MXPA98009070A - Confeccionadora of paper with yarns in direction of machine and in transversal direction of maquina-apila - Google Patents

Abstract

The present invention provides a papermaking fabric having a system of machine direction yarns, of flat monofilaments (hereinafter referred to as MD yarns) which are stacked to control the permeability of the fabric. The yarn system MD comprises at least one upper and lower yarn. Preferably, each upper MD yarn is matched in a vertically stacked orientation with a lower Md yarn. Preferably, multiple layers of capped CMD yarns are provided which are maintained in the stacked ratio by the flat stacked MD yarns to provide an adequate volume of voids within the fabric. In one embodiment characterized by low permeability, at least the MD yarns of the upper layer are spun from flat monofilaments which are woven contiguously with respect to each other.

Description

YARN PAPER MANUFACTURER WITH YARNS- MACHINE ADDRESS AND ADDRESS TRANSVERSAL OF MACHINE-STACKED BACKGROUND OF THE INVENTION This application is a continuation in part of the pending US patent application, serial number 08 / 524,800, filed on September 7, 1995 with the title FABRICS OF PAPER OF A SINGLE LAYER , which in turn is a continuation of the American patent application serial number 08 / 228,158, filed on August 10, 1994 with the title FABRIC OF PAPER THAT HAS FLOATING THREADS OF PLANE YARNS, granted on September 12, 1995 as Patent Number 5,449,026, which in turn is a continuation of the North American patent application serial number '08 / 043,016, filed on April 5, 1993 with the title PAPER CONFECCIONADORA OF PAPER WITH YARNS IN ADDRESS OF MACHINE, STACKED, which in turn is a continuation of the American patent application number 07 / 855,904, filed on April 13, 1992 with the title of PAPER CONFECCIONADORA OF PAPER WITH YARNS IN ADDRESS OF MACHINE, STACKED, with its patent granted on April 6, 1993 as patent number 5,199,467, which is a continuation of the American patent application number 07 / 534,164, filed on June 6, 1990, with the title TELE CONFECCIONADORA OF PAPER WITH YEARS IN ADDRESS OF MACHINE, STACKED , whose patent was granted on March 14, 1992 with the number 5,103,874.

Field of the Invention The present invention relates to papermaking fabrics and in particular to fabrics consisting of flat monofilament yarns. Description of the Related Art The papermaking machines generally consist of 3 sections: forming, pressing and drying. Papermaking fabrics are used to transport a continuous sheet of paper through the paper making equipment during the manufacture of the latter. The requirements and convenient characteristics of the papermaking fabrics vary according to the specific section of the machine, ie that section where the respective fabrics are used. With the development of synthetic yarns, it has come to use monofilament yarns configured in the construction of papermaking fabrics. Thus, for example, US Pat. No. 4,290,209 discloses a fabric woven with warp yarns, of flat monofilaments. U.S. Patent No. 4,755,420 discloses a non-woven construction in which the papermaking fabric comprises spirals that are made from flat monofilament yarns. Numerous weavings are known in the art that are used to obtain different results. For example, US Pat. No. 4,438,788 discloses a dryer fabric having 3 layers of yarns in the machine's transverse direction, interwoven with a system of machine direction yarns, of flat monofilaments, in such a way that yarns are created floating on the upper face and at the same time on the lower face of the fabric. The floating yarns tend to provide the cloth with a smooth surface. Permeability is an important criterion in the design of such papermaking fabrics. Specifically with respect to fabrics made to run at high speeds in modern dryers, it is convenient to give the dryer fabrics a relatively low permeability. U.S. Patent No. 4,290,209 discloses the use of warp yarns, of flat monofilaments, which are woven contiguously with respect to each other to provide a fabric with reduced permeability. However, even when flat warp yarns are adjoiningly woven together, additional auxiliaries are needed, such as, for example, fill yarns to reduce the permeability of the fabric. As noted in that patent, it is convenient to avoid the use of voluminous and fluffy filler yarns to reduce permeability because they make the fabric susceptible to pick up foreign substances or retain water. U.S. Patent No. 4,290,209 and U.S. Patent No. 4,755,420 indicate practical limitations in the so-called aspect ratio (is the ratio of the width to height, in cross section) of warp yarns in the machine direction, which define the structural bond of a cloth. The highest practical aspect ratio disclosed in those patents is 3: 1 and preferably this aspect ratio will be less than 2: 1. U.S. Patent No. 4,621,663, assigned to the same assignee of the present invention, discloses an attempt to use yarns with a high aspect ratio (of the order of 5: 1 and more) to define the surface of a dryer fabric, papermaking . As disclosed in said patent, a woven base fabric is provided to support surface yarns with their high aspect ratio. The woven base fabric comprises conventional • round yarns and provides a structural support and at the same time a stability to the fabric disclosed in that patent.

U.S. Patent No. 4,815,499 discloses the use of flat yarns in the context of a forming fabric. Said patent discloses a composite fabric consisting of an upper and a lower fabric, interconnected by linker yarns. The aspect ratio used for such yarns in the machine direction, flat type, both in the upper and lower fabric, is well below 3: 1. SUMMARY OF THE INVENTION The present invention provides a papermaking fabric having a system of machine direction yarns, of flat monofilaments (hereinafter referred to as MD yarns, - as an international abbreviation), which are stacked to control the permeability of the fabric. The yarn system MD comprises at least one upper and lower layer of yarns. Preferably, each upper MD yarn is matched in an orientation stacked vertically with a lower MD yarn. The fabric has a variety of industrial uses. For example, it can be used as a base fabric for a wet pressing felt, for making paper, or also as a drying fabric. Preferably, multiple layers of stacked CMD yarns (international abbreviation of the yarns extending in the transverse direction of the machine) are provided, which are kept in this piled up relationship thanks to the stacked, flat type MD yarns to provide a adequate hollow volume, inside the fabric. Preferably 3 layers of stacked CMD yarns are provided. In an embodiment which is characterized by low permeability, at least the upper MD yarns are flat monofilament yarns woven in contiguous form to one another. Preferably, yarns of the same type and of the same size are used throughout the yarn system in the machine direction, also for the upper and lower MD yarns. When 3 layers of CMD yarns are used, the CMD yarns of the middle layer preferably contain a smaller diameter than the yarns of the upper and lower layer, of CMD type, when it is desired that the fabric be used as a base fabric, for pressing. For drying fabrics, the CMD yarns are preferably all the same. It is an object of the present invention to provide a papermaking fabric having a controlled permeability with yarns in machine direction, planes and fabrics. Other objects and advantages will be apparent in the course of the following description, which presents those currently preferred embodiments. Other objects and advantages will be apparent to those skilled in the art after they have taken note of the detailed description of a presently preferred embodiment. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a papermaking fabric made in accordance with the teachings of the present invention. Figure 2 is a cross-sectional view of the fabric shown in Figure 1, following line 2-2. Figure 3 is a cross-sectional view of the fabric shown in Figure 1 following the line 3-3. Figure 4 is a cross-sectional view of a tissue construction according to the prior art. Figure 5 illustrates the effective spinning structure of that fabric shown in Figure 1, which is inside the finished fabric and which only shows two stacked, representative MD yarns. Figure 6 is a schematic view of a second embodiment of a fabric made in accordance with the present invention. Figure 7 is a cross-sectional view of the fabric shown in Figure 6, following line 7-7. Figure 8 is a cross-sectional view of the fabric shown in Figure S, following the line. Figure 9 is a top view of a third embodiment of a fabric made in accordance with the present invention. The figure 10 is a side view of the third embodiment of a fabric made in accordance with the present invention. Figure 11 is a front view of the third embodiment of a fabric made in accordance with the present invention. Figure 12 is a schematic view of the third embodiment of a fabric made in accordance with the present invention and showing only a first pair of stacked MD yarns. Figure 13 is a schematic view of the third embodiment of a fabric made in accordance with the present invention and showing only a second pair of stacked MD yarns. Figure 14 is a schematic view of the third embodiment of a fabric made in accordance with this invention and showing only a third pair of stacked MD yarns. Figure 15 is a schematic view of the third embodiment of a fabric made in accordance with the present invention and showing only a fourth pair of stacked MD yarns. Figure 16 is a cross-sectional view of the fabric shown in Figure 9, following line 16-16. Figure 17 is a cross-sectional view of the fabric shown in Figure 9, following line 17-17. Figure 18 is a top view of a fourth embodiment of a fabric made in accordance with the teachings contained in the present invention. Figure 19 is a side view of the fourth embodiment of a fabric made in accordance with the present invention. Figure 20 is a view of the fabric shown in Figure 19, following the line 20- ^ 0. Figure 21 is a schematic view of the fourth embodiment of a fabric made in accordance with the present invention and showing 4 stacked MD yarns. Figure 22 is a schematic view of the fourth embodiment of a fabric made in accordance with the present invention showing the second layer of four stacked MD yarns. Figure 23 is a cross-sectional view of the fabric shown in Figure 18, following line 23-23. Figure 24 is a cross-sectional view of the fabric shown in Figure 18, following line 24-24.

Figure 25 is a cross-sectional view of the fabric shown in Figure 18, following line 25-25. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment will be described with reference to the Figures that appear in the drawing and in which the numerical references represent equal elements in all the representations. Referring to FIGS. 1 to 3, a papermaking dryer 10 is shown, comprising an upper, middle and lower layer of yarns in the machine's transverse direction (hereinafter CMD) 11, 12, 13, respectively, interwoven with a system of MD 14-19 yarns that are woven sequentially into a selected repeating design. The yarn system MD comprises upper MD yarns 14, 16, 18 which are interwoven with CMD yarns 11, 12 and lower MD yarns 15, 17, 19 which are interwoven with CMD yarns 12, 13. The upper MD yarns 14, 16 , 18 define floating yarns on the upper face of the fabric 10, as they are woven on top of two yarns of the upper layer CMD 11, which fall inside the fabric to be knitted on an inner knuckle below a layer CMD yarn half 12 and below a yarn CMD 11 to then rise to the surface of the fabric to continue with the repetition of the yarn. The floating yarns above the CMD yarns of the upper layer 11 of the upper MD yarns 14, 16, 18 are offset so that all of the CMD yarns of the upper and middle layer 11, 12 are held within the fabric. As will be recognized by those skilled in the art, the knitting pattern, disclosed, with respect to Figures' 1-3, gives rise to the fact that the upper face of the fabric will have the pattern of a twill fabric. Although this twill pattern of two floating threads, shown in Figures 1, 2 and 3 is a preferred embodiment, those of ordinary skill in the art will recognize that the length of the floating yarn, the number of MD yarns in design repetitive the ordering of MD yarns can be selected according to preference so that other patterns will also be produced, whether twill type or not. As best seen in Figures 2 and 3, the lower MD yarns, 15, 17 and 19 are woven directly below the upper MD yarns 14, 16, 18, respectively in a vertically stacked relationship. The lower yarns are woven in an inverted image of their respective upper yarns. Each lower MD yarn 15, 17, 19 floats below two CMD yarns of the lower layer 13, goes up to enter the fabric passing over a CMD 13 yarn, to form a knuckle around a CMD yarn of the layer half 12 and then return the yarn to the underside of the fabric to continue with its repetitive floating system below the following two CMD yarns of the lower layer 13. With respect to each pair of stacked yarns, the inner knuckle, formed around of the CMD yarns of the middle layer 12 by a single MD yarn, is hidden by the floating yarn of the other MD yarn. For example in Figures 1 'and 3, the lower MD yarn 15 is represented as knitting a knuckle above the CMD yarn 12 while the MD-14 yarn is weaving its floating yarn over the CMD 11 yarns to hide this way the inner knuckle of the lower MD yarn 15. Similarly, with respect to Figures 1 and 3, the upper MD yarn 18 is represented as knitting a knit below the CMD yarn 12 as long as it is hidden by the lower MD yarn .19 floats below the CMD yarns 13. The upper MD yarns 14, 16, 18 according to Figure 18 are woven contiguously with respect to each other. This maintains its alignment in the parallel machine direction, in a respective manner, and reduces the permeability. Such narrow fabric of yarns in the machine direction is known in the art as a 100% filling of the warp., as explained in US Pat. No. 4,290,209. As taught in said patent (and used in the present application), the actual warp count within a woven fabric can vary between about 80% and 125% in a single layer and is anyway considered as a 100% fill. % of the warp. The stacking of yarns MD 14, 16 and 18 also serves to force MD 15, 17 and 19 yarns into their stacked position below the respective yarns MD 14, 16, 18. Preferably MD 15 yarns, 17 and 19 have the same size as the MD 14, 16 and 18 yarns so that they are similarly woven with 100% warp filling. The result of this is the general fabric according to the preferred embodiment having a 200% filling of the warp, with MD yarns. Since the lower MD yarns 15, 17 and 19 are also preferably woven with a 100% warp finish, they also have the effect of maintaining the upper MD yarns 14, 16, 18 in a stacked relation to to the lower MD yarns 15, 17, 19. Consequently the respective pairs of yarns MD 14 and 15, 16 and 17, 18 and 19 are double locked in their position, and in this way improve the stability of the fabric. As noted in U.S. Patent No. 4,290,209, it has been recognized that flat yarns in the machine direction will be woven in a narrower contact around the yarns in the transverse direction of the machine than round yarns. However, the aspect ratio of 3: 1 was considered to be a practical limit for such woven yarns in order to preserve the overall stability of the fabric. The present system of stacked MD yarns retains the stability and strength in the machine direction of the fabric, and allows the use of yarns with a higher aspect ratio, in order to more effectively control the permeability. The high aspect ratio of MD yarns results in reduced permeability. Yarns with a high aspect ratio are wider and thinner than conventional flat yarns that have aspect ratios less than 3: 1 and the same cross-sectional area. An equal cross-sectional area means that comparable yarns have essentially the same linear force. The greater width of the yarns of high aspect ratio translates into less interstices over the width of the fabric than in the case of conventional yarns so that there is a smaller number of openings in the fabric through which the yarns can pass through. liquids. The relative thinness of the yarns with a high aspect ratio allows the flat MD yarns to support ie more efficiently backs up the yarns in the machine's transverse direction to reduce the size of the interstices between the yarns in the machine direction and in the cross direction of the machine. For example, in Figure 4 a woven fabric with a single-layer system of a warp in the machine direction, flat, having a cross-sectional width of 1.5 units and a cross-sectional height of one unit, is illustrated. Say an aspect ratio of 1.5: 1. Such a fabric could be replaced by a fabric that had the current system of double stacking of MD yarns, woven with MD yarns that have a double width, that is, a total of 3 units and with half the height, or 0.5 units . Such MD yarns have a four times higher aspect ratio of 6: 1, as illustrated in Figure 3. When MD yarns are thinner and wider, the permeability will be controlled more efficiently, while the force in the machine direction will be controlled. of the fabric will remain basically unchanged since the cross-sectional area of the MD yarns over the width of the fabric remains the same. For the previous example, illustrated by Figures 3 and 4, the fabric with the unique conventional system, of MD yarns, has six conventional contiguous flat yarns over 9 units of the width of the fabric, which has an area in cross section of 9 square units, that is 6 * (lu. * 1.5u.). Yarns with a high aspect ratio, which are thinner and wider, woven like contiguous stacked MD yarns, define a fabric having three couples stacked of MD yarns over 9 units of fabric width. Thus this fabric also has a cross-sectional area of 9 square units, ie (3 '(0.5u. * 3u.)) + (3 * (0.5u 3u.)) Over 9 units of fabric width. In one example, the fabric was woven according to Figures 1, 2 and 3 in which the CMD yarns 11, 12 and 13 were spun from polyester monofilaments with a diameter of 0.6 mm, interwoven with MD yarns, 14-19, which they were flat polyester monofilament yarns with a width of 1.12 mm and a height of 0.2 mm. Therefore, the aspect ratio of flat MD yarns was 5.6: 1. The fabric was woven with 48 warp ends for each inch or for every 2.54 cm with a loom tension of 40 PLI (pounds per linear inch) (7.14 K / cm) (kilogram per lineal centimeter) and with 12.5 minced or passed CMD yarns per inch, or for every 4.92 cm, in each layer (there are three layers in total). The fabric was heat consolidated in a conventional thermal fixing apparatus under temperature, tension and time conditions within the known ranges for polyester monofilament yarns. For example, conventional polyester fabrics are thermally fixed within the parameters of 340- * > F to 380- ^ F ((171.11-: to 362.22- ^ C) of temperature, 6 to 15 PLI of tension (1.07-2.68 K / cm) in a time of 3 to 4 minutes, however, due to its structure Stable, the fabrics of the present invention are more tolerant to variations in the parameters of the thermal fixation.The fabric exhibited a warp modulus of 6000 PSI (ie 6000 pounds per square inch, (438 K / cm2), measured by ASTM D-1682-64 from the American Society for Testing and Materials, the fabric stretched less than 0.2% in its length during thermal fixation, which makes the manufacture of fabrics very reliable according to the teachings of the present invention with a view to achieving the desired dimensional characteristics compared to conventional fabrics The resulting thermally fixed fabric had 12.5 CMD yarns per inch (4.92 CMD yarns per cm), per layer, with a MD warp filling equivalent to 106% both with respect to MD yarns sup as the bottom, which results in an effective fill •? e the warp of 212% for the fabric. The finished fabric has a permeability of 83 CFM, as measured by the ASTM D-737-75 standard. As illustrated in Figure 5, when the fabric 10 is woven, the three layers of CMD yarns 11, 12, 13 are compressed. This compression together with the relatively thin dimension of the MD yarns reduces the caliber of the fabric. Accordingly, the general gauge of the fabric can be kept relatively low and not much larger than conventional woven fabrics without stacked pairs of MD yarns. In the previous example, the caliber of the finished fabric was 0.050 inches (1.27 mm). Those skilled in the art will recognize that whether either the upper MD yarns 14, 16, 18 or the lower MD yarns 15, 17, 19 are woven with a 100% warp filling the general warp fill for the stacked fabric will be notably greater than 100%, which will contribute to the reduction of the permeability of the fabric. The instant fabric having stacked MD yarns will be recognized as having a significantly greater percentage of a warp fill than those fabrics having an effective warp fill of 125% of non-stacked MD yarns, which is achieved by stacking as well as by stacking. lateral undulation of the warp cords. Although the 200% warp fill is preferred, a 100% fill fabric can be woven for either the upper or lower MD yarns with a lower fill grade for the other MD yarns by using yarns that are not as wide as those MD yarns woven with a 100% warp fill. For example the upper yarns 14, 16, 18 could have a width of 1 unit with the yarns of the lower layer 15, 17, 19 having a width of 0.75 units, which would result in a fabric having about 175% Warp filling. Such variations can be used to achieve a selected degree of permeability. As an alternative, such variations could be used to make a forming fabric. In such a case the lower MD yarns would be woven with a 100% warp fill to define the machine side of the fabric and the upper MD yarns would be woven with a considerably smaller percentage of fill to provide a more open paper forming surface. . Referring to Figures 6, 7 and 8, there is shown a second preferred embodiment of a fabric 20 made "in accordance with the teachings of the present invention." The papermaking fabric 20 comprises a single layer of interwoven CMD 21 yarns. with a system of stacked MD yarns 22-25, which are woven in a selected repetitive pattern. The yarn system MD comprises the upper MD yarns 22, 24 that define floating yarns on the upper face of the fabric 20 when weaving over 3 yarns CMD 21, dropped into the fabric in order to form a knuckle around the next CMD 21 yarn, and then keep floating above the next 3 yarns CMD 21 in the repetitive system. The lower MD yarns 23, 25 are woven directly below the respective upper MD yarns 22, 24 in a vertically stacked relationship. The lower MD yarns are woven in an inverted image of their respective upper MD yarns. Each lower MD yarn 23, 25 floats below three CMD yarns 21, is woven up around the next CMD yarn forming a knuckle and then follows in the repeating system to float below the following three CMD yarns 21.

As can be seen with respect to Figures 6 and 8, the knuckles formed by the lower MD yarns 23, 25 are hidden by the floating yarns defined by the upper MD yarns 22, 24, respectively. Similarly, the knuckles formed by the upper MD yarns 22, 24 are hidden by the floating threads of the lower MD yarns 23/25, respectively. The gauge of the fabric near the knuckle area shown in Figure 8 has a tendency to be somewhat larger than the gauge of the fabric in the non-knuckle CMD 21 yarns, as shown in Figure 7. However, the CMD yarns 21 around which the knuckles are formed are curled, which reduces the caliper of the fabric in that area as illustrated in Figure 8. Additionally, CMD yarns of a slightly larger size may be used for the CMD yarns 21, shown in Figure 7, and which do not have MD knits in the shape of knuckles around them. A fabric to be used as a dryer fabric was woven according to Figures 6 to 8, in which the CMD 21 yarns were composed of polyester monofilament yarns with a diameter of 0.7 mm, interwoven with MD 22-25 yarns, which were spun yarns. flat polyester monofilaments with a width of 1.12 mm and a height of 0.2 mm. Thus the aspect ratio of flat MD yarns was 5.6: 1. The fabric was woven with 22 CMD-type minced yarns per inch, that is, 2.54 cms, which corresponds to 8.66 yarns per cm. The fabric was fixed thermally with the use of conventional methods. The fabric exhibited a modulus of 6000 pounds per square inch, or 438 kgs x cm¿. The fabric stretched less than 0.2% in its length during heat fixation. The resulting fabric had 22 CMD yarns per inch, ie 8.66 CMD yarns x cm with a 106% MD warp fill both with respect to the upper yarns and the MD type lower yarns, which resulted in an effective filling of the warp of 212% for the fabric. The finished fabric had a caliber of 0.048 inches or 1.22 ir-m. with an air permeability of 60 CFM, that is, 101.94 m3 / hr. A fabric to be used as a base fabric for a press felt was woven according to Figures 6 to 8 in which the CMD 21 yarns were constructed of alternating nylon yarns with 0.019 inch (0.48 mm) and 0.012 inch (0.30 mm) diameter. ), interwoven with monofilament yarns in machine direction, nylon, flat condition, 0.30 mm by 0.90 m. The fabric was woven with 15 to 19 pitches per inch (5.91 to 7.48 pitches per cm) for CMD yarns and 45 to 48 ends per inch (17.72 to 18.90 ends per cm) for MD yarns. A base fabric with a higher permeability was woven with the same design but using 0.30 mm by 0.85 mm nylon flat yarn for machine direction yarns instead of using wider nylon yarns of 0.30 mm by 0.90 mm. To complete the pressing felt, wool-shaped material laminated to the base fabric was applied by needles in a conventional manner. The preferred inverted woven fabric of the lower MD yarns facilitates the creation of seam loops at the end of the fabric which allows the ends of the fabric to be joined. By forming a seam loop, the upper MD yarns extend beyond the end of the fabric and the respective lower yarns are returned by a distance selected from the end of the fabric. Then the upper MD yarns are folded back, on themselves, to be rewoven in the space vacated by the lower MD yarns returned or trimmed. When the upper MD yarns are woven in reverse to within the space previously occupied by the lower MD yarns, their curling coincides with the pattern of the lower MD yarns to thereby lock the resulting end loops in position. Similarly, MD yarns can be woven in reverse., alternating, so that they are firmly pressed against the end of the fabric in such a way that the loops formed at the opposite end of the fabric can be interlaced in those spaces provided by the MD yarns that do not form loops to sew the fabric by inserting of a pivot pin through the interwoven end loops. In view of the fact that the yarns in the machine direction, upper and lower, are stacked, the resulting end loops are orthogonal to the plane of the surface of the fabric and have no twist. In conventional reverse weaving techniques, the yarns defining the loops are normally returned into the fabric in a space adjacent to the yarn itself. Such conventional formation of the loops inherently imparts a twist to the seam loop; see U.S. Patent No. 4,438,788, Figure 6. Referring to Figures 9-17 there is shown a third preferred embodiment of a cloth 150 made in accordance with the teachings of the present invention, which is particularly suitable for use as a base fabric for a press felt. The fabric 150 has an upper, middle and lower layer of yarn in the transverse direction of the machine 151, 152 and 153, respectively, interwoven with a system of yarns MD 154 to 161 inclusive, which are woven sequentially in a selected, repetitive pattern. The MD yarn system has flat, stacked, top and bottom MD yarns, which are repeated in four pairs of yarns MD 154 and 155, 156 and 157, 158 and 159, and 160 and 161. The MD yarn system is interwoven with the yarns of the three layers CMD 151, 152 and 153. The stacked pairs of the MD yarns are repeated with respect to 12 CMD yarns, ie four of each of the layers of CMD yarns. The relative stacking of the MD yarns as well as the CMD yarns is shown in Figures 10-17. The MD yarns of the upper layer 154, 156, 158 and 160 are woven exclusively with the CMD yarns belonging to the upper and middle layer 151 and 152 and preferably define inner knuckles below the CMD yarns of the middle layer 152 and the outer knuckles above the CMD yarns of the upper layer 151. As best seen in Figure 9, the repetition of the upper MD yarns preferably defines a pattern in the form of crow's feet with respect to the four belonging CMD yarns to top layer 151, however MD yarns may be arranged to define a regular twill pattern. The MD yarns of the lower layer 155, 157, 159, 161 are woven in a similar manner as the MD yarns of the upper layer, but with respect to the middle and lower layer of CMD yarns, 152 and 153, respectively. The MD yarns of the lower layer 155, 157, 159 and 161 are woven in such a way that the inner knuckles are defined by the lower MD yarns 155, 157, 159 and 161 above the CMD yarns of the middle layer 152 that remain aligned vertically with the outer knuckles defined by the yarns of the upper layer, MD, 154, 156, 158, 160 above the CMD yarns of the upper layer. Similarly, the MD yarns of the lower layer 155, 157, 159 and 161 are knitting outside below the CMD yarns of the lower layer 153, which are aligned vertically with the inner knuckles that are defined by the yarns of the MD layer. upper 154, '156, 158 and 160, below the CMD yarns of the middle layer 152. A base fabric for press felt produced according to the third embodiment, shown in Figures 9 to 17, is preferably woven with 15 to 19 CMD yarns per inch (5.91 - 7.48 CMD yarns per cm), in each layer, with the use of hylon yarns with a diameter of 0.5 mm for the upper layer CMD and lower CMD, and nylon yarns with diameter 0.3 mm for the average CMD layer. The fabric is preferably woven at an intensity of 45 to 48 MD yarns per inch (17.72 to 18.90 MD yarns per cm), either in the low permeability or high permeability version. In the low permeability version, MD nylon yarns with a width of 1.06 mm and a height of 0.25 mm are used to produce a permeability of the base fabric in the range of 90 to 200 CFM (152.91 - 339.8 m3 / hr). In the high permeability version, MD nylon yarns with a width of 0.85 mm and a height of 0.30 mm are used to produce a permeability in the base fabric in the range of 200 to 400 CFM (339.8 to 679.6 rnVhr).

To form a press felt, a laminated wool is applied with needles on the woven base fabric in a conventional manner, thereby obtaining a weight in the preferred range of 2.2 to 2.6 ounces per square foot (671.22 to 793.26 g / m2). Preferably, a laminated wool weight of 2.3 ounces per square foot (701.73 g / m2) is used. A dryer fabric produced according to the third embodiment, shown in Figures 9 to 17, is preferably woven with 15 to 19 CMD yarns per inch (5.91 to 7.48 CMD yarns per cm) in each layer using polyester yarns with a diameter of 0.5 mm. The fabric is preferably woven with 45 to 48 MD yarns per inch (17.72 to 18.90 MD yarns per cm) from a polyester yarn with a width of 1.06 mm and a height of 0.25 mm to produce a permeability in the base fabric in the range of 90 to 200 CFM (152.91 to 339.8 m3 / hr). Referring to FIGS. 18 to 25, a fourth alternate embodiment of a papermaking fabric 110 is shown, which is also particularly suitable for use as a base fabric for press felt. The fabric 110 has top, middle and bottom layers of the CMD yarns 111, 112, and 113, respectively, interwoven with an MD yarn system in the machine direction 114 to 121, which are woven in a selected repeating pattern. As best seen in Figures 21 to 25, the repeat in the system of the MD yarns is defined by a first group of stacked MD yarns 112 to 117 and a second group of stacked MD yarns 118 to 121 which are repeated with respect to 12 yarns CMD 111-113, four yarns of each layer, that is to say of the upper, middle and lower layer, give CMD yarns. The MD yarn system includes an inner, upper MD yarn layer, defined by MD 115, 119 yarns that are woven exclusively with the yarns of the upper and middle layer of CMD, 111, 112, knuckling over the alternate yarns CMD of the upper layer 111, and below the alternating CMD yarns of the middle layer 112. The inner, upper, MD yarns 115, 119 are both woven between alternating pairs of CMD yarns of the upper and middle layer III, 112, within the repetitive web system. The MD yarn system also includes a layer of MD yarns, inner, lower, defined by yarns MD 116, 120 which are woven exclusively with the yarns of the middle and lower CMD layer 112, 113 to thereby form knuckles above the yarns. alternating CMD yarns of the middle layer 112 and below the CMD yarns 113, belonging to the lower layer and which are also alternated. MD yarns, inner and lower 116, 120 are woven between alternate pairs of CMD yarns of the middle layer and lower layer 112, 113, within the repeating fabric system. The knuckles defined by the layers of yarns Inner, upper and inner, lower MDs are vertically aligned in a manner similar to the layers of the MD yarns, upper and lower, of the embodiment disclosed in Figures 9 to 17. The '' MD yarn system also it includes a layer of MD yarns with an upper face defined by yarns MD 114, 118 that are woven exclusively with the CMD yarns, of the upper layer 111, with a floating yarn above three and a knuckle below one, of the yarns. CMD yarns of the upper layer 111 within the repeating system. The knuckles defined by the spinning of the upper face layer 114 are aligned vertically with the knuckles defined by the inner, upper MD yarn, 115, below the yarns of the middle CMD layer 112, while the knuckles defined by the yarn of the upper face layer 118 are vertically aligned with the knuckles defined by the MD yarns, upper, inner, 119 below the CMD yarns of the middle layer 112. The MD yarn system also includes a layer of MD yarns lower face, defined by yarns MD 117, 121 which is woven exclusively with the CMD yarns of the lower layer 113 with a floating yarn below three and a knuckle above one of the CMD yarns of the lower layer 113 within the repetitive system . The knuckles defined by the spinning of the lower face layer 117 are vertically aligned with the knuckles defined by the inner, lower MD yarn 116 above the yarns 112 of the middle layer CMD; the knuckles defined by the spinning of the bottom face layer 121 are vertically aligned with the knuckles * defined by the inner lower MD yarns 120 above the average CMD layer yarns 112. As a result of the repetitive pattern, alternating yarns CMD in each layer of CMD yarns is curled to a markedly greater degree toward the knuckle fabric by the MD yarn system, as best seen in Figures 21, 22 and 25. None of the MD yarns weave knuckles around the other yarns alternating CMD of each upper, middle and lower CMD layer 111, 112 and 113. Thus a balanced fabric system similar to the balanced system described with respect to the single-layer embodiment CMD illustrated above, is defined within a fabric of Multiple CMD layers. Those of ordinary skill in the art will recognize that the MD yarn system could include four groups of MD yarns stacked within the repeating system to define a twill or twill surface pattern. However, as illustrated above, only two groups of yarns MD 114-117 and 118-121 are required for the preferred construction of the fabric.

A base fabric for press felt that is produced according to the fourth embodiment shown in Figures 18-25 is preferably woven with 15 to 19 CMD yarns per inch (5.91 to 7.48 CMD yarns per centimeter), in each layer , with the use of nylon yarns with a diameter of 0.5 mm for the upper and lower layer of the CMD type and nylon yarns with a diameter of 0.3 mm are used for the average CMD layer. The fabric is preferably woven with 90 to 96 MD yarns per inch (35.43 to 37.8 MD yarns per cm) either in its low permeability or high permeability version. In the low permeability version, MD nylon yarns with a width of 1.06 mm and a height of 0.25 mm are used to produce a permeability in the base fabric in the range of 90 to 200 CFM (152.91 to 339.8 m3 / hr) . In the high permeability version, MD nylon yarns with a width of 0.85 mm and a height of 0.30 mm are used to produce a permeability in the base fabric in the range of 200 to 400 CFM (339.8 to 679.6 m / hr). The addition of layers of upper and lower face MD yarns does not substantially affect the permeability of the fabric in contrast to those fabrics made according to the third embodiment illustrated in Figures 9 to 17. The floating yarns of the yarns MD of the upper and lower face layer provide a softer support surface, however, the inclusion of such yarns does not reduce the vacuum volume of the base fabric in contrast to those fabrics made according to the third embodiment depicted in Figures 9 to 17. To form a press felt, a wool laminated on the woven base fabric is applied with needles in a conventional manner, having a weight in the preferred range of 2.2 to 2.6 ounces per square foot. (671.22 to 793.26 g / m2). Preferably a laminated wool weight of 2.3 ounces per square foot is used. (701.73 g / m2). In the preferred embodiment with low permeability, the upper face MD yarns 114 and 118 are woven contiguously with respect to one another. This maintains its respective parallel alignment in the machine direction and reduces permeability.This form of compact fabric of the yarns in the machine direction is known in the art as 100% warp filling, as explained in FIG. U.S. Patent No. 4,290,209.As taught in said patent (and is used in the present application), the actual warp count on a woven fabric can vary from about 80% to 125% in a single layer and can anyway be considered as a 100% filling of the warp, the stacking of yarns MD 114 and 118 also serves to force yarns MD 115-117 and 119-121 into their stacked position below the respective yarns MD 114, 118 Preferably MD 115-117 and 119-121 yarns have the same size as MD 114 and 118 yarns so that similarly they will be woven with 100% warp filling. preferred embodiment with its low permeability has a 400% fill of the warp, with MD yarns. A dryer fabric produced according to the fourth embodiment shown in Figures 18 to 25 is preferably woven with 15 to 19 CMD yarns per inch (5.91 to 7.48 CMD yarns per cm) in each layer with the use of polyester yarns with a diameter of 0.5 mm. The fabric is preferably woven with an intensity of * 90 to 96 MD yarns per inch (35.43 to 37.8 MD yarns per cm) starting from a polyester MD yarn with a width of 1.06 mm and a height of 0.25 mm to produce a fabric which has a permeability in the range of 90 to 200 CFM (152.91 to 339.8 m3 / hr). While the present invention has been described in terms of the preferred embodiment, other variations that fall within the scope of the invention as defined in the claims will be apparent to those led in the art.

Claims (23)

1. CLAIMS 1. A papermaking fabric comprising: a system of MD yarns of interwoven flat monofilaments with a system of said CMD yarns in a selected repeating pattern, said CMD yarn system includes at least one upper, intermediate and lower layer of yarns. CMD yarns stacked in vertical alignment, and the MD yarn system includes a first subsystem of flat MD yarns that are interwoven with the upper and intermediate layer of CMD yarns and a second subsystem of flat MD yarns that are woven with the CMD yarn layer , intermediate and bottom such that each of the MD yarns of the second subsystem is stacked in vertical alignment with a flat MD yarn of the first MD yarn subsystem.
2. 2. A papermaking fabric according to claim 1 further comprising laminated wool material applied with needles over interwoven MD and CMD yarns.
3. 3. A papermaking fabric according to claim 1 wherein the MD yarns of the first subsystem have an aspect ratio of at least 3: 1 and are woven with a 100% fill of the warp.
4. 4. A papermaking fabric according to claim 1 wherein the MD and CMD yarns are polyester.
5. 5. A papermaking fabric according to claim 1 wherein the MD and CMD yarns are nylon yarns.
6. 6. A papermaking fabric according to claim 1 wherein the CMD yarns of the upper and lower layer have a round cross section and have a first diameter and the CMD yarns of the intermediate layer have a round cross section and possess a second diameter smaller than the first diameter.
7. 7. A papermaking fabric according to claim 6 wherein the CMD yarns of the intermediate layer have a diameter of 0.3 mm and the CMD yarns of the upper and lower layer have a diameter of 0.5 mm.
8. 8. A papermaking fabric according to claim 1 wherein the MD flat yarns are 1.06 mm by 0.25 mm and the fabric has a permeability in the range of 90-200 CFM (152.91 to 339.8 rnVhr).
9. A papermaking fabric according to claim 1 wherein the MD flat yarns are 0.85 mm by 0.30 mm and the fabric has a permeability in the range of 200 to 400 CFM (339.8 to 679.6 m3 / hr).
10. A papermaking fabric according to claim 1 further comprising a third subsystem of flat yarns MD which are interwoven with the CMD yarns of the upper layer such that each of the MD yarns of the third subsystem is stacked into vertical alignment with a flat MD yarn of the first MD yarn subsystem.
11. 11. "A papermaking fabric according to claim 10 further comprising a fourth subsystem of flat MD yarns that are interwoven with the CMD yarns of the lower layer so that each of the MD yarns of the fourth subsystem is stacked in vertical alignment with a flat MD yarn of the first MD yarn subsystem.
12. 12. A papermaking fabric according to claim 11 wherein the flat yarns MD of the third subsystem are woven with floating yarns above at least three CMD yarns of the upper layer.
13. A papermaking fabric according to claim 12 in which the flat MD yarns of the fourth layer are woven with floating yarns below at least three CMD yarns of the lower layer.
14. A papermaking fabric according to claim 11 which further comprises laminated wool material applied with needles over interwoven MD and CMD yarns.
15. 15. A papermaking fabric according to claim 11 wherein the MD yarns of the third subsystem have an aspect ratio of at least 3: 1 and are woven with a 100% warp fill.
16. 16. A fabric for making paper according to claim 11 in which the MD and CMD yarns are polyester.
17. 17. A papermaking fabric according to claim 11 in which the MD and CMD yarns are nylon yarns.
18. 18. A papermaking fabric according to claim 11 wherein the CMD yarns of the upper and lower layer have a round cross section and have a first diameter and the GMD yarns of the intermediate layer have a round cross section and possess a second diameter smaller than the first diameter.
19. 19. A papermaking fabric according to claim 18 wherein the CMD yarns of the intermediate layer have a diameter of 0.3 mm and the CMD yarns of the upper and lower layer have a diameter of 0.5 mm.
20. 20. A papermaking fabric according to claim 11 wherein the MD flat yarns are 1.06 mm by 0.25 mm and the fabric has a permeability in the range of 90 to 200 CFM (152.91 to 339.8 rnVhr).
21. 21. A papermaking fabric according to claim 11 wherein the MD yarns are 0.85 m by 0.30 mm and the fabric has a permeability in the range of 200 to 400 CFM (339.8 to 679.6 m3 / hr).
22. 22. A papermaking fabric according to claim 11 which is woven in a repeating pattern in which two groups of four stacked MD yarns are repeated with respect to a total of 12 CMD yarns, four CMD Yarns from each of the upper, intermediate and lower layers of CMD yarns.
23. 23. A papermaking fabric according to claim 11 wherein the stacked MD yarns form alternating knuckles that impart a higher degree of crimping over the alternating CMD yarns of each layer relative to the other CMD yarns.