Efecto de la temperatura de termotratamiento en el comportamiento eléctrico de la madera de pino radiata

Se analiza el efecto de la temperatura del termotratamiento sobre la conductividad eléctrica de la madera de pino radiata. Sobre probetas de madera de pino radiata de procedencia País Vasco (España), termotratada a 190ºC y 210ºC por el método Thermowood así como sobre piezas testigo de la misma especie, procedencia y dimensiones, acondicionadas todas ellas hasta masa constante a 20ºC/40%HR, 20ºC/65%HR y 20ºC/90%HR se evaluó la resistencia eléctrica (longitudinal y transversal) y, posteriormente, se ajustó el modelo Samuelson para modelizar en cada tipo de material la relación humedad de la madera-resistencia eléctrica. Se concluye que la temperatura empleada en el tratamiento térmico de la madera afecta no sólo a la humedad de equilibrio sino, también, a su conductividad eléctrica, siendo máximo este efecto en el tratamiento efectuado a 210ºC

Improving stem quality assessment based on national forest inventory data: an approach applied to Spanish forests

20 Pág.Key message: This paper proposes a methodology that could be considered as a base for a harmonized protocol for stem-quality reporting in Europe while conducting National Forest Inventories, in order to cost-efficiently obtain a visual wood quality proxy. The importance of the variables selected, the limitations identified, and some improvements to the methodology are suggested. Forest areas with better wood quality, which in turn it would be useful for breeding programs, can be easily detected. Context: The establishment of harmonized standards or indicators that allow us to determine the quality of the wood present in a forest prior to its exploitation has long been demanded by the European forestry sector, although agreed methodologies for the evaluation of wood quality in standing trees, which is one of the sector’s most urgent requirements, have not, as yet, been implemented. Aims: To develop a protocol that visually characterizes wood quality on standing trees in a cost-effective way for the National Forest Inventory (NFI). After some improvements, it can be considered as a base for a European harmonized protocol. Methods: In this article, we analyze the implementation, in the NFI, of a visual wood-quality assessment methodology in forests of Central Spain based on the different European standards as well as on research papers addressing this issue. Results: The silvicultural practices employed are of the utmost importance to obtain the best wood quality, regardless of the species. Several areas with higher wood quality were identified as well as areas most affected by specific pests in the studied region. The impact of the variables measured (e.g., branchiness, crookedness, maximum branch diameter) is discussed. Conclusion: It is feasible to estimate a proxy for wood quality on standing trees in the NFI. Furthermore, after studying the inventory data provided, several enhancements are proposed, not only to improve wood-quality estimates but also to optimize fieldwork costs. Harmonizing NFIs to assess and map European standing wood quality can be achieved.This work was supported by the Spanish Ministry of Agriculture, Fishing and Food (Encomienda de Gestión. EG17-042 “Soporte científico a la generación de información Forestal”).Peer reviewe

Evaluation at industrial scale of electric-driven heat pump dryers (HPD)

Electric-driven heat pump drying is evaluated in lumber from different softwoods (Maritime, radiata and Scot pines) and hardwoods (Iroko, Beech). The evaluation was carried out at industrial scale being controlled by five different driers over a two-year period. Up to 235 different cycles of drying were evaluated. Specific energy consumption seems to be between 0.64 kWh/l to 0.73 kWh/l in softwoods and between 1.0 to 1.3 kWh/l in hardwoods. These values are much lower than those usually reported for the traditional kiln drying. In moderate permeable lumber, the overall duration of drying is very similar to traditional kiln drying, but is longer in the case of very permeable softwoods. This drying technology seems to be efficient when drying lumber, at least when medium temperatures (65-70°C) are involved. © Springer-Verlag 2004

Practical evaluation and operation of superheated steam drying process with different softwoods and hardwoods

Die Holztrocknung mit überhitztem Wasserdampf wird an Bauholz aus verschiedenen Laub- und Nadelholzarten bewertet. Größere Probleme bei Nadelholz hänge mit dessen hohem Harzgehalt zusammen. Probleme bei Laubhölzern ergeben sich aus deren Wegsamkeit und der Tendenz zu Kollabieren und Risse zu bilden. Die Brauchbarkeit der Temperaturmessung im Innern des Holzes zur Kontrolle des Endpunktes der Trocknung wird ebenfalls bewertet

Solar drying of sawn lumber in Spain

Im spanischen Holzforschungsinstitut in Madrid wurde die Wirksamkeit der Solartrocknung von Schnittholz im Vergleich zur Freilufttrocknung untersucht. Die 2 m3-Trockenkammer wurde unter Kostenoptimierung aus vorgefertigten Sandwichbauteilen mit in die Dachflächen integrierten Kollektoren erstellt, zur Trocknungssteuerung jedoch mit einem halbautomatischen Kontrollsystem ausgerüstet, dessen Funktionsweise ausführlich beschrieben wird. Das Trocknungsverhalten der Solaranlage wurde über zwei Jahre in 10 Versuchstrocknungen unter Berücksichtigung des Trocknungsverlaufs, der Anfangs- und Endfeuchten, der Betriebssicherheit sowie der Effizienz untersucht. Bei Ausnutzung der Solarenergie war die Holztrocknung von ua∼70 bis 80% auf ua∼8 bis 10% bis zu 3,5mal schneller als bei der Freilufttrocknung. Die Holzqualität nach der Solartrocknung war besser sowohl im Vergleich mit der Freiluft- als auch im Vergleich mit der konventionellen Frischluft-/Ablufttrocknung. Obwohl die Ergebnisse wesentlich von den klimatischen Gegebenheiten am Trocknerstandort abhängen, wird die Ausnutzung der Solarenergie zur Schnittholztrocknung auch für nördlich gelegene Regionen als lohnend beurteilt

Long-term deformation of MDF panels under alternating humidity conditions

Creep tests were carried out on 19 mm thick commercial MDF panels, raw and overlaid with melamin resin-impregnated 80 g/m2 paper. The tests were carried out under cyclic environmental conditions with relative humidity levels of 30%-90%, a steady temperature of 20 °C, 3 different stress levels, 20%, 30% and 40%, and using mid-span loading. The relative creep of the MDF panels was considerably higher than that in particleboards with similar characteristics. Creep behaviour of the raw panels seems to be strongly influenced by melamin coating of the boards' surfaces but not by the edge coating, except when both were combined. This study debates the convenience of comparing the Theological behaviour of MDF and particleboards by means of the relative creep

Structural characterization of Pinus radiata D. Don timber from Pais Vasco (Spain) according to standard modifications

In the last decades in Europe the promulgation of Practice Codes, Directives and Harmonised Standards of obliged fulfilment for the member countries was promoted. They affect to wood in construction and are essential to improve the material in the structural use. Due to the dynamic character proper of standards, and necessary for their functionality, these suffer modifications in the time that are necessary to check in the really existing material. In this work, a representative sampling on one of the usual species of wood in the construction in Spain, as it is the radiata pine, was carried out, looking for the veracity of the available material in the market both in qualities and sections. The standard methodology stipulated for the characterization was applied. Additionally, in each piece, the visual classification criteria established in the Spanish standard UNE 56.544 for the estimation of the strength grades, was applied. The results set forth the conclusions obtained after the application of the last changes of the regulation for the determination of mechanical properties, which are involved in the analyses of the structural characterization of timber and determine the final strength assignation

Improving the prediction of strength and rigidity of structural timber by combining ultrasound techniques with visual grading parameters

The present study explores the possibility of using longitudinal ultrasound transmission to evaluate the bending strength and modulus of elasticity in structural timber made from the two species most commonly found in Spanish construction and rehabilitation works Scots pine (Pinus sylvestris L) and Laricio pine (Pinus nigra Arn.). An analysis of 1305 Scots pine and 852 Laricio pine beams shows that ultrasound transmission velocity alone can predict neither the bending strength nor the modulus of elasticity and that other predictive variables are required. A series of models are proposed based on ultrasound transmission velocity measurements, the relative size of the largest face and edge knots, length and density. After running models for each species individually and for the two jointly, a single model is found to be suitable for both. The models proposed explain from 63 to 73 per cent of bending strength and modulus of elasticity variability

Structural Tali timber (Erythrophleum ivorense A. Chev.;Erythrophleum suaveolens Brenan.) Assessment of strength and stiffness properties using visual and ultrasonic methods

The physical and mechanical properties (density, bending strength and stiffness) of 82 sawn pieces of Tali wood (Erythrophleum ivorense A. Chev.;Erythrophleum suaveolens Brenan.) from Guinea and Cameroon were estimated using the EN 408 (2003) test standard. Timber pieces had a cross section of 80 mm×80 mm and 200 mm×250 mm and were visuallygraded according to British Standard BS 5756 (1997) in a single HS grade. The efficacy of this test was analyzed. The velocity of propagation of ultrasound waves had previously been measured by means of equipment specially designed for structural timber (Sylvatest Duo). The results of visual grading according to BS 5756 (1997) show very low output with an excessive percentage of rejected pieces. Due to this, modifications are proposed to some of the specifications with the aim of reducing this percentage. Furthermore, visual grading does not facilitate to clearly separate the mechanical properties of HS grade and rejected pieces. The use of ultrasonic measurements shows good accuracy for the evaluation of stiffness properties, but not for strength. Visual grading makes it possible to reach a strength class of D50, while ultrasonic method could be used as an added parameter for grading