Stock inlet

Details Stock inlet Stock inlet

2000-07-31

2001-10-16

Chin, Peter (Department: 1731)

Paper making and fiber liberation

Apparatus

Running or indefinite length product forming and/or treating...

C162S336000, C162S216000

Reexamination Certificate

active

06303004

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 199 36 330.7, filed on Aug. 2, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a stock inlet, in particular a multi-layer stock inlet, of a paper machine having at least one stock suspension supply, a diffusor block with a multitude of tubular elements, and a stock inlet aperture which has a number of suspension conduits running the width of the machine, which are formed between a top and bottom wall of the stock inlet aperture by at least two, preferably three, dividing elements which run the width of the machine and through which the stock suspension is conveyed onto a wire or between two wires, with the suspension conduits having a first region I and a second region II disposed downstream, with the first region I being constituted by flat boundary surfaces, which run the width of the machine and converge in the flow direction, and with each dividing element having a sharper convergence of its surfaces in the second region II than in the first region I.
2. Discussion of Background Information
A similar stock inlet is known, for example, from the Applicant's U.S. Pat. No. 5,599,428. Among other things, this document shows a stock inlet in FIG. 6, which has a stock inlet aperture with three internal dividing elements that separate the stock suspension of the individual layers of this stock inlet from one another. In the aperture outlet region, the dividing elements first have a widening and then a tapering (convergence) which should lead to there being only minimal mixing tendencies between the individual suspension layers that are brought together after the dividing elements.
A problem of these known stock inlets lies in the fact that the paper produced therewith has a striped structure, known as “tiger stripes,” running the width of the machine, whose origin has not yet been definitively explained. These stripes, which are distinguished by alternating areas of higher and lower luster and extend in the machine direction, are particularly undesirable in high-quality papers and should be prevented to the greatest extent possible.
The Applicant's as yet unpublished DE 199 02 621.1 describes a stock inlet with lamellas to counteract tiger stripes. Lamellas of this kind also have a particularly positive effect on the jet quality.
U.S. Pat. No. 5,876,564 discloses building up angular momentum in the turbulence generator in order to increase the lateral strength and to keep the L/C ratio as low as possible, which is of particular interest for gap formers. A disadvantage of such an angular momentum generator, however, is the low jet quality and poor formation.
SUMMARY OF THE INVENTION
The object of the invention is to produce a stock inlet of the type mentioned at the outset in which both the highest possible strength as well as the greatest possible jet stability and best possible formation are simultaneously assured. Furthermore, the striped structure (tiger stripes) in the paper should be prevented or at least mitigated.
This object is attained according to the invention in that the tubular elements of the diffusor block are associated with a turbulence generating element in order to produce secondary turbulence currents in the partial suspension flows conveyed through these tubular elements, which turbulence currents overlap the primary current of these partial suspension flows, and in that all of the dividing elements of the stock inlet aperture have a contour and disposition which produce a second region II of equal length with an identical cross sectional course for each suspension conduit.
The term cross sectional course is understood to mean the change and absolute magnitude of the free area that is flowed through with regard to a position in the operational direction of the machine, with the variation of flow directions not being initially taken into consideration.
A high strength as well as a high jet stability and favorable formation are achieved simultaneously as a result of this embodiment. The disadvantages previously associated with angular momentum generators are consequently eliminated. Moreover, the striped structure (tiger stripes) in the paper are prevented or at least mitigated.
In particular, the turbulence generating element can be embodied in the manner described in U. S. Pat. No. 5,876,564. The use of these turbulence generating elements and the corresponding process for mixing the partial suspension flows can also be provided in the manner described in U.S. Pat. No. 5,876,564. To this end, the disclosure of this U.S. Pat. No. 5,876,564 is also included in its entirety in the disclosure of the current application.
In a suitable embodiment of the stock inlet according to the invention, the rotating motion of a each secondary turbulence current is generally oriented around the longitudinal axis of the respective tubular element.
It is also particularly advantageous for each secondary turbulence current to be generated so that a generally helical total flow is produced in the respective tubular element.
For example, the turbulence generation can be produced by means of a corresponding geometry and/or property of the inner surface of each tubular element or of each tubular insert.
In a preferred practical embodiment, the turbulence generating element includes at least one insert and/or yoke that is associated with each tubular element
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and by means of which the respective partial suspension flow can be correspondingly influenced in order to generate the secondary turbulence current.
It is advantageous if at least one yoke or insert is designed for a pressure-induced influence of the applicable partial suspension flow and preferably includes at least one pressure impulse generating element. In this connection, each tubular element or tubular insert can be associated with, for example, at least two and preferably two to twelve pressure impulse generating elements.
In a suitable practical embodiment, at least one pressure impulse generating element is provided which is constituted by an acoustic element.
In certain instances, it can also be advantageous for at least one pressure impulse generating element to be provided that is constituted by an electromagnetic element.
In a suitable practical embodiment, at least one tubular element or at least one tubular insert is provided, which has an inlet provided as a flat section for receiving the stock suspension from a distributor and an outlet provided as an elongated section that feeds into the stock inlet aperture.
It is also advantageous if at least one tubular insert is provided which can be inserted into the diffusor block in order to receive stock suspension from a distributor.
In a preferred practical embodiment of the stock inlet according to the invention, at least one insert is provided which is constituted by a body disposed inside a respective tubular element, which body has at least two blades and, in order to generate turbulence, can be correspondingly acted on by at least one, preferably at least three magnet rings encompassing the tubular element and spaced apart from one another in the longitudinal direction of the tubular element.
The body can have two to twelve blades, for example.
In a suitable practical embodiment, the body is provided with external blades.
Fundamentally, however, an embodiment is also conceivable in which a preferably annular body is provided with internal blades.
According to the invention, the cross section of the suspension conduits can increase or decrease in the second region. It is also possible for there to be a uniform cross section in region II.
It is advantageous for the second region II to directly follow the first region I viewed in the flow direction.
It is also advantageous for the dividing elements to have a tapering in the end region, with the degree of convergence of the surfaces of the tapering

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