FILTRE A VIDE ROTATIF DE BOULETAGE

ROTARY PELLETIZING VACUUM FILTER

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
An improved rotary vacuum filter for producing
filtration blanks or what may be termed pellets from slurries,
especially for example, iron ore slurries. Known
rotary filters utilize spiked deflecting rollers to remove iron
ore agglomerates from interstices in a lattice-like belt. The
use of a spiked deflecting roller necessitates the use of a
metal belt which is difficult to produce since the belt must
be sufficiently flexible to both pass around the deflecting
roller and lie sealingly against the surface of a vacuum drum
without permitting entry of outside air. This problem is over-
come by the present invention which provides a vacuum filter
whereby dehydrated iron ore agglomerates are easily released
undamaged from the belt without impairing the suction effect
produced by the drum. The rotary vacuum filter according to
the present invention comprises a filter drum adapted to rotate
about a horizontal axis while partly immersed in a filter trough
filled with slurry, the filter drum is provided with a filter
lining and a suction area, a forming belt, divided like a lattice,
lies against the filter lining over the entire suction area of
the drum and is adapted to rotate therewith, the forming belt
extends from the drum over a deflecting roller arranged at a
distance from the drum, the deflecting roller having a diameter
smaller than a diameter of the drum, the belt adapted to be
lifted off the said drum at an end of the suction area by means
of the deflecting roller and being returned thereto before being
immersed in the filter trough, the lattice forming belt having
walls made of resiliently flexible material, interstices in the
lattice for holding filtration blanks, said interstices being
tapered conically towards a surface of the belt lying against
the filter drum whereby filtration blanks are removed from the
interstices by squeezing action as the belt passes around the
deflecting roller.

Revendications

The embodiments of the invention in which an exclu-
sive property or privilege is claimed are defined as follows:-
1. Apparatus for filtering slurries and for the manufac-
ture of pellets from filter cakes, said apparatus comprising:
a filter drum adapted to rotate about its axis while
partly immersed in the slurries, the filter drum being provided
with a filter lining and a suction area and an endless forming
belt, divided like a lattice which lies against the filter
lining over the entire suction area of the drum and which is
adapted to rotate therewith, the forming belt extends from the
drum over a deflecting roller arranged at a distance from the
drum whereby the pellets which are separated from the filter
cakes are removed from the interstices in the lattice, charac-
terized by the fact that the lattice forming belt has walls
made of resiliently flexible material, and that said interstices
are tapered conically toward a surface of the belt lying against
the filter drum.
2. A rotary vacuum filter according to claim 1, wherein
the taper of the interstices in the lattice amounts approximate-
ly 1:10.
3. A rotary vacuum filter according to claims 1 or 2,
wherein an additional deflecting roller is located in a return
path of the belt from the deflecting roller to the drum, the
location of the additional deflecting roller being such that
the lattice forming belt extends substantially horizontally
between the two deflecting rollers.
4. A rotary vacuum filter according to claims 1 or 2,
wherein an auxiliary device is arranged adjacent and above a
return run of the forming belt from the deflecting roller to
the drum, the auxialiary device adapted to remove filtration
pellets remaining in the interstices after the belt has passed
around the deflecting roller.

Description

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The invention relates to a rotary vacuum filter for
producing filtration blanks or what may be termed pellets from
slurries, especially , for example, iron ore slurries.
Many iron ores must be subjected to wet mechanical
dressing in order to enrich them by removal of the gangue. The
slurry thus produced must then be dehydrated and converted to
a grain size suitable fo~ ~he subsequent metallurgical process.
German Patent 1 920 219 and German Patent of Addition 1 925 876
discloses a method in which the two operations of dehydrating
and moulding are combined with one another.
Dehydrating of the slurry is preferably carried out
in so-called rotary vacuum filters comprising a filter drum
rotating about a horizontal axis, the lower part of the said drum
being immersed in a filter trough filled with the slurry. The
filter drum is provided with a filter lining permeable to water.
A negative pressure produced in the interior of the drum causes
the s-lurry to be deposited by suction in a layer on the submerged
surface of the drum. This deposit is then removed from the
trough by the continuously rotating drum. The rotation of the
drum removes still more water from the layer of sludge. The
dehydrated ore cake is removed from the surface of the drum by
appropriate means before the surface of the drum is again
immersed in the iron ore slurry.
Division of the dehydrated filter cake is achieved by
arranging a lattice-like belt on the surface of the drum, the
interstices of the belt being such as to produce, during the
dehydrating process, agglomerates of iron in the form of cubes,
or the like. The lattice-like forming belt which rotates with
the filter drum, is so arranged that it is lifted from the drum
at the end of the suction area by means of a deflecting roller
located at a distance from the drum, the forming belt being
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returned to the drum before again being immersed in the filter
trough.
The surface of the deflecting roller is provided with
spikes to expel the iron ore agglomerates from the interstices
in the belt. As a result, the spikes must be very accurately
matched with the interstices. The use of the spiked roller has
necessitated the use of a metal forming belt. However, it is
extremely difficult to produce a lattice belt made of metal
since the belt must be flexible in order to pass around the
spiked roller. Further, a high degree of accuracy is required
in order to ensure that the spikes enter the interstices. Another
problem is to ensure that the lattice belt lies sealingly against
the surface of the drum so that no outside air is drawn into
the drum.
The present invention proposes to improve this known
vacuum filter so that the dehydrated iron ore agglomerates are
easily released undamaged from the lattice belt without impair-
ing the suction effect produced within the drum. This is
achieved by providing a belt having walls made of resiliently
flexible material, the belt having interstices therein which
are tapered conically towards the surface of the belt which lies
against the filter drum. As a result, the lattice belt lies
sealingly against the filter drum over the entire suction area.
Furthermore, since the diameter of the deflecting roller is con-
siderably smaller than that of the drum, the said belt is bent
so sharply around the deflecting roller that most of the pieces
of iron ore are released by the squeezing action and easily
fall out of the interstices. The conical design of the inter-
stices, which are open at the bottom, prevents the iron ore
agglomerates therein from adhering to the filter lining when the
belt is lifted from the drum, as well as from falling out on the

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way to the deflecting roller.
In accordance with a broad aspect of the invention
there is provided an apparatus for filtering slurries and for
the manufacture of pellets from filter ca~es, said apparatu~
comprising: a filter drum adapted to rotate about its axis
while partly immersed in the slurries, the filter drum being
provided with a filter lining and a suction area and an endless
forming belt, divided like a lattice which lies against the
filter lining over the entire suction area of the drum and
which is adapted to rotate therewith, the forming belt extends
from the drum over a deflecting roller arranged at a distance
from the drum whereby the pellets which are separated from the
filter cakes are removed from the interstices in the lattice,
characterized by the fact that the lattice forming belt has
walls made of resiliently flexible material, and that said
interstices are tapered conically toward a surface of the belt
lying against the filter drum.
In one preferred embodiment of the invention, an
additional deflecting roller is arranged in the return path of
the belt just above the point of immersion, such that the belt
runs approximately horizontally between the two deflecting
rollers. The advantage of this is that the belt approaches the
surface of the drum at a steeper angle, thus enlarging the suc-
tion area.
In case any pieces of iron ore fail to drop out of
the interstices when the lattice belt passes around the deflect-
ing roller, according to a further embodiment of the invention
an auxiliary device for shaking, beating, or blowing such pieces
out of the said belt is arranged immediately above the return
run of the belt. This auxiliary device may be a blower, or a
beating or vibrating device.
The invention will now be described with reference to
-3-

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the accompanying drawings which illustrate one embodiment of
the present invention.
Figure 1 i~ a ~ide elevation of a diagrammatic re-
presentation of the drum filter according to
the invention,
Figure 2 is an enlarged vertical section of the lattic~
forming belt of Figure 1, taken along the
! line II-II, and
Figure 3 is a plan view of the enlarged section of
the belt of Figure 2.
' m e drum filter illustrated in Figure 1 consists of a
filter drum 1 which rotates about a horizontal axis, the lower
part of the said drum being immersed in a filter trough 2 filled
with iron ore slurry. This slurry is produced by wet mechanical
dressing and is fed continuously from a mixing container 3,

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through a feed means 4, into trough 2. The slurry is fed into
trough 2 at such a rate that the depth of immersion of the filter
drum therein remains constant.
Filter drum 1 is provided with a filter lining 5 which
is permeable to water. The slurry in filter trough 2 is drawn
through the filter lining 5 by means of a vacuum device arranged
within the interior of the drum. As filter drum 1 continues to
rotate, the slurry is brought to the desired degree of dryness.
The vacuum device is well known in the art and consists of
suction cells 6 arranged closely below filter lining 5, the cells
6 being connected by means of suction lines 7 to a control disc
8 located on the axis of the drum. The control disc 8 rotates
against a control head, not shown, which is connected to a
suction pump, also not shown. The design of the control head
is such that suction is applied only to suction lines 7 in
rotational area ~ of the drum. None of the remaining suction
lines is connected to the pump.
Arranged on filter lining 5 is a lattice-like divided
forming belt 9, the interstices in the belt 9 being tapered
conically towards the suction side thereof, that is, towards
the side of the belt which lies against the filter drum, as
best seen in Figures 2 and 3. The belt 9 is made of a resiliently
flexible material and is lifted from filter drum 1 at the end of
the suction area by means of a deflecting roller 10 arranged at
a distance from filter drum 1. The belt 9 is returned to the
drum 1 before being immersed in filter trough 2. The conicity
(a-b):c of the interstices tapering towards the suction side of
the belt is of the order of 1:10. Although a part of the
effective surface area of the filter lining 5 is lost due to the
thickening of belt webs 14 towards the suction side of the belt,
this loss is compensated for by the fact that the thickness of

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the layer of sludge deposi.ted on drum 1 may be considerably
greater than if the sludge were deposited by suction without
the use of a lattice belt.
Arranged in the return run of the belt, just above the
point of immersion, is an additional deflecting roller 11, by
means of which lattice belt 9 is caused to travel approximately
horizontally towards drum 1. Also, located beneath deflecting
roller 10 is a conveyor belt 12 for carrying away the pieces
of iron ore 15 released from lattice belt 9. Most of these
pieces are released from the interstices due to the resulting
squeezing action as the belt passes around deflecting roller 10
and fall onto conveyor belt 12.
In order to re'ease any iron ore agglomerates 15
remaining in lattice belt 9, as well as to ensure that all of
the interstices in the belt are ready to receive the new slurry,
it is desirable to arrange between the two deflecting rollers
10, 11 and just above the belt 9, an auxiliary device 13, whlch
may be in the form of a blowing, a beating, or a vibrating device.
Any pieces of iron ore thus released also drop onto conveyor
belt 12.
If conveyor belt 12 is suitably designed, iron ore
blanks lS may be simultaneously burned or sintered in order to
provide them with the strength required for the subsequent -
metallurgical process.