Abstract:
The present invention is a grooved belt, or surface roll where applicable, and a method for making these belts or rolls, comprising placing a chemically reactive material on a partially completed belt surface, and depositing an elastomeric material onto the chemically reactive material which reacts and forms a bond therewith to create a pattern. Placement of the elastomeric material is used to create the grooves, for example. The grooves are formed without machining and the resulting belt surface is smooth and uniform without cuts or cracks.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to the field of papermaking, particularly to a method of making a grooved belt, or roll cover where applicable, used in papermaking machines and processes. The invention concerns using ribbon placement to create the grooves without machining the belt surface. 
     BACKGROUND OF THE INVENTION 
     During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric. 
     The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet. 
     The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation. 
     It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section. 
     Rising energy costs have made it increasingly desirable to remove as much water as possible from the web prior to its entry into the dryer section. As the dryer drums are typically heated from within by steam, costs associated with steam production may be substantial, especially when a large amount of water must be removed from the web. 
     Traditionally, press sections have included a series of nips formed by pairs of adjacent cylindrical press rolls. In recent years, the use of long press nips of the shoe type has been found to be more advantageous than the use of nips formed by pairs of adjacent press rolls. This is because the longer the time a web can be subjected to pressure in the nip, the more water can be removed there, and, consequently, the less water will remain behind in the web for removal through evaporation in the dryer section. 
     The present invention relates, in part, to long nip presses of the shoe type. In this variety of long nip press, the nip is formed between a cylindrical press roll and an arcuate pressure shoe. The latter has a cylindrically concave surface having a radius of curvature close to that of the cylindrical press roll. When the roll and shoe are brought into close physical proximity to one another, a nip, which can be five to ten times longer in the machine direction than one formed between two press rolls, is formed. Since the long nip may be five to ten times longer than that in a conventional two-roll press, the so-called dwell time, during which the fibrous web is under pressure in the long nip, may be correspondingly longer than it would be in a two-roll press. The result is a dramatic increase in the dewatering of the fibrous web in the long nip relative to that obtained using conventional nips on paper machines. 
     A long nip press of the shoe type requires a special belt, such as that shown in U.S. Pat. No. 5,238,537 to Dutt (Albany International Corp.), the teachings of which are incorporated herein by reference. The belt is designed to protect the press fabric, which supports, carries and dewaters the fibrous web, from the accelerated wear that would result from direct, sliding contact over the stationary pressure shoe. Such a belt must be provided with a smooth, impervious surface that rides, or slides, over the stationary shoe on a lubricating film of oil. The belt moves through the nip at roughly the same speed as the press fabric, thereby subjecting the press fabric to minimal amounts of rubbing against the surface of the belt. 
     Belts of the variety shown in U.S. Pat. No. 5,238,537 are made by impregnating a woven base fabric, which takes the form of an endless loop, with a synthetic polymeric resin. Preferably, the resin forms a coating of some predetermined thickness on at least the inner surface of the belt, so that the yarns from which the base fabric is woven may be protected from direct contact with the arcuate pressure shoe component of the long nip press. It is specifically this coating which must have a smooth, impervious surface to slide readily over the lubricated shoe and to prevent any of the lubricating oil from penetrating the structure of the belt to contaminate the press fabric, or fabrics, and fibrous web. 
     The base fabric of the belt shown in U.S. Pat. No. 5,238,537 may be woven from monofilament yarns in a single or multi-layer weave, and is woven so as to be sufficiently open to allow the impregnating material to totally impregnate the weave. This eliminates the possibility of any voids forming in the final belt. Such voids may allow the lubrication used between the belt and shoe to pass through the belt and contaminate the press fabric or fabrics and fibrous web. The base fabric may be flat-woven, and subsequently seamed into endless form, or woven endless in tubular form. 
     When the impregnating material is cured to a solid condition, it is primarily bound to the base fabric by a mechanical interlock, wherein the cured impregnating material surrounds the yarns of the base fabric. In addition, there may be some chemical bonding or adhesion between the cured impregnating material and the material of the yarns of the base fabric. 
     Long nip press belts, such as that shown in U.S. Pat. No. 5,238,537, depending on the size requirements of the long nip presses on which they are installed, have lengths from roughly 10 to 35 feet (approximately 3 to 11 meters), measured longitudinally around their endless-loop forms, and widths from roughly 6 to 35 feet (approximately 2 to 11 meters), measured transversely across those forms. The manufacture of such belts is complicated by the requirement that the base fabric be endless prior to its impregnation with a synthetic polymeric resin. 
     It is often desirable to provide the belt with a resin coating of some predetermined thickness on its outer surface as well as on its inner surface. By coating both sides of the belt, its woven base fabric will be closer to, if not coincident with, the neutral axis of bending of the belt. In such a circumstance, internal stresses which arise when the belt is flexed on passing around a roll or the like on the paper machine will be less likely to cause the coating to delaminate from either side of the belt. 
     Moreover, when the outer surface of the belt has a resin coating of some predetermined thickness, it permits grooves, blind-drilled holes or other cavities to be formed on that surface without exposing any part of the woven base fabric. These features provide for the temporary storage of water pressed from the web in the press nip, and are usually produced by grooving or drilling in a separate manufacturing step following the curing of the resin coating. 
     The present invention relates particularly to a grooved press belt which could be used in a long nip press or also in a conventional press. In addition, the present invention relates to a grooved roll cover. 
     In the case of conventionally grooved belts, a machining process is typically used to create the surface grooves. The grooves define channels and are separated from one another by what may be referred to as land areas. The width and depth of the grooves and the number of grooves per inch dictate the void volume of the grooved belt surface. In addition, the need for the belt to flex dictates certain material characteristics. For instance, the material must be sufficiently flexible to conform to the belt path and still be rigid enough so as not to collapse under press loads. In this regard, it is noted that elastomers such as urethane have been successfully used heretofore. 
     Roll covers are manufactured in a variety of ways, using varied materials such as rubber, rubber-like materials, polymers or metal alloys. Current methods of manufacturing roll covers include “laying up” sections of uncured mats of polymeric compounds onto a roll body, sometimes with textile reinforcement. This forms a roll cover of several sections, which is finished by heat curing to form a continuous cover. This cover is ground and may undergo other surface finishing steps. Finally, grooves are cut in a circumferential pattern in the surface to assist sheet dewatering in the press nip. Another method used to form roll covers is to spiral wind a semi-solid resin onto a body, followed by curing and surface finishing. Again, grooves are cut in the surface to assist dewatering in the nip. Yet another method is to cast or mold a resin-fiber system onto a mandrel or roll body, forming a composite system. Other covers may be formed of mixtures of resins (i.e., “alloys” of resins), metals and resins, ceramics, and the like. 
     Also in the case of conventional grooved rolls, the surface grooves are typically created by machining the roll cover surface. Again, the width and depth of the grooves and the number of grooves per inch dictate the void volume of the grooved surface. It is also noted that there are many different materials used to create grooved roll surfaces. 
     During the machining of grooves especially in belts, the interior walls (the sides of the lands separating the grooves) of synthetic surface material are left with microscopic surface cuts created by the action of the machine tool. These microscopic cuts can constitute crack initiation sites which may lead to larger cracks and eventual failure or delaminating of the land area on either side of the groove. In this connection, U.S. Pat. No. 5,171,389 is directed toward a method of making a grooved void-volume belt for use on a long nip press. After applying an adhesive, a strip of material having a groove already formed therein is wound about a partially completed belt and suitably attached. This, among other things, avoids having to cut grooves in the belt surface. 
     The present invention provides an approach towards forming grooves or other patterns on both belt and roll surfaces without machining using ribbon placement to create the grooves. 
     SUMMARY OF THE INVENTION 
     The present invention is directed towards a method of making a grooved belt or surface roll. A chemically reactive material is first placed on the surface of the partially processed belt or roll. A second material is then deposited as a ribbon on the chemically reactive surface to create a pattern of grooves. Advantageously, the placement of the ribbon is used to create the grooves therebetween and no machining is required. This eliminates the potential problem of cracking and delamination of the belt or roll surface. The resulting ribbon is smooth and uniform. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the method by which the belt of the present invention may be manufactured; 
         FIG. 2  illustrates using the placement of the ribbons to create the grooves; 
         FIG. 3A  illustrates the strip profile of the prior art; and 
         FIG. 3B  illustrates exemplary profiles of the ribbons of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention, as illustrated in  FIG. 1 , will now be described in the context of making a shoe press belt used in papermaking machines and the process of making it. However, it should be noted that the invention is also applicable to the manufacture of a roll or roll cover used in a papermaking machine. 
     Continuing to refer to  FIG. 1 , the belt may include a base structure or substrate which may be any conventional belt base substrate known in the art, including woven, nonwoven, spiral-link, MD or CD yarn arrays, knitted fabric, extruded mesh, and spiral wound strips of woven and nonwoven materials. These substrates may comprise yarns of any of the varieties used in the production of paper machine clothing, such as monofilament, plied monofilament, multifilament and plied multifilament yarns. These yarns may be obtained by extrusion from any of the polymeric resin materials used for this purpose by those of ordinary skill in the art. Accordingly, resins from the families of polyamide, polyester, polyurethane, polyaramid, polyolefin and other resins suitable for the purpose may be used. 
     The present invention can be, produced by using a device similar to that shown in  FIG. 1 . For the present invention, the device has (A) a mandrel  11  for supporting a belt substrate  10  (or roll cover base where applicable) during production of the belt; (B) means for applying (not shown) a chemically reactive material  12  on the belt substrate  10 ; (C) means for depositing  14  a second material  16  onto the belt substrate  10  to form a pattern. For example, material  16  may be elastomer ribbons placed so as to form grooves therebetween; (C) means for mounting (not shown) the depositing means  14  for movement in at least one direction relative to the surface of the belt substrate  10 ; and (D) means to control (not shown) the movements and to control the depositing of the second material  16  from the depositing means  14 . 
     In the example of the present invention illustrated in  FIG. 1 , a belt forming mandrel  11  is provided. The belt substrate  10  can and usually does have at least a partial impregnation of resin already. The inside surface (that is, the surface against the mandrel  11 ) also has a smooth layer of resin applied by any means known in the art. Initially, a thin film of chemically reactive elastomeric material  12  is placed on the belt substrate  10  to create a chemical bond between the substrate  10  and the second material  16  to be deposited. In this connection, the thin layer  12  must be chemically reactive for the time which is required to apply the second material  16 . With the embodiment shown in  FIG. 1 , this second material is a liquid elastomeric ribbon stream  16 . To deposit this ribbon stream  16 , a chemical mixing head  14  containing the elastomeric material is so angled and controlled to traverse the width of the belt substrate  10 . In this way, each revolution of the mandrel leaves a ribbon deposition of raised land areas with grooves on either side. That is, the placement of the ribbons  16  is used to create the grooves.  FIG. 2  shows the distribution of the small liquid elastomer ribbons which nestle next to each other to form the lands  20  and the shaped grooves  22 . Advantageously, the elastomer is engineered so that it turns from a liquid to a solid in a sufficiently short time (i.e., seconds), thus allowing the ribbon of material to retain its shape. The resulting ribbon laid surface  24  is uniform and smooth without cuts or cracks. 
     It should be understood that the mixing head  14  shown in  FIG. 1  may have either one port or multiple ports. However, a mixing head  14  having multiple ports is preferred. In this connection, it is noted that the number of ports and dimensions thereof, and the amount of material being applied determine the size and shape of the ribbons  16 . It is further noted that the greater the surface speed of the belt substrate  10 , the greater the amount of material must be pumped through the ports. In this connection, controlling precisely the traverse speed of the mixing head  14  is very important, since the ribbon lay must match each previous pass. It should be further understood that the weld lines (i.e., where the respective ribbons start and end) should also match when making the ribbon pattern. 
     It is evident from this disclosure that a superior grooved belt or surface roll can be produced using the aforedescribed method. In this way, the direct deposition of the ribbons to produce the grooves eliminates the problems caused by the machining of grooves as practiced in the prior art. More specifically, the present invention uses the ribbons&#39; placement to create the grooves. The resulting ribbon laid surface is uniform and smooth without cuts and cracks that lead to delamination of the belt or roll surface. 
     Further, by controlling the mixing head, a relatively greater amount of material (or lesser amount, as the case may be) may be applied to the desired region of the belt or roll surface in a controlled manner in a controlled geometry in three planes (x, y and z). Where applicable, this permits the formation of, for example, a crown formed as part of a roll cover, or the formation of other variations in the diameter of the surface along the cross machine direction. 
     It is noted that the present invention differs from the aforementioned U.S. Pat. No. 5,171,389 in that the present invention specifies first placing a chemically reactive layer  34  (see  FIG. 3B ) onto the belt surface prior to depositing the elastomeric ribbon stream, whereas the &#39;389 patent instead mentions merely preapplying an adhesive. In addition, while both the &#39;389 patent and U.S. Pat. No. 5,208,087 (Stigberg) specify strips  30  having a groove already formed therein ( FIG. 3A ), the present invention instead uses the ribbons&#39;  32  placement or gelling time to create the groove ( FIG. 3B ). This is a major distinguishing feature. Other distinctions will be apparent to those skilled in the art. 
     Although preferred embodiments have been disclosed and described in detail herein, their scope should not be limited thereby rather their scope should be determined by that of the appended claims.