Abstract:
The present invention relates to an assembly of forming elements which together define in a papermaking apparatus a discontinuous supporting surface for a papermaking suspension to permit drainage and micro-turbulence to be accurately controlled, and to the papermaking apparatus per se.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to an assembly of forming elements which together define in a papermaking apparatus a discontinuous supporting surface for a papermaking suspension to permit drainage and micro-turbulence to be accurately controlled, and to the papermaking apparatus per se.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the papermaking industry, various forming elements are deployed to promote the drainage of water from paper stock in its transformation from a papermaking suspension (or slurry) of fibres, water and chemicals (eg fillers) into a self-supporting web of cellulose fibres commonly referred to as a sheet (ie a sheet of paper or board). De-watering takes place in the forming area at the “wet end” of a papermaking apparatus, a typical one of which is illustrated schematically by way of example in  FIG. 1 . Thus in  FIG. 1 , parallel papermaking wires  1  (or mesh or a belt) move in direction A and are supported from beneath by discrete forming elements which include forming boards  2 , spaced apart foils  3  and low vacuum blades  4 . Suction box covers  5  together with Uhle box covers  8  constitute dewatering elements.  
         [0003]     Crucial to the formation of the sheet of paper (or board) in the forming area is the drainage of the papermaking suspension and the micro-turbulence generated in the papermaking suspension which serves to eliminate agglomeration thereby enhancing the uniformity of the papermaking suspension. The harmonic pitch of the papermaking apparatus is the spacing on the paper table of the forming board, forming foils and gravity foils which together determine the natural harmonics of the wet end of the papermaking apparatus and which is established at the time that the papermaking apparatus is designed to give the desired drainage and micro-turbulence. It can be a disadvantage of conventional papermaking apparatus that the design is specified in accordance with certain grades of paper (or board) and certain types or quality of pulp.  
         [0004]     Referring again to  FIG. 1 , the papermaking suspension is ejected from a flow box or head box (not shown) onto the papermaking wire  1 . Commonly the forming board  2  which is a solid unitary element may do little more than help to direct the papermaking suspension flow onto the moving papermaking wires  1  prior to de-watering. However the forming board  2  may be provided with grooves or slots to generate micro-turbulence. GB-A-2190932 discloses a solid forming board (known commercially as the TURBOFORM™ board) in the surface of which one or more transverse, open-ended slots are provided. The depth of the slots may be varied by an insert to achieve the requisite degree of micro-turbulence in the papermaking suspension whilst permitting limited drainage. However the TURBOFORM™ board is able to take little or no account of the natural harmonic pitch of a papermaking apparatus. Moreover the TURBOFORM™ board is generally of little use in a slow speed papermaking apparatus.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention seeks to improve the versatility of a papermaking apparatus by introducing into the forming area an assembly of forming elements which together define a discontinuous supporting surface for the papermaking suspension. More particularly, the present invention relates to an assembly of forming elements which takes account of and enhances the natural harmonic pitch of the papermaking apparatus to accurately control in the forming area the drainage of and micro-turbulence in the papermaking suspension thereby satisfying a demand from customers for improved paper quality (eg improved fibre and fines dispersal throughout the sheet).  
         [0006]     Thus viewed from one aspect the present invention provides an assembly of forming elements including: 
        a primary blade capable of being positioned adjacent one or more supply means at the wet end of a papermaking apparatus;     a first secondary support blade coupled to a leading face of the primary blade by a first drainage deckle; and     optionally n consecutive additional secondary support blades and n consecutive additional drainage deckles, wherein a trailing face of the first additional secondary support blade is coupled to a leading face of the first secondary support blade by the first additional drainage deckle and a trailing face of the second to n th  additional secondary support blades is coupled respectively to a leading face of the first to n-1 th  additional secondary support blades by the second to n th  additional drainage deckle respectively, wherein n is an integer of one or more, 
 
 whereby the upper surface of the primary blade, the first secondary support blade, the first drainage deckle, the n additional drainage deckles and the n additional secondary support blades together define a discontinuous surface for supporting a papermaking suspension being carried by a carrier from the wet end to an output end of the papermaking apparatus. 
       
 
         [0010]     Viewed from a further aspect the present invention provides a papermaking apparatus capable of making a sheet of paper (or board) from a papermaking suspension, said apparatus comprising:  
         [0011]     one or more supply means for introducing the papermaking suspension into a wet end of the apparatus;  
         [0012]     a carrier for carrying the papermaking suspension from the wet end to an output end of the apparatus; and  
         [0013]     an assembly of forming elements which include: 
        a primary blade positioned adjacent the one or more supply means;     a first secondary support blade coupled to a leading face of the primary blade by a first drainage deckle; and     optionally n consecutive additional secondary support blades and n consecutive additional drainage deckles, wherein a trailing face of the first additional secondary support blade is coupled to a leading face of the first secondary support blade by the first additional drainage deckle and a trailing face of the second to n th  additional secondary support blades is coupled respectively to a leading face of the first to n-1 th  additional secondary support blades by the second to n th  additional drainage deckle respectively, wherein n is an integer of one or more, 
 
 whereby the upper surface of the primary blade, the first secondary support blade, the first drainage deckle, the n additional drainage deckles and the n additional secondary support blades together define a discontinuous surface for supporting the papermaking suspension. 
       
 
         [0017]     It will be apparent that the assembly of forming elements largely making up the forming area of the papermaking apparatus of the invention may be advantageously extended to any desired length to achieve the requisite formation characteristics simply by adding additional secondary support blades and additional drainage deckles (ie by increasing n). Moreover, in sharp contrast to conventional rigid forming boards, the forming elements of the papermaking apparatus of the invention may be assembled into the papermaking apparatus quite straightforwardly to the desired length. To exemplify its improved versatility, the papermaking apparatus may be used with a broader range of paper (or board) grades (eg varying in weight) than has hitherto been possible irrespective of the carrier speed.  
         [0018]     The upper surfaces of the forming elements together present a discontinuous supporting surface (paper table) to the papermaking suspension. This discontinuous surface serves intrinsically to generate micro-turbulence in the papermaking suspension. For this purpose, the profile, thickness and/or relative positioning of the primary blade, the first secondary support blade, the first drainage deckle, the n additional drainage deckles and the n additional secondary support blades may be varied to suit the requirements of the papermaking process. Typically the discontinuous supporting surface is irregularly discontinuous. For example the discontinuous supporting surface may be stepped (eg irregularly stepped).  
         [0019]     Preferably the upper surfaces of the primary blade, the first secondary support blade and the n consecutive additional secondary support blades are substantially coplanar at a first height and the upper surface of at least one (preferably each) of the first drainage deckle and n consecutive additional drainage deckles is at a height different from the first height. Particularly preferably the upper surfaces of the primary blade, the first secondary support blade and the n consecutive additional secondary support blades are substantially coplanar at a first height and the upper surface of each of the first drainage deckle and n consecutive additional drainage deckles is at a height different from the first height whereby to define a discontinuous surface which is stepped. More preferably the upper surfaces of the first drainage deckle and n consecutive additional drainage deckles are substantially coplanar at heights different from each other and from the first height whereby to define a discontinuous surface which is substantially irregularly stepped. Alternatively (if desired) the upper surfaces of the first drainage deckle and n consecutive additional drainage deckles are substantially coplanar at a common height different from the first height whereby to define a discontinuous surface which is substantially regularly stepped  
         [0020]     Alternatively or additionally the upper surfaces of at least one of (preferably each of) the first drainage deckle and n consecutive additional drainage deckles is angled (eg angled at a height different from the first height). Typically the upper surface is angled downwardly from trailing to leading edges of the upper surface. The difference between the first and second height and any degree of angling may be judiciously chosen to generate the desired micro-turbulence into the papermaking suspension. For example, each of the first drainage deckle and n consecutive additional drainage deckles may be angled at a different angle to fine tune the micro-turbulence. Typically the angle is in the range 1-4° from the horizontal.  
         [0021]     Additionally or alternatively at least one (preferably more than one eg each) of the first drainage deckle and n consecutive additional drainage deckles generates micro-turbulence in the papermaking suspension by extrinsic means. In a preferred embodiment, at least one (preferably more than one eg each) of the first drainage deckle and n additional drainage deckles is adapted to transmit a means for generating micro-turbulence in the papermaking suspension. Preferably the means for generating micro-turbulence is sourced externally and may be a physical means or electromagnetic radiation. For example, the means for generating micro-turbulence may be pulses of fluid (eg gas or liquid such as water) or vibrations (eg sonic vibrations).  
         [0022]     Preferably the upper surface of at least one (preferably more than one eg each) of the first drainage deckle and n consecutive additional drainage deckles comprises a groove adapted to transmit fluid (eg water) onto its upper surface. Typically the groove is a closed end groove (ie a groove extending downwardly from and transversely along the upper surface remote from its opposing edges). The transverse end walls of the groove may be curved (eg semicircular).  
         [0023]     Preferably the groove is adapted to transmit pulses of fluid (eg water) onto its upper surface. Preferably to an end wall of at least one (preferably more than one eg each) of the first drainage deckle and n consecutive additional drainage deckles extends a transverse slot (eg a transverse substantially circular slot) outwardly from a transverse end wall of the groove. Particularly preferably to a first and second end wall of at least one (preferably more than one eg all) of the first drainage deckle and n consecutive additional drainage deckles extends respectively a first and a second transverse slot (eg a transverse substantially circular slot) outwardly from a first and second transverse end wall of the groove respectively. The or each transverse slot is in fluid communication with the groove and therefore with the upper surface so that pulses of fluid (eg water) may be transmitted therethrough onto the upper surface. The depth of the groove, the nature of the means for generating micro-turbulence and the manner in which the means for generating micro-turbulence is applied may be judiciously chosen to refine the micro-turbulence generated intrinsically in the papermaking suspension (eg by dampening or amplifying the micro-turbulence imparted by the natural harmonic pitch of the forming elements) which in turn assists fibre formation and dispersal of fines throughout the sheet (ie improves sheet quality).  
         [0024]     The first drainage deckle and n additional drainage deckles may couple the leading and trailing faces of a first and second consecutive forming element in any convenient manner. Preferably the leading and trailing faces of the drainage deckle engage the first and second consecutive forming elements through male and female portions (eg interlocking male and female portions) of any convenient coupling arrangement. The male and female portions may be a tongue and groove or a dovetail-type arrangement. Preferably the male and female portions are a tongue and groove. More preferably the trailing face of the drainage deckle bears a tongue adapted to engage a complementarily shaped groove on the leading face of the first forming element and the leading face of the drainage deckle bears a groove adapted to be engaged by a complementarily shaped tongue on the trailing face of the second forming element.  
         [0025]     The thickness and/or profile of the first drainage deckle and n additional drainage deckles may be different but are preferably largely the same and may (in practice) be judiciously chosen to accurately control drainage of and micro-turbulence in the papermaking suspension as discussed above. Typically the trailing and leading faces of the drainage deckle are substantially perpendicular to the upper and lower surfaces. The upper edge of the leading face typically comprises a shoulder and the upper edge of the trailing face is chamfered.  
         [0026]     The primary blade may be positioned immediately after the one or more supply means and support the carrier substantially at the point where (in use) the papermaking suspension flows onto the carrier. Typically the trailing face of the primary blade tapers downwardly and forwardly and the leading face is substantially non-tapered (ie substantially perpendicular to the upper and lower surfaces) and incorporates the male or (preferably) female portion (eg a groove) of any convenient male/female coupling arrangement (eg a tongue and groove). The upper edge of the leading face typically comprises a shoulder and the upper edge of the trailing face is chamfered. The primary blade is normally (but not necessarily) the same thickness as each of the first and n additional secondary support blades. The lower face may be adapted to enable the primary blade to be mounted on the forming box (eg by incorporating the male or (preferably) female portion of any convenient male/female coupling arrangement such as a dovetail type arrangement or (preferably) T-bars/T-slots).  
         [0027]     The carrier may be a wire (or wires), belt, mesh or other arrangement driven between the wet end and the output end in a conventional manner. The carrier may be at least partly composed of fabric, metal or plastic which may be woven or otherwise manipulated.  
         [0028]     The one or more supply means may be head boxes or flow boxes as desired.  
         [0029]     The first secondary support blade and n optional additional secondary support blades (which may be different but are preferably the same) support the carrier largely in the area where sheet formation takes place (the forming area). Typically the trailing face of the first secondary support blade and n optional additional secondary support blades is substantially perpendicular to the upper and lower surfaces and incorporates the female or (preferably) male portion (eg a tongue) of any convenient male/female coupling arrangement (eg a tongue and groove). The upper edge of the leading face typically comprises a shoulder and the upper edge of the trailing face is chamfered. The first secondary support blade and n optional additional secondary support blades are normally (but not necessarily) the same thickness as the primary blade. The lower face may be adapted to enable the first secondary support blade and n optional additional secondary support blades to be mounted on the forming box (eg by incorporating the male or (preferably) female portion of any convenient male/female coupling arrangement such as a dovetail type arrangement or (preferably) T-bars/T-slots).  
         [0030]     By substituting the forming elements of a conventional papermaking apparatus with the assembly as hereinbefore defined, the natural harmonic pitch of the conventional papermaking apparatus is advantageously enhanced in a controlled manner.  
         [0031]     Viewed from a yet further aspect the present invention provides a method for constructing a papermaking apparatus as hereinbefore defined comprising:  
         [0032]     (a) obtaining a conventional papermaking apparatus comprising one or more conventional forming elements in the forming area;  
         [0033]     (b) substituting at least one (preferably all) of the one or more conventional forming elements with an assembly of forming elements which include: 
        a primary blade positioned adjacent the one or more supply means;     a first secondary support blade coupled to a leading face of the primary blade by a first drainage deckle; and     optionally n consecutive additional secondary support blades and n consecutive additional drainage deckles, wherein a trailing face of the first additional secondary support blade is coupled to a leading face of the first secondary support blade by the first additional drainage deckle and a trailing face of the second to n th  additional secondary support blades is coupled respectively to a leading face of the first to n-1 th  additional secondary support blades by the second to n th  additional drainage deckle respectively, wherein n is an integer of one or more,        
 
         [0037]     whereby the upper surface of the primary blade, the first secondary support blade, the first drainage deckle, the n additional drainage deckles and the n additional secondary support blades together define a discontinuous surface for supporting the papermaking suspension.  
         [0038]     In accordance with an embodiment of the method of the invention, the conventional forming elements include a conventional forming board and the primary blade of the assembly functionally replaces the conventional forming board. The primary blade may be (but is not necessarily) the same width as the forming board and is generally the same length.  
         [0039]     In accordance with an embodiment of the method of the invention, the conventional forming elements include one or more forming foils and the first and n optional additional secondary support blades functionally replace the one or more forming foils. In this embodiment, n will be determined by the user in accordance with the demands of the application.  
         [0040]     In a preferred embodiment of the method of the invention, the forming elements are mounted individually on existing T-bars of the forming box of the conventional papermaking apparatus thereby retaining the harmonic pitch of the conventional papermaking apparatus but refining it accordingly. In contrast, the rather more cumbersome rigid TURBOFORM™ board is mounted in the conventional papermaking apparatus on at least two T-bars simultaneously.  
         [0041]     Viewed from an even yet further aspect the present invention provides a kit of parts comprising one or more of the forming elements selected from the group consisting of a primary blade as hereinbefore defined, a first secondary support blade as hereinbefore defined, n additional secondary support blades as hereinbefore defined and n consecutive additional drainage deckles as hereinbefore defined, said one or more of the forming elements capable of being assembled into an assembly as hereinbefore defined.  
         [0042]     The present invention will now be described in a non-limitative sense with reference to the accompanying Figures in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0043]      FIG. 1  is a side perspective view illustrating the present invention;  
         [0044]      FIG. 2  illustrates schematically an isolated side view of a first embodiment of the assembly of forming elements of the invention;  
         [0045]      FIG. 3  illustrates schematically an isolated side view of a second embodiment of the assembly of forming elements of the invention;  
         [0046]      FIG. 4  illustrates a primary blade;  
         [0047]      FIG. 5  illustrates a secondary blade;  
         [0048]      FIG. 6  illustrates a drainage deckle of the first embodiment;  
         [0049]      FIG. 7  illustrates a drainage deckle of the second embodiment;  
         [0050]      FIG. 8  illustrates a conventional papermaking apparatus in use; and  
         [0051]      FIG. 9  illustrates a papermaking apparatus of the invention in use. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0052]      FIG. 2  illustrates schematically an isolated side view of the assembly of forming elements  1  of a first embodiment of a papermaking apparatus of the invention. The assembly of forming elements  1  includes a primary blade  2  positioned immediately after the one or more supply means (not shown), a first secondary support blade  3 , first and second consecutive additional secondary support blades  4   a  and  4   b , a first drainage deckle  5  and first and second additional drainage deckles  6   a ,  6   b . The assembly of forming elements  1  defines a discontinuous upper surface for supporting the papermaking suspension carried by a papermaking wire  7 .  
         [0053]     The primary blade  2  is illustrated alone in  FIG. 4 . A trailing face  42   a  of the primary blade  2  tapers downwardly and forwardly. A leading face  41   a  of the primary blade  2  is perpendicular to the upper and lower surfaces and is provided with a shoulder  42  at its upper edge. The lower surface incorporates T-shaped slots  49   a ,  49   b  which engage T-shaped bars on the forming box.  
         [0054]     The first secondary support blade  3  and first and second additional secondary support blades  4   a ,  4   b  are the same and are illustrated alone in  FIG. 5 . A trailing face  2  la of the first secondary support blade  3  and first and second additional secondary support blades  4   a ,  4   b  is perpendicular to the upper and lower surfaces and is provided with a chamfer  500  at its upper edge. A leading face  21   b  of the first secondary support blade  3  and first and second additional secondary support blades  4   a ,  4   b  is perpendicular to the upper and lower surfaces and is provided with a shoulder  501  at its upper edge. The first secondary support blade  3  and first and second additional secondary support blades  4   a ,  4   b  are the same thickness as the primary blade  2 . The lower surface incorporates a T-shaped slot  59   a  which engages a T-shaped bar on the forming box.  
         [0055]     The upper surfaces of the primary blade  2 , the first secondary support blade  3  and the first and second consecutive additional secondary support blades  4   a  and  4   b  are substantially coplanar at a first height.  
         [0056]     The first drainage deckle  5 , first additional drainage deckle  6   a  and second additional drainage deckle  6   b  are essentially (but not precisely) the same and are illustrated alone in perspective view in  FIG. 6 . The upper surfaces  65  of each of the first drainage deckle  5 , first additional drainage deckle  6   a  and second additional drainage deckle  6   b  are at heights different from the common height of the primary blade  2 , the first secondary blade  3  and the first and second additional secondary support blade  4   a ,  4   b  whereby to define a discontinuous surface which is substantially irregularly stepped. Moreover the upper surface  65  of each of the first drainage deckle  5 , first additional drainage deckle  6   a  and second additional drainage deckle  6   b  is angled at a different angle in the range 1-4°. The difference between the heights creates voids  11   a ,  11   b  and  11   c . The voids  11   a ,  11   b  and  11   c  and the variable angling of the upper surfaces  65  of the first drainage deckle  5 , first additional drainage deckle  6   a  and second additional drainage deckle  6   b  contribute to the generation of micro-turbulence in the papermaking suspension.  
         [0057]     The trailing face  21   a  of the first additional secondary support blade  4   a  is coupled to the leading face  21   b  of the first secondary support blade  3  by the first additional drainage deckle  6   a  and the trailing face  21   a  of the second additional secondary support blade  4   b  is coupled to the leading face  21   b  of the first additional secondary support blade  4   a  by the second additional drainage deckle  6   b . The trailing face  1   a  of the first secondary support blade  3  is coupled to the leading face  41   a  of the primary blade  2  by the first drainage deckle  5 .  
         [0058]     The first drainage deckle  5  and first and second additional drainage deckles  6   a ,  6   b  couple the leading and trailing faces of the forming elements by a tongue and groove arrangement.  
         [0059]     For example, a trailing face  71   a  of the drainage deckle  5  bears a tongue  72  adapted to engage a complementarily shaped groove  73  on the leading face  41   a  of the primary blade  2  and the leading face  74   a  of the drainage deckle  5  bears a groove  75  adapted to be engaged by a complementarily shaped tongue  76  on the trailing edge of the first secondary support blade  3 .  
         [0060]      FIG. 3  illustrates schematically an isolated side view of the assembly of forming elements  31  of a second embodiment of a papermaking apparatus of the invention which is particularly useful in slow speed papermaking apparatus. The assembly  31  is largely the same as the assembly  1  described for the first embodiment hereinbefore but has a different first drainage deckle  35  and first and second additional drainage deckles  36   a ,  36   b  (see  FIG. 7 ). Each of the first drainage deckle  35  and first and second additional drainage deckles  36   a ,  36   b  is adapted to introduce micro-turbulence into the papermaking suspension by extrinsic means. Each of the first drainage deckle  35  and first and second additional drainage deckles  36   a ,  36   b  comprises a closed end groove  301  extending downwardly from and transversely along the upper surface  300 . To an end wall  302  of each of the first drainage deckle  35  and first and second additional drainage deckles  36   a ,  36   b  extends a first transverse circular slot  303  outwardly from the groove  301 . To an opposing end wall  304  of each of the first drainage deckle  35  and first and second additional drainage deckles  36   a ,  36   b  extends a second transverse circular slot  305  outwardly from the groove  301 . Through the slots  303 ,  305  may be transmitted pulses of water which reach the upper surface  300  through the groove  301  and generate micro-turbulence in the papermaking suspension.  
         [0061]     To illustrate the general improvements in the generation of micro-turbulence,  FIGS. 8 and 9  illustrate respectively a papermaking suspension during dewatering in a conventional papermaking apparatus and a papermaking apparatus of the invention.  
         [0062]     It will be understood that this disclosure, in many respects, is only illustrative. Changes may be made in details, particularly in matters of shape, size, material, and arrangement of parts without exceeding the scope of the invention. Accordingly, the scope of the invention is as defined in the language of the appended claims.