Smaller, thinner, and lower quality plywoods may only have their plies (layers) arranged at right angles to each other. Some better-quality plywood products will by design have five plies in steps of 45 degrees (0, 45, 90, 135, and 180 degrees), giving strength in multiple axes.
The The Plywood
There is little record of the early implementation of the rotary lathe and the subsequent commercialization of plywood as we know it today, but in its 1870 edition, the French dictionary Robert describes the process of rotary lathe veneer manufacturing in its entry Déroulage.[6] One can thus presume that rotary lathe plywood manufacturing was an established process in France in the 1860s. Plywood was introduced into the United States in 1865[7] and industrial production there started shortly after. In 1928, the first standard-sized 4 ft by 8 ft (1.22 m by 2.44 m) plywood sheets were introduced in the United States for use as a general building material.[4]
Artists use plywood as a support for easel paintings to replace traditional canvas or cardboard. Ready-made artist boards for oil painting in three-layered plywood (3-ply) were produced and sold in New York as early as 1880.[8]
Softwood plywood is usually made either of cedar, Douglas fir or spruce, pine, and fir (collectively known as spruce-pine-fir or SPF) or redwood and is typically used for construction and industrial purposes.[10]
Hardwood plywood is made out of wood from dicot trees (oak, beech and mahogany) and used for demanding end uses. Hardwood plywood is characterized by its excellent strength, stiffness, durability 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. Hardwood plywood has excellent surface hardness, and damage- and wear-resistance.[11]
Tropical plywood is made of mixed hardwood species of tropical timber. Originally from the Asian region, it is now also manufactured in African and South American countries. Tropical plywood is superior to softwood plywood due to its density, strength, evenness of layers, and high quality. It is usually sold at a premium in many markets if manufactured with high standards. Tropical plywood is widely used in the UK, Japan, United States, Taiwan, Korea, Dubai, and other countries worldwide. It is used for construction purposes in many regions due to its low cost. However, many countries' forests have been over-harvested, including the Philippines, Malaysia and Indonesia, largely due to the demand for plywood production and export.[12]
High-strength plywood, also known as aircraft plywood, is made from mahogany, spruce and/or birch using adhesives with an increased resistance to heat and humidity. It was used in the construction of air assault gliders during World War II and also several fighter aircraft, most notably the multi-role British Mosquito. Nicknamed "The Wooden Wonder" plywood was used for the wing surfaces, and also flat sections such as bulkheads and the webs of the wing spars. The fuselage had exceptional rigidity from the bonded ply-balsa-ply 'sandwich' of its monocoque shell; elliptical in cross-section, it was formed in two separate mirror-image halves, using curved moulds.
Howard Hughes' H-4 Hercules was constructed of plywood. The plane was built by the Hughes Aircraft Company employing a plywood-and-resin Duramold process.[13] The specialized wood veneer was made by Roddis Manufacturing in Marshfield, Wisconsin.[14]
In the United Kingdom single-ply sheets of veneer were used to make stove pipe hats in Victorian times, so flexible modern plywood is sometimes known there as "hatters ply",[citation needed] although the original material was not strictly plywood, but a single sheet of veneer.
Marine plywood is manufactured from durable face and core veneers, with few defects so it performs longer in both humid and wet conditions and resists delaminating and fungal attack. Its construction is such that it can be used in environments where it is exposed to moisture for long periods. Each wood veneer will be from tropical hardwoods, have negligible core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond. It uses an exterior Weather and Boil Proof (WBP) glue similar to most exterior plywoods.
Marine plywood can be graded as being compliant with BS 1088, which is a British Standard for marine plywood and IS:710 is Bureau of Indian Standards (BIS) for marine grade plywood. There are few international standards for grading marine plywood and most of the standards are voluntary. Some marine plywood has a Lloyd's of London stamp that certifies it to be BS 1088 compliant. Some plywood is also labeled based on the wood used to manufacture it. Examples of this are Okoumé or Meranti.
Other types of plywoods include fire-retardant, moisture-resistant, wire mesh, sign-grade, and pressure-treated. However, the plywood may be treated with various chemicals to improve the plywood's fireproofing. Each of these products is designed to fill a need in industry.
Baltic Birch plywood is a product of an area around the Baltic Sea. Originally manufactured for European cabinet makers but now popular in the United States as well. It is very stable composed of an inner void-free core of cross-banded birch plys with an exterior grade adhesive. The face veneers are thicker than traditional cabinet grade plywood.
Plywood production requires a good log, called a peeler, which is generally straighter and larger in diameter than one required for processing into dimensioned lumber by a sawmill. The log is laid horizontally and rotated about its long axis while a long blade is pressed into it, causing a thin layer of wood to peel off (much as a continuous sheet of paper from a roll). An adjustable nosebar, which may be solid or a roller, is pressed against the log during rotation, to create a "gap" for veneer to pass through between the knife and the nosebar. The nosebar partly compresses the wood as it is peeled; it controls vibration of the peeling knife; and assists in keeping the veneer being peeled to an accurate thickness. In this way the log is peeled into sheets of veneer, which are then cut to the desired oversize dimensions, to allow it to shrink (depending on wood species) when dried. The sheets are then patched, graded, glued together and then baked in a press at a temperature of at least 140 C (284 F), and at a pressure of up to 1.9 MPa (280 psi) (but more commonly 200 psi) to form the plywood panel. The panel can then be patched, have minor surface defects such as splits or small knot holes filled, re-sized, sanded or otherwise refinished, depending on the market for which it is intended.
Plywood for indoor use generally uses the less expensive urea-formaldehyde glue, which has limited water resistance, while outdoor and marine-grade plywood are designed to withstand moisture, and use a water-resistant resorcinol-formaldehyde or phenol-formaldehyde glue to prevent delamination and to retain strength in high humidity.[15]
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. Plywood produced to "E0" has effectively zero formaldehyde emissions.[16]
Exterior glued plywood is suitable for outdoor use, but because moisture affects the strength of wood, optimal performance is achieved where the moisture content remains relatively low. Subzero conditions do not affect the dimensional or strength properties of plywood, making some special applications possible.
Plywood is also used as an engineering material for stressed-skin applications. It has been used for marine and aviation applications since WWII. Most notable is the British de Havilland Mosquito bomber, with a fuselage made of birch plywood sandwiching a balsa core, and using plywood extensively for the wings. Plywood was also used for the hulls in the hard-chine Motor Torpedo Boats (MTB) and Motor Gun Boats (MGB) built by the British Power Boat Company and Vosper's, American PT boats, and the Higgins landing craft critical to the D-Day landings. Plywood is currently successfully used in stressed-skin applications.[citation needed] The American designers Charles and Ray Eames are known for their plywood-based furniture, as is Finnish Architect Alvar Aalto and his firm Artek, while Phil Bolger has designed a wide range of boats built primarily of plywood. Jack Köper of Cape Town designed the plywood Dabchick sailing dinghy, which as of 2015[update] is still sailed by large numbers of teenagers.
Plywood is often used to create curved surfaces because it can easily bend with the grain. Skateboard ramps often utilize plywood as the top smooth surface over bent curves to create transition that can simulate the shapes of ocean waves.
There are coating solutions available that mask the prominent grain structure of spruce plywood. For these coated plywoods there are some end uses where reasonable strength is needed but the lightness of spruce is a benefit, e.g.:
In order not to overload its original stone walls, this townhouse in a peaceful neighborhood in the Spanish city of Palma de Mallorca gets a second-floor extension of lightweight plywood, bringing its usable floor area up to 2,000 square feet.
Working with 96" x 48" poplar plywood boards, the architects created a framework that gave them the chance to investigate and test out a structural system that integrates local materials and craft techniques with factory processes.
This plywood structure creates ornate patterns on both the ground-floor and second-floor ceilings, so both the old lower level and new upper level are linked through a geometric rhythm that resembles the arabesque ornamentations in the old town of Palma. 2ff7e9595c
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