IMPROVEMENTS IN THE MANUFACTURE OF STEEL AND IRON, AND IN THE MANUFACTURE OF REFRACTORY BRICKS
Year: 1878

page_text: LETTERS PATENT to Sidney Gilchrist Thomas, of 3, Queen's Road Villas,
Queen's Road, Battersea Park, in the County of Surrey, for the Invention of
IMPROVEMENTS IN THE MANUFACTURE OF STEEL AND IRON, AND IN THE
MANUFACTURE OF REFRACTORY BRICKS."
Sealed the 11th February 1879, and dated the 14th October 1878.
PROVISIONAL SPECIFICATION left by 'the said Sidney Gilchrist Thomas
at the Office of the Commissioners of Patents on the 14th October 1878.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Queen's Road, Battersea
Park, Surrey. "IMPROVEMENTS IN THE MANUFACTURE OF STEEL AND IRON, AND
IN THE MANUFACTURE OF REFRACTORY BRICKS."
In carrying out the improvements in the manufacture of iron and steel detailed
in the Specifications of my Patents, No. 908 and 289, in the present year, I find
that refractory basic bricks, especially suitable for lining Bessemer converters and
open hearth steel furnaces, may, by the application of a very intense heat, be made
from natural magnesian limestone, in which there is present naturally or with
which there is mixed artificially from two to five or six per cent. of silica and allumina
together, or a stone with a very small per-centage of allumina and silica, but a con-
siderable amount of oxide of iron may be used, care being taken that not so much
oxide of iron is present as to render the mixture unrefractory. In all cases, arti-
ficial mixtures, as of a nearly pure magnesian limestone mixed with from three to
four or five per cent. of oxide of iron may be used when a natural stone of the
desired composition is not obtainable.
The temperature at which the bricks are fired (after slow drying) must be
exceedingly high (exceeding an ordinary white heat); a kiln fired by a regenerative
gas furnace will conveniently supply the intense temperature which is requisite.
Ordinary fire-clay kiln temperatures are not sufficient. Instead of grinding the
stone before making into bricks, blocks of natural stone of moderate size and of the
above-mentioned composition may be used after the same intense firing.

page_text: I also, when using basic bricks in the Bessemer converter, find that the requisite
basic slag may be produced by adding from six to ten times the weight of lime that
there is of silicon present in the pig treated, without any oxide of iron (or at all
events with very little) being added. The lime should preferably be very highly
heated, and may be either a magnesian lime or an ordinary non-silicious lime. It
is generally desirable that the slag should be present in such quantity as not to
contain more than from twelve to fourteen per cent. of phosphoric acid.
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 12th
April 1879.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Queen's Road, Battersea
Park, in the County of Surrey. "IMPROVEMENTS IN THE MANUFACTURE OF STEEL
AND IRON, AND IN THE MANUFACTURE OF REFRACTORY BRICKS."
This Invention consists in certain improvements having relation to the same
object as Inventions detailed in the Specifications of my Patents, Nos. 908 and 289
and 3975 in the year 1878, viz., the manufacture of refractory basic furnace
lining materials, especially suitable for lining Bessemer converters and open hearth
steel furnaces, and the treatment of phosphoretic pig iron in Bessemer converters
lined with such materials.
In carrying out the manufacture of refractory basic furnace linings, I have some-
times found it desirable and convenient in order to diminish the amount of silica
and alumina which is imparted to the slag from the wear of the lining material,
and to prepare a lining material from local kinds of magnesian limestone in which
the silica and alumina together amount to less than five per cent., though to more
than two per cent. of the whole; and I find that by subjecting bricks or blocks
moulded from such material in a pulverulent and slightly moist state to extremely
intense firing before use, a dense shrunk material very useful as a furnace lining
may be produced from limestone of this character. I do not however regard it as
desirable to use a stone with less than about three and a half per cent. of silica and
alumina together unless there is two or three per. cent of oxide of iron also present;
astone with a very small per-centage of silica and alumina but with three to five
per cent. of oxide of iron may also be used, care being of course taken that not
enough oxide of iron is present to impair the refractory character of the material.
I consider the following compositions to be good ones:--
'
per cent.
{
Silica.
2 to 4
1 to 2
Alumina.
1 to 3
1 to 2
Oxide of iron.
0 to 212
21 to 4.
2
Less advantageously, limestone low in magnesia or even chalk may be used when
a limestone high in magnesia is not obtainable, the more magnesia there is present
the better.
i
In all cases, artificial mixtures, as of a nearly pure magnesian limestone with
from three to five per cent. of oxide of iron (such as blue billy) or with three or four

page_text: per cent. of clay intimately mixed together, and preferably ground together in a
mortar mill, may be used. The greatest care must however be taken to make the
inixture regular and the composition even. The grinding should also be very fine
indeed. The slightly moist mass resulting from grinding the limestone is made
into bricks, preferably under great pressure.
The bricks are best made of moderate size and thickness, say 9 inches, by
4 inches, by 3 inches.
The bricks or blocks are subjected, after drying at a moderate temperature, to a
very intense firing. . I find that the less silica and alumina the stone contains the
more intensely must the bricks or blocks be fired to get the compact hard dense
shrunk structure which I find it requisite to obtain before limestone can be advan-
tageously used for forming furnace linings. The firing may be conducted in any
kiln in which a very intense temperature can be raised. The heat used for burning
ordinary fire-clay bricks is not high enough, nor will a heat which suffices for
firing limestone bricks containing ten or twelve per cent. of silica and alumina give
satisfactory results when burning my present bricks with low per-centages of silica
and alumina; when there is much oxide of iron present, however, the temperature
is not necessarily quite so intense. The kiln should, like those employed in burning
my previously referred to basic bricks, be lined with my basic lime bricks or best
silica bricks, and the floor formed with my lime bricks or lime blocks. The draft,
as in pottery kilns, should be a down draft and the flue holes evenly distributed
over the bottom. The bricks or blocks should not generally be stacked to a greater
height than four (4) feet.
A kiln fired by a regenerative gas furnace will conveniently supply the necessary
intense temperature; if this is not used a very large fire-grate area must be
provided.
The firing should be at first gradual, say for 24 or 36 hours after drying. It is
then pushed so as to give a very intense white heat, and kept at this for from 48 to
80 hours, according to the size of the kiln.
The cooling must be very gradual, and all access of cold air to the heated bricks
carefully avoided. The bricks or blocks, before use, should be kept very dry, and
are best used soon after they are taken from the kiln.
The bricks should be used with a basic cement. I use these highly-fired shrunk
bricks or blocks to grind up as a material for making basic cements, cement made
from. lime fired at ordinary temperatures being very inferior. The ground brick
mixed with a small quantity of solution of silicate of soda makes a good cement.
In carrying out the Bessemer process and treating phosphoretic pig iron, as
referred to in my Specification, No. 289, in the year 1878, in a converter lined
with these or other basic lime bricks, I find that the requisite highly basic earthy
slag should contain, to obtain the best results, a minimum of about forty per cent.
of lime and magnesia together, and I find that this description of slag is most
advantageously produced by adding to the metal in the converter a large amount
of lime (which may with advantage be magnesian lime) with little or, in some
cases, no iron ore. I operate in the following manner :—
Before running the metal into the converter, I throw into the converter an
amount of lime (preferably very hot) nearly equal in weight to twice the weight of
the silicon and phosphorus contained in the charge, or a mixture formed by calcining
a mixture of ground limestone and iron ore in the proportion of 1 ton of limestone
to 1 cwt. or even 2 cwt. of ore.
I then blow for from six to ten minutes, till the heat is sufficiently raised to
allow the rest of the bases to be added. I then turn down and add a somewhat
smaller amount than was first added (say 2/3 of the first amount) of either lime
alone (if the pig treated is high in manganese) or of a mixture of 3 or 4 parts of
lime to one of iron oxide ore. This addition should also be very hot. It may be
conveniently prepared by calcining at a high temperature a mixture of six or eight
parts of limestone, preferably a magnesian limestone containing with very little
silica one of iron ore, such as hoematite or blue billy.'

page_text: The heat of the converter flame may be conveniently utilised for heating these
basic additions. The converter is then quickly turned up and the blow finished.
When the metal is working very hot the whole amount of base may be added at
once, before the pig is run in, but this is not generally desirable. The total amount
of bases added should not be less with the ordinary wear of the bottoms than about
six times the weight of the silicon in the charge. I prefer not to use pig with
more than 2 per cent. of silicon. If however the bottoms last less than six blows,
the amount of bases is proportionately reduced, as a large amount of the base will
be derived from this source. The object to be kept in view in making the addition
is to have a slag containing over 40 per cent. of lime and magnesia, under 20 per
cent. of silica, and under 14 per cent. of phosphoric acid, assuming all the phos-
phorus of the pig to go into the slag as phosphoric acid.
Having thus described the nature of my said Invention, and the manner of
performing the same, I would have it understood that I claim,
First. The manufacture of hard shrunk lime bricks or moulded blocks suitable
for lining Besseiner converters and furnaces in which steel and iron is operated on,
from limestone of the character herein defined, and firing the same at an intense
heat, substantially as described.
Second. The method, substantially as described, of treating phosphoretic pig iron
in a Bessemer converter provided with a calcareous lining by the addition of lime
with or without a little oxide of iron, substantially in the manner and proportions
indicated.
In witness whereof, I, the said Sidney Gilchrist Thomas, have hereunto set
my hand and seal, this Tenth day of April, in the year of our Lord One
thousand eight hundred and seventy-nine.
SIDNEY GILCHRIST THOMAS. (L.S.)