Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
1998-11-04
2001-05-22
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C162S217000, C162S300000, C162S301000
Reexamination Certificate
active
06235158
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a wet section of a machine to manufacture a fibrous material web, especially a paper or cardboard web, with a double-screen segment, in which two sieves are guided approximately parallel to one another and into which a fibrous material suspension is guided, a roll, around which the double-screen segment is looped; apparatus arranged on the roll for the immobilization of the fibrous material suspension in the doublescreen segment for the formation of the fibrous material web, and apparatus to further drain the fibrous material web.
2. Discussion of Background Information
Furthermore, the invention relates to a method for the manufacture of a fibrous material web, especially a paper or cardboard web with the steps to guide two screens in a double-screen segment approximately parallel to one another and around a roll, to introduce a fibrous material suspension into the double-screen segment, to immobilize the fibrous material suspension on the roll in the double-screen segment while forming the fibrous material web, and to drain the fibrous material web further.
Such a wet section and a method of this kind for the manufacture of a fibrous material web are generally known, e.g., from EP-A-0 607 549.
In the present context, a wet section is to be understood as the section located before the drying section of a paper or cardboard machine, that is normally the arrangement of head box, screen section, and press section. It is given that especially the screen section and the press section do not necessarily have to lie in sequence behind each other. So, for example, pressing elements can be contained in the actual screen section.
The wet section bears particular significance in the manufacture of paper webs. In the wet section, the immobilization of the fibrous material suspension, which has been supplied in fluid form, takes place. The fibers which initially float freely in the suspension thereby are “immobilized” relative to one another via the removal of water. Prior to or during the immobilization, irregularities which appear can be compensated only insufficiently or not at all through subsequent sections of the paper machine.
The construction of such a wet section is typically a compromise between different, competing demands, including web run speed, web width, regularity of the characteristics of the finished paper web, surface quality, as well as compactness of the machine, the lowest possible inclination toward contamination, easy access for cleaning, as little expense as possible, etc.
Double-screen segments are used in wet sections in so-called gap-formers as well as in so-called hybrid-formers. Two continuous screens are guided thereby over a segment, the double-screen segment, parallel to each other.
In gap-formers, the two screens are guided over a forming roll as a support body, with the fibrous material suspension being introduced from a head box into an opening formed by the two screens and lying near to the forming roll.
In known wet sections, the two screens are guided over another segment parallel to one another following the looping around the forming roll; typically, forming strips and/or draining media such as suction boxes are arranged in this other segment in order to assist the draining of the fibrous material suspension, i.e., the “immobilization,” or the further draining of the fibrous material web in this other segment; see for example EP-B-0 489 094.
The noted forming strips preferably are pressed flexibly onto one of the two screens, each with a force which can be selected. It is thereby possible to optimize the so-called formation (transparency) in the finished paper.
The screen section known from EP-B-0 489 094 has a very big length, however, and exhibits a large number of individual parts.
Furthermore, a wet section in the prior art is disclosed in the German patent application 196 34 995.8.
In this wet section, similar to that in EP-A-0 607 549, an upper screen and a lower screen are looped around a forming roll and hereafter guided parallel to each other to a screen-suctioning roll, which serves further draining of the formed fibrous material web after the immobilization. In the vicinity of the suctioning zone of the screen-suctioning roll, the upper screen is lifted from the web, so that the fibrous material web remains on the lower screen.
In EP-A-0 607 549, mentioned at the outset, the two screens are guided parallel from the forming roll to a screen-suctioning roll which serves the further draining of the web. In the vicinity of its suctioning zone, the outer screen is lifted from the web and the inner screen so that the web remains behind the double-screen segment on the inner screen.
SUMMARY OF THE INVENTION
The problem which forms the basis of the invention consists thus of indicating a wet section which is compact, inexpensive to manufacture, and can be maintained cost-effectively.
This problem is solved with the wet section noted at the outset in that the roll is a combined forming and draining roll, which exhibits a forming sector, on which the immobilization media are arranged, as well as a draining sector located in the direction of the running screen behind the forming sector; at least a predominant portion of the draining media are arranged on the draining sector.
The problem is also solved with the process noted at the outset for the manufacture of a fibrous material web, moreover, in that the immobilization occurs in a forming sector of the roll and at least a predominant part of the subsequent draining occurs in a draining sector of the roll located in the direction of the running screen behind the forming sector.
The problem is completely solved in this way.
With the invention, a so-called “mono-suctioning roll” former is realized. Departing from the previous basic concept of wet sections, in which only the immobilization or a part of the immobilization process occurs on a forming roll, in accordance with the invention not only the immobilization of the fibrous material suspension is attained on the combined forming and draining roll, but also a substantial, additional draining of the likewise formed fibrous material web. Thus, the fibrous material web, running from the combined forming and draining roll (below, combination roll), can, if necessary, be transported directly into a press section or even directly into a drying section. Hereby, a multiplicity of individual elements, especially an additional screen-suctioning roll, is spared. The wet section in accordance with the invention can hereby be manufactured more cost-effectively arid is extremely compact. Fewer replacement parts must be provided during operation, so that even the maintenance of the wet section is especially cost-effective. Because for the maintenance of wet sections, a reserve roll must be kept available for every type, in order to minimize machine down times. With the wet section in accordance with the invention, only the combination roll thus must be provided in duplicate, and not respectively a combination roll and an additional screen-suctioning roll. The single combination roll enables large web widths and high belt running speeds.
Preferably, the outer screen facing away from the roll is guided so that it is lifted in the vicinity of the draining sector away from the fibrous material web.
The fibrous material web, formed and drained further, remains on the screen facing the combination roll. Following this it can be conveyed directly or after a suitable diversion into another section of the paper machine.
Since the combination roll in the draining sector always exhibits suctioning segments for draining, one of the same can be used as a separating suctioning segment (as with known, conventional suctioning rolls).
With a preferred embodiment, the fibrous material web exhibits a dry content of at least 10%, and preferably at least 12%, in the area of its runoff from the combination roll.
In conventional forming rolls, the dry content of the fibrous material suspension or web in t
Dahl Hans
Esslinger Klaus
Kotitschke Gerhard
Kraft Wilfried
Mayer Wolfgang
Greenblum & Bernstein P.L.C.
Hastings Karen M.
Voith Sulzer Papiermaschinen GmbH
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