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  • 1.
    Myronycheva, Olena
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Karlsson, Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sehlstedt-Persson, Margot
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Distribution of low-molecular lipophilic extractives beneath the surface of air- and kiln-dried Scots pine sapwood boards2018Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 13, nr 10, artikel-id e0204212Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 2.
    Karlsson, Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Myronycheva, Olena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sehlstedt-Persson, Margot
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Multivariate modeling of mould growth in relation to extractives in dried Scots pine sapwood2017Ingår i: Proceedings IRG Annual Meetin, 2017, artikel-id 17-20629Konferensbidrag (Refereegranskat)
    Abstract [en]

    Influence of extractives on mould growth on Scots pine sapwood dried in air or in kiln was studied. Boards were sprayed with water mixtures of spores of the fungal species Penicillium sp., Aspergillus sp., Mucor sp., Paecilomyces sp., Trichoderma sp., treated at a temperature of 22ºC at 90% RH, classified into a percentage of covered area. Acetone and water extracts were isolated and analyzed for sugars, nitrogen, ash, resin/fatty acids, glycerol, and phenols. A multivariate Orthogonal Partial Least Squares (OPLS) regression model was developed to study relations between the extent of mould coverage of boards and chemical content. The model describes 51% variability in X and 69% in Y with prediction power of 55%. The results indicated that total acetone soluble extractives and sugars like glucose contributed to increased mould growth whereas fatty acids prevent mould growth.

  • 3.
    Ekevad, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Guo, Xiaolei
    Nanjing Forestry University.
    Potential Yield Increase with Reduced Saw Kerf Deviations when Curve Sawing2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Curve sawing with circular saw blades introduces saw kerf deviations due to the combination of the flat sawblade and the curvature of the saw kerf in log or cant direction. Deviations for a double arbor resaw used for curve sawing, are that the saw kerf becomes wider at top and bottom and that the desired rectangular cross sections of the boards become distorted. The yield loss due to the saw kerf deviation in practice for a sawmill was of interest in this study. Earlier and very approximate guesses and simple estimates have been indicating that the loss of income for a sawmill in Sweden producing 200’ m3 of sawn timber may be about 2 MSEK/year (0.22 Meuro/year). In this study calculations were based on true log data and assumed sawing conditions for a sawmill. A true mixed input log assortment (78458 spruce and pine logs taken into the log yard of a sawmill in northern part of Sweden) was used as basis. Individual curvature of these logs was taken into consideration but the calculation was still approximate because not all facts about sawing patterns, log classes etc. for an actual sawmill were known. Instead one single sawing class was used for the calculation of saw kerf deviation.

     

    Results show that the direct yield loss given the assumed input data was 0.61 %-units. This corresponds roughly to the income loss 0.2 Meuro/year mentioned above. Besides from the yield increase there are other advantages gained if the saw kerf deviation can be reduced.

  • 4.
    Ekevad, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Guo, Xiaolei
    Nanjing Forestry University, Faculty of Material Science & Engneering, Nanjing Forestry University.
    Li, Rongrong
    Nanjing Forestry University, Nanjing Forestry University, Faculty of Material Science & Engneering.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Curve sawing effects on board dimensions when rip-sawing with a circular saw blade2016Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 11, nr 3, s. 135-141Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 5.
    Sehlstedt-Persson, Margot
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Marklund, Birger
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Myronycheva, Olena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Hyveldjupets inverkan på mögelbenägenhet hos råspont av furu och gran2016Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Råspont av furu och granbrädor hyvlas av splintvedsrika sidbrädor. Råvaran till råspont postad som sidutbyte har ett rikt innehåll av kolhydrater i splintveden, speciellt i vinteravverkat timmer där furusplint normalt har högre näringsinnehåll än gransplint. Risken för mögelangrepp på råspont är stor om det omgivande klimatet är gynnsamt för mögeltillväxt - ett tilltagande problem i och med ett allt fuktigare och varmare klimat. Hög luftfuktighet i kombination med näring som anrikats mot virkesytorna under forcerad virkestorkning kan snabbt leda till missprydande mögelangrepp på råspont som används i t.ex. underspikning av takfot, takluckors insida i ouppvärmda vindar i småhus, väggar i carport mm. Tidigare studier har visat att det är fullt möjligt att styra näringsvandringen i till en utvald sida av brädorna under torkningsprocessen genom dubbelläggning av brädor och att därefter hyvla bort dessa ytor. I praktiken är detta dock svårt att industrialisera då dubbelläggning av brädor vid sågverken är slumpvis vad gäller vilka sidor som läggs ihop i kombination med att brädorna vanligen har olika längder.Numera bearbetas oftast alla ytor av råspont jämfört med tidigare där begreppet ”rå” innebar att en flatsida lämnades obearbetad. Denna flatsida profilhyvlas med ett finprofilerat vågformat rillstål på märgsidan dvs. den brädsida som inte har vankant. Projektets syfte har varit att undersöka ifall det rilldjup som idag används är tillräckligt för att avlägsna den näringsanrikade veden för att undvika mögelpåväxt i långtidsanvändning. I studien har torkade, dubbellagda 22x100 mm furu och gran brädor som hyvlats med ett hyveldjup mellan 0 – 1,9 mm, jämförts i ett forcerat, korttids mögeltest. Resultaten av detta mögeltest med mögelarterna Penicillium sp. Paecilomyces sp. och Rhyzopus sp., som använts vid indirekt kontaminering av försökmaterialet visar följande•En tydlig trend kan ses för furu med avtagande mögelgrad vid ökande hyveldjup. För att ytorna ska klassas som bra-acceptabla i praktiskt bruk bör inte mögelgraden överstiga mögelgrad 2. Enligt resultat i denna studie bör därför hyveldjupet för furu vara minst 1,5 mm. •För gran är resultaten inte lika entydiga men även här verkar ett hyveldjup på minst 1,5 mm vara lämpligt. Träslagens mögelbenägenhet är vid detta hyveldjup ungefär likvärdig. •Om hyveldjupet är mindre än 1,5 mm är furu betydligt mer mögelbenägen än gran och risken stor att splinten angrips av mögel. •Vid rillhyvling bör därför rillans ”toppar” ligga 1,5 mm in i virket.

  • 6.
    Öhman, Micael
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Grubii, Victor
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Moistening of the wood surface before planing for improved surface quality2016Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 11, nr 3, s. 156-163Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 7.
    Grubii, Victor
    et al.
    Luleå tekniska universitet.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Influence of Wetting on Surface Quality during Scots Pine Planing2015Konferensbidrag (Refereegranskat)
  • 8.
    Öhman, Micael
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Grubii, Victor
    Remoistering of the wood before planing: a method for improved quality2015Ingår i: Proceedings of the 22nd International Wood Machining Seminar / [ed] Roger Hernández; Claudia B. Cáceres, Quebec city, Kanada: Universite Laval , 2015, s. 245-251, artikel-id 5Konferensbidrag (Refereegranskat)
    Abstract [en]

    It is beneficial if the machining of wooden products is done at a moisture content equal to the climate the product is meant to be used in. For indoor products in central heated houses such moisture content is about 5-10%. For planing this is often a too low moisture content showing an increased risk of poor surface quality due to severe torn grain. Contrary to this too high moisture content will result in a fuzzy grain surface and problems with swelling and shrinkage of the product. The roughness of a machined wooden surface is affected by a number of different parameters like cutting tool geometry, machine settings and wood structure. The latter is the hardest to control since the surface quality is a result of the local combination of density, grain direction and moisture content. The larger 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.This study showed that by wetting the surface before machining, in this case planing, the average surface quality could be increased. No time dependences could be shown, wetting short before planing did show as good improvements as wetting treatment for 30 minutes or more.The study was based on a total of 120 test surfaces of Scots pine (Pinus silvestris L.). In order to maximize the variation in grain angle and density variations the test surfaces contained both clear wood as well as green knots.

  • 9.
    Ekevad, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Cristovao, Luis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Grönlund, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Geometry of kerf when curve sawing with a circular rip-saw2014Ingår i: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 72, nr 6, s. 809-814Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 10.
    Sandberg, Dick
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Vaziri, Mojgan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Trischler, Johann
    Linnæus University, Forestry and Wood Technology.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    The role of the wood mechanical industry in the Swedish forest industry cluster2014Ingår i: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 29, nr 4, s. 352-359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The forest and forest products form one of the most important basis for the transfer to a biobased economy in Sweden. About 75% of the area covered by forest in Sweden is used industrially to produce raw material for the wood-refining industries. Every year, this cluster uses 75 million m3 of roundwood and has an export value of € 12 billion. This review paper is devoted to the wood mechanical industry, i.e. the industry which turns the forest into sawn timber, packaging, construction wood, furniture and interior fittings. The sawmills consume about half of the volume of softwood which is felled, and about two thirds of the sawn timber goes to export without any further refining within the country. Nevertheless, in spite of the relatively low degree of refinement in the sawmill and the fact that the sawmills in general over time have a very low profitability, they are responsible for 70–80% of the forest owners' profits on the sale of timber. An increased upgrading of the sawn timber within the country is desirable from a national economic viewpoint – increased employment opportunities, increased export income etc. It should then in the first place be for products with a higher added value, such as furniture and fittings. Today, the refinement value is 15–20 times higher for products from joinery and furniture industries compared that of the sawn timber and the added value of the wood within the building industry is only about 1.5 times.

  • 11.
    Ekevad, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Cristovao, Luis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Grönlund, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Geometry of Kerf when Curve Sawing with a Circular Rip-Saw2013Ingår i: Proceedings of the 21th International Wood Machining Semina: August 4th – 7th, Tsukuba International Congress Center, Japan, 2013, s. 206-213Konferensbidrag (Refereegranskat)
    Abstract [en]

    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 inherent flat geometry of circular sawblades. 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 sawblade and with a double arbour circular saw with two sawblades is viewed upon. Input parameters in the study for the double arbour saw are blade diameter, overlap, margin between blades, cant height, curve centre horizontal position and curve radius. Output is the geometry of the kerf that is cut by the teeth. Theoretical 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 become wider at the top and bottom of the cant than in the middle. Sawing takes place not only in the front part of the blades but also on the back of the blades (back sawing). Parts of the cutting edges of the teeth are cutting when back sawing and not the whole of the width of the teeth. A result is that boards that are cut out of the cant get 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.

  • 12.
    Fredriksson, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Song, Haitong
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Determination of crosscutting safety zone for finger-jointed Pinus sylvestris furniture components2012Ingår i: Forest products journal, ISSN 0015-7473, Vol. 62, nr 2, s. 107-113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A common problem with finger-jointed wooden furniture components is chipping in the finger joints due to fiber deviations around sound knots. To avoid this, a fixed size safety zone between defects and crosscuts is used, but can lead to an excess of material cut away in the crosscutting operation. To reduce chippings in finger joints while maximizing recovery, an adaptive strategy was developed for setting the safety zone size between sound knots and finger joints in Scots pine (Pinus sylvestris L.) furniture components. The strategy was based upon modeling the risk of chipping the finger joint depending on the knot measurement. The model was used in an adaptive strategy in order to minimize the expected loss due to cutting away material around knots, compared with the cost of rejecting components in later stages due to chipped finger joints. Thus, each knot was assigned a unique safety zone. The strategy was tested using computer simulation of the finger-jointing process, and a sensitivity analysis was performed in order to quantify the effect of variations in the input data. The results show that the adaptive strategy improves recovery by at least 3 percent in the process of turning lumber into finger-jointed furniture components. It is very robust toward variations in knot size measurements (e.g., by scanning equipment), but less robust toward variations in crosscutting precision.

  • 13.
    Forsman, Samuel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Björngrim, Niclas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Bystedt, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Laitila, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Bomark, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Need for innovation in supplying engineer-to-order joinery products to construction: a case study in Sweden2012Ingår i: Construction Innovation, ISSN 1471-4175, E-ISSN 1477-0857, Vol. 12, nr 4, s. 464-491Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 in planning and coordination, assembly information, and spatial measuring through information modelling and spatial scanning technology. This is likely to result in an increased level of prefabrication, decreased assembly time, and increased predictability of on-site work. Originality/value – The role of supplying ETO joinery-products is a novel research area in construction. There is a need to develop each segment of the manufacturing industry supplying construction and this paper contributes to the collective knowledge in this area. The focus is on the possibilities for innovation in the ETO joinery-products industry and on its improved integration in the construction industry value chain in general.

  • 14.
    Forsman, Samuel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Bystedt, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Interaction in the construction process: System effects for a joinery-products supplier2011Ingår i: Lean Construction Journal, ISSN 1555-1369, E-ISSN 1555-1369, Vol. 2011, s. 1-18Artikel i tidskrift (Refereegranskat)
    Abstract [sv]

    Denna fallstudie beskriver svagheter i den samverkan som sker i byggprocessen vid upphandling av specialsnickerier. Resultaten visar på att informationen i processen är bristfällig och att dess överföring inte är säkrad. Kompetens att förädla och modellera information behöver utökas. En stor del av tiden tillförs inget värde till produkten vilket försvårar kommunikationen i värdekedjan vilket påverkar produktens kvalité. Mycket av problemen kan undvikas genom ökad interaktion mellan leverantören, föreskrivande arkitekter, och angränsande processer. En ökad grad av standardisering för samverkan och informationsutbyte, samt att minska systemberoende buffertlager för att öka andelen tid för värdeskapande aktiviteter, är andra förbittrare av prestanda i denna process.

  • 15.
    Öhman, Micael
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Nyström, Jan
    Modelling distribution and amount of compression wood by the shape of the green bow within planks of Norway spruce2003Ingår i: IWSS 5: Proceedings / Fifth International conference om image processing and scanning of wood, March 23 to 26, 2003, Bad Waltersdorf, Austria, Europe, Joanneum research , 2003, s. 13-24Konferensbidrag (Övrigt vetenskapligt)
  • 16.
    Johansson, Marie
    et al.
    Chalmers University of Technology.
    Nyström, Jan
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Prediction of longitudinal shrinkage and bow in Norway spruce studs using scanning techniques2003Ingår i: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 49, nr 4, s. 291-297Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 x 95 x 2500 mm and 45 x 120 x 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 x 10 x 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.

  • 17.
    Öhman, Micael
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Nyström, Jan
    Measurement of green plank shape for prediction and elimination of compression wood2002Ingår i: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 17, nr 4, s. 377-384Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 18.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Methods for avoiding the negative effects of compression wood2001Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This is a study of how the selection of raw material and sawing methods affects the magnitude of bow, spring and twist as well as the yield of accepted wall studs when graded with respect to straightness. The focus was on the relation between compression wood in butt logs of Norway spruce (Picea abies (L.) Karst) and the straightness of wall studs, in order to improve the sawmills ability to satisfy the customer demands by straighter sawn products. The following aspects of compression wood in the production process were examined:

  • 19.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    The measurement of compression wood and other wood features and the prediction of their impact on wood products2001Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Wood is a complex and highly variable biological material formed to give the tree best possible conditions for sustaining life. Thus every piece of wood is possessed of unique qualities. The great challenge in the process of manufacturing wood products has always been to select pieces of wood with properties that fulfil requirements for the product. The importance of selecting the right piece of wood will increase along with demands from customers for products with specific properties, such as moisture content, warp, strength, biological and aesthetic features. In order to supply customers with the products they request, a considerably improved selection of the raw material is needed. The earlier an accurate selection can be done, the better. To improve this selection or pregrading process, knowledge of the relationships between different features and different aspects of quality, as well as methods for measuring external and internal features, must be developed. The main objective of this work was to contribute to improved predictability of the quality of dried sawn products using the features both of logs and of sawn green products as input. This work was divided into two parts: Part one focused on the possibility of learning how to predict the quality grades of centre planks by manually inspecting longitudinal radiograph images (LRI) that depict the density variation within a log. In a survey respondents were interviewed regarding their interpretations of the density related features visible in the LRIs of Scots pine logs (Pinus silvestris L). The purpose was to be able to use these interpretations in predicting the final quality of planks sawn from the logs. The LRIs were reconstructed with the aid of an X-ray CT scanner. Part two focused on the relationship between compression wood (CW) in foremost butt logs of Norway spruce (Picea abies (L.) Karst) and the warp of the sawn products, on how to detect CW and on how to predict warp. The logs used in the study were chosen among logs delivered to and sawn at commercial sawmills located in the northern part of Sweden in order to assure that conditions in the study match those extant in commercial sawmills. The most important findings in this thesis are: Longitudinal radiograph images of the density variation within a log can be a powerful aid in manual grading of logs with respect to the quality of the resulting sawn products. The shape of the sawn, but not dried, centre planks is an indicator of both the amount and distribution of compression wood. Basing the cutting of planks on their shapes while still green can considerably increase the total length of acceptably straight dried products. This improvement is achieved through the elimination of compression wood.

  • 20.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Correspondences between manually estimated compression wood in Norway spruce and the warp of the sawn timber1999Ingår i: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 57, nr 5, s. 391-396Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Compression wood is regarded as a serious defect which affects the warp and machinability of sawn timber. To handle these problems, different regulations have been developed regarding grading of sawlogs and of sawn timber. This study is an attempt to clarify the relation between the amount of visible compression wood in Norway spruce (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.

  • 21.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Modelling compression wood in sawn timber of Scot pine and Norway spruce1999Ingår i: Connection between silviculture and wood quality through modelling approaches and simulation softwares: third workshop : La Londe-Les-Maures, France, 1999 : proceedings / [ed] Gérard Nepveu, Nancy: INRA Editions, 1999Konferensbidrag (Refereegranskat)
  • 22.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Plank grade indicators in radiograph images of Scots pine logs1999Ingår i: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 57, nr 5, s. 359-363Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is possible today to detect the internal structure of a log by using X-ray scanning technology. By visual inspection of a longitudinal radiograph image (LRI) of a log, it is possible to manually predict the coming grade of the centre planks. The objective of this study was to identify the features of Scots pine logs visible in the LRI's that were of importance in a manual grading process. The identification of useful features was determined by a survey among respondents connected to the wood and sawmill industry. The test logs originate from the Swedish stem bank and the evaluation of the results was based on the statistical method of partial least square regression (PLS). This study shows that useful indicators of the true grade of the centre planks were the knots and knot-related features as well as the butt swell and the heart wood fraction of the log.

  • 23.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Grade prediction of Pinus sylvestris logs with the aid of a radiograph image log1998Ingår i: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 13, s. 83-89Artikel i tidskrift (Refereegranskat)
  • 24.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Prediction of the properties of sawn timber by visual inspection of sawlogs1998Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
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