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.