He said an 8x8ft line can produce 200 million ft2 of plywood annually, with single lines for peeling, drying, lay-up, pressing, composing and panel handling. Investment is lower because of less machinery, such as forklifts, and floor space required, he said. Blocks are peeled down to 21’2in on high-speed lathes using double or triple spindles. A 45-opening hot press for 8x8ft has the capacity of a 90-opening 4x8ft press. An 8x8ft lay-up line has twice the capacity of a 4x8ft line. The six-deck, 20ft-wide, dryer handles a combination of 8x8ft and 4x8ft veneer. Veneer is scanned and sorted after drying. Stacks are equalised for 48 hours before grading to reduce re-dry. Most veneer goes directly to lay-up. Randoms are composed into 8x8ft core.
An 8x8ft mill peels blocks of 11in diameter or greater to ensure sufficient full sheets. Randoms are clipped at the peeling line or left as 8x4ft material and dried. Defects are removed at the composer. Annual production of 200 million ft2, 3’8in basis, requires 20 operators per shift. When indirect labour is added, the labour is about one man-hour per m3 or 1,200ft2, 3’8in basis, per hour. Christian Blyt, GreenHus Design Ltd, traced the 12-year development of ‘Corelam’ corrugated plywood. He plans to market it next year. He describes it as being comprised of at least three layers of veneer laminated with thermal bonding adhesive in different radii and profiles. At least one layer’s grain is perpendicular to the others, providing structural and dimensional stability.
Tensioned backing sheets on both sides of the package permit the veneers to move with low friction relative to each other, without fracturing, to compensate for the differing bending radii of the individuals. A series of cylinders on the upper layer of the press fire in sequence from the centre out, pressing the corrugations into the panel with fixed opposing profiles in the bottom section. Aspen is a prolific tree species which has emerged as an important North American raw material, with LVL one of the newer uses. Andre Klemarewski, Raute Wood Ltd, New Westminster, British Columbia, Canada, described progress. He said the world’s first aspen LVL mill, started in Quebec in 1990, produces 25,000m3 annually. It processes 4ft blocks since it was already operating a 4ft lathe and green end. The firm has added a second such mill in Quebec. Drying the aspen veneer requires special consideration, taking it from 70-120% down to 3.5%. This is done by closely controlling dryer temperatures to maintain re-dry levels within a strict window.
Mr Klemarewski said LVL may have 32 plies, including three veneer grades, and each grade with tight side up and down. Fast and correct veneer feeding is important for high, and quality, LVL production. He said modern lines have up to six primary veneer feeders, plus a replacement veneer feeder and the top face veneer feeder, which is positioned downstream of a glue applicator. Harry E Moore, Metriguard, Inc, Pullman, Washington, US, said improved grading technology now permits material throughput of up to 600fpm with greater accuracy for the best utilisation of raw veneer in the final LVL or plywood. He said the measurement of stress wave velocity has always been the limiting factor in material throughput. Adding a second stress wave detector wheel on a standard ultrasonic stress wave grader permits operation up to the maximum foreseeable speed, 180m/minute and beyond, achievable by modern veneer dryers. Roman Réh, Association of Wood Processing Manufacturers of the Slovak Republic, Zvolen, reported six medium and small plywood mills producing 38,000m3 per year in Slovakia, while plywood consumption is about 40,000m3 annually.
Chunping Dai, Forintek Canada Corp, Vancouver, BC, said, "Although it has been declining in production, plywood is still one of the major panel sectors in Canada and the US. This year’s total production is projected to be around 16.6bn ft2, 3’8in basis (14.7 million m3) He said LVL production this year is projected to be 70m ft2 (two million m3). He added that North American MDF production capacity is significant, but no new MDF mills have been built in the past few years. Canada has six MDF mills. Forintek continues major research and development work. The light-transmission method for moisture detection is an important development. Incisor roller bars have made significant improvements in veneer handling and pressing. "Veneer grading has become increasingly important for the LVL industry to tackle resource variation for consistent high-stiffness products," said Forintek’s Brad Jianhe Wang.
He said stress grading has gained momentum over veneer visual grading to maximise value recovery. Forintek developed a veneer grading optimiser computer software program to improve the work. The program, equipped with a database, can accommodate and analyse either on-line or off-line data of veneer properties such as thickness, density, UPT and MOE. It links veneer grades with final veneer products and provides flexible product lay-up options and stiffness/strength predictions by mixing species, grades and ply orientations. As to LVL international standards, Tom Williamson, APA declared, "While North America has long been a dominant producer of LVL, many other countries are now manufacturing the product. This makes it vitally important that international standards under ISO be developed to ensure equality in performance for this product as it is exported from one country to another".
He said the major market for LVL has shifted to beams and headers in residential construction. Mr Williamson warned that producing countries have developed their own LVL standards which are not always compatible with one another. To make changes to harmonise these standards under an ISO standard requires each country involved to consider adopting provisions that may or may not be compatible with their own national standards. This is difficult in many instances. Spencer Alkan, Forintek, explained an experimental system for x-ray log scanning defect detection to analyse logs for particular uses. He said preliminary simulation showed a great potential for detecting internal defects and clear wood regions which cannot be visually detected. Bryan Wolowiecki, The Coe Manufacturing Co, Painesville, Ohio, US, explained Coe’s Automatic Dryer Efficiency Control System which provides optimised dryer performance, maximum thermal efficiency, minimised average process exhaust flow to pollution abatement equipment, no exhaust leakage and a better working environment for mill staff. It also minimises oxygen during drying. He said this provides for improved veneer colour and quality through reducing veneer oxidisation and resulting surface inactivation.
Jori Sopanen, Raute Oy, Nastola, Finland described a single-operator automatic glue line employing foam glue. He enumerated the features: only one operator per shift; low-cost foam glue; high product quality due to accurate spread control; and single-sided gluing and production flexibility due to free selection of panel lay-up configurations and step-less adjustments of gluing widths. He said the foam glue has a low spread rate compared with purely liquid glues, an easily adjusted accurate spread rate, excellent coverage even on rough surfaces, shorter pressing time, less waste due to the closed-loop system, and good pre-tack. Conrad Kevin Groves of Forintek described ‘GlueMap’, an optical scanning system developed by his organisation for on-line veneer glue distribution. Under simulated on-line mill conditions they found it effective for measuring plywood glue distribution variations on Douglas fir and lodgepole pine veneer.
He said the scanning system can be used to render glue distribution maps in real time to easily detect problems as they occur online. He said large fluctuations in glue distribution have been observed, demonstrating that a permanent glue deficiency detecting system could provide valuable feedback to minimise problems such as poor bonding and delamination. The system uses a near infrared camera in the 800-1,100nm wavelength which can view through a surface coating to show thickness variations. Pasi Kenola, Mecano Group, Kajaani, Finland, concluded, "The ability of machine vision technology and its various applications to eliminate many manual functions while instilling confidence in the decision-making capabilities of machinery will go a long way toward satisfying industry’s need to do more with less. "In the future we can expect to see machine vision become even smarter, with integration of Artificial Intelligence, more sophisticated camera and scanning technology, faster and more reliable computers, more open architecture, and a higher level of usability," he concluded.
