Plywood
June 1, 2009 by blogtopia
Filed under Definitions
Plywood is a type of engineered wood made from thin sheets of wood, called plies or wood veneers. The layers are glued together, each with its grain at right angles for greater strength. There are usually an odd number of plies, as the symmetry makes the board less prone to warping. The adhesives used in plywood have become a point of concern. Both urea formaldehyde and phenol formaldehyde are carcinogenic in very high concentrations. As a result, many manufacturers are turning to low formaldehyde emitting glue systems, denoted by an "E" rating ("E0" possessing the lowest formaldehyde emissions). Plywood produced to "E0" have effectively zero formaldehyde emissions.
A common reason for using plywood instead of plain wood is its resistance to cracking, shrinkage, twisting/warping, and its general high degree of strength. In addition, plywood can be manufactured in sheets far wider than the trees from which it was made. It has replaced many dimensional lumbers on construction applications for these reasons.
US plywood grades
June 1, 2009 by blogtopia
Filed under Definitions
Plywood grades are determined by a veneer quality on the face and back of each panel. The first letter designates quality of face veneer (best side), while the second letter denotes the surface quality of the back of the panel. The letter "X" indicates the panel was manufactured with scrap wood as the center plies, not "exterior" as is commonly thought. The A-D rating is only good for construction (softwood) plywood, not for hardwood plywoods such as oak or maple.
"A": Highest grade quality available. Can be defect free or contain small knots, providing they are replaced with wooden plugs (the fillers having a "boat" or an "American football" shape) or repaired with synthetic patch. This grade may contain occasional surface splits that are repaired with synthetic filler. The surface is always sanded and provides for smooth paintable face quality.
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Plywood Applications
June 1, 2009 by blogtopia
Filed under Definitions
Plywood is used in many applications that need high-quality, high-strength sheet material. Quality in this context means resistance to cracking, breaking, shrinkage, twisting and warping.
Exterior glued plywood is suitable for outdoor use, but because moisture affects on the strength of wood, optimal performance is achieved in end uses where woods moisture content remains relatively low. On the other hand subzero conditions don’t affect on plywood’s dimensional or strength properties which opens some special application possibilities.
Types of Plywood
June 1, 2009 by blogtopia
Filed under Definitions
A vast number of varieties of plywood exist for different applications. Softwood plywood is usually made either of Douglas fir or spruce, pine, and fir (collectively known as Spruce-pine-fir), and is typically used for construction and industrial purposes.
Hardwood plywood is used for some demanding end use. Birch plywood is characterized by its excellent strength, stiffness and resistance to creep. It has a high planar shear strength and impact resistance, which make it especially suitable for heavy-duty floor and wall structures. Oriented plywood construction has a high wheel carrying capacity. Birch plywood has excellent surface hardness, damage and wear resistance.
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