Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
1999-01-27
2001-07-31
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C162S300000, C162S301000
Reexamination Certificate
active
06267846
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a twin wire former and method of manufacturing a fibrous material web with a twin wire former, and more particularly, to a twin wire former and method for manufacturing a fibrous material web, such as a paper web, from a fibrous suspension.
2. Discussion of Background Information
Twin wire formers are known in related art apparatus. One such apparatus is disclosed in European Patent No. EP 0489094. This document disclosed a twin wire former with two wire belts, which jointly constitute a twin wire zone. At the beginning of the twin wire zone, the two wire belts jointly form a wedge-shaped inlet gap, which receives the fibrous suspension directly from a headbox. The two wire belt are thus known as a “gap former.” Directly at the wedge-shaped inlet gap, the two wires travel by way of a rotatable forming roller. Downstream from the forming roller with respect to the rotational direction thereof, the two wire belts contact forming strips and/or forming shoes inside the twin wire zone.
In other embodiments of twin wire formers, the two wires travel in a generally horizontal direction or ascend diagonally inside the twin wire zone. Consequently, the drainage devices disposed inside the perimeter of the upper wire require relatively high suction to remove the water. In other embodiments, the two wire belts travel in a generally vertical direction upward from the bottom, at the inlet gap. The belts travel by way of a forming roller, which is embodied as a suction roller. In drainage boxes disposed above the forming roller, a few deflection surfaces are necessary to remove the water, possibly requiring a suction connection.
Twin wire formers according to above-noted European Patent No. EP 0489094 may be useful, especially when a forming roller is disposed directly at the inlet gap. Because of the presence of this forming roller, the two wires are guided along a sharply curved path about the circumference of the forming roller immediately downstream of the inlet gap. This sharply curved path is required because the sleeve of the forming roller has a small radius in comparison with the large radius of a forming shoe disposed at the inlet gap. When the suspension stream coming out of the headbox enters the wedge-shaped inlet gap, a large portion of the suspension flows almost in a straight line through the top wire. From the top wire, the water stream breaks up rapidly and uniformly over the width of the machine. Rapid and uniform breakup of the water stream contributes to rapid and uniform web formation. High quality finished fibrous material webs may be produced by this twin wire former, even though the web is rapidly formed.
The disposition of the forming roll at the beginning of the twin wire zone enables both the top wire and bottom wire to be stretched tautly, which creates longitudinal tension, thereby preventing the forming of wire tubes in the travel direction. Additionally, keeping the top wire taut in the lateral direction contributes to uniform web formation, particularly in the critical beginning region of the web formation. Keeping the top wire taut in the lateral direction additionally helps prevent the defect known as “longitudinal striping” in the paper.
However, a disadvantage of the twin wire former known from the above reference EP 0489094 is that during operation, a large amount of energy is used for the production of suction. Furthermore, the starting up of this twin wire former is sometimes difficult when there is a backup of water in the machine.
The trade journal “Das Paper” [Paper] 1970, No. 10A, pp. 779 to 784, disclosed a twin wire former with a twin wire zone that steeply travels in a downward direction. The convexly curved forming shoe that both wires wind around is provided before a forming roller around which both wires wind.
SUMMARY OF THE INVENTION
The present invention provides a twin wire former and method for manufacturing a fibrous material web from a fibrous suspension using a twin wire former. The device of the present invention comprises a movable bottom wire belt and a movable top wire belt converging at a twin wire zone. The twin wire zone has a first section, a second section and an end section. A rotating forming roller is disposed at the first section of the twin wire zone, the top wire and the bottom wire forming a wedge-shaped inlet gap at the first section of the twin wire zone, the inlet gap being adapted to receive the fibrous suspension from a headbox. The bottom wire belt and the top wire belt form the fibrous web therebetween at the second section of the twin wire zone, and the second section of the twin wire zone has at least one drainage element. The invention also comprises a separating device adapted to separate one wire belt from the other wire belt. The twin wire zone has a section disposed in a steep downward direction downstream of the forming roller in relation to the movement of the wire belts.
The steep downward direction of the twin wire zone may be an angle between about 10 and 50 degrees from the vertical, and is preferably between about 10 and 45 degrees from the vertical.
The twin wire former may also include a deflection device for deflecting the bottom wire belt and the top wire belt from the steep downward direction section, to a generally horizontal direction.
In another aspect of the invention, the invention may also comprise a breast roller disposed upstream from the forming roller in relation to the movement of the top wire, the breast roller being adapted to guide the top wire. The breast roller and the headbox together may then be pivoted about a rotational axis of the forming roller.
Furthermore, the invention may comprise a convexly curved forming shoe disposed against the top wire at the steep downward direction section of the twin wire zone. At least one deflector disposed against the bottom wire may be provided opposite the forming shoe. The invention may further comprise at least one forming strip flexibly disposed against the bottom wire, opposite the forming shoe.
A further aspect of the invention may provide at least one forming strip flexibly disposed against the top wire at the circumference of the forming roller.
According to another aspect of the invention a first and a second balanced-pressure drainage element (which may be fluid permeable and/or perforate) at the steep downward direction section of the twin wire zone may be provided, the first balanced-pressure drainage element being stationary and disposed against the top wire belt. The second balanced-pressure drainage element is flexibly disposed opposite the first balanced-pressure drainage element against the second wire belt. These elements may be embodies as plates or plate segments.
A convexly curved guide plate, which may be perforated, may also be disposed alongside and downstream from the forming roller in relation to the movement of the wire belts, the top wire belt and the second wire belt being adapted to travel over the convexly curved guide plate, the convexly curved guide plate further resting against the top wire.
Additionally, inside the twin wire zone, the top wire belt and the bottom wire belt may be configured so that they only come into contact with the forming roller, the forming shoe and the suction device. The separating device may be a stationary separating suction device disposed against the bottom wire at the steep downward direction section of the twin wire zone.
Furthermore, at least one additionally suction device may be provided at the steep downward direction section of the bottom wire, and a removal device adapted to remove the fibrous web material from the bottom wire at a point downstream from the at least one additional suction device may also be provided.
The top wire belt and the bottom wire belt may also be adapted to be conveyed by a wire suction roller at a point downstream from the steep downward direction section. The wire suction roller may be disposed against an inside perimeter of the top wire. The wire suction
Brunnauer Erich
Halmschlager Gunter
Prinz Günther
Ronning James
Schmidt-Rohr Volker
Greenblum & Bernstein P.L.C.
Hastings Karen M.
Voith Sulzer Papiertechnik Patent GmbH
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