IMPROVEMENTS IN AND CONNECTED WITH APPARATUS OR MACHINES FOR GRINDING OR REDUCING ORES AND MINERAL SUBSTANCES
Year: 1872

page_text: PROVISIONAL SPECIFICATION left by David Stevens at the Office
of the Commissioners of Patents, with his Petition, on the 19th
February 1872.
I, DAVID STEVENS, of Godolphin Mills, Townshend, near Hayle, in the
County of Cornwall, Metallurgist, do hereby declare the nature of the
said Invention for "IMPROVEMENTS IN AND CONNECTED WITH APPARATUS OR
MACHINES FOR GRINDING OR REDUCING ORES AND MINERAL SUBSTANCES," to be as
follows:-
The object of my Invention is to provide apparatus or machines in
which mineral and other hard substances can be expeditiously and
inexpensively ground or reduced both in the dry and wet state to a finely
divided condition. For that purpose I have devised and perfected
apparatus or machines which for convenience in enabling others to
readily grasp my improvements may be described as having somewhat
5 of a resemblance, both in the general arrangement of parts and their
motions, to horizontal millstones and appliances employed in grinding
grain. Thus there is common to both (1) supporting framework, (2) bed
or stationary grinding surface, (3) runner grinding surface supported on

page_text: and operated by a vertical adjustable spindle, and (4) an enclosing case.
The parts of my apparatus or machines are however constructed, formed,
and arranged in an entirely different and a novel manner, as will appear
from the description immediately following:
First. As means for providing durable and keen grinding surfaces, I
form the bed or stationary grinding surface of two metals of different
degrees of hardness. This is effected by casting around a number of
projecting pieces of hard iron or other metal a soft iron or other metal,
the ends of the projecting pieces being flush with the soft metal so as
together to form a true and smooth surface. And I form the runner
surface, which is preferably not continuous although it may be so, of
hard iron or other hard metal. The grinding surfaces just described may
be horizontal, but I prefer them formed as described under the second
head hereafter set down.
A modification under the said first part of my Invention consists in
making the bed or stationary surface of soft iron or other suitable metal,
and the runner of hard iron or other suitable metal, or vice versa.
Second. As means for retaining the ore or other material a sufficient
length of time between grinding surfaces constructed as described under
the above first head in constructing the bed or stationary grinding surface
of a concave form, and the runner of a corresponding convex outline.
Third. As means for ensuring that the grinding surfaces of the runner
shall receive the ore or other material freely, I bevel the leading edges of
the shoes at the furrows or separations, and lead them from excentric
points at the eye to the skirt. These shoes may be removable from the
body or frame of the runner if desired.
Fourth. As means for facilitating the entrance of ore or material
between the grinding surfaces, I construct the runner with openings so
that the ore or material may enter therethrough as well as through the
eye.
Fifth. As means for preventing the ore or material to be reduced from
escaping past the driving spindle down through the bed, and also from
damaging the spindle, I attach firmly to the bed and lead upwards near
to the top of the spindle a sleeve, and over the top of the spindle and
encircling the sleeve I pass a thimble which revolves with the spindle
and couples to the runner. This arrangement is more particularly useful

page_text: in wet grinding; for dry grinding the material to be reduced may be fed
through the openings in the runner mentioned under the third head.
The discharge for the ground or reduced ore or material may in this, as
also under the above first, second, third & fourth heads, be placed at or
near the circumference of the bed or stationary grinder.
Sixth. As means for ensuring when wet grinding is being effected that
only the very finely ground ore or material shall escape in constructing
the case water-tight, and leaving an opening near its centre around a
rising cylindrical piece secured to the runner. Around the said opening
I form a channel, and connect thereto a leadaway spout. The advantage
of this is that only the finest particles held in suspension will float
towards the centre, the coarser and gritty particles being made to circulate
by the centrifugal action of the runner near the periphery of the case.
The fine particles and liquid may be conveyed to settling tanks, or to
other machines for subsequent treatment.
Seventh. As means for determining the fineness at which the ground
material during wet grinding shall flow away, I make the case adjustable
so that it can be raised or lowered. The higher the case the finer will be
the effluent product.