IMPROVEMENTS IN ATTRITION MILLS
Year: 1884

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I SYDNEY PITT of Sutton in the County of Surrey Gentleman do hereby declare
the nature of my invention for "IMPROVEMENTS IN ATTRITION MILLS and in
what manner the same is to be performed to be particularly described and
ascertained in and by the following statement :—
This invention relates to attrition mills for reducing ores and other hard
substances, of a class in which is employed a rotary recessed head combined with a
suitable case, such rotary head serving to put the particles of the mass in motion
upon one another in order that such mass inay furnish its own grinding surfaces,
the rotary head being the agent for keeping the particles in motion. In the
practical operation of this mill I have found that owing to the rapidity with which
the material is reduced to flour and the small size of the mill in comparison with
the labor it performs, the flour tends to collect and clog, and its free escape is
prevented. It is desirable that a screen be combined with the mill to facilitate
the discharge of the flour and to prevent escape of granular particles with such
flour in other words to sift the products of the mill.
The object of my present invention is to combine in one device means for
sifting the material and preventing clogging of the flour, and to this end my
invention consists, first, in an annular or other proper shaped screen of large area
and suitably reticulated or foraminous material contained within the case and in
this instance constituting the reducing chamber and through which the ground
material must pass in making its oxit from the mill, this screen being preferably
secured to the top of said case.
The drawings accompanying this specification represent in Figure 1 a perspectivo
elevation and in Figure 2 a longitudinal sectional elevation.
In said drawings A represents a mill of the class before alluded to, such mill
consisting briefly in two heads or discs A' A¹ chambered in front, and at rear each
secured to the front end of a horizontal rotary shaft B, mounted in suitable
standards CC, and provided with a pulley B¹. D in the drawings represents a
practically circular box or case, the two sides of which are shown at D' E and
its annular periphery at E¹, the two sides being formed with circular openings to
receive the front end of the rotary head A. To the upper front corner of the

page_text: case D I add a hopper F which communicates with the interior of said case, and
through which material is fed to the latter.
In carrying out my present improvements I employ a screen G composed of a
band of woven wire cloth or other suitable foraminous, reticulated, slotted, or open
work material; this band being formed in this instance annular in shape and
secured at its upper part to the wall of the mill over the rotary head A¹. The
screen G is of less diameter than that of the case, and both the hopper and rotary
head communicate with the interior of the screen. The material fed through the
hopper is disturbed and put in motion by the rotations of the heads, its particles
are reduced by attrition among themselves, and the flour, as it becomes reduced to
the proper fineness, escapes through the meshes of the screen. As will be scen
by inspection of the accompanying drawings, the screen practically constitutes the
case to contain the material being reduced, the case D serving to prevent flour or
dust from escaping into the atmosphere.
By constructing an annular screen I am enabled to provide a very large
screening surface which permits of free outlet and ready escape of the products of
the mill.
I do not confine myself to a screen of perforated sheet metal or woven wire as a
series of parallel wires or slotted plates may bo employed as alternatives. I prefer
a screen composed of perforated sheet metal plates, as shown in the drawings.
Having now particularly described and ascertained the nature of iny said
Invention, and in what manner the same is to be performed, I declare that what
I claim is:
First. The combination with a mill of the class hereinbefore named of a screen,
substantially as explained.
Second. In combination the rotary recessed head, the case, and a suitable
screen.
Dated this 16th day of January 1881