Scielo RSS <![CDATA[Maderas. Ciencia y tecnología]]> vol. 7 num. 2 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<B>INDUSTRIAL EVALUATION OF RE-DRY STRATEGY FOR SOFTWOOD LUMBER</B>]]> This paper presents an experimental evaluation of the first commercial scale dry-sort-redry (DSRD) strategy for drying of 2x4 Pacific coast hemlock (PCH) lumber. The DSRD strategy is a methodology designed to reduce final moisture content variability in kiln dried lumber by complementing conventional drying with radio frequency vacuum (RFV) drying technology. The strategy′s objective is to avoid producing over-dried lumber in conventional drying by setting the target moisture content to a value much higher than those usually used in industry. Then, RFV drying technology is implemented to quickly and efficiently re-dry the lumber that remains wet (under-dried) after the first conventional pass. Six experimental tests were performed in an industrial sawmill with the intention of studying the effect of target moisture content on the properties and quality of the dried lumber. In all cases, the first drying pass was performed in a 260m³ industrial heat-and-vent conventional kiln, and the re-drying of wets was performed in a 75m³ RFV kiln. Additionally, a mathematical model developed for prediction of data dispersion in lumber drying was calibrated with experimental data, and used to simulate the DSRD strategy under other hypothetical conditions. The results of the study demonstrate that the DSRD strategy reduces drying time, shrinkage and kiln drying degrade in comparison with a single conventional pass <![CDATA[<B>MEASUREMENT OF COLOUR DEVELOPMENT IN <I>PINUS RADIATA</I> SAPWOOD BOARDS DURING DRYING AT VARIOUS SCHEDULE</B>]]> Colour changes, such as kiln brown stain, that develop in Pinus radiata boards during kiln drying can reduce the value of the final wood products and result in significant losses due to downgrade or waste of dried wood by removing the darkened surfaces. This study measured how colour developed in Pinus radiata sapwood boards under different drying schedules. The boards used in these experiments were 40×100×800mm, cut from the same log and were end- and edge-matched. Boards were dried at eight different schedules using temperatures from 50°C to 120°C and relative humidities from 14% to 67%. Separate boards were dried for 5 equal intervals through each schedule and colour profiles measured through the boards using a surface reflectance spectrophotometer. Lightness, L* on a greyscale was used as an indication of colour change (darkening). The results show that there is generally a greater decrease in lightness with higher temperature schedules and also with slower, higher relative humidity, schedules. This suggests that both temperature and drying time are significant factors in the formation of colour during drying. The most significant changes in colour occurred near the board surfaces, indicating kiln brown stain <![CDATA[MATHEMATICAL MODELLING AND EXPERIMENTAL INVESTIGATION OF DEHUMIDIFIER DRYING OF RADIATA PINE TIMBER]]> A dynamic kiln-wide wood drying model was developed previously to solve the integral form of the unsteady-state mass, momentum and energy balance equations in the air side. For the wood side, an empirical model, characteristic drying curve, for the internal moisture movement is used, which was obtained for low and medium temperature drying of Pinus radiata, with a medium velocity of 1.4-4.1 m s-1. As part of the research programme to improve the design and control of dehumidifier wood drying kilns, the wood drying model has been assessed using the experimental data measured under drying conditions similar to those in dehumidifier kiln. It is noted that close agreement between the modelled results and the experimental data can be obtained for Pinus radiata drying processes with a medium air velocity (<; 5 m s-1). However, larger discrepancy between the modelled results and the measured data has been observed with a higher velocity (8 m s-1). To solve this problem a new characteristic drying curve, based on a two-zone diffusion model, has been used in the kiln-wide wood drying model and more accurate results have been obtained <![CDATA[<b>ESTUDIO DE LA VELOCIDAD DEL SECADO DE RENOVALES DE CANELO DRIMYS WINTERI</b>]]> En este trabajo se estudia experimentalmente la velocidad del secado artificial a temperaturas convencionales de renovales de canelo Drimys winteri. El diseño experimental incluye los programas de secado y el espesor de la madera. Seis ensayos son realizados usando madera de 25 y 50 mm de espesor, en un horno convectivo de 0.3 m³. La madera para los ensayos experimentales proviene de bosques de renovales creciendo en la zona de Lanco (X Región, Chile). Los resultados muestran que la velocidad del secado es limitada por la tendencia a los defectos del secado de los renovales de canelo. Las curvas de secado carecen de la etapa de velocidad de secado constante, la velocidad de secado máxima se encuentra en el rango de 1.72 x10-2 y 2.99x10-2 (%/h) y el contenido de humedad crítico varía entre 87 y 116 %<hr/>This is an experimental study at conventional temperatures of the wood drying rate of canelo Drimys winteri regrowth. The experimental design include as a variables the drying schedule and the wood thickness. Six run are realized in 25 and 50 mm of wood thickness using a pilot drier with 0.3 m³ capacity. Canelo regrowth from Lanco (X Region, Chile) are utilized in this experiments. The results show that the wood drying rate is conditioned by the drying defects tendency of canelo regrowth. Also the drying curves are not constant drying rate and they have a maximal drying rate between 1.72 x10-2 and 2.99x10-2 (%/h) and the critical moisture content are among 87 and 116 % <![CDATA[<b>SECADO DE <em>EUCALYPTUS NITENS</em><strong> Y </strong><em>GLOBULUS </em><strong>Y SU APROVECHAMIENTO EN BLOCKS, PISOS Y MUEBLES</strong></b>]]> Ensayos de secado en madera radial y tangencial de Eucalyptus nitens y globulus fueron realizados en laboratorios de la Universidad del Bío-Bío en el marco del Proyecto FONDEF D98I1018 y posteriormente validados a escala industrial. A escala de laboratorio, la escuadría utilizada fue de 30 mm de espesor, 1.8 m de largo y ancho aleatorio. A escala industrial en tanto, fue de 32 mm de espesor, largos de 2.1 y 2.8 m, con anchos variables. En general, los programas de secado fueron suaves, con temperaturas no superiores a los 50°C, con un bajo potencial de secado e incluyeron tratamientos de vaporizado para recuperar colapso y reducir tensiones de secado. Se evaluaron contenidos de humedad inicial y final, densidad básica, gradientes de humedades, grietas, contracciones, tensiones y alabeos, determinando finalmente su aprovechamiento en pisos, blocks y muebles. Los resultados indican que la madera de Eucalyptus nitens presenta una fuerte evaporación superficial, generando altos gradientes de humedad, contracciones prematuras a nivel de superficie y tensiones de secado bajo el P.S.F, originando grietas superficiales e internas. Cuando el colapso es severo, debido a la baja resistencia mecánica de la pared celular de la madera, se generan grietas superficiales e internas en la madera. El mejor aprovechamiento se obtuvo para madera radial, donde el Eucalyptus globulus registró entre 52 y 81% para blocks, entre 48 y 91% para piso y entre 38 y 89% para muebles. El Eucalyptus nitens registró entre 60 y 71% en blocks, entre 59 y 61% para piso y entre 52 y 63% para muebles. La pérdida por nudos en Eucalyptus globulus fluctuó entre 3 y 22% en madera radial y entre 5 y 24% para madera tangencial. Para Eucalyptus nitens, en tanto, fluctuó entre 12 y 19% y entre 15 y 34% para los cortes antes señalados. La pérdida por grietas en Eucalyptus globulus varió entre 3 y 10% para madera radial y entre 15 y 21% para tangencial. En el Eucalyptus nitens ésta fluctuó entre 3 y 13% y entre 5 y 38%. Lo anterior, permite concluir que la madera de corte radial es la mejor opción para ser utilizada en estas aplicaciones<hr/>Drying tests on both Eucalyptus nitens and globulus radial and tangential timber were carried out at Universidad del Bío-Bío Laboratories, under the approach of the D98I1018 FONDEF Project to be later validated at an industrial scale. A 30 mm-thick, 1.8 meter-long and random with scantling was used at a laboratory level, while the one applied at industrial level showed 32 mm of thickness, the lengths of which ranging from 2.1 to 2.8 meters, and variable widths. As general rule, mild drying programs were used, at temperatures not higher than 50°C, and having low drying potential. In turn, such programs included steaming based treatment with the purpose of overcoming collapse and reduce drying tensile. The following was assessed: initial and final moisture content, basic density, moisture gradients, checks, shrinkage, tensile and warpage, to finally specify their utilization in flooring, blocks and furniture. Outcomes have shown that Eucalyptus nitens timber features a high surface evaporation, thus generating high moisture gradients, early shrinkage at surface level, along with below P.S.F. drying related tensile, which, in turn, brings about surface and internal checks. When collapse turns to be severe, and because of timber cell wall mechanical strength, both surface and internal checks show up. A better utilization was achieved for radial timber, where Eucalyptus globulus values ranged from 52 to 81% in the case of blocks, form 58 to 91% with respect to flooring, and between 38 and 89% in the case of furniture. Eucalyptus globulus figures ranged from 60 to 71% for blocks, from 59 to 61% for flooring, and between 52 and 63% in the case of furniture. Losses caused by knots in Eucalyptus globulus ranged from 3 to 22% in the case of radial timber, while the tangential one featured a 5 to 24% variation. On the other hand, Eucalyptus nitens timber showed variations from 12 to 19%, and from 15 to 34% for the above mentioned cuts. Check related losses in Eucalyptus globulus ranged from 3 to 10% in the case of radial timber, while tangential wood showed a 15 to 21% variation. Eucalyptus nitens featured variations from 3 to 13% and between 5 and 38%. Out of the above we may conclude that radial cut timber turns out to be the best option when being used in such applications <![CDATA[<B>A REVIEW OF THE CONFIGURATION OF BORDERED PITS TO STIMULATE THE FLUID FLOW</B>]]> As the bordered pits have generally been thought to have an influence on the refractory nature of softwoods, structural behaviour of this conducting pathways is discussed according to the published literature. Various theories on the role of bordered pits to axial flow are expounded in respect to preservative treatment. Pit aspiration is also reviewed <![CDATA[<B>CARACTERIZACIÓN FÍSICA Y MECÁNICA DE PINUS TAEDA ORIGEN MARION EN PLANTACIONES DE DIFERENTES EDADES Y DETERMINACIÓN DE USOS POTENCIALES, MISIONES, ARGENTINA</B>]]> As the bordered pits have generally been thought to have an influence on the refractory nature of softwoods, structural behaviour of this conducting pathways is discussed according to the published literature. Various theories on the role of bordered pits to axial flow are expounded in respect to preservative treatment. Pit aspiration is also reviewed <![CDATA[<b>DURABILIDAD NATURAL DE LA MADERA DE CINCO ESPECIES APTAS PARA LA INDUSTRIA DE LA CONSTRUCCIÓN</b>]]> As the bordered pits have generally been thought to have an influence on the refractory nature of softwoods, structural behaviour of this conducting pathways is discussed according to the published literature. Various theories on the role of bordered pits to axial flow are expounded in respect to preservative treatment. Pit aspiration is also reviewed