The invention generally concerns seamed press felts for use in the manufacture of paper and similar products in a papermaking or like machine. It is particularly concerned with seams for spirally wound, multiaxial press felts formed with four layers. The novel construction assists to reduce sheet marking at the seam.
The present invention concerns press felts for use in the press section of papermaking machines. In the manufacture of paper products, a stock slurry consisting of about 1% papermaking fibers and others solids dispersed in about 99% water is delivered at high speed and precision from a headbox slice onto a rapidly moving forming fabric, or between two forming fabrics, in the forming section of a papermaking machine. The stock is subjected to agitation and is dewatered by various means through the forming fabrics, leaving behind a loosely cohesive and wet web of fibers. This web is then transferred to the press section where a further portion of water is removed by mechanical means as the web, supported by one or more press felts, passes through at least one, and usually a series, of press nips where water is essentially squeezed from the nascent sheet and into the press felt. The water is accepted by the press felt and, ideally, does not return to the web. The resulting sheet is then passed to the dryer section which includes a series of rotatable dryer drums, or cans, that are heated by steam. The sheet is directed around and held in contact with the periphery of these drums by one or more dryer fabrics so that the majority of the remaining water is removed by evaporation.
Press felts play a critical role in the manufacture of paper products. The known press felts are produced in a wide variety of styles designed to meet the requirements of the papermaking machines on which they are installed, and the paper grades being manufactured. They are generally assembled using a woven or nonwoven base fabric structure into which is needled one and usually multiple layers of a fibrous nonwoven batt. The batt provides a smooth surface upon which the paper product is conveyed, acts as a reservoir to trap water expressed at the press nip, and provides a measure of resiliency to the press felt as it passes through the nip. The base fabrics are typically woven from monofilament, cabled monofilament, multifilament or similar multicomponent yarns; they may also be arranged as nonwoven planar arrays. The component yarns are usually comprised of an extruded polymeric resin, typically a polyamide.
The base fabrics may be of single layer or multilayer construction, or they may be formed from two or more layers which are laminated together. They may be woven endless, so that the resulting fabric resembles a tube with no seam; such fabrics must be prepared to the length and width of the machine for which they are intended, and must be slipped onto the press section in a manner similar to a sock. An example of such a fabric is provided in U.S. Pat. No. 7,118,651. In a variant modified endless weaving technique, the weft yarns are used to form seaming loops at the widthwise fabric edges during manufacture; when installed on the papermaking machine, these yarns will be oriented in the intended machine direction (MD) allowing the fabric to be joined by bringing the loops from each side together and inserting a pin, or pintle, through the resulting channel formed by the intermeshed loops. An example of a modified endless woven fabric may be found in U.S. Pat. No. 3,815,645. The base fabrics may also be flat woven, using one or more layers of warp or weft yarns; a seam is typically formed at each end allowing the fabric to be joined on the machine. An example of a flat woven base fabric may be found in U.S. Pat. No. 7,892,402. All of the above constructions require that the base fabric be woven to the full width and length of the machine for which they are intended.
In an effort to reduce manufacturing time and costs, so-called “multiaxial fabrics” have recently been introduced for the production of press felts. Multiaxial press felts are well known and are described in U.S. Pat. Nos. 5,360,656; 5,268,076; 5,785,818 and others. The base fabrics of these press felts are comprised of a plurality of spirally wound and edgewise joined turns of a material strip including at least machine direction (MD) oriented yarns. The material strip is usually a flat woven fabric which is narrower than the width of the intended base fabric of which it is a component; it has also been proposed to use nonwoven arrays of MD yarns as the material strip component. Regardless of whether the component is woven or nonwoven, during assembly each turn of the material strip is directed about two opposing rollers such that its component MD yarns are canted at a small angle that is from about 1° to about 8° to the intended MD of the finished fabric; see prior art
For the seamed press felt, and particularly in the case of multiaxial fabric based press felts, there are several seam related issues. These include differences in the physical characteristics of the fabric in the seam area resulting in different resiliency and different air permeability, which can result in sheet break due to lower strength of the paper sheet at the seam mark, as well as marking of the finished paper. The seam region is thus usually recognized as the most critical area of the finished fabric.
One previously proposed solution was to insert so-called “stuffer yarns” into the base fabric adjacent the seam. These stuffer yarns are usually multicomponent yarns which, due to their larger surface area in comparison to monofilaments, offer greater opportunity for anchorage of the batt material during a needling process to provide more uniformity. However, the results here are inconsistent at best and still leave very perceptible marks on the finished sheet being processed/transported by the press felt.
It would be desirable to provide a press felt base fabric construction which improves upon the known sheet marking issues at the seam, particularly for multiaxial press felt constructions. The seam constructions provided herein address some or all of these issues.
In one aspect, a seamed press felt is provided that includes a base fabric having a CD width and an MD length with two opposing MD ends that are joined to form a continuous belt. MD oriented yarns form uniform loops at the two opposing MD ends that are interdigitated to define a pintle channel extending the CD width, and CD oriented yarns are connected to the MD oriented yarns. Loop open spaces are located within the loops on each of the two opposing MD ends in a seam region, with the loop open spaces being defined between a last one of the CD yarns at each of the two opposing MD ends and the pintle channel. In order to reduce the seam mark in the finished paper product, a stuffer package is located in the loop open spaces on each of the two opposing MD ends. The stuffer package includes at least one CD stuffer monofilament yarn having a diameter at least as large as a diameter of the CD oriented yarns, and at least two CD cabled monofilaments, each said cabled monofilament including at least 3 monofilament strands. A stitch, preferably in the form of a zig-zag stitch, extends through at least a portion of the stuffer package and a portion of the base fabric at each of the two opposing MD ends. The zig-zag stitch holds the at least one monofilament yarn and a first subset of the at least two cabled monofilaments in place in the loop open spaces, and a second subset of the at least two cabled monofilaments is free-floating in the loop open spaces. A pintle extends through the pintle channel to form a seam.
In one embodiment, a single one of the CD stuffer monofilament yarns is used in the loop open spaces on each of the two opposing MD ends. The single one of the CD stuffer monofilament yarns preferably has a diameter that is about 0.5-1.2 mm.
Alternatively, two of the CD stuffer monofilament yarns are used in the loop open spaces on each of the two opposing MD ends. These CD stuffer monofilament yarns preferably have a diameter that is also about 0.5-1.2 mm.
In one presently preferred arrangement, there are no more than two of the CD stuffer monofilament yarns in the loop open spaces on each of the two opposing MD ends.
In another aspect, the at least two CD cabled monofilaments includes four of the CD cabled monofilaments, and the first subset includes two of the CD cabled monofilaments and the second subset includes the other two of the CD cabled monofilaments.
In each case for use as a papermaking press felt, batt fibers are needled to the base fabric.
Preferably, an air permeability of the press felt across the seam region is within 15% of an air permeability of the press felt outside of the seam region. More preferably, the air permeability of the press felt across the seam region is within 10% of an air permeability of the press felt outside of the seam region.
In one arrangement, the base fabric can be woven. It is also possible for the base fabric to be a non-woven.
In one preferred arrangement, the at least one CD stuffer monofilament is made of polyurethane.
In one preferred arrangement, the at least one CD stuffer monofilament yarn has a diameter of at least 0.5 mm.
In one preferred arrangement, the CD cabled monofilaments have a diameter of at least 0.5 mm.
In embodiments where the press felt is a nonwoven multiaxial press felt, the base fabric may comprise a plurality of spirally wound turns of a first fabric structure, the first fabric structure including a first planar yarn array of the MD oriented yarns comprising single polymeric monofilaments arranged at a first density, at least two layers of a hot melt adhesive web having a first melting temperature, one of the layers of the hot melt adhesive located on each side of the first planar yarn array is used to attach an array of CD oriented yarns. Each adjacent one of the wound turns of the first fabric structure is oriented at an angle to the MD and is bonded to an adjacent turn to provide a flattened continuous double layer tube.
A preferred assembly method provides that the base fabric is collapsed so that it forms a flattened tube with two folded ends and the seam loops are located at the folded ends.
The foregoing Summary and the following detailed description and claims will be best understood when read in conjunction with the drawings which show the presently preferred embodiments of the invention. In the drawings:
Certain terminology is used in the following description for convenience only and is not limiting. The words “top,” “bottom,” “upper” and “lower” designate directions in the drawings to which reference is made. The words “interior” and “exterior” refer to directions within or outside of the two layers of the base fabric. A reference to a list of items that are cited as “at least one of a, b, or c” (where a, b, and c represent the items being listed) means any single one of the items a, b, or c, or combinations thereof. “A” or “an” refer to one or more of the item noted. “MD” refers to a machine direction in the papermaking machine from the headbox to the dryer section and is the longitudinal direction of the press felt. “CD” refers to the cross-machine direction, or a direction perpendicular to the machine direction in the plane of the fabric. The term “PS” refers to the paper side surface of the fabric, which is the surface upon which the paper product is carried through the papermaking machine. “MS” refers to the machine side of the fabric and is the surface opposite to the PS. Unless otherwise specified, the term “yarn” or “yarns” refers to a continuous length of either single or cabled polymeric monofilament such as would be used in the manufacture of the base fabrics, while the term “fiber” or “fibers” refers to relatively small diameter polymeric materials such as those commonly used in batt or scrim materials which fibers have a very small dtex (mass in grams per 10,000 meters of fiber). “Seam region” refers to the exposed yarn loops of the MD yarns at the CD fold areas at the opposing MD ends of the press felt. “Orthogonal” or “perpendicular” as used herein with respect to the CD and MD yarns means generally within about 85° to 95° based on the deviation from true perpendicular created by the spiral winding of the MD yarns in the first yarn array. The terms “left”, “right”, “up”, “down” are used in relation to the drawings and have the meanings usually assigned. The term “about”, unless otherwise noted, means +/−10% of the noted value. Additional definitions for terms used herein are as follows:
Additional Definitions:
“Press felt base fabric”: a woven or nonwoven assembly of yarns provided as an endless structure or continuous loop including two superimposed layers joined (when laid flat) at two opposing fold areas, including continuous MD yarns passing around the folds. The assemblies can take the form of: a) an endless woven structure, b) a modified endless woven structure, c) a flat woven fabric folded at two locations to provide a double layer assembly, d) a fabric formed according to a multiaxial assembly process, or e) a nonwoven structure assembled to provide any of the previous assemblies. The present invention is applicable to all of the above, but it is particularly suitable for use in both woven and nonwoven multiaxial base fabric constructions. All of the base fabrics, with the possible exception of those which are endless woven, are post processed to provide seam loops formed by the MD oriented component yarns allowing the fabric to be joined and thus rendered endless. These base fabrics provide the finished press felt with the physical properties (strength, void volume, resiliency) necessary for it to survive the rigors of the machine environment in which it will be used, while providing a rugged carrier for the batt fibers.
Referring to
In the case of a multiaxial press felt base fabric 30, as well as other double layer base fabrics, the double layer formed by collapsing the fabric tube is connected together in a needling process in which one or more layers of a nonwoven fibrous batt material 28 (shown in
After the needling process, it is necessary to again free the yarn loops 14 of excess batt fiber so that the seam region can accommodate the pintle 18 or similar retaining means that is passed through the loops 14 as the finished fabric is joined on the machine for which it is intended. The batt fiber material 28 in this fold region is typically cut and brushed back to form a flap of nonwoven material which is laid back over and reattached at the seam region to minimize any discontinuity there.
The needled press felt 31 is then subjected to heatsetting and various other known finishing steps so as to stabilize it. Following these steps, the finished nonwoven press felt is ready for installation in the press section of a paper machine. The press felt 31 may be installed by passing it through the press section at slow speed while attached to one end of the previous press felt, bringing together the opposed seam regions, intermeshing the loops 14 formed by the MD yarns 12 at the fold regions, and then inserting the pintle 18 or similar joining wire or device through the pintle channel 19 provided at the seam region to close the fabric 31.
As shown in
Still with reference to
In order to complete the press felt 131, those skilled in the art will recognize that batt fibers 28 (as described above) are needled to the base fabric 130.
The zig-zag stitch 160 has the advantage that part of the stuffer package 150 is held in position and does not float. In comparison to the prior art seamed press felt 31, as the loops 14 are interdigitated, the stuffers 21 floating in the loop open areas 42 are pushed together by the ends of the loops 114 and moved toward the respective bodies of the fabric 30. During needling of the batt 28, this then entangles them against the fabric and accordingly, two much open area remains within the seam region adjacent to the pintle channel 19. In the case of the present invention, by anchoring some of the stuffer package yarns, preferably including the CD stuffer monofilament yarns 152A, 152B as well as a subset of the CD cabled monofilaments 154A, 154B in position, they cannot migrate toward the body of the base fabric 130 when the opposing seam loops 114 are interdigitated.
In the preferred arrangement, an air permeability of the press felt across the seam region is within 15% of an air permeability of the press felt outside the seam region and more preferably is within 10%.
As discussed above, the press felt according to the invention can include a woven base fabric 130 as well as a non-woven base fabric 130.
The monofilament stuffer package 150 prevents the collapse of the MD loops 114 that form the pintle channel 119 and also reduces the elongation of the loops 114 by filling a greater percentage of the loop void area. Further, based on the increased fill provided by the stuffer package 150, the air permeability as well as the pressure become more uniform in the region of the seam, resulting in less seam marking.
With respect to
The graphs in
Referring to
In the preferred embodiments, both the MD yarns 112 and the CD yarns 116 are preferably polyamide monofilaments or cabled yarns. These can be formed of polyamide-6/10 or any other suitable polyamides or co-polymers thereof. Monofilaments formed of polyurethane polymers could also be used. The CD stuffer monofilament yarns 152A, 152B are preferably polyurethane, and preferably have a diameter of 0.5 mm or greater. The CD cabled monofilaments 154A-D are preferably formed of polyamide-6/10, and preferably also have a diameter of 0.15 mm or greater. Exemplary cabled monofilaments could be formed from 0.20 mm diameter monofilaments cabled in a 1×3, 2×3, 2×2, 2×4, 2×5, or 2×6 configuration. The cabled monofilaments could also be formed from 0.15 mm diameter monofilaments cabled in a 1×3, 2×3, 2×2, 2×4, 2×5, or 2×6 configuration. Other suitable polyamides or co-polymers thereof could be used for either or both the CD stuffer monofilament yarns 152A, 152B and the CD cabled monofilaments 154A-D. The zig-zag stitch 160 is also formed of a polyamide.
Having thus described the present invention in detail, it is to be appreciated and will be apparent to those skilled in the art that many physical changes, only a few of which are exemplified in the detailed description of the invention, could be made without altering the inventive concepts and principles embodied therein. It is also to be appreciated that numerous embodiments incorporating only part of the preferred embodiment are possible which do not alter, with respect to those parts, the inventive concepts and principles embodied therein. The present embodiment and optional configurations are therefore to be considered in all respects as exemplary and/or illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all alternate embodiments and changes to this embodiment which come within the meaning and range of equivalency of said claims are therefore to be embraced therein.
The following documents are incorporated herein by reference as if fully set forth: U.S. Provisional Patent application No. 63/048,251, filed Jul. 6, 2020.
Filing Document | Filing Date | Country | Kind |
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PCT/US2021/035828 | 6/4/2021 | WO |
Number | Date | Country | |
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63048251 | Jul 2020 | US |