Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Apparatus and rnethQti for_pressi~~ a-~paper ~e'~
FIELD OF THE INVENTION
The present invention relates to a press device having an extended nip
intended for
pressing a running paper or paperboard web. The invention further relates to a
procedure for
controlling the pressure curve in the machine direction by such a press nip.
More specifically,
the invention relates to a shoe press of the type which comprises a support
which supports a
press shoe adjacent to a counter roll or another backing member in such a way
that the press
shoe and the backing member form an extended nip between themselves, and which
furthermore comprises a hydraulic or pneumatic arrangement for urging the
press shoe
towards the backing member in order to apply a pressure onto the web passing
through the
nip.
The press device and procedure according to the invention can particularly
advantageously be utilised for wet-pressing of moist paper or paperboard webs,
but also for
calendering or other finishing of dried paper or paperboard. It may also be
contemplated that
the pressing device according to the invention and the procedure is utilized
for other fibre
webs than paper and paperboard.
BACKGROUND OF THE INVENTION
For a long time, shoe press devices, i.e. presses having an extended nip, have
been
employed when manufacturing different paper and paperboard grades, primarily
for wet-
pressing in order to increase the dryness of the web, but also for calendering
and other
finishing in order to improve surface properties or other physical properties
of the web.
As a result of their longer nips, shoe press devices provide a number of
advantages in
comparison to conventional roll presses, such as higher dryness at the same
nip pressure, or a
pressing at a lower nip pressure but with maintained dryness which is more
gentle to the
sheet.
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In oFder to ~ulate the press nip conditions in a shoe pre~uch as the pressure
curve
in the machine direction throughout the nip, it is often desirable to be able
to displace the
pressure shoe forward or backward in the machine direction, to thereby affect
the pressure
curve through the press nip in such a way that the press power is at its
highest in the
beginning and lower towards the end of the press nip, or vice versa. At such
regulation the
pressure shoe will, in principle, follow an arc-shaped line of movement
centred in the central
axis of the counter roll.
The reason for the desirability of a regulated pressure curve in the machine
direction
throughout the press nip is, among others, that different qualities of paper
or paperboard have
different optimal pressure curves.
U.S. Patent No. 4,713,147 describes a shoe press with an extended press nip in
a paper
machine, in order to remove water from a wet fibrous and porous paper or
paperboard web.
The press comprises a rotating press roll and at least one loading shoe, which
is pressed
towards the press roll to form a prolonged pressing zone. The loading shoe is
capable of
rotating around an axis parallel to the axis of the press roll. The web to be
dewatered is
passed through the pressing zone together with at least one felt that receives
water from the
web. The loading shoe is supported on a carrier frame by supporting means. The
center of
gravity of the supporting force exerted by the supporting means at the shoe is
displaceable in
the dewatering direction of the web in order to allow adjustment of the
pressure pattern
generated in the pressing zone when different paper qualities are processed.
The
displacement of the center of gravity is performed either mechanically, by
displacing the
supporting means in relation to the shoe, or hydraulically, by varying the
pressures in two
separate pressure cushions in the supporting means.
Further, SE-C2-510 609 describes a shoe press for a paper or paperboard
machine
comprising a pressing shoe and a counter roll, between which is formed an
extended nip for a
paper or paperboard web, and a circulated flexible belt. The shoe press
further comprises at
least one press cylinder arranged between a horizontal beam and the press
shoe, in order to
press the latter against the counter roll. The press shoe is arranged on top
of the press
cylinder, 'whereby there is a device for anchoring the press cylinder to the
horizontal beam,
which can be disconnected. After the disconnection of the anchoring device,
the press
cylinder may be affected by eccentric members for displacement in the machine
direction, and
for the regulation of the pressure profile of the shoe press.
In the publication EP 0 933 471, corresponding to U.S. Patent No. 6,083,352,
the
disclosure of which is incorporated herein by reference, a shoe press is
disclosed which
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reduces the probler~originating from the thermal expansion of t~press shoe,
since it has the
ability to tolerate relatively Large eIongations of the press shoe across the
machine direction,
and also other deformations of the press shoe. The disclosed shoe press
comprises a press
shoe extending in the cross-direction along the entire width of a web running
through the
press, and a plurality of articulated hydraulic Loading cylinders supported by
a support and
spaced apart along the shoe. The loading cylinders define working chambers
which can be
pressurised by hydraulic fluid, so as to enable the cylinders to force the
press shoe away from
the support and towards a~counter roll or other backing member for applying
pressure to the
web being carried through the nip defined between the shoe and the backing
member. Each
loading cylinder comprises a piston member disposed within a cylinder member.
Either the
piston or the cylinder comprises a two-part member having a first member fixed
relative the
press shoe and a second member fixed relative to the support, while the
remaining piston or
cylinder comprises a coupler. Since the press shoe of the shoe press disclosed
in EP 0 933
471 also can be moved or tilted in the machine direction in relation to the
support, the shoe
press comprises a stop member restricting the movement of the shoe forward in
the machine
direction.
Further, the applicants' own Swedish, still unpublished patent application SE
9901636-
2 describes a shoe press for a paper or a paperboard machine. The shoe press
comprises a
press shoe and a counter roll, which between themselves form an extended nip
for passage of
a paper or paperboard web and an endless flexible belt therethrough, and at
least one press
cylinder arranged between a horizontal beam included in the support system of
the shoe press
and the press shoe, for pressing the press shoe against the counter roll. The
cylinder or piston
of the press cylinder is mounted in bearings to swivel around an axis in
relation to which the
axis forming a symmetry axis for the work space of the press cylinder is
eccentric. The shoe
press further possesses maneuvering members for swivelling of the cylinder or
piston of the
press cylinder in order to regulate the pressure profile of the shoe press,
which maneuvering
members comprise an actuating device extending outside the mantle.
In U.S. Patent No. 5,676,799 a device is described, with an extended press nip
for
treatment of a fiber web. At the device at least one press surface is formed
by a belt subjected
to pressure from at least one cylinder-piston unit by way of a hydraulic
contact pressure
device, consisting of at least one supporting element, whereby a supply of
pressurised fluid
for pressure pockets of the supporting element is insured by one of the parts
of the piston-
cylinder unit being permanently connected to a part of the supporting element,
whereas the
other part of the piston-cylinder unit is kept movable in the machine
direction and in the
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direction of web d~lacement on one of the elements, and where~the supporting
element is
supported by way of a stop attached to the supporting part.
Many of the previously known arrangements for affecting the pressure curve in
the
machine direction of e.~ctended press nips may be experienced as unnecessarily
complicated
and expensive, and often require an appreciable amount of time to make the
adjustments
necessary when switching from one pressure curve to another.
Further, there is a frequent risk that the desired adjustment of the pressure
curve in the
,machine direction is disturbed during operation, which may lead to problems
concerning
operability and quality.
SUMMARY OF THE INVENTION
Accordingly, the first object of the present invention is to provide a press
device
having an extended nip for pressing a running paper or paperboard web that
allows
adjustments between different pressure curves in a simple, cheap and reliable
manner.
This first object of the present invention is achieved, in accordance with one
preferred
embodiment of the invention, by a press device comprising a press shoe
directed across the
machine direction, arranged in order to form an extended nip in cooperation
with a backing
member for passage of the web during pressing, and a support that supports the
press shoe in
a manner displaceable towards the backing member by way of several loading
cylinders
arranged along the press shoe in order to make possible the application of
pressure to the web
during pressing. At least some of the loading cylinders comprise a first end
intended to be
fixed to the press shoe and a second end intended to be fixed to the support,
whereby each of
the loading cylinders have a main axis in their longitudinal direction. The
press shoe is
arranged for displacement between different positions in relation to the
support and the
backing member for controlling a pressure curve in the machine direction
throughout the
press nip, whereby a stop member is arranged downstream of the press shoe.
According to the invention the stop member is thereby arranged for
displacement
between, and fixation at, different stop positions in the machine direction,
whereby at least
some of the loading cylinders or the support comprise members, eccentrically
arranged
relative to one or some of the main axes, that can be brought into various
eccentric positions
relative to the main axes, in such a way that the present eccentric position
and the present stop
position controls the position of the press shoe during the pressing, and
thereby the pressure
curve in the machine direction throughout the press nip.
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A second ot~t of the invention is to provide a procedure ~ controlling the
pressure
curve in the machine direction throughout the press nip in the press device
according to the
invention. This second object of the present invention is reached, in
accordance with a
preferred embodiment of the invention, by a procedure, in which the press nip
is provided by
a press device according to the invention, comprising a press shoe, a backing
member, a
support, and several loading cylinders, at least some of which comprise a
first end intended to
be fixed to the pressure shoe, and a second end intended to be fixed to the
support, each of the
loading cylinders having a main axis in its longitudinal direction. The press
shoe can be
displaced between different positions in relation to the support and the
backing member in
order to control the pressure curve, whereby a stop member is provided
downstream of the
press shoe.
According to the invention the pressure curve in the machine direction is
controlled by
the extended press nip by displacement of members, eccentrically arranged in
relation to one
or more of the main axes, of the support or the loading cylinders, from a
first eccentric
position to a second eccentric position in relation, to the main axes, while
the stop member is
transferred from a first stop position to a second stop position, in such a
way that the second
eccentric position and the second stop position causes the position of the
press shoe to change
from a first position to a second position in relation to the support and the
backing member.
Further objects of the present invention will be apparent from the following
description, while the characteristics that realise the achievement of the
fiuther objects are
stated in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, the invention will be described in greater detail with
reference to the
drawings, in which .
Fig. 1 a shows a schematic sectional view seen across the machine direction of
a shoe
press device according to a preferred embodiment of the invention, with its
press shoe in~a
first position,
Fig. 1b shows a schematic sectional view across the machine direction of the
shoe
press device of Fig. 1 a, but this time with its press shoe in a second
position,
Fig. 2a shows a schematic sectional view seen across the machine direction of
a shoe
press device according to a specially preferred embodiment of the invention,
with its press
shoe in a first position, and
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Fig. ~b shows a schematic sectional view seen across the machine direction of
the shoe
press device according to Fig. 2a, but this time with its press shoe in a
second position.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In the attached figures 1 a and 1 b is shown a schematic sectional view of a
shoe press
device according to a preferred embodiment of the invention, in Fig. 1 a with
its press shoe
101 in a first position, and in Fig. 1 b with the press shoe 1 O 1' in a
second position.
In the attached figures 2a and 2b is shown a schematic sectional view of a
shoe press
device according to a specially preferred embodiment of the invention, in Fig.
2a with its
press shoe 201 in a first position, and in Fig. 2b with its press shoe in a
second position.
A press shoe 101; 201 in the first position (Fig. 1 a and 2a) will generate a
predominantly "symmetrical" pressure curve in the machine direction by way of
the extended
press nip whereby the pressure rises from a low initial value to a pressure
maximum and
subsequently drops again.
A press shoe 101'; 201' in the second position (Fig. 1 b and 2b), on the other
hand, will
generate a pressure curve with a low pressure in the beginning of the press
nip that increases
towards the end of the press nip, i.e. a pressure curve with its maximum
pressure displaced
towards the end of the press nip, compared with the case when the press shoe
101; 201 is in
the first position (Fig. 1 a and 2a). One might, of course, contemplate a
number of different
positions for the press shoe of the shoe press device according to the
invention.
The shoe press device according to the invention is intended for pressing of a
continuous paper or paperboard web and comprises a press shoe I01, 101'; 201,
201' aligned
across the machine direction MD, which press shoe is arranged to form an
extended press nip
103, 103'; 203, 203', together with a backing member 102; 202, for the passage
of the web
104; 204 during pressing.
The press device according to the invention further comprises a support 105;
205 that
supports the press shoe in a manner mobile towards the backing member by way
of several
loading cylinders 106; 206, arranged along the press shoe in order to make
possible the
application of pressure to the web during pressing.
At least some of the loading cylinders 106; 206 comprise a first end 110; 210,
intended
to be fixed to the press shoe 101;101'; 201, 201', and a second end 111; 211,
intended to be
fixed to the support 1 O5, 205. Thus, an embodiment in which some of the
cylinders are not
fixed to the press shoe and/or the support, but rather are retained in or
controlled in their
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intended positions in some other appropriate way, is conceivable within the
scope of the
invention.
Each of the loading cylinders 106; 206 possess a main axis X; Y in their
longitudinal
direction. By main axis is thereby understood an axis extending predominantly
in the
direction of.extension of a loading cylinder.
As evident from the above, the press shoe of the press device according to the
invention is arranged for displacement between different positions 101, 101';
201, 201' with
respect to the support and the backing member for controlling a pressure curve
in the machine
direction MD throughout the press nip 103, 103'; 203, 203'.
A stop member 107, 107'; 207, 207' is arranged downstream of the press shoe of
the
pressing device according to the invention. Different types of stop members
for restricting the
mobility of the shoe in the machine direction, and also in the direction
opposite to the
machine direction, are already known through the prior art documents discussed
above.
The stop member 107, 107'; 207, 207' of the press device according to the
invention is
arranged for displacement between, and fixing in different stop positions A,
B; C, D in the
machine direction MD. Thus, in the embodiments shown in Fig. 1 a - 1 b and 2a -
2b the stop
member can be brought to, and fixed in, two different defined stop positions.
One might also
contemplate embodiments within the scope of the invention, with stop members
that can be
moved to, and fixed in, more than two different defined stop positions.
At least some of the loading cylinders 106; 206 or the support 1 O5; 205 of
the press
device according to the invention comprise members 108, 109, 108', 109'; 208,
208',
arranged eccentrically with regard to one or some of the main axes X; Y, which
may be
brought in different eccentric positions E, F; G, H with respect to the main
axes X; Y. During
the pressing the current eccentric position E, F; G, H, and the current stop
position A, B; C, D,
will control the position of the press shoe 101, 101'; 201, 201', and thereby
also the
abovementioned pressure curve in the machine direction MD throughout the press
nip 103,
103'; 203, 203'. -
According to one preferred embodiment of the invention, shown in the figures 1
a and
1b, the eccentrically arranged members are constituted by recesses 108, 109;
108', 109' in the
first end 110, intended to receive male members 112, 113 for fixation to the
press shoe 101,
101'. In this embodiment the male members 112; 113 are constituted by sliding
guides
pressed into the recesses 108, 109; 108', 109', and into the corresponding
recesses of the
press shoe. One might also contemplate advantageous embodiments with recesses
in the
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second end; intend to receive male members for fixation to the support, or
recesses in the
support, intended to receive male members for fixation to the second end.
In a particularly preferred embodiment of the press device according to the
invention,
the eccentrically arranged members are constituted by male members 208; 208'
of the first
end 210, intended to be received in recesses 214 in the press shoe 201; 201'
for fixation of
said press shoe 201, 201'. One might also contemplate advantageous embodiments
with male
members at the second end, intended to be received in recesses in the support
for fixation to
said support, or male members at the support, intended to be received in
recesses at the
second end for fixation to the second end.
The male members mentioned above, may thus be constituted by separately
penetrable
parts 112, 113, or by protrusions 208, 208' which are integrated into the
press shoe, the first
end 210, the second end, or into the support.
In the particularly preferred embodiment the fixation of the first and/or
second ends
comprises that the male members mentioned above provide a recess or a cavity
for reception
of a dowel 215, a locking pin, or a similar member extending through a passage
formed in the
press shoe 201, the first end, the second end, or in the support. Thus, in the
particularly
preferred embodiment as shown in Fig. 2a and 2b, a locking pin 215 extends
through a
passage in the press shoe 201.
In a particularly advantageous embodiment of the press device according to the
invention, the stop member 107, 107'; 207, 207' is fined in the present stop
position A, B; C,
D, at least by a spacer element 116, 116'; 216, 216' in a recess in the
support, abutting the
stop member. The spacer element has a geometric design, which in a first
position 116; 216
enables said abutment in a first A; C stop position, and which in a second
position 116'; 216'
enables said abutment in a second B; D stop position in the machine direction
MD. Of course,
one might also contemplate embodiments within the scope of the invention, in
which the
spacer element (or the spacer elements) allows abutting contact with the stop
member in more
than two stop positions.
In the embodiments shown in Fig. 1 a - 2b the spacer element consists of a
ledge
running across the whole width of the stop member across the machine
direction, and which
may be rotated around its longitudinal axis in order to provide the different
stop positions.
One might also contemplate embodiments with a plurality of shorter spacer
elements that may
be rotated or twisted in order to provide the different stop positions, or
less advantageous
embodiments with replaceable spacer elements of several different dimensions.
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According to one embodiment of the press device, at Ieast some of the loading
cylinders 106; 206 comprise at least one cylinder part, coupled in a sliding
manner to at least
one piston part 118; 218 in a sealed manner by contacting gaskets 119; 219,220
to form at
least one work chamber 121; 221, inside which the pressure of a pressurising
medium may be
reduced in order to generate a shortening, or increased in order to generate
an extension of the
loading cylinder 106; 206. In this embodiment the cylinder part 117; 217
provides the first
end 110; 210.
In an alternative embodiment (not shown) the piston part instead consists of a
cylindrical coupling part, which in a sliding and sealed manner connects the
first cylinder part
to a second cylinder part. Thus, in this embodiment at least some of the
loading cylinders
have three parts sliding with respect to each other, whereby the coupling part
advantageously
is a substantially cylindrical sleeve, the inner part of which constitutes
part of the work
chamber.
It is, on the other hand, possible to conceive embodiments of the press device
according to the invention, in which the piston part (Fig. la - 2b) or the
coupling part is a
massive, substantially cylindrical body I 18; 218, at one or both ends of
which is formed a
work chamber 121; 221, and, in the case of several work chambers, in which the
cylindrical
body comprises one or more channels between the two ends for pressure
connection between
the work chambers.
In yet another alternative embodiment of the press device according to the
invention,
the first and second cylinders are solid, substantially cylindrical bodies, in
which one end is
surrounded by the coupling part in order to form the work chamber.
The backing member 102; 202 of the press device according to the invention is
preferably a rotating counter roll, and a flexible belt I22; 222, preferably
in the form of a
sleeve, is arranged in an endless loop to run between the press shoe 101,
101'; 201, 201' and
the paper or paperboard web 104, 204 during the pressing.
At the pressing, the paper or paperboard web 104; 204 passing through the
press nip
103, 103'; 203, 203' is preferably supported by one or more water-receiving
fabrics. Such
fabrics, for example press felts, are well known in the art.
The press device according to the invention is particularly advantageously
utilised for
wet pressing or calendering of a paper or paperboard web.
In the following, a procedure according to the invention, for controlling the
pressure
curve in the machine direction MD through an extended press nip in a press
device will be
described, when appropriate with reference to the attached figures la - 2b.
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The press m~I03, 103'; 203, 203' is thus provided by a die according to the
invention, comprising a press shoe 101, 101'; 201, 201', a backing member 102;
202, a
support 105, 20~, and a number of loading cylinders 106, 206.
At least some of the loading cylinders comprise a first end 110; 210, intended
for
fixation to the press shoe 101, 101'; 201, 201', and a second erid 111; 211,
intended for
fixation to the support 105; 205, whereby each of the loading cylinders 106;
206 has a main .
axis X; Y in its longitudinal direction. One may thus contemplate embodiments
of the
invention, where not all of the loading cylinders are fixed to the press shoe
and/or the support.
The press shoe may be moved between different positions 1 O l, 101'; 201, 201'
in
relation to the support and the backing member for controlling the
abovementioned pressure
curve, whereby a stop member 107,107'; 207, 207' is provided downstream of the
press shoe,
and thus limits the mobility of the press shoe in the machine direction.
In the procedure according to the invention the pressure curve is controlled
in the
machine direction MD through the extended press nip 103; 203 by members 108,
109; 208,
eccentrically arranged with respect to one or more of the main axes X; Y, at
the support or the
loading cylinders 106; 206 being moved from a first eccentric position E; G to
a second
eccentric position F; H with respect to the main axes, while the stop member
116; 216 is
displaced from a first stop position A; C to a second stop position B; D. The
second eccentric
position F; H and the second stop position B; D will control the position of
the press shoe
from a first position 101; 201 to a second position 101'; 201' with respect to
the support 105;
205 and the backing member 102; 202. As evident from the above, this will
change the
pressure curve in the machine direction through the extended press nip.
In a preferred embodiment of the procedure according to the invention, the
eccentric
members are provided in the form of recesses 108, 109; 108', 109' in the first
end 110,
receiving male members 112; 113 in such a way that the first end is fixed to
the press shoe
101; 101'. One may also contemplate embodiments of the procedure according to
the
invention (not shown) with eccentrically arranged members in the form of
recesses in the
second end, which receive male members in such a way that the support is fixed
to the second
end.
In a particularly preferred embodiment of the procedure according to the
invention, the
eccentrically arranged members are provided in the form of male members 208;
208' of the
first end 210, received in recesses 214 in the press shoe 201; 201' in such a
way that the first
end is fixed to the press shoe. One may also contemplate embodiments in the
shape of male
members of the second end, received by recesses in the support in such a way
that the second
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end is fixed to the support, or in the shape of male members of the support
that are received
by recesses in the second end in such a way that the support is fixed to the
second end.
In the particularly preferred embodiment of the procedure according to the
invention, a
recess or a cavity is advantageously provided in said male members 208; 208',
and a passage
is provided in the press shoe 201, in the first end or the second end, whereby
a locking pin
215, a peg, a locking screw, or a similar member is introduced into the recess
or the cavity by
way of the passage in order to fix the first and/or second ends.
In a particularly advantageous embodiment of the procedure according to the
invention
the stop member 107, 107'; 207, 207' is fixed in the present stop position A,
B; C, D, at least
by a spacer element 116, 116'; 216;216' in a recess of the support, abutting
the stop member.
In this embodiment the spacer element is initially brought into a first
position 116; 216 in
order to provide the abutment in a first stop position A;C, and is thereafter
brought into a
second position ~ 16'; 216' in order to provide the abutment in a second stop
position B; D in
the machine direction.
In another advantageous embodiment of the procedure according to the
invention, a
first number of the abovementioned plurality of loading cylinders 206 are
double-acting,
while a second number of said plurality of loading cylinders are single-
acting. By double-
acting is herein understood a loading cylinder with the capability of
generating force in its
extending direction as well as in its shortening direction, while single-
acting designates a
loading cylinder with the capability of generating force only in its extending
direction. In this
embodiment the fixation is performed by said male members 208; 208' only at
the first
number of loading cylinders 206, whereby the first number is smaller than the
second number,
and particularly advantageously less than a third of the second number. This
embodiment
considerably shortens the switching time between different pressure curves,
because the
eccentrically arranged members of the non-fixated loading cylinders may be
rapidly rotated or
displaced to a desired location, without any particular disengaging from the
press shoe, when
the non-fixated loading cylinders are in a pressure-less condition and do not
contact the press
shoe.
In the case when the shoe press device according to the invention comprises
both
double-acting (possessing both extension and shortening power) and single-
acting (possessing
extending power only) loading cylinders 106; 206, the double-acting loading
cylinders 206
are advantageously of the type that is shown in the figures 2a and 2b, while
the single-acting
loading cylinders 106 advantageously are of the type shown in the figures 1 a
and 1 b. It is
possible, though, to contemplate embodiments within the scope of the
invention, in which
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both double-acting and single-acting loading cylinders are of the same type,
or in which the
loading cylinders are of some other suitable type within the scope of the
appended patent
claims.
The present invention shall in iio way be construed as being limited to what
has been
described herein in connection with the different embodiments, or what has
been shown in the
attached figures. Rather, the scope of the invention is defined by the
appended patent claims.
The mechanic and hydraulic, alternatively pneumatic, components being part of
the
shoe press device according to the invention have not been described in detail
herein, since
such components sliould be well known to those skilled in the art, and
furthermore have been
described and illustrated in above mentioned EP 0 933 47I.
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