Note: Descriptions are shown in the official language in which they were submitted.
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The invention concerns a dewatering device.
Dewatering devices are used for thickening fibre
suspensions in, for example, paper-making processes. one
type of such device is shown in German Patent No. 21 38 072
and has a perforated dewatering drum as a first dewatering
stage followed by press rolls that are parallel to one
another and to the drum. Two wire belts partly loop about
both the dewatering drum and the press rolls to form one
less press gap than the number of press rolls.
This device has already been improved in that the
headbox which supplies the suspension to the area of the
wire belt which directly loops partly around the dewatering
drum and is located before the dewatering drum has been
coordinated with an area before the approach point of the
other wire belt to this wire belt. The suspension has been
fed to the former wire belt and between the first and the
second wire an entrance gap has been formed immediately
before the dewatering drum, by a suitable reversal of the
second wire. Thus it was possible to collect liquid passing
through the former wire already in the area of the
applicator device and, thus, remove it from the suspension
already at an early stage.
It is an object of the present invention to
fashion such a device in such a way that a greater
throughput may be achieved and, most of all, the entering
substance density can be reduced through a greater efficacy
of the initial dewatering process.
According therefore to the present invention,
there is provided a dewatering device, specifically for
thickening fibre suspensions, with a perforated dewatering
drum as a first dewatering stage and with, following the
dewatering drum, press rolls that are parallel to one
another and to the dewatering drum, and two wire belts which
partly loop around both the dewatering drum and the press
rolls forming between the press rolls, corresponding to
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their number n, a corresponding number n-l of press gaps,
characterized in that an entrance gap is formed by a
bow-shaped sliding guideway for the wire belt situated
radially inward on the dewatering drum, with the radius of
curvature k of the bow-shaped sliding guideway amounting to
at least three times the outside radius of the dewatering
drum 4 and the outside radius R of the dewatering drum 4
amounting to at least twice the smallest outside radius i of
the press rolls.
The amount of suspension entering the entrance gap
greatly determines the throughput of the dewatering device
for a given setting of a speed of rotation of the dewatering
drum or a revolving speed of the wires. The bow-shaped
guideway at the entrance gap provides a relatively gentle
increase of the squeeze pressure of the wires that increases
toward the drum. As a result, the liquid is squeezed out
very well forming sort of a fleece, whereas it would
otherwise be easily possible for the suspension to splash
out of the entrance gap sideways. This bow-shaped sliding
guideway favourably extends in the area of the entrance gap
across a 15 circular sector.
The invention will be explained hereafter with the
aid of an embodiment illustrated in the drawings, with the
figure showing a basic cross-section of the belt type
squeeze filter.
The belt type squeeze filter features two wire
belts 1 and 2 which jointly and partly loop around both the
peripherally perforated dewatering drum 4 and the following
press rolls 9-13. The radially inner wire belt 2 proceeds
additionally across reversing rolls 25 and 27 and the,
relative to the dewatering drum, radially outer wire belt 1
loops around the dewatering rolls 28-31. Formed in the area
of the dewatering drum 4 between the reversing roll 25 and
the drum 4 is an entrance gap guideway 6. The guideway 6 is
formed as an upwardly convex surface in the form of a bow
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and located radially inward in relation to the loop of the
wire belt 2 which is in direct contact with dewatering drum
4 so as to support the belt 2, which is preferably of a low
friction material and partly perforated in the way of a
screen. This makes it possible for the water (liquid)
pressed out of the suspension int he entrance gap to drain
into the collection trough 38. The suspension is applied on
the wire belt 2, which is in intimate contact with the
dewatering drum 4, by the headbox 40, to which the
suspension is supplied by the inlet socket 41. Passing
through the wire belt 2, the liquid quantity that drains
already here proceeds as well to the collection box 38.
The dewatering drum 4 has a perforated
circumference, with preferably a wire covering placed on a
perforated cylinder. The dewatering drum is sideways sealed
by plates 34 which are provided with drain openings 35O The
dewatering drum is mounted with its ends in a bearing 32
each supported by the upper support beam.
Of the following press rolls 9-11 of the bottom
row and 12 and 13 of the top row, two adjacent press rolls
of the two rows always form among each other a press gap.
The press rolls 14 and 15 of the upper row are supported by
hydraulic piston/cylinder units 14 and 15 bearing on the
upper support beam 20. The centre axis of the press
elements 14 and 15 are inclined at an angle of about 70 and
in the running direction of the wire toward the connecting
plane of the lower row of press rolls 9-11. As a result,
the upper press rolls 11 and 13 are forced onto the lower
press rolls 9-11 in such a way that two press gaps will be
formed at the upper press rolls. In the order of the press
gaps, increasing squeeze pressures between 100 and 600 N/cm
are applied.
The water (liquid) squeezed out is collected in
the lower collection trough 36 and removed through the drain
socket 37. The entire device bears on a base plate by way
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of supports 45 and 46 which act on the lower crossbeam 21.
Additionally, the upper crossbeam 20 bears on the lower
crossbeam 21 via lateral support columns 22 and 23. As
indicated at 35,33, the reversing rolls are supported by
similar bearings, except here for the reversing roll 28,
which for reason of creating the wire tension is supported
through a swivel arm 51 and a hydraulic pressure element 52.
the set up for the upper reversing roll 27 of the other wire
belt 2 is similar, with the lever 53 and the pneumatic
pressure element 54 being provided for that purpose. These
pneumatic pressure elements, in turn, act on levers 54 and
56, respectively.
The radius of curvature k of the bow-shaped
sliding guideway 3 amounts to at least three times the
outside radius R of the dewatering drum 4, and the outside
radius R of the dewatering drum 4 amounts to at least twice
the smallest outside radius i of the press rolls 9-13.
Preferably the radius k is 4 times the radius R. The guide
6 extends over a sector of approximately 15-.
This belt type squeeze filter affords the
additional advantage that, due to the relatively gentle,
technologically very favourable dewatering process, a
relatively low initial substance density can be used in the
area of the entrance gap 6. Due to the good dewatering
effect, nearly the same leaving substance density as with
previous dewatering devices of this type is obtained
nonetheless. Depending upon stock type, entrance stock
densities may range here between 2.5 and 2.9%.
It is preferred that the press rolls 9-11 and
13,14 lie in a horizontal plane or are inclined to the
horizontal plane at an angle of 25 or less.
