Note: Descriptions are shown in the official language in which they were submitted.
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A DRUM FILTER APPARATUS
FIELD OF THE INVENTION
The present invention relates to a a drum filter apparatus according
to the preamble of claim 1.
BACKGROUND OF THE INVENTION
Filtration is a widely used process whereby a slurry or solid liquid
mixture is forced through a media, with the solids retained on the media and
the liquid phase passing through. Examples of filtration types include depth
filtration, pressure and vacuum filtration, and gravity and centrifugal
filtration.
lo Both pressure and vacuum filters are used in the dewatering of
mineral concentrates. Pressure filtration is based on the generation of an
overpressure within a filtration chamber. Consequently, solids are deposited
onto the surface of the filter medium and filtrate flows through the filter
medium
into the filtrate channels. Pressure filters often operate in batch mode
because
continuous cake discharge is more difficult to achieve.
Vacuum filtration is based on producing a suction within the filtrate
channels and thereby forming a cake of mineral on the surface of the filter
medium. The most commonly used filter types in vacuum filters are filter
cloths
and ceramic filters. There exists several types of vacuum filters, ranging
from
belt filters to drums. The invention is, however, related to rotary vacuum
drum
filters.
Rotary vacuum drum filters are used for the filtration of relatively
free filtering suspensions on a large scale, such as the dewatering of mineral
concentrates. The dewatering of mineral concentrates requires large capacity
in addition to producing a cake with low moisture content. The vacuum drum
filter may comprise a cylindrical support structure rotating around a
longitudinal
shaft forming a centre axis for the drum. There are a plurality of filter
plates
arranged on the outer surface of the cylinder. Each filter plate forms a
portion
of the cylindrical outer surface of the cylinder. Each filter plate is during
each
revolution of the shaft displaced for a certain period into a slurry basin
situated
below the shaft. The filter plate rises out of the basin when the revolution
of the
shaft proceeds. When the filter plate is submerged in the slurry basin a cake
forms onto the outer surface of the filter plate due to the vacuum within the
filter plate. Once the filter plate comes out of the basin, the pores are
emptied
as the cake is deliquored for a predetermined time which is essentially
limited
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by the rotation speed of the drum. The cake can be discharged by a back-
pulse of air or by scraping, after which the cycle begins again. The filter
plates
are advantageously made of porous ceramic.
The filter plates are in prior art solution attached with bolts to the
drum. There are fastening points provided with holes passing through the
filter
plate. A fastening flange is positioned into each hole in the filter plate.
The
fastening flange comprises a hole passing through the fastening flange. The
filter plate is fastened by bolts passing through the hole in the fastening
flange
in the filter plate. The holes passing through the filter plate will reduce
the filter
area in the outer surface of the filter plate. The holes and the bolts passing
through the filter plate will also increase the risk of leakage.
BRIEF DESCRIPTION OF THE INVENTION
An object of the present invention is to present a drum filter appa-
ratus with an improved fastening arrangement for the filter plates in the appa-
ratus.
The object of the invention is achieved by a fastening arrangement
in a drum filter apparatus according to the independent claim 1. Preferred em-
bodiments of the invention are disclosed in the dependent claims.
The drum filter apparatus comprises a cylindrical drum that is sup-
ported with a rim structure on a rotatable shaft having a centre axis, an
outer
surface of the drum comprises a number of individual filter plates forming an
essentially continuous cylindrical filter surface, each filter plate comprises
an
inner surface and a curved outer surface forming the filter surface of the
filter
plate, each filter plate is attached through at least three fastening points
to the
rim structure. The fastening arrangement at each of the at least three
fastening
points comprises:
a first recess extending from the inner surface of the filter plate into
a portion of the filter plate so that the outer surface of the filter plate
remains
unbroken,
a fastening flange positioned at least partly in the first recess and
being firmly attached to the filter plate,
a longitudinal fastening member comprising a first end portion and a
second opposite end portion, the first end portion being attached to the fas-
tening flange and the second end portion being attached to the rim structure,
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at least one snap locking means positioned in the fastening flange
or in the rim structure or in both and providing snap locking of the fastening
member to the filter plate or to the rim structure or to both, wherein
the filter plate is mounted on the drum by pressing the filter plate ra-
dially to the drum so that the snap locking means locks the filter plate to
the rim
structure of the drum.
The fastening arrangement in the drum filter apparatus according to
the invention will eliminate the holes passing through the filter plate. The
outer
surface of the filter plate will thus be unbroken, which leads to a bigger
effec-
tive filter area in the filter plate. It is only the outer surface of the
filter plate that
functions as the filter surface in the filter plate. The inner surface and the
edge
surfaces of the filter plate are impervious to water.
The fastening arrangement in the drum filter apparatus is identical in
all fastening points in the filter plate. This fact will lower the production
costs of
the fastening arrangement compared to a situation where the fastening ar-
rangements in the different fastening points are different.
The fastening arrangement in the drum filter apparatus according to
the invention makes the connection and the disconnection of the filter plates
to
the drum fast and efficient. The connection and the disconnection of the
filter
plates to the drum could be done e.g. by a vacuum lifter.
The fastening arrangement in the drum filter apparatus according to
the invention makes it easy to regulate the rigidity of the fastening of the
filter
plate to the drum. This can be done by changing the snap locking means. The
snap locking means is in one advantageous embodiment a spring ring posi-
tioned in a second groove within the second recess. The spring load is propor-
tional to the cross sectional area of the spring ring. The rigidity of the
fastening
of the filter plate can thus be altered by changing the cross sectional area
of
the spring ring.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention will be described in greater detail by
means of example embodiments with reference to the accompanying draw-
ings, in which
Figure 1 is a perspective top view of a drum filter apparatus,
wherein the inventive fastening arrangement may be applied,
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Figure 2 is a perspective top view of the drum of figure 1 with some
of the upper filter plates being removed,
Figure 3 is a cross section of the drum of figure 2,
Figures 4 is a cross section of a filter plate showing a prior art fas-
tening arrangement to the right in the figure and a fastening arrangement ac-
cording to the invention to the left in the figure,
Figure 5 shows the fastening flange of the inventive fastening ar-
rangement in figure 4,
Figure 6 shows the fastening member of the inventive fastening ar-
rangement in figure 4,
Figure 7 shows the fastening flange of figure 5 and the fastening
member of figure 6 in an assembled form,
Figure 8 is a cross section of a filter plate showing a second embod-
iment of a fastening arrangement according to the invention,
Figure 9 shows the fastening flange and the fastening member in a
disassembled form.
Figure 10 shows a third embodiment of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
Figure 1 is a perspective top view illustrating a drum filter apparatus
in which the inventive fastening arrangement may be applied. The drum filter
apparatus 10 comprises a frame 8, a cylindrical drum 20 supported within the
frame 8, a slurry basin 9 under the drum 20. The drum 20 comprises a shaft 25
that is supported at both ends with bearings 11, 12 on the frame 8. The shaft
and thereby also the drum 20 is rotatated by an electric motor 7 through a
25 gear. The drum 20 rotates around a centre axis X-X forming the
longitudinal
centre axis X-X of the shaft 25.
Figure 2 is a perspective top view illustrating the drum of figure 1
and figure 3 is a cross section of the drum 20 of figure 1. The drum 20 is
supported with a rim structure 21 at the axial X-X middle point of the drum 20
and at both ends of the drum 20. The rim structure 21 can be supported on the
shaft 25 e.g. by a disc structure or by spokes. The rim structure 21 comprises
further a plurality of support members 22 attached to each rim 21. The support
members 22 are formed of straight bars having a rectangular cross section.
The support members 22 are attached to the rim 21 by axially X-X directed
bolts passing through the support members 22 and being screwed into holes in
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the side surface of the rim structure 21. The support members 22 are arranged
on the circumference of a circle having the centre on the centre axis X-X.
Each
ceramic filter plate 23 is attached to two opposite support members 22 so that
an outer surface 23B of the filter plates 23 forms the cylindrical outer
filter sur-
5 face of the drum 20. The axial X-X length of the drum 20 is divided into
two
sections. A first ring R1 of filter plates 23 is positioned on the first
section of the
drum 20 and a second ring R2 of filter plates 23 is positioned on the second
section of the drum 20. The filter plate 23 comprises a planar inner surface
23A, a curved outer surface 23B and edge surfaces connecting the side edges
of the inner surface 23A and the side edges of the outer surface 23B of the
filter plate 23. The curvature of the outer surface 23B of the filter plates
23 co-
incides with the circumference of the outer surface of the drum 20. The centre
of the radius R forming the circumference of the outer surface of the drum 20
is
on the longitudinal centre axis X-X of the drum 20.
The number of the ceramic filter plates 23 on the drum 20 may vary
depending on the size of the drum 20. The diameter of the drum 20 may be in
the order of 1 to 5 meter and the length of the drum 20 may be in the order of
2
to 10 meter. The filtering area of the filter plates 23 may be in the order of
10 to
200 m2. A lower portion of the drum 20 is submerged in the slurry basin 9. The
outer surface 23B of the ceramic filter plate 23 has a microporous structure
so
that water can enter into the filter plate 23. The interior of the filter
plate 23 is
porous so that water can travel within the filter plate 23. The inner surface
23A
of the filter plate 23 and the edge surfaces of the filter plate 23 are
impervious
to water. This means that water can penetrate into the filter plate 23 only
through the outer surface 23B of the filter plate 23.
Each filter plate 23 is also provided with a tube connector 29 in
order to provide a fluid duct from the interior of the the filter plate 23 to
a
collector piping 30 provided in the drum 20. The tube connector 29 in each
filter plate 23 is connected to a radial inner tube 31 supported on the
support
member 22 and passing through the support member 22. The inner end of the
radial inner tube 31 is connected to an axial tube 32 passing in the axial X-X
direction through the drum 20. The axial tubes 32 are at one end of the drum
20 connected to radial outer tubes 33. The radial outer tubes 33 extend from
the outer edge of the drum 20 to the shaft 25 of the drum 20. The radial outer
tubes 33 are connected to a distributing valve 13 disposed on the shaft 25 of
the drum 20. The distributing valve 13 transmits vacuum or overpressure to the
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filter plates 23. The distributing valve 13 may comprise zones such that a
part
of the filter plates 23 are subjected to a higher vacuum or overpressure and a
part of the filter plates 23 are subjected to a smaller vacuum or
overpressure. If
a long drum 20 is used, it can be advantageous to have a distributing valve 13
at both ends of the drum 20.
The vacuum system providing the vacuum through the collector pip-
ing 30 to the filter plates 23 is not shown in the figures. The pump for
removing
the filtrate from the collector piping 30 is also not shown in the figures. It
is
possible to arrange reverse flushing or backwash either such that some of the
filtrate or clean water from an external water source is led back to the
collector
piping 30 by means of a backwash system, such as a backwash pump.
As the drum 20 rotates, the filter plates 23 move into and through
the basin 9. Each filter plate 23 goes through different process phases during
one revolution of the drum 20. In a cake forming phase, the liquid is passing
through the outer surfaces 23B of the filter plate 23 into the interior of the
filter
plate 23 when it travels through the slurry, and a cake is formed on the outer
surface 23B of the filter plate 23. The filter plate 23 enters the cake drying
phase after it leaves the basin 9. If cake washing is required, it is done in
the
beginning of the drying phase. In the cake discharge phase the cake is
scraped off from the outer surface 23B of the filter plate 23 by ceramic
scrapers so that a thin cake is left on the outer surface 23B of the filter
plate
23. There is thus a small gap between the scraper and the outer surface 23B
of the filter plate 23. In the backflush phase of each rotation, water
(filtrate) is
pumped in a reverse direction from the inside of the filter plate 23 through
the
filter plate 23 to the outside of the filter plate 23. The backflush water
washes
off the residual cake and cleans the pores of the filter plate 23.
Figure 2 shows that each filter plate 23 comprises fastening points
P1, P2, P3 comprising holes passing through the filter plate 23 in a radial
direction. The filter plates 23 are attached to the support members 22 by
bolts
70 passing through the holes in the fastening points P1, P2, P3. Two fastening
points P1, P2 are positioned at the axial X-X outer edge of the filter plate
23
and one fastening point P3 is positioned at the axial X-X inner edge of the
filter
plate 23.
Figures 4 is a cross section of a filter plate showing a prior art fas-
tening arrangement 50 to the right in the figure and a fastening arrangement
100 according to the invention to the left in the figure.
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The prior art fastening arrangement 50 shown to the right in figure 4
comprises at each fastening point P1, P2, P3 a first hole 45 passing through
the filter plate 23, a fastening flange 60, a rubber bushing 80 and a bolt 70.
The fastening flange 60 comprises an upper portion 61 forming essentially a
cylinder and a second lower portion 62 forming essentially a collar. The upper
portion 61 is fitted within the first hole 45 in the filter plate 23 and the
collar like
lower portion 62 is fitted against the inner surface 23A of the filter plate
23. The
fastening flange 60 can be attached by glue to the filter plate 23. The
fastening
flange 60 comprises further a second hole 63 extending through the fastening
flange 60 from the upper portion 61 to the lower portion 62. The second hole
63 has a first diameter within the upper portion 61 and a second smaller diam-
eter within the lower portion 62 of the fastening flange 60. A landing 64 is
thus
formed within the second hole 63. The end part 71 of the bolt 70 will thus
seat
against the landing 64 when the bolt 70 is tightened. A first end of the
cylindri-
cal rubber bushing 80 extends partly into the lower portion 62 of the
fastening
flange 60. A second opposite end of the cylindrical rubber bushing 80 is
seated
against the upper surface of the support member 22. The exterior threads at
the outer end 72 of the bolt 70 are received by corresponding interior threads
in a hole in the support member 22. Tightening of the bolt 70 will press the
filter
plate 22 tightly against the upper surface of the support member 22. The first
hole 45 passing through the filter plate 23 at each fastening point P1, P2, P3
will reduce the effective filtering area of the filter plate 23. The upper
curved
filtering surface 23B of the filter plate 23 is broken at each hole 45.
The fastening arrangement according to the invention 100 shown to
the left in figure 4 comprises at each fastening point P1, P2, P3 a first
recess
46 made into the filter plate 23, a fastening flange 110, a rubber bushing 130
and a fastening member 120. The first recess 46 extends from the lower sur-
face 23A of the filter plate 23 into a portion of the filter plate 23. The
opposite
surface of the filter plate 23 remains unbroken at the first recess 46. The
cylin-
drical bushing 130 corresponds to the cylindrical bushing 80 in the prior art
fastening arrangement. A first end of the cylindrical rubber bushing 130 ex-
tends partly into the lower portion 112 of the fastening flange 110. A second
opposite end of the cylindrical rubber bushing 130 is seated against the upper
surface of the support member 22 or extends partly into the support members
22.
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Figure 5 shows the fastening flange of the inventive fastening ar-
rangement. The fastening flange 110 comprises a first portion 111 forming es-
sentially a cylinder with a closed end and a second portion 112 forming essen-
tially a collar. The first portion 111 is fitted within the first recess 46 in
the filter
plate 23 and the second portion 112 is fitted against the lower surface 23B of
the filter plate 23. The fastening flange 110 can be attached by glue to the
filter
plate 23. The fastening flange 110 comprises further a second recess 113 ex-
tending from the second portion 112 towards the first portion 111 of the fas-
tening flange 110 i.e. in the same direction as the first recess 46. There is
fur-
l() ther a circular second groove 114 extending radially into the inner
surface of
the second recess 113 within the first portion 111 of the fastening flange
110.
Figure 6 shows the fastening member of the inventive fastening ar-
rangement. The longitudinal fastening member 120 has an essentially cylindri-
cal form and comprises a first end portion 121 and an opposite second end
portion 122 provided with an external thread. The first end portion 121 of the
fastening member 120 comprises a first circular groove 123 extending radially
into the outer surface of the first portion 121 of the fastening member 120.
The
second end portion 122 of the fastening member 120 comprises further a grip-
ping portion 125 with two parallel planar side surfaces. The two parallel side
surfaces form gripping surfaces for an adjustable wrench or fork wrench.
Figure 7 shows the fastening flange and the fastening member in an
assembled form. This figure shows that first snap locking means 140 is fitted
into the second groove 114 in the fastening flange 110.
The fastening member 120 can be attached to the support member
22 by threading the second end portion 122 of the fastening member 120 into
a corresponding hole 75 in the support member 22. There are exterior threads
at the second end portion 122 of the fastening member 120 and interior
threads in the corresponding hole 75 in the support member 22. The hole 75
can either extend only into a portion of the support member 22 or pass through
the support member 22. The cylindrical rubber bushing 130 can then be
pushed on the fastening member 120. The filter plate 23 can then be fastened
to the fastening members 120 protruding in a radial direction from the upper
surface of the support member 22 by pushing the filter plate 23 on the fas-
tening members 120 so that the first end portions 121 of the fastening mem-
bers 120 glide into the corresponding second recesses 113 in the first portion
111 of the fastening flange 110. The filter plate 23 will be locked to the fas-
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tening member 120 by the spring ring 140 setting into the circular first
groove
123 on the fastening member 120. A first end of the cylindrical rubber bushing
130 will extend partly into the lower portion 112 of the fastening flange 110
and
a second opposite end of the cylindrical rubber bushing 130 will seat against
the upper surface of the support member 22 or extend partly into the support
member 22.
Figure 8 is a cross section of a filter plate showing a second embod-
iment of a fastening arrangement according to the invention and figure 9
shows the fastening flange and the fastening member in a disassembled form.
Figure 9 illustrates the porous structure of the filter plate 23. The
fastening
flange 110 corresponds essentially to the fastening flange shown in figure 5.
The fastening flange comprises a first portion 111 having essentially the form
of a cylinder and a second portion 112 having essentially the form of a
collar.
The first portion 111 is within the recess 46 in the filter plate 23 and the
second
portion 112 is seated against the inner surface 23A of the filter plate 23.
The
longitudinal fastening member 120 forms advantageously an integral part of
the fastening flange 110. The fastening member 120 is essentially cylindrical
and comprises a first end portion 121 and a second end portion 122. The se-
cond end portion 122 of the fastening member 120 is incorporated with the
second portion 112 of the fastening flange 110. The first end portion 121 of
the
fastening member 120 is provided with a first circular groove 123 extending
radially into the outer surface of the fastening member 120. There is a third
recess 115 extending in a direction opposite to the direction of the first
recess
46 into the support member 22 in the rim structure 21. The third recess 115
receives the first end portion 121 of the fastening member 120. The third re-
cess 115 comprises a second circular groove 116 extending radially into the
surface of the third recess 115. The second circular groove 116 is provided
with second snap locking means 141. The support member 22 is also provided
with axial X-X holes 22A through which the support member 22 can be fas-
tened to the rim 21 of the drum 20. The cylindrical rubber bushing 130 corre-
sponds to the cylindrical rubber bushing 130 in figure 4. The rubber bushing
130 is positioned between the fastening flange 110 and the support member
22.
Figure 10 shows a third embodiment of the invention. This third em-
bodiment corresponds to the second embodiment shown in figure 9 except that
the fastening member 120 is in this embodiment fastened at both ends with
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snap lock means. The fastening member 120 has an essentially cylindrical
form and comprises a first end portion 121 and an opposite second end portion
122. The first end portion 121 of the fastening member 120 is fastened with
first snap lock means 140 to the fastening flange 110. The second end portion
5 122 of the fastening member 120 is fastened with second snap lock means
141 to support member 22. Both snap lock means 140, 141 are advantageous-
ly identical. The first snap lock means 140 comprises a first spring ring posi-
tioned in a circular groove 114 in a second recess 113 in the fastening flange
110. The second snap lock means 141 comprises a second spring ring posi-
10 tioned in a circular groove 116 in a third recess 115 in the support
member 22.
The fastening member 120 comprises a first circular groove 123 in the first
end
portion 121 and a second circular groove 124 in the second end portion 122.
The first circular groove 123 and the second circular groove 124 extend radial-
ly into the outer surface of the fastening member 120. The rubber bushing 130
is positioned between the fastening flange 110 and the support member 22.
The support member 22 is also provided with axial X-X holes 22A through
which the support member 22 can be fastened to the rim 21 of the drum 20.
The longitudinal fastening member 120 has advantageously an es-
sentially cylindrical form with a circular cross section in all embodiments in
the
invention.
The cylinder hat like form of the fastening flange 110 is an advanta-
geous form. The fastening flange 110 can be attached with glue from the cylin-
drical outer surface of the first portion 111, from the outer bottom surface
of the
first portion 111 and from the planar lower surface of the second portion 112
to
the filter plate 23. There is thus a fairly big fastening area for the glue
between
the fastening flange 110 and the filter plate 23. The fastening flange 110
could,
however, also have some other form. The fastening flange 110 should com-
prise a second recess 113 or have the fastening member 120 fixedly attached
to the second recess 113 and have a form that fits into the first recess 46 in
the
filter plate 23.
The fastening flange 110 and the fastening member 120 are
advantageously made of acid-proof steel. The fastening flange 110 is naturally
tightly fitted in the recess 46 in the filter plate 23. The outer diameter of
the first
portion 111 of the fastening flange 110 corresponds to the inner diameter of
the recess 46 in the filter plate 23. The depth of the recess 46 in the filter
plate
23 corresponds to the depth of the first portion 111 of the fastening flange
110.
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The fastening member 120 is also tightly fitted in the second recess 113 in
the
fastening flange 110 and/or in the second recess 115 in the rim structure 21,
22.
The filter plate 23 comprises in the figures three fastening points P1,
P2, P3. Two fastening points P1, P2 are at the outer ends of the drum 20 and
one fastening point P3 is at the middle of the drum 20 in the axial direction.
Three fastening points P1, P2, P3 are needed in order to achieve a firm
attachement of the filter plate 23. There could naturally be more than three
fastening points P1, P2, P3 if a need for further fastening points would for
some reason arise.
The axial X-X length of the drum 20 is divided into two sections so
that there are two rings R1, R2 of filter plates 23 in the drum 20. There
could
naturally be more than two rings R1, R2 of filter plates 23 on the drum 20 or
only one ring of filter plates 23 on the drum 20. The appropriate number of
rings R1, R2 of filter plates 23 on the drum 20 depends on the length of the
drum 20.
The fastening of the filter plates 23 to the drum 20 need not
necessary be through the support members 22. It might be possible to fasten
the filter plates 23 directly to the rims 21 of the drum 20. The inner surface
23A
of the filter plates 23 would thus have to be curved. The fastening of the
filter
plates 23 would thus be to the curved outer surface 23B of the rims 21.
In embodiments described herein, a material to be filtered is
referred to as a slurry, but embodiments of the invention are not intended to
be
restricted to this type of fluid material. The slurry may have high solids
concen-
tration, e.g. base metal concentrates, iron ore, chromite, ferrochrome,
copper,
gold, cobalt, nickel, zinc, lead and pyrite.
Upon reading the present application, it will be obvious to a person
skilled in the art that the inventive concept can be implemented in various
ways. The invention and its embodiments are not limited to the examples de-
scribed above but may vary within the scope of the claims.
