Reversible foil blade having multi-activity zones

Abstract

A reversible foil blade for a papermaking machine providing for a plurality of activity zones wherein the drainage and sheet activity characteristics of the blade can be independently and separately predetermined, established, and controlled. The shape of the foil blade is designed to provide both leading and trailing edges that each form an angle less than 90° with the horizontal, the paper sheet and conveying forming fabric, thereby providing different drainage and sheet activity characteristics when the blade is reversed and installed in a reverse orientation.

I claim:  
     
         1 . A foil blade for paper machines comprising 
 a first orientation of the foil blade having a leading edge angle α 1  that is less than 90 degrees from the horizontal;    an entry surface positioned at the angle α 1 ;    and a tee slot to facilitate the mounting, installation and/or removal of the blade on the paper machine, such that when the foil blade is installed on a paper machine in the first orientation the leading edge angle is the first portion of the foil blade that is traversed by a conveying fabric and by a sheet being formed on the paper machine, thereby providing a predetermined and controlled effect of the blade on drainage and sheet activity.    
     
     
         2 . The foil blade according to  claim 1 , wherein reversing of the blade with respect to the machine direction changes the sheet activity and drainage associated with the blade while the paper machine is running.  
     
     
         3 . The foil blade according to  claim 1 , wherein the leading edge angle α 1  is between about greater than zero and 10 degrees.  
     
     
         4 . The foil blade according to  claim 1 , further including an exit angle α 2  that is less than 90 degrees from the horizontal and is formed by an exit surface positioned at the opposite end of the blade from the entry surface.  
     
     
         5 . The foil blade according to  claim 1 , wherein the exit angle α2 is between about greater than zero and 10 degrees.  
     
     
         6 . The foil blade according to  claim 1 , further including at least one surface discontinuity following the entry surface, wherein the at least one surface discontinuity produces separate and independent drainage and activity characteristics for the blade.  
     
     
         7 . The foil blade according to  claim 6 , wherein the surface discontinuity is at least one groove surface.  
     
     
         8 . The foil blade according to  claim 6 , wherein the surface discontinuity is at least one recessed surface.  
     
     
         9 . The foil blade according to  claim 6 , wherein the surface discontinuity is at least two groove surfaces.  
     
     
         10 . The foil blade according to  claim 6 , wherein the surface discontinuity is at least two recessed surfaces forming the entry and exit of a convex surface.  
     
     
         11 . The foil blade according to  claim 1 , wherein the tee slot is centered.  
     
     
         12 . The foil blade according to  claim 1 , wherein the tee slot is offset from the center of the blade.  
     
     
         13 . The foil blade according to  claim 1 , further including a first flat surface that defines the acceleration distance of the first activity zone.  
     
     
         14 . The foil blade according to  claim 13 , wherein the first flat surface is between about 0.25 inches to about 3 inches.  
     
     
         15 . The foil blade according to  claim 13 , wherein reversal of the blade makes the first flat surface define the acceleration distance of a different activity zone.  
     
     
         16 . The foil blade according to  claim 1 , further including a first divergent surface having an angle between about 0 to about 15 degrees, which defines the exit angle of the first activity zone and produces a first activity zone exit drainage.  
     
     
         17 . The foil blade according to  claim 16 , wherein reversal of the blade makes the first divergent surface define a convergent nip of a different activity zone.  
     
     
         18 . The foil blade according to  claim 16 , wherein the first divergent surface further includes a surface discontinuity to define fabric deflection at the exit angle of the first activity zone.  
     
     
         19 . The foil blade according to  claim 1 , further including a first convergent surface having an angle between about 0 to about 15 degrees, which defines an entry nip into a second flat surface.  
     
     
         20 . The foil blade according to  claim 19 , wherein the second flat surface is between about 0.25 to about 3 inches.  
     
     
         21 . The foil blade according to  claim 19 , wherein reversal of the blade makes the first convergent surface become a divergent surface and defines an exit angle of the first activity zone and produces a first activity zone exit drainage.  
     
     
         22 . The foil blade according to  claim 1 , further including a first doctoring surface to doctor water at the entry of the fabric to the blade and second doctoring surface to prevent fiber build-up at the exit of the fabric from the blade.  
     
     
         23 . The foil blade according to  claim 22 , wherein reversal of the blade changes the first doctoring surface to prevent fiber build-up at the blade exit and the second doctoring surface to doctor water at the blade entry.  
     
     
         24 . A foil blade for paper machines comprising 
 a first orientation of the foil blade having a leading edge angle α 1  that is less than 90 degrees from the horizontal;    an entry surface positioned at the angle α 1 ;    and a tee slot to facilitate the mounting, installation and/or removal of the blade on the paper machine, such that when the foil blade is installed on a paper machine in the first orientation the leading edge angle is the first portion of the foil blade that is traversed by a conveying fabric and by a sheet being formed on the paper machine, thereby providing a predetermined and controlled effect of the blade on drainage and sheet activity and wherein reversing of the blade with respect to the machine direction changes the entry angle from affecting activity to function as an exit angle affecting drainage.    
     
     
         25 . The foil blade according to  claim 24 , wherein reversing of the blade with respect to the machine direction changes the sheet activity and drainage associated with the blade while the paper machine is running.  
     
     
         26 . A foil blade for paper machines comprising 
 a first orientation of the foil blade having a leading edge angle α 1  that is less than 90 degrees from the horizontal;    an entry surface positioned at the angle α 1  having a first flat surface F1;    an angle θ 1  of the conveying fabric with the horizontal at fabric entry to the blade and an angle θ 3  of the conveying fabric with the horizontal at fabric exit from the blade;    a second entry surface positioned at the angle α 3  having a second flat surface F2;    wherein a first activity zone is produced according to the formula    acceleration ( a )=(fabric speed) 2 ×(θ 1 +α 2 )/ F 1;    and a tee slot to facilitate the mounting, installation and/or removal of the blade on the paper machine, such that when the foil blade is installed on a paper machine in the first orientation the leading edge angle is the first portion of the foil blade that is traversed by a conveying fabric and by a sheet being formed on the paper machine, thereby providing a predetermined and controlled effect of the blade on drainage and sheet activity.    
     
     
         27 . The foil blade according to  claim 26 , wherein reversing of the blade with respect to the machine direction changes the sheet activity and drainage associated with the blade while the paper machine is running such that a reverse first activity zone is produced according to the formula  
       acceleration ( a )=(fabric speed) 2 ×(α 4 +θ 3 )/ d,    
       where d is the distance over which the fabric changes direction and α 4  is the angle that the fabric forms with the blade when it enters the reversed orientation.  
     
     
         28 . The foil blade according to  claim 26 , wherein the drainage and activity characteristics of the blade are set forth as follows:  
       Acceleration at zone 1=(fabric speed) 2 ×(θ 1 +α 2 )/ F 1 Acceleration at zone 2=(fabric speed) 2 ×(θ 2 +α 2 )/ d  Acceleration at zone 3=(fabric speed) 2 ×(θ 2 +α 4 )/ F 1 Acceleration at zone 4=(fabric speed) 2 ×(θ 3 +α 4 )/ d  Drainage˜α 4 ×L5  
       where d is the distance over which the fabric changes direction, and θ 1  is the angle of the fabric with the horizontal H at activity zone 1, θ 2  is the angle of the fabric with the horizontal H at activity zone 2, and θ 3  is the angle of the fabric with the horizontal H at activity zone 4.  
     
     
         29 . The foil blade according to  claim 27 , wherein the drainage and activity characteristics of the blade are set forth as follows:  
       Acceleration at zone 1=(fabric speed) 2 ×(θ 1 +α 3 )/ F 2 Acceleration at zone 2=(fabric speed) 2 ×(θ 2 +α 3 )/ d  Acceleration at zone 3=(fabric speed) 2 ×(θ 2 +α 4 )/ F 1 Acceleration at zone 4=(fabric speed) 2 ×(θ 3 +α 1 )/ d  Drainage˜α 4 ×L1  
       where d is the distance over which the fabric changes direction, and θ 1  is the angle of the fabric with the horizontal H at activity zone 1, θ 2  is the angle of the fabric with the horizontal H at activity zone 2, and θ 3  is the angle of the fabric with the horizontal H at activity zone 4.  
     
     
         30 . A method for using a foil blade for paper machines comprising the steps of: 
 providing a foil blade having a leading edge angle α 1  that is less than 90 degrees from the horizontal; an entry surface positioned at the angle α 1 ; and a tee slot to facilitate the mounting, installation and/or removal of the blade on the paper machine;    installing the foil blade in a first orientation such that when the foil blade is installed on a paper machine in the first orientation the leading edge angle is the first portion of the foil blade that is traversed by a conveying fabric and by a sheet being formed on the paper machine, thereby providing a predetermined and controlled effect of the blade on drainage and sheet activity.    
     
     
         31 . The method according to  claim 30 , further including the step of removing the foil blade from the machine, reversing its direction with respect to the conveying fabric travel direction, and reinstalling the blade on the machine.