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OSB-production before the press

Oriented strand board, or OSB, is an engineered wood product formed by layering strands (flakes) of wood in specific orientations. In appearance it has a rough and variegated surface with the individual strips (around 2.5 by 15 cm each) lying unevenly across each other in the direction of their grain.

It is manufactured in wide mats from cross-oriented layers of thin, rectangular wooden strips compressed and bonded together with wax and resin adhesives (95% wood, 5% wax and resin). The layers are created by shredding the wood into strips, these are sifted and then oriented on a belt or wire cauls. The mat is made in a forming line, the layers are built up with the external layers aligned in the panel direction and internal layers cross-oriented. The number of layers placed is determined partly by the thickness of the panel but is limited by the equipment installed at the manufacturing site, however individual layers can also vary in thickness to give different finished panel thicknesses. Typically a 15 cm layer will produce a 15 mm panel thickness. The mat is placed in a thermal press to compress the flakes and bond them by heat activation and curing of the resin that has been coated on the flakes. Individual panels are then cut from the mats into finished sizes. Most of the worlds OSB is made in the USA and Canada in large production facilities. The largest production facilities can make over 1,000,000,000 square feet of OSB per year.

Different qualities in terms of thickness, panel size, strength, and rigidity can be imparted to the OSB by changes in the manufacturing process. OSB panels have no internal gaps or voids, and are water-resistant, although they do require additional membranes to achieve impermeability to water. The finished product has similar properties to plywood, but is uniform and cheaper. It has replaced plywood in many environments, especially the North American structural panel market. The most common uses are as sheathing in walls, floors, and roofs.

While OSB does not have grain like a natural wood, it does have a specific axis of strength. This can be seen by observing the alignment of the surface wood chips. The most accurate method for determining the axis of strength is to examine the ink stamps placed on the wood by the manufacturer.

There is some debate over the environmental impact of OSB. It allows producers to use tree species such as aspen or poplar that are unfit for standard veneer plywood or lumber. The production method uses almost all the wood of the harvested trees, and small, young trees and lower quality fast growing species can be used. Due to the type of resins used in wood-based structural use panels like OSB, they emit very low levels of formaldehyde. The emission levels have been found to be not more than 10% of the criteria of key national standards.

All wood-based structural use panels can be cut and installed with the same ease and types of equipment used with solid wood. In 2001, 19.4 million m³ of OSB panel was produced in the US. The US is Canada's largest OSB market, receiving 98% of its export product in 2005.Review of Canadian Structural Panel Market

Some manufacturers add zinc borate, 2ZNO.303.3.5H20, a powder which is toxic to termites and molds and fungus but not mammals in applied doses. Buyers should ask whether zinc borate is added to their purchase.

OSB is commonly known as Sterling board in the United Kingdom.

• Fiberboard
• Glued laminated timber
• Hardboard
• Masonite
• Medium-density fiberboard
• Particle board
• Plywood
• Pressed wood

• Choosing Between Oriented Strandboard and Plywood