Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a screen compris-
ing a screen frame with supporting elements for a screen
deck inserted in the screen frame, and fastening means
for the screen deck.
Many different fastening methods have been used in
the mounting of screens for dynamic screening machines.
According to, for example, DE-OS 2,849,838 published
September 13, 1979 - Hein L~hm~nn AG, a snap-on system
has been used in which the separate screen elements have
been snapped onto enlarged supporting elements. Similar
modes of fastening are utilized in DE-GM 78 38 335 pub-
lished April 5, 1979 - Gummi-Kueper GMBH and Co. KG and
DE-OS 2,749,489 published June 1, 1978 - Binder and Co.
In some cases, fastening has been accomplished by pro
jections on the underside of the screen cloths and ex-
pansion means adapted to urge said projections into
engagement with recesses provided in the supporting
elements of the screen frame. Such constructions are
shown in, for example, U.S. patent specification 4,141,821
issued February 27, 1979 - Steinhaus GMBH and also in
U.S. patent specification 3,745,736 issued July 17, 1973
- A. Fisher et al.
However, the above-mentioned screening machines
with small individually fastenable screen elements are
not often used since they necessitate reconstruction of
existing screening machines. The most commonly used
variant of screening machines makes use instead of screen
cloths oP substantial size, very often 1-2 m2 per unit.
This type of screen cloths are fastened in the
screen frames by providing the screen cloth units with
hooks by which the screen cloth units are clamped between
opposed edges of the screen frame. An example of such a
clamping method is disclosed in DE-OS 2,005,376, published
August 19, 1971 - Gummi-Kueper GMBH and Co. KG.
This fastening method is utilized for the majority
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of all screening machines which at present are manufactured
all over the world, as a result oE which the frame con-
structions of most screening machines are of a similar
kind. As will appear from some of the above-mentioned
publications, it has been tried to divide the screen
deck into smaller units which are readily exchangeable
to facilitate rapid exchange o a worn section and also
to afford an opportunity for rapidly shifting from one
hole size to another within a section of the screen deck.
The disadvantage of known smaller screen elements
is that the frame construction of the screening machines
used on the market must be redesigned or completed be-
fore the readily exchangeable screen element systems
according to, for example, DE-OS 2,754,374 published
June 13, 1979 - Gummi-Kueper GMBH a~d Co. KG can be
utilized.
It is one object of the present invention to pro-
vide a far-reaching simplification of prior art screen
constructions with smaller screen elements and to allow
of a simpler and cheaper mounting on location, without
necessitating any essential alteration of the frame
construction of the screening machine.
According to the present invention, it is re~uired
in a screen comprising a screen frame with supporting
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elements for a screen deck mounted in the screen frame
and fastening means for the screen deck, that the said
screen deck comprises several elongated screen elements
placed adjacent each other and havin~ stiffening ele-
ments which are included in the screen elements and
which, upon mounting in the screen frame, are prestress-
ed against the supporting elements by elastic deforma-
tion.
The invention thus is based on the idea that the
separate screen elements forming said screen deck should
be formed as elongated and rigid plank-like elements
and, upon m~unting, be subjected to an elastic deforma-
tion in order to provide the required holding-down force
against the supporting elements of the screen frame.
Compared with the conventional systems where the
separate screen cloths are provided at their edges with
retention hooks by which the cloths are prestressed,
the present invention makes it much easier to apply
the requisite holding-down force against the supporting
elements of the screen frame. Thus~ if the screen frame
is designed in such a manner that the supporting ele-
ments force the screen elements to curve convexly, the
screening elements can be formed with straight stif-
fening elements. One end of the screen elements is then
secured to the frame, and the screen elements are bent
over the supporting elements to be secured underneath
a hold-down rib at the opposite side of the screen
frame. The force required for bending the screen ele-
ments will be considerably less than a force directedin the plane of the screen elements and applied in order
to stretch the screen elements to such an extent that
the same holding-down force is obtained.
The screening system according to the invention
can be utilized not only for screening machines in which
the screen decks are curved convexly, but also in screen-
ing machines with planar decks~ In such a case, it is
possible, according to a development o~ the invention,
to plastically deform the stiffening elements in a di-
rection opposite to the elastic deformation to which
the stiffening elements are subjected during mounting
of the screen elements in the screening machine. In
the present invention, it is best if the stiffening
elements~ when the screen elements are mounted in the
screen frame, are subjected to an elastic deformation
whose spring-back force resultant is at least as large
as an inertia resultant acting on the screen elements
in the opposite direction, when the screen elements
are used in a dynamic screening machine. If it should
be difficult ko obtain such a strong elastic deforma-
tion, it is possible, according to the present inven-
tion! to increase the holding-down force by utilizing
permanent magnets which preferably are mounted in the
supporting elements of the screen frame and which are
caused to act against magnetic inserts in the screening
cloth. These magnetic inserts may consist of the said
sti~fening elements.
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The present invention therefore provides a screening
system comprising a screen frame with supporting elements
for a screen deck inserted in the screen frame, and fast-
ening means for the screen deck which comprises several
screen elements placed adjacent each other and having
screen stiffening means consisting of stiffening elements
which are included in the screen elements and which are
pre-stressed against the supporting elements by elastic
deformation upon mounting in the screen frame, wherein the
screen elements each have a length to width ratio of at
least 3:1, and wherein the stiffening elements are mounted
in the screen frame with an elastic deformation whose
spring-back force resultant is at least as large as an
inertial force resultant acting on the screen deck in a
direction opposite to the spring-back force resultant when
the screen deck is used in a dynamic screening machine.
In a preferred embodiment the screen elements have a
length to width ratio of at least 4:1, preferably at least
5:1. By this arrangement, the stiffening elements will
lie closer to one another, and thus the total holding-down
force will be greater, without it being necessary, upon
mounting of the individual elements, to exert an inconven-
iently great force on the free ends of the elements when
they are bent down and mounted in the screen frame.
In a still further embodiment the stiffening elements
are mounted in the screen frame with an elastic deformation
whose spring-back force resultant is at least as large as
an inertial force resultant acting on the screen deck in a
direction opposite to the spring-back force resultant when
the screen deck is used in a dynamic screening machine.
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I~ permanent magnets are utilized for providing
or lmproving tne holding-down force, these magnets should
be disposed on the supporting elements of the screen
frame, preferably by being connected therewith via elas-
tlc dampers.
The invention will be described in more detail
in the following, reference being had to the accompa-
nying drawings ln which
Fig. 1 is a perspective view of an example of a
screen element in accordance with the present invention;
Fig. 2 is a perspective view of parts of the screen
frame of a screening machine to illustrate ~he mounting
of the screen elements;
Fig. 3 is a perspective view of another embodiment
o~ a screen element according to the present invention;
Fig. 4 is a longitudinal section oE a part of a
screening machine with screen elements accorairlg to
a further embodiment of the invention;
Fig~ 5 is a section along line V-V in Fig. 4; and
Fig. 6 is a section along line VI-VI in Figl 4;
Fig. 7 is a transverse section through a further
embodiment of the screening system where the screening
deck is divided into two juxtaposed areas.
Fig. 1 shcws a screen element consisting of an
elastomer~ for instance natural or synthetic rubber~
such as polyurethane. The screen element has holes 2
made during the manufacture of the element. Reinforcing
or stiffening elements 3 are insertea along the longi-
tudinal sides of the screen elementO These reinforcing
elements are made of rigid material and may consist
of metallic square tubes~ as illustrated in the draw-
ings. If necessary, the screen elements may also bereinforced with a suitable number of laid-in stiffening
elements 4 extending at right angles to the stiffening
or reinforcing elements 3. The screen element is then
formed for overlap jointing by being provided with a
recess 5 at one long side and an overlap flange 6 at
the other long side.
Fig. 2 shows an example of a screen frame in a
screening machineO The screen frame has side members
7, hold-down ribs 8 and longitudinal supporting elements
9. The side members 7 also are provided with supporting
surfaces 10. In the embodiment illustrated, the support-
ing surfaces 10 and the supporting elements 9 are mount-
ed at different levels, such that the screen elements
1 will curve upwardly over the supporting elements 9.
As will appear from Fig. 2, the screen elements
are mounted by ~lamping their one ends against the sup-
porting surface 10 by means of the hold-down rib 8,
whereupon the elements are pressed down over the sup-
porting elements 9 by being subjected to a force in
the direction of the arrow 11. Finally, the elements
1 are retained in this elastically deformed position
by securing the hold-down rib 8 to the left in Fig. 2.
The present invention thus utilizes the elasticity
or spring ~orce provided by the stiffening elements
3 in order to obtain the requisite holding-down action
against the supporting elements 9 during the subsequent
use of the screening machine. The holding-down action
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can be very large if an appropriate material is select-
ed for the stiffening elements 3. These elements may
consist of, for example, metallic material which is
rigid and can be subjected to heavy elastic deformation
without surpassing the 0.2~ yield strength during mount-
ing. However, the stiffening elements 3 may also be
formed of other materials, such as glass fiber rods
or other rigid bars placed in the screening cloth ele-
ments either at the long side edges only, as is shown
in Fig. 1, or at suitable intervals in the lateral di-
rection of the screen elements (= the screening direc-
tion of the screQning machine).
In the embodiment according to Figs. 1 and 2, the
invention has been utilized in connection with a screen-
ing machine with a convexly curved screen deck. As has
been mentioned above, the invention may also ~e utilized
with screening machines in which the finished screen
deck i5 planar, in which case the stiffening elements
may have been subjected to a plastic predeformation
(see Fig. 3) such that the screen elements are curved
in à direction opposite to the elastic deformation im-
parted to them during mounting. In Fig. 3, this plastic
predeformation is illustrated by the arrows 12 which
indicate the amount by which the screen elements de-
viate from a straight line 13.
If it is desired, according to a further development
of invention, to strengthen the holding-down force or
to avoid deformation of the screen elements during mount-
ing, it is possible in accordance with Figs. 4-6, to pro-
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vide a holding-down force by means of permanent magnets
13 which, by means of resilient holders 14 serving as
dampers, are mounted on the longitudinal supporting
elements 9 of the screen frame. In the embodiment illu-
strated, the holders 14 are fi~edly mounted on the lon-
gitudinal supporting elements 9 by means of a holder
plate 15 secured by means of bolts 16 (Fig. 5) or by
welding (Fig. 6).
The permanent magnets 13 attract the stiffening
elements 3 which are inserted in the screen elements
and which, in this instance, must consist of magnetic
material to be able to function as armatures. As will
appear from Fig. 4, the magnets 13 can be placed at
suitable intervals across the screening surface, such
that the magnets can be used for retaining the stif-
fening elements 3 of two juxtaposed screen elements.
The use o~ magnetic retention means makes mounting and
dismounting much simpler than in known mounting systems.
With magnets, the magnetic force can be used as the
only retention force, but it is also possible to utilize
the above-mentioned deformation of the screen elements
to produce a more powerful holding~down action.
The invention has been described above with refe-
rence to a screen frame in which *he screening cloth
elements extend from one side to the other. However,
the invention may be used also with screening machines
designed in a different manner, in which the screening
deck is divided into two or more juxtaposed areas, as
shown in Fig. 7.
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