Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Patent
1997-05-29
1999-05-11
Hastings, Karen M.
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
100174, 210407, 210396, 162323, B30B9/20
Patent
active
059024569
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to apparatus for dewatering material suspensions. More particularly, the present invention relates to apparatus comprising a pair of cooperating press rolls, which between themselves form a press nip and in which the press rolls are formed with liquid permeable shell surfaces, whereby the material suspension, for example, a pulp suspension, is dewatered by liquid being pressed through these surfaces by means of an overpressure. The material is finally dewatered to the desired dry matter content in the nip between the rolls.
BACKGROUND OF THE INVENTION
The shell surface of the types of press rolls discussed above consists of a perforated metal sheet, which is welded onto a roll body. In order to achieve a high capacity, the total open area must be large, and at the same time the apertures must be sufficiently small so as to prevent fibers from following along with the liquid through the apertures. In order to solve these problems, the press roll can be covered with a wire cloth on the outer surface of the perforated shell sheet. Such a wire permits liquid flow even along the shell surface. This, in turn, permits the perforations to be given a greater size, whereby the capacity is increased without risking increased fiber passage. Wire-covered press rolls have proven to be particularly advantageous for mechanical pulp, which contains a large amount of fine material. Compared with a perforated metal sheet, the wire cloth permits a smaller amount of fine material to pass through the apertures.
The rolls are generally rotatably mounted on two parallel shafts, and are usually immersed into a trough, which encloses at least the lower half of the rolls. The material suspension is supplied to the space between the rolls and the trough. This space is sealed from the surroundings so that an overpressure can be maintained in the trough whereby the dewatering is facilitated. The pulp is moved from the trough upwards through the nip, where it is simultaneously dewatered. Doctor blades are located after the nip, for the purpose of removing the dewatered pulp web from the rolls. The pulp is then removed by a conveyor for transfer to subsequent processing steps.
By means of this type of dewatering, dry matter contents of up to about 55 to 60% can be obtained. The equipment required for removing the dewatered pulp web from the rolls and for transferring the pulp from below to the conveyor, however, is complicated and sensitive to operational breakdowns. In many cases when a maximum dry matter content is not required, therefore, a simpler dewatering apparatus would be sufficient and quite desirable.
SUMMARY OF THE INVENTION
In accordance with the present invention, these and other objects have now been accomplished by means of a simplified method and a simpler dewatering apparatus in which the dewatered pulp can readily be taken off and conveyed from the apparatus. Thus, by means of the apparatus according to the present invention, the dry matter content of the pulp can be increased from about 0.5 to 8% up to about 8 to 30%, and preferably from about 1 to 5% up to about 8 to 15%.
In accordance with the present invention, apparatus is provided for dewatering a material suspension comprising a pair of cylindrical, rotatable, liquid-permeable press rolls juxtaposed with each other so as to form a nip therebetween, whereby the material suspension can pass between the nip in order to be dewatered and to form a material web therefrom, a pair of doctor blades disposed below the nip, each of the pair of doctor blades being associated with one of the pair of press rolls for removing the material web from the pair of press rolls, and a sealed casing enclosing at least the upper portion of the pair of press rolls, the sealed casing including an inlet for the material suspension, the pair of doctor blades being coupled to each other whereby the pair of doctor blades are movable relative to the nip so as to alter the distance between the pair of doctor blades and nip when the si
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patent: 5107757 (1992-04-01), Oshita et al.
patent: 5667642 (1997-09-01), Luthi
Haggstrom Bert
Sundqvist Ingemar
Swardh Olof
Hastings Karen M.
Sunds Defibrator Industries AB
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