Parallel strand lumber

If lumber were used to do to the same job as OSB, an excess of 8 billion more board feet of lumber would be needed annually, and this lumber would have to come from laiger, higher quality, more expensive trees. It is easy to understand why OSB is considered as the wood product of future in the construction business. Veneer lumber, parallel strand lumber, and laminated strand lumber are also rapidly moving into the market as engineered wood products.25,26... 

Figure 10.18. Three examples of structural composite lumber (top to bottom) laminated veneer lumber (LVL), parallel strand lumber (PSL), and oriented strand lumber (OSL).

Parallel strand lumber (PSL) is defined as a composite of wood strand elements with the wood elements primarily oriented along the length of the member the average length of the strands must be a minimum of 150 times that of the least dimension. 

Parallel strand lumber is manufactured from veneer about 3 mm (1/8 in.) thick, that is clipped into strands about 19 mm (3/4 in.) wide and 0.6 m (24 in.) long. The produet was designed to use waste material from the roundup lathe as well as other less than full-width veneer arising from plywood manufacture (Chapter 11). Species eommonly used for PSL include Douglas fir, southern pines, western hemlock and yellow poplar, but there is no restriction on the use of other species. 

Parallel strand lumber (PSL) was introduced to market by MacMillan Bloedel Ltd in the 1980s. Figure 11.11 shows the PSL manufacturing process. Residues from plywood and LVL plants can be used as the raw materials for the PSL - mainly Douglas fir, hemlock, southern pine, or yellow poplar. 

Technically, there is no length limit for parallel strand lumber since a continuous pressing operation is used. However, considering handling restrictions, PSL billets are usually cut to 20 m lengths, by up to 280 x 480 mm in section. The billets are recut to desired dimensions for use as beams, headers, columns, and studs. 

Figure 11.13. A 300 x 375 mm continuous press, for the manufacture of parallel strand lumber (Churchland, 1988). Four drive drums draw the strands into the press. The throat acts as a prepress reducing the thickness of the loose mat to 35-40% of its imconsolidated thickness. Both platens and side dams apply compressive forces to the mat that is ciued by microwave energy admitted through ceramic windows in the side dams. These are transparent to microwave energy and yet sustain the full compressive forces on the edge of the product.

Parallel strand lumber (PSL) Strands from softwood veneer PF s Headers, beams, columns and posts industrial uses such as bridge structures and power poles and with CCA pressure treatment, post, beams and columns for decks, balconies, car-ports 280 by 430 cross section (11 by 17), length up to 66 ft ... 

Veneers - for plywood, laminated veneer lumber (LVL), and parallel strand... 

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