Web product with isotropic fiber orientation

Abstract

Methods and apparatus to enhance paper and board forming qualities with insert tubes and/or a diffuser block in the paper forming machine headbox component which generates vorticity in the machine direction (MD) which is superimposed on the streamwise flow to generate a swirling or helical flow through the tubes of the diffuser block. Tubes of the diffuser block are designed such that the direction of the swirl or fluid rotation of the paper fiber stock may be controlled and the direction thereof is controlled in such a way to provide effective mixing, coalescence and merging of the jets of fluid emanating from the tubes into the converging section, i.e., nozzle chamber of the headbox. A specific flow inside the headbox distributes the fibers in an isotropic form, i.e., uniform in all directions, in the sheet substantially eliminating the MD preferential fiber orientation to produce an isotropic and uniform sheet. Also disclosed is the effective mixing of the jets generating cross-machine direction (CD) shear between the rows of jets that form at the outlet of the tubes inside the nozzle chamber of the headbox to align paper fibers in the cross-machine direction.

What is claimed is:  
     
         1 . A paper forming machine headbox component for receiving a paper fiber stock and generating a jet therefrom for discharge upon a wire component moving in a machine direction (MD), the headbox component comprising: 
 a distributer for distributing stock flowing into the headbox component in a cross-machine direction (CD), the distributer effective for supplying a flow of said stock across the width of the headbox in the machine direction;    a nozzle chamber having an upper surface and a lower surface converging to form a rectangular outlet lip defining a slice opening for the jet;    a diffuser block coupling said distributer to said nozzle chamber, said diffuser block comprising a multiplicity of tubular elements disposed between said distributer and said nozzle chamber, said tubular elements being oriented axially in the machine direction, a plurality of the tubular elements having a longitudinal axes in the direction of the flow of stock, and the tubular elements arranged within the diffuser block as a matrix of rows and columns for generating multiple jets of said stock flowing into said nozzle chamber; and    said tubular elements being oriented axially generate an axial vorticity which prevents fiber orientation in the machine direction in an initial converging section of said nozzle chamber being effective for swirling said stock in controlled pairs of axial vortices along the longitudinal axes of the tubular elements as said stock flows through said tubular elements promoting mixing of the jets of said stock as said jets flow into said nozzle chamber from the tubular elements to form a uniform flow of stock at the slice opening for the jet.    
     
     
         2 . A headbox component as recited in  claim 1  wherein said diffuser block orienting said tubular elements axially in the machine direction generates machine direction strain and acceleration in said nozzle chamber with a gradual convergence rate near the slice which is not strong enough to orient the fibers in the machine direction.  
     
     
         3 . A headbox component as recited in  claim 2  wherein the fibers in the forming jet will be isotropic, uniformly oriented in all directions.  
     
     
         4 . A headbox component as recited in  claim 1  wherein said tubular elements comprise a closed core with a spiral section followed by the open core in the downstream section for enhanced swirl in a small diameter tube.  
     
     
         5 . A paper forming method for receiving a paper fiber stock and generating a jet from a headbox component for discharge upon a wire component moving in a machine direction (MD), the method comprising: 
 distributing stock flowing into the headbox component in a cross-machine direction (CD), to a distributer effective for supplying a flow of the stock across the width of the headbox in the machine direction;    converging the flow of the stock with a nozzle chamber having an upper surface and a lower surface to form a rectangular outlet lip defining a slice opening for the jet;    coupling the distributer to a diffuser block and nozzle chamber having a multiplicity of tubular elements being disposed and oriented axially therebetween in the machine direction with longitudinal axes in the direction of the flow of stock, the tubular elements being arranged within the diffuser block as a matrix of rows and columns for generating multiple jets of the stock flowing into the nozzle chamber; and    generating controlled axial vortices along the longitudinal axes of the tubular elements as the stock flows through said tubular elements promoting mixing of the jets of the stock as the jets flow into the nozzle chamber from the tubular elements to form a uniform flow of stock at the slice opening.    
     
     
         6 . A method as recited in  claim 5  wherein the tubular elements are oriented axially to generate an axial vorticity which prevents fiber orientation in the machine direction in an initial converging section of the nozzle chamber.  
     
     
         7 . A method as recited in  claim 5  wherein the tubular elements are oriented axially in the machine direction to generate machine direction strain and acceleration in the nozzle chamber with a gradual convergence rate near the slice which is not strong enough to orient the fibers in the machine direction.  
     
     
         8 . A method as recited in  claim 7  wherein the generating step isotropically orients the fibers in the forming jet in all directions.  
     
     
         9 . A web product being formed from paper fiber stock, comprising: 
 generating a jet from a headbox component for discharge upon a wire component moving in a machine direction (MD);    distributing the paper fiber stock into the headbox component in a cross-machine direction (CD);    converging the flow of paper fiber stock in a nozzle chamber;    coupling a diffuser block between the distributor and the nozzle chamber to provide a multiplicity of tubular elements being disposed and oriented axially therebetween in the machine direction with longitudinal axes in the direction of flow of the paper fiber stock for generating multiple jets of stock flowing into the nozzle chamber; and    generating controlled axial vortices along the longitudinal axes of the tubular elements as the paper fiber stock flows therethrough to form a uniform flow of stock at the slice opening to provide isotropic fiber orientation in the web product.    
     
     
         10 . A web product as recited in  claim 9 , wherein the process for producing the web product comprises generating machine direction strain and acceleration in the nozzle chamber with a gradual convergence rate near the slice.  
     
     
         11 . A web product as recited in  claim 9 , comprising providing a closed core with a spiral section within the tubular elements followed by an open core in the downstream section.  
     
     
         12 . A web product as recited in  claim 9 , wherein the tubular elements generate controlled axial vortices as the paper fiber stock flows therethrough.  
     
     
         13 . A web product as recited in  claim 9 , wherein the MD/CD fiber orientation ratio is approximately unity indicating fibers being substantially uniformly oriented in all directions in the web product.  
     
     
         14 . A web product as recited in  claim 9 , wherein the elastic content of the web product indicates orientation distribution of strength in the web product as being substantially uniform from the MD to the CD directions.