Potential market gain for Canadian softwood plywood in residential construction could arise from the emerging Chinese market to build massive numbers of affordable apartments and the upcoming rebuilding effort in Japan following the earthquake and tsunami disaster. Compared to the main Chinese species (poplar), common BC species, such as Douglas-fir, spruce and hem-fir, have competitive advantages in the aspects of log diameter, wood properties and veneer quality and processing productivity. For non-residential construction, Canadian plywood concrete forms also offer competitive advantages over Chinese overlaid poplar counterparts due to their higher stiffness and strength. However, the production cost has to be kept to below US$ 500/m3 for a profit margin. Further, three-ply and four-ply Canadian softwood plywood panels are ideally suited for the base materials of multi-layer composite floor, which currently is gaining momentum in China and other countries.
A sizeable increase in industrial and remodelling market is anticipated for the Canadian plywood industry. This will be mainly driven by a number of specialty plywood products, such as container floor and pallet, light truck, utility vehicle, trailer and camper manufacturing. However, these products are not commonly manufactured by larger commodity manufacturers in Canada. China is currently the largest global supplier of container floors, most of which are made from imported plywood, bamboo and poplar veneer. To meet their stringent requirements and gain a market share, Canadian plywood industry should take appropriate actions in adjusting veneer thickness, veneer grade, veneer treatment, and panel lay-up.
Japan has developed customized products such as oversized plywood for wall applications, and termite/mould resistant plywood for above ground and ground-contact applications. China has developed numerous new value-added veneer products for niche markets. Such products include marine plywood, sound reducing plywood, non-slip plywood, metal faced plywood, curved plywood and medium density fiberboard (MDF) or particleboard (PB)-faced plywood.
In order to stay competitive in the global market, Canadian plywood industry needs to:
remove the trade constraints between softwood plywood and hardwood plywood,
remove in-plant manufacturing barriers to deal with both softwood and hardwood processing,
diversify products for both appearance and structural based applications, and
develop new value-added products for niche markets.
This study suggests the following opportunities for Canadian plywood producers to
incorporate naturally decay-resistant species such as cedar as surface veneer and/or perform veneer or glueline treatment to make marine and exterior plywood for improved durability,
characterize veneer properties from the changing resource for better utilization,
peel some thinner and higher quality veneer for making specialty plywood,
conduct stress grading in combination with visual grading to maximize value recovery from the available resource,
increase the flexibility of panel lay-up for domestic/overseas markets and various applications,
develop mixed species plywood by mixing available hardwood species such as birch, maple, alder, aspen veneer (as overlay materials) with softwood plywood to achieve better appearance and higher performance,
develop new structural composite lumber (SCL) products such as veneer strand lumber (VSL) from low quality logs, particularly beetle-killed, and random veneer or waste veneer,
develop new drying, pressing and adhesive technologies for processing high moisture veneer, particularly hem-fir and spruce, to improve productivity and bond quality and reduce panel delamination,
develop light weight and strong hybrid plywood panels for furniture applications, by adding MDF or PB on the face of plywood,
develop hybrid plywood for floor applications to reduce thickness swell and increase dimensional stability and stiffness,
develop hybrid cross-laminated timber (CLT) panels from lumber, plywood and laminated veneer lumber (LVL) for low- and mid-rise residential and non-residential applications, and
develop a series of new product standards for specialty plywood.
A market research study for each product opportunity is recommended to develop a solid business case for each.
In plywood mills finished panels are manually graded and sorted based on specific defects. The panel edges are especially difficult to grade by human visual inspection due to the small nature of different defects, especially at higher line speeds. This can result in misread errors that can be costly.
In this project a prototype scanner, based on 3D laser profilometry, was developed by FPInnovations and demonstrated in two Canadian plywood mills for automatic edge grading. At both mills, panels were scanned on the production line in real time, collecting full length, 3-dimensional edge profiles in the x, y and z coordinate fields that were then analyzed by computer software sub-routines to identify defects for each panel. The data was processed to categorize groups of data points, depending on the edge profile depth (z-axis) variation, length (x-axis) and height (y-axis) into the specific defect categories of core, top and bottom edge void, core gap and core overlap, based on the values of predetermined edge profile thresholds.
Results from the two mill tests showed that the scanner was effective with a correct identification rate greater than 80%. The lack of panel hold-downs at each mill resulted in extreme height variation of the panel edges and this limited the defect detection accuracy. Based on the tests, the technology for automated edge grading is feasible. Longer term mill evaluations are recommended with adequate panel hold-downs in place before confirming that this technology is ready for commercialization.
Wood failure evaluation is the key criterion for predicting the long-term durability of plywood. At present, the conventional visual method for plywood wood failure evaluation is slow and subjective. Evaluations can be influenced by factors such as: room lighting, wood species, sample treatment, and readings from prior samples. An automated wood failure evaluation system using image analysis techniques could potentially be programmed to consider all the variables and respond with consistent wood failure values regardless of the machine operator's experience level. This report describes the results of a six-month study in which a system for automated plywood wood failure determination was compared with conventional visual wood failure evaluation. It was built upon research undertaken in the 1996/97 year in which the feasibility of the approach was initially established. In the research reported previously, a colour optical imaging system was assembled and suitable wood failure algorithms were compiled with promising results. The imaging system was 100 % effective in reproducing sample values. The data were discussed with the project liaisons and a three-month comparison with Canply readings was suggested. In this study, machine evaluation of 4,150 samples was compared with readings of monthly plywood mill quality control samples. The sampling was designed to include all British Columbia plywood mills and all categories of commercial plywood production. The differences in average values for wood failure between human and machine evaluation were found to be less than plus or minus 5% in the majority of cases. In addition, 93 % of ‘set average' readings fell in the plus or minus 10% range of deviation expected of human wood failure readers. Agreement on readings of individual samples within each set was not quite as good with 72% falling in the plus or minus 15% range.
Wood failure evaluation is the key criterion for predicting the long-term durability of plywood. At present, the conventional visual method for plywood wood failure evaluation is slow and subjective. Even experienced evaluators can show significant differences in their evaluations on the same plywood specimen and an individual evaluator can make different wood failure estimates on the same specimen at different times. Differences among evaluators can be as high as 50% for some samples. Evaluations can be influenced by room lighting, the wood species, sample treatment, and readings from prior samples. An automatic wood failure evaluation system using image analysis techniques could potentially be programmed to consider all the variables and respond with consistent wood failure values regardless of the experience level of the machine operator. This report describes the results of a one-year project in which a system for automatic plywood wood failure determination was investigated. A color optical imaging system was assembled and the preliminary work of compiling suitable algorithms was completed with promising results. The imaging system was 100% effective in reproducing individual sample values. Samples were sorted according to plywood type and test method to develop appropriate program algorithms for each category. The wood failure program was then further developed to automatically detect wood species and test method, thus avoiding the need for specimen separation prior to evaluation. Based on nearly 1200 samples in four categories, the differences in average values of wood failure between human evaluation and machine vision were found to be less than plus or minus 5%. In addition, a minimum of 85% of individual machine readings fell in the plus or minus 15% range of deviation expected of human wood failure readers. The imaging system was more accurate for light-colored specimens (i.e., Canadian Softwood Plywood) than darker-colored specimens (i.e., Douglas fir ) and for specimens where resin had been applied by spray. In order to make the imaging system more reliable and robust, the algorithm parameters now need to be fine-tuned based on a larger sample database.
Delamination currently accounts for approximately 85% of customer complaints about plywood as a sub-flooring product. It has become an urgent issue to many of our plywood members. It is estimated that by merely reducing 1% delamination in a 250 million ft2 (3/8 –in basis) plywood mill, the potential annual savings will be approximately $650,000. To help reduce plywood delamination, the key objective of this project was to develop a generic best practice checklist as a guide for manufacturing plywood.
A generic best practice checklist for manufacturing plywood was compiled with a focus on the following four key checkpoints: veneer peeling, veneer drying, panel gluing/lay-up and hot pressing. Key process variables at each checkpoint were determined as follows: peeling related veneer surface roughness and thickness variation, drying related veneer moisture content (MC) variation and surface inactivation, veneer temperature, glue coverage and dryout, and pressing time and pressure. Some technical issues were proposed to revisit as a strategy to reduce panel delamination. Among them include optimal lathe bar gap and pitch profiles, and proper knife sharpening for peeling, reduction of veneer overdry during drying, real-time adjustment of glue spread for adequate glue coverage, and use of optimum pressing time/pressure for adequate level of panel compression and glue curing. The resulting generic checklist can be modified for individual mill use.
Through literature review, pilot plant tests, and mill trials, the main causes of panel delamination were identified as: 1) glue dryout from long assembly time and high veneer temperature; 2) low panel compression, light glue spread or glue skips due to rough veneer; 3) little glue transfer due to veneer surface inactivation; 4) inadequate glue cure due to heavy glue spread, overwet veneer, sap wet spots, and short pressing time; and 5) combined effects of the above. It was found that veneer surface roughness had a significant effect on plywood gluebond quality, and excessive roughness and combined effect of veneer roughness, overdry, and glue dryout, were key causes of the low percentage wood failure. A statistical model was also developed from mill trials to predict the percentage wood failure in terms of veneer temperature, open assembly time and glue spread. The model helps establish an operating window for each key variable and adjust the gluing/layup process to reduce glue dryout. Furthermore, a practical method was developed to determine the optimum pressing parameters to achieve target gluebond quality while minimizing plywood thickness loss.
In this work, the properties of aspen veneer from two mills (A and B) were compared. The comparisons between the incised veneer and non-incised veneer for mill A were made in terms of veneer thickness, ultrasonic propagation time (UPT), density and MOE. The aspen veneer was further characterized for LVL/plywood products by tailoring veneer grades to the requirements of final veneer products. In addition, MOE-based veneer stress grading and UPT-based veneer stress grading were compared for the aspen veneer. The advantages of MOE-based veneer stress grading over UPT-based veneer stress grading were identified in terms of veneer grade MOE and volume breakdown. The main results are summarized as follows:
1) Aspen veneer properties change from mill to mill. The differences in aspen veneer density and MOE between mill A and B are significant with mill A producing denser and stronger aspen veneer.
2) For aspen veneer in the mill A, the distribution shapes of veneer thickness, UPT, density and MOE between the non-incised and incised veneer are quite similar. Although the differences in veneer thickness, UPT and density between the non-incised veneer and incised veneer are identified as significant, the difference in veneer MOE is not significant due to the effect of both veneer UPT and density. The incised veneer has a slightly higher variation in thickness and is also slightly thicker compared to the non-incised veneer. This could due to the change of lathe settings or the property variation of aspen species as indicated with the veneer density variation.
3) Of the aspen veneer from mill A, using the optimum UPT thresholds, about 27.5 ~ 30.9% can be extracted through veneer stress grading to make 2.0 million psi LVL; about 43.4 ~ 59.9% can be sorted out for 1.8 million psi LVL; and the remaining 12.6 ~ 25.7% can be used for 1.5 million psi LVL or for plywood. It was also found that the incised aspen veneer generates 3.4% less of top stress grade G1 but 16.5% more of stress grade G2 compared to the non-incised aspen veneer if performing the optimum UPT-based stress grading.
4) The MOE-based veneer stress grading not only results in a smaller variation in MOE of each grade, but also higher volume percentages of stress grades G1 and G2 compared to the UPT-based veneer stress grading. This smaller variation in MOE of each stress grade will be very beneficial to the industry and structural applications since higher design stress can be assigned for the wood structural components. Also the higher percentages of stress grades G1 and G2 with the MOE-based veneer stress grading has significant economical implications and should be recognized by the industry.
5) To maximize mill profits, veneer sheets need to be periodically sampled and analyzed using the VGrader software. The optimum grading thresholds for the specific veneer can be established for on-line veneer stress grading based on the current market and requirements of final veneer products, providing a real solution to characterize and make best use of the specific veneer for LVL/plywood products.