The present invention broadly relates to a wet press and, more specifically, pertains to a new and improved construction of a wet press for dewatering a web of material.
Generally speaking, the wet press of the present invention comprises a rotating or rotatable roll and a contact pressure device. The web of material is guided between the rotating or rotatable roll and the contact pressure device in a press nip conjointly with at least one water-absorbent belt along a portion of the circumference of the rotating or rotatable roll. The contact pressure device comprises a hydrostatic pressure element. The hydrostatic pressure element comprises a support shoe movable in the pressing direction. The support shoe comprises at least two pressure pockets or recesses sequentially arranged in the direction of travel of the web of material in the press nip. The pressure pockets are connected with a common pressure chamber by conduits. The common pressure chamber is supplied with a suitable pressure medium.
In other words, the wet press of the present invention for dewatering a web of material comprises a rotatable roll and a contact pressure device, the contact pressure device and the rotatable roll defining therebetween a press nip. The wet press also comprises at least one water-absorbent belt, the web of material being guided conjointly with the water-absorbent belt through the press nip between the contact pressure device and the rotating roll and along a portion of the circumference of the rotatable rolI. The web of material has a predetermined direction of travel. The contact pressure device comprises a hydrostatic pressure element having a predetermined direction of pressing. The hydrostatic pressure element comprises a support shoe movable in the predetermined direction of pressing. The support shoe comprises at least two pressure pockets arranged sequentially in the direction of travel of the web of material in the press nip, a common pressure chamber supplied with a suitable pressure medium and conduits connecting the pressure pockets with the common pressure chamber.
Such wet presses are disclosed, for example, in the German Pat. No. 2,313,920, and serve for dewatering, for instance, a paper web or pulp web or another fibrous material. The web of material is guided through a press nip conjointly with, for instance, a water-absorbent felt belt and a water-impervious contact pressure belt. The press nip is formed by a roll and a hydrostatic pressure element. In this manner, a uniform contact pressure is attained in the press nip over a certain length of the web of material in the direction of travel, so that the dewatering of the web of material to be expressed is significantly better than in wet presses having two rolls acting only in one line transverse to the web of material. The dewatering performance is, however, not optimal since the contact pressure or pressing force in the press nip remains practically constant over the entire length.
It is known to the art, for instance from the German Pat. No. 3,105,276, or the U.S. Pat. No. 3,783,097, granted Jan. 1, 1974, to provide a successively increasing contact pressure or pressing force in a press nip of predetermined length in a wet press having a roll and a contact pressure device cooperating with the roll. This effect is attained in such wet presses by arranging a plurality of pressure chambers or a plurality of hydraulically actuatable bearing shoes sequentially in the direction of web travel. For attaining a contact pressure or pressing force increasing in the direction of web travel, the individual pressure chambers or bearing shoes arranged sequentially must be supplied with a suitable pressure medium at a different and successively increasing pressure. This, however, requires a complicated regulation of the pressure in the individual pressure chambers and a multiplicity of control devices and control conduits. Furthermore, a plurality of independent bearing elements are necessary in the direction of web travel which complicates construction to an undesirable degree. Furthermore, a pressure drop arises between the bearing shoes which leads to an undesirable re-moistening of the web of material.