Note: Descriptions are shown in the official language in which they were submitted.
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The inventiDn relates tD a tensioning device For woven
Fabrics, screen bottoms and the like prDvided with
tension edges, tension folds or the like, particu-
larly For the tensioning or Fine and Finest metallic
woven Fabrics for the purpose oF sieving, sifting
and Filtering, the tensioning device having two par-
allel arranged longitudinal stays which, tDgether
with two transverse stays connected at right angles
or at nearly right angles to the front side, Form a
10 similar rigid frame and in which, iF required, the
space limited by the frame is sub-divided by means
of a number oF longitudinal and transverse tie-rods
into several or multiple parcels oF identicel or
different size.
~evices For the Fastening and tensioning oF Filter
Fabrics to their supports are known. In drum-type
Filters, For example, the woven fabric placed on the
outside circumFerence is Fastened and tensioned by
means of several pressure ledges which ere pushed
into grooves in the drum shell~ In this device, the
ledges have to be Fixed by means oF screws, which
damage the Fine-meshed, sensitive Filter fabric ln
many places. The tightening oF the required large
number o~ screws is also time-consum;ng and diFfi-
cult. In annther device, the Filter fabric is at- Z
tached to a shaFt in order to be tensionçd by rotat-
ing the shaFt. This device used also in Filter screens
with Flat surFace has the shortcoming that the ten-
sioning on drum-type or arched Filter fabric carri-
~30 ers is difficult and uneven over the drum oircumFer-
ence as the filter fabric is applied on -the whole cir-
cumference, which results in a continuously increasing
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friction. In the field of screens, and particularly of vibra-
tor~screens, devices are known in which the scrQen fabric is
attached at both its ends to a fold-shaped plate bordering
which is en~aged by a screw-actuated tensioning device. ~lso
in this design the tensioning of the sieve fabric is compli-
cated and uneven.
In order to avoid this, Federal ~epublic of Germany Patent No.
618,786 has proposed a device for the fastening and tensioninc3
of woven fabrics, and particularly of filter fabrics, on their
carrier, in which the ends of the fabric width are fixed to
carrier elements on the free edge opposite the hinge axis, said
elements being of a valvular design and swivelling into the insert
ply of the fabric width.
In a further development of this device, Fecleral Republic of
Germany Patent l~o. ~66,466 has made known a tensioning frame for
woven fabric screens with at least one tensioning edge provlded
on a rotary adjustable clamp bracket on the frame, in wllic~h either
the tensionin~ edge of the clamp bracket or its opposite tension-
incJ edge of the frame is flexibly mounted in the known manner
in the tensioning direction of the screen fabric with respect to
the brackets, i.e. to tlle frame, the tensioning edge opposite
to t~e clamp opposite to the clamp bracket is made up of a
tensionin~ rail movably mounted on the frame by means of inter-
mediate rubber hlocks, cup or leaE sprincJs and the like.
The two devices described above have a cornmon feature, namely
that very high tensions are often required for the tensionin~
of the screen fabric; hence it is not only necessary to pro-
vide very strong spring members, but a very high force is also
required in order to push the clamp bracket down into
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the plane of the tensionin~ frame after having previously
attached the screen fabric to the opposite tensioning ed~es.
This can be achieved often only with great effort and by using
special tensioning tools, for example screw clamps. Besides,
the not inconsiderable danger of accidents also exists, es-
pecially when the screen fabric, which is under great tension,
has to be changed, that is removed from the frame. In this
case namely, the frame clamp bracket, after loosening the ar-
resting device holding it in the plane of the tensioning frame,
under the tension of the screen fabric, can suddenly sprin~ up-
wards with great force, which can easily result in shop accidents.
In vibratory screens, in which one of the tensionin~ ed~es is
flexibly supported over spring members operatin~ in opposite
direction to the screen tensioning, but which do not include,
however, any swivelling clamp bracket serving as carrier for
one of the tensioning ed~es, the provision of additional ad~
justing means which enable the variation of the distance between
the opposite lying tensioning edges and the adjustment of the
working stroke of the spring members is already known. This
makes it possible to apply the screen bottom onto the fra~ with-
out any pre-tensionin~ and to produce the desired screen tension-
in~ then by an appropriate adjustment of the spacin~ of the
opposite tensioning as disclosed in French patent No. 015,0~S.
In another known vibratory screen U.S. Patent No. 1,999,769 it
is not the tensioning edges lying opposite in longitudinal dir-
ection which are supported flexibly but rather the two tensioning
edges lying laterally opposite to one another, namel~ in the clamp
shaped brac];ets suspended in the inside walls of the screen frame.
On these brac~ets are mounted th~ bars which~
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penetrate the screen frame side walls, said bars carrying at their
free ends a screw thread with adjustin~ nut ancl spring members
between the latter and the screen frame external side. The
screen is fully tensioned as a function of said spring members
and ~y means of the bars and clamp shaped brackets, whereby the
tensioning of the screen can be adjus~ed as desired by operating
the adjusting nuts mounted on the bars.
In order to utilize the advantages of the devices described above
and to avoid at the same time their negative ~e~s,~ Lal Republic of
Germany Patent No. 1,133,22~ discloses a tensioning frame for
woven fabric screens with parallel opposite lying tensioning
edges, one of said edges ~eing mounted rigidly on the frame whereas
the other edge is supported fleYibly against the screen tension by
means of spring members in telescopic cylinders, where~y one of the
two tensioning edges is designed as swivelable clamp bracket
mounted on the frame, said tensionin~ screen distinguishing itself
in that the maxium spacing of the two opposite lying tensioning
edges is adjustable in the known manner by means of the wor~ing
stroke of the sprincJ members which determine the position of
the stops, whereby the piston rod of the telescopic cylinclers
hincJed on one transverse rail of the frame is provided with an
extension passed throucJh the spring member as well as the cylinder
front ~ace, said extension carrying at its free end, passed througl
a clamping led~e of its clamp brac~et, a screw thread as well as
nut wllich forms the adjustahle stop.
~ll the devices described above are imperfect, nowever, in
that they do not ma}e it possible to compensate the variation in
the parallelism of the opposite lying tensioning edges or
tensioning folds,
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caused`by machining tolerances and /or inherent to
the type o~ woven ~abric to be tensioned, without
producing thereby different tensions o~ the ~abric
in dif~erent ~abric zones. The tensioning ~rames
provided with a clamp bracket swivelable in the ten-
sioning plane o~ the fabric screen are completely
useless when it is necessary to stretch fine and
~inest metallic woven fabrics, and particularly
those which have a high blinding tendency, which
10~ have tD be equipped with beating members in order
tD reduce the blinding tendency.
In ~act, it is possible .to stretch on one tension-
ing ~rame o~ the type described above at the same
time two superimposed screen ~abrics, the bottom
one o~ which has preferably a larger mesh size and
in the tensioning direction a predetermined greater
length than the ~ine or finest ~abric, so that when
the two ~abrics are tensioned jointly the bottom
one is tensioned less and hits upwards against the
20.\ tightlier stretched ~abric. In this manner, the blind-
ing tendency o~ the ~iner ~abric is countered, but
at the same time the wear rate o~ the fine or ~inest
~abrio is accelerated.
A ~urther possibility o~ counteracting the blinding
tendenoy o~ the ~ine or ~inest screen ~abric would
consist in providing underneath the screen Fabric `.
stretohed on a ~rame o~ the type described above
oeating members in the ~orm o~ balls or ralls made
oF rubber or rubber-elastio plastios, whereby said
beating members are sù$oended by means oF oords and
the like under the screen fabric or attached to it.
This is, however, a very complicated and expensive-
solution, the ef~iciency o~ which depends addition-
ally on the uni~orm arrangement and distribution of
the beating members. ~ "
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Consequently, in the screening and filtering or
si~ting DF asbestos fibres, the solution adopted
is to nail the fine and finest woven fabrics 5Up- ~.
plied in rolls on a similarly rigid wooden frame.
To counter the blinding tendency, the area limited
by the wooden frame is sub-divided by means of lDn-
gitudinal and transverse wooden ledges into parcels
of identical or approximately identical size, where-
by a coarser woven ~abric is nailed on the rear side
f the wooden frame so that each parcel ~orms an
area enclosed by the fine or ~inest ~abric on one
side and by the coarse'fabric on the other side,in
which loose ball or roll-shaped beating members are
introduced, which are thrown upwards in irregular
sequence and with a varying intensity against the
fine or finest fabric due to the movements of the
machine.
This simple and proven mode of operation, whioh
seems initially to require only limited expendi-
;20 tures~ involves however major inherent deficienciesand disadvantages. In fact, if there is a change in
. the Fibre structure, which happens quite often, the
woven fabric being used has to be replaced as a rule
by another one with a mesh size consistent with the
changed Fibre structure. This could be achieved by
ha~ing available a number of frames carrying screen
I fabrics oF various mesh sizes; however~ in view of
.the size oF the plants for asbestos fibre winning~
this would make the method o~ operation economical-
~30 ly inef~icient~
Instead of th;s it is usual today, at changing Fibrestructure, to tear down the still serviceable screen
- fabric in use and to nail on a brand-new woven fab-
ric with a mesh size matched to the modified fibre
structure, which will be torn down also, in turn,
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as soon as the ~ibre structure has changed ayain.
This involves the des~ruction Dr the still useable,
generally not worn out fabric upon i~s remDval rrom
the frame, an unjustifiable wasie in view oF the in-
creasing shor~age of raw materials, which leads to
an avoidable and ecDnomically unacceptable enhancing i~
oF the cost Df asbestos fibre winning.
The purpose o~ the invention described hereunder is
to remedy this situation, the consequent aim oF said
invention being to provide, on the basis of the ad-
vantages oF the devices described above, a woven
Fabric tensioning Frame which enables a quick, non-
destructive and easy replacement oF the fabric and
the compensation to a large extent oF any possible
parallelism variations, which counteracts eFficient-
ly the blinding tendency, which ensures a longer
service liFe Df the screen ~abrios, which warrants
an easier handling oF the Frame through a reduced
dead weight at higher carrying capacity, and which
permits in addition the tensioning of coarser Fab-
rics as well as o~ screen bottoms made oF rubber or
plastics.
The present invention solves this task by means of
a tensioning Frame of the type designated initially
in that a tensioning rail can be associated to eac~h
oF the parallel transverse stays~ whereby at least
one oF said tensioning rails can be mounted movably
in the tensionin9 plane and the tensioning direction
thereby changing the spaoing of the tensioning rails
and hinge-connec~ed preFerably in the tensioning
plane tD an adjusting device, which can be ~ixed,
in turn, in ar. adjustbble position in the longitu-
dinal stays preFerably without changing thereby ~he - ~1
predetermined tensloning Force.
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To this end, each of the longitudinal stays includes in the
area of at least one of its two ends on its inside a slot-
shaped opening, which is penetrated by t11e end part of an
adjusting bracket which engages in turn with its end part a guide
made up of elements, whereas the hole provided in the head part
of the adjusting brac]cet is penetrated by a bolt, a pin, a screw
or the like perpendicular to the screen plane, over which the
tensioning rail is hinged swivelably to the adjusting bracket
in the tensioning plane. The guide elements are penetrated by
a tensioning spindle, and attached mutuall~ spaced to it. The
tensioning spindle can be provided with a threaded part at one of
its ends, which is guided in a threaded hole of a shiftable
bearing located in the interior of the longitudinal stay. With
this type of tensioning spindle, it is advantageous to provide
the possibly available spring, e.g. the spring cup set, in a
heavier design. As an alternative solution, the tensioning
spindle can be provided with a threaded section at both ends,
one of whicll engages the threaded hole of a shiftable bearing,
while the other one penetrates a threaded bush, which is con-
nected in turn unshiftably to the front side end of th~ longi-t-
udinal stay.
The shiftable bearing and the guide bush are actuated by a
s~rin~, particularly by a spring cup set, which is threaded on
the tensioning s~indle and arranged between the bearing and
the guicle bush.
The longitudinal stays are friction-locked to prism blocks. The
longitudinal stays to~ether with the prism blocks can consist
thereby of a one-sided design casting section, e.g. made of
aluminium or of an aluminium alloy, which includes in the area
of the longitudinal stays, on its bottDm side, at least stage-
wise openlngs, for example a continuous slot.
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Furthermore, the lnngitudinal stays can be designed
as hollDw sections, e.g. rectangular tubes, and the
prism blocks can be provided with two extensions at
to each other~ one o~ which engages the ~ront
side Df the longitudinal stay while the other one
engages the adjacent front side of the transverse
stay, whereby each prism block has a shaped ~ace on
its upper part, the shape and pDsition of which are
matched to thst of the tensioning edge or tension-
ing fold of the woven fabric or the like.
At least tWD prism blocks of each frame have a hole
_ passing thro~gh the side ~acing the longitudinal
stay, in which the threaded bush i5 possibly fixed.
A wide-meshed screen fabric or the like is attached
on the rear side o~ the longitudinal and transverse
stays~ and the space formed by the longitudinal ~nd
transverse stays is sub-divided by means o~ longi-
tudinal and tr~nsverse tiu-bars ~nto ~everal Dr
multiple psrcels of identical or different size,
2~ and a number of ball- or roll-shaped beating bodies
are introduced in each parcel, whereby the trans-
verse tie-bars have pre~erably on one side an in-
clined rebounding surfece sloped in the transport
direction.
The invention is represented in Figs. i to 4J
they show:
Fig. 1 the ten5ioning device in three-dimensional
representation~
Fig. 2 the adjusting device operating in the screen
plan~
Fig. 3 a prism block, also in three-dinensional
representation~
Fig. 4 the area of two successive tensioning devices.
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109~
As illustrated by Fig. 1, the tensiDning device
consists ~f tw~ longitudinal stays 1, parallel tD
one another and ~rictionally connected ~ver two
transverse stays 2. In the represented example, a
tensioning rail 3 is associated only to the ri~ht-
hand transverse stay 2, said tensioning rail being
shi~tably mounted in the tensioning plane and adjust-
able by ~eans of the adjusting device 4. It is in
the spirit n~ the invention to provide also the left-
hand transverse stay with a shi~table tensioningrailJ the statements hereunder apply therefore anal-
ogously also to such a case.
The longitudinal stays 1 consist pre~erably o~ a
light metal, e.g. aluminium, and are designed as
hollow sections~ whereas the transverse stays 2 are
an angle section o~ light metal, such as aluminium.
The tensioning rail 3 is a C-shaped section~ also
made o~ a light material, which is hinge-connected
at both ends to an adjusting device 4, which i5 lo-
cated in turn in the front side end of a longitudi-
nal stay 1.
For the tensioning o~ coarser or wide-meshed wire
fabrics or screen bottoms of rubber or plastics the
tensioning frame can include a number of transverse
tie-bars 23 oF simple design arranged transversally
to the screening direction, i.e. to the longitudi-
nal stretch of stays 1, the mounting faces o~ which
are arranged in a common plane or in di~ferent planes.
In the specially selected case of the tensioning o~
~ine and finest fabrics, the space formed by the
longitudinal and transverse stays 1,2 is sub-divided
~into several or multiple parcels Z4 of identical or
different size, whereby the transverse stays 2~ have
pre~erably an angular cross-section, which forms on
one side an inclined rebounding surface 25 sloped
in the screening or transport direction.
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On th~ rear side ~f th~ longitudinal and transverse
stays 1,2 there is fixed interchangeably pre~erably
a wide-mesh~d fabric 21 Dr the like, which fcrms
together with the longitudinal and transverse stays
22,23 bnx-shaped, open-~op parcels 24, in which a
number of loDse ball- or roll-shaped beating bodies
27 are introduced, said bodies bounding during the
operation upwards against the tensioned fine or
finest fabric which covers the parcels 24 from above.
In order to increase the effect of the beating ele-
ments 27, it is possible to arrange the bars 28, and
particularly round bars, in the parcels 24 trans-
versally to the screening or transport direction~
said bars being mounted preferably directly over
the wide-meshed ~abric 21. This ensures that a twist
is imparted to the beating bodies 27.
As explained already initially, fine and finest wo-
ven fabrics present fabrication-caused inaccuracies
or edge lengths, which act counter to the need o~ a
uniForm application of the tensioning force to the
screen Fabric. In order to remove this e~fect~ it
is proposed in accordanoe with the invention to
mount the shiftable tensioning rail 3 swivelably ~
in the screening plane and to connect it horizontal-
ly shiftable to the adjusting device.
To this end, the tensioning rail 3 is connected
swivelably at its ends over a bolt~ pin, screw or
the like to an adjusting bracket 7, whereby the bolt
or the like penetrates the vertical hole 9 of the
adjusting braoket 7~ which penetrates~in turn with
its end part 6 a slot 5 provided on the inside of
the longitudinal sta~ 1 and engages a guide7 which
is Formed by two guide elements 8 spaced-mounted on
a guide bush 14. The guide bush 14 is penetrated in
turn by a tensioning spindle 10, which has a threaded
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psrt 11 at both ends, one o~ which ~or example has
a right-hand thread and penetrates the threaded hole
12 of a bearing member 13 shi~table in the inside
of the longitudinal stay 1, while the other threaded
part 11 has for example a left-hand thread and pene-
trates a threaded bush 15, which is connected in
turn unshi~tably to the Front slde end or the lon-
gitudinal stay 1. Holding-down devices 31, e.g.three
selF-lubrica~ing bearings ~ixed in fork-shaped lugS,
can ensure an additional ~astening o~ $he tension-
ing rail ~, whereby a free leg oF the tensioning
rail reaches underneath the holding-down device.
ln order to enable an aùtomatic re-tensioning in
case of lengthening oF the screen Fabric, the shift-
able bearing 12 and the guide bush 14 are actuated
by a spring and particularly a cup spring set 16,
which is mounted on the tensioning spindle 10 and
arranged between the bearing 12 and the guide bush 14.
Fig. 2 shows a cross-section through the adjusting
device 4 represented in Fig. 1~ The adjusting device
i5 looated in the inside o~ the longitudinal stays 1.
It includes an adjusting bracket 7, which is rigid-
ly connected to the slide bush 14, whereby two slide
bearings 29 carry the slide bush 14. The slide bush
14 engages in the area o~ one oF its ends the cylin-
drical extension 30 aF the shi~ting bearing 13l
which is penetraked by the tensioning spindle 10
and threaded on the spring set 16.
As an alternative solution it is possible to pro-
vide an adjusting device with a tensioning spindle,
in which the tensioning spindle has a threaded part
only at Dne end~ e.g. in the area oF the shiFting
bearing. Such an adjusting device, which is not
shown, cDnsists basically oF the same elements. On-
ly the threaded bush 15 can be eliminated. Further-
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morel the spring se~ can be o~ a heavier design.
In this adjusting device, the adjusting spindle head
does nDt project out of the prism block bore.
Fig. 2 shows additionally another cross-section
thrDugh the adjusting device. This illustrates a
section along the line A - B o~ the main dra~ing of
Fig. 2. As ayainst the main drawing o~ Fig. Z, the
longitudinal stay 1 is designed in the form o~ a
oasting section in this example. The material used
therefor is preferably a light metal~ e.g. aluminium
or an aluminium alloy. The longitudinal stay 1 con-
sists mainly o~ a hoilow section, which includes on
its bo'tom side at least stagewise openings, e.g. a
slot, into which parts of the adjusting device can
be introduced. Furthermore, one or more recesses
can be provided on the top side o~ the longitudinal
stay 1, which form, in oonjunction with a web, e.g.
a heavy clamp pin, a lug. This enables an easy mount-
ing and dismounting of the complete ~rame by means
of lifting hooks. The bottom side of the longitudi-
nal stay is equipped at least in the area of its
ends with a stop face. The prism blocks can Form
together with the longitudinal stays the one-piecs
casting section. however, it is also possible to
make the prism blocks separate From the longitudi-
nal stays designed as casting sections~ and to at-
tach them then rigidly to the longitudinal stays~
e.g. by welding.
Fig. 9 shows a prism block za, which has two exten-
sions 17,18 at right angles to one another, of which
the extension 17 engages the front end o~ the lon-
gitudinal stay 1 and the extension 18 engages the
adjacent -~ront side oF the transverse stay 2. Each
prism block ZO has a shaped face 19 on its upper
part, the shape and position of which are matched
to those oF the tensioning edge or of the tension-
ing fold of the screen fabric 26. As illus~rated,
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the prism block 20 is penetrated in the direction of its
extension 17 ~y a hole, in which the guide bush 15 is fixed.
Holding-down devices 31 can be provided on the prism blocks 20
in the area of the extension 18~
The shaped face 1~ of the prism block 20 has a positive effect
particularly when two or more tenslonincJ devices are arran~ed
successively on a screening or sifting machine, as shown in
Fig. 4; this arrangementsimplifiæ the tensioning or detensioning
of the woven fabric or screen bottom.
The longitudinal or transverse stays 1, 2 as well as the long-
itudinal and transverse tie-bars 22, 23 are made preferably of
a liyht metal, e.g. aluminium.
Fig. 4 is a cross-section through the two transverse stays of
adjacent frames, with a tensioning rail 3 associated to the left-
hand stay. The tensioning rall 3, with a mainly C~shaped cross-
section, reaches with its free lower leg underneath the holcling-
down device 31 which is in the form o~ a roller, and is thereby
additionally secured. A wire fabric, Eor example, is attached
to the other upper leg of the tensioning rail 3. The riyht-
~ hand transverse stay has an S-shaped cross-sectional clesign.
The upper leg fixes thereby a wire fabric, whereas the lower
le~ forms a supporting surface. I~he space defined by the lower
le~ as well as a mainly perpenclicular and a central stay is e~uippecl
towards the screening surface with a stop 32, e.g. a rouncl wire
running parallel to the transverse stay and welded at the ends.
The stop 32 prevents the escape of the beating elements, e.g.
beating balls, intro~uced in this space. These beating elements
protect the transverse stays against clogging by excessive sedi-
mentation. Furthermore, these beating elements can serve also
to prevent a pressing down- _
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D~ the central stay and or the upper leg. Cons2-
quently, the upper leg cannot be li~ted by the clamp-
ing ~orces acting upon it and resulting frDm the ten-
sioning o~ the ~abric or o~ the screen bottom, which `~
makes it pDssible to ensure a reliable ~astening o~
the ~abric or o~ the screen bottom.
Patent cl~ims
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