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.
A software, by which virtual 3-D subalpine fir (Abies lasiocarpa [Hook] Nutt) logs can be re-created, visualized, and theoretically sawn an infinite number of times, was developed. The software also facilitates obtaining data for determining quantitative variation of clear wood, wet-wood, and knot patterns within the tree stems.
Results based on the quantitative calculations showed that there are two general patterns of wet-wood within the sub-alpine fir stems. The first pattern is called wet-pocket and the second pattern is called wet-streak. Wet-streak patterns are generally confined to the medullary-inner heartwood regions in the outer heartwood and heartwood-sapwood transition zones of the tree stems, mostly associated with dead knots. Wet-pocket patterns consist of portions occurring in mid regions in close proximity to the base and regions mostly around partially dead knots of the tree stems. Both wet-wood patterns usually converge at the nodes and extend along the branch axes, forming a connection with the exterior boundary only around branches.
Numerical analysis of the results showed that the volume of both types is more prevalent in the lower-stem regions, becoming less prevalent towards the living crown. The radial extension of wet-wood types with radial distance from the tree centre was variable, with a maximum diameter of 22 cm. Both wet-wood volumes increased with increasing tree age and diameter class independent of age. However, the percentage of total wet-wood volume decreased with increasing DBH, increased stem height and showed no clear trend with age class. Total amounts of wet-wood ranged up to 27 per cent in individual stems. A weak relationship was found between dead knot-pattern and wet-streak pattern volumes, while a moderate high relationship was found between partially dead knot and wet-pocket volumes. A weak relationship was found between external tree characteristics and both wet-wood distributions.
As a result, some promising trends emerged for a better understanding of wet-wood and knot pattern variations as influenced by tree stem locations, DBH, and age. The developed software may offer a compelling technique for assisting subalpine fir log processing decisions. However, the destructive data collection method used in this study is “error-prone”. Therefore, an interesting alternative would be the use of more accurate non-destructive scanning techniques, such as CT-scanning, to verify the trends identified here through more deliberate sampling at other forest sites. A new study is already underway to meet this need.
Work is underway to prepare a preliminary design of a 3-storey office building using this new modular construction system. This application is helping to understand and improve configurations of prefabricated column and beam modules proposed for the new construction system. The use of standardized prefabricated connections in modules and between modules will contribute to the quality of construction and ease of design. The development of a flexible modular prefabricated construction system based on engineered wood products will also simplify the conceptual design process. The conceptual design of a class of buildings will only require selection of a few specific prefabricated column and beam modules with predetermined load carrying capacities, which may be guaranteed by testing or analysis.
Building construction - Design - Computer simulation
Continuous drying is still in its relatively early stages and mills are currently dealing with process adjustments to obtain desired throughput and quality of the final product. Field measurement carried out in 2015-16 illustrated a number of opportunities for process optimization involving each of the three main stages of current continuous kilns. Simulations of industrial continuous drying at laboratory level performed in 2016-17 were successful and allowed the evaluation of each of the drying stages to be fully characterized (lumber temperatures, drying schedule conditions of dry and wet bulb temperatures). Thus, different drying schedules provided an excellent opportunity to examine the impact of schedule conditions on drying defects, drying rates and kiln residence times.
The main objectives of the project for 2017-18 were to simulate continuous drying in laboratory conditions for different products, products mix, species and green sort groups. In addition, a detailed evaluation of potential technologies was carried out to explore the concept of dynamically adjusting speed (push rates), based on drying rates and moisture content.
Piecewise regression was used to identify the optimum push rate and suggest design modifications of continuous kilns. This method proved to be efficient in identifying potential reductions in drying time for different sorts of sprue/pine (SP) lumber without compromising the quality of the final product. Simulations also allowed identifying the push rate of 2 feet/h to satisfactorily dry green hem-fir 2-inch lumber.
Initial tests showed that mid-sort sub-alpine (moisture content below approximately 70%) could not be mixed with wet sort SP in a continuous kiln operating at push rate of 4.2 feet/hr because only 73% of the sub-alpine sort dried below 21%. Decreases in push rate will reduce the percentage of sub-alpine fir wets but will also increase the amount of over-dried lumber. Changes in kiln configuration may reduce the drying time but increase the percentage of over-dried lumber.
The results indicated that additional laboratory tests are required to develop drying schedules and temperature profiles in the main drying zone of continuous kilns, drying times and final moisture content distribution.
This report presents the main factors to consider in evaluating the economic impact of using a dispersed block layout rather than traditional clearcuts separated by narrow leave strips. The costs related to the construction, maintenance, and restoration of roads, as well as travel by forestry machines and haul trucks and the indirect harvesting costs, are illustrated using a hypothetical example. An Excel spreadsheet is available so readers can perform comparative analyses based on their own operating conditions.
In an effort to promote the adoption of manufacturing strategies that more closely match the Eastern resource supply, simulation work was conducted with SAWSIM to investigate the benefits of implementing innovative conversion technologies such as: computer optimized bucking (COB), curve sawing technology, and cant optimization technology.
Simulation results for COB clearly indicate that the implementation of computer optimized bucking generates significantly better volume and value recovery than achievable from operator derived bucking solutions.
Comparison of curve sawing and cant optimization simulation results show that both technologies have the potential to improve present efficiency levels by at least 10 percent.
FERIC and the Faculty of Forestry of the University of British Columbia (UBC) developed a computer model, for use at the cutblock level, to predict the net revenue of coastal second-growth stands that are to be clear-cut or partial cut. Cruise data and company sort descriptions are used to predict volume by sort and timber value. Productivity and cost data from within the model, or as defined by the user, determine the total harvesting costs for an operation. Net revenue is obtained by subtracting the harvesting cost from the timber value. At two harvesting sites near Powell River, B.C., the predicted total volumes and timber values were within 5% and 3% of scaled volumes and actual values, respectively.
The increase in forest road grades on the coast of British Columbia has led to hauling safety concerns. To investigate this issue and to develop guidelines for hauling on these steep grades, the Forest Engineering Research Institute of Canada (FERIC) installed instrumentation on a coastal off-highway truck to measure braking energy requirements during typical steep grade descents. FERIC used the data to develop a computer model for predicting brake performance for steep grade descents and to develop descent guidelines for several operating conditions.
Statistical process control (SPC) involves using statistical techniques to analyze and monitor the variation in manufacturing processes and maintain processes to fixed targets. The use of SPC will greatly enhance the in-mill quality control program. To demonstrate the benefits of applying SPC in general panelboard products, the current member mill application of SPC was first reviewed in this study. Mill visits and a survey were conducted to identify and prioritize the areas for improvement in plywood manufacturing. Key process variables were determined in terms of product performance, productivity and material recovery. Subsequently, different SPC statistics/control charts were reviewed and effective tools for process control were selected. A two-step sampling and statistical analysis method was established for panelboard quality control with a given confidence level. Coupled with this panelboard quality control module, an integrated computer software program, PanelSPC®, was developed for mill data acquisition, data analysis and decision-assistance. The software helps establish histograms and X-bar and Range (R) (or standard deviation, s) control charts for a given process variable and can perform process capability analysis.
To address the No. 1 issue, i.e., panel delamination in plywood manufacturing, a practical SPC approach was established. A cause-and-effect diagram was first constructed to identify the checkpoints and key variables involved in the manufacturing process. A histogram chart (Pareto) was then established to: 1) find the root causes of panel delamination due to a low percent wood failure; and 2) identify potential process variables overlooked in the current practice. Mill and laboratory studies were conducted to investigate the effect of key variables on panel gluebond performance using an experimental design approach. The results revealed that panel pressing time and compression ratio (CR) had a tremendous effect on panel gluebond quality. This led to a new direction to reducing panel delamination.
As a case study, a production data set of dry Douglas-fir heart veneer width was collected and imported into the PanelSPC® software for statistical analysis. With this off-line SPC tool, the distribution, X-bar and R control charts of the dry veneer width were established. The trial control limits were computed and then revised for continuous production monitoring. The assignable causes were subsequently identified to maintain the dry veneer width under statistical control with less variability. However, in this case, the dry veneer width was still centered incorrectly with many sheets being out of the specification limit. This problem was ultimately tracked to the wider clipping width resulting from inaccurate green veneer sorting. It was demonstrated that with a proper application of SPC, the assignable causes and upstream (in this case) or downstream problems can be detected. By adjusting veneer drying control and green veneer moisture sorting, dry veneer width can be tightly controlled, resulting in approximately 1.9% recovery improvement or about $300,000~$450,000 annual savings for an average plywood mill.
With the off-line PanelSPC® tool, sources of process variability can be detected and the manufacturing process can be modified and better controlled to attain greater material recovery, increased product quality and productivity.
