THE BLAST FURNACE
Up the dark tower shoots the elevator with its “buggy” of coke. Its
speed is not conditioned to the comfort of man, who is not supposed to
be a passenger, except the occasional laborer whose duty as buggy-pusher
requires his presence on twelve-hour shifts at the top. So we, whose
exploratory proclivities have led us at the office to sign away our
lives for grant of a pass to the blast furnace, find our breath about
taken from us with the first mad dash into the darkness of the climb.
That stone tower had looked much more innocent from below.
But now the rickety elevator has as suddenly emerged into the light
again and stopped abruptly at the charging floor which extends across
the chasm to the top of the furnace.
As the smoke-begrimed buggy-pushers rush the buggy of coke across to the
furnace bell, we have opportunity to notice that we are a full hundred
feet above ground. Just here, seemingly so close that we can put our
hands on them, in a row, are the round steel tops of the four stoves
which are for the purpose of preheating the blast. The huge pipes, dust
arresters, tanks, and buildings, all so necessary to the plant, look
almost like a tangled mass from our high station, while the charging
floor upon which we stand, the shoulder-high steel fence around it, the
furnace top, the adjacent stoves and in fact everything for a half mile
around us, is colored yellow-red with iron dust. We understand the
reason for this when the buggies of ore which have succeeded the coke
are dumped into the funnel-shaped depression around the conical bell at
the center. As the huge bell is lowered and the charge slides in there
is considerable blowing out of the fine ore dust, which, in fact,
continually “oozes” out of all crevices under the heavy pressure of the
blast inside.
[Illustration:
HAND-FED BLAST FURNACE
]
Day and night, month in and month out, during the life of the fire-brick
lining of the furnace, this routine of charging, first coke, next the
theoretically correct charge of analyzed iron ores, then limestone, in
rotation goes on. From 6 A.M. to 6 P.M. and from 6 P.M. to 6 A.M. on
twelve-hour shifts, alternating gangs of laborers push the buggies
across to the furnace top, dump and return them to the elevator already
up with another load.
The incessant quiver of the iron plates beneath our feet with the
rumbling and groaning from the inside of this monster are disquieting
and the thought constantly recurs: “What if this powerful creature
should just now rebel, as quite occasionally occurred in the old days
when all of its moods had not been so well understood?” For this king of
metallurgical devices, though gentle and obedient as a lamb under proper
treatment, is a domineering fury when it has dyspepsia as occurs
whenever its attendants are remiss in their attentions to its diet.
“Those explosion doors just below the furnace top—are they in working
order and would they be adequate?” But whether, as in recorded
instances, the whole furnace top is torn off as evidence of its wrath,
or its displeasure is exhibited in a milder way, we much prefer to be
absent. The thought is disquieting and we are glad to leave.
[Illustration:
CINDER OR SLAG FLOWING INTO LADLES
]
[Illustration:
“FIREWORKS” AT THE CINDER-NOTCH
]
Unwilling to test again the elevator for the downward trip, we take to
the narrow iron stairway which leads from the top of the furnace to the
ground. But this is worse than the elevator, for the stair treads are
very narrow and made only of three slender iron rods. To our palpitating
hearts they seem to give very insecure foothold and the gaps show that
there is nothing but earth beneath us, and that a hundred feet below. To
make matters worse, before we creepingly get half way down some visitors
below have stopped to watch our slow and trembling steps and our nervous
clutch on the low “stingy” hand rail. We hear them innocently inquire of
one another why we move so slowly. We wish that we could appear brave,
especially before the women in the party, but we could not move with
greater alacrity if our lives depended upon it.
Once below again with our breath regained, things are more interesting.
The red-hot molten slag which has just been tapped out is running from
the furnace along a long trough into a ladle six feet high resting upon
a car on the railway track alongside the “cast house,” as the huge
structure which houses the lower part of the furnace is called. This
smoking, molten slag stream gives off a powerful sulphur smell and
throws a lurid glare over everything round about.
[Illustration:
THE SLAG DUMP
]
The furnace superintendent is just explaining to the other party that
No. 2 furnace has been “hanging” for a couple of days and is still
dangerous. “If you realize,” said he, “the great weight of coke, ore,
and limestone in that furnace, you can see what a splash it would make
if the clogged, bridged part with all above it should fall suddenly into
the molten pool in the ‘hearth’ of the furnace. Two years ago No. 1
broke out and the molten metal caught and burned to death one of our men
and injured several others. ‘Hanging’ does not occur when the furnace is
working right, but failure of the charge to come down evenly is very
serious sometimes. A blast furnace is like a coquette; she has to be
handled just so, and even then you cannot always be sure what she is
going to do next.
“Oh yes,—where does the iron come from? Well, we often read nowadays of
a man and his ‘affinity.’ Now the chemist has used that word ‘affinity’
for years to describe the liking or attraction of one chemical ‘element’
for another; in fact, that is where this recent colloquial use of the
word originated. Iron ore is nothing more nor less than metallic iron,
the element, chemically combined with oxygen, another element which
constitutes one-fifth of the air we breathe. Under conditions produced
in the blast furnace, though for centuries wedded to iron, oxygen
deserts him for her ‘affinity’ carbon, which is best known to you as
coke, coal, or charcoal. The iron, now free, becomes molten at the high
temperature encountered (about 2800° to 3000° F.) and descends into the
‘hearth’ or bottom of the furnace, while oxygen and her new partner
escape out of the top of the furnace in gaseous form. When molten iron
has accumulated in the hearth to the extent desired it is tapped out as
you will soon see.
[Illustration:
DIAGRAMMATIC SKETCH OF BLAST FURNACE
]
“The limestone charged has ‘affinity’ for dirt and certain other
impurities of the ore which it removes in molten form as the ‘cinder’ or
‘slag’ which is there running into the ladle. When cold, this cinder is
a dark greenish-black, glassy substance, which of recent years has come
to be used to a certain extent in the manufacture of Portland cement but
is mainly used for filling-in purposes. Some is crushed and utilized in
concrete mixtures and for road building. In Chicago considerable land
has been ‘made’ by dumping slag into the lake, and South Chicago is
reported as standing on a swamp which has been filled in with slag from
the steel works there.
[Illustration:
OLD-FASHIONED PIG BED
]
“This immense furnace is simply a strong steel shell lined two or three
feet thick with fire bricks. At the ‘bosh,’ which is the region where
the greatest heat is produced, hollow bronze plates are inserted among
the bricks of the lining through which circulating cold water keeps the
bricks from being fused.
“The hot gases which are led from the upper part of the furnace through
that brick-lined ‘downcomer’ are burning in three of those ‘stoves’ to
heat them, while cold, clean air from the blowing engines is coming
through the other stove, which, ten minutes ago, when it was put on
blast, was the hottest of the four. It is now giving up part of its
accumulated heat to the blast on its way to the furnace. Switching the
cold incoming air every little while from a partially cooled stove
through a hotter one while allowing the former to reheat, provides
continuous blast of a temperature of 800° to 1400° F. The ‘hot blast’
idea originated about 1830 with James Neilson, a gas engineer of
England, and its introduction revolutionized the blast furnace industry
and made the highly efficient modern practice possible.
[Illustration:
FURNACE AND SAND BED READY FOR IRON
]
“This big pipe above our heads which encircles the furnace is the
‘bustle pipe.’ It also has to be lined with fire bricks. The hot blast
is distributed by this ‘bustle pipe’ to the tuyères here—these L-shaped
pipes—which shoot it directly into the furnace. Through the peep-holes
in the tuyères you can get a glimpse of the dazzling interior of the
furnace. The blast of heated air is causing the coke to burn fiercely
there so that it melts the iron, which farther up in the furnace has
been forced to part from the oxygen, as I explained to you.”
[Illustration:
LAYOUT OF BLAST FURNACE PLANT
]
But now six men with a long steel bar are starting to break through the
two or three feet of clay with which the “tap hole” of the monster
furnace is plugged, and our informant hurries away.
[Illustration:
SKIP HOIST AT WORK. SKIP DUMPING INTO HOPPER
]
For ten minutes with strong sledge blows the tappers struggle to break
through the plug of burned clay. Meanwhile the monotonous whistle of the
heavy blast into and through the bustle pipe and tuyères goes on and the
discharge pipes of the water-cooling plates empty into the gutter around
the furnace bottom the water which has been circulating to keep the
inner bricks from fusing.
[Illustration:
SECTION OF BLAST FURNACE SHOWING FILLING ARRANGEMENT, BINS AND ORE
BRIDGE
]
And now a shout and the strong red glow throughout the cast house tell
us that the tap hole is open and the iron is running down the main
channel of the sand bed. Past the plugged entrances to the lateral
branches runs the molten iron stream to the end of the cast house nearly
one hundred feet distant where it divides, filling the laterals on each
side and from them running into many open molds arranged like the teeth
of a comb. Each of these molds is about five feet long. They form the
“pigs,” and the laterals what are known as “sows.” As each lateral and
its molds fill, the lateral ahead of it is opened and the process
repeated, laterals and pigs filling up simultaneously on opposite sides
of the main channel till the whole cast house floor is filled nearly up
to the furnace with the red smoking metal.
[Illustration:
SAND CAST PIG IRON
]
There are few sights more glorious than the cast house with bed just
filling with metal, and especially is it so at night. The strong
yellow-red light of the flaming metal issuing from the furnace and the
intense glow of that already in the bed illuminates everything in and
about the building. But already, before the furnace is empty, the
workmen are spraying with water the earliest cast pigs. Covering them
with a light layer of sand they venture upon them with thick-soled shoes
and break the “pigs” from the “sows” with sledge hammers.
This is the old-fashioned “sand cast” pig iron. After remelting in the
cupola furnaces of neighboring towns and casting into stove parts or
other forms it is known as “cast iron”; through “puddling” in
reverberatory or special furnaces it becomes “wrought iron”; after
decarbonizing treatment in steel furnaces of various design it is
changed into the wonderful material called “steel.”
Pig iron is thus the _intermediate_ or _semi-raw_ material from which
practically all of our various iron and steel products are made and the
transition product through which they pass.
[Illustration:
MACHINE CAST PIG IRON
]
But the romantic period of the hand-fed furnace and the gloriously
beautiful pig beds at casting time are rapidly passing; in fact, are
almost past. Modern “skip-hoists” carrying automatically dumped buckets
or cars charge the furnace more economically than even low-waged
laborers can do it. The two charging cars alternate, one filling at the
bottom in the stock house while the other is dumping through the double
bell at the top of the furnace. Furnaces are now tapped by power driven
drills which make quick work of a formerly difficult operation. Instead
of running it into the sand bed, the molten iron from the furnace is
nowadays run into ladles alongside the cast house as is the cinder which
was described above. If the metal is to be made into pigs it goes to the
pig casting machine, where the traveling iron molds very quickly convert
the entire cast into “chilled cast” pigs. At the top of the incline
these pigs which have been cooling under sprays of water fall from the
traveling molds into railroad cars below which deliver them to the
consumer.
[Illustration:
HOW PIG IRON IS NOW CAST INTO TRAVELING MOLDS
]
[Illustration:
UPPER END OF CASTING MACHINE WHERE PIGS ARE DUMPED FROM TRAVELING
MOLDS INTO RAILWAY CARS
]
In large steel works the greater part of the molten iron is not cast
into pigs at all but while yet molten is directly charged into the
open-hearth or Bessemer furnaces which convert it at once into steel of
which the greater part is made into plate, rails, or other shapes before
being allowed to cool. Even the gas is recovered nowadays. Its journey
through the “dust arrester” rids it of most of its dust, after which
filters and washers clean it thoroughly. That not required for the
heating of the stoves is used for firing the steam boilers about the
plant and as fuel for batteries of huge gas engines which in large
plants have been installed to generate low-priced electric current.
It should be noted that in modern practice iron is mined, loaded,
transported to the furnaces, unloaded, charged and made into pigs or
converted into steel and even into the finished products with
practically no hand labor, all operations being performed by machinery.
Though a “direct” process for converting the ore into wrought iron or
steel has been long sought, a method has never been found, except that
used in the very small way followed by the old iron-workers with their
crude furnaces. It has always proved commercially advantageous to make
pig iron in the blast furnace as an intermediate step and then by a
second step convert it into wrought iron, steel, etc. So the ore is
brought from the mines to the furnace, the coke and limestone arrive
from another region, and batteries of huge blast furnaces through the
country make from them the pig iron.
BLAST FURNACE DATA AND ANNUAL PIG IRON PRODUCTION
═════╤══════════╤══════════╤══════════╤════════════════════════════════
Year │ Average │ Average │ Average │ Tons Pig Iron Produced During
│Height[1] │ Cu. Ft. │ Daily │ Year
│ of Blast │ Capacity │Output in │
│ Furnace │ of Blast │Tons Each │
│ │ Furnace │ │
─────┼──────────┼──────────┼──────────┼──────────┬──────────┬──────────
„ │ „ │ „ │ „ │ United │ Great │ Germany
│ │ │ │ States │ Britain │ and
│ │ │ │ │ │Luxemberg
─────┼──────────┼──────────┼──────────┼──────────┼──────────┼──────────
1850 │ 30′│ 2000│ 29│ 565,000│ │
1860 │ │ │ │ 920,000│ │
1870 │ │ │ │ 1,865,000│ 5,963,000│ 1,391,000
1880 │ 70′│ 8200│ 117│ 3,835,000│ 7,749,000│ 2,729,000
1890 │ 90′│ 18200│ 360│ 9,000,000│ 7,904,000│ 4,658,000
1900 │ 100′│ 24000│ 600│13,790,000│ 9,003,000│ 7,550,000
1905 │90 to 100′│ 24000│ 600│23,000,000│ 9,746,000│10,988,000
1910 │90 to 100′│ 24000│ 600│27,300,000│10,380,000│14,495,000
1912 │90 to 100′│ 24000│ 600│30,000,000│ 9,037,000│17,869,000
1913 │90 to 100′│ 24000│ 600│31,000,000│10,654,000│19,292,000
─────┴──────────┴──────────┴──────────┴──────────┴──────────┴──────────
Footnote 1:
No advantage has been found in furnaces having a height of over 110
feet.
The chemical laboratory plays a very important rôle in iron making.
Analyses made of each car or boat load of ore by the furnace chemists
representing the buyer must check very closely the analyses made by the
mine chemists for the seller, as the price of every ton of ore is based
on its iron and its phosphorus contents and the percentages of certain
other constituents present. In calculating the “burden” or charges for
the furnace, each of these constituents is estimated in pounds actually
present per charge, losses or gains during the journey through the
furnace are allowed for, and by combining the various ores the charges
are so made up that the resulting iron will be of certain desired
composition. The closeness of actual composition obtained to calculated
results is startling.
Truly this is an age of efficiency.
Though technical information and statistics are not to be inflicted upon
our readers to any extent in this series of articles, it may not be
amiss to give one table of interesting figures which show the increase
in height and capacity of furnaces from 1850 to the present time. During
this period the annual production of pig iron in the United States has
risen from 565,000 to 31,000,000 long tons (2240 pounds). It will be
noted that since 1887, when we passed Great Britain, the United States
has been the champion pig iron producer of the world.
The record production of a single blast furnace to date was that of one
of the United States Steel Corporation’s furnaces at Duquesne, Penn.,
which produced 900 tons of pig iron in one day.