Micael Öhman

Prediction of longitudinal shrinkage and bow in Norway spruce studs using scanning techniques

Straightness is one of the most important properties for making timber an attractive material for modern mechanized building. Several studies have shown that a lack of straightness is one of the main reasons for choosing materials other than timber in the construction industry. This paper presents a way to model moisture-induced bow from longitudinal shrinkage data predicted from an analysis of images of the surface of Norway spruce studs. For this study, eight studs (45 × 95 × 2500 mm and 45 × 120 × 3000 mm) of Norway spruce timber were selected. Bow in these studs was measured at two moisture contents below the fiber saturation point. The studs were then split into three slices 11 mm thick, and the surfaces of these slices were scanned to obtain color information and images of the tracheid effect. The slices were cut into sticks with dimensions of 10 × 10 × 200 mm. The longitudinal shrinkage coefficient of these sticks was measured. A multivariate model was created to model the longitudinal shrinkage coefficient data from the information in the images. The predicted longitudinal shrinkage data was used to model bow. The mean value of the measured longitudinal shrinkage was 0.0121 (SD 0.0123). The root mean square error of prediction (RMSEP) for the multivariate model was 0.0079, which is regarded as good. Thus, it was possible to model moisture-induced bow with good accuracy using the predicted longitudinal shrinkage data.

Measurement of green plank shape for prediction and elimination of compression wood

The objective of this study was to predict the amount and the distribution of compression wood (CW) within a Norway spruce [ Picea abies (L.) Karst.] plank based on green plank curvature. The findings indicated a possibility of predicting the longitudinal distribution of CW from the green plank curvature. Areas free from CW showed a typical concave shape in relation to the centre of the log, while CW was present when a convex shape was shown. The larger the magnitude of convex curvature, the higher the concentrations of CW that could be found, and a larger fraction of dried planks was rejected due to excessive warp. This study also determined what information can be used to eliminate areas of high concentrations of CW by cutting and how cutting affects the grading results with respect to warp. Over 50% of the plank length showing a high concentration of CW (>30% of the cross-cut volume) was successfully cut off. Cutting strategies based on predicted CW concentrations resulted in a 10-40% increase in accepted plank length.

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

Need for innovation in supplying engineer‐to‐order joinery products to construction: A case study in Sweden

Purpose – The construction industry has been criticized for not keeping up with other production industries in terms of cost efficiency, innovation, and production methods. The purpose of this paper is to contribute to the knowledge about what hampers efficiency in supplying engineer‐to‐order (ETO) joinery‐products to the construction process. The objective is to identify the main contributors to inefficiency and to define areas for innovation in improving this industry.Design/methodology/approach – Case studies of the supply chain of a Swedish ETO joinery‐products supplier are carried out, and observations, semi‐structured interviews, and documents from these cases are analysed from an efficiency improvement perspective.Findings – From a lean thinking and information modelling perspective, longer‐term procurement relations and efficient communication of information are the main areas of innovation for enhancing the efficiency of supplying ETO joinery‐products. It seems to be possible to make improvements...

Geometry of kerf when curve sawing with a circular rip-saw

Rip-sawing following the curvature of a crooked log means advantages for yield. However, the possibility to saw in a narrow curve with a circular saw blade is limited because of the inherently flat geometry of circular saw blades. For a double arbour circular saw the situation is even more problematic because the two blades have a certain overlap and thus, the two arbours are not positioned in the same horizontal position. In this study, a theoretical geometrical study of the creation of a kerf with a single circular saw blade and with a double arbour circular saw with two saw blades was examined. Results for stiff saw blades show that the kerfs become in general curved and inclined (tilted) in the vertical direction and also that the width of the kerfs for double arbour saws becomes wider at the top and bottom of the cant than in the middle. Additionally, the sawn boards obtain varying thickness along their width because of the varying kerf width. A comparison with experimental thickness data from four test sawings at a sawmill indicates that the theoretical results are valid and that curve sawn boards become thinner than straight sawn boards.

Moistening of the wood surface before planing for improved surface quality

Abstract The roughness of a machined wooden surface is affected by a number of factors such as cutting tool geometry, machine settings and wood structure. The influence of wood structure on wood surface quality is difficult to control since the surface roughness is dependent on the local combination of density, grain direction and moisture content (MC). The greater the variation in wood features, the more difficult it is to find a combination of tools and machine settings that will give a high surface quality. The purpose was to study the impact of a surface wetting treatment before planing in order to reduce torn grain in the wood surface near knots in sawn timber of low MC. The study was based on a total of 120 specimens of Scots pine (Pinus sylvestris L.). To maximize the variation in grain orientation and density, the specimens contained both clear wood and knots. The results showed that when the surface was moistened before planing, chipped and torn grain in areas of deviating grain close to knots decreased. The response to wetting was rapid, wetting less than 30 s before planing gave as good an improvement as treatment time of 30 min or more.

Grade prediction of Pinus sylvestris logs with the aid of a radiograph image of the log

Today the internal structure of a log can be detected using X‐ray scanning technology. The objective of this study was to investigate the potential of grading a log by visual inspection of its longitudinal radiograph image (LRI). The grading accuracy of the LRI method was compared with the accuracy of a conventional manual log grading method. The grading accuracy was expressed as the ability to predict the grade of the centre planks of a log before the log was sawn. The grading results of the LRI method were determined by interviewing respondents connected with the wood and sawmill industry. The statistics of the conventional log grading method originate from the Swedish Stem Bank. The evaluation of the results was based on conventional statistical methods, unpaired significance tests and confidence intervals for means. This study shows that it is possible to grade logs by using LRIs. The grading accuracy is equal to, or better than, conventional log grading done by skilled graders from the Measurement So...

Distribution of low-molecular lipophilic extractives beneath the surface of air- and kiln-dried Scots pine sapwood boards

During industrial wood drying, extractives migrate towards the wood surfaces and make the material more susceptible to photo/biodegradation. The present work provides information about the distribution, quantity and nature of lipophilic substances beneath the surface in air- and kiln-dried Scots pine (Pinus sylvestris L.) sapwood boards. Samples were taken from knot-free sapwood surfaces and the composition of lipophilic extractives, phenols and low-molecular fatty/resin acids layers at different nominal depths below the surface was studied gravimetrically, by UV-spectrometry and by gas chromatography-mass spectrometry (GC-MS). The concentration of total extractives was significantly higher in kiln-dried than in air-dried samples and was higher close to the surface than in the layers beneath. The scatter in the values for the lipophilic extractives was high in both drying types, being highest for linoleic acid and slightly lower for palmitic, oleic and stearic acids. The amount of fatty acids was low in kiln-dried boards, probably due to a stronger degradation due to the high temperature employed. The most abundant resin acid was dehydroabietic acid followed by pimaric, isopimaric, and abietic acids in both drying types. It is concluded that during kiln-drying a migration front is created at a depth of 0.25 mm with a thickness of about 0.5 mm.

Curve sawing effects on board dimensions when rip-sawing with a circular saw blade

Abstract Curve sawing means advantages for yield and quality of sawn boards. However, for circular saw machinery deviations of saw kerfs give losses of valuable board volume. Deviations give thinner boards but also slight cupping of the cross sections. Theoretical calculations show that even with moderate (large) curve radii, these saw kerf deviations are typically 0.2–0.6 mm for normal circular saw machinery and Swedish log material. The test sawing reported here was made in order to give experimental values that can be compared to theoretical values. Fifty normal logs and 50 curved with top diameter 236–248 mm were cut with sawing pattern 3X with center boards 51 × 149 mm. The average curve radius of the curved cants that were cut in the resaw was 132 m (bow height 19 mm) and the theoretical saw kerf deviation for this radius is 0.31 mm. The experimental results show that the thickness reduction at the measuring points for curve sawn boards compared to straight sawn boards was in average 0.19 mm to be compared with the theoretical value of 0.20 mm. Cupping was more difficult to measure but results seem to agree well between theory and experiments.