| 1. |
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| 2. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Basic knowledge of wood properties for improved performance of laminated Veneer products
- 2013
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Ingår i: Pro Ligno. - Brasov : Publishing House of Transilvania University of Brasov. - 1841-4737 .- 2069-7430. ; 9:4, s. 549-556
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Bio-based adhesives at laminated veneers
- 2012
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Ingår i: Proceedings of the 8th meeting of the Northern European Network for Wood Science and Engineering (WSE). - Kaunas, Lithuania. - 9786090205815 ; , s. 221-225
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Konferensbidrag (refereegranskat)
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| 4. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Chipless Machining; Challanges in Manufacture of Laminated Veneer Products
- 2015
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Ingår i: Proceedings of the 22nd International Wood Machining Seminar, IWMS 22.. - Qubec City : Universite Laval. - 9780994796400 - 9780994796400 ; , s. 155-164
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Konferensbidrag (refereegranskat)abstract
- 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 modelis 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.
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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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Development of novel structural connections - Inspiration from furniture industry
- 2021
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Ingår i: World Conference on Timber Engineering 2021, WCTE 2021. - Santiago, Chile : World Conference on Timber Engineering (WCTE).
-
Konferensbidrag (refereegranskat)abstract
- The presented project aims to develop prototypes for building connections inspired by the furniture and interior industry and explore them with representatives from the timber construction industry. The long-term vision is that actors from furniture and building industry together develop a smart system for assembly of building elements, which provide higher precision, faster and more efficient assembly than what is available today. The prototype connection developed in this project shows that the idea is ripe for full-scale investigation. Laboratory tests showed promising results due to the high failure loads obtained with very high stiffness.
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| 7. |
- 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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| 8. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Downtime causes in a production cell for laminated veneer products
- 2017
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Ingår i: 23<sup>rd</sup> International Wood Machining Seminar Proceedings. - Warsaw, Poland : The Polish Chamber of Commerce of Furniture Manufacturers. - 9788394804602 ; , s. 28-35
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Konferensbidrag (refereegranskat)abstract
- 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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| 9. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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EXPERIMENTAL AND NUMERICAL ANALYSES OF A CONNECTION FOR CLT STRUCTURES
- 2023
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Ingår i: Proceedings of the 2023 World Conference on Timber Engineering (WCTE). - Oslo, Norway : Curran Associates, Inc.. ; , s. 1154-1159
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Konferensbidrag (refereegranskat)abstract
- Although building systems made of cross-laminated timber (CLT) have become common in Sweden in the past 20 years and they have developed rapidly during the same period, steps remain to be taken to simplify the assembly of such systems, especially at construction sites. Current construction methods, however, remain labour-intensive and thus show room for improvement.This paper describes a novel connection for the assembly of building elements made of CLT. Simple and inexpensive, the connection is fairly insensitive to manufacturing tolerances and enables rapid, more efficient construction than the connections for CLT structures currently used. Test results show the excellent strength and stiffness of the connection, which also allows the replacement of numerous fasteners, including nails and screws, with only a single steel rod.
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| 10. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Formstabilitet i underlägg för dukning
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this study, a coaster intended for table setting has been investigated regarding shape stability in relation to the surrounding climate. The coaster was made up of paper, some of which was printed, and a fibreboard that was bonded together.Symmetry in a construction is desirable for high shape stability, which is known since before. The fact that the surfaces have a similar moisture absorption contributes to the symmetry. Boards that have a harder surface than the opposite should be sanded so that both surfaces of the board have a similar moisture absorption. The orientation of the components in a laminate can reduce or increase the asymmetry if the surfaces have different moisture absorption capacity. Symmetrical construction as well as symmetrical moisture absorption are beneficial for high shape stability.
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| 11. |
- Blomqvist, Lars, 1962-, et al.
(författare)
-
Framtidens resurseffektiva KL-trä – en spaning
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Korslimmat trä (KL-trä) för byggnadsändamål är en produkt som togs fram i Centraleuropa i mitten av 1990-talet. Syftet med förstudien är att i samverkan utforska förslag för hur en framtida resurseffektivare KL-träprodukt kan utformas. Målet är att ta fram underlag för utveckling och genera en samling kring frågan. Det finns en medvetenhet för de omvärldsfaktorer som påverkar byggandet med KL-trä. Det finns en ökad efterfrågan på trä i byggsektorn och det finns ett dynamiskt tänkesätt för att ersätta betong med KL-trä. Ökad användning av skogsråvara, global uppvärmning och minskad tillgång via begränsningar i skogsbruk väcker frågor. Vilken råvara har vi i framtiden, vilka trädslag och hur ser tillgången ut? Det resulterande materialet har analyserats utifrån de olika perspektiven som representeras av intressentgrupperna i värdekedjan för byggande med KL-trä. Rapporten avslutas med projektidéer som framkom under arbetet med förstudien.
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| 12. |
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| 13. |
- 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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| 14. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Influence of different pressing parameters on urea-formaldehyde adhesive-bond strength in laminated veneer products
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the present study was to investigate the relationships between contact pressure, temperature, hardener content and pressing time fixed at different levels and the strength of the UF adhesive bond, in order to develop a model to predicting the bonding strength. Bond strength was measured with the Adhesive Bonding Evaluation System, and a linear model for predicting adhesive bond strength using four independent variables was developed (R2 = 0.75). The strongest parameter was pressing time, followed by hardener content and temperature, all of which explained variation in bond strength at the same level. Pressure had no significant influence on the bond strength.
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| 15. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Influence of pressure on bond-line shear strength in laminated veneer products
- 2022
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Ingår i: Wood Material Science & Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 17:6, s. 1020-
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the bond-line strength of different bonding pressure of veneers in dry (9% moisturecontent) and wet (immersed in water) conditions was investigated. The results show that peeledEuropean beech veneers need approximately 0.5– 1.2 MPa pressure to achieve a proper bond-linewhen a urea-formaldehyde adhesive was used. The pressure variation within this range did notsignificantly affect the strength of the dry veneer, but the strength of the wet veneers decreasedas the bonding pressure increased. The type of failure varied, especially for the wet veneers. Athigh pressure, the wood were stronger than the cohesive strength of the adhesive and thestrength of the adhesion between the adhesive and the wood. High pressure, however, caused acompression of the bond-line and resulted in a lack of adhesion.
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| 16. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Influence of veneer orientation on shape stability of plane laminated veneer products
- 2014
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Ingår i: Wood Material Science & Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 9:4, s. 224-232
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 17. |
- Blomqvist, Lars, 1962-
(författare)
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Laminated Veneer Products : Shape Stability and Effect of Enhanced Formability on Bond-Line Strength
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 18. |
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| 19. |
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| 20. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Moisture-induced distortion of laminated veneer products
- 2013
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Ingår i: Proceedings of the 9<sup>th</sup> meeting of the Northern European network for wood science and engineering (WSE). - Hannover, Germany. ; , s. 178-183
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Konferensbidrag (refereegranskat)abstract
- 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, andconsider the orientation of the veneers and the species.
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| 21. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Resource utilization in a production cell for laminated veneer products
- 2017
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Ingår i: Pro Ligno. - Brasov, Romania : PRO LIGNO Foundation. - 1841-4737 .- 2069-7430. ; 13:4, s. 142-147
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 22. |
- Blomqvist, Lars, 1962-
(författare)
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Shape stability of laminated veneer products : a review – defining and achieving shape stability
- 2015
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Ingår i: International Wood Products Journal. - : Taylor & Francis. - 2042-6445 .- 2042-6453. ; 6:2, s. 89-95
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 23. |
- 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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| 24. |
- Blomqvist, Lars, 1962-
(författare)
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Shape stability of laminated veneer products
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 25. |
- Blomqvist, Lars, 1962-, et al.
(författare)
-
Shape stability of laminated veneer products : an experimental study of the influence on distortion of some material and process parameters
- 2013
-
Ingår i: Wood Material Science & Engineering. - : Taylor & Francis Group. - 1748-0272 .- 1748-0280. ; 8:3, s. 198-211
-
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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| 26. |
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| 27. |
- Blomqvist, Lars, 1962-, et al.
(författare)
-
Spin-off från möbelindustrin till byggbranschen
- 2019
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- There is a deficit of housing in Sweden and it is built too little to compensate for this according to the National Board of Housing, Building and Planning, which, among other things, indicate resource shortages as a reason.The furniture and construction industry have much in common. However, the furniture industry has a larger share of industrial production, which means production at a lower cost. By retrieving production ideas in other industries, there is an opportunity to radically renew and transform the (wood) construction industry and thus streamline the construction process. Historically, cross-sectoral spin-off effects have been shown to generate success factors.The goal of this project is to develop prototypes for building connections inspired by the furniture and interior industry and explore them together with industry actors. This, in turn, serves as an inspiration for a larger project, together with industry actors aiming at developing systems for assembly of building elements, which provide higher precision and are faster to perform than today's system. The pilot developed in this project shows that the idea is ripe for a more full-scale investigation.
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| 28. |
- Blomqvist, Lars, 1962-, et al.
(författare)
-
Stress distribution in veneers under lamination and simultaneously bending : an experimental and numerical investigation
- 2023
-
Ingår i: Wood Material Science & Engineering. - : Taylor & Francis Group. - 1748-0272 .- 1748-0280. ; 18:3, s. 995-1002
-
Tidskriftsartikel (refereegranskat)abstract
- Laminated veneer products (LVPs) are veneers glued together into a predetermined shape. Experimental and numerical investigations were performed under lamination and simultaneously bending of veneer laminate to study the stress distribution in the laminate. Laminates of different thicknesses were made of peeled veneers of European beech. The veneers were coated with adhesive, inserted in a mould which had the shape of a semicircle, and finally pressed at 20 degrees C to a laminate. Two Teflon-polymer films including sensors for measurement of the contact pressure were placed on both sides of the laminate to measure the local contact pressure (contact stress) between the laminate and the mould. At the beginning of the bending process, the contact stresses were locally distributed over the laminate in a similar pattern as in a three-point bending; after the laminate was further bent, the stress distribution rearranged to be as in four-point bending. In the end of the moulding, the local contact stresses increased over the entire laminate and reached a 'peak-value' over bent area in the middle part of the mould. A finite-element model was created to study the bending process. Regarding the overall development of the contact stress variations, the experimental and the numerical results agreed.
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| 29. |
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| 30. |
- Blomqvist, Lars, 1962-, et al.
(författare)
-
Säkerhet och organisation vid CNC-maskiner i träindustrin
- 2002
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Denna rapport är en redovisning av projektet Säkerhet och organisation vid CNC-maskiner i träindustrin. Målsättningen med detta projekt har varit att utveckla, beskriva och sprida kunskap om arbetssätt, arbetsorganisation och kringutrustning vid arbete med träbearbetande CNC-maskiner. Sådant arbete är förknippat med stora risker, vilket bl a beror på maskinernas komplexitet, höga varvtal samt korta bearbetningstider i kombination med manuell hantering av arbetsstycken. Det sistnämnda innebär att en operatör ofta arbetar nära en maskins arbetsområde samtidigt som maskinen är i drift. Innehållet i denna rapport bygger på en inledande litteraturstudie, en inventering av olycksfall och incidenter samt fallstudier vid tre företag och en gymnasieskola.
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| 31. |
- Blomqvist, Lars, 1962-, et al.
(författare)
-
Temporary buildings in reusable lightweight material design
- 2016
-
Ingår i: Proceedings of the 2016 World Conference on Timber Engineering (WCTE). - Vienna : Vienna University of Technology.
-
Konferensbidrag (refereegranskat)abstract
- 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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| 32. |
- Blomqvist, Lars, 1962-, et al.
(författare)
-
The effect of veneer modification on the bond-line strength in laminated veneer products
- 2015
-
Ingår i: Pro Ligno. - Brasov, Romania : Transilvania University. - 1841-4737 .- 2069-7430. ; 11:4, s. 43-49
-
Tidskriftsartikel (refereegranskat)abstract
- A major problem in the manufacture of three-dimensional laminated veneer products (LVP) is damage due to stretching and/or buckling of the veneer. To reduce or eliminate this problem, veneer densification or adding a strengthening layer to the veneer can be an alternative. To study how veneer modification influences the veneer-to-adhesive bond strength, three methods of modification were studied in relation to an unmodified reference veneer: (1) densified veneer, (2) veneer pre-bonded with paper 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 and polyvinyl acetate (PVAc) adhesive, and (c) with a PVAc adhesive. Densification, pre-bonding with paper, and NW with UF/PVAc adhesive mixture resulted in no or only a slight decrease in strength of the bond-line compared to the reference. NW glued with UF or PVAc adhesive showed a considerable reduction in the strength of the bond-line. The climatic cycling had no significant influence on the bond strength.
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| 33. |
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| 34. |
- Blomqvist, Lars, 1962-, et al.
(författare)
-
The influence of veneer modification on adhesive bond strength
- 2014
-
Ingår i: Proceedings of 10th Meeting of the Northern European Network for Wood Science & Engineering (WSE). - Edinburgh : Edinburgh Napier University.. ; , s. 150-155
-
Konferensbidrag (refereegranskat)
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| 35. |
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| 36. |
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| 37. |
- Johansson, Jimmy, et al.
(författare)
-
Influencing factors to enable automation of wood furniture production
- 2016
-
Ingår i: Proceedings of the 12th meeting of the Northern European Networkfor Wood Science and Engineering (WSE). - Riga, Latvia : Latvian State Institute of Wood Chemistry. - 9789934149818 - 9789934149825 ; , s. 208-213
-
Konferensbidrag (refereegranskat)abstract
- 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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| 38. |
- Johansson, Marie, 1973-, et al.
(författare)
-
Prefabricerade ytterväggselement för KL-trästommar
- 2023
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Prefabricated external wall elements for CLT systems This is a first pre-study to how building with cross-laminated timber (CLT) as a frame system in buildings could be made more efficient using prefabricated exterior wall elements as frame completion for CLT buildings. In carrying out this study, CLT building in Sweden as a rule involves an efficient frame erection of the CLT elements, but with a relatively slow phase to assemble the exterior frame completion. External frame completion of CLT buildings is usually carried out on construction scaffolding, where the layers of insulation and surface layer are built up on site. Prefabrication of the outer layers of the CLT frame that is lifted into place has the potential to save a lot of labor time and thus costs. The report presents requirements and practical aspects that must be taken into account in order for prefabricated exterior wall elements to be feasible in terms of requirements and in practice. The purpose of the report has also been to give tips, inspiration and ideas to consider when producing prefabricated exterior wall elements. In the study, an example solution has been developed with the aim of being wood based to as high degree as possible. The result shows that with relatively simple means it is possible to build a prefabricated wall element that meets established requirements. It is desirable that the outer wall elements are hung in place with the minimum possible finishing work on the facade. When it comes to the division of external wall elements, it is practical to follow a similar division and measurements as for the CLT boards to facilitate handling, assembly and lifting. It should be avoided to have sockets (window panes, door holes and the like) that are broken in its interface between the external wall elements to facilitate uniformity in the dimensioning of the elements. The study shows that it is realistic to create prefabricated exterior wall elements for CLT frames.
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| 39. |
- Sandberg, Dick, 1967-, et al.
(författare)
-
Formstabilitet hos formpressade hyllplan.
- 2007
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 40. |
- Sandberg, Dick, 1967-, et al.
(författare)
-
Formändringar hos formpressade fönsterkarmar vid ändrad fuktkvot.
- 2006
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 41. |
- Sandberg, Dick, 1967-, et al.
(författare)
-
Fuktkvotsvariation i fanerbuntar vid ändrad relativ luftfuktighet.
- 2006
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 42. |
- Sandberg, Dick, 1967-, et al.
(författare)
-
Inverkan av fanerens fuktkvot på formstabiliteten hos skiktlimmade skal.
- 2006
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 43. |
- Sandberg, Dick, 1967-, et al.
(författare)
-
Inverkan av fiberorienteringen på formstabiliteten hos skiktlimmade skal.
- 2006
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 44. |
- Sandberg, Dick, 1967-, et al.
(författare)
-
Inverkan av limmets torrhalt på formstabiliteten hos skiktlimmade fanerprodukter.
- 2006
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 45. |
- Sandberg, Dick, 1967-, et al.
(författare)
-
Inverkan av limspridningen på formstabiliteten hos skiktlimmade skal
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 46. |
- Sandberg, Dick, 1967-, et al.
(författare)
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Inverkan av ojämn limspridning på formstabiliteten hos skiktlimmade skal - Förstudie.
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 47. |
- Sandberg, Dick, 1967-, et al.
(författare)
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Klimat i produktionslokaler vid Svensson & Linnér AB.
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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:FanerlagretTorkenPresshallenTemperatur 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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| 48. |
- Sandberg, Dick, 1967-, et al.
(författare)
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Material- och produktionsparametrars betydelse för formstabiliteten hos skiktlimmade fanerprodukter
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Denna rapport redovisar ett antal undersökningar som har genomförts för att belysa några material- och produktionsparametrars betydelse för formstabiliteten hos Skiktlimmade fanerprodukter. Produkterna tillverkas av faner som formas genom sammanlimning under tryck och där faneren kan vara orienterade i olika riktningar i förhållande till varandra för att åstadkomma ökad styrka och förbättrad formstabilitet jämfört t.ex. solitt trä. En vanlig benämning för metoden är också formpressning.Skiktlimmade skal har tillverkats under industriella förhållanden, där ett antal parametrar har varierats för att försöka utröna dessa parametrars inverkan på formstabiliteten. Den enda parameter som skilde försöken från de normala produktionsförhållandena var att samtliga faner konditionerades till avsedd fuktkvot innan försöken genomfördes. Formändringar hos skalen bestämdes i samtliga studier direkt i anslutning till pressningen, efter en viss tids lagring av skalen i produktionslokalen och/eller efter konditionering i klimatrum vid låg respektive hög relativ luftfuktighet.De parametrar som studerades var:träslag, dvs. svarvade faner av rödbok och björk;varianter av ett limsystem baserat på urea-formaldehyd, dvs. olika fukthalter hos limmet, olika typer av härdare (flytande respektive pulver) och tillsats av s.k. filler;inverkan av avvikande fuktkvot hos enskilda faner som skulle pressas till ett skal;inverkan av hur faneren matades genom limspridaren (vid applicering av lim med vals) och ojämn applicering av lim på faneren innan pressningen;inverkan av avvikande fiberorientering hos enskilda faner i ett skal; samtinverkan av att produkten utsattes för varierande relativ luftfuktighet.De slutsatser som kunde dras angående ovanstående uppräknade parametrars inverkan på formstabiliteten var:Bok är ett mer ”rörligt” träslag jämfört med björk och uppvisade överlag sämre formstabilitet än björk.Variationen i egenskaper hos det nu studerade limsystemet hade liten praktisk betydelse för produktens formstabilitet.Variation i fuktkvot mellan de faner som limmades samman till en produkt visade sig kunna få förödande konsekvenser för slutproduktens formstabilitet.Om faner med avvikande fuktkvot (i den genomförda studien var dessa faners fuktkvot 14 %-enheter högre) var osymmetriskt placerade i konstruktionen gav detta upphov till försämrad formstabilitet, dvs. såväl ökad spring-back som ökad skevhet.Något avvikande fuktkvot (3 %-enheter) hos ytfaneren inverkade inte menligt på formstabiliteten.För att uppnå god formstabilitet vid skiktlimning behövde faneren vara väl konditionerade, så att en så liten fuktgradient som möjligt uppkom i den limmade konstruktionen.Storleken på spring-back, men inte skevhet, direkt efter pressningen påverkades av hur faneren matades igenom valsspridaren och av på fanerarket ojämnt applicerad limmängd. Dock hade dessa faktorer inte en avgörande betydelse för produktens formstabilitet.Fiberorienteringen i enskilda faner var avgörande för deformationer och formstabilitet hos de studerade produkterna.Snedfibrighet på endast någon grad kunde under vissa omständigheter medföra deformationer och försämrad formstabilitet i sådan omfattning att slutprodukten blev obrukbar.Snedfibrighet i längsgående faner resulterade i skevhet, medan snedfibrighet i spärrfaner resulterade i kupning hos de nu studerade produkterna (studie 6). Spring-back påverkades i liten utsträckning av snedfibrighet hos faneren.Fanerark med snedfibrighet som limmades så att fiberorienteringen blev i motsatt riktning för faner på vardera sidan om symmetrilinjen (i tjockleksriktningen hos konstruktionen), så kallad korslimning, gav den absolut sämsta förutsättningen för att erhålla en formstabil produkt. Hade däremot faneren snedfibrighet med samma riktning på vardera sidan om symmetrilinjen begränsade detta läggningssätt skevhet som en följd av snedfibrighet.Formen hos produkterna ändrades i takt med omgivningens variationer i temperatur och framförallt i relativ luftfuktighet pga. att träet tar upp och avger fukt. Varierande fuktinnehåll (vilket i praktiken är mycket svårt att förhindra) kan frigöra spänningar som finns inbyggda i produkten, vilket resulterar i formändring. Detta kan ske trots att produkten under produktion bedömdes vara spänningsfri. Storleken på de deformationer som orsakas av variationer i det omgivande klimatet beror på produktens utformning/konstruktion, det aktuella klimatets nivå och varaktighet, samt olika material- och processparametrar, t.ex. de ovan nämnda, som kan inverka på formstabiliteten.Resultaten från de nu genomförda studierna visar tydligt att material- och processparametrar kan ha stor inverkan på skiktlimmade produkters formstabilitet. Fiberorienteringen i enskilda faner och skillnader i fuktinnehåll mellan faner som resulterade i fuktgradienter hos slutprodukten har identifierats som de viktigaste parametrarna som påverkar deformationer och formstabilitet hos de nu studerade produkterna.
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| 49. |
- Sandberg, Dick, 1967-, et al.
(författare)
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Produktivitetsmätning vid skiktlimning- störningsanalys vid CNC-bearbetningen.
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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:Diskutera gemensamt hur stopptiderna kan minskas utifrån vad som framkommit i studien och utifrån allas erfarenheter och upprätta en åtgärdslista.Sätt operativa mål för vilken produktivitetsnivå man vill sträva mot.Ta till vara på erfarenhet från tidigare perioder då det fanns en rutin för hur man organiserade arbetet inför ett ställ.Genomför SMED-analys vid något vanligt förekommande ställ för att fördela inre ställtid till yttre ställtid och genomför insatser för att reducera ställtiderna.Utarbeta rutiner för hur arbetet vid CNC-bearbetning ska organiseras.
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| 50. |
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