Patent Publication Number: US-6712941-B2

Title: Forming board for papermaking machine with adjustable blades

Description:
FIELD OF THE INVENTION 
     This invention relates generally to papermaking, and more particularly to equipment employed with papermaking machines. 
     BACKGROUND OF THE INVENTION 
     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 rollers. 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 gravity alone or with assistance from one or more suction boxes located on the lower surface (i.e., the “machine side”) of the upper run of the fabric. 
     After leaving the forming section, the paper web is transferred to a press section of the paper machine, in which it is passed through the nips of one or more pairs of pressure rollers covered with another fabric, typically referred to as a “press felt.” Pressure from the rollers removes additional moisture from the web; the moisture removal is often enhanced by the presence of a “batt” layer on the press felt. The paper is then conveyed to a drier section for further moisture removal. After drying, the paper is ready for secondary processing and packaging. 
     The paper stock is fed onto the forming fabric from a device known as the “headbox”, which applies a jet of stock onto the forming fabric. A “breast roll” is located beneath the headbox and serves as the upstreammost roll over which the forming fabric is conveyed. In many paper machines, and particularly more modem machines, a “forming board” is located just downstream of the breast roll, typically in the area beneath the portion of the forming fabric that receives the jet of paper stock. In this location, the forming board can support the forming fabric against deflection due to the force of the jet, and can provide well-defined drainage for the paper stock. 
     A typical forming board includes a series of blades (usually formed of ceramic or, more recently, polyethylene) that extend substantially parallel to one another across the width of the fabric and that are separated by gaps that extend in the cross-machine direction. The degree of open area provided by the gaps can impact the amount of drainage occurring at the forming board. Many forming boards also include a lead blade with a wedge-shaped “nose” on its leading edge that serves to “doctor” water beneath the lead blade. 
     Because the configuration of the forming board can impact drainage, which, in turn, can impact paper quality, the sizes of the blades and the spacing therebetween should be considered carefully during design and installation. In fact, in many paper mills, the blade positions are adjusted for each different type of paper made on the machine. Also, often the paper mill will match the forming board blade size and spacing to match that of other foil units that are positioned downstream of the forming board, and it is typically desirable to position the blades such that the gaps between blades are of uniform width. With some forming boards, the degree of open area is altered by installing blades of different widths (which can be somewhat laborious, particularly if numerous adjustments are required to attain acceptable paper machine performance). For other forming boards, spacing between blades can be adjusted manually, with each blade being repositioned and fixed into place. However, this type of adjustment can not only be time-consuming, but also may result in the spacing between blades being non-uniform. Thus, it would be desirable to provide a forming board having a configuration that would enable the open area to be adjusted without the installation of replacement blades and that would provide substantially uniform spacing between the blades automatically. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a forming board for a papermaking machine. In a first embodiment, the forming board comprises: a support; a transversely-extending lead blade attached to the support, the lead blade having an upper surface; a plurality of transversely-extending trailing blades, each of the trailing blades having an upper surface, a leading edge and a trailing edge; a mounting unit for each of the plurality of trailing blades, the mounting unit being attached to a respective trailing blade and to the support such that the upper surfaces of the lead blade and the trailing blades are substantially coplanar and such that gaps are defined between the trailing edges and leading edges of adjacent blades, the gaps being of substantially uniform width; and a drive unit attached to the mounting unit and to the support, the drive unit being configured to drive the trailing blades simultaneously to different longitudinal positions relative to the support, wherein the widths of the gaps vary but remain substantially uniform for each different longitudinal position. In this configuration, the gaps between the blades of the forming board can be maintained at substantially uniform width as the positions of the blades are adjusted for different paper grades. 
     In certain embodiments, the drive unit comprises a longitudinally extending positioning shaft, the positioning shaft being rotatably mounted to the support, and each trailing blade is mounted to the support via a mounting unit that engages the positioning shaft. In some of such embodiments, the positioning shaft includes a plurality of threaded sections, each of the threaded sections having a different thread pitch, and each mounting unit includes a threaded bore that is complimentary to one of the threaded sections of the positioning shaft. 
     As a second aspect, the present invention is directed to a forming board for a papermaking machine comprising papermaking machine, comprising: a support; a transversely-extending lead blade fixed to the support, the lead blade having an upper surface; a plurality of transversely-extending trailing blades, each of the trailing blades having an upper surface, a leading edge and a trailing edge, the blades being attached to the support such that the upper surfaces of the lead blade and the trailing blades are substantially coplanar and such that gaps are defined between the trailing edges and leading edges of adjacent blades; and a drive unit attached to the support and with the trailing blades, the drive unit being configured to drive the trailing blades simultaneously between a first position, in which the each of the gaps has a first width, the first widths of each of the gaps being substantially uniform, and a second position, in which each of the gaps has a second width that is different from the first width, the second widths of the gaps being substantially uniform. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a partial side view of a papermaking machine with a forming board of the present invention. 
     FIG. 2 is an enlarged side view of the forming board of FIG. 1, with the trailing blades in a first position in which the blades are separated by relatively narrow gaps. 
     FIG. 3 is an enlarged side view of the forming board of FIG. 1, with the trailing blades in a second position, in which the blades are separated by relatively wide gaps. 
     FIG. 4 is a partial cutaway top view of the forming board of FIG. 1 with the trailing blades removed. 
     FIG. 5 is an enlarged side view of the shaft of the forming board of FIG.  1 . 
     FIG. 6 is a greatly enlarged partial side view of the shaft and mounting portion of a trailing blade shown in FIG. 5 taken along lines  6 — 6  thereof. 
     FIG. 7 is a greatly enlarged partial side view of the shaft and mounting portion of a trailing blade shown in FIG. 5 taken along lines  7 — 7  thereof. 
     FIG. 8 is a greatly enlarged partial side view of the shaft and mounting portion of a trailing blade shown in FIG. 5 taken along lines  8 — 8  thereof. 
     FIG. 9 is a greatly enlarged partial side view of the shaft and mounting portion of a trailing blade shown in FIG. 5 taken along lines  9 — 9  thereof. 
     FIG. 10 is an enlarged end view of a lateral edge of the forming board of FIG. 1 supported by an end bulkhead. 
     FIG. 11 is an enlarged partial end view of an internal bulkhead for supporting the forming board of FIG.  1 . 
     FIG. 12 is a top view of the internal bulkhead of FIG.  11 . 
     FIG. 13 is a side view of the internal bulkhead of FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more particularly hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The invention, however, be embodied in many different forms and is not limited to the embodiments set forth herein; rather, these embodiments are provided so that the disclosure will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like components throughout The dimensions and thicknesses for some components and layers may be exaggerated for clarity. 
     The present invention relates to a fourdrinier papermaking machine, in which paper stock is dispensed and conveyed along a processing path. In the description of the present invention that follows, certain terms are employed to refer to the positional relationship of certain structures relative to other structures. As used herein, the term “forward” and derivatives thereof refer to the general direction paper stock travels as it moves along the machine; this term is intended to be synonymous with the term “downstream”, which is often used in manufacturing environments to indicate that certain material being acted upon has advanced farther along in the manufacturing process than other material. Conversely, the terms “rearward” and “upstream” and derivatives thereof refer to the directions opposite, respectively, the forward and downstream directions. Together, the forward and rearward directions comprise the “longitudinal” dimension. As used herein, the terms “outer”, “outward”, “lateral”, and derivatives thereof refer to the direction defined by a vector originating at the longitudinal axis of a given structure and extending horizontally and perpendicularly thereto. Conversely, the terms “inner”, inward”, and derivatives thereof refer to the direction opposite that of the outward direction. Together, the inward and outward directions comprise the “transverse” dimension. 
     In addition, the discussion that follows is directed to a forming board of a paper machine. The present invention is equally applicable to a gravity foil, which is typically positioned just downstream of the forming board. Thus, when the term “forming board” is used herein, it is intended that the term include both forming board units and gravity foil units. 
     Referring now to the figures, a fourdrinier paper machine, designated broadly at  20 , is illustrated in FIG.  1 . The paper machine  20  includes a head box  24  that dispenses paper stock through an outlet  25  (known in the industry as the “slice”). A transversely-extending breast roll  22  is positioned beneath the outlet  25 . An endless forming fabric  26  extends longitudinally and engages the breast roll  22  at its upstreammost end. A forming board  28  is positioned below the upper surface of the forming fabric  26  just downstream of the breast roll  22 . The forming board  28  includes a lead blade  74  and a plurality of trailing blades  84  (four trailing blades  84  are illustrated herein) that are disposed transversely and support the upper run of the forming fabric  28 . Paper stock P is dispensed from the head box  24  onto the upper surface of the forming fabric  26 , which travels around the breast roll  22  and over the blades  74 ,  84  of the forming board  28  as indicated by the arrows in FIG.  1 . 
     Referring again to FIG.  1  and also to FIGS. 2-4, the forming board  28  includes a support  30  that is fixed relative to the head box  24  and breast roll  22 . The support  30  provides mounting points for the components of the forming board  28  and can take a variety of configurations, one of which is best illustrated in FIGS. 1,  2  and  4 . The support  30  shown therein includes an upstream mounting portion  30   a , an intermediate mounting portion  30   b , a downstream mounting portion  30   c , internal bulkheads  40  (two of which are shown in FIG.  4  and one of which is shown in FIGS.  11 - 13 ), end bulkheads  42  (one of which is shown in FIGS.  4  and  10 ), and a plurality of tee bar support assemblies  44 . The upstream mounting portion  30   a  provides a mounting location for the lead blade  74 , each of the intermediate and downstream mounting portions  30   b ,  30   c  defines a mounting platform for a portion of a blade positioning assembly  90 , and the internal and end bulkheads  40 ,  42  provide mounting locations for the trailing blades  84 . These components are described in greater detail below. 
     Referring to FIGS. 11-13, in which an exemplary internal bulkhead  40  is shown, each internal bulkhead  40  includes a longitudinally-extending, vertically-projecting upper end  41  upon which a tee bar support assembly  44  is mounted. The tee bar support assembly  44  includes a base member  46  that is fixed (typically welded) to the upper end  41  and extends longitudinally. A slide plate  50  (typically formed of TEFLON® polymer or another low friction material) extends longitudinally and rests atop the base member  46 . A plurality of transversely-extending tee bar supports  52  rest upon the upper surface of the slide plate  50  at spaced intervals, with their transverse edges extending beyond the transverse edges of the slide plate  50 . 
     The tee bar supports  52  are positioned and spaced such that each aligns along a transverse axis with tee bar supports  52  mounted on other internal bulkheads  40  (see FIGS.  4  and  11 - 13 ). One of four trailing blade support bars  80  overlies each set of aligned tee bar supports  52  and extends transversely to span the distance between the end bulkheads  42 . The trailing blade support bars  80  are held in place with pairs of capture members  48   a ,  48   b . The capture members  48   a ,  48   b  are fastened to the underside of the tee bar supports  52  with bolts  51  that are inserted through the capture members  48   a ,  48   b , into and through the tee bar supports  52 , and into the trailing blade support bars  80 . Each of the capture members  48   a ,  48   b  has a small lip  49  that underlies the underside of the slide plate  50 , such that the slide plate  50  is clamped between the capture members  48   a ,  48   b  and the tee bar support members  52 , but is free to slide thereon upon loosening of the bolts  51 . 
     Referring now to FIG. 10, each end bulkhead  42  supports the ends of the trailing blade support bars  80  through an end slide assembly  54 . The end slide assembly  54  includes a slide plate  58  that extends longitudinally and overhangs the end bulkhead  42  inwardly. The trailing blade support bars  80  rest upon the upper surface of the slide plate  58  and are clamped thereto by capture members  56  bolted via bolts  57  to the underside of the trailing blade support bars  80 . 
     Referring now back to FIGS. 1-3, the trailing blades  84  (usually between 2 and 7 are employed in a paper machine, and herein four are illustrated) are attached to the support  30  via a series of trailing blade capture members  82 , each of which is fixed to the upper surface of each trailing blade support bar  80 . The trailing blade capture member  82  has an upwardly-extending T-shaped cross-sectional projection  83 . The trailing blades  84  include a complimentary T-shaped cavity that receives the projection  83  such that the trailing blades  84  can be slid transversely onto the trailing blade capture member  83 . Gaps  86  are formed between the trailing and leading edges of adjacent blades. The trailing blades  84  are typically between about 2.5 and 4.0 inches in width, and the gaps  86  are typically between about 0.75 and 1.75 inches. 
     Referring again to FIG. 1, the lead blade  74  is attached to the support  30  via a transversely-extending lead blade support bar  70 , which rests on the upstream mounting portion  30   a  of the support  30 . Two capture members  72 , each with an upwardly-extending T-shaped projection  73 , are positioned above and fixed to the support bar  70 . The lead blade  74  can be slid transversely into place on the capture member  72  in much the same manner as the trailing blades  84  are attached to the capture members  82 . 
     Referring again to FIG.  1  and also to FIG. 4, the positioning assembly  90  includes a transversely-extending drive shaft  92 . The drive shaft  92  is rotatably mounted in drive shaft bearings  94  that are fixed to the intermediate mounting portion  30   b  of the support  30 . The drive shaft  92  has a worm portion  96 . A positioning shaft  100  extends longitudinally and is mounted in two positioning shaft bearings  102 , one of which is fixed to a vertical panel  30   d  between the upstream and intermediate mounting portions  30   a ,  30   b  via a bracket  103 , and the other of which is fixed to the downstream mounting portion  30   c  via a bracket  105 . The positioning shaft  100  has a toothed portion  98  that engages and is driven by the worm portion  96  of the drive shaft  92 . In addition, the positioning shaft  100  has four threaded portions  104   a ,  104   b ,  104   c ,  104   d  (see FIGS.  6 - 9 ). Each of the threaded portions  104   a ,  104   b ,  104   c ,  104   d  resides directly beneath a respective trailing blade  84 . A threaded positioning nut  112  or other mounting unit depends from the support bar  82  of each of the trailing blades  84  and receives a respective threaded portion  104   a ,  104   b ,  104   c ,  104   d.    
     As shown in FIGS. 6-9, the thread pitch on each of the threaded portions  104   a ,  104   b ,  104   c ,  104   d  differs (and, in turn, the thread pitch of each positioning nut  112  matches that of its mating threaded portion), with the result that, as the positioning shaft  100  rotates within its bearings  102 , the positioning nuts are driven longitudinally different longitudinal distances. Consequently, the trailing blades  84  move different longitudinal distances. The thread pitches of the threaded portions  104   a ,  104   b ,  104   c ,  104   d  are selected so that, as the trailing blades  84  move, the gaps  86  between the adjacent edges of the trailing blades  84  widen or narrow, but remain substantially uniform with each other. As an example, the diameters and pitches of the threaded portions  104   a ,  104   b ,  104   c ,  104   d  can be selected as shown in Table 1 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Threaded Portion # 
                 Shaft Diameter (in) 
                 Thread Pitch (threads/in) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 104a 
                 0.75 
                 32 
               
               
                 104b 
                 1.00 
                 16 
               
               
                 104c 
                 1.00 
                 10.667 
               
               
                 104d 
                 0.75 
                 8 
               
               
                   
               
            
           
         
       
     
     Those skilled in this art will recognize that other combinations of shaft diameter and thread pitch will also enable the gaps between the trailing blades  84  to remain substantially uniform as they change in width. 
     Adjustment of the trailing blades  84  is achieved by rotating the drive shaft  92 . This can be accomplished with a drive motor (not shown) or by manual rotation of the drive shaft  92  with a handle (also not shown). Rotation of the drive shaft  92  causes the worm portion  96  to rotate. Because the toothed portion  98  of the positioning shaft  100  engages the worm portion  96 , the positioning shaft  100  rotates also. Rotation of the positioning shaft  100  and its threaded portions  104   a ,  104   b ,  104   c ,  104   d  drives the trailing blades  84  to different longitudinal positions, but the gaps  86  remain substantially uniform with each other. The trailing blades  84  are free to move longitudinally relative to the internal and end bulkheads  40 ,  42  due to the sliding interaction between the slide plates  50 ,  58  and, respectively, the tee bar supports  52 ,  60  and their capture members  48   a ,  48   b ,  56 . 
     Those skilled in this art will appreciate that other forming board configurations may also be suitable for use with the present invention. For example, different numbers of trailing blades may be employed; they may have different widths, or the gaps therebetween may have different widths. Further, the support on which the forming board is mounted may have a different configuration, depending on the configuration of the blades. The positioning unit may also take a different configuration; for example, the positioning shaft may be driven directly with a crank or other rotating device, or the drive shaft may be coupled to the positioning shaft through other design techniques. Also, the positioning unit may be configured such that multiple positioning shafts are used in order maintain uniformity of gaps between the trailing blades. The configuration of the tee bar assembly may also differ, although the unit should support the trailing blades from beneath and allow them to be driven longitudinally. 
     The foregoing embodiments are illustrative of the present invention, and are not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein.