Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
2003-05-16
2004-09-28
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S900000, C162S904000, C442S270000, C442S239000, C442S247000, C428S060000, C428S192000
Reexamination Certificate
active
06797121
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of manufacturing a press felt, the method comprising forming a laminated base fabric having at least two superimposed, independent, woven layers, each layer having its own warp yarns and weft yarns; assembling the base fabric from one or more base fabric modules into one closed loop; providing for assembly jointing edges at the opposing edges of the base fabric; and attaching at least one batt fibre layer to the base fabric after the assembly.
The invention further relates to a press felt, which comprises a woven base fabric and at least one batt fibre layer, and in which the base fabric comprises at least two superimposed, independent layers, each layer having its own warp yarns and weft yarns, the base fabric further comprising at least one base fabric module, which base fabric module is provided with necessary jointing edges, of which jointing edges one or more base fabric modules are joined into a closed loop base fabric.
The invention also relates to a base fabric, which comprises at least two superimposed, independent layers, each layer having its own warp yarns and weft yarns, and which base fabric comprises at least one base fabric module which is provided with necessary jointing edges, of which jointing edges one or more base fabric modules are joined into a closed loop base fabric.
BACKGROUND OF THE INVENTION
The aim of a press section in a paper machine is to drain a web as efficiently as possible without causing any deterioration in the quality of the web, however. From the viewpoint of energy consumption, it is most advantageous to remove as much water as possible already at the press section, whereby there is less need to dry the paper web at subsequent sections of the paper machine. Depending on the press structure, the press section of the paper machine employs a press felt on one or both sides of the web to be dried, into which press felt the water in the web is absorbed. The purpose of the press felt is to transport the water away after pressing without allowing it to migrate back into the web. In pressing, the paper web is conveyed on the felt to a gap between two rolls, i.e. so-called nip. Typically, there are one to four nips in succession, and in each nip water is pressed out of the web into the felt. Consequently, the felt should be such that the water can well be absorbed into the felt pressed in the roll nip. The press felts comprise a base fabric that provides the felt with a necessary space for water, for instance. To make the felt surface smooth, batt fibre is needled onto a base fabric surface facing the paper web. The batt fibre thus prevents markings from being produced on the web to be drained. In addition, by means of the batt fibre the water retention capacity of the felt can be adjusted to a desired level such that water is prevented from migrating back from the felt into the web, i.e. so-called rewetting is prevented. Further, the press felt should endure pressing, in order not be permanently compressed, and thereafter, easily blocked.
Even though non-woven arrays of yarns and corresponding structures have also been developed, the base fabric of the press felt is still typically manufactured by weaving, because better stability is achieved by a woven structure. Further, weaving allows better formation of a base fabric to suit each purpose, because there are more structural alternatives. Several alternative ways to weave the base fabric are known. The base fabric can be woven on a weaving machine directly into an endless loop. In that case, the weft yarns, transversal while being woven, are in the machine direction during use on the paper machine, whereby the width of the weaving machine limits the length of the base fabric to be manufactured. Using this technique, it is difficult to manufacture sufficiently long base fabrics for all press types. Further, it is possible to weave base fabrics provided with seam loops, and a necessary number of the base fabrics can be connected to form a closed loop. The seam loops at the ends of the base fabrics to be connected are intermeshed and engaged by inserting a seam yarn in a channel formed by the seam loops. The base fabric with seam loops can be woven by the known methods as flat weaving or horseshoe weaving. When woven as a plane, the weft yarns form seam loops on both edges of the fabric. Horseshoe weaving, in turn is carried out endless, so that only one edge of the fabric is provided with seam loops formed by weft yarns. Thus the base fabric can be assembled from a plurality of flat, or correspondingly, horseshoe portions, which are interconnected at their ends to form one longer entity. The press felts with seam loops have a drawback that at the seam the base fabric is different from other portions, whereby the properties of the felt at the seam area are different. In addition, the attachment of the batt fibre to the base fabric is difficult at the seam loop area, where yarn density is lower. During use, the felt is subjected to tensile stress, because of which the seam area, in particular, tends to deform. This weakens the adherence of the batt fibre even further and affects the permeability properties of the seam area.
BRIEF DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a novel and improved press felt for a paper machine, a base fabric and a method of manufacturing the press felt.
The method of the invention is characterized by arranging, in assembling the base fabric, prior to batt fibre attachment, transverse jointing edges of one or more base fabric modules edge on edge, substantially closely against one another, and connecting them at the resulting butt seam to form a closed loop.
Further, the press felt of the invention is characterized in that the base fabric modules to be connected are substantially as wide as the press felt and that, prior to attaching the batt fibre, the transverse jointing edges of the base fabric modules are arranged with a butt seam edge on edge, substantially closely against one another, to form a closed loop of a desired length.
Further still, the base fabric of the invention is characterized in that the base fabric modules to be connected are substantially as wide as the press felt and that the transverse jointing edges of one or more base fabric modules are arranged with a butt seam edge on edge, substantially closely against one another, and connected at the butt seam to form a closed loop of a desired length.
The basic idea of the invention is to form a base fabric having a laminated structure for the press felt, i.e. multi-layered base fabric having at least two superimposed, independent layers. Each of these independent layers comprises weft yarns and warp yarns of its own. According to the inventive idea, the base fabric is assembled of one or more base fabric modules to form a closed loop of a desired length. For assembly, at least one base fabric module edge, transverse to the paper machine direction, is provided with a jointing edge. On assembly, the jointing edges of one or more base fabric modules are interconnected with a butt seam. Each of the base fabric portions to be connected is substantially as wide as the press felt, i.e. seen in the lateral direction the press felt is continuous. Typically, one or more batt fibre layers are attached to the base fabric, preferably by needling.
Thanks to the butt seam according to the invention, the properties in the seam area of the laminated base fabric now substantially correspond to those in the rest of the base fabric. Thus, the base fabric can be formed more freely than before of a plurality of different base fabric modules. It is possible to form the base fabric modules by different solutions, as regards the shape, the yarn material, the dimensions and the thread count, the weave, the number of superimposed laminated layers, etc., whereby different base fabrics can be customized for different press sections.
In general, the laminated felts have an advantage that it is easier to provide the laminated felts with a s
Hyvönen Kari
Rehakka Heikki
Virtanen Tauno
Chin Peter
Hug Eric
Oliff & Berridg,e PLC
Tamfelt Oyj ABP
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