This invention relates to the retention of filter elements, principally
in the art of vertically rotating disc filters, each composed of a plurality of
Examples of such filters are described in US 3,283,906 (Crane) and
US 3,331,512 (Vore). Each segment comprises a generally wedge shaped hollow plate
with perforated surface webs, covered on each side with an appropriate filter cloth.
Liquid is drawn into the cavities within the plate, through the filter cloths by
suction achieved by known means, as the respective sector is dipped into an unfiltered
slurry or other prefiltrate. Particles above the retention threshold of the filter
cloths are retained by the filter cloths, whilst liquid and fine particles below
the threshold pass into the interior of the segment plate, and are pumped therefrom.
On emergence from the bath of unfiltered slurry, to be exposed to the air, the
cake of retained particles on the filter cloth can be removed by scrapers or other
Disc filters of this kind are commonly used in filtration of minerals
such as coal dust, ores or the like. Each filter disc may comprise 8 to 12 sectors,
each from 0.4 to 1.8m in height, and two or three skilled workers may be needed
to fit and remove each sector, which in known filters is required in order to remove
old filter cloths, and fit replacements. A complete installation may comprise up
to 200 filter wheels or more and the operation of changing filter cloths may take
several days, as each sector may occupy 2-3 workers to remove, dress and re-fit
so that each wheel may represent a full day's work for each team employed.
In our previous application WO-97/24170, we describe a filter apparatus,
such as a drum filter or a segmented disc filter, wherein filter panels are covered
on one side with a filter cloth which is held along at least some of it's edges
by a slotted tube received in a channel in a panel separating member, and the slotted
tube receives an elastomeric retaining bead formed on the edge of the filter cloth.
An object of the invention is to provide means for the retention of
filter cloths on the segments of a disc filter; which will enable the filter cloths
to be removed and replaced quickly and easily, and without removal of the segment
from the wheel.
According to the invention, filtration apparatus comprises a filter
disc made up of a plurality of wedge-shaped segments, the segments being separated
by radially extending elongate members and each segment comprising perforated plates
enclosing an interior volume, and a filter cloth each covering a respective face
of the segment, characterised in that the elongate members each comprise a hollow
core to receive a sector dividing stem and are provided with a pair of grooves
at each opposite side each groove receiving an edge bead on the edge of a respective
filter cloth for retaining the edges of the filter cloths.
The filtration apparatus is preferably a vertical disc filter of the
kind described above, but may be a horizontal pan disc filter, comprising a similar
assembly of a plurality of segments.
In a preferred embodiment, the elongate member comprises an extrusion
of profiled cross section of a hard plastics material, such as polypropylene, polyethylene
or polyamide or a blend of two or more thereof, or of a lightweight metal such
as aluminium or an alloy thereof. Two grooves may be provided at each side of the
member to receive the edges of two filter cloths, one on each face, of each of
the sectors abutting the elongate member.
The bead on each filter cloth edge is preferably an elastomeric extrusion,
of e.g. natural or synthetic rubber or the like, which can be deformed to be forced
into the respective groove, or to be pulled out from it. The bead may be formed
with flaps or rods between which an edge of a filter cloth may be received, and
secured for example by at least one of stitching or welding. It is noted that the
bead is preferably made of a softer material than the elongate member.
The grooves of the elongate member are preferably circular in cross
section, set deeper than their radius, so that they present an orifice slit which
is less than the diameter of the groove, thereby forcing compression of the bead
for insertion or withdrawal, and acting to retain the bead in normal use.
A preferred embodiment of the invention will now be described by
way of example, with reference to the accompanying drawings, wherein:-
- Fig. 1 is a diagrammatic view of one segment of a vertical disc filter
embodying the invention;
- Fig. 1a is a detail of an edge cap;
- Fig. 1b is a side view of a lock-down bar used to secure a filter cloth
near the hub of the disc;
- Fig. 2 is a detailed sectional view of an elongate member in place between
two adjacent disc segments;
- Fig. 3 is a sectional view of the edge of a filter cloth used in the
- Fig. 4 is a cross section of the elongate member.
In the preferred embodiment of the invention, a vertical disc filter
comprises a plurality of generally wedge-shaped segments 11, 12, 13. Each segment
comprises perforated plates 14 enclosing an interior to which vacuum is applied
to draw water in through the perforations of the plates and filter cloths 15, 16
covering the plates, to be removed via the hub of the disc.
The disc segments are separated by generally radial sector stems 17
which provide mechanical strength to the construction of the disc.
The radially outer edges of the segments are covered by rectangular
trough-shaped sector caps 18, which also clamp the outer edges of the filter cloths
The radially inner edges of the filter cloths 15, 16 are secured by
a lock-down bar 19 on each face of the segment, secured by Tec screws. The bar
19 can be easily secured and released, using a screwdriver.
The radially extending edges of each segment are separated by elongated
members 20, in the form of extrusions from e.g. polyamide. The members 20 each
have an axial passage 21, through which extends a respective sector stem 17.
The member 20 is generally rectangular in shape and is situated between
the adjacent sector plates 14, 15 of adjacent segments, with the longer faces in
abutment with the plates. The shorter faces of the member 21 are each provided
with a pair of circular cross sectioned grooves 22, 23 in the upper face and 24,
25 in the lower face. Each groove opens with a slot which is narrower than the
diameter of the groove. For example, the diameter of the groove is typically 9mm,
whilst the width of the slot is typically 4mm.
Each groove 22, 23, 24, 25 receives an edge bead 26 on the edge of
a respective filter cloth 15, 16. Each edge bead 26 is secured to the filter cloth
by means of flaps 27 between which the cloth is inserted, and secured by stitching
The edge bead 26 is of a flexible or at least deformable synthetic
material, or a rubber or the like. The bead 26 is capable of being deformed to
enter the slot of the respective groove, or to be pulled out from the groove.
In use, a disc filter is dressed by simply removing the respective
sector caps 18 to release the radially outer edges of the filter cloths, then
the lock-down bars 19 are detached. The used filter cloths can then be removed
by pulling the edge beads 26 from their respective grooves in the elongate member
20. Replacement clean filter cloths are fitted by the reverse procedure, that is
pushing their edge beads 26 into the grooves in the member 20, and then securing
the lock-down bars 19 and the sector caps 18.
Instead of requiring two or three workers over an hour, because the
sector does not have to be disconnected, changing filter cloths on a segment can
be carried out by one person in about 10 minutes. Consequently, dressing a complete
installation of 200 disc filters may take about 400 man-hours, as opposed to 7200
man-hours approximately for the prior art installation.
Existing installations may be modified to conform with the invention.
In a pan filter or a rotary drum filter, the elongate members would
be solid with no passage through the middle.
The elongate member may be divided so that separate members are provided
on the opposite faces of the filter disc.