Abstrict
The invention relates to a filter cloth for a filter press and
to a method for producing said filter cloth. The inventive filter
cloth has a filtration section through which the filtrate reaches
a filter element of the filter press, and an edging section which
rests against the edge of the filter element. The filtration area
is provided with a cloth that differs from that of the edging section.
The filtration area is woven from monofil yarns while multifil yarns
are woven into the edging section.
Claims
1. Filter cloth for a filter press (50), having a filtration area
(12) through which filtrate can pass into a filter element (52)
of the filter press (50), and a border area (14) which is provided
for application to an edge (54) of the filter element (52), characterized
in that the filtration area (12) has a fabric differing from that
of the border area (14), that the filtration area (12) is preponderantly
woven from monofilament yarns and that preponderantly multifilament
yarns are woven in the border area (14).
2. Filter cloth according to claim 1, characterized in that the
filtration area (12) is exclusively woven from monofilament yarns.
3. Filter cloth according to claim 1 or 2, characterized in that
in the border area (14) are woven both multifilament yarns and monofilament
yarns.
4. Filter cloth according to claim 3, characterized in that in
the border area (14) the multifilament yarns are preponderantly
located on the side of the filter cloth (10) facing the filter element
(52).
5. Filter cloth according to one of the claims 1 to 4, characterized
in that it is constructed as a double layer fabric, that a lower
fabric layer facing the filter element (52) is a backing fabric
(22) and that an upper fabric layer is constructed as a filtration-active
layer (24).
6. Filter cloth according to one of the claims 1 to 5, characterized
in that a border area (14) located in the discharge direction of
a filter cake formed has on its top side remote from the filter
element (52) preponderantly monofilament yarns.
7. Filter cloth according to one of the claims 1 to 6, characterized
in that in the filtration area (12) the monofilament yarns are preponderantly
located on the side of the filter cake (10) which is remote from
the filter element (52).
8. Method for the manufacture of a filter cloth (10) for a filter
press (50) according to one of the claims 1 to 7, characterized
in that a filtration area (12) is woven differently from the border
area (14), that the filtration area (12) is preponderantly woven
from monofilament yarns and that in the border area (14) preponderantly
multifilament yarns are woven.
9. Method according to claim 8, characterized in that the filter
cloth (10) is manufactured from a length of fabric (40), which is
produced with a width corresponding to a desired side length of
the filter cloth (10).
10. Method according to claim 9, characterized in that along the
marginal edge (42) of the length of fabric (40) and corresponding
to the desired border area (14) of the filter cloth (10), multifilament
yarns are used as warp threads.
11. Method according to claim 10, characterized in that in accordance
with the other side length of the rectangular filter cloth (10)
in transversely directed portions (44) of the length of fabric (40)
use is made of multifilament yarns as weft threads for forming the
border area (14).
Description [0001] The invention relates to a filter cloth for a filter press,
having a filtration area through which filtrate can pass into a
filter element of the filter press, and a border area which is provided
for application to an edge of the filter element. The invention
also relates to a method for the manufacture of the filter cloth
for a filter press.
[0002] A filter press is a discontinuously operating filtration
device, which is more particularly used in the raw material, foodstuffs,
pharmaceutical and chemical industries. The filter press generally
comprises a large number of parallel-linked, plate-like filter elements,
between which are located filter cloths. The filter elements may
not only be plate-like, but can also have a different shape. The
faces of the plate group are bounded by a fixed wall or cover plate
and a movable pressure plate. The pressure plate presses together
the plate-like filter elements, which are made from metal, plastic
or some other suitable material and as a result the filter press
is closed. Subsequently a suspension to be filtered is introduced
into the filter press, filtrate passing through the filter cloth
whilst forming a filter cake thereon and is led off via corresponding
channels on the plate-like filter element. For removing the filter
cake formed, the axial tensile force is relieved and the plate-like
filter elements separated. The filter cake formed on the individual
filter cloths is ejected or is scraped off by means of a doctor
blade.
[0003] As a result of the method the axial force for pressing together
the filter elements must be so high that it significantly exceeds
the filling pressure of the suspension to be filtered. The filter
cloth used for a filter press not only serves as a filtering medium,
but also as a seal along the filter element edge, where the adjacent
filter elements are pressed against one another. To ensure that
this sealing function is adequately performed, particularly at the
contact surface between the filter element edge and the filter cloth,
said filter cloth must have an adequate deformability, so that liquid
passages are prevented.
[0004] However, in the vicinity of the filtration surface of the
filter cloth a very dimensionally stable, robust filter cloth structure
is desired.
[0005] It is known to weave a filter cloth from monofilament yarns,
which are also known as plastic wires. However, a fabric formed
from monofilament yarns is unsuitable for sealing the edges of the
filter elements, because the wire-like yarns do not adequately elastically
deform under the axial contact pressure and tend to break during
prolonged operational loads.
[0006] Therefore multifilament yarn fabrics are used for filter
cloths for filter presses. Such multifilament yarns, which is also
understood to cover hereinafter staple fibre yarns, comprise a plurality
of fibres, which leads to an improved deformability under pressure
and therefore a desired sealing action. However, a disadvantage
of such multifilament yarn fabrics is that in the filtration area
solid attachments form between the individual fibres of a multifilament
yarn and such fabrics mat together and/or clog after a relatively
short operating period. Thus, multifilament yarn filter cloths when
used on a filter press require relatively frequent replacement or
cleaning, which reduces the degree of utilization of a filter press
and leads to corresponding costs when replacing said filter cloths.
[0007] The object of the invention is to provide a filter cloth,
which permits a particularly economic operation of a filter press.
A further object is to provide an economic method for the manufacture
of such a filter cloth.
[0008] The first part of the object is achieved by a filter cloth
having the features of claim 1. According to the invention, the
second part of the object is achieved by a method having the features
of claim 8. Preferred embodiments of the invention are given in
the dependent claims.
[0009] The filter cloth according to the invention is characterized
in that the filtration area has a fabric differing from that of
the border area, that the filtration area is preponderantly woven
from monofilament yarns and that preponderantly multifilament yarns
are woven in the border area.
[0010] In this way, in the case of the filter cloth according to
the invention, it is possible to combine the advantages of a monofilament
fabric and a multifilament fabric. Through the use of monofilament
yarns in the filtration area it is possible to ensure a particularly
robust and consequently long-life filtering medium, even under relatively
rough operating conditions in a filter press. As a result of the
smooth yarn surface of the monofilament yarn a reliable and substantially
complete discharge of the filter cake from the filtration area is
ensured. In addition, the monofilament fabric ensures a high shear
strength and excellent dimensional stability. The use of multifilament
yarns in the border area, which engages on the projecting edge of
the filter element, ensures an adequate deformability, which is
essential for a good sealing function. Whereas in the case of multifilament
filter cloths of a conventional nature, through having to take account
of the sealing function, the filter cloth openings are relatively
fine throughout, the filter cloth according to the invention permits
a significant freedom of design with regard to the size of the openings
in the filtration area. The openings preferably have a size between
10 and 100 um. The filter cloth can also be used in other filters,
in which there is a similar problem of a simultaneous filtering
and sealing function.
[0011] To a certain extent there can also be multifilament yarns
in the filtration area. A particularly robust, long-life filter
cloth for a filter press is obtained according to the invention
in that the filtration area is woven exclusively from monofilament
yarns.
[0012] It is also possible to provide only multifilament yarns
in the border area. According to a further development of the invention,
in the border area are woven both multifilament yarns and monofilament
yarns. Through the combination of the two yarns in the border area
it is ensured that on the one hand an adequate deformability and
elasticity is ensured through the multifilament yarns and on the
other the monofilament yarns ensure an adequate stability against
tearing. Preferably preponderantly multifilament yarns are used
in the border area to ensure a good sealing function.
[0013] To ensure an adequate sealing function in the aforementioned
embodiment, it is preferable for the multifilament yarns in the
border area to be located preponderantly on the side of the filter
cloth facing the filter element. Thus, the contact surface between
the edge of the filter element and the filter cloth being supported
is particularly problematical with regards to sealing. On pressing
together two facing filter elements with filter cloths spread out
thereon, the contact surface between the individual filter cloths
is scarcely problematical, because even on pressing together two
monofilament fabrics an adequate seal against the passage of liquid
is ensured. Conversely in the filtration area the monofilament yarns
are preponderantly on the filter cake side in order to ensure a
good and substantially complete discharge of the filter cake.
[0014] According to a further development of the invention the
filter cloth is constructed as a double layer fabric, a lower fabric
layer facing the filter element is a backing fabric and an upper
fabric layer is constructed as a filtration-active layer. The upper
fabric layer can be adjusted in such a way that there is a desired
opening size for the passage of filtrate. For this purpose relatively
fine yarns can be used, whereas the lower fabric layer can be made
from a wide meshed fabric with relatively thick yarns.
[0015] According to the invention the use time of the filter cloth
can be increased in that a border area located in the discharge
direction of a filter cake formed is provided on its top surface
remote from the filter element preponderantly or exclusively with
monofilament yarns. During filter cake discharge over the marginal
area, the problem arises that filter cake residues can stick to
the filter cloth in said marginal area. On closing the filter press
again, these residues constitute a very considerable burden for
the filter cloth, so that such residues frequently cause damage
to the filter cloth. A fabric of monofilament yarns with smooth
top surface ensures a reliable sliding off of the filter cake and
consequently reduces the filter cloth damage risk. The filter cloth
can be produced with an angular, round or other shape. For so-called
tower filter presses with progressively circulating filter cloth
belt, the filter cloth can be constructed as an annular, closed
belt with a plurality of transverse borders.
[0016] The method according to the invention for the manufacture
of a filter cloth for a filter press is characterized in that the
filtration area is woven differently from the border area, that
the filtration area is preponderantly woven from monofilament yarns
and that in the border area preponderantly multifilament yarns are
woven. In this way the aforementioned filter cloth according to
the invention can be economically manufactured.
[0017] According to a further development of this method, it is
particularly economically advantageous for the filter cloth to be
made up from a length of fabric and for the latter to be produced
in a width corresponding to a desired side length of the filter
cloth. The filter cloth for a filter press with predetermined filter
element dimensions can in this way be woven and finished, e.g. heat
treated and/or stretched and can be produced by simply cutting to
length the length of fabric.
[0018] Preferably, along the marginal edges of the length of fabric
and corresponding to the desired border area of the filter cloth,
multifilament yarns are used as warp threads. As opposed to this,
for forming the filtration area monofilament yarns are used here
as warp threads. In these areas monofilament yarns are also used
as weft threads.
[0019] According to another embodiment of the method according
to the invention, corresponding to the other side length of the
quadrangular filter cloth in transversely directed portions of the
length of fabric multifilament yarns are used as weft threads for
forming the border area. This method permits simple manufacture
of the filter cloth according to the invention with the specifically
constructed filter areas and border areas by weaving, finishing
and making up.
[0020] The invention is further illustrated hereinafter by preferred
embodiments described in greater detail relative to the attached
drawings, wherein show:
[0021] FIG. 1 A part cross-sectional view through a filter press
during filtration.
[0022] FIG. 2 A perspective view of a filter press with separated
filter elements.
[0023] FIG. 3 A plan view of the length of fabric for producing
a filter cloth according to the invention.
[0024] FIG. 4 A part cross-sectional view through a fabric of a
filter cloth according to the invention.
[0025] The basic operating principle of a filter press 50 and the
arrangement of the filter cloth 10 according to the invention is
diagrammatically illustrated by FIGS. 1 and 2. The filter press
50 comprises several plate-like filter elements 52, which have a
central filtration portion provided with outflow channels and surrounded
by a frame-like, projecting edge 54. The arrangement of the outflow
channels and the edge 54 on the filter elements 52 is bilateral.
A filter cloth 10 is placed on both sides of the filter element
52 and a one-piece filter cloth 10 can be used by turning over on
one side of the filter element 52.
[0026] For filtration operation the filter press 50 is closed,
in that the parallel filter elements 52 are pressed axially against
one another. The edges 54 of the individual filter elements 52 are
adjacent to one another, the filter cloth 10 resting on the edge
54 sealing the contact surface. In accordance with arrow P1 a suspension
to be filtered can be introduced under pressure into the cavity
between the filter elements 52. Accompanied by the formation of
a filter cake at the filtration area 12 of the filter cloth 10,
the filtrate penetrates through the filter cloth 10 and runs out
through the outflow channels in the filter elements 52 and central
channels in accordance with the arrow P2. On reaching a given filter
cake height the filter press 50 is opened in accordance with FIG.
2, the filter cake formed on the filter cloth 10 dropping downwards
or being scraped off.
[0027] To comply with the different conditions during filtration
operation, the border area 14 of the filter cloth 10 according to
the invention and which rests on the raised edge 54 of the filter
element 52, has a fabric formed preponderantly from multifilament
yarns. However, in its filtration area 12, the so-called filtration
window, the filter cloth 10 has a fabric formed preponderantly from
monofilament yarns.
[0028] The manufacture of a filter cloth 10 according to the invention
will be explained in conjunction with FIG. 3. The filter cloth 10
is made up from a length of fabric 40 produced by a conventional
weaving method by weaving longitudinally directed warp threads with
transversely directed weft threads. The length of fabric 40 is woven
and finished in accordance with a desired width of the filter cloth
10 and in accordance with the desired border area 14 along the marginal
edges 42 monofilament yarns are used as warp threads. In a transversely
directed portion 44, which is also intended to serve as a border
area 14 as so-called transverse borders of the filter cloth 10 to
be made up, additionally multifilament yarns are used as weft threads.
The width of the transversely directed portion 44 is designed for
a turn round the edge 54 of the filter element 52 or roughly twice
as large as the desired width of the border area 14. In the latter
case cutting of the filter cloth 10 from the length of fabric 40
would take place in the centre of portion 44, so that the filter
cloths 10 can be made up without waste from the length of fabric
40. In other areas of the length of fabric 40 mainly monofilament
yarns are used both as warp threads and weft threads.
[0029] FIG. 4 is a part cross-sectional view through a filter cloth
10 according to the invention with a double layer fabric. Said double
layer fabric comprises a lower backing fabric 22 facing the filter
element, whilst on the so-called filter cake or satin side there
is a finer meshed fabric as filtration-active layer 24. In all there
are an upper weft thread 26, a central binding thread 28 and a lower
weft thread, which are woven with fine, upper warp threads 32 and
lower, larger warp threads 34.
[0030] The upper weft threads 26 and the upper, fine warp threads
32 form the filtration-active layer 24, whereas the upper weft thread
26 is always a monofilament yarn. Corresponding to the arrangement
in a border area 14 or a filtration area 12, the upper warp threads
32 can be multifilament or monofilament yarns.
[0031] The lower backing fabric 22 is formed by the lower warp
threads 34 and the lower weft threads 30 and said threads can be
multifilament yarns in a border area 14. The central binding threads
28 serve to provide a reliable connection of the filtration-active
layer 24 with the underlying backing fabric 22. |