Note: Descriptions are shown in the official language in which they were submitted.
CA 02293515 1999-12-10
SCREEN BASKET FOR FIBER SUSPENSIONS
AND METHOD FOR THE PRODUCTION THEREOF
The invention relates to a screen for fiber suspensions
having a shape which is essentially rotationally symmetrical
in relation to a screen axis, with a first circumferential
side of the screen forming an inlet side and the other,
second circumferential side thereof forming an outlet side
of the screen for the fiber suspension, with a series
of profiled bars extending transversely to the
circumferential direction of the screen, the profiled bars
being arranged at equal spacings from one another in the
circumferential direction of the screen and forming slot-
shaped screen openings between them, and with at least two
supporting rings lying in planes extending perpendicularly to
the screen axis and being arranged in spaced relation to one
another in the direction of the screen axis, each of the
supporting rings having in its first edge region facing the
screen inlet side a series of cutouts which are open at their
edge towards the screen inlet side and into which the
profiled bars are inserted in such a way that they project
with part of their cross section in a radial direction over
the first edges of the supporting rings.
Such so-called bar screen baskets are known, in particular,
from EP-B-0 417 408 and DE-A-39 27 748 corresponding thereto,
from EP-A-0 499 154 and DE-A-41 04 615 corresponding thereto,
and from EP-A-0 705 936.
These publications describe various methods for fixing the
profiled bars in the cutouts of the supporting rings, and in
all these bar screen baskets the inner circumference thereof
forms the inlet side for the fiber suspension to be sorted.
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To produce the bar screen basket according to EP-H-0 417 408
the cutouts open at their edge are produced in initially
straight or only slightly bent profiled bar supports which
are later bent to form closed supporting rings. The cutouts
open at their edge have such a shape that they each form an
undercut at a radial spacing from the first edge of the
profiled bar supports into which the cutouts open, and the
cross-sectional shape of the profiled bars is adapted to the
configuration of the cutouts such that a projection of the
profiled bar cross section engages in this undercut, and the
profiled bars are thus held positively in the cutouts and are
prevented from sliding out of the cutouts transversely to the
longitudinal direction of the profiled bar supports. When the
profiled bar supports are then bent into closed supporting
rings the resulting narrowing of the cutouts causes the
profiled bars to be clamped in the cutouts of the supporting
rings. Bath the profiled bar supports and the supporting
rings of this known bar screen basket which are finally
produced from these have a cross-sectional shape
corresponding to a flat rectangle.
The bar screen basket according to EP-A-0 499 154 or
DE-A-41 04 615 differs from this known bar screen basket only
in that the configuration of the undercuts of the cutouts of
the profiled bar supports and of the projections of the
profiled bars engaging in these undercuts allows the profiled
bars to be introduced transversely to their longitudinal
direction into the open-edged cutouts of the profiled bar
supports, which results in a type of snap closure, by means
of which the profiled bars are prevented from sliding out of
the cutouts of the profiled bar supports again transversely
to their longitudinal direction. Therefore, whereas in
the manufacture of the bar screen basket according to
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EP-B-0 417 408 the profiled bars are pushed into the cutouts
of the profiled bar supports in their longitudinal direction,
in the manufacture of the bar screen basket according to EP-
A-0 499 154 the profiled bars are introduced into the cutouts
of the profiled bar supports transversely to the longitudinal
direction of the profiled bars. In the manufacture of the bar
screen basket according to EP-A-0 499 154, too, the profiled
bar supports are then bent into closed supporting rings and
the profiled bars are thereby clamped in the cutouts.
In the bar screen basket according to EP-A-0 705 936, the
profiled bars have a T-shaped cross section and the open-
edged cutouts of the supporting rings have the shape of a
rectangular slot into which there is inserted in the radial
direction from the inside the rib of a profiled bar forming
the foot of the T-shaped cross section. Clamping rings are
then placed around the supporting rings so as to compress the
supporting rings and thereby decrease the diameter in the
radial direction, in order to clamp the aforementioned ribs
of the profiled bars in the supporting ring cutouts.
Screen baskets with quite.a different diameter are used in
so-called sorters for fiber suspensions for the production of
paper, cardboard and the like, but for cost reasons one
endeavors to always use profiled bars which have identical
cross-sectional shapes and cross-sectional dimensions. In the
bar screen baskets according to EP-B-0 417 408 and EP-A-0 499
154, the size of the clamping forces by means of which the
profiled bars are held firmly in the supporting rings does,
however, depend to quite a considerable degree upon the
diameter of the supporting rings into which the profiled bar
supports are formed after insertion of the profiled bars
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into the open-edged cutouts of the profiled bar supports,
unless one were to vary the configuration or dimensions of
the cutouts to be produced in the profiled bar supports in
dependence upon the diameter of the bar screen basket to be
produced, a measure which naturally results in an increase in
the manufacturing costs - cutouts designed independently of
the screen basket diameter result in clamping forces which
decrease progressively as the screen basket diameter
increases. Furthermore, in the manufacture of the bar screen
baskets known from EP-8-0 417 408 and EP-A-0 499 154, the
profiled bars may shift in the longitudinal direction of the
bars relative to the profiled bar supports, which may cause
an obstruction during the bending of the profiled bar
supports into closed supporting rings - it is only by this
bending operation that the profiled bars are clamped in the
cutouts, and, of course, in a finished bar screen basket the
one or other ends of all profiled bars must lie in the same
plane extending perpendicularly to the screen axis.
The fixing of the profiled bars in the supporting rings
disclosed in EP-A-0 705 936 is presumably problematic not
only because the attachment and closure of the clamping rings
pressing the supporting rings radially inwardly appears
difficult if sufficiently high clamping forces are to be
generated, but, in addition, this known bar screen basket
also necessitates manufacture and attachment of the clamping
rings.
The object underlying the invention was to produce a bar
screen basket and a method for its production which not only
enable relatively simple fixing of the profiled bars in an
accurate and lasting manner on the supporting rings but also
open up the possibility of manufacturing screen baskets with
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quite a different diameter using profiled bars with one and
the same cross section and profiled bar supports with one and
the same cutout shape.
To achieve this object one departs from a screen for fiber
suspensions having a shape which is essentially rotationally
symmetrical in relation to a screen axis with a first
circumferential side of the screen forming an inlet side and
the other, second circumferential side thereof forming an
outlet side of the screen for the fiber suspension, with a
series of profiled bars which extend transversely to the
circumferential direction of the screen, are arranged at
equal spacings from one another in the circumferential
direction of the screen and form slot-shaped screen openings
between them, the cross sections of the profiled bars each
having an elongate shape with a first end region facing away
from the screen outlet side and a second end region facing
away from the screen inlet side, and with at least two
supporting rings made of a plastically deformable material,
lying in planes extending perpendicularly to the screen axis
and being arranged in spaced relation to one another in the
direction of the screen axis, each of the supporting rings
having in its first edge region facing the screen inlet side
a series of cutouts open at their edge towards the screen .
inlet side, the shape of the cutouts - viewed in the
direction of the screen axis - corresponding to the
configuration of the second cross-sectional end regions of
the profiled bars lying in the cutouts and forming at a
radial spacing from the first edge of the supporting ring
facing the screen inlet side an undercut in which a
projection of the profiled bar cross section engages so that
the profiled bars are held positively in a radial direction
in relation to the screen axis and in the circumferential
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direction of the screen with their second cross-sectional end
regions in the supporting ring cutouts, the profiled bars
projecting in a radial direction over the first edges of the
supporting rings, and being clamped with their second cross-
sectional end regions in the supporting ring cutouts as a
result of a plastic deformation of the supporting rings.
Such a screen is designed in accordance with the invention
such that the supporting rings have on the side of the
profiled bars facing the screen outlet side such plastically
deformed regions that as a result of a displacement of
supporting ring material in the direction towards the screen
inlet side, the profiled bar projections are pressed in this
direction against the undercuts.
Accordingly, when manufacturing an inventive screen basket,
on the side of each profiled bar facing the screen outlet
side, supporting ring material is displaced in the direction
towards the adjacent profiled bar, more specifically, such
that this profiled bar is thereby displaced somewhat by the
displaced supporting ring material and/or by a displacement
of that edge region of the cutout holding this profiled bar
which faces the screen outlet side relative to the supporting
ring in the direction towards the screen inlet side and is.
thereby pressed with its projection in this direction against
the undercut formed by the supporting ring cutout and is thus
also fixed precisely and lastingly in the radial direction of
the screen basket. At the same time, the profiled bars
previously pushed in their longitudinal direction into the
cutouts are also fixed in the longitudinal direction of the
bars.
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As the inventive way of attaching the profiled bars on the
supporting rings or on the profiled bar supports does not
presuppose any definite design of the regions of the profiled
bars projecting inwardly or outwardly in a radial direction
in relation to the screen axis over the supporting rings,
these regions can, in accordance with the invention, also be
designed in a novel and particularly advantageous way:
In the known so-called bar screen baskets - on viewing a
certain screen basket - all profiled bars are of identical
design, and each profiled bar has the same cross section
throughout its entire length. In contrast to this known
design of the profiled bars, it is now proposed, in
accordance with the invention, that profiled bars arranged
one behind the other in the circumferential direction of the
screen be designed differently at their first longitudinal
sides facing away from the screen outlet side such that the
profiled bars impart to a fiber suspension flowing in the
circumferential direction of the screen at the screen inlet
side an axial flow component oriented in the direction of the
screen axis or increase such an axial flow component. For
this purpose, the profiled bars could be provided at their
aforementioned first longitudinal sides, for example, with
grooves or ribs which form an acute angle with the
circumferential direction of the screen and thus form
conveying or deflecting surfaces disposed at an incline at
the inlet side of the bar screen basket for the fiber
suspension to be sorted circulating there.
When mention is made hereinabove of profiled bars arranged
one behind the other in the circumferential direction of the
screen, this is not to be interpreted so narrowly that all
profiled bars or profiled bars following one another directly
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in the circumfea:ential direction of the screen must be
designed in accordance with the invention at their first
longitudinal si<ies, although, such configurations are
preferred. The profiled bars do also not have to be designed
in accordance with the invention over the entire length of
the profiled bars at their first longitudinal sides, as it
may, under certain circumstances, be sufficient to provide
only in an axial section of the screen means which allow an
axial flow component to accur or which increase such a
flow component - the advantage achievable thereby will be
explained hereinbelow.
Profiled bars to be used in accordance with the invention can
be produced relatively simply when the profiled bars project
at their first longitudinal sides section-wise to a varying
extent over they first supporting ring edges. Profiled bars of
such configuration can be produced, for example, from
extruded profi.l.ed bars with the same cross section throughout
by machining, such as milling, being carried out section-
wise. If the profiled ba:r sections pro~eoting to a varying
extent over thE: supporting rings are then arranged on the bar
screen basket :Ln the fashion of a helical pattern, they
impart to a fiber suspensian flowing in the circumferential
direction of the screen at the screen inlet side not only an
axial flow component oriented in the direction of the screen
axis or cause .an increase in such an axial flow component,
but the profiled bar sections projecting over the supporting
rings to a varying extent also bring about a loosening-up of
the so-called rejected material, whereby the risk of damage
to sorters aontai.ning bar screen baskets is reduced:- ~n
sorters for fiber suspensians, the inside circumference of
the bar screen. basket usually forms its inlet side, and
inside the screen basket there rotates around the axis
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thereof a rotor which is provided with blades which move past
the inlet side of the screen at a short distance therefrom,
extend either parallel to the screen axis or form a small
acute angle with the direction thereof and serve to generate
positive and negative pressure pulses in the fiber suspension
to be sorted at the inlet side of the screen. Fibers, fiber
agglomerations and impurities contained in the fiber
suspension to be sorted which do not pass through the screen
openings of the screen basket (i.e. the so-called rejected
material) have the tendency to collect at those flanks of the
rotor blades which are located at the front in the direction
of rotation, and such agglomerations of rejected material can
result in breakage of the screen basket if they become
"wedged" between a rotating rotor blade and the screen
basket. In so-called pressure sorters into which the fiber to
be sorted flows under pressure and in which the screen basket
is acted upon at one axial end thereof with the fiber
suspension to be sorted, while that part of the fiber
suspension to be sorted which does not pass through the
screen openings leaves the screen basket at its other axial
end, the fiber suspension flowing along essentially in the
circumferential direction of the screen under the influence
of the rotor at the inlet side of the screen basket always
also has an axial flow component oriented in the direction.of
the screen axis, namely on account of the above-described
flow of the fiber suspension to be sorted into the screen
basket, and due to the fact that the rejected material leaves
the screen basket at its other end. Consequently, the above-
described rejected material agglomerations travel along the
rotor blades and increase more and more unless the rotor is
not provided with continuous blades over its entire axial
length, but - as known per se - has blade sections between
which there are gaps and which are often also offset in
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relation to one another in the circumferential direction of
the rotor. Similarly to these gaps between the blade sections
of a rotor, the profiled bar sections arranged in accordance
with the invention and projecting over the first supporting
ring edges also result in a loosening-up of rejected material
agglomerations and thus reduce the risk of damage to the bar
screen basket.
The invention also relates to a method for the manufacture of
a screen for fiber suspensions having a shape which is
essentially rotationally symmetrical in relation to a screen
axis, with a first circumferential side of the screen forming
an inlet side and the other, second circumferential side
thereof forming an outlet side of the screen for the fiber
suspension, with a series of profiled bars extending
transversely to the circumferential direction of the screen,
the profiled bars being arranged at equal spacings from one
another in the circumferential direction of the screen and
forming slot-shaped screen openings between them, and the
cross sections of the profiled bars each having an elongate
shape with a first end region facing away from the screen
outlet side and a second end region facing away from the
screen inlet side, and with at least two ring-shaped profiled
bar supports made of plastically deformable material lying.in
planes extending perpendicularly to the screen axis and
arranged in spaced relation to one another in the direction
of the screen axis, each of the profiled bar supports having
in its first edge region facing the screen inlet side a
series of cutouts open at their edge towards the screen inlet
side, the shape of the cutouts - viewed in the direction of
the screen axis - corresponding to the configuration of the
second cross-sectional end regions of the profiled bars lying
in the cutouts, and forming at a radial spacing from the
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first edge of the profiled bar support facing the screen
inlet side an undercut in which a projection of the profiled
bar cross section engages so that the profiled bars are held
positively in a radial direction in relation to the screen
axis and in the circumferential direction of the screen with
their second cross-sectional end regions in the cutouts of
the profiled bar supports and project with their first cross-
sectional end regions in a radial direction over the first
edges of the profiled bar supports, wherein the profiled bar
supports are first provided with cutouts which are somewhat
larger than the second cross-sectional end regions of the
profiled bars and the profiled bars are then inserted into
the profiled bar support cutouts and clamped by a plastic
deformation of the profiled bar supports in their cutouts.
Such a process is configured in accordance with the invention
such that the profiled bar supports are plastically deformed
on the side of the profiled bars facing away from their first
edges such that as a result of a displacement of profiled bar
support material in the direction towards the first profiled
bar support edges, the profiled bar projections are pressed
in this direction against the undercuts.
When hereinabove mention is made of the fact that the
profiled bar supports are first provided with cutouts which
are somewhat larger than the second cross-sectional end
regions of the profiled bars, this statement is not to be
understood in the sense that the profiled bar support cutouts
first have to be somewhat larger in each direction than the
second cross-sectional end regions of the profiled bars as
the inventive solution to the set object only makes it
necessary to displace profiled bar support material in the
direction towards the first profiled bar support edges in
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order to press the profiled bar projections in this direction
against the undercuts formed by the profiled bar support
cutouts.
As will be apparent from the aforesaid, in the manufacturing
method according to the invention one can start with straight
or only slightly bent profiled bar supports in whose cutouts
the profiled bars are clamped by displacement of profiled bar
support material, whereupon the profiled bar supports are
bent to form closed rings. It is, however, equally possible
to reshape the profiled bar. supports with or without profiled
bars into closed supporting rings and to only then fix the
profiled bars inserted in the supporting ring cutouts by
displacement of profiled bar support or supporting ring
material in the cutouts. If the profiled bars are already
fixed on the profiled bar supports which have not yet been
reshaped into supporting rings, the advantage is gained over
the prior art according to EP-B-0 417 408 and EP-A-0 499 154
that already before the bending of the profiled bar supports
into closed supporting rings, a firm grid is obtained whose
profiled bars can no longer shift relative to the profiled
bar supports, more particularly, also not while the profiled
bar supports are being reshaped into closed supporting rings.
The displacement of profiled bar support or supporting ring
material to be carried out in accordance with the invention
could, for example, be brought about by deforming by means
of rolling the edge region of a profiled bar support or
supporting ring facing away from the cutout openings and
initially having a rectangular cross section between two
pressure rolls with axes tilted in relation to one another
and in relation to the plane of the supporting ring or
profiled bar support such that the deformation brings about
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a displacement of material in the direction towards the
profiled bars. Alternatively, one could coin, for example,
using a coining die, in the immediate vicinity of each
profiled bar on one or both sides of the supporting ring or
profiled bar support in the latter a discrete recess for each
profiled bar. However, embodiments are preferred wherein the
deformed supporting ring or profiled bar support regions
comprise pressed-in grooves which extend along the entire
series of screen bars, in particular, in the immediate
vicinity of the profiled bars.
In general, the supporting rings will consist of a suitable
metal or a suitable metal alloy. It is, however, in
principle, also possible to use instead a plastic material
sufficiently resistant to wear, which - possibly by heating -
can undergo sufficient plastic deformation, yet does not tend
to creep, thus resulting in a reduction in the clamping
forces fixing the profiled bars in the supporting rings in
the course of time.
After the profiled bar supports have been bent into rings,
the latter are closed by the ends of the profiled bar
supports being welded to each other. This results in inherent
tensions in the supporting rings which, above all, in sorters
in which positive and negative pressure pulses are generated
in the fiber suspension with the aid of a rotor near the
screen basket, may lead to permanent breakages in the
supporting rings. To avoid this risk it is proposed, in
accordance with the invention, that the welded supporting
rings be made to undergo a heat treatment at least in the
region of their weld joints in order to reduce or completely
eliminate the inherent tensions caused by the welding. If the
heat treatment is carried out before the fixing of the
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profiled bars in the cutouts of the supporting rings, it is
also not necessary to limit the heat treatment narrowly to
the actual weld joint in order to prevent the clamping forces
fixing the profiled bars in the supporting rings from being
reduced by the heat treatment.
Metallic profiled bars are preferred, although, in principle,
profiled bars made of another material are also conceivable,
e.g. made of a sufficiently hard plastic sufficiently
resistant to bending stress or of a ceramic material. It is
also recommended to use for the profiled bars a material
whose stability is greater than the stability of the material
used for the supporting rings or the profiled bar supports in
order that during the deforming of the profiled bars or
supporting rings and the resulting pressing of the edges of
the supporting ring or profiled bar support cutouts against
the profiled bars, notches will be prevented from occurring
in the profiled bars, which with the alternating compression
stress on the screen in a sorter with a rotor rotating at the
screen inlet side or screen outlet side, could lead to
permanent breakages on the profiled bars.
Further features of particularly preferred embodiments of the
inventive screen and the inventive manufacturing method will
be apparent from the attached claims and/or the following
description and the appended drawings of two particularly
advantageous embodiments of the inventive screen and the
manufacture thereof. The drawings show:
Figure 1 a perspective and mainly schematic
illustration of the first embodiment of the
inventive bar screen basket showing only a
few profiled bars;
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Figure 2 a plan view of the bar screen basket shown in
Figure 1, in which, again, only a few
profiled bars were drawn;
Figure 3 a plan view of a relatively short section of
a still stretched or straight profiled bar
support with three profiled bars shown in
cross section, which have already been pushed
into cutouts in the profiled bar support, but
have not yet been fixed thereon, i.e., prior
to the inventive plastic deformation of the
profiled bar support;
Figure 4 an illustration corresponding to Figure 3,
but after the inventive plastic deformation
of the profiled bar support for the purpose
of displacement of profiled bar support
material in the direction towards the
profiled bars;
Figure 5 a section taken on line 5-5 in Figure 4;
Figure 6 an illustration corresponding to Figure 5,
but including two rolling tools for the
invention plastic deformation of the profiled
bar support;
Figure 7 an illustration of the second embodiment
corresponding to Figure 4;
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Figure 8 part of an unwinding of the second embodiment
of the inventive bar screen basket, more
specifically, in a view of its inlet side
seen in the direction of arrow X from Figure
7; and
Figure 9 a side view of the region of a profiled bar
of the second embodiment projecting over the
supporting rings, seen in the direction of
arrow R from Figure 7, but wherein only part
of the length of this profiled bar is shown.
It is first pointed out, in addition, that Figure 5 could
also represent a section corresponding to line 5-5 in Figure
2, and Figure 6, consequently, the rolling tools acting upon
the already closed supporting ring.
Figures 1 and 2 show that the bar screen basket consists of
three supporting rings 10, 12 and 14 and of a plurality of
profiled bars 16, with the latter extending parallel to a
screen axis 18 and the supporting rings lying in planes
perpendicular to the screen axis. As will be apparent from
the following, in the illustrated screen basket the profiled
bars 16 are designed and arranged such that the inlet side 20
for the fiber suspension to be sorted is located at the inner
circumference of the screen basket, the outlet side 22 for
the fiber suspension which has passed through the screen
basket at the outer circumference thereof. Each of the, in
particular, identically designed supporting rings 10, 12 and
14 has a cross section in the form of a flat rectangle and
possesses an upper flat side 24, a lower flat side 26, an
outer edge 28 and an inner edge 30.
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Figure 3 shows a short section of a still straight profiled
bar support 10' which is later to be bent into the closed
supporting ring 10. The first edge of the profiled bar
support 10' corresponding to the inner edge 30 of the
supporting ring 10 was designated 30', the second edge of the
profiled bar support 10' corresponding to the outer edge 28
of the supporting ring 10 was designated 28', and the upper
flat side of the profiled bar support visible in Figure 3 was
designated 24'. For each profiled bar 16, the profiled bar
support 10' has a cutout 34 into which a profiled bar 16 can
be pushed in the direction of the longitudinal extent of the
profiled bar. All cutouts 34 are to have the same
configuration and the same dimensions, and the same applies
to the profiled bars 16. The cross section of a profiled bar
is approximately mushroom-shaped with a mushroom head forming
a first cross-sectional end region 16A and an approximately
club-shaped mushroom foot forming a second cross-sectional
end region 16B, with the configuration of the second cross-
sectional end region 16H corresponding to the configuration
of the cutout 34 if one disregards a relatively small play of
the profiled bar 16 in the cutout 34 recognizable in Figure
3.
The shape of the cutout 34 whose flanks extend
perpendicularly to the upper and lower flat sides of the
profiled bar support 10' is designed such that the cutout 34
has a constriction 34A. Between the latter and the end of the
cutout 34 facing the second edge 28' of the profiled bar
support 10' the cutout 34 forms an undercut 34B in the region
of which the edge of the cutout 34 has an approximately
straight flank 34C which forms with a plane designated 40 in
Figure 3 and extending perpendicularly to the drawing plane
of Figure 3 an acute angle a which opens in the direction
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towards the second edge 28' of the profiled bar support 10'.
After the profiled bar support 10' has been reshaped into the
closed supporting ring 10, the plane 40 forms a diameter
plane of the bar screen :gasket .
The second cross-sectional end region 16B of the profiled
bars 16 forms a projection 16C which engages the undercut 34B
of the associated cutout 34 and so even prior to the
inventive deformation of the profiled bar support 10',
the profiled bar 16 cannot be pulled upwards out of the
cutout 34 in accordance with Figure 3. As Figure 3 also
shows, the outer circumference of each profiled bar 16
already lies in the region of the second cross-sectional end
region 16B of the profiled bar prior to the inventive
deformation of the profiled bar support 10' overall at least
almost free of play against the edge of the associated cutout
34 with the exception of a relatively narrow gap between the
flank 34C of the cutout 34 and the projection 16C of the
profiled bar. This gap is closed by the inventive deformation
of the profiled bar support 10' in the following way:
An upper pressure roll 60 is pressed from above and a lower
pressure roll 62 from below (see Figure 6) against the
profiled bar support 10' (in the given case, against the
supporting ring 10). The pressure rolls are freely rotatable
about axes 60' and 62', respectively, parallel to one another
and to the flat sides of the profiled bar support 10' or the
supporting ring 10. (The axes 60', 62' also extend
perpendicularly to the longitudinal direction of the profiled
bar support 10' and radially to the screen axis 18). Hy
controlling the pressure with which they are pressed in
accordance with Figure 6 in the vertical direction against
the profiled bar support 10' or the supporting ring 10, the
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pressure rolls 60 and 62 are guided past all of the profiled
bars 16 along the profiled bar support 10' or around the
supporting ring 10 and thus produce with their displacement
ribs 60A and 62A, respectively, recognizable in Figure 6, at
the upper and lower flat sides of the profiled bar support
10' or the supporting ring 10 (the same naturally applies
accordingly to the supporting ring 12 and the supporting ring
14) in the immediate vicinity of the profiled bars 16 a
channel 70A and 70B, respectively, and owing to the inventive
configuration of the profile of the displacement rib 60A and
62A, respectively, recognizable in Figure 6, a bead 72A and
72B, respectively, cast up against the profiled bars 16 so
that owing to this displacement of material, the profiled
bars 16 are displaced upwards to a slight extent in
accordance with Figure 3 (including the lower edge area of
each of the cutouts 34 in accordance with Figure 3), and, in
this way, as will be apparent from Figure 4, the previously
present gap between the flank 34C of the cutouts 34 and the
projection 16C of the profiled bars 16 is closed with the
result that the profiled bars are clamped in the cutouts. The
angle a recognizable in Figure 3 is expediently of such
dimensions that after the inventive deformation self-locking
occurs between the flank 34C and the flank of the projection
16C pressed against the latter.
If one assumes that Figure 4 represents a section taken from
Figure 2 and does not show the profiled bar support 10', but
already the upper supporting ring, one recognizes that also
after reshaping of the profiled bar supports into closed
supporting rings, the profiled bars 16 form between them
slot-shaped screen openings 80 which extend parallel to the
screen axis 18 and are open between the supporting rings 10,
12 and 12, 14, i.e., the inlet side 20 communicates via the
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screen openings 80 with the outlet side 22 of the screen
basket.
In the first cross-sectional end regions 16A, the profiled
bars 16 are provided at the screen inlet side 20 with
inclined flanks 82 and 84 and with rear flanks 86 and 88. The
inclined flanks 82 and 84 form with the plane 40 recognizable
in Figure 3 acute angles which may be of the same or
different size, and the rear flanks 86 and 88 lie, in
particular, prior to performance of the inventive
deformation, against the first edge 30' of the profiled bar
support 10'.
In sorters in which a rotor rotates in a known way in the
fiber suspension to be sorted adjacent to the inlet side 20
of the screen basket, the first cross-sectional end regions
16A of the profiled bars 16 generate, in particular, with
their inclined flanks 82 and 84 in the fiber suspension to be
sorted microturbulences which counteract the formation of a
considerable fiber fleece at the screen inlet side 20 and a
clogging of the screen openings 80.
As extremely fine screen openings are required for the
processing of fiber suspensions in modern sorters and high
material densities (high fiber component of the fiber
suspensions to be processed) are used, it is also necessary
to generate with the above-mentioned rotor of the sorter high
pressure and suction pulses in the fiber suspension in order
to counteract clogging of the screen openings. These high
pressure and suction pulses result in correspondingly high
forces acting on the profiled bars, and, therefore, these
must permanently have a firm hold in the supporting rings.
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This requirement can be met in a simple way with the present
invention as the profiled bars are firmly clamped in the
cutouts of the supporting rings by the inventive displacement
of material, more particularly, also in the case of large
screen basket diameters and, consequently, correspondingly
small bendings when reshaping the profiled bar supports into
the supporting rings.
The second embodiment shown in Figures 7 to 9 differs from
the first embodiment according to Figures 1 to 6 only in the
design of the first longitudinal sides of the profiled bars
facing away from the screen outlet side, more specifically,
in the design of the first cross-sectional end regions of the
profiled bars with which the latter project over those edges
of the supporting rings which face the screen inlet side.
Therefore, in Figures 7 to 9, as far as possible, the same
reference numerals were used as in Figures 1 to 6, but with
the addition of two primes.
The illustration in Figure 7 is intended to correspond to the
illustration in Figure 4, but with the modification that
Figure 7 does not show a profiled bar support which is still
straight, but the unwinding of a circular ring-shaped
supporting ring which, consequently, was illustrated in
Figure 7 as a straight element.
In the second embodiment, a supporting ring 10 " holds a
series of profiled bars 16I " , 16II " and 16III " , which
project with their first cross-sectional end regions 16IA,
16IIA and 16IIIA over the edge 30 " of the supporting ring
" facing the screen inlet side 20 " (see Figure 7).
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As is apparent i:rom Figures 8 and 9; each of the profiled
bars 16I " , 1617: " and 16:L I I " has in the longitudinal
direction of ths: bar a periodically repeated series of cross-
sectional end reagions 16IA, 16IIA and 16IIIA following one
another in the 7Longitudinal directian of the bar and hence
in the longitud_Lnal direction of the bar a periodically
repeated series of sections with a varying projection
following one another ira the longitudinal direction of the
bar. The profil~ad bars 7..6I' ' , 16II' '' and 16III' ' thus differ
from one anothe:c essentially only in that the series of
profiled bar se~~tions fc>rmed by the cross-sectional end
regions 16IA, 16IIA and 16IIIA are offset in relation to one
another in the :Longitudinal direction of the bar.
Furthermore, in the second embodiment, the screen has several
identical groups of profiled bars following one another in
the circumferential directian of the screen, each of these
groins being formed by three profiled bars, namely a profiled
bar 16I" , a profiled bar 1~6 I 1 " and a profiled bar 16III" ,
which follow one anothev in the above-indicated sequence.
In Figures 7 anal 8, the arrow R was drawn to indicate that
direction in which the :fiber suspension to be sorted flows
along the inlet. side 20 " of the screen, but in a sorter with
a rotor the arrow R also indicates the direction of rotation
of the rotor, i.n particu.~ar, that direction in which blades
or so-called cleaning wings of the rotor pass the inlet side
20 " of the screen. Thus,, i:n the illustrated embodiment, the
first cross-secaional end regions always follow one another
in the sequence~-i6IIIA, :L6IIA and 16IA in the direction R tn
an axial screen section.
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As shown in Figure 7, the first cross-sectional end regions
16IA, 16IIA and 16IIIA prr~ject to a varying extent into the
fiber suspension to be sorted, i.e., they project to a
varying extent over the inner edges 30 " of the supporting
rings. The differences in the projections were designated D1
and Dz in Figure 7, and D1 and Dz can be different in size or
equal in size - Dland DZ values of approximately equal size
being preferred. In particular, in screen baskets for so-
called pressure sorters Dland DZare at the most equal to
1 mm, preferably 0.5 to 0.8 mm, and, in particular,
approximately 0.5 to approximately 0.6 mm. In Figure 8, the
lengths of the cross-sectional end regions 16IA, 16IIA and
16IIIA measured in the direction of the screen axis or in the
longitudinal direction of the profiled bar were designated
L1, L2 and L3. In the illustrated, preferred embodiment L1, Lz
and L3 are of identical size, which means that the cross
sections of the cross-sectional end regions 16IA, 16IIA and
16IIIA are not to change over their axial length, but this
obviously does not necessarily have to be the case. In a
screen of approximately circular-cylindrical configuration,
Ll, LZ, L3 are each preferably approximately 15% to
approximately 30% of the axial length of the screen, in
particular, equal to 1/5 to 1/4 of the screen length. With an
axial screen length of, for example, 800 mm, L1, LZ, L3 thus
each lie in a range of 150 to 200 mm.
As is apparent from Figure 8, the cross-sectional end regions
or profiled bar sections 16IA, 16IIA and 16IIIA which are
of different height or project to a varying extent are
arranged in accordance with the invention in a special
pattern on the inlet side 20 " of the inventive screen such
that a fiber suspension to be sorted flowing past the screen
inlet side in the direction of arrow R in Figure 8 contains
CA 02293515 1999-12-10
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an axial flow component or an increased axial flow component
in the direction of the screen axis, i.e., is deflected
downwards in accordance with Figure 8, as there is adjacent
to a row of profiled bar sections 16IIIA, 16IIA, and 16IA
which follow one another in the direction R and project to an
increasing extent in the direction R, in the downwardly
adjoining axial screen section a row of like profiled bar
sections, but which is offset in relation to the first-
mentioned row opposite to the direction R, more particularly,
by the dimension of the so-called division of the screen,
i.e., by the spacing of the longitudinal center planes of two
adjacent profiled bars measured in the direction R. Such an
offset is preferred although, in principle, also twice as
large an offset is possible.
