element is grey, malleable and ductile and has exceptional magnetic
readily oxidizes in moist air and is attacked by many corrosive
seldom appears pure. It is nearly always found as iron ore which
is a compound of iron and oxygen, or of iron, oxygen and carbon
joined with other substances such as limestone and clay.
is set free from its ore in a blast furnace which is a tower built
of iron plates and lined with firebrick. At the base there is a
taphole which can be opened to let the molten iron run off, and
above it the blast pipes enter carrying the blast of hot air to
keep combustion. The gases are driven off through a taphole and
the air blast passes to be heated before it enters the furnace.
The charge, which is introduced at the top, consists of alternate
layers of iron ore to provide the iron; limestone to act as flux,
and coke or coal to supply heat and produce the carbon monoxide
which is the active reducing agent.
iron which is released from the ore, sinks to the bottom of the
furnace and is driven off through the taphole into sand moulds outside
the furnace where it solidifies giving the blocks known as pig irons,
the process being continuous.
was known to the ancient world and probably its first samples examined
were of meteoric origin. The Egyptian, Hebrew and Assyrian names
for this metal mean, "the metal of heaven" thus indicating
that the first known specimens were of heavenly origin. It is said
that the working of iron ore was. first practised on a large scale
in ancient Egypt.
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iron is hard and brittle and cannot be shaped with a hammer. It
is used to make wrought iron and steel and for castings. For these,
suitable pig iron is remelted and poured into moulds shaped according
to the article required.
iron is brittle. It generally cannot be forged, that is heated and
shaped. It resists rusting much better than wrought iron. It is
particularly used for railings, gratings, pipes and stoves.
oldest form of iron used by man is wrought iron which is made by
releasing suitable pig iron from most of its impurities.
iron is melted in a puddling furnace with the oxides of iron which
oxidize the impurities; the oxygen from the ore combines with the
carbon in the pigs, the metal is puddled with long rakes through
the furnacedoor, and at a certain stage in the manufacture, the
metal begins to set and become sticky; then it is rolled into a
ball mixed with slag which is afterwards squeezed out as much as
possible by rolling and hammering. This material is malleable, tough
and very resistant to shock. Today there are very few uses for this
material because commercial mild steel serves the same general purposes
and is much cheaper. It has now a few applications such as nails,
chains, horse-shoes, anchors and ornamental ironwork.
is an alloy of iron and carbon which is made of pig iron by
removing the excess of carbon and the undesirable components
by means of oxidation reactions. It is hard, strong and resistant.
are three principal methods to manufacture steel: the Bessemer
converter, the open-hearth and the electric process.
the first, suitable molten pig iron is put into the Bessemer converter,
which is a barrel-shaped furnace supported on piers. Compressed
air penetrates through the holes in the bottom and oxidizes the
impurities which go to form a slag. At the same time, the iron is
oxidized and to correct this, an alloy of manganese, iron and carbon
is added once the blast is shut off.
manganese deoxidizes the iron forming manganese oxide which goes
into the slag and the carbon dissolves in the iron and converts
it into steel. The steel is then put into moulds.
The open-hearth process is very commonly employed. Pig iron and
scrap iron are put into a steel furnace heated to a very high temperature
by producer gas derived from coal. The impurities of the iron are
oxidized; manganese is added to deoxidize the iron and provide the
molten steel is put into moulds through a taphole in the bottom
of the furnace.
furnaces are used for special types of steel and alloys such as
chromium steels, manganese steels and others.
iron is melted by an electric are and the oxidation of impurities
is carried out by iron ore. This process has several advantages:
it produces the purest steel; it gives good steel out of impure
materials and the composition can be better regulated than by other
change in the carbon content may give rise to a large change in
the properties of steel which also depend on the method by which
it is cooled. Thus, sudden cooling or chilling produces a
brittle metal while if it is slowly cooled or annealed, a soft,
ductile kind is produced. By tempering the steel we may get properties
intermediate to the two extremes.
steel is an alloy of iron with about 16 % of chromium so as to resist
corrosion. It was invented in Sheffield in the year 1913.
Gordon process for making stainless steel gives ordinary steel a
coating of stainless steel which makes the whole absolutely rustless.
and steel and their mixtures are called ferrous metals.
are given a special name because they constitute the main metals
used in our age. All the other metals and their alloys belong to
the non-ferrous metals.
has been using iron for three thousand years, but pure iron is too
soft to use in tools. It is the most important metal of the contemporary
world and enormous quantities of it are made each year. For instance,
about 25,000,000 tons are produced in Great Britain annually while
the production in the United States is of over 100,000,000 per year.
us see how iron is treated to make cast iron, wrought iron and steel:
in a blast furnace (I ton of pig iron is made with2 tons of
ore, 1/2 ton of limestone, 1 ton of coke, 4% tons of air)
iron : made in a foundry
iron : in a puddling furnace
: made by several processes
steels special steels made in electric furnaces
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