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.
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.
Within the limits of this study, the results indicate that it is quite possible to develop new Engineered Structural Lumber products from MPB wood and to maximize its value for uses in traditional and next generation wood buildings. New product and processing technologies have to be developed first to convert severely dried and checked MPB wood into competitive structural lumber products. Further research and development, particularly in stranding technology for dry logs is recommended.
In this study, several types of oriented strandboard (OSB) panels were compared including those prepared using a novel method involving the application of plastic film directly to the OSB faces by hot-pressing. Different edge seal methods were also evaluated. A flooring simulation test involving both water spray and drying cycles was used to evaluate the dimensional stability performance of the OSB panels. In total, three tests were carried-out to evaluate the swelling properties of OSB panels with different edge seal and face plastic cover combinations.
Results showed that when plastic coated panels were installed in the flooring simulation set-up and then sealed around the edges with tape, the edge and inside edge thickness swelling could be significantly reduced compared to control panels. Also, the panels with a plastic covering on both faces warped less and recovered better after air-drying compared to panels with plastic film on the top face only.
This study has shown that when panels are first coated with plastic by hot-pressing and then sealed around the edges with tape after installation, thickness swell and warping can be minimized. This method is especially promising for providing sufficient protection of OSB when used in flooring applications which are exposed to short-term exposure to wetness due to weather exposure.
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.
Phenolic glue extenders/fillers from mountain pine beetle (MPB)-attacked wood (sander dust, bark and wood particles) were developed as substitutes for corncob to reduce the costs of plywood manufacturing. Laboratory tests of the bonding performance of plywood panels produced with these new glue mixes generally exceeded the standard requirements for Canadian plywood in terms of wood failure percentage under both vacuum-pressure and boil-dry-boil conditions. All alternative extenders/fillers, except one: mountain pine beetle bark, increased the viscosity of glue mixes. The glue mix formulations may need to be adjusted in commercial production to minimize the impact on the glue application process.
Among these alternative glue extenders/fillers, sander dust is the most promising substitute for corncob since it is a by-product from the production of medium density fiberboard (MDF) production or particleboard, and as such has little value. With little treatment, it can be applied in a phenol-formaldehyde (PF) glue mix to partially or fully substitute for corncob. This will reduce cost and ensure a steady supply of extenders/fillers.
It is recommended that a mill trial be conducted to confirm and quantify the economic benefits.
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.
Veneer incising at the lathe, a new technology developed at Forintek, has been increasingly applied in the Canadian softwood plywood industry. The benefits include reducing veneer curl-up and spin-outs and increasing veneer recovery. However, a comprehensive study of the effect of veneer incising on veneer stress grading and LVL strength properties has not been thoroughly undertaken. In response to requests from our Forintek member mills, this report investigated the effect of veneer incising on the veneer stress grading and strength properties of spruce LVL products. Both incised veneer and non-incised veneer were peeled with blocks from same log using a Forintek mini-lathe equipped either with incisor bar or smooth roller bar. Then veneer sheets were randomly and proportionally sampled from the peeled veneer ribbon. These veneer sheets were stress wave tested and used to make LVL panels. The t-test was used to examine the significance of the differences in veneer stress wave time (equivalent to UPT) and LVL panel mean strength properties. The results showed that:
Veneer incising did not significantly affect veneer stress grading (identified by the measurement of veneer stress wave time or UPT), veneer density and veneer MOE.
Veneer incising also had no significant effect on the spruce LVL conventional hot pressing times for the core temperature to rise to 1050C and LVL compression ratio.
Further, there were no significant differences in LVL edgewise bending MOE, MOR and block shear strength parallel to grain between the non-incised and incised veneer. However, the difference in mean LVL block shear strength through-the-thickness between the non-incised veneer and incised veneer was significant. The block shear strength through-the-thickness using the incised veneer was slightly lower compared to that using the non-incised veneer using a glue spread level of 32 lbs/1000 ft2 per single glueline. A previous study showed that at higher glue spread levels normally used for LVL, 40 lbs/1000 ft2 per single glueline, the block shear strength through-the-thickness was slightly higher for the incised veneer compared to that using the non-incised veneer.
VGrader, Veneer Grading Optimizer, was developed at Forintek to assist mills to optimize on-line veneer stress grading operations. So far, more than 10 copies of VGrader 1.0 software have been delivered to Forintek member mills. The software can recommend the optimum grading thresholds through analyzing the properties of veneer to help mills deal with “what-if” scenarios when veneer species, log source and diameter as well as final veneer products change. By tailoring veneer grades to the market requirements of LVL/plywood products, the software serves as a useful tool to characterize specific veneer for end use and help optimize veneer on-line stress grading and products lay-up options.
During the past year, the VGrader software has been upgraded to deal with either UPT-based (ultrasonic signal propagation time) veneer stress grading or E-based (modulus of elasticity) veneer stress grading or veneer visual grading. The software has also been upgraded to accommodate UPT data either from mills or laboratory testing of veneer samples. A direct linkage between laboratorial measurement span and desired wheel-span of the on-line grading system was also setup. The current version of the software is VGrader 3.0. To help mills optimize current on-line stress grading operations, the proper procedures to find the optimum UPT thresholds were established.
The proper procedures are as follows:
1) Sample veneer sheets representative of veneer population in the mill and perform stress wave testing for sampled sheets using a portable stress wave timer. Alternatively, full-size veneer sheets can be sampled right after the on-line grading system with UPT data being recorded for each veneer sheet;
2) Measure other relevant veneer properties such as thickness, density, moisture and knots;
3) Calibrate the stress wave time (or UPT) to find its zero offset value;
4) Store all measurement data into a VGrader compatible database;
5) Use the upgraded VGrader software to examine the distribution of veneer attributes/properties such as thickness, UPT, density and MOE;
6) Derive required veneer MOE based on the performance requirements of target veneer products;
7) Establish stress grading constraints and using VGrader 3.0 to perform computerized veneer stress grading through adjusting the UPT or E thresholds and examining the change of statistical veneer MOE, densities and volume breakdown per grade until all the grading constraints are satisfied;
8) Convert the optimum set of UPT or E thresholds from the VGrader software into those used for on-line veneer grading system to perform stress grading;
9) Make veneer products and test them to validate the grading results.
An example of establishing the above procedures was also demonstrated.
It is important to improve drying productivity since this process is the bottleneck in plywood production. To address this issue, we evaluated the veneer moisture content (MC) distribution and the accuracy of radio frequency (RF) sensors both in the laboratory and in mill trials in this study.
We analyzed the distribution of green veneer moisture content (MC) and density from sapwood to heartwood for lodgepole pine logs via veneer peeling in the Forintek’s composites pilot plant. The results show that the MC distribution appears to be a dual-peak pattern both for heartwood and for sapwood. The position of the first peak is more consistent whereas the second peak varies more among logs. This information is useful for determining the proper number of green veneer sorts and the optimum cut-off MC level for each sort.
Readings of the radio frequency (RF) sensor are affected by veneer species, veneer density, veneer thickness, temperature, green veneer MC, grain angle, and distance between the sensor source and veneer surface. Of these variables, veneer density, veneer species and the distance are found to be the three main factors affecting the readings of the sensor. Based on the measurement results from different species, we conclude that the RF sensor is only suitable for measuring green veneer MC below 80%.
The correlation between readings of the sensor and green veneer MC varies from species to species. In general, this correlation could be improved using an exponential or a power equation. The readings of mill sensor are more inconsistent than those of the lab sensor for the heart sort veneer. The lab sensor underestimates MC for the heart sort veneer and overestimates MC for the sap sort veneer. However, the mill sensor overestimates in both positive and negative ways for each sort. To improve the accuracy of the readings, the sensor needs to be calibrated based on the species and veneer thickness, and the distance between the sensor source and veneer surface has to be kept as small as possible. However, this is not practical for the spruce, pine and subalpine fir (SPF) group since these species are not separated on a commercial basis.
We conducted three mill visits to: 1) measure the distribution of green veneer MC for different veneer sorts, and 2) assess the accuracy of current green veneer sorting. The results demonstrate that the accuracy of moisture sorting differs among mills and species, and the species mix like SPF generates larger MC variation within each sort. In general, the heart veneer sort is well done, but there is a significant overlapping between light-sap and sap veneer sorts. This indicates that the current industrial RF sensors cannot ideally sort higher MC veneer. The results also show that there is potential for more accurate green veneer sorting which would result in a 5% increase in drying productivity. This improvement would generate more than $1 million in annual savings per mill.