Paper making and fiber liberation – Processes and products – Conditioning – preparing or repairing of apparatus
Patent
1993-11-18
1995-06-27
Hastings, Karen M.
Paper making and fiber liberation
Processes and products
Conditioning, preparing or repairing of apparatus
162205, 1623583, 1623584, 162901, D21F 302
Patent
active
054276535
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a press and a method for modifying a press for use in the press section of a papermaking, cellulose or board manufacturing machine. More specifically, the invention relates to the field of shoe presses, being a type of presses having a press nip extended in the machine direction.
A shoe press generally comprises a rotary press roll, a substantially stationary pressure shoe, and a press belt running in an endless path around the pressure shoe between this and the press roll and having a substantially impermeable inner surface facing the pressure shoe. The pressure surface of the shoe facing the press roll is arcuate by a curvature corresponding to the radius of the press roll. The press nip formed between the press roll and the shoe is intended to receive, between the press roll and the outer side of the press belt, a web, such as a paper web, from which water is to be removed. The water which is pressed out of the paper web by the press is initially taken up by one or more press felts, generally one press felt in the form of a sandwich structure provided on each side of the paper web. In operation, the rotating roll feeds the paper web, the felt or felts, as well as the press belt jointly through the press nip.
The extent of the pressure surface of the shoe in the machine direction may be in the order of 25 cm (10 inches), which is several times longer than the nip in a traditional roll press with two rolls, and (for a given web speed) results in a corresponding increase of the press time. Hence, a shoe press enables considerably enhanced dewatering of the paper web.
In a shoe press, between the shoe and the inner surface of the press belt, there is traditionally provided for friction-reducing oil lubrication by means of an oil film. The oil film is produced by conducting pressurised oil through one or more oil ducts provided in the interior of the shoe and opening at its pressure surface. The press belt serves to maintain the oil film established between the press belt and the shoe in place and, therefore, must be oil-impermeable. In this way, the oil is also prevented from fouling the paper web and the felt or felts.
Another demand placed on the press belt in a shoe press is that the inner surface of the press belt must be smooth to expose a good sliding surface to the shoe. As known in the art, a good sliding surface can be achieved by providing a base weave of the press belt with a layer of plastic, which then also makes the press belt oilproof. Such press belts provided with a plastic layer are known from EP-A-01,194,601 (Albany Int. Corp.), U.S. Pat. No. 4,564,551 (Best), U.S. Pat. No. 4,946,731 (Dutt), U.S. Pat. No. 4,559,258 (Kiuchi), and JP 63-247061 (Ichikawa Umou Co. Ltd).
In addition to the above-mentioned two demands placed on the press belt in a shoe press--oil tightness and a smooth inner sliding surface--the belt must also be strong to have a long service life and be dimensionally stable so as not to be stretched during mounting or in operation. Moreover, the press belt must be given a uniform thickness when manufactured.
To sum up, the following demands are thus placed on a press belt in a shoe press:
Hitherto, it has been difficult to meet all these demands (1-5) on a press belt in a shoe press. Especially, a dimensionally unstable press belt causes problems in shoe presses of the short-belt type, which in the context of this invention means a shoe press which, in addition to the features mentioned above, is distinguished by the press shoe being integrated in the outer periphery of a usually cylindrical, non-rotating element, the outer periphery of which defines the endless path of the press belt. Rotary sealing means are arranged at each end of the cylindrical element in order, together with the running press belt, to retain the oil film in a closed space. As compared with shoe presses of the long-belt type, which lack the above-mentioned non-rotating, cylindrical elements and the rotary sealing means and in which the press be
REFERENCES:
patent: 3981084 (1976-09-01), Sobota
patent: 4431045 (1984-02-01), Josefsson
patent: 4559258 (1985-12-01), Kiuchi
patent: 4564551 (1986-01-01), Best
patent: 4946731 (1990-08-01), Dult
patent: 5043046 (1991-08-01), Laaputti
patent: 5175037 (1992-12-01), Merckens et al.
Aberg Bo-Christer
Andersson Nils
Albany Nord skafilt AB
Hastings Karen M.
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