The impact of log-end splits and spring on sawn recovery of 32-year-old plantation Eucalyptus globulus Labill.

Thirty dominant or co-dominant, straight trees were selected from a 32-year-old thinned plantation of Eucalyptus globulus Labill. Growth strain at tree surface at breast height was estimated using a CIRAD-forêt method. Log-end splits in the butt logs were measured. The butt logs were quarter-sawn following a pre-determined sawing pattern. The most common dimensions of sawn boards were 28×105×3000and 28×77×3000?mm.The volume of the curved-edge off-cuts was estimated for each butt log. The end splits in the dried sawn boards were measured and the volume of the wood containing the splits in the boards calculated. The estimated reduction in sawn recovery due to removing the curved edges in the slabs was equivalent to 6% of the log volume. The estimated reduction in recovery due to end-docking log-end splits was equivalent to 1% of the log volume, or approximately 4% of the dried board volume. For a sawmill processing 40000?m³ of logs per annum, this could translate into an annual loss of $?758000 (log volume) and $?385000 (board volume). These numbers are high in the context that end splits in these logs overall were quite mild and the estimated strain at tree surface was moderate.     

Value optimized log rotation for strength graded boards using computed tomography

A possible application for an industrial computed tomography scanner in a sawmill is finding an optimal rotational position of logs with respect to knots and outer shape. Since a computed tomography scanner is a great investment, it is important to investigate potential profitability of such an investment for different production strategies. The objective of this study was to investigate the potential value increase of the sawn timber of Norway spruce (Picea abies (L.) Karst.) by rotating logs to their optimum position prior to sawing compared with sawing all logs in horns down position. The production strategy evaluated by log breakdown simulation in this case study was to produce strength graded timber of the center boards, while the side boards were appearance graded. This case study showed an average value increase with respect to the value of center boards, side boards and chips of 11 %.     

Modeling the effect of length on yield of sawn timber grades in Norway spruce (Picea abies (L.) Karst.)

The aim of the study was to model and analyse the effect of length on grade yield of timber from different stem parts in Picea abies, and to use the models to simulate the cost of reduced grade yield due to increased length. The boards were simulated having lengths ranging from 20 to 60 dm starting at stump level, 4 m above stump level and 8 m above stump level, respectively. Logistic regression models showed that length had a significant effect on grade yield, and this length effect was stronger in strength grading according to INSTA 142 (IN) compared to appearance grading according to Nordic Timber (NT). The length effect was most pronounced in butt logs, and somewhat greater in middle logs compared to top logs. Also a smaller length effect in inner boards compared to boards farther from the pith was found for IN-grading. The cost of the decrease in grade yield with increasing length will depend on the assumptions about the price gap between the grades. Current market prices in both grading rules gave a decrease in value of the sawn timber in stock by about 6% with an increase in the log length from 45 to 60 dm. In addition, a decrease in yield of timber in longer logs will amplify this effect, while a higher efficiency in the production process will diminish it.     

Drying of tangentially-sawn regrowth Tasmanian Eucalyptus obliqua

The Tasmanian sawmilling industry has traditionally been heavily focused on the processing of mature eucalypt timbers. However, the available log supply has contained an increasingly high proportion of younger, smaller regrowth logs. In response to this change, the Tasmanian sawmilling industry carried out an experimental program aimed at determining a means of processing regrowth Eucalyptus obliqua into high quality sawn and dried timber similar to that available from mature logs. Initial investigations revealed that application of conventional processing techniques to the production of dried machined tangentially sawn (“backsawn”) 25 mm and 19 mm thick boards did not produce commercially viable results. Two possible techniques for reducing drying degrade were investigated: storing boards for some time prior to drying and periods of zero airflow applied intermittently during drying. Neither technique proved effective. Quartersawn timber was found to undergo less surface checking and endsplit than did backsawn. Thinner boards showed no decrease in drying degrade when compared to thicker boards.     

In-forest assessment of timber stiffness in Norway spruce (Picea abies (L.) Karst.)

The objective of this study is to identify easily obtainable predictors for the mean timber stiffness of a forest stand. The most robust predictor is found to be the average taper of the trees in a stand, expressed as the tree height divided by the diameter at breast height (H/D-ratio). In a simple linear regression, the mean H/D-ratio of a stand yielded a R ²-value of 82 % in explaining the mean modulus of elasticity of boards from the corresponding stand. As a practical approach, exclusion of timber from stands with an H\D-ratio under a certain threshold is implemented. This shows an increase of six to ten percentage points in the C30-portion depending on the combinations of strength classes produced with a Dynagrade strength-grading machine. This must be considered a substantial improvement in grade yield and makes such pre-sorting in the forest very attractive since the H/D-ratio can easily be measured in forest inventories or by harvesters.     

Modulus of elasticity of I-214 young poplar wood from standing trees to sawn timber: influence of the age and stand density

The poplar wood industry chain from planted forests takes a strategic position for the creation of a competitive, profitable, and highly technological bioeconomy in the world. Niche sectors such as buildings can find in poplar wood an effective ally to reduce its carbon footprint and ecological backpack. For the poplar wood, it is important to understand the huge significance of the proper silvicultural management of a plantation and to characterize the raw material. In this context, this paper carries out such characterization for the particular case of young plantations of the clone I-214 (Populus × euroamericana (Dode) Guinier), commonly used for its high growth rate. The acoustic non-destructive characterization of poplar wood is carried out from standing trees, logs and sawn timber and then compared with the one obtained through destructive mechanical tests. The study shows that growth parameters are highly affected by the age and moderately affected by stand density, while mechanical properties are strongly affected by the age and less affected by the stand density. The study also shows high values of the linear regression coefficients between the mechanical properties obtained on standing trees, logs, and sawn timber using non-destructive and destructive methods (R²?=?0.7 for all three cases), greater than those obtained for other species. A good linear fitting was obtained between the tree and log velocities (R²?=?0.76) and between the tree and log elastic moduli (R²?=?0.85). Consequently, the evaluation of the mechanical properties employing the optimized acoustic protocol provides a reliable characterization for the poplar wood.

     

The influence of material properties on the amount of twist of spruce wood during kiln drying

The development of twist in Norway spruce boards (Picea abies Karst.) during normal temperature kiln drying was researched. Tangentially oriented boards were sawn from diametrical radial planks, from which the basic wood properties, i.e. linear shrinkage and grain angle, were determined. The unrestrained boards were kiln dried using a selected drying schedule. During the controlled drying process the moisture content (MC) and twist of the boards were measured. Twist was generally induced by the shrinkage of wood below the fibre saturation point, and increased in proportional to the decrease in MC. The earlier appearance of twist, with regard to MC and drying time, was confirmed in the case of boards sawn from the central part of logs. The final twist amounted to between 10 and 20°/m in the case of boards close to the pith, and decreased to less than 4°/m in the case of boards sawn at a radius of 70 mm from the centre of the logs. Ring curvature had the highest impact on the final twist of the dried boards, followed by grain angle and tangential shrinkage.     

Machine strength grading of Argentinean<Emphasis Type="Italic"> Eucalyptus grandis</Emphasis>

The present paper reports the results of an investigation regarding the possibility of machine strength grading sawn timber of Argentinean Eucalyptus grandis. In order to assess the usefulness of each parameter for predicting the mechanical properties of this timber species, and to propose strength, stiffness and density profiles, an empirical research project with four samples of beams and one sample of boards subjected to bending, and another sample of boards subjected to tension parallel to the grain, was carried out. The results obtained with specimens in structural sizes reveal the more important single and combined parameters for machine strength grading this timber species, and allow to analyse strength, stiffness and density profiles in comparison with the international strength class system established in the European standard EN 338.     

Modeling the longitudinal variation of sawn timber grades in Norway spruce (Picea abies (L.) Karst.)

Grades derived from visual assessments of sawn timber are determined by the worst part of each piece. Since grade varies longitudinally in timber, grade yield will decrease if the average length of timber increases. The variation in grade is caused by longitudinal variation in knot properties and other features as they appear on the sawn surface taken into account during grading. The objective of this study is to describe and analyze this variation in Picea abies. The study consisting of 768 boards for which all features that could lead to downgrading were recorded noting position, type and size. Based on this information, all boards were graded according to appearance by Nordic Timber, and strength by INSTA 142. Logistic regression models of grade as a function of position in the stem were developed, and the dependence between responses was taken into consideration by using General Estimating Equations (GEE). The models showed a decreasing trend in grade from the butt end toward the top end of the trees, and the effect was more pronounced in strength grading than in appearance grading. Models with binomial response and different correlation structures were tested, and it was shown that both independent and autoregressive correlation structures could be used. This suggests that a multinomial ordinal logistic regression with a GEE-approach with an independent correlation structure is appropriate for modeling grade in this study.     

Processing and wood properties of four ages of Eucalyptus obliqua

Trees of naturally regrown Tasmanian Eucalyptus obliqua L’Herit. of four different ages were sawn into 28 mm thick boards and then dried and milled together following best conventional industry practice. Younger logs had a lower proportion of heartwood and older logs had longer end splits. There was no significant difference between groups in unconfined shrinkage, drying rate, strength, stiffness or hardness. Boards cut from the youngest age class shrank significantly less but had higher variation in density, hardness and stiffness when compared to other age groups. They also suffered significant internal check. A much lower proportion of the youngest boards reached the highest value visual grade when compared with other groups.     

Selecting trees for structural timber

Twenty-eight cubic metres of timber (i.e. a total of 2248 boards) cut from 108 Pinus radiata trees from two 25-year-old plantations from Canterbury and Nelson in the South Island of New Zealand were tested in tension. Within- and between-tree variations of stiffness, strength and density were examined. Comparisons between density and stiffness for selecting trees for structural timber indicated that stiffness is the better parameter for selecting superior trees within the natural population of a forest stand; and the quality and grade recovery of structural timber would be increased significantly if trees were to be selected on the basis of stiffness. These conclusions apply to both stands although regional differences are evident with the Nelson timber being somewhat stiffer.     

Evaluating vacuum and steam process on hardwood veneer logs for export

There is an immediate need to develop and adopt new treatment technologies for eliminating insect pest and tree pathogens from veneer logs moved in trade. This is largely due to the current phase-out of methyl bromide and the uncertainty associated with the efficacy of potential alternatives. Vacuum and steam in combination has a proven and reliable record for commercially sanitizing a variety of commodities, including cotton, spices and textiles among others. This study was designed to evaluate basic parameters of vacuum and steam application on five high value hardwood veneer log species in an effort to ascertain the feasibility of continued treatment development. Relative heating rates to log center, damage and value loss assessment due to treatment, and overall energy used during treatment were recorded for logs treated individually in a flexible polymer chamber. At 200 mm Hg vacuum, time to reach 56 °C for 30 min to core ranged from 17 to 29 h, depending on density and log diameter. End checking varied by species, but veneer sawn from logs was largely unaffected in terms of yield and value. Energy used during treatments ranged from 54 to 205 kWh for individual logs. Results suggest that vacuum and steam as a phytosanitary treatment for hardwood veneer logs has potential and should be explored further.     

Sortierverfahren für die kombinierte maschinelle und visuelle Festigkeitssortierung

The aim of this study was to show the possibility of the classification of structural timber into strength class C35 according to EN 338 by using combined visual and machine strength grading techniques. Three different visual-machine strength grading combinations are devised for allocating sawn timber into strength class C35. They are composed on the one hand of the visual grading according to DIN 4074-1 and on the other hand of machine strength grading of green or dry sawn timber by measuring the dynamic MOE or the apparent density of sawn timber. In order to allocate sawn timber into strength class C35 the machine settings for these combinations were estimated. The grading results show that combinations based on the dynamic MOE are suitable for strength grading of lamellae for glued laminated timber and joists. Combinations based on apparent density are also suitable for strength grading lamellae for glued laminated timber.     

Simulated and realised industrial yields in sawing of maritime pine (Pinus pinaster Ait.)

A sawing simulation software was evaluated by comparison with a real situation in the industrial sawing of maritime pine (Pinus pinaster Ait.) stems. At an operational sawmill sawing yields were measured for the conversion of logs with two sawing patterns: production of boards and production of boards and lumber. The simulation used the WoodCIM® optimisation software with similar sawing set-ups and dimensionally matching virtual logs obtained from cross cutting of 3D mathematical reconstructions of maritime pine stems. The virtual maritime pine stems and the sawing simulation software showed potential to evaluate the impact of raw material and process characteristics on the production performance. The simulated sawing yields corresponded closely to the industrial yields for the production of boards (57% volume yield). For production of lumber and boards, the simulation allowed to obtain a higher volume (45% vs. 53%). The negative impact of resin production on the sawing yields was estimated by comparing the industrial yields of resin tapped trees with matching virtual logs and showed a loss of 11% sawn wood volume, increasing with log diameter.     

Correspondences between manually estimated compression wood in Norway spruce and the warp of the sawn timber

Picea abies L.) and the warping of the sawn timber in terms of bow, spring and twist as well as further deformation after ripping of the dried products. The amount of compression wood was defined and measured on logs according to the methods of the Swedish Timber Measurement Council (Regulations for measuring of round wood) and on the sawn timber according to the Nordic Timber. The impact of two different drying schedules was also investigated. The study shows that visible compression wood in both the butt end of the log and within the sawn timber was a rather poor indicator of the warp of the dried sawn timber. In no comparison did the correlation coefficient, r, exceed 0.3. In contrast to this, the correlation between the amount of compression wood and the warp of secondary products was fair, r = 0.79. This means that it should be possible to identify sawn timber less suitable for secondary processing by the amount of compression wood. The corresponding correlation between compression wood in the butt end of the log and the warp of the secondary products was r = 0.46. No significant differences could be shown in the degree of warp, as related to compression wood, between sawn timber or secondary products, dried at a wet-bulb temperature of 55 °C/117 h, LT-schedule, and a dry-bulb temperature of 110 °C/24 h, HT-schedule, respectively.

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r  = 0,79). Es sollte also m?glich sein, weniger geeignete Schnittware anhand ihres Druckholzanteils auszusortieren. Die Korrelation zwischen Druckholzanteil am Stammende und der Verwerfung im Schnittholz betrug 0,46. Für das Ausma? der Verformungen wurde kein signifikanter Unterschied zwischen den beiden Tocknungsbedingungen (55 °C/117 h und 110 °C/24 h) gefunden.

     

Untersuchung der Holzqualität von Traubeneichen aus unterschiedlich dicht begründeten Beständen

Logs taken from two stands of Quercus petraea Liebl. (age appr. 120 years) established in different density of stocking were comparatively investigated in view of dimension and quality. Afterwards the logs were cut into boards which were graded according to DIN 68 370. The logs of the stand with wide seeded strips showed clearly stronger dimensions and roughly better quality properties in the middle and lower part of stems. The results of the log and timber grading show a significant better quality for the wood coming from the stand which was established by wide seeded strips. Also the timber volume produced out of that stand was 18% higher compared with the narrow spaced stand which has been natural regenerated.     

Wood density and annual growth variability of <Emphasis Type="Italic">Picea abies</Emphasis> (L.) Karst. growing in the Ukrainian Carpathians

The purpose of this study was to increase knowledge of the variability of wood density and annual growth of Norway spruce growing in the Ukrainian Carpathians. The material consisted of 21 trees which were cut between 600 m and 1200 m asl from south-west and north-east expositions of the mountain Dovshka. The ovendry and relative wood density increased from the bottom (630 m asl) to the top (1190 m asl) of the mountain and was related to increasing number of tree rings in 1 cm, whereas the width of annual rings decreased expressively. Three significant categories of altitude (forest types) of Norway spruce timbers were estimated for the mountain forest stands. The highest average ovendry wood density (413 kg m^?3) and number of tree rings in 1 cm (17.1) were characterized by spruce trees growing at the wet rocky bilberry spruce forest (above 1000 m asl). Wood density and annual growth are two variables which were significantly correlated with each other and the altitude (R = 0.5–0.6).     

Radiometrisches Verfahren für die Holzsortierung

Grading according to DIN 4074 (quality specifications for coniferous sawn timber) is of great importance both for the security of timber structures and the economic use of the raw timber. According to this standard, timber grading is based on visual characteristics. In order to objectify timber grading as far as possible, great efforts have been made to achieve timber grading by machines. GreCon, Alfeld, has developed a procedure to determine the density of timber and thus even its content of knots by isotopic γ-radiation. Tests proved that this procedure is suitable for grading of boards and planks. The results show a good correspondence between mean bending strength of machine graded and visually graded timber according to DIN 4074. It is furthermore possible to apply this procedure to other grading rules, for instance the ECE-recommendations.     

Prediction of the mechanical properties of lumber by stress-wave velocity and Pilodyn penetration of 36-year-old Japanese larch trees

The objective of this study was to obtain basic knowledge for the prediction of the mechanical properties of Japanese larch lumber (Larix kaempferi) on the basis of tree properties, such as the stress-wave velocity (SWV) and Pilodyn penetration value (Py). The values of the correlation coefficient between the SWV of a standing tree and the dynamic Young’s modulus (DMOE) of logs, which were obtained at various heights, gradually decreased with an increase in the log sampling height, indicating that the SWV of a tree is affected by wood properties at the measuring position. A significant correlation between the SWV of trees and the average modulus of elasticity (MOE) of lumber was found (r =0.834). A significant negative correlation between the Py of a tree and the average modulus of rupture (MOR) of lumber was also found (r=-0.859). A high coefficient of determination for an obtained regression curve was found when both the SWV and Py of a tree were used for evaluating the average MOE or MOR of lumber. These results indicate that the average MOE and MOR of lumber can be predicted by using the SWV and Py of the Japanese larch tree.     

Reduction of the surface colour variability of thermally modified <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> wood by colour pre-grading and homogeneity thermal treatment

A new method that consists of combining wood pre-grading by surface colour followed by the application of homogeneity thermal treatments is proposed to reduce the surface colour variability of the thermally modified blue gum wood. To identify the conditions of the homogeneity thermal treatment for two pre-graded groups with different initial surface colours (pinkish and yellowish), the effects of applying 25 different thermal treatment intensities to such groups were analysed. The effects of this method on mass loss and volumetric swelling were also analysed. Results show that an optical pre-grading of the wood samples and treatments under different conditions can reduce the colour variability of the blue gum wood samples, as well as the volumetric swelling. Mass loss was not homogenised after the treatment, but the difference of masses between the two groups was similar to their untreated state. The application of this new methodology may be of interest for the sawn timber industry to bring more uniform boards on the markets and to promote Eucalyptus globulus as a price-competitive and sustainable alternative timber.