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Blomqvist, L., Berg, S. & Sandberg, D. (2019). Distortion in laminated veneer products exposed to relative-humidity variations: experimental studies and finite-element modelling. BioResources, 14(2), 3768-3779
Open this publication in new window or tab >>Distortion in laminated veneer products exposed to relative-humidity variations: experimental studies and finite-element modelling
2019 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, no 2, p. 3768-3779Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Raleigh, NC: North Carolina State University, 2019
Keywords
Birch, Cup, FEM, Veneer, Wood, Twist
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-81623 (URN)000466449000091 ()
Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2019-05-28Bibliographically approved
Blomqvist, L., Nilson, H., Johansson, J. & Landscheidt, S. (2017). Downtime causes in a production cell for laminated veneer products. In: Marcin Zbiec and Kazimierz Orlowski (Ed.), 23rd International Wood Machining Seminar Proceedings: . Paper presented at 23rd International Wood Machining Seminar, 28-31 May, 2017, Warsaw, Poland (pp. 28-35). Warsaw, Poland: The Polish Chamber of Commerce of Furniture Manufacturers
Open this publication in new window or tab >>Downtime causes in a production cell for laminated veneer products
2017 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
Warsaw, Poland: The Polish Chamber of Commerce of Furniture Manufacturers, 2017
Keywords
adhesive, air, CNC, dust, robot, vacuum
National Category
Wood Science Production Engineering, Human Work Science and Ergonomics
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-64451 (URN)9788394804602 (ISBN)
Conference
23rd International Wood Machining Seminar, 28-31 May, 2017, Warsaw, Poland
Projects
Flexible automation in manufacturing of laminated veneer products
Funder
Knowledge Foundation, 20150229
Available from: 2017-05-29 Created: 2017-05-29 Last updated: 2019-05-20Bibliographically approved
Blomqvist, L., Johansson, J., Landscheidt, S. & Nilson, H. (2017). Resource utilization in a production cell for laminated veneer products. Paper presented at The International Conference Wood Science and Engineering in the Third Millennium (ICWSE 2017), Brasov, Romania, Nov. 2-4. Pro Ligno, 13(4), 142-147
Open this publication in new window or tab >>Resource utilization in a production cell for laminated veneer products
2017 (English)In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 13, no 4, p. 142-147Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Brasov, Romania: PRO LIGNO Foundation, 2017
Keywords
CNC, robot, stiffness, vibration
National Category
Wood Science Production Engineering, Human Work Science and Ergonomics
Research subject
Technology (byts ev till Engineering); Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-69645 (URN)
Conference
The International Conference Wood Science and Engineering in the Third Millennium (ICWSE 2017), Brasov, Romania, Nov. 2-4
Projects
Flexible automation in manufacturing of laminated veneer productsProWOOD
Funder
Knowledge Foundation, 20150229
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2019-09-06Bibliographically approved
Johansson, J., Blomqvist, L., Nilson, H. & Landscheidt, S. (2016). Influencing factors to enable automation of wood furniture production. In: Bruno Andersons and Arnis Kokorevics (Ed.), 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. Paper presented at 12th Annual Meeting of the Northern European Network for Wood Science and Engineering WSE, 12-13 September, 2016, Riga (pp. 208-213). Riga, Latvia: Latvian State Institute of Wood Chemistry
Open this publication in new window or tab >>Influencing factors to enable automation of wood furniture production
2016 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
Riga, Latvia: Latvian State Institute of Wood Chemistry, 2016
Keywords
industrial robot, laminated veneer products, production development, process development
National Category
Wood Science Robotics
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-56536 (URN)978-9934-14-981-8 (ISBN)978-9934-14-982-5 (ISBN)
Conference
12th Annual Meeting of the Northern European Network for Wood Science and Engineering WSE, 12-13 September, 2016, Riga
Projects
Flexible automation in manufacturing of laminated veneer products
Funder
Knowledge Foundation
Available from: 2016-09-15 Created: 2016-09-15 Last updated: 2019-05-20Bibliographically approved
Blomqvist, L. (2016). Laminated Veneer Products: Shape Stability and Effect of Enhanced Formability on Bond-Line Strength. (Doctoral dissertation). Växjö: Linnaeus University Press
Open this publication in new window or tab >>Laminated Veneer Products: Shape Stability and Effect of Enhanced Formability on Bond-Line Strength
2016 (English)Doctoral 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. 

Abstract [sv]

Denna avhandling berör två områden inom tillverkning av plan- och formpressade fanerprodukter. Det första avser formstabiliteten hos dessa och om det är möjligt att förbättra densamma. Det andra har sin utgångspunkt i modifiering av faner för ökad formbarhet och huruvida dessa modifieringar påverkar limfogens styrka.

Plan och formpressade fanerprodukter består av faner som sammanfogats med lim till en förutbestämd form. Metoden används främst för tillverkning av möbler och inredningar. Avvikelse från avsedd form hos produkterna är ett stort problem för både tillverkare och kunder. Orsakerna till avvikelser i form kan relateras till både materialet och processen men också till hur produkten används. Studier har genomförts för att utvärdera inverkan av olika material- och processparametrar på formstabiliteten hos några utvalda produkter. De undersökta parametrarna var träslag (rödbok och björk), limsystem (baserade på urea- formaldehyd), limspridning, klimat, jämviktsfuktkvot, fiberorintering hos faner samt orienteringen av faner i den specifika produkten.

För att kunden till skiktlimmade produkter ska erhålla en formstabil vara krävs att tillverkarna tar hänsyn till grundläggande fakta om trä. Detta material avger och tar upp fukt i förhållande till omgivande klimat, vilket innebär att trä krymper och sväller. Detta sker dessutom med varierande magnitud i olika riktningar av träet. Denna variation är även träslagsspecifik. Att ha en förståelse för detta beteende är grunden för tillverkning av formstabila träprodukter.

Symmetri definieras i denna avhandling med att faneregenskaperna är balanserade i laminatet. Detta innebär att det motsatta faneret på vardera sidan av det mittersta faneret i laminatet har liknande egenskaper. Om faneren sammanläggs och pressas på ett asymmetriskt sätt blir produkterna skeva eller kupade. Avvikelsen från önskad form kan vara liten direkt efter pressningen men kan öka avsevärt i samband med fuktkvotsvariationer. Asymmetri kan uppstå genom att faner med avvikande fiberorientering ingår i sammanläggningen eller att faneren läggs asymmetriskt. Det kan även uppstå om faner med olika jämviktsfuktkvot sammanlimmas på ett icke symmetriskt sätt. En försvårande faktor är att även de sprickor som uppstår när faneren tillverkas genom svarvning eller knivskärning inverkar på formstabiliteten. I en korsvis limmad tre-lagers plywood ska fanerens sida med sprickor vara orienterad åt samma håll för hög formstabilitet.

För att uppnå formstabila produkter bör faneren vara konditionerade till en enhetlig jämviktsfuktkvot och vara rätfibriga, dvs. att fiberriktningen sammanfaller parallellt med ytornas kanter. Som nämnts tidigare bör även fanerets sida med sprickor beaktas. Slutanvändarens, det vill säga kundens, klimat bör styra fanerens måljämviktsfuktkvot som tillsammans med tillförd fukt från limmet påverkar produktens jämviktsfuktkvot i tillverkningsprocessen. Dessutom ska läggningen vara symmetrisk.

Vid formpressning kan faneren utsättas för sådana sträckningar, dvs. töjningar, att bristningar uppkommer. Därför finns det olika sätt att förstärka faneren främst i transversell riktning där faneren är som svagast. Detta kan ske genom olika bearbetningar och/eller pålimningar. Dessa förbehandlingar av faner för förbättrad formbarhet kan dock hindra limmet från att tränga in i träytan vilket tester visat. Därför är det viktigt att kontrollera att förbehandlingen inte påverkar limfogens styrka. 

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2016. p. 120
Series
Linnaeus University Dissertations ; 247/2016
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-52014 (URN)978-91-88357-13-7 (ISBN)
Public defence
2016-05-02, Weber, Hus K, Växjö, 13:00 (English)
Opponent
Supervisors
Available from: 2016-04-11 Created: 2016-04-09 Last updated: 2019-05-20Bibliographically approved
Blomqvist, L., Pfriem, A. & Johansson, J. (2016). Temporary buildings in reusable lightweight material design. In: Proceedings of the 2016 World Conference on Timber Engineering (WCTE): . Paper presented at WCTE 2016, World Conference on Timber Engineering, August 22-25, 2016, Vienna, Austria. Vienna: Vienna University of Technology
Open this publication in new window or tab >>Temporary buildings in reusable lightweight material design
2016 (English)In: Proceedings of the 2016 World Conference on Timber Engineering (WCTE), Vienna: Vienna University of Technology , 2016Conference paper, Published 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.

Place, publisher, year, edition, pages
Vienna: Vienna University of Technology, 2016
Keywords
Lightweight materials, Temporary housing, Automated production, Pre-manufacture, Connection, Form stability, Wood modification, Wood veneer
National Category
Wood Science Building Technologies
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-55847 (URN)2-s2.0-85010971969 (Scopus ID)
Conference
WCTE 2016, World Conference on Timber Engineering, August 22-25, 2016, Vienna, Austria
Available from: 2016-08-30 Created: 2016-08-30 Last updated: 2019-08-12Bibliographically approved
Blomqvist, L., Berg, S. & Sandberg, D. (2015). Chipless Machining: Challenges in Manufacture of Laminated Veneer Products. In: Roger Hernández and Claudia B. Cáceres (Ed.), Proceedings of the 22nd International Wood Machining Seminar, IWMS 22: Volume 1 - Oral Presentations. Paper presented at 22nd International Wood Machining Seminar, June 14-17, 2015 Quebec City, Canada (pp. 155-164). Quebec City, Canada: Université Laval
Open this publication in new window or tab >>Chipless Machining: Challenges in Manufacture of Laminated Veneer Products
2015 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
Quebec City, Canada: Université Laval, 2015
Keywords
finite element modelling, shape stability
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-44800 (URN)978-0-9947964-0-0 (ISBN)
Conference
22nd International Wood Machining Seminar, June 14-17, 2015 Quebec City, Canada
Available from: 2015-06-18 Created: 2015-06-18 Last updated: 2019-02-27Bibliographically approved
Blomqvist, L. (2015). Shape stability of laminated veneer products: a review – defining and achieving shape stability. International Wood Products Journal, 6(2), 89-95
Open this publication in new window or tab >>Shape stability of laminated veneer products: a review – defining and achieving shape stability
2015 (English)In: International Wood Products Journal, ISSN 2042-6445, E-ISSN 2042-6453, Vol. 6, no 2, p. 89-95Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Taylor & Francis, 2015
Keywords
Fibre angle, Moisture content, Relative humidity, Symmetry, Wood
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-43592 (URN)10.1179/2042645315Y.0000000004 (DOI)000218999800009 ()2-s2.0-84940938537 (Scopus ID)
Available from: 2015-06-03 Created: 2015-06-03 Last updated: 2018-04-18Bibliographically approved
Blomqvist, L., Sterley, M., Sandberg, D. & Johansson, J. (2015). The effect of veneer modification on the bond-line strength in laminated veneer products. Paper presented at The International Conference Wood Science and Engineering in the Third Millennium (ICWSE 2015), Brasov, Romania, Nov. 5-7. Pro Ligno, 11(4), 43-49
Open this publication in new window or tab >>The effect of veneer modification on the bond-line strength in laminated veneer products
2015 (English)In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 11, no 4, p. 43-49Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Brasov, Romania: Transilvania University, 2015
Keywords
densification; HMA; pre-bonding, PVAc; strengthening; THM processing; UF; wood
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-47309 (URN)
Conference
The International Conference Wood Science and Engineering in the Third Millennium (ICWSE 2015), Brasov, Romania, Nov. 5-7
Available from: 2015-11-16 Created: 2015-11-16 Last updated: 2019-05-20Bibliographically approved
Blomqvist, L., Sandberg, D. & Johansson, J. (2014). Influence of veneer orientation on shape stability of plane laminated veneer products. Wood Material Science & Engineering, 9(4), 224-232
Open this publication in new window or tab >>Influence of veneer orientation on shape stability of plane laminated veneer products
2014 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 9, no 4, p. 224-232Article in journal (Refereed) Published
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.

Keywords
adhesive, distortion, lamination, plywood, thermo-hydro-mechanical processing, THM, wood
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-34541 (URN)10.1080/17480272.2014.919022 (DOI)2-s2.0-84911408156 (Scopus ID)
Available from: 2014-06-02 Created: 2014-06-02 Last updated: 2019-05-20Bibliographically approved
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