Abstract:
A papermaker&#39;s fabric having a system of primary machine direction yarns which form seaming loops at each end of the fabric and a system of secondary machine direction yarns. A system of cross-machine direction yarns are interwoven with the primary and secondary systems of machine direction yarns in a weave pattern that provides adjacent balancing yarns that maintain the seam loops in substantially vertical alignment.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a woven fabric for use in a paper, cellulose or board manufacturing machine that is seamed by interlocking loops along each of two fabric edges to form an endless woven fabric. 
     2. Description of the Prior Art 
     As will be known to those skilled in the art, papermaking machines generally include three sections which are referred to as the forming, press and dryer sections. A felt is generally employed to transport the formed, wet sheet through the press and dryer sections of the papermaking equipment. The felt must be particularly adapted to specific conditions encountered in papermaking. 
     Typically, such felts include a supporting base, such as a woven fabric, and a paper carrying or supporting layer fixed to the base. The paper carrying or supporting layer is generally softer and smoother than the base layer. The support layer is often a non-woven batt material which has been affixed to the base and has homogeneous characteristics as to permeability, compaction and drainage. Slight irregularities or imperfections in the support layer are undesirable in virtually all papermaking operations. Inconsistencies in the felt thickness, gauge or weight can cause undesirable vibrations during operation of the equipment. 
     In press fabrics, the batt material is often anchored to a base fabric which is provided with end loops to join the fabric. Many of these fabrics are woven as endless loops in patterns that provide the seaming loops at each end of the fabric. Standard woven loop base constructions frequently include two layers of weft yarns in a low density, symmetrical construction. However, these base fabrics typically provide limited batt anchorage and sheet support due to low surface contact area. This necessitates the use of a third, topical laminate structure, having a higher density of weft or warp yarns. The laminate is generally bound to the primary base by means of filament entanglement during a post weaving needling process. This process can be costly and time consuming. 
     Another problem associated with endlessly woven seamed fabrics is seaming of the fabric. Standard endlessly woven loop seam products are made with stacked weft pairs, formed by looping around a forming monofilament. A common problem associated with this type of loop formation is non-uniform loop alignment, both in the vertical and horizontal axis, when the forming wire is removed. This misalignment creates a seam that is difficult to mesh. 
     FIGS. 1-3 show representative loop misalignments experienced in common prior art endlessly woven seams. Generally, as a loom weaves the loops in an endless weave construction, it naturally offsets the returning weft position slightly from its outgoing weft position. It is possible to maintain the weft yarns in a stacked relationship throughout the fabric through the balanced weave of the warp yarns. However, the last warp yarn  2  does not have a balancing yarn on one of its sides and, therefore, an unbalanced crimp force is applied to the weft yarns in the loop area, as shown by the arrows in FIG.  2 . As a result, the two weft yarn passes which form each loop are not balanced by warps and the loops tend to be misaligned. 
     A similar misalignment of the loops occurs in flat woven fabrics wherein the tie back portion of the warp yarn is offset from the outgoing portion of the warp yarn during loop formation. 
     The present invention combines two high density structures during the weaving process, with the primary base construction being used to form endless type seam loops. This is achieved by means of unique weave patterns that stitch in a higher density weft layer of yarns to provide greater batt anchorage and maintain a stacked weft arrangement in the base for uniform, vertically aligned, loop formation. 
     SUMMARY OF THE INVENTION 
     The present invention generally relates to a papermaker&#39;s fabric of a type having a system of primary machine direction yarns which form seaming loops at each end of the fabric. The fabric also includes a system of secondary machine direction yarns and a system of cross-machine direction yarns. The cross-machine direction yarns are interwoven with the primary and secondary systems of machine direction yarns in a weave pattern that provides adjacent balancing yarns that maintain the seam loops in substantially vertical alignment. A method of forming the papermaker&#39;s fabric is also provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of prior art end loops. 
     FIG. 2 is an elevation view of the prior art end loops along the line  2 — 2  in FIG.  1 . 
     FIG. 3 is a side elevation view of the prior art end loops along the line  3 — 3  in FIG.  1 . 
     FIG. 4 is a schematic perspective view of a portion of the fabric according to the present invention. 
     FIG. 5 is an end elevation view of a portion of the fabric according to the present invention. 
     FIG. 6 is a schematic view showing the weaving progression of the weft yarns. 
     FIG. 7 shows a position of the weft yarn after the fabric of FIG. 6 is removed from the loom and opened. 
     FIG. 8 is a cross section taken along the line  8 - 8  in FIG.  6 . 
     FIG. 9 is a weave pattern diagram for the preferred embodiment of the base fabric of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment will be described with reference to the drawing figures wherein like numerals represent like elements throughout. 
     Referring to FIGS. 4 and 5 the preferred fabric  100  generally comprises a base fabric  110  with batt material  112  attached thereto. The base fabric  110  comprises three layers of machine direction (MD) yarns  114 ,  116  and  118  interwoven with a system of cross-machine direction (CMD) yarns  120 . MD layers  114  and  116  are woven in stacked pairs and form seam loops  122  at each end of the base fabric  110 . The third layer MD yarns  118  extend above MD layers  114  and  116  and are substantially parallel thereto. In the preferred embodiment, two third layer MD yarns  118  are provided for every pair of stacked MD yarns  114  and  116 . 
     The fabric  110  is preferably endless woven using a two shuttle loom. The first shuttle weaves the lower and intermediate MD layers  114  and  116  and the second shuttle weaves the upper MD layer  118 . As shown in FIG. 6, the base fabric  110  is woven on the loom doubled over upon itself. That is, the base fabric  110  is woven with an upper weaving layer  130  and a lower weaving layer  132  which are opened after weaving as shown in FIG. 7 to provide a base fabric  110  which is approximately twice the length of the fabric on the loom. Reference to position of the yarns relative to one another is the relative position after the fabric is opened, unless otherwise specified. 
     The CMD yarns  120  interweave with all three MD yarn layers  114 ,  116  and  118 . As shown in FIGS. 5 and 8, the CMD yarns  120  preferably include two CMD subsystems  120   a, b.  Upper CMD subsystem yarns  120   a  weave exclusively with the middle and upper MD layers  116  and  118  and the lower CMD subsystem yarns  120   b  weave exclusively with lower and middle MD layers  114  and  116 . 
     The base fabric  110  has a weave which preferably repeats on sixteen (16) CMD yarns and thirty-two (32) MD yarns. As shown in FIG. 8, CMD yarns  1 ,  4 ,  5 ,  8 ,  12 ,  13  and  16  make up the upper CMD subsystem  120   a  and CMD yarns  2 ,  3 ,  6 ,  7 ,  10 ,  11 ,  14  and  15  make up the lower CMD yarn subsystem  120   b.  The upper CMD subsystem yarns  120   a  weave exclusively with the intermediate and upper layer MD yarns  116  and  118 . Each upper subsystem CMD yarn  120   a  preferably weaves, relative to the intermediate and upper MD layers  116 ,  118 , over two, under four, over two and under four in a given repeat. For example, as shown in FIG. 8, warp yarn  16  weaves over MD yarns  4  and  5 , under MD yarns  8 ,  12 ,  13  and  16 , over MD yarns  20  and  21 , and under MD yarns  24 ,  28 ,  29  and  32 . The lower CMD subsystem yarns  120   b  preferably weave in a standard “N” pattern relative to the lower and intermediate MD layers  114 ,  116 . For example, CMD yarn  14  weaves over weft yarns  5  and  6 , between MD yarns  13  and  14 , under MD yarns  21  and  22 , and between MD yarns  29  and  30  in a given repeat. 
     As can be seen in FIG. 8, the intermediate MD yarns  116  interweave with both CMD subsystem layers  120   a,b,  to integrate the fabric. This weave pattern integrates the three MD layers  114 ,  116 ,  118  while maintaining the seam loops  122  in substantial vertical alignment. Loop alignment is maintained by the balanced weave of the end upper CMD yarn  120   a  which counterbalances the unbalanced crimp force of the end lower CMD yarn  120   b.    
     The fabric  110  may be flat woven or endless woven. The preferred method of endless weaving the fabric  110  will be described with reference to FIGS. 6-9. FIG. 9 shows a weave pattern diagram for the base fabric  110  wherein the filled boxes indicate where a warp yarn or cord is over a respective weft yarn. Weaving of the fabric will be described with reference to positioning of the cords only, but it will be understood that the warp heddles are positioned for each shuttle pass in accordance with the desired weave pattern. 
     The base fabric  110  is preferably woven using a two shuttle loom. Referring to FIGS. 6-9, the first shuttle is thrown across the loom with all of the cords LC, RC 1 , and RC 2  lowered. The right cord RC 1  is then raised and the first shuttle is thrown back across the loom, thereby looping around the end right cord RC 1 . This first shuttle pass is depicted as 1 and 2 in FIG.  6 . The end right cord RC 1  remains raised and the second shuttle is thrown across the loom from the side opposite the first shuttle. The three left cords LC, RC 1 , and RC 2  are raised as the second shuttle is thrown back across the loom. This second shuttle pass is depicted as  3  and  4  in FIG.  6 . The first shuttle then weaves weft yarns  5  and  6 . The left cord LC and the inner right cord RC 2  are raised and the first shuttle is thrown across the loom. All three cords LC, RC 1 , and RC 2  are raised and the first shuttle is thrown back across the loom, thereby weaving weft yarns  5  and  6  in the lower fabric layer and looping around the end right cord RC 1 . To weave weft yarn  7 , both right cords RC 1  and RC 2  are raised and the second shuttle is thrown across the loom. The left cord LC and the end right cord RC 1  are raised and the second shuttle is thrown back across the loom to weave weft yarn  8 . At the transition of each shuttle back to the upper weaving layer  130 , a turning fold is formed as is known in endless weaving. The shuttles weave in the same pattern across the width of the fabric  110  with the heddles being adjusted to provide the desired weave pattern. 
     To open the fabric  110  after the desired width is formed, the right end cord RC 1  is removed and the left and inner right cords LC and RC 2  are replaced with yarns consistent with the remainder of the warp yarns. Removal of RC 1  provides the loops  122  at both ends of the fabric. As can be seen in FIG. 6, in the preferred weaving arrangement, the upper weft yarn passes  3 ,  4  and  7 ,  8  will be joined at the loop end of the woven fabric  110  as represented at  150 . To facilitate opening of the fabric  110 , these weft yarns are cut at  150 . It will be understood that various other weaving patterns can be used which will leave these ends separate, thereby eliminating the need for cutting of the upper weft layer yarns. 
     As can be seen in FIG. 9, the upper layer MD yarns  118  substantially increase the number of entanglement points on the upper surface of the base fabric  110 . The increase in entanglement points allows greater adherence of the batt material  112  to the base fabric  110 .