There
are
two main methods of melting iron.
The oldest is through a blast furnace, known as a cupola where a bed of
coke is ignited.
Above, where the air comes into the furnace, are layers
of coke and metal.
The air is forced into the furnace through
vents ( Tuyeres ) and the oxygen in the air super heats
the coke to above 1500 deg. C..
This heat travels up the furnace and melts the
layer of metal above the coke.
When the metal melts it flows down
through
the coke into the well at the bottom.
When one layer of metal is melted
the next layer of coke drops down and melts the metal layer above.
This
happens continuously with new metal being charged at the top.
Our
furnace
melts at 3 tonnes/hour.
When there is sufficient metal in the well
below
the tuyeres it is removed through the tapping hole, flows down a trough
and into the ladle.
The tapping hole is then bunged with a piece of
clay
on the end of a rod, which in turn is removed when more metal is
collected. |
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1997 saw the arrival of a new cupola to replace
the original which had celebrated its 40th Birthday.
Environmental controls meant we had to have a
water gas scrubber fitted to the top, unfortunately the existing
structure was not strong enough to take the weight.
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The cupola is basically just a steel shell
with various holes for blast air in, metal and coke in, molten metal
and
slag out. The new furnace arrived in 3 basic parts and was erected and
bolted together, it stands 45 feet into the air with the latter
sections
lifted into place by a mobile crane.
To stop the shell from melting when the heat is on,
ceramic bricks, forming a circle, are used to line the inside of the
furnace
building up to form an internal chimney. This in turn is sealed by
gannister,
a clay and aggregate mixture used to fill the cracks between the
bricks.
Metal ,when it is molten, stills weighs the
same, so the head pressures can squeeze the liquid through the tiniest
of gaps. This can then weaken the outer shell allowing the extremely
hot
metal to cut through the thin outer shell, like the proverbial hot
knife
through butter.
So we take all precautions to ensure the furnace
is sealed and have an effective method developed in case of
emergencies.
Finally. the furnace area was treated to
a new roof to shelter the operatives.
The swelling at the top forms the water spray and
collection area, it is accessed by the ladder on the left hand side.
The
furnace sways in the wind, but the climb to the top allows a good view
up and down the valley. |
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Electric melting.
This is more like cooking and gives a greater control
of the metal chemistry than with cupola melting. What you put in you
can
get out, with predictable losses of certain elements. It is more
suitable
for producing SG and Nickel Irons.
The material is loaded into a ceramic pot.
Electrical coils surrounding the pot induce a frequency into the metal
causing excitation of the molecules. Temperature increases causing the
iron to melt. Cooling water coils surround the pot to stop the coils
from
melting.
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Similar to the cupola the the electric furnace
is constructed with an internal chimney and lined with a ceramic powder
which is fused into position to form a pot. Our electric furnaces are
raised above ground level for ease of filling, a platform for
material storage and instruments surround the furnaces
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When the metal has reached the correct chemistry
and temperature the whole floor and pot section is tilted forward to
pour
the metal into ladles attached to craneage. The ladles are then taken
to
various moulds for casting.
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