ball drops. Balls are usually of half a ton weight. Heavy scrap is also cut
up with the oxy-acetylene flame.
Steel-melting Furnaces.—These are only used to a very moderate
extent outside the great steel works. Some of the larger iron foundries
make what steel castings they require in preference to sending away for them.
Special designs of furnaces are provided for such cases. Instead of the
great open-hearth furnaces which will melt 50 tons, or the immense Bessemer
converters, small " Baby " con-
verters are used, the Robert,
one of the earliest, and the
Tropenas being most common.
The small furnace can be used
for casts as low as 10 cwt.
The melting is so rapid that
two successive melts can be
poured into the ladle for a
single cast. Ferro-alloys can
be added in the ladle to pro-
duce just the amount of recar-
burization desired. The waste
of metal is rather large, and
the upkeep costly.
These converters are made
in capacities of from |- ton to
2 tons, and they are made to
tilt for pouring the. charge.
The blast is brought in at one
side only through tuyeres, and
is directed through the metal,
or over its surface. A pressure
of from 3 to 4 Ib. per square
inch is necessary. This is
supplied from a blower. A
cupola supplies the molten
metal, which must be melted much hotter than that for the iron foundry,
besides which more heat is required to melt the scrap steel included.
The latter may amount to from 25 to 50 per cent of the charge.
Brass-melting Furnaces.—While few iron foundries possess a steel
plant, there are not many of fair dimensions destitute of a department for
the melting of the brasses and bronzes. Castings in these alloys enter into
nearly all constructions, and the delays and risks attendant upon getting
castings from distant firms render the brass foundry a most valuable annexe
to that of iron. A few years ago there was little choice in the matter of
furnaces, now they rival the cupolas, both in variety and increased efficiency.
Natural draught with coke fuel, blast, oil fuel, and electricity, each with
many variations, are now employed regularly.
Fig. 61.—Pig Iron Breaker