IMPROVEMENTS IN THE MANUFACTURE OF BASIC BRICKS, AND IN THE MATERIALS USED IN THE MANUFACTURE OF METAL CASTINGS
Year: 1881

page_text: LETTERS PATENT to Sidney Gilchrist Thomas, of 27, Tedworth Square,
London, for an Invention of "IMPROVEMENTS IN THE MANUFACTURE OF
BASIC BRICKS, AND IN THE MATERIALS USED IN THE MANUFACTURE OF
METAL CASTINGS."
PROVISIONAL SPECIFICATION left by the said Sidney Gilchrist Thomas
at the Office of the Commissioners of Patents on the 8th October 1881.
SIDNEY GILCHRIST THOMAS, of 27, Tedworth Square, London.
"IMPROVEMENTS
IN THE MANUFACTURE OF BASIC BRICKS, AND IN THE MATERIALS USED IN THE
MANUFACTURE OF METAL CASTINGS."
Magnesia has hitherto not been successfully used on a large scale for the manu-
facture of bricks, owing to the unsuitable methods employed in the manufacture
of such bricks.
By my Invention I make good magnesia bricks as follows:-I tako ordinary
magnesia or magnesite or hydrate of magnesia, which later may be made by
precipitating by magnesian-lime the magnesia from dolomite which has been
dissolved in hydrochloric acid; I prefer it to be as pure as possible and free from
silica, and I burn it at an intense white beat, preferably for not less than forty-
cight hours, until it has shrunk to about half its original bulk. It may be advan-
tageously made up into rough bricks for convenience of burning, and is best burnt
in a down draft kiln preferably fired by gas, or it may be burnt in a cupola at an
intenso white heat; I then grind the burnt and thoroughly shrunk material, and
mix it with a little water or tar; it is then made into bricks of the desired form,
with or without pressure; the bricks aro then dried at a moderate temperature,
and preferably burnt again at a white heat. Such bricks may be advantageously
used for lining converters and furnaces, and basic twyers may be prepared in the
same way. I also employ this highly calcined and shrunk magnesia as a material
for making moulder's sand or loan. It is especially used for steel castings which

page_text: are very hard to make with ordinary moulding sand, as it does not stick to the
.metal and is quite infusible. It may be used by itself moistened with a little
water or for some castings in admixture with a little clay or silicate of soda or tar
to give it coherence.
In the manufacture of basic lime bricks it has been found that a considerable !
economy is obtained by building in magnesia bricks, mado as herein described,
between the courses of dolomite or lime bricks, in this way the excessivo shrinkage
of the lime bricks is counteracted by the non-shrinkage of the magnesia bricks,
and the lime bricks may be piled twenty or thirty courses high instead of eight
or ten courses, thus resulting in a notable economy of fuel.

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
8th April 1882.
SIDNEY GILCHRIST THOMAS, of 27, Tedworth Square, London.
"IMPROVEMENTS
IN THE MANUFACTURE OF BASIC BRICKS, AND IN THE MATERIALS USED IN THE
MANUFACTURE OF METAL CASTINGS."
Magnesia has hitherto not been successfully used on a large scale in the manu-
facture of bricks, this being chiefly owing to the unsuitable methods used in the
manufacture of such bricks. I have found that for the manufacture of hard,
durable, and refractory magnesian bricks the following process must be adopted:
I tako magnesia or carbonate or hydrate of magnesia, which latter may be obtained
by reprecipitating by magnesian limo magnesia from a solution of dolomite in
hydrochloric acid or in any other known way. The magnesia should not contain
more than five per cent. of silica. If the magnesia or carbonate or hydrate of
magnesia contains less than about five per cent. of silica it may be (particularly if
it bo in a state of powder) mixed with enough clay to give it about five per cent.
of silica and two or three per cent. of alumina and oxide of iron, but the pure
magnesia is however to be preferred when the bricks are to be exposed to a very
intense heat; the material, with or without this mixture, is then burnt in rough
bricks or blocks at an intense white heat either in lime lined cupolas or kilns, but
preferably in regenerative or continuous gas kilns with a down draught. This
burning may be performed very rapidly, a short exposure to a very intense heat
being all that is necessary; thus in a cupola the material may be drawn every
twelve hours; a very intense white heat is however absolutely necessary for success,
the object being to produce an intensely shrunk material; I then take this shrunk
magnesia and grind it with either water, tar, or crude hydrocarbon oils to form a
plastic mass, coke dust or plumbago in proportion not exceeding twenty per cent.
may be ground up with the magnesia; if a light brick is desired the mass is then
made into bricks either by hand or machine, but preferably using considerable
pressure; they are then dried, after which they are fit for use for some purposes,
but I prefer particularly when they are to be exposed to a very high heat that
they should be again fired in a gas or other kiln at a full white heat. I have also
found that from this highly calcined and shrunk magnesia an excellent material for
making moulder's sand or loam may be formed.
It is especially suited for steel castings, as it is quite infusible, does not stick to
the casting, and castings formed in it are particularly sound. For this purpose it
may be used by itself or mixed with graphite, clay, or coke dust, and moistened
with water, or tar, or oil, according to the purpose for which it is to be used. In
carrying out the manufacture of basic or lime bricks I have found that the
inconvenience and loss resulting from the great shrinkage of the bricks in the kiln
may be avoided in the following mannor:-Bricks of shrunk magnesia prepared as
herein described are inserted as binding courses in the kiln between every sixth or
seventh row in height of the lime bricks, thus in a vertical section of a kiln full of
bricks we have six or seven courses of lime bricks followed by a course of magnesia
bricks, on which again there will be six or seven courses of lime bricks, then a
course of magnesia bricks and so on; in this way the excessive shrinkage of the
lime brick is counteracted by the non-shrinkage of the magnesia brick, and the
lime bricks may be piled twenty or thirty courses high instead of eight or ten
courses high, which leads to a very great economy of fuel.

page_text: Having thus described my Invention, what I claim and desire to secure by
Letters Patent is,-
The herein described improvements in the manufacture of basic bricks, and in
the materials used in the manufacture of metal castings, consisting in,―
1st. The preparation of magnesia for the manufacture of magnesian bricks by
firing it at an intense white heat, and the subsequent treatment herein described.
2nd. The herein described method of interposing courses of magnesian bricks
between the courses of lime bricks when firing lime bricks in kilns, substantially
ns and for the purposes set forth.
3rd. The preparation and employment of highly shrunk magnesia for moulder's
loam or sand, especially for steel castings, all as herein before described and for the
purposes set forth.
In witness whereof, I, the said Sidney Gilchrist Thomas, have hereunto
set my hand and seal, this Sixth day of April, in the year of our Lord Ono
thousand eight hundred and eighty two.
Signed, sealed, and delivered in
the presence of
HENRY B. HATCHWELL,
14, Southampton Bldgs.,
London, W.C.
SIDNEY GILCHRIST THUMAN.
(L.S.)