Iron foundry basics
Practical Action
Tuyeres "H" are the nozzles (usually made from cast-iron) which feed the air supply needed for the
combustion to the correct position in the cupolette.
A metal tapping spout "F" is provided at the front of the cupolette and the working bottom is
made to slope towards this, thus giving a supply of molten metal when the hole is tapped. When no
molten metal is required, this hole is plugged.
A slag hole "E" is provided at the back of the cupolette, positioned about 8" (200 m/m) or 9" (230
m/m) below the centres of the tuyeres and midway between two tuyeres, to prevent the slag
chilling, thus allowing it to run freely.
A charging hole "C" is positioned in the upper section of the cupolette. Coke, pig-iron, scrap iron
and flux is loaded through hole from the charging floor "K".
Cupolette Operation
A fire is first lit on the working bottom of the furnace and coke is added in small quantities until it
reaches the level of the tuyeres. The fire is drawn up by natural draught until the coke is at white
heat, the air for this being drawn in through the open fettling and slag holes. This operation may
take some considerable time, particularly with new furnaces, which are being warmed for the first
time.
When the coke has reached white heat, the fettling hole is closed with sand and covered with the
steel plate. More coke is added to bring it to its final level about 1 metre above the level of the
tuyeres and the height is checked by a measuring rod, or for convenience a chain, inserted at the
charging hole. Care should be taken to see that the coke is at white heat, before any charges are
loaded.
Cupolette Charges
Charges are put on to fill the furnace to the level of the charging hole. Alternatively charges of
mixed pig and scrap iron and coke (mixed with limestone at about 20% of the coke weight) are
made. When the cupolette is full (level with charging hole), the air blast is switched on and in 5 to
7 minutes, molten metal will be seen passing the tuyeres.
Note: Scrap iron should be broken into pieces not more than 12" long, before loading into
cupolette, with a mixture of pig.
Ratio of charges:
35 Ibs (15 KG) of good quality coke, together
with 71bs (3 KG) of limestone, for every charge
of 2'12 cwts (125 KG) of pig and scrap iron.
Metal is allowed to collect in the well, until sufficient has accumulated for a tap to be taken. A 'tap'
which is taken from "F" (tapping spout) means allowing a flow of molten metal from the cupolette
into a
ladle, which has been carefully positioned at the end of the chute. This is done by perforating the
refractory plug with a pointed end steel bar, and replacing it after drawing off the amount of metal
required, with a new plug of damp clay inserted in to the tapping spout with a mushroom headed
steel bar.
In the meantime, further charges of piq-iron and coke are added through the charging hole to
replace the metal melted. This procedure continues until the end of the melt. Slag is tapped from
the slag spout at intervals of 45 to 60 minutes, or whenever it is considered that too great an
accumulation of slag has built up in the furnace. It is desirable to bott (close) the slag hole with
ordinary moulding sand, rather than refractory clay as used elsewhere, the reason being that
because of the infrequent tapping that is required through the slag hole, refractory clay tends to set
very hard and may be difficult to penetrate for the next tap.
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