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Improvement of shape stability by high-temperature treatment of Norway spruce Effects of drying at 120 °C with and without restraint on twist

Verbesserung der Formstabilität von Fichte (Picea abies) durch Hitzebehandlung Effekt des Trocknens bei 120 °C mit und ohne Belastung auf die Verdrehung

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Abstract

During drying, timber changes its shape mainly due to shrinkage anisotropy, radial differences in longitudinal shrinkage and spiral grain. The warp, causing severe downgrading of the timber, can be reduced by restraint and appropriate climate treatments of different types. The research presented here is part of a larger project on the improvement of shape stability of Norway Spruce (Picea abies) by high-temperature treatment. In this part, a method for determining twist as well as results for a drying temperature of 120 °C are presented. The effects of presteaming, drying and steaming with and without restraint on the size of twist in Norway Spruce were investigated in laboratory scale. Short-term twist-reducing effects as well as the permanency of the reduced distortions in subsequent moisture cycling were investigated. Results show a clear dependency of twist on the distance from the pith. Furthermore, the twist is reduced in restrained specimens sawn close to the pith. This effect is permanent even after exposure to subsequent moisture cycling.

Zusammenfassung

Während der Holztrocknung treten Formänderungen des Holzes hauptsächlich aufgrund der anisotropen Schwindung, der radial unterschiedlichen longitudinalen Schwindung und des Drehwuchses auf. Die zu grosser Deklassierung führenden Verformungen können durch Belastung während der Trocknung und geeignete Trocknungsprogramme vermindert werden. Die hier vorgestellte Forschungsarbeit ist Teil eines grösseren Projektes über die Verbesserung der Formbeständigkeit von Fichte (Picea abies) mit Hilfe von Hochtemperaturtrocknung. Es werden Methoden zur Bestimmung der Verdrehung und Ergebnisse für eine Trocknungstemperatur von 120 °C diskutiert. Die Wirkung von Dämpfen, Trocknung und Konditionierung mit und ohne äusserer Belastung auf die Verdrehung wurde an Fichte im Labormassstab untersucht. Sowohl die kurzfristige Verringerung der Verdrehung als auch die Beständigkeit dieser Verbesserung während Feuchtewechsel wurden untersucht. Die Ergebnisse zeigen eine deutliche Abhängigkeit der Verdrehung vom Abstand von der Markröhre. Die Verdrehung konnte in marknahen, eingespannten Proben verringert werden. Dieser Effekt bleibt auch nach mehreren Feuchtewechseln bestehen.

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Authors and Affiliations

  1. Division of Structural Engineering, Lund Institute of Technology, Lund University, 118, 22100, Lund, Sweden

    E. Frühwald

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  1. E. Frühwald
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Frühwald, E. Improvement of shape stability by high-temperature treatment of Norway spruce Effects of drying at 120 °C with and without restraint on twist. Holz Roh Werkst 64, 24–29 (2006). https://doi.org/10.1007/s00107-005-0039-y

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  • DOI: https://doi.org/10.1007/s00107-005-0039-y

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