Textiles: weaving – Fabrics – Drier felts
Patent
1995-02-10
1997-03-25
Falik, Andy
Textiles: weaving
Fabrics
Drier felts
D21F 100
Patent
active
056135270
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention describes a forming screen for the sheet forming zone of a paper machine and consists of a multi-layer, especially flat-woven material made of synthetic material threads with longitudinal threads which run in machine direction and cross threads which run crosswise whereby a first group of cross threads is located in the plane of the paper side and floats across longitudinal threads whose number is at least equal to the number of the cross threads, across which the longitudinal threads float on the paper side and whereby the plane of the machine side is formed exclusively by a second group of cross threads.
DESCRIPTION OF THE PRIOR ART
A customary paper machine in general consists of three successive zones. In the individual zones the sheet is drained or dried in different manner. During the process, the sheet is supported and guided by so-called paper machine coverings.
For this purpose a forming screen is used for this purpose in the first zone, the so-called sheet forming zone. The liquid to pulpy fibrous material is applied to the screen. With the help of gravity, supported by suction boxes which create negative pressure, the fibrous material is drained to a point in which a continuous, if very sensitive, sheet of paper with a high fluid content is generated at the end of the forming screen. The sheet is removed from the forming screen and brought to the second zone, the so-called press section. There the sheet is subjected to high pressure between two rollers so that the water is drained. It is supported by press felts which in general consist of a base fabric and a spunbonded material which is pinned to it at least on the paper side. In the third zone, the drying zone, the sheet for the most part is drained thermally. It is guided over heated drying cylinders with hardly any pressure. The sheet is supported by so-called skeleton screens whereby the skeleton screens can be made of material or wire link conveyors.
Due to the different types of draining in the different zones of the paper machine, the respective paper machine coverings-- forming screen, press felts and skeleton screen-- must meet different requirements. This means that in general they all have a very different structure. This applies especially to water permeability, thickness of the material, endurance, etc. Paper machine coverings which are used in one zone in general can never be used in another zone.
The forming screen must meet special requirements. This is due to the fact that the forming screens above all must form a sheet of paper out of a liquid mass and that-- contrary to the pressing and drying zone-- there is no continuous sheet of paper. This means that when a forming screen is designed, special attention must be given to the behavior of the different fibers with regard to the forming screen. This is a requirement which is not necessary in the pressing and drying zones since there already is a continuous sheet of paper which reaches these zones. Often times the requirements contradict each other, i.e. a compromise must be reached. This means that a forming screen must have good separation capabilities, i.e. on one hand it must retain the paper fibers on the paper-side surface of the forming screen and on the other hand it must drain the material well. This characteristic of retaining the fibers on the forming screen must be combined with the ability to prevent the fibers from being pulled into the forming screen and causing a sheet sealing. The sheet sealing not only means that the material is not draining very well, but that it is harder to remove the sheet at the end of the forming screen since it is interlaced with the screen.
Another requirement which is especially important for forming screens, is a very long service life. Contrary to the paper machine coverings used in the pressing and drying zones, a forming screen is guided over deflection pulleys but also over rigid machine parts which means that it is subjected to high friction forces. Especially when suction boxes are invol
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Maher Liam
Zimmermann Daniel
Berenato, III Joseph W.
Falik Andy
Siebtuchfabrik AG
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