IMPROVEMENTS IN THE MANUFACTURE OF PLASTER OF PARIS
Year: 1883

page_text: PROVISIONAL SPECIFICATION: left by John: Thomlinson at the Office of the
Commissioners of Patents on the 12th July 1883.
.
.POSK
JOHN THOMLINSON of the Knothill Plaster and Cement Works near Carlisle
"IMPROVEMENTS IN THE MANUFACTURE OF PLASTER OF PARIS "
«
This Invention has for its object improvements in the manufacture of plaster of
Paris.
"The manufacture is usually carried on at present by a process which is termed
Boiling."
The raw stone, known as plaster stone, gypsum and alabaster (all these names
are used) arrives in the mill from the quarries or mines in waggons in pieces
varying from the size of a turnip to the size of a man's head and upwards.
The process of boiling consists of passing the lumps of stone through a Blake's
stone crusher from which the crushed stone passes to the millstones and is ground
to a powder.
The cooking or getting rid of the water it contains is generally performed as
follows.
Over a series of flues from a furnace is laid a cast iron floor of a circular form,
and from the face of the cast iron floor brick work is built up about two feet high
to form the edge of the circle or pan or boiler as it is commonly called.
The boilers are made from 12 to 20 feet in diameter they are loaded with from 2
to 3 or more tons of the raw ground stone, the material being from 6 to 10 inches
deep. There is an upright shaft with two scrapers like plough shares being slowly
moved round amongst the powder. A large furnace underneath is kept going to
its fullest extent and in time the material begins to bubble and boil like in from 3
to 4 hours when all the water contained has been converted into steam the bubbling
ceases and the cooking is complete, the boiler slowly empties upon the floor from
which the hot plaster is filled into sacks.
The constant heating and cooling of the plates cause such expansion and
contraction that the joints open and the flues become soon filled with plaster,
the boilers are almost constantly under repairs and there is great waste of heat.
Directly the material on the pan begins to boil, the fine light particles begin to
fly about and soon the whole mill becomes a dense thick cloud of plaster and in
[Price 21

page_text: this condition is the mill constantly while outside all is white and thick with plaster
for a considerable distance round about."
According to my Invention I render the process continuous so that the piece of
stone may be put into the stone crusher carried to the millstones ground carried on
through a cooking or boiling apparatus in passing through which it becomes
cooked and thence passing on to be cooled and delivered direct into the sacks in a
cold condition. Thus from its being put into the breaker until it is complete it has
made mechanical progress to the end without further labour.
To accomplish this I cause the mineral to go direct from the millstones to the
following description of a cooking or boiling process.
In an oblong chamber made with fire brick and a proper furnace and chimney
to heat that chamber I place a tube made preferably of copper or of sheet iron or
thin boiler plates or other material. This tube revolves slowly and the ground
stone goes direct into this tube from the millstones, the tube is set at an angle in
the heated chamber, such angle and the speed of the tube being adjustable.
In connection with the cooking or boiling apparatus I erect a stive or dust
receiving room and by an exhaust fan I carry all the dust which now so seriously
flies all over the works into this room thus saving it and keeping the mill free
from dust,
After the material leaves the cooking or boiling apparatus it is cooled as it
travels along and is finally delivered into sacks.