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
The invention claimed is:
1. Filter cloth for a filter press, comprising: a filtration area
defining a filter cake side and through which filtrate can pass
into a filter element of the filter press; and a border area surrounding
the filtration area and adapted for sealing application to a corresponding
peripheral edge of the filter element; wherein the filtration area
has a fabric differing from that of the border area, and the filtration
area is preponderantly woven from monofilament yarns and preponderantly
multifilament yarns are woven in the border area, and wherein the
multifilament yarns used in the border area are interwoven with
the monofilament yarns of the filtration area.
2. Filter cloth according to claim 1, wherein the filtration area
is exclusively woven from monofilament yarns.
3. Filter cloth according to claim 1, wherein in the border area
both multifilament yarns and monofilament yarns are woven.
4. Filter cloth according to claim 3, wherein in the border area
the multifilament yarns are preponderantly located on a side of
the filter cloth facing the filter element.
5. Filter cloth according to claim 1, wherein 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.
6. Filter cloth according to claim 1, wherein the border area is
located in a discharge direction of a formed filter cake and has
on a top side remote from the filter element preponderantly monofilament
yarns.
7. Filter cloth according to claim 6, wherein in the filtration
area the monofilament yarns are preponderantly located on a side
of the filter cake remote from the filter element.
8. Method for manufacture of a filter cloth for a filter press
according to claim 1, wherein the filtration area is woven differently
from the border area, the filtration area is preponderantly woven
from monofilament yarns, and in the border area preponderantly multifilament
yarns are woven, and wherein the multifilament yarns used in the
border area are interwoven with the monofilament yarns of the filtration
area.
9. Method according to claim 8, wherein the filter cloth is manufactured
from a length of fabric, produced with a width corresponding to
a desired side length of the filter cloth.
10. Method according to claim 9, wherein along a marginal edge
of the length of fabric and corresponding to the border area of
the filter cloth, multifilament yarns are used as warp threads.
11. Method according to claim 10, wherein the filter cloth is rectangular,
and wherein in accordance with another side length of the rectangular
filter cloth in transversely directed portions of a length of fabric
multifilament yarns are used as weft threads for forming the border
area.
Description 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.
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.
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.
However, in the vicinity of the filtration surface of the filter
cloth a very dimensionally stable, robust filter cloth structure
is desired.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The invention is further illustrated hereinafter by preferred embodiments
described in greater detail relative to the attached drawings, wherein
show:
FIG. 1 A part cross-sectional view through a filter press during
filtration.
FIG. 2 A perspective view of a filter press with separated filter
elements.
FIG. 3 A plan view of the length of fabric for producing a filter
cloth according to the invention.
FIG. 4 A part cross-sectional view through a fabric of a filter
cloth according to the invention.
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.
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.
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.
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.
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.
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.
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. |