EXTENDED NIP PRESS WITH IMPROVED PRESS SHOE AND PRESSURE APPLYING APPARATUS

PRESSE PRESENTANT UN PINCEMENT ETENDU ET UN SABOT PERFECTIONNE ET APPAREIL D'APPLICATION DE PRESSION

English Abstract

An extended nip press (10) with an improved press shoe (22) and pressure
applying apparatus. The press (10) includes a backing roll (14), a shoe (22),
a belt (58), one or more felts (54) for passing between the shoe (22) and the
backing roll (14) with the web (W), and a pressure applying apparatus for
selectively forcing the shoe (22) toward the backing roll (14), such that the
belt (58), the one or more felts (54) and the web (W) are urged against the
backing roll (14) to establish a pressure zone (P) between the shoe (22) and
the backing roll (14). The pressure applying apparatus is operable to vary the
pressure profile of the pressure zone (P). The pressure applying apparatus
engages the shoe (22) at three or more points on the shoe (22), spaced in the
machine direction. The pressure applying apparatus includes three hydraulic
pressure applying devices (34a, 34b and 34c) which are independently operable
to vary the pressure profile. The press shoe (22) has a stiffness value in the
range of approximately five million to fifty million mm4/meter width, and the
pressure profile can be varied by flexing the press shoe (22).

French Abstract

L'invention concerne une presse (10) présentant un pincement étendu et un sabot perfectionné (22), ainsi qu'un appareil d'application de pression. La presse (10) comprend un rouleau de soutien (14), un sabot (22), une bande (58) ainsi qu'un ou plusieurs feutres (54) destinés à passer, avec la nappe de papier (W), entre le sabot (22) et le rouleau de soutien (14), et elle comprend également un appareil d'application de pression destiné à pousser de manière sélective le sabot (22) vers le rouleau de soutien (14) de façon que la bande (58), le ou les feutre(s) (54) et la nappe de papier (W) soient poussés contre le rouleau de soutien (14), afin d'établir une zone de pression (P) entre le sabot (22) et le rouleau de soutien (14). On peut commander cet appareil d'application de pression de façon à faire varier le profil de pression de la zone de pression (P). Ledit appareil entre en contact avec le sabot (22) au niveau d'au moins trois points situés sur le sabot et espacés dans le sens de la machine, et il comprend trois dispositifs d'application de pression (34a, 34b et 34c) que l'on peut commander de manière indépendante afin de faire varier le profil de pression. Le sabot (22) présente une valeur de rigidité se situant dans une gamme comprise entre environ 5 et 50 millions de mm?4¿/mètre largeur, le profil de pression pouvant être modifié par flexion du sabot (22) de la presse.

Claims

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2. A press as set forth in claim 22, characterized in
that the first, second and third points are respectively
located on parallel first, second and third pivot lines
extending in the cross machine direction, and the pressure
applying apparatus (134a, 134b, 134c) selectively forces
the shoe (122) toward the backing roll (14) on any one, two
or three of the first, second and third pivot lines.
3. A press as set forth in claim 2, characterized in
that the pressure applying apparatus includes first, second
and third pressure appyling devices (134a, 134b, 134c)
engaging the shoe (122) on the first, second and third
pivot lines, respectively.



-12/A-



6 . A press as set forth in claim 3, characterized in
that the shoe has therein first, second and third grooves
(230a, 230b, 230c) extending along the first, second and
third pivot lines, respectively, wherein the pressure
applying apparatus includes first, second and third pivot
rods (232a, 232b, 232c) respectively disposed in the first,
second and third grooves (230a, 230b, 230c) for pivotal
movement of the shoe (222) about the pivot rods, and
wherein the first, second and third pressure applying
devices (234a, 234b, 234c) respectively engage the first,
second and third pivot rods (232a, 232b, 232c).
7. A press as set forth in claim 3, characterized in
further comprising a frame (19) on which the backing roll
(14) is rotatably mounted, and in that the pressure
applying devices (134a, 134b, 134c) extend between the
frame (19) and the shoe (122).
8. A press as set forth in claim 3, characterized in
that the first, second and third pressure applying devices
respectively include first, second and third hydraulic
assemblies (134a, 134b, 134c).
9. A press as set forth in claim 8, characterized in
that the pressure applying apparatus includes a control
system (50) for controlling the supply of hydraulic fluid
to each of the hydraulic assemblies (134a, 134b, 134c).
10. A press as set forth in claim 9, characterized in
that the control system (50) includes first, second and
third valves (52a, 52b, 52c) for controlling the supply of
hydraulic fluid to the first, second and third hydraulic
assemblies (134a, 134b, 134c), respectively.



-13/A-



11. A press as set forth in claim 22, characterized in
that the shoe (122) has a stiffness value in the range of
approximately five million to fifty million mm4/meter
width.
12. A press as set forth in claim 22, characterized in
that the shoe (122) has a length of approximately 0.5 m
(twenty inches).
14. A press as set forth in claim 22, characterized in
that the pressure profile is substantially constant along
at least one-third of the length of the shoe (122).




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16. A press as set forth in claim 25, characterized in
that the shoe (22) has a length of approximately 0.5 m
(twenty inches).
17. A press as set forth in claim 25, characterized in
that the pressure profile is substantially constant along a
substantial portion of the length of the shoe (22).



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18. A press as set forth in claim 17, characterized in
that the pressure profile is substantially constant along
at least one-third of the length of the shoe (22).
19. A press as set forth in claim 25, characterized in
that the pressure applying apparatus (34a, 34b, 34c)
includes a corresponding plurality of independently
extendable assemblies (34a, 34b, 34c).
20. A press as set forth in claim 19, characterized in
that the extendable assemblies (34a, 34b, 34c) exert
parallel forces.



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22. An extended nip press (110) for dewatering a
moving paper web (W) in a papermaking machine having a
machine direction and a cross machine direction, the press
(110) comprising:
a backing roll (14) having an axis of rotation (18),
a shoe (122) including a concave inner surface
complementary with and facing the backing roll (14),
a belt (58),
one or more felts (54) for passing between the shoe
(122) and the backing roll (14) with the web (W), and
a pressure applying apparatus (134a, 134b, 134c) for
selectively forcing the shoe (22) toward the backing roll
(14) at any one or more of a plurality of points on the
shoe (22), the plurality of points on the shoe (122) being
spaced in the machine direction,
the pressure applying apparatus including a
corresponding plurality of pressure applying devices (134a,
134b, 134c), each of the plurality of pressure applying
devices (134a, 134b, 134c) engaging the shoe (122) at a
respective one of the plurality of points such that the
belt (58), the one or more felts (54) and the web (W) are
urged against the backing roll (14) to establish a pressure
zone (P) between the shoe (122) and the backing roll (14),
the pressure zone (P) having a pressure profile in the
machine direction, the pressure applying apparatus (134a,
134b, 134c) being operable to vary the pressure profile,
characterized in that the pressure applying devices
(134a, 134b, 134c) exert non-parallel forces on the shoe
(122),
wherein the pressure applying device (134a, 134b,
134c) each exert a force in a respective plane including
the backing roll axis of rotation (18).


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25. An extended nip press (10) for dewatering a moving paper web
(W) in a papermaking machine having a machine direction and a cross
machine direction, the press (10) comprising:
a backing roll (14),
a shoe (22) including a concave inner surface complementary with
and facing the backing roll (14)
a belt (58),
one or more felts (54) for passing between the shoe (22) and the
backing roll (14) with the web (W), and
a pressure applying apparatus (34a, 34b, 34c) for selectively
forcing the shoe (22) toward the backing roll (14) at any one or more
of at least first, second and third points on the shoe (22), the
first, second and third points being spaced in the machine direction,
such that the belt (58), the one or more felts (54) and the web (W)
are urged against the backing roll (14) to establish a pressure zone
(P) between the shoe (22) and the backing roll (14), the pressure zone
(P) having a pressure profile in the machine direction, the pressure
applying apparatus (34a, 34b, 34c) being operable to vary the pressure
profile,
characterized in that the first, second and third points are
respectively located on parallel first, second and third pivot lines
(33a, 33b, 33c) extending in the cross machine direction, wherein the
pressure applying apparatus (34a, 34b, 34c) selectively forces the
shoe (22) toward the backing roll (14) on any one, two or three of the
first, second and third pivot lines (33a, 33b, 33c),
the pressure applying apparatus includes first, second and third
pressure applying devices (34a, 34b, 34c) engaging the shoe (22) on
the first, second and third pivot lines (33a, 33b, 33c), respectively,
and
the shoe (22) has therein first, second and third grooves (30a,
30b, 30c) extending along the first, second and third pivot lines
(33a, 33b, 33c), respectively, wherein the pressure applying apparatus
(34a, 34b, 34c) includes first, second and third pivot rods (32a, 32b,
32c) respectively disposed in the first, second and third grooves
(30a, 30b, 30c) for pivotal movement of the shoe (22) about the pivot
rods (32a, 32b, 32c) and wherein the first, second and third pressure
applying devices (34a, 34b, 34c) respectively engage the first, second
and third pivot rods (32a, 32b, 32c).

Description

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BACKGROUND OF THE INVENTION
This invention relates to an extended nip press
apparatus for pressing water from a web of paper. More
particularly, the invention relates to an improved
press shoe and an improved pressure applying apparatus
for an extended nip press.
An extended nip press dewaters a wet paper web by
applying a pressing force to the web across a wide
area, or extended nip, rather than at a narrow point
contact. This application of force increases the
quality of the finished paper product.
Optimization of the pressing operation is a
function of the machine speed, the nip load applied,
the pressure profile of the nip, and the grade of the
paper being produced. The optimal pressure profile at
a given machine speed and nip load ensures that the
finished paper product is of superior quality.
A typical extended nip press includes a rotating
cylindrical backing roll and a rigid press shoe having
a complementary curved concave facing surface. The
press shoe is pivotally mounted and is hydraulically
actuated to apply pressure against the backing roll.
To dewater the paper web, the web is passed
between the press shoe and the rotating backing roll.
A felt is normally provided on each side of the web,
and a rotating belt is provided between the surface of
the press shoe and the felt, if provided, or the web
surface. Lubricant is sprayed between the belt and the
press shoe so that the belt provides a sliding contact
with the press shoe surface. Thus, the rotating belt,
the felt(s), and the web travel through the extended
nip between the surface of the press shoe and the
surface of the backing roll.
In DE-A-4 425 915, there is disclosed an extended nip
press for dewatering a moving paper web in a papermaking
machine according to the preamble of the independent
claims.
U.S. Patent No. 4,425,190 (Cronin) discloses an
extended nip press in which the press shoe is pivotally
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WO 98/58122 PCT/EP97/03161
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supported by a single pivot rod and actuated by a
single piston. While this press generally operates
well and provides dewatering over an extended nip, the
optimal pressing operation is limited due to the rigid
geometry.of the press shoe and its range of movement or
adjustability, relative to the backing roll when in
operation. The pressure profile on the web is
optimized at a given combination of machine speed and
nip loading force. If the machine speed or the nip
load changes so that the pressure profile is not
optimal, however, the press shoe cannot be adjusted to
return to an optimal condition due to the single fixed
pivot.
U.S. Patent No. 4,973,384 (Cronin) discloses an
extended nip press having some flexibility at setting
an optimal pressure profile. In this press, the press
shoe has a plurality of parallel grooves serving as
adjustable pivot points for the press shoe. The single
pivot rod supporting the press shoe can be positioned
in any of these grooves to change the pressure profile.
This adjustment is time-consuming and costly. Also,
this press has limited flexibility because the pressure
profile at each pivot point is fixed and cannot be
adjusted to overcome non-optimal conditions while the
machine is in operation.
U.S. Patent No. 5,167,768 (Cronin et al.)
discloses an extended nip press having increased
flexibility at setting an optimal pressure profile. In
this press, the rigid press shoe is pivotally supported
on two .parallel rods, each of which is supported by a
separate piston. The pistons operate to apply
different forces to the pivot rods to bias the facing
surface of the press shoe with different forces. By
being able to apply force to the press shoe at two
points, the pressure profile can be altered so that a
more controlled application of pressure is provided.
This control is achieved independently of maximum nip
load, machine speed, or paper grade. The press
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establishes a variable, more gentle pressure profile
providing increased flexibility in operating the
machine at a greater speed while maintaining the
optimization of the pressing operation.
SUMMARY OF THE INVENTION
While the extended nip press disclosed in U.S.
Patent No. 5,167,768 provides increased flexibility at
setting an optimal pressure profile, the optimization
of the pressing operation is still limited by the fixed
pivot locations and the rigid press shoe. The present
invention provides an improved extended nip press which
overcomes the limitations of earlier extended nip
presses. The extended nip press of the present
invention provides greater flexibility in optimizing
press operating conditions.
More particularly, the invention provides an
extended nip press comprising a backing roll, a shoe, a
belt and one or more felts for passing between the shoe
and the backing roll with the web. The extended nip
press also comprises a pressure applying apparatus for
selectively forcing the shoe toward the backing roll at
any of at least first, second and third points on the
shoe, the first, second and third.points being spaced
in the machine direction. The belt, the felts and the
web are urged against the backing roll to establish a
pressure zone between the shoe and the backing roll.
The pressure profile of the pressure zone can be varied
by the pressure applying apparatus. In the preferred
embodiment, the pressure applying apparatus includes
first, second and third hydraulic assemblies. Also,
the hydraulic assemblies are preferably independently
controlled by a control system including a
corresponding valve for each hydraulic assembly.
The invention also provides an extended nip press
comprising a flexible shoe having a stiffness value in
the range of five million to fifty million mm4/meter
width. The pressure applying apparatus is selectively
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operable to flex the shoe and thereby vary the pressure
profile of the pressure zone. In the preferred
embodiment, the shoe has a length of approximately
twenty inches, and the pressure profile is
substantially constant along a substantial portion,
e.g. at least one-third, of the length of the shoe.
Additionally, the invention provides an extended
nip press including a pressure applying apparatus for
selectively forcing the shoe toward the backing roll at
any one or more of a plurality of points on the shoe,
the pressure applying apparatus including a
corresponding plurality of pressure applying devices
that exert non-parallel forces on the shoe.
Preferably, the pressure applying devices each exert a
force in a respective plane including the backing roll
axis of rotation, such that the force is perpendicular
to the surface of the backing roll.
Further, the invention provides a method =or
controlling the pressure profile in an extended nip
press. The method includes the following steps:
providing the shoe with a stiffness value in the range
from five million to fifty million mm4/meter width;
selectivEly forcing the shoe toward the backing roll at
any one or more of at least first, second and third
points on the shoe, the first, second and third points
being spaced in the machine direction, such that the
belt, the one or more felts and the web are urged
against the backing roll to establish a pressure zone
between the shoe and the backing roll, the pressure
zone having a pressure profile in the machine
direction; and controlling the force applied at each of
the first, second and third points so as to flex the
shoe and vary the pressure profile.
An advantage of the extended nip press of the
present invention is that the press provides greater
flexibility in optimizing the pressing operation. The
~.mproved extended nip press provides a longer and more
gradual pressure profile. The pressure profile can be
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varied by the selective application of two or more
loads to the press shoe. Additionally, the pressure
profile can be varied by the flexing of the flexible
press shoe.
Another advantage of the extended nip press is
that the press is adjustable "on the run", during
pressing operations. This increases the efficiency of
the pressing operation.
Other features and advantages of the invention
will become apparent to those skilled in the art upon
review of the following detailed description, claims
and drawings.
DESCRIPTION OF THE DRAWINGS
Fig. 1 is a partial cross-sectional view of an
extended nip press embodying the invention.
Fig. 2 is a graph of the pressure profile achieved
by the extended nip press shown in Fig. 1.
Fig. 3 is a partial cross-sectional view of an
extended nip press that is a second embodiment of the
invention.
Fig. 4 is a partial cross-sectional view of an
extended nip press that is a third embodiment of the
invention.
Before one embodiment of the invention is
explained in detail, it is to be understood that the
invention is not limited in its application to the
details of the construction and the arrangements of the
components set forth in the following description or
illustrated in the drawings. The invention is capable
of other embodiments and of being practiced or being
carried out in various ways. Also, it is understood
that the phraseology and terminology used herein is for
the purpose of description and should not be regarded
as limiting.
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DESCRIPTION OF THE PREFERRED EbIBODIMENT
An extended nip press 10 embodying the invention
is partially illustrated in Fig. 1. The extended nip
press 10 is part of a papermaking machine (not
otherwise shown) having a machine direction (right to
left in Fig. 1) and a cross-machine direction (into and
out of the paper in Fig. 1). The extended nip press 10
dewaters a wet paper web W by applying pressure to the
web W in a pressure zone or extended nip P. The web W
moves generally in the machine direction and in a
direction of travel indicated by arrow 12.
It should be understood that the extended nip
preys 10 can be either an open extended nip press or a
closed extended nip press. In an open extended nip
press, the longitudinal ends of the extende3 nip press
are open so that the operating elements, such as the
press shoe and pressure applying apparatus described
below, are open to the surrounding work area. In a
closed extended nip press, the longitudinal ends of the
extended nip press are closed by a suitable cover so
that the operating elements are substantially sealed to
contain operating fluids and to protect the operating
elements from any environmental contaminants.
The extended nip press 10 includes a rotating
cylindrical backing roll 14 having an axis of rotation
18. The backing roll 14 is mounted on a frame 19 for
rotation in the direction indicated by arrow 20. The
backing roll 14 is driven by a drive mechanism (not
shown ) ..
The extended nip press 10 also includes a press
shoe 22 having a concave upper surface 26. The surface
26 is complementary to the surface of the backing roll
14 and faces the backing roll 14. Grooves 30a, 30b and
30c are defined in the lower surface of the press shoe
22. The grooves 30a, 30b and 30c are spaced apart in
the machine direction and are parallel to each other
and to the axis 18. The grooves 30a, 30b and 30c
extend in the cross-machine direction. In the
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illustrated construction, the grooves 30b and 30c are
defined by flexible locators 31b and 31c fixed to the
underside of the shoe 22. Pivot rods 32a, 32b and 32c
are positioned in respective grooves 30a, 30b and 30c.
The locators 31b and 31c allow relative movement in the
machine direction between the pivot rods 32b and 32c
and the s'~oe 22. This is explained more fully below.
The grooves 30a, 30b and 30c and corresponding pivot
rods 32a, 32b and 32c provide respective pivot lines
33a, 33b and 33c for the press shoe 22. In the
illustrated construction, the central pivot line 33a is
in a generally vertical plane including the axis 18 of
the backing roll 14.
The press shoe 22 is made from a suitable material
such as mild steel having a stiffness value (or."I"
value) such that small deflections of the press shoe 22
are possible over its length. In the preferred
embodiment, the press shoe 22 has a length'of
approximately 20 inches in the machine direction, and
the press shoe 22 can be deflected up to 1 mm. In
other constructions, the length of the press shoe 22 is
preferably between 10 and 30 inches, although it can be
greater or less. The preferable range of stiffness
values for the press shoe 22 is from 5x106 to 107
mm"/meter width, although it can be greater or less.
The flexing of the press shoe 22 allows the profile of
the pressure applied to the web W to be varied. This
is discussed below in greater detail.
The press shoe 22 is supported by a pressure
applying apparatus for selectively forcing the press
shoe 22 towards the backing roll 14. The pressure
applying apparatus includes pressure applying devices
or extendable assemblies 34a, 34b and 34c engaging
respective pivot rods 32a, 32b and 32c. The extendable
assemblies 34a, 34b and 34c are spaced apart in the
machine direction. The extendable assemblies 34a, 34b
and 34c are parallel and exert parallel forces. In
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_g_
other embodiments, the extendable assemblies 34 may be
non-parallel.
The extendable assemblies 34a, 34b and 34c are
preferably hydraulic. Each extendable assembly 34 is a
piston and cylinder assembly including a piston.rod 38
and a cylinder 42. The cylinders 42 are supported on
the frame 19, and the extendable assemblies 34 extend
between the frame 19 and the press shoe 22. Each
piston rod 38 engages the respective pivot rod 32 at a
point on the corresponding pivot line 33.
The pressure applying apparatus also includes a
control system 50 for controlling the supply of
hydraulic fluid to each extendable assembly 34. The
control system 50 includes valves 52a, 52b and 52c for
independently controlling the supply of hydraulic fluid
to extendable assemblies 34a, 34b and 34c,
respectively. The extendable assemblies 34a, 34b and
34c are independently actuated so that the pressure
applied to the press shoe 22 is varied dependent upon
the amount of pressure applied by each of the
extendable assemblies 34a, 34b and 34c and to the
respective pivot rods 32a, 32b and 32c.
The extended nip press 10 also includes a felt 54
which is positioned on one side of the paper web W
between the web W and the surface of the backing roll
14. A second felt (not shown) may be provided on the
other side of the web W. The extended nip press 10
also includes a rotating belt 58 positioned between the
surface.26 of the press shoe 22 and either the second
felt, if provided, or the web W. A nozzle (not shown)
is positioned at the upstream end of the press shoe 22
and sprays lubricant between the rotating belt 58 and
the surface 26 of the press shoe 22.
In operation, the web W, the felt 54, and the
rotating belt 58 travel at a machine speed between the
backing roll 14 and the surface 26 of the press shoe
22. The press shoe 22 is forced towards the backing
roll 14 by the extendable assemblies 34a, 34b and 34c
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to apply a nip load pressure to the web W. The
pressure zone or extended nip P is created by the
pressure of the press shoe 22 and the backing roll 14.
The optimal pressure profile of the pressure zone
P is shown in Fig. 2. By independently actuating the
extendable assemblies 34 and by flexing the press shoe
22, the pressure profile can be adjusted so that the
profile is substantially constant over a substantial
portion of the length of the press shoe 22. In the
preferred embodiment, the pressure profile is
substantially constant along at least one-third of the
length of the press shoe 22 at a pressure of
approximately 3,OU0 kPa. It should be understood that
in other embodiments of the invention the maximum
pressure and the pressure profile can vary greatly
depending on various factors.
In other embodiments, the pressure applying
apparatus can include only two or more than three
extendable assemblies 34 so that the press shoe 22 can
be loaded at only two or more than three points.
As mentioned above, the flexible locators 31b and
31c allow relative movement between the pivot rods 32b
and 32c and the shoe 22. Such relative movement can
occur as a result of flexing of the shoe 22, thermal
expansion of the shoe 22, or, in embodiments in which
the assemblies 34 are not parallel, the angle of the
assemblies 34.
An extended nip press 110 that is a second
embodiment of the invention is illustrated in Fig. 3.
Except as noted below, the extended nip press 110 is
substantially identical to the extended nip press 10
illustrated in Fig. 1, and common elements have been
given the same reference numerals.
The extended nip press 110 includes a press shoe
122. The press shoe 122, like the press shoe 22, is
flexible and is preferably 20 inches in length. The
pressure applying apparatus includes pressure applying
devices or extendable assemblies 134a, 134b and 134c
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engaging respective pivot rods 32a, 32b and 32c. The
extendable assemblies 134a, 134b and 134c are non-
parallel and each exerts a force in a respective plane
including the axis 18 of the backing roll 14, such that
the force is perpendicular to the surface of the
backing roll 14. In other words, the assemblies 134a,
134b and 134c extend radially of the backing roll 1~.
An extended nip press 210 that is a third
embodiment of the invention is illustrated in Fig. 4.
Except as noted below, the extended nip press 210 is
substantially identical to the extended nip presses 10
and 110 illustrated in Figs. 1 and 3, and common
elements have been given the same reference numerals.
The extended nip press 210 includes a press shoe
222. The press shoe 222, like the press shoe 22, is
flexible and preferably 20 inches in length. Grooves
230a, 230b, 230c and 230d are defined in the lower
surface of the press shoe 222. The grooves 230a, 230b,
230c and 230d are spaced apart in the machine
direction, are parallel to each other and to the axis
18, and extend in the cross-machine direction. Pivot
rods 232a, 232b, 232c and 232d are positioned in
respective grooves 230x, 230b, 230c and 230d.
The pressure applying apparatus includes pressure
applying devices or extendable assemblies 234a, 234b,
234c and 234d engaging respective pivot rods 232a,
232b, 232c and 232d. The extendable assemblies 234a,
234b, 234c and 234d are non-parallel and each exerts a
force i~n a respective plane including the axis 18 of
the backing roll 14.
Various features of the invention are set forth in
the following claims.
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Representative Drawing