Plywood is a type of engineered wood made from thin sheets of wood veneer, called plies or veneers. Engineered wood, also called composite wood, "man made wood" or "manufactured wood" includes a range of derivative Wood products which are In Woodworking, veneer refers to thin slices of wood usually thinner than 3 mm (1/8 inch that are typically Glued onto core panels (typically Wood The layers are glued together, each with its grain at right angles to adjacent layers for greater strength. There are usually an odd number of plies, as the symmetry makes the board less prone to warping [1], and the grain on the outside surfaces runs in the same direction. The plies are bonded under heat and pressure with strong adhesives, usually phenol formaldehyde resin,[2] making plywood a type of composite material. Glue or adhesive is a compound that adheres or bonds two items together The earliest commercial synthetic Resin is based on a Phenol formaldehyde resin (PF with the commercial name Bakelite, and is formed from an Elimination Composite materials (or composites for short are engineered Materials made from two or more constituent materials with significantly different physical or chemical Plywood is sometimes called the original engineered wood. Engineered wood, also called composite wood, "man made wood" or "manufactured wood" includes a range of derivative Wood products which are [3]
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. Wood is hard fibrous lignified structural tissue produced as secondary Xylem in the stems of Woody plants notably trees but also shrubs It has replaced many dimensional lumbers on construction applications for these reasons. Lumber or timber is Wood in any of its stages from felling through readiness for use as structural Material for Construction, or In the fields of Architecture and Civil engineering, construction is a process that consists of the Building or assembling of Infrastructure
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Types of plywood
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, and is typically used for construction and industrial purposes. Softwood is a generic term used in Woodworking and the Lumber industries for Wood from Conifers (needle-bearing trees from the order Pinales Douglas-fir is the common name applied to coniferous Trees of the Genus Pseudotsuga in the family Pinaceae. Spruce refers to Trees of the genus Picea, a genus of about 35 species of Coniferous Evergreen trees in the Family Pinaceae This article is about the tree For other uses of the term "pine" see Pine (disambiguation. Firs ( Abies) are a genus of between 45-55 species of Evergreen conifers in the family Pinaceae. [4] Decorative plywood is usually faced with hardwood, including red oak, birch, maple, lauan (Philippine mahogany) and a large number of other hardwoods. The term hardwood is used to describe Wood from broad-leaved angiosperm Trees mostly Deciduous, but not necessarily in the case of tropical Red oak may refer to Lobatae, a kind of oak tree Agkistrodon contortrix, a venomous snake species found in North Birch is the name of any Tree of the genus Betula ( Bé-tu-la) in the family Betulaceae, closely related to the Acer ( maple) is a Genus of Trees or Shrubs They are variously classified in a family of their own the Aceraceae, or Dipterocarpaceae is a family of 17 genera and approximately 500 species of mainly Tropical lowland Rainforest Trees The family name from The name mahogany is used when referring to numerous varieties of dark-colored wood originally the wood of the species Swietenia mahagoni, known as West
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 rot, and use a water resistant phenol-formaldehyde glue to prevent delamination and to retain strength in high humidity. In construction marine plywood is a specially treated Plywood that is designed to resist rotting in a high-moisture environment This article is about structural materials For delamination in embryology see Embryogenesis. Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity.
The most common varieties of softwood plywood come in three, five or seven plies with a metric dimension of 1. 2 m × 2. 4 m or the slightly larger imperial dimension of 4 feet × 8 feet. Plies vary in thickness from 1/10" through 1/6" depending on the panel thickness. Roofing can use the thinner 5/8-inch plywood. Vietnam roofjpg|thumb|The roofs of Vietnam.]] A roof is the covering on the uppermost part of a Building. Subfloors are at least 3/4-inch depending on the distance between floor joists. A joist in Architecture and Engineering, is one of the horizontal supporting members that run from wall to wall wall to beam or beam to beam to support a Ceiling Plywood for flooring applications is often tongue and grooved. Tongue and groove or T&G is a method of fitting similar objects together edge to edge used mainly with Wood: Flooring, Parquetry, panelling The mating edge will have a "groove" notched into it to fit with the adjacent "tongue" that protrudes from the next board. This keeps the boards from slipping past each other providing a solid feeling floor when the joints do not lie over joists. Tongue & groove flooring plywood is typically 1" in thickness.
High-strength plywood, known as aircraft plywood, is made from mahogany and/or birch, and uses adhesives with increased resistance to heat and humidity. It was used for several World War II fighter aircraft, including the British-built Mosquito bomber. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including A fighter aircraft is a Military aircraft designed primarily for air-to-air combat with other Aircraft, as opposed to a Bomber, which is designed WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout
Plywood production
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. A sawmill is a facility where logs are cut into boards Sawmill process A sawmill's basic operation is much like those of 100 years ago a log enters The log is peeled into sheets of veneer which are then cut to the desired dimensions, dried, patched, glued together and then baked in a press at 140 °C (280 °F) and 19 MPa (2800 psi) to form the plywood panel. The panel can then be patched, resized, sanded or otherwise refinished, depending on the market for which it is intended.
History
Plywood has been made for thousands of years; the earliest known occurrence of plywood was in Ancient Egypt around 3500 BCE when wooden articles were made from sawn veneers glued together crosswise. Ancient Egypt was an Ancient Civilization in eastern North Africa, concentrated along the lower reaches of the Nile River in what is now This was originally done due to a shortage of fine wood. Thin sheets of high quality wood were glued over a substrate of lower quality wood for cosmetic effect, with incidental structural benefits. This manner of inventing plywood has occurred repeatedly throughout history. Most high quality English furniture makers working in the eighteenth and nineteenth centuries (and since) have used veneering as a technique. In addition to making the most out of the highest quality materials available, it reduces prices and improves stability of construction. The irregularities of grain which confer decorative interest often result in uncontrollable warping and cracking if any attempt is made to use the wood in thicknesses much greater than those characterizing cabinet-making veneers (typically 1-2mm).
Modern plywood, in which the veneer is cut on a rotary lathe from softwood logs, is of relatively recent origin, invented by Immanuel Nobel. A lathe (ˈleɪð is a Machine tool which spins a block of material to perform various operations such as Cutting, Sanding, Knurling Immanuel Nobel (1801-1872 Swedish engineer architect inventor and industrialist The first such lathes were set up in the United States in the mid 19th century. The United States of America —commonly referred to as the Plywood has been one of the most ubiquitous building products for decades.
One of the earliest applications of mass-produced modern plywood manufacturing in the United States was recorded in Portland, Oregon by the Portland Manufacturing Company. The owner, Thomas J. Autzen helped develop a bonding technology, which greatly shortened the drying and manufacturing process. Thomas J Autzen (1888 – 1958 was a German-American pioneer in Plywood manufacturing best known for establishing a philanthropic foundation to support the construction of His early engineering contribution played an important role in making plywood one of the most abundant and affordable building products ever produced.
In India, waterproof plywood is also known as "kitply". Though Kitply is a brand, it has become a generic designation, since the company that makes it pioneered the use of waterproof plywood in India.
The landscape historian John Stilgoe has theorized that the 4' x 8' dimensions of a standard sheet are due to the space required for moving a mule into a barn.
Plywood advantages
1. High uniform strength - wood is 25-45 times stronger along the grain than across the grain. Crossing the adjacent sheets tends to equalise the strength in all directions.
2. Freedom from shrinking, swelling and warping - Solid wood exhibits considerable movement across the grain but generally negligible shrinkage or swelling in a longitudinal plane. The balanced construction of a plywood panel with the grain direction of adjacent veneers at right angles tends to equalise stress, thus reducing shrinkage, swelling and warping.
3. Non-splitting qualities solid wood splits fairly readily along the grain. Plywood by virtue of the crossed laminations can be nailed or screwed near the edges without damage from splitting.
4. Availability of relatively large sizes - Sawn timber can be obtained in fairly long lengths but only in relatively narrow widths. Plywood can be sold in sizes up to 6 ft * 25 ft and by the scarf jointing of small sheets up to 6 ft *40 ft, however 6 ft*3 ft is the most common size.
5. Economical and effective utilisation of figured wood - Twenty sheets of veneer can be sliced from 1 inch of solid wood, when glued to a core of cheaper material a high grade panel is produced. This procedure thus effects distinct economies in the use of figured or the more valuable woods. In addition to facilitating the utilisation of attractive but fragile face veneers to give results which cannot be duplicated in solid construction. More effective utilisation is obtained by the matching of veneer in such a manner that the decorative effect due to the natural figure in the wood is enhanced by the regularity or symmetry of the design.
6. Dense woods can be sliced and bonded into plywood panels for use in furniture construction whereas furniture fabricated from solid timber would be far too heavy.
7. Ease of fabrication of curved surfaces - The trend of modern architectural design is to feature curved surfaces. The desired shapes can be readily fabricated in plywood construction, utilising male and female forms, or a single forming a vacuum press or autoclave
8. One of the important aspects in the manufacture of plywood is that it results in the conservation of timber by the elimination of the waste which occurs in sawing e. g. sawdust. Waste is confined to the small core which remains after peeling, and from the veneer which is lost in rounding up the log, and the elimination of such defects as knots and splits.
US plywood grades
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. [5] 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.
"B": Second highest quality veneer grade. Normally a by-product of downgraded "A" quality veneer. Solid surface, but may contain small diameter knots and narrow surface splits. Normally repaired with wooden plugs or synthetic filler. The surface is normally sanded smooth.
"C": Considered to be a lower end face quality, but a reasonable choice for general construction purposes. May contain tight knots up to 1½ inches diameter, some open knot holes, some face splits, and discoloration. Some manufactures may repair the defects with synthetic filler. Panels are typically not sanded.
"D": Considered to be the lowest quality veneer and often used for the back surface for construction grade panels. Allows for several knots, large and small, as well as open knots up to 2½ inches diameter. Open knots, splits, and discoloration are acceptable. "D" grade veneers are neither repaired nor sanded. This grade is not recommended for permanent exposure to weather elements.
Plywood applications
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. 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, which was primarily made out of wood. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout Plywood is currently successfully used in stressed-skin applications. In Mechanical engineering, stressed skin is a type of rigid construction intermediate between Monocoque and a rigid frame with a non-loaded covering . The American designers Charles and Ray Eames and Phil Bolger are famous for their plywood-based furniture. Charles (1907-1978 and Ray (1912–1988 Eames (ˈiːmz were American designers married in 1941 who worked and made major contributions in many fields of design Charles (1907-1978 and Ray (1912–1988 Eames (ˈiːmz were American designers married in 1941 who worked and made major contributions in many fields of design Philip C Bolger (1927-) prolific boat designer was born and lives in Gloucester Massachusetts.
References
- ^ Plywood basics
- ^ Handbook of Finnish Plywood, Finnish Forest Industries Federation, 2002, ISBN 952-9506-63-5 [1]
- ^ "Milestones in the History of Plywood", APA - The Engineered Wood Association. Accessed October 22, 2007. Events 202 BC - Hannibal Barca, leader of the Carthaginians, is defeated by the Roman legions under Scipio Africanus Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. "plywood is often called the original engineered wood product because it was one of the first to be made by bonding together cut or refashioned pieces of wood to form a larger and integral composite unit stronger and stiffer than the sum of its parts. "
- ^ O'Halloran, p. 221.
- ^ Education - Plywood
See also
- Engineered wood
- Fiberboard
- Glued laminated timber
- Hardboard
- Masonite
- Marine plywood
- Medium-density fiberboard
- Oriented strand board
- Particle board
- Pressed wood
Further reading
- APA - The Engineered Wood Association (formerly known as the American Plywood Association)
- Canadian Plywood Association - Plywood Manufacturing Process, Grades and Specifications, Engineering Design Values, Technical Literature, Mill Contact Info, Environmental Practices, International Certification, Hobby Ply-Plans
- Sellers, Terry. Engineered wood, also called composite wood, "man made wood" or "manufactured wood" includes a range of derivative Wood products which are Fiberboard is a type of Engineered wood product that is made out of Wood fibers Types of fiberboard (in order of increasing density include Particle board Glued laminated timber, also called "gluelam" or "glulam" is a type of structural Timber product composed of several layers of dimensioned Lumber Hardboard, also called high-density fiberboard, is a type of Fiberboard, which is an Engineered wood product Masonite is a type of Hardboard invented by William H Mason. It is formed using the Mason method using Wooden chips and blasting them into long fibers In construction marine plywood is a specially treated Plywood that is designed to resist rotting in a high-moisture environment Medium-density fiberboard ( MDF or MDFB) is an Engineered wood product formed by breaking down Softwood into Wood fibers often in Oriented strand board, or OSB, or waferboard or Sterling board (UK is an Engineered wood product formed by layering strands (flakes of Particle board, or particleboard, (called "chipboard" in some countries is an Engineered wood product manufactured from Wood particles such Pressed wood is any Engineered wood building and furniture construction material made from Wood veneers particles or wood fibers bonded together with an 1985. Plywood and Adhesive Technology. New York: Dekker. ISBN 0-8247-7407-8
- Yahoo about Article On Plywood Grades
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