| 1. |
- Ah Shenga, Pedro, et al.
(författare)
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Log sawing positioning optimization and log bucking of tropical hardwood species to increase the volume yield
- 2017
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; 12:4, s. 257-262
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Tidskriftsartikel (refereegranskat)abstract
- The sawmill industry is a very important link in the Mozambique forest products value chain, but the industry is characterized by undeveloped processing technology and high-volume export of almost unrefined logs. The low volume yield of sawn timber has been identified as a critical gap in the technological development of the industry. To improve the profitability of the industry, there is thus a need to develop methods and techniques that improve the yield. In this paper, different positioning of logs prior to sawing and the possibility of increasing the volume yield of crooked logs by bucking the logs before sawing have been studied. A computer simulation was used to study the cant-sawing and through-and-through sawing of the logs to determine the volume yield of sawn timber from the jambirre (Millettia stuhlmannii Taub.) and umbila (Pterocarpus angolensis DC.) species. The optimal position, i.e. the position of the log before sawing that gives the highest volume yield of sawn timber for a given sawing pattern when the positioning parameters, offset, skew and rotation, are considered gave a considerable higher volume yield than the horns-down position. By bucking very crooked logs and using the horns-down positioning before sawing, the volume yield can be of the same magnitude as that obtained by optimal positioning on full-length (un-bucked) logs. The bucking reduces the crook of the logs and hence increases the volume yield of sawn timber.
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| 2. |
- Bachtiar, Erik Valetine, et al.
(författare)
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Properties of adhesive films used in cultural assets
- 2022
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis Group. - 1748-0272 .- 1748-0280. ; 17:2, s. 147-150
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Tidskriftsartikel (refereegranskat)abstract
- The hygroscopic nature of wood leads to large moisture fluctuations in the material that may influence the mechanical performance of glued wood products. Adhesives based on bone, fish and hide have a long tradition for the gluing of wood and can be found in wooden structures in our cultural heritage. In this study, selected sorptive and mechanical properties of animal adhesives have been compiled and compared to those of synthetic polyurethane adhesives. Bone, fish and hide adhesives show a high moisture uptake at high relative humidity, which confirms the low moisture resistance of such adhesives. The modulus of elasticity and ultimate tensile strength of the films based on animal adhesives are considerably reduced when the moisture content is increased.
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| 3. |
- Báder, Mátyás, et al.
(författare)
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Wood densification processing for newly engineered materials
- 2018
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Ingår i: Proceedings of the 5th International Conference on Processing Technologies for the Forest and Bio-based Products Industries (PTF BPI 2018), Freising/Münich, September 20-21. - Kuchl. ; , s. 255-263
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Konferensbidrag (refereegranskat)abstract
- Wood is a renewable, bio-based material with a mixture of different properties and qualities, used in numerous applications. Beside many species with high wood qualities several species suffer due to a number of disadvantages, where low hardness and abrasive resistance are characteristic for low-density species. This paper presents examples of on-going European research projects and industrial processes mostly related to wood densification methods. Wood densification is a classical thermohydro-mechanical (THM) wood treatment process, through which density is increased by mechanical compression of wood perpendicular to the grain, by impregnation of cell lumens or cell walls with solutions or melted substances (resins, waxes), or by a combination of both. The purpose is to produce newly designed and engineered materials and products with new property profiles, which would potentially find new markets. In general, the THM processes consist of three stages: plasticization of the wood cells, followed by the actualcompression, and finally solidification of the compressed wood in order to prevent elastic spring-back and the moisture-induced set-recovery. The wood densification process refers but is not limited to solid wood and might apply to whole wood pieces, or to local areas within given pieces only. Another THM method is the mechanical compression of wood parallel to the grain, which leads to a product with high flexibility. A European wood research network, represented by the authors of this contribution, has extended experience in many wood modification processes, as demonstrated through ongoing researches and case studies in this paper
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| 4. |
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| 5. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Contact free measurement of complex shapes in the wood industry
- 2011
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Ingår i: Mechano-chemical transformations of wood during THM processing. - Biel, Switzerland : Bern University of Applied Sciencs, Architecture, Wood and Civil Engineering. - 9783952378700 ; , s. 143-144
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Konferensbidrag (refereegranskat)abstract
- There is an increasing need to update and correct information about product geometry in the wood manufacturing industry. Changes in machinery or personnel can be the cause of that need. Manual measurement takes time and diff erent ways of digitizing the geometry of the products have therefore been developed.In this study, two methods (3D-coordinate measurement and optical scanning) have been tested together in order to determine the position of a product in relation to the processing machine, and to optically scan the product geometry. The aim was to identify and evaluate methods to digitize product geometry into a CAD-model for the wood industry. Th e seat shell measured was fitted in the CNC-machine where the processing later would be performed.The methodology used has made it possible to create a CAD-model from the physical model. Based on the experience from this methodology, it would be recommended to continue by creating of a tool that minimizes the need for after processing, i.e. the adjustment of certain coordinates manually.
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| 6. |
- 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. ; 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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| 7. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Improving the performance of bended laminated veneer products
- 2011
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Ingår i: Mechano-chemical transformations of wood during THM processing. - Biel, Switzerland : Bern University of Applied Sciencs, Architecture, Wood and Civil Engineering. - 9783952378700 ; , s. 147-148
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Konferensbidrag (refereegranskat)abstract
- Laminated bending of veneers mean that dried, thin veneers or thin wood sheets are glued together under influence of pressure and eventually increased temperature. At the same time the product is given its desired shape, most often curved. This thermo hydro mechanical process offers several benefits. For example thick bends of small radiuses of any species of wood may be formed and poor quality wood containing knots, splits and other defects may be utilised. Laminated bends can usually be set more readily and made to conform better to the shape of the form than similar bends of solid wood. Further no softening treatment is generally required before the pieces are bent. However, there are also disadvantages e.g. more technical skill and better equipment are usually required than for solid wood bending. The presence of glue may be somewhat detrimental to the machines used for the final cleaning up of the bent pieces. Further the glue lines which are usually visible on the sides may be an aesthetical unappreciated effect [1],[2].The quality of the laminated bended veneer products are obtained as an interaction between the process, the veneers and the glue [3]. In industries designing and producing these products it is of interest to obtain better understanding of how processing- and material parameters affect the product quality. With an improved understanding of the material and processing parameters it may be possible to increase the efficiency of wood utilisation and promote the development of new processes and products that manipulate the viscoelastic nature of wood. In particular the possibilities to obtain narrower radius of curvature and better possibilities of bending in more than one plane would be advantageous.This study has focused on the moisture content (MC) and the grain angle orientation in the veneers. These two specific aspects were assumed to have a great influence on spring-back and distortions of the laminated bended veneer products. Spring-back and distortions were therefore studied in separate tests where MC and the grain angle orientation was varied separately in manufactured laminated bended wood products. After manufacturing the products were exposed to variations in humidity and temperature whereupon the spring-back and distortions were measuredThree tests were performed. For the first and the second test a seat shell was selected as test product, figure 1a. To the third test another product was selected, figure 1b. This product was a small bookshelf. The company producing this shelf had experienced large problems considering distortions of this product. Further the product was very simple in shape with only one bend and therefore suitable for measurements.In the first test the influence of MC of the veneers was investigated. In the second and third test the influence of grain angle of the veneers was studied.For the study veneers of birch and beech were selected in the production. For the first and third study only birch veneers were used. The veneers were initially conditioned to equilibrium moisture contents (EMC) according to setups in different test groups. For the first study a test group was also built up from veneers taken directly out of production to study the industrial conditions. The seat shells in this test group contained veneers conditioned to EMC 4 %, except for the surface veneers that had been stored in the production hall. The humidity and temperature conditions in this room corresponded to MC 7 %.The manufacturing of the products were performed in industrial conditions. In the tests the products were built up from a number of veneers and the studied factors were varied between the veneers in a controlled manner.The results from the first test showed that the MC of the veneers influenced the spring-back and the distortions. A large moisture gradient between veneers and especially unsymmetrical placements of these in the construction were especially critical. The results from the second and third tests showed that grain angle deviation has large effect on the distortions of the products. Even a small grain angle deviation as in study two (5°) resulted in large problems with distortions. The study also showed that when crossing two or more veneers with deviating grain angles there were cases when these faults interacted and multiplied the distortions. In production grain angle deviations can be a result of inaccurate placement of the veneers during pressing, incorrect cutting of the veneers, inherent from the growth of the tree or a combination of these factors. Deviations of the grain angle were, however, shown to have only small effects on spring-back.
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| 8. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Shape stability of laminated veneer products : How to decrease the negative effects of fibre deviation?
- 2013
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Ingår i: Forest Products Society (FPS) 67th International Convention. - Madison : Forest Products Society.
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Konferensbidrag (refereegranskat)abstract
- A shortcoming of the laminated bending process is that the products may become distorted after moulding and during use. Annually, significant financial losses have incurred in the furniture and interior design industries as a result of distorted products. In this study, we have examined the influence of deviation of fibre orientation of individual veneers on distortion of a moulded shell to find ways to improve shape stability of laminated veneer products.Ninety cross-laminated shells, consisting of 7 veneers of Birch (Betula pubescens Ehrh.) with a total thickness of 3.6 mm, were studied. The in-plane dimensions of the veneer were 400x660 mm. All the veneers were straight-grained, but to simulate deviation in fibre orientation some of the individual veneers were oriented 7 degrees relative to the main orientation of the other veneers in the laminate. Distortion was determined directly after moulding and after storage in a changing relative humidity.The results show the well-known fact that deviation of fibre orientation of the veneers in the laminate influences the shape stability of the product. The results from this study, however, also show how the placement of the abnormal veneers in the laminated veneer products influences the degree of distortions. From this basic knowledge some improvements for production of laminated veneer products were suggested.
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| 9. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Shape stability of laminated veneer products : an experimental study of the influence on distortion of some material and process parameters
- 2013
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis Group. - 1748-0272 .- 1748-0280. ; 8:3, s. 198-211
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Tidskriftsartikel (refereegranskat)abstract
- Laminated bending of veneers is a common used and important process for manufacture of components primarily for furniture and interior purposes. According to the use, such products are in general very sensitive to variations in the intended shape, i.e. distortion can be of great problem and more or less destroy the use of the final product. The most critical mode of distortion is twist, but also other changes in shape may be of interest to keep low. The causes to distortion of laminated bended veneer products can be of material (veneer, adhesive and the combination of these), design, processes and climate nature and there is a challenge to know which parameters which are of major importance for distortion, both directly after moulding and when the products are in use.In this study, the influence of type of UF-adhesive hardener, i.e. liquid or powder, water content of adhesive, adhesive distribution, variation of moisture content of glued veneers, and fibre orientation of veneers, on twist and position for a 3D-veneer construction (a chair seat shell) has been studied. Distortion, i.e. twist and position, has been determined directly after moulding and after moisture cycling. The moisture cycling was to simulate and accelerate conditions that the shells are subjected in use. The aim of the work is to study how the above mentioned material and process parameters influence the shape stability of the products.The results show that the climate, i.e. how a certain level of temperature and relative humidity influence the moisture content of the moulded product, has a clear impact on the distortion of the product in use. An increase in moisture content results in a significant increase in distortion and vice versa. The level to which the moulded products distort during climate variation can be controlled through controlling material, design and process parameter during moulding. Of the studied parameter mentioned above, a deviation in fibre orientation of the veneers in the moulded assembly is the most critical parameter to have under control to minimize distortion. The fibre deviation mainly results in an increase in twist. A high moisture content of a veneer vis-à-vis the rest of the veneers in the assembly before moulding, will result in increased position and twist of the moulded product in use. The difference of moisture content between veneers and the position of veneers with high moisture content in the assembly will influence the level of distortion. Other studied parameter also influences the distortion to a lesser extent and can in these cases be related to the moisture distribution in the mouldings.
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| 10. |
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