English Oak - thermomechanically densified and thermally modified timber
Densification and thermal modification change wood properties in different ways depending on the treatment conditions and the wood species. In the presented investigations, densification and thermal modification were applied consecutively. The primary objective of this treatment combination was the compensation of reduced mechanical properties due to the thermal modification by densification. The combined processes were applied to five European wood species: poplar (Populus nigra L.), beech (Fagus sylvatica L.), Norway spruce (Picea abies Karst.), English oak (Quercus robur L.) and European ash (Fraxinus excelsior L.). Depending on the mean density of the species, a thermo-mechanical densification of 43 or 50% was imposed to improve mechanical strength parallel to the grain. Subsequently, the densified material was thermally modified in the so-called Vacu3-process at 230 °C and 20 or 80% vacuum and at 240 °C and 20% vacuum. The thermal modification resulted in changing wood colour, mechanical strength, hardness, dimensional stability and durability. All the wood modification processes were carried out at industrial scale after pre-tests at laboratory scale. The modified material was characterized regarding flexural properties, static and dynamic hardness, structural integrity, abrasion resistance, moisture dynamics, dimensional stability, and durability against white, brown and soft rot fungi. In summary, the test results showed that the consecutive application of thermo-mechanical densification and thermal modification leads to significantly improved durability whilst mechanical properties at least for beech, ash and poplar remained and the material is dimensionally stable.
- Shaker method: described by Brischke et al. (2005); Specimens of 35 (ax.) by 8.5 by 8.5 mm³ were placed in polyethylene flasks (V = 500 ml) together with 400 g of steel balls (diameter 6 mm) and moved in an overhead shaker at 28 revolutions min− 1 for 72 h
- Density distribution: was determined based on X-ray measurements (Grecon DAX 6000), Specimen size 50 by 50 by approx. 20 mm³ (longitudinal by width by thickness)
- Brinell hardness test: transverse to the grain, ball indenter with a diameter D = 10 mm, Fmax = 1000 N
- The samples were manufactured and conditioned at 20 °C/65% RH prior to the various tests. Reference not densified and not thermally treated.
Physikalische Eigenschaften
| Name | Wert | Genauigkeit | Bemerkung | Messverfahren und -bedingungen |
|---|---|---|---|---|
| Dichte | 622 kg/m³ | σ = 89.5 kg/m³ | Reference | X-ray measurements |
| 1202.4 kg/m³ | σ = 133.6 kg/m³ | Only densified | X-ray measurements | |
| 674.9 kg/m³ | σ = 98.6 kg/m³ | Densified, 230 °C/20% | X-ray measurements | |
| 735.8 kg/m³ | σ = 65.3 kg/m³ | Densified, 230 °C/80% | X-ray measurements | |
| 672.9 kg/m³ | σ = 74.7 kg/m³ | Densified, 240 °C/20% | X-ray measurements | |
| Mechanische Eigenschaften | ||||
| Abrieb | 18.2 % | σ = 6.7 % | Reference | Shaker method |
| 50 % | σ = 23.4 % | Densified, 230 °C/20%, 43% DoD | Shaker method | |
| 49.3 % | σ = 7.3 % | Densified, 230 °C/80%, 43% DoD | Shaker method | |
| 62.6 % | σ = 3.6 % | Densified, 240 °C/20%, 43% DoD | Shaker method | |
| Biege-Elastizitätsmodul | 10065 MPa | σ = 2568 MPa | Reference | DIN 52186, three-point bending test |
| 18102 MPa | σ = 1831 MPa | Densified, 43% DoD | DIN 52186, three-point bending test | |
| 9996 MPa | σ = 2702 MPa | Densified, 230 °C/20%, 43% DoD | DIN 52186, three-point bending test | |
| 8246 MPa | σ = 1671 MPa | Densified, 230 °C/80%, 43% DoD | DIN 52186, three-point bending test | |
| 6919 MPa | σ = 3202 MPa | Densified, 240 °C/20%, 43% DoD | DIN 52186, three-point bending test | |
| Biegefestigkeit | 110 Pa | σ = 28 Pa | Reference | DIN 52186, three-point bending test |
| 219 Pa | σ = 30 Pa | Only Densified, 43% DoD | DIN 52186, three-point bending test | |
| 43 Pa | σ = 18 Pa | Densified, 230 °C/20%, 43% DoD | DIN 52186, three-point bending test | |
| 34 Pa | σ = 3 Pa | Densified, 230 °C/80%, 43% DoD | DIN 52186, three-point bending test | |
| 39 Pa | σ = 26 Pa | Densified, 240 °C/20%, 43% DoD | DIN 52186, three-point bending test | |
| Brinell-Härte | 3.59 HB | σ = 0.30 HB | Reference | EN 1534 (2010) |
| 8.54 HB | σ = 0.88 HB | Only densified, 43% DoD | EN 1534 (2010) | |
| 3.37 HB | σ = 0.46 HB | Densified, 230 °C/20%, 43% DoD | EN 1534 (2010) | |
| 2.91 HB | σ = 0.27 HB | Densified, 230 °C/80%, 43% DoD | EN 1534 (2010) | |
| 3.24 HB | σ = 0.33 HB | Densified, 240 °C/20%, 43% DoD | EN 1534 (2010) | |
Daten bereitgestellt von
Technische Universität Dresden, Professur für Ingenieurholzbau und baukonstruktives Entwerfen
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- Brischke C, Koch S, Rapp AO, Welzbacher CR (2005) Surface properties of thermally treated wood—wear, abrasion and hardness. In: Militz H, Hill C (eds) Wood modification: processes, properties and commercialisation. Proceedings of the 2nd European Conference on Wood Modification, Göttingen, Germany, 6–7 October 2005, pp 371–375
Die in diesem Dokument enthaltenen Informationen wurden im Rahmen der zitierten Arbeit erhoben und werden als korrekt erachtet. Die aufgeführten Werte sind jedoch beeinflussbar durch Verarbeitungsbedingungen, Modifikationen, Werkstoffzusätze und Umgebungseinflüsse und befreien den Anwender nicht von eigenen Prüfungen und Versuchen. Eine rechtlich verbindliche Zusicherung bestimmter Eigenschaften oder der Eignung für einen konkreten Einsatzzweck durch den Datenanbieter kann aus den Angaben nicht abgeleitet werden.
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