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.
This study was conducted with the aim of assessing the effects of log storage time and conditions at a BC mill yard on veneer production under mill production conditions. The second objective was to validate the FPInnovations LogdryTM drying model for developed for wood piles in Eastern Canadian mills. The software was used to generate drying rate predictions under the BC mill’s prevailing weather conditions and storage times for comparison with some measured residual moisture contents of Douglas fir logs kept in storage at the mill for six and nine months, sampled and peeled in a laboratory trial in 2016.
The 2016 lab trials suggested little effect of lengthy (winter) storage up to 9 months but mill experience suggests this is excessively long and logs deteriorate in terms of veneer production and quality considerably earlier. Unfortunately due to experimental circumstances the mill peeling trials for the 9 month stored logs were unable to provide an accurate assessment of the true effect on production. Mills trials indicated % heavy sap had remained fairly stable largely within the mill target of 14% to 17% over the storage periods. During the mill trials there were unavoidable heavy confounding effects of different average diameter for log groups and peeler knife condition affecting the expected veneer production variables.
The trials also demonstrated how pile size and height play a major role in protecting logs from drying; with very dry logs having a deleterious effect on veneer production. Logs held in small piles for 12 months or more, even with artificial ‘drying retardants’ such as end sealant and tarping were too dry for reliable peeling, causing very rapid knife wear, spinouts, veneer break-up and line blockages and significant lost recovery. The % heavy sap offtakes from these trials were just 2% to 4%.
LogDryTM provides a fairly good estimate of likely drying rate trends of mid-sized (35 cm/14” to 41 cm/16” range) Douglas fir under the BC mills historic weather conditions over 6 and 9 months.
LogDryTM (Birch setting) was closest to measured log MC in large diameter (46 cm/18”) logs but the Aspen setting was closer to measured MC in small logs (<30 cm/12”). In the limited sample of logs available from the mill in 2016 the 12” logs were much drier after 9 months storage than the model predicted, even on the Aspen setting. Further sampling of piled logs in the small diameter range is needed to verify this observation.
LogDryTM was used to estimate drying rates of logs stored before or after Summer. Modelling indicated a shorter viable storage window for logs delivered before Summer compared to just before Winter, especially in the 6-month range. Residual log MCs were very similar after 12 months regardless of start time.
Further work is required to better calibrate LogdryTM for major Western Canadian species, particularly Douglas fir, Spruce and Lodgepole pine, and reduce the calculation time for simulations. Further adjustment may be needed for simulating real drying rates in very small logs. The model assumption of similar residual MC after 12 months regardless of start time also needs to be verified.
A total of 48 peeler blocks and 256 mini-billets were sampled from mills to investigate the effects of yard storage time, and artificial yard drying and sprinkling on residual moisture contents (MCs) and veneer quality. MC in fresh and stored log inventories varied greatly across mills according to geographic location of their wood supply zones, bark damage and loss, and storage time and conditions. The main findings were as follows:
1. DF logs supplied by three BC mills from the Cariboo, Thompson Okanagan, or Kootenay regions were highly variable in wood MC.
2. Winter-cut DF logs with high sapwood MC stored had good bark retention and high moisture retention over 6 and 9 winter-spring months. No effects on veneer peeling roughness from longer-term winter storage up to 9 months.
3. Summer-cut logs had little or no residual bark, or the bark slipped off very easily during debarking. Exposed, bark-free summer-cut logs can dry and crack on edges and ends very quickly, within a few weeks.
4. A marked decline in veneer quality with piling time in Summer for spruce and DF, suggesting an optimum window of processing of such exposed logs of about two weeks. Veneer quality and recovery suffered markedly once the logs had fully air dried mainly because of edge splits creating natural fragmentation of the ribbon.
5. Mills receiving dry-zone logs with much lower MC have a very limited storage window, especially over winter. As little as 2-3 weeks if bark is damaged or missing.
6. Veneer quality could not be definitively tied to log residual MC. Under the controlled laboratory conditions used here it was observed that peeling quality could still be good at low sapwood MC (35-40%) and or very high (MC>100%). Whether this is still the case in mill production is unknown.
7. Logs must never be allowed to fall below FSP and develop edge-checks or deep end checks.
8. Wax emulsion end sealants were effective at hampering drying and end checking on high MC logs, but not effective on low MC logs.
9. Sprinkling retained log freshness and peel quality in high MC DF for several months and prevented log drying and end splitting as well as inner log staining. Ends absorbed considerable extra moisture. Some variability in peel quality was noted.
10. The prototype EM1000 Ground Penetrating Radar could only be reliably used in log edge mode in DF. The unit would also require re-calibration for the very high sapwood MC in spruce and wet-zone DF logs.
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.
There is a need to demonstrate how novel timber-concrete composite floors can span long distances and be a practical alternative to other traditional structural systems. Better understanding of the fire behaviour of these hybrid systems is essential. To achieve this, the fire-resistance of a timber-concrete composite floor assembly, using BC wood products, will be evaluated in accordance with
CAN/ULC-S101 . A 2 hr fire resistance rating will be targeted, as this is the current requirement in high-rise buildings for floor separations between occupancies.
The structural behaviour of this type of system will also be assessed from conducting pull-out tests of the shear connectors.
In conjunction with previous test data, the results of this test will be used to develop an analytical model to assess the structural and fire-resistance of timber-concrete composite floors. 301010618
A new laser-based system was successfully developed in the pilot plant for veneer thickness and roughness measurements. This system was tested for both green and dry spruce veneer. The comparisons were made between the green veneer measurement and dry veneer measurement, and between the laser-based system measurement and actual digital measurement. A linear mixed effect model was used to estimate the within-sheet and between-sheet variations of veneer thickness and roughness and their causes.
A good correlation was found between the laser-measured thickness and caliper-measured thickness. The laser-measured average roughness could also capture the trend of veneer surface roughness determined by the visual classification. Thus, the new laser-based system can be a useful tool for measuring both veneer thickness and roughness.
For veneer thickness, the within-sheet variation seemed to be larger than the between-sheet variation, and the laser-based measure had a larger variation than the digital-based measure for both green and dry veneer sheets. With the green veneer, higher veneer moisture content and density would lead to a larger difference between the two measurements. The laser-based method tended to classify more "thick" sheets than the digital-based method, but this tendency was not obvious with the dry veneer. Such tendency also became negligible by factoring in either veneer moisture content or density. Thus, in the real applications, the accuracy of the new laser system can be improved for measuring green veneer thickness with a calibration of moisture content and/or density.
For veneer roughness, the within-sheet variation was again larger than the between-sheet variation, and the dry veneer had a larger variation than the green veneer. Further, the tight side variation was generally larger than the loose side variation. The above information is deemed useful for establishing an overall veneer quality criterion for industrial applications. Further work is scheduled to adopt the new laser-based system for real-time measurement of green veneer thickness and roughness.
Tolerant hardwood forests provide a wide array of products, such as logs varying in value from $45 - 1700/m3. Using production models suitable for commodity based forests does not maximize the value comiing from this type of forest.
By marketing the wood asket in terms of an enhanced product range and new market opportunities, more wealth can be generated from this resource. This report presents results from a study aimed at increasing the recovery of high-value logs from a roundwood operation in Central Ontario. During the study, the overall focus on maximizing high-value log recovery at the stump increased the total volume of preferred grades available for local mills while less than 1% ofharvested log and veneer grades were sold outside of Ontario. Log makers and logging staff were trained in the identificaiton and specifications of new grades. Extracting and protecting these products was supported by the nteraction and communication of the variou logging staff. This created a feedback loop within the logging operation, and assisted in adjustment and refinement of the process.
While this study was completed in 2009-2010, the contractor continued to operate under this value recovery approach. The contractor acknowledges this change in operating focus has had a significant role in the company's continued survival during this current industry downturn.
Les forêts de feuillus tolérants fournissent une vaste gamme de produits, notamment des billes dont la valeur varie de 45 à 1700 $/m3. L'utilisaton de modèles de production convenant aux produits de commodité ne maximise pas la valeur qu'on peut tirer de ce type de forêt.
Potential market gain for Canadian softwood plywood in residential construction could arise from the emerging Chinese market to build massive numbers of affordable apartments and the upcoming rebuilding effort in Japan following the earthquake and tsunami disaster. Compared to the main Chinese species (poplar), common BC species, such as Douglas-fir, spruce and hem-fir, have competitive advantages in the aspects of log diameter, wood properties and veneer quality and processing productivity. For non-residential construction, Canadian plywood concrete forms also offer competitive advantages over Chinese overlaid poplar counterparts due to their higher stiffness and strength. However, the production cost has to be kept to below US$ 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.
This work provides scientific support for, and confirms, what most mills already use as rough and dirty rules of thumb as best practices for manufacturing plywood: i.e. dry veneer should be pressed when its temperature is 100°F or less; average veneer moisture can be 4 %; assembly times should not exceed 20 minutes; and glue spreads should be approximately 32 lbs. per M ft2 SGL.
In addition, this report used the data generated to formulate multivariate statistical models that could be used to develop or enhance existing in-mill process control software, and/or quality procedures at member operations.
This report documents the results of an extensive investigation of plywood dryout and delamination. The study included laboratory and mill tests of key manufacturing variables used in the production of phenol formaldehyde (PF) bonded plywood. Relationships between key variables and plywood quality were used to develop a statistical equation to quantify the effect of veneer moisture content, temperature, assembly time and glue spread rate on wood failure percentage. Testing methods using vacuum/pressure boil-dry-boil, and 6-cycle soak were used and a new multi-step pressing schedule was examined. The following are the main findings:
Veneer with a low moisture content (MC) level is more likely to create glueline dryout than high MC sheets when PF resin is used. Although veneer with a high MC level could minimize the occurrence of dryout, PF gluing systems accept a maximum allowable veneer MC (peak moisture) range of 6 to 8%.
Sheets having temperatures over 100°F are strongly correlated with dryout problems.
An excessively long assembly time approaching 20+ minutes could significantly affect bonding, especially when veneer or ambient temperatures are high.
Increasing glue spread rate can be used to minimize dryout caused by high veneer temperature and low veneer MC; however, a higher glue cost per M ft2 is incurred.
Flexure tests cannot be relied upon to detect bond quality as bending strength is heavily influenced by surface panel properties.
During the mill study, it was learned that variations within each of the above mentioned controllable factors could not be avoided in a mill situation. Good manufacturing process control can ensure that all variables stay within ideal ranges and occurrences of dryout are minimized. The statistical models developed during this project could, possibly, be used to develop or enhance process control software.
A multiple-step hot-pressing schedule, capable of improving plywood bonding properties with or without sacrificing volume recovery, was developed to minimize bond problems caused by dryout. Existing mill presses may be able to implement this approach seamlessly or after a few minor adjustments have been made. Some mills may have to peel thicker veneer to compensate for increased veneer compression associated with multi pressing and in doing so sacrifice log recovery. Pressing schedules illustrated in this study indicate that press production is not sacrificed as single or multi-step pressing time is identical for most thicknesses.
Laboratory tests showed that wood failure percentage figures from a glueline shear test, a standard method for evaluating bond quality, are useful glue dry-out indicators for softwood plywood.
An attempt to develop a tack strength test that could assist in evaluating dryout was unsuccessful as excessive variation was present within recorded data.