Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR CLEANING OF SCREEN-CLOTHS
IN PARTICULAR AT VIBRATING SCREENING EQUIPMENT
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The invention concerns a method and an apparatus fo~
cleaning of screen cloths especially for vibrating multi
deck screening equipment where a screen cloth is held
between tensioning profiles and tensioned in the
direction of the flow of material on the screen cloth by
means of at least one tensioning device connected to ak
-~ least one of the tensioning profiles.
When a sticky material is fed through vibrating
screening equipment there is frequently a tendency for
the matexial to stick to the screen cloth and such an
adherence is ofken difficult to remove. Further
difficulties can appear when a material contains
particles which are nearly the same size as the mesh
aperture of the screen cloth and thereby can wedge into
the mesh.
-~ These two kinds of problems with screen cloth often
result in a more or less rapid reduction of the screening
capacity in that th3 screening surface is reduced by the
adherence of the material.
`~ It has already been suggested that the removal of
par~icles adhering to the apertuxes of the mesh could be
made by means o~ applying bouncing or hammering devices
to the screen cloth whereby the wedging particles are
knocked out of the mesh. With binding caused by sticky
or particulate and sticky materials these bouncing or
hammering devices have hardly been effective. In this
~- case it has so far often been necessary to stop the
screening equipment from time to time and thoroughly
clean the screen cloth. Such an effort is hardly
commercially defensible because of the downtime of the
" equipment and loss of produ~tion.
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Other equipment is known where a screen cloth can be
slackened in a direction which is at right angle to the
flow of material on the screen cloth (U5 - P 3655045).
The disadvantage of that system is, however, that the
waves of the fluttering are oriented in ~he direction of
the flow of material thereby forcing it to accumulata in
the troughs or nodes and thus creating individual flows
instead of the even distribution of material across the
screen cloth which is desired and important for the
;~ 10 screening process.
As the load of material on a screen cloth always is
heaviest on its first part and binding of both kinds most
fre~uently appear in this region it is important to
concentrate the f luttering there. With a transversely
tensioned system this is impossible; on the contrary, one
can expect that the heavier load of material on the first
part of screen cloth will limit its fluttering movement
more than the relatively less loaded second part.
The present invention aims at avoiding the
disadvantages of the known equipment and solving the
problem so that a sufficient cleaning of the screen cloth
is possible also during the continuous operation of the
;- screening machine, i.e. without any real loss of
production.
It is therefore suggested that, according to the
invention, during the continuous vibration of the
screening equipment the screen cloth is slackened
~- longitudinally until the particles sticking to the screen
cloth or being wedged into the mesh are removed by the
fluttering of the screen cloth and after that the screen
cloth is tensioned again. This process of slackening and
tensioning of the screen cloth could also be repeated.
It can further be organized so that appropriate intervals
~; are automatically arranged by means of a timing device.
Thereby the degree of slackening of the screen cloth
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should be possible to define, ad~ust and repeat and,
depending upon type of screen cloth as well as frequency
and amplitude of vibration, preferably ad~ustable between
2 and ~ mm.
The slackening of the screen cloth gives a
fluttering movement which brings an intensive shaking out
and removal of binding or adhered particles so that the
screen cloth is kept optimally clean and thereby
maintaining maximum possible capacity.
An apparatus to perform the method according to the
invention could have tensioning devices which engage the
tensioning profiles of the screen cloth and which are
equipped with pneumatical cylinders connected to a
compressed air supply in a fashion that is in principle
already known. The tensioning profiles of the screen
cloth could also be connected to the frame of the
equipment by means of tensioning springs and the
~- slackening of the screen cloth could then be made bymeans of electromagnetic devices. It could be suitable
to link the tensioning device to the tensioning profiles
of the screen cloth through guides by means of flexible
oints e.g. hinges, leaf springs etc.
It has proven advantageous to arrange covering or
deflecting plates for the material above the tensioning
~; 25 profiles and devices.
In order to increase the cleaning effect there could
~` be supporting or hammering profiles at the screen cloth.
According to a broad aspect the invention relates to
:~ a method for cleaning screen cloths, particularly screen
cloths mounted in a multi-deck screening apparatus having
vibratory mechanisms, comprising the steps of: mounting
a screen cloth so as to be held between at least firs~
and second tensioning proiles, tensioning said screen
cloth between said tensioning profiles in a direction of
flow of material on said screen cloth with a tensioning
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device coupled to at least one of said tensioning
profiles, operating said screening equipment so as to
vibrate said screen cloth and during said step of
operating said screening equipment, decreasing a
longitudinal tension of the screen cloth to flutter the
screen cloth until at least some of the particles which
have adhered to wires forming the screen cloth are
removed and retentioning said screen cloth.
According to another broad aspect the invention
relates to an apparatus for cleaning screen cloths,
particularly screen cloths mounted in a multi-deck
screening apparatus having vibratory mechanisms, wherein
each said screen cloth is mounted and held between at
least first and second tensioning profiles and tensioned
in the direction of flow of material on said screen
cloth; comprising: a tensioning device coupled to at
least one of said tensioning profiles to control the
tension of the screen cloth, means for reducing the
tension applied by said ~ensioning device so as to
slacken said screen cloth as said screen cloth is
vibrated by a respective vibrating mechanism whereby
s particles which have adhered to wires forming the said
screen cloth are at least partially removed and means for
retentioning said screen cloth following such partial
removal.
With reference to the enclosed drawings the
invention will be further explained. The drawings show:
Figure 1 is a schematic view of a multi-deck
screening apparatus with three screen cloths;
Figure 2 is an arrangement of a screen cloth with
tensioning device in a screening equipment frame, in side
view;
- Figure 3 is a partial view from above showing this
screen cloth with tensioning device; and
Figure 4 is another example of a tensioning device
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with the screen cloth in a frame of a screening
equipment.
In the drawings, the screen cloths are indicated by
10 which at one end are fitted to stationary tensioning
profiles 11. The other end of the screen cloths 10 are
connected to moveable tensioning profiles 12. In the
example as shown in figure 1 to 3 the tensioning profiles
12 are connected through guides 21 to tensioning devices
14 which are fitted to the frame of the screening
equipment 13 and which are equipped with a pneumatic
cylinder for e.g. air or oil. When the pneumatic
` pressure is increased the piston of the cylinder moves
to the xight in the direction of the arrow and tensions
the screen cloths. When the pressure is reduced the
lS piston moves in the direction of the arrow to the let
and the screen cloth 10 is slackened. The tensioning
system could also be organized in a reverse fashion so
~; that an increased pressure slackens the screen cloth and
a reduced pressure tensions it. The pneumatic medium is
brought to the cylinder 14 through khe conductor 18.
Fig. i shows the arrangement of three screen cloths 10
~; with tensioning devices 14 in a screening apparatus 20,
;~ equipped with vibrating devices 19.
The arrangement according to figure 4 shows how the
screen cloth is tensioned by means of the tensioning
profile 12 being mounted of the frame of the screening
equipment 13 by means of tensioning springs 15. In this
case the slackening of the screen cloth 10 is achieved by
the tensioning profile 12 being pulled to the let in the
direction of the arrow by m ans or electromagnets 16.
When the eIactromagnets are switched off the springs 15
retension the screen cloth.
There are of course also other suitable tensioning
devices which fit the scope of this invention.
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