Method for compensating for faults in a paper web

Abstract

Method for compensating for uneven shrinkage in a paper web in the press and drying sections of a paper machine, in which there is at least one open draw. In the method, a flow guide/guides are used in the head box, by means of which the machine direction orientation tendency of the fibres is reduced in the edge areas of the web and the angle of detaching of the web from the centre roll is adjusted, by directing onto the web an air jet that is located in the cross direction and the pressure of which can be adjusted in the said direction.

1 . Method for compensating for faults, like uneven shrinkage, in a paper web in the press and drying sections of a paper machine, in which there is at least one open draw,
 characterized in that   the paper web, which has a property naturally or induced by a differing release angle from the centre roll of the press section over its width, is fed to the press and drying sections of the paper machine and   the web's ( 4 ) release angle is adjusted by directing an air jet at the web ( 6 ), which is located in cross-direction of the web and the pressure of which can be adjusted in the said direction.   
     
     
         2 . Method according to  claim 1 , characterized in that, in order to compensate for the great shrinking tendency of the edge areas of the web, a flow guide/guides are used, the length of which in the edge areas of the web is greater that in the centre area, in order to reduce the machine direction orientation of the fibres. 
     
     
         3 . Method according to  claim 1 , characterized in that the pressure of the air jet, in the cross direction of the web, on the web ( 4 ) detaching from the centre roll ( 3 ) of the press section, is adjusted in such a way that it is greater in the edge areas of the web than in the centre area of the web. 
     
     
         4 . Method according to any of the above claims, characterized in that the release angle of the web from the roll is monitored in real time and the result of the monitoring is used directly and immediately to correct the pressure profile, in order to equalize the release angle of the web over the width of the web. 
     
     
         5 . Method according to  claim 4 , characterized in that a suitable measuring device, for example a laser camera/cameras is/are used for the monitoring.