Earlywood and latewood in softwood
June 1, 2009 by blogtopia
Filed under Definitions
In temperate softwoods there often is a marked difference between latewood and earlywood. The latewood will be denser than that formed early in the season. When examined under a microscope the cells of dense latewood are seen to be very thick-walled and with very small cell cavities, while those formed first in the season have thin walls and large cell cavities.
The strength is in the walls, not the cavities. Hence the greater the proportion of latewood the greater the density and strength. In choosing a piece of pine where strength or stiffness is the important consideration, the principal thing to observe is the comparative amounts of earlywood and latewood. The width of ring is not nearly so important as the proportion and nature of the latewood in the ring.
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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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