IMPROVEMENTS IN GRINDING MILLS
Year: 1881

page_text: LETTERS PATENT to Alfred Julius Boult, of 323, High Holborn, in the County
of Middlesex and Kingdom of Great Britain, Engineer and Patent Agent, for
an Invention of "IMPROVEMENTS IN GRINDING MILLS." A communication
by William Nelson Cosgrove, of Faribault, Rice County and State of Minnesota,
and Robert Morrell, of Passaic, Passaic County and State of New Jersey, in the
United States of America.
COMPLETE SPECIFICATION filed by the said Alfred Julius Boult at the
Office of the Commissioners of Patents on the 25th October 1881.
ALFRED JULIUS BOULT, of 323, High Holborn, in the County of Middlesex and
Kingdom of Great Britain, Engineer and Patent Agent. "IMPROVEMENTS IN
GRINDING MILLS." A communication by William Nelson Cosgrove, of Faribault,
Rice County and State of Minnesota, and Robert Morrell, of Passaic, Passaic
County and State of New Jersey, in the United States of America.
This Invention relates to that class of grinding mills in which the grain is
subjected to repeated grindings or reductions by successive pairs of cooperating
grinding rolls, and in which the fine flour and middlings are separated and
removed from the product of each grinding or reduction, and the remaining
portions of such product passed to the next pair of rolls, and so on throughout the
machine. The Invention consists in the improved construction of certain parts of
the mill, and in the several novel combinations and sub-combinations, which I will
now proceed to describe, reference being had to the accompanying Drawings, in
which
Fig. 1 is a side elevation of the machine with a portion of the casing broken
away; Fig. 2, a rear view with the rear casing removed; Fig. 3, a detail view
showing the construction of the screens or sieves, and the manner of adjusting
them with respect to the brushes. Similar letters of reference in the several
Figures denote the same parts.

page_text: 5
In the Drawing, a represents the hopper into which the grain to be ground is
fed; a¹ a feed roller working in the lower part of the hopper; a² a hinged or
swinging gate hung on journals at opposite ends of the hopper, and cooperating
with the rollers a¹ to regulate the feed of the grain from the hopper, as will be
hereinafter inore particularly described; a³ a screw for adjusting the gate a²;
b, b, represent the first pair of grinding rolls; c, a revolving fan onto which the
product of the first grinding falls; d, a concave screen or sieve partially surrounding
the fan; e, openings in the casing for the admission of air to the fan; f, a trunk
into which the fine flour and middlings are forced through the screen by the
operation of the fan; g, an inclined deflector for directing the fine flour and 1
middlings into said trunk; h, perforations in the inclined deflector for the
admission of air; i, an exhaust fan for drawing out of the trunk f the fine light
dust, and forcing it to a suitable dust receiver for subsequent treatment. 6, 6,
the second pair of grinding rolls to which the product of the first grinding is
delivered by the revolving van c. Below this second pair of rolls is arranged 1
another fan and its cooperating sieve and deflector, and below them again a third
pair of rolls, and so on throughout the machine, as many pairs of rolls, fans, etc.,
being employed as may be desired or found necessary.
aro
jis a conveyor at the bottom of the machine to which the separated fine flour
and middlings pass by gravity from the trunk, and to which also the products of ?
the last grinding is delivered. One of the rolls of each pair is provided with a
pulley k, and is preferably revolved by means of a belt which passes over all said
pulleys and also over lap pulleys m, and is driven from a main driving pulley n,
as shown,
A tightening pulley n' is employed to give proper tension to the belt.
The shafts of the fans aro provided with pulleys o, and are in turn driven by
means of belts ? passing around said pulleys, and also around other pulleys q on
the opposite ends of the lap-pulley shafts. The shaft of the pulley roll of each
pair of the rolls is provided with a gear which meshes with a smaller gear s
on the shaft of the cooperating roll so as to cause a differential motion of the two
rolls.
The difference in the speed of the two rolls can be regulated as desired. I have
found by actual test of a machine containing five pairs of rolls, each of a diameter
of ten inches and a length of thirty six inches, that excellent results can be
obtained by giving the rolls of the first two pairs a relative speed of two and one
half to one, the rolls of the third pair a relative speed of two and one quarter to
one, the rolls of the fourth a relative speed of two to one, and of the rolls of the
fifth or last pair a relative speed of one and one half to ono, and I recommend that
substantially these relative rates of speed be followed.
A simple change of gears will however enable the relative speed to be altered,
as will be readily understood. The shafts of the rolls of each pair aro journalled
in boxes, as shown, and one roll is preferably adapted to be adjusted nearer to or
farther from the other by means of adjusting screws t applied to its boxes, in order
that the material may be ground more or less fine, and that the process of gradual
reduction may be effectively carried out.
The grinding rolls may be plain or corrugated, though I prefer them corrugated.
The corrugations inay be formed in any suitable manner, but I recommend that
they be formed by grooving the rolls spirally, as such form of dressing I have
found by practice to operate admirably. Any suitable form of fan may be employed
to effect the separation of the ground product. In the Drawings I have shown
three forms, one (the upper or first one) consisting merely of two pulleys or heads
mounted on the shaft, to which are attached at suitable distances a part longitudinal
strips or bars carrying brushes n which project against or in close proximity to
the screens; another (the second) consisting of the same arrangement with the
addition of blades v between the brush strips, and another (the third or lower one)
in which blades only are used, the brushes being entirely omitted. Any or all of
5

page_text: these forms of fan or any other suitable form may be employed. I prefer
however to employ the form in which both blades and brush strips are provided,
as not only is a blast of air produced and forced through the screen by such an
arrangement, but the screen or sieve is also kept clear by the sweeping action of
the brushes. The screens or sieves may be of any suitable material, but are
preferably made of steel wire woven to the proper mesh. The frames in which
they are placed are preferably inade in sections, hinged together as shown in Fig. 3,
and provided with slots and adjusting screws to enable the screens to be adjusted
nearer to or farther from the fans as occasion may require. Heretofore in machines
of this class it has been customary to employ in connection with the revolving
roller in the bottom of the grain hopper a sliding gate capable of adjustment to
and from the roller tangentially, so as to regulate the slit or aperture through
which the grain passes, but such arrangement is defective because when the machino
stops any grain remaining in the hopper passes out by its own gravity through
the obliquo discharge opening and falls between the rolls, thereby clogging said
rolls, so that when the machine is again started up the belts will run off, thus
causing much annoyance and delay. In my improved feeding arrangement the
edge of the swinging gate stands at or near the centre of the roller, and conse-
quently the feed takes place through a lateral instead of an oblique opening, and
when the roller ceases to rotate the feed also ceases, because the weight of the
grain in the hopper alone is not sufficient to force out the grain through such
lateral opening unassisted by the action of the feed roller. The gate is arranged
so as to swing inward away from the point of discharge, so as to at all times
preserve the lateral opening. The operation of the mill is as follows:-
Grain being fed into the grain hopper passes thenco to the first pair of rolls,
where it is ground or given its first reduction. The resulting ground product falls
onto the first revolving fan, and is by it thrown against the screen, the greater
part of the fine flour and middlings being separated and forced out through the
screen by the contact of the fans and the air blast produced thereby and into the
trunk, while the remaining material is carried by the fan over the screen and falls
onto the next pair of rolls. A portion of the current of air induced by the exhaust
fan at the top of of the trunk draws through and cools the descending coarse
material and passes in through the openings in the inclined deflectors and through
the flour and middlings and assisted by the currents from the several separating
fans carries off up through the trunk all the fino light dust from the flour and
middlings and conveys it to a dust receiver of any approved form.
The several pairs of rolls are adjusted a little nearer together than the first pair,
and the material falling upon them is by them still further reduced and falls upon
the second fan, which acts upon it in a manner similar to the first fan. Continuing
through the mill the material is subjected to still further reduction and separations
until it finally falls onto the conveyor at the base of the mill, where mingling with
the flour and middlings descending through the trunk, the whole is conveyed off
and elevated to the separators or purifiers for further treatment. In the arrange-
ment shown in the Drawings the flour and middlings from all the screens and fans
are delivered into a common trunk with a single exhaust at the top.
obvious, however, that instead of such arrangement separate trunks may be
provided for each screen and fan and a separate exhaust provided for each
trunk.
.
It is
The separating fans should be of a size and driven at a rate of speed propor-
tioned to the size and speed of the grinding rolls, so as to properly and effectively
act upon the product of each grinding without on the one hand allowing it to
accumulate or back up or on the other hand carry it off too fast. I recommend
that for use in connection with rolls ten inches in diameter said fans be made
about 30 inches in diameter, and that the screen or sieves be of proper relative
size. Inasmuch as the product of the first grinding is comparatively coarse and
contains but little fine flour and middlings, and as the yield of fine flour and

page_text: middlings from each successive grinding is greater by reason of the greater
reduction, I recommend also that each successive separating brush be made
somewhat larger than its predecessor, and that a screen of increased area be
provided for it in order that the capacity of the separating means may be
increased in proportion as there is an increase in the amount of material to be
separated.
It will be observed that by this arrangement of grinding rolls, separating fans,
screens, etc., in the manner herein described and shown, the passage of the material
through the mill is effected almost entirely by gravity, all elevating and conveying
machinery being dispensed with between the several reductions. While I have
described the operation of the mill upon wheat alone, it is evident that it is also
adapted to the grinding of middlings as well. When so used, plain smooth rolls
are employed instead of corrugated ones.
Having now fully described my Invention, what I claim is,--
1st. In a grinding mill the combination with two or more pairs of grinding rolls, 1
the rolls of each pair of which run at differential speed, with a revolving separating
fan between each pair of rolls and the next succeeding pair of rolls, and a concave
screen or sieve cooperating with each fan, whereby the ground product is delivered
directly onto the fans which operate to force the fine flour and middlings out
through the screens, and to deliver the remaining material to the next pair of rolls ?
for further reduction, substantially as described.
2nd. In a grinding mill the combination with two or more pairs of grinding
rolls, the rolls of each pair of which run at differential speed, with a revolving fau,
between each pair of rolls and the rolls of the next succeeding pair of rolls, having
both blades and brushes and a concave screen or sieve cooperating with each fan, i
substantially as described for the purpose specified.
3rd. In a grinding mill the combination of two or more pairs of grinding rolls,
the rolls of each pair of which run at differential speed, with a revolving fan
between each pair of rolls and the rolls of the next succeeding pair, onto which the
ground product is directly delivered, concave screens or sieves cooperating with 3
the fans, an air trunk into which fine flour and middlings forced through the
screens are delivered, and an exhaust for drawing off the fine dust from said air
trunk, substantially as described.
4th. In a grinding mill the combination, substantially as described, of the two or
more pairs of grinding rolls, the rolls of each pair of which run at differential
speed, the revolving fan and screen arranged between each pair of rolls, the air
trunk into which the separated flour and middlings are delivered, perforated
inclined deflectors for directing the material into said trunk, and an exhaust at the
top of the trunk, whereby a current of air is made to pass through the coarse
material as it falls from each fan to the next pair of rolls to cool it, and whereby
also the fine dust is drawn out of the trunk and delivered to a suitable dust
receiver for further treatment.
5th. In a grinding mill the combination, substantially as described, of the several
pairs of grinding rolls, the rolls of each pair of which move at differential speed,
the concave screens between each pair of rolls and the rolls of the next succeeding
pair, the rotary separating fans onto which the ground material is directly delivered,
and by which the fine flour and middlings are forced out through the screens, and
the remaining material delivered directly to the next pair of rolls, with the trunk
into which the fine flour and middlings are delivered by the exhaust and conveyor
at the bottom of the machine, all said parts being combined to operate substantially
as described.
6th. In a grinding mill of the character described, the combination with the
revolving separating fans of the cooperating screens rendered adjustable toward
und from the fans, substantially as described for the purpose specified.
7th. In a grinding mill the combination with the honner of the feed roller!

page_text: working in the bottom thereof, and the swinging gate arranged to swing inward
so as to leave a lateral discharge opening, substantially as described for the purpose
specified.
In witness whereof, I, the said Alfred Julius Boult, have hereunto set my
hand and seal, this Twenty fifth day of October, in the year of our Lord
One thousand eight hundred and eighty one.
ALFRED J. BOULT. (L.S.)