Belt for pulp or paper machine with sensors for detecting pressure during operation and press using same

Abstract

A pressure-sensing belt for a shoe press or the like includes: a substantially cylindrical polymeric belt having a longitudinal axis, a radially inner surface, and a radially outer surface; a plurality of reinforcing cross-machine (CD) fibers extending parallel to the longitudinal axis for the length of the belt between the inner and outer surfaces; a plurality of reinforcing machine direction (MD) fibers extending circumferentially relative to the longitudinal axis between the inner and outer surfaces; and a plurality of piezoelectric fibers extending within the belt, the piezoelectric fibers each having a sensing portion and a signal-carrying portion.

Description

BELT FOR PULP OR PAPER MACHINE WITH SENSORS FOR DETECTING PRESSURE DURING OPERATION AND PRESS USING SAMERelated Application

[0001] The present application claims priority from and the benefit of U.S. Provisional Patent Application No. 63 / 501,893, filed May 12, 2023, the disclosure of which is hereby incorporated herein by reference.Field of the Invention

[0002] The present invention relates generally to nip presses, and more particularly to shoe presses.Background of the Invention

[0003] In the conventional fourdrinier papermaking process, a water slurry, or suspension, of cellulosic fibers (known as the paper "stock") is fed onto the top of the upper run of an endless belt of woven wire and / or synthetic material that travels between two or more rolls. The belt, often referred to as a "forming fabric," provides a papermaking surface on the upper surface of its upper run which operates as a filter to separate the cellulosic fibers of the paper stock from the aqueous medium, thereby forming a wet paper web. The aqueous medium drains through mesh openings of the forming fabric, known as drainage holes, by gravityor vacuum located on the lower surface of the upper run (z.e., the "machine side") of the fabric.

[0004] After leaving the forming section, the paper web is transferred to a press section of the paper machine, where it is passed through the nips of one or more presses (often roller presses) covered with another fabric, typically referred to as a "press felt." Pressure from the presses removes additional moisture from the web; the moisture removal is often enhanced by the presence of a "batt" layer of the press felt. The paper is then transferred to a dryer section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.

[0005] Over the last 35 or 40 years, a “shoe press” has been developed for the press section of the papennaking machine. A shoe press includes a roll or similar structure that mates with a “shoe” of an opposed roll or press structure; the surface of the shoe is somewhat concave and approximates in curvature the convex profile of the mating roll. This arrangement can increase the width of the nip in the direction of paper travel, thereby enabling greater amounts of water to be removed therein.

[0006] Endless belts or blankets have traditionally been used in shoe press operations. The belt overlies and contacts the shoe of the press; in turn, the press felt overlies the shoe press belt, and the paper web overlies the press felt. The shoe press belt and press felt travel through the nip and, in doing so, convey the paper web through the nip. The press felt travels over a set of rollers arranged around the shoe. In older embodiments, shoe press belts were also driven by sets of drive rollers arranged around the shoe. In some newer configurations, however, the shoe press belt is clamped or otherwise fixed to the edges of circular head plates located on either end of the shoe, such that rotation of the head plates causes the shoe press belt to rotate and travel through the nip.

[0007] Given the performance requirements, a shoe press belt should be sufficiently flexible to pass around the drive rollers or head plates and through the shoe and sufficiently durable to withstand the repeated application of pressure within the nip. Because of these performance parameters, most endless belts are formed entirely or predominantly of a polymeric material (often polyurethane). Many shoe press belts also include reinforcing fibers or a reinforcing fabric between or embedded in polymeric layers. Also, shoe press belts may be configured to encourage water to pass from the paper web. To this end, some shoe press belts have grooves or blind-drilled holes in the surface adjacent the press felt that serve to vent water from the paper that is exiting the press felt.

[0008] As the paper web is conveyed through the nip, it can be very important to understand the pressure profile experienced by the paper web. Variations in nip pressure can impact the amount of water drained from the web, which can affect the ultimate sheet moisture content, thickness, and other properties. Excessive nip pressures can cause crushing or tearing of the web. Of course, in a shoe press the pressure typically varies at different locations in the nip, both along and transverse to the direction of paper travel, and can also vary over time. As a result, it would be desirable to have a reliable technique and apparatus for determining the pressure distribution and area of the nip in a shoe press.Summary

[0009] As a first aspect, embodiments of the invention are directed to a pressure-sensing belt for a shoe press or the like. The belt comprises: a substantially cylindrical polymeric belt having a longitudinal axis, a radially inner surface, and a radially outer surface; a plurality of reinforcing cross-machine (CD) fibers extending parallel to the longitudinal axis for the length of the belt between the inner and outer surfaces; a plurality of reinforcing machine direction (MD)fibers extending circumferentially relative to the longitudinal axis between the inner and outer surfaces; and a plurality of piezoelectric fibers extending within the belt, the piezoelectric fibers each having a sensing portion and a signal-carrying portion.

[0010] As a second aspect, embodiments of the invention are directed to a shoe press that employs a belt as described above.Brief Description of the Figures

[0011] Figure 1 is an end view of a shoe press of the present invention.

[0012] Figure 2 is a front section view of the lower roll and shoe press belt of the shoe press of Figure 1.

[0013] Figure 3 is a perspective view of the shoe press belt of Figure 1 with the outer polymeric layer removed to reveal the CMD fibers.

[0014] Figure 4 is an enlarged partial end view of the shoe press belt of Figure 1 illustrating reinforcing and piezoelectric fibers.

[0015] Figure 5 is an enlarged partial perspective view of the shoe press belt of Figure 1 with the outer polymeric later removed to show the reinforcing CMD fibers and piezoelectric fibers.

[0016] Figure 6 is a schematic front view of an exemplary piezoelectric fiber employed in the shoe press belt of Figure 1.

[0017] Figure 7A is a schematic front view of another exemplary piezoelectric fiber that can be employed with the shoe press belt of Figure 1.

[0018] Figure 7B is a schematic front view of the piezoelectric fiber of Figure 7A shown with the piezoelectric core cleaved.

[0019] Figure 8 is a partial perspective view of the shoe press belt of Figure 1 with the sensing portions of the piezoelectric fibers shown at different lengths to enable sensing of different axial locations on the shoe press belt.

[0020] Figure 9 is a front section view of the shoe press shown in Figure 2 with the processing unit illustrated schematically.Detailed Description of the Invention

[0021] The present invention now is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0022] Like numbers refer to like elements throughout. In the figures, the thickness of certain lines, layers, components, elements or features may be exaggerated for clarity. Broken lines illustrate optional features or operations unless specified otherwise.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the tenns "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. As used herein, phrases such as "between X and Y" and "between about X and Y" should be interpreted to include X and Y. As used herein, phrases such as "between about Xand Y" mean "between about X and about Y." As used herein, phrases such as "from about X to Y" mean "from about X to about Y."

[0024] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and / or clarity.

[0025] It will be understood that when an element is referred to as being "on", "attached" to, "connected" to, "coupled" with, "contacting", etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, "directly on", "directly attached" to, "directly connected" to, "directly coupled" with or "directly contacting" another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed "adjacent" another feature may have portions that overlap or underlie the adjacent feature.

[0026] Referring now to Figures 1 and 2, a shoe press, designated broadly at 20, is illustrated therein. The shoe press 20 includes a lower roll 22 and a mating upper roll 24 that define therebetween a nip 25 through which a web or sheet, such as a paper web 37, can travel. Each of the lower and upper rolls 22, 24 defines a respective axis Al, A2; the axes Al, A2 are essentially parallel with one another and substantially perpendicular to the direction MD that the web 37 travels. As can be seen in Figure 1, press felts 35, 36 are positioned between the lower and upper rolls22, 24; the press felts 35, 36 are driven around respective sets of drive rollers 35a, 36a by the lower and upper rolls 22, 24. The web 37 is conveyed by and between the press felts 35, 36.

[0027] Referring again to Figures 1 and 2, the lower roll 22 includes a beam 26 that extends parallel to tire axis Al. At either end, the beam 26 includes a round shaft 28 that engages and is supported by a bracket 30. A shoe 32 with a concave pressing surface 33 extends upwardly from the beam 26. The shoe 32 is mounted onto the beam 26 such that it can be controllably biased upwardly; the biasing of the shoe 32 can be accomplished with, for example, a hydraulic system (not shown). A circular head plate 34 is rotatably mounted on each shaft 28 spaced apart from the end of the shoe 26. Bearings 37 enable the head plates 34 to be rotated on the shaft 28.

[0028] A substantially cylindrical shoe press belt or sleeve 40 is mounted about the perimeter of each head plate 34 such that its longitudinal axis is substantially parallel with the axis Al. The shoe press belt 40 is fixed to tire head plates 34 (by clamping or the like) such that, as the head plates 34 rotate about the shafts 28, they cause the shoe press belt 40 to rotate also. Typically, the shoe press belt 40 is between about 40 and 84 inches in diameter and between about 120 and 480 inches in length.

[0029] As shown in Figure 1, the lower and upper rolls 22, 24 are positioned relative to each other so that the upper roll 24 causes the shoe press belt 40 to deflect from a cylindrical configuration and conform to the configuration of the pressing surface 33 of the shoe 32. The pressing surface 33 of the shoe 32 is shaped to be substantially complimentary to the convex profile of the upper roll 24, with the result that the nip 25 has significant width and is extended in the direction MD (this dimension is typically between about 3 and 12 inches). Both the shoe 32 and the upper roll 24 can be adjusted to control the magnitude and distribution of the pressure in the nip 25; in particular, the shoe 32 may be pivotable about an axisparallel to axis Al that enables the pressure to be adjusted along the direction of web travel MD. As the shoe press belt 40 rotates with the head plates 34, portions thereof are deflected by the contact surface 24a of the upper roll 24 to contact the contact surface 33 of the shoe 32.

[0030] Those skilled in this art will recognize that the present invention may be suitable for shoe presses of other configurations. For example, the lower roll 22 may include a fixed shaft and a hydraulic shoe (such as that available from Voith Group, Heidenheim, Germany under the tradename NipcoFlex), or may be replaced with a shoe alone, wherein the shoe press belt is guided across the shoe by a set of drive rollers. The upper roll 24 may be hydraulically supported (as is the case with the NipcoFlex press mentioned above), may include an adjustable convex shoe (such as that available from Voith Group under the tradename NipcoFlex), or may lack adjustability. Other exemplary shoe presses include those available from Valmet (SymBelt), Bellmer (TURBOPRESS) and Beloit (ENP-C). Also, the lower and upper members may be oriented such that the concave pressing surface of the shoe is presented by the upper member of the shoe press and the convex pressing surface is presented by the lower member of the shoe press. These and other configurations of suitable shoe presses are described and illustrated in Joint Textbook Committee of the Paper Industry, Pulp and Paper Manufacture, Vol. 7, 267-70 (Third Edition, 1991). Alternative configurations should include a shoe with a concave pressure surface that is adjustable and a mating structure (such as a roll or opposed convex shoe) that form a nip through which a shoe press belt travels.

[0031] Figures 3-5 illustrate the shoe press belt 40 in greater detail. The majority of the shoe press belt 40 comprises a polymeric material, such as polyurethane or rubber, that serves as a matrix 42. Typically, the material comprising the entire matrix 42 will be the same, but it need not be; the matrix 42may comprise layers of different materials. An exemplary material for use in the matrix 42 is a polyurethane material having a Shore A hardness value of between about 55 and 100.

[0032] As can be seen in Figure 4, the shoe press belt 40 also includes reinforcing yarns or fibers. One set of fibers 44 is routed in the MD direction (i.e., they extend circumferentially within the matrix 42 of the shoe press belt 40, often as a single continuous helically-wound fiber). Another set of fibers 46, which is located radially outwardly of the MD fibers 44, is routed in the CMD direction (i.e., they extend axially within the matrix of the shoe press belt 40). The fibers 44, 46 may be any that are known to be suitable for inclusion for reinforcement of a shoe press belt 40. The fibers 44, 46 may be formed of any size and formed of any material suitable for use in a shoe press belt; exemplary fibers include those formed of polyester, nylon, or ultra high molecular weight polyethylene (UHMWPE), which may have a denier of between about 1,000 and 1,200 and may be twisted in 2, 3 or 6 plies. The fibers 44, 46 may be included in any density / frequency, but are typically spaced so that 8-12 fibers are present per inch.

[0033] The fibers 44, 46 are included in the shoe press belt 40 to provide reinforcement in the machine and cross-machine directions. As used herein, the fibers 44, 46 are intended to encompass both woven fabrics (such as those illustrated in U.S. Patent No. 5,196,092 to Stigberg) and reinforcing structures such as those shown, which include the constructions described and illustrated in U.S. Patent No. 5,525,194 to Jermo, the disclosures of which are hereby incorporated herein in their entireties.

[0034] The radially outward surface of the matrix 42 of the shoe press belt 40 may include grooves or the like that may improve the dewatering capacity of the shoe press belt 40. Such grooves typically are MD grooves, although they may also include holes and the like. Exemplary groove patterns are illustrated anddescribed in U.S. Patent No. 8,083,899 to Kawamata, the disclosure of which is hereby incorporated herein by reference in full.

[0035] As shown in Figure 5, the shoe press belt 40 also includes a plurality of piezoelectric fibers 100 that serve as pressure sensors. The piezoelectric fibers 100 are configured so that they include a sensing portion 102 that generates a signal under pressure, and a signal-carrying portion 104 (see Figure 6) that carries the signal from the sensing portion 102 to a processing unit 56 (described below). As an example, the sensing portion 102 may be formed of a piezoelectric material such as piezoelectric polymers, piezoelectric ceramics and piezoelectric composites. The signal carrying portion 104 may be any type of communications cable in which information generated by the sensing portion 102 can pass; exemplary materials for the signal-carrying portion may be magnet wire or other conductive wire (insulated or uninsulated). In some instances, the piezoelectric fiber 100 may also include a non-conducting portion 106 (see Figure 6) that extends beyond the piezoelectric portion (e.g., a polyester fiber).

[0036] In some instances, the piezoelectric fiber 100 may be one layer or component of a multilayer or multi-component fiber; for example, the piezoelectric fiber 100 may be the core of a multilayer fiber that also includes an outer protective sheath formed of a different material (see Figure 7A).

[0037] The piezoelectric fibers 100 are shown herein as CD fibers, although in some embodiments piezoelectric fibers may also be included in the machine direction. Typically, the piezoelectric fibers 100 are positioned substantially equidistant from each other about the circumference of the shoe press belt 40; for example, the piezoelectric fibers 100 may be separated by approximately 15 degrees, such that the shoe press belt 40 includes 24 piezoelectric fibers 100.

[0038] In the illustrated embodiment, and as shown in Figure 9, each of the piezoelectric fibers 100 is configured so that the sensing portion 102 thereof islocated at a different axial location on the shoe press belt 40. (As an example, a first of the sensing portions 102 may be located adjacent one end of the shoe press belt 100, a second of the sensing portions 102 may be located 12 inches from that end of the shoe press belt 100, a third of the sensing portions may be located 24 inches from that end of the shoe press belt 100, and so on for the full length of the shoe press belt 40. This type of arrangement permits measurement of pressure at different axial locations on the shoe press belt 40, which can provide an operator with a complete profile of pressure along the length of the shoe press belt 40. Such a pressure profile can enable the operator to identify and correct issues in the correct location of the paper machine. The sensing portions 102 are typically positioned substantially equidistant from each other along the length of the shoe press belt 40, but other configurations, such as those in which sensing portions 102 are more concentrated in one or more areas of particular interest, may also be used.

[0039] In one embodiment, each of the piezoelectric fibers 100 is co-located or combined with one of the CD fibers 46; for example, each piezoelectric fiber 100 may be wrapped around a CD fiber 46 in a helical fashion, or the piezoelectric fiber 100 may be routed adjacent a CD fiber 46. This embodiment may have an advantage in being able to utilize the existing CD fiber 46 as a supportive “backbone” for the piezoelectric fiber 100, such that the piezoelectric fiber 100 need not extend the entire length of the shoe press belt 40. In such an embodiment, it may be desirable to secure the end of the piezoelectric fiber to the CD fiber via an adhesive or the like.

[0040] In another embodiment, each of the piezoelectric fibers 100 replaces one of the CD fibers 46 in the matrix 42, such that the total number of CD fibers (i.e., CD fibers 46 plus piezoelectric fibers 100) is unchanged. In such an embodiment, the piezoelectric fiber 100 extends the full length of the shoe press belt 100 (see Figures 6 and 7A). In this configuration, each of the piezoelectricfibers 100 may be modified to provide a sensing portion at a different axial location along the length of the shoe press belt 40. This may be achieved by replacing the portion of the piezoelectric fiber 100 opposite the signal-carrying portion 104 with a nonconductive material (shown at 106 in Figure 6). In another version, the piezoelectric core of a multi-layer fiber may be cleaved at a desired location, such that a signal is sent only for the portion of the piezoelectric fiber 100’ prior to the cleaving location (Figure 7B). Other variations may also be possible.

[0041] Each of the piezoelectric fibers 100 is operatively connected with a processing unit (schematically represented at 56 in Figure 9). The processing unit 56 may be mounted on one of the head plates 34, above one end of the shoe press belt 40, or at another convenient location. As one example, the processing unit 56 may be a wireless voltage reader mounted just above one end of the shoe press belt 40 (see Figure 9), such that it can read the voltages present in the signal-carrying members as each passes under the voltage reader. Alternatively, the piezoelectric fibers may be hard-wired to the processing unit 56.

[0042] The processing unit 56 may also include a device or sensor that can identify which piezoelectric fiber 100 is producing the signal being read. This can be achieved in several ways. One example is to mount an RFID tag or transmitter that is associated with each piezoelectric fiber 100 such that, as the shoe press belt 40 rotates during operation, an RFID reader detects the RFID tag and can correlate the signal being received with the correct piezoelectric fiber 100. As another example, the piezoelectric fibers 100 may be sufficiently separated from each other circumferentially that only one fiber is present in the nip at a time, such that identifying which fiber 100 is sending a signal may be simplified.

[0043] The processing unit 56 includes a signal transmitter 58 that is in communication with a signal receiver 62 mounted remotely from the shoe press 20.The signal receiver 62 is hard-wired to a personal computer 64 or other data processing device (such as the distributive control system of a paper mill) that can process signals from the transmitter 58 into useful, easily understood information. It is preferred that a wireless communication mode, such as RF signaling (e.g., Bluetooth® protocol), be used to transmit the data from the processing unit 56 to the receiver 62.

[0044] The shoe press belt 40 can be constructed by any manner known for the construction of shoe press belts, such as casting, molding, extrusion, or the like. One construction method is discussed in U.S. Patent No. 7,014,733 to Gustafson et al. the disclosure of which is hereby incorporated herein by reference in full.

[0045] A shoe press belt 40 that includes piezoelectric fibers 100 as described above can provide real-time information about operational parameters in the nip, such as the magnitude and distribution of pressure, nip width, strain, and stress. Such information can enable an operator to adjust the shoe press 20 as desired for the papermaking operation at hand. For example, it may be desirable to adjust the shoe 32 so that pressure within the nip 25 remains at a certain magnitude. As another example, it may be desirable to adjust the shoe 32 so that the peak pressure experienced in the nip 25 is located toward the “downstream” end of the nip 25 rather than in the center, as doing so can improve the quality of paper formed therein.

[0046] It is also contemplated that a belt of the present invention may be suitable for other uses. These may include, for example, other locations on a papermaking machined (e.g., calendering belts and Clupak blankets), belts for pulp machines, and belts for tissue machines.

[0047] It is also contemplated that pressure-sensitive materials other than piezoelectric fibers may be employed.

[0048] The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

That Which is Claimed is:

1. A pressure-sensing belt, comprising: a substantially cylindrical polymeric belt having a longitudinal axis, a radially inner surface, and a radially outer surface; a plurality of reinforcing cross-machine (CD) fibers extending parallel to the longitudinal axis for the length of the belt between the inner and outer surfaces; a plurality of reinforcing machine direction (MD) fibers extending circumferentially relative to the longitudinal axis between the inner and outer surfaces; and a plurality of piezoelectric fibers extending within the belt, the piezoelectric fibers each having a sensing portion and a signal-carrying portion.

2. The belt defined in Claim 1, wherein the polymeric belt comprises polyurethane.

3. The belt defined in Claim 1 , wherein said polyurethane has a Shore A hardness value of between about 55 and 100.4 The belt defined in any of Claims 1-3, wherein each of the sensing portions of the piezoelectric fibers is positioned at a different axial location.

5. The belt defined in any of Claims 1-3, wherein each of the piezoelectric fibers includes a non-conductive portion and extends the length of the belt.

6. The belt defined in Claim 5, wherein each of the piezoelectric fibers is positioned to replace one of the reinforcing CD fibers.

7. The belt defined in any of Claims 1-3, wherein each of the piezoelectric fibers is co-located with one of the reinforcing CD fibers.

8. The belt defined in Claim 7, wherein each of the piezoelectric fibers extends less than the length of the belt.

9. The belt defined in Claim 8, wherein each of the piezoelectric fibers is helically wrapped about a corresponding one of the reinforcing CD fibers.

10. The belt defined in any of Claims 1-3, wherein the sensing portions comprise a piezoelectric polymer, and the conducting portions comprise a magnet wire.

11. The belt defined in any of Claims 1-3, wherein said outer surface includes a plurality of recesses for venting water.

12. The belt defined in any of Claims 1-3, wherein said piezoelectric fibers are spaced substantially equidistant from each other along a circumference of the belt.

13. The belt defined in any of Claims 1-3, further comprising at least one piezoelectric fiber routed in the MD direction.

14. A shoe press, comprising: a first member having a convex pressing surface; a second member comprising a shoe with a concave pressing surface substantially complimentary to said convex pressing surface, said second member further comprising a pair of substantially circular head plates rotatably mounted on axially opposed ends thereof; a belt as defined in Claim 1 mounted to the head plates; and a processing unit in communication with the piezoelectric fibers that processes signals generated by the sensing portions.

15. The shoe press defined in Claim 14, wherein said first member comprises an elongate roll.

16. The shoe press defined in Claim 14, further comprising an endless press felt positioned to be conveyed between said belt and said pressing surface of said second member.

17. The shoe press defined in Claim 14, wherein the processing unit is mounted above one end of the belt in axial alignment with the shoe.

18. The shoe press defined in Claim 17, wherein said processing unit comprises a signal transmitter, and wherein said shoe press further comprises a signal receiver and a display device operatively associated with said signal transmitter.

19. The shoe press defined in Claim 17, wherein an identifier is associated with each of the piezoelectric fibers, the identifier configured to provide a signal to the processing unit indicating the indent of the associated piezoelectric fiber.

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