Patent Application
20070006934
1. Field of the Invention
The present invention relates to compound paper making fabrics, especially to forming fabrics, for use in a paper machine to manufacture a fibrous web.
2. Discussion of Background Information
Various styles of paper making fabrics, especially forming fabrics are known in the art.
EP 1 294 981 discloses a compound forming fabric for use in the forming section of a paper making machine comprising a paper side fabric and a wear side fabric being bound together by pairs of binding threads forming part of the weave pattern of the paper side fabric and part of the weave pattern of the wear side fabric and alternate from weaving with the paper side fabric to weave with the wear side fabric and vice versa, thereby crossing each other by forming crossing points. The forming fabric according to EP 1 294 981 shows per wear side weave repeat two crossing points. The structure has a high number of crossing points each of which destroys the planarity of the paper contacting side of the paper side fabric resulting in markings of the paper sheet.
In EP 0 432 413, a compound forming fabric for use in the forming section of a paper making machine is disclosed whereby a paper side fabric and a wear side fabric are bound together by pairs of binding threads forming part of the weave pattern of the paper side fabric and part of the weave pattern of the wear side fabric and alternate from weaving with the paper side fabric to weave with the wear side fabric and vice versa. According to EP 0 432 413, the number of paper side weft yarns is similar to the number of wear side weft yarns, resulting in a structure having a relative coarse paper contacting surface because of the relative low number of paper side weft yarns per length unit, thereby leading to marking of the paper sheet formed on the fabric.
The present invention is directed towards providing a paper making fabric, especially a forming fabric, having improved smoothness of the paper contacting side leading to improved, and therefore less marking, of the paper sheet.
According to the present invention there is provided a compound paper making fabric, especially a forming fabric, with a paper side fabric having paper side threads and with a wear side fabric having wear side threads, the paper side fabric and the wear side fabric being superimposed onto one another and connected by binding threads weaving with the paper side threads and with the wear side threads both extending in cross direction relative to the binding threads, the binding threads forming part of the weave pattern of the paper side fabric and forming part of the weave pattern of the wear side fabric. The binding threads alternate from weaving with the paper side fabric to weave with the wear side fabric and vice versa, thereby crossing each other by forming crossing points, wherein the wear side weave pattern being repeated by wear side repeat units. Further, the binding threads alternate such that an average of one or less than one crossing point per wear side weave repeat unit is formed, and the ratio of the paper side threads to the wear side threads is greater than or equal to 1.0.
Additionally, according to the present invention the number of crossing points is reduced to create an optimum balance to fulfil the requirement of achieving good binding between the paper side and the wear side fabric, thereby achieving as the least possible crossing points that destroy the planarity of the paper contacting surface as well as leading to hydraulic marking on the paper sheet caused by the disturbance of the regular inner structure of the fabric. By further providing a ratio of paper side threads to wear side threads, both weaving with the binding threads and being greater than or equal to 1.0, the planarity and smoothness of the paper contacting surface can be improved. leading to a paper contacting surface having less tendency for marking the paper sheet compared to those from prior art fabrics.
It is understood that according to the present invention each wear side repeat unit or each second or each third repeat unit or each repeat unit being higher in number can comprise a crossing point.
In the preferred embodiment the ratio of paper side threads to wear side threads is 3:2 or 2:1. These threads can be weft threads in the case that the binding threads are warp threads and warp threads in the case that the binding threads are weft threads.
According to a preferred embodiment of the present invention the diameter of the paper side threads is less than the diameter of the wear side threads. The use of thicker yarns on the wear side compared to the yarns on the paper side leads to a fabric having a planar and smooth paper contacting surface and having a high wear resistance.
According to another embodiment of the present invention, at each crossing point the first of the binding threads extends in a direction thereby floating under a first number of consecutive paper side threads before passing under a wear side thread, and the second of the binding threads extends in a direction opposite to the direction of the first binding thread thereby floating under a second number of consecutive paper side threads before passing under a wear side thread, wherein the first number is not equal to the second number.
According to another embodiment of the present invention the whole paper side fabric is formed by the paper side threads weaving with the binding threads and the whole wear side fabric is formed by the wear side threads weaving with the binding threads.
The present invention if 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:
a shows the weave paths of 16 consecutive binding threads B1 to B16 forming the full weave repeat by weaving with paper side weft threads 1, 3, 5, 6, 8, 10, 11, 13, 15, 16, 18, 20, 21, 23, 25, 26, 28, 30, 31, 33, 35, 36, 38 and 40 and by weaving with wear side threads 2, 4, 7, 9, 12, 14, 17, 19, 22, 24, 27, 29, 32, 34, 37 and 39.
The binding threads are arranged in pairs, for example, pair B1,B2; pair B3,B4 etc., such that each pair together weaves a full weave path on the paper side and on the wear side. By doing this the binding threads alternate from weaving with the paper side threads to weave with the wear side threads and vice versa, thereby crossing each other by forming two different types of crossing points A and B. This is best illustrated in
The weave pattern of the wear side is formed by wear side repeat units a through h having eight wear side threads. The weave pattern on the paper side is a linen binding weave pattern.
The embodiment shown in
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.
