Cristina Coelho

Method for evaluating the influence of wood machining conditions on the objective characterization and subjective perception of a finished surface

A method for evaluating the influence of the operating parameters of wood machining (planing, sanding) on the quality of a finished surface was established. The influence of each of the operations involved was studied using different strategies. For the planing operation, three levels were established (Level 1, 2 and 3) by determining different values for each of the major process parameters (tool rotation speed, feed speed, depth of cut). For both, surface preparation and polishing, two levels were established with a fixed setup. Finally, as finishing products, two different transparent coatings were selected (water-borne and solvent-borne). The quantitative evaluation of the state of the surface was assessed by means of an artificial vision system for the determination of the pseudo-roughness of wood surfaces. A filtering method based on fast Fourier transforms was applied and it was possible to derive three criteria for evaluating the resulting profile.

Low formaldehyde emission MDF overlaid with wood veneer: bonding problems assessment

Abstract The aim of this work is to assess wood bonding problems in medium density fibreboard (MDF) surfacing with decorative wood veneer (beech). Three sets of tests were carried out. The first set was carried out using automatic bonding evaluation system (ABES) in order to assess the bond strength development rate of two UF resins produced according to different processes. The second set permitted the study of the behaviour of bonding between MDF and beech veneer using ABES, and for this purpose a special MDF sample was designed. These MDF samples were pressed to conventional beech test strips and pulled at any given time immediately after pressing. A third set of tests were performed in a pilot hot-press used for MDF surfacing with beech veneer. Different operating conditions were tested (pressing time and resin type). The quality of bonding between wood veneer and MDF was evaluated using the surface soundness test (EN311). The tensile load required to pull off a defined surface area of overlaid panel was recorded and it was observed that in all samples the failure mode occurred within the underlying board. An analysis of variance test was performed to evaluate the significance level of the effects of the different factors on surface soundness. The main conclusion of this work is that the MDF surfacing operation seems to induce degradation in the MDF surface layers, probably due to the presence of urea, which could be responsible for a decrease in the surface soundness, which was mostly observed for longer pressing times.

Impact of thermal treatment on bonding performance of UF/PVAc formulations

Abstract Polyvinyl acetate (PVAc) adhesives present several advantages: ready to use, short setting time, flexible joint, easy to clean and long storage life. On the other hand, formaldehyde-based adhesives are less expensive and give a rigid bond. In this work, the combination of a PVAc glue and UF resin for surfacing MDF with wood veneer was assessed. The reactivity of different mixing ratios was evaluated using ABES (automated bonding evaluation system) machine as well as the wettability of beech veneers after different heat pre-treatments. The obtained results have shown that a mixture of PVAc/UF could be used for surfacing MDF with beech veneer without loss of mechanical properties, when compared with pure PVAc.