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1、PlywoodSoftwood plywood made from spruceContents 1History 2Structural characteristics 3Typeso 3.1Softwood plywoodo 3.2Hardwood plywood 3.2.1Tropical plywoodo 3.3Special-purpose plywood 3.3.1Aircraft plywood 3.3.2Decorative plywood (overlaid plywood) 3.3.3Flexible plywood 3.3.4Marine plywood 3.3.5Oth
2、er plywoods 4Production 5Sizes 6Grades 7Applicationso 7.1Softwood plywood applicationso 7.2Hardwood (Birch) plywood applicationso 7.3Tropical plywood applications 8See also 9References 10External linksPlywoodis a manufactured wood panel from the family of manufactured boards (such as MDF, Chipboard
3、etc.) made from thin sheets ofwood veneer. Plywood layers (called veneers or plys) are glued together, with adjacent plies having theirwood grainrotated relative to adjacent layers up to 90 degrees.All plywoods bind resin and wood fiber sheets (cellulosecells are long, strong and thin) to form acomp
4、osite material. This alternation of the grain is calledcross-grainingand has several important benefits: it reduces the tendency of wood to split when nailed at the edges; it reduces expansion and shrinkage, providing improved dimensional stability; and it makes the strength of the panel consistent
5、across all directions. There is usually an odd number of plies, so that the sheet is balancedthis reduces warping. Because plywood is bonded with grains running against one another and with an odd number of composite parts, it is very hard to bend it perpendicular to the grain direction of the surfa
6、ce ply.Smaller thinner plywoods and lower quality plywoods (see Average-quality plywood photo below and right) may only have their plys (layers) arranged at right angles to each other, though many better quality plywood products will by design have five plys in steps of 45 degrees (0, 45, 90, 135, a
7、nd 180 degrees), giving strength in multiple axes. The highest quality specialty plywoods often have plys at 30 degrees (0, 30, 60, 90, 120, 150, and 180 degrees) in seven layers, or have nine layers with two layers of 45 and 135 degrees in the sandwich. The smaller the step rotations the harder it
8、is to manufacture, increasing manufacturing costs and consequently retail price.HistoryIn 1797 the Englishman Sir Samuel Bentham applied for patents covering several machines to produce veneers. In his patent applications, he described the concept of laminating several layers of veneer with glue to
9、form a thicker piece the first description of what we now call plywood.1Samuel Bentham was a British naval engineer with many ship-building inventions to his credit. Veneers at the time of Bentham were Flat sawn, Rift sawn or Quarter sawn; i.e. cut along or across the log manually in different angle
10、s to the grain and thus limited in width and length.About fifty years laterImmanuel Nobel, father ofAlfred Nobel, realized that several thinner layers of wood bonded together would be stronger than one single thick layer of woodcitation needed; understanding the industrial potential oflaminated wood
11、he invented therotary lathe.citation neededThere 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 dictionaryRobertdescribes the process of rotary lathe veneer manufacturing in its
12、 entryDroulage.2Once can thus presume that rotary lathe plywood manufacture was an established process in France in the 1860s. Plywood was introduced into the United States in 18653and industrial production started shortly after. In 1928, the first standard-sized 4 ft by 8 ft (1.2 m by 2.4 m) plywoo
13、d sheets were introduced in the United States for use as a general building material.4As forartists use of plywood as support for easel paintings, replacing traditional canvas or cardboard; a recent JSTOR article has brought to light that ready-madeartist boardsfor oil painting in three-layered plyw
14、ood (3-ply) were produced and sold in New York as early as 1880.5It is evident that there was an application precedent going back several years. When considering the advantage of simply cutting raw board to wanted measure, one might safely assume that the progressive phalanges among late 19th centur
15、y French artists embraced this new support for their paintings from the very beginning of the national manufacture (1860s).Structural characteristicsA typical plywood panel has face veneers of a higher grade than the core veneers. The principal function of the core layers is to increase the separati
16、on between the outer layers where the bending stresses are highest, thus increasing the panels resistance tobending. As a result, thicker panels can span greater distances under the same loads. In bending, the maximum stress occurs in the outermost layers, one intension, the other incompression. Bending stress decreases from the maxi
