Arrangement for transferring a web from the press section to the

Details Arrangement for transferring a web from the press section to the Arrangement for transferring a web from the press section to the

1991-10-02

1992-12-08

Hastings, Karen M.

Paper making and fiber liberation

Apparatus

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

162290, 34116, 34117, D21F 304, D21F 504

Patent

active

051695014

DESCRIPTION:

BRIEF SUMMARY
The invention concerns an arrangement for transferring a fiber material web, preferably a paper web (hereafter briefly referred to as "web"), from the press section to the dryer section of a paper machine. Concerned is thus an arrangement where a continuous belt passing through the last press gap of the press section and fashioned as a water-absorbent felt belt serves a dual function: The felt belt absorbs in the usual way at least part of the water pressed out of the web in the press gap and removes it. Additionally, this felt belt carries the web from the press section to the dryer section, where it passes together with the web at least over the first drying cylinder of the dryer section. Therefore, this felt belt will hereafter be called "transfer felt".
An arrangement of that type is known from the European patent document 0346659. In detail, it has the following features: The last press of the press section has only a single felt belt, namely a bottom belt which at the same time performs the function of a transfer felt. Thus, the web to be dewatered makes direct contact with the upper roll of the last press. Therefore, this upper roll has a smooth and generally hard shell surface, for instance fashioned from granite or artificial stone. It is generally known that with such arrangement the web adheres behind the press gap for a distance to the upper roll and must be pulled off under application of a certain tensile stress. In the process, the web runs for at least a short distance freely, i.e., without backing by the transfer felt. Besides, it is inevitable that the web, which here is still relatively moist and possesses thus only a low strength, suffers a certain elongation. This elongation is undesirable because it has a negative effect on the quality properties of the finished web; for instance, an undesirable cross contraction of the web results thereof. Even more aggravating, the mentioned elongation takes place irregularly across the web width, because the web edges are mostly more heavily stretched than the middle region of the web. This creates disuniform quality properties of the finished web, measured across the width of the web.
Another characteristic of the above proposal consists in arranging the first drying cylinder of the dryer section within the loop of the transfer felt. Thus, the web will not make direct contact with this first drying cylinder. Resulting thereof--especially at high operating speeds--is the risk that the paper web, due to centrifugal force, will lift off the transfer felt at the first drying cylinder.
Known from the U.S. Pat. No. 4,648,942 is an arrangement where the last press has the following characteristics: The web passes there between two felt belts through the press gap and from there to a separating device arranged in the bottom felt; the web separates there from the top felt and continues on with the bottom felt until it is transferred to the dryer section by means of the first drying wire of the dryer section and by means of a pickup suction roll. In the last press, the bottom roll is fashioned as a long-gap press roll; that is, this roll has a flexible revolving (hose or web type) and liquidtight pres element which by means of a press shoe can be pressed onto the top roll. A disadvantage of this arrangement is constituted in that the web very early on, i.e., as long as it is till relatively moist and soft, makes contact with the relatively hard and coarse drying wire. This entails the risk that the drying wire will leave permanent impressions behind in the paper web. Such impressions may be acceptable in the case of coarse paper grades, for instance such used for wrapping purposes, but not for printing and writing papers. Besides the adherence of the paper web to the relatively coarse surface is not always guaranteed, especially at high speeds.
The problem underlying the invention is t provide an arrangement for transferring a web from the press to the drying section of a paper machine that meets all of the following requirements; no point travel freely (i.

REFERENCES:
patent: 1868617 (1932-07-01), Tompkins
patent: 3250019 (1966-05-01), Beachler
patent: 3981084 (1976-09-01), Sobota
patent: 4000035 (1976-12-01), Scheil et al.
patent: 4219383 (1980-08-01), Valkama
patent: 4483745 (1984-11-01), Wicks et al.
patent: 4561939 (1985-12-01), Justus
patent: 4648942 (1987-03-01), Wanke

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