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- Blomqvist, Lars, 1962-, et al.
(författare)
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Distortion in laminated veneer products exposed to relative-humidity variations : Experimental studies and finite-element modelling
- 2019
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Ingår i: BioResources. - Raleigh, NC : North Carolina State Univ Dept Wood & Paper Sci. - 1930-2126 .- 1930-2126. ; 14:2, s. 3768-3779
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Tidskriftsartikel (refereegranskat)abstract
- A shortcoming of the laminated bending process is that the product may become distorted after moulding. This study focused on the influence of fibre orientation deviation for individual veneers on the distortion of a moulded shell. The distortion of 90 cross-laminated shells of the same geometrical shape, consisting of seven peeled birch veneers, were studied under relative humidity variation. All the veneers were straight-grained in the longitudinal-tangential plane, but to simulate a deviation in fibre orientation, some of the individual veneers were oriented at an angle of 7° relative to the main orientation of the other veneers in the laminate. A finite element model (FEM) was applied to study the possibility of predicting the results of a practical experiment. The study confirms the well-known fact that deviation in fibre orientation influences shape stability. The results also show how the placement of the abnormal veneer influences the degree of distortion. From this basic knowledge, some improvements in the industrial production were suggested. However, the FE model significantly underestimated the results, according to the empirical experiment, and it did not show full coherence. The survey shows the complexity of modelling the behaviour of laminated veneer products under changing climate conditions and that there is a great need to improve the material and process data to achieve accurate simulations. Examples of such parameters that may lead to distortion are density, annual ring orientation in the cross section of the veneer, the orientation of the loose and tight sides of the veneer, and parameters related to the design of the moulding tool.
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| 3. |
- Dvinskikh, Sergey, 1963-, et al.
(författare)
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Moisture content profiles and uptake kinetics in wood cladding materials evaluated by a portable nuclear magnetic resonance spectrometer
- 2011
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis Group. - 1748-0272 .- 1748-0280. ; 6:3, s. 119-127
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Tidskriftsartikel (refereegranskat)abstract
- We have evaluated the capability of nuclear magnetic resonance (NMR) technology based on small portable magnets for in situ studies of the local moisture content in wood. Low field and low resolution 1H NMR with a unilateral permanent magnet was used to monitor and map the moisture content of wood cladding materials of various types in a spatially resolved manner. The results show that portable NMR equipment based on small open-access permanent magnets can be successfully used for non-invasive monitoring of the moisture content in various extended wood specimens. The moisture content was measured with a depth resolution of 0.2 mm and a maximum penetration depth of 3 mm. This makes the technique suitable for e.g. in situ local moisture content measurements beneath a coating layer in the claddings and it is also possible to relate the moisture level to specific properties of the wood material.
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| 4. |
- Neyses, Benedikt, 1986-, et al.
(författare)
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Continuous densification of solid wood – The belt press approach
- 2022
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Ingår i: Proceedings of the 10th European Conference on Wood Modification. - Nancy : University of Lorraine, Faculty of Science and Technology, Laboratory of Study and Research on the Wood Material (LERMaB). ; , s. 76-79
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Konferensbidrag (refereegranskat)abstract
- The densification, i.e., transverse compression of solid wood can lead to improvements in the mechanical properties, and this can expand the areas of application for low-density wood species. For the past one hundred years, many efforts have been made to mass-produce densified wood products, but despite being available on the market, they remain niche products with low annual production volumes. One of the main reasons for this is that all available densified wood products are produced in a batch-type process, which limits the achievable process speed and integration into the continuous wood processing chain. For this reason, we propose a continuous surface densification process using a bespoke belt press – similar in principle to those used to produce MDF panels. The belt-press is capable of densifying full-sized wood boards at processing speeds of up to 60 m min-1. The primary belt for densification can be heated to temperatures above 160°C, while a subsequent belt functions as a cooling stage. During the densification process, the belt press can log the pressing forces, moments, and temperature. Preliminary tests with Scots pine specimens of 120 mm in width and 38 mm in thickness resulted in a twofold increase in peak density, after a pressing time of two minutes at 120°C. The resulting density profiles were similar to those obtained in studies using a static hot press. As the belt press can be fed with a continuous stream of boards, it has a higher net throughput than a static hot press. Further studies continue with the aim to evaluate different aspects relevant to the large-scale industrial production of densified wood products.
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| 5. |
- Sandberg, Dick, 1967-, et al.
(författare)
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Crack formation due to weathering of radial and tangential sections of pine and spruce
- 2006
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; 1:1, s. 12-20
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Tidskriftsartikel (refereegranskat)abstract
- The development of cracks and changes in appearance have been investigated on radial and tangential sections of pine (Pinus sylvestris L.) and spruce (Picea abies Karst.) after exposure outdoors for 61 months. The degradation of the sections has also been studied at the micro-level.The annual ring orientation was the most important factor affecting crack development on weathering. After 61 months of outdoor exposure, the tangential sections of spruce had 1.7–2.2 times greater mean total crack length per area unit than the corresponding radial sections. In pine, the total crack length per area unit on the tangential sections was 2.2–2.6 times greater than that on the radial sections. Tangential and radial sections show the same colour change as a result of weathering.Tangential sections have more and deeper cracks than radial surfaces. The cracks on the tangential sections occur frequently in both earlywood and latewood. On radial sections, cracks occur primarily at the annual ring borders, but to a certain extent also in the earlywood.Decomposition of the cell wall takes place in both radial and tangential cell walls and cracks tend to follow the fibril orientation in the S2-layer of the cell wall. The radial cell wall of the earlywood has a large number of pits which are degraded at an early stage.
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| 6. |
- Sandberg, Dick, 1967-
(författare)
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Simuleringsverktyg för skiktlimning – nulägesanalys av processen och prioriterade arbetsområden. : Simulation Tools for laminated bending of veneer - state of the art for the process and priority work.
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Denna rapport är en dokumentation av villkor och förutsättningar som gäller vid skiktlimning av faner för inredning och möbler inom delprojektet ”Skiktlimning av björk och bok” vid AB Åberg & Söner i Lönsboda.En analys av skiktlimningsprocessens status ger vid handen:Stora kunskapsluckor finns om de grundläggande fenomenen vid skiktlimning.Tydlig förändring av processerna sker mot:- mer avancerade produkter- korta serier- korta leveranstider- fokusering på pris och kvalitetSkiktlimning är ett av de få områden där svensk trämanufakturindustri har möjlighet att konkurrera mot låglöneländer.Ett framtidsscenario är att om 5 till 10 år kommer i stort sett alla beställningar via arkitekter och designers till företaget på elektronisk väg. Ritningarna är gjorda med hjälp av något CAD program. På grund av kravet på korta ledtider och utvecklingen mot allt mer avancerade produkter måste man kunna öppna och läsa olika CAD-program och utifrån dessa ritningar kunna avgöra om det är möjligt att i sin tillverkning tillverka den önskade produkten. Till sin hjälp i denna situation är företaget i behov av ett simuleringsverktyg i form av en matematisk modell som man har tillgång till. Med hjälp av detta verktyg skall risken kunna beräknas för att lokala brott i faneren inträffar, sprickor och limsläpp uppstår, samt att andra orsaker vid produktionen förorsakar kassaktioner av den färdiga eller nära färdiga produkten. Ytterligare ett önskemål är att det ritningsunderlag som man i digital form får från arkitekter i dess ursprungsform kan ligga till grund för tillverkningen. En analys av dagens tillverkning i relation till de framtida behoven som företaget kommer har genomförts och redovisas med förslag.
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| 7. |
- Sandberg, Dick, 1967-, et al.
(författare)
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The Concept of Value Activation : the PrimWood Method for Improved Properties.
- 1998
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Ingår i: Timber and Wood Composites for the Next Century.
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Konferensbidrag (refereegranskat)abstract
- Value Activation is an integrated R&D programme carried out for the last eight years at the Royal Institute of Technology, Wood Technology and Processing. The name Value Activation refers to the basic understanding ofwood, where at present there are properties that are not fully exploited, but with help of a new sawing pattern could be fully utilized. The basic idea lies at an industrial level producing radially sawn timber with good profitability and with a lesser and mostly a controllable moisture movement. In short it implies an activation of values of timber, that has not been exploited in ordinary industrial production to date. This paper gives one example how the basic ideas in the concept ofValue Activation have been implemented to the industry. A new manufacturing system, the Prim Wood Method, has been proposed in order to improve the utilization of wood. One basic idea within this method is a new sawing pattern called star-sawing, which produces timber with two different shapes, viz., timber with rectangular and triangular cross sections. This method facilitates an efficient production of radially sawn timber with vertical annual rings, and without pith and juvenile wood. The triangles produced in star-sawing are used for producing high quality, knot free panels with vertical annual rings, PrimWood Prism. In this process, the timber is finger-jointed to form knot-free lengths and glued together into a block. This block can then be divided according to thickness into boards with vertical annual rings. In star-sawing, a certain volume of clear pieces will be obtained which are relatively long, i.e. longer than 1 metre. It is not desirable to finger-joint these boards, but instead to manufacture PrimWood Prism without a finger-joint. The first full-scale industrial plants based on the Value Activation concept are now in production in nothern Sweden. At full capacity, the saw mill will produce around 18000 m3 of star-sawn pine a year and shift. The plant for Prim Wood Prism will produce around 5 000 m3 a year and shift. The company is expect to generate two to three times the usual value from each log.
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