Shoe for an extended-nip press

A shoe in an extended-nip press arranged to be placed in a nip between a back-up roll and a belt-mantle roll inside the belt mantle. The shoe is pressed by an actuator, e.g., a cylinder device, towards the back-up roll, while the web/felt or felts is/are placed between the back-up roll and the belt mantle. The shoe has at least one chamber provided for hydraulic fluid into which a fluid is passed from a duct. The shoe has a first curved face, whose curve radius is substantially equal to the curve form of the back-up roll. The shoe has a second face which forms the bottom of the chamber provided for hydraulic fluid. The second face joins the first face and has a larger curve radius than the first face. At a joint between the first face and the second face, the tangents of the faces are substantially the same.

BACKGROUND OF THE INVENTION 
The present invention relates to a shoe in an extended-nip press of the 
type, e.g., present in paper machines. The present invention also relates 
to a method for using the shoe in an extended-nip press to obtain a 
desired pressure profile, usually a linear profile. 
The optimal shape of the pressure curve in an extended-nip press is 
triangular, i.e., the pressure rises in a linear manner from zero to a 
maximum value. In prior art shoes for extended-nip presses, the rise of 
pressure has been unsatisfactory. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a new and improved shoe 
for an extended-nip press by whose means it is possible to come closer to 
the optimal triangular shape of the increase in pressure for the pressure 
curve. 
In accordance with the present invention, the novel shoe has a first face 
in the area of the trailing side, when considered in the direction of 
running of the web. The radius R.sub.1 of the first face corresponds to 
the curve radius of the back-up roll. The first face is followed by a 
second face which is also curved and which determines the shape of the 
bottom of the hydrostatic chamber. The second face is constructed having a 
radius R.sub.2. At the joint between the first face and the second face, 
the radii R.sub.1 and R.sub.2 are situated on the same line, while the 
radius R.sub.2 is slightly longer than the radius R.sub.1. In relation to 
the hydrostatic chamber, the area at the inlet side of the chamber 
comprises a third face which has the same curve radius R.sub.1 as the 
first face on the shoe, i.e., the third face corresponds to the curve form 
of the backup roll K. In the present invention, at the joint between the 
first face and the second face, the tangents of the faces are the same. As 
a result of this construction, in an arrangement in accordance with the 
present invention, a substantially linear, triangular curve of pressure 
increase is obtained. This type of curve provides substantial advantageous 
over the prior art devices. 
The manufacture of a shoe in accordance with the present invention takes 
place so that as a first step, the bottom part/parts of the hydrostatic 
chamber, i.e. hydrostatic pocket, are machined, e.g., or turned, to form a 
radius R.sub.2 in the second face portion and form the partition walls of 
the hydro-static chamber/chambers with radius R.sub.1. After this step, 
the face of the shoe proper, i.e., the first face and the third face, are 
machined to define radius R.sub.1. 
A shoe in accordance with the present invention for an extended-nip press 
is mainly characterized in that the shoe has a first curved face, whose 
radius of curvature is substantially equal to the curve form of the 
back-up roll. The shoe has a second face which forms the bottom of the 
chamber provided for hydraulic fluid. The second face joins the first face 
and is constructed with a larger curve radius than the first face and so 
that, at the joint between the first face and the second face, the 
tangents of the faces are substantially the same. 
The shoe in accordance with the present invention is placed in an 
extended-nip press wherein a nip is defined by a back-up roll and a 
belt-mantle roll. The shoe, in an interior of the belt mantle, is pressed 
by actuator means towards the back-up roll while a web runs on at least 
one felt between the back-up roll and the belt mantle. The shoe has at 
least one chamber in the second face portion for a lubricant, e.g., 
pressurized or hydraulic fluid. Further, the shoe may include a third face 
portion situated in an inlet side of the shoe at which the web enters the 
nip. The third face portion has a radius of curvature substantially equal 
to the radius of curvature of the first face portion, i.e., the radius of 
the back-up roll. The web is pressed between two corresponding surfaces 
having the same curvature, i.e., between the back-up roll and the first 
and third face portions. A planar face portion may be arranged in a 
direction substantially tangential to the third face portion and preceding 
the third face portion at the inlet side of the shoe, i.e., in the running 
direction of the web through the nip. 
The shoe preferably includes a plurality of chambers arranged in a 
direction of width of the web and partition walls to separate the chambers 
from one another. Top edges of the partition walls have a shape 
corresponding to the radius of curvature of the first face portion so that 
in the area of the partition walls, the shoe has a uniform, curved surface 
corresponding to the curvature of the back-up roll. 
In a preferred embodiment, the shoe has at least three interconnected 
parts. The first part constitutes the second face portion and forms a 
bottom of the chambers. The second and third part are arranged adjacent to 
the first part and constitute the first face portion and the third face 
portion which have a radius of curvature substantially equal to that of 
the back-up roll. 
The present invention also relates to a method for providing a 
substantially linear pressure increase in a shoe of an extended-nip press. 
In the method, a back-up roll and a belt-mantle roll are arranged to 
define a nip through which a web runs on at least one felt. A shoe, in 
accordance with the present invention, is an interior of the belt mantle 
of the belt-mantle roll and is pressed against the back-up roll. As such, 
a first curved face portion in the shoe has a radius of curvature 
substantially equal to the curvature of the back-up roll, and a second 
curved face portion of the shoe, adjacent to the first face portion, has a 
chamber therein and a radius of curvature larger than the radius of 
curvature of the first face portion. By passing a pressurized fluid to the 
chamber through ducts, the shoe is loaded to provide a desired pressure 
profile, which is ideally a linear pressure profile. 
Also, the first and second face portions may be arranged so that tangent 
lines to the first and second face portions are substantially the same at 
a joint between them. A third face portion of the shoe may be arranged at 
an inlet side of the shoe at which the web enters the nip. The third face 
portion has a radius of curvature substantially equal to the radius of 
curvature of the first face portion, i.e., the back-up roll. A plurality 
of chambers are arranged in a direction of width of the web and separated 
by partition walls. 
In the following, the invention will be described with reference to some 
preferred embodiments of the invention illustrated in the figures in the 
accompanying drawings. However, the invention is not confined to these 
embodiments alone.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a side view of a prior art extended-nip press. Press felts 
H.sub.1 and H.sub.2 are passed through a nip N while a web W is placed in 
the middle of the felt draw. The nip N is formed between the rolls mounted 
on the frame R, e.g., a back-up roll K.sub.1 and a belt-mantle roll 
K.sub.2. A shoe 10 in accordance with the present invention may be placed 
in the extended-nip press inside the belt mantle S so that it is pressed 
against the felt-mantle face S'. Thus, an area L of the nip N becomes 
substantially long as the resilient belt mantle S follows the curve form 
and the surface form of the back-up roll K.sub.1 over the entire length L 
of the shoe 10. 
FIGS. 2 and 3 show a shoe 10 in accordance with the present invention for 
use in an extended-nip press. The shoe 10 has a first face 11 whose curve 
form R.sub.1 corresponds to the radius, i.e., the curve form, of the 
back-up roll K.sub.1. The shoe 10 has a second face 12 which forms the 
bottom of hydrostatic pockets or chambers 12',12", 12"'. The hydrostatic 
pockets 12',12" . . . define a hydrostatic space for pressure fluid. The 
face 12 is shaped to conform to the curve radius R.sub.2. At a joint C 
between face 11 and face 12, the tangents t.sub.1 and t.sub.2 of the two 
faces 11 and 12 are the same. In addition to the curved bottom 12 and by 
an end wall 14, the hydrostatic chambers 12',12" . . . are also defined by 
partition walls 13',13" . . . arranged substantially in the transverse 
direction of the web. 
The top edges of the partition walls 13',13" . . . have a curvature 
corresponding to the curve radius R.sub.1, which corresponds to the curve 
form of the back-up roll K.sub.1. One or more ducts 15', 15",15'" open 
into each of the chambers 12',12" . . . , in order to pass pressurized 
fluid into the chambers 12',12",12"'. The center of curvature of the top 
edge of the partition walls 13',13" . . . is denoted by O.sub.1 which is 
the same as that of face 11 and a third face 16. 
The function of the partition walls 13',13",13"' . . . is to operate as 
limiting means, or parts, which permit a maximum uniform distribution of 
the hydrostatic pressure across the length of the shoe without causing 
detrimental effects of outside interfering factors and impulses on the 
pressure formation. By means of the vertical end wall 14, the face 12 is 
joined by the third face 16 which has a curvature corresponding to the 
same curve radius R.sub.1 as the back-up roll K.sub.1. 
FIG. 3 is a sectional view taken along the line I--I in FIG. 2. With 
reference to this figure, the shoe in accordance with the present 
invention is described in greater detail. The first face 11 joins the 
second curved face 12 smoothly at the point C. At the point C, the tangent 
t.sub.1 of the face 11 is the same as the tangent t.sub.2 of the face 12. 
Thus, when the radii R.sub.1 and R.sub.2 related to the point C are 
examined, the centers of curvature O.sub.1 and O.sub.2 of the faces 11 and 
12 are placed on the same straight line which intersects with point C. The 
radius R.sub.2 of the face 12 is slightly longer, and larger as shown, 
than the curve radius R.sub.1 of the face 11. The ratio R.sub.2 /R.sub.1, 
i.e., the ratio of the radii of curvature, is preferably in a range from 
about 1.05 to about 1.5 and even more advantageously in a range from about 
1.1 to about 1.3. 
During construction of the shoe 10, the adjustable variables are the length 
L.sub.1 of the first face 11, the length L.sub.2 of the second face 12, 
and, in the inlet area of the web W into the shoe, the length L.sub.3 of 
the face 16 and the length L.sub.4 of face 17 in the lateral area. The 
face 17 is preferably a straight planar face that is connected to the 
radius R.sub.1 substantially tangentially. Further, the shoe 10 comprises 
an initial rounding, or rounded portion, 18 arranged before face 17 in the 
running direction of the web and a final rounding 19 arranged after face 
11 in the running direction of the web. The overall length (L) of the shoe 
is L=L.sub.1 +L.sub.2 +L.sub.3 +L.sub.4. 
A particularly advantageous form of the pressure curve in the shoe in 
accordance with the present invention is obtained with a construction in 
which the ratio of radii R.sub.2 /R.sub.1 is as small as possible, 
preferably in a range from about 1.1 to about 1.3, and wherein the length 
L.sub.2 of the hydrostatic chamber 13 is as large as possible. Also, 
preferably the face 11 in the area of the trailing edge of the shoe is 
relatively short and, in an extreme case, may be omitted entirely. The 
overall length of the shoe 10 is preferably in a range from about 120 mm 
to about 150 mm. 
FIG. 4A shows the formation of the pressure curve from the initial rounding 
18 to the final rounding 19 in an embodiment in which the overall length L 
of the shoe is about 250 mm. FIG. 4B shows the formation of the pressure 
curve in an embodiment in which the overall length L of the shoe is about 
150 mm. From FIGS. 4A and 4B, it is seen that the rise of the pressure 
curve is substantially linear, and, in a corresponding manner, the 
lowering or decrease of the pressure curve is as steep as possible. 
FIG. 5 shows a mode of construction and formation of the shoe in accordance 
with the present invention. The bottom parts 12 of the hydrostatic pockets 
12',12",12"' are first turned, or machined, so that they have a radius 
R.sub.2, and thereafter, the partition walls 13',13",13"' are turned with 
the radius R.sub.1. The faces 11 and 16 of lateral parts 20b,20c are 
turned with the radius R.sub.1. The parts 20b,20c are fixed, for example 
by means of screws, to the middle part 20a of the construction, e.g., to 
its side projections 20a',20a". The middle part 20a includes the 
hydrostatic chambers 12', 12", 12"'. 
FIG. 6 shows a hydraulic diagram of a hydrostatic loading shoe 10 in 
accordance with the present invention. A lubricant, preferably hydraulic 
fluid, is passed from the fluid container 21 by means of a fluid pump P, 
along a duct 22 into a capillary duct 15/ducts 15', 15" . . . in the shoe 
10 as shown in FIG. 2. Through the capillary duct 15/ducts 15', 15", 15"' 
. . . the fluid flows through the face 12 into the chambers 12', 12". . . 
The shoe 10 is loaded hydraulically by loading means, e.g., cylinder 
devices 24a, 24b, by means of their pistons 24a, 24b, in relation to the 
length of the hydrostatic shoe 10, from both ends of the shoe 10. The 
hydraulic cylinders 24a,24b can be loaded independently from one another, 
and in this manner, it is possible to vary the loading of the shoe so as 
to obtain a desired pressure curve. 
The pressurized fluid is passed from the fluid container 21, from the duct 
25, by means of a regulation pump P.sub.2 into the duct 26 and further 
into the ducts 26a,26b. Ducts 26a,26b may include proportionally 
adjustable valves 27a,27b, or other compatible regulation means, to 
regulate the loads applied by the pistons 24a,24b. The return ducts 
28a,28b from the cylinder 24a,24b are connected with the duct 29 which 
comprises a valve 30. When the block 30a of the valve 30 is switched on, 
the fluid flow passes through the valve 30 into the hydraulic-fluid 
container 21. When the block 30b of the regulation valve 30 is switched 
on, the flow is passed from the pump P.sub.2 into the cylinders 24a,24b 
and into the cylinder spaces at the side of the piston rod. As shown in 
FIG. 6, the overflow of the fluid is passed from the overflow space 31 
along the duct 32 into the fluid container 21. 
The examples provided above are not meant to be exclusive. Many other 
variations of the present invention would be obvious to those skilled in 
the art, and are contemplated to be within the scope of the appended 
claims.