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.
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.
Advantages of incising veneer at the lathe are discussed in comparison with the traditional veneer incisor located prior to drying. The mechanism and design factors of veneer lathe incising are outlined and explained. A prototype incisor bar was designed and fabricated for mill trials, which indicate that it is feasible to incise veneer at the lathe by replacing a regular Big Bar with an incisor bar. The introduction of teeth to a Big Bar not only adds the incising function to the lathe, but also significantly increases the drive torque on the core, thereby reducing spin-outs. In addition, incising results in faster drying, reduced blows in pressing and flatter veneer. Trials under normal production conditions prove that the proposed incisor design works well for spruce. However, high pitch content presents plug-up problems for peeling Douglas fir. Further work is recommended to eliminate plug-ups, overcome pitch problems and optimize the incisor bar design.
Based on extensive results from laboratory and mill studies, this report focuses on the characterization of green veneer moisture content (MC) and development of a mathematical model for green veneer MC variation, establishment of the optimum clipping width and Forintek’s improved green veneer sorting method for common softwood and hardwood species. Further, the economic benefits of improved green veneer clipping and sorting were analyzed. Finally, a computer simulation program, VSort, was developed to assist mills in performing optimum green veneer clipping and sorting.
The key results show that:
the MC distribution appeared to be a dual-peak pattern for common softwood and hardwood species: one for heartwood veneer and the other for sapwood veneer, characterized by means and standard deviations of the two normal distributions. The position of the first peak (heartwood) was more consistent whereas the second peak (sapwood) varied more among logs;
the green veneer clipping should be based on the green veneer sorts with each of them having a target clipping width, which can be determined based on the shrinkage measurement of sapwood and heartwood of each species and the minimum allowable clipping width in the mill;
the green veneer sorting should be based on peak veneer MC and the size of wet spots on each veneer sheet instead of average veneer MC used currently in the mill;
with improved clipping strategy, veneer recovery can be improved by 1.0 to 2.0%, which can translate to an annual savings varying from $200,000 to $400,000 per mill;
with improved green veneer sorting strategy using Forintek’s new light transmission method, veneer drying productivity can be improved by 4.0 to 8.0% for green Douglas-fir veneer. The improvement in drying productivity also depends on the species and mill situation. Further, the improved veneer sorting helps significantly reduce the amount of overdried veneer. The improved green veneer sorting will translate to an annual savings varying from $400,000 to $800,000 per mill;
the VSort model can successfully characterize the MC distribution for common softwood and hardwood species and the relationship between peak veneer MC and average veneer MC in terms of clipping width. It can also assist mills perform optimum green veneer clipping, and establish the optimum cut-off MC levels of each sort for improved veneer drying and reduced energy consumption.
In order to help the plywood industry improve veneer production from new high-tech veneer lathes, this report evaluates present veneer block conditioning methods and techniques for possible areas of enhancement and identifies the need for new innovative instrumentation technology.
Hot pressing is a critical stage in plywood and laminated veneer lumber (LVL) manufacturing. In this study, a new hot pressing method was developed for plywood and LVL products, which integrated both pressure control and position control in one pressing cycle. The optimum pressing parameters and resulting benefits of this method were determined for panels made from stress graded Douglas-fir, white spruce and mountain pine beetle (MPB) veneer through laboratory tests and for white spruce-lodgepole pine-subalpine fir (SPF) veneer through full-size panel tests. The method was further successfully applied in a mill trial using an industrial multi-opening plywood press.
This report addresses issues about productivity, recovery and quality concerning veneer peeling in plywood mills. It was demonstrated that green veneer can be composed using a stitching technique. The maximum stitching speed was 50 ft/min which was slower than a current veneer composer. Stitched veneer did not have a significant effect on bending properties, but shear strength was slightly reduced which could be caused by the existence of stitching threads between the glueline.
The roller bar diameter size had a significant influence on veneer quality. In general, peeling veneer with a 1” diameter roller bar resulted in the smoothest veneer with the most uniform thickness. The veneer thickness and roughness between 1.0” and 2.56” diameter roller bars were significantly different, but the difference in veneer quality between 1.75” and 2.56” diameter roller bars was not significant. Further, the difference in veneer quality between 1.0” and 1.75” diameter roller bars was not significant except for veneer roughness.
Knife height also had a significant effect on veneer quality. Setting the knife at the spindle center proved to be the best. Veneer thickness at this setting was consistently closest to the target, and had the smoothest surfaces and smallest lathe checks. Average veneer thickness was lowest as well. While higher or lower settings created rougher veneer, higher settings were more forgiving than lower ones. For best results, the peeling knife should therefore be set at 0.0” to 0.015” above the spindle center.
Incisor teeth pattern affected veneer quality. Narrower teeth and a wider gap resulted in better veneer quality in terms of veneer curl-up (flatness) and green and dry veneer thickness variations. However, the effect of incisor teeth patterns on veneer roughness and lathe checks seemed to be negligible.
The validation tests revealed that an optimum lathe setting for the smooth roller bar was the following: pitch angle (PA) =89.50, vertical gap (VG)=0.425” and horizontal gap (HG) = 0.1”, and the optimum lathe setting for the incisor bar was the following: PA=90.50, VG=0.388” and HG=0.1” to 0.11” when peeling 1/8-inch veneer.
The peeling computer program VPeel® was successfully upgraded to allow users to define profiles of pitch angle and horizontal gap. This feature will help the veneer product industry to define optimum lathe settings.