The present application claims priority under 37 CFR 119 of German Patent Application, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of Invention
The present invention relates to papermaking fabrics for use in papermaking machines, in particular for use in the dryer section of a papermaking machine.
2. Description of Prior Art
Papermaking fabrics commonly are made by weaving weft yarns with warp yarns. During weaving on the weaving loom, the shafts together with its corresponding warp yarns are alternately lifted and lowered to enable the insertion of weft yarn shoots extending in cross direction to the warp yarns. The rate of weaving and therefore the weaving speed mainly is limited by the insertion rate of the weft yarns and the number of weft yarns in a fabric design. As the weaving is a very labour intensive manufacturing method the manufacturing costs are significantly influenced by the weaving speed and the number of weft yarns per unit of running length.
It is the object of the present invention to provide a papermaking fabric that can be fabricated faster and therefore less cost intensive to produce compared to those known in the art.
It is another object of the present invention to provide a papermaking fabric that is less sensitive to contamination as those known in the art.
It is also an object of the present invention to provide a papermaking fabric, especially a dryer fabric, having increased surface contact points or area on both sides of the fabric.
According to a first aspect of the invention there is provided a papermaking fabric having a system of warp yarns interwoven with a system of weft yarns. The papermaking fabric according to the invention is characterized in that the system of weft yarns comprise groups of weft yarns, each of the groups being formed by a plurality of adjacent weft yarns weaving in the group side-by-side the same weave path with the warp yarns.
By providing a papermaking fabric having weft yarn groups, each of which is formed by a plurality of adjacent weft yarns, wherein the adjacent weft yarns in each of the groups weave side-by-side the same weave path with warp yarns the weft yarns of each group can be inserted during weaving of the fabric at the same time. In this manner, weaving speed can be increased with the effect of faster production of the fabric at a lower cost.
Fabric designs known in the art normally provide weft yarns being separated by the interlacing of warp yarns by forming interstices, resulting in increased air permeability. By providing a plurality of adjacent weft yarns weaving side-by-side the same weave path with the warp yarns of the present invention, the number of interstices is reduced. This results in reduction of the air permeability of the fabric with the advantage of less air carriage for the application in high speed papermaking machines, especially for papermaking machines having a production speed of 1000 meter per minutes or more. Further, by forming less interstices, the fabric according to the present invention has less ability to trap contaminations coming from the paper producing process.
According to an embodiment of the present invention, it is foreseen that the system of weft yarns further comprise ungrouped weft yarns. In this manner the system of weft yarns is formed by groups of weft yarns and by ungrouped weft yarns. By way of example the system of weft yarns comprise groups of two adjacent weft yarns, the two adjacent yarns in each group weave—like a single yarn—the same weave path with the warp yarns and wherein between each group two ungrouped weft yarns are located weaving different weave paths in relation to each other.
According to another embodiment of the invention the system of weft yarns is only being formed by groups of weft yarns. In this case each of the weft yarns of a first group weave the same weave path with the warp yarns wherein the weft yarns of a second group weave the same weave path, being different to the weave path of the first group.
Depending on the specific application of the fabric the adjacent weft yarns in a group can have the same dimension. This can, for example, be the case if the paper contacting side of the fabric should be as flat as possible. A possible weave structure can be in this case an asymmetrical weave where the warp yarns float over two or more groups of weft yarns of the same dimension.
The weft yarns and/or warp yarns of the fabric according to the invention preferably have round and/or rectangular cross section and/or preferably being monofilament yarns.
For other applications it can be suitable if the adjacent weft yarns in a group have different dimensions. This is especially the case when different weft yarns in a group have to fulfill different functions.
In addition it is possible that the adjacent weft yarns in a group have the same composition or that they have different compositions. The later case can again be feasible if different yarns in the group have to fulfill different functions, for example, a first of them needs to have hydrophobic properties, whereas a second of them needs to have enhanced abrasion resistance properties.
For dryer fabrics application according to a preferred embodiment of the present invention, the system of warp yarns is interwoven with the system of weft yarns in a single-layer weave.
According to another preferred embodiment of the present invention the warp yarns alternately weave over and under the groups of weft yarns, wherein adjacent warp yarns do not weave side-by-side over or under the same group of weft yarns.
In this manner, the weave structure of the fabric according to the invention is a plain weave in the sense that each of the groups of weft yarns is regarded as being a single yarn.
This embodiment is especially advantageous for the application of the fabric as a dryer fabric in a paper making machine operating at a machine speed of about 1000 m/min omr more or 1200 m/min or more. For such high speed machines often a single tier dryer configuration is used. In this configuration vacuum rolls and stabiliser boxes are provided to produce under pressure to hold the paper web against the fabric surface to improve tail threading and sheet runnability.
By providing a weave structure with warp yarns which alternately weave over and under the groups of weft yarns, wherein adjacent warp yarns do not weave side-by-side over or under the same group of weft yarns, a discontinuous surface on at least the paper contacting side of the fabric is generated. This discontinuous fabric surface has straight channels in weft direction, being in most cases of application the cross machine direction, which are connected by channels formed between warp yarns which weave over the groups of weft yarns. These channels form a channel matrix. The channel matrix allows the formation of an under pressure network between the paper side of the fabric and the paper, thereby increasing the sheet runnability.
Further the weave structure according to this preferred embodiment provides an improved bending stiffness in weft direction, which is in many cases the cross machine direction (CD-direction) of the fabric in the paper making machine, compared to fabrics known in the art. The increased bending stiffness in CD-direction reduces the tendency of the fabric for edge curl and therefore improves the runnability of the fabric.
Additionally, the preferred weave structure provides reduced contamination affinity at the same time as the fabric can be cleaned more easily compared to fabrics known in the art.
It is understood that if the fabric of the invention has grouped weft yarns as well as ungrouped weft yarns, the warp yarns alternately weave over and under the groups of weft yarns and the ungrouped weft yarns, wherein adjacent warp yarns do not weave side-by-side over or under the same group of weft yarns and the same ungrouped weft yarns (as can be seen for example in
The single-layer weave further can be one of a broken twill weave, a straight twill weave, and a matt weave. It is also possible to have combinations of the before mentioned weave designs.
For further reduction of the permeability of the fabric on the one hand and for further reduction of the contamination affinity according to a preferred embodiment of the present invention it is foreseen that said warp system comprise groups of warp yarns, each of the groups being formed by a plurality of adjacent warp yarns weaving in the group side-by-side the same weave path with said weft yarns. By way of example the weft system can be formed of groups of two adjacent weft yarns weaving the same weave path and the warp system can be formed of groups of four adjacent warp yarns weaving the same weave path.
According to a preferred embodiment it is foreseen that the groups of warp yarns alternately weave over and under the groups of weft yarns, wherein adjacent groups of warp yarns do not weave side-by-side over or under the same group of weft yarns.
The advantages set out in the above discussion where single warp yarns alternately weave over and under the groups of weft yarns are fully applicable for this embodiment and will therefore be no further point of discussion.
Preferably the fabric according to the present invention is woven flat. In this case at least some of the warp yarns form seaming loops or hold a spiral or other means at the lengthwise ends of the papermaking fabric so that it can be joined endless. In the case that the fabric according to the invention is woven flat the weft yarns extend along the intended CD direction in the papermaking machine and the warp yarns extend along the intended MD direction in the paper making machine.
The fabric according to the invention is suitable for use in the different sections of the papermaking machine. Therefore the papermaking fabric can be a forming fabric or a press fabric or a dryer fabric.
According to a second aspect of the present invention a paper making machine comprising a dryer section is provided, wherein the dryer section is a single tier dryer section comprising a dryer fabric according to the invention. The most benefit of the fabric according to the present invention in terms of sheet runnability can be achieved if the paper making machine is one that operates at a machine speed at about or greater than 1200 m/min or more.
According to a third aspect of the present invention a highly productive and cost saving method of manufacturing a papermaking fabric with a woven structure being formed by weaving of weft yarns with warp yarns comprising the step of inserting a plurality of weft yarns at the same time by one weft shoot such that said plurality of weft yarns weave side-by-side the same weave path with said warp yarns is provided.
The present invention is further described in the detailed description which follows, in reference to the noted drawing by way of non-limiting example of exemplary embodiment of the present invention, and wherein:
The particulars shown herein are by way of example and for purposed of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.
In
Fabric 1 is repeated by weave repeat units being formed by the warp yarns 2a, 2b and the weft yarns 3a, 4a, 3b, 4b.
As can be seen the weft yarn system 5 is only formed by said groups 3a, 4a and 3b, 4b of weft yarns.
The single-layer weave shown in
a shows a cross sectional view of the dryer fabric of
b shows a cross sectional view of the dryer fabric of
By way of example warp yarn 2a weave over weft yarn group 3a, 4a and under weft yarn group 3b, 4b wherein adjacent warp yarn 2b weaves under weft yarn group 3a, 4a and over weft yarn group 3b, 4b.
c shows a cross sectional view of the dryer fabric of
The spacing between the yarns shown in
Further adjacent weft and/or warp yarns can also be equally spaced.
To increase planarity of the paper contacting surface of the dryer fabric 1, to decrease air permeability and to decrease contamination affinity it further could be advantageous to provide at least some of the weft or warp yarns with a flat cross section, e.g. with a rectangular cross section having an aspect ratio of width to height of 2:1, preferably 5:1, most preferably of 10:1.
The dryer fabric 10 is woven as a single-layer fabric has a warp yarn system 7 with warp yarns 2a, 2b and a weft yarn system 5 with weft yarns 3a, 3b, 3a, 4a, 4b and 6a, 6b, 6c, 6d. As can be seen according to the invention weft yarns 3a, 3b, 4a, 4b are arranged in groups of two adjacent weft yarns 3a, 4aand 3b, 4b weaving in said group side-by-side the same weave path with said warp yarns 2a, 2b.
In contrast to the dryer fabric 1 shown in
Accordingly, the weft yarn system 5 is formed by said groups 3a, 4a and 3b, 4b of weft yarns and by ungrouped weft yarns 6a, 6b, 6c, 6d.
As can be seen the warp yarns 2a, 2b alternately weave over and under the groups of weft yarns 3a,4a and 3b,4b and the ungrouped weft yarns 6a to 6d, wherein adjacent warp yarns 2a, 2b do not weave side-by-side over or under the same group of weft yarns e.g. 3a,4a and the same ungrouped weft yarns e.g. 6a.
Accordingly, the single-layer weave shown in
Fabric 10 is repeated by weave repeat units being formed by the warp yarns 2a, 2b and the weft yarns 3a, 4a, 3b, 4b, 6a to 6d.
The spacing between the yarns shown in
To increase planarity of the paper contacting surface of the dryer fabric 10, to decrease air permeability and to decrease contamination affinity it further could be advantageous to provide at least some of the weft or warp yarns with a flat cross section, e.g. with a rectangular cross section having an aspect ratio of width to height of 2:1, preferably 5:1, most preferably of 10:1.
The dryer fabric 100 is woven as a single-layer fabric having a warp yarn system 7 with warp yarns 2a, 2b, 8a, 8b and a weft yarn system 5 with weft yarns 3a, 3b, 4a, 4b. As can be seen according to the invention weft yarns 3a, 3b, 4a, 4b are arranged in groups of two adjacent weft yarns 3a, 4a and 3b, 4b, weaving in said group side-by-side the same weave path with said warp yarns 2a, 2b, 8a, 8b.
In contrast to the dryer fabric 1 and 10 shown in
a shows a cross sectional view of the dryer fabric 100 of
b shows a cross sectional view of the dryer fabric of
Fabric 100 is repeated by weave repeat units being formed by the warp yarns 2a, 2b, 8a, 8b and the weft yarns 3a, 4a, 3b, 4b.
The spacing between the yarns shown in
Further adjacent weft and/or warp yarns can be equally spaced.
The fabrics 1, 10100 shown in the
Further the weft and/or warp yarns of the weft yarn system 5 and/or the warp yarn system 7 are preferably monofilament yarns.
As can be seen all the warp yarns 2a, 2b alternately weave over and under the groups of weft yarns 3a, 4a and 3b, 4b. Further it can be seen that the adjacent warp yarns 2a and 2b do not weave side-by-side over or under the same group of weft yarns 3a, 4a or the same group of weft yarns 3b,4b. Therefore the weave structure of the fabric 1 can be regarded as a plain weave in the sense that each of the groups 3a, 4a and 3b, 4b weaves side-by-side like a single yarn.
Further it can be seen that a discontinuous surface on the paper contacting side 16 of the fabric 1 is generated. This discontinuous fabric surface 16 has straight channels 13 in weft- or cross machine direction (CD-direction), which are connected by channels 14 formed between warp yarns 2a which weave over the groups of weft yarns 3a, 4a. The channels 13 and 14 form a channel matrix 15. These channel matrix 15 allows the formation of an under pressure network between the paper side 16 of the fabric 1 and the paper and thereby increasing the sheet runnability.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.
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