Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR PRODUCING A ROTATIONALLY SYMMETRICAL, IN
PARTICULAR, CYLINDRICAL SCREENING DEVICE
BACKGROUND OF THE INVENTION
I. Field of the Invention
[0002] The invention relates to a method for producing a rotationally
symmetrical, in
particular, cylindrical screening device with a plurality of profile bars. Bar
holders are
provided with cut-outs open at the edge that are shaped to -outs essentially
correspond in
a complementary manner to bases of the profile bars, and the profile bars are
inserted
parallel to one another into the cut-outs open at the edge of the bar holders.
The bar
holders are subsequently formed into rings having an interior circumference on
which the
cut-outs are located. As a result of forming the rings, the cut-outs narrow
and clamp the
profile bars.
2. Discussion of Background Information
[0003] A known example for the use of screening devices that can be
produced
according to the method of this type is the screening of fibrous suspensions,
as carried out
in pressurized screens of the paper-producing industry. The fibers contained
in the
suspension are thereby to pass through the screen, whereas the undesirable
solid
components are rejected at the gap and guided out of the screening device
again. Since
the openings have an essentially oblong shape, i.e., are slots or gaps,
fibrous particles are
let through more easily than the cubic ones, even if both types should be
present in a
similar magnitude. A very good elimination effect of non-fibrous contaminants
from
fibrous suspensions is thus rendered possible with a screening technology of
this type. A
use for separating different fiber components, the so-called fiber
fractionation, is also
conceivable. A high precision of the slot shape over the entire screen surface
is,
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however, a prerequisite. With high demands, cylindrical screening devices, so-
called
screen baskets, are generally used.
[0004] DE 39 27 748 Al shows a possible method for producing screen baskets of
this
type, in which method the profile bars are clamped by plastic deformation of
the support
rings provided with recesses for the bars. Profile bars particularly suitable
for production
methods of this type are used for this. By this method, it was possible to
make
production considerably cheaper. The method is used with screen baskets where
the bars
are inserted on the interior edge of the support rings. A bar arrangement of
this type is
chosen if the suspension is to pass through the slots from the inside outward
(centrifugal
mode of operation). For the centripetal mode of operation, i.e., with a
suspension flow
from the outside inward, e.g., screening devices according to DE 44 35 538 Al
can be
used.
[0005] Screening devices produced by the use of the method according to the
invention
are preferably used in pressurized screens of the paper-producing industry. It
is thereby
important that the dimensions of the screen openings are maintained with very
low
tolerances. In order to keep them unclogged, scrapers are generally necessary,
which are
moved past the screen surface at a narrow distance and which generate
hydraulic
impulses.
Screening devices for use in pressurized screens must therefore be
manufactured very precisely and must withstand high stresses.
SUMMARY OF THE INVENTION
[0006] The invention provides a method with which screening devices can be
produced
in an even more favorable economical manner. It is also to be usable for
different sizes
of screening devices without any great expenditure. The screening devices
produced are
to be of high precision and strength, so that they can be used in pressurized
screens.
[0007]
According to the invention, the bending forces required for forming are
transferred at at least two locations on the sides of the bar holders that are
not provided
with cut-outs and that the bar holders are connected to one another at their
two abutting
ends after the forming into complete rings.
[0008] By the method according to the invention, it is rendered possible to
carry out in
particular the process of forming in a precise and relatively simple manner.
The bending
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forces required for forming are applied on the circumference of the bar
holders. In this
stage of the production process, i.e., before the final forming into a closed
cylinder is to
be carried out, the as yet unfinished screening device is composed of a bent
part, the
radius of curvature of which is still larger than the radius of curvature of
the finished
screening device. The bar holders are thus still open at their respective
ends, which will
be formed into butt joints. The ends mentioned are brought into contact with
each other
to form the butt joints by the final forming process, or at least brought
close enough for a
fixing to be possible, e.g., by welding. The shape of the formed component is
determined
by the bending forces and/or bending moments introduced on the circumference.
The
counterforce customarily hitherto applied with the aid of a mating shape,
e.g., a so-called
bending mandrel, acting within the component can be omitted. As is known, a
mating
shape of this type has a surface that is complementary to the desired shape of
the
component to be bent. Overall, the bending machine, which is a large,
expensive
apparatus, is simplified considerably. Furthermore, the bending machine can
easily be
reset to screening devices of different diameters, since as a rule only the
control program
needs to be changed.
[0009] The present invention is directed to a method for producing a
rotationally
symmetrical screening device with a plurality of profile bars. The method
includes
inserting profile bars parallel to each other into cut-outs open on an
interior
circumference edge of bar holders and forming the bar holders into rings,
thereby
narrowing the cut-outs and clamping the profile bars. The forming of rings
includes
transferring bending forces to at least two locations on sides of the bar
holders not
provided with the cut-outs. The method further includes connecting abuttable
ends of the
bar holders to one another.
[0010] According to a feature of the invention, the rotationally symmetrical
screening
device can be cylindrical.
[0011] In accordance with another feature of the present invention, the
profile bars can
include base portions insertable into the cut-outs, and the cut-outs may be
shaped to
essentially correspond in a complementary manner to the base portions of the
profile
bars.
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[0012] According to the invention, the location for introducing the bending
forces can
essentially extend over an axial extension of the screening device. The
location can be
fixed on the bar holder during forming.
[0013] In accordance with still another feature of the invention, the bending
forces can
act both radially inward and in the circumferential direction.
[0014] Further, during the forming, no forces influencing the forming are
transferred to
the interior circumference surface of the bar holder to be formed into a ring.
[0015] According to another feature, no mating shape is used during the
forming.
[0016] The
method can further include applying the bending forces during the
connecting of the abuttable ends of the bar holders. Further, complete rings
can be
formed by the connecting of the abuttable ends of the bar holders.
[0017] The method may also include clamping the bar holders during the forming
in
bending devices applying the bending forces.
[0018]
According to still another feature, the bending forces can be introduced at a
maximum of four locations, and four bending devices can be used to introduce
the
bending forces at the maximum of four locations. Further, respectively two
bending
devices may form a bending group which, in interaction, transfers a bending
moment to
the bar holders.
[0019] In accordance with another feature of the invention, the bending forces
can be
introduced at six locations, and four bending devices and two backing rolls
may be
arranged to introduce the bending forces at the six locations. Moreover,
respectively two
bending devices and one backing roll can form a bending group which, in
interaction,
transfers a bending moment to the bar holders.
[0020] According to still another feature of the instant invention, the
abuttable ends of
the bar holders may be connected to one another by welding.
[0021] In
accordance with another feature, the forming and the connecting of the
abuttable ends of the bar holders can be carried out with a same machine.
[0022] According to a further feature of the invention, the bar holders can be
assembled
from segments before the forming.
[0023] Further,
the profile bars can be inserted into a bar holder having an open
cylinder shape in which the abuttable ends are spaced from each other.
Moreover, the
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forming can include forming a butt joint comprising the abuttable ends. The
method can
also include welding the butt joint.
[0024] In accordance with still yet another feature of the present
invention, a screen
basket for a pressurized screen usable in the paper-producing industry, is
produced by the
above-noted method.
[0024a] In accordance with a further aspect of the present invention, there
is provided
a method for producing a rotationally symmetrical screening device with a
plurality of
profile bars, comprising: inserting profile bars parallel to each other into
cut-outs open on
an interior circumference edge of bar holders; forming the bar holders into
rings, thereby
narrowing the cut-outs and clamping the profile bars, wherein the forming of
rings includes
transferring bending forces to at least two locations on sides of the bar
holders not provided
with the cut-outs; and connecting abuttable ends of the bar holders to one
another.
[0025] Other exemplary embodiments and advantages of the present invention
may
be ascertained by reviewing the present disclosure and the accompanying
drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The present invention is further described in the detailed
description which
follows, in reference to the noted plurality of drawings by way of non-
limiting examples
of exemplary embodiments of the present invention, in which like reference
numerals
represent similar parts throughout the several views of the drawings, and
wherein:
[0027] Figure 1 illustrates a principle of forming according to the method
of the
present invention;
[0028] Figure 2 diagrammatically illustrates the forming;
[0029] Figure 3 illustrates a perspective view of a finished screen basket;
[0030] Figure 4 illustrates a part of a slotted screen produced according
to the
invention;
[0031] Figure 5 illustrates a part of a drilled screen produced according
to the
invention; and
[0032] Figure 6 diagrammatically illustrates a bending machine for carrying
out the
method according to the invention.
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DETAILED DESCRIPTION OF THE PRESENT INVENTION
100331 The particulars shown herein are by way of example and
for purposes of
illustrative discussion of the embodiments of the present invention only and
are presented
in the cause of providing what is believed to be the most useful and readily
understood
description of the principles and conceptual aspects of the present invention.
In this
regard, no attempt is made to show structural details of the present invention
in more
detail than is necessary for the fundamental understanding of the present
invention, the
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description taken with the drawings making apparent to those skilled in the
art how the
several forms of the present invention may be embodied in practice.
[0034] Figures la and lb show the principle of deformation in two sketches.
Figure la
indicates a bar holder 1 in a state in which the forming (into a ring or
cylinder) according
to the invention has not yet been completed, thus the disconnected abuttable
ends 6 and 7
are still distant from one another. This means a radius of curvature of bar
holder 1 (as an
open cylinder) is larger than the circle 5 (shown in dashed line), which
corresponds to a
radius of curvature for the finished cylinder. The bending forces are
transferred to bar
holder 1 at locations 8 and 9. Forces directed radially inward, forces in the
circumferential direction or bending moments can be applied individually or in
combination as bending forces ¨ as indicated by vectors in the exemplary
illustration.
The bending devices used in the technical implementation of the method are to
be moved
during the forming such that abuttable ends 6 and 7 come closer or come into
(abutting)
contact with each other to form a butt joint. This process is illustrated in
Figure lb.
After this forming is finished and the bending forces are removed, the
screening device
has a cylindrical shape, the projection of which is the circle 5.
[0035] As shown in somewhat more detail in Figure 2, the bar holder 1 can
be
composed of several (e.g., three as illustrated in the exemplary embodiment)
segments
21, 22, and 23, which have already been connected to one another, e.g.,
welded, in a
previously performed process step. Some of profile bars 2 are also shown drawn
in this
representation, which have been inserted on the interior circumference of bar
holder 1.
With respect to this representation, it is to be noted that a screening device
must be
provided with at least two bar holders 1 (and usually more than two) but only
a single bar
holder is visible here as this illustration depicts a top view. In order to be
able to transfer
forces as well as, if required, bending moments to bar holders 1 in a
technical
embodiment of the method according to the invention, four bending devices 10,
11, 12,
and 13 are used according to Figure 2, i.e., the bending forces are
transferred to bar
holders 1 at four locations. Bending devices 10, 11, 12, and 13 can
advantageously be
equipped such that a projecting part of bar holder 1 is clamped during the
bending
process. Respectively, two bending devices, e.g., 10 and 11, or 12 and 13, can
thereby
interact such that they jointly produce a bending moment. As already
mentioned, it is
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advantageous to move the bending devices during forming such that bar holders
1 come
together at their ends 6 and 7 to form a butt joint. In other cases, they can
rotate slowly
and thus bring the ends 6 and 7 together in a butt joint. It is advantageous
to design the
abuttable ends 6 and 7 such that the required dimensioning of the screening
device is
ensured in particular when these abuttable ends come into contact with each
other a butt
joint is formed. A very precise manufacturing is thus possible.
[0036] It can be expedient to provide one or more nip rolls 14 on the interior
contour to
support the clamping of bar holders 1 in the bending devices and/or form a
counter hold
for bending devices 12 and/or 13. They are usually not designed to apply
bending forces
for forming the bar holders 1.
[0037] The subsequent process step, in which a fixed connection of the
abuttable ends 6
and 7 is produced, e.g., by welding, is not shown in this representation.
Advantageously,
the bending forces are only withdrawn after the connection has been made at
the butt
joints.
[0038] A finished screen basket produced according to the invention is
shown
diagrammatically and in perspective in Figure 3. It is shown that four bar
holders 1 are
used in this case, on the interior circumference of which bar holders profile
bars 2 are
clamped (only a few are drawn). Profile bars 2 are thereby aligned in an
axially parallel
manner.
[0039] As shown in Figure 4, profile bars 2 are inserted into cut-outs 4 of
bar holders 1
with their bar bases 3. They can be arranged such that a slot-shaped screen
opening 20 is
respectively located between them. In practice, slots of this type often have
a width
between 0.08 and 2 mm. Screen baskets of this type are known, e.g., from EP 0
417 408.
But it is also possible to produce drilled screen baskets with the aid of the
method
according to the invention. Figure 5 shows an example of this, in which figure
drilled
strips 15 are located between profile bars 2', which strips are provided with
cylindrical
and/or conic screen openings 16 (or combinations of both). A screening device
of this
type is described, e.g., in DE 196 35 189. With respect to Figures 4 and 5 it
is to be noted
as well that the curvature of bar holders 1 or 1' is not visible in these
partial
representations.
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10040] In a roughly diagrammatic manner, Figure 6 shows a bending machine
17
suitable for carrying out the method. The operating principle and the
situation in the
course of production corresponds approximately to what is represented in
Figure 2.
Bending machine 17 according to Figure 6 thus also has four bending devices
10, 11, 12,
and 13, which can also be referred to as bending towers with a perpendicular
arrangement
of the machine. They can be constructed such that it is possible to
intermittently clamp
the projections of bar holders 1. Bending machine 17 has a frame 18 with
support
elements 19 (merely roughly indicated) for the components to be bent.
Advantageously,
the bending devices 10, 11, 12, and 13 are laterally moveable in this frame,
so that the
method according to the invention can be carried out in the manner already
described.
Expediently, the bending devices 10, 11, 12, and 13 have a height that renders
it possible
to introduce the bending forces over the entire axial extension A of the
finished screening
device.
[0041] It is noted that the foregoing examples have been provided merely
for the
purpose of explanation and are in no way to be construed as limiting of the
present
invention. While the present invention has been described with reference to an
exemplary embodiment, it is understood that the words which have been used
herein are
words of description and illustration, rather than words of limitation.
Changes may be
made, within the purview of the appended claims, as presently stated and as
amended,
without departing from the scope and spirit of the present invention in its
aspects.
Although the present invention has been described herein with reference to
particular
means, materials and embodiments, the present invention is not intended to be
limited to
the particulars disclosed herein; rather, the present invention extends to all
functionally
equivalent structures, methods and uses, such as are within the scope of the
appended
claims.
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