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  • 1.
    Blomqvist, Lars
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Laminated Veneer Products: Shape Stability and Effect of Enhanced Formability on Bond-Line Strength2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns two aspects of the manufacture of laminated veneer products (LVPs). The first aspect is related to the possible improvement of the shape stability of LVPs, and the second has its starting point in the modification of the veneer for enhanced formability as well as the question of whether and how these modifications affect the bond-line strength.

    LVPs are veneers bonded with adhesive into predetermined shapes, mostly for the production of furniture and interior fittings. Since any deviation from the intended shape is a problem for both manufacturer and customer, various studies have sought to evaluate the influence of different materials and process parameters on shape stability. Parameters studied have included wood species (beech and birch), an adhesive system based on urea formaldehyde, the adhesive distribution on the veneer, climate, moisture content and fibre orientations of the veneers, as well as the orientation of the individual veneers in a multiply.

    Manufacturers of LVPs must consider some basic facts about wood in orders adequately to provide shape-stable LVPs to customers. Wood emits and absorbs moisture in relation to the surrounding climate, and this can lead to shrinkage and swelling. Such moisture induced movements differ in the wood’s different directions, and the magnitude is specific for the species. A thorough understanding of this is the basis for achieving shape-stable LVPs.

    Symmetry is defined in this thesis such that the veneer properties are balanced in the laminate. This means that opposite veneers on either side of the centre veneer have similar characteristic. An LVP will become distorted if the veneers are asymmetrically oriented before the press. Deviation from the desired shape can be small immediately after the pressing, but it may increase significantly with moisture content (MC) variations. Asymmetry may result when veneers with different fibre orientations are included in the laminate or when the veneers are placed asymmetrically. It may also occur if veneers with different MCs are bonded together asymmetrically. One aggravating factor is that the lathe checks that are introduced when the veneers are peeled or sliced from the log affect the shape stability. In 3-ply crosswise-oriented plywood, the veneer surfaces on which the lathe checks occur should be oriented in the same way for high shape stability.

    Based on existing knowledge, the production of shape-stable LVPs requires that the veneers are conditioned to a uniform MC and sorted with regard to fibre orientation and the side with lathe checks before bonding. End-user climates should govern the MC of the veneers and the moisture added with the adhesive during the process. Straight-grain veneers and symmetry should always be the goal.

    Moulding can cause stretching, i.e. strain, of the veneers depending on the curvature of the mould. To prevent the veneers from rupture, there are various ways to strengthen the veneers particularly in the transverse direction in which the veneer is weakest. However, tests have shown that these pre-treatments of veneers for enhanced formability can prevent the adhesive from penetrating the wood surface. It is therefore important to confirm that the pre-treatment does not affect the bond-line strength. 

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    Lars Blomqvist, Doctoral Thesis (Kappa)
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  • 2.
    Blomqvist, Lars
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Shape stability of laminated veneer products2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is about the shape stability of laminated veneer products.

    Laminated veneer products consist of veneers bonded together with adhesive into a predetermined shape. Such products are used in several contexts but especially in furniture manufacture. Deviation from the intended shape is a problem for both manufacturers and customers of the final products. The shape stability of laminated veneer products depends on a variety of material and process parameters, and this thesis identifies several important factors that influence shape stability. The purpose of this thesis is to find ways to decrease distortion and improve shape stability so that product quality can be improved.

    Different ways of measuring shape stability, both in an industrial environment and in a more research-based context, are presented in this thesis. Various studies have been conducted to evaluate the influence of different material and process parameters on shape stability. The parameters studied were species (beech and birch), adhesive system (bio-based adhesives, adhesive systems based on urea formaldehyde), adhesive distribution on the veneer, climate, moisture content and fibre orientations of the veneers, as well as orientation of the individual veneers in an assembly.

    The results clearly show that the fibre orientation of the veneer strongly influences the shape stability of a laminated veneer product. This means that products can show considerable distortion (particularly twist) if the fibre orientation of the veneer is orientated in an unsuitable way in the assembly before moulding. The effect of fibre orientation on shape stability can be very small directly after moulding, but it increases considerably when the moulded product is subjected to a change in moisture content. In general, a change in moisture content leads to distortion. Moisture change alone, however, results in a controlled distortion.

    An asymmetrical construction coupled with different moisture contents of the veneers in an assembly before moulding will result in poor shape stability of the product. Other studied parameters had a low impact on shape stability, although beech resulted in more distortion and poorer shape stability than birch.

    In order to produce shape-stable laminated veneer products, the veneers should be conditioned to a uniform moisture content and sorted with regard to fibre orientation before bonding. The orientation of the veneers is highly important regarding both fibre orientation and the loose or tight side of the veneer. If shape stability is the main target, the loose sides of peeled and sliced veneers should be oriented in the same manner.

  • 3.
    Blomqvist, Lars
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Shape stability of laminated veneer products: a review – defining and achieving shape stability2015In: International Wood Products Journal, ISSN 2042-6445, E-ISSN 2042-6453, Vol. 6, no 2, p. 89-95Article in journal (Refereed)
    Abstract [en]

    Laminated veneer products (LVPs) consist of veneers bonded together with an adhesive into a predetermined shape. Deviation from the intended shape is a problem for both manufacturers and customers of the final products. The shape stability of LVP depends on a variety of material and process parameters, and this review identifies several important factors that influence shape stability, the purpose being to find ways of decreasing distortion and improving shape stability so that product quality can be improved.

    The review ends to the following statements:

    The fibre orientation of the veneer strongly influences the shape stability of LVP. The products can show considerable distortion (particularly twist) if the fibre orientation of the veneer is oriented in an unsuitable way in the assembly before moulding.

    The effect of fibre orientation on shape stability can be very small directly after moulding, but it can increase considerably when the moulded product is subjected to a change in moisture content (MC). In general, a change in moisture leads to distortion. Moisture changes alone, however, result in a controlled distortion.

    The orientation of the loose and tight sides of the veneers in LVP affects the shape stability.

    An asymmetrical construction, coupled with different levels of moisture in the different veneers in an assembly before moulding, will result in poor shape stability of the product.

    The choice of wood species affects shape stability. Beech shows more distortion and poorer shape stability than birch.

    Based on existing knowledge to produce shape-stable LVP, the veneers should be conditioned to uniform MC and sorted with regard to fibre orientation and loose or tight side of the veneer before bonding. End-user climates should govern the veneers’ MC and added moisture from the adhesive during the process. Straight grain veneers and symmetry should always be sought.

    This review reveals several areas that need to be further clarified in order to achieve shape-stable LVP, for example the influence of adhesive, the distribution of pressure, temperature, stresses and strains during moulding and the development of numerical methods to better predict the final shape.

  • 4.
    Blomqvist, Lars
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Simulering och mätning av yttryck vid formpressning2008Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
  • 5.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Berg, Sven
    Luleå University of Technology, Sweden.
    Sandberg, Dick
    Luleå University of Technology, Sweden.
    Chipless Machining: Challenges in Manufacture of Laminated Veneer Products2015In: Proceedings of the 22nd International Wood Machining Seminar, IWMS 22: Volume 1 - Oral Presentations / [ed] Roger Hernández and Claudia B. Cáceres, Quebec City, Canada: Université Laval , 2015, p. 155-164Conference paper (Refereed)
    Abstract [en]

    A laminated veneer product (LVP) consists of veneers bonded together with adhesive under pressure into a predetermined shape and, in general, under increased temperature to shorten the curing time of the adhesive. The process is commonly used in furniture design to manufacture complex forms such as thin shells. In the industrial production of LVP and when the ready-for-use components are exposed to climate variations, rejection due to distortion of the laminates is a major problem. The shape stability depends on a variety of material and process parameters, and this study has focused on the influence of fibre deviation in a single veneer. Recent research on the shape stability of LVP and how distortion is influenced by various material and production parameters is presented. A finite-element model for LVP is introduced and the use of this model is exemplified by predicting the shape of a LVP with fibre distortion in a single veneer. The results show that it is possible to improve the shape stability of LVP if knowledge of various material and process parameters is implemented in the manufacturing process, and that a simulation based on a model of the wood material can be helpful in estimating the risk of an undesired deformation of the product.

  • 6.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology. RISE Research Institutes of Sweden, Sweden.
    Berg, Sven
    Luleå University of Technology, Sweden.
    Sandberg, Dick
    Luleå University of Technology, Sweden;Czech University of Life Sciences Prague, Czech Republic.
    Distortion in laminated veneer products exposed to relative-humidity variations: experimental studies and finite-element modelling2019In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, no 2, p. 3768-3779Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Blomqvist, Lars
    et al.
    Trätek.
    Bronsek, Anders
    Trätek.
    Oscarsson, Jan
    Trätek.
    Svensson, Nils
    Trätek.
    Säkerhet och organisation vid CNC-maskiner i träindustrin2002Report (Other academic)
  • 8.
    Blomqvist, Lars
    et al.
    Trätek.
    Hagström, Lina
    Trätek.
    Oscarsson, Jan
    Trätek.
    3D-modeller i träindustrin som konkurrensmedel vid e-handel2002Report (Other academic)
  • 9.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Landscheidt, Steffen
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Nilson, Henrietta
    Linnaeus University, School of Business and Economics, Department of Organisation and Entrepreneurship.
    Resource utilization in a production cell for laminated veneer products2017In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 13, no 4, p. 142-147Article in journal (Refereed)
    Abstract [en]

    The concept of productivity is often used to determine how well resources are used in an operation, and it is usually determined as the ratio of what is consumed in the production. Laminated veneer products are considered complicated products often taking complex shapes, using a raw material with high variation, and requiring machining processes that create scrap material that needs to be handled. Therefore, maintaining high productivity in industries producing such products may become challenging. This study reports on productivity measurements in a production cell consisting of an adhesive, pressing and a processing station. The study seeks to increase the understanding of production-related problems in this industry. This research has been based on productivity measurement as well as on interactive discussions between researchers and workers. Measurement of cycle times indicated bottlenecks in the processing cell. The discussion led via cycle times, processing residues and chatter marks to an examination of the foundation and rigidity of the CNC-machine in the processing cell. The study indicated that the performance of the CNC machine did not correspond to expectations. The machine was too weak to handle the required output in an efficient manner. Thus, there is a need to determine the performance expected before a machine or machine group is purchased. An update of the existing purchasing literature and its dissemination will support the crystallization of the purchasing process as a way forward to support the industry.

  • 10.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sandberg, Dick
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Basic knowledge of wood properties for improved performance of laminated Veneer products2013In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 9, no 4, p. 549-556Article in journal (Refereed)
    Abstract [en]

    To ensure success in the production of laminated veneer products, it is necessary to acquire a sound basic understanding of the behaviour of the wood, and to understand the inherent reactions of wood to adhesive, heat, moisture, strain and stress. This can ensure an efficient wood utilization and promote the development of new processes and products that take advantage of the visco-elastic nature of wood.

     

    A shortcoming of the laminated bending process is that the products may become distorted after moulding and during use. In this study, we have examined how the performance of laminated veneer products can be improved through the implementation of basic knowledge of wood in the design and production process.

     

    The results show that the material and process parameters and storage in a changing relative humidity have a clear impact on distortion. Fibre orientation of the veneers in the moulded assembly was the most critical parameter to control. Fibre deviations mainly resulted in twist of the product. A moisture content in one veneer deviating from that of the rest of the veneers in the assembly before moulding resulted in distortion of the laminated veneer products both after moulding and during use. To decrease the negative effect of fibre orientation and moisture content on shape stability, the veneer should be straight-grained and well-conditioned to a moisture level adapted to the use of the final product. Special care should also be taken to orientate the veneers during assembly before moulding.

  • 11.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Jimmy
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Sandberg, Dick
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Contact free measurement of complex shapes in the wood industry2011In: Mechano-chemical transformations of wood during THM processing / [ed] Parviz Navi and Andreas Roth, Biel, Switzerland: Bern University of Applied Sciencs, Architecture, Wood and Civil Engineering , 2011, p. 143-144Conference paper (Refereed)
    Abstract [en]

    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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  • 12.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Jimmy
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Sandberg, Dick
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Improving the performance of bended laminated veneer products2011In: Mechano-chemical transformations of wood during THM processing / [ed] Parviz Navi and Andreas Roth, Biel, Switzerland: Bern University of Applied Sciencs, Architecture, Wood and Civil Engineering , 2011, p. 147-148Conference paper (Refereed)
    Abstract [en]

    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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  • 13.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sandberg, Dick
    Luleå tekniska universitet.
    Modification of surface veneer to reduce damage in laminated veneer products during manufacturing2014In: Final Cost Action FP0904, Recent Advances in the Field of TH and THM Wood Treatment, May 19-21, Skellefteå, Sweden: Book of abstracts / [ed] Dick Sandberg and Mojgan Vaziri, Luleå: Luleå tekniska universitet, 2014, p. 50-51Conference paper (Refereed)
  • 14.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sandberg, Dick
    Luleå tekniska universitet, Luleå University of Technology.
    Moisture-induced distortion of laminated veneer products2014In: Forest Products Society (FPS)  68th International Convention, 2014Conference paper (Refereed)
  • 15.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sandberg, Dick
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Moisture-induced distortion of laminated veneer products2013In: Proceedings of the 9th meeting of the Northern European network for wood science and engineering (WSE): September 11-12, 2013, Hannover, Germany / [ed] Christian Brischke & Linda Meyer, Hannover, Germany, 2013, p. 178-183Conference paper (Refereed)
    Abstract [en]

    Laminated veneer products consist of veneers bonded together with adhesive into a predetermined shape. Since wood is a hygroscopic material and also anisotropic by nature, laminated veneer products are especially shape-sensitive to changes in moisture content. A deviation from the intended shape is a problem for both the manufacturers and users of the final products and annually such deviations cause great economic losses in the manufacturing industry.

     

    To illustrate the influence of moisture on distortion and shape stability, studies have been performed in industrial conditions and in a laboratory environment. Veneers of beech and birch and a seat shell moulded from these veneers were used in the study. Distortion, i.e. spring-back, position and twist, has been determined directly after moulding and during subsequent moisture and drying cycles.

     

    The distortion follows more or less slavishly the changes in relative humidity around the product. The distortion is generally small directly after moulding but, after the laminates have been exposed to a variation in relative humidity, the distortion increases. Some of the problems of poor shape stability that may arise later in the bending process can be reduced if attention is paid to moisture content and fibre orientation already in the production of the veneer.

     

    To achieve good shape stability of laminated veneer products in practice, the following should be followed by the manufacture industry:

    • develop      cooperation with suppliers of veneer and set requirements of veneer with regard      to deviation of the fibre orientation, and require that the veneer be dried      and conditioned to a moisture content consistent with production,
    • control      incoming veneers with respect to fibre orientation and moisture content,
    • plan warehousing      of veneers and ensure adequate conditioning, and
    • consider      the orientation of the veneers and the species.
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  • 16.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sandberg, Dick
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Shape stability of laminated veneer products: an experimental study of the influence on distortion of some material and process parameters2013In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 8, no 3, p. 198-211Article in journal (Refereed)
    Abstract [en]

    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.

  • 17.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sandberg, Dick
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Shape stability of laminated veneer products: How to decrease the negative effects of fibre deviation?2013In: Forest Products Society (FPS)  67th International Convention, Madison: Forest Products Society , 2013Conference paper (Refereed)
    Abstract [en]

    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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  • 18.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sandberg, Dick
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Shape stability of THM-processed laminated veneer products glued with bio-based adhesive systems2013In: Evaluation, processing and predicting of THM treated wood behaviour by experimental and numerical methods / [ed] Carmen-Mihaela Popescu and Maria-Cristina Popescu, Iasi, Romania, 2013, p. 99-100Conference paper (Refereed)
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    Abstract
  • 19.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sandberg, Dick
    Luleå tekniska universitet, Luleå University of Technology.
    Veneer modification for improved formability when moulding laminated veneer products2014In: Forest Products Society (FPS)  68th International Convention, 2014Conference paper (Refereed)
  • 20.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Jimmy
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Sandberg, Dick
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Kifetew, Girma
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    The influence of individual veneer orientation on the shape stability of planar lamination2012In: Current and Future Trends of Thermo-Hydro-Mechanical Modification of Wood. Opportunities for new markets? / [ed] Mathieu Pétrissans and Philippe Gérardin, Nancy, France, 2012, p. 160-162Conference paper (Refereed)
  • 21.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Nilson, Henrietta
    Linnaeus University, School of Business and Economics, Department of Organisation and Entrepreneurship.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Landscheidt, Steffen
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Downtime causes in a production cell for laminated veneer products2017In: 23rd International Wood Machining Seminar Proceedings / [ed] Marcin Zbiec and Kazimierz Orlowski, Warsaw, Poland: The Polish Chamber of Commerce of Furniture Manufacturers , 2017, p. 28-35Conference paper (Refereed)
    Abstract [en]

    Productivity is often used to determine how well resources are used for an operation. Most often, the ratio of what is produced to what is required to produce it determines productivity. Laminated veneer products are considered complicated products often with complex shapes, a raw material with high variation, and machining processes that create scrap materials that need to be handled. Therefore, keeping a high productivity in the industries producing such products may become challenging. This study reports productivity measurements in a production cell consisting of an adhesive, pressing and processing station. The study seeks to increase understanding of production-related problems in this industry. The research has been using productivity measurement as well as interactive discussions between researchers and workers.

    Measurement of downtime causes were made for 20 days, for a total of approximately 300 hours. The production cell had 1,299 minutes of stops. Of those, 450 minutes were one-time events. The rest were intermittent disturbances. Many of them could be explained by the dust-laden air and processing residues but were also related to veneer and adhesive. There is a need for determining material and processing parameters; however, the first priority is cleaning the factory.

    From a social perspective, some other issues must be added to the discussion of this paper. First and foremost, the business has gone through a transformation from a family business to a privately held firm. From the non-family employee’s view, this is a huge change. This has resulted in unclear roles and responsibilities within the company, which has also affected the productivity of the company.

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  • 22.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Pfriem, Alexander
    Eberswalde University for Sustainable Development, Germany.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Temporary buildings in reusable lightweight material design2016In: Proceedings of the 2016 World Conference on Timber Engineering (WCTE), Vienna: Vienna University of Technology , 2016Conference paper (Refereed)
    Abstract [en]

    There is a growing need and market for temporary buildings for various purposes, including largeconstruction projects in the tourism and events sectors or in civil protection. This paper gives an overview about the useof reusable lightweight materials in temporary buildings. Based on a project proposal submitted to the 7th framework, anew concept of temporary buildings is proposed. This concept combines the advantages of the premanufacturing of asmall number of parts and wooden components and a flexible and modular erection of the temporary building. Thefocus is on fast establishment with a maximum of three persons. A flexible and modular extension is possible.Assembling and disassembling the individual components with novel connect systems, adapted from the furnitureindustry, is proposed.This project aims to bring these concepts into new temporary buildings with new, reusable, and flexible lightweightdesign.

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  • 23.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Rowell, Roger
    University of Wisconsin-Madison.
    Bio-based adhesives at laminated veneers2012In: Proceedings of the 8th meeting of the Northern European Network for Wood Science and Engineering (WSE) / [ed] Antanas Baltrušaitis and Kristina Ukvalbergiené, Kaunas, Lithuania, 2012, p. 221-225Conference paper (Refereed)
  • 24.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sandberg, Dick
    Luleå tekniska universitet, Luleå University of Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Influence of veneer orientation on shape stability of plane laminated veneer products2014In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 9, no 4, p. 224-232Article in journal (Refereed)
    Abstract [en]

    One of the most important quality aspects of a laminated veneer product is its shape stability under changing relative humidity (RH). This study aimed to establish an understanding of how the orientation of individual veneers in the laminate, i.e., orientation according to fibre orientation and orientation of the loose (the side with ‘lathe checks’) or tight side of the veneer, affects the shape stability. Three-ply laminates from peeled veneers of beech (Fagus sylvatica L.) were studied. The four types of laminate were the following: loose sides of all veneers in the same direction (cross and parallel centre ply) and loose sides of the outer veneers facing inward (cross and parallel centre ply). Four replicates of each type yielded 16 samples. The samples were exposed to RH cycling at 20% and 85% RH at 20°C, and the shapes of the samples were determined. The shape stability was influenced by the veneer orientation. Laminations with the middle veneer perpendicular to the top and bottom veneer (cross-laminated) showed the best shape stability, especially when the loose sides of the veneers were oriented the same direction. In parallel-laminated veneers, the laminates with opposite directions of the loose sides in the two outermost veneers showed the best shape stability. The major explanation of the behaviour of the laminates is that the loose side expanded more than the tight side from the dry to the humid climate, which was shown by optical 3D deformation analysis (ARAMISTM). After RH cycling, the laminates with cross plies showed visible surface checks only when the tight side was facing outwards.

  • 25.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sterley, Magdalena
    SP Technical Research Institute of Sweden.
    Sandberg, Dick
    Luleå University of Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    The effect of veneer modification on the bond-line strength in laminated veneer products2015In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 11, no 4, p. 43-49Article in journal (Refereed)
    Abstract [en]

    A major problem in the manufacture of three-dimensional laminated veneer products (LVP) isdamage due to stretching and/or buckling of the veneer. To reduce or eliminate this problem, veneerdensification or adding a strengthening layer to the veneer can be an alternative. To study how veneermodification influences the veneer-to-adhesive bond strength, three methods of modification werestudied in relation to an unmodified reference veneer: (1) densified veneer, (2) veneer pre-bonded withpaper and hot melt adhesive (HMA), (3) veneer pre-bonded with non-woven polypropylene (NW)fabric glued to the veneer (a) with a urea formaldehyde (UF) adhesive, (b) with a mixture of UF andpolyvinyl acetate (PVAc) adhesive, and (c) with a PVAc adhesive. Densification, pre-bonding withpaper, and NW with UF/PVAc adhesive mixture resulted in no or only a slight decrease in strength ofthe bond-line compared to the reference. NW glued with UF or PVAc adhesive showed a considerablereduction in the strength of the bond-line. The climatic cycling had no significant influence on the bondstrength.

  • 26.
    Blomqvist, Lars
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sterley, Magdalena
    SP Wood Technology.
    Sandberg, Dick
    Luleå tekniska universitet, Luleå University of Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    The influence of veneer modification on adhesive bond strength2014In: Proceedings of the 10th meeting of the Northern European network for wood science and engineering (WSE) / [ed] Peter Wilson, Edinburg, Scotland, 2014, p. 150-155Conference paper (Refereed)
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  • 27.
    Johansson, Jimmy
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Blomqvist, Lars
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Nilson, Henrietta
    Linnaeus University, School of Business and Economics, Department of Organisation and Entrepreneurship.
    Landscheidt, Steffen
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Influencing factors to enable automation of wood furniture production2016In: Proceedings of the 12th meeting of the Northern European Networkfor Wood Science and Engineering (WSE): Wood science andengineering – a key factor on the transition to Bioeconomy / [ed] Bruno Andersons and Arnis Kokorevics, Riga, Latvia: Latvian State Institute of Wood Chemistry , 2016, p. 208-213Conference paper (Refereed)
    Abstract [en]

    The wood furniture industry in Sweden has an identified need of technological development in order to stay competitive. Especially the necessity to focus on automation has been identified. In the industry there are often needs to handle large levels of customization at the same time as keeping the production effective. This requires flexible automation solutions, often described as automated equipment that can rapidly be reconfigured for new products.Before automated applications are implemented in an industry there are issues to solve related to organisational, human and technological aspects. Based on this, the project - Flexible automation in manufacturing of laminated veneer products was initiated. The project is running since January 1, 2016 and is a two year national Swedish project. The aim of the project is to investigate challenges concerning automation in the wood furniture industry and especially focusing on bended laminated veneer products.In the project a case-study with the aim of identifying factors important for successful automation implementation in an involved wood manufacturing industry was performed. Key persons and staff of the company were asked to tell their life stories and a process mapping of the production was conducted.The results indicate a problematic relation between the management and the production staff, which partly can be referred to the shift from a family business to a private owned firm. Based on the process mapping, internal transport and handling are identified improvement areas. Productivity is disturbed by stops caused by processing residues and poorly defined materials. There is potential for improvement by adapting a process-oriented approach and defining the materials used.The case–study confirms the need to consider organizational and human aspects in production before initiating production. The study concludes the need to consider the special aspects of the wood material in production development.

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  • 28.
    Johansson, Jimmy
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Blomqvist, Lars
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sandberg, Dick
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Challenges using dielectric heating for THM processing of solid wood2013In: Evaluation, processing and predicting of THM treated wood behaviour by experimental and numerical methods / [ed] Carmen-Mihaela Popescu and Maria-Cristina Popescu, Iasi, Romania, 2013, p. 55-56Conference paper (Refereed)
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  • 29.
    Sandberg, Dick
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Blomqvist, Lars
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Formstabilitet hos formpressade hyllplan.2007Report (Other academic)
    Abstract [sv]

    Denna rapport beskriver inverkan av snedfibrighet i enskilda fanerark på formstabiliteten hos en 3,6 mm tunn formpressad konstruktion av björk.

    Totalt har 6 provgrupper á 15 skal tillverkats och testats. Genom olika orientering av faneren så att vissa ämnen fått avvikande fiberorientering i den limmade konstruktionen och inverkan av snedfibrighet har därmed kunnat studeras.

    Resultaten visar att snedfibrighet i enskilda fanerark medför försämrad formstabilitet hos den formpressade produkten. Snedfibrighet ger framförallt skevhet hos produkten, men kan i vissa fall även medföra ökad rörelse vid ändrad fuktighet i andra rörelseriktningar, samt kupning av konstruktionen.

    Fanerark med snedfibrighet som limmas så att fiberorienteringen blir i motsatt riktning för faner på vardera sidan om symmetrilinjen i tjocklek för konstruktionen, så kallad korslimning, ger den absolut sämsta förutsättningen för att erhålla en formstabil produkt.

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  • 30.
    Sandberg, Dick
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Blomqvist, Lars
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Formändringar hos formpressade fönsterkarmar vid ändrad fuktkvot.2006Report (Other academic)
    Abstract [sv]

    I denna rapport beskrivs hur förändringar i relativ luftfuktighet inverkar på formstabiliteten hos formpressade ämnen till fönsterkarmar. Karmämnena ärr uppbyggda av 29 faner som har formats till en öppen halvrund form (ungefär formen av ett C).

    Totalt tillverkades och testades 21 formpressade karmämnen. Ämnena hade följande dimensioner efter pressningen: bredd 260 mm, tjocklek 55 mm och innerdiameter 570 mm. Samtliga faner hade en och samma orientering i den formpressade konstruktionen, nämligen så att fiberorienteringen följde böjen.

    Efter formpressningen konditionerades ämnena i ett klimatrum vid 20°C och 18 % RF under 16 dygn. En uppfuktning i 90 % RF genomfördes sedan under 32 dygn och därefter konditionerades ämnena vid 20°C/20 % RF under 49 dygn.

    Avståndet mellan ämnets fria ändar och ämnets tjocklek bestämdes vid några olika tillfällen under klimatcyklingen.

    Resultaten visar att de karmämnen som studerats i denna undersökning har dålig formstabilitet med avseende på förändringar av det omgivande klimatet (RF). Den formförändring som är mest kritisk är avståndet mellan de fria ändarna, som ska vara inom intervallet 569 ±4 mm, det vill säga minsta respektive största tillåtna innerdiameter är 565 respektive 573 mm. Efter torkning av karmämnena under 49 dygn i 20°C och 20 % RF uppvisade 38 % av ämnena ett för litet avstånd mellan de fria ändarna.

    Karmämnena bör innan tillverkning av fönstren förvaras på ett sådant sätt att det inte torkar ut, för att förhindra att de formändras (diametern minskar) utöver de gränser som tillåts. En genomgång av de klimat som produkten skall användas vid, lagrings- och produktionsförhållanden där ämnena förekommer, samt fanerfuktkvot och tillförd fuktmängd via limmet, skulle kunna ge vid handen om processen kan förfinas för att minska rörelserna hos karmämnena.

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  • 31.
    Sandberg, Dick
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Blomqvist, Lars
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Fuktkvotsvariation i fanerbuntar vid ändrad relativ luftfuktighet.2006Report (Other academic)
    Abstract [sv]

    Denna studie behandlar inverkan av felaktig belimning av faneren vid tillverkning av skiktlimmade sittskal av bok och björk. Tre olika sätt att belimma faneren testades:

    1)  Jämn limmängd över hela fanerarket.

    2)  Ökad limmängd på ett över faneret diagonalt område.

    3)  Ökad limmängd på ena halva av faneret i dess längdriktning.

    Faner av bok och björk med dimensionen 1055 x 500 mm2, togs ut ur den ordinarie produktionen och konditionerades vid klimatet 20°C och 20 % relativ luftfuktighet (RF) under 30 dygn, vilket motsvarar en jämviktsfuktkvot på 4,5 %. 15 sittskal av respektive provgrupp tillverkades, dvs. totalt 90 sittskal.

    Skevhet och så kallad spring-back uppmättes direkt efter pressningen, efter konditionering i torrt klimat (20°C /18 % RF), efter uppfuktning i 20°C /90 % RF, samt efter en påföljande torkning och konditionering i torrt klimat (20°C /20 % RF).

    Undersökning visar tydligt att en måttlig variation över de enskilda fanerarken av pålagd mängd lim inte har en avgörande betydelse för hur formpressade produkter deformeras efter pressningen. Denna slutsats görs med reservation för att endast en limtyp (karbamidlim) och ett uppvärmningssystem (eluppvärmning, trögt verktyg) har testats.

    Resultaten antyder att avvikande fiberorientering hos faneren i sittskalen kan vara orsaken till ökad skevhet.

  • 32.
    Sandberg, Dick
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Blomqvist, Lars
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Inverkan av fanerens fuktkvot på formstabiliteten hos skiktlimmade skal.2006Report (Other academic)
    Abstract [sv]

    Syftet med denna studie var att undersöka hur olika fuktkvot hos ingående faner inverkar på deformationer hos skiktlimmade fanerprodukter.

    Skevhet och spring-back (återfjädring) har undersökts hos totalt 90 sittskal av modell VISIT 180 tillverkade av björkfaner. Sittskalen har tillverkats med olika fuktkvot i de ingående faneren.

    Omedelbart efter pressningen av sittskalen var spring-back och skevhet i stort sett likvärdiga för de olika provgrupperna.

    Efter 13 dygns konditionering av sittskalen i produktionslokalen kraftig minskning i spring-back för de sittskal som hade osymmetrisk fuktkvotsfördelning i sittskalen vid pressning (provgrupp 1 och 2), medan övriga sittskal uppvisade en måttlig (normal) förändring. Förändringen av spring-back var störst i provgrupp 1, där hela den konkava halvan av sittskalet var tillverkad med faner med hög fuktkvot.

    För skevheten har medelvärdet mer än fördubblats i samtliga grupper efter 13 dygns lagring av sittskalen i produktionslokalen. Den största ökningen har skett i provgrupp 1, dvs. för de sittskal med störst fuktkvotsgradient vid pressningen. Ökningen av skevheten i de övriga grupperna var likvärdig, dock uppvisade sittskal tillverkade av väl konditionerade faner liten rörelse underlagringen.

    För att få kontroll över spring-back och skevhet vid tillverkning av böjda och skiktlimmade produkter är det viktig att fuktkvotsvariationen mellan ingående faner är liten. Att faner med avvikande fuktkvot blir symmetriskt placerade i konstruktionen minskar effekten av för stor fuktgradient, men leder ändå till en betydande ökning i rörlighet hos det färdiga sittskalet.

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  • 33.
    Sandberg, Dick
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Blomqvist, Lars
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Inverkan av fiberorienteringen på formstabiliteten hos skiktlimmade skal.2006Report (Other academic)
    Abstract [sv]

    Denna rapport beskriver inverkan av snedfibrighet hos faner på formstabiliteten hos formpressade sittskal. Undersökningen har genomförts på totalt 29 stycken sittskal av rödbok och björk som efter tillverkning har konditionerats vid 20°C och 20 % RF (relativ luftfuktighet) respektive 20°C och 90 % RF, varvid skevhet och så kallad spring-back bestämdes.

    Sittskalen tillverkades av rakfibriga faner som i vissa fall lades samman utan någon avvikelse i fiberorientering erhölls i förhållande till sittskalets utbredning. I andra fall orienterades ytfaneren på sittskalets fram- respektive baksida med ca. +5 och -5 graders avvikelse. I ett tredje fall orienterades faneren närmast under ytfaneren, som var snedlagda ± 5°, i motsatt riktning ± 5° i förhållande till ytfaneren. Spärrfaner med ”orolig” fiberstruktur testades också.

    Resultaten visar tydligt att en måttlig avvikande fiberorientering i formpressade sittskal är förödande för sittskalens formstabilitet. Snedfibrigheten resulterar i skevhet hos sittskalen, som under vissa omständigheter kan bli så stor att skalen inte går att använda till slutprodukter.

    Resultaten visar också att korsläggning av faneren, det vill säga att snedfibrigheten i faneren får olika riktning på olika sidor om den limmade konstruktionens symmetrilinje ger en additiv effekt på skevheten. På motsvarande sätt ger en korsläggning på samma sida av konstruktionens symmetrilinje en reducerad skevhet.

    Öppningsvinkeln mellan sits och ryggbricka (i denna rapport benämnd spring-back) påverkas i liten utsträckning av snedfibrigheten hos faneren, likväl som spärrfaner med orolig fiberstruktur har haft liten inverkan på spring-back och skevhet hos sittskalen i denna undersökning.

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  • 34.
    Sandberg, Dick
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Blomqvist, Lars
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Inverkan av limmets torrhalt på formstabiliteten hos skiktlimmade fanerprodukter.2006Report (Other academic)
    Abstract [sv]

    Denna undersökning har syftat till att studera inverkan av några olika limsystems torrhalt på skevhet och spring-back (återfjädring) hos skiktlimmade produkter; i detta fall sittskal.

    Skevhet och spring-back har bestämts för totalt 86 sittskal till stolen VISIT 180, tillverkade av 1,5 mm björkfaner (ytfaner 1,3 mm). Mätningarna har utförts dels direkt efter pressningen, dels efter en längre tids lagring i a) produktionslokalen respektive b) i klimatrum där skalen utsattes för en cykel av uppfuktning och uttorkning.

    Fem limsystem från Casco Products har testats.

    Skillnaden i spring-back mellan limsystemen är inte av någon praktisk betydelse. Förändring av sittskalens fuktkvot alternativt omgivningens relativa luftfuktighet har större inverkan på spring-back än inverkan av de olika limsystemens fukthalt.

    Sittskal limmade med system 3 (pulverhärdare) uppvisar större skevhet än produkterna limmade med systemen 1 och 2 (flytande härdare) och system 4 (pulverhärdare), Samtliga av dessa limsystem har högre fukthalt än system 3. Detta visar att ökad fukthalt i limmet inte behöver innebära ökad skevhet hos produkterna.

    Sittskal limmade med limsystem 2 uppvisade en mycket liten förändring av skevheten över tiden och när sittskalen fuktcyklades. Det motsatta förhållandet gällde för sittskal limmade med system 4. Inblandning av filler (system 5) har medfördt ökad skevhet hos sittskalen.

    Utifrån de testades limsystemen är flytande härdare och låg fukthalt att föredra ur deformationssynpunkt hos de färdiga produkterna, framför limsystem med pulverhärdare eller hög fukthalt. Filler bör i möjligaste mån undvikas.

    [1] Fukthalten som avses är kg H2O/kg färdigblandat lim.

    [2] Det lim som Svensson & Linnér normalt använder i sin produktion av skiktlimmade produkter.

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  • 35.
    Sandberg, Dick
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Blomqvist, Lars
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Inverkan av limspridningen på formstabiliteten hos skiktlimmade skal2006Report (Other academic)
    Abstract [sv]

    Denna studie behandlar inverkan av felaktig belimning av faneren vid tillverkning av skiktlimmade sittskal av bok och björk. Tre olika sätt att belimma faneren testades:

    1)             Jämn limmängd över hela fanerarket.

    2)             Ökad limmängd på ett över faneret diagonalt område.

    3)             Ökad limmängd på ena halva av faneret i dess längdriktning.

    Faner av bok och björk med dimensionen 1055 x 500 mm2, togs ut ur den ordinarie produktionen och konditionerades vid klimatet 20°C och 20 % relativ luftfuktighet (RF) under 30 dygn, vilket motsvarar en jämviktsfuktkvot på 4,5 %. 15 sittskal av respektive provgrupp tillverkades, dvs. totalt 90 sittskal.

    Skevhet och så kallad spring-back uppmättes direkt efter pressningen, efter konditionering i torrt klimat (20°C /18 % RF), efter uppfuktning i 20°C /90 % RF, samt efter en påföljande torkning och konditionering i torrt klimat (20°C /20 % RF).

    Undersökning visar tydligt att en måttlig variation över de enskilda fanerarken av pålagd mängd lim inte har en avgörande betydelse för hur formpressade produkter deformeras efter pressningen. Denna slutsats görs med reservation för att endast en limtyp (karbamidlim) och ett uppvärmningssystem (eluppvärmning, trögt verktyg) har testats.

    Resultaten antyder att avvikande fiberorientering hos faneren i sittskalen kan vara orsaken till ökad skevhet.

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  • 36.
    Sandberg, Dick
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Blomqvist, Lars
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Inverkan av ojämn limspridning på formstabiliteten hos skiktlimmade skal - Förstudie.2006Report (Other academic)
    Abstract [sv]

    Denna förstudie behandlar inverkan av felaktig belimning av faneren vid tillverkning av skiktlimmade sittskal av björk.

    Vid belimningen av faneren applicerades limmet avsiktligt så att en förhöjd limmängd erhölls enligt två sätt:

    a)              på fanerets ena långsida (i rygg-sitsriktningen),

    b)             diagonalt över faneret.

    Fem sittskal av vardera appliceringsmodellen har testats och jämförts med totalt 60 stycken korrekt limmade sittskal.

    Felaktig limpåläggning som medför att mängden lim fördelas olika i den skiktlimmade konstruktionen har stor inverkan på formstabiliteten hos det färdiga sittskalet. Effekten blir ökad skevhet, medan spring-back påverkas marginellt.

    Denna förundersökning visar att limpåläggningens inverkan på formstabiliteten behöver undersökas närmare.

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  • 37.
    Sandberg, Dick
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Blomqvist, Lars
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Klimat i produktionslokaler vid Svensson & Linnér AB.2007Report (Other academic)
    Abstract [sv]

    I den nu genomförda undersökningen har klimatet, dvs. temperaturen och den relativa luftfuktighet, bestämts vid tre för produkten väsentliga platser i produktionslokalen hos Åberg & Söner i Lönsboda, nämligen i:

    • Fanerlagret
    • Torken
    • Presshallen

    Temperatur och relativ luftfuktighet har loggats med logger Tinytag Ultra 2 vid dessa platser under perioden oktober 2005 till juni 2006.

    Följande slutsatser har kunnat dras:

    • I fanerlagret har RF under den period mars-juni 2006 legat på en nivå som motsvarar en jämviktsfuktkvot på 7,5-12 % vid 20°C. Detta innebär att problem kan uppstå vid limningen (HF) och torkning av faneren är därmed att rekommendera. Torkning av faneren är att rekommendera med tanke på variationen i leveransfuktkvot hos faneren och att faneren lagras i buntar som medför att en fuktutjämning går mycket långsamt.
    • Torken fungerar tillfredsställande och det klimat som denna var inställd på under mätperioden bör ge en slutfuktkvot hos faneren mellan 2,5 % och 4,1 %.
    • Klimatet i presshallen varierar i samklang med utomhusklimatet. Det innebär att under vintrar med minusgrader och regnfattiga vårar så kommer klimatet i lokalen att motsvara ca 5 % jämviktsfuktkvot. Under övrig tid på året kommer produkter som förvaras i lokalen att fuktas upp mot 8-10 % fuktkvot.
    • Ur aspekten fanerens fuktkvot, så bör presshallen och fanerlagret inte förses med en befuktningsanläggning. Snarare bör det ordnas så att fanerens fuktkvot har möjlighet att utjämnas mot en lägre nivå.
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  • 38.
    Sandberg, Dick
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Blomqvist, Lars
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Johansson, Jimmy
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Material- och produktionsparametrars betydelse för formstabiliteten hos skiktlimmade fanerprodukter2007Report (Other academic)
    Abstract [en]

    This report describes a number of investigations carried out to illustrate the importance of various material and production parameters for the shape stability of laminated veneer products. The moulded products are manufactured from veneers which are shaped by being glued together under pressure, the veneers being oriented in various directions in relation to each other to achieve greater strength and a better shape stability than that of solid wood.

    The laminated veneer shells have been manufactured under industrial conditions, where a number of parameters have been varied in order to assess the influence of these parameters on the shape stability. The tests differed from normal production conditions only in that all the veneers were conditioned to a defined moisture content before the tests were carried out. The change in shape of the shells has been determined immediately after pressing, after a certain period of storage in the production premises and/or after the shells have been conditioned in a climate chamber at low and high relative atmospheric humidities.

    Factors studied were:

    • wood species, i.e. peeled veneers of beech and birch;
    • variations of an adhesive system based on urea-formaldehyde, i.e. various moisture ratios in the adhesive, various types of hardener (liquid or powder) and the addition of a filler;
    • the influence of different moisture content in the individual veneers to be pressed to a laminate;
    • the influence of how the veneers are fed through the adhesive spreader (in a roller application of the adhesive) and of an uneven application of the adhesive on the veneer before pressing;
    • the influence of different fibre orientations in the individual veneers in a laminate; and
    • the influence of exposure of the product to a varying relative atmospheric humidity.

    The conclusions which could be drawn regarding the influence of different parameters on the shape stability were:

    • Beech is a more “mobile” wood species than birch and showed overall a poorer shape stability than birch.
    • The variations in properties of the adhesive systems studied had little practical importance for the shape stability of the product.
    • Differences in moisture content between the veneers glued together into a product had serious consequences for the shape stability of the final product.
      • If veneers with different moisture ratios were placed asymmetrically in the structure, (in this study the moisture content was 14 %-units higher) the shape stability was worse, i.e. a greater spring-back and a greater twist.
      • A slight difference in moisture content (3 %-units) in the surface veneers did not greatly influence the shape stability.
      • To achieve a good shape stability in the laminate, the veneers should be well conditioned, so that as small a moisture gradient as possible arises in the laminated structure.
      • The magnitude of the spring-back, but not the twist, immediately after lamination was influenced by how the veneers were fed through the roller spreader and by the evenness of application of adhesive to the veneer sheet. These factors did not however have a decisive influence on the shape stability of the products.
      • The fibre orientation in the individual veneers was decisive for the deformation and shape stability of the products studied.
        • A grain deviation of only a few degrees could under certain conditions lead to deformations and a deterioration in shape stability so severe that the final product was useless.
        • A grain deviation in the longitudinal veneer resulted in twist, while a deviation in the cross veneer resulted in cupping in the products studied (Study 6). The spring-back was influenced to a small extent by a grain deviation in the veneers.
        • Gluing veneer sheets with a grain deviation so that the fibre orientation was in the opposite direction for veneers on each side of the symmetry line (in the thickness direction of the structure), so called cross-gluing, gave the absolutely worst conditions for obtaining a shape-stable product. Conversely, having the grain deviation in the same direction on each side of the symmetry line reduced the tendency to twist.
        • The shape of the laminated veneer products depended on the moisture content of the veneers of which the product was made, i.e. the product shape followed the variations in the temperature and in particular the relative atmospheric humidity of the surroundings. Variations in moisture content (which in practice are very difficult to prevent) can release stresses built into the product, and this can lead to deformations. This can occur even if the product during production is assessed to be free from stresses. The magnitude of the deformations which follow from the variations in the climate surrounding the product depend on the design/structure of the product, the level and duration of the prevailing climate, and the various material and process parameters, e.g. those mentioned above, which can influence the shape stability.

    The results of this investigation show clearly that material and process parameters can have a great influence on the shape stability of laminated veneer products. The fibre orientation in the individual veneers and differences in moisture content between the veneers which result in moisture gradients in the final product have in this study been identified as the most important parameters influencing the deformation and shape stability of these products.

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  • 39.
    Sandberg, Dick
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Blomqvist, Lars
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Svensson, Nils
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Produktivitetsmätning vid skiktlimning- störningsanalys vid CNC-bearbetningen.2006Report (Other academic)
    Abstract [sv]

    Denna studie redovisar produktivitetsmätningar för två 5-axliga CNC-maskiner (maskin B och E) för bearbetning av skiktlimmade produkter vid företaget Svensson & Linnér AB.

    Studien visar att organisationen klarar av att producera med en acceptabel produktivitet när satserna är stora. När satsstorlekarna sjunker ökar stopptiderna dramatiskt. Som ett exempel visar studien att stopptiden i maskin B är 12 % när satsstorleken är över 600 detaljer. Vid maskin E och där satsstorleken igenomsnitt är 32 detaljer är stopptiden 33 %.  En stor del av stopptiden beror på organisatoriska orsaker och en kraftig minskning av störningar kan erhållas genom att förbättra organisationen och planering för respektive maskin.

    Då utvecklingen går mot allt kortare serier måste stor energi läggas på att reducera stopptiderna. Det finns många goda exempel från till exempel bilindustrin där man lyckats att nå långt i detta arbete. Den så kallade SMED-metoden är ett exempel på ett kraftfullt verktyg för att radikalt minska ställtiderna vid en maskin utan att det behöver innebära några större investeringar.

    När stopptiderna tenderar att öka, ökar också riskexponeringen för olyckor och tillbud. En orsak till detta är den ökade stress som blir när kravet på produktiviteten ökar på grund av ökad konkurrens, samtidigt som produktionen i den egna verksamheten går mot allt mindre satsstorlekar.

    Utifrån den nu genomförda studien ges följande åtgärdsförslag:

    1. Diskutera gemensamt hur stopptiderna kan minskas utifrån vad som framkommit i studien och utifrån allas erfarenheter och upprätta en åtgärdslista.
    2. Sätt operativa mål för vilken produktivitetsnivå man vill sträva mot.
    3. Ta till vara på erfarenhet från tidigare perioder då det fanns en rutin för hur man organiserade arbetet inför ett ställ.
    4. Genomför SMED-analys vid något vanligt förekommande ställ för att fördela inre ställtid till yttre ställtid och genomför insatser för att reducera ställtiderna.
    5. Utarbeta rutiner för hur arbetet vid CNC-bearbetning ska organiseras.
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