Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to the sorting of particulate material. In this
specification the word "material" includes any material that is in a
particulate form and refers particularly to ores in the mining industry.
Many industries produce materials that are uneconomic to process by
standard means as they are either co"lamillated by foreign bodies or have
a low grade. These materials are generally not processed at all and are
discarded.
SUMMARY OF THE INVENTION
The invention provides, in the first instance, apparatus for sorting a
particulate material which includes a drum which is mounted for rotation
about its axis, means for feeding the particulate material into the drum
which, due to centrifugal force produced by its rotation, causes the
particulate material to adhere to an inner surface of the drum, means for
detecting the presence of at least one predetermined characteristic in the
particulate material, and means for separating particles with the
predetermined characteristic from the remaining particles.
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The separating means may comprise at least one removal device which is
responsive to the detection means. In one embodiment of the invention
the drum may be made from a solid or semi-permeable material and the
material is removed from an inner surface of the drum by one or a plurality
of the removal devices. Each removal device may be a suction de~ice.
In an alternative arrangement the removal means comprises at least one
fluid ejection device which is responsive to the detection means. The
drum inner surface may then be a perforated or slotted surface, or
otherwise be formed with a plurality of apertures, and the fluid ejection
device or devices may be directed from outside the drum, through the
drum wall, to the particles adhering to the inner surface.
The fluid ejection devices may co""" ise compressed air jets, water jets or
the like.
Depending on the type of particulate material mechanical separation
devices may also be employed. These may for example comprise flapper
gates or similar devices which are moveable to free selected particles
directly from the inner surface of the drum.
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The drum may for example be made from wedge wires and be similar to a
trommel. The wedge wires may extend across the drum thereby forming
a surface which includes a plurality of very fine slots.
Material remaining in the drum, after removal of those particles which
possess the predetermined characteristic or characteristics, may be
removed from the drum by means of suction, water spray, air jet or by
means of a mechanical scraper.
The predete, ~ eJ characteristic or characteristics depend on the nature
of the material which is being sorted. The invention is not limited in this
regard. For example the predetermined characteristic may comprise any
one of the following diverse features: a photometric effect, reflectance or
absorbtion criteria, radio-active emissions, a magnetic or conductive
effect, optical fluorescence or the like. It may be that the predetermined
characteristic or characteristics are emitted only in response to suitable
stimulation. Thus it falls within the scope of the invention to stimulate the
particles so that those particles which possess the predetermined
characteristic or characteristics emit a signal which is indicative of the
presence thereof.
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For example, in the sorting of diamonds, the particulate material may be
subjecte~l to a X-ray source which stimulates the emission of fluorescence
by the diamonds.
The invention provides, in a second instance, a method of sorting a
particulate material which includes the steps of subjecting the particulate
material to a centrifugal force thereby to form a layer of the material,
detecting the presence of at least one predetermined characteristic in
particles in the layer of material, and removing particles with the
predetermined characteristic from the layer of material.
The particulate material may be subjected to the centrifugal force by
feeding material into a rotating drum so that a layer of the material is
dispersed on an inner surface of the drum. Preferably the drum rotales at
a speed which is sufficiently high to ensure that substantially a mono-layer
of the particulate material is formed.
The material may be fed continuously into the drum and the material
remaining in the drum, after removal of the particles with the
predetermined characteristic or characteristics, may be removed
continuously from the drum.
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Removal of material from the drum may be effected by means of suction
or by means of fluid pressure or by mechanical means.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further described by way of example with reference to the
accompanying drawings in which:
Figure 1 is a somewhat schematic side view of sorting apparatus
according to the invention,
Figure 2 is a block diagram of control circuitry for the sorting apparatus of
Figure 1,
Figure 3 is a schematic view in elevation of a drum in the apparatus of
Figure 1, and
Figure 4 is a sectioned side view, on an enlarged scale, of a drum suitable
for use in the apparatus of Figure 1.
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DESCRIPTION OF PREFERRED EMBODIMENT
Figures 1 and 2 of the acco""~anying dr~r;"~s illustrate sorting apparatus
- 10 according to one form of the invention. The apparatus includes a drum
- 12 which is mounted for rotation about a horizontal axis. The drum is
driven by means of an electrical motor 14 and, where required, use is made
of a gear box or similar drive l, ~"s",;ssion system, not shown, between the
motor and the drum.
The rotational speed of the drum is monitored by means of a sensor 16.
A signal produced by the sensor, which is indicative of the rotational
speed of the drum, is applied to a control module 18 which in turn operates
to drive the motor 14 so that the rotational speed of the drum is known and
kept substantially constant.
The sensor or control module may include suitable switching circuitry to
adjust the rotational speed of the drum to a fixed desired speed and to
stop the motor in the case of a malfunction.
- A feed chute 20 extends into the drum, in a lower region of the drum. The
feed chute may be of any suitable construction and may for example
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cG~ l an endless conveyor belt which carries particulate material into the
- drum, depositing the material at one or a number of points onto an inner
surface 22 of the wall of the drum.
Three collecting chutes 24,26 and 2~ extend from the interior of the drum.
The drum is rotaled in the direction of an arrow 30 and the chutes are
spaced from one another in this direction of rotation. The chutes 24 and
26 are relatively low capacity chutes while the chute 28 has a higher
capacity.
The chutes are oriented so that material entering the upper mouth of a
chute moves under gravity action down the chute.
The apparatus 10, in this example of the invention, is intended to be used
for the sorting of diamondiferous particulate material. It is known that
diamonds can be excited, by means of suitable X-ray sources, to emit
fluorescence. To make use of this characteristic an X-ray source or a
plurality of X-ray sources 32 are placed in line, in the interior of the drum,
extending across the horizontal length 46 of the drum. The arrangement
is such that the whole drum surface which passes in front of the array of
X-ray sources is irradiated with X-rays. One or a plurality of X-ray
detectors 34 are similarly positioned across the interior of the drum, to
detect X-ray emissions which may be stimulated by the X-ray sources. The
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position of each X-ray detector is known with respect to the horizontal
length of the drum. Each X-ray detector therefore monitors a particular
track, of a predetermined width, on the inner surface 22 of the drum.
An air or water ejector 36, or a plurality of the eje~tors, are positioned
opposite the mouth of the chute 24.
A second array of X-ray sources 38, and a corresponding array of X-ray
detectors 40, are positioned downstream of the chute 26. The X-ray
sources 38 are similar to the sources 32 and the detectors 40 are similar
to the .leteclors 34. Air or water ejectors 42, similar to the ejectors 36, are
positioned opposite the mouth of the chute 26.
Additional air or water ejeclola 44 are positioned opposite the mouth of the
chute 28.
Rerere"ce should be made to Figure 3 which schematically illustrates the
ejectors 36 and 42 extending in two arrays which are spaced from one
another in the rotational direction 30 of the drum and which extend across
the horizontal width 46 of the drum.
The drum 12 includes a wall which is formed with a plurality of apertures.
The apertures may be provided in any suitable way and the drum wall may
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for example be formed with a plurality of perforations. Alternatively,
howcver, as is shown in the partial cross-sectional illustration of the drum
in Figure 4, the drum is formed from a plurality of wedge wires 48 which
extend across the drum surFace to form a plurality of very fine slots 50
. between adjacent wedge wires.
Material which is to be sorted is fed via the chute 20 into the interior of the
drum. The drum is rotated by means of the motor 14 and, due to
centrifugal force, the material is caused to adhere to the inner surface of
the drum. Preferably the rotational speed is sufficiently high, or
altematively use is made of mechanical dispersion devices, to ensure that
the material on the inner surface of the drum is held in a mono-layer with
the particulate material separated so that individual particles are
identifiable.
The rotating material is presented to the X-ray sources 32 and the
diamonds in the material are stimulated to emit fluorescence. The
fluorescing particles are detected by the detectors 34 and control signals
are fed by the . Ietectors to the control module 18. As the rotational speed
of the drum is known and as the position of each particle, in the
longitudinal sense, is known from the particular detector 34 which detects
the emission of fluorescence from the particle in question, it is possible for
the control module 18 to cause the cor,es~o"~ ,y ejector 36 to be actuated
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as the fluorescent particle p~sses the mouth of the chute 24. By firing the
ejector at the right time an air or water jet is directed through the
appropriate portions of the corresponding slots 50 and the particle or
particles adhering to the inner surface 22 are displaced from the drum and
are directed into the chute 24.
In this example of the invention there are two stimulating and detection
sections. Thus after the particulate material has passed the chute 24, the
material is again subjected to X-ray stimulation by means of the sources
38 and fluorescing particles are detected by the detectors 40 and are then
displaced by the ejectors 42 into the chute 26.
Material remaining on the inner surface 22 is displaced into the chute 28
by means of the ejectors 44. These ejectors could be replaced by means
of a mechanical scraper device 52 which simply removes all material from
the surface 22 and directs it into the chute 28.
The material which is fed via the chute 20 into the interior of the drum, may
be fed in wet or dry form. For very hne wet material the bottom of the drum
could be in a trough of water. The material is flung onto the inner surface
22 by the ce.,l-irugal force ye,.e.dled due to the drum rotating and most of
the moisture is moved. The material remains in a stable position on the
surface 22 and is transported, preferably in a mono-layer.
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The control module 18 calculates whether the detected particles are of
accept or reject quality. The accepted particles, which are the minority
part of the feed, are removed by means of the accept ejectors 36 and 42.
~he principles of the invention may be used with particulate material which
ranges in size from a fine size to relatively coarse material.
It is not necessary to make use of gas or fluid ejectors. These devices
could be replaced by means of suction systems which suck selected
particles from the inner surface 22. In this variation of the invention the
drum wall may be solid or be made from a semi-permeable material.
The invention has been described with reference to the removal of desired
con".onenls from the particulate material. The invention can be used in a
different sense in that contaminants can initially be removed from the
- 20 particulate material and the remaining material, which is then the desired
component, can be collected in the chute 28. For example if the particulate
material includes a food product such as rice or beans then damaged
grains or beans can be removed, or dangerous inclusions such as glass
or grit can be separated from the food product. This sorting technique is
based on visual dirrer~nces which are detectable without prior stimulation.
