U.S. patent application number 11/801818 was filed with the patent office on 2008-01-31 for backflushable filtering apparatus for molten material and distribution unit for a filter device of this type.
This patent application is currently assigned to EREMA Engineering Recycling Maschinen Und Anlagen Gesellschaft m.b.H.. Invention is credited to Helmut Bacher, Wolfgang Dreu, Helmuth Schulz, Georg Wendelin.
Application Number | 20080023392 11/801818 |
Document ID | / |
Family ID | 32111254 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080023392 |
Kind Code |
A1 |
Bacher; Helmut ; et
al. |
January 31, 2008 |
Backflushable filtering apparatus for molten material and
distribution unit for a filter device of this type
Abstract
A backflushable filtering apparatus for a molten material,
particularly for a plastic melt, comprises a housing (1) in which a
sieving arrangement (17) is provided which includes at least two
sieving sections (16) separated from one another. The melt to be
filtered is supplied to the sieving sections (16) through at least
one distributor (3). The distributor (3) includes at least one
control body (9) for backflushing which is moveable within a
housing (53) that is provided with an inlet opening (4) for the
material to be filtered. The control body (9), in a filtering
position, unblocks the influx of material to be filtered to all
sieving sections (16) through connection channels (23). However, in
a backflushing position, the control body (9) interrupts the influx
of material to the filtering section (16) to be backflushed and
interconnects the connection channel (23) of the sieving section
(16) flushed back with a discharge channel (28) located in the
control body (9). At least the majority of the circumference of the
control body (9) is surrounded by a distribution space (7) for the
material to be filtered which is situated within its housing (53).
The distribution space (7) is connectable through the connection
channels (23) to all sieving sections (16) in communication with
the distributor (3). Guiding channels (6) lead from the inlet
opening (4) to the regions of the two front ends (61, 62) of the
distribution space (7). These front ends (61, 62) are situated in
the region of the outermost connection channels (23) or outside the
region of all connection channels (23). The discharge channel (28),
which leads away from the control body (9), may be caused to
communicate with the connection channel (23) of the respective
sieving section (16) to be flushed back through a flush back
channel (27) of at least one cross-piece (14) of the control body
(9) which overbridges the distribution space (7).
Inventors: |
Bacher; Helmut; (St.Florian,
AT) ; Schulz; Helmuth; (Linz, AT) ; Wendelin;
Georg; (Linz, AT) ; Dreu; Wolfgang; (Linz,
AT) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
EREMA Engineering Recycling
Maschinen Und Anlagen Gesellschaft m.b.H.
Unterfeldstrasse 3
Freindorf
AT
A-4052
|
Family ID: |
32111254 |
Appl. No.: |
11/801818 |
Filed: |
May 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10525884 |
Feb 24, 2005 |
7267234 |
|
|
PCT/AT03/00322 |
Oct 27, 2003 |
|
|
|
11801818 |
May 10, 2007 |
|
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Current U.S.
Class: |
210/411 |
Current CPC
Class: |
B29C 48/55 20190201;
B29C 48/6912 20190201; B29C 48/273 20190201; B29C 48/69 20190201;
B29C 48/03 20190201; B29C 48/268 20190201; B29C 48/2554
20190201 |
Class at
Publication: |
210/411 |
International
Class: |
B01D 35/16 20060101
B01D035/16 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 2002 |
AT |
A1629/2002 |
Claims
1-21. (canceled)
22: Distributor for a backflushable filtering apparatus, comprising
a housing (53) and a control body (9) for backflushing moveable
therein, to which the material to be filtered is supplied through
an inlet opening (4) and which, in filtering position, unblocks the
influx of this material to at least two connection channels (23)
which may be interconnected to sieving section (16) of the
filtering apparatus, whereas in a flush back position, the control
body (9) interconnects one of these connection channels (23) with a
discharge channel (28) situated in the control body (9), the inlet
opening (4) communicating with a distribution space (7) arranged in
the housing (53) and whose majority surrounds the control body (9),
characterized in that the inlet opening (4) communicates with the
distribution space (7) via two guiding channels (6) which discharge
at its front ends (61, 62) into the distribution space (7) within
the region of the outermost connection channels (23) or outside the
region of all connection channels (23).
23: Distributor according to claim 22, characterized in that the
control body (9) comprises at least one cross-piece (14) at its
circumference which overbridges the distribution space (7) and
surrounds a flush back channel (27) communicating with the
discharge channel (28), said cross-piece sealingly engaging an area
of the inner wall of the housing (53).
24: Distributor according to claim 22, characterized in that the
control body (9) is a slider (37) displaceable in the housing (53)
or is a rotary piston (8) rotatable in the housing (53), said
rotary piston (8) comprising at least two cross-pieces (14) which
are offset relative to each other both in axial direction and in
circumferential direction of the rotary piston (8).
25: Distributor according to claim 22, characterized in that at
least one additional guiding channel (60) leads into the
distribution space (7) between the two guiding channels (6) leading
to its two front ends (61, 62).
26: Distributor according to claim 22, characterized in that at
least two control bodies (9) are disposed within a common housing
(53), wherein a distribution space (7) is assigned to each one of
these control bodies (9), which distribution space is supplied in
the region of its front ends (61, 62) via guiding channels (6).
Description
[0001] The invention relates to a backflushable filtering apparatus
for a molten material, particularly for a plastic melt, comprising
a housing in which a sieving arrangement is provided which includes
at least two sieving sections separated from one another, to which
the melt to be filtered is supplied via at least one distributor
which includes at least one control body for backflushing, moveable
within a housing that is provided with an inlet opening for the
material to be filtered, said control body, in a filtering
position, unblocking the influx of material to be filtered to all
sieving sections through connection channels, while in a
backflushing position interrupting the influx of material to the
filtering section to be backflushed and interconnecting the
connection channel of the sieving section flushed back with a
discharge channel located in the control body and leading away from
it, at least the majority of the circumference of the control body
being surrounded by a distribution space for the material to be
filtered which is situated within the housing of the distributor,
said distribution space being connectable through the connection
channels to all sieving sections in communication with the
distributor. Furthermore, the invention relates to a distributor
for such a filtering apparatus.
[0002] A filter apparatus of the initially described kind which can
be back-flushed, has become known (EP 1245366 A2, DE 19730574 C1).
Within these constructions, the control body is constituted by a
control piston that can be shifted within its housing in
longitudinal direction and has a central peripheral groove which is
in flow connection with the inlet opening and via which the
material to be filtered is supplied either to two piston-shaped
sieve carriers or, if it has to be back-flushed, only to one of
these sieve carriers. In the back-flushing position a conduit that
leads to the central discharge channel of the control body is in
connection with the downstream side of the back-flushed sieve.
Within this, the expenditure caused by two separated sieve carrier
pistons is of disadvantage as well as the reason that such a
construction is limited to only two sieves. Further, material to be
filtered may stay for a longer time within the peripheral groove of
the control body so that there is the danger of coking of this
material.
[0003] Within another back-flushable filter apparatus (AT 407611
B), the control-body is constituted by a rotatable piston bearingly
supported for rotation within its housing, which piston is
intersected crosswise to its axis by two radial through-passage
conduits which in the filtering position connect the inlet opening
with two sieve section of the sieving arrangement. Each one of
these sieve sections is formed by a filter element disposed within
the housing of the filter device. By rotation of the rotational
piston around its longitudinal axis one of the two through-passage
conduits can be so rotated that the flow of the material to be
filtered to the associated filter is blocked, however this filter
which has to be back-flushed is connected with a discharge channel
for impurities which have to be carried off the back-flushed
filter, which discharge channel is disposed within the rotatable
piston. Within this, it is of disadvantage within the temporary
blocking of the supply conduit during the back-flushing process
that the material positioned within the conducting conduit leading
from the inlet opening to the rotatable piston stands still and
therefore tends to coking. Further, it is difficult to extend such
a filter apparatus to more than two sieve sections.
[0004] It is an object of the invention to improve a filtering
apparatus of the kind mentioned at the outset so that a continuous
flow through all channels is ensured which lead to the sieving
sections during the filtering procedure, thus avoiding coking of
the material to be filtered, on the one hand, while the apparatus
may be enlarged to any number of sieving sections desired without
any problem, on the other hand. This object is achieved according
to the invention in that guiding channels lead from the inlet
opening to the regions of the two front ends of the distribution
space, that said front ends are situated in the region of the
outermost connection channels or outside the region of all
connection channels, and that the discharge channel may be caused
to communicate with the connection channel of the respective
sieving section to be flushed back through a flush back channel of
at least one cross-piece of the control body which overbridges the
distribution space. In this way, the flow to the connection
channels is always directed from the exterior to the middle so that
no dead corners will exist in which plastic material could remain
during the filtering procedure, thus affecting its quality. A
distribution space with such a flow will continuously be flown
through by the material to be filtered, independently of whether a
sieving section is just backflushed or not.
[0005] By arranging a plurality of cross-pieces off-set relative to
each other, this construction may be enlarged to a high number of
sieving section without any problem, nevertheless always ensuring
backflushing section by sections. It is also advantageous that the
sieving section flushed back has not necessarily to be moved during
flushing back procedure so that a sieve carrier, commonly used for
holding a sieving section, does not wear off by the back flushing
procedure. The sieve carrier, being stationary during backflushing
procedure, will therefore not introduce burnt or decomposed parts
of melt into the melt that has already been filtered. Moreover, the
apparatus may also be operated in an easier manner, because, by
simply moving the control body into a position different from the
previous position, one sieve section after the other may be blocked
against the flow of melt, while concurrently connecting it with the
discharge channel, independently of the number of existing sieving
sections.
[0006] Within the scope of the constructive possibilities of
realization, there are two basic variants: the control body may be
a slider displaceable in the housing, that surrounds it, the
connection channels leading to the individual sieving sections
being offset relative to each other in sliding direction of the
slider, on the one hand. On the other hand, the control body may be
a rotary piston, rotatable about its longitudinal axis within its
housing, which is supported in a sealed manner at its two front
ends in its housing, but is surrounded in-between by the
distribution space. Though the former construction requires more
space due to the longitudinal sliding motion of the slider, it is
theoretically unlimited with respect to the number of sieving
sections, while the latter construction is more space-saving.
[0007] According to a preferred embodiment of the invention, a
particularly advantageous construction consists in that the
connection channels extend only in the housing, which surrounds the
control body, and that sieve nests of the housing of the filtering
apparatus, which contain the sieving sections, immediately join the
outer surface of the housing of the control body within the region
of the respective orifice of a connection channel. This results in
a very short path between the distribution space and the individual
sieving sections. The consequence is that, having terminated the
backflushing procedure, the dirty flush back mass existing in the
above-mentioned path is as small as possible, thus not affecting
substantially the filter function of the corresponding sieving
section in the following filtering procedure.
[0008] It is especially favorable if, according to the invention,
the sieving arrangement comprises a plurality of sieving sections
arranged in at least one array, the orientation of which being
parallel to the longitudinal direction of the distribution space.
These numerous sieving sections separated from one another can each
separately be flushed back, and, in the case of a suitable
arrangement, can be flowed through centrally in relation to the
connection channels, and therefore also can centrally be flushed
back, which enhances the efficiency both of the filtering
performance and of backflushing.
[0009] It is convenient to form each sieving station with a
perforated support plate and a perforated backflushing plate, at
least one sieving layer being situated in-between. Both plates, as
mentioned above, support the sieving layer during filtering
procedure and the backflushing procedure, and prevent in this way
any deformation of the sieving layer. Such a construction can
easily be formed in such a manner that at least one sieving section
is separated from the adjacent sieving section by a partition
arranged upstream in filtering position, and a connection channel
leads to each one of the sieving sections. This results in an
increase of the number of sieving sections being independent from
one another, and therefore an improvement of the entire filtering
performance. The perforated support plate and the perforated
backflushing plate may be made arcuate, the convex side being
upstream in filtering position. This results in an enlargement of
the sieving surface, and the resulting sieving space corresponds
better to the occurring flow conditions. At least one sieving
section may comprise a rectangular or square sieving surface,
optionally with rounded corners, which results in an increase of
the active filtering surface that is flown through in a uniform
manner.
[0010] In order to favour splitting up the supplied melt fluid to
centrally disposed sieving sections, at least one additional
conducting conduit may end in the distribution space between the
two conducting conduits leading to the front ends of the
distribution space.
[0011] Further, it is possible to provide at least two control
bodies within a common housing, each one of which is supplied in
the region of the front ends of its distribution space via
conducting channels. This may contribute to enhance the uniformity
of supplying the sieving sections. Further, this facilitates the
common backflushing of more than one sieving section. Further,
thereby the backflushing distances for the screened-off impurity
particles to be backflushed are made even shorter, and the material
demand for backflushing is decreased.
[0012] The distributor for a backflushable filtering apparatus
according to the invention is based on a construction which
comprises a housing and a control body for backflushing moveable
therein, to which the material to be filtered is supplied through
an inlet opening and which, in filtering position, unblocks the
influx of this material to at least two connection channels which
may be interconnected to sieving sections of the filtering
apparatus, whereas in a flush back position, the control body
interconnects one of these connection channels with a discharge
channel situated in the control body, the inlet opening
communicating with a distribution space arranged in the housing and
whose majority surrounds the control body. On this base, the
construction according to the invention of this distributor is
characterized in that the inlet opening communicates with the
distribution space via two guiding channels which discharge at its
front end into the distribution space within the region of the
outermost connection channels or outside the region of all
connection channels. As has been mentioned above, this results in
the advantage that the flow to the connection channels is always
directed from the exterior to the middle, and dead corners are
avoided in which material to be filtered could remain for a long
period.
[0013] At least one additional conducting conduit may lead to the
distribution space between the two conducting channels leading to
the front ends of the distribution space.
[0014] Further characteristics and advantages of the invention will
become apparent from the description of embodiments schematically
illustrated in the drawings.
[0015] FIG. 1 shows a cross-section of a first embodiment having a
single distributor formed as a rotary piston.
[0016] FIG. 2 is a cross-section along the line II-II of FIG.
1.
[0017] FIG. 3 shows an embodiment having two distributors as a
cross-section similar to that of FIG. 1, and
[0018] FIG. 4 is a cross-section along the line IV-IV of FIG.
3.
[0019] FIG. 5 shows an embodiment having two distributors formed as
sliders in a cross-sectional view similar to that of FIG. 3, the
two distributors being in filtering position.
[0020] FIG. 6 shows a cross-section similar to that of FIG. 5
wherein, however, the left-side distributor is in flush back
position.
[0021] FIG. 7 shows a cross-section of an embodiment having two
sieving arrangements, each of which being sub-divided in partial
sieving surfaces.
[0022] FIG. 8 shows a cross-section, similar to that of FIG. 7, of
a variant having a single sieving arrangement which is sub-divided
into five partial sieving surfaces which may be flushed back
independently from one another.
[0023] FIG. 9 shows a cross-section along the line IX-IX of FIG.
8.
[0024] FIG. 10 shows an embodiment comprising partial sieving
surfaces which are formed as a rectangle.
[0025] FIG. 11 shows schematically an embodiment wherein a single
distributor is associated to two opposite sieving arrangements.
[0026] FIG. 12 shows schematically the combination of a filtering
apparatus and a device for plastifying and agglomerating plastic
material.
[0027] FIG. 13 shows an embodiment having additional guide
channels.
[0028] FIG. 14 shows an embodiment having two control bodies.
[0029] The embodiment of FIGS. 1 and 2 comprises a housing 1 for a
sieve carrier 2 as well as a housing 53 for a distributor 3
associated to it. The housing 53 comprises an inlet opening 4 for
the influx of a melt to be filtered which is particularly formed by
a molten thermoplastic material. The material flowing in the
direction of arrow 5 into the inlet opening 4 reaches two guide
channels 6 leading to both front ends of a distribution space 7
which surrounds the majority of the circumference of a control body
9 of the distributor 3 formed as a rotary piston 8. This
distribution space 7, at both its front ends 61, 62, is closed by
cylindrical portions 10, 11 of the rotary piston 8 with which the
rotary piston 8 is supported in a borehole 12 of the housing 1 so
as to be rotatable about its longitudinal axis, but sealed. The
control body 9 comprises between the two cylindrical portions 10,
11 a plurality of cross-pieces 14 extending through the
distribution space 7 which are offset relative to each other in
circumferential direction of the distribution space, each of which
being formed by a knob-like salient 54 of the outer surface of the
control body 9. The surface of each cross-piece 14 or of the
salient 54 forming it which faces the wall of the borehole 12 is
adapted to the shape of the borehole 12 so that the cross-piece 14
sealingly engages an area of the wall of the borehole 12.
[0030] The sieve carrier 2 is formed as a cylindrical piston
arranged in a borehole 15 of the housing 1. At the side facing the
distributor 3, the sieve carrier 2 carries a plurality of sieving
sections 16 arranged side-by-side in its longitudinal direction, a
single one of them being represented in FIG. 2 for the sake of
simplicity. These sieving sections 16 together form a sieving
arrangement 17 for filtering the material supplied to it. The
individual sieving sections 16 are separated from one another by
partitions 18 arranged upstream of each sieving arrangement 17 and
extending substantially perpendicularly to the longitudinal axis 19
of the sieve carrier 2. Each sieving section 16 comprises a
perforated support plate 20 arranged downstream during filtering
procedure, and a perforated backflushing plate 21 arranged
upstream. Between the two plates 20, 21 is a sieving layer 22 which
exerts the real filtering effect. The two plates 20, 21 serve to
absorbing the pressure exerted by filtered or backflushed melt, and
the perforations provided in the two plates 20, 21 are large enough
that they do not substantially interfere with the flow of melt
supplied or of the filtrate. The perforated support plate 20 and
the perforated backflushing plate 21 are arcuate, the convex side
being upstream during filtering procedure. To each sieving section
16, a connection channel 23 is assigned through which melt supplied
from the distribution space 7 may flow to the corresponding sieving
section 16. As is shown in FIG. 2, all connection channels 23 are
between both front ends of the distribution space 7 defined by the
cylindrical portions 10, 11 of the control body 9, and also between
the orifices 55 of the guide channels 6 into the distribution space
7 so that all connection channels 23 serving for filtering are
always flown through from the front ends of the distribution space
7. Under this flow condition, the melt, supplied by the guide
channels 6, passes the cross-pieces 14. This has the advantage that
no dead regions can develop in the distribution space 7 wherein
plastic material can dwell for a prolonged period without moving,
thus being liable to be thermally damaged. In an extreme case, the
outermost connection channels 23, i.e. the connection channels 23
situated in the array of connection channels 23 at both ends of
this array, may be opposite the two guide channels 6 so that these
two guide channels 6 are located in the region of the outermost
connection channels 23.
[0031] In filtering position, the control body 9 of the rotary
piston 8 is caused by a device merely schematically illustrated to
assume such a rotary position that none of the cross-pieces 14,
which are offset relative to each other in circumferential and
longitudinal direction of the rotary piston 8, is opposite to one
of the connection channels 23. Therefore, the melt to be filtered
is able to flow unimpededly from the whole distribution space 7
into all connection channels 23 and, thus, to the sieving sections
16 which are behind. The sieving layer 22 of each sieving section
16 retains impurities, the filtrate reaches a collection space 25
behind all sieving sections 16, and flows from it off the housing 1
through a discharge channel 34 in the direction of arrow 57 to a
discharge opening 26.
[0032] If, however, one of the sieving sections 16 is to be flushed
back, the control body 9 is turned by means of the device 24 in
such a manner that the cross-piece 14 opposite the sieving section
16 to be flushed back is moved in front of the associated
connection channel 23. The area engagement of the front surface of
the cross-piece 14 of the wall of the borehole 12 acts as a sealing
so that the flow of melt to be filtered is blocked for the
corresponding connection channel 23. However, this connection
channel 23 is moved into communication with a flush back channel 27
passing through the cross-piece 14 and extending radially or
obliquely (FIG. 2) within the rotary piston 8. All flush back
channels 27 discharge into a discharge channel 28, extending
centrally along the longitudinal axis 13 of the rotary piston 8,
through which the mass flushed back reaches either ambient or a
collection chamber not shown in the direction of arrow 29.
[0033] When flushing back a sieving section 16, the conditions
mentioned above remain unchanged for all other sieving sections,
i.e. these other sieving sections 16 will continue to filter, and
only for the sieving section to be flushed back, the associated
connection channel 23 will be closed by the cross-piece situated in
front of it with respect to the incoming material to be filtered
from the distribution space 7. For the sieving section 16 to be
flushed back, purified filtrate from the collection space 25 flows
through the perforate supporting plate 20, and in reverse
direction, as compared with the filtering procedure, through the
sieving layer 22 and entrains therefrom the accumulated impurities
which will be discharged from the sieving section 16 flushed back
through the perforations of the perforated backflushing plate 21
and will be directed through the respective connection channel 23
into the flush back channel 27 and from it into the discharge
channel 28. Therefore, no backflushed material will reach the
distribution space 7.
[0034] In order to be able to perform the flushing back procedure
just described for each individual sieving section 16,
independently from the other sieving sections, the cross-pieces 14
at the circumference of the rotary piston 8 are offset relative to
each other both in longitudinal direction and in circumferential
direction so that one respective cross-piece 14 may be moved into
sealing engagement with that wall portion of the borehole 12 which
surrounds the connection channel 23, while the other cross-pieces
14 are far enough from their associated connection channels 23 that
the flow of the mass to be filtered into these connection channels
23 is not disturbed.
[0035] As shown, the sieve carrier 2 has not necessarily to be
moved for backflushing. This is advantageous, because in this way
the sieve carrier does not wear off for backflushing, and no burnt
or decomposed melt particles can possibly reach the already
filtered melt through any gap between the housing and the discharge
channel in the sieve carrier. However, the sieve carrier 2 may be
displaced in direction of its longitudinal axis 19 by a device 30
merely schematically illustrated, in order to make individual or
all sieving sections 16 in the housing 1 accessible so that a
change of any sieving section may be carried out in a simple
manner. This makes it possible to form the housing for the sieve
carrier 2 and the distributor 3 integral, as shown in FIGS. 1 and
2. An alternative would be to form the housing in two pieces, the
parting line 31 represented in dotted lines in FIG. 1 being
arranged in such a manner that the whole sieving arrangement 17 is
accessible for an exchange of any sieving section after having
removed the housing 53 which contains the distributor 3. Another
possibility for arranging such a parting line, thus constructively
separating the two housings 1, 53, is given by the parting line 58,
also shown in dotted lines in FIG. 1, which suitably passes through
the connection channels 23. In both cases, it is possible to flange
the housing of the control body 9 of the distributor 3 to the
housing 1 of the sieve carrier 2. An embodiment with separated
housings 1, 53 has the advantage that the distributor 3 and the
sieve carrier 2 form constructively independent components and can
be machined or exchanged independently from each other for either
an exchange (e.g. when worn off) or a repair. Therefore, the
distributor can form a component which may be obtained separately
on the market.
[0036] It is suitable to dimension the length of the connection
channels 23 as short as possible which improves the performance of
backflushing.
[0037] As shown, material flows through all connection channels 23
and the whole distribution space 7 both when filtering and when
flushing back. Therefore, coking or other thermal damage of the
material supplied cannot occur.
[0038] The arcuate shape of the sieving arrangement 17, apart from
the enlargement of the sieving surface, has also the advantage that
a very high pressure can be absorbed during filtering. If desired
or required, however, an additional supporting body 32 may be
arranged at that side of the sieving arrangement 17 which is
downstream during filtering and may conveniently be formed so as to
be favorable for the flow, e.g. as a rib having an orthorhombic
cross-section (FIG. 1).
[0039] In a likewise manner, it may be suitable in some cases to
support the convex side of the sieving arrangement 17, in addition
to the support by the partitions 18, by transverse ribs 33 in order
to better absorb the pressure occurring during backflushing.
[0040] The embodiment according to FIGS. 3 and 4 is substantially a
duplication of the construction according to FIGS. 1 and 2.
Accordingly, two sieving arrangements 17 are provided which are
arranged in common back to back in a single sieve carrier 2, a
distributor 3 being assigned to each of them. The construction of
each of these sieve arrangements 17 and of each of these
distributors corresponds to the constructions described with
reference to FIGS. 1 and 2. The stream to each one of both
distributors 3 flows via two guide channels 6. A discharge channel
34 leads from the collection space 25 being in common to both
sieving arrangements 17 to a discharge opening 26 which, in
contrast to the construction according to FIGS. 1 and 2, is
situated at the same side of the housing 1 as the inlet opening 4.
The direction of flow of the material to be filtered in the guide
channels 6 is represented by arrows 35.
[0041] It may be seen in FIG. 4 that it is possible to combine the
cross-pieces 14 of two adjacent back flushing channels 27 to form a
single cross-piece 14'. Furthermore, it is suitable to provide a
throttle 36 at the discharge end of the discharge channel 28 in
order to prevent a drop in pressure within the overall system
during backflushing. As may be seen, the rotary piston 8
represented at left in FIGS. 3 and 4 is in that position in which
all sieving sections 16 filter, whereas the rotary piston 8
represented at right in FIGS. 3 and 4 is in that position in which
the connection channel 23 represented on the upper side of FIG. 4
is closed for filtering, the sieving section 16 assigned to this
connection channel being, however, flushed back, while the mass
flushed back is directed into the discharge channel 28 through the
flush back channel 27 arranged in the cross-piece 14 which is in
blocking position.
[0042] The embodiment according to FIGS. 5 and 6, instead of rotary
pistons as a control body 9, has sliders 37 displaceable in
longitudinal direction of the distribution spaces 7 and connected
to tie rods 38 which may be displaced to and fro in the direction
of double arrows 39 by the devices 24. At the side opposite to the
tie rods 38, each slider 37 is connected to a tube forming an
elongation 40 of the slider 37 and containing in its interior the
discharge channel 28, while being sealingly guided in longitudinal
direction in the borehole 12. Each one of these sliders 37 may be
displaced into a position in which it is outside the region of the
connection channels 23, which position is represented for both
sliders 37 in FIG. 5 and corresponds to the filtering position in
which the influx of the mass to be filtered is unblocked to all
sieving sections 16. In the operational position shown in FIG. 6,
the right-hand slider 37 is also outside the region of the
connection channels 23, but the left-hand slider 37 is in a
position in which its flush back channel 27 is communicating with
the connection channel 23 of the second sieving section 16 (when
counted from the top of FIG. 6). As may be seen from FIGS. 5 and 6,
the orifices 55 of the guide channels 6 into the distribution
space, also in this construction, are outside the region of the
connection channels 23 and outside the extreme boundary positions
of the slider 37 to ensure a flow to the connection channels 23
from the exterior and to avoid dead regions.
[0043] As may be seen, the slider 37 has only to have a single
cross-piece 14 for the functions described above. However, the
slider 37 may also have two or more cross-pieces 14 arranged in an
array, their direction coinciding with the direction of
displacement of the slider 37. In this way, simultaneous
backflushing of two or more sieving sections 16 is possible. Of
course, it should be provided that the slider 37 as a whole, i.e.
with all its cross-pieces, may then displaced into a position where
it is outside of all connection channels 23 in order to ensure a
simultaneous filtering position of all sieving sections 16.
Moreover, it has to be made sure for a reliable function that the
slider 37 cannot inadvertently be turned about its longitudinal
axis 59. This can be ensured in a simple way by an appropriate
cross-section of the elongation 40 and of the borehole 12 which
receives this cross-section, e.g. by a rectangular
cross-section.
[0044] Although the construction according to FIGS. 5 and 6
requires more space in the direction of double arrow 39, it has the
advantage to enable a simpler construction of the control body 9
and, above all, has the advantage that the number of sieving
sections 16 arranged side-by-side in the array is theoretically
unlimited.
[0045] The construction, that is only schematically illustrated in
FIG. 7, has also a rotary piston 8 as a control body 9 which may be
turned in the direction of arrow 41 about its longitudinal axis by
the device 24, while its end portions 10, 11 are sealingly
supported in the borehole 12. For the sake of simplicity, only two
of the cross-pieces 14 of the control body 9 are represented of
which the lower cross-piece 14 is in flush back position, whereas
the upper cross-piece 14 unblocks the path of the mass to be
filtered from the distribution space 7 into the opposite connection
channel 23. The difference to the constructions described up to now
is that the sieving sections 16 are distributed onto two sieving
arrangements 17, each of which being in a sieve nest 42, and the
two sieve nests 42 being spaced and offset to each other in the
direction of the longitudinal axis of the distribution space 7. The
filtrate is discharged from both filtering arrangements 17 through
a discharge channel 34 each, these two channels 34 combining in the
discharge opening 26.
[0046] In the embodiment according to FIGS. 8 and 9, there is also
a rotary piston 8 as a control body 8 whose construction and
arrangement is similar to that of FIG. 7. The difference to FIG. 7
is, however, that the sieve carrier 2 has only a single sieve nest
42 in which a sieving arrangement 17 sub-divided into a plurality
of sieving sections 16 is located. The sieving sections 16 are
separated from one another by partitions 18, thus being separately
flown through and flushed back. The partitions 18 extend parallel
to each other from side wall to side wall of the sieve nest 42 and,
at the same time, form a support of the sieving arrangement 17 in
backflushing direction. It may be seen that the connection channels
23 are suitably arranged in such a manner that they are
respectively centered with respect to the sieving section 16
supplied by the respective connection channel 23 in order to ensure
as uniform an influx onto the whole active surface of the sieving
section 16 as possible.
[0047] FIG. 10 shows that the individual sieving sections are not
necessarily circular or formed of circular segments. To the
contrary, the invention offers the possibility to shape the sieving
sections as a rectangle or square which results in the advantage of
an enlarged active sieving surface and a more uniform flow through,
as compared with circular segments. The corners of a rectangular or
square sieving section may be rounded in order to avoid dead angles
for the flow.
[0048] Of course, in all embodiments, more than one sieve carrier
may be provided, and on each sieve carrier a plurality of sieve
nests may be arranged, the number of sieving sections per sieve
nest theoretically being also unlimited.
[0049] FIG. 11 shows a variant in which two sieving arrangements
17, being opposite to each other and arranged back to back in the
sieve carrier 2, are supplied with the material to be filtered by a
distributor 3 in common via the connection channels 23 and are
backflushed over the same connection channels 23. As compared to
the embodiments described up to now, this variant has the advantage
of a smaller and more space saving construction, but requires
longer connection channels 23.
[0050] FIG. 12 shows the combination of a backflushable filtering
apparatus 43 according to the invention, and a device 44 for
plastifying or agglomerating plastic material. This device 44
comprises a housing 45 wherein two screw portions 46, 47 are
supported interconnected by still another screw portion 48 situated
between them and acting as a sealing means, the conveying direction
of this portion being opposite to the conveying direction of the
screw portions 46, 47 indicated by an arrow 49. In this way, the
thermoplastic material conveyed by the screw portion 46 is forced
to flow through an opening of the wall of the housing 45 in the
direction of the arrow 56 to the distributor 3 of the filtering
apparatus 43 via a channel 50. From its discharge opening 26, the
filtrate flows in the direction of arrow 52 through a channel 51
into another opening of the wall of the housing 45 and flows, thus,
back to the screw position 47, postponed in conveying direction,
which conveys the filtered plastic material to an extruder nozzle
or any other outlet.
[0051] The sieve carrier 2 is not necessarily a piston having a
circular cross-section. To the contrary, it may in many cases be
favorable to form the sieve carrier 2 as a flat slider, e.g. having
a rectangular cross-section, which prevents in a simple manner any
undesired rotation of the sieve carrier 2 about its longitudinal
axis.
[0052] Within the embodiment according to FIG. 13, which is similar
to that of FIG. 2, additional guiding channels 16 are provided
which branch off the two guide channels 6 leading to the front ends
61, 62 of the distribution space 7 which is disposed between these
two front ends 61, 62. These additional guide channels 60,
suitably, have a smaller cross section than the guide channels 6,
and, of course, they are so disposed that, when the rotary piston 8
is rotated, there is no direct connection to the backflushing
channels 27. These additional guide channels 60 offer an advantage
in distributing the supplied melt fluid to the centrally disposed
sieving sections 16 and, in general, with respect to an improvement
of the flow characteristics. This embodiment, therefore, is
particularly suitable for constructions in which a plurality of
sieving sections 16 are disposed side by side in axial direction of
the sieve carrier 2.
[0053] The embodiment according to FIG. 14 differs from that
according to FIG. 1 in that two control bodies 9 are disposed
within a common housing 53. An own distribution space 7 is assigned
to each one of these control bodies 9, wherein the construction of
each control body 9 corresponds to the construction described in
connection with FIG. 1. Each distribution space 7 is supplied on
its both front ends via the guide channels 6. This embodiment has
the advantage of still shorter backflushing distances for the
impurity particles to be flushed off, and further the volume of
clean melt necessary for the backflushing process is decreased.
Within this, the transverse ribs 33 are suitable for additional
subdividing the sieving arrangement 17 into several sieving
sections 16 to which the distributors 9 are assigned.
[0054] Of course, it is also possible to assign to each control
body an own housing and, if desired, to supply via more than one
inlet opening 4.
* * * * *