Scielo RSS <![CDATA[Maderas. Ciencia y tecnología]]> http://www.scielo.cl/rss.php?pid=0718-221X20020001&lang=es vol. 4 num. 1 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.cl/img/en/fbpelogp.gif http://www.scielo.cl <![CDATA[<B>LA TRAYECTORIA CIENTÍFICA DEL Dr. WALTER G. KAUMAN</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-221X2002000100001&lng=es&nrm=iso&tlng=es <![CDATA[<b>FUNDAMENTAL PHENOMENA IN WOOD RFV DRYING WITH 50-Ohm AMPLIFIER TECHNOLOGY</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-221X2002000100002&lng=es&nrm=iso&tlng=es Radio frequency/vacuum drying (RFV) experiments were conducted on thick (200-250 mm) softwoods by using a 50-Ohm amplifier as the radio frequency (RF) source. The power densities selected were low to ensure highest quality of the final product and that no internal checking will occur. The effect of dryer pressures and power densities on the drying kinetics and product quality was examined for two different wood species. A number of experimental observations and drying characteristics are analyzed and discussed in detail. The concept of the identity drying card is applied and useful information concerning the drying mechanisms and the relevant phase transitions is obtained <![CDATA[INFLUENCE OF SAWING ORIENTATION ON MOISTURE MOVEMENT THROUGH SOFTWOOD BOARDS]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-221X2002000100003&lng=es&nrm=iso&tlng=es Earlywood, formed at the beginning of the growth period each year in temperate regions, has tracheids that are thinner-walled and larger in diameter than those laid down later in the season, the latewood. As a consequence, the permeability to moisture movement differs, particularly as some of the pits in the latewood tracheids may close or aspirate. Boards sawn from a log will have the orientation of the growth rings (representing seasonal accumulation of woody material) at various angles to the long dimension of the boards. The extreme cases, known as flat-sawn and quarter-sawn, respectively, represent the situations where the growth rings lie parallel to the long dimension or at right angles to it. Tests were undertaken on the drying behaviour of both flat-sawn and quarter- sawn, 50mm-thick sapwood boards of Pinus radiata dried under so-called high-temperature conditions, 120/70°C, with an air velocity over the boards of 5m s-1 in a single-board drying tunnel. Moisture-content profiles were determined by slicing samples after various stages of drying. In the wet core, the moisture distribution was uniform with quarter-board boards, but showed "peakiness" corresponding to the latewood zones in flat-sawn boards. With either orientation, there is a thin dry layer below fibre saturation at the surface, which in the case of flat-sawn boards is one growth-ring-wide. Quarter-sawn boards dry more slowly than flat-sawn boards due to different drying mechanisms, and these differences in drying behaviour is also reflected in differences in strain development as the wood tries to shrink in conformity with the local moisture content <![CDATA[<B>EFFECTS OF SAWING PATTERN ON DRYING RATE AND RESIDUAL DRYING STRESSES OF PINUS RADIATA LUMBER</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-221X2002000100004&lng=es&nrm=iso&tlng=es Flatsawn and quartersawn Pinus radiata (radiata pine) sapwood boards were dried in a tunnel dryer in three runs using three drying schedules. These schedules represented low temperature (LT), accelerated conventional temperature (ACT) and high temperature (HT) drying. In each run, the boards were assembled in the dryer in two vertically matched layers with the flatsawn and the quartersawn boards being alternatively placed side by side. The samples were weighed at pre-set drying times. After drying, all of the samples were cut to two halves, one half for oven drying to determine the moisture content during drying and the remaining half for stress assessments. For LT and ACT drying, the quartersawn boards dried slower than the flatsawn boards, but for HT drying the difference between the quartersawn and the flatsawn boards was not statistically significant. The transverse residual drying stress in the quartersawn boards was, in general, lower than the flatsawn boards and the difference was most apparent for the LT drying <![CDATA[<b>FLUID MIGRATION IN TWO SPECIES OF BEECH (FAGUS SILVATICA AND FAGUS ORIENTALIS)</b>: <b>A PERCOLATION MODEL ABLE TO ACCOUNT FOR MACROSCOPIC MEASUREMENTS AND ANATOMICAL OBSERVATIONS</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-221X2002000100005&lng=es&nrm=iso&tlng=es The aim of this study is to visualise, measure and understand the pathway of liquid and gas at both macroscopic and microscopic levels on specimens of beech (Fagus silvatica and Fagus orientalis). The permeability to air and to water has been measured using devices developed in our laboratory. The extension of the area coloured by dyed water is available as well. At the microscopic level, the permeability has been calculated using Poiseuille's equation from the vessel diameters determined on cross sections by image processing. Using dyed water, the proportion of active vessels is also reported at different distances from the injection surface. Our data confirm that the permeability decreases significantly when the sample distance increases. Moreover, the value extrapolated for a zero-length sample is similar to the value predicted from the vessel diameters. This observation stands for both for sapwood and heartwood, in spite of the great permeability difference noticed between these zones. At the microscopic level, the percentage of active vessels decreases with the increase of sample total length and the increase of the distance from the injection point. Several simulations performed using a bond percolation model confirmed our experimental results obtained at the macroscopic and microscopic levels <![CDATA[MODELACIÓN DEL SECADO CONVENCIONAL DE COIGÜE: PARTE 2: RESULTADOS EXPERIMENTALES]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-221X2002000100006&lng=es&nrm=iso&tlng=es Un modelo fenomenológico unidimensional basado en el coeficiente global de transferencia de materia (Kx) es utilizado para representar la cinética del secado convencional del coigüe (Nothofagus dombeyi). Este modelo consiste en un conjunto de cuatro ecuaciones diferenciales parciales no lineales de primer orden el cual es discretizado de acuerdo al método de diferencias finitas y resuelto como un problema de valor inicial. Para determinar Kx se realizaron cuatro experimentos de secado variando el espesor y la velocidad del aire. El valor de éste coeficiente osciló entre 1,87 · 10-5 y 3,37 · 10-5 kg/m²·s. El modelo predijo adecuadamente el comportamiento transiente de la humedad durante el secado de la madera de coigüe. Kx varió con el espesor de la madera pero no con la velocidad del aire<hr/>A one-dimensional phenomenological wood drying model is used to describe the conventional drying kinetic of Chilean coigüe Nothofagus dombeyi. The model is based on a global mass transfer coefficient (Kx), it consists of a system of four 1st order coupled partial differential equations and is finite differenced and solved like a initial value problem. In order to determine Kx four drying cycles were performed varying the wood thickness and the drying air velocity. The model suitably predicted the humidity transient behavior during the coigüe wood drying. Kx varied with the wood thickness but not with the air velocity. The value of this coefficient oscillated between 1,87· 10-5 and 3,37 · 10-5 kg/m²s <![CDATA[<b>CONTRIBUTION TO THE THEORY OF CELL COLLAPSE IN WOOD</b>: <b>INVESTIGATIONS WITH EUCALYPTUS REGNANS</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-221X2002000100007&lng=es&nrm=iso&tlng=es Total collapse is considered as the sum of "liquid tension collapse" and "stress collapse". An equation is derived giving total collapse as a linear function of wood temperature and, to a smaller extent, of collapse-free shrinkage. The parameters of the equation depend only on surface tension data and on structural and rheological properties of the wood. To test the theory, Eucalyptus regnans cubes of 7/8 in. edge length were dried at temperatures ranging from 70 to 285°F, using two levels of humidity at each temperature. In addition, specimens measuring 7/8 by 7/8 by 3 in. were dried at 150°F and low humidity. The results show good agreement with theoretical values for wood temperatures up to about 190°F. For higher temperatures or very low humidities collapse is found to be significantly time-dependent. Collapse in small end-sealed cubes is shown to be of the same order as that in the thickness of boards of rectangular cross section, but the latter collapse less in width <![CDATA[<B>LA PARTICIPACION DEL DOCTOR WALTER KAUMAN EN LA CREACION DEL INSTITUTO FORESTAL DE CHILE</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-221X2002000100008&lng=es&nrm=iso&tlng=es Total collapse is considered as the sum of "liquid tension collapse" and "stress collapse". An equation is derived giving total collapse as a linear function of wood temperature and, to a smaller extent, of collapse-free shrinkage. The parameters of the equation depend only on surface tension data and on structural and rheological properties of the wood. To test the theory, Eucalyptus regnans cubes of 7/8 in. edge length were dried at temperatures ranging from 70 to 285°F, using two levels of humidity at each temperature. In addition, specimens measuring 7/8 by 7/8 by 3 in. were dried at 150°F and low humidity. The results show good agreement with theoretical values for wood temperatures up to about 190°F. For higher temperatures or very low humidities collapse is found to be significantly time-dependent. Collapse in small end-sealed cubes is shown to be of the same order as that in the thickness of boards of rectangular cross section, but the latter collapse less in width <![CDATA[<B>RECUERDOS DE LA PERMANENCIA DEL Dr. Walter Kauman EN CHILE</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-221X2002000100009&lng=es&nrm=iso&tlng=es Total collapse is considered as the sum of "liquid tension collapse" and "stress collapse". An equation is derived giving total collapse as a linear function of wood temperature and, to a smaller extent, of collapse-free shrinkage. The parameters of the equation depend only on surface tension data and on structural and rheological properties of the wood. To test the theory, Eucalyptus regnans cubes of 7/8 in. edge length were dried at temperatures ranging from 70 to 285°F, using two levels of humidity at each temperature. In addition, specimens measuring 7/8 by 7/8 by 3 in. were dried at 150°F and low humidity. The results show good agreement with theoretical values for wood temperatures up to about 190°F. For higher temperatures or very low humidities collapse is found to be significantly time-dependent. Collapse in small end-sealed cubes is shown to be of the same order as that in the thickness of boards of rectangular cross section, but the latter collapse less in width