Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
1999-05-13
2001-07-03
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C162S301000, C162S352000
Reexamination Certificate
active
06254727
ABSTRACT:
CROSS-REFERENCE OF RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 198 28 237.0, filed Jun. 25, 1998, the disclosure of which is expressly incorporated by reference herein in its entirety
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a twin-wire (i.e., a two-wire) former. More particularly, the present invention is directed to a twin-wire former used in the formation of a web of fibrous material from a fiber suspension, in particular as part of a paper production machine.
2. Discussion of the Background Information
German patent application 196 52 485.7 discloses a twin-wire former having two endless circulating wire belts or bands, which together form a twin-wire zone. The web of fibrous material forms between the twin-wire bands in the region of the twin-wire zone. At the twin-wire zone, the twin-wire bands move together over a forming roll, by which one wire band (the “inner wire band”) comes into direct contact with the forming roll. At the reel-off point of the twin-wire bands from the forming roll, the other wire band (the “outer wire band”) contacts at least one support device extending crosswise over the wire band, such as a skimmer. This skimmer may be rigidly attached to the frame of the machine or preferably) pressed against the outer wire band (for example, by a pneumatic hose). In each such embodiment, transitory divergence of the twin-wire bands (wire separation) is undesirable, and should be avoided using the skimmer at the reel-off point by applying tension to the wire bands in the direction of travel of the fiber web. However, divergence of the twin-wire bands is still occasionally observed, even though tension is applied as noted above. Such divergence disrupts the proper formation of the web.
By using a skimmer that can be pressed against the outer wire band, the position of the skimmer automatically adjusts to the actual layer thickness of the fiber suspension located between the twin-wire bands. A similar technique is shown in WO 95/34713. Nonetheless, disruptions of proper web formation are still observed in the finished web. For example, in a nonuniform basis weight-crosswise profile, the paper web makes a cloudy impression (on observation against a light source), whereby the cloudiness is sometimes strong and/or nonuniform. In other words, the quality of the “formation” is unsatisfactory.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming the drawbacks of the prior art. This is accomplished by providing a twin-wire former that reduces divergence of the wire bands, to thereby improve the overall quality of the resultant web.
The above is further accomplished by forming a vacuum zone, for example, by a so-called foil skimmer, in the region of the reel-off point of the wire bands from the forming roll on the side of the outer wire band. Such a foil skimmer, disclosed in, for example, DE 91 05 328 and U.S. Pat. No. 5,262,009, the disclosure of which is expressly incorporated by reference herein in its entirety, has a slide surface in contact with the wire band and a so-called foil surface connected thereto, which is tilted counter to the direction of travel of the wire, whereby it diverges from the wire band in the direction of travel of the wire. A vacuum zone is thereby created in the wedge opening between the outer wire band and the foil surface through the motion of the wire band.
The aforementioned vacuum zone acts to increase the quality of the finished paper web, i.e., it largely avoids defects in the basis weight-crosswise profile and the observed cloudiness. In other words, significantly improved “formation” quality is obtained. This effect appears to derive from the fact that a similar vacuum develops in the wedge that is always present between the inner wire band reeling off and the jacket of the forming roll, The present invention establishes a counter balancing vacuum zone on the outer band. In other words, the vacuum generated by the foil skimmer (or a vacuum shoe, a vacuum box, etc.) counteracts the vacuum developing on the forming roll such that the negative effect of the latter is neutralized, or at least reduced.
The slide surface of the foil skimmer preferably contacts the outer wire band by flexibly pressing against the outer wire band. Thus, the advantage is obtained that the foil skimmer automatically adapts to different suspension depths. For this purpose, the foil skimmer (seen in a cross-section through the foil skimmer) is preferably supported in its downstream region (relative to the belt travel direction) by a hinge (i.e., a joint) on a stationary or adjustable component, and is pressed against the outer wire in its upstream region by means of a flexible positioning device, such as a pneumatic hose.
According to an exemplary embodiment of the present invention, a twin-wire former adapted to form a web of fibrous material is provided. First and second endless circulating wire bands define a twin-wire zone therebetween, and are adapted to form the web of fibrous material therebetween. A forming roll is provided. The first and second wire bands run over the forming roll in the twin-wire zone, where the first wire band contacts the forming roll. A reel-off point is the point at which the first and second wire bands separate from the forming roll. At least one support device extends crosswise over the second wire band. The support device is disposed in a region of the reel-off point, and contacts the second wire band. Movement of the second wire band relative to the at least one supporting device creates an area of reduced air pressure therebetween.
The at least one support device is preferably a skimmer having a slide surface contacting the second wire band, and a foil surface connected thereto in a direction of travel of the wire. The skimmer is preferably pressed flexibly at the slide surface against the second wire band. A downstream region of the skimmer is preferably supported by a hinge, and an upstream region of the skimmer is preferably supported by a flexible adjustment device. The flexible adjustment device is preferably a pneumatic hose.
In another feature of the exemplary embodiment, a distance between the hinge and the second wire band is variable to vary an angle of inclination between the foil surface and the second wire band, and thereby vary the magnitude of the reduced air pressure.
For a further feature of the exemplary embodiment, a position of the at least one support device is movable along a direction substantially parallel to a direction of travel of the second wire band. The at least one support device is preferably one of a suction shoe and a suction box, and is preferably flexibly pressed against the second wire band. The at least one support device is also preferably disposed inside a loop defined by the second wire band, and the forming roll is disposed inside a loop defined by the first wire band, in which the first wire band is below the second wire band. The at least one support device is also preferably disposed inside a loop defined by the second wire band, and the forming roll is disposed inside a loop defined by the first wire band, in which the first wire band is above the second wire band.
In accordance with another feature of the exemplary embodiment, the first and second wire bands run upwardly or downwardly between the forming roll and the at least one support device.
According to another embodiment of the present invention, a twin-wire former adapted to form a web of fibrous material is provided. First and second endless circulating wire bands are adapted to form the web of fibrous material therebetween, A forming roll is provided. The first and second wire bands run over the forming roll such that the first wire band contacts the forming roll. A reel-off point is defined by the point at which the first and second wire bands separate from the forming roll. At least one support device extending crosswise over the second wire band, is disposed in a region of the
Greenblum & Bernstein P.L.C.
Hastings Karen M.
Voith Sulzer Papiertechnik Patent GmbH
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