Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Patent
1998-01-05
1999-08-10
Hastings, Karen M.
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
162357, 162369, 492 20, D21F 310, D21F 160
Patent
active
059353864
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a suction box as defined in the preamble of claim 1.
In the following, both the invention and prior art are described mainly in connection with paper machines, yet without limiting the invention exclusively to paper machines. Therefore, the term `paper machine` in this application refers to paper or cardboard machines in general or machines used in pulp manufacture to produce webs containing cellulose fibers.
In paper machines, suction rolls are used for the dewatering of the web being produced, both after the head box and in the press section. A suction roll is a roller with perforations in the whole area of its jacket and with a suction box inside it, the suction box being attached or pressed to the interior surface of the suction roll, with a sealing between them. The purpose of the suction box is to suck water from the web and to draw air through the web to remove moisture from it with the air.
As the machines are operated at increasing speeds, i.e. with increasing speeds of rotation of the rolls, the operation of the suction rolls has become ineffective. A vacuum draws water into the perforations in the suction roll and somewhat into the roll, but the centrifugal force prevents most of the water from entering the suction box itself. The centrifugal force even returns some of the water back into the perforations in the suction rolls and to the outside of the suction roll. For this reason, the water removed from the web remains on the underside of the web, keeping it wet. After the suction stage, the water splashing out from inside the roll again wets the web or, in the press section, the felt. The perforations in the roll contain plenty of water rotating with the roll, and some of this water is also passed to the supply side of the web, wetting the web or the felt. Moreover, the water remaining in the perforations of the roll and the particles contained in the water tend to block the perforations, increasing the power requirement of the suction pumps.
In an attempt to enhance the operation of the suction rolls, the vacuum level in the suction box has been increased, which naturally means an increased power required by the vacuum pumps. This is about the only effect this measure has produced. The increase in the speed of the machines has been achieved by increasing the efficiency of the drying section or by increasing the machine length or the steam consumption.
SUMMARY OF THE INVENTION
The object of the present invention is to eliminate the drawbacks described above. A specific object of the invention is to present a new type of suction box structure which allows more efficient dewatering of a wet web by a suction roll and more efficient drainage of the water from the suction roll into the suction box.
As for the features characteristic of the invention, reference is made to the claims.
The suction box of the invention in a machine for manufacturing a web containing cellulose fibers is inside a rotating suction roll provided with a perforated jacket. The suction box comprises a suction chamber having a suction inlet placed against the interior surface of the suction roll and a suction connection for creating a negative pressure in the suction chamber and drawing water through the perforations in the suction roll into the suction chamber. According to the invention, the suction inlet of the suction box is provided with ribs or slats forming suction slits placed longitudinally relative to the suction roll near its interior surface. Thus, the invention is based on the observation that by reducing the cross-sectional flow area of the suction inlet, the velocity of flow can be increased so that the water drawn through the perforations in the suction roll will continue flowing in the same direction even after the perforations, getting into the slits of the lattice and further into the suction box. Ribs or slats correctly directed also direct the water drops emerging from the perforations towards the suction box.
The ribs preferably form a latti
REFERENCES:
patent: 2520327 (1950-08-01), Nilson
patent: 2714839 (1955-08-01), Mazer
patent: 3072180 (1963-01-01), Jodrey
patent: 3272692 (1966-09-01), Hayes et al.
patent: 3880711 (1975-04-01), Hayes, Jr.
patent: 4735686 (1988-04-01), Skytta
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