Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
1997-12-22
2001-04-24
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C162S305000, C162S358300, C162S358200
Reexamination Certificate
active
06221214
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 196 54 200.6 filed Dec. 23, 1996, 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 wet section of a machine for producing a fibrous material web, specifically a paper or a cardboard web, which includes at least one press unit that includes a nip through which the fibrous material web, which has been preformed in a web forming section, is guided.
The present invention also relates to a method for treating a fibrous material web in an elongated nip of a press section of a machine for producing a fibrous material web. The method includes preforming the fibrous material web in a forming section of the machine, guiding the fibrous material web, which has a dry matter content of approximately 15%, to at least one elongated nip and pressing the fibrous material web in at least one elongated nip.
2. Discussion of Background Information
The wet section of machines for producing a fibrous material web, particularly for producing either a paper or a cardboard web, occur after the web forming region and after the fibers have achieved a certain immobility gradient. Further drainage of the wet fibrous material web has, in the past, primarily been achieved by elements that essentially operate through the use of suction, such as, for example, particular foils, register rolls, suction boxes, suction rolls, or the like. Connecting this type of drainage to the machine incurs considerable expense, especially where, for example, the element requires a large amount of space or, for example, where generating the vacuum consumes an excessively large amount of costly energy. In addition, depending on the type of material, the drainage screen, which rubs over the mostly stationary drainage elements, may result in a relatively short screen service life.
In a wet section of the type discussed in EP-A-0 359 696, a press function is integrated into the screen region to eliminate a web pick-up point. The press point provided in the screen region includes a suction roll and an open roll. Either the relevant nip is not very hard, i.e. having a high linear force, or the nip is very short and soft, which can be attributed to a low linear force. Neither of these operations is suitable for removing the required quantity of water from the fibrous material web with the lowest possible pressure gradients when there are low dry matter contents, i.e. when the fibrous material web is still wet.
SUMMARY OF THE INVENTION
The present invention provides the ability to drain the pre-formed wet fibrous material web of a wet section of a machine while utilizing a minimal expenditure of energy, a small amount of space, and a correspondingly low operating cost.
The invention provides at least one long-nip press or elongated nip press, which is elongated in the web travel direction. The nip is positioned in a region or area where the dry matter content of the preformed fibrous material web coming into the nip is less than or equal to about 15%, and preferably, is less than or equal to about 12%.
The present invention may be used, for example, on gap formers, hybrid formers, fourdrinier wires, multistage fourdrinier wires, and/or the like. The nip length can be adapted to the respective types of production. Because the relevant press point is disposed closer to the headbox, the fibrous material web is warmer during pressing, which further increases the drainage capacity. In addition, lower screen wear is produced and the energy costs are clearly reduced. The pressing occurs in an extremely gentle fashion, wherein the progression of pressing power can be predetermined by a corresponding shoe embodiment (e.g. the length or shape or form of the shoe).
In fact, the pressure applied to the fibrous material web may increase in the traveling direction of the fibrous material web from approximately 1 bar to approximately 20 bars. Preferably, the pressure increases from about 1 bar to between about 5 and 10 bars.
At least one screen associated with the web forming zone is guided through the elongated nip. In particular industrial applications, it is advantageous to guide two screens associated with the web forming zone through the nip.
The fibrous material web, which is preformed in the web forming zone, can also be delivered to the nip by a water-absorbing belt. The fibrous material web is transferred onto the water-absorbing belt before the elongated nip. The water-absorbing belt can be, for example, a felt band, a screen belt, and/or a perforated belt.
Another embodiment of the invention provides for at least one belt being positioned on both sides of the fibrous material web and then being guided through the nip. The belts on either side of the fibrous material web are designed to be the same, i.e, symmetrical.
In this instance, starting from the fibrous material web, a support belt that supports the fibrous material web and is preferably comprised of fine woven cloth, a belt of porous woven cloth that serves to absorb and transport water, and a waterproof belt, are provided on each side of the web. In this instance, the support belt is preferably a felt band and/or screen belt.
It is also possible to provide a thick felt band and a waterproof belt, respectively, on each side of the web, starting from the fibrous material web.
However, it is also conceivable to provide a belt comprised of a fine woven cloth, a porous, coarse belt, and a waterproof belt, respectively, on each side of the web, starting from the fibrous material web. The belt comprised of fine woven cloth can, for example, be a screen belt.
In another suitable embodiment of the wet section according to the invention, at least one belt is on both sides of the fibrous material web and is respectively guided through the nip. The belts on either side of the fibrous material web are not the same, that is, they are asymmetrical.
For example, one asymmetrical belt design includes a felt band and a waterproof belt on one side of the web and a screen belt, a porous, coarse belt, and a waterproof belt provided on the other side of the web.
With an asymmetrical design like this, it is also possible, starting from the fibrous material web, to provide a waterproof belt on one side of the web and a screen belt, a porous, coarse belt, and a waterproof belt on the other side of the web.
In the embodiment, it is preferable to have an elongated nip formed between a rotating, flexible press belt, which is guided by at least one press shoe, and an opposing press face. Consequently the elongated nip can be formed, in particular, by a press shoe.
Because the pressing power exerted at low dry matter contents is relatively low, the region between the press shoe and the flexible press belt may be lubricated in a suitable fashion with water. As a result, there is also the possibility, in particular, of using the relevant press shoe in a continuous loop that is open on its end faces and to use an open system in which the shoe length can be relatively large.
According to one embodiment of the invention, the continuous loop formed by the rotating, flexible press belt may be open on its two end faces.
To form the first elongated nip that the web fibrous material web approaches, preferably, a press shoe is provided that includes a press face. The press face is at least substantially smooth on the jacket or flexible press belt side. In this instance, the woven cloths that travel through the nip may undergo less mechanical bending stress. Thus, the cloths or fabrics may be thicker and, thus, absorb more water.
Preferably, the wet section includes a headbox that is also supplied with dilution water.
According to one embodiment, the wet section is adapted to be used in combination with at least one other long-nip press or elongated nip press and a transfer zone where the fibrous material web is transferred to a dryer section. Preferably, the fibrou
Esslinger Klaus
Kotitschke Gerhard
Mayer Wolfgang
Meschenmoser Andreas
Morhardt Günther
Greenblum & Bernstein P.L.C.
Hastings Karen M.
Voith Sulzer Papiermaschinen GmbH
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