Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
2000-01-05
2002-04-16
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S343000, C162S216000, C162S336000
Reexamination Certificate
active
06372092
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.,C. §119 of German Patent Application No. 199 02 623.8, filed on Jan. 23, 1999, 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 relates to a headbox of a paper machine having at least one material suspension supplying system, at least one subsequent region for producing turbulence, and one headbox nozzle having one first and one second dividing wall running the width of the machine. The headbox nozzle has a first path in which the total cross-section of the headbox nozzle, i.e., total free cross-sectional surface flowed through by suspension, steadily and continuously decreases such that a second, shorter path immediately follows the first path.
2. Discussion of Background Information
A headbox similar in general to the above-noted headbox is disclosed in commonly assigned U.S. Pat. No. 5,599,428. In this patent, different variations of multi-layer headboxes, which are provided with differently constructed or formed separating lamellas, are disclosed.
Paper manufactured using headboxes of the above-noted type has the problem of insufficient crosswise stiffness SCT
cross
, which can cause disruptions in operation when used, e.g., in modem copying systems or in printers with automatic paper feed. Further, it would be advantageous for a breaking length ratio L/Q, where L is lengthwise in a machine direction and Q is crosswise to the machine direction, after sheet formation to be reduced to a range of between approximately 0,6 and 1.0, if possible.
SUMMARY OF THE INVENTION
The present invention provides a headbox that improves the crosswise stiffness of manufactured paper in which breaking length ration L/Q can be reduced, if possible.
The inventors of the instant invention recognize that the crosswise stiffness of the paper improves substantially if care is taken, by appropriately shaping the headbox nozzles, especially in the end region, to ensure that the fibers in the material suspension in the end region of the nozzle are turned more strongly in the z direction lying parallel to the sheet surface and, if possible, stretched as well.
Accordingly, the instant invention is directed to headbox of a paper machine with at least one material suspension supplying system, at least one following region for producing turbulence, and one headbox nozzle with one first and one second dividing wall running the width of the machine. The headbox nozzle has a first path in which a total cross-section of the headbox nozzle, i.e., the total free cross-sectional surface flowed through by the suspension in the respective machine section, steadily and continually decreases, and a second, shorter path immediately following the first path. Further, the second path has a continually widening total cross-section that extends toward an end of the headbox nozzle, which causes a flow deceleration in the end region of the headbox nozzle so that no substantial turbulence arises. The speed profile hereby caused stretches fibers in the suspension in the z direction and improves the crosswise stiffness of the finished paper. An additional positive side effect of this influence on the suspension is that the breaking length ratio L/Q decreases and can take on values between approximately 0.6 and 1.0.
According to an exemplary embodiment of the invention, an additional third path, which directly follows the second path, can be positioned to extend to the end of the headbox nozzle. In this manner, the second path has a continually widening total cross-section and the third path can have a steadily and constantly decreasing total cross-section. It may be advantageous for the length of the third path to be shorter than the length of the second path, and for the length of the second path to be shorter than the length of the first path. By selecting the corresponding ratios of the path length, it is possible to increase or decrease the crosswise stiffness stimulating effect. As such, the length of the third path should remain shorter than the length of the second path. This length ratio prevents the fiber orientation achieved in the second path from being overcompensated in the third path.
The first path can be positioned to begin immediately downstream of the turbulence producing region. Further, the total cross-section of the headbox nozzle can be formed, at least across one part of the headbox nozzle, by only one suspension conduit. In this way, no separation elements for separating individual levels are present in this region. This arrangement can reduce edge effects, and the height of the flow cross-section available at one unit can correspond to the total cross-section, so that a better fiber orientation in the z direction can be achieved.
For example, when the headbox is employed as a multiple layer headbox, it can be advantageous for the total cross-section of the headbox nozzle to include several suspension conduits, at least over a part of the headbox nozzle length, which are formed, e.g., by at least one separating element that extends across width of the machine and that is arranged between the first and second dividing walls. Moreover, it can be particularly advantageous for all suspension conduits to have the same cross-section progression without exception so that the same acceleration and deceleration ratios are provided for the suspension flowing through each conduit. It may also be advantageous for all suspension conduits without exception to have a congruent form, and be symmetrically congruent. Not only does this allow even progression of the acceleration and deceleration in the suspension conduits, but it also allows the vector field in each suspension conduit to be identical along the entire length.
In another exemplary embodiment, the degree of divergence in the region of the second path can be the same for all suspension conduits.
For example, when utilizing internal separating elements, the divergence of the individual suspension conduits can be achieved in that the separating elements in the region of the second path are arranged to have a taper. Here, it can be advantageous for the degree of convergence of the surfaces of the tapering ends of all separating elements to be the same so as to achieve as unified a flow ratio as possible across the cross-section of the headbox.
It may be further advantageous for the progression of the upper wall and/or lower wall, at least in the second region, to be constructed or formed symmetrically to the progression of the surface of the neighboring separation element. In this manner, the outermost suspension conduits can be constructed as identically to the innermost suspension conduits as possible.
Further, the headbox according to the present invention includes a turbulence producer with a plurality of diffusion tubes in which the diffusion tubes are arranged in rows running across the width of the machine and the separating elements are arranged to begin between the rows of diffusion tubes.
In a headbox provided for a gap former, the upper and lower walls of the headbox can be and, preferably should be, made equal in length.
In accordance with features of the instant invention, it is contemplated that the individual elements can be utilized in various combinations without departing from the scope of the invention.
Accordingly, the present invention is directed to a headbox of a paper machine that includes at least one material suspension supplying system, and a headbox nozzle that includes a first dividing wall having a machine width and a second dividing wall having a machine width, The first and second dividing walls are arranged to form a first path in which a total nozzle cross-section steadily and continually decreases in a material flow direction and to form a second path, arranged to follow the first path, in which a total nozzle cross-section continually increases in the material flow direction.
According to a feature of the instant inventio
Bubik Alfred
Henssler Joachim
Holzer Walter
Müller Karl
Prössl Jürgen
Hastings Karen M.
Voith Sulzer Papiertechnik Patent GmbH
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