Patent Publication Number: US-7584768-B2

Title: Woven belt for a machine for producing web material and method for manufacturing such a woven belt

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a woven belt for a machine for producing web material, in particular forming mesh, including at least two woven layers with warp threads extending in a belt longitudinal direction and weft threads extending in a belt transverse direction, wherein a first of the woven layers provides a web material contact side and a second of the woven layers provides a machine contact side and the woven layers are joined together by tie warp threads. In addition this invention relates to a method with which such a woven belt can be manufactured. 
   2. Description of the Related Art 
   In the case of woven belts of the type used for example as forming meshes on machines for producing web material such as paper or paperboard, an elementary requirement is that there should be as little tendency as possible to marking in the web material to be produced. This means that the structure of the woven belt should impress itself as little as possible in the web material to be produced because such an impression of the structure, generally referred to as marking, impairs the quality of the produced web material. 
   Markings are produced above all when a very regular tie structure or weave structure exists in the woven belt. Hence there is a general endeavor to make the repeat lengths in both the warp direction and the weft direction, meaning in general the size of a warp/weft repeat, as large as possible. In this way it is possible to obtain a greater diversity of variation of the mutual tie points of warp threads and weft threads as well as an accordingly greater irregularity of said tie points. 
   What is needed in the art is a woven belt for a machine for producing web material and a method for manufacturing such a woven belt, by way of which an improved weave structure with a smaller tendency to marking is obtained. 
   The term “tendency to marking” is understood in this context to mean for example a line-shaped marking which extends for example in the warp or weft direction or in a diagonal direction thereto. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the invention, the present invention provides a woven belt for a machine for producing web material, in particular forming mesh, including at least two woven layers with warp threads extending in a belt longitudinal direction and weft threads extending in a belt transverse direction, wherein a first of the woven layers provides a web material contact side and a second of the woven layers provides a machine contact side and the woven layers are joined together by tie warp threads, wherein the first woven layer is woven with at least 26 different warp runs, the structure-forming warp threads woven into the first woven layer and the weft threads of the first woven layer having a maximum floating length of 3 in relation to each other, wherein, when the tie warp threads for providing structure-forming tie thread pairs are arranged in pairs relative to each other so that where a tie warp thread of a respective structure-forming tie warp thread pair is integrated into the first woven layer then the other tie warp thread of this structure-forming tie warp thread pair is integrated into another woven layer, then changeover points at which the tie warp threads of the structure-forming tie warp thread pairs cross each other for switching between the first woven layer and the other woven layer are distributed irregularly within a warp/weft repeat, or wherein, when the tie warp threads are integrated into the first woven layer with no structure-forming effect and tie onto tie-on points over weft threads of the first woven layer, then the tie-on points within a warp/weft repeat are distributed irregularly. 
   In the case of the inventive woven belt it is first clear that said belt is a warp-tied woven belt, meaning that the connection between various woven layers is produced by warp threads. Said threads can be provided either as structure-forming warp thread pairs which contribute to forming the structure where they are integrated into the woven layer providing the web material contact side or which produce a strong connection between woven layers by switching between said layers. On the other hand provision can be made for so-called non-structure-forming tie warp threads which are not integrated primarily into the woven layer providing the web material contact side and which are tied only to a few points, so-called tie-on points, over weft threads of the first woven layer and thus produce the connection between various woven layers. 
   By providing at least 26 different warp runs, meaning at least 26 different ways in which the warp threads integrated into the first woven layer are tied in relation to the weft threads of the first woven layer, a very large repeat length is produced and extends over at least 26 warp threads. This makes it possible in turn for the changeover points of so-called structure-forming tie warp thread pairs or the tie-on points of non-structure-forming warp threads within a respective warp/weft repeat to be positioned with great freedom of variation such that the occurrence of a regular pattern of such changeover points or tie-on points can be avoided so that said points are distributed irregularly in a respective repeat. 
   The first woven layer (G 1 ) can be woven with 32 or more, 38 or more or 45 or more different warp runs. 
   According to another particularly advantageous aspect provision is made on the inventive woven belt for each structure-forming tie warp thread pair within a warp/weft repeat to have at least two changeover points and for all the changeover points on no more than two, preferably on no structure-forming tie warp thread pairs to lie on the same weft threads of the first woven layer. 
   The measure of providing within one warp/weft repeat no more than three structure-forming tie warp thread pairs on which all changeover points lie on the same weft threads of the first woven layer contributes to the changeover points within a respective warp/weft repeat being distributed irregularly. 
   It is advantageous for there to be at least one changeover point on at least half of the weft threads within a warp/weft repeat. 
   In order to obtain a stable connection of the woven layers to each other while at the same time obtaining as irregular a distribution as possible of the tie-on points of non-structure-forming tie warp threads it is proposed for each non-structure-forming tie warp thread within a warp/weft repeat to have at least two tie-on points in the first woven layer and for all tie-on points on no more than two, preferably on no non-structure-forming tie warp threads to lie on the same weft threads of the first woven layer. In this case provision can also be made for there to be within one warp/weft repeat no more than three non-structure-forming tie warp threads on which all tie-on points lie on the same weft threads of the first woven layer. 
   On the non-structure-forming tie warp threads it is also possible to increase the irregularity of the distribution of tie-on points within a warp/weft repeat by there being at least one tie-on point on at least half of the weft threads of the first woven layer within a warp/weft repeat. 
   The other woven layer can be the second woven layer, which generally means that such a woven belt is then constructed with two woven layers. 
   In addition provision can be made for the number of structure-forming tie warp thread pairs or the number of non-structure-forming tie warp threads to be smaller than or equal to the number of warp threads in the first woven layer which do not contribute to the connection of the woven layers. 
   In order to produce, in particular on the web material contact side, a comparatively high density of warp threads and weft threads and a correspondingly dense weave structure it is proposed for the number of warp threads of the first woven layer to be greater than or equal to the number of warp threads of the second woven layer. In addition provision can be made for the number of weft threads of the first woven layer to be greater than or equal to the number of weft threads of the second woven layer. 
   It is possible that all warp threads within a warp repeat have different warp runs. 
   On the inventive woven belt a contribution to a reduced tendency to marking is made in addition by at least half of the floatings between the structure-forming warp threads woven into the first woven layer and the weft threads of the first woven layer relative to each other having a floating length of less than 3. 
   A very irregular tie pattern can also be obtained by at least two, preferably all of the at least 26 different warp thread runs being formed not by shifting of another warp thread run in the warp direction. 
   According to another aspect of the invention, the present invention provides a method for manufacturing a woven belt for a machine for producing web material, in particular forming mesh, including at least two woven layers with warp threads extending in a belt longitudinal direction and weft threads extending in a belt transverse direction, wherein a first of the woven layers provides a web material contact side and a second of the woven layers provides a machine contact side and the woven layers are joined together by tie warp threads, wherein the first woven layer is woven with at least 26 different warp runs, the structure-forming warp threads woven into the first woven layer and the weft threads of the first woven layer having a maximum floating length of 3 in relation to each other, wherein, when the tie warp threads for providing structure-forming tie thread pairs are arranged in pairs relative to each other so that where a tie warp thread of a respective structure-forming tie warp thread pair is integrated into the first woven layer then the other tie warp thread of this structure-forming tie warp thread pair is integrated into another woven layer, then changeover points at which the tie warp threads of the structure-forming tie warp thread pairs cross each other for switching over between the first woven layer and the other woven layer are distributed irregularly within a warp/weft repeat, or wherein, when the tie warp threads are integrated into the first woven layer with no structure-forming effect and tie onto tie-on points over weft threads of the first woven layer, then the tie-on points within a warp/weft repeat are distributed irregularly. 
   The use of at least 26 shafts generally means that at least 26 different warp thread runs are generated, resulting in a correspondingly long warp repeat. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  shows a warp/weft repeat of a woven belt for producing web material, wherein warp lifts are indicated by a dark field, warp lowerings by a bright field and changeover points of structure-forming tie warp thread pairs with an “X”; 
       FIGS. 2   a  to  2   f  show the warp thread runs of the warp threads or warp thread pairs  1  to  36  shown in  FIG. 1 ; 
       FIG. 3  shows a representation of a warp/weft repeat corresponding to  FIG. 1 , wherein warp lifts are indicated by black fields, warp lowerings with white fields and tie-on points of tie warp threads with an “X”; 
       FIGS. 4   a  to  4   g  show the warp thread runs of the structure-forming warp threads drawn in  FIG. 3  and the tie warp threads. 
   

   Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, and more particularly to  FIGS. 1 and 2   a  to  2   f , there is shown a first example of a tie structure of a woven belt constructed according to the principles of the invention for a machine for producing web material, for example a paper machine. Such a woven belt can be used on a paper machine as a so-called forming mesh. 
     FIG. 1  shows the tie pattern of a warp/weft repeat R. In this case the adjacent columns  1  to  36  designate respectively the runs of warp threads while the lines  1  to  42  orthogonal thereto represent weft thread runs. In particular it should be noted that the tie pattern illustrated here is that of a woven layer providing a web material contact side of a woven belt constructed with two woven layers G 1  and G 2  (see  FIG. 2   a ). In  FIG. 1  a respectively black marked field indicates a so-called warp lift, meaning a condition in which looking from the web material contact side a warp thread runs over a weft thread. The white marked fields indicate warp lowerings, meaning positions at which a respective warp thread runs under a weft thread of the first woven layer G 1 . The fields marked with “X” indicate changeover points (explained below) in which so-called structure-forming warp threads switching from one of the woven layers G 1 , G 2  into the other of the woven layers cross each other. 
   If  FIG. 2   a  is considered, for example, then the runs marked in  FIG. 1  with  1  to  7  and the structure-forming warp threads woven in the first woven layer G 1  are shown. A basic difference in the way the warp threads forming the first woven layer G 1  are integrated is that for example the warp threads  2 ,  4 ,  6  in  FIG. 2   a  and also designated as Ko in the following figures are woven solely in structure-forming manner into the first woven layer G 1 , meaning that they are tied only to the weft threads  1  to  42  of this first fabric layer. By contrast the “warp threads” designated in  FIG. 2   a  with  3 ,  5  and  7  and also appearing with corresponding numbering in  FIG. 1  are formed respectively by a pair of tie warp threads which switch at the respective changeover points A between the first woven layer G 1  and the second woven layer G 2 . Such structure-forming tie warp thread pairs, designated in  FIGS. 2   a  to  2   f  as sBK, are formed respectively from two individual warp threads, which in some regions are tied to the weft threads of the first woven layer G 1  and thus lie in structure-forming manner on the surface or in the first woven layer G 1 , but which in some regions are also tied to weft threads of the second woven layer G 2  and thus produce a connection between the two woven layers G 1  and G 2 . In order to obtain a continuous structure in the first woven layer G 1 , when one of these tie warp threads of a respective structure-forming tie warp thread pair switches from the first woven layer G 1  into the second woven layer G 2 , then the other tie warp thread of such a structure-forming tie warp thread pair switches from the second woven layer G 2  into the first woven layer G 1 , thus creating a changeover point A at a respective crossover point. 
   From  FIG. 2   a  to  2   f  and also from  FIG. 1  it is evident that in each case a warp thread Ko woven only into the first woven layer changes with such a structure-forming tie warp thread pair sBK, which actually becomes visible in the finished weave pattern on the surface of the woven belt as only a single warp thread. 
   In order to obtain the greatest possible irregularity in a respective warp/weft repeat on an inventively constructed woven belt and, in so doing, to suppress as far as possible the occurrence of marking effects in the web material to be produced, the tie structure as illustrated in  FIGS. 1 and 2   a  to  2   f  is constructed with very great irregularity. Various aspects contribute to this irregularity. For example, each of the warp threads used in the warp/weft repeat R, meaning each warp thread Ko and each tie warp thread contributing to a structure-forming tie warp thread pair sBK, has a different warp run than the other warp threads of said repeat R. This means that actually 54 different warp runs exist in the repeat shown in  FIG. 1  for the first woven layer G 1  alone. There are namely 18 different warp runs of the warp threads Ko and 2×18 (=36) different warp runs for the structure-forming tie warp thread pairs sBK. A warp run in the context of the current invention is in each case the run of a respective warp thread in relation to the weft threads of the first woven layer G 1 . By using these many different warp runs, which on account of the pair-wise joining together of certain warp threads to form the respective structure-forming tie warp thread pairs are recognizable on the woven belt actually as 36 different thread runs 1 to 36, it is possible to produce a warp/weft repeat which extends in warp direction over at least 36 “warp threads”, wherein in this case the warp threads actually visible on the surface are considered, meaning the structure-forming tie warp thread pairs sBK are interpreted only as a single warp thread existing in the first woven layer G 1 . Actually a total of 54 warp threads contributes to these 36 recognizable “warp threads”. 
   If use is then made on such a woven belt for the running-side woven layer, meaning the second woven layer G 2 , of three different warp runs, which are repeated for example periodically on the warp threads Ku respectively woven into only the second woven layer G 2 , then the tie structure presented in  FIG. 1  requires actually 57 different warp runs. For production with a so-called high-shaft machine this means that at least 57 shafts are required to weave such a tie structure. 
   Another contribution to a greatest possible irregularity is the fact that none of the warp runs are generated only by shifting another of the warp runs by a predefined number of wefts. Each of the warp runs actually forms a completely independent pattern in conjunction with the weft threads viewed in connection therewith. 
   In addition it is evident above all from  FIG. 1  that the distribution of changeover points A, represented there in each case by a field marked with “X”, is not subject to any regularity. On the one hand there are structure-forming tie warp thread pairs sBK, on which there are 2 changeover points A within the repeat R, while on other structure-forming warp thread pairs there are 3 changeover points. However, to provide as uniform a connection as possible between the two woven layers G 1 , G 2 , each structure-forming warp thread pair sBK has at least 2 changeover points A. In addition steps should be taken to ensure that the number of structure-forming tie warp thread pairs sBK, on which the changeover positions A are in each case on the same wefts, is kept as small as possible. Advantageously there should be no more than three structure-forming tie warp thread pairs on which all changeover points lie on the same weft threads. Also it is advantageous to configure the distribution of changeover points A on the weft threads  1  to  42  as evenly as possible. Hence there should be a changeover point A on at least half of all the weft threads. 
   Another contribution to as irregular as possible a structure with the smallest possible tendency to marking is made on the inventively constructed woven belt by the fact that the floating length of the structure-forming warp threads in the first woven layer G 1 , meaning the warp threads Ko in the case of the tie shown in  FIGS. 1 and 2   a  to  2   f  and the warp threads of the respective structure-forming tie warp thread pairs sBK, has a floating length of no more than 3 with regard to the weft threads of the first woven layer G 1 . Actually it is evident from the illustrated example that on the two warp threads Ko  10  and  20  there is respectively one floating which extends over three weft threads, namely the weft threads  36 ,  37  and  38  in the case of the warp thread Ko  10  and the weft threads  38 ,  39  and  40  in the case of the warp thread Ko  20 . All other floatings extend over fewer than three weft threads. Here it has proven to be particularly advantageous for at least half of the existing floatings to extend over fewer than three threads, meaning fewer than three warp threads or fewer than three weft threads. 
   Another embodiment of an inventively constructed woven belt or a tie structure therefor is shown in  FIGS. 3 and 4   a  to  4   g . Here, too,  FIG. 3  shows a warp/weft repeat R, which extends over 36 structure-forming warp threads woven into the first woven layer G 1  and over 42 weft threads of both the first woven layer G 1  and the second woven layer G 2 . The connection between the two woven layers G 1  and G 2  is effected in this case by tie warp threads BK which in the essential region of their extension are woven into only the second woven layer G 2 , meaning that they are tied there over or under the weft threads  1  to  42  of this second woven layer G 2 . At so-called tie-on points A′, however, said tie warp threads BK are tied to weft threads of the first woven layer G 1 . In the case of the tie warp thread BK arranged between the structure-forming warp threads  1  and  2  of the first woven layer G 1 , said tie-on points A′ are formed in each case on the weft threads  2 ,  20  and  35  of the first woven layer G 1 , meaning the tie warp thread BK runs there over the weft threads of the first woven layer G 1 . Before and afterwards it switches from the second woven layer G 2  into the first woven layer G 1  or back into the second woven layer G 2 . Because said tie warp threads on the surface of the first woven layer G 1  occur only in the region of the tie-on points A′ and otherwise do not appear in the first woven layer G 1 , they are not referred to as structure-forming because they do not make a notable contribution to the structure of the first woven layer G 1 . 
   The greatest possible irregularity is assured also on the tie structure shown in  FIGS. 3 and 4   a  to  4   g . Here, too, a contribution is made by the first woven layer being woven with a multiplicity of different warp runs. This applies initially to the structure-forming warp threads Ko occurring in the first woven layer G 1 , which in  FIG. 3  are numbered from  1  to  36 . All the warp runs of these 36 warp threads Ko differ from each other by respectively different tie patterns with the weft threads  1  to  42  of the first woven layer G 1 , wherein here again none of the warp runs can be generated solely by shifting another warp run in the warp direction. Different warp runs are selected also for the tie warp threads which occur solely at the tie-on points A′ in the first woven layer G 1 , which results among other things in a completely irregular distribution of the tie-on points A′. Such non-structure-forming tie warp threads BK are thus available here for a warp/weft repeat  18  so that the total number of warp runs of warp threads Ko and BK, which occur in the first woven layer G 1 , again lies at  54 . Combined with the three different warp runs for the warp threads Ku woven into only the second woven layer G 2  this results in a total number of 57 different warp runs within a warp/weft repeat. Hence such a weave or such a tie structure also requires the use of a high-shaft machine with at least 57 shafts. 
   In addition it should be noted that for the tie structure shown in  FIGS. 3 and 4   a  to  4   g  with regard to the floating of structure-forming warp threads in the first woven layer G 1 , meaning the warp threads Ko and the weft threads  1  to  42  of the first woven layer woven thereto, the same applies of course as for the preceding embodiment. Here, too, the maximum floating length should not exceed the number 3. Such a floating extending over 3 weft threads can be seen for example on warp thread Ko  29  in  FIG. 4   f . The majority of floatings is selected such that they extend over a maximum of two respectively other threads, meaning warp threads or weft threads. 
   With regard to the irregular positioning of the tie-on points A′ within a respective repeat it should also be noted that said tie-on points should be selected preferably such that on no more than three tie warp threads BK do the tie-on points A′ lie respectively on the same weft threads. To the extent that there are such tie warp threads which have all the tie-on points A′ on the same weft threads the same as other tie warp threads BK, steps should be taken to ensure that they do not lie directly side by side but are separated by at least one differently integrated tie warp thread. Also care should be taken to ensure that, as is evident in  FIG. 3 , tie-on points A 1  exist on as many as possible of the weft threads existing in such a repeat. At least half of the weft threads should be tied respectively to a tie warp thread BK in order to form such a tie-on point A′. 
   In the manner previously described it is thus possible to create a tie structure for a woven belt for a machine for producing web material, for example paper or paperboard, on which the occurrence of regular tie patterns is suppressed as far as possible on the one hand through the provision of very large repeats and on the other hand through a very irregular distribution of for example the changeover points A or the tie-on points A′ within the respective repeats. A very short floating length also contributes to this. As a result it is possible to obtain a woven belt on which not only is the tendency to marking reduced but a very uniformly distributed connection of the woven layers to each other over the entire woven belt can be maintained. 
   Finally it should also be noted that the illustrated examples with 54 different warp runs of the first woven layer, meaning the woven layer providing the web material contact side, are of course not limiting for the current invention. It is also possible to use smaller numbers of warp runs or shafts in the weaving process in order to produce comparatively large repeats. For example, it is possible of course for a certain number of warp runs to be repeated within a respective repeat, thus producing repeats which have for example 26 different warp runs and extend over 40 or more warp threads or structure-forming warp thread pairs. The number of 26 different warp runs has proven to be advantageous. It is also possible to use 30 different warp runs or 36 different warp runs as a lower limit, thus resulting in correspondingly larger repeats. 
   The previously described inventively constructed woven belt can also be used in particular for the production of voluminous paper, in particular tissue paper or bulky tissue paper. When assigned to such voluminous paper, which therefore has a lower gsm (grams per square meter) substance, the warp and weft specifications can then be selected accordingly, for example the density and diameter of the warp threads and/or weft threads, which are interrelated variables. 
   While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.