Abstrict
A fastening strip for fastening a filter cloth against the filter
surface of a solid-liquid separator. The solid-liquid separator
comprises at least one filter element provided with a fastening
groove for the fastening strip. The filter cloth is fastened to
the filter element by means of the fastening strip, whose fastening
portion is inserted into the fastening groove. The fastening strip
is an elongated piece having a substantially T-shaped cross section
and comprising a fastening portion and a support portion transverse
to the fastening portion. The support portion provides a protective
edging that extends to a distance from the edges of the fastening
groove.
Claims
What is claimed is:
1. A fastening strip for fastening a filter cloth to the filter
element of a solid-liquid separator, wherein the solid-liquid separator
comprises a body portion rotatable around its horizontal axis, two
or more adjacent filter elements arranged on the periphery of said
body portion, each filter element comprising at least one filter
surface provided with holes, against which surface the filter cloth
is arranged, and at least one fastening groove arranged in connection
with the filter element, in which groove the fastening strip is
to be arranged for fastening the filter cloth; and the fastening
strip is an elongated piece having a substantially T-formed cross
section and comprising (a) a fastening portion made from flexible
material and so dimensioned that it is deformed when inserted into
said fastening groove and generates a fastening force and (b) a
support portion that is transverse to the fastening portion and
remains outside the fastening groove and is dimensioned so as to
extend to a predetermined distance from the edge of the fastening
groove.
2. The fastening strip of claim 1, wherein at least the surface
on the side of the sector element of the support portion is curved.
3. The fastening strip of claim 1, wherein the support portion
narrows towards the transverse edges of the fastening strip.
4. The fastening strip of claim 1, wherein the support portion
comprises a flat portion on the surface opposite to the sector element.
5. The fastening strip of claim 1, wherein the fastening portion
comprises two flexible projecting portions, between which is a gap
that allows said projecting portions to move towards one another,
the projecting portions acting as a spring.
6. The fastening strip of claim 1, wherein the fastening portion
is made from flexible compressible material.
7. A filter unit for a disc filter, wherein the disc filter comprises
a body portion that is rotatable around its horizontal axis and
on whose periphery are arranged two or more filter units that form
a disciform structure; the filter unit comprises a sector element,
a filter cloth and a fastening strip; the sector element comprises
a neck portion for fastening the sector element to the body portion
of the disc filter, a flat substantially triangular hollow blade
portion comprising an outer edge at the edge opposite to the neck
portion, lateral faces transverse to the direction of rotation and
flank surfaces in the direction of rotation; the flank surfaces
of the sector element are provided with holes and act as filter
surfaces; the filter cloth is arranged against said filter surfaces,
the sector element comprises at least one fastening groove, wherein
a fastening strip is arranged for fastening the filter cloth on
the sector element; and the fastening strip is an elongated piece
having a substantially T-formed cross section and comprising (a)
a fastening portion made from flexible material and so dimensioned
that it is deformed when inserted into said fastening groove and
generates a fastening force and (b) a support portion that is transverse
to the fastening portion and remains outside the fastening groove
and extends to a predetermined distance from the edge of the fastening
groove.
8. The filter unit of claim 7, wherein the fastening groove is
arranged at the outer edge of the blade portion, a tubular filter
bag that is made from filter cloth and open at both its ends, and
comprises a wider end and a narrower end, is arranged around the
sector element, the narrower end of the filter bag is fastened by
means of fastening elements around the neck portion of the sector
element, and the edges of the wider end of the filter bag are fastened
to the fastening groove of the sector element by means of the fastening
strip.
9. The filter unit of claim 7, wherein the fastening groove is
arranged at least on one lateral face of the blade portion of the
sector element, a substantially triangular filter bag made from
filter cloth and having a closed wider end and an open narrower
end is arranged around the sector element, the side of the filter
bag comprises an opening from which the filter bag is arranged onto
the sector element, the edges of said opening are fastened by means
of the fastening strip to the fastening groove at the lateral face
of the blade portion, and the narrower end of the filter bag is
fastened by means of the fastening elements around the neck portion
of the sector element.
10. A drum filter comprising a body portion, which is an elongated
tubular piece rotatable around its horizontal axis, a plurality
of filter elements arranged adjacent each other on the periphery
of the body portion, the filter elements comprising hollow spaces
substantially in the shape of a toroidal sector in the longitudinal
direction of the body portion, the periphery of the filter elements
being provided with holes, and the outer peripheries of adjacent
filter elements together forming the filter surface of the drum
filter, one or more fastening grooves provided on the periphery
of the drum filter, and a filter cloth fastened by means of one
or more fastening strips to said one or more fastening grooves,
the filter cloth being arranged against the filter surface of the
drum filter, and wherein the fastening strip is an elongated piece
having a substantially T-formed cross section and comprising (a)
a fastening portion made from flexible material and so dimensioned
that it is deformed when inserted into said fastening groove and
generates a fastening force, and (b) a support portion that is transverse
to the fastening portion and remains outside the fastening groove
and extends to a predetermined distance from the edge of the fastening
groove.
11. The drum filter of claim 10, wherein the fastening groove is
longitudinal with respect to the body portion.
12. The drum filter of claim 11, wherein the filter cloth is a
preformed tubular piece drawn onto the drum filter and tightened
against the filter surface of the periphery of the drum filter by
means of one or more fastening strips.
13. The drum filter of claim 11, wherein the filter cloth comprises
at least one sheet-like piece arranged around the periphery of the
drum filter, the longitudinal edges of the filter cloth being fastened
by means of the fastening strip to the fastening groove on the periphery
of the drum filter, the filter cloth forming an endless loop around
the drum filter.
Description FIELD OF THE INVENTION
[0001] The invention relates to a fastening strip for fastening
a filter cloth against the filter surface of a solid-liquid separator
filter element. The filter element comprises a fastening groove,
in which the fastening strip is arranged. The invention further
relates to a filter unit in a solid-liquid separator, the filter
unit comprising a filter element and a filter cloth, and a fastening
strip for joining them together.
BACKGROUND OF THE INVENTION
[0002] Solid-liquid separators are used for separating liquid and
solids from a mixture of solids and liquid. Solid-liquid separators
include disc and drum filters, for example. FIG. 1 shows the former.
A disc filter 1 typically comprises several substantially triangular
sector elements (blades) 2, fastened at joint faces provided in
their neck portions 3 to a rotary body 4 of the disc filter. In
this case, adjacent sector elements form a disciform (disc-shaped)
structure around a tubular body. Each sector element is hollow and
flank surfaces serving as its filter surfaces are provided with
holes. Onto the sector element is arranged a filter bag made from
filter cloth and serving as a filtering layer. The filter disc is
rotated in direction A around the horizontal axis of the body portion
in a basin 5 containing a mixture 6 of solids and liquid. During
the filtration stage, when the sector element is submersed in the
mixture in the basin, suction acts inside the sector element, whereby
the liquid in the mixture penetrates the filter cloth and is allowed
inside the sector element through the holes on the filter surface.
The liquid is led from the sector element along a flow duct in the
neck portion of the sector element to the tubular body of the disc
filter for further processing. During filtration, solids adhere
to the filter cloth in the flank surfaces of the sector elements.
Before the next filtration step, the solids cake has to be discharged,
and a pressure pulse is therefore applied to the inside of the sector
element, the pressure pulse releasing the solids cake from the surface
of the filter cloth. The released solids are led by means of doctor
blades or corresponding cleaning surfaces to a discharge chute 26
from both flank surfaces of the disc.
[0003] The filter cloth to be arranged onto the sector elements
of the disc filter is usually designed in advance as a cylindrical
tube corresponding to the shape of the sector element and it comprises
an open narrower end, i.e. a first end, and an open wider end, i.e.
a second end. Such a filter bag is arranged in place by pulling
it via the neck portion onto the sector element. The narrower end
of the bag is then fastened around the neck portion of the sector
element by means of clamping elements. The clamping element may
be any known clamping element. The periphery of the sector element
is provided with a fastening groove, to which the wider end of the
tubular filter cloth is fastened in a first step by means of an
elongated fastening strip. The fastening of the sector elements
to the body portion and the fastening of the wider end of the filter
cloth are then secured with a clamp 15, which is tightened around
the periphery of the filter disc by means of supporting bars 30
or the like. The filter cloth is caught between the clamp and the
sector element. As the fastening strip is inserted into the fastening
groove of the sector element, it pushes the filter cloth along with
it to the fastening groove thus sealing the end of the filter bag.
The fastening strip also tightens the filter cloth arranged around
the sector element against the sector element. A presently used
fastening strip is for example a rope or a bar made from flexible
material, such as rubber, which is hammered into the fastening groove
with a hammer. The cross section of the fastening strip is round,
which makes it difficult to aim hammer blows at the curved outer
surface of such a strip. Hammer blows very typically also hit the
structure of the sector element, damaging the sector element that
is made from plastic or corresponding material. Furthermore, missed
blows may damage the filter cloth. A further drawback in the prior
art is that, during the discharge of the cake, the filter bag expands
against the sharp edges of the clamp. A continuous reciprocating
movement causes scuffing, which wears the filter cloth.
SUMMARY OF THE INVENTION
[0004] The object of the present invention is to provide a novel
and improved arrangement for fastening a filter cloth to a solid-liquid
separator.
[0005] The invention relates to a fastening strip for fastening
a filter cloth to the filter element of a solid-liquid separator,
wherein the solid-liquid separator comprises a body portion rotatable
around its horizontal axis, two or more adjacent filter elements
arranged on the periphery of said body portion, each filter element
comprising at least one filter surface provided with holes, against
which surface the filter cloth is arranged, and at least one fastening
groove arranged in connection with the filter element, in which
groove the fastening strip is to be arranged for fastening the filter
cloth; the fastening strip is an elongated piece having a substantially
T-formed cross section and comprising; a fastening portion made
from flexible material and so dimensioned that it is deformed when
inserted into said fastening groove and generates a fastening force;
and a support portion that is transverse to the fastening portion
and remains outside the fastening groove and is dimensioned so as
to extend to a predetermined distance from the edge of the fastening
groove.
[0006] The invention also relates to a filter unit for a disc filter,
wherein: the disc filter comprises a body portion that is rotatable
around its horizontal axis and on whose periphery are arranged two
or more filter units that form a disciform (disc-shaped) structure;
the filter unit comprises a sector element, a filter cloth and a
fastening strip; the sector element comprises a neck portion from
which it can be fastened to the body portion of the disc filter,
a flat substantially triangular hollow blade portion comprising
an outer edge at the edge opposite to the neck portion, lateral
faces transverse to the direction of rotation and flank surfaces
in the direction of rotation; the flank surfaces of the sector element
are provided with holes and act as filter surfaces; the filter cloth
is arranged against said filter surfaces and the sector element
comprises at least one fastening groove, wherein a fastening strip
is to be arranged for fastening the filter cloth to the sector element;
the fastening strip is an elongated piece having a substantially
T-formed cross section and comprising: a fastening portion made
from flexible material and so dimensioned that it is deformed when
inserted into said fastening groove and generates a fastening force;
and a support portion that is transverse to the fastening portion
and remains outside the fastening groove and extends to a predetermined
distance from the edge of the fastening groove.
[0007] The invention further relates to a drum filter comprising
a body portion, which is an elongated tubular piece rotatable around
its horizontal axis, a plurality of adjacent filter elements arranged
on the periphery of the body portion, the filter elements comprising
hollow spaces substantially in the shape of a toroidal sector in
the longitudinal direction of the body portion, the periphery of
the filter elements being provided with holes, and the outer peripheries
of adjacent filter elements together forming the filter surface
of the drum filter, one or more fastening grooves provided on the
periphery of the drum filter, a filter cloth fastened by means of
one or more fastening strips to said one or more fastening grooves,
the filter cloth being arranged against the filter surface of the
drum filter, and wherein the fastening strip is an elongated piece
having a substantially T-formed cross section and comprising a fastening
portion made from flexible material and so dimensioned that it is
deformed when inserted into said fastening groove and generates
a fastening force, and a support portion that is transverse to the
fastening portion and remains outside the fastening groove and extends
to a predetermined distance from the edge of the fastening groove.
[0008] The essential idea of the invention is that a liquid-solid
separator filter element comprises or has in association therewith
one or more fastening grooves for a fastening strip. A filter cloth
serving as a filtering layer is arranged against the perforated
filter surface of the filter element, whereupon it is tightened
and fastened in place by means of the fastening strip. The fastening
strip is an elongated piece having a substantially T-formed cross
section and comprising a fastening portion that is inserted into
the fastening groove, and a support portion that is transverse to
the fastening portion and remains outside the fastening groove,
on both sides thereof. At least the fastening portion of the fastening
strip is made from flexible material so as to allow the fastening
portion to be deformed to some degree when inserted into the fastening
groove and thus produce a fastening force, which, together with
friction, keeps the fastening strip firmly in place in the fastening
groove of the filter element. The support portion of the fastening
strip settles substantially in the direction of the surface of the
filter element and extends to a predetermined distance from the
edge of the fastening groove.
[0009] An advantage of the fastening strip of the invention is
that it is easier to install than prior art fastening strips. The
support portion of the fastening strip protects the filter element
and the filter cloth from blows and other damage during installation.
Furthermore, the support portion of the fastening strip dampens
the movements of the filter cloth resulting from the changes in
the pressure acting inside the filter element. This prevents scuffing
of the filter cloth and the resulting wear.
[0010] The essential idea of a preferred embodiment of the invention
is that at least the lower surface of the support portion of the
fastening strip is curved, whereby the support portion settles against
the curved outer surface of the filter element.
[0011] The essential idea of a second preferred embodiment of the
invention is that the support portion of the fastening strip is
made from flexible material and that the support portion narrows
from the middle portion towards the edges, whereby the edges of
the support portion are flexible.
[0012] The essential idea of a third preferred embodiment of the
invention is that the upper surface of the support portion of the
fastening strip comprises a substantially flat surface in the middle
portion of the support portion. Hammer blows are substantially easier
to aim at this so-called hammering surface during installation of
the fastening strip.
BRIEF DESCRIPTION OF THE FIGURES.
[0013] FIG. 1 is a schematic side view of a typical disc filter.
[0014] FIG. 2 is a schematic side view of a filter unit of a disc
filter.
[0015] FIG. 3 is a schematic sectional view of the filter unit
of FIG. 2, seen from direction B.
[0016] FIG. 4 is a schematic side view of another filter unit of
a disc filter.
[0017] FIG. 5a is a schematic view of a sector element of the filter
unit of FIG. 4, seen from direction B.
[0018] FIG. 5b is a schematic view of the filter bag of the filter
unit of FIG. 4, seen from direction B.
[0019] FIG. 6 is a schematic end view of a fastening strip according
to one embodiment of the invention before it is installed in the
fastening groove of a sector element.
[0020] FIG. 7 is a schematic end view of a fastening strip according
to another embodiment of the invention installed in the fastening
groove of a sector element.
[0021] FIG. 8 schematically shows an application of a fastening
strip of another embodiment of the invention.
[0022] FIG. 9 schematically shows a drum filter, in which the filter
cloth is fastened by means of a fastening strip of the invention.
[0023] FIG. 10 is a schematic end view illustrating the fastening
of a filter cloth to the filter surface of the filter elements of
a drum filter according to an embodiment of the invention.
[0024] FIG. 11 is a schematic end view of illustrating another
embodiment for fastening a filter cloth to a drum filter.
[0025] The figures are simplified views of the invention. Like
reference numbers are used for like parts.
DETAILED DESCRIPTION OF THE INVENTION
[0026] FIGS. 2 and 3 show a filter unit of a disc filter. The filter
unit comprises a sector element 2 comprising a neck portion 3 and
a flat substantially triangular blade portion 7. The sector element
2 is hollow, and flank surfaces 8 in its blade portion 7 comprise
holes 9 through which filtered liquid, that has penetrated a filter
cloth 10, is allowed inside the sector element 2. The filter cloth
10 is pre-formed as a bag corresponding to the shape of the sector
element 2, both ends of the bag being open to allow the bag to be
pulled onto the triangular sector element 2 via the neck portion
3 when the sector element 2 is detached from the body portion 4
of the filter. The narrower end of the bag is sealed tightly against
the neck portion 3 of the sector element. A known fastening element
11 is used to seal the bag by pressing the mouth portion of the
bag tightly against the neck portion 3. The edge opposite to the
neck portion, i.e. a periphery 12 of the sector element 2, is provided
with a fastening groove 13 in which the edges of the wider end of
the filter bag are arranged and locked in place by means of an elongated
fastening strip 14 to be placed in the fastening groove. The fastening
strip 14 is preferably a uniform piece equal in length to the outer
edge of the sector element and has a cross section that comprises
a fastening portion 16 to be inserted into the fastening groove
13 and a support portion 19 that is transverse to the fastening
portion and settles in the direction of the periphery of the sector
element. The fastening groove 13 is dimensioned slightly narrower
than the fastening portion 16 of the fastening strip 14. Therefore,
the fastening portion 16 is deformed when inserted in place into
the fastening groove 13. The fastening portion 16 is made from flexible
compressible material or alternatively it comprises a flexible portion
acting as a spring when being installed in place. The deformation
of the fastening portion produces a fastening force that keeps the
fastening strip and the filter cloth in place in the fastening groove.
FIG. 3 shows a clamp 15, arranged around the filter disc, for securing
the fastening of the filter units.
[0027] Alternatively, in accordance with FIG. 4, a substantially
triangular filter bag 10 is arranged around the sector element 2,
the wider end of the filter bag being closed and the narrower end
open. In this embodiment, at least one side of the filter bag is
provided with an opening 40 shown in FIG. 5b, from which it can
be laterally arranged onto the sector element 2. Further, at least
one lateral face of the sector element transverse to the direction
of rotation A is provided with a fastening groove 13 shown in FIG.
5a, extending from the periphery 12 of the sector element to the
neck portion 3 for the fastening strip 14, The opening 40 at the
side of the filter bag 10 is closed by sealing the edges of the
opening to the fastening groove 13 by means of the fastening strip
14. The narrower end of the filter bag 10 is sealed against the
neck portion 3 in a conventional manner by means of suitable fastening
elements 11. This solution replaces arrangements wherein the opening
at the side of the filter bag is provided with a zipper or the like.
[0028] An advantage of this embodiment of the invention is that
the filter bag is simpler and less expensive than prior art filter
bags. Furthermore, in this embodiment of the invention, the filter
bag can be tightly fastened onto the sector element upon installation.
A support portion 19 in the fastening strip 14 arranged in the fastening
groove 13 at the lateral faces of the sector element 2 remains between
the lateral faces of the adjacent sector elements, and this ensures
that the fastening strip remains in the fastening groove. In addition,
the support portion 19 of the fastening strip may act between the
sector elements as an element that dampens vibration.
[0029] FIG. 6 shows the fastening strip 14 made, for example, by
extrusion from a flexible material, such as a suitable rubber, plastic
or a combination thereof. In this embodiment, the fastening portion
16 of the fastening strip 14 comprises two projections 17, between
which a gap 18 forms so as to allow the projections to move towards
one another when the fastening portion 16 is arranged in the fastening
groove 13. A lower surface 20 in the support portion 19 of the fastening
strip is curved, whereby it settles against the curved periphery
12 of the sector element. An outer surface 21 in the support portion
19 is also curved. The curvatures of the lower and upper surfaces
of the support portion are preferably arranged such that the support
portion 19 narrows from the middle towards its outer edges. Hereby,
the edges of the support portion are flexible, allowing the filter
cloth 10 to expand in a controlled manner supported by the flexible
edges when a pressure pulse is applied inside the sector element
2 for discharging the solids cake. At the same time, the support
portion 19 protects the filter cloth 10 and prevents it from rubbing
against the clamp 15. The support portion 19 also protects the filter
cloth 10 and the periphery 12 of the sector element 2 from damage
upon installation. The support portion 19 is preferably so dimensioned
that it substantially covers the entire periphery 12 of the sector
element 2.
[0030] FIG. 7 shows an embodiment of the fastening strip 14, wherein
transverse protrusions 28 are formed in the projection portions
17 of the fastening portion 16 to increase the fastening force.
The upper surface 21 of the support portion 19, preferably the middle
of the support portion, further comprises a flat surface 22, a so-called
hammering surface, which substantially facilitates aiming the hammer
blows at the fastening strip 14 during installation.
[0031] As distinct from the previous figures, FIG. 8 shows an embodiment
wherein the wider edge of the filter bag is not inserted into the
fastening groove 13 by means of the fastening strip 14. Instead,
the fastening strip 14 is first installed in the fastening groove
13, whereupon the edges of the filter cloth 10 are folded in an
overlapping manner and fastened to the upper surface 21 of the support
portion 19 by means of suitable fastening elements 23, such as rivets,
nails, glue or the like. In this case, the fastening strip 14 acts
as an exchangeable installation base.
[0032] Another embodiment of the fastening strip 14 is shown in
FIG. 8, wherein the fastening portion 16 comprises a single projection
17 with an intermediate portion 31 extending outward to contact
the side walls of the fastening groove 13.
[0033] FIGS. 9, 10, and 11 are perspective views of a drum filter
24. FIG. 11 shows a basin 5, in which the filter drum is rotated
around a horizontal axis during filtration. The mixture 6 to be
filtered is led along a feed duct 25 into the basin and the solids
cake is led from the surface of the filter to a discharge chute
26. The drum filter comprises a tubular body portion 4, on whose
periphery adjacent filter elements 27 are arranged longitudinally
with respect to the body portion. The cross sections of the filter
elements 27 are substantially hollow spaces in the shape of a toroidal
sector 29, whose peripheries 32 are provided with holes 9 and act
as filtering surfaces. A filter cloth 10, acting as a filtering
layer, is arranged against the filtering surface 32. Liquid that
has penetrated the filter cloth 10 is allowed through the holes
9 of the filtering surface 32 inside the filter element 27 for subsequent
processing. Each filter element 27 forms a separate space, inside
of which suction or a pressure pulse is applied during operation,
depending on whether the filter element 27 is in a filtering or
a cake discharge stage.
[0034] FIG. 10 is an end view of a drum filter 24, wherein a fastening
groove 13 in the direction of the longitudinal axis of the drum
filter is arranged between adjacent filter elements 27. Each filter
element 27 may have a separate filter cloth 10 fastened against
the filter surface 30 of the filter element 27 by means of the fastening
strip 14 of the invention, arranged in a fastening groove 13. Upon
installation of the fastening strip 14, the fastening strip 14 pushes
the longitudinal edges of the filter cloths 10 of adjacent filter
elements 27 along with it into the fastening groove 13 and keeps
them tightly in place.
[0035] Alternatively, the filter cloth 10 may be composed of only
one piece that covers the entire periphery of the drum filter 24.
In this case, the filter cloth 10 can be fastened with one fastening
strip 14 as a closed loop around the drum as shown in FIG. 11. If
required, a fastening strip 14 can be arranged between each adjacent
filter element in accordance with FIG. 8, whereby the fastening
strips 14 ensure that the filter cloth 10 remains in place and dampen
any extensive expansion of the uniform filter cloth 10. The filter
cloth may also be a tubular piece that is pulled onto the drum filter
in the longitudinal direction of the drum filter. The tubular filter
cloth is then tightly fastened, by means of fastening strips, against
the filter surfaces 32 of the periphery of the drum filter.
[0036] Since the support portion 19 of the fastening strip 14 extends
a distance outside the outer surface of the filter cloth 10 in the
radial direction of the drum filter 24, the support portion 19 produces
a discontinuity at the fastening groove 13 in the solids cake formed
on the surface of filter cloth 10. At the fastening strip 14, the
solids cake remains thinner, thereby breaking more easily than in
prior art solid-liquid separators, when the cake is discharged.
The fastening strip used in a drum filter can be of a similar type
as the ones used in a disc filter.
[0037] Furthermore, each filter element 27 of the drum filter 24
may be a detachable elongated cassette, a separate filter bag being
disposed around each cassette. The filter bag is an elongated tubular
piece made from filter cloth, at least one end of the bag being
open allowing it to be pulled longitudinally onto the filter element.
In this case, in the gap between adjacent filter elements 27, a
fastening strip 14 according to the invention can be arranged for
tightening the filter cloth 10 tightly against the filter surface
32, thus improving the filtration result and preventing any damage
to the filter cloth 10. Further, the support portion 19 of the fastening
strip 14 prevents solids from penetrating in the fastening gap 13
between the filter elements, thus facilitating the discharge of
the solids cake from the filter cloth 10.
[0038] The drawings and the related description are only intended
to illustrate the inventive idea. The details of the invention may
vary within the scope of the claims. |