BESSEMER STEEL
The “Manufacture of Malleable Iron and Steel without Fuel” was the
startling title of a scientific paper read in 1856 before the British
Association for the Advancement of Science. This was the announcement to
the world of Henry Bessemer’s invention of the process for making iron
and steel which led to the greatest commercial development the world has
seen.
To those of us who have had little or no experience along manufacturing
lines the announcement seems strange enough, but metallurgists,
engineers and manufacturers who know how serious is the matter of fuel
bills realize at once how revolutionary the claim of Bessemer must have
seemed to men of those days.
As occurs with so many new things the idea was scoffed at; Bessemer’s
scheme was one purporting to give “something for nothing” and—well, it
could not be.
It was ridiculous!
And why should it not have seemed strange when we consider that up to
that time fuel had been required in all metallurgical processes. In the
old Catalan furnace and the types that preceded it, in the Finery Fire,
the Walloon and the several other refining furnaces fuel had to be
provided without stint. The lowest proportion that seventy years of
experiment and practice had brought about in Cort’s puddling process was
one ton of coal per ton of iron, while the blast furnace required at the
least four-fifths of a ton of coke for each ton of pig iron produced.
[Illustration:
KELLY’S FIRST TILTING CONVERTER
]
Whether Bessemer, an Englishman of French descent, or William Kelly, an
American of Irish descent, of Eddyville, Ky., first conceived the idea
of the “pneumatic” process is a moot question. Considerable evidence
substantiates the claim that the latter first hit upon the scheme and
during the ten years between 1846 and 1856 had considerable success with
its development. Perhaps Bessemer had heard of Kelly’s experiments.
There is no proof that he did. Whether he did or not, the fact remains
that he quite independently and very fully developed the process in
England, and with great business sagacity and energy made it the success
that it is.
As fortune has withheld from Kelly and from this country credit which
was deserved, it is desirable to tell briefly the part which he had in
the development of this process that with a single furnace converts pig
iron into steel at the rate of a thousand tons in 24 hours and first
made mild steel available as a building material.
In 1846 Kelly, with a brother, bought the Suwanee Iron Works, near
Eddyville, Ky. After about a year they encountered the same difficulty
that charcoal iron manufacturers usually have encountered—the failure of
the supply of fuel. This difficulty Kelly, a better inventor than
business man, apparently had not foreseen. His business was threatened
unless some other way of refining his iron was found.
[Illustration:
CRUCIBLE WITH WHICH BESSEMER’S FIRST EXPERIMENTS WERE CONDUCTED
]
One day while watching the operation of his Finery Fire he noticed that
the blast of air from the tuyère made the molten iron where it impinged
very much whiter and apparently hotter than the rest. Like other iron
makers, he had always supposed that a blast of cold air chilled molten
iron.
It appears that Kelly was not long in surmising the truth. In a few days
he had rigged up a crude apparatus and made soft iron from which a
horseshoe and a horseshoe nail were fashioned by a blacksmith.
[Illustration:
FIXED CONVERTER OF 1856 WITH SIX TUYÈRES ABOUT THE SIDES
]
Being conservatives, Kelly’s customers were not slow in informing him
that they did not want iron made by anything other than the “good old
process” and he was obliged to accede to their demands or lose their
trade.
Like Galileo, however, he had not really surrendered. In the woods near
by he built and experimented with seven successive “converters,” as the
furnaces are called in which Bessemer steel is made.
Upon learning that Bessemer of England had been granted a United States
patent (1856), Kelly came before the patent office and proved that he
had several years before used the same process. The priority of his
invention was acknowledged, and a patent was granted to him also (1857).
[Illustration:
BOTTOM BLOWING TILTING CONVERTER
]
Financial troubles and finally bankruptcy handicapped him. However, the
Cambria Steel Co., of Johnstown, Pa., became interested and let him
experiment with his process at the company’s plant. Here in 1857 he
built his first “tilting” converter. His first public demonstration
resulted in failure and ridicule, but a few days later he was
successful. Steel makers bought interests in his patent, which at its
expiration in 1870 was renewed by the United States Patent Office, while
renewal of Bessemer’s patent was refused.
[Illustration:
IN 1858 BESSEMER ERECTED HIS FIRST CONVERTER OF THE FORM GENERALLY
USED TO-DAY
]
The Kelly Pneumatic Process Company, which was organized to operate
under Kelly’s patents, built a converter at an iron works at Wyandotte,
Michigan. Here the first pneumatic process steel ever made in this
country in other than an experimental way was “blown” in 1864.
Meanwhile Alexander L. Holley, an American engineer, had obtained for
another American company the right to manufacture steel here under
Bessemer’s patents. He built a plant at Troy, New York, which began
making steel in 1865.
[Illustration:
EVEN THE DETACHABLE BOTTOM—TO FACILITATE REPAIRS—WAS THOUGHT OF AND
PATENTED BY BESSEMER—1863
]
It was soon decided to merge the interests of the two companies and in
1866 this was done, the process thereafter being known as the Bessemer
Process. During the early years of the process here Holley became very
well known. As consulting engineer he designed practically all of the
Bessemer plants which were built during the first ten or fifteen years.
To the majority of the people of the United States to-day Kelly and his
parallel part in the great invention are practically unknown, and thus
not only he but the United States is without credit which should be
ours.
Fortunately Kelly did not entirely fail to profit financially as so many
times is the case with inventors. He received a total of about $500,000.
Bessemer’s return from his process is said to have approximated
$10,000,000 and he was knighted by the British sovereign.
More intimate details regarding Kelly and his work may be found in
_Munsey’s Magazine_ for April, 1906, where H. Casson gives information
which he received direct from several of the men who knew and worked
with Kelly.
While apparently not the originator of the process, Bessemer is without
any doubt entitled to most of the credit he received. There is no proof
that he had heard of Kelly’s experiments when he began his own or that
he was aided by Kelly’s discoveries. He worked out the details of the
process independently, as had Kelly, and it was Bessemer who put it on a
commercial basis.
As has occurred with other new processes Bessemer’s first licensees were
not particularly successful. When those who had bought the right to use
his process had failed in their efforts to use it, and become
discouraged as most of them did, he quietly bought back their rights and
went ahead with his development of the process. Perhaps no man ever
exhibited more perseverance in continuing experiments and development
under very discouraging conditions than did Henry Bessemer. He had
faith.
[Illustration:
SECTIONAL VIEW OF A MODERN CONVERTER SHOWING AIR DUCT AND TUYÈRES
]
He had a genius for invention and was thorough in his experimental work.
Practically no type of converter has since been brought out that he did
not think of and try, and the process has been modified in but one or
two important particulars in the years that have passed.
The essential part of the Bessemer process is the blowing of air through
molten cast iron to remove the metalloids by which cast iron differs
from steel and wrought iron, as has been explained before.
This being the essential point, and at first thought the lack of fuel
seeming so peculiar, we must describe what happens during the Bessemer
“blow.”
[Illustration:
POURING CHARGE OF MOLTEN PIG IRON INTO CONVERTER
]
Technically speaking, the metalloids are “oxidized.” Oxidation is the
chemical uniting of oxygen, generally from the air, which has 21 per
cent of this element, with another element or material such as iron,
silicon, carbon, wood, coal, etc. If the oxidation is slow as in the
“rusting” of iron, the resulting heat dissipates as fast as it is
generated and the change is hardly noticeable. If, however, the reaction
occurs rapidly and with vigor enough, we say that the material “burns.”
The latter sort of oxidation is what we call “combustion.”
The affinity between the metalloids and oxygen has been noted by us
before, but in those cases most of the oxygen came from a different
source.
In the wrought iron process most of it was furnished by the iron ore or
scale which was stirred into the metal, or by the slag which covered the
“bath.” In the Bessemer, or as it was first known in America, “Kelly’s
air blowing process,” the oxygen of the air blown through the molten
metal directly oxidizes or burns out the carbon, silicon, and manganese.
The extremely rapid oxidation of these furnishes the heat.
The iron, then, furnishes its own fuel and _no outside combustible is
needed_.
How can this be?
In every ton of molten cast iron there are approximately 70 pounds of
carbon, 25 pounds of silicon, and 15 pounds of manganese or a total of
about 2000 pounds of these metalloids in the fifteen-ton charge of
molten metal which goes into the ordinary steel plant converter.
We know that if burned in a furnace this ton of high grade fuel would
generate much heat. Burned _inside_ of the mass of molten metal it
generates exactly that same amount of heat and the heat is applied with
such rapidity, directness and efficiency that the molten iron which had
a temperature of 2300° F., say, when charged, in nine or ten minutes has
become steel with a temperature of about 3000° F. simply through this
rapid oxidation of its 4 to 6 per cent of metalloids.
How the blast under 15 to 30 pounds per square inch is applied through
little nozzles in the bottom of the modern “converter” and the several
types of vessels with which Bessemer experimented in the course of his
investigations are shown in the illustrations.
Nor is it necessary that the air be blown through the metal. Air blown
upon its surface accomplishes practically the same purpose, and in many
of the steel foundries of to-day smaller converters of this
“surface-blown” type are used for producing steel for castings. The
large steel plants, however, use the larger “bottom-blown” converter.
Two or three of these vessels, working with proper metal from the
“mixer,” produce an immense tonnage of steel each 24 hours.
The “mixer” is quite necessary. It is a large vessel or furnace holding
and keeping hot from 75 to 300 or more tons of metal from the blast
furnace. It mixes and equalizes irons of various compositions, so that
the converters have the advantage of uniform and hot metal with which to
work.
In addition it is made to perform a “refining” service. By mixing into
the metal a quantity of manganese, considerable of the sulphur present
(a deleterious substance) is removed.
The fifteen or twenty minute blowing of 15 tons of metal in the big
egg-shaped converters of a steel plant presents a spectacle which, when
once observed, will never be forgotten.
One sees a little “dinky” engine come shooting into the converter
building with its ladle of molten iron from the “mixer.” With America’s
time saving routine not a single minute is lost while emptying the metal
into the converter, now in a horizontal position. Almost before the
ladle is out of the way, the converter swings to the upright position
with the blast already on, for otherwise the metal would flow into the
tuyère holes at the bottom.
[Illustration:
COMPARISON OF INGOTS
A. From Four Pot Crucible Furnace: Each Heat 400 Pounds in 4 Hours or
100 Pounds an Hour, Each Heat Pours 4 Ingots 3 × 3 × 36″. B. From
Fifteen Ton Bessemer Converter: 30,000 Pounds in 20 Minutes or
90,000 Pounds an Hour, Each Heat Pours 6 Ingots 19 × 20 × 62″. C.
From Fifty Ton Open-Hearth Furnace, 100,000 Pounds in 8 Hours or
12,500 Pounds an Hour, Each Heat Pours 6 Ingots 24 × 32 × 72″.
]
Reddish-brown smoke and a shower of sparks come from the converter.
These gradually develop into a flame.
The blast shows considerable partiality in selecting for its first
attention the metalloids silicon and manganese, in preference to the
iron itself or any other of the metalloids present. After from three to
five minutes half of the silicon and manganese have been burned out. If
the temperature of the metal and other conditions have become right the
carbon then begins to burn. This gives a change in the nature of the
flame which becomes large and of a dazzling whiteness.
The metal is hot—very hot—so much so that pieces of cold steel often
must be dropped in to cool it somewhat. This is known as “scrapping” the
charge.
An experienced blower can judge through every period of the operation of
the condition of his metal and just how things are progressing.
After some minutes the flame begins to waver and later “drops”; i.e.,
there is scarcely a flame at all. This signal, which is very definite to
an experienced man, cannot be lightly disregarded. Oxygen has affinity
for iron as well as for the metalloids and it is only because of its
greater love for silicon, manganese and carbon that it has thus far
largely neglected the iron. With the metalloids mentioned out of the
way, as they are when the drop occurs, the iron will begin to burn. Were
the “blowing” continued we would shortly have no iron left, but in its
place a mass of iron oxide and slag.
Thus we see that during the first minutes of the blow, more than
one-half of the silicon and manganese are burned. The remainder of these
and all of the carbon are removed in the subsequent five or six minutes.
At the end of this short blowing period we have practically pure iron.
[Illustration:
TWO CONVERTERS IN OPERATION AND A THIRD POURING
]
The metal is not yet in condition to pour well, however, largely because
of the dissolved air and gases which it holds. Something akin to the
“killing” of the steel which we observed in the crucible process must be
accomplished or ingots from it will be spongy. And, having practically
no carbon, it is not yet “steel.”
Bessemer, knowing that the finished steel should contain carbon, tried
to stop the blow long enough before the drop of the flame to leave
exactly the desired amount of this element. He found this difficult to
do and therefore uncertain. It was found to be far better to blow until
the drop of the flame and then put back sufficient carbon to give the
proper composition.
An English metallurgist named Mushet discovered that addition of
manganese ridded the metal of injurious gases and oxides and what is
known as “red-shortness.” After a period of difficulty without it
Bessemer acknowledged the necessity of manganese and adopted its use. It
had before this been used in crucible steel.
Upon turning down the converter at the drop of the flame, the blast is
turned off and a smaller ladle is run in on a track above. This brings a
molten mixture of irons, usually known as “spiegel” or “spiegeleisen”
which contains just enough carbon, manganese and silicon to give to the
whole of the molten metal in the converter the metalloids needed to make
of it steel of the composition desired. This addition also accomplishes
the “deoxidation” of the metal. By deoxidation we mean that the iron is
relieved of the oxygen and gases which have remained as a result of the
blast. This is necessary in order to give proper fluidity for pouring
and the best physical properties to the finished steel.
After “recarburization,” as this addition of manganese-silicon-carbon
metal is called, the steel and slag are quickly poured out into a ladle
waiting below from which the steel is “teemed” (i.e., poured), through a
“nozzle” or hole in the bottom into ingot molds arranged on trucks on
the railroad track which runs through the building.
[Illustration:
TEEMING THE FINISHED STEEL INTO THE INGOT MOLDS
]
When the molds have been filled and a strong crust develops on the steel
the cars are pulled to the “stripper” where the molds are removed,
leaving the white-hot ingots standing on the cars.
The ingots mentioned in the chapter on Cementation and Crucible Steel
were usually small enough that one pot of 100 pounds of metal filled the
mold. A four pot furnace therefore produced 400 pounds. Now for the
first time, we are talking in _tonnage_ figures. Instead of a batch of
steel making four 3″ × 3″ × 36″ ingots of 100 pounds each, the ordinary
“heat” of Bessemer steel from the 15–ton converter gives six or seven
ingots about 18″ × 20″ × 60″ in size. Each of these weighs about two
tons. The total is 30,000 pounds.
From the stripper the ingots go to the gas-fired soaking pits where the
molten interiors of the ingots gradually solidify by cooling while the
outer crusts are reheated. After equalizing the temperatures of
exteriors and interiors in this way, the ingots are white-hot again and
ready for rolling.
[Illustration:
MOLDS BEING STRIPPED FROM INGOTS
]
The purpose for which the steel is intended, of course, determines the
shapes and sizes into which the ingots are rolled. For rails they are
rolled down directly, each ingot making about six rails, of
thirty-three-foot length. For most other purposes the ingots are rolled
in the slabbing mill into billets or slabs which are of intermediate
shapes and sizes which are reheated and further rolled down into axles,
bars, shapes, wire or other products.
Meanwhile the converter which we saw emptied has not been idle. The
American steel engineer has genius for mechanical efficiency and all
parts of a great steel plant are so co-ordinated that enormous
quantities of material can be handled with not a moment lost between
trips. Almost before the ladle of steel had swung away from the
converter’s mouth, any remaining slag was dumped from the converter by
further tipping, the vessel returned to receiving position and the ladle
car, back again from the mixer, poured in the next charge.
Thus blow after blow is made without loss of time.
Repairs are allowed to take no longer than is absolutely necessary. When
the lining around the tuyères gets too badly cut by the action of the
air and metal the bottom is removed, another one is quickly substituted
and the steel making goes on.
Blowers, ladlemen, cranemen, pourers, patchers, vesselmen, sample boys
and the other workmen are relieved by their “partners” at the end of
each shift, each man of necessity working until relieved—twelve,
twenty-four, or even thirty-six hours, for there must be no delay. So
day and night, through the entire week from Monday morning at six, when
they begin, until the next Sunday morning at six, when the plant shuts
down for a brief spell, the converters go on turning out three heats per
hour or four to five hundred per week each.
It has been mentioned that most of Bessemer’s first licensees failed
with the new process. The reasons for this were various, but one in
particular was the attempt of many to use metal of high phosphorus
content. Bessemer soon discovered that no phosphorus was removed during
the “blow” and that, as phosphorus in quantity over one-tenth of one per
cent was detrimental to steel, it was necessary to use raw material
which had little of this element.
This could be done, but it barred many pig irons otherwise good.
Fortunately Swedish and many English irons had low phosphorus. Germany’s
vast beds of high phosphorus ores, however, were useless for the
purpose.
For twenty years this situation existed, during which time many
metallurgists endeavored to make the process applicable to irons which
contained high phosphorus. After long study and many experiments the
problem was solved by Sidney Thomas, an English metallurgist. With a
cousin, Percy Gilchrist, he made hundreds of blows with a toy converter
holding only eight pounds of iron.
Bessemer’s linings had been of sand, clay and other earths which are
known chemically as “acid” materials. By using “basic” materials such as
limestone, dolomite, etc., for the converter lining and additions of
limestone or burnt lime to the charge before and during the blow to make
and keep the slag “basic,” Thomas was able to make the phosphorus burn
after the carbon had been removed. Therefore, a three or four minute
“after blow” following the “drop” of the carbon flame took out the
phosphorus,—again, with generation of heat.
So there are two varieties of the process—the acid Bessemer and the
basic Bessemer, but the former, only, is used in this country as we have
few high phosphorus ores. The analogous open-hearth processes, which are
next to be described, are both used in this country with the basic
open-hearth greatly in the lead.
However, the basic Bessemer process of Thomas and Gilchrist is credited
with making Germany’s great industrial development possible.
════╤════════════════════════════════════╦═══════════════════════════════════
Year│ TABLE NO. 1 ║ TABLE NO. 2
│ Materials Used for Rails[6] ║ Total Steel Made by Processes[6]
────┼──────────┬────────────┬────────────╫─────────────┬────────────┬────────
│ Wrought │ Bessemer │Open-Hearth ║ Bessemer │Open-Hearth │Crucible
│ Iron │ Steel │ Steel ║ Steel │ Steel │ Steel
────┼──────────┼────────────┼────────────╫─────────────┼────────────┼────────
1849│ =21,710=│ │ ║ │ │
1850│ =39,360=│ │ ║ │ │
1855│ =124,000=│ │ ║ │ │
1860│ =183,000=│ │ ║ │ │ No Data
1865│ =318,000=│ │ ║ │ │
1867│ =410,000=│ 2,280│ ║ =2,679=│ │
1868│ =445,970=│ 6,450│ ║ =7,589=│ │
1869│ =521,370=│ 8,620│ ║ =10,714=│ 893│
1870│ =523,000=│ 30,360│ ║ =37,500=│ 1,339│
1875│=448,000=↘│ 260,000│ ║ =335,000=│ 8,080│ 35,180
1880│ 441,000│ ↘=852,000=│ 12,160║ =1,074,000=│ 110,850│ 64,660
1885│ 13,000│ =959,000=│ 4,280║ =1,515,000=│ 133,000│ 57,600
1890│ 14,000│ =1,868,000=│ 3,590║ =3,689,000=│ 513,000│ 71,200
1895│ 5,810│ =1,300,000=│ 700║ =4,909,000=│ 1,137,000│ 68,700
1900│ 695│ =2,384,000=│ 1,330║ =6,685,000=│ 3,398,000│ 100,500
1905│ 318│ =3,192,000=│ 183,000║ =10,941,000=│ 8,971,000│ 102,200
1906│ 15│ =3,391,000=│ 186,000║ =12,276,000=│ 10,980,000│ 127,500
1907│ 925│ =3,380,000=│ 253,000║=11,668,000=↘│ 11,550,000│ 131,000
1908│ 71│ =1,349,000=│ 572,000║ 6,117,000│↘=7,837,000=│ 63,600
1909│ │ =1,767,000=│ 1,257,000║ 9,331,000│=14,494,000=│ 107,400
1910│ 230│=1,884,000=↘│ 1,751,000║ 9,413,000│=16,505,000=│ 122,300
1912│ │ 1,100,000│↘=2,105,000=║ 10,328,000│=20,780,000=│ 121,500
1913│ │ 818,000│ =2,528,000=║ 9,546,000│=21,600,000=│ 121,200
1914│ │ 324,000│ =1,526,000=║ 6,221,000│=17,175,000=│ 89,900
1915│ │ 327,000│ =1,775,000=║ 8,287,000│=23,679,000=│ 113,800
1916│ │ 440,000│ =2,270,000=║ 11,059,000│=31,415,000=│ 129,700
────┴──────────┴────────────┴────────────╨─────────────┴────────────┴────────
Footnote 6:
In United States—long tons of 2,240 pounds.
The well-known “Thomas Slag” which is in demand as a fertilizer on
account of its phosphorus content is the by-product of the basic-lined
converter.
An idea of what the invention of the Bessemer process meant to railroad
development alone may be gained by studying for a moment Table No. 1.
Wrought iron was our first material for rails, but, being very soft, it
did not give long service. But a short time was required for Bessemer
steel to displace it for rails when steel became available. The greater
uniformity, strength and hardness of the alloy gave such excellent
wearing properties that few rails of iron were laid after the year 1880.
During recent years rails have been made of greater and greater strength
and hardness to keep pace with the fast increasing weight, speed and
frequency of railroad trains, steel being susceptible to much
modification of properties.
Now it appears that Bessemer steel is giving way to other products which
show even superior properties.
What happened in the railroad world to a great extent has happened
elsewhere, as the figures of Table No. 2 show. They are a barometer
which indicates what has been our industrial development and our advance
in civilization.