History of Wrought Iron:
CHARCOAl IRON There are two
types of wrought iron, the iron of antiquity, now known as charcoal iron. This
was the metal that blacksmiths used to before the turn of the eighteenth
century. Iron was melted directly by heating ore in a forge with charcoal, which
served as both a fuel and a reducing agent..While still hot the iron and slag
mixture was removed as a lump and worked (wrought) and welded the iron into a
coherent mass. Charcoal Iron can withstand corrosion for hundereds of
PUDDLE IRON In the nineteenth
century the demand for stronger wrought iron, brought to the industry a method
to mass produce puddle iron. This new wrought iron with a higher tensile
strength and a smallincrease in carbon content making the chemical composition
and consistency easier to control.
Carbon: A naturally abundant
nonmetallic element that occurs in many inorganic and in all organic compounds,
exists freely as graphite and diamond and as a constituent of coal, limestone,
and petroleum, and is capable of chemical self-bonding to form an enormous
number of chemically, biologically, and commercially important
molecules.Carbon is added to iron to make steel.
Carbon Steel is a metal, a combination of two
elements, iron and carbon, where other elements are present in quantities
too small to affect the properties. With a low carbon content it has the same
properties as iron, soft but easily formed. As carbon content rises the metal
becomes harder and stronger but less ductile.
Cast iron usually refers to grey cast iron, but can
mean any of a group of iron-based alloys containing more than 2% carbon
(alloys with less carbon are carbon steel by definition). It is
made by remelting pig iron, often along with substantial quantities of
scrap iron and scrap steel, and taking various steps to remove undesirable
contaminants such as phousphorus and sulfer, which weaken the material.
Carbon and silicon content are reduced to the desired levels, which may be
anywhere from 2% to 3.5% for carbon and 1% to 3% for silicon depending on the
application. Other elements are then added to the melt before the final form is
produced by casting.
Mild steel is the most common form
of steel as its price is relatively low while it provides material
properties that are acceptable for many applications. Mild steel has
medium carbon contents (up to 0.8%) and is therefore neither extremely
brittle nor ductile. It is also often used where large amounts of steel need to
be formed, for example as structural steel. Another popular use is in steel wire
mesh.MILD STEEL:With it's higher and greater strength mild steel has
superiority over wrought iron in it's strength and consistency which it gives a
much wider range of it's application, it also can be hardened by heat
treatment. Mild steel has just about replaced wrought iron in the last century.
Mild steel does tend to corrode
steel, alloy of iron, carbon, and small
proportions of other elements. Iron contains impurities in the form of silicon,
phosphorus, sulfur, and manganese; steelmaking involves the removal of these
impurities, known as slag, and the addition of desirable alloying
industry, the business of processing iron ore into steel,
which in its simplest form is an iron-carbon alloy, and in some cases, turning
that metal into partially finished products or recycling scrap metal into steel.
The steel industry grew out of the need for stronger and more easily produced
metals. Technological advances in steelmaking during the last half of the 19th
cent. played a key role in creating modern economies dependent on rails,
automobiles, girders, bridges, and a variety of other steel products.
Iron working can be traced as far back as 3,500 B.C. in Armenia. The Bessamer process, created
independently by Henry Bessemer in England and William Kelly in the United
States during the 1850s, allowed the mass production of low-cost steel; the
open-hearth process, first introduced in the United States in 1888, made it
easier to use domestic iron ores. By the 1880s, the growing demand for steel
rails made the United States the world's largest producer. The open-hearth
process dominated the steel industry between 1910 and 1960, when it converted to
the basic-oxygen process, which produces steel faster, and the electric-arc
furnace process, which makes it easier to produce alloys such as stainless steel
and to recycle scrap steel.
After World War II, the U.S. steel industry faced increased competition from
Japanese and European producers, who rebuilt and modernized their industries.
Later, many Third World countries, such as Brazil, built their own steel
industries, and large U.S. steelmakers faced increased competition from smaller,
nonunion mills (“mini-mills”) that recycle scrap steel. The U.S. produced about
half of the world's steel in 1945; in 1999 it was the second largest producer,
with 12% of the world market, behind China and ahead of Japan and Russia.
Since the 1970s, growing competition and the increasing availability of
alternative materials, such as plastic, slowed steel industry growth; employment
in the U.S. steel industry dropped from 2.5 million in 1974 to to less than a
million in 1998. Global production stood at 773 million tons in 1997, down from
786 million tons in 1988. U.S. steel production has remained constant since the
1970s at about 100 million tons, but 50% of that total is now produced by
mini-mill companies. An increase in U.S. demand during the 1990s was largely met
by imports, which now account for from about a fifth to a quarter of all steel
used annually in the United States. The old-line U.S. steelmakers, losing market
share and with higher wage, health, and retirement costs, experienced a string
of bankruptcies beginning in the late 1990s, leading to industry and union
pressure for protective tariffs, which were imposed by President George W. Bush
in 2002 on most steel from non-NAFTA industrialized nations. Later reduced, the
tariffs were found in 2003 to be illegal under World Trade Organization rules,
and President Bush reversed the tariffs.
Aluminum: Aluminium is a
soft and lightweight metal with a dull silver-gray appearance. Aluminium
is about one-third as dense as steel or copper is malleable
ductile, and easily machined and cast; and has excellent corrosion resistance and
durability due to the protective oxide layer. It is also nonmagnetic
and nonsparking and is the second most malleable metal (most being gold) and the
sixth most ductile.Whether measured in terms of quantity or value, the use of
aluminium exceeds that of any other metal except iron and it is important
in virtually all segments of the world economy.Aluminium alloys form vital
components of aircrafts and rockets as a result of their high strength
to weight ratio. Aluminium was selected as the
material to be used for the apex of the Washinton Monument, at a time when
one ounce cost twice the daily wages of a labourer.
Aluminium was, when it was first discovered, extremely difficult to separate
from the rocks it was part of. Since the whole of Earth's aluminium was bound up
in the form of compounds, it was the most difficult metal on earth to get,
despite the fact that it is one of the planet's most common. The reason is that
aluminium is oxidized very rapidly and that its oxide is an extremely stable
compound that, unlike rust on steel, does not flake off. The very reason for
which aluminium is used in many applications is why it is so hard to
produce.Recovery of this metal from scrap (via recycling) has become an important
component of the aluminium industry. Recycling involves simply melting the
metal, which is far less expensive than creating it from ore. Refining aluminium
requires enormous amounts of electricity; recycling it requires only 5% of the
energy to produce it. A common practice since the early 1900's, aluminium
recycling is not new. It was, however, a low-profile activity until the
late 1960's when the exploding popularity of aluminium beverage
can finally placed recycling into the public consciousness.
Electric power represents about 20 to 40% of the cost of producing aluminium,
depending on the location of the aluminium smelter. Smelters tend to be located
where electric power is plentiful and inexpensive, China is currently
(2004) the top world producer of aluminium.