Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02625843 2008-03-27
CENTRIFUGAL SEPARATOR OF HEAVIER PARTICULATE MATERIALS FROM
LIGHT PARTICULATE MATERIALS IN A SLURRY USING A RING IN THE
COLLECTION RECESS
This invention relates to a centrifugal separator of heavier particulate
materials from light particulate materials in a slurry.
BACKGROUND OF THE INVENTION
In U.S. Patents 4,608,040, 4,776,833, 5,222,933, 5,421,806,
5,230,797 and 5,338,284 of Benjamin Knelson and now assigned to the present
Assignee is disclosed a centrifugal separator of the type including a
rotatable bowl
having a peripheral wall of generally frusto-conical shape on which is
provided' a
plurality of axially spaced, annular recesses. The particulate material
containing
fractions of different specific gravity to be separated is fed in slurry form
through a
feed duct to a position at or adjacent a base of the bowl so that the feed
materials
flow outwardly onto and pass over the peripheral wall with heavier particulate
materials collecting in the annular recesses while lighter particulate
materials escape
from the bowl through the open mouth. In the above patents, all of the annular
recesses are fluidized by the injection of fluidizing water through holes in
the
peripheral wall at the respective recesses thus acting to fluidize the
collecting
material within the recesses,
A further arrangement is disclosed in U.S. Patent 5,586,965, issued
December 24th, 1996 of the above inventor in which the number of recesses is
reduced and a frusto-conical lead-in section of the bowl is provided which is
free
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2
from fluidized recesses so that the feed material is deposited onto the lead-
in section
and flows over that lead-in section prior to reaching the first annular
recess. In this
arrangement there are provided discharge ports at the base of the recess or
recesses which are opened by valves periodically so that the concentrate is
discharged from the recess on an effectively continuous basis as opposed to
the
batch collection basis of the above patents.
In US Patent 5,601,523 issued February 11l" 1997 of the above
inventor there is disclosed a continuous machine of the above type where at
each
discharge port is provided a guide body which is generally a spherical ball
located in
the recess in front of the port. The balls are supported by a ring which
extends
around the recess at the mouth of the recess.
Further developments of this continuous machine are shown in US
Patent 6,149,572 issued November 21st 2000 where at each discharge port each
spherical ball is located in the recess in front of the port by a support bar
which
extends across the recess.
It is also known, as shown in a brochure of a machine manufactured
under the above patents to provide a diffuser ring which extends around the
recess
at the mouth leaving gaps between the top and bottom of the ring and the edge
of
the recess through which the heavier materials pass for collecting in the
recess and
for discharge through the ports as the valves are opened.
A further arrangement is disclosed in U.S. Patent 5,895,345, issued
April 20th, 1999 of the above inventor in which the amount of fluidizing water
is
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reduced by supplying water only to some of the recesses of the bowl which are
reduced in depth. This includes a lowermost section of the wall which has no
fluidized recesses in a row of the shallower non-fluidized recesses.
SUMMARY OF THE INVENTION
It is one object of the invention to provide a centrifugal separator of
heavier particulate materials from light particulate materials in a slurry and
an insert
member which can be used in an apparatus of this type as a retrofit.
According to one aspect of the invention there is provided an
apparatus for separating intermixed particulate materials of different
specific gravity
in a slurry, comprising:
a centrifuge bowl having a base and a peripheral wall surrounding an
axis passing through the base and generally upstanding from the base to an
open
mouth;
a mounting arrangement for rotating the bowl around the axis;
a feed duct having a discharge mouth adjacent the base of the bowl for
feeding the slurry into the bowl during rotation of the bowl so that, during
rotation of
the bowl, the intermixed particulate materials flow over the peripheral wall
of the
bowl from the base for collection of heavier particulate materials on the
peripheral
wall and for discharge of the lighter particulate materials in the slurry from
the open
mouth;
a launder for collecting the lighter particulate materials in the slurry
discharged from the open mouth;
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an annular recess having a mouth at the peripheral wall over which the
materials pass when fed from the supply duct as the materials pass to the open
mouth of the bowl for collection of the heavier materials in the annular
recess;
the annular recess comprising an annular upper wall and an annular
lower wall each extending generally outwardly from the peripheral wall;
the annular upper wall and the annular lower wall including at least
portions thereof which converge together toward a base of the annular recess
spaced outwardly of the peripheral wall;
fluidizing openings in the annular recess at or adjacent the base at
angularly spaced positions for fluidizing said heavier materials in the
annular recess;
I a plurality of valve controlled discharge ports in the annular recess at
angularly spaced positions for generally radially outward discharge of
collected
heavier materials from the annular recess for substantially continuous
operation;
and an annular ring extending continuously around the annular recess;
the annular ring having an annular inner portion mounted at the mouth
of the annular recess leaving a space above and below the ring for passage of
materials into the recess from the bowl;
the annular ring having an annular outer portion extending from the
inner portion generally radially outwardly into the recess to a position
between the
converging portions of the walls of the recess;
wherein the outer portion has an outermost face facing outwardly to
the base and the discharge ports therein with the outer portion being shaped
and
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arranged relative to the recess that the space between the outermost face and
the
discharge ports is open to cause the outermost face to act as a control
surface of the
materials in the recess at the discharge port.
Preferably the outer portion of the ring has top and bottom walls which
5 converge toward the base of the recess.
The top and bottom walls may converge in steps or may be rounded
and preferably are arranged such that a spacing from of the top and bottom
walls
from the converging portions increases in an outward direction.
Preferably the top and bottom walls are symmetrical but this is not
necessary as the operation is not symmetrical so that the spacing from the
wall of
the recess at the top may be wider than the spacing at the bottom.
Preferably the annular upper wall and the annular lower wall each
include an inner portion inwardly of the converging portions which are
substantially
radial in direction and wherein the inner portion of the ring has top and
bottom walls
which are also substantially radial.
Preferably the inner portion of the ring has an inwardly facing surface
which is substantially flat.
Preferably the inner portion of the ring has an inwardly facing surface
which is substantially coplanar with the mouth at peripheral wall.
According to a second aspect of the invention there is provided an
apparatus for separating intermixed particulate materials of different
specific gravity
in a slurry, comprising:
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a centrifuge bowl having a base and a peripheral wall surrounding an
axis passing through the base and generally upstanding from the base to an
open
mouth;
a mounting arrangement for rotating the bowl around the axis;
a feed duct having a discharge mouth adjacent the base of the bowl for
feeding the slurry into the bowl during rotation of the bowl so that, during
rotation of
the bowl, the intermixed particulate materials flow over the peripheral wall
of the
bowl from the base for collection of heavier particulate materials on the
peripheral
wall and for discharge of the lighter particulate materials in the slurry from
the open
mouth;
a launder for collecting the lighter particulate materials in the slurry
discharged from the open mouth;
an annular recess having a mouth at the peripheral wall over which the
materials pass when fed from the supply duct as the materials pass to the open
mouth of the bowl for collection of the heavier materials in the annular
recess;
the annular recess comprising an annular upper wall and an annular
lower wall each extending generally outwardly from the peripheral wall;
the annular upper wall and the annular lower wall including at least
portions thereof which converge together toward a base of the annular recess
spaced outwardly of the peripheral wall;
fluidizing openings in the annular recess at or adjacent the base at
angularly spaced positions for fluidizing said heavier materials in the
annular recess;
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a plurality of valve controlled discharge ports in the annular recess at
angularly spaced positions for generally radially outward discharge of
collected
heavier materials from the annular recess for substantially continuous
operation;
and an annular ring extending continuously around the annular recess;
the annular ring having an annular inner portion mounted at the mouth
of the annular recess leaving a space above and below the ring for passage of
materials into the recess from the bowl;
' the annular ring having an annular outer portion extending from the
inner portion generally radially outwardly into the recess to a position
between the
converging portions of the walls of the recess;
wherein the outer portion has top and bottom walls which converge
toward the base of the recess.
According to a third aspect of the invention there is provided an insert
member for use in an apparatus for separating intermixed particulate materials
of
different specific gravity in a slurry, the apparatus comprising:
a centrifuge bowl having a base and a peripheral wall surrounding an
axis passing through the base and generally upstanding from the base to an
open
mouth;
a mounting arrangement for rotating the bowl around the axis;
a feed duct having a discharge mouth adjacent the base of the bowl for
feeding the slurry into the bowl during rotation of the bowl so that, during
rotation of
the bowl, the intermixed particulate materials flow over the peripheral wall
of the
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bowl from the base for collection of heavier particulate materials on the
peripheral
wall and for discharge of the lighter particulate materials in the slurry from
the open
mouth;
a launder for collecting the lighter particulate materials in the slurry
discharged from the open mouth;
an annular recess having a mouth at the peripheral wall over which the
materials pass when fed from the supply duct as the materials pass to the open
mouth of the bowl for collection of the heavier materials in the annular
recess;
the annular recess comprising an annular upper wall and an annular
lower wall each extending generally outwardly from the peripheral wall;
the annular upper wall and the annular lower wall including at least
portions thereof which converge together toward a base of the annular recess
spaced outwardly of the peripheral wall;
fluidizing openings in the annular recess at or adjacent the base at
angularly spaced positions for fluidizing said heavier materials in the
annular recess;
a plurality of valve controlled discharge ports in the annular recess at
angularly spaced positions for generally radially outward discharge of
collected
heavier materials from the annular recess for substantially continuous
operation;
the insert member comprising an annular ring;
the annular ring being shaped and arranged so as to extend
continuously around the annular recess;
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the annular ring having an annular inner portion shaped and arranged
so as to be mounted at the mouth of the annular recess leaving a space above
and
below the ring for passage of materials into the recess from the bowl;
the annular ring having an annular outer portion shaped and arranged
so as to extend from the inner portion generally radially outwardly into the
recess to
a position between the converging portions of the walls of the recess;
wherein the outer portion has an outermost face facing outwardly to
the base which is free from elements attached to the ring member.
According to a fourth aspect of the invention there is provided an insert
member for use in an apparatus for separating intermixed particulate materials
of
different specific gravity in a slurry, the apparatus comprising:
a centrifuge bowl having a base and a peripheral wall surrounding an
axis passing through the base and generally upstanding from the base to an
open
mouth;
a mounting arrangement for rotating the bowl around the axis;
a feed duct having a discharge mouth adjacent the base of the bowl for
feeding the slurry into the bowl during rotation of the bowl so that, during
rotation of
the bowl, the intermixed particulate materials flow over the peripheral wall
of the
bowl from the base for collection of heavier particulate materials on the
peripheral
wali and for discharge of the lighter particulate materials in the slurry from
the open
mouth;
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a launder for collecting the lighter particulate materials in the slurry
discharged from the open mouth;
an annular recess having a mouth at the peripheral wall over which the
materials pass when fed from the supply duct as the materials pass to the open
5 mouth of the bowl for collection of the heavier materials in the annular
recess;
the annular recess comprising an annular upper wall and an annular
lower wall each extending generally outwardly from the peripheral wall;
the annular upper wall and the annular lower wall including at least
portions thereof which converge together toward a base of the annular recess
10 spaced outwardly of the peripheral wall;
fluidizing openings in the annular recess at or adjacent the base at
angularly spaced positions for fluidizing said heavier materials in the
annular recess;
a plurality of valve controlled discharge ports in the annular recess at
angular9y spaced positions for generally radially outward discharge of
collected
heavier materials from the annular recess for substantially continuous
operation;
the insert member comprising an annular ring;
the annular ring being shaped and arranged so as to extend
continuously around the annular recess;
the annular ring having an annular inner portion shaped and arranged
so as to be mounted at the mouth of the annular recess leaving a space above
and
below the ring for passage of materials into the recess from the bowl;
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the annular ring having an annular outer portion shaped and arranged
so as to extend from the inner portion generally radially outwardly into the
recess to
a position between the converging portions of the walls of the recess;
wherein the outer portion has top and bottom walls shaped and
arranged so as to converge.
In principle therefore concentrated slurry migrating up the wall of the
concentrator and over the lead-in surface enters the concentrating recess
through
the lower opening at the base of the concentrate grade ring. The shape of the
back
of the concentrate grade enhancer serves to take up voidage volume and thus
reduce the available space for particles to accumulate. As a result, lighter
gangue or
waste particles are replaced by the denser target particles. In this way the
grade of
the concentrate is increased because there are less gangue particles present.
The concentrate capture ring in concentrators has hitherto been
deemed to be the final holding point before the concentrates are withdrawn
from the
concentrator. The concentrate present there was therefore the final product.
By
introducing the concentrate grade enhancer ring a further step of upgrading is
introduced by forced exclusion of the light gangue particles.
The arrangements described herein can be used in batch machines
where the bowl is stopped periodically to discharge collected materials from
the
collection recesses or in a continuous machine using a plurality of valve
controlled
discharge ports in the annular recess at angularly spaced positions for
generally
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radially outward discharge of collected heavier materials from the annular
recess for
substantially continuous operation.
The number of collection recesses can vary in machines of this type
depending on requirements bearing in mind that the number of recesses is
generally
smaller in continuous machines and larger in batch machines. The minimum
number of recesses is therefore a single recess and the number can be
considerably
greater as required. Where definitions used herein refer to a"recess", it will
be
appreciated that this may be the only recess or may be one of a number of such
recesses.
The description and definition of the arrangements herein use for
convenience the terms "inward" and "outward" and these terms are used in
relation
to the axis of the bowl so that the former defines a direction toward the axis
and the
latter a direction away from the axis.
The description and definition of the arrangements herein use for
convenience the terms "upper" and "lower", "top" and "bottom" and these terms
are
used in relation to a normal orientation of the bowl. However it will be
appreciated
that the bowl can be placed or may in fact be used in orientations different
from the
normal upright orientation.
The description and definition of the arrangements herein use for
convenience the term "annular" which is used to indicate that the element
concerned
is an element which continuously surrounds the axis and is not intended to
imply or
specify any particular shape of the element in cross section or in plan.
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The description and definition of the arrangements herein use for
convenience the term "radial" which is used to indicate a direction generally
toward
or away from the axis and is not intended to indicate that the direction lies
directly
along a radius of the axis.
Devices of this type are typically be used where the heavier particles
are to be collected and the lighter particles are gangue or waste. However in
some
cases this relationship is reversed.
BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the invention will now be described in conjunction
with the accompanying drawings in which:
Figure 1 is a vertical cross sectional view through an apparatus
according to the present invention.
Figure 2 is a vertical cross sectional view through one half of the bowl
only of the apparatus of Figure 1.
Figure 3 is a horizontal cross sectional view through the bowl only of
the apparatus of Figure 1.
In the drawings like characters of reference indicate corresponding
parts in the different figures.
DETAILED DESCRIPTION
The centrifugal separation apparatus as shown in Figures 1 to 3
comprises a bowl generally indicated at 10 having a base 11 and an open mouth
12.
A feed duct 13 comprises a vertical pipe mounted on a central axis 14 of the
bowl for
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feeding a slurry 15 downwardly onto the base 11 of the bowl. The bowl 10
includes
a peripheral wall 16 so that the slurry moving outwardly to the peripheral
wall under
centrifugal forces passes over the peripheral wall for collection of heavier
materials
into a collection recess 17 and for discharge of lighter materials and water
over the
open mouth 12. While one recess is shown, the number of recesses can be
increased if required.
The material collecting in the recess 17 is discharged radially
outwardly through a series of discharge ports at spaced positions around the
recess.
Each discharge port forms part of a discharge port and valve assembly 19.
The materials discharged from the open mouth are collected within a
first launder 20 for coliection and transportation to a discharge area. The
heavier
materials collected within the recess 17 is discharged from the assembly 19
and
collected within a middle launder 21.
The bowl 10 is mounted on a shaft 22 for rotation about the axis 14.
U.S. Patent. No. 5,222,933 discloses further details of the base of the bowl
including
a base plate 1 1A and a bottom discharge opening 11 B. U.S. Patent Nos.
5,601,523
discloses various constructional features of the above machine. Construction
of the
shaft is shown in U.S. Patent No. 5,601,524. Further the general shape of the
bowl
including a lower frusto-conical portion 16 which directs the feed material
across the
recesses 17 and 18 is shown in U.S. Patent No. 5,586,965. The further patents
can
be referred to for further details of the construction if required.
The construction of the bowl in the area of the recess 17 is shown in
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more detail in Figures 2 and 3. Thus the collection area of the bowl comprises
a
metal bottom plate 24 and a metal top plate 25. The metal bottom plate 24 is
attached to the first conical inclined section 16A of the wall of the bowl. In
between
the metal plates 24 and 25 is provided the recess 17, which is molded or
formed
5 from a polyurethane material so as to be substantially rigid to provide some
resilience and wear resistance. It is well known that centrifuge bowls
accommodate
significant levels of wear and for this purpose the use of polyurethane as a
manufacturing material is well established.
This conical wall 16A forms a smooth run up zone or lead-in surface so
10 that the feed material move outwardly from the base 11A onto the surface
16A and
moves in a smooth flow to the recess 17 which is outward of the upper end of
this
surface. This surface is selected to be smooth in the belief that a smooth
surface
avoids disruption and thus aids both recover and grade of the target dense
particles.
The recess 17 is generally annular defining a cylindrical outer surface
15 28 and extends outwardly from the upper end of the surface 16A. The recess
17
has a horizontal top wall 26 and horizontal bottom wall 27. The latter is
attached to
the top surface of the plate 24 and is located in position on the plate by
guides pins
29 at spaced positions around the annular plate 24, the guide pins being
received
within a recess 30 formed in the wall 27. Similarly the top ring 25 has a
bottom
surface sitting in contact with the top surface of the wall 27 and a top
surface
carrying an outlet guide plate 25A extending from the mouth 12 to the launder
20.
The whole structure including the recess 17, the top plate 25 and the bottom
plate
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16
24 is clamped together by a series of bolts 31 at angularly spaced positions
around
the structure. Each bolt 31 has a head received within a recess in the top
plate 25A.
The recess 17 has a recess upper side surface 17A of the wall 26 and
a lower side surface 17B of the wall 27 which converge outwardly to a flat
base 17C
with the base being annular and lying in a cylindrical surface surrounding the
axis of
the bowl. The shape and arrangement of the recesses is similar to that
disclosed in
U.S. Patent No. 5,601,523. Each recess has a plurality of fluid injection
openings 39
and 40 for injecting fluidizing water into the recess adjacent the base of the
recess
so the fluidizing water can flow through the recess and mix with the materials
in the
recess as described in the prior patents of Knelson. In this arrangement, as
is best
shown in Figure 2, the injection openings are arranged to a first series of
injection
openings 40 located in the upper wall 17A adjacent to but spaced inwardly from
the
base 17C. A second series 39 of injection openings is arranged in the lower
wall
17B again at a position adjacent to but spaced from the base 17C. Both sets of
injection openings lie in a common cylindrical surface surrounding the axis of
the
bowl with the cylindrical surface spaced inwardly from the cylindrical surface
containing the base 17C. Thus the injection openings are arranged to inject to
the
fluidizing water in a direction lying in a surface parallel to the axis.
As shown in Figure 3, there is a series of such injection openings 39
and 40 at angularly spaced positions around the bowl. The injection openings
lie in
the cylindrical plane 41 but are inclined to a line 42 fying centrally of the
base 17C so
as to inject the water in a direction tending to flow in a direction 43 which
is opposite
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17
to direction 44 of rotation of the bowl. Each injection opening is shaped with
a first
wider portion 39A and a second narrower portion 39B with the second portion
having
a mouth breaking out on the respective side wall. The length of the narrower
portion
is as short as reasonably practical so as to maintain the duct forming the
injection
opening at the wider dimension 39A for communication of fluid therethrough
with
reduced possibility for blockages. However it is required that the mouth of
the
injection opening at the side wall be relatively small so as to provide a jet
of the
fluidizing water entering the recess at the side wall with that jet having
sufficient fluid
flow to cause a significant jet of the fluidizing liquid across the base
toward the
opposite side wall.
The construction of the fluidizing water supply system from the hub to
the ducts 39, 40 and the assembly 19 is shown in more detail in US Patent
6,149,572.
The assembly 19 comprises a duct 53 which is formed integrally from a
resilient material and extends from a mouth 54 to an outer discharge end 55.
The
duct 53 includes a valve portion 56 and a tapered duct portion 57 extending
from the
mouth 54 to the valve portion 56. The duct defines an inner surface through
which
the heavier materials are discharged from the recesses to the launder 21. The
tubular duct portion 57 has an outer surface which is generally cylindrical
and
projects forwardly from the assembly 19. The mouth 54 is arranged as an
annular
surface lying in a plane at right angles to a central axis of the duct and
surrounding
the tapered tubular portion 57 and inside the outer surface. For each
discharge
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assembly, the recess has an opening into which the mouth can project from a
chamber located between the recessed and the outer surface of the recess 17.
Thus a forward portion of the mouth 54 projects slightly proud of the base 17C
of the
recess. The mouth 54 is thus substantially aligned with the jet from the inlet
openings 39 and 40. In this way the jet from the inlet openings passes across
the
mouth in a sweeping action. The pressurized fluid for activating the valve
portion is
supplied to the valve through a pipe 19A.
The constriction of the hub and the supply of fluidizing liquid through
the hub from the shaft and the supply of compressing fluid through the hub
from the
shaft is described and illustrated in detail in U.S. Patent No. 5,601,524 and
therefore
will not be described in detail herein.
It will be noted however that the fluidizing liquid is supplied through a
single source through the shaft and then connects to a plurality of angularly
spaced
supply ducts to the pipes 47. The pressurizing fluid, which is generally air,
for the
valves is supplied through two supply ducts to the pipes 19A.
In normal operation of the bowl as shown herein, the feed material is
separated so that the heavier particles collect within the recess 17 and the
lighter
particles and water escape over the mouth 12. The heavier particles are then
discharged by periodic opening of the pinch valves to allow release of a plug
of
collected heavier particles. At least one fluidization hole is aligned in
front of each
pinch valve exit jet to blow material away from the entrance to the exit jet.
The
recess 17 is V-shaped to direct material to the pinch valve. it can also be
flattened
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19
out in front of the fluidization holes so as to prevent material from
compacting in an
otherwise elliptically exposed hole. In the event that the larger particles
accumulate
to a situation where blockage cannot be prevented, it is necessary to halt
operation
of the device, that is to halt the feed 15, to halt rotation of the bowl and
to effect
discharge of the heavier particles collected within the recess. As these
heavier
particles are generally the larger particles which have been collecting, it
may not be
necessary to collect the materials as concentrate but this can be done if
preferred.
The above arrangement is substantially as described and shown in
previous patents of the present Assignees.
In the present application two further significant modifications are
made which enhance the operation of the general device described above.
Firstly a device inserted to enhance the separation of dense particles
from light waste or gangue particles which consists of a series of sequential
steps
running up the lower wall of the concentrator, called the Run Up Zone.
There is thus provided in the bowl an insert member 70 mounted on
the wall 16A which defines a lead-in surface 71 which extends axially of the
peripheral wall from a lower end 72 on the peripheral wall arranged for
receiving said
feed materials from the discharge mouth 13A of the duct 13 to an upper end 73
of
the lead-in surface at the recess 17. The lead-in surface is arranged such
that in the
bowl it is generally increasing in diameter from the lower end 72 to the upper
end 73
so that the upper end is of greater diameter than the lower end. This
generates a
flow upwardly and outwardly which accelerates and moves toward the recess 17.
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The lead-in surface 71 is shaped to define a series of axially spaced
surface portions 74A to 74D each surrounding the axis with the portions being
arranged in a row with each surface portion of the row being directly after
the
previous surface portion in the row. Each surface portion 74A of the row is of
5 smaller diameter than a subsequent portion 74B of the row. Each surface
portion
74A of the row has a trailing edge 74C which connects directly to a leading
edge of
the subsequent surface portion 74B of the row by an outwardly extending step
75.
The lead-in surface thus includes a plurality of step portions 75 thereon
at axially spaced positions thereon with the step portions 75 arranged to
provide a
10 repeated tumbling action in the feed materials as the feed materials rnove
over the
lead-in surface.
The surface portions 74A, 74B are inclined outwardly and upwardly
relative to a cylindrical surface and the steps 75 are substantially radial.
However
these angles are not essential and may be less aggressive so that the steps 75
are
15 inclined outwardly and upwardly to a radial plane at an angle greater than
the
surface portions 74A.
The surface portions 74A etc extend in a row substantially continually
from the base to the at least one recess. However this is not essential and
there
may be steps portions only over a part of the length of the surface 71, in
which case
20 a remaining part of the length of the lead-in surface 71 is frusto-conical.
In the principle of operation, slurry introduced into the concentrator is
accelerated by contact with the spinning surface 71 of the concentrator. As it
is
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21
accelerated, the denser and coarser particles become more concentrated against
the wall and as a result the slurry becomes thicker and more viscous in
proximity of
the wall. This thickening is counterproductive to the desired separation of
particles
as their relative mobility is impaired as a result. By introducing the series
of steps
75, the thick slurry tumbles over the edge of the steps on its migration up
the cone
wall. With each tumbling action an opportunity is afforded for particles to
sort
themselves with the target denser particles moving closer to the wall under
the force
of the centrifugal gravity field and so displacing lighter waste or gangue
particles. In
this way the recovery of the denser target particles is increased as more find
their
way towards the wall where they are captured. The purity of the concentrate is
also
increased because more of the lighter gangue particles, which contaminate the
concentrate, are rejected by the denser target particles.
The insert member 70 can be formed into the centrifugal concentrator
either at the time of manufacture by casting the liner in the required shape,
or a
separate insert piece can be formed as an insert and retrofitted into
concentrators
already existing.
The height of the steps and the length of the surface portions can be
varied between wide limits to obtain different angle of the wall as it
increases in
diameter toward the recess 17. The intended effect is that the feed materials
as
they flow over the surface pass over the step between each surface portion in
turn
with both the step and the surface portion being arranged to have some effect
on the
materials.
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22
An increased effect can be provided by adding fluidizing ports in the
lead-in surface for supplying fluidizing liquid onto the surface as the feed
material
flow over the surface. The fluidizing ports can be located in the surface
portions 74A
or in the steps 75. Suitable ducts to the exterior of the bowl can be provided
to
supply the fluidizing water or the insert member itself may carry a supply
duct. The
angle of the dust through the insert member to the surface may be selected tso
that
the water passes through the surface at a required angle to mix with the feed
materials as they pass over the surface and tumble over the steps.
It will be appreciated that the steps move continually outwardly without
any return portions extending inwardly since such portions act to define
additional
shallow recesses on the surface which merely act to collect additional
material and
thus are filled and do not affect the flow of the material passing over the
filled recess.
Any kind of geometry or steps can be used on this surface that is in the
run-up zone that disrupts the flow and could potentially achieve the same
benefits.
One example is the use of golf ball dimples which can be attached onto the
surface.
In all these cases the additional elements form an array of steps extending in
both
angular and axial direction so that the material tumbles over these steps as
previously explained. The steps do not need to be annular, that is fully
surrounding
the axis.
The annular recess 17 has a mouth 80 at the peripheral wall defined
by a bottom edge 81 and a top edge 82 over which the materials pass after the
materials emerge from the last surface portion of the lead-in surface 16 of
the bowl.
CA 02625843 2008-03-27
23
The recess 17 is defined by the upper surface 17A and the lower surface 17B
each
extending generally outwardly from the peripheral wall. The annular upper wall
and
the annular lower wall each include portions 17E and 17D thereof which
converge
together toward the base 17C of the annular recess spaced outwardly of the
peripheral wall. Adjacent the mouth 80, the surfaces 17A and 17B each include
a
vertical portion 17F followed by a horizontal portion 17G immediately at the
mouth.
Thus the spacing across the mouth is defined by the portions 17G which is
greater
than the spacing between the inner ends of the converging portions 17D and
17E.
Into the recess is mounted an annular ring 84 extending continuously
around the annular recess. The annular ring has an annular inner portion 85
mounted at the mouth 80 of the annular recess leaving a space above and below
the
ring at the portions 17G and inwardly of the vertical portions 17F for passage
of
materials into the recess from the bowl. The annular ring has an annular outer
portion 86 extending from the inner portion 85 generally radially outwardly
into the
recess to a position between the converging portions 17E and 17D of the walls
of
the recess. The outer portion 86 has an outermost face 87 facing outwardly to
the
base 17C and the discharge ports therein. The ring is intended as a guide
surface
for the materials and is not a support for other guide surfaces so that the
outermost
face 87 defines relative to the recess and particularly the base of the recess
a space
between the outermost face and the discharge ports. This space is open so that
the
outermost face 87 acts as a control surface of the materials in the recess at
the
discharge port.
CA 02625843 2008-03-27
24
The outer portion 86 of the ring has top and bottom walls 88 and 89
which converge toward the base of the recess so that they tend to follow the
convergence of the portions 17D and 17E of the recess. As shown the top and
bottom walls 88 and 89 are stepped rather than smooth so that they converge in
steps. However the top and bottom walls can also be smoothly rounded. The top
and bottom walls 88, 89 are also arranged such that a spacing from of the top
and
bottom walls from the converging portions 17D and 17E increases in an outward
direction with the face 87 being spaced from the base by a distance even
greater
than the spacing of the walls from the converging portions. Thus there is a
point of
closet approach on the converging portions which then opens up again outward
of
the ring. The top and bottom walls are symmetrical. The inner portion 85 of
the ring
has top and bottom walls which are also substantially radial and thus parallel
to the
portions 17G of the recess at the mouth 80. The inner portion 85 of the ring
has in
inwardly facing front surface 90 which is substantially flat and is
substantially
coplanar with the mouth 80 at peripheral wall.
The ring 84 is mounted in the recess 17 by a series of upstanding
brackets 95, 96 which extend between the top of the ring and the top wall of
the
recess and between the bottom of the ring and the bottom wall of the recess.
These
simply span the space and act to prevent axial and radial movement. The
brackets
are located at angularly spaced positions around the ring so as to maintain
the ring
at the required axial position within the recess to prevent flexing. The ring
is molded
from the wear resistant material commonly used in the bowl. V-shaped cuts 98
are
CA 02625843 2008-03-27
provided extending from the outer surface 87 to the brackets and simply make
the
production of piece easier by adding relief for flexing. They may or may not
face the
pinch valves.
Two anti rotation locks 97 to prevent angular movement are also
5 provided at respective ones of the brackets 95, 96 and are mounted in the
annular
recess 17 to prevent rotation of ring 84.
The toroidal concentrate collection ring 84 has been found to increase
the grade of the resulting concentrate. The ring has a flat inner face edge
across the
mouth of the concentrator and a rounded back edge protruding into the inner
part of
10 the concentrate collecting recess. Concentrated slurry migrating up the
wall of the
concentrator and over the stepped run up zone enters the recess through the
lower
opening at the base of the concentrate grade enhancer. The shape of the outer
face
of the concentrate grade enhancer ring 84 serves to take up voidage volume and
thus reduce the available space for particles to accumulate. As a result,
lighter
15 gangue or waste particles are excluded at the expense of the denser target
particles.
In this way the grade of the concentrate is increased because there are less
waste
particles present.
The concentrate capture recess in concentrators has hitherto been
deemed to be the final holding point before the concentrates are withdrawn
from the
20 concentrator. The concentrate present there was therefore the final
product. By
introducing the concentrate grade enhancer ring a further step of upgrading is
introduced by forced exclusion of the light waste particles.
CA 02625843 2008-03-27
26
The concentrate grade enhancer can be installed into the concentrate
collection recess of the concentrator, either at the time of manufacture, or
as a
retrofit. The concentrator is then operated in the normal mode of operation
without
any further special consideration.
The ring 84 can have any kind of shape that takes out ring volume.
Since various modifications can be made in my invention as herein
above described, and many apparently widely different embodiments of same made
within the spirit and scope of the claims without department from such spirit
and
scope, it is intended that all matter contained in the accompanying
specification shall
be interpreted as illustrative only and not in a limiting sense.
