Abstract:
A former for a machine for the production of a fibrous web, particularly a paper or cardboard web including a headbox equipped with at least one stock suspension feed, one turbulence block equipped with several channels and/or a tube generator equipped with several channels, and a headbox nozzle whose suspension jet strikes an exposed or open surface of a dewatering belt, specifically a wire. Turbulence generating elements are allocated to at least a section of the channels and/or the headbox nozzle, in order to create turbulent flows in the suspension substreams in the channels, or in the headbox nozzle. The side of the suspension stream facing away from the dewatering belt is covered at least partially by a wall. A danger of the suspension stream bursting open is reduced to a minimum. In addition, swirling motions of considerably higher intensity than occur on conventional Fourdrinier wire formers are now permissible.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a machine a machine for the production of a fibrous web, and, more particularly, to a former and former headbox.  
         [0003]     2. Description of the Related Art  
         [0004]     With suction formers, a longitudinal orientation of the fibers occurs at an appropriate increase in the operating speed of the paper machine in question. This may limit the scope of application of such suction formers to low operational speeds.  
         [0005]     A relatively strong transverse orientation of the fibers, as well as a low longitudinal/transverse ratio can be achieved (see for example U.S. Pat. No. 5,876,364) through transverse movements that are indicated through various swirl-producing bodies in the turbulence block. However, a consequence of these transverse motions is the inherent danger of the suspension stream that is delivered by the headbox of the respective former bursting open when encountering an open surface, for example on the Fourdrinier wire.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides an improved former and former headbox whereby the cited problems are eliminated.  
         [0007]     The present invention provides a former, particularly a suction former of a machine for the production of a fibrous web, particularly a paper or cardboard web comprising a headbox equipped with at least one stock suspension feed, one turbulence block equipped with several channels and/or a tube generator equipped with several channels, and a headbox nozzle whose suspension jet strikes an exposed or open surface of a dewatering belt, specifically a wire. Turbulence generating elements are allocated to at least a section of the channels and/or the headbox nozzle, in order to create turbulent flows in the suspension substreams in the channels, or in the headbox nozzle. The side of the suspension stream facing away from the dewatering belt is covered at least partially by a wall. Based on this configuration, the danger of the suspension stream bursting open is reduced to a minimum. In addition, swirling motions of considerably higher intensity than occur on conventional Fourdrinier wire formers are now permissible.  
         [0008]     The wall can be stationary or in motion. A stationary wall can, for example, be allocated to the headbox on which it can be installed adjustably. The wall can in addition, be permeable to water or impermeable to water. A movable wall or a wall in motion can be in the embodiment of an additional dewatering belt, that can specifically be in the form of a revolving wire.  
         [0009]     In the coverage area the wall can possess an at least partially curved progression and/or an at least partially straight progression. Moreover, in a practical embodiment the lower wall has a maximum length of 90%, preferably of 60%, especially of 30% of the length of the upper wall. In a preferred practical embodiment of the former in accordance with the present invention, at least some of the channels are equipped with the turbulence generating inserts. Such turbulence generating inserts can basically be provided in the channels of a respective turbulence block and/or in the channels of a respective tube generator.  
         [0010]     In hitherto conventional suction formers or in twin wire formers eddies occur in pairs in opposite rotational directions, that can lead to stripes. These are known as the so-called “Taylor-Görtler-Eddies” in Central Europe. The stripes occur especially in curved dewatering surfaces.  
         [0011]     The present invention provides an improved former, particularly a suction former or twin wire former for a machine for the production of a fibrous web, specifically a paper or cardboard web, in which the previously cited problems are eliminated.  
         [0012]     In accordance with an additional aspect of the present invention a former, specifically a suction former or twin wire former of a machine for the production of a fibrous web, specifically a paper or cardboard web is provided or this purpose; comprising a headbox that is equipped with at least one stock suspension feed, one turbulence block equipped with several channels and/or a tube generator equipped with several channels and a headbox nozzle. Turbulence generating elements are allocated to at least a section of the channels in order to create turbulent flows that rotate in the same direction in the suspension substreams in the channels. Same directional turbulence movement suppresses the undesirable stripes.  
         [0013]     In a functional practical embodiment of the present invention helix type spirals are installed in at least a section of the channels in order to create turbulent flows that rotate in the same direction. Such helix type spirals can, for example, be installed in the channels of a turbulence block and/or in the channels of tube generator. The creation of turbulences through the means of helix type spirals can for example occur as described in U.S. Pat. No. 5,876,464.  
         [0014]     Alternatively, or in addition, turbulent flows that are rotating in the same direction can be created particularly by the fact that, in a headbox comprising a tube generator, the supply of stock suspension through nozzles into a respective tube channel occurs asymmetrically and preferably at least essentially tangentially to the tube wall, relative to a center plane progressing in longitudinal direction through the tube channel. Advantageously, the stock suspension is fed through nozzles only on one side of the center plane respectively. Preferably, suspension supplied to the relevant pipe channels is fed into the various pipe channels through nozzles always on the same side of the respective center planes.  
         [0015]     In contrast to Fourdrinier wires, the previously discussed, deliberately produced turbulences are kept very small in the sheet formation zone in other types of formers, particularly in suction and twin wire formers, since the surface of the suspension is “covered”, resulting in improved sheet formation, even at an increased stock consistency. In addition the headbox can be equipped with at least one feed for dilution water, air, chemicals and/or similar substances. The supply of dilution water, air, chemicals and/or similar substances may essentially occur in axial direction of a respective channel.  
         [0016]     In accordance with an advantageous embodiment of the present invention, the wall can be located in an area opposite the forming roll and can be at least partially curved according to a radius of curvature that is preferably larger than or equal to the radius of the forming roll. Basically however, a smaller radius is also feasible, at least in sections. The wall can for example be stationary. Thereby it would preferably cover the circumferential surface of the forming roll, that is in a range of approximately 100 to approximately 400 mm. The stationary wall can particularly be rigid, deflection resistant or not deflection resistant.  
         [0017]     In accordance with an additional advantageous design of the present invention whereby the wall is again provided in an area opposite the forming roll and is curved, at least partially, according to a curvature radius that is preferably larger than or equal to the radius of the forming roll, the wall can be movable or in motion and can be formed by an additional dewatering belt, particularly a revolving wire. In this instance, the wall preferably covers a circumferential area of this forming roll that is in the range of approximately 100 mm to approximately 1500 mm and/or corresponds with a circumferential angle of the forming roll of approximately 25° to approximately 120°.  
         [0018]     The additional dewatering belt that forms the wall can be routed around a breast roll, prior to the area covering the forming roll, when viewed in the direction of belt travel. The curvature radius of the wall in the area covering the forming roll is preferably larger than the radius of the breast roll, or respectively the corresponding curvature radius of the wall in the area of this breast roll.  
         [0019]     The headbox nozzle can be sectioned by at least one lamellar plate. A configuration without lamellar plates is also feasible. In a functional advantageous design at least one lamellar plate and/or at least one nozzle wall exhibit contours, especially swirl-producing washboard contours.  
         [0020]     Alternatively, or in addition, at least one lamellar plate and/or at least one nozzle wall can have contours that serve to generate turbulent motion. At least one lamellar plate and/or at least one nozzle wall can for example be equipped with at least one interference body. Preferably the at least one interference body of the at least one nozzle wall is in the form of preferably a discontinuous tapering of the cross section. This formation provides a fluidic ideal turbulence chamber. In addition, at least one lamellar plate has a length not exceeding 70% of the length of the headbox nozzle.  
         [0021]     In order to attain a sufficient effect, the headbox nozzle should be as short as possible. The headbox nozzle should preferably be shorter than approximately 400 mm. It is also advantageous if the outlet cross section of the channels or pipes is at least essentially round, since a square outlet cross section would dampen the effect.  
         [0022]     In accordance with the present invention a headox is furthermore disclosed especially for a former of the relevant type previously described. Such a headbox includes at least one stock suspension feed, one turbulence block equipped with several channels and/or a tube generator equipped with several channels and a headbox nozzle. Turbulence generating elements are allocated to at least a section of the channels in order to create turbulent flows that rotate in the same direction in the suspension sub-streams in the channels.  
         [0023]     In accordance with an additional aspect of the present invention a headbox, particularly for a former of the type previously described is provided, including at least one stock suspension feed, one turbulence block equipped with several channels and/or a tube generator equipped with several channels and a headbox nozzle. Turbulence generating elements are allocated to at least a section of the channels in order to create turbulent flows, rotating in the same direction, in the suspension sub-streams in the channels. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0025]      FIG. 1  is a partially schematic side view of an embodiment of a suction former of the present invention whose headbox includes a turbulence block that is equipped with turbulence generating inserts, and that is equipped with a stationary preferably adjustable wall, that covers the suspension stream, at least partially, on one side;  
         [0026]      FIGS. 2-2   d  are cross-sectional views of various designs of the turbulence generating inserts of the present invention, viewed in the direction of arrow V in  FIG. 1 ;  
         [0027]      FIG. 3  is a schematic cross-sectional view of a headbox equipped with tube generator, as viewed along line I-I in  FIG. 4 , whereby the feeding of the stock suspension through nozzles into a respective tube channel occurs asymmetric and at least essentially tangential to the tube wall;  
         [0028]      FIG. 4  is a schematic longitudinal section of an embodiment of the headbox of the present invention;  
         [0029]      FIG. 5  is a schematic longitudinal section of an embodiment of headbox of the present invention including a turbulence block or tube generator into whose channels, at least into sections, helix type spirals or helix are installed;  
         [0030]      FIG. 6  is a schematic side view of an embodiment of a former of the present invention with a movable wall, or a wall in motion that is formed by an additional dewatering belt and is located in an area opposite the forming roll and that covers a certain circumferential length of this forming roll;  
         [0031]      FIG. 7  is a schematic longitudinal sectional view of an embodiment of a headbox nozzle, of the present invention that is sectioned by at least one lamellar plate, whereby at least one lamellar plate is equipped with at least one interference body;  
         [0032]      FIG. 8  is a schematic perspective view of an embodiment of a headbox nozzle of the present invention that is sectioned by at least one lamellar plate, whereby at least one lamellar plate has a washboard contour; and  
         [0033]      FIG. 9  is a schematic side view of an embodiment of a headbox of the present invention sectioned by at least one lamellar plate, whereby the upper and lower nozzle wall respectively are contoured. 
     
    
       [0034]     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a schematic side view of a former  10 , which in this example is a suction former of a machine for the production of a fibrous web that may specifically be a paper or cardboard web.  
         [0036]     A headbox  12  that is allocated to this former  10  includes a stock suspension feed  14 , at least one turbulence block  18  that is equipped with several channels  16  and a headbox nozzle  20  whose suspension stream  22  strikes an exposed, that is an open surface  24 ′ of dewatering belt  24 , which in this example is a wire.  
         [0037]     Turbulence generating elements  26 , in this example turbulence generating inserts, are allocated to at least one section of channels  16 , in order to create turbulent flows  28  in the suspension substreams that are guided through the channels (also see  FIG. 2 ). These turbulent flows  28  are illustrated schematically in  FIGS. 2-2   d , which show front views of various designs of the turbulence generating inserts, in the direction of arrow V in  FIG. 1 .  
         [0038]     The side of suspension stream  22  facing away from the dewatering belt  24  is covered at least partially by wall  30 . In the present example wall  30  is stationary, installed preferably adjustably on headbox  12 . As can be seen in  FIG. 1 , wall  30  can, for example, be connected via link  32  with headbox nozzle  20 . Wall  30  that is mounted on headbox nozzle  20  in this manner can be adjusted through pivoting by adjustment elements  34 . Headbox nozzle  20  can, for example, be sectioned by at least one lamellar plate  36 .  
         [0039]     As can be seen in  FIG. 1 , wall  30  is curved at least slightly in the area of coverage. Wall  30  can, for example, be located in an area opposite forming roll  38 . In the present example wall  30  is curved in accordance with a radius of curvature R 1 , that is larger than the radius R 2  of the forming roll  38 .  
         [0040]     Wall  30  can include an upper wall shown at  30  and lower wall  30 ′. Lower wall  30 ′ has a lower wall length not greater than 90%, preferably 60%, especially 30% of an upper wall length.  
         [0041]     Stationary wall  30  can for example cover a circumferential length L of forming roll  38 , that is in a range of approximately 100 to approximately 400 mm. In  FIG. 1  the circumferential angle of forming roll  38  resulting from a respective circumferential length L is indicated as “α”. The stationary wall may be rigid, deflection resistant or not deflection resistant. Curvature radius R 1  of wall  30  can, if necessary, be larger than or equal to radius R 2  of forming roll  38 . In certain instances a smaller curvature radius R 1  is also feasible.  
         [0042]     In the example illustrated in  FIG. 1  an additional dewatering belt  40 , especially a wire is provided that is brought together with dewatering belt  24  at a location A. Furthermore, at least one disturbance body  60  of at least one nozzle wall  30  is designed as preferably a discontinuous tapering of cross section  64  (shown as broken lines). The tapering of the cross section may however also occur continuously and/or randomly.  
         [0043]     In the present example wall  30  is impermeable to water. As can be seen especially from the following design examples, this type of wall may basically also be water permeable, especially if a movable wall or a wall in motion is provided in the embodiment of a dewatering belt, such as especially a wire.  
         [0044]      FIGS. 3 and 4  are schematic illustrations of headbox  12  including tube generator  42  that is equipped with several channels  16  whereby turbulence generating elements are allocated to at least a section of channels  16 , in order to create turbulent flows  28  that rotate in the same directions in the suspension sub-streams in the relating channels  16 . The turbulence generating elements in the present example include nozzles  44  through which the supply of stock suspension into a respective tube channel  16  occurs asymmetrically and at least essentially tangentially to tube wall  46 . Supply of the stock suspension through the nozzles occurs asymmetrically, relative to center plane E progressing in longitudinal direction through tube channel  16 . In the present example this is always only on one side of this center plane E. As can be seen in  FIG. 3 , feeding into the various tube channels  16  through the nozzles always occurs on the same side of the center plane E, for example the right side in  FIG. 3 , resulting in same directional rotation of the various turbulent flows  28 .  
         [0045]     As can be seen in  FIGS. 3 and 4 , in addition to stock suspension feed  14 , headbox  12  can additionally be equipped with at least one inlet  48  for dilution water, air, chemicals and/or other substances. As seen in  FIG. 4  the supply of dilution water, air, chemicals and/or similar substances can essentially occur in an axial direction of a respective channel. Again, headbox nozzle  20  can be provided with or without lamellar plates. A turbulence block  18  can also be provided alternatively or in addition to the tube generator  42 .  
         [0046]     As illustrated in particular in  FIG. 4 , an intermediate chamber  50  can be provided, for example, following tube generator  42  which is equipped with rotation channels  16 . In the available design example the rotational flow is produced by the asymmetric or tangential inflow of suspension.  
         [0047]      FIG. 5  is a schematic longitudinal sectional view of another design form of a headbox  12 , including tube generator  42 . A turbulence block can again be provided alternatively or in addition. In the present example helix-type spiral or helix  52  are installed in at least a section of channels  16  of tube generator  42 , or in the turbulence block, for the purpose of producing turbulent flows rotating in the same direction. As can be seen in  FIG. 5 , headbox  12  also includes stock suspension feed  14 , a headbox nozzle  20  and a stationary, preferably adjustable wall  30 . Headbox nozzle  20  can be sectioned by at least one lamellar plate  36 , or can also be configured withouth lamellar plates. Helix-type spirals  52  can be configured and installed specifically so that same-directionally rotating turbulent flows again occur. Moreover, a respective rotational flow initiated by a relating helix-type spiral  52  can be produced, for example, as described in U.S. Pat. No. 5,876,564. In the design form illustrated in  FIG. 5  an acceleration segment a of the headbox is followed by a section b that shows helix-type spirals  52 . This is followed by a section c, for example constant deceleration or acceleration, further followed by an additional acceleration section d. A deceleration occurs in a subsequent section e.  
         [0048]      FIG. 6  is a schematic partial illustration of former  10  that is equipped with a movable wall  30 , or a wall in motion, that is formed by an additional dewatering belt  54  and that is located in area opposite forming roll  38  and that covers a certain circumferential length L of forming roll  38 . Former  10  also includes dewatering belt  24  that is routed around forming roll  38  and is formed particularly by a wire, and has headbox  12  whose suspension stream  22  is directed into the area between forming roll  38  and breast roll  56 , around which dewatering belt  54  that forms wall  30  is routed prior to the area that covers forming roll  38 , viewed in direction of belt travel  1 . Dewatering belt  54  can also specifically be a wire. After forming roll  38 , two dewatering belts  24 ,  54  are run over an additional forming element  58 .  
         [0049]     In an area opposite forming roll  38  movable wall  30  that is formed by dewatering belt  54  is curved, at least partially according to a curvature radius R 1  that is preferably larger than or equal to radius R 2  of forming roll  38 . Movable wall  30  can, for example, cover a circumferential length L of the forming roll  38  that is in a range of approximately 100 to approximately 1500 mm and/or corresponds with a circumferential angle a of forming roll  38  of approximately 25° to approximately 120°. As can be seen in  FIG. 6 , the additional dewatering belt  54  that forms wall  30  can be routed around breast roll  56 , prior to the area covering forming roll  38 , when viewed in direction of travel  1 . Curvature radius R 1  of wall  30  in the area covering forming roll  38  is preferably larger than radius R 3  of the breast roll, or respectively the corresponding curvature radius R 3  of wall  30  in the area of this breast roll  56 .  
         [0050]      FIG. 7  is a schematic longitudinal sectional view of headbox nozzle  20  that is sectioned by at least one lamellar plate  36 , whereby at least one lamellar plate  36  is equipped with at least one interference body  60  in order to provide a turbulence generating profile. Moreover, at least one lamellar plate  36  has a length not exceeding 70% of the length of the headbox nozzle  20 . At least one lamellar plate  36  and/or at least one nozzle wall  20 ′,  20 ″ can have contours that serve to generate turbulent motion.  
         [0051]      FIG. 8  is a schematic, perspective partial view of headbox nozzle  20  that is sectioned by at least one lamellar plate  36 , whereby at least one lamellar plate  36  has a swirl-producing contour, in this example a washboard contour. At least one lamellar plate  36  and/or at least one nozzle wall  20 ′,  20 ″ can possess this type of swirl-producing contour, for example in the form of a washboard contour.  
         [0052]      FIG. 9  is a schematic longitudinal view of headbox  20 , that is sectioned by at least one lamellar plate  36 , where the upper and lower nozzle wall  20 ′ or  20 ″ respectively are contoured so that turbulence generating edges  62  are created in the flow area.  
         [0053]     In order to achieve an appropriate effect a respective headbox nozzle  20  should be as short as possible, whereby headbox nozzle  20  is preferably shorter than approximately 400 mm. The outlet cross section of channels  16  or pipes is preferably at least essentially round, since a square cross section would dampen the effect.  
         [0054]     Other desired combinations of the various former variations, as well as of the various headbox variations are feasible.  
         [0055]     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.