School of Infrastructure.
Plywood is a a manufactured wood panel made from
thin sheets of wood veneer Plywood layers (called
veneers or plys) are glued together.
Plywood was invented, in the 19th century, by Immanuel
Nobel, father of Alfred Nobel. Nobel realized that
several thinner layers of wood bonded together would
be stronger than one single thick layer of wood, and
invented the rotary lathe used in plywood
A typical plywood panel has face veneers of higher
grade than the core veneers.The principal function of
the core layers is to increase the separation between the
outer layers where the bending stresses are highest, thus
increasing the panel's resistance to bending.In bending,
the maximum stress occurs in the outermost layers, one
in tension, the other in compression.
Shear stress, by contrast, is higher in the center of the
panel, and zero at the outer fibers.
The most common dimension is 1.2m×2.4m
or the slightly larger imperial dimension of
4 feet × 8 feet. Plies vary in thickness from
1.4 mm to 4.3 mm. The amount of plies
depends on the thickness and grade of the
Types of plywood:-
4. Decorative plywood.
And Other types.
1.SoftPlywood :-Softplywood is usually made either
of cedar, Douglasfir or spruce, pine,
and fir (collectively known as spruce-pine-firor SPF) or
redwood and is typically used for construction and
2.Hard Plywood:-Hardplywood usually made up of
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. Birch plywood has excellent surface
hardness, and damage- and wear-resistance.
3.Tropical Plywood:- Tropical plywood is made of
mixed species of tropical wood. Tropical plywood is
superior to softwood plywood due to its density,
strength, evenness of layers, and high quality.
Tropical plywood is widely used in the UK, Japan,
United States, Taiwan, Korea, Dubai, and other
It is the preferred choice for construction
purposes in many regions due to its low cost.
However,in many countries’ forests have been over-
harvested, including the Philippines, Malaysia and
Indonesia, largely due to the demand for plywood
production and export..
4.Decorative plywood:-Usually faced with hard
woodincluding ash, oak, redoak, birch, maple, mahog
any , rose wood, teak and a large number of other
Formica, metal and resin-impregnated paper or
fabric bonded are also added on top of plywood at
both side as a kind of ready for use in the decoration
field. This plywood is a lot easier to dye and draw on
than any other plywoods.
5.MarinePlywood:-Marine plywood is manufactured from
durable face and core veneers,so it performs longer in
humid and wet conditions and resists to fungal attack.
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. Marine plywood
is frequently used in the construction of docks and boats.
It is much more expensive than standard plywood.
Other types of plywoods include fire retardant,
moisture-resistant, 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.
Production:-Plywood production requires a good
log, called a peeler, which is generally straighter and
larger in diameter.
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).
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
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 .
Plywood for indoor use generally uses the less
expensive urea-formaldehyde glue, which has
limitedwater 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
Grades:- Grading rules differ according to the country
of origin. Most popular standard is the British
Standard (BS) and American Standard (ASTM). List
some general indication of grading rules:
A-Face and back veneers practically free from all
A/B-Face veneers practically free from all defects.
Reverse veneers with only a few small knots or
A/BB-Face as A but reverse side permitting jointed
veneers, large knots, plugs, etc.
B-Both side veneers with only a few small knots or
B/BB-Face veneers with only a few small knots or
discolorations. Reverse side permitting jointed
veneers, large knots, plugs, etc.
BB-Both sides permitting jointed veneers, large
knots, plugs, etc.
WG-Guaranteed well glued only. All broken knots
X-Knots, knotholes, cracks, and all other defects
Plywood is often used to create curved surfaces
because it can easily bends. It has been used for
marine applications since WWII.
Softwood plywood few applications:-
Floors, walls and roofs in house constructions.
Wind bracing panels.
Vehicle internal body work.
Packages and boxes.
Hardwood plywood few applications:-
High-end loud speakers.
Insulation boxes for Liquefied Natural Gas (LNG)
Floors, walls and roofs in transport vehicles.
Wind turbine blades.