Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 2020/007499 CA 03096277 2020-10-06
PCT/EP2019/000199
SCREENING DEVICE
Description
The invention is concerned with a screening device, which is preferably
designed in
the form of a screen basket, wherein the screening device has screening slots
or
screening gaps which are formed between profiled screen bars, and the screen
bars
are received at their foot area in receiving recesses of support elements,
with the
receiving recesses suited to the foot area geometry, and are permanently
attached to
the support elements.
Such screening devices are also referred to as "bar screen devices". These
screening devices can be designed in a flat shape as screening plates or in a
rounded shape as screen baskets.
DE 10 2014 011 679 Al discloses profiled screen bars and screening devices,
which
are preferably designed in the form of a screen basket. These devices have
specially
profiled screen bars in such a way that the respective radii upstream and
downstream of the slot-generating flanks in the head area of the screen bar
have a
common center point. The screening device produced from such screen bars is
cylindrical and can be subdivided into segments or regions viewed in axial
direction,
with the regions with different profile depths respectively, always having an
essentially constant slot width. The production of these specially designed
screen
bars and their head area are complex, and hence there is a need for a more
cost-effective production of screening devices of the type involved here.
DE 196 09 316 C2 discloses a method for the production of a screening device
with
controlled, uneven sorting slots as well as screening devices and their use.
The
adjustability of the profile depth in a cylindrical bar screen basket is known
therefrom.
The screen basket has variable slot widths and/or different profile depths,
wherein
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both core sizes can be varied at all times. A screening device, preferably in
the form
of a screen basket with a cylindrical configuration, is created from these
known profile
bars.
Finally, DE 44 32 842 Al discloses a sorting device with a conical
configuration, with
the slot widths varying in the direction of the flow path from the stock inlet
side to the
reject outlet side in such a way that the slot width becomes smaller in the
direction of
the flow path from the stock inlet side to the reject outlet side.
The aim of the invention is therefore to provide a screening device made of
conventional screen bars, which have a triangular profile, for example, in
which the
sorting efficiency is improved, a low tendency towards clogging is
established, and
higher throughput rates can be achieved as a more gentle sorting process can
be
realized overall
According to the invention, a screening device is provided for this purpose,
preferably
in the form of a screen basket, with screening slots or screening gaps formed
between profiled screen bars, in which screening device the screen bars are
received
at their foot area in receiving recesses of support elements, with the
receiving
recesses suited to the foot area geometry, and are permanently attached to the
support elements, and which screening device is characterized in that the
profile bars
are arranged in such a way that with a constant slot width between adjacent
profile
bars in axial direction of the screen basket, the profile depth increases from
the stock
inlet side to the reject outlet side, and that the diameter of the screening
device on
the stock inlet side is greater than on the reject outlet side.
The screening device according to the invention is configured in such a way
that
different profile depths and/or different angles of a tangent to the outer
surface of the
screen device are established, but essentially a constant slot width is
available, so as
to be able to realize in the throughput direction of the screening device from
the stock
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inlet side to the reject outlet side screening or sorting treatments with
different
implementation conditions. As a result, higher throughput rates can be
realized and,
in particular, an improved sorting efficiency is obtained. In the screening
device
according to the invention, the screen bars have a common profile and are, for
example, triangular in profile.
When, in the invention, the screen bar in the upper area of the screen basket
is
shallower or has a smaller profile depth, smaller flow eddies, less turbulence
are
obtained and the likelihood of dirt particles being pressed through the
screening slots
or screening gaps is reduced. Thus, the screening device according to the
invention
attains an overall more efficient and gentle sorting process.
The thickening of the fiber suspension increases steadily in the direction of
the reject
outlet side. To prevent the sorting process from coming to a standstill due to
the risk
of clogging, a greater profile depth is realized in the area in direction of
the reject
outlet side. As a result, the turbulences can be increased in this region,
paper fibers
in the suspension can be better fluidized, and the tendency to clogging
decreases. In
the region towards the reject outlet side, the dirt load is also thickened and
concentrated. This dirt load increases wear, so that the greater profile depth
in this
region increases the volume of material in the flow, thereby improving the
creep
strength and increasing the service life of the profile or screen basket.
According to preferred embodiments, the profile depth can increase
continuously
starting from the stock inlet side to the reject outlet side. As an
alternative, the profile
depth can increase incrementally from the stock inlet side to the reject
outlet side.
According to preferred embodiments of screening devices, the screen bars can
be
aligned axially to the screen basket axis, or alternatively be aligned
linearly inclined to
the screen axis. Or, according to a further preferred embodiment, the screen
bars
can be aligned discontinuously curved with respect to the screen basket axis.
The
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alignment of the screen bars is chosen according to requirements and in
accordance
with the screening tasks and the screening treatments.
In particular, the profile bars have an essentially triangular profile. The
slot width can
be in a range from 0.05 mm to 0.8 mm, preferably from 0.1 mm to 0.4 mm.
The profile bar width is preferably in a range from 2.0 mm to 8 mm, and
preferably
between 2.0 mm and 4.0 mm.
The invention will be explained in more detail hereinafter on the basis of
preferred
embodiments with reference to the accompanying drawing, without any limiting
character. The drawing shows in:
Fig. 1 a schematic view of a screen basket according to the invention with
at least
two different screening regions between stock inlet side (inflow) and a
reject outlet side (reject);
Fig. 2 a schematic sectional view of a screen basket according to Fig. 1 in
cooperation with a rotor equipped with blades;
Fig. 3 a schematic sectional view of another configuration of a screening
device
in cooperation with a likewise conically configured rotor;
Fig. 4 a schematic view of a detail of a screening device in which the
screen bars
are aligned axially to the screen basket axis;
Fig. 5 a further preferred embodiment of a variant of a screening device in
which
the screen bars are aligned linearly inclined with respect to the screen
basket axis; and
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Fig. 6 a schematic view of a detail of a variant of a screening device in
which the
screen bars are aligned discontinuously curved with respect to the screen
basket axis.
In the figures of the drawing, same or similar parts are provided with the
same
reference signs.
Fig. 1 shows an exemplary embodiment of a screening device, generally
designated
with 1 and subdivided into at least two different treatment zones A, B in
through flow
direction from the stock inlet side (inflow) to the reject outlet side
(reject). The inflow
on the stock inlet side 2 and the reject on the reject outlet side 3 are
indicated by
arrows. The flow direction of the accepted stock is also indicated by arrows
in
conjunction with the designation "Accept".
On the right-hand side of Fig. 1, the corresponding arrangement of profile
bars 4 is
illustrated by way of an enlarged detail illustration next to the treatment
zones A, B.
As can be seen overall from Fig. 1, the profile bars 4 are arranged in such a
way that
with a constant slot width w between adjacent profile bars 4 in axial
direction of the
screen basket, the profile depth t increases from the stock inlet side to the
reject
outlet side, and the diameter of the screening device 1 on the stock inlet
side 2 is
greater than on the reject outlet side 3. The screening device 1 according to
the
invention is thus configured conically in a predetermined manner and in such a
way
that the diameter of the stock inlet side 2 is greater than on the reject
outlet side 3.
Illustrated in treatment zone A are three screen bars 4 lying next to one
another,
which have a profile width Br, a distance from profile bar 4 to profile bar 4
of P1, a
profile bar head width b1 and a profile depth t1, with 4 screening slots or
screening
gaps being formed between adjacent profiled screen bars 4, which have a slot
width w.
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The screen bars 4' in the treatment zone B have a profile head width Br, a
distance
from profile bar 4' to profile bar 4' of P2, a profile bar head width b2, with
the profile
depth being indicated with t2.
As can be seen from this illustration, the screen bars 4 are arranged in the
preferred
example in the treatment zone A with a profile depth t1, and the profile bars
4' are
arranged in the treatment zone B with a profile depth t2. The slot width w is
constant
in each of both treatment zones A, B. The profile depth t1 in the treatment
zone A is
smaller than the profile depth t2 in the treatment zone B, or, in other words,
the
profile depth t, designated there with t1, increases from the treatment zone A
to the
treatment zone B to t2. Furthermore, the diameter of the screening device 1 on
the
stock inlet side (inflow) 2 is greater than on the reject outlet side 3
(reject).
Fig. 2 schematically illustrates a screening device 1 according to Fig. 1 in
conjunction
with an internally running rotor 6 which is equipped with a blade 7. Since the
screening device 1 according to the invention is of conical configuration, the
gap
between the blades 7 and the inner wall of the screening device 1 is smaller
in Fig. 2,
starting from the stock inlet side 2 in the direction of the reject outlet
side 3. As a
consequence, the sorting efficiency can be significantly increased.
Fig. 3 shows an alternative embodiment in which the screening device 1
interacts
with an internally running rotor 6', which is also equipped with blades 7'.
Though the
design is realized here such as to configure the rotor 6' also conical as is
the
screening device 1, but the diameter of the rotor 6' becomes smaller starting
from the
stock inlet side 2 in the direction of the reject outlet side 3. As a result,
the blades 7'
also follow the conical configuration of the screening device 1. The gap
between the
blades 7 of the rotor 6' and the inner wall of the conically configured
screening
device 1 therefore remains approximately constant, starting from the stock
inlet
side 2 to the reject outlet side 3.
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According to Fig. 4, the profile bars 4, 4' are aligned axially to the screen
basket
axis 4 as preferred embodiment of the screening device 1.
In Fig. 5, the profile bars 4, 4', serving as screen bars, are aligned
linearly inclined at
an angle a in relation to the screen basket axis as preferred embodiment of
the
screening device 1.
Finally, as is apparent from Fig. 6, the profile bars 4, 4' are
discontinuously curved
and aligned in relation to the screen basket axis as preferred embodiment of
the
screening device 1.
Of course, the invention is not limited to the details described above, but
numerous
changes and modifications are possible, which the person skilled in the art
will make
if necessary, without departing from the spirit of the invention. In
particular, it is
essential in the invention that the profile bars 4, 4' are arranged such as to
be
assigned to the corresponding treatment zone, so that the profile depth t1, t2
starting
from the stock inlet side 2 to the reject outlet side 3 increases while the
slot widths w
between adjacent profile rods 4, 4' in the screen basket axis direction is
constant,
and the diameter of the screening device 1 on the stock inlet side 2 is
greater than on
the reject outlet side 7, so as to establish a conical configuration of the
screening
device 1 in accordance with the invention is obtained. In this way, the
screening
device 1 can be suited in the through flow direction to the respective
requirements,
circumstances and treatment conditions and can be tailored accordingly in a
targeted
manner.
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6. Screening device according to one of claims 1 to 3, characterized in
that the
screen bars (4, 4') are aligned discontinuously curved in relation to the
screen
basket axis.
7. Screening device according to one of the preceding claims, characterized
in
that the profile bars (4, 4 ') have an essentially triangular, common profile.
8. Screening device according to one of the preceding claims, characterized
in
that the slot width (w) is in a range from 0.05 mm to 0.8 mm, preferably 0.1
to
0.4 mm.
9. Screening device according to one of the preceding claims, characterized
in
that the profile bar width (b1, b2) is in a range from 2.0 mm to 8 mm,
preferably 2.0 mm to 4.0 mm.
Date Recue/Date Received 2020-10-06
