Des visites industrielles auprès des producteurs et des utilisateurs de panneaux collés sur chant ont été effectuées afin de définir ce qu’est un collage sur chant de qualité pour les produits d’apparence. Lors des visites, des panneaux collés avec joints de bonne et de mauvaise qualité ont été recueillis pour examen au laboratoire de Forintek. Des mesures effectuées au microscope ont permis d’établir à 0.05 mm la valeur maximale acceptable de largeur du joint de colle d’un panneau. Les principales causes de joints problématiques propres à l’opération de délignage des bandes sont l’éclatement des fibres du bois sur l’arête, la trop grande rugosité de la surface sur chant et la mauvaise rectitude du trait de scie bien que l’angle d’équerre de la scie constitue aussi un paramètre critique. La proportion de panneaux rejetés en usines reliés à ces causes varie de 0.5 à 3 %.
Des mesures de rugosité sur un échantillon de bandes recueillies en usines ont permis d’établir des valeurs représentatives de rugosité sur chant de bandes utilisées à la production industrielle de panneaux. Des mesures de rugosité sur des bandes délignées en laboratoire ont démontré les effets importants du modèle de scie et de la vitesse d’alimentation, ou avance par dent, sur les valeurs de rugosité sur chant. Des mesures effectuées sur des bandes délignées à partir de scies usées ont démontré que la rugosité sur chant ne permet pas de détecter le niveau d’usure d’une scie, les valeurs moyennes de rugosité étant similaires à celles de bandes délignées à l’aide de scies bien affûtées.
Suite à la fabrication de panneaux en laboratoire à partir de bandes présentant une large gamme de rugosité sur chant, des mesures ont démontré l’augmentation de la largeur des joints de colle, l’augmentation de la proportion des joints de largeur supérieure à 0.05 mm (trop apparents) et la diminution de la résistance en cisaillement des joints de colle avec l’accroissement de la rugosité sur chant des bandes. Les paramètres de collage (type de colle, pression aux serres, température ambiante, etc.) furent gardés constants pour la fabrication de l’ensemble des panneaux.
Finalement, en fonction des résultats obtenus dans le cadre de cette étude, des valeurs de rugosité sur chant Ra et Rt de 9 µm et 80 µm respectivement peuvent être considérées comme des valeurs permettant la fabrication à grand volume de panneaux avec joints de colle de qualité, une augmentation de la rugosité sur chant résultant en des joints de colle plus apparents.
Mill visits to manufacturers and users of edge-glued panels were conducted in order to characterize the quality of edge-glued joints in appearance products. During these visits, panels with gluelines of good and poor quality were collected for further analysis in Forintek’s laboratory. Microscopic measurements served to determine that the maximum acceptable width of glue joints in edge-glued panels is 0.05 mm. The main causes of troublesome gluelines resulting from ripping operations are splintering at the juncture of the edge and flat surface, excessive edge roughness, and uneven straightness of the saw kerf, although the right angle of the saw is also a critical parameter. The percentage of mill-rejected panels as a result of these problems ranges from 0.5% to 3%.
A series of edge roughness measurements taken from a sample of strips from participating mills set the stage for the development of representative roughness values for the edges of strips used in the industrial production of edge-glued panels. Edge roughness measurements taken from strips ripped in the laboratory showed the impact of various factors on edge roughness values: saw blades, feed speed and chip load. Measurements taken from edges ripped with worn saw blades indicated that edge roughness cannot be used to determine saw blade wear values because average roughness values obtained with such blades were found to be similar to those of strips ripped with well-sharpened saws.
Following the laboratory assembly of panels using strips exhibiting a wide range of edge roughness, measurements revealed that edge roughness contributes to increased glueline width, a greater proportion of gluelines wider than 0.05 mm (too apparent) and a reduction in glueline shear strength. Glueing parameters (type of glue, clamp pressure, ambient temperature, etc.) were constant throughout the production of laboratory panels.
Finally, the results of this study suggest that edge roughness values of 9 µm for Ra and 80 µm for Rt allow large-volume manufacturing of panels with good quality gluelines and that an increase in edge roughness will result in more apparent gluelines.
6.1 Effect of refining process conditions on the dimensional stability of the panels
In this project, a study was carried out to investigate the effects of different refining parameters on the properties of dry-process fibreboard, in particular, high density fibreboard as the substrate for flooring products. Refining temperature (as quantified by steam pressure), retention time of preheating, refining specific energy, and speed of the refining were investigated as factors contributing to the physical and mechanical properties of fibreboard. A total of 18 different refining runs were carried out, and 36 laboratory high density fibreboards were produced. The experiment results show that panel stability can be improved substantially and thickness swell can be reduced by optimizing a ‘fit for purpose’ refining strategy.
Work reported in this study was carried out with the key objective of evaluating fasteners holding capacity in commercial wood panels for the purpose of exploring potential markets or expanding existing ones for OSB and other panel products in the upholstered furniture industry.
In order to have a better understanding of the upholstery furniture industry, visits were made to major upholstered furniture manufacturers in the Montreal area in November and December of 2003. These visits provided the research group with a comprehensive knowledge on the various types of wood materials and processing technologies being used at these plants, including ways of connecting the various components of the frames. Interviews with the plants staff indicated that fasteners holding capacity in OSB and other panel products are some of the major issues that are currently limiting the increased use of wood-based panels in the upholstered furniture industry.
In order to better understand the relationship between the fasteners holding capacity and the density distribution in panels, a comprehensive testing program was established. A total of 20 panels of medium density fiberboard (MDF), 16-mm thick, particleboard (PB), 16 mm thick, and oriented strand board (OSB), 11 mm, 15 mm, and 18 mm thick, with 4 replications each, were scanned using a commercial X ray system to obtain in-plane (horizontal) density distribution of the full size panels. In addition, basic panel properties (i.e., bending strength (MOR) and stiffness (MOE), internal bond (IB) and density profile) were determined. Sampling of test specimens from mapped panels was carried out in such away to cover low and high horizontal density zones.
Fasteners holding capacity tests including; lateral resistance of screws, edge and face withdrawal and head pull-through resistance of screws and staples were carried out. Correlations between fasteners holding capacities and localized horizontal density distributions were established in order to investigate how density distribution within the plane of the panel could affect the fasteners holding capacity. Investigations on the fasteners holding capacity in panel specimens subjected to static and cyclic loadings were made as well for the purpose of examining the effect of repeated cycles of loading and unloading events (i.e., short-term fatigue).
Findings from this study indicated that poor fasteners holding capacity especially on the edge of the panel is one of the key panel attributes that is currently limiting the use of OSB and other wood panel products in the upholstered furniture. Fastener driven in low density points or zones may fail at much lower load level than that driven in high density points with failure initiating at those low density zones and progressing to other zones from there (i.e., loaded end or edge distance). For the type of cyclic loading regimes used in this study (90 cycles at different load levels), no significant differences were observed.
Recommendations are given on how to improve the panel attributes in order to increase the fasteners holding capacity and resolve some of the technical issues limiting the market access of wood panel products in the upholstered furniture industry.
This report summarizes the research project carried out at Forintek’s Eastern Laboratory entitled Properties of MDF in Relation to Wood fibre Characteristics and Processing. This project included two phases. In the first phase, 10 types of raw materials, including wood, bark, and tops, were selected to cover large range of wood characteristics. The samples were classified by wood species (e.g., the less desirable red pine species), fast growing and short rotation (e.g., hybrid poplar), residue type (e.g., tops and bark), and forest management regime (e.g., commercial thinnings). The basic properties of raw materials, such as basic density, pH, and buffering capacity, were determined. The effects of raw material acidity on the curing behaviours of UF resins were investigated, and the properties of MDF panels manufactured using each sample at fixed manufacturing conditions were compared. The impact of bark content on MDF properties was also studied. In the second phase, two types of raw materials (black spruce tops and bark) were selected for the optimization of process parameters, including refining and hot pressing. The effects of refining conditions on pH and buffering capacity of refined fibres as well as on the properties of MDF panels were investigated. Optimal refining and hot-pressing parameters were established for manufacturing MDF products with black spruce tops and bark. Based on the results of this study, the following conclusions can be made:
Buffering capacity and pH differ among species and type of raw materials. Bark has higher acid and alkaline buffering capacities and a lower pH value than wood of the same species due to their extractives. Ten-year-old poplar wood has a higher pH than six year old poplar wood, tops, and bark.
The pH value of the raw fibre materials studied decreases with increased absolute and relative acid buffering capacity due to the increased absolute acidity mass in the solution.
At lower levels of added catalyst, the effect of raw materials pH on UF resin gel time is significant, while it is insignificant at higher catalyst contents. This may be due to the acidity of wood, which is the main source of acid catalyst in mixtures with lower levels of added catalyst. In contrast, at higher levels of added catalyst, the catalyst is the main source of acid catalyst. With higher catalyst contents, all studied raw materials mixed with UF resin result in a longer gel time than with UF resin alone. The gel time of UF resin/wood mixture does not correlate to acid buffering capacity or alkaline buffering capacity, but there is a strong relationship between gel time and both absolute acid buffering capacity and relative acid buffering capacity.
The reaction enthalpy of UF resin increases with catalyst content. The activation energy and peak temperature of curing UF resin generally decrease with increased catalyst content at lower catalyst levels. However, with further increases in catalyst content, the changes in activation energy and peak temperature are insignificant. The hydrolysis reaction of cured UF resin occurs during the latter stages of the curing process at both lower-level (<0.2%) and higher-level (>0.7%) catalyst contents. This indicates that there is an optimal range of catalyst content for UF resin. The curing enthalpy of UF resin decreases with increased amounts of wood raw materials; this is due to the effect of diffusion induced by wood materials and the changes in the phase of curing systems. This suggests the curing reactions reach a lower final degree of conversion for wood/resin mixtures than for UF resin alone.
Hybrid poplar MDF panels show better mechanical properties than jack pine panels; the mechanical properties of jack pine panels are better to those of red pine and white spruce panels. The dimensional stability is the best in jack pine panels among the materials studied (poplar, red pine, and white spruce).
The effect of refining on wood pH is significant, but it is insignificant on bark pH. The pH values of the wood from all species studied reduced after refining.
The effect of bark on the modulus of rupture (MOR) and modulus of elasticity (MOE) of MDF panels is more significant than the effects on IB and other physical properties, such as thickness swelling (TS), water absorption (WA), and linear expansion (LE). All properties of MDF panels (except TS and, in one case, MOR) made with up to 40% bark meet the ANSI standard.
When black spruce tops are used as raw material for MDF, steam pressure is more important than retention time during the refining process in order to achieve better panel properties. The panels show very good mechanical properties and dimension stability under optimal refining conditions even without the addition of wax.
In the new 2005 edition of the National Building Code of Canada, the permissible deflections under earthquake conditions will be much more restrictive and could potentially become the governing factor for the design of wood frame construction.
To proactively respond to the code changes, this three-year project was to develop design procedures for determining the stiffness or deflection of shearwalls and diaphragms under these extreme seismic and wind load events. While investigating the formulae for predicting deflections, issues related to the overall strength or load carrying capacity of shearwalls were also addressed.
Using a “mechanics-based” approach, deflection formulae were developed for unblocked shearwalls, two-sided shearwalls (gypsum wallboard on one side and wood-based panels on the other side), and shearwalls without hold-downs. In collaboration with staff from the Canadian Wood Council, these deflection formulae will be submitted for implementation in the next edition of the Canadian Standard for Engineering Design in Wood (CSA O86), which in turn forms the basis for acceptance under the National Building Code.
The work has also helped to address the following issues in the CSA O86:
· Height limitations for unblocked shearwalls (currently capped at 2.44m)
· The use of diagonal lumber as sheathing for walls and diaphragms. This information, which is particularly important in upgrading wood buildings to new code requirements, addresses concerns raised by designers.
Technical information generated from this project was disseminated in the wood engineering community and CSA O86 committee meetings. Two papers entitled “Lateral Resistance of Tall Unblocked Shearwalls” and “Deflections of Nailed Shearwalls and Diaphragms” were presented at the 8th World Conference on Timber Engineering in Lahti, Finland in June 2004. An article entitled “Racking Performance of Tall Unblocked Shearwalls” has been submitted to the ASCE Journal of Structural Engineering for publication. Another article entitled “Performance of Shearwalls with Diagonally Sheathed Lumber” is being prepared and will be soon submitted to the ASCE Journal of Structural Engineering.
By proactively responding to future design code changes, this project will allow the construction industry to take advantage of various shearwall options in their designs of wood frame buildings, and will assist the wood products industry to maintain its competitive advantage in existing and new markets situated in seismic and high wind zones such as those around the Pacific Rim and in the South Eastern United States.