Method to improve the formation of a paper or paperboard web by pre-pressing in a twin-wire former

Abstract

A method and apparatus for improving forming of a web of paper or paper board employing prepressing during web forming. Forming wires are brought together over at least one roll or alternatively two rolls. The web then passes, sandwiched between two wires through one or more pressure nips which may be one or more roll nips or an extended nips. The pressure nip may be formed as the web travels between the two fabrics, one of them being a forming wire, along a straight path or alternatively as the web travels partially around a roll. The web is then sandwiched between a wire and a fabric, which may be a felt or a belt, and passed through another press nip which may be one or more roll nips or an extended nip.

What is claimed is:  
     
         1 . A method for improving the structure of a paper web in a forming section of a paper making machine comprising: 
 ejecting a suspension of paper pulp from a head box between a pair of forming fabrics so that a paper web starts to be formed between the forming fabrics; and    continuing web formation by pressing the web between two fabrics by passing the fabrics and the web sandwiched therebetween through at least one pressure nip formed by a pair of rollers such that water in the web is partially removed from the web.    
     
     
         2 . The method of  claim 1 , wherein at least one of the forming fabrics passes through the at least one pressure nip.  
     
     
         3 . The method of  claim 1 , wherein the paper pulp ejected from the head box between the forming fabrics has a dry content above about 2%.  
     
     
         4 . The method of  claim 3 , wherein the paper pulp ejected from the head box between the forming, fabrics has a dry content above about 3%.  
     
     
         5 . The method of  claim 3 , wherein the paper pulp ejected from the head box between the forming fabrics has a dry content of less than about 12%.  
     
     
         6 . The method of  claim 5 , wherein the paper pulp ejected from the head box between the forming fabrics has a dry content of less than about 10%.  
     
     
         7 . The method of  claim 1 , wherein at least one of the fabrics passing through the at least one pressure nip is a wire.  
     
     
         8 . The method of  claim 7 , wherein both of the fabrics passing through the at least one pressure nip are wires.  
     
     
         9 . The method of  claim 1 , wherein one of the fabrics passing through the at least one pressure nip is a water absorbing felt.  
     
     
         10 . The method of  claim 1 , wherein one of the fabrics passing through the at least one pressure nip is a non-water absorbing belt.  
     
     
         11 . The method of  claim 1 , wherein the at least one pressure nip is formed by a pair of press rolls.  
     
     
         12 . The method of  claim 1 , wherein the a t least one pressure nip comprises an extended nip press.  
     
     
         13 . An apparatus for improving the structure of a paper web in a forming section of a paper making machine comprising: 
 a pair of endless first fabrics supported so that a surface of one of said first fabrics travels proximate a surface of the other of said first fabrics along a portion of the length of said first fabrics;    a head box positioned to eject a suspension of paper pulp therefrom between said first fabrics so that the ejected paper pulp starts to form a web between said first fabrics;    a pair of endless second fabrics supported so that a surface of one of said second fabrics travels proximate a surface of the other of said second fabrics along a portion of the length of said second fabrics, said pair of second fabrics positioned to receive the paper web from said pair of first fabrics; and    at least one pressure nip positioned to press the web between said second fabrics by passing said pair of second fabrics and the web sandwiched therebetween through said at least one pressure nip, the web being pressed such that water in the web is partially removed from the web, said at least one pressure nip being formed by a pair of rollers.    
     
     
         14 . The apparatus of  claim 13 , wherein at least one of said second fabrics is at least one of said first fabrics.  
     
     
         15 . The apparatus of  claim 13 , wherein neither of said second fabrics is either of said first fabrics.  
     
     
         16 . The apparatus of  claim 13 , wherein at least one of said second fabrics is a wire.  
     
     
         17 . The apparatus of  claim 16 , wherein both of said second fabrics are wires.  
     
     
         18 . The apparatus of  claim 13 , wherein one of said second fabrics is a water absorbing felt.  
     
     
         19 . The apparatus of  claim 13 , wherein one of said second fabrics is a non-water absorbing belt.  
     
     
         20 . The apparatus of  claim 13 , wherein said at least one pressure nip is formed by a pair of press rolls.  
     
     
         21 . The apparatus of  claim 13 , wherein said at least one pressure nip comprises an extended nip press.  
     
     
         22 . The apparatus of  claim 14 , wherein one of said second fabrics is a water absorbing felt.  
     
     
         23 . The apparatus of  claim 14 , wherein one of said second fabrics is a non-water absorbing belt.