This invention relates to a press for dewatering material suspensions, possibly in connection with liquid treatment.

A press comprises two co-operating press rolls, which between them¬ selves form a roll nip. The rolls are arranged in a vat, to which the material suspension, for example a pulp suspension, is supplied. The rolls are formed with liquid-permeable shell surfaces, and the suspension is dewatered in that liquid by means of overpressure is pressed in through these surfaces. The final dewatering to the desired dry matter content of the material takes place in the nip between the rolls. The dry matter content there can be up to 35-55%.

The shell surface of the press rolls consists of a perforated metal sheet welded on a roll body. In order to achieve high capacity, the total open area shall be large at the same time as the apertures shall be small to prevent fibers from following along with the liquid through the apertures. For solving these problems, the press roll is provided with a wire cloth on the outside of the perforated shell sheet. The wire allows liquid flow even along the shell surface. This implies, that the perforations can be given a greater size so as to yield a higher capacity without causing the risk of increased fiber passage. The use of press rolls covered with wire has proved to be especially advantageous for mechanical pulp, which contains a greater amount of fine material. The wire cloth, compared with a perforated metal sheet, implies that a smaller amount of fine material is allowed to pass through.

The rolls immersed in the vat are rotary on two parallel shafts, so that the vat encloses at least the lower half of the rolls. The material suspension is supplied to the space between the rolls and vat. This space is sealed toward the ambient, so that an overpressure can be maintained in the vat in order thereby to fac¬ ilitate dewatering. Seals are provided at the upper edge of the

vat both, toward the end walls of the rolls and along the shell surf¬ aces of the rolls. The seal at the end walls normally consists of an hydraulically applied plastic strip, and to the shell surface, norm¬ ally a bar is applied, mostly by hydrostatic pressure. Between the rolls, the nip and the pulp web passing through continuously serve as a seal toward the ambient.

After the nip, doctor means are located, the object of which is to remove the dewatered pulp web from the rolls. The doctor means norm¬ ally comprise a steel or plastic blade, which abuts obliquely the ^• .shell surface of the roll. The pulp is thereafter removed by means of a con¬ veyor for subsequent processing steps.

It was found that the use of sealing bars of the type normally used at press rolls with shell surfaces of perforated metal sheet is not at all suitable at press rolls covered with wire cloth. There is a great risk that the wire cloth gets wedged and deformed and that at the same time the efficiency decreases.

The present invention offers a solution for the aforesaid problems. The characterizing features of the invention are apparent from the attached claims.

The invention is described in greater detail in the following, with reference to an embodiment thereof shown in the accompanying drawing, in which

Fig. 1 is a cross-section of a press according to the invention, and Fig. 2 shows a sealing device on an enlarged scale.

The device shown in Fig. 1 comprises two cylindric rotary liquid- -permeable press rolls 10, the shell surface of which consists of a perforated metal sheet welded on a roll body. On the outside of the perforated sheet, a wire cloth 11 is applied which preferably is made of plastic wires. The rolls 10 are partially immersed in a vat 12 so that spaces 13 are formed between the rolls and vat. Said

spaces 13 communicate with inlets 14 for the pulp suspension. Between the rolls 10, the spaces 13 contract to form a nip 15.

The spaces 13 are sealed toward the ambient by seals 16 toward the shell surfaces of the rolls 10, and by seals 17 applied to the end walls of the rolls, The pulp web in the nip 15 acts as a seal between the rolls.

After the nip 15, doctor means 18 are located to remove the pulp web coming from the nip 15. The seal 16 between the vat 12 and the shell surface of each of the rolls 10 consists of a flexible steel strip 21 extending along the entire length of the roll. The steel strip 21 is attached in a holder 20 on the upper edge of the vat 12, in such a manner that the strip is directed inward to the roll 10 and bent so that its leading end abuts the rolls. A blade 19 of flexible seal¬ ing material, preferably rubber, is located on that side of the steel strip 21 which is remote from the roll, so that the blade 19 raises together with the steel strip and extends all the way to the roll. The ^' leading end of the steel strip 21 extends past the leading end of the blade 19 and can be designed with a clearance. The blade 19 has a length in axial direction exceeding the axial length of the steel strip 21 so as to form a seal to the seals 17 at the end walls of the roll in the vat corners.

Due to the design of the seal 16, overpressure can be maintained in the space 13 without causing the risk of deformation of or damage on the wire cloth. The seal has a simple and effective design and can easily be installed and replaced, when required. Normally, the seal¬ ing blade 19 and the steel strip 21 are replaced.

The invention, of course, is not restricted to the embodiment shown and described, but can be varied within the scope of the invention idea.