Martinsburg herald. [volume] (Martinsburg, W. Va.) 1881-1920, 1913-12-20
Flux Limestone at Marti1sburg
6 r eRIMsLEY in manufacturers Record

/ In the smelling of iron ore, and
IN the conversion Of pig.iron into steel
In the open-hearth furnace, a fiux
must be used to aid In the fusion and
to remove impurities Crushed ZINE.
stone has proved to be superior to
all other materials for this purpose.
Iron ore as used today In the Pitts.
burg district contains about As to so
per cent. metallic iron, mixed with
silica, alumlna, phosphorus, etc, as
impurities The ore is practically
hnfuslble at any ordinary tempera-
ture, but when mixed with limestone
In the blast furnace it is readily
fused The acid impurities of the
ore unite with the basic lime and
magnesia OF the limestone, forming a
fused Stag which is drawn off, leaving
the metallic iron which is NODDED in
to pigs more or less free from i'm.
purties.
II the limestone fiux used contains
considerable percentage of impur-
ties itself, the stone adds to the bur
den Of the work in the furnace The
efficiency Of the limestone will be
lowered IN at least three important
ways. First, portion of the lime
/ viii be required to neutrallte the
silica and aluminium of the stone, SO
that more pounds of impure limestone
are required than of pure rock This
! involves greater cost of stone to the
charge. Second, the larger charge OF
limestone required involves more fuel
and thus higher fuel cost to fuse
this additional stone and Stag Third,
there is involved a higher manufac.
turing cost through decreased out.
put with use OF lower grade lime.
stone.
A limestone with over 4 per cent.
silica Is not desirable in the blast
furnace, while in open-hearth steel
work practically all contracts require
/ the silica to run under / per cent.
1t requires 1000 to 1900 pounds OF
limestone flux to the ton OF pig-iron
made in the Pittsburg district. In
this district nearly 100000 tons Of
limestone fux are used a year The
other Pennsylvania and Maryla al
furnaces use over 100000 tons. Most
of this stone comes from Pennsyl-
vania, where the freight distance
from quarries is less than from Mar.
t}nsburg, but this stone averages
about per cent silica
The three factors given above
which lower the efficiency of an lm-
pure limestone as fux can be deter
mined by mathematical calcu'a alton so
as to prove in cents per ton tine actual
additional cost of using a 3 per cent.
silica limestone over that of / per
cent. In the Pittsburg district the
use of the Martinsburg limestone in
blast furnaces will save &C cents per
ton of stone over the use of the Penn
sylvania per cent. stone, and is
therefore practically worth that much
more per ton, though at present the
cost of the furnaces is the same ex-
cept that certain companies quarry
their own stone.
The influence OF magnesia in the
limestone on its fiuxing value is a
disputed subject among engineers. It
Is claimed by some that it has little
or no value in removal of sulphur
from the ore. 1t, however, has the
same property as lime in combining
with the silica of the ore, but to a
slightly less degree. The proportion
of magnesium carbonate in the limo
stone used in the Pittsburg district
is so small that its effects need not
be considered.
In this country it 10 almost the
universal practice to use raw lime
stone rather than the calcined. Theor-
etically, the calcined rock would be
better, but practical tests show but
lite advantage and many disadvan.
tages. The use of raw stone involves
a large fuel loss which is at present
impossible to offset 1t is estimated
that 1900 pounds of limestone through
its content of carbonic acid will re-
move from the furnace 220 pounds
of coke but this loss appears to con
tinue even when the stone is first
calcined, and there is also a loss OF
the Gnely-divided lime in the strong
air blast
Low silica limestone is in demand
in manufacture OF open-hearth steel
Until the year 1890 practically all
the steel in this country was made
by the Bessemer process, which re.
quires no limesone in 1890 two
IA frde Of he A..