Runnability of Web in a Material Web Machine

Abstract

A runnability device, for example a runnability box such as a suction box, is for achieving improved runnability of a web when the web (W) progresses supported by a wire ( 61 ) to a closing gap between a roll and the wire. The runnability device ( 10 ) is located on the side of the wire before the roll and extends over the width of the web so that there is a slot between the wire and the runnability device. The runnability device comprises devices ( 11 ) for directing a vacuum from the side of the wire over the width of the closing gap so that the vacuum in the edge area (E) of the web wire is greater than in the central area of the web wire. A characteristic feature of the invention is that the vacuum device ( 11 ) which creates the vacuum effect is adjustable in the cross-direction of the web wire.

1 . A runnability device in a material web machine comprising: 
 a roll in the web machine;    a wire arranged to travel in a machine direction over the roll to form a closing gap with the roll, the closing gap having edge areas with a central area therebetween, the wire having a first side which engages the roll;    a web arranged to travel in a machine direction over the roll with the wire to define with the wire a web wire, wherein the web wire has edge areas with a central area therebetween and;    a runnability device located on the first side of the wire, and positioned before the said roll and which extends essentially over the width of the wire so that there is a slot between the wire and the runnability device;    wherein the runnability device further comprises vacuum devices for directing a vacuum from the first side of the wire over the width of the web wire or over the width of the closing gap in the cross-machine direction such that the edge areas of the web wire or the edge areas of the closing gap are connected to a first source of vacuum which has a greater vacuum than a second source of vacuum, which second source of vacuum is connected to the central area of the web wire or the central area of the closing gap; and    wherein at least one adjustable device which is arranged to connect the first source of vacuum to one edge area is mounted to be adjustable in a cross-machine direction.    
   
   
       2 . The runnability device of  claim 1  wherein the at least one adjustable device comprises vacuum seals.  
   
   
       3 . The runnability device of  claim 2  wherein the vacuum seals comprise at least two labyrinth seals located at a distance from each other.  
   
   
       4 . The runnability device of  claim 3  wherein the labyrinth seals have essentially straight counter faces and form between them an air slot connected to the first source of vacuum.  
   
   
       5 . The runnability device of  claim 3  wherein the second source of vacuum is at least one of the labyrinth seals.  
   
   
       6 . The runnability device of  claim 2  wherein the first source of vacuum is a nozzle device which employs the ejection principle.  
   
   
       7 . The runnability device of  claim 6  wherein the nozzle device is a blow nozzle, having two wall sections located at a distance from each other, and wherein the wall sections have shaped counter faces, which are directed towards each other and which define between them a blow slot.  
   
   
       8 . The runnability device of  claim 7 , wherein the second source of vacuum is formed by at least one wall section of the blow nozzle.  
   
   
       9 . The runnability device of  claim 1  wherein the at least one adjustable device mounted to be adjustable in a cross-machine direction is adjustable in a Z-direction with respect to the wire so that a vacuum effect intensity can be adjusted in the machine direction.  
   
   
       10 . The runnability device of  claim 1 , wherein the at least one adjustable device mounted to be adjustable in a cross-machine direction comprises: 
 an adjustable width suction slot so that velocity of the air flow in the suction slot can be influenced to adjust vacuum intensity at the edge areas of the web wire and/or in the edge areas of the closing gap.    
   
   
       11 . The runnability device of  claim 1  wherein the wire does not touch the at least one adjustable device.  
   
   
       12 . The runnability device of  claim 1  wherein the at least one adjustable device is arranged to wear to correspond to a shape taken by the wire.  
   
   
       13 . The runnability device of  claim 11 , wherein the at least one adjustable device is constructed of polytetrafluoroethylene.  
   
   
       14 . A runnability device in a dryer section of a paper machine, having an impingement blowing hood positioned above a plurality of vacuum rolls and a wire extending in a machine direction between said plurality of vacuum rolls, and the wire positioned between the impingement blowing hood and the vacuum rolls, the wire having a first side which engages the rolls and the wire having a first edge area and a second edge area with a central area therebetween, the runnability device comprising: 
 a vacuum box positioned between two of said plurality of vacuum rolls, the vacuum box spaced from the wire first side to define a slot, and extending in a cross machine direction with respect to the wire;    at least one first source of vacuum;    a second source of vacuum which has less vacuum than the at least one first source of vacuum;    a first sealing device mounted for cross machine direction motion, and arranged to separate a first edge portion of the vacuum box from a central portion of the vacuum box;    a second sealing device mounted for cross machine direction motion, and arranged to separate a second edge portion of the vacuum box from the central portion of the vacuum box, the central portion of the vacuum box being between the first edge portion of the vacuum box and the second edge portion of the vacuum box;    wherein the first edge portion of the vacuum box is connected to the at least one first source of vacuum to draw a vacuum on the first edge area of the wire;    wherein the central portion of the vacuum box is connected to the second source of vacuum to draw a vacuum on the center area of the wire; and    wherein the second edge portion of the vacuum box is connected to the at least one first source of vacuum to draw a vacuum on the second edge area of the wire, or is connected to a second first source of vacuum to draw a vacuum on the second edge area of the wire.    
   
   
       15 . The runnability device of  claim 14  further comprising: 
 a first nozzle device which is arranged to employ the ejection principle, and which forms the at least one first source of vacuum; and    a second nozzle device which is arranged to employ the ejection principle and which forms the second first source of vacuum.    
   
   
       16 . The runnability device of  claim 15  wherein the first nozzle device is made up of two wall sections located at a distance from each other, wherein the wall sections have shaped counter faces, which are directed towards each other and wherein a border is located between them which defines a blow slot having a curved convergent gap part, followed by a reduction zone having a small flow cross-section, and followed by an out-flow zone; and 
 wherein the second nozzle device is made up of two wall sections located at a distance from each other, wherein the wall sections have shaped counter faces, which are directed towards each other and wherein a border is located between them which defines a blow slot having a curved convergent gap part, followed by a reduction zone having a small flow cross-section, and followed by an out-flow zone    
   
   
       17 . The runnability device of  claim 14  wherein the first sealing device and the second sealing device are labyrinth seals.  
   
   
       18 . The runnability device of  claim 14  wherein the first sealing device comprises a pair of spaced apart labyrinth seals, said pair of labyrinth seals defining the first edge portion of the vacuum box; and 
 wherein the second sealing device comprises a pair of spaced apart labyrinth seals, said pair of labyrinth seals forming the second edge portion of the vacuum box.