IMPROVEMENTS IN THE MANUFACTURE OF STEEL AND IRON, AND IN FURNACES EMPLOYED IN THIS MANUFACTURE
Year: 1878

page_text: LETTERS PATENT to Sidney Gilchrist Thomas, of 3, Queen's Road Villas, Queen's
Road, Battersea, in the County of Surrey, for the Invention of "IMPROVEMENTS
IN THE MANUFACTURE OF STEEL AND IRON, AND IN FURNACES EMPLOYED IN
THIS MANUFACTURE."
Sealed the 22nd March 1878, and dated the 22nd January 1878.
PROVISIONAL SPECIFICATION left by the said Sidney Gilchrist Thomas at
the Office of the Commissioners of Patents on the 22nd January 1878.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Queen's Road, Battersea,
in the County of Surrey. "IMPROVEMENTS IN THE MANUFACTURE OF STEEL AND
IRON, AND IN FURNACES EMPLOYED IN THIS MANUFACTURE.”
My improvement consists in the removal of phosphorus from pig iron into and
with the slag produced in the manufacture of iron and steel by the Bessemer and
Martin and Siemens-Martin processes, and similar open hearth processes.
In these processes as at present carried out very little or no phosphorus is
removed from the metal under treatment, either into the slag or otherwise.
In carrying out my improvements in these processes, my constant object is to
produce a basic slag.
In carrying out the Bessemer process I use a basic or but slightly silicious lining
for the converter, and I add to the metal in the converter such a quantity of a basic
body, preferably non-silicious iron ore or lime, though common salt, carbonate of
soda nitrate of soda (or other alkaline bodies), may be used as will secure the slag
being of a highly basic character.
I prefer that the linings should be of the kind described in my Provisional
Specification, No. 4422, 1877, but they may be made of other basic substances, as
lime or alumina, with or without binding material, as clay or oxide of iron.
I am aware that it has been proposed to use certain of these substances as linings
for Bessemer converters, and also that it has been proposed to add lime, oxide
of iron, and other bodies to the contents of the Bessemer converter which, as is
well known, is in, practice always lined with a highly silicious material, such as

page_text: fire-clay or gannister. Now I find the addition of basic substances to the contents
of a converter lined with silicious substances is followed by a rapid destruction of
the lining, and it is also on this account difficult to produce a basic slag. I there-
fore, when adding these substances, use basic linings, i.e., linings containing but
little silica, the use of which I consider essential to render technically advantageous
the addition of these substances.
In carrying out the Martin or Siemens-Martin or other open hearth processes for
the manufacture of iron or steel, it has been hitherto the practice to work with a
silicious slag (containing on the average considerably above 45 per cent. of silica),
and sand is sometimes added with a view to render the slag sufficiently silicious.
My improvements in these processes consist in working with a basic slag, and to
admit of this I make either the whole or those parts of the furnace in contact with
the molten metal of lime and silicate of soda or other of the materials detailed in
my Provisional Specification, No. 4422, 1877; by observing this condition the slag
produced in the course of the process will sometimes be of a basic character. To
assist this end I however add lime, oxide of iron, or salt or carbonate of soda when
the slag is not otherwise sufficiently basic; 1 may point out that the addition of
lime and basic substances, when the hearth of the furnace is constructed of sand,
will not answer the purpose I have in view.
The whole or those parts of the above furnace which are in contact with the
molten metal may also be composed of burnt lime, or preferably limestone, or of
alumina with or without the addition of a small quantity of clay or other-binding
material.
All these basic lining materials may be used either as bricks or be rammed into
an iron casing.
As a binding material silicate of soda may be advantageously employed; it is
applicable to all furnaces in which a lining of lime, limestone; or such like material
is employed.
In case it be preferred to retain the silica bricks now in use for the roof of the
furnace, the silica bricks should not be allowed to come into direct contact with the
basic material forming the hearth or side, but be separated by a layer of best
plumbago bricks or other non-fluxing refractory material.
According to my improvements in working the Martin or Siemens-Martin process
therefore, the process throughout is so conducted that at no time is the slag
silicious.
It is desirable not to allow the slag to contain more than 25 per cent. of silica.
By these means it is possible to use both in the Siemens-Martin and Martin pro-
cesses, and also in the Bessemer process, pig iron containing a considerable per-
centage of phosphorus, and a considerable amount of sulphur, and yet make good
merchantable steel and cast metal, and this without the use of expensive alloys of
manganese, such as ferro-manganese.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Sidney Gilchrist Thomas in the Great Seal Patent Office on the 20th
July 1878.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Queen's Road, Battersea,
in the County of Surrey. "IMPROVEMENTS IN THE MANUFACTURE OF STEEL AND
IRON, AND IN FURNACES EMPLOYED IN THIS MANUFACTURE,”
My improvements in the manufacture of steel and ingot iron consist in
effecting the removal of phosphorus from pig iron into and with the slag produced
in operating by the Bessemer process, and the Siemens-Martin, Siemens, and other
similar open hearth processes by causing highly basic slags to be produced and
maintained.
In these processes as at present carried out little or no phosphorus is removed,
either into the slag or otherwise.
In carrying out my improvements in these processes, my constant object is to
produce a highly basic slag, in which alone phosphorus can be retained and removed.
To effect this in carrying out the Bessemer process, I use a basic lining for the
converter, and I add to the metal in the converter such a quantity of a basic body,
namely, lime and oxide of iron, or a mixture of these, as will secure the slag being
highly basic, particularly during the latter part of the blow. By highly basic I
mean that the amount of silica in the slag in which it is desired to remove phos-
phorus should be less than thirty-three per cent. as a maximum, and it should
preferably be less than twenty-five per cent, while when a very phosphoretic
pig is being treated, it is desirable that the final alag should contain considerably
less than twenty per cent. of silica. To obtain this result a large quantity of basic
material should be thrown into the converter.
I prefer to make this addition in the following manner:-Before tapping the
molten metal into the converter I throw into the converter an amount of newly
burnt lime broken in small pieces, nearly equal in weight to the silicon contained
in the charge of pig to be operated on. If, however, on account of the coldness of
the converter or any other reason there is cause to believe that the metal will not
blow hot enough, the amount of lime thrown in is reduced. The metal is then run
in and blown in the usual way, till sufficient heat has been developed in the metal
to enable the basic addition mentioned in the next paragraph to be made without
cooling the metal to such an extent as to prevent its being subsequently success-
fully tapped. The vessel is then turned down and molten iron ore or other oxide
of iron (which should be as non-silicious as possible) is thrown in together with
newly burnt non-silicious lime.
It is preferable to throw in a molten mixture of oxide of iron and lime, these
bodies having been previously melted together. The total weight of this basic
addition should not (when the pig treated is very phosphoretic) generally be less
than four times the weight of the silicon originally contained in the charge unless
the metal does not blow hot or a very manganiferous pig is treated.
A little oxide of manganese may be added with the other bases. Immediately after
the basic addition has been made, the vessel is turned up and the blow is finished.
Before making the usual addition of spiegel, the slag may be tapped off as
recommended in my Patent, No. 4422, in the year 1877, or if this be not done, it is
preferable to add the spiegel simply in red hot lumps (and not molten), providing
the metal is hot enough to allow of this being done. If the metal is not hot enough
to allow of this being safely done, the spiegel should be so added as to pass through
as little slag as possible.
Whether molten oxide of iron or a molten mixture of oxide of iron and lime
are used, its fusion should take place in a basic lined cupola (preferably blown
with a hot blast) or air furnace, so that as little silica as possible may be intro-
duced into the charge..

page_text: It is desirable that the molten basic material should be transferred very rapidly
⚫ from the furnace in which it is melted to the converter, either by using a very
short runner (which should have a basic lining), or it should be tapped into a basic
lined ladle, and so rapidly conveyed to the converter. It will otherwise set before
reaching the converter.
The objects to be kept in view are to let the basic addition be as hot as possible
and as free as possible from silica.
Lime and peroxide of iron readily melt together in many different proportions.
A mixture, in which from two to three parts of limestone, or from one to two of
lime is mixed with one part of oxide of iron, is a suitable one to use..
It is essential that when using these basic additions for the removal of phosphorus
the converter should be lined with a refractory basic substance.
The basic substance I prefer to use is magnesian lime in the form of very highly
fired bricks prepared from magnesian limestone, mixed with a little highly aluminous
limestone or clay, this being one of the linings referred to in my Provisional
Specification of the 6th of March 1878.
I am aware that it has been proposed to add small quantities of lime, and of oxide
of iron and other hodies to the contents of the Bessemer converter, such converter
having been hitherto lined only with highly silicious substances.
I am also aware that a few pounds of limestone is in practice sometimes added
to the contents of the converter, but this is of no avail in producing a basic slag, or
for the elimination of phosphorus.
I am also aware that certain basic substances have been suggested as suitable
for lining Bessemer converters.
Now I wish to point out that the addition of basic substances to a converter
with a silicious lining is followed by a rapid destruction of the lining, so that
it is commercially impossible to obtain by this means a sufficiently basic slag to
secure the removal (to any considerable extent) of phosphorus, even when a large
quantity of base is added. Nor can phosphorus be commercially removed by the
use of such basic linings as have been suggested, unless a large quantity of basic
material be added to the charge so as to obtain economically a highly basic
slag.
I do not claim the mere use of a basic lining in the Bessemer converter, nor the
mere addition of basic material to the Bessemer charge, but I claim the addition to
the contents of a Bessemer converter lined with a basic substance of basic oxides,
in such manner as to obtain a highly basic slag, and to effect the removal of
phosphorus, substantially as herein described.
In carrying out the Martin or Siemens-Martin or other similar processes for the
manufacture of steel and ingot iron, it has hitherto been the practice to work with
a silicious slag, namely, one containing on the average over forty-five per cent. of
silica, and sand has been even sometimes added with a view to render the slag
silicious.
My improvements in these processes consist in working with a very basic slag.
To admit of this it is necessary to make the interior of the furnace, or at least the
hearth of the furnace, and all those parts which are in contact with the molten 4
metal or slag, of some refractory basic substance. For this purpose I prefer to use
either highly calcined magnesian lime, bricks made from magnesian limestone
mixed with a little clay, or highly aluminous limestone, this being one of the linings
referred to in my Provisional Specification of the 6th March 1878, or I use finely
ground highly magnesian limestone intimately mixed with about eight or ten per 5
cent. of its weight of a solution of silicate of soda of a specific gravity of 1.4 to 1.5
rammed hard round the bottom of the furnace so as to form the hearth.
If the magnesian limestone be not naturally aluminous, a little clay may be
added to it and ground up with it.
Aluminous limestone may also be used with silicate of soda instead of magnesian 5
limestone to form the hearth of the furnace, but care must be taken that not
enough alumina or alumina and oxide of iron is present to make the limestone

page_text: fusible. Nor is it desirable that more than seven or eight per cent. of silica be
present in the limestone used. I do not however confine myself to these methods
of forming a basic lining.
When silica bricks, such as are now generally employed, are used for the roof of
the furnace, and those parts of the sides which are not in contact with the charge,
which is often a desirable course, these silica bricks should not of course be allowed
to come into direct contact with the basic material of the hearth or sides, but be
separated from it by a layer of plumbago, bricks, or of coke mixed with clay or
with clay and silicate of soda solution or other non-fluxing refractory material.
In order to make the slag highly basic I add at intervals lime or limestone, and
oxide of iron in quantity sufficient to prevent the per-centage of silica in the slag
rising at any rate above thirty-three per cent., and I prefer to keep it at a considerably
lower point. Both the lime and oxide should be as little silicious as possible.
The lime and oxide may be conveniently used in the form of a fusible mixture,
such as from one and a half to two parts of lime for one of oxide of iron.
If any considerable part of the charge already consists of iron ore (as it is
desirable should be the case), it will be only necessary to add lime,
The character of the slag may be judged of by the workman from time to time,
taking out a sample and ascertaining if it has a glassy or silicious fracture and
appearance which is to be avoided.
The more phosphorus and silicon there is present in the metal used, the greater
will be the amount of base required to be added.
It is desirable that the slag should not contain more than twenty-five per cent.
of silica, and preferable, particularly when very phosphoretic materials are being
treated, that it should contain less than twenty per cent. If it contains more
than thirty-three per cent., only a small proportion of the phosphorus will be
removed.
I am aware that iron ore and sometimes lime are thrown into the furnace in
carrying out these processes. This however is not done with the view of rendering
the slag highly basic, so as to enable the phosphorus to be removed, nor is this
result obtained, owing chiefly to the silicious character of the hearth.
What I claim is,-
Conducting the Siemens-Martin, Siemens, and such like processes for the manu-
facture of steel.in furnaces having basic linings, and (in combination with the use of
such furnace linings) maintaining the slag in the furnaces in a highly basic state,
substantially in the manner described.
I claim also the use of magnesian or aluminous limestone mixed with silicate of
soda as a lining for the Siemens furnace, as herein described.
By my improvements in the Bessemer process, and also in the Siemens-Martin,
Martin, and other similar processes, pig iron, containing much phosphorus may be
used, and yet good merchantable steel and ingot iron produced, and this without it
being necessary to use expensive alloys of manganese, such as ferro-manganese.
In witness whereof, I, the said Sidney Gilchrist Thomas, have hereunto set my
hand and seal, this Eighteenth day of July, in the year of our Lord One
thousand eight hundred and seventy-eight.
THOMAS
L
SIDNEY GILCHRIST THOMAS. (L.S.)