MXPA06004799A - Belt with variable grooves - Google Patents

Abstract

A belt (16) for use in a papermaking process, such as in a long nip press having a cylindrical press roller (12) and an arcuate pressure shoe (14) which define a nip (10). The belt has a nip load zone (36) which passes through the nip during an operation. The belt comprises a substrate (28) having a coating (34) on at least one surface thereof The substrate is in the form of an endless loop and has a longitudinal or machine direction. The coating has a plurality of grooves (42, 44) running in the machine direction, wherein grooves (44) in a center portion (64) of the nip load zone have at least one of a depth, width, cross-sectional shape, or spacing which is different from that of grooves (42) in outer portions (62) of the nip load zone so as to vary the void volume of the nipe load zone in a cross-machine direction in a desired manner.

Description

BAND WITH VARIABLE GROOVES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fibrous network that is processed in a paper product in a papermaking machine. More specifically, the present invention relates to a method and device for pressing operations associated with the production of paper. 2. Description of the Related Art During the papermaking process, a fibrous network of cellulosic fibers is formed on a forming wire by depositing a fibrous mixture therein in the forming section of a papermaking machine. A large amount of water is drained from the mixture in the forming section, after which the newly formed network is led to a press section. The press section includes a series of pressure zones in which the fibrous network is subjected to compressive forces applied to remove the water therefrom. The network is finally led to a drying section including heated drying drums around which the network is directed. The heated drying drums reduce the water content of the network to a desirable level through evaporation to produce a paper product. The increase in energy costs makes it increasingly desirable to remove as much water as possible from the network before it enters the drying section. Since drying drums are frequently heated from the inside by steam, the costs associated with steam production can be substantial, especially when it is necessary to remove a large amount of water from the network. Traditionally, the press sections have included a series of pressure zones formed by pairs of adjacent cylindrical pressure rollers. In recent years, it has been found that the use of shoe-type extended pressure zones is more advantageous than the use of pressure zones formed by adjacent pressure roller pairs. This is because the network takes more time to pass through a prolonged pressure zone than through one formed by pressure rollers. The longer the network can be subjected to the pressure in the pressure zone, the more water can be removed from there and, consequently, the less water will be removed in the network through the evaporation in the drying section. The present invention relates to shoe type prolonged pressure zone presses. In this variety of press for prolonged pressure zone, the pressure zone is formed between a cylindrical pressure roller and an arcuate pressure shoe. The latter has a cylindrically concave surface having a radius of curvature close to that of the cylindrical pressure roller. When the roller and the shoe enter in close physical proximity to each other, a pressure zone is formed, which can be five to ten times greater in the machine direction than one formed between two pressure rollers. Since the zone of prolonged pressure is five to ten times greater than in a conventional two-roll press, the so-called drying time of the fibrous network in the prolonged pressure zone is correspondingly greater under the same pressure level per square inch. in the pressure force used in a two-roll press. The result of this prolonged pressure zone technology has been a dramatic increase in the drainage of the fibrous network in the prolonged pressure zone compared to conventional pressure zones in paper machines. A shoe type prolonged pressure zone press requires a special band, such as that shown in Pat. of E.U. No. 5,238,537. This band is designed to protect the pressing fabric that supports, carries and drains the fibrous network, from the accelerated wear that would result from the direct sliding contact on the stationary pressure shoe. Such a band should be provided with a soft waterproof surface that travels or slides over the stationary shoe in a film of lubricating oil. The web moves through the pressure zone at approximately the same speed as the web of thought, thus subjecting the press fabric to minimum degrees of friction against the surface of the web. The bands of the variety shown in Pat. from E.U. No. 5,238,537 are made by impregnating a woven base fabric, which takes the form of an endless band, with a synthetic polymeric resin. Preferably, the resin forms a coating of some predetermined thickness over at least the inner surface of the band, so that the strands from which the base fabric is woven can be protected from direct contact with the arched pressure shoe component of the press. of prolonged pressure zone. It is specifically this coating that must have a smooth waterproof surface to slide easily over the lubricated shoe and to prevent part of the lubricating oil from penetrating the structure of the belt contaminating the fabric or press fabrics, and the fibrous network. The base fabric of the band shown Pat. of E.U. No. 5,238,537 can be woven of monofilament strands in a single or multi-layered fabric, and woven sufficiently open to allow the impregnated material to completely impregnate the fabric. This eliminates the possibility of voids forming in the final band. Such voids may allow the lubrication used between the web and the shoe to pass through the web and contaminate the web or press fabrics and the fibrous web. The base fabric may be of flat weave and subsequently be sewn endless, or woven endless in tubular form. When the impregnated material is cured to a solid condition, it is first attached to the base fabric by mechanical interconnection, where the cured impregnated material surrounds the strands of the base fabric. In addition, there may be some bond or chemical adhesion between the cured impregnated material and the material of the strands of the base fabric. Prolonged pressure zone press bands, such as those shown in Pat. of E.U. No. 5,238,537, depending on the size requirements of the prolonged pressure zone presses in which they are installed, have lengths of approximately 13 to 35 feet (approximately 4 to 11 meters), measured longitudinally around their endless band forms , and widths of approximately 100 to 450 inches (approximately 250 to 1125 centimeters), measured transversely through these shapes. It will be appreciated that the manufacture of such webs is complicated by the requirement that the base fabric be endless before it is impregnated with a synthetic polymeric resin. It is often desirable to provide the band with a resin coating of some predetermined thickness on its outer surface as well as on its inner surface. By covering both sides of the band, your woven base fabric will be closer to, if not coincident with, the neutral axis of the band fold. In such a circumstance, the internal stresses that arise when the band is bent when passing around the roller or the like in a papermaking machine will be less likely to cause the coating to dislodge on either side of the web. Further, when the outer surface of the band has a resin coating of some predetermined thickness, it allows the formation of grooves, concealed perforations, or other cavities or voids in that surface without exposing any part of the woven base fabric. These characteristics provide a temporary storage of the pressed water of the network in the pressure zone. In fact, for some press configurations of prolonged pressure zone, the presence of some vacuum volume, provided by slots, hidden perforations or the like, on the outer surface of the band is necessary. Although an attempt is made to preserve the consistency and drainage properties of the network as constantly as possible throughout the papermaking process, a variation inevitably occurs. The characteristics of the network, such as the moisture content, may change over time. The moisture content of the network can affect the strength and quality of the final product. For example, an excessively variable moisture content in the profile (CD) in the transverse direction can lead to variable characteristics of the sheet, such as curling, and the decrease in product quality. Therefore, there is a need to control the CD moisture profile during the papermaking process. In contrast to the bands of the prior art, the present invention can provide an improved web with a variable vacuum volume to correct (flatten) the CD moisture profile of the sheet. Specifically, the band of the present invention, for example, can provide grooves of variable depth in the area of the band subjected to compression forces in the pressure zone. The variable depth grooves improve the band's CD moisture profile, thus improving the quality of the product. Alternatively, the present invention may provide grooves having shapes, dimensions and / or sizes, widths and lengths, varying or different in the area of the web subjected to compression forces in the pressure zone. Still further, the present invention may vary the orientation and / or the number of slots in this area in combination with any of the above variants. SUMMARY OF THE INVENTION Accordingly, the present invention is a web for a papermaking process. Specifically, the band can be used in a pressurized zone press where the press has a cylindrical pressure roller and an ate pressure shoe which jointly define a pressure zone therebetween. The present band has a pressure loading zone and two flange zones and is operable in such a way that the pressure charging zone passes through the pressure zone during any operation. The band comprises at least one layer having a resin coating on at least one surface thereof, in which the band is in the form of an endless band having a longitudinal or machine direction. The resin layer has a plurality of grooves that include a number of first grooves and a number of second grooves' running in a direction substantially parallel to the longitudinal direction in a central portion of the pressure loading zone, in which the The number of first slots has at least one of, a depth, cross-sectional shape, size, or width or a combination thereof, different from that of the number of second slots. The present invention will now be described in more complete detail with frequent reference to the drawings identified below.

BRIEF DESCRIPTION OF THE FIGURES The following detailed description, given by way of example and without intending to limit the present invention only to the same, will be better appreciated in conjunction with the accompanying drawings in which like reference numerals denote similar elements and parts, in which: Figure 1 is a cross-sectional side view of a prolonged pressure zone press; Figure 2 is a cross-sectional view of a band according to an embodiment of the present invention; and Figure 3 is a separate view of the pressure loading zone of the band illustrated in Figure 2. DETAILED DESCRIPTION OF THE PREFERRED MODALITY A detailed embodiment of the present invention will be described in the context of a shoe press band of prolonged pressure zone. A prolonged pressure zone press is shown for draining a processed fibrous web in a paper product in a papermaking machine, in a cross-sectional side view in Figure 1. The pressure zone 10 is defined by a roller of cylindrical pressure 12 and an arcuate pressure shoe 14. The arcuate pressure shoe 14 has approximately the same radius of curvature as the cylindrical pressure roller 12. The distance between the cylindrical pressure roller 12 and the arcuate pressure shoe 14 it can be adjusted by a hydraulic means or the like operatively attached to the arcuate pressure shoe 14 to control the loading of the pressure zone 10. The cylindrical pressure roller 12 can be a controlled crown roller equaled to the arcuate pressure shoe 14 to obtain a level of pressure profile of the pressure zone transverse to the machine. A sheet moisture profile CD such as a "smile" or "gathers" configuration is often presented. Its mechanical correction is sometimes inefficient or not sufficiently satisfactory. The extended pressure zone press band 16 extends in a closed band through the pressure zone 10, separating the cylindrical pressure roller 12 from the arcuate pressure shoe 14. The press fabric 18 and the fibrous web 20 processed on a sheet of paper they pass together through a pressure zone 10 as indicated by the arrows in Figure 1. The fibrous web 20 is supported by the press fabric 18 and comes into direct contact with the pressure roller cylindrical soft 12 in the pressure zone 10. Alternatively, the fibrous web 20 may pass through the pressure zone 10 trapped between the two pressing fabrics 18 (the second press fabric is not shown). The prolonged pressure zone press band 16, which also moves through the pressure zone 10 as indicated by the arrows, i.e., clockwise as shown in Figure 1, projects the press fabric 19 from a direct sliding contact against the arcuate pressure shoe 14, and typically slides thereon on a lubricating oil film. The prolonged pressure zone press band 16, therefore, is impervious to oil, so that the press fabric 18 and the fibrous web 20 will not be contaminated thereby. Figure 2 is a cross-sectional view of a band according to an embodiment of the present invention. As shown therein, the band 16 may include a pressure charging zone 36 and flange regions 38. The pressure charging zone 36 is the area of the band that can pass between the pressure roller 12 and the hot shoe. of arcuate pressure 14 and that can be found in compression therefrom, and it is the area of the band to which this invention is directed. The flange zones 38 define the areas in the web from the flanges of the web 37 to the pressure charging zone 36 and have a configuration known to those skilled in the art. The pressure charging zone 36 may have a flange area 38 on both sides thereof in a direction of the belt transverse to the machine. The pressure charging zone 36 and the flange area 38 also extend in the direction of the operating or longitudinal band of the machine. The band 16 may include at least one layer, such as a structure or base substrate layer 28, shown in Figure 3. However, the web 16 may also contain additional layers. The layer 28 can be a non-woven structure in the form of a strand assembly 30 in the transverse or transverse direction to the machine (seen from the side in Figure 3), and strands 32 in the longitudinal or machine direction, which, depending on the application they can be joined together in their mutual coupling points to form a fabric. The layer 28 can alternatively be woven. The transverse strands being warp threads woven on, under and between the longitudinal strands. It should be understood that the layer 28 may be of flat weave, and subsequently bonded endlessly with a seam. It should be further understood that the layer 28 can be woven into a single layer fabric, or any other fabric pattern that is known to those skilled in the art. In addition, the layer 28 may be a woven or braided fabric or a spiral binding band of the type shown in Pat. of E.ü. No. 4,567,077 for Gauthier, whose teachings are incorporated herein by reference. The layer 28 can also be extruded from a polymeric resin material in the form of a sheet or membrane, which can subsequently be provided with openings. Still alternatively, at least one layer 28 may comprise non-woven mesh fabrics, such as those shown in Pat. commonly assigned from E.ü. No. 4,427,734 for Johnson, whose teachings are incorporated herein by reference. In addition, layer 28 may be produced by spirally winding a web of woven, non-woven, sewn, braided, extruded or non-woven mesh material according to the methods shown in Pat. of E.U. commonly assigned NO. 5,360,656 to Rexfelt et al., Whose teachings are incorporated herein by reference. The layer 28 may therefore comprise a spirally woven ribbon, wherein each spiral turn is joined to the next by a continuous joining line endless layer 28 in a longitudinal direction. A prolonged pressure band or pressure shoe having such a layer is described in the Pats. of E.U. commonly assigned Nos. 5,792,323 and 5,837,080, the teachings of which are incorporated herein by reference. A resin such as a polymer resin 34 is deposited, coated, impregnated or otherwise disposed on at least one surface of the strip 16. The polymer resin 34 may be coated or otherwise disposed on the outer surface 24. of the band 16, that is, the surface that makes contact with the press fabric 16 that is in use in a prolonged pressure press. In addition, the polymer resin may be coated or otherwise disposed on the inner surface 22 of the web 16, i.e., the surface that slides over the arcuate pressure shoe 14 when the web is in use in a pressurized press prolonged Alternatively, the polymer resin can be coated on both the inner surface 22 and the outer surface 24 of the strip 16. The polymeric resin can impregnate the layer 28, and make the band 16 impermeable to oil, water and the like. The polymeric resin coating 34 may be of polyurethane, and may be a 100% solids composition thereof. The use of a 100% solids resin system, which by definition lacks a solvent material, prevents the formation of bubbles in the polymer resin during the curing process through which it proceeds after its application in layer 28. Other coating material may also be used, for example, rubber or rubber-like compounds. In any case, the resin layers can be the same or different, with the same or different level of hardness. The inner surface 22 and / or the outer surface 22 can also be sprayed and polished after the polymer resin has cured to provide the polymer resin coating with a smooth surface, uniform. After the polymeric resin has been cured, slots 26 may be provided on the outer surface 24 of the strip 16. Specifically, the variable depth slots 26 may be cut, punched or otherwise provided in the pressure loading zone 36 (ie, the area of the band undergoing compression, which is commonly a portion of the total width of the band) and oriented in order to run in the longitudinal direction. In one embodiment of the present invention, the slots 26 run parallel to each other, however, other orientations are considered within the scope of the present invention. Alternatively, to the cut, perforated, etc., the slots 26 can be printed on the outer surface 24 by a printing type device before the polymeric resin has cured, or they can be molded on the surface 24 (such as, when the web 16 is manufactures, using a molding process). As will be appreciated, other possible ways of forming the grooves 26 will be readily apparent to the person skilled in the art. Note that although the term "grooves" is referred to, what actually happens is the creation of voids or void volume in the band a order to receive the liquid that enters. The variation of such volume of vacuum in the band can be achieved by varying the shapes, dimensions, spacing and orientation of. the "slots" or any combination thereof. Figure 3 is a separate view of the pressure loading zone 36 illustrated in Figure 2. Figure 3 also shows a separate view of the first slot 42 and the second slot 44 on the external surface 24. Also note that all the Numerical dimensions are used for illustrative purposes only and should not be considered exclusive in any way. The first slot 42 and the second slot 44 have a first depth 46 and a second depth 48, respectively. In addition, the first slot 42 and the second slot 44 have a first external width 50 and a second external width 52, and a first internal width 54 and a second internal width 56, respectively. In addition, the first slot 42 and the second slot 44 can be continuous or discontinuous in the longitudinal direction. Also, the first groove 42 and the second groove 44 may be spaced apart from adjacent grooves by a so-called land area 58 and a second land area 60. The first land area 58 and the second land area 60 may be considered narrow cured polymer resin pillars running in the machine direction on the outer surface 24 of the strip 16. The first and second slot depths 46, 48 can have values of approximately 1.10 mm and 1.5 mm, the first internal and external widths 54, 50 may have values of approximately 0.85 mm and 1.18 mm, and the second internal and external widths 56, 52 may have values of approximately 0.85 mm and 1.35 mm, respectively. The first land area 58 and the second land area 60 may have widths of approximately 2 mm and 1.88 mm, respectively. As will be appreciated, other configurations, dimensions, spacings and orientations of the first and / or second slots 42, 44, and the first and / or second land areas 58, 60 may be used and are considered within the scope of the present invention. . As shown in Figure 3, the pressure charging zone 36 may include a central portion 64, intermediate portions 66, and external portions 62. The grooves 26 of the central portion 64, intermediate portions 66, and outer portions. 62 may have different sizes, orientations, shapes and / or depths or combinations thereof. For example, the central portion 64 may include grooves of a single width and depth; alternatively it may include a number of first slots 42 and a number of second slots 44. The slots within the central portion 64 may be arranged in any manner. That is, the arrangement of such slots could be a first slot 42 followed by a second slot 44 followed by a first slot 42 and so on, or a number of first slots followed by a number of second slots followed by a number of first slots. and so on. In addition, the central portion 64 may include slots having more than two different sizes, orientations, shapes and / or depths that could be arranged in any combination. Additionally, one or both of the intermediate portions 60 and the outer portions 62 may also include grooves having different sizes, shapes and / or depths and which may be arranged in any manner such as those previously described. Still further, an outer portion 62 or an intermediate portion 66 may have a different groove shape on one side of the pressure load zone 36, on that of the other. For example, the intermediate portions 66 may include a stepwise depth-of-slot gradation. As shown in Figure 3, the intermediate portion 66 includes grooves having an initial depth of approximately 1.4 mm at location 72, a depth of approximately 1.3 m at location 71, and a depth of 1.2 mm at location 70 that change in increments of .10 mm every 460 mm. Such an arrangement may be particularly useful in embodiments in which the central portion 64 has grooves of a depth of approximately 1.5 mm, and an outer portion with grooves of a depth of 1.1 mm.

This essentially results in an increase in the volume of vacuum in the central portion 64 which decreases as it goes towards the outer portions 62. Briefly, the arrangements and groove characteristics can be optimized to flatten or improve the CD profile of moisture typically existing in the transition from a shorter depth in the outer portions to greater depths in the central portion 64. Note that there may even be areas without grooves or zero depth depending on the moisture profile for which they are adjusted. Although grooves having a cross-sectional shape such as those shown in Figure 3 have been described, and provided by cutting or forming, the present invention is not limited thereto. For example, the slots may have other shapes in cross section and may be obtained by other means. As an example, the slots 26 can be provided by a cutting device (such as a piercing type device) that cuts or forms slots in a spiral orientation about the circumference of the band either in a clockwise or in a clockwise direction. counter clockwise proceeding in a substantially longitudinal direction. In such a situation, the slots may be arranged in any combination. In one arrangement, a groove having a spiral cross-section in the clockwise direction followed by a groove having a counter-clockwise cross-section followed by a groove having a cross-section spirally in the direction of clockwise. the direction of the clock hands and so on. In addition, each of the grooves 26 may not be perfectly parallel to the longitudinal direction, but may vary therefrom. Additionally, a number of slots 26 may be oriented so as to run in a direction that forms an angle (such as up to 45 degrees) to a line parallel to the longitudinal direction. In essence, the principle involves changing the void volume of the slots in these zones (two ridges and the center) in such a way that, for example, the area with the least available vacuum volume will be able to accept less water. For example, in a typical "shirred" sheet moisture profile CD, the edges of the sheet are drier than the center of the sheet. By reducing the vacuum volume of the areas of the two edges of the web, less water will be removed from the web in these areas, so that the sheet moisture profile leaving the pressing area will be flatter. Similarly, for a typical "smile" sheet moisture profile CD, the vacuum volume is inverted. The modifications to the foregoing will be obvious to those of ordinary skill in the art, but will not modify the invention beyond the scope of the appended claims.

Claims (22)

1. CLAIMS 1. An endless belt for use in a shoe press having a cylindrical pressure roller and an arcuate pressure shoe which together define a pressure zone therebetween, said band including a pressure loading zone having a width in the direction transverse to the machine, said band being operable in such a manner that during operation, said band with said pressure loading zone passes through said pressure zone, said band comprising: a substrate; at least one layer re-covered on at least one side of said substrate; a desired pattern in said layer including grooves; and said desired pattern being such that said pressure loading zone has a void volume across the width of the pressure loading zone said void volume being the result of the grooves having different width, shape in cross section , separation, or a combination of one or more of these features together with or in conjunction with a different depth in order to vary said vacuum volume in a desired manner. The band according to claim 1, wherein said pressure loading zone includes two external portions each located on one side of a central portion. The band according to claim 2, wherein said pressure loading zone includes two intermediate portions each located on one side of said central portion and between said central portion and said external portions. The band according to claim 3, wherein said coated layer has a plurality of grooves in at least one of said two outer portions. The band according to claim 3, wherein said coated layer has a plurality of slots in at least one of said intermediate portions. The band according to claim 1, wherein said coated layer has a plurality of slots in said outer portion. The band according to claim 1, wherein said substrate is one selected from the group consisting of woven fabrics, non-woven fabrics, knitted fabrics, braided fabrics, extruded sheets of polymeric material and non-woven mesh fabrics. , and a spiral binding band. The band according to claim 1, wherein said substrate is a tape of spirally wound material in a plurality of turns, each turn being joined to those adjacent to it by a continuous joining line, said tape material being selected from the group consisting of woven fabrics, non-woven fabrics, knitted fabrics, braided fabrics, extruded sheets of polymeric material, non-woven mesh fabrics, and a spiral binding band. 9. The band according to claim 1, wherein said coated layer is a polymeric resin, rubber or rubber-like composite. The band according to claim 2, wherein the grooves have a depth that is greater in the central portion. The band according to claim 3, wherein the depth of said grooves decreases in a stepwise function from the central portion through the intermediate portion and the outer portion. The band according to claim 11, wherein the intermediate portion includes grooves of two or more depths. The band according to claim 1, wherein said desired pattern includes portions or a portion having no grooves. The band according to claim 1, wherein said grooves are formed in a repeat pattern of different widths and depths. The band according to claim 2, wherein said grooves formed in said central portion have a greater width than the grooves formed in said outer portion. 16. A method for adjusting the moisture profile of a shoe press band comprising the steps of: providing a substrate having a coated layer on at least one surface thereof, forming a desired pattern in said layer including grooves; and creating said desired pattern such that said pressure loading zone has a void volume across the width of the pressure loading zone which is the result of the grooves having different width, cross-sectional shape, spacing, or a combination of one or more of these features together with or in conjunction with a different depth in order to vary said vacuum volume in a desired manner. The method of claim 16, wherein grooves are formed in a central portion of said pressure loading zone having a greater depth than the grooves formed in an outer portion of the pressure loading zone. The method of claim 16, wherein said substrate is one selected from the group consisting of woven fabrics, non-woven fabrics, knitted fabrics, braided fabrics, extruded sheets of polymeric material and non-woven mesh fabrics, and a spiral binding band. The method of claim 16, wherein said substrate is a tape of spirally wound material in a plurality of turns, each turn being joined to those adjacent to it by a continuous bond line, said tape material being selected from the group. which consists of woven fabrics, non-woven fabrics, knitted fabrics, braided fabrics, extruded sheets of polymeric material, non-woven mesh fabrics, and a spiral binding band. The method of claim 16, wherein said coated layer is a polymeric resin, rubber or rubber-like composite. The method of claim 16, wherein at least part of said desired pattern has no slots. 22. An endless belt for use in a shoe press having a cylindrical pressure roller and an arcuate pressure shoe which together define a pressure zone therebetween, said band including a pressure loading zone having a width in one cross-machine direction, said band being operable such that during operation, said band with said pressure loading zone passes through said pressure zone, said band comprising: a substrate; at least one coated layer on at least one side of said substrate; a desired pattern in said layer including grooves; and said desired pattern being such that said pressure loading zone has a void volume across the width of the pressure loading zone said void volume being the result of the grooves having different width, shape in cross section , separation, or a combination of one or more of these features together with or in conjunction with a different depth in order to vary said vacuum volume such that the volume of vacuum in the central portion of the pressure loading zone is greater than the volume of vacuum in the outer portion of the pressure loading zone.