Note: Descriptions are shown in the official language in which they were submitted.
Extended nip press
The present invention relates to a press for removing
liquid from a web of paper, cellulose or other material
where the travelling web is subjected to pressing force for
a longer time than in a conventional roll press.
The object of the invention is to provide an extended nip
press which is simpler and cheaper than the earlier
constructions.
Various extended nip presses have been disclosed by e.g. US
Patent Specifications Nos. 3,970,515, 3,808,096, 3,783,097
and 3,748,225.
The extended nip press according to the invention comprises
two endless belts which are impervious to liquid and form an
extended nip press; at least one belt which is pervious to
liquid and/or liquid absorbing which together with the
material web travels through the nip; a pressure member
which together with the inner surface of one of the liquid
impervious belts forms a pressure compartment/compartments
for exerting pressure onto the material web along its whole
width in the nip, and a supporting member which contacts the
inner surface of the other liquid imper~7ious belt and is
provided with a slide surface.
Compared with the extended nip presses disclosed by the
patent specifications mentioned above the construction
according to the inventions provides the following
advantages:
- A beam acts as the pressing element which is
relatively easy to design sturdy enough to avoid
detrimental deflection.
- As the construction allows the pressing beams to be
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mounted semi-stationary in relation to each other
and their distance from each other can be adjusted,
the sealing requirement is not as high as in
constructions where the pressing element must
follow the variations of the web thickness.
The sealing strips of the pressure members are the
only mechanically moving elements in the press.
Due to its simple structure the press is easy to
open for change of sealing strips. Thus the
sealings may be made of a relatively wearing
material which makes it easier to find a suitable
elastic material.
As the web can be made to travel through the nip
e.g. rectilinearly it is possible to avoid
subjecting the web to unnecessary bends which may
decrease its strength.
Since the press zone can easily be devided into
smaller zones and their pressures separately
adjusted, optimal pressing can be obtained.
Since the press can, due to its mechanical
construction, be built very long, the effect of
several presses is obtainable by this press and
thus the press section can be decisively
simplified.
There are only few wearing parts and they are in-
expensive.
As the beams are connected to each other, i.e. the
power system is internal, the other construction of
the machine can be made fairly slight.
- Since the beams need only be adjusted in relation
to each other, they can easily be detached for
change of felt or press belt. Further more,
cantilevering of the beams is very easy to arrange.
The invention is described below in more detail with
reference to the drawings attached where
Fig. 1 is a schematic cross section of an embodiment of
the apparatus according to the invention,
Fig. 2 is a schematic cross section of the press nip area
of Fig. 1 in a larger scale,
Fig. 3 is a schematic cross section of another embodiment
of the apparatus according to the invention,
Fig. 4 is a schematic cross section of yet another
embodiment of the apparatus according to the
invention.
The press illustrated in figures 1 and 2 consists of two
beams 1 and 2 mounted semi-stationary in relation to each
otherO The distance of the beams from each other can be
adjusted and they are disposed in a transverse position in
relation to the travelling direction of a paper web 3. The
upper beam 1 acts as a supporting member of an endless water
impervious belt 4, and the lower beam 2 as a pressing member
of an other endless water impervious belt 5, directing the
pressing force to belt 5 whereby the belts together form a
press nip. Rolls 6 guide the web to run through the nip.
The paper web 3 and a water pervious and/or absorbing belt
7, e.g. press felt, and possibly yet another water pervious
belt ~ provided to increase the dewatering capacity, e.g. a
fabric wire, are guided to travel through the nip.
In order to create pressure in the nip the beam 2 is
provided with movable, preferably elastic, the pressing zone
defining sealing strips 9, which are in sealing contact with
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khe inner surface 10 of the endless belt 5 whereby a closed
pressure chamber 11 is formed wich is supplied by liquid,
e.g. water or other appropriate pressurized medium. Beam 1
has a substantially plane slide surface 12 along which the
inner surface 13 of the endless belt 4 travels. Lubricant
may by known methods be supplied between the belt and the
slide surface e.g. on the front side of the beam.
Beams 1 and 2 are positioned in relation to each other so
that the sealing strips 9 are able to compensate both the
deflection of the beam and the variations in the thickness
of the material web, belts and the fabric-wire.
By forming the slide surface 12 optimal geometry can be
obtained for the nip (e.g. linear).
By designing appropriately the outlet side 14 of the slide
surface 12 the web is made to quickly detach itself from
the felt 7, whereby rewetting of the web is prevented.
The lenght of the nip is chosen for optimal pressing whereby
the length is a function of speed and dewatering. The pre-
sumptive optimal length varies from 10 cm to 1 m.
In the embodiment illustrated in Figure 3 the beam is
provided with several transverse sealing strips 15 in such a
way that a plurality of subsequent pressure compartments 16
are formed which can be provided with different pressures.
In this manner e.g. a gradually increasing pressure can be
created in the nip.
In the embodiment illustrated in Figure 4 several transverse
supporting strips 18 provided with slide surfaces 17 have
been formed in the beam forming pressurized compartments 19
between them. In this way an efficient lubrication and good
guiding has been provided for the rnoving belk 4.
