Press roll for web material

Details Press roll for web material Press roll for web material

1982-09-21

1985-05-21

Smith, William F.

Paper making and fiber liberation

Apparatus

Running or indefinite length product forming and/or treating...

29113AD, 29116AD, 100118, 100 93RP, 100153, 162205, 162358, D21F 302, D21F 308

Patent

active

045184607

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a press roll, which cooperates with an associated roll, for pressing web material, and is particularly for use in a paper making machine for pressing out the water from a web of fibrous material supported by a felt or support fabrics. The press roll is provided with a device having an elastically deformable outer shell in order to form an elongated nip and an inner shell for supporting the outer shell on its periphery.
It is known to use such a lengthened nip in order substantially to increase the removal of water as compared with ordinary press rolls. In the case of graphic papers, for instance, the solids content of the web can in this way be increased from between 40 to 45% absolute dryness to between 55 to 60% absolute dryness. In the case of toilet papers it is important that, in addition to the increase in the dryness, the product can be very positively influenced with respect to its required softness by an extended nip. Upon the cooperation of two rolls, at least one of which has a deformable outer shell arranged on a stationary roll shell, a longer nip will be obtained in the direction of the web. Such a roll is known, for instance, from German Provisional Patent AS No. 25 22 657. The roll shown there is intended, in particular, for use as backup impression cylinder in rotary printing. However, it is not suitable for a higher pressure such as is necessary in particular for the removal of water from webs of paper. The upper pressure limit is about 25 kgf/cm and its life is very short. A rubber covering, for instance, heats up and leads to the destruction of the web.
In order to obtain a lengthened press nip with higher pressure it is known, particularly in the construction of paper making machines, to conduct the support felt together with the web of paper between two rotating belts against which hydrostatic pressure members are pressed from both sides over a given length. Due to the special shape and development of the pressure members a given pressure profile can be obtained along the web (see U.S. Pat. No. 3,808,092). The sealing of such a device from the outside is, however, very critical. It is particularly problematical if the pressure members are to be lifted off from the web. This cannot be done without previously drawing off the oil.
It is furthermore known to press a rotating band by means of a pressure shoe hydrostatically against a rotating roll (see U.S. Pat. No. 3,853,698). In this case also it is very difficult to seal it against the emergence of oil on its sides. Even with expensive seals such a design cannot be made completely tight. This is very detrimental for operation. Dirt can settle on the exposed part of the band. It is therefore necessary that it be scraped off before entrance. In this case also, the hydrostatic character is very detrimental upon the opening and closing of the press shoe.
A tube roll for pressing a web of material against a drying cylinder is also known. The tube-like outer shell of that tube roll is supported on a co-rotating inner shell over self-contained segment tubes which are distributed along the inner periphery of the outer shell and which can be inflated in the nip to the application pressure (see German Provisional Patent AS No. 19 23 784). Such a device requires a special control device by which the segment tubes which are present at the time in the nip are acted on by pressure. This results in a relatively complicated and expensive construction, in which, in particular, the seal between the parts which rotate with respect to each other is very problematical. The tube segments are unsuitable for high pressures, because pressure can be produced only by a gas. When employing non-compressible liquid pressure fluids, as are necessary for the production of higher pressures, excessively high flow velocities in the feed and discharge lines of the individual chambers would occur at high machine speeds of more than 200 meters per minute, leading to cavitation.
The object of the present invention is to develop a press roll o

REFERENCES:
patent: 2430868 (1947-11-01), Francis, Jr.
patent: 3808092 (1974-04-01), Busker
patent: 3853698 (1974-12-01), Mohr
patent: 3974026 (1976-08-01), Emson et al.
patent: 4069569 (1978-01-01), Meckel
patent: 4287021 (1981-09-01), Justus et al.

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