Improvements in Magnetic Separators.
Year: 1891

page_text: Date of Application, 17th Nov., 1891
Complete Specification Left, 27th July, 1892-Accepted, 10th Sept., 1892)
PROVISIONAL SPECIFICATION.
Improvements in Magnetic Separators.
WILLIAM DURANT HOFFMAN of Brewster in the County of Putnam and
State of New York, United States of America, Engineer, do hereby declare the
nature of this invention to be as follows:-
The object of this invention is to provide a facile means for effecting the com-
plete separation of the substances of what ferruginous ores are composed, so that
the resultant products of the separation may be classified with great nicety.
For this purpose, the attractive power of magnets is employed in a manner which
will create a molecular movement of the crushed material which is intended to be
assorted.
The machine to which the magnets are adapted, is provided with an endless
travelling apron or carrier belt, onto which the crushed ore is delivered at a
regulated rate from a fixed hopper fitted with an adjustable shute.
This apron, which is furnished with raised edges, is held taut by a pair of
drums, one of which is loose on its shaft and closed at its ends, while the other is
keyed to its shaft, which is the driver. The shaft of the loose drum is mounted on
the main frame of the machine, and the driving shaft, with its drum, is carried by
a frame, which is adjustable by screws. or otherwise, to maintain the apron at a
proper tension.
Underlying the apron between the two drums, is a series of magnets consisting
of parallel bars of a length equal to the width of the apron, the adjacent bars
having opposite polarities.
The shaft which carries the loose drum is hollow, and it is closed by a partition
at its middle, while on either side of this partition it is pierced with holes. Air,
drawn or forced into one end of this shaft, passes out of the holes into the closed
drum, and entering the holes on the other side of the partition, passes out from the
opposite end of the hollow shaft, and eventually escapes into the atmosphere.
The current of air thus made to circulate in the drum, is designed to cool a set
of electro-magnets, which are mounted upon the hollow shaft, and occupy the
forward half of the internal space of the drum.
Overlying the apron, and forming an air-tight cover to the machine, is a casing
which extends from the hopper to and beyond the loose drum, and then descends to
the ground, to form, with a return plate that reaches up near to the underside of
the drum, a receptacle for a portion of the crushed material that is to be
assorted.
This casing is divided into two compartments by a vertically adjustable partition,
and the inner side of this receptacle is also made vertically adjustable. Beyond
this receptacle (below the apron), is a partition, which is adjustable towards and
from the receptacle, and serving to assort the particles which remain attached to the
apron while passing over the receptacle, but which fall when they leave the sphere
of attraction of the electro-magnet.
The receptacle is provided with weighted valves, which yield as the assorted
material accumulates, and thus discharge it therefrom.
Fitted to an opening in the casing immediately over the receptacle, is an
exhaust chamber, connected with a fan, which, when set in action, causes a
current of air to flow past the bend of the apron in the direction opposed to
its travel.
To this exhaust chamber, the hollow shaft is connected, and thus the circulation
of air through the drum, as already explained, is maintained.

page_text: .
Let it now be supposed that the crushed material in the hopper is allowed to
flow onto the travelling apron, and that the exhaust just mentioned is set in action
as the pulverized ore comes within the field of the first group of magnets; the
particles subject to magnetic influence are attracted towards the nearest pole, and
at the same time are carried along by the apron past the succession of opposite
poles. As the said particles pass the successive poles of the magnet, they will not
follow a line parallel with the apron, but will assume positions, under the influence
of the magnetic lines of force, 'in the forins of curves, from one pole to the nearest
pole of opposite polarity. The degree of curvature will depend upon the strength
of the magnetic force, and the distance between the poles of opposite polarity.
By following these curves, and at the same time being moved along by the
apron, the material to be separated assumes a rising and falling, or wave-like
motion.
This motion results :-
First, in the gathering together of the magnetic particles from the mass, by their
attraction for each other, and by the force tending to draw them toward the nearest
magnetic pole, and consequently nearest the apron; and
Secondly, in tending to bring particles of the greatest specific gravity nearest
to the bottom of the mass, on the apron, and consequently nearest the poles of
the magnet.
This wave-like motion causes an expulsion of the slightly magnetic
or non-magnetic material, and that of least specific gravity, towards the top of the
mass on the apron, and results finally in a stratification of the substances to be
separated, the most magnetic and heaviest portions being brought closest to the
apron, and the lighter and non-magnetic, or slightly magnetic particles, farthest
from the apron.
The motion of the particles of the mass of material, as ahove described, results
in an effective scouring action, which tends to clean their surfaces, and thereby
free them from such impurities as slightly adhere to them, as, for example,
phosphorus and silica, in the case of magnetic iron ore. These non-magnetic
impurities thus freed, are expelled from the magnetic portions of the mass by
the above described action, and arrange themselves in the stratum farthest from
the apron.
In such a stratified condition, the mass to be separated passes from the field of
'the first group of 'magnets into the field of the electro-magnets in the loose drum,
and as the apron follows its path around the periphery of the loose drum, the
magnetic particles of the mass, just before it leaves the horizontal line of the
apron's motion, once more assume the direction of the line of force in curves from
one pole to its nearest opposite pole, and a magnetic force sufficiently strong to act
upon the entire stratum of partially separated magnetic particles, is now brought
into action. The nou-magnetic and lighter particles forming the upper stratum,
'will, under the horizontal motion imparted to them by the apron, leave the magnetic
stratum in a trajectory, as the apron begins to follow around the periphery of the
loose drum, and this stratum will be assisted in separating itself from the magnetic
stratum by the lifting and wedging action of the upward current of air which it
meets. The amount of the upper stratum which shall finally escape, and be per-
manently separated. from the lower stratum, is determined by the adjustment of
the partition in the receptacle, the discharge from which is automatically effected
'as above described.
After passing beyond the receptacle, the less magnetic material falls from the
apron, while the more magnetic is still carried round, and finally leaves the apron,
after the latter has carried it beyond the holding force of the last pole of the
magnet. The adjustable plate outside the receptacle serves to separate this last
mass of material as it falls from the apron, and secure a predetermined percentage
of purity in that portion which is the most magnetic.
If thought desirable, a farther cleaning and separating may be effected by locating
a second group of horizontal magnets in proximity to the lower portion of the
apron, so as to hold the magnetic stratum within its field, as it leaves the last pole

page_text: of the electro magnets in the loose drum; the position of the preparatory or
stratifying magnet inay be varied as desired.
Dated this 17th Novemba 1901
NEWTON & SON,
Agents for the Applicant.
Improvements in Magnetic Separators.
I, WILLIAM DURANT HOFFMAN of Brewster in the County of Putnam and
State of New York, United States of America, Engineer, do hereby declare the
nature of this invention and in what manner the same. is to be performed, to be
particularly described and ascertained in and by the following statement :-
My invention relates to an improvement in magnetic separators, in which a pre-
paratory or stratifying magnet is arranged to act upon the mass of material at a
point intermediate of the feed, and the means for effecting the final separation.
In separating ore in large quantities by magnetism, it has been found that on
account of the thickness of the mass or layer delivered to the action of the
magnets and carried through the magnetic field, thereby bringing the magnetic
particles nearest the magnetic poles within a stronger magnetic field than the
outside portion of the mass, the magnetic force sufficient to ensure the separation
of the magnetic particles nearest the surface, is not strong enough to cause an
attraction and separation of the magnetic particles farthest from the inagnetic
poles, and a loss thereby ensues. On the other hand, if the magnetic field is made
strong enough to attract the magnetic particles farthest from the poles, it is then
sufficient to hold the lean or slightly magnetic particles nearer the poles with
sufficient force to carry them through the magnetic field, without releasing, and
thereby prevent a complete separation.
These objections are especially marked in separators where the magnetic
particles are picked out of the mass against the action of gravity, in separators
which employ a revolving drum or vertical or inclined belts as conveyors,
and in separators where the material is brought into actual contact with the
magnetic poles.
The object of my present invention is to overcome the above-named objections,
and to provide a magnetic separator, which will effect the complete separation of a
great mass of material, so that the resultant products of the separation may be
classified with great nicety.
A practical embodiment of my invention is represented in the accompanying
drawings, in which :-
Fig. 1 is a view of the separator in vertical longitudinal section, the magnets
being shown in end elevation;
Fig. 2 is a top plan view; &
Fig. 3 is a view in detail, showing the drum for conveying the material
within the field of the curved line of magnets, and the parts in immediate
contact therewith.
A represents the supporting frame, having hinged at one end the auxiliary
frame the latter forming a support for the drive shaft c. The hinged connection
of the frame a with the frame A, is shewn at e, and the means for holding the
frame in the desired adjustment with respect to the frame A, consists of a
screw T pivotally secured to the frame a, and provided with suitable adjusting
nuts t, at the point where it passes through a stationary portion, a' of the main
frame A. The drive shaft is mounted in suitable bearings b, and has fixed
thereto a drive pulley R, by means of which motion. is communicated, to the shaft v
from a source of power not shewn. The shaft is also provided with a loose
pulley R', located in proximity to the pulley R, for the purpose of shifting the

page_text: belt, to throw the machine out of action. The said shaft has fixed thereon a
drum or pulley B, for the support, at one end, of an endless apron D.
The opposite end of the apron D is supported upon a drum C, loosely mounted
upon a hollow shaft i, supported in suitable hangers or standards c, fixed to the
main frame A. The supports are preferably formed in half sections, which
embrace the opposite sides of the hollow shaft i, and are adapted to be drawn
firmly together, to clamp the shaft between them, by means of bolts d, which, in
the present instance, also serve to hold the support a firmly to the main frame A.
The shaft is preferably provided with bearing collars m, on which the bearings m³,
fixed in the ends of the drum C, are seated.
The tension of the apron D may be maintained as desired, by swinging the
auxiliary frame a toward and away from the drum C by means of the adjusting
screw T.
A feed hopper E is fixed to the supporting frame A in position to feed the
material to be separated upon the apron near the drum B, a shute F being hinged
to the base of the hopper, and resting at its free end upon the apron, for the purpose
of receiving the material from the bottom of the hopper, and distributing it in an
even layer across the face of the apron. This shute also serves to seal the air
blast. An adjustable gate Q serves to determine the amount of opening at the
base of the hopper, and hence the rapidity of the feed.
A casing Y, arranged a short distance above the apron, extends from the
hopper E to a point beyond the drum C, and thence downwardly at the end of the
machine, and along beneath the drum C, forming, together with the apron, a
substantial enclosure for the passage of the material to be separated, from the
time it leaves the shute F, until it is finally separated.
Partitions L, M, and N, located at intervals within the casing Y, between it and
the apron, serve to determine the size of the passage in proximity to the apron, to
cut off such portions of the material as may be desired. The portions of the said
partitions Land M nearest the apron are hinged, so that they may be swung
toward and away from the apron, and the several partitions L, M, and N are
further provided with sliding sections r, s, and t, to further determine the points
of separation. The partition N, which forms the final separation of the highest
grade from the inferior grade of material, is supported upon a slide
on ways P.
P, which moves
The lower ends of the spaces separated by the partition L, are provided with
gates S and S', which are held normally closed by means of weights Wand W,
here shown as supported in sliding adjustment upon arms ww', and intended to
hold the gates closed under such tension, so that there will always remain the
bottoms of said spaces, in proximity to the gates, a mass of material sufficient to
seal the gates against the entrance of any considerable amount of air, and at the
same time he subject to be opened, to allow the discharge of the material, when
the mass of a predetermined weight has accumulated therein.
Intermediate of the point where the material is fed upon the belt and the point
where the finishing of the separation takes place, (around the periphery of the
drum C), I locate a magnet H, which may be either a permanent magnet or an
electro magnet, in the present instance shown as an electro-magnet. The magnet H
consists of a connected series of poles 1, each alternate pole being the opposite
polarity of that adjacent thereto, the said magnet being located in proximity to
the underside of the apron D.
be
Within the drum C, I locate a magnet I, which, like the magnet H, may
either permanent or electro,-in the present instance shown as an electro, and
consisting of a series of poles o, radiating from a centre toward the periphery of
the drum C, and located in proximity thereto.
series of poles o
In practice, I prefer to extend the
a little more than one-half the distance along the periphery of
the drum C. The poles of the magnet 1, like those of the magnet H, are arranged
so that each alternate pole shall be the opposite polarity to one adjacent thereto.
The magnet I is supported upon a suitable frame, which is here shown as having

page_text: a removable half section j', adapted to partially embrace the hollow shaft i, and
serve, together with the frame, to clamp the magnet I, in the desired rotary
adjustment, upon the shaft. The said magnet I may also be adjusted with the
drum C by the rotation of the entire shaft within its supports c.
The hollow shaft i serves as a convenient housing for the wires which lead to
the magnet I, and it is further provided with a central partition X, transverse of
its longitudinal axis, and is perforated upon opposite sides of said partition, as
shown at a, and has one of its ends connected with an air exhaust conduit n. The
air exhaust conduit n also communicates with a chamber G, which, by means of a
sliding gate or valve K, opens communication into the space between the casing Y
and the apron, so that when a suitable exhaust mechanism of any well known or
approved form, not shown herein, exerts an exhaust through the conduit n, and the
gate K is open, it will draw a blast of air between the partition M and the face of
the apron, and thence upwardly between the partition L, and the face of the apron,
in the opposite direction from that in which the apron D is travelling, and will at
the same time draw a current of air into the open end of the shaft i, and thence
outwardly through the openings a into the space within the drum C, thence through
the openings upon the opposite side of the partition X, through the end of the
shaft connected with the conduit n.
It is obvious that air might be forced through the shaft i by a blower, instead
of being drawn through by an exhauster. The current of air along the outer
surface of the apron D performs a cleaning and scouring action, which will be
hereinafter referred to, while the current of air through the shaft i, and thence
within the drum B, serves to cool the magnet I. The travelling apron D is
provided with marginal ribs g to prevent the material from escaping from its
edges.
The operation is as follows:-
The apron D, having been set in motion in the direction indicated by the arrows,
an upward current of air along the periphery of the drum Chaving been
established by the exhaust mechanisin, and the electre magnets having been.
energised, the material to be separated is allowed to pass from the hopper E onto
the shute F, and is fed thence upon the apron D, which carries it along within the
field of the magnet H.
As the said material comes within the field of the magnet H, the particles subject
to magnetic influence are attracted towards nearest pole, and at the same time are
carried along by the apron past the succession of opposite poles. As the said
particles pass the successive poles of the magnet, they do not follow the line
parallel with the apron D, but assume positions, under the influence of the magnetic
lines of force, which are in the forms of curves from the end of one pole to the
end of the nearest pole of opposite polarity. The degree of curvature will depend
upon the strength of the magnetic force, and the distance between the poles of
opposite polarity.
By following these curves, and at the same time being moved along by the apron,
the material to be separated assumes a rising and falling, or wave-like motion.
This motion results :-
First, in the gathering together of the magnetic particles from the mass by
their attraction for each other, and by the force tending to draw them toward the
nearest magnetic pole, and consequently nearest the apron, and :-
Secondly, in tending to bring particles of greatest specific gravity nearest to
the bottom of the mass on the apron D, and consequently nearest the poles of the
magnet. The above described wave-like motion causes an expulsion of the slightly
magnetic or non-magnetic material, and that of least specific gravity, towards the
top of the mass on the apron, and results finally in a stratification of the substance
to be separated, the most magnetic and heaviest portions being brought closest to
the apron, and the lighter and non-magnetic, or slightly magnetic particles, farthest
from the apron.
The jigging motion or violent agitation of the particles of the
nass of material as above described results in an effective scouring action, which

page_text: tends to clean their surfaces, and thereby free them from such impurities as slightly
adhere to them, as, for example, phosphorus and silica, in the case of magnetic
iron ore.
These non-magnetic impurities thus freed, are expelled from the magnetic
portions of the mass by the above described action, and arrange themselves in the
stratum farthest from the apron. In such a stratified condition, the mass to be
separated passes from the field of the magnet H into the field of the magnet I.
As the belt follows its path around the periphery of the drum C, the mass, just
before leaving the horizontal line of the apron's motion, enters the field of the
magnet I, and the magnetic particles once more assume the directions of the line
of force, in curves from one pole to its nearest opposite pole. In the form in which
I have represented the magnet I, the poles o being farther apart that the poles
of the magnet H, the curves which the magnetic particles assume will be less
sharp. The magnetic particles having been arranged by the preparatory magnet H
into a stratum in proximity to the surface of the belt, it becomes feasible to
employ a magnetic force sufficiently strong to act upon the entire stratum of
partially separated magnetic particles.
The non-magnetic and lighter particles forming the upper stratum, will, under
the horizontal motion imparted to them by the apron, leave the magnetic stratum
in a trajectory as the apron begins to follow around the periphery of the drum C,
and will be assisted in separating itself from the magnetic stratum by the lifting
and wedging action of the upward current of air, following along between the
periphery of the drum C and the upper portion of the partition L. Just what part
of the upper stratum shall be allowed to finally escape and be permanently
separated from the lower stratum, is determined by means of the partition L and
its sliding section ». Such portion as passes over the section falls to the base
of the space between the casing Y and the partition L, and as it accumulates in
a sufficient quantity, automatically opens the gate S¹ and escapes.
The magnetic stratum follows the path of the apron D around the periphery of
the drum C, by reason of the attraction to the magnet I, and its wave-like motion
is continued, constantly gathering the more highly magnetic particles closer to
the poles, and consequently to the apron D. This wavelike motion also continues
to expel to the surface all the slightly magnetic substances which gradually Hy
from the surface under the centrifugal force, and as the mass passes the transverse
horizontal axis of the cylinder, being aided by the force of gravity. During its
passage around the periphery of the drum C, a scouring action is kept up upon
the surface of the mass by the opposing current of air, and by the agitation of
the mass, which effectually brings all of the particles into contact with the air
current. The intensity of the air current may be regulated by the speed of the
exhauster, and by the adjustments of the several slides in the partitions.
The slightly magnetic particles, together with such non-magnetic particles as
were not at first separated from the mass, fall from the surface of the apron into
the space between the partitions L and M, and as they accumulate in sufficient
quantities, are automatically discharged through the gate S¹.
After passing the partition M, the less magnetic material continues, first, to
fall from the apron, while the more magnetic is still carried forward, and finally
leaves the apron after the latter has carried it beyond the holding force of the last
pole of the magnet I. The adjustable partition N serves to separate this last mass
of material as it falls from the apron, so as to retain a predetermined percentage
of purity in that portion which is the most magnetic.
It is obvious that a farther cleaning and separating might be effected, if found
desirable, by locating a magnet similar to the magnet H in proximity to the lower
portion of the apron D, so as to hold the magnetic stratum within its field, as it
leaves the last pole of the magnet I, and that the position of the preparatory or
stratifying magnet H may be varied in its position between the feed and the
finishing magnet I, as may be desired.
It will be observed that the action of the magnet H, is solely that of stratifying
or separating the material into layers, together with the resultant scouring, as set

page_text: forth, while the finishing is performed by the second magnet, which segregates the
material forming each layer.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
1. In a magnetic separator, mechanism for completing the separation, a stratifying
magnet located in advance of the completing mechanism, and means for conducting
the material to be operated upon within the field of the stratifying magnet,
substantially as set forth.
2. In a magnetic separator, a feeding device, a finishing magnet, a stratifying
magnet located intermediate of the feed and finishing magnet, and means for
conducting the material to be operated upon successively within the fields of the
stratifying and finishing magnets, substantially as set forth.
3. In a magnetic separator, a feeding device, a finishing magnet, a stratifying
magnet located intermediate of the feed and finishing magnet, and an endless apron
for conducting the material to be operated upon within the fields of the stratifying
and finishing magnets, substantially as set forth.
4. In a magnetic separator, the combination with an endless apron, means for
feeding the material to be operated upon onto the apron, and mechanisın for
completing the separation, of a stratifying magnet located intermediate of the feed
and finishing mechanism, and comprising a series of poles of opposite polarity
located in proximity to the belt, substantially as set forth.
5. The combination with an endless apron, and means for feeding the material
to be operated upon outo the apron, of a stratifying inagnet and a finishing magnet,
each comprising a series of poles of opposite polarity, and arranged to act
successively upon the material as it passes along the apron, substantially as set
forth.
6. In a magnetic separator, the combination with an endless apron and a
separating magnet located in proximity thereto, of drums forming supports for the
opposite ends of the apron, and a swinging frame in which one of said supporting
drums is mounted, and means for adjusting the frame, and hence the drum, toward
and away from the opposite drum, to determine the tension of the apron, substantially
as set forth.
7. The combination with the separating magnet arranged in curved form, and
the hollow perforated shaft at the centre of the curved magnet, of the partition
within said hollow shaft, and means for directing a current of air through the
shaft, for cooling the magnets, substantially as set forth.
8. The combination with the separating magnet and the endless apron extending
in proximity to the magnet, of the casing arranged at a short distance from the
endless apron, to form an air conduit between the two, and the feed shute hinged to
its support, and resting with its free end upon the apron, for distributing the
material evenly upon the apron, and sealing the air conduit at the feed end of the
casing, substantially as set forth.
9. The combination with the separating magnet arranged in curved form, the
hollow shaft at the centre, and the endless apron in proximity to the curved
magnet, of a conduit for the air in proximity to the outer face of the apron, an
air chamber, an adjustable gate for opening and closing communication between
the chamber and the air conduit in proximity to the apron, and an exhaust conduit
in communication with the air chamber, substantially as set forth.
Dated this 27th day of July 1892.
NEWTON & SON,
Agents for the Applicant.