Plywood
Plywood is a composite material manufactured from thin layers, or "plies", of wood veneer that have been stacked and glued together.
All plywoods bind resin and wood fibre sheets (cellulose cells are long, strong and thin) to form a composite material.
This alternation of the grain is called cross-graining and has several important benefits: it reduces the tendency of wood to split when nailed at the edges; it reduces thickness swelling and shrinkage, providing improved dimensional stability; and it makes the strength of the panel consistent across all directions.
In his patent applications, he described the concept of laminating several layers of veneer with glue to form a thicker piece – the first description of what we now call plywood.
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] There were experiments with gluing plywood with phenolic resins, mostly in the form of an alcoholic solution or powder, which, however, did not provide sufficient accuracy of application.
Hardwood plywood is made out of wood from dicot trees (oak, beech and mahogany) and used for demanding end uses.
It has a high planar shear strength and impact resistance, which make it especially suitable for heavy-duty floor and wall structures.
Tropical plywood is widely used in the UK, Japan, United States, Taiwan, Korea, Dubai, and other countries worldwide.
However, many countries' forests have been over-harvested, including the Philippines, Malaysia and Indonesia, largely due to the demand for plywood production and export.
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.
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.
Aviation-grade plywood is manufactured to a number of specifications including those outlined since 1931 in the Germanischer Lloyd Rules for Surveying and Testing of Plywood for Aircraft and MIL-P-607, the latter of which calls for shear testing after immersion in boiling water for three hours to verify the adhesive qualities between the plies meets specifications.
Aircraft grade plywood is made from three or more plies of birch, as thin as 0.40 millimetres (1⁄64 in) thick in total, and is extremely strong and light.
[citation needed] At 3⁄8 inch (9.5 mm) thick, mahogany three-ply "wiggle board" or "bendy board" come in 4 by 8 feet (1.2 m × 2.4 m) sheets with a very thin cross-grain central ply and two thicker exterior plies, either long grain on the sheet, or cross grain.
Wiggle board is often glued together in two layers once it is formed into the desired curve, so that the final shape will be stiff and resist movement.
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.
Each wood veneer will be from tropical hardwoods and have negligible core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond.
In the UK, one can find builders' merchants advertising a grade of ply as "marine ply" that does not conform to BS 1088 - generally online adverts for these products will include a caveat along the lines of "not suitable for boat In India,marine ply is popularly called "Kitply" after the brand which popularised the concept of water proof marine plywood in the 1980"s. Other types of plywoods include fire-retardant, moisture-resistant, wire mesh, sign-grade, and pressure-treated.
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 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.
Programme for the Endorsement of Forest Certification (PEFC) Forest Stewardship Council (FSC), Leadership in Energy and Environmental Design (LEED), Sustainable Forestry Initiative (SFI), and Greenguard are all certification programs that ensure that production and construction practices are sustainable.
Skateboard ramps often utilize plywood as the top smooth surface over bent curves to create transition that can simulate the shapes of ocean waves.
