Patent Publication Number: US-7588663-B2

Title: Multiple mode headbox

Description:
BACKGROUND OF THE INVENTION 
     In the manufacture of paper sheets, including creped tissue paper, a headbox is used to deposit the papermaking stock onto a forming wire, where the stock is partially dewatered to form a paper web. While headboxes are well known in the art, a problem heretofore has been the inability to make very uniform sheets utilizing both high consistency and low consistency approach flows in a single headbox. As such, a need exists for a headbox that incorporates functionality to use both high consistency and low consistency flows to make uniform basis weight sheets. 
     SUMMARY OF THE INVENTION 
     Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through the practice of the invention. 
     The present disclosure is directed toward a multiple mode headbox which includes a support surface, two or more chambers, and an adjustable roof. The chambers include a plurality of nozzles, the nozzles being adapted to optionally supply papermaking fibers to the support surface. The adjustable roof is positioned to adjust over a range of movement such that it defines a forming zone between the support surface and at least one chamber in a first mode and between the support surface and at least one different chamber in a second mode. 
     In certain embodiments, the headbox also may include one or more distributors connected to each chamber, each distributor including pulp fibers, staple fibers, and mixtures thereof. The support surface may define apertures in communication with one or more vacuum boxes. The adjustable roof may define a forming zone between the support surface and one chamber. The forming zone may be suitable for forming a high consistency wood pulp sheet. The adjustable roof may define a forming zone between the support surface and at least two chambers in which the forming zone may be suitable for forming a low consistency long fiber sheet. The range of movement of the adjustable roof may be controlled by a controller. The adjustable roof may be positioned in a first planar region in the first mode and in a second planar region in the second mode. 
     In another exemplary disclosure, a multiple mode headbox is disclosed which includes a support surface, a first chamber and a second chamber, and an adjustable roof. Each chamber includes a plurality of nozzles, the nozzles being adapted to optionally supply papermaking fibers to the support surface. The adjustable roof is positioned to adjust over a range of movement such that a first mode defines a forming zone between the support surface, the first chamber, and the second chamber, and a second mode defines a forming zone between the support surface and the second chamber. 
     In still another exemplary embodiment of the present disclosure, a process for forming a web is disclosed which includes providing a headbox comprising a support surface, a first chamber, a second chamber, and an adjustable roof. The first chamber and the second chamber each include a plurality of nozzles, the nozzles being adapted to optionally supply papermaking fibers to the support surface. The adjustable roof is positioned to adjust over a range of movement. An aqueous suspension of fibers is supplied to the forming zone. A forming fabric is passed through the forming zone to receive the aqueous suspension of papermaking fibers. The adjustable roof is controlled such that a first mode defines a forming zone between the support surface, the first chamber, and the second chamber, and a second mode defines a forming zone between the support surface and the second chamber. 
     Other features and aspects of the present disclosure are discussed in greater detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present disclosure, including the best mode thereof to one of ordinary skill in the art, is set forth more particularly in the specification, including reference to the accompanying Figures in which: 
         FIG. 1A  represents one embodiment of a headbox for making paper webs in accordance with one embodiment of the present disclosure; 
         FIG. 1B  is represents the embodiment illustrated in  FIG. 1A  with the roof of the headbox in an alternate position in accordance with one embodiment of the present disclosure; 
         FIG. 2A  represents a perspective view of the headbox of  FIG. 1A  in accordance with one embodiment of the present disclosure; and 
         FIG. 2B  is represents a perspective view of the headbox of  FIG. 1B  in accordance with one embodiment of the present disclosure. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present disclosure. 
     DETAILED DESCRIPTION 
     It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present disclosure, which broader aspects are embodied in the exemplary construction. 
     The invention will now be described in greater detail with reference to FIGS.  1 A, 1 B,  2 A, and  2 B which depict one embodiment of a multiple mode headbox  10  according to the present disclosure. As described in more detail as follows, a headbox of the present disclosure incorporates functionality to allow for production of both high consistency and low consistency paper sheets. 
     In this regard, the term “paper” is used herein to broadly include writing, printing, wrapping, sanitary, and industrial papers, newsprint, linerboard, tissue, napkins, wipers, towels, or the like. Paper webs can be manufactured using a variety of devices, such as suction breast roll formers, twin wire formers, crescent roll formers, or the like and any such devices can be used in connection with the present disclosure. Conventional papermaking apparatuses and operations as would be known in the art can be used with respect to the stock preparation, forming fabrics, web transfers, creping, drying and the like. Such conventional apparatuses and processes are well known to those skilled in the art and need not be discussed or illustrated in detail herein for an appreciation and understanding of the present invention. 
       FIGS. 1A ,  1 B,  2 A, and  2 B depict a headbox  10  for making a paper web from an aqueous suspension of papermaking fibers. The headbox  10  includes two chambers  22  that each have a plurality of nozzles  24 . The nozzles  24  deposit the aqueous suspension of papermaking fibers  26  onto the surface of a forming fabric  12  in a forming zone  14 . The forming fabric  12  forms an endless loop traveling between the headbox in the direction of arrow  100 . The forming process allows partial dewatering of a newly-formed paper web to varying consistencies. 
     The headbox  10  includes a support surface  16  that defines a plurality of apertures  18 . The apertures  18  can open to one or more vacuum boxes  20  located within the headbox  10  beneath the support surface  16  and operatively connected to a vacuum source. The vacuum box  20  provides a controlled amount of vacuum in the forming zone  14 . The vacuum box  20  can include section dividers that divide the vacuum box  20  into multiple sections. 
     The headbox  10  receives a suspension of papermaking fibers through one or more distributors  28  operatively connected to the one or more chambers  22 . Each distributor  28  can provide one or more types of fibers. Many fiber types may be used for the present disclosure including hardwood or softwoods, straw, flax, milkweed seed floss fibers, abaca, hemp, kenaf, bagasse, cotton, reed, and the like. All known papermaking fibers may be used, including bleached and unbleached fibers, fibers of natural origin (including wood fiber and other cellulosic fibers, cellulose derivatives, and chemically stiffened or crosslinked fibers) or synthetic fibers (synthetic papermaking fibers include certain forms of fibers made from polypropylene, acrylic, aramids, acetates, and the like), virgin and recovered or recycled fibers, hardwood and softwood, and fibers that have been mechanically pulped (e.g., groundwood), chemically pulped (including but not limited to the kraft and sulfite pulping processes), thermomechanically pulped, chemithermomechanically pulped, and the like. Mixtures of any subset of the above mentioned or related fiber classes may be used. As described previously, the nozzles  24  deposit the aqueous suspension of papermaking fibers  26  onto the surface of a forming fabric  12  in a forming zone  14 . 
     The fibers can be prepared in a multiplicity of ways known to be advantageous in the art. Useful methods of preparing fibers include dispersion to impart curl and improved drying properties, such as disclosed in U.S. Pat. No. 5,348,620 issued Sep. 20, 1994 and U.S. Pat. No. 5,501,768 issued Mar. 26, 1996, both to M. A. Hermans et al. and U.S. Pat. No. 5,656,132 issued Aug. 12, 1997 to Farrington, Jr. et al.; which are incorporated herein by reference. 
     The headbox  10  also includes an adjustable roof  30  having a proximal edge  32  and an opposite distal edge  34 . The adjustable roof  30  is configured to adjust over a range of movement. In this regard, the proximal edge  32  is connected to a chamber  22  such that the adjustable roof  30  defines a forming zone  14  between the support surface  16  and the chamber  22  to which the proximal edge  32  is connected. The adjustable roof  30  can be connected to the chamber by any method as would be known in the art including locking pins or the like. The sealing of the proximal edge  32  of the adjustable roof  30  can be accomplished by pressure pushing a sliding seal  36  against the chamber  22  to which the adjustable roof  30  is to be connected. The sliding seal  36  can be any material as would be known in the art so long as it serves to effectively seal the connection between the proximal edge  32  and the chamber  22 . The adjustable roof  30  can also move by any method as would be known in the art including mechanical devices, hydraulics, pneumatics or the like. The movements of the adjustable roof  30  can be controlled by a computer controller such as a programmable logic controller or the like. 
     It has been determined that the adjustable roof as described herein allows a single headbox the functionality to operate in multiple modes. For example, with reference to  FIGS. 1A and 2A , a headbox is depicted in a low consistency mode in which the complete headbox is utilized to form long fiber sheets. The adjustable roof  30  is situated such that both chambers are enclosed in the forming zone  14  and the long forming distance results in low consistency sheets being formed. Referring to  FIGS. 1B and 2B , the adjustable roof  30  is positioned such that only one chamber is enclosed in the forming zone  14 , and as a result, this arrangement favors the formation of a high consistency sheet being formed. In this regard, the terms low consistency and high consistency refer to the consistency of sheet being formed as would be generally understood by one of ordinary skill in the art. 
     As depicted in  FIGS. 1A ,  1 B,  2 A, and  2 B, the adjustable roof is positioned in a first planar region in the first mode and in a second planar region in the second mode. 
     The adjustable roof  30  can be straight, articulated or somewhat curved, with the distal edge  34  in close proximity to the support surface  16 . For instance, the adjustable roof  30  can have a hinge point that allows the angle of the adjustable roof  30  to vary so as to allow control of the distance between the adjustable roof  30  and the support surface  16 . The forming zone  14  is located between the adjustable roof  30  and the support surface  16 . The distal edge  34  of the adjustable roof  30  may ride on the web as it is formed. 
     Under normal conditions, the expected contact between the adjustable roof  30  and the formed sheet operates to seal the vacuum box  20 . Alternatively, the distal edge  34  of the adjustable roof may be spaced from the forming fabric, such as from about 0.8 to about 3 millimeters. 
     The length of the adjustable roof  30 , measured between the proximal edge  32  and distal edges  34 , is fixed. In some embodiments, the distance can be adjustable. For a roof of fixed length, the distal edge  34  of the roof after the stock has been dewatered may ride on the surface of the sheet, depending on the length of the forming zone required for that particular set of forming conditions. 
     In some embodiments, the adjustable roof  30  is formed from a rigid material having adequate durability and strength to operate in a commercial environment under the loads present. However, the adjustable roof  30  can also be formed from flexible materials. Suitable materials for forming the adjustable roof  30  include LEXAN (Polycarbonate, General Electric, Pittsfield, Mass.), glass or carbon-fiber reinforced epoxy resins, other polycarbonate materials, fiberglass or other composites, stainless steel or the like, where machining or fiber orientation can achieve the correct rigidity. 
     To improve web formation by creating turbulence within the suspension of papermaking fibers, the adjustable roof  30  may include turbulence generating features disposed on a surface of the adjustable roof  30  facing the forming zone  14 . The turbulence generating features may include, for example, a plurality of projections extending outward from the inner surface of the adjustable roof  30  that are designed to provide micro-turbulence to the fluid flow near the roof surface, but without disturbing the sheet. 
     Another aspect of the invention concerns a method of forming a paper web. In one embodiment, the method includes providing a headbox that has a support surface, a first chamber, a second chamber, and an adjustable roof. The first chamber and said second chamber of the headbox each have a plurality of nozzles adapted to optionally supply papermaking fibers to the support surface and the adjustable roof is positioned to adjust over a range of movement. An aqueous suspension of fibers is supplied to the forming zone and a forming fabric is passed through the forming zone to receive the aqueous suspension of papermaking fibers. The adjustable roof is controlled such that a first mode defines a forming zone between the support surface, the first chamber, and the second chamber, and a second mode defines a forming zone between the support surface and one of the first or second chambers. 
     The web is formed on a forming fabric that travels through the forming zone between the adjustable roof and the support surface. The forming fabric is sandwiched between the support surface and a distal edge of the adjustable roof, with the forming fabric and the aqueous suspension generally traveling at the same speed. The term “forming fabric” refers to an endless mesh belt adapted to drain water away from the papermaking fibers and provide support as the web is being formed. Suitable forming fabrics comprise synthetic fabrics and are available from fabric suppliers such as Lindsay Wire and Albany International. 
     In particular embodiments, the method also includes the step of controlling the velocity of the aqueous suspension and the level of vacuum to achieve removal of water from the forming zone. The aqueous suspension that is under the adjustable roof is desirably under a slight positive pressure and thus positive pressure with respect to atmospheric pressure. The positive pressure will force water from the sheet through the fabric. The fluid will drain more slowly as the sheet builds on the fabric and resistance is increased. 
     There are a number of variables that will increase the length and/or time for the formation to take place under the adjustable roof. These include basis weight, speed, furnish, and consistency. The drainage of free water from the aqueous suspension should be completed before reaching the distal edge of the adjustable roof. To achieve complete drainage of free water, the operator can decrease the flow rate of the aqueous suspension, increase the vacuum, or change the length of the vacuum zone under the forming fabric. 
     The operating parameters of headbox such as vacuum levels, headbox orientation and other operating parameters such as the fan pump speed can be adjusted as will be recognized by those skilled in the art in order to achieve the desired sheet properties. The fiber type, fiber consistency, and other factors will need to be taken into consideration, but by the nature of the invention, are less critical to operation with improved formation. 
     These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.