Docstoc

Wood _ Plastics

Document Sample
Wood _ Plastics Powered By Docstoc
					Construction & Materials
 Assignment: Wood & Plastics

        Section: E

     BSCE 01113167



Name: Moazzam Khalid



Submitted to: Sir Usama
                                       Wood/Timber



Introduction
Those who work with wood should have a basic understanding of wood anatomy so
they will be familiar with how different anatomical features influence wood properties
and, in turn, how these properties react to different treatments and uses of the wood.
This publication introduces the reader to wood characteristics that are common to both
hardwoods and softwoods. Trees can be divided into two classes based on different
anatomical characteristics, monocotyledonous and dicotyledoneae. (For more
information on the classification of trees, request a copy of FOR-61 from your local
Extension office). There are no commercially important monocot trees in the United
States, although some items made from such woods as bamboo, palm, and rattan, are
often imported into this country. Although these monocots produce woody stems, their
anatomy is quite different from that of dicots and will not be discussed in this
publication.




Common Characteristics of Tree Structure
Chemical Composition of Wood All wood is composed of cellulose, lignin, ash-forming
minerals, and extractives formed into a cellular structure. The characteristics and
amounts of these components and differences in cellular structures result in significant
variations. Some woods are heavier, some lighter, some stiffer, some more flexible,
some harder, some softer, and some easier to work with than others. It is these
differences that make wood such a unique material. It is beyond this publication to do
more than mention the different chemical compositions of wood. Because harsh
chemicals are needed to separate some of these components from others, wood
scientists do not know everything about the structures and functions of some of these
chemicals. In addition, the components themselves are somewhat altered during the
separation processes.



Composition of wood:

   I.      Cellulose
Cellulose is the principal component of the cell walls of trees. It also makes up the cell
walls of other plants, including all the higher plants, most algae, and some fungi. It is the
most important component for its effect on the properties of wood. Hemicelluloses,
composed of shorter molecules than cellulose, makes up a large part of wood. It is also
important for some properties of wood.
    II.    Lignin
Lignin can be thought of as the glue that holds the wood (cellulose and hemicelluloses)
together. Lignin is important because it gives rigidity to the cells so that a tree can grow
large and tall.

    III.  Ash
The ash content of wood is made up of inorganic minerals, primarily calcium,
potassium, and magnesium. Manganese and silica are two other common
minerals.Extractives Common characteristics that we use to identify different woods
with the naked eye come from extractives in the wood. Without extractives, wood would
have to be identified solely by its anatomical structure. Extractives are made up of an
extremely wide range of organic compounds. These chemical compounds are not part
of the wood but accumulate there. The amounts and types of extractives help to
determine the wood’s permeability to liquids and influence other wood properties such
as density, hardness, and compressive strength. Extractives give certain woods their
resistance to insect or fungi attack. (For more information about insect and decay
resistance, see FOR-54.) Many useful chemicals are made from the extractives found in
trees. They also cause the odors and colors attributed to most woods. In a number of
woods, such as cherry, walnut, and mahogany, the extractive colors make these woods
very valuable for furniture, wood paneling, and other products. In general terms, the
chemical composition of wood from trees found in the United States, on an oven-dry
basis, can be summarized as follows:

Cellulose 40 to 50 percent
Hemicelluloses 20 to 35 percent Lignin 15 to 35 percent
Ash less than 1 percent
Miscellaneous compounds usually 1-2 percen
Uses of wood in construction:
    Mostly it’s used in:
    roof building
    construction of ships
    harbors / docks
    as piles under water
    construction of walls and floorings
    as a support for construction projects

Types of wood:

HARDWOODS


OAK: Oak is the most widely used hardwood. There are more than 60 species of oak
grown in the U.S., which can be separated into two basic varieties; white and red. The
red variety is also known as black oak (a reference to its bark).
Properties: Oak is a heavy, strong, light colored hardwood. It is ring porous, due to the
fact that more and larger conductive vessels are laid down early in the summer, rather
than later. Prominent rings and large pores give oak a course texture and prominent
grain. Oak also has conspicuous medullary rays which can be seen as "flakes" in
quarter sawed oak lumber.

Uses: Oak is the most popular wood used to craft American and English country
designs. It is also used for Gothic and William & Mary reproductions, as well as many
transitional and contemporary pieces.




MAPLE: There are 115 species of maple. Only 5 commercially important species grow
in the U.S. Two of the five are hard rock maple and sugar maple.

Properties: Maple is so hard and resistant to shocks that it is often used for bowling
alley floors. Its diffuse evenly sized pores give the wood a fine texture and even grain.
Maple that has a curly grain is often used for violin backs (the pattern formed is known
as fiddleback figure). Burls, leaf figure, and birds-eye figures found in maple are used
extensively for veneers. The Birds eye figure in maple is said to be the result of stunted
growth and is quite rare.

Uses: Maple is used extensively for American colonial furniture, especially in medium
and lower priced categories. It can also be stained to simulate cherry wood, which it
resembles.




MAHOGANY: Mahogany, also known as Honduras mahogany is a tropical hardwood
indigenous to South America, Central America and Africa. There are many different
grades and species sold under this name, which vary widely in quality and price.
Mahogany which comes from the Caribbean is thought to be the hardest, strongest and
best quality. Logs from Africa, though highly figured, are of slightly lesser quality.
Philippine mahogany has a similar color, but is not really mahogany at all. It is a much
less valuable wood, being less strong, not as durable or as beautiful when finished.

Properties: Mahogany is strong, with a uniform pore structure and poorly defined annual
rings. It has a reddish - brown color and may display stripe, ribbon, broken stripe, rope,
ripple, mottle, fiddleback or blister figures. Crotch mahogany figures are widely used
and greatly valued. Mahogany is an excellent carving wood and finishes well.

Uses: Mahogany is used extensively in the crafting of Georgian, Empire and Federal
reproduction furniture. Mahogany is also used in styles ranging from Victorian furniture
reproductions to Contemporary.




CHERRY: Cherry is grown in the Eastern half of the U.S.. It is sometimes called
fruitwood. The term fruitwood is also used to describe a light brown finish on other
woods.

Properties: A moderately hard, strong, closed grain, light to red-brown wood, cherry
resists warping and checking. It is easy to carve and polish.

Uses: Cherry veneers and solids are used in a variety of styles. Cherry has been called
New England mahogany and is often used to craft 18th century, Colonial and French
Provincial designs.




WALNUT: Walnut is one of the most versatile and popular cabinet making woods. It
grows in Europe, America and Asia. There are many different varieties.

Properties: Walnut is strong, hard and durable, without being excessively heavy. It has
excellent woodworking qualities, and takes finishes well. The wood is light to dark
chocolate brown in color with a straight grain in the trunk. Wavy grain is present toward
the roots, and walnut stumps are often dug out and used as a source of highly figured
veneer. Large burls are common. Walnut solids and veneers show a wide range of
figures, including strips, burls, mottles, crotches, curls and butts. European walnut is
lighter in color and slightly finer in texture than American black walnut, but otherwise
comparable.

Uses: Walnut is used in all types of fine cabinet work, especially 1 8th century
reproductions.
ROSEWOOD: Very hard and has a dark reddish brown color. It is fragrant and close
grained. It is hard to work and takes high polish. Used in musical instruments, piano
cases, tool handles, art projects, veneers and furniture.




TEAK: True teak is indigenous to Southeast Asia, but similar wood species also grow in
Africa.

Properties & Uses: Teak is a yellow to dark brown hardwood which is extremely heavy,
strong and durable. Often strongly figured, teak may show straight grain, mottled or
fiddleback figures. It carves well, but because of its high value, is often used as a
veneer. Scandinavian modern, and oriental furniture styles are often crafted of teak.

SOFTWOODS



PINE: Pine is a softwood which grows in most areas of the Northern Hemisphere. There
are more than 100 species worldwide.

Properties: Pine is a soft, white or pale yellow wood which is light weight, straight
grained and lacks figure. It resists shrinking and swelling. Knotty pine is often used for
decorative effect.

Uses: Pine is often used for country or provincial furniture. Pickled, whitened, painted
and oil finishes are often used on this wood.
ASH: There are 16 species of ash which grow in the eastern United States. Of these,
the white ash is the largest and most commercially important.

Properties: Ash is a hard, heavy, ring porous hardwood. It has a prominent grain that
resembles oak, and a white to light brown color. Ash can be differentiated from hickory
(pecan) which it also resembles, by white dots in the darker summerwood which can be
seen with the naked eye. Ash burls have a twisted, interwoven figure.

Uses: Ash is widely used for structural frames and steam bent furniture pieces. It is
often less expensive than comparable hardwoods.




HICKORY: There are 15 species of hickory in the eastern United States, eight of which
are commercially important.

Properties: Hickory is one of the heaviest and hardest woods available. Pecan is a
species of hickory sometimes used in furniture. It has a close grain without much figure.

Uses: Wood from the hickory is used for structural parts, especially where strength and
thinness are required. Decorative hickory veneers are also commonly used.



BEECH: The American beech is a single species which grows in the eastern half of the
United States.

Properties & Uses: Beech is a hard, strong, heavy wood with tiny pores and large
conspicuous medullary rays, similar in appearance to maple. This relatively inexpensive
wood has reddish brown heartwood and light sapwood. Beech is often used for frames,
a variety of bent and turned parts. Quarter sliced and half round cut beech veneers are
commonly used.



BIRCH: There are many species of birch. The yellow birch is the most commercially
important. European birch is fine grained, rare and expensive.

Properties & Uses: Birch is a hard, heavy, close grained hardwood with a light brown or
reddish colored heartwood and cream or light sapwood. Birch is often rotary or flat
sliced, yielding straight, curly or wavy grain patterns. It can be stained to resemble
mahogany or walnut.
CEDAR: Several species of cedar grow in the southern United States, Central and
South America.

Properties & Uses: Cedar is a knotty softwood which has a red-brown color with light
streaks. Its aromatic and moth repellent qualities have made it a popular wood for lining
drawers, chests and boxes. Simple cases and storage closets are also constructed from
this light, brittle wood.




REDWOOD: Indigenous to the Pacific United States, redwood trees grow to more than
300 feet tall and 2,500 years old.

Properties & Uses: The best quality redwood comes from the heartwood which is
resistant to deterioration due to sunlight, moisture and insects. It is used to craft outdoor
furniture and decorative carvings. Redwood burls have a "cluster of eyes" figure. They
are rare and valuable.



HEMLOCK: Light in weight, uniformly textured. It machines well and has low resistance
to decay and nonresinous. Used for construction lumber, planks, doors, boards,
paneling, sub flooring and crates.



FIR: Works easy and finishes well. Uniform in texture and nonresinous. Has low
resistance to decay. Used in furniture, doors, frames, windows, plywood, veneer,
general millwork and interior trim.


SPRUCE: Strong and hard. Finishes well and has low resistance to decay. Has
moderate shrinkage and light in weight. Used for masts and spars for ships, aircraft,
crates, boxes, general millwork and ladders.
ADVANTAGES OF WOOD

Thermal Properties:

As we know, many, materials change in size and volume as the temperature changes.
They expand with increasing of the temperature. This means linear and volumetric
expansion. The expansion. The expansion causes decrease in the strength of materials.
Steel, which is inorganic and non-combustible and therefore has an advantage against
fire, but when used in buildings, it expands and collapses as a result of increase in heat.

Wood does not practically expand against heat. On the contrary, by the effect of heat, it
dries out and gains strength. The only time wood expands a little is when the humidity
level is below 0%, and this is only scientifically significant. In practice, the humidity level
of wood does not drop under 5% even in the driest climate.

The coefficient of thermal conductivity of the wood is very low. Aluminium transmits heat
7000 times, steal 1650 times, marble 90 times and glass 23 times faster than wood. For
this reason, wood is used for making matches, handles of hardware equipment, ceilings
and wall coverings.

Specific heat of wood is high. That means high amount of energy is needed to increase
and decrease the temperature of one-kilogram of wood. Wood requires almost twice
amount of heat energy than stones and concrete; similarly, three times of energy is
needed for heating or cooling steel.

Acoustic Properties:

Sound isolation is based on the mass of the surface. Wood, as a light material, is not
very perfect for sound isolation; But it is ideal for sound absorption. Wood prevents echo
and noise by absorbing sound. For this reason it is extensively used in concert halls.

Sound velocity is faster in woods than gases and liquids, and it is close to that of
metals. Sound energy loss as a result of friction is also significantly low in woods due to
its lightness and structure. Because of such properties, wood is extensively used in
musical instruments.

Electrical Properties:

Resistance to electrical current of a completely dry wood is equal to that of fhenol
formaldehit. An oven dried wood is a very good electrical insulator. To some extent air
dried wood is the same. Unfortunately electrical resistance of wood is lowered by
increasing the moisture content. The resistance of wood saturated with water. Static
electricity that is dangerous for human health is not observed in wood unlike metal,
plastic and other materials. For this reason wood is preferred as a healthy material.

Mechanical Properties:

Although wood is a light material, its strength is quite high. For instance, while the
tensile strength of wood with 0,6/cm3 specific gravity is 100 N/mm2, the tensile strength
of steel with 7,89/cm3 specific gravity is 500 N/mm2. Dividing tensile strengh by specific
gravity gives the breaking length and quality of material. This figure means the breaking
length of the material, when hung as a result of its own weight. While the breaking
length of steel is used for construction is 5.4 km, chrome mobile steel is 6.8 km,
hardened bow steel is 17.5 km, breaking length of spruce wood is 19.8 km, and
laminated wood made of beech is 28.3 km. For this kind of properties, wood and
laminated wood is used in wide-gap constructions like health centers and sport halls.

Aesthetic Properties:

Wood is a decorative material when considered as an aesthetic material. Each tree has
its own color, design and smell the design of a tree does change according to the way it
is sliced. It is possible to find different wooden materials according to color and design
preference. It can be painted to darker colors of varnished, and can be given bright or
mat touches.

Oxidation Properties:

Although wood has oxidation characteristics in some way, it is not the kind of oxidation
seen in metals. Metals get rust, wood doesn’t. For such characteristics, use of wood is
preferred to avoid rust when necessary.

Working Properties:

It is easy to repair and maintain wood. While old woods can be renewed by special
touches other materials are highly difficult and costly to maintain and to repair.
Therefore they are usually disposed of.

Variation:

There are more than 5000 kinds of woods in the world. Their specific gravity,
macroscopic and microscopic structures are different. Accordingly, their physical,
thermal, acoustic, electrical and mechanical properties are also different. Because of
this variety, it is possible to find wood suitable for needs. For instance, for heat isolation
and sound absorption woods in lightweight are used. Similarly, heavy ones are used for
construction purposes.
DISADVANTAGES OF WOOD

There are some disadvantages of wood but they are easy to disregard, and eliminate as
long as the cause is known.

Shrinkage and Swelling of Wood:

Wood is a hygroscopic material. This means that it will adsorb surrounding condensable
vapors and loses moisture to air below the fiber saturation point.

Deterioration of Wood:

The agents causing the deterioration and destruction of wood fall into two categories:
Biotic (biological) and abiotic (non-biological).

Biotic agents include decay and mold fungi, bacteria and insects.

Abiotic agents include sun, wind, water, certain chemicals and fire.

Biotic Deterioration of Wood:

Woods are organic goods. Like any organic good, wood is a nutritional product for some
plants and animals. Humans can not digest cellulose and the other fiber ingredients of
wood, but some fungi and insects can digest it, and use it as a nutritional product.
Insects drill holes and drive lines into wood. Even more dangerously, fungi cause the
wood to decay partially and even completely.

Biological deterioration of wood due to attack by decay fungi, woodboring insects and
marine borers during its processing and in service has technical and economical
importance.

Fungi:

It is necessary to give some short information about fungi agents to take measures
against the wood deterioration.

Physiological requirements of wood destroying and wood inhabiting fungi:

A favorable temperature.

The temperature must be 25-30°C for optimum growth of most wood rotting fungi. But
some of them can tolerate temperature between 0-45°C.

An adequate supply of oxygen
Oxygen is essential for the growth of fungi. In the absence of oxygen no fungi will grow.
It is well known that storage of wood under water will protect them against attacks by
fungi.

Moisture

Generally wood will not be attacked by the common fungi at moisture contents below
the fiber saturation point. The fiber saturation point (FSP) for different wood lies
between 20 to 35% but 30% is accepted generally.

It is recommended that wood in service must have a moisture content at least 3% less
than FSP to provide desirable safety against fungi.

Nutrients

Wood is an organic compound and consists of 50% carbon. That means that wood is a
very suitable nutrient for fungi because fungi derive their energy from oxidation of
organic compounds. Decay fungi wood rotters can use polysaccharides while stain fungi
evidently require simple forms such as soluble carbohydrates, proteins and other
substances present in the parenchyma cell of sapwood. Additionally, the presence of
nitrogen in wood is necessary for the growth of fungi in wood.

Insects:

Insects are only second to decay fungi in the economic loss they cause to lumber and
wood in service. Insects can be separated into four categories: Termites, powderpost
beetles, carpenter ants and marine borers.

Termites

There are two types of termites: Subterranean termites damage wood that is untreated,
moist, in direct contact with standing water, soil, other sources of moisture.

Dry wood termites attack and inhabit wood that has been dried to moisture contents as
low as 5 to 10%. The damage by dry wood termites is less than subterranean termites.

Powderpost beetles

Powderpost beetles attack hardwood and softwood. At risk is well seasoned wood as
well as freshly harvested and undried wood.

Carpenter ants

Carpenter ants do not feed on wood. They tunnel through the wood and create shelter.
They attact most often wood in ground contact or wood that is intermittently wetted.
Carpenter bees

They cause damage primarly to unpainted wood by creating large tunnel in order to lay
eggs.

Marine borers

They attack and can rapidly destroy wood in salt water and brackish water.



                                        Plastic

Introduction to Plastics

The name Plastic is derived from the Greek word plastikos, which means able to be
shaped. Plastic materials consist of long chain molecules (polymers). Available in many
colors and in transparent form, plastics can be rubbery or rigid. Plastic shapes include
sheet, rod, hex, pipe, cubes, balls, tubes, etc.



Plastics are used on a daily basis throughout the world. The word plastic is a common
term that is used for many materials of a synthetic or semi-synthetic nature. The term
was derived from the Greek plastikos, which means “fit for molding.” Plastics are a wide
variety of combinations of properties when viewed as a whole. They are used for
shellac, cellulose, rubber, and asphalt. We also synthetically manufacture items such as
clothing, packaging, automobiles, electronics, aircrafts, medical supplies, and
recreational items. The list could go on and on and it is obvious that much of what we
have today would not be possible without plastics.

One way plastics changed the world was in cost. It was so much cheaper to
manufacture than other materials and the various ways it could be used was
staggering. For instance, the use of polymers, which are substances with a higher
molecule mass and which have a large number of repeating units, is common today.
There are synthetic polymers, which are produced on a large scale and have many
properties and uses. And there are naturally occurring polymers, which include
starches, cellulose, proteins, and latex. Polymers are molecules (monomers) that join
together like a chain with one or more monomers. The polymers are changed
depending on the incorporation of these monomers. If the atoms in the monomers are
combined with the polymer, it is called an addition polymer. When some of the atoms of
the monomers are released into small molecules, as in liquid, then the polymer is called
a condensation polymer. A double bond between carbon atoms is most common in
addition polymers.
In the early part of the twentieth century, a big boom occurred in polymer chemistry
when polymer materials such as nylon and Kevlar came on the scene. Much of the work
done with polymers focuses improvement while using existing technologies, but
chemists do have opportunities ahead. There is a need for the development of new
applications for polymers, always looking for less expensive materials that can replace
what is used now. Chemists have to be more aware of what the market yearns for, such
as products with a green emphasis, polymers that break down or are environmentally
friendly. Concerns such as these have brought new activity to the science arena and
there are always new discoveries to be made.



Plastic Properties

Plastics have numerous properties that make them superior to other materials in many
applications. Plastics generally have:

      Resistance to corrosion and chemicals
      Low electrical and thermal conductivity
      High strength-to-weight ratio
      Colors available in a wide variety and transparent.
      Resistance to shock
      Good durability
      Low cost
      Easy of manufacture
      Resistance to water
      Low toxicity

Applications of Plastic

Plastics are one of the most common materials in countless products and applications
including:

      Appliances
      Auto interior panels, side shields, fender liners, head liners
      Bottles
      CD and cassette boxes
      Cutlery
      Displays
      Disposable cups
      Electrical connectors
      Electronic enclosures
      Eyeglasses
      Food packaging
      Fridge liners
      ID cards
      Instrument panels
      Jars
      Lenses
      Microwavable packaging
      Name tags
      Outdoor signs
      Packaging
      Pallets
      Pipes
      Plates
      Seat backs
      Security shields
      Shutters
      Trays
      Window frames
      Windows
      Windshields

Types of Plastic Materials

Plastic materials include:

      Polypropylene (PP)
      Polystyrene (PS)
      High impact polystyrene (HIPS)
      Acrylonitrile butadiene styrene (ABS)
      Polyethylene terephthalate (PET)
      Polyester (PES)
      Polyamides (PA) (Nylons)
      Poly(vinyl chloride) (PVC)
      Polyurethanes (PU)
      Polycarbonate (PC)
      Polyethylene (PE)
      etc.



Advantages

In electrical installations, electrical boxes are used to install electrical devices, make
splices and install light fixtures. This leads to a choice of types of boxes, plastic or metal
boxes. Plastic boxes are nonconductive and easy enough to install. They have two
nails, both on one side of the box, that allow the box to be fastened to the studs in your
home. Plastic boxes have markings on the side that show different depths that the box
can be set out to allow flush alignment with the outer wall of drywall or wall surface. This
allows the outlet, switch, or light fixture to sit flush against the box opening and the wall
face for proper alignment and installation.

Disadvantages

Plastic boxes have their disadvantages also. Along with the box being plastic, the nail
brackets are also plastic. They are easily broken off when installing a box or when you
have to take a box off and reinstall one. Once this bracket clip is damaged or broken off,
your mounting options are all but gone.

One look at the face opening of the box and you’ll notice there are two screw holes that
make it possible to install a switch, outlet, or other device to the box. As with anything
plastic, the threads inside the mounting holes are threaded and they are easily stripped
if the screws are not installed properly.

Quite often, you may be tempted to put any old screw into these holes, but the threads
are usually set to a 6-32 thread. In the event the threads do become stripped, you may
be able to still use the box by installing a short drywall screw into the hole, that is, if it
isn’t cracked or damaged. We want the screw to firmly hold the device in place so that it
doesn’t short out.

As for mounting light fixtures and ceiling fans, I recommend using metal boxes.
Although there are some plastic boxes that are designed to support these fixtures, I
personally have little faith in the plastic threads that support a fixture over my head. And
while we are discussing that matter, keep in mind to use the specially designed light
fixture and fan mounting boxes that come complete with mounting brackets. These
setups are specifically designed to handle the weight that some of these lights and fans
have.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:5
posted:8/22/2013
language:
pages:16
Description: This is an assignment template so that you can understand how to make assignments in universities.