Note: Descriptions are shown in the official language in which they were submitted.
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AN APPARATUS FOR WASHING AND/OR DEWATERING PULP
Technical Field
The present invention relates to an apparatus for washing and/or dewater-
ing pulp comprising a first press roll and a second press roll, each press
roll being
rotatable about an axis of rotation and having a permeable outer surface, and
a
vat in which the press rolls are installed. The press rolls define a press nip
be-
tween them, in which press nip the pulp is pressed, and the apparatus is
arranged
to feed the pulp in the direction of rotation of the press rolls through the
press nip.
The apparatus comprises a first pair of bearing housings provided with
bearings in
3w which the ends of the first press roll are journalled, and each bearing
housing of
the first pair and the first press roll are movable in relation to the second
press roll
to vary the press nip. The apparatus also comprises a second pair of bearing
housings provided with bearings in which the ends of the second press roll are
journalled.
Background of the Invention
When producing cellulose-based products, a roll press is frequently used
for washing and dewatering the cellulose-based pulp. The pulp is passed
between
two co-operating press rolls installed in the roll press, the press rolls
having a
perforated outer surface, a so called mantle surface, whereby the outer
surface is
permeable to liquid pressed out of the pulp, and the pulp is pressed in the
roll nip,
or the press nip, between the press rolls, whereby liquid is pressed out of
the pulp.
The roll press also includes one or more washing zones prior to the press nip.
One example of such a roll press is disclosed in EP 1 035 250, where the
axes of rotation of the press rolls are lying in substantially the same
horizontal
plane. The pulp is fed in the direction of rotation of the press rolls through
the
press nip and the pulp passes the press nip between the press rolls from below
upwards.
In prior art roll presses, it is known to provide a press roll which is
laterally
movable relative to the other to vary the press nip between the press rolls.
The
cross-section of the press nip, or the distance between the press rolls, is
one of
the operating parameters which affect the quality of the washed and dewatered
pulp. US 3,730,079 discloses a roll press comprising two press rolls rotatable
about parallel axes, wherein one of the press rolls is laterally movable
relative to
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the other to vary the cross-section of the therebetween press nip. Pressing
force is
applied to the laterally movable press roll by a plurality of separate lirk
systems
actuated by individual fluid pressure operated actuators. Pneumatically
expansible
tubes or springs are provided to force the movable press roll away from the
other.
The object of this press is to maintain the axes of the press rolls parallel
while
permitting relative lateral movement of the press rolls.
The Object of the Invention
There is a need for an improved processing of pulp in an apparatus for
washing and dewatering pulp comprising two rotatable press rolls, which more
ac-
to curately provides pulp with the quality which is desired, and which
increases the
capacity of the apparatus. In order to attain an improved processing of pulp
it is
important to obtain an adequate determination of the linear load which acts on
the
pulp in the press nip and is affected by the torque of the press rolls.
In most prior art apparatus having a stationary rotatable first press roll and
35 a rotatable second press roll which is laterally movable relative to the
first press
roll to vary the press nip, the lateral movement of the second press roll is
attained
by friction rails, normally made of a plastic material, on which the bearing
hous-
ings, provided with bearings in which the laterally movable second press roll
is
journalled, rest and slide. The linear load is determined by measuring the
load on
20 the bearing housings of the movable second press roll. The load cells used
for
determining the linear load are thus situated between the sliding bearing
housings
and the casing housing the press rolls, often behind the sliding bearing
housings in
their direction of motion/sliding. During operation when the bearing housings
slide
back and forth on the friction rails, the frictions rails are subjected to
wear, and the
25 friction between the sliding bearing housings and the friction rails is
therefore not
the same over time but is continuously changing. The wear on the friction
rails
negatively affects the determination of the linear load and is a source of
errors.
Consequently, the linear load can not be adequately determined.
Further, the bearing housings, the end casing members, or gables, to
30 which the bearing housings are attached, and the region between the sliding
bearing housings and the casing housing where the load cell is positioned in
prior
art are exposed to the heat from the vat. When there is a change in vat
tempera-
ture there is also a temperature change in the region of the load cell. Thus,
in prior
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art, the load cell is affected by heat and temperature changes which
deteriorates
the performance of the load call, This affects the determination of the linear
load
and is a source of errors.
Because of poor determination of the linear load based on deteriorated
performance of the load cell, the process can not be controlled efficiently
enough,
and pulp having the quality which is desired can not be produced from the roll
press.
The object of the present invention is thus to provide an improved
processing of pulp in an apparatus for washing and/or dewatering pulp
comprising
io two rotatable press rolls.
Summary of the Invention
The above-mentioned object is achieved by providing an apparatus of the
kind mentioned in the introductory part of the description, having the
features that
each bearing housing of the first pair and the opposite bearing housing of the
sec-
and pair are connected to each other by an adjusting device, which adjusting
de-
vice is adapted to force the first press roll away from and towards the second
press roll, respectively, and that the adjusting device is connected to at
least one
measuring member adapted to provide measurement values by means of which
the linear load acting on the pulp in the press nip is determined.
By the present invention, the at least one measuring member for measur-
ing the forces acting on the bearing housing is situated at a position where
the in-
fluence of the heat from the vat and the resulting heat changes is minimal,
whereby the performance of the measuring member is radically improved and
gives an accurate measurement of the forces acting on the bearing housing, and
consequently, the linear load acting on the pulp in the press nip can be more
accu-
rately and efficiently determined. Hereby, the processing of pup is
efficiently im-
proved. Further, because of the more suitable environment of the measuring
member according to the present invention, the measuring member is subjected
to
less wear, as the heat exposure is lower and the temperature around the measur-
ing member is kept at a more even level. However, the innovative position of
the
measuring member also provides for an easy and uncomplicated replacement of
the measuring member if necessary.
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The adjusting device is advantageously controlled by a control system, or
a control device, which controls the processing of the apparatus by setting
one or
several variable operating parameters, which setting is based on measurements
and determinations of several control parameters, inter alia the linear load.
The at
lest one measuring member is advantageously connected to the control system,
or the control device which may comprises a processing means, e,g, a CPU (Cen-
tral Processing Unit).
According to an advantageous embodiment of the apparatus according to
the present invention, the apparatus comprises determination means for deter-
{o mining the linear load based on the measurement values. When determining
the
liner load based on the measurement values, the determination means are
adapted to take into account design parameters which are specific for the
design
of the overall apparatus, for example the geometry of the bearing housings,
the vat
pressure profile etc., or the determination means can be calibrated based on
pre-
Ã5 vious measurements on the apparatus.
According to advantageous embodiments of the apparatus according to
the present invention, the adjusting device is directly connected, or directly
at-
tached, to the at least one measuring member.
According to another advantageous embodiment of the apparatus accord-
20 ing to the present invention, the at least one measuring member is mounted
to the
adjusting device.
According to a further advantageous embodiment of the apparatus accord-
ing to the present invention, the at least one measuring member comprises at
least one force sensor, the adjusting device is attached to the bearing
housing of
25 one of the pairs by a first set of complementary attachment means, and said
first
set comprises the at least one force sensor for measuring forces acting on
that set
of complementary attachment means to determine the linear load acting on the
pulp in the press nip.
The above-mentioned object is also attained by providing an apparatus of
30 the kind mentioned in the introductory part of the description, having the
features
that each bearing housing of the first pair and the opposite bearing housing
of the
second pair are connected to each other by an adjusting device, which
adjusting
device is adapted to force the first press roll away from and towards the
second
press roll, respectively, that the adjusting device is attached to the bearing
housing
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of one of the pairs by a first set of complementary attachment means, and that
said first set comprises at least one force sensor for measuring forces acting
on
that set of complementary attachment means to determine the linear load acting
on the pulp in the press nip.
5 According to an advantageous embodiment of the apparatus according to
the present invention, the attachment means of the first set comprise an
attach-
ment element and at least one recess which the attachment element engages, and
the attachment element is provided with said at least one force sensor. Tests
per-
formed by the inventors of the present invention have shown that this position
of
the force sensor is especially advantageous in order to accurately determine
the
linear load.
According to a further advantageous embodiment of the apparatus accord-
ing to the present invention, the at least one force sensor is included in a
cylindri-
cal load cell, and the attachment element is cylindrical and houses the lead
cell,
This embodiment provides for an efficient installation of force sensors at the
above-mentioned location,
According to another advantageous embodiment of the apparatus accord-
ing to the present invention, the attachment element and the recess are
pivotable
in relation to each other. Tests performed by the inventors have shown that
this ar-
rangement of the attachment element and the recess is advantageous in order to
accurately determine the linear load.
According to still another advantageous embodiment of the apparatus ac-
cording to the present invention, the adjusting device is pivotally attached
to the
bearing housing of one of the pairs via a first pivot axis by the first set
and pivotally
attached to the bearing housing of the other pair via a second pivot axis by a
sec-
ond set of complementary attachment means, and the first and second pivot axes
are displaced in relation to the axes of rotation of the press rolls.
By the arrangement where the first and second pivot axes are displaced in
relation to the axes of rotation of the press rolls, the adjusting device is
subjected
to less stress and forces, as would be the case if the adjusting device was at-
tached to the bearing housing via the axes of rotation, whereby the adjusting
de-
vice can be less strong and have a less complicated, or less advanced,
structure,
and the adjusting device can thus be more light-weight and less expensive to
pro-
duce.
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According to yet another advantageous embodiment of the apparatus ac-
cording to the present invention, each bearing housing of the first pair is
pivotable
about a third pivot axis which is displaced in relation to the axis of
rotation of the
first press roll and in relation to the first and second pivot axes, and the
bearing
housings of the first pair are adapted to move the first press roll in
relation to the
second press roll by pivoting about their third pivot axes. In addition to the
source
of errors because of the wear on the friction rails, the inventors of the
present in-
vention have also found that the force of the friction between the rails and
the
sliding bearing housing is also dependent on the vat pressure, i.e. the
pressure
to within the vat, and other sources of errors. In prior art, a determination
of the linear
load which must take the friction between the friction rails and the sliding
bearing
housing into account to a considerable extent can not present a satisfactory
and
accurate enough value of the linear load. By this embodiment, the above-men-
tioned friction rails can be excluded, and by laterally moving the first press
roll
Ã5 relative to the other press roll by the innovative pivoting of the bearing
housings of
the first press roll about the third pivot axis, the friction in connection
with the
movement of the first press roll to vary the press nip is in principal
unchanged
during long term operation, since the contact surfaces pivoting in relation to
each
other about the third pivot axis are not sensitive to wear, and if subjected
to wear,
20 the wear's effect on the friction between said contact surfaces is minimal.
Conse-
quently, the accuracy of the determination of the linear load based on load
cells
measuring the load on the bearing housings is further improved, whereby a
further
improved processing of pulp in an apparatus for washing and dewatering pulp is
provided.
2.5 Further, since the friction rails can be excluded, there is no longer a
need
for replacing worn out friction rails by new friction rails, which also
reduces the
costs for maintenance, since no stop of the roll press is necessary because of
any
change of friction rails.
According to an advantageous embodiment of the apparatus according to
30 the present invention, the adjusting device is attached to the bearing
housing of
the first pair by said first set of complementary attachment means. Tests per-
formed by the inventors have shown that this position of the force sensor,
i.e. in
connection with the pivotable bearing housing, is advantageous in order to
accu-
rately determine the linear load.
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According to another advantageous embodiment of the apparatus accord-
ing to the present invention, the apparatus comprises a casing which houses
said
vat and the two press rolls, and each bearing housing of the first pair is
pivotally
attached to the casing via its third pivot axis. This pivotally attachment can
be ef-
s fected by a first means and a second means which are complementary to each
other and pivotable in relation to each other, where the bearing housing of
the first
pair is provided with said first means and the casing is provided with said
second
means. For example, a pin can be provided on the casing and a recess can be
provided in the bearing housing, which recess is complementary to and engaged
i o by the pin. The pin and recess are pivotable in relation each other about
the third
pivot axis. Instead, the bearing housing could be provided with the pin and
the
casing could be provided with the recess.
The vat pressure tends to elevate the movable press roll in an upward di-
rection. In prior art apparatus, the weight of the end casing members, Le. the
ga-
15 bles, of the apparatus, must be great so that the casing can withstand the
forces of
the vat pressure on the laterally movable press roll. The innovative
attachment of
the first press roll to the casing, advantageously to the end casing members,
via
the third pivot axis balances the upward force originating from the vat
pressure,
and the casing including the end casing members can be manufactured using less
20 material, providing end casing members and a casing of a reduced weight
which
still efficiently withstand the forces originating from the vat pressure.
Further, in prior art apparatus there is a need for a strong, bulky and heavy
mechanism which applies a force on the movable first press roll and its
bearing
housings in the direction towards the stationary press roll to counter act the
force
25 produced in the press nip which forces the movable press roll away from the
sta-
tionary press roll. Further, the overall casing must be strong and heavy to
handle
the forces originating from the press nip. Because of the innovative
attachment of
the first press roll to the casing, advantageously to the end casing members,
via
the third pivot axis, the weight and size of said mechanism can be reduced and
the
30 weight of the casing can be further reduced. Since said mechanism and the
casing
of the apparatus can thus be produced using less material, providing a low-
weight
apparatus, the apparatus is easier to transport and install, and also less
expensive
to manufacture.
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According to an advantageous embodiment of the apparatus according to
the present invention, the adjusting device is in the form of a pneumatic or
hydrau-
lic driving device and comprises a housing adapted to contain fluid, and the
at
least one measuring member comprises at least one pressure sensor for measur-
ing the pressure of the fluid provided to the housing to determine the linear
load
acting on the pulp in the press nip. By measuring the pressure of the fluid
provided
to the driving device, the linear load can be determined in an efficient way.
The
pressure measuring equipment can be easily mounted to the apparatus, even to
apparatuses already manufactured and installed on site. The fluid can be a gas
or
a liquid, for example oil, but other fluids for the driving device may also be
used.
According to a further advantageous embodiment of the apparatus accord-
ing to the present invention, the at lest one pressure sensor is adapted to
meas-
ure the pressure of a fluid situated in the housing of the adjusting device,
The
measurement values of the pressure of a fluid situated in the housing are
advan-
tageous for determining the linear load. Alternatively, the at least one
pressure
sensor can be adapted to measure the pressure of a fluid situated in a fluid-
carry-
ing line which connects the housing to a fluid reservoir.
According to another advantageous embodiment of the apparatus accord-
ing to the present invention, the housing houses a piston which divides the
inner
space of the housing into a first chamber and a second chamber, and the at
lest
one pressure sensor is adapted to measure the pressure of the fluid of both
the
first chamber and the second chamber. By measuring the pressure of both the
first
and the second chamber, the pressure difference therebetween can be provided,
which is advantageous for determining the linear load.
Alternatively, the at least one pressure sensor can be adapted to measure
the pressure of a fluid situated in a fluid-carrying first line which connects
the first
chamber to a fluid reservoir and the pressure of a fluid situated in a fluid-
carrying
second line which connects the second chamber to a fluid reservoir. The appara-
tus may also comprise determination means adapted to determine the difference
between the fluid pressure of the first line and the fluid pressure of the
second line,
and adapted to determine the linear load based on the pressure difference be-
tween the first and second lines.
According to yet another advantageous embodiment of the apparatus ac-
cording to the present invention, the apparatus comprises determination means
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adapted to determine the difference between the fluid pressure of the first
cham-
ber and the fluid pressure of the second chamber, and adapted to determine the
linear load based on the pressure difference between the first and second cham-
bers. This is an efficient way to provide a good determination of the linear
load
based on pressure measurement on the adjusting device.
According to still another advantageous embodiment of the apparatus ac-
cording to the present invention, the adjusting device is in the form of a
hydraulic
driving device. By using a hydraulic driving device, an efficient control of
the mov-
able press roll and of the size of the press nip is achieved. However, also
other
io devices for adjusting the distance between the press rolls are possible,
such as
devices based on electromechanics.
According to another advantageous embodiment of the apparatus accord-
ing to the present invention, the first pivot axis is positioned between the
axis of
rotation of the first press roll and the press nip, and the second pivot axis
is posi-
Ã5 tioned between the axis of rotation of the second press roll and the press
nip.
Hereby, the longitudinal extension of the adjusting device can be reduced and
thus
be manufactured using even less material making it even less expensive to pro-
duce.
According to still another advantageous embodiment of the apparatus ac--
0 cording to the present invention, where the adjusting device is pivotally
attached to
the bearing housing of the first pair via said first pivot axis, when the axes
of rota-
tion of the two press rolls are in the same plane which is substantially
parallel to
the plane on which the apparatus rests, the third pivot axis and the first
pivot axis
are positioned on different sides of said plane in which the axes of rotation
of the
25 two press rolls lie.
By the above-mentioned innovative attachments of the adjusting device,
where the first pivot axis is displaced in relation to both the third pivot
axis and the
axis of rotation of the first press roll, the adjusting device is subjected to
less stress
and forces in relation to an adjusting device attached to the bearing housing
via
30 the axis of rotation.
By the above-mentioned displacements of the first pivot axis from the third
pivot axis, a "leverage effect" is attained, whereby less force is required to
force
the movable first press roll towards the other stationary press roll. The
longer dis-
tance between the third pivot axis and the first pivot axis, the more
prominent the
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"leverage effect" becomes, and the adjusting device is also subjected to less
stress and forces during operation and can thus be less strong and have a less
complicated, or less advanced, structure, and can thus be made of less
material.
The axes of rotation of the two press rolls can be in the same plane which
is substantially parallel to the plane on which the apparatus rests and, and
the
movable press roll is then laterally movable in relation to the other, or the
axes of
rotation of the press rolls can be positioned in other ways.
Further advantageous embodiments of the apparatus according to the pre-
sent invention and further advantages of the apparatus according to the
present
Ão invention emerge from the detailed description of preferred embodiments.
Brief Description of the Drawings
The present invention will now be described, for exemplary purposes, in
more detail by way of embodiments and with reference to the enclosed drawings,
in which:
Fig. 1 is a schematic view of an embodiment of the apparatus according
to present invention;
Fig. 2 is a schematic view illustrating bearing housings of the apparatus
of Fig. 1;
Fig. 3 is a schematic section view illustrating a set of complementary at-
tachment means of a first embodiment of the apparatus according
to the present invention;
Fig, 4 is a schematic view of the set of complementary attachment
means of Fig. 3 seen from above; and
Fig. 5 is a schematic cut-away view illustrating an embodiment of an
adjusting device of a second embodiment of the apparatus ac-
cording to the present invention.
Detailed Description of Preferred Embodiments
Fig. 1 schematically shows an embodiment of the apparatus for washing
and dewatering cellulose-containing pulp according to the present invention
pro-
vided with an embodiment of the system according to the present invention sche-
matically illustrated with blocks. The apparatus comprises a first rotatable
press
roll 102 and a second rotatable press roll 104, each press roll 102, 104
having a
permeable outer surface 106, 108 which is perforated, i.e. provided with
apertures,
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Whereby the outer surface 106, 108 is permeable to filtrate pressed out of the
pulp.
The shape of the apertures is normally circular, but any shape is possible.
The
press rolls 102, 104 comprise a number of filtrate channels 110 radially
inwards of
the outer surface 106, 108 to lead evacuated filtrate away, The two press
rolls
102, 104 defines a press/roll nip 112 between them, in which press nip 112 the
pulp is pressed, and are arranged to rotate in opposite directions, the left
press roll
104 being arranged to rotate in counter clockwise direction and the right
press roll
102 being arranged to rotate in clockwise direction. The apparatus is arranged
to
feed the pulp in the direction of rotation of the press rolls 102, 104 through
the
press nip 112. The axes of rotation of the press rolls 102, 104 being in
substan-
tially the same horizontal plane, and the apparatus is arranged to feed the
pulp
through the press nip 112 in a substantially vertical direction from below
upwards.
One of the press roll 102, 104, herein the first press roll 102, is laterally{
movable in
relation to the other press roll 104 to vary the press nip 112 under the
operation of
i5 the apparatus. The processing of the pulp in the apparatus is determined by
a set
of variable operating parameters which are variable during operation. The
cross-
section of the press nip is on of these operating parameters.
The apparatus comprises a casing 113 which includes a vat 114, 116, 118
in which the press rolls 102, 104 are installed, the vat 114, 116, 118 partly
enclos-
e ing the outer surface 106, 108 of each press roll 102, 104, whereby a gap
124,
125 for each press roll 102, 104 is defined, limited by the vat 114, 116, 118
and
the outer surface 106, 108 of the respective press roll 102, 104. The vat 114,
116,
118 can be pressurized and comprises a first side vat segment 114 which partly
encloses the outer surface 106 of the first press roll 102, and a second side
vat
25 segment 116 which partly encloses the outer surface 108 of the second press
roll
104, In the gap a vat pressure is built up during operation which tends to
elevate
the press rolls 102, 104 in an upward substantially vertical direction.
Said casing 113 comprises a first casing member 115 which extends be-
tween the ends of the first press roll 102 and to which the first side vat
segment
30 114 is mounted, and a second casing member 117 which extends between the
ends of the second press roll 104 and to which the second side vat segment 116
is
mounted. The first casing members 115 is pivotable about a first axis 121 and
the
second casing members 117 is pivotable about a second axis 123, whereby the
casing members 115, 117, together with their side vat segments 114, 116, are
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movable between a closed position and an opened position for providing access
to
the press rolls 102, 104. Further, the vat 114, 116, 118 comprises a central
vat
segment 118 partly enclosing the outer surface 106, 108 of the press rolls
102,
104 between the press nip 112 and the side vat segments 114, 116.
s The apparatus comprises a first pulp distribution device 126 for
distributing
pulp on the first press roll 102 and a second pulp distribution device 128 for
dis-
tributing pulp on the second press roll 104. The pulp distribution devices
126, 128
are arranged to distribute pulp to the gap 124 along the whole length of each
press
roll 102, 104. The pulp distributed on the outer surface 106, 108 of the press
roll
ire 102. 104 forms a mat on the press rolls 102, 104. Herein, the pulp
distribution de-
vice 126, 128 is in the form of a pulp distribution screw. However, other
kinds of
pulp distribution devices are possible. The pulp distribution device 126, 128
can
also comprise several separate pulp distribution means distributed one after
the
other along the longitudinal extension of the press roll 102, 104. Each pulp
distri-
]s bution device 126, 128 is connectable to a pulp supplying system via
connection
means 140, 142, and the supplying system supplies pulp to each pulp
distribution
device 126, 128.
The apparatus also includes a pulp transport screw (not shown), which for
example can be in the form of a pulp disintegrating screw or a shredder screw,
to-
20 wards which the pulp which has been pressed in the press nip 112 is
conveyed.
The pulp transport screw extends parallelly to the longitudinal axes of the
press
rolls 102, 104, and is arranged to disintegrate the pulp and transport the
pulp axi-
ally away from the press for further processing.
With reference to Fig. 2, the apparatus includes a first pair of bearing
25 housings 202 provided with bearings 204, in which bearings 204 the ends of
the
first press roll 102 are journalled, and a second pair of bearing housings 206
pro-
vided with bearings 208, in which bearings 208 the ends of the second press
roll
104 are journalled. In Fig. 2, only one of the bearing housings 202 of the
first pair
and the opposite bearing housing 206 of the second pair are shown. The casing
i0 113 of the apparatus includes two end casing members 210 (only one end
casing
member is shown in Fig. 2) between which the press rolls 102, 104 are
installed,
and each end casing member 210 comprises a beam 212 to which both a bearing
housing 202 of the first pair and the opposite bearing housing 206 of the
second
pair are attached. The bearing housing 202 of the first pair is pivotally
attached to
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the beam 212 via a third pivot axis 214 which is displaced in relation to the
axis of
rotation 216 of the first press roll 102, and the bearing housings 202 of the
first pair
are adapted to move the first press roll 102 in relation to the second press
roll 104
by pivoting about their third pivot axes 214. The bearing housings 206 of the
sec-
and pair are fixedly attached to the beam 212. The pivotally attachment of the
bearing housings 202 of the first pair to the beam 212 is effected by a pin
215 pro-
vided on each bearing housing 202 and a recess 217 provided in each beam 212,
which recess 217 is complementary to and engaged by the pin 215. The pin 215
and recess 217 are pivotable in relation each other about the third pivot axis
214.
The apparatus rests on a plane, and the axis of rotation 218 of the second
press roll 104 and the axis of rotation 21$ of the first press roll 102 are in
the same
plane which is substantially horizontal and substantially parallel to the
plane on
which apparatus rests. The third pivot axis 214 and the axis of rotation 216
of the
first press roll 102 lie in the same plane which is transverse to the plane on
which
the apparatus rests.
Each bearing housing 202 of the first pair and the opposite bearing hous-
ing 206 of the second pair are connected to each other by an adjusting device
220, in the form of a hydraulic driving device, more precisely a hydraulic
cylinder in
the disclosed embodiment. The adjusting devices 220, one provided at one end
of
the apparatus and the other provided at the other end of the apparatus, are
adapted to force the laterally movable press roll 102 away from the stationary
sec-
ond press roll 104 and towards the second press roll 104 for providing a
specific
distance between the press rolls 102, 104 and for keeping this distance. The
ad-
justing device 220 is pivotally attached to the bearing housing 202 of the
first pair
via a first pivot axis 222, which is displaced in relation to the third pivot
axis 214
and the axis of rotation 216 of the first press roll 102, and pivotally
attached to the
bearing housing 206 of the second pair via a second pivot axis 224, which is
dis-
placed in relation to the axis of rotation 218 of the second press roll 104.
The ad-
justing devices 220 are adapted to perform the lateral movement of the first
press
roll 102 by pivoting the bearing housings 202 of the first pair about their
third pivot
axes 214.
The third pivot axis 214 and the first pivot axis 222 are positioned on differ-
ent sides of the plane in which the axes of rotation 216, 218 of the press
rolls 102,
104 lie, which plane is substantially parallel to the plane on which the
apparatus
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14
rests. The first pivot axis 222 is positioned between the axis of rotation 216
of the
first press roll 102 and the press nip 212, and the second pivot axis 224 is
posi-
tioned between the axis of rotation 218 of the second press roll 104 and the
press
nip 212. The adjusting device 220 is pivotally attached to the bearing housing
202
of the first pair by means of a first set 226 of complementary attachment
members,
and the adjusting device 220 is pivotally attached to the bearing housing 206
of
the second pair by means of a second set 228 of complementary attachment
members.
In this embodiment, the complementary attachment members of the first
io set 226 generally correspond to the complementary attachment members of the
second set 228. With reference to Figs. 3 and 4, the complementary attachment
members of the first set 226 Will now be described in more detail. The
adjusting
device 220 is provided with a first attachment member of the first set 226,
which
includes a circular-cylindrical attachment element 302. The bearing housings
202
Ã5 of the first pair is provided with a second attachment member of the first
set 226,
which includes a recess 304 which is complementary to the cylindrical
attachment
element 302. Alternatively, the adjusting device may be provided with the
recess
304, and the bearing housings 202 of the first pair may be provided with the
circu-
lar-cylindrical attachment element. The attachment element 302 engages the rem
20 cess 304, and the attachment element 302 and the recess 304 are pivotable
in
relation to each other about the first pivot axis 222.
According to a first embodiment of the apparatus according to the present
invention, the attachment element 302 houses a cylindrical load cell 306
provided
with several force sensors 308 for measuring forces acting on the cylindrical
at-
25 tachment element 302, which measurement then is used for determining the
linear
load acting on the pulp in the press nip 112, Hereby, a load measuring is
provided,
which corresponds more accurately to the force originating from the press nip
and
acting on the first press roll 102, which results in an improved and more
effective
determination of the linear load, whereby a further improved processing of
pulp is
30 provided. The above-mentioned measuring is performed at both adjusting
devices
220. The load cell 306 may be connected to a control device including a CPU
and
determination means adapted to determine the linear load based on forces
acting
on the first set 226 of complementary attachment means and measured by the
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load cell 306, in view of the design of the overall apparatus, for example the
ge-
ometry of the bearing housings, the vat pressure profile etc.
Fig. 5 shows a schematic cut-away view illustrating an embodiment of an
adjusting device 501 of a second embodiment of the apparatus according to the
present invention. The apparatus comprises two adjusting devices 501, one ad-
justing device 501 being provided at one end of the apparatus and the other ad-
justing device 501 being provided at the other end of the apparatus. The
adjusting
device 501 is in the form of hydraulic driving device 501 and comprises a
housing
502 adapted to contain an oil-based liquid. The adjusting device 501 is
provided
l0 with a circular-cylindrical first attachment element 302 and a circular-
cylindrical
second attachment element 504. The first attachment element 302 is adapted to
be connected to one of the bearing housings 202, in a similar way as
previously
disclosed in connection with the first embodiment of the apparatus but without
the
load cell 306, and the second attachment element 504 is adapted to be
connected
15 to the other bearing housing 206 opposite the bearing housing 202 to which
the
first attachment element 302 is connected. In a conventional way, the housing
502
of the adjusting device 501 houses a piston 506 which divides the inner space
of
the housing 502 into a first chamber 508 and a second chamber 510, and the pis-
ton 506 is axially movable in relation to the housing 502. A piston rod 512 is
mounted to the piston 506 and to the first attachment element 302. In a conven-
tional way, each chamber 508, 510 is provided with a connection means 514, 516
for the inlet and outlet of pressurized oil, and each connections means 514,
516 is
connected to an oil reservoir 518 via an oil-carrying line 520, 522, or
conduit, and
via a pump device 524 which controls the flow of the oil between the oil
reservoir
518 and the chambers 508, 510. Via the connections means 514, 516, the pump
device 524 axially displaces the piston 506 in relation to the housing 502 by
in-
creasing and decreasing, respectively, the oil volume of the respective
chamber
508, 510. The adjusting device 501 is provided with a first pressure sensor
526 for
measuring the pressure of the fluid situated in the first chamber 508 and with
a
second pressure sensor 528 for measuring the pressure of the fluid situated in
the
second chamber 510. Each pressure sensor 526, 528 is directly attached and
mounted to the adjusting device 501. The apparatus includes a control device
530
including a CPU and determination means 532 adapted to determine the differ-
ence between the fluid pressure of the first chamber 508 and the fluid
pressure of
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16
the second chamber 510. The determination means 532 is adapted to determine
the linear load based on the pressure difference between the first and second
chambers 508, 510, in view of the design of the overall apparatus, for example
the
geometry of the bearing housings, the vat pressure profile etc. The control
device
530 may also be adapted to control the pump device 524 and consequently the
adjusting device 501. The above-mentioned measuring of the pressures is per-
formed at both adjusting devices 501, and consequently, in this embodiment the
pressure of four housing chambers is measured.
According to another embodiment of the apparatus according to the pre-
1o sent invention, the adjusting device may be connected to both at least one
load
cell and at least one pressure sensor.
By the present invention, the performance and the flexibility of a roll press
are improved since the press nip can be more efficiently controlled based on a
more accurate and more easy determination of the linear load, whereby the
capac-
ity of the apparatus is improved, and a desired quality of the pressed pulp is
at-
tained in an efficient way.
