Press roll for treating a material shaped in the form of a web

Flexible press sleeve for a press roll for treating a web includes an inside surface including a longitudinal press area adapted to be pressurized with a press shoe by directing pressure radially outward, and a flexible section on at least one end of the press area having a greater flexibility than a flexibility of the press sleeve outside the flexible section, without causing a significant weakening of the press sleeve within the flexible section. A press shoe includes the press roll and a mating roll forming a press opening with the press roll. A method of treating a web includes draining a fibrous pulp web by using the press shoe.

CROSS-REFERENCE OF RELATED APPLICATION 
The present invention claims the priority under 35 U.S.C. .sctn.119 of 
German Patent Application No. 196 52 545.4 filed on Dec. 17, 1996, the 
disclosure of which is expressly incorporated by reference herein in its 
entirety. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a press roll for treating material shaped 
in the form of a web, in particular to drain a fibrous pulp web, with a 
flexible press sleeve which has an inside that, in order to determine the 
longitudinal press area, can be pressurized with a press shoe by directing 
pressure radially outward. The invention furthermore relates to a press 
shoe for treating material shaped in the form of a web with a press roll 
and a mating object, in particular a mating roll, that creates a press 
opening with the press roll. 
2. Discussion of Background Information 
The flexible press sleeve of a rotating press roll of the type mentioned at 
the outset is typically pressed radially against a mating object, for 
example a rotating mating roll, with the aid of a press shoe positioned 
radially inside the press roll, whereby the friction occurring between the 
press shoe and the interior surface of the press roll is reduced by an oil 
film provided between these two elements. The fibrous pulp web to be 
drained is guided through the press opening created between the press roll 
and the mating roll and drained by the pressure present in the press 
opening. 
A problem of conventional devices is that the press sleeve of a press shoe 
in operation is not only stressed by the surface pressure in the press 
opening but is also dynamically stressed by a changing bending strain. The 
areas of the press sleeve located on both ends of the press shoe are most 
affected by this dynamic bending strain. The curvature in this section of 
the press sleeve changes from convex to concave or vice versa, depending 
on whether the press sleeve, relative to its horizontal center position, 
is bent outward by the press shoe, or pressed radially inward by the 
mating roll. This constantly repeating curvature change represents high 
mechanical strains to these press sleeve sections and leads to increased 
crack formations across the press sleeve. 
SUMMARY OF THE INVENTION 
An object of the present invention is to construct a press sleeve and a 
press shoe of the type mentioned at the outset so that the danger of crack 
formation in the press sleeve due to dynamic straining in the press shoe 
end sections is avoided or at least reduced. 
This task is accomplished for a press sleeve of the type mentioned at the 
outset, wherein the press sleeve has a flexible section on at least one 
end of the press area with a greater flexibility than the flexibility in 
the area of the press sleeve outside the flexible section, without causing 
a significant weakening of the press sleeve within the flexible section. 
By providing a special flexible section with an increased flexibility on 
one end of the press section area or on both ends of the press area, it is 
ensured that the curvature changes occurring due to dynamic strain do not 
lead to crack formations in this flexible section of the press sleeve. In 
accordance with the invention, the flexible section must be constructed 
such that no significant weakening of the press sleeve occurs, since 
otherwise the risk reduction with respect to crack formations, achieved by 
increasing the flexibility, would be offset. A weakening of the press 
sleeve in the press shoe end sections could, for example, result in crack 
formations in the press sleeve caused by the tensile loads attacking these 
sections during operation so that, in effect, the danger of crack 
formations would even be increased. 
In a preferred embodiment of the invention, the flexible section extends 
from an area within the press area to an area outside the press area. This 
ensures that the flexible section having the required flexibility and at 
the same time the required stiffness is placed at the location of the 
press sleeve that undergoes the heaviest strain due to dynamic loading. 
The heavily-strained area of the press sleeve extends into the press area, 
in particular when the width of the fibrous pulp web to be treated is 
smaller than the width of the press shoe and therefore the width of the 
press area is determined by the press shoe, so that the required 
flexibility of the press sleeve also must be ensured in the end sections. 
The flexible section can thereby be arranged symmetrically or 
asymmetrically around the edge of the press area. 
In another embodiment of the invention, the press sleeve has a smaller 
thickness in the area of the flexible section than the press area portion 
located outside the flexible section. The press sleeve thickness thereby 
decreases radially outward. The reduced press sleeve thickness produces 
the desired press sleeve flexibility, whereby the thickness is only 
reduced as far as being able to maintain the required stability of the 
press sleeve. The continuous reduction of press sleeve thickness, in 
particular radially outward, ensures that the flexibility of the press 
sleeve increases axially outward from the edge zones of the press area to 
obtain the desired flexibility in the section of the press sleeve that 
undergoes the heaviest strain. A continuous reduction thereby ensures that 
no stability failures occur in the axial direction of the press sleeve. 
In another preferred embodiment of the invention, the press sleeve within 
the flexible section comprises, at least sectionally, a material with 
higher flexibility than outside the flexible section, in particular an 
elastomeric material. The material used can be adjusted optimally to the 
operating requirements by using different materials inside and outside the 
flexible section of the press sleeve. The material for the edge zones of 
the press area and for the adjoining area of the press sleeve must have a 
relatively high flexibility and at the same time a high tensile strength, 
while the press sleeve material inside the press area is to be optimized 
to the high press forces occurring in the press opening. 
In accordance with the present invention, a flexible press sleeve for a 
press roll for treating a web includes an inside surface including a 
longitudinal press area adapted to be pressurized with a press shoe by 
directing pressure radially outward. The flexible press sleeve also 
includes a flexible section on at least one end of the press area having a 
greater flexibility than a flexibility of the press sleeve outside the 
flexible section, without causing a significant weakening of the press 
sleeve within the flexible section. 
In a further embodiment, the flexible section extends from an area within 
the press area to an area outside the press area. 
In a further embodiment, the press sleeve in an area of the flexible 
section has a smaller thickness than in an area of the press area located 
outside the flexible section. 
In a still further embodiment, the thickness of the flexible section is 
continuously reduced toward an outside. 
In a still further embodiment, the press sleeve has an outer surface which 
drops off within the flexible section toward an end of the press sleeve. 
In a still further embodiment, the outer surface of the press sleeve forms 
an oblique surface. 
In a still further embodiment, the oblique surface may extend at an angle 
.alpha. of about .ltoreq.3.degree. to the outer surface of the press 
sleeve located outside the flexible section. Further, the oblique surface 
may extend at an angle .alpha. of about .ltoreq.2.degree. to the outer 
surface of the press sleeve located outside the flexible section. Still 
further, the oblique surface may extend at an angle .alpha. of about 
.ltoreq.1.degree. to the outer surface of the press sleeve located outside 
the flexible section. 
In a further embodiment, at least a portion of the press sleeve within the 
flexible section includes a material having higher flexibility than a 
material of the press sleeve outside the flexible section. 
In a still further embodiment, the material having higher flexibility 
comprises a soft, elastomeric material. 
In a further embodiment, the flexible section may have an axial width of at 
least about 20 mm. Further, the flexible section may have an axial width 
of at least about 30 mm. Still further, the flexible section may have an 
axial width of at least at least about 50 mm. 
In a further embodiment, the flexible section may overlap the press area by 
at least about 10 mm. Further, the flexible section may overlap the press 
area by at least about 20 mm. Still further, the flexible section may 
overlap the press area by at least about 30 mm. 
In accordance with another embodiment of the present invention, a press for 
treating a web, includes a press roll including a press shoe and a 
flexible press sleeve. The press sleeve has an inside surface including a 
longitudinal press area adapted to be pressurized with the press shoe by 
directing pressure radially outward, and the press sleeve further 
including a flexible section on at least one end of the press area having 
a greater flexibility than a flexibility of the press sleeve outside the 
flexible section, without causing a significant weakening of the press 
sleeve within the flexible section. The press shoe also includes a mating 
roll forming a press opening with the press roll. 
In accordance with yet another embodiment of the present invention, a 
flexible press sleeve for a press roll for treating a web includes a 
longitudinal press area and a flexible section on at least one end of the 
press area having a greater flexibility than a flexibility of the press 
sleeve outside the flexible section, without causing a significant 
weakening of the press sleeve within the flexible section. 
The present invention also involves a method of treating a web including 
draining a fibrous pulp web by using a press. The press includes a press 
roll including a press shoe and a flexible press sleeve. The press sleeve 
having an inside surface including a longitudinal press area adapted to be 
pressurized with the press shoe by directing pressure radially outward, 
and the press sleeve further including a flexible section on at least one 
end of the press area having a greater flexibility than a flexibility of 
the press sleeve outside the flexible section, without causing a 
significant weakening of the press sleeve within the flexible section. The 
press shoe also includes a mating roll forming a press opening with the 
press roll. 
Further embodiments and advantages can be seen from the detailed 
description of the present invention and the accompanying figures.

DETAILED DESCRIPTION 
The particulars shown herein are by way of example and for purposes of 
illustrative discussion of the preferred embodiments of the present 
invention only and are presented in the cause of providing what is 
believed to be the most useful and readily understood description of the 
principles and conceptual aspects of the invention. In this regard, no 
attempt is made to show structural details of the invention in more detail 
than is necessary for the fundamental understanding of the invention, the 
description taken with the drawings making apparent to those skilled in 
the art how the several forms of the invention may be embodied in 
practice. 
FIG. 1 displays a portion of a press sleeve 1 comprising an elastomeric 
matrix 2 containing longitudinal and cross threads 3, 4. 
The press sleeve 1 makes contact with a portion of its inside surface 5 on 
the outer surface of a press shoe 6. The press sleeve 1 is preferably made 
of polyurethane. A lubricant 7, for example in the form of oil, is 
provided between the inside surface 5 of the press sleeve 1 and the press 
shoe 6 in order to enable the press sleeve 1 to glide on the press shoe 6 
in a relatively frictionless manner. 
The press shoe 6 is pressed axially outward against the inside surface 5 of 
the press sleeve 1 by pressure units that are not illustrated, so that the 
contact surface defines a press area 8 of the press sleeve 1. 
The press sleeve 1 contains a flexible section 9 in which the outer surface 
10 of the press sleeve 1 extends at an angle .alpha. with respect to the 
outer surface 10 of the press sleeve 1 located outside the flexible 
section 9. The outer surface 10 thereby creates an oblique surface 11 
inside the flexible section 9 and extends over the entire circumference of 
the press sleeve 1. In a press sleeve 1 mounted parallel to the 
longitudinal axis of the press roll, the oblique surface 11 is therefore 
sloped at the angle .alpha. with respect to the longitudinal axis. 
The thickness of the press sleeve 1 decreases along the oblique surface 11 
in the direction of the press sleeve edge, so that the flexibility of the 
press sleeve 1 in flexible section 9 and beyond, up to the press sleeve 
end, is higher than inside the press area 8. The oblique surface 11 
gradually joins the portion of the press sleeve 1 located outside the 
flexible section 9, so that no discontinuities are created on the outer 
surface of the press sleeve 1 that reduce the stability of the press 
sleeve 1. 
Due to the low degree of inclination of the oblique surface 11, the 
reduction of the thickness of press sleeve 1 is so small that a weakening 
of the press sleeve 1 as a result of reducing the thickness practically 
does not occur. 
The oblique surface 11 extends at an angle .alpha. of about 
.ltoreq.3.degree., preferably .alpha. about .ltoreq.2.degree., and more 
preferably .alpha. about .ltoreq.1.degree. to the outer surface 10 of the 
press sleeve 1 located outside the flexible section 9. The axial width of 
the flexible section 9 measures at least about 20 mm, preferably at least 
about 30 mm, and more preferably at least about 50 mm. The flexible 
section 9 overlaps the press area 8 by at least about 10 mm, preferably at 
least about 20 mm, and may overlap by at least about 30 mm or even at 
least about 40 mm. In other words, the flexible section 9 extends over the 
press area 8 by at least about 10 mm, preferably at least about 20 mm, and 
may extend over each other by at least about 30 mm or even at least about 
40 mm. 
FIG. 2 shows an embodiment wherein an elastomeric element 12, having a 
higher degree of flexibility than that of the elastomeric matrix 2, is 
used inside the flexible section 9 of the press sleeve 1. The elastomeric 
element is preferably made of softer polyurethane. The illustrated 
embodiment shows a recess 13 located on the outer surface 10 of the press 
sleeve 1. The recess 13 extends in a ring-shaped manner over the 
circumference of the press sleeve 1 and is used to insert the elastomeric 
element 12. The elastomeric element can be connected with the elastomeric 
matrix 2 with the aid of conventional methods, such as gluing, 
vulcanizing, etc. 
It is furthermore possible to arrange the elastomeric element 12 not in a 
ring-shaped manner, but in individual sections along the circumference of 
the press sleeve 1. 
In principle it is also possible to insert the elastomeric element 12 into 
the inner surface 5 of the press sleeve instead of the outer surface 10 of 
the press sleeve, or that the elastomeric element 12 extends over the 
entire thickness of the press sleeve 1. 
While the illustrated embodiments form the outer surface 10 of the press 
sleeve in a smooth manner, it is also possible to form holes, grooves or 
other types of recesses in the outer surface 10 in order to improve the 
drainage of the fibrous pulp web to be treated. 
It is also possible to combine the embodiment illustrated in FIG. 1 with 
the embodiment illustrated in FIG. 2, i.e., to increase the flexibility by 
reducing the press sleeve thickness as well as using a softer elastomeric 
material inside the flexible section 9. 
It is noted that the foregoing examples have been provided merely for the 
purpose of explanation and are in no way to be construed as limiting of 
the present invention. While the invention has been described with 
reference to a preferred embodiment, it is understood that the words which 
have been used herein are words of description and illustration, rather 
than words of limitation. Changes may be made, within the purview of the 
appended claims, as presently stated and as amended, without departing 
from the scope and the spirit of the invention in its aspects. Although 
the invention has been described herein with reference to particular 
means, materials and embodiments, the invention is not intended to be 
limited to the particulars disclosed herein; rather, the invention extends 
to all functionally equivalent structures, methods and uses, such as are 
within the scope of the appended claims.