Method for determining paper strength

Abstract

The present invention provides a method for determining at least one strength property of a fibrous web during its production, in particular a paper web, paperboard web or tissue web, having the following steps: determining the web draw and the tension of the fibrous web resulting therefrom; determining the actual state of at least one controlled variable influencing the strength property of the fibrous web; and determining the actual state of the at least one strength property of the fibrous web by way of a model which creates a dependency of the strength property on the web draw, the web tension and the at least one controlled variable.

1 . A method for determining at least one strength property of a fibrous web during production of the fibrous web, the fibrous web produced by a paper machine, said method comprising the steps of: 
 determining a web draw and a tension of the fibrous web resulting from said web draw;    determining an actual state of at least one controlled variable influencing the at least one strength property of the fibrous web; and    determining an actual state of the at least one strength property of the fibrous web dependent on the strength property on said web draw, said web tension, and said at least one controlled variable.    
   
   
       2 . The method according to  claim 1 , further comprising the steps of: 
 comparing said actual state of the at least one strength property with a desired state of the at least one strength property; and    changing said actual state of the at least one controlled variable in order to establish said desired state of the at least one strength property.    
   
   
       3 . The method according to  claim 1 , wherein said web draw and said web tension resulting therefrom are determined in a winding-up area of the paper machine.  
   
   
       4 . The method according to  claim 1 , wherein said model takes account of at least one of a type of the fibrous web, a plurality of specific characteristics of a production process used, and a design of the paper machine producing the fibrous web.  
   
   
       5 . The method according to  claim 1 , wherein said web draw, said web tension, and said at least one controlled variable are determined online.  
   
   
       6 . The method according to  claim 1 , wherein said model takes account of a plurality of measured values of the at least one strength property.  
   
   
       7 . The method according to  claim 6 , wherein said plurality of measured values is determined in a laboratory.  
   
   
       8 . The method according to  claim 1 , wherein said at least one controlled variable includes several said controlled variables, said model taking account of said several controlled variables.  
   
   
       9 . The method according to  claim 1 , wherein said at least one controlled variable comprises a composition of a pulp suspension used for producing the fibrous web.  
   
   
       10 . The method according to  claim 9 , wherein said at least one controlled variable comprises a composition of a fibrous material used for producing the fibrous web.  
   
   
       11 . The method according to  claim 1 , wherein said step of determining said web draw includes the substep of determining a plurality of said web draws at various points of a production process of the fibrous web, said at least one controlled variable is a ratio of said plurality of web draws at said various points of said production process of the fibrous web.  
   
   
       12 . The method according to  claim 11 , wherein said ratio is a ratio of said web draw upstream from a last press nip of a press section of said paper machine to a web draw downstream from said last press nip of said press section.  
   
   
       13 . The method according to  claim 1 , wherein the at least one strength property of the fibrous web comprises a bursting strength, at least one of a longitudinal and a transverse elongation at break, a tensile strength, and a breaking length.  
   
   
       14 . The method according to  claim 1 , further comprising the step of determining a transverse profile of the at least one strength property by the fibrous web being cut into several sections extending respectively over a subwidth of the fibrous web and by said web draw and said web tension resulting therefrom then being determined for each said section.  
   
   
       15 . The method according to  claim 14 , wherein said transverse profile of the at least one strength property is determined in a reel cutting area of the paper machine.