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Neyses, B., Scharf, A. & Sandberg, D. (2023). Continuous densification of wood with a belt press: how knot features impact the densification outcome. Wood Material Science & Engineering, 18(4), 1587-1596
Open this publication in new window or tab >>Continuous densification of wood with a belt press: how knot features impact the densification outcome
2023 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 18, no 4, p. 1587-1596Article in journal (Refereed) Published
Abstract [en]

Densification, i.e. the transverse compression of sawn timber has been studied and commercialised for well over 100 years but remains an expensive niche product with low annual production volumes. One reason for this is the reliance on time-consuming batch processes in a hot press. To solve this, a continuous densification process using a belt press, capable of densifying full-sized sideboards was developed. However, there is insufficient knowledge about the effect of knots on the densification outcome. The objective of this study was to assess how different knot parameters affect the densified wood in terms of damage and deformation to the knot itself and the surrounding wood material. Multivariate data analysis methods were applied to a dataset of 171 knots, described by 23 variables. The data showed that it is possible to densify knots in a continuous process without causing damage. Especially sound knots are often unproblematic, even at relatively large sizes, while densifying dead knots often resulted in unacceptable damage to the knot or the surrounding wood. From a material selection standpoint, any knots bleeding into the board edge and dead knots greater than 20 mm in diameter should be avoided altogether.

Place, publisher, year, edition, pages
Taylor and Francis Ltd., 2023
Keywords
Compression of wood, full-size samples, surface densification, wood defects, wood industry
National Category
Wood Science Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-99295 (URN)10.1080/17480272.2023.2228278 (DOI)001012945900001 ()2-s2.0-85163005843 (Scopus ID)
Funder
The Kempe FoundationsLuleå University of Technology
Note

Validerad;2023;Nivå 2;2023-11-08 (joosat);

Full text license: CC BY-NC-ND

Available from: 2023-08-08 Created: 2023-08-08 Last updated: 2023-11-08Bibliographically approved
Scharf, A., Neyses, B. & Sandberg, D. (2023). Continuous densification of wood with a belt press: the process and properties of the surface-densified wood. Wood Material Science & Engineering, 18(4), 1573-1586
Open this publication in new window or tab >>Continuous densification of wood with a belt press: the process and properties of the surface-densified wood
2023 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 18, no 4, p. 1573-1586Article in journal (Refereed) Published
Abstract [en]

Thermo-mechanical densification of sawn timber results in improved mechanical properties, but densified wood remains a fairly expensive niche product, partially because of high-cost batch processing. Densification in a continuous process could address this problem and was shown to be possible in previous research. The outcomes were limited to proofs-of-concept, partially due to insufficient cooling capabilities of the used densification equipment, resulting in high spring-back. Therefore, a novel continuous process using a belt press to densify full-sized sawn timber has been conceived. The press ensures almost constant contact between the wood and the heating and cooling elements. The study aimed to analyse how the processing temperature, speed and compression ratio affected the density profile, spring-back, set-recovery, Brinell hardness, and bending properties. Results showed a density increase concentrated close beneath the surface in contact with the heating element and approx. 20% spring-back. Belt speeds above 2 m min−1 caused higher spring-back due to the reduced contact time between the wood and the heating element. Brinell hardness increased by up to 250% at a compression ratio of 27% while bending properties were unaffected. Belt temperature and speed were shown to be critical factors to consider for the future optimisation of the belt-press process.

Place, publisher, year, edition, pages
Taylor & Francis, 2023
Keywords
Compression of wood, set-recovery, mechanical properties, density profile
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-97745 (URN)10.1080/17480272.2023.2216660 (DOI)2-s2.0-85161407224 (Scopus ID)
Funder
Luleå University of Technology, CT WOOD Centre of ExcellenceThe Kempe Foundations
Note

Validerad;2023;Nivå 2;2023-11-08 (joosat);

Full text license: CC BY-NC-ND 4.0

Available from: 2023-05-31 Created: 2023-05-31 Last updated: 2023-11-08Bibliographically approved
Scharf, A., Lemoine, A., Neyses, B. & Sandberg, D. (2023). The effect of the growth ring orientation on spring-back and set-recovery in surface-densified wood. Holzforschung, 77(6), 394-406
Open this publication in new window or tab >>The effect of the growth ring orientation on spring-back and set-recovery in surface-densified wood
2023 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 77, no 6, p. 394-406Article in journal (Refereed) Published
Abstract [en]

Wood under thermo-mechanical densification behaves differently depending on the cross-sectional growth ring orientation (GRO) relative to the direction of compression. This influences the degree of cell damage, but also the shape-memory effects occurring when the compression load is released (spring-back) and when the timber is re-moistened (set-recovery). To study how the GRO influences the shape-memory effects, Scots pine specimens were separated into three distinct groups of GRO (Flat, Inclined, Hybrid) and then thermo-mechanically surface-densified. Spring-back and set-recovery were determined by thickness measurements and by digital image correlation. A GRO parallel to the densified surface, resulted in a low spring-back and a high set-recovery which were uniform over the width of the specimen. Specimens with a GRO between 15 and 45° to the densified surface showed high spring-back and low set-recovery, indicating cell-wall damage. Spring-back mainly occurred in the non-plasticised region immediately below the heated surface region and elasto-plastic rolling-shear deformation along individual growth rings occurred. The GRO of softwood subjected to thermo-mechanical densification determines if an applied load results in rolling shear-deformation or radial compression. This in turn determines where in the cross-section and when in the process the cells deform and if this deformation occurs below or above the glass-transition temperature.

Place, publisher, year, edition, pages
Walter de Gruyter, 2023
Keywords
densification, digital image correlation, rolling shear, shape-memory, wood compression
National Category
Wood Science Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-96487 (URN)10.1515/hf-2023-0004 (DOI)000967647600001 ()2-s2.0-85153381478 (Scopus ID)
Funder
Luleå University of Technology, CT WOOD
Note

Validerad;2023;Nivå 2;2023-06-29 (sofila);

Available from: 2023-04-14 Created: 2023-04-14 Last updated: 2023-06-29Bibliographically approved
Scharf, A., Neyses, B. & Sandberg, D. (2022). Accelerating wood densification – Are we going too fast?. In: Brischke, C. & Buschalsky, A. (Ed.), Proceedings of the 18th Annual Meeting of the Northern European Network for Wood Science and Engineering (WSE): . Paper presented at 18th Annual Meeting of the Northern European Network for Wood Science and Engineering (WSE 2022), September 21-22, 2022, Goettingen, Germany (pp. 44-46). Goettingen: Georg-August-University of Goettingen
Open this publication in new window or tab >>Accelerating wood densification – Are we going too fast?
2022 (English)In: Proceedings of the 18th Annual Meeting of the Northern European Network for Wood Science and Engineering (WSE) / [ed] Brischke, C. & Buschalsky, A., Goettingen: Georg-August-University of Goettingen , 2022, p. 44-46Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Goettingen: Georg-August-University of Goettingen, 2022
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-93281 (URN)
Conference
18th Annual Meeting of the Northern European Network for Wood Science and Engineering (WSE 2022), September 21-22, 2022, Goettingen, Germany
Available from: 2022-09-27 Created: 2022-09-27 Last updated: 2022-09-30Bibliographically approved
Neyses, B., Scharf, A. & Sandberg, D. (2022). Continuous densification of solid wood – The belt press approach. In: Candelier, K., Collet, K., Dumarçay, S. et al. (Ed.), Proceedings of the 10th European Conference on Wood Modification: . Paper presented at 10th European Conference on Wood Modification (ECWM10), Nancy, France, April 25-26, 2022 (pp. 76-79). Nancy: University of Lorraine, Faculty of Science and Technology, Laboratory of Study and Research on the Wood Material (LERMaB)
Open this publication in new window or tab >>Continuous densification of solid wood – The belt press approach
2022 (English)In: Proceedings of the 10th European Conference on Wood Modification / [ed] Candelier, K., Collet, K., Dumarçay, S. et al., Nancy: University of Lorraine, Faculty of Science and Technology, Laboratory of Study and Research on the Wood Material (LERMaB) , 2022, p. 76-79Conference paper, Published paper (Refereed)
Abstract [en]

The densification, i.e., transverse compression of solid wood can lead to improvements in the mechanical properties, and this can expand the areas of application for low-density wood species. For the past one hundred years, many efforts have been made to mass-produce densified wood products, but despite being available on the market, they remain niche products with low annual production volumes. One of the main reasons for this is that all available densified wood products are produced in a batch-type process, which limits the achievable process speed and integration into the continuous wood processing chain. For this reason, we propose a continuous surface densification process using a bespoke belt press – similar in principle to those used to produce MDF panels. The belt-press is capable of densifying full-sized wood boards at processing speeds of up to 60 m min-1. The primary belt for densification can be heated to temperatures above 160°C, while a subsequent belt functions as a cooling stage. During the densification process, the belt press can log the pressing forces, moments, and temperature. Preliminary tests with Scots pine specimens of 120 mm in width and 38 mm in thickness resulted in a twofold increase in peak density, after a pressing time of two minutes at 120°C. The resulting density profiles were similar to those obtained in studies using a static hot press. As the belt press can be fed with a continuous stream of boards, it has a higher net throughput than a static hot press. Further studies continue with the aim to evaluate different aspects relevant to the large-scale industrial production of densified wood products.

Place, publisher, year, edition, pages
Nancy: University of Lorraine, Faculty of Science and Technology, Laboratory of Study and Research on the Wood Material (LERMaB), 2022
Keywords
belt press, densification process, wood compression, process development, thermo-mechanical processing
National Category
Agricultural Science, Forestry and Fisheries Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-90640 (URN)
Conference
10th European Conference on Wood Modification (ECWM10), Nancy, France, April 25-26, 2022
Funder
The Kempe Foundations
Note

Funder: Luleå University of Technology, CT Wood

Available from: 2022-05-14 Created: 2022-05-14 Last updated: 2022-09-30Bibliographically approved
Scharf, A., Neyses, B. & Sandberg, D. (2022). Hardness of surface-densified wood. Part 1: material or product property?. Holzforschung, 76(6), 503-514
Open this publication in new window or tab >>Hardness of surface-densified wood. Part 1: material or product property?
2022 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 76, no 6, p. 503-514Article in journal (Refereed) Published
Abstract [en]

The established methods for testing the hardness of wood are of questionable value for assessing the performance of surface-densified wood, since the density profile beneath the densified surface is an important property that needs to be considered. The purpose of this study was to evaluate the influence of the density profile of surface-densified wood and the hardness test parameters, such as indenter geometry and applied load on the measured hardness. The influence of the density profile varied considerably depending on the hardness test parameters. This can make a comparison of hardness values of surface-densified wood prone to misinterpretation. The selection of hardness test parameters should either be product-specific, or the density profile itself should be used to evaluate the hardness of surface-densified wood. A strong influence of the density profile on the indentation depth development during the hardness tests indicates the possibility of predicting the density profile based on the hardness test methods.

Place, publisher, year, edition, pages
Walter de Gruyter, 2022
Keywords
Brinell hardness, density profiles, ionic liquids, Janka hardness, wood compression
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-89776 (URN)10.1515/hf-2021-0151 (DOI)000765921500001 ()2-s2.0-85126561094 (Scopus ID)
Funder
Luleå University of Technology, CT Wood
Note

Validerad;2022;Nivå 2;2022-06-29 (sofila)

Available from: 2022-03-22 Created: 2022-03-22 Last updated: 2022-09-30Bibliographically approved
Scharf, A., Neyses, B. & Sandberg, D. (2022). Hardness of surface-densified wood. Part 2: prediction of the density profile by hardness measurements. Holzforschung, 76(6), 515-524
Open this publication in new window or tab >>Hardness of surface-densified wood. Part 2: prediction of the density profile by hardness measurements
2022 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 76, no 6, p. 515-524Article in journal (Refereed) Published
Abstract [en]

The density profile of surface-densified wood has a major influence on the indentation resistance of the material. A method that can predict the density profile in surface-densified wood from measurements of the indentation in a hardness test was established. The combined information of hardness and density profile is expected to better assess the performance of surface-densified wood. Density profile and hardness test data for surface-densified Scots pine have been subjected to a partial least squares analysis to determine the relationship between the indentation depth measured during a hardness test and the density profile measured by X-ray densitometry. Among seven different hardness tests, which varied in test force and indenter geometry, the Brinell method according to the EN 1534 standard showed the highest correlation between the indentation-versus-time curve and the density profile. The mean absolute error for the prediction of density profiles in an external test set was 5–10%, indicating that the method proposed in this study can be used to replace X-ray densitometry in process control and process design.

Place, publisher, year, edition, pages
Walter de Gruyter, 2022
Keywords
densification, partial least squares regression, wood compression
National Category
Wood Science Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-89846 (URN)10.1515/hf-2021-0232 (DOI)000766098800001 ()2-s2.0-85126548618 (Scopus ID)
Funder
Luleå University of Technology, CT WOOD
Note

Validerad;2022;Nivå 2;2022-06-29 (sofila)

Available from: 2022-03-25 Created: 2022-03-25 Last updated: 2022-09-30Bibliographically approved
Neyses, B. & Scharf, A. (2022). Using machine learning to predict the density profiles of surface-densified wood based on cross-sectional images. European Journal of Wood and Wood Products, 80(5), 1121-1133
Open this publication in new window or tab >>Using machine learning to predict the density profiles of surface-densified wood based on cross-sectional images
2022 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 80, no 5, p. 1121-1133Article in journal (Refereed) Published
Abstract [en]

Over the past decades, the surface densification of solid wood has received increased attention. However, the inhomogeneous density distribution in the densification direction might be a challenge with regard to process control within a large-scale production process, as the density profile governs many relevant properties of surface-densified wood. Currently, the measurement of density profiles relies on sensitive X-ray equipment and is difficult to integrate into an on-line process. Hence, in this study, three machine learning approaches were applied to predict the density profiles of surface-densified Scots pine specimens, only based on visual image acquisition—a technology that is ubiquitous in the wood industry: partial least squares (PLS) regression, artificial neural networks (ANN), and convolutional neural networks (CNN). The machine learning models were trained on images of the specimen cross-sections as input data, and X-ray density profiles as output data. There were 1850 observations, and the model performance was evaluated on external test sets. The models had mean absolute percentage errors of the predicted values between 9 and 18%; the CNN achieving the smallest error (9.24%). A deeper analysis of the data revealed that the ANN approach performed inconsistently between observations. PLS regression predicted the main density peak to a high accuracy but could not model other features. Only the CNN could reliably model the main density peak, wide growth rings, and the important region between the specimen surface and the main density peak. The ability of the models to generalise to untypical new data was improved by augmentation of the training data.

Place, publisher, year, edition, pages
Springer Nature, 2022
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-91623 (URN)10.1007/s00107-022-01826-2 (DOI)000805899400002 ()2-s2.0-85131522286 (Scopus ID)
Note

Validerad;2022;Nivå 2;2022-09-29 (hanlid)

Available from: 2022-06-20 Created: 2022-06-20 Last updated: 2022-10-07Bibliographically approved
Scharf, A., Sandberg, D. & Neyses, B. (2021). Continuous Densification of Solid Wood – the Belt-press Approach. In: Ginta Laureckienė (Ed.), Proceedings of the 17th Annual Meeting of the Northern European Network for Wood Science and Engineering - WSE 2021: . Paper presented at The 17th Annual Meeting of the Northern European Network for Wood Science and Engineering (WSE 2021), Kaunas, Lithuania, October 14-15, 2021 (pp. 29-31). Kaunas: Kaunas University of Technology
Open this publication in new window or tab >>Continuous Densification of Solid Wood – the Belt-press Approach
2021 (English)In: Proceedings of the 17th Annual Meeting of the Northern European Network for Wood Science and Engineering - WSE 2021 / [ed] Ginta Laureckienė, Kaunas: Kaunas University of Technology , 2021, p. 29-31Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Kaunas: Kaunas University of Technology, 2021
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-87923 (URN)
Conference
The 17th Annual Meeting of the Northern European Network for Wood Science and Engineering (WSE 2021), Kaunas, Lithuania, October 14-15, 2021
Note

ISBN för värdpublikation: 978-609-02-1762-7

Available from: 2021-11-17 Created: 2021-11-17 Last updated: 2022-09-30Bibliographically approved
Scharf, A., Neyses, B. & Sandberg, D. (2021). Cupping distortion of surface-densified wood intended for flooring. In: Marketta Sipi; Juha Rikala (Ed.), Proceedings of the 16th Annual Meeting ofthe Northern European Network for Wood Science and Engineering–WSE2020: . Paper presented at 16th Annual Meeting ofthe Northern European Network for Wood Science and Engineering (WSE2020), Helsinki, Finland (online), December 1-2, 2020 (pp. 50-52). Helsinki, Finland: University of Helsinki
Open this publication in new window or tab >>Cupping distortion of surface-densified wood intended for flooring
2021 (English)In: Proceedings of the 16th Annual Meeting ofthe Northern European Network for Wood Science and Engineering–WSE2020 / [ed] Marketta Sipi; Juha Rikala, Helsinki, Finland: University of Helsinki , 2021, p. 50-52Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Helsinki, Finland: University of Helsinki, 2021
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-83379 (URN)
Conference
16th Annual Meeting ofthe Northern European Network for Wood Science and Engineering (WSE2020), Helsinki, Finland (online), December 1-2, 2020
Note

ISBN för värdpublikation: 978-952-94-4383-3

Available from: 2021-03-23 Created: 2021-03-23 Last updated: 2022-09-30Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-1489-0839

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