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 Melting
Furnaces
To get answers to the following questions on
melting furnaces, please select one of the links below:
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| 1. |
What is ‘cokeless’
cupola and where can I find more information about it? |
| 2. |
Is it possible to produce
both gray iron and SG iron from the same cupola? |
| 3. |
Can I melt iron ore directly
instead of pig iron in a cupola? |
| 4. |
What are the advantages of
oxygen enrichment in cupola melting? |
| 5. |
What is long campaign cupola? |
| 6. |
What is the typical range
of oxidation loss in a cupola? |
| 7. |
What are the advantages of
hot-blast cupola? |
| 8. |
What is a rotary furnace? |
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| 1. |
What is ‘cokeless’ cupola and where
can I find more information about it? |
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A cokeless cupola melts iron using fuels such as natural
gas, propane or diesel oil in place of coke. The cokeless
cupola, which was invented over 30 years ago, has suddenly
come in limelight in India due to the Supreme Court’s
order, banning the use of coal within the Taj Trapezium
Zone (TTZ), in December 1996. The TTZ is an area of 10,400
sq. km around the Taj Mahal (Agra). A large number of
foundries, which were located within the TTZ, were affected
by the order.
Inspite of being in existence for a number of years, high
capital and operating costs and sophisticated control
requirements have limited the adoption of coke-less cupolas
to only a handful of larger foundry units in Europe. Almost
all the cokeless cupolas are operated in duplexing mode
with electric furnaces.
For more information on cokeless cupola, the reader
may refer to www.cokeless.co.uk |
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| 2. |
Is it possible to produce both gray iron and
SG iron from cupola? |
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Technically, it is possible to produce both gray and
ductile iron from the same cupola. However very good planning
and control on charge is required. A few changes such
as reduced manganese and chromium in charge metallics
and additional coke boosters are needed while switching
from gray iron to ductile iron production. The melt chemistry
needs to be closely monitored to detect a rapid drop in
manganese and chromium, signalling a change to ductile
iron. Increase in carbon content of the melt is achieved
by lowering the air blast. |
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| 3. |
Can I melt iron ore directly instead of pig
iron in a cupola? |
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Very large foundries have used the cupola for conversion
of iron oxide to iron, a sort of mini-blast furnace, for
smelting and melting together. A much larger cupola is
needed in such cases because any carbon reduction of iron
oxide takes time and additional coke, which inevitably
slows down the melting rate. |
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| 4. |
What are the advantages of oxygen enrichment
in cupola melting? |
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Oxygen helps to raise the melt temperature and increase
the melting rate. It is usually introduced at the tuyere
level after suitably modifying the tuyeres. The amount
of oxygen in the blast air usually varies between 1% to
4%. Oxygen enrichment is common in United States and Europe,
especially in large cupolas. However oxygen enrichment
is difficult to justify in terms of cost (of oxygen) in
small-scale foundry units. |
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| 5. |
What is long campaign cupola? |
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Most recent cupola installations in Europe are of long
campaign hot blast type. The operating period of the cupola
could range from a few weeks to several months. The shell
and tuyeres of long campaign cupolas are usually water-cooled
and high quality refractories (alumina type) are used
in the cupola well. Some advantages of a long campaign
cupola are listed below.
- One cupola is sufficient to meet the
melting requirements
- Saving in space
- Savings in coke and limestone
- Slag extraction is simpler and easier
- Less refractory consumption
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| 6. |
What is the typical range of oxidation loss
in a cupola? |
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Typical ranges of oxidation loss in an acid lined cupola
are as follows:
Silicon - 10 - 15% loss
Manganese - 20 - 30% loss
Sulphur - 20 - 50% gain
Phosphorus - 1 - 20% gain
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| 7. |
What are the advantages of hot-blast cupola? |
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Some advantages of hot blast operation are energy savings,
lower sulphur pick-up and higher carbon pick-up. However,
these benefits are substantially reduced if the blast
air temperature is below 400oC. Since it difficult to
pre-heat blast air upto 400oC by heat exchange with stack
gases, requirement for secondary oil firing and recuperator
maintenance increase the operating cost substantially. |
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