Harvest the Wood
One of the benefits of oriented strand board (OSB) is that it uses small-diameter logs from a fast-growing species chosen for its mill and plant geography, such as Aspen, Southern yellow pine, poplar, or black poplar. Look for manufacturers that work with forests that are managed responsibly (such as FSC- or SFI-certified land) and gather raw materials from a close radius (say, 50 to 150 miles). Once the logs are on site, they are stacked or, in northern areas during colder months, placed in large ponds that are heated by wood burners powered by the mill’s scrap wood. These ponds unfreeze, wash, and soften the logs.
Break it Down Now
The logs are debarked—bark is often reused as fuel for plant operations—and fed into stranders, where knives in either ring or fan configurations (with perhaps 30 to 50 blades per strander) slice and dice the entire log into strands that are generally 3 to 6 inches long, 1 inch wide, and 0.03 inch thick. No wood is wasted here: Strands are screened to weed out the undesirable, which are fed into wet fuel bins for reuse. Doing this before drying the strands eliminates excess energy use, and OSB plants usually keep a reserve of strands on hand in case a strander goes down for a knife change, so that the line can run continuously.
Strand Together Under Pressure
After tumbling through a dryer where temperatures may range from 1,500 F at the inlet to 200 F at the outlet, the strands are blended with a concoction of resins and waxes that varies by manufacturer, wood mix, time of year, and other factors. Strands are then layered into 3- to 8-inch-deep mats on a continuous belt that is roughly 8- to 12-feet wide, and the length of these mats are cut to fit a plant’s presses. Environmental controls should clean exhaust air, and wet electrostatic precipitators, high heat, and beds of media may filter out any ash or VOCs before discharge. Then it’s time to press: Mats are baked above 400 F and under pressure—which varies by board thickness, but is generally around 1,300 psi.
Cool It, Cut It, Deliver It
Coming out of the presses (whose exhaust air is often treated by regenerative catalytic oxidizers or regenerative thermal oxidizers before it is released), the OSB boards are cut to size, with most panels trimmed to 4 feet by 8 feet, and scrap edges and dust reused as fuel sources for the line. Boards may receive modifications such as a radiant barrier or tongue-and-groove cuts. After quality control checks, the boards are then bundled for delivery. Scroll below for a selection of OSB products on the market.