Weyerhaeuser uses strong scraps
By Amie Silverwood
Oct. 17, 2014 - The sky is the limit for wooden structures, and the 66-foot-long beams at Weyerhaeuser’s parallel strand lumber mill carry the weight of inspiration. Not only are these beams strong, but they’re also made from a waste material. Weyerhaeuser has developed an engineered wood that rips unwanted veneer into strands that are then woven to create structural beams. The company calls this finished product Parallam PSL.
The concept of parallel strand lumber (PSL) was flushed out in 1975 when a team of researchers under MacMillan Bloedel set out to produce a high strength wood-based material. The first PSL plant was completed in 1982 with the first commercial sale of the product for Expo ’86. Over the years, the process has been improved to make bigger, longer beams and production and sales have picked up steadily.
Weyerhaeuser owns the patent on the production process and there are currently only two plants that use it: the Weyerhaeuser plant in Delta, B.C., and one in Buckhannon, W.V. Much of the equipment is designed in-house because the process is a tightly guarded secret and constantly being tweaked.
Graeme Dick is the Plant Technical Director for Weyerhaeuser’s parallel strand lumber plant in Delta, B.C. who took Canadian Forest Industries on a tour of the plant. “A lot of the equipment here was innovated by the people who work on the floor. So we involve ourselves in the process and then our maintenance or electrical staff make it a reality.”
Veneer with broken corners, splits and random widths are all consumed at the plant and turned into massive beams for mid-rise and open concept houses. “Above your garage door, down the center of your open concept home, large, straight beams are required. It could be a steel beam, one of our competitors, or Parallam PSL. Our hope is that it’s Parallam PSL,” says Graeme Dick.
According to Dick, there are three types of beams offered by Weyerhaeuser in its Trus Joist-branded family of engineered wood products. “TimberStrand LSL, Microllam LVL and Parallam PSL, with increasing strength and stiffness properties,” Dick explains.
As housing sales pick up, PSL has the potential to reach more of the market. New building codes that allow for up to six storeys of wood frame housing is good news for the mill; initiatives such as Wood First support the use of engineered wood products as well.
The company has managed to penetrate the local home building market and maintains a strong foothold in California. “Much of our product stays here in Vancouver,” says Dick.
But there isn’t enough local development to support the plant without relying on outside markets. Only 30 to 40 per cent of the product is used locally with the vast remainder going to the Western United States and Japan. But once the California market fully recovers, the mill will have reached full stride.
In order to make LDL or plywood, the veneer has to be large, square and clear of visual defects. But because the process of making PSL cuts the veneer into narrow strands, what would otherwise be scraps are saved from the hog. “Although the veneer may be poor in visual grade, it is very good quality in terms of strength,” Dick explains. “The other benefit we have is that we pull from a 100 per cent Douglas Fir supply. It’s a very good fibre source, strong and dimensionally stable.”
As the veneer comes into the plant, the higher visual grade is run on an automatic feeder into a jet box dryer. Narrow sheets and low visual grade veneer runs through screen dryers, made by Babcock (now Grenzebach BSH). These lower grade pieces of veneer are fed manually into the screen dryers that carry the veneer through the drying process.
“We run veneer through the screen dryer that we don’t think we’ll be able to automatically transfer through the process,” he points out. “It’s this ability to process and utilize veneer that would otherwise be unusable in our competitor products that helps distinguish Parallam PSL.”
According to Dick, the process requires a unique moisture content range. To achieve these internal specifications, the mill maintains an ongoing dialogue with its key dry veneer suppliers.
Once the sheets have been dried to the appropriate moisture content, they are then clipped into long strands and go through a glue application process. A rotating conveyor system moves back and forth carrying the resin-coated strands and gently dropping them into a trough. The back-and-forth movement of the conveyor system ensures the strands are deposited in an offset pattern throughout the length of the billet.
The layered veneer is preheated and enters the press where it is condensed before the resin is cured with microwaves.
The microwaves activate the molecules in the glue, heating it to a point of full cure. Because of the thickness of the product, microwave technology must be used to penetrate to the centre of the beam to completely cure the resin.
The billets are made in a continuous press, with the billet length only limited by handling capability. After the billet exits the press, it is remanufactured on site to the customer’s order, which includes the product length, depth and width.
Monitored for quality
The product is tested regularly to ensure it meets structural requirements. “Throughout the day, we complete small- and large-scale testing as part of our Quality Management System,” he says. The results are entered into the database and carefully monitored. The plant is audited by a third-party inspector to make sure the company is in compliance with its accreditation.
“We have one full-time lab technician for every shift, we have two daytime lab technicians, and we currently have co-op students as well.”
The whole process is also closely monitored on a series of cameras posted throughout the facility. During the tour, Tony Deschamps and Russell Petrie are keeping an eye on the cameras. “The press operator is watching the veneer go into the glue dip, watching it come out of the glue dip, as it comes out of the press, and he has the camera focused on certain aspects of the process looking for any potential mechanical complications.”
Deschamps’ job is to make sure the process produces a high-quality product at the optimal rate. Not only does he have access to cameras strategically placed to monitor all of the intricacies of the press, but he also has access to a process historian that provides background on how the plant operated under different conditions. If there is a malfunction, he can decide whether the plant must be shut down immediately or if the issue can be resolved without impacting the final product.
“He [the press operator] has all these HMI screens to make sure we have the right glue mix, the right wood mix, making sure we’re making a certain mat height and density because combined, it will have an impact on our mechanical properties,” says Dick. “He’s watching the press performance. This is a continuous press with many moving parts. If any of these parts fail, you could potentially have a catastrophic failure in the press.”
If this seems like a big job for one press operator to undergo, it doesn’t faze Deschamps, who is quite confident in his role. “I do have a lot of alarms that tell me if anything starts to look a little different. I react to it pretty quickly.”
Once the mat is pressed and the resin is set, one long billet emerges to be sent to remanufacturing to be cut to the customer’s specifications. The plant makes a combination of the five sizes of billets each week so that the lead time is minimal. Once it has been cut to order, it is put through an automated strapping machine and then wrapped. Finished products are shipped by truck, rail or container for export markets.
The plant runs five days a week, for 24 hours a day, employing 121 people but the company plans to run the mill around the clock all week, implementing a four shift schedule in the near future. When U.S. housing starts pick up, Weyerhaeuser will be there to prop up the market with its “trash turned treasure.”