IMPROVEMENTS IN THE MANUFACTURE OF STEEL AND IRON, AND IN THE FURNACES USED FOR SUCH 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 THE
FURNACES USED FOR SUCH MANUFACTURE."
Sealed the 7th May 1878, and dated the 6th March 1878.
PROVISIONAL SPECIFICATION left by the said Sidney Gilchrist Thomas at
the Office of the Commissioners of Patents on the 6th March 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 THE FURNACES USED FOR SUCH MANUFACTURE."
In carrying out the improvements in the manufacture of steel and iron detailed
in my Provisional Specifications of the 23rd November 1877 and 22nd January
1878, I find that various other basic mixtures may be advantageously used, as the
material for forming the lining of the Bessemer converter, and the interior of the
furnace employed in the open hearth processes for the manufacture of steel or cast
malleable metal, so as to enable a basic slag in which phosphorus is removed to be
produced. Thus I find that blast-furnace slag or ore-furnace copper slag, or clay, or
Portland cement, or other similar hydraulic cements; or the natural silicates of
magnesia or borax, when ground up with limestone, give it sufficient tenacity to
form a satisfactory basic lining or fire-brick without materially diminishing its
refractory character.
Carbonate of magnesia, magnesia, magnesian limestone, or carbonate of baryta
may sometimes be substituted for limestone.
Čertain natural limestones which contain a considerable proportion of silica or of

page_text: silica and alumina, such as lias limestone and other hydraulic limestones, may be
ground up and sometimes used without any admixture, though it is generally
desirable to add a little silicate of soda.
Ordinary lime or limestone cannot be successfully used by itself on a commercial
scale. If so much silica is present in a hydraulic limestone as to make it non-
refractory it should be mixed with a purer limestone before being used.
I find a mixture of eighty-six parts of limestone, eight or nine of glassy blast-
furnace slag, and five of silicate of soda solution, a good one.
Though silicious substances may be advantageously used as a binding material
only a sinall quantity should be used, and the total silica present in the mixture
should not exceed about ten or twelve per cent. as a maximum.
The tuyeres used in the converter I make of approximately the same materials as
the lining. Thus I find a mixture of eighty-five parts of ground limestone, with
ten parts of clay and five of a solution of silicate of soda, makes an excellent
tuyere. I also make tuyeres of a mixture of limestone and oxide of iron in the
proportion of from two to four parts of oxide of iron to one hundred parts of
ground limestone..
The ladle into which the converted metal is tapped should be lined with one of
the basic mixtures above described.
These mixtures may, in all cases, either be rammed into an iron casing, or they
may be made into bricks before being used.
The bricks, and also the tuyere, should be well burnt before being used, having
been previously dried at a low heat.

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 5th
September 1878.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Queen's Road, Battersea,
in the County of Surrey. "LMPROVEMENTS IN THE MANUFACTURE OF STEEL AND
IRON, AND IN THE FURNACES USED FOR SUCH MANUFACTURE."
In carrying out the improvements in the manufacture of steel and iron detailed
in the Specifications of my Patents, No. 4422 in the year 1877 and No. 289 in the
present year, I find that certain basic mixtures other than those therein claimed
may be advantageously used as the material for forming the lining of the Bessemer
converter, and the interior of the various furnaces employed in the open hearth
processes for the manufacture of steel or ingot iron, so as to enable a basic slag in
which phosphorus is removed to be produced. Thus I find that alumina and silica,
when intimately mixed with limestone (particularly the magnesian limestones), in
certain proportions, give it, when exposed for a sufficient period to an intense heat,
sufficient strength and cohesiveness to form a satisfactory basic lining material.
The silica and alumina necessary for this purpose may be either present naturally
or be introduced artificially, as in the form of clay or aluminous shale, or aluminous
blast-furnace slag.
The substance which I find by far the most advantageous to use is a highly
magnesian limestone (the more magnesian the better) containing naturally sufficient
silica and alumina to produce, when fired at a very high temperature, a strong
coherent refractory substance. A highly magnesian limestone containing about
eight per cent. of silica, three and a half per cent. of alumina, and two per cent. of
oxide of iron is a suitable one. To improve its coherence the ground material may
be tempered with clay water. If this description of magnesian limestone is not
readily available a purer magnesian limestone may be used after being ground up
with a very aluminus limestone (this being preferably also magnesian), so as to give
a composition as regards alumina and silica approximating to that quoted in the
preceding paragraph; or a material of similar composition may be obtained by
grinding a comparatively pure magnesian limestone with clay or highly aluminous
blast-furnace slag (the slag being preferably also a magnesian one), or with
aluminous shale.
Aluminous non-magnesian limestone is in all cases inferior to magnesian limestone
for my purpose, but when the lining can be always kept perfectly dry and magnesian
stone is not available it may be used.
Magnesia or carbonate of magnesia mixed with the binding materials above
mentioned may sometimes be used instead of limestone, but its cost is almost
prohibitive. A small quantity of magnesia may, however, often be mixed with the
imagnesian limestone materials before mentioned with advantage.
From three to four and a half per cent. of alumina, from six to eight or nine per
cent. of silica, and from one to two per cent. of oxide of iron may be taken generally
to represent the limits for the most favorable proportions of binding material in a
good lining material before calcination.
As a general rule the more alumina there is present (so long as the refractory
character of the mixture is unimpaired) the better; but if much oxide of iron is
present there should be comparatively little alumina, and vice versa, as oxide of
iron is very apt to cause fusibility.
Though silica is a most excellent binding material there are limits beyond which
its presence becomes injurious. Thus the total silica present in the uncalcined
material should not exceed eleven per cent. as a maximum.
As the composition of magnesian limestone is very variable, and a small excess of
alumina or oxide of iron will greatly affect the character of the material, it is best
in all cases when new materials are used to prepare trial bricks approximately of
the desired composition, and to expose them after drying to a full white heat for,

page_text: say, twelve or twenty-four hours. If they fuse, the proportion of alumina or oxido
of iron is too high. If they are tender after removal or soon become so on exposure
to the air, the amount of binding material present is too small. If, however, a
compact hard brick is formed the composition may be generally considered as
satisfactory.
The purer varieties of lime or limestone by itself cannot be successfully used for
basic linings, the presence of a minimum of about six per cent. of silica and alumina
being essential to make a tolerable material.
To make basic bricks, which is the form in which the materials above described
should be used for lining the Bessemer converter, I proceed as follows:-The
material, such as has been above described, is finely ground and moistened, and
moulded into bricks under considerable pressure. The bricks are dried slowly and
then fired for a considerable period at an intense white heat. When fired at
ordinary temperatures the bricks are soft and disintegrate on exposure to the air.
The temperature in the kiln should be high enough and continued for a sufficient
period to cause the whole of the alumina and silica present to enter into combination
with the lime and magnesia. The kiln should preferably be one with a down draft,
and the basic bricks should be separated from the silicious bricks forming the floor,
etc., of the kiln by a layer of neutral material such as tale or steatite.
I have found a good brick made from an aluminous limestone containing equal
amounts of carbonate of magnesia and carbonate of lime to contain, after firing,
fourteen per cent. silica, six per cent, of alumina, and three and a half per cent. of
peroxide of iron. A good brick will generally contain less than eighty per cent. of
line and magnesia after firing, and more than seventy per cent.
The bricks should always be kept as dry as possible both before and during use.
The converter bottom may be rammed with a mixture of magnesian limestone
and silicate of soda solution, prepared as described in my Specification No. 4422 in
the year 1877. This mixture may also be used as the basic cement in which it is
necessary that the bricks should be set; or the bottom may be partly formed of
basic bricks and partly rammed either with the basic material herein described or
with the silicate of soda mixture; or it may be entirely ramined with the basic
material herein described.
Bessemer twyers may be formed of the same material as bricks, and used either
simply dried or fired at a high temperature; when fired they have a tendency to
become deformed by shrinkage. Twyers made as described in my Patent No. 4422,
1877, may also be used with these linings.
In the Siemens-Martin, Pernot, or other open-hearth steel furnaces I line the
hearth with the basic material already described, preferably in the form of bricks.
The other parts of the furnace may also sometimes be lined with these basic bricks;
or I line the hearth with the basic material herein described carefully raminer, the
flame being allowed to play on the hearth for a sufficient time to cause the formation
of silicates and aluminates of lime and magnesia, and thereby secure a compact
lining before the charge is introduced.
When the hearth of a Siemens' or other open-hearth furnace is lined with a basic
mixture it is often useful for convenience of repair to have the hearth of the furnace
mounted on a carriage, so that it may be readily removed when it requires repairs,
and a fresh hearth put in its place, as has been often before proposed.
It will be readily understood that when the roof of the furnace is of silica bricks
it must be separated from the basic hearth by some non-fluxing material, such as
silicate of magnesia or plumbago bricks.
It is to be understood that these basic linings are to be used in conjunction with
the mode of rendering the slag basic by basic addition, as already sufficiently
described in my Patent No. 289 of the present year.
Having thus described the nature of ny said Invention and the manner of
performing the same, I would have it understood that it has before been proposed
to employ as the lining of a Bessomer converter limestone (or lime) "containing as
little silica as possible," and with or without a little oxide of iron; and it has been

page_text: proposed to prepare this material for use by making it into bricks to be employed
either unburnt or burnt, presumably at the temperature at which clay or fire-clay
bricks are commonly burnt; to this therefore, which in my experience is not
practically successful, I make no claim, but what I claim is,-
First. Lining Bessemer converters with basic bricks formed of the natural or
artificial mixtures herein described, and fired at an intense white heat.
Second. Lining the hearth or the interior of open-hearth steel furnaces with basic
bricks prepared as herein described.
Third. Lining the hearth of open-hearth steel furnaces with the basic mixtures
herein described, used as a rammed lining, and highly fired.
In witness whereof, I, the said Sidney Gilchrist Thomas, have hereunto set
my hand and seal, this Fourth day of September, in the year of our Lord One
thousand eight hundred and seventy-eight.
SIDNEY G. THOMAS. (L.S.)