each of the three size classes are given in Table 2.4. Full results are in Table 2.8 and Table 2.9. Diameter class (cm) Total log volume (m 3 ) Mean (SD) % heartwood Board volume (m 3 ) Mean (SD) green sawn recovery (%) 25 (20 to 32.5) (7.8) (10.8) 40 (33 to 47.5) (3.5) (10.8) 55 (48 to 60) (4.5) (10.7) Table 2.4. Combined log volumes and board volumes, mean percentage heartwood and mean green sawn recoveries of boards from ten logs in each of three size classes of jarrah logs Mean percentage heartwood shows the expected increasing trend with increasing log size, because sapwood width tends to remain constant and sapwood will become a decreasing proportion of the cross-sectional area. It is well documented that green sawn recovery increases with increasing log diameter (assuming similar log quality) Wood density and shrinkage The green density, basic density, and moisture content of samples from each treatment are given in Table 2.5. Full results are in Table Diameter class MC% Green density (kg/m 3 ) Basic density (kg/m 3 ) (cm) Mean SD Mean SD Mean SD 25 ( ) ( ) (48 60) Table 2.5. Moisture content, green and basic density of jarrah samples from three diameter classes The results indicated significantly lower basic density in the two smaller diameter classes, resulting in a higher green density in the 55 cm class because the density of wood is approximately 50 per cent greater than that of water. Moisture content in that class was lower because of the greater proportion of wood. Unrestrained tangential and radial shrinkage were measured on 1 mm thick slices. The grain of the wood prevented slicing thinner than this with the guillotine used at Timber Technology for drying research. The results indicated significant differences between diameter classes, although the proportions of tangential shrinkage to radial shrinkage were similar to those reported by Kingston and Risdon (1961) for 25 mm (1 inch) square sections (Table 2.6). Jarrah obviously behaves differently to the ash-type eucalypts with regard to unrestrained 31

38 shrinkage of thin slices, because the latter have significantly greater shrinkage than pieces with larger dimensions. Diameter class Tangential shrinkage (%) Radial shrinkage (%) (cm) Mean SD Mean SD 25 ( ) ( ) (48 60) Mature* *Published data from Kingston and Risdon (1961) Table 2.6. Unrestrained tangential and radial shrinkage of jarrah from three diameter classes The samples from the largest diameter class had lowest shrinkage and least variation, with a coefficient of variation of 22.9 per cent. In comparison, the coefficients for 25 cm and 40 cm diameter classes were 32.6 per cent and 42.2 per cent respectively. It should be taken into account that a single board was randomly selected from the ten boards milled from each log, but overall it is logical that the largest trees had lower and more uniform shrinkage Board evaluation Board evaluation results are given in Table Boards downgraded because of wood quality The hundred boards from each of the three diameter classes were graded before stripping for drying, taking into account that if wood quality was below grade, drying could not improve that grade. Boards were separated by a commercial grader into select and non-select grades, and a major objective was to monitor the effects of drying on boards that were originally graded as select. Grades are shown in Table End splits (before drying) With end splits, the data confirmed the variation between trees, with only a few trees in each diameter class having boards with end splits. It was anticipated that there would be a gradation based on diameter class in the number of boards affected by end splits, with the highest level of stress in boards from the smallest diameter class. However, the 40 cm class was most affected by end splits, with 43 boards with end splits compared with 22 boards in the 25 cm class and 20 boards in the 55 cm class. There was a gradation in the mean length of splits from the 25 cm class to the 55 cm class, ranging from 156 mm (25 cm class) to 221 mm (40 cm class) to 309 mm (55 cm class). A better indication of the occurrence of end splits in the three diameter classes is the total length (3432 mm, 9503 mm and 6180 mm respectively from smallest to largest diameter class) End splits (after drying) The mean length of end splits increased in each of the three diameter classes, as would be expected with the effect of drying stresses. However, the greatest increase (35 per cent) was in the boards from the 25 cm class logs, compared with 23 per cent from the 40 cm class and 13 per cent from the 55 cm class. 32

39 Spring Although most of the sawn production was backsawn boards, there are inevitably some quartersawn and intermediate boards (growth rings between 30º and 60º angle to the face), and the random sampling of ten boards from the production from the largest diameter class was expected to be a factor. However, the numbers of boards with 10 mm or greater spring were three, four and seven respectively in the 25 cm, 40 cm and 55 cm classes. Boards with spring cannot be straightened during drying, unlike those with bow, but dressing the boards on a straightening planer removed the effect. The exceptions were one board in the 40 cm class and two boards in the 55 cm class where dressing apparently upset the balance of stresses caused by drying. Twist and cupping were not a problem Surface checks Surface checks were not a problem, except where included heart was involved. Every board with included heart had drying defects, and the 25 cm class had 16 boards with heart, the 40 cm class 14 boards and the 55 cm class only two boards Skip The boards were milled at a nominal 28 mm thickness, however there were some with skip after drying and dressing to 90 x 20 mm dimensions. The number of boards with skip were six, four and five respectively in the smallest to largest classes Upgrading boards Some boards originally downgraded because of low wood quality could be upgraded by docking, dressing further or ripping along the length. Before drying, the boards downgraded to non-select due to included heart, gum veins and pockets and knots (based on AS 2796:1999). In some boards the split heart was along one edge of the board, and ripping to 70 mm width produced select material. Similarly, some boards could be dressed to 15 mm thickness to remove skip from the initial dressing, while others would not benefit. The number of boards that could be upgraded to select are also given in Table % of boards: % with spring exceeding AS 2796: Diameter class (cm) select upgraded with included Flooring Lining heart Table 2.7. Grade by diameter class and spring Strength and hardness testing Strength testing was performed on 10 samples from each size class, each mm. 3 point bending tests loaded on a radial face as detailed by Mack (1979), specified in Australian Standard 2878:2000 were performed by the University of Tasmania. Results are shown in Table Janka hardness tests were performed at two sites on each of ten specimens from each size class. Results are shown in Table

40 Size class Log No. Mean dub Mean diam heartwood Mean dub Mean diam heartwood Log volume Vol heart % heart (cm) butt (mm) butt (mm) crown (mm) crown (mm) (m 3 ) (m 3 ) Total / Mean (SD) (7.8) Total / Mean (SD) (3.5) Total / Mean (SD) (4.5) Table 2.8. Mean log diameters, volumes and percentage heartwood of jarrah from three diameter classes 34

41 Diameter class (cm) Tree No.* DBHOB (cm) Log volume (m 3 ) Board volume (m 3 ) Green sawn recovery (%) 25 Y Y Y Y Y Y Y Y Y Y Mean (SD) 29.0 (2.3) 45.6 (10.8) 40 R R R R R R R R R R Mean (SD) 40.3 (3.8) 53.1 (10.8) 55 W W W W W W W W W W Mean (SD) 54.9 (4.0) 55.0 (10.7) * Y = 25 cm diameter class, R = 40 cm diameter class, W = 55 cm diameter class. Table 2.9. Mean dbhob and green sawn recoveries of jarrah boards from individual logs 35

42 Diameter class (cm) Sample No Tangential shrinkage (%) Radial shrinkage (%) 25 Y Y Y Y Y Y Y Y Y Y Mean (SD) 7.4 (2.5) 4.3 (1.4) 40 R R R R R R R R R R Mean (SD) 8.0 (2.8) 4.5 (1.9) 55 W W W W W W W W W W Mean (SD) 5.5 (1.3) 3.5 (0.8) Table Unconfined tangential and radial shrinkage of jarrah from three different size classes Log No. Board No. Green Mass (g) O.D. Mass (g) M.C. % Green Volume (cm 3 ) Green Density (kg/m 3 ) Basic Density (kg/m 3 ) 25 cm 1 Y Y Y Y Y Y Y Y Y Y Y Y Y Y

43 8 Y Y Y Y Y Y MEAN SD cm 1 R R R R R R R R R R R R R R R R R R R R MEAN SD cm. 1 W W W W W W W W W W W W W W W W W W W W MEAN SD Table Moisture content, green density and basic density of jarrah 37

44 Property End splits: Numbered end Other end Total splits 25 cm class (yellow) 40 cm class (red) 55 cm class (white) Before drying After drying Before drying After drying Before drying After drying Mean No. Mean No. Mean No. Mean No. Mean No. (SD) boards (SD) boards (SD) boards (SD) boards (SD) boards No. boards (89) 109 (49) 156 (98) (125) 185 (85) 243 (158) (128) 154 (116) 221 (165) (132) 184 (104) 278 (185) (189) 258 (217) 309 (278) Mean (SD) 288 (202) 243 (121) 291 (195) No. split both ends Total length of end splits Spring 3 25 (-)* (-) (8) 2 10 (-) Surface ** Full ** Full - - 2** Full checks length length- length Skip (269) (598) MC% (1.0) (1.0) (1.1) Downgraded (heart, gum, knots) Upgraded Dock 11 Dress 5 Rip 8 * Standard deviation was not calculated for fewer than five boards. ** Almost exclusively the effect of included heart Table Effect of drying on wood quality of regrowth jarrah boards Dock 18 Dress 1 Rip 4 Dock 15 Dress 1 Rip 2 38

45 Adjusted to 12% MC* No Max load Width Depth Load/Deflection MOE MOR MC MOE MOR SD SD (kn) (mm) (mm) to PL (kn/mm) (GPa) (MPa) (%) (GPa) (MPa) (MOE) (MOR) SD Density at Comment 12% (kg/m 3 ) Yellow (25 cm) Half sapwood? (pale) Half sapwood? (pale) Half sapwood? (pale) Mean Red (40 cm) "Carroty" grain. Brittle failure Mean White (55 cm) Mean Overall Mean Std Dev *MOE adjusted to 12% MC at 1.5% per 1%MC; MOR adjusted at 4% per 1%MC as per AS 2878 Table Jarrah strength testing results summary - measurements by Timber Research Unit, University of Tasmania 39

46 No 1st test kn 2nd test kn Mean kn MC % Orientation Yellow (25 cm) Tangential Tangential Tangential Tangential Radial Radial Radial Tangential Tangential 84(2) Tangential Mean Std Dev Mean Red (40 cm) Tangential Radial Radial Tangential Tangential Tangential Tangential Tangential Tangential Tangential Mean Std Dev Mean White (55 cm) Tangential Radial Tangential Tangential Tangential Tangential Tangential Tangential Tangential Tangential Mean 8.9 Std Dev Mean Overall Mean 8.7 Std Dev 1.5 Radial Mean 7.5 Tangential Mean 8.8 Radial means hardness of a quartersawn face Tangential means hardness of a tangentially sawn (backsawn) face Table Jarrah Janka hardness testing results measurements by the Timber Research Unit, University of Tasmania 40

47 Plate 2.1. Typical regrowth jarrah Plate sided planing 2.5. Analysis Heartwood proportion There was a significant difference (ANOVA) between heartwood proportion in the three groups, except when comparing 25 and 40 cm groups. Heartwood proportion was higher in larger logs Green timber properties There was a significant difference (ANOVA) between initial moisture content in the three groups, except when comparing 25 and 40 cm groups. Initial MC was lower in larger logs. There was a significant difference (on ranks) between basic density in the smallest and largest log groups only, with higher density in the larger logs. There was no significant difference in tangential unconfined shrinkage at 10% MC between groups Drying There was no noticeable difference in drying rate between the three groups Dry evaluation Shrinkages in thickness and width were not measured prior to machining. There was no trend with board size of dry endsplit, although the nature of this data makes analysis problematic (most boards have no endsplit, so distribution is non-normal) Strength There was no significant difference between groups for either MOE or MOR. Summary results and comparison with published data for mature jarrah are shown in Table

48 Yellow (25 cm) Red (40 cm) White (55 cm) Overall Strength properties adjusted to 12%MC MC (%) MOE (Gpa) MOR (Mpa) Strength Group (MOE)* Strength Group (MOR)* Group Density (kg/m 3 ) Mean SD Mean SD Mean SD Mean SD Bolza and Kloot (1963) Table Summary strength data and comparison with published results for mature timber * Based on AS/NZS 2878: Hardness There was no significant difference between groups for Janka hardness Janka hardness (kn) MC % Mean SD Yellow (25 cm) Red (40 cm) White (55 cm) Overall Bolza and Kloot (1963) 8.5 Table Summary hardness data and comparison with published results for mature timber 42

49 Plate 2.3. Typical jarrah boards. From left, 2 each of 55 cm, 40 cm, 25 cm batches. 43

50 Plate 2.4. Typical jarrah boards. From left, 2 each of 55 cm, 40 cm, 25 cm batches. 44

51 3. Queensland regrowth spotted gum (Corymbia citriodora) Matt Armstrong Horticulture and Forestry Sciences Department of Primary Industries and Fisheries, Queensland Government Methodology Site Thirty-three trees were selected from a current sale area of Allies Creek State Forest (S E ), 90 km north-west of Kingaroy, Queensland. The logs were milled at Queensland Sawmills Pty Ltd, Allies Creek (Plates 3.1, 3.2) Tree selection As Queensland s regrowth hardwood forests are generally not made up of even-aged stands, tree selection for the Queensland component of the project was based on diameter class. Three distinct diameter classes were selected: cm, cm and cm DBHOB. These diameter classes respectively represent: the majority of the current cut, trees that will increasingly make up a larger proportion of the cut, and the type of tree that may have to be harvested to sustain current log yields. Crown assessment, using the Grimes technique (Grimes 1978), was utilised for the identification of suitable study trees. The Grimes technique was developed as a simple crown assessment method for use in spotted gum ironbark forests. The technique uses five crown factors to assess a tree s vigour. They are: Crown position, scored out of 5; Crown size, scored out of 5; Crown density, scored out of 9; Dead branches, scored out of 5; Epicormic growth, scored out of 3 (with ½ increments). Each of the factors are first scored independently and then totalled. In past research (Grimes 1978), regression analysis has indicated that all these factors are correlated with diameter increment. Total crown scores can be used to predict Diameter: Mean Annual Increment (d.m.a.i), using the equation: d.m.a.i. = t t 2 (R 2 = ), where t = total score To classify the tree s growth based on general qualitative groupings, Grimes (1978) assigned total crown scores to the following groupings: Less than 12 points - Very poor d.m.a.i Poor Average Good Excellent 45

52 While this system was designed to assess current standing trees and predict future increments, it is possible to use the system to make generalisations about past growth rates. It can be assumed that trees of similar diameter and total crown score have had similar growth rates and are therefore of a similar age, and that trees fitting into distinctly different diameter classes with similar total crown scores (as in this study) are distinctly younger or older. It is for this purpose that the Grimes crown assessment method has been used in this study, that is, to ensure that the trees within each diameter class are of a similar age, and that between groups, the trees are of a distinctly different enough age to allow data comparison with the greater national data set. The assessments were also made to ensure that trees of similar vigour and growth habit were selected. For this study only dominant and co-dominant trees were selected. Suppressed, slow growing trees, and bendy trees were excluded due to the possibility that such trees could have properties uncharacteristic of the species. All of the study trees were selected from a current sale area within Allies Creek State Forest. Ten trees from each of the diameter classes were selected. A further three trees were selected from the cm diameter class group, to ensure that 100 boards from each group would be produced. Each tree was marked and assessed for Grimes score, DBHOB (cm) and total height (m) Harvesting Upon felling each tree was assessed for pipe, bend, spiral grain and other potential defects in accordance with the allowable defects detailed in Table 3.1. Also measured were total tree height, height to 30cm underbark diameter (UB) & 20 cm UB and the worst face split and log split, on the large-end log face. The selected trees were snigged prior to the commercial harvest of the sale area. Each tree that was assessed as a suitable study tree had a batch and tree number scribed onto the large-end log face, along with a bush number and the merchandised log centre diameter. To avoid leaving suitable logs in the forest, the trees were merchandised in the bush to a variety of lengths depending on form and diameter, with a minimum set at 3.8 m (Bush logs). Logs were left with the bark on and stored in the mill s log yard for two weeks before processing. Water sprays are not commonly used in Queensland and were therefore not used in this instance. Size Class (cm) Pipe max. (cm) Allowable bend max. Spiral grain max. Non-pipe defect including limbs max. (% of circumference) :10 1 in :7 1 in :5 1 in 8 30 Table 3.1: Allowable limits for log defect Pre-processing measurements Eighteen hours prior to processing, end-splitting was re-measured on the large-end log face, before each bush log was merchandised into a 3.8 m butt log (study log), and an extra log (which had no further part in the study). From the 3.8 m butt log a disc was removed from each end to produce a 3.6 m study log. All discs were numbered with the tree number and either a B or T for Butt end or Top end, respectively. Each log was not re-numbered but colour-coded by painting both log ends with either: Blue for the cm batch; Red for the 46

53 35-30 cm batch; or Green for the cm batch. Each log was then sorted into their respective batches for processing (Plates 3.1 and 3.2). Immediately before processing, log-end splitting was measured on the small-end log face Processing Sawing took place on a Saturday when the mill was not commercially operating; the logs were processed batch by batch. All logs were sawn predominately into either 100 x 25 or 75 x 25 mm boards (nominal), with a small amount of 50 x 25 mm material to reduce waste. The logs were initially broken down on a Canadian single-saw line-bar carriage system and then sent to a one-man single-saw line-bar resaw bench before going past a docking saw. Boards were only docked for severe wane or want or for any other defect that compromised the structural integrity of the board, which could have posed a risk to machinery or staff. Similar sawing patterns were used for the cm & cm batches. On the break-down saw the log was continuously rotated, removing a flitch and/or slab each side of the log until a nominal 100 mm sized cant was produced. All logs from these batches were taper sawn using the line-bar. The flitches, slabs and tapered cant were re-sawn on the bench. The objective of this sawing pattern was to remove, in full lengths, the maximum amount of good wood from the outer zones of the logs. Logs from the smallest diameter class (25-20 cm) were sawn using an alternative sawing pattern due to their size. Figure 3.1 represents the sawing pattern used. Saw cuts 1 & 2 were done on the break-down saw. Both cuts were put in parallel to the pith, with saw cut 2 being approximately 50 mm or 37.5 mm off the pith. The resultant cant was then sent to the bench where saw-cut 3 was put in, parallel to the pith, to create a sized cant of either 100 or 75 mm width. The cant was then sawn through from the round-back for the first couple of passes and then later from the alternate sawn face, as it was easier to put the sawn face against the fence. The cant was sawn through and through, i.e. not taper sawn Figure Sawing pattern used for the small diameter logs (25 20 cm class). 47

54 Racking Prior to racking each board was tallied and assessed for: Length (m); Width and Thickness (mm) measured in approximately the middle of the board using vernier callipers; End-splits (mm) length of the longest split was measured at both ends ( numbered and other ), end-split on pith boards was not assessed due to the confounding factor of heartshake; Bow (mm) - if greater than 10mm (bow less than 10 mm is well within the limitations set by Australian Standards); Surface checking (length of board downgraded) measured on the top (inner) and bottom (outer) surface. Only 100 boards from each batch required the full assessment, however to avoid bias in batches where the number of boards was well in excess of 100, all boards were assessed and then 100 were randomly selected for inclusion in the study and analysis. Board number, from for each batch, was scribed onto each board during racking. Spring was not measured as boards were backsawn, so any spring was minimal and within the allowances of Australian Standards. Boards from each batch were racked out separately. Within a batch, the 100 and 75 mm boards were sorted prior to racking to minimise handling when the boards were machined Sample boards Five sample boards were used per pack. Ten sample boards would have been preferred, however due to the design of the kilns only one side of the pack is accessible during drying. The five sample boards were located as indicated in Figure 3.2. Each sample board was approximately 350 mm long, colour coded and numbered. Figure 3.2: Positioning of Sample Boards within a pack. An additional 100 mm sample, adjacent to the sample board, was also cut, colour coded, numbered and wrapped in plastic for later assessment of basic density and unconfined shrinkage. A further mm samples were cut from randomly selected boards for later assessment of basic density Treatment Each pack of timber was then vacuum-pressure treated with CCA preservative formulation to H3 in accordance with the Timber Utilisation and Marketing Act (TUMA). After treatment all sample boards were removed from the pack and had a 25mm section removed from either end for green MC calculation. They were then weighed, end-sealed and placed back in the rack. 48

55 All boards were then end-sealed with a clear wax emulsion to slow drying and reduce drying related defects Drying schedule Following air drying, the pack was placed in a gas assisted solar kiln. Two MC probe were inserted into the boards within the pack to monitor MC (kiln probe No 5 & 6). Sample boards were regularly weighed and measured during drying to monitor moisture loss and associated board shrinkage Grading After drying the boards were dressed to either 82x19mm T&G flooring or 65x19mm DAR decking. Sawmill employees graded the dressed boards on site to Australian Standard AS Timber-Hardwood-Sawn and milled products, using a minimum grade length of 0.9m. Grade lengths were demarcated on each board by the use of crayon marks, using a similar code to that used for automatic docking saws. The boards were then stacked and sent to the Department of Primary Industries and Fisheries Salisbury Research Centre. At the Salisbury Research Centre each board s graded length and reason for downgrade were recorded, along with end-split (both ends), distortion (Spring & Bow >10mm and Twist), length degraded by surface checking and length degraded by skip Mechanical properties Twenty five small clears were tested for MoE and MoR in accordance with the Mack Australian Method (Mack, J.J. 1979) which is based on BS 373:1957 Methods of Testing Small Clear Specimens of Timber. Ten samples were tested for Janka hardness in accordance with the Mack Australian Method (Mack, J.J. 1979) which is based on BS 373:1957 Methods of Testing Small Clear Specimens of Timber Moisture content, density & heartwood proportion From each batch of boards twenty samples were assessed for basic density and moisture content. Basic density was measured using the volume displacement method. Further to this, basic density was also assessed on samples cut from discs. A disc was taken from the top and bottom of each log. The heartwood/sapwood proportions were then measured at two locations on each disc. Two diametrically opposed wedges were cut from each disc, with each wedge being cut into a sapwood section and three heartwood sections of equal length. The basic density of each section was assessed using the volume displacement method. The heartwood sections were labelled H1 (outer heartwood section), H2 (middle heartwood section) and H3 (inner heartwood section) Results Tree selection In total 33 trees were selected. Upon felling no tree was assessed as unsuitable. Excessive pipe is not uncommon in typical spotted gum resource, however the fact that each selected tree was of vigorous growth and form would most likely indicate that the trees were not of sufficient age to have developed excessive pipe. 49

56 Grimes scores, as presented in Table 3.2, show that the average total crown score was 19, which represents average bordering on good growth. Overall there was no significant difference (p=0.01) in total Grimes scores between the batches, indicating similar vigour and growth habit. Batch All (13 trees) (10 trees) (10 trees) DBHOB (cm) Individual Grimes Assessments Total Tree Height (m) CP CS CD DB E Total Grimes Score Mean Min Max Mean Min Max Mean Min Max Mean Min Max. Table 3.2: Grimes Assessment Scores Log data Table 3.3 summarises the data for the bush logs. Batch Full log length (m) Height (m) to (including Diameter u.b.(mm) at: stump) 30cm ub 20cm ub large end mid small Vol (m 3 ) na All Note: volume was calculated using Newton s formula; length value was rounded down to 0.1 m intervals in volume calculations. Table 3.3: Bush Log Data Mean values Study log data are summarised in Table 3.4. Whilst the mean large end diameter for the cm diameter class batch of logs was within the targeted values, the mean large end diameters for the next two batches was slightly under the targeted values. This is most likely due to the disparity between over-bark and under-bark measurements. The logs in each batch are still distinctly different enough, based on diameter and log volume, to meet the project s objectives. 50

57 Batch Diameter UB(mm) at: (3.6m log) Large end Small Vol (m 3 ) All Note: volume was calculated using Smalian s formula; length value was rounded down to 0.1 m intervals in volume calculations Table 3.4: Study Log Data Mean values Mean end-split data for each batch are summarised in Table 3.5. Due to the differing mean log diameters in each class, the severity of the log face end-splits can be difficult to determine when looking at the raw data. By calculating the proportional length of the mean log face endsplit to the mean log face radius, expressed as a percentage of radius (Table 3.6), for each batch, it can be seen that there was a trend of worsening (longer) splits with increasing diameter. A similar trend was found for log splitting up the log bole (Table 3.5). Batch End - splits (mm) - large end End - splits (mm) - small end felling log face up log log face up log log face up log All Table 3.5: Mean Log End-split Data Mean values Batch Large end (%) Small end (%) Table 3.6: Proportional length of the log face end-splits measured on the logs just prior to processing Green-off-saw (GOS) tally and recovery Green-off-saw (GOS) recovery was calculated for each batch by dividing the tallied sawn volume (based on nominal dimensions and with restricted docking as described in section 3.3.5) by log volume. The smallest diameter class batch of logs, cm, had the highest GOS recovery of 39%. This is contrary to anecdotal evidence and empirical data from several previous hardwood sawing studies which showed that small diameter logs generally result in lower GOS recovery. The next two batches produced GOS recoveries of 33%. One explanation for the variation in GOS recovery across the batches may be that the alternate sawing pattern used for the logs in the 20-25cm batch resulted in less waste. This may 51

58 indicate that sawing parallel to the pith results in higher GOS recovery, however, parallel sawing maximises the number of boards being produced from the inner heartwood zone, where the greatest amount of defect normally occurs. Green off saw recovery (%) Group (cm) Figure 3.3: Green off saw recovery Green board assessment Between the batches there were no significant differences in length, width, thickness or endsplit. However the boards from the cm batch had significantly more bow (p=0.05) than the other two batches. As the occurrence of bow is often linked to growth stress (Armstrong 1999), this may indicate that the smaller diameter logs have higher levels of growth stress. Bow is more tolerable than spring for milled products. Surface checking occurred predominately in boards from the cm batch and only on the outer backsawn surface (ie surface on bark side). These results indicate that surface checking could potentially become an issue of increasing significance to industry as it shifts towards a smaller diameter resource. Batch Boards Length (m) Width (mm) Thickness (mm) End split numbered end (mm) End split other end (mm) Bow >10mm (mm) Surface check - Outer surface (m) Surface check - Inner surface Mean Count Mean Count Mean Count Mean All 79.7 Count Table 3.7: Green Board Assessment Data. Mean thickness separated for two widths sawn, nominally 100 and 75mm. Even though there were no significant differences in width or thickness between the groups it is still worth assessing the data. Figures 3.4 to 3.7 show the frequency with which boards from 52

59 each batch were sawn to a specific dimension. It can be seen that boards from the cm batch (Blue) were consistently sawn to wider and thicker dimensions than boards from the cm batch (Red) and cm batch (Green). This may indicate sizing and handling difficulties with the smaller logs. Besides the actual dimension of the logs in this size class, another contributing factor may have been the significantly higher levels of distortion (found in the boards from this batch) or the different sawing pattern. These factors could potentially have a negative effect on the productivity level of mills cutting smaller dimensioned logs, which are not specifically set up to handle the smaller resource. 60% 50% 40% 30% 20% 10% 0% More % 60% 40% 20% 0% More mm Figure 3.4. Width variation, 100mm boards mm Figure 3.5. Width variation, 75mm boards 50% 40% 30% 20% 10% 0% More % 40% 30% 20% 10% 0% More mm mm Figure 3.6. Thickness variation, 100mm boards Figure 3.7. Thickness variation, 75mm boards Drying The processed green boards were air-dried for 30 days under cover prior to being put into the gas-assisted solar kiln. The average moisture content of the boards upon entering the kiln was 19.5% as calculated using the sample boards, or 30.5% as measured using the kiln s MC probes. As the standard deviation of the MC of the sample boards was only 1.8%, it would appear that the kiln s probes might not be accurate at relatively high MCs. The boards were dried in the kiln for a further 23 days with a final average MC of 11.3%. It should be noted that as the boards continued to lose moisture the difference between the average MC reading from the kiln s probes and the average MC of the sample boards narrowed until both were at 11.3% when the timber was removed from the kiln (Figure 3.8). Between batches there was a small amount of variation in MC both prior to and after kiln drying. The boards from the batch had the lowest initial and final moisture contents of 17.4% and 10.4% respectively. Batches and dried down to a similar final MC of approximately 11.5% (Table 3.8). 53

60 Mean MC during kiln drying MC /04/ /04/ /04/ /04/ /04/ /05/ /05/ /05/ /05/ /05/ /05/ /05/2004 Kiln's probes 5+6 MC sample boards Figure 3.8. Mean moisture content loss during kiln drying All batches Batch 21/04/ /04/2004 3/05/ /05/ /05/ % 14.5% 12.6% 11.2% 10.4% % 15.3% 14.3% 12.5% 11.6% % 16.9% 14.3% 12.6% 11.8% Table 3.8: Mean moisture content loss during kiln drying Separate batches The mean dimensional change in the width and thickness of the sample boards during kiln drying is presented in Figure 3.9. It should be noted that as the sample boards were a combination of 100 and 75mm wide boards the means appears as a nominal figure only. Width (mm) /04/ /04/ /05/ /05/ /05/ Thickness (mm) Thickness Width Figure 3.9: Width & thickness of all sample boards during kiln drying Figures 3.10 and 3.11 present the data for thickness measurements alone. No clear trend can be seen between batches. 54

61 /4 26/4 3/5 10/5 14/ /4 3/5 10/5 14/ Figure 3.10 Thickness of sample boards Figure 3.11: Change in thickness Recovery Overall, the sawn recovery (proportion of green off saw material making grade to Australian Standard AS Timber-Hardwood-Sawn and milled products) was relatively high, with recoveries of 87.3%, 84.8% and 91.6% for batches 20-25, and respectively (Figure 3.12). By grade, batch had a proportionally lower volume of select grade boards and a higher proportion of High Feature grade boards when compared to the two other batches (made up of larger diameter logs see Figure 3.13). Whilst the trees from the batch produced a similar volume of GOS material, the lower proportion of boards meeting the grade requirements for select grade would significantly devalue the timber sawn from this batch of logs. Conversely, Batch had the highest recovery of select grade boards while having the lowest GOS recovery % 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% Figure 3.12: Sawn recovery by batch to AS % 60% 40% 20% 0% 75.2% 69.3% 50.9% 30.6% 25.3% 18.3% 18.5% 6.4% 5.4% Select Medium Feature High feature Proportion of total sawn volume in grade Figure 3.13: Recovery Grade by batch 55

62 Boards sawn from all three batches had a high incidence of tight gum vein, which is typical of the species. Between batches there appeared to be a negative trend (i.e. higher incidences with decreasing diameter) in the incidence rate of knot related defect, overgrowth of injury, insect damage and heart-shake. This may indicate that there is an relationship between age and the occurrence/severity of these defects. Typical boards from each batch are shown in Plates Distortion Percentage of boards exceeding the AS (Standards Australia 1999) allowances for distortion are shown in Table 3.9. No obvious trends between distortion and batches were noted. % boards outside AS distortion allowance Spring, for Batch Bow, for Spring, for lining or flooring flooring decking Twist Table 3.9. Percentage of boards outside AS distortion tolerances End-splitting Table 3.10 presents the results of end splitting measurements and includes the number or count of boards effecting by end-splitting within each category and a corresponding mean length of board affected. No clear trend in end-splitting could be determined between the batches (Table 3.10). Batch had the lowest level of end-splitting, both before and after drying, while batch had the highest. Growth in endsplit from drying is shown in Figure Batch Green Dry Number end Other end Number end Other end Mean (mm) Count Mean (mm) Count Mean (mm) Count Mean (mm) Count All Table End-splitting data 56

63 All 0 Mean (mm) Count Mean (mm) Count Number end Other end Figure End-split growth (mm) from green to dry. 57

64 Tight Knots Loose Knots Knot Hole Wane Count Want End Splits Comp Fracture Decay Overgrowth Of Injury Tight Gum Vein Loose Gum Vein Checks Heart Shake Insect Damage Natural Feature Stain Bark Encased Knot Shake Figure Defect summary by batch

65 Surface checking No clear trend in surface checking could be determined between the batches (Table 3.11). Batch had the highest level of surface checking when green, while batch went from not having any surface checking in the green state to having the highest level after drying and dressing. Growth in surface checking from drying is shown in Figure Batch Green Dry Top Surface Other Surface Top Surface Other Surface Mean (cm) Count Mean (cm) Count Mean (cm) Count Mean (cm) Count All Table 3.11: Surface checking data Mean (cm) Count Mean (cm) Count All Top Surface Other Surface Figure Change in length of board degraded by Surface Checking from green to dry Skip Similarly to end-splitting and surface checking, batch had the lowest level of skip after dressing (Table 3.12). Batch Dry Top Surface Other Surface Mean (cm) Count Mean (cm) Count All Table 3.12: Length of board degraded by skip Overall, the boards sawn from the logs of batch had the highest recovery of select grade material and the lowest level of negative attributes such as end-split, surface checking and skip. Boards sawn from the logs of Batch had the highest levels of negative attributes, however the batch still produced a reasonable proportion of select grade material. The boards 59

66 sawn from the smallest diameter batch of logs, batch 20-25, had a good GOS recovery, however only a low proportion of the boards made select grade due to higher incidences of knots, heart shake and insect damage. The boards also had relatively high levels of combined end-splits, indicating that the material may have had relatively high levels of internal stresses that were released during processing Mechanical properties Bending tests on small clears indicated that the samples from each batch were strength group SD2. As can be seen from the MOE and MOR means presented in Table 3.13 (complete results in Table 3.19), there was a trend of decreasing MOE and MOR with increasing diameter, however the differences between the groups did not prove significant (p=0.05). Batch MOE (Gpa) MOR (Mpa) Bolza and Kloot (1963) Table 3.13: Summary strength data and comparison with published values for mature material. The Janka hardness tests (Table 3.14, 3.20) indicated that the samples from each batch were of a similar hardness with no significant difference between groups (p=0.05). Batch Janka hardness (kn) Bolza and Kloot (1963) 10.1 Table 3.14: Summary Janka hardness data and comparison with published values for mature material Moisture content, density and heartwood proportion. Table 3.15 presents the moisture content and density data assessed on the twenty samples cut from the boards of each batch. No trend between groups is evident. batch MC Oven Dried Basic Density % % % 864 Table 3.15: MC and Density data Table 3.16 presents the disc basic density data. The data indicate that there is a positive trend between density and log diameter. Other trends that are evident are: decreasing density up the log, relatively lower sapwood density, and decreasing density towards the pith. Sample Batch Butt discs Top discs Sap H1 (outer) H2 (middle) H3 (inner) Mean Table 3.16: Basic density from discs Table 3.17 presents the heartwood/sapwood proportion data. The data indicate a slight trend towards decreasing heartwood proportion with decreasing diameter. 60

67 Heartwood/sapwood proportion Batch Butt disc Top Disc Average Heart Sap Heart Sap Heart Sap % 26% 74% 26% 74% 26% % 24% 73% 27% 74% 26% % 20% 78% 22% 79% 21% Table 3.17: Heartwood proportion Unconfined shrinkage Unconfined shrinkage was measured on five slices in the radial and tangential directions. Fit points at FSP and EMC are shown in Table Summary results and comparison with published data are shown in Table Tangential shrinkage (shrinkage across the width of backsawn boards) and shrinkage ratio (tangential : radial shrinkage) were much higher than the published values for mature timber, indicating that this regrowth may be less stable in terms of both width and cupping when subjected to atmospheric changes in service. Radial EMC Tangential EMC Class Mean % Std Dev Mean % Std Dev Kingston and Risdon (1961) Table 3.18: Unconfined shrinkage summary and comparison with published data. Plate 3.1. Experimental logs Plate 3.2. Queensland Sawmills 61

68 Report No: Date of Issue: Client: Modulus of Elasticity and Modulus of Rupture of Small, Clear Timber Samples in Bending to BS 373 (modified by JJ Mack 1979) The results reported herein apply only to this sample of specimens as provided by client. Defln Device Upper Span (mm) Nom. Width (mm) Nom. Th'ss (mm) Testing Machine Load Range (kn) Lower Span (mm) Amsler Adjusted to 12% MC: Sample No. M.C. (%) Breadth (mm) Depth (mm) MOE (Gpa) MOR (Mpa) Adj MOE Adj MOR B B B B B B B B B B B B B B B B B

69 B B B B B B B B R R R R R R R R R R R R R R R R R R R R R R R R R G

70 G G G G G G G G G G G G G G G G G G G G G G G G Table Complete strength testing data for spotted gum 64

71 B B B B B B B B B B Mean R R R R R R R R R R Mean G G G G G G G G G G Mean Table Complete Janka hardness (kn) results for spotted gum FSP EMC FSP EMC Batch Sample # Shrink (%) MC (%) Shrink (%) MC (%) Shrink (%) MC (%) Shrink (%) MC (%) Table Complete unconfined shrinkage results 65

72 Plate 3.3. Typical boards from cm DBHOB logs 66

73 Plate 3.4. Typical boards from cm DBHOB logs 67

74 Plate 3.5. Typical boards from cm DBHOB logs 68

75 4. Victorian regrowth silvertop ash (Eucalyptus sieberi) Trevor Innes Timber Research Unit, University of Tasmania 4.1. Methodology Sample Material Three age classes were sampled; see Table 4.1. A minimum of 100 sample boards for each experimental group was required, with no more than 10 boards cut from any log. Twelve logs were sampled for the 1955 batch, ten for the 1965 batch and twenty for the 1975 batch. Trees were either co-dominant or dominant and not edge trees, and were selected as being representative of the stand. A suitable size class was chosen for each stand, with all of the logs selected being within that size class; see Table 4.1. The three age classes were from three separate coupes, chosen for being single-aged with trees of appropriate size for sawlog. Each log was identified by a colour (from Table 4.1) and a number. Year Size class DBHOB (cm) Colour green pink blue Table 4.1. Colour codes for Victorian timber Pre-felling Prior to felling, the following measurements were made for trees: breast height diameter over bark; tree stems/ha; and approximate tree height Post-felling For each tree: total height, height to 30 cm under bark small end diameter and height to 20 cm under bark small end diameter were measured; most logs were sawn over-length to suit the forwarder and then recut to 3.1 m length on the small end once loaded on the truck; both ends of logs were painted with appropriate colour from Table 4.1 above and endsealed following felling and cross-cutting; each log was marked with tree number; and length of longest endsplit up log on both small and large ends was measured. Logs were then transported to Fenning s Bairnsdale sawmill and stored under waterspray, separately from general mill stock, until sawing Log processing at sawmill endsplit of both ends of each log was re-measured prior to sawing; 69

76 approximately 50 mm thick discs were cut from the butt end of each log, labelled and transported to the laboratory; logs were re-end coated and colour coded with a different colour on the freshly cut end so that individual logs could be tracked through the sawmill (Plate 4.1); logs were backsawn to 28 mm thickness, width of 100, 75 or 50 mm (nominal dry) following standard practice. Experimental groups were kept separate; log breaking down was by single bandsaw to 28 mm thickness with boards cut on a single circular saw (Plates 4.2 and 4.3) to 100, 75 or 50 mm nominal width. Each of the three log batches was processed individually, with all boards free of want and wane for their whole length bundled for later selection of trial boards (Plate 4.4). Falldown boards were recovered by the mill for docking. Immediately after removal from the sorter, boards were moved under cover for selection of trial material; and a maximum of 10 boards per log were selected with wider boards preferred, block stacked, tightly wrapped on all sides with plastic and transported to the TRU laboratory, Launceston Drying for each board the following measurements were made: Length, Width, Thickness, Endsplit (numbered end), Endsplit (other end), Bow (if greater than 10 mm), Spring (if greater than 10 mm), Twist (if greater than 2.5 mm per 25 mm width), Length degraded by surface check on each side. Endsplit was measured as the length of board affected by the longest end split at each end of the board. This is the length of board that would have to be docked to remove all end-splitting; racks were hand built by TRU staff with rack sticks at 350 mm centres; six 300 mm long sample boards were used per rack of 100 boards, 3 on each side of the rack. MC, width and thickness were monitored throughout the trial; an additional 100 mm long sample was cut adjacent to each MC sample board for determination of unconfined shrinkage, initial MC and basic density; and another 14 boards were randomly selected from each pack for determination of unconfined shrinkage (four boards only), initial MC and basic density. Either one or two samples were cut from each log (number of logs per batch varied due to requirement for numbers of boards). Boards were dried in a 10 m 3 kiln belonging to the Forests and Forest Industry Council (FFIC) located at Neville Smith Timber s (NST) Mowbray, Tasmania site see Plate 4.5. The kiln was constructed specifically for experimental predrying of Tasmanian eucalypts and so generally controls very well at low temperatures (typically within 0.5 C). The predrying schedule used is shown in Table 4.2. When sample boards indicated that MC had fallen to approximately 20%, timber was reconditioned and final dried to the schedules shown in Table 4.2. Following final drying, racks were transported to the TRU laboratory. 70

77 Time (days) Dry bulb temperature (deg C) Wet bulb temperature (deg C) Air speed (m/s) Predrying schedule Time (hours) Temperature (deg C) Comments 0-2 Ambient-98 Weights fitted, heat up Doors opened, charge allowed to cool for 14 hours Reconditioning schedule Time (hours) Dry bulb temperature (deg C) Wet bulb temperature (deg C) Air speed (m/s) Final drying schedule Table 4.2. Drying schedule Dry measurements MC sample boards were measured, oven dried and weighed; following assessment of width and thickness (Plate 4.6) and removal of samples for strength and hardness testing, boards were transported to NST Mowbray and machined to 19 mm thickness, Plate 4.7, by removing 2.5 mm from the bottom surface and the rest from the top; a qualified commercial grader then graded boards to Australian Standard 2796 on each side (disregarding machining skip) over the whole board length except lengths affected by endsplit; see Plate 4.8 and Table 4.7. boards were assessed in the laboratory for total length degraded by endsplit each end, machining skip and surface check on each side. Bow (if greater than 10 mm), spring (if greater than 10 mm) and twist (if greater than 2.5 mm per 25 mm width) were measured over a 2.4 m length of each board. Mean MC of each board was measured by resistance meter; a correction of -2 was applied as required by Australian/New Zealand Standard AS/NZS (Standards Australia 1997); 71

78 a 100 mm length was then removed from the end of each board and the freshly cut end evaluated for internal check (Plate 4.12) and sawing orientation. Boards were scored with either no internal check, or internal check present without attempting to categorise severity; and oven dry MC was measured on a 25 mm long full cross-section sample from each board. Australian Standard AS 2796 (Standards Australia 1999) describes four grades based on features and desired aesthetic appearance. The three grades commonly used are select, Medium Feature Standard and High Feature Grade. Grading was performed by a qualified commercial grader, who assigned the full length of each wide face a single grade, ignoring length affected by end splits and ignoring machining skip. Note that AS 2796 is generally applied on all four faces. For this study, the edges were not graded as they were not machined since boards were of varying width. The two wide faces were graded separately as many products expose only one face, for example flooring or architraves. Amount of distortion allowable in various products is also specified by AS 2796 (Standards Australia 1999). Backsawn orientation was defined as all growth rings making an angle of less than 45 with the wide surfaces; quartersawn was defined as this angle being less than 45 ; transitional sawn was defined as having a mixture of backsawn and quartersawn parts. An additional 25 mm long full-width sample was cut for measurement of oven-dry MC Disc measurements a count of growth rings was made on discs to verify age. Radial sections cut from several disc samples were assessed by a dendrochronologist; and sapwood, heartwood and heart width were measured across two diameters at right angles on each disc Green measurements initial MC and basic density were measured on twenty samples per group (see Drying section above); and unconfined shrinkage in radial and tangential directions were measured for ten of the twenty samples from each group. Unconfined shrinkage is the shrinkage undergone by a thin slice of wood (approximately 0.8 mm thick) allowed to dry naturally in the laboratory, unaffected by drying gradients and stresses. Board shrinkage is lower than unconfined shrinkage due to the restraining effect resulting from moisture gradients due to drying; early in drying, the surface of boards is under tension, while later in drying the middle parts are under tension. This tension induces a set in the board, reducing overall shrinkage. From each curve of shrinkage versus moisture content, three points were selected for reporting: green MC (zero shrinkage), and shrinkage and moisture content at both FSP and EMC Strength and hardness measurements ten dry samples per experimental group (a maximum of one per log) were used for hardness and strength testing. They were cut from the same boards as the MC sample boards, plus another four taken from the 14 boards initially sampled for shrinkage, 72

79 initial MC and basic density. Each sample originated from a different source log. They were cut prior to machining as 20 mm thickness was required for strength testing; 400 mm samples were cut 100 mm clear of endsplit, at least 200 mm from the board end. They were then machined to give a 100 mm long hardness sample and a mm MOE/MOR sample; strength and stiffness testing was carried out as described by Mack (1979), in the section Static bending, centre point loading, as specified in Australian Standard 2878:2000 (Standards Australia 2000). Timber was loaded in the radial direction; and hardness was measured using the Janka hardness test as described by Mack (1979). Two points were tested for each sample. Samples rejected because of defect were replaced with other samples cut from the same board if possible, otherwise replacement samples were cut from boards from the same log. Strength testing was performed on a calibrated Instron tensile testing machine located at FurnTech, Launceston. Modulus of elasticity (MOE) was calculated by fitting a straight line by eye to the first part of the load-deflection trace. Modulus of rupture (MOR) was also calculated. These were corrected to values at 12% MC based on the oven-dry MC of each sample by adjusting bending strength by 4% for each 1% difference in MC and MOE by 1.5% for each 1% difference in MC. Adjustments were negative for MC below 12% and positive for MC above 12%. This complies with the rules of Australian Standard AS 2878 (Standards Australia 2000). A strength group was calculated for each sample and experimental group using the rules of AS Janka hardness testing was also conducted using FurnTech s Instron. Oven dry MC was measured for each sample, as was sawing orientation, that is, whether the test face was a radial or tangential surface Results Logs Trees were felled on the 24 th of January They were end-sealed before transport to Fenning s Bairnsdale sawmill the following morning. Logs were stored there under waterspray until sawing. Tree and log measurements are shown in Table 4.3. Logs were all graded as D+ under Victorian log grading rules. No A or B grade was possible due to presence of Amrosia spp. stain and pinhole. Only one log had endsplitting at falling (1965 log number 2, split length 18 cm). Some logs had falling shakes, which were disregarded for this study. 73

80 Dom/ Codom stem DBH OB (cm) Total height (m) Height to 200 SED UB (m) Height to 300 SED UB (m) 3 m sawlog Prior to sawing Sawn logs Endsplit length small end (cm) Endsplit length large end (cm) Mean dia scanned (mm) Log no. SED (cm) LED (cm) Length (cm) Vol (m 3 ) E. sieberi South East Fibre Exports Private Property. Harvested and regenerated 1955/1960. Thinned from below 1999/2000 to approx 350 stems/ha. Log grade C & D. GPS / :GREEN **1 C C C C * C D C C C C D C Mean E. sieberi Brunts Tk, (831/506/0002). Harvested and regenerated 1965/66. Thinned from below 1990/1991 to approx 350 stems/ha. Log grade C. GPS / : PINK. 1 C D D D D D D C D D Mean Table 4.3. Summary log data. DBHOB diameter at breast height over bark; SED small end diameter; LED large end diameter; UB under bark continued below 74

81 Dom/ Codom stem DBH OB (cm) Total height (m) Height to 200 SED UB (m) Height to 300 SED UB (m) 3 m log Prior to sawing Sawn logs Endsplit length small end (cm) Endsplit length large end (cm) Mean dia scanned (mm) Log no. SED (cm) LED (cm) Length (cm) Vol (m 3 ) E. sieberi Dyers Ck Tk. Harvested and regenerated 1975/76. Thinned from below 2004 to approx 300 stems/ha. Log grade C & D. GPS / : BLUE 1 D D D D D D D D D D D D D D D D D D D D Mean Table 4.3. Summary log data. DBHOB diameter at breast height over bark; SED small end diameter; LED large end diameter; UB under bark continued from above 75

82 Log No Discs Disc measurements are shown in Table 4.4. A dendrochronologist assessed radial samples from several discs for age, see Appendix 2. Results were inconclusive. Mean Pith Radius Mean Heart Width Mean Heart Mean Mean Mean Heart Mean Mean Sap Prop. Pith Heart Sap Prop. Pith Heart Width (%) Radius Width Width (%) Radius Width Mean Sap Width Heart Prop. (%) Table 4.4. Disc measurements. Dimensions in mm. Heartwood proportion is a % of volume Sawing Logs were sawn at Fenning s Bairnsdale sawmill on 27 th January Logs were identified by colour (Table 4.1) so that source log could be identified for each board. The sawmill has a scanning system that determines log volume; individual log volumes are shown in Table 4.3. They also have a tallying sorter; results are shown in Table 4.5. Total fall-down was m 3. Board nominal width (mm) Thickness (mm) Batch Min Max Mean SD No. boards % of volume Sawn recovery from log (%) 1965 No. boards % of volume No. boards % of volume Table 4.5. Board width recovery, thickness and sawn recovery from log (nominal dry dimension basis, not including fall-down) Wood properties Initial moisture content and basic density were assessed on twenty samples from each batch; results are shown in Table 4.6. Radial and tangential unconfined shrinkage was measured for 10 samples from each batch. Results are shown in Table 4.7 as three points fitted to each 76

83 shrinkage curve: initial MC, and shrinkage and MC at fibre saturation point and at equilibrium Initial Basic Initial Basic Initial MC density MC density MC (%) (kg/m 3 ) Board (%) (kg/m 3 ) Board (%) Basic density (kg/m 3 ) Board Mean Mean Mean SD SD SD Table 4.6. Initial moisture content and basic density of randomly selected samples 77

84 Radial shrinkage fits (%) Tangential shrinkage fits (%) Green FSP EMC Green FSP EMC Batch Board MC MC Sr MC Sr MC MC St MC St C C C C C C Mean Mean C C Mean Table 4.7. Unconfined shrinkage measured on ten randomly selected samples from each batch. Shrinkage curves fitted by three points at initial moisture content, fibre saturation point, and equilibrium moisture content. C indicates a slice that collapsed; St tangential shrinkage; Sr radial shrinkage Drying A Vaisala temperature and RH probe located at the centre of the stack entry face was logged every 10 minutes for the duration of the trial. Results are shown in Figure 4.1. Note that the kiln only runs on weekdays. The commercial site housing the kiln had steam supply problems at the time of the trial, so it wasn t run for five days every week, leading to the poor control recorded. Drying progress of the samples is plotted in Figure 4.2. Thickness of the sample boards is plotted in Figure 4.3 to give an indication of shrinkage in thickness and recovery from reconditioning. Dry width and thickness of sample boards is shown in Table

85 Temperature (deg C) and Relative Humidity (% Time (days) Relative Humidity Temperature Figure 4.1. Recorded temperature and relative humidity during the trial Dry evaluation and grading Summary board shrinkage and moisture content results are shown in Table 4.6. Grading results are shown in Table 4.7, endsplit results in Table 4.8, surface checking, machining skip and internal checking results in Table 4.9, distortion results in Table 4.10 and sawn orientation results in Table Thickness (mm) Shrinkage (%) Moisture content (%) Green Dry Width Thickness Meter Oven dry Min Max Mean Std Dev Min Max Mean Std Dev Min Max Mean Std Dev Table 4.6. Summary of dry dimensional recovery and moisture content measured by resistance meter and oven drying of all boards Grade Top surface Bottom surface Both sides 1955 select Standard 7 11 High Feature select Standard High Feature select Standard High Feature Table 4.7. Percentage of boards in each grade (to AS 2796) on each face and percentage of boards with both faces graded select 79

86 Total length (m) Green Loss to endsplit Length (m) % of overall length Total length (m) Dry Loss to endsplit Length (m) % of overall length Table 4.8. Total length of board processed and length lost to endsplit Top surface Bottom surface Surface check Skip Surface check Skip Internal check Table 4.9. Percentage of overall board length (disregarding endsplit) degraded by surface check or machining skip on both surfaces and percentage of boards affected by internal check. Green Dry Bow Spring Twist Bow Spring Twist Table Percentage of boards with distortion exceeding AS 2796 allowance for 19 mm thick flooring. Backsawn Quartersawn Transitional Table Percentage of each batch by sawing orientation Strength testing Results are shown in Table

87 Hardness Results are shown in Table No. 1st test (kn) 2nd test (kn) Mean (kn) MC % Orientation R T T T T T T T T T Mean 6.0, Std Dev R R R T T T T T T T Mean 6.2, Std Dev R R R T T T T T T T Mean 5.1, Std Dev Overall: Mean 5.8, Std Dev 1.3 Table Hardness test results. Orientation R indicates that a radial face was tested; T indicates a tangential face. 81

88 Properties adjusted to 12%MC* Max load Width Depth Load/Deflection to MOE MOR MC MOE MOR SD SD Density Batch No. (kn) (mm) (mm) PL (kn/mm) (GPa) (MPa) (%) (GPa) (MPa) (MOE) (MOR) SD (kg/m 3 ) Mean Mean Mean *MOE adjusted to 12% MC at 1.5% per 1%MC; MOR adjusted at 4% per 1%MC Overall Mean Std Dev Table Strength test results for silvertop ash mm clears loaded in the radial direction 82

89 120.0 Average moisture content (% Pink 10 Pink 18 Pink 46 Pink 54 Pink 85 Pink 93 Green 10 Green 18 Green 48 Green 56 Green 85 Green 94 Blue 10 Blue 17 Blue 55 Blue 62 Blue 103 Blue Drying time (days) Figure 4.2. Sample board moisture content during drying. Green 1955; Pink 1965; Blue

90 120.0 Width (mm) Pink 10 Pink 18 Pink 46 Pink 54 Pink 85 Pink 93 Green 10 Green 18 Green 48 Green 56 Green 85 Green 94 Blue 10 Blue 17 Blue 55 Blue 62 Blue 103 Blue Drying time (days) Figure 4.3. Sample board width during drying. Green 1955; Pink 1965; Blue

91 35 Thickness (mm Pink 10 Pink 18 Pink 46 Pink 54 Pink 85 Pink 93 Green 10 Green 18 Green 48 Green 56 Green 85 Green 94 Blue 10 Blue 17 Blue 55 Blue 62 Blue 103 Blue Drying time (days) Figure 4.4. Sample board thickness during drying. Green 1955; Pink 1965; Blue

92 Plate 4.1. Log sealing after cutting discs Plate 4.5. Racked timber ready for predrier Plate 4.2. Log breaking down Plate 4.6. Pre-machining evaluation Plate 4.3. Resaw Plate 4.7. Machining Plate 4.8. Commercial grading to AS 2796 Plate 4.4. Bundled boards prior to selection 86

93 Plate Typical boards from 1955 Eucalyptus sieberi logs. 87

94 Plate 4.9. Typical boards from 1965 Eucalyptus sieberi logs 88

95 Plate Typical boards from 1975 Eucalyptus sieberi logs. 89

96 Plate Typical internal checking, from 1965 Eucalyptus sieberi logs 4.3. Analysis Logs and discs There was a significant difference (ANOVA on ranks) between heartwood proportion for the 1965 and 1975 groups, but not comparing other pairs. Means were 86%, 83% and 75% for the 1955, 1965 and 1975 groups respectively. There was no significant difference in endsplit formed prior to sawing between the three groups Green timber properties Timber from 1975 logs had significantly higher initial MC and lower basic density than that from 1965 logs (Table 4.6). Data failed a normality test, so an ANOVA on ranks was performed using Dunn s test to compare groups. There were no statistically significant differences between the three groups in radial or tangential unconfined shrinkage. Mean shrinkage of each group and a comparison with published data for mature timber are shown in Table Mean radial shrinkage (%) Mean tangential shrinkage (%) mature Table Radial and tangential unconfined shrinkage and comparison with published values. Mature figures from Kingston and Risdon (1961) Drying Figure 4.2 shows no noticeable difference in drying rate between the three groups. Moisture content variation decreased as drying progressed, though there was still wide variation in MC (20-40%) before final drying. Small samples used for prediction of MC of sample boards resulted in inaccurate predictions (hence final drying was started too early). This indicates substantial variation in MC along the length of boards. There was a poor correlation between 90