IMPROVEMENTS IN THE MANUFACTURE OF STEEL AND MALLEAble iron, anD IN FURNACES THEREFOR
Year: 1872

page_text: LETTERS PATENT to Friedrich Hahn, of Berlin, Germany, now of
Finsbury Circus, in the City of London, Professor of Chemistry,
for the Invention of "IMPROVEMENTS IN THE MANUFACTURE OF STEEL
AND MALLEAble iron, anD IN FURNACES THEREFOR.
COMPLETE SPECIFICATION filed by the said Friedrich Hahn at the
Office of the Commissioners of Patents, with his Petition and
Declaration, on the 16th November 1872, pursuant to the 9th
Section of the Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, FRIEDRICH
HAHN, of Berlin, Germany, now of Finsbury Circus, in the City of
London, Professor of Chemistry, send greeting.
WHEREAS I am in possession of an Invention for "IMPROVEMENTS IN
THE MANUFACTURE OF STEEL AND MALLEABLE IRON, AND IN FURNACES THEREFOR,"
and have petitioned Her Majesty to grant unto me, my executors,
administrators, and assigns, Her Royal Letters Patent for the same,
and have made solemn Declaration that I am the true and first Inventor
thereof.

page_text: NOW KNOW YE, that I, the said Friederich Hahn, do hereby declare
that the following Complete Specification, under my hand and seal,
fully describes and ascertains the nature of the said Invention and in
what manner the same is to be performed, in and by the following
statement, reference being had to the accompanying Drawing forming
a part of this Specification.
My said Invention has for its object the direct conversion of iron ore
or pig iron into cast steel or malleable or bar iron in the blast
furnace, and without the use of separate processes and apparatus or
appliances therefor, that is to say, by my process I convert crude cast
iron into malleable iron in a blast furnace, and without subjecting it to
puddling or other treatment after it has been taken from the said
furnace, and I convert cast iron into cast steel in the same furnace by'
the same process without puddling, cementing or other subsequent
treatment.
In manufacturing steel and malleable iron according to my improved
process, I first melt the iron ore or pig iron and cause the molten cast
iron to descend through a chamber or passage which is supplied with
heated air by a suitable blast. And in passing through the heated air
the crude metal is by the means herein-after described fully exposed
thereto, and being acted upon by the oxygen in the same, is thereby
decarburized and also freed from the various impurities usually existing
in iron ore or pig iron.
By this process I obtain a material that is perfectly homogeneous,
and as I require none of the machinery or apparatus ordinarily employed
in the manufacture of wrought iron and cast steel and use no chemicals,
but produce steel or bar iron by the same furnace that is employed
for the production of cast iron, and by a process which forms a con-
tinuation of the melting of the iron ore or pig iron I avoid the cost of
machinery, fuel, and labour and other expenses involved in the special
processes heretofore employed for the production of malleable iron and
steel, and am enabled to supply the same at a price but slightly exceed-
ing that of cast iron. This improved process is carried into effect by
means of a suitable blast furnace provided with the necessary arrange-
ments for conducting the molten cast iron through the heated air.
In the accompanying Drawing I have shown a furnace constructed
according to my Invention.

page_text: Figure 1 is a vertical central section of the said furnace; Figure 2 is
a horizontal section on the line × ×, Figure 1; Figure 3 is a vertical
section on the line y, y, Figure 2, and in a plane at right angles to
Figure 1; like letters indicate the same parts throughout the Drawing.
The
upper part of the blast furnace wherein the ore or pig iron is melted
is constructed in the ordinary manner. Immediately below the pit a
of the furnace I place a receiving hearth into which the molten cast
iron descends. This hearth has a dished or concave form and is of such
a depth as will permit the retention of a proper quantity of molten iron
to ensure a uniform discharge therefrom. The said hearth has an
opening for removing the scum. or dross. It also has an aperture d,
through which the molten metal passes away from the said hearth, the
said opening being provided with a guard to prevent the escape of the
slag with the molten iron. Below this last mentioned aperture is a
vertical passage or channel at the bottom of which I arrange another
hearth f for receiving the metal from the first or upper hearth. In the
said passage or channel I place bars g made of fire-clay or other suitable
refractory material which are arranged horizontally in rows from the
top to the bottom of the said passage, as clearly shewn in Figure 3.
These bars should be triangular or circular, in transverse section, and so
arranged that the bars of each row lie over the spaces between the bars
in the next row. The object of this peculiar arrangement of the said
bars is the separation or division of the molten metal descending the
passage e, and its diversion from a vertical direction for the purposes
herein-after explained. All the portions of the furnace with which the
molten iron comes in contact must be constructed of fire-clay or other
refractory material.
The said furnace is provided with the usual blast apparatus for
supplying the air required for maintaining combustion therein, and it
also has another blast for supplying the heated air to the aforesaid
vertical channel or passage e. The ordinary furnace blast is supplied by
pipes which enter the furnace just above the first or upper hearth b,
and this blast may be either cold or hot; the lower blast is admitted
into the vertical channel or passage e just above the lower hearth f.
This lower blast must be heated to prevent its chilling the iron during
the process of decarburizing and refining the same in the vertical

page_text: passage, and I prefer for this purpose to make use of the gases from
the furnace. These gases are conducted into a heater constructed as
follows:-i is a chamber in which are placed a number of small tubes j,
whose ends open into a fire-place k. The gases from the furnace are
conducted into this fire-place where they are burned, the volatile pro-
ducts of combustion passing through the tubes j and 1 to the furnace,
cold air is forced into the chamber i wherein it is heated by contact with
the pipes before it enters the vertical passage or channel e, as clearly
shown in Figure 3; the hot air chamber is provided with three tuyeres
or nozzles, 12, 13, for admitting the hot air at different parts of the
vertical passage e; the said nozzles are provided with valves whereby
they may be opened or closed.
If I desire to produce bar iron I admit the lower blast at the bottom
of the vertical passage by closing the nozzles 1, 2, and opening the
nozzle ³, but in making cast steel I admit the said blast only through
the nozzle, and if desired I can produce a metal midway between bar
iron and cast steel by closing the nozzles ",, and opening the nozzle .
I can regulate the intensity of the blast by the said valves or other
suitable contrivances and therefore I can control the oxidation of the
carbon in the molten metal with great exactness.
In the conversion of cast iron into steel the excess of carbon must
be removed from the crude metal, and to make good wrought or bar iron
it must be all or nearly all removed from the crude metal. This object
as herein-before explained is accomplished in my process as the molten
cast iron descends through the hot air in the vertical channel or passage
from the upper to the lower hearth.
It will be obvious that the success of my process depends greatly
upon the manner in which the molten cast iron is brought into contact
with the heated air as it descends through the latter. To ensure the
free and effectual exposure of the cast iron during its descent in the said
chamber, and the action of the oxygen of the air upon the crude metal
I arrange the bars g in the peculiar manner above described. The
aperture whereby the iron is discharged from the upper hearth bis
made long and narrow so that the molten iron escapes therefrom in a
broad thin stream or layer. The aforesaid bars divide this stream into
drops or small streams and change the direction and position of the
particles of metal as they fall from one row of bars to the next row, so

page_text: that all portions of the metal are fully exposed to the hot air and the
removal of the carbon by oxidation is effected under the most favorable
conditions. Moreover any impurities such as sulphur, arsenium, phos-
phorous or silicon contained in the iron are oxidized and carried off.
In the manufacture of steel a small quantity of nitrogen is taken up
from the air; and in some cases I use a small quantity of titanic acid
to ensure the combination of the required quantity of nitrogen with the
steel.
In the manufacture of iron or steel from iron ore, according to this
Invention, the furnace is charged and the ore reduced by the combustion
of coal or other fuel in the usual manner. As the ore is reduced the
molten iron drops from the pit a into the hearth b. Accumulating in
this hearth it rises to the level of the opening d, flows therefrom, and
falls down the vertical passage e, striking the bars g in its descent, and
being thereby separated and tossed from side to side, and otherwise
agitated and scattered as it falls so that all portions of the iron are
freely and fully exposed to the heated air as they pass through it, and
when the molten iron is received in the lower hearth fit will be freed
from its impurities and from its excess of carbon. The degree of
decarburization is regulated by the nozzles 1, 2, 3, as above set forth.
As the iron is at the same time and by the same process freed from
the carbon and its various impurities, it is unimportant whether the ore
or pig iron is melted down with either coke or coal. The sulphur,
arsenium, phosphorous, and silicon oxidize at a much lower temperature
than the carbon, and are carried off before the oxidation of the carbon
takes place. The high temperature of the air blast accelerates the
process of oxidation, and the more nearly the heat of the air approaches
that of the molten cast iron the more perfect will be the oxidation.
The lower hearth f is provided with a suitable tapping hole for the
discharge of the metal therefrom, and when this metal has been drawn
from the said hearth it will be good sound homogeneous metal either
steel or bar iron as required and will be quite ready for use without
further treatment.
It will be understood from the above description that my process is
continuous, that is to say, there is no interruption thereof from the time
the iron ore or pig iron is placed in the furnace till it is withdrawn from
the lower hearth, and I produce either steel or bar iron or an

page_text: intermediate metal by a very slight variation of the blast as hercin
described.
I do not confine myself to the particular form of furnace above
described, as the construction of the same may be varied, and I may
utilize existing furnaces of various forms by adding to the same an 5
arrangement of hearths with the air passage and blast, as shewn.
Having thus fully described my said Invention and the manner of
performing the same, I wish it understood that I claim,―
First. The process herein described whereby I produce in a blast
furnace by the admission of heated air to a descending stream of molten 1
iron, and without any apparatus separate from the said blast furnace, or
any treatment subsequent to the removal of the metal therefrom,
homogeneous cast steel, malleable iron, or a metal intermediate between
the same.
Second. A blast furnace so constructed that the metal melted or I
reduced therein may be discharged in the condition of cast iron, or may
be converted into cast steel, malleable iron, or an intermediate metal by
regulating the admission of heated air to a stream of molten cast iron
descending through the same.
Third. In a blast furnace the upper and lower receiving hearths 2
arranged as described and connected by a vertical passage or channel
which is supplied with heated air as herein described and for the purpose
set forth.
Fourth. Providing the said vertical passage or channel with bars of
fire-clay or other refractory material arranged in the peculiar manner 2
set forth for the purpose specified.
In witness whereof, I, the said Friedrich Hahn, have hereunto sct
my hand and seal, this Thirteenth day of November in the year
of our Lord One thousand eight hundred and seventy-two.
F. HAHN. (L.S.)
1
Witness,
WM. ROBT. LAKE.