Laminated Veneer Lumber (LVL) and plywood are the two major veneer-based wood composite products. During LVL/plywood manufacturing, the hot pressing process is crucial not only to the quality and productivity, but also to the performance of panel products. Up to now, the numerical simulation of the hot-pressing process of LVL/plywood products is not available.
To help understand the hot-pressing process of veneer-based wood composites, the main objective of this study was to develop a computer simulation model to predict heat and mass transfer and panel densification of veneer-based composites during hot-pressing. On the basis of defining wood-glue mix layers through the panel thickness, a prototype finite-element based LVL/plywood hot-pressing model, VPress®, was developed to simulate, for the first time, the changes of temperature, moisture and vertical density profile (VDP) of each veneer ply and glueline throughout the pressing cycle. This model is capable of showing several important characteristics of the hot-pressing process of veneer-based composites such as effect of glue spread level, veneer moisture, density, platen pressure and temperature as well as pressing cycles on heat and mass transfer and panel compression. Experiments were conducted using several different variables to validate the model. The predicted temperature profiles of the veneer plies and gluelines (especially at the innermost glueline) by the model agree well with the experimental measurements. Hence, the model can be used to evaluate the sensitivity of the main variables that affect hot-pressing time (productivity), panel compression (material recovery) and vertical density profile (panel stiffness). Once customized in industry, the new model will allow operators to optimize the production balance between productivity, panel densification and panel quality or stiffness. This hot-pressing model is the first step in facilitating the optimization of the pressing process and enhanced product quality.
In the construction of buildings, the timber-concrete (TCC) system can be a cost-competitive solution for floors with longer spans, since the mechanical properties of the two materials are used efficiently. Furthermore, the additional mass from the concrete improves the acoustic performance compared to a timber floor system alone. Nevertheless, TCC floors are not commonly used in buildings in Canada, due to the absence of technical guidelines for such types of structural systems in this country.
The new technologies, incising, moisture tolerant phenolic adhesives and steam pressing were evaluated for the manufacture of laminated veneer lumber (LVL). Both 8- and 13-ply incised spruce LVL panels were prepared using these new technologies. The results showed that both steam pressing and self-generated steam from wet face and back veneers accelerated temperature rise in the innermost glueline of 13-ply incised spruce LVL panels. This would help facilitate faster production rates for LVL manufacture. Bond quality and edge bending values were determined for the steam-pressed 8-ply and 13-ply incised spruce LVL panels. In all cases the average % wood failure was above 90% indicating excellent adhesion between the moisture tolerant adhesive and wood. The modulus of rupture and modulus of elasticity values measured for the steam-pressed incised spruce LVL samples compared very favourably with those for a commercial Norway spruce 15-ply LVL product.
Six impregnating phenol formaldehyde (PF) resins having low to moderate molecular weight were synthesized and evaluated for their wood veneer penetration and curing properties. Based on the results from the penetration and curing properties studies, a PF resin designated as B-2 was used to impregnate subalpine fir, white spruce and lodgepole pine veneer. LVL panels, 12 x 12 inch, were prepared with these veneers. Both modulus of rupture (MOR) and modulus of elasticity (MOE) were increased by 10 to 15% for the resin-impregnated LVL made from each of the SPF species. Edgewise bending results for specimens cut from 2 x 4 foot white spruce LVL panels showed an increase of 15% both for MOR and MOE for the resin impregnated specimens. As well, the dimensional properties (% edge swelling and % water uptake) of the SPF LVL panels were improved by 50% using the patented Forintek resin impregnation method.
A series of plywood and laminated veneer lumber (LVL) panels were prepared using veneers with higher than normal moisture contents in face and back layers. The purpose of the work was to evaluate the effects of self-generated steam on the pressing times and panel warpage. Panels made with 6% and 10% m.c. faces and backs were compared with control panels made with all dry veneer. Thirteen- ply 40 mm (1 5/8 inch) thick panels were evaluated for press times and thin 9.5 mm (3/8 inch) panels were evaluated for cupping and bowing. Normal plywood press temperatures and adhesives were used. All panels were made with incised 3.2 mm (1/8 inch) SPF veneers. The project demonstrated that substantially shorter press times and more dimensionally stable panels can potentially be made using higher moisture content outside veneers.
A series of plywood and laminated veneer lumber (LVL) panels were prepared using incised veneers in the second phase of this two year project. The primary purpose of the work was to evaluate the effects of steam injection on the pressing times. A secondary objective was to expand the study of warpage in three-ply and four-ply plywood which was begun in phase one. Thirteen-ply 40 mm (1 5/8 inch) thick panels were evaluated for press times and thin 9.5 mm (3/8 inch) and 12.5 mm (1/2 inch) panels were evaluated for cupping and bowing. Press temperatures of 150 degrees C, 175 degrees C and 204 degrees C were used with a commercial adhesive mix for the LVL study while normal plywood pressing conditions were used for the plywood. For the plywood warpage study, the effect of lathe check orientation and species mix were evaluated. The lathe check orientation had little effect while the surface veneer species had a pronounced effect on the warpage in the plywood. Steam used for injection was heated to 260 degrees C at 450 KPa (65 psi) with a super-heater. All panels were made with incised 3.2 mm (1/8 inch) SPF veneers. The project demonstrated that steam injection can shorten press times by fifty percent if incised veneers are used.
Forintek has completed a two-year investigation of the NLGA SPS 6 Standard, Special Products Standard for Structural Face-Glued Lumber. The NLGA SPS 6 Standard prescribes product specifications and qualification and quality control requirements for structural products created by edge-gluing and/or fingerjoining lumber segments. Under the NLGA SPS 6 Standard, the design values assigned are based on the visual grade and the stress level achieved in qualification tests on the glue joints.
The project assessed the effect of the following three factors on strength of the NLGA SPS 6 product:
1. Tension proof-loading;
2. Relative location of fingerjoints in adjacent members when fingerjoined material is edge-glued;
3. Strength of the material used to make the NLGA SPS 6 product.
Results showed a positive effect of proof-loading, a minor effect of staggering of fingerjoints, and a highly significant effect of density of raw material on tensile stress of edge-glued specimens. It was confirmed that SPS6 products of greater commercial value can be obtained from lower grade lumber. However, visual grading of SPS 6 products proved to be more difficult than visual grading of lumber, because grade-determining wood characteristics were sometimes hidden in the bond line, and could not be properly identified.
The findings of this project can be used to fine tune the NLGA SPS 6 standard and the other NLGA fingerjoint and face-glued lumber product standards. The project will help the wood industry maximize the utilization of their raw material resource, resulting in increased profitability.
A lathe monitoring system has been developed and successfully tried in a mill. The system can measure the position, the hydraulic driving pressure and contact pressure of the backup rolls, the position and the hydraulic driving pressure of the roller bar, the position and contact pressure of the knife carriage against the peeler block and the driving torque of the spindle motor. Some of the monitored data points required additional sensors which were then connected to and then downloaded directly from the lathe controller, i.e., PLC and VME. The results showed that the lathe parameters vary significantly with time and knife position. The backup roll offsets control the lathe performance and peeling quality, particularly spin-out rate and veneer thickness variation. The best results seemed to come from the combination of tighter outer offset and looser inner offset.
Further work is needed to fine tune the software program for user-friendly data analyses. More mill tests are required to understand the interactions between the backup rolls, the roller bar, the knife and the block.
FPInnovations launched a multi-year research project to measure mid- to high-rise wood buildings’ natural frequencies and damping ratios to expand the database and validate or adapt the existing equations to estimate the natural frequencies. Two high-rise wood buildings equipped with an anemometer and accelerometers are also being constantly monitored to study how the wind excites the building.
This report investigated the effect of veneer incising (incisor teeth patterns) on conventional hot-pressing time and compression behavior of spruce LVL/plywood. The 4 factors taken into account were panel type (LVL or plywood), number of panel layers, veneer moisture content and veneer type. Three veneer types were considered: non-incised veneer, lightly-incised (lathe-incised) veneer and heavily-incised veneer (similar to veneer incising in front of dryer). The three veneer moisture levels considered were 0%, 3% and 6%. The number of panel layers used was 5, 9 and 13. A mixed-level experimental design was employed. Using a statistical software program, JMP, the main factors affecting the LVL/plywood hot-pressing time were identified.