Method and apparatus for detecting and counteracting a deformation of the stock discharge gap in a headbox of a paper machine

摘要

The invention relates to a method and an apparatus for detecting and counteracting a deformation of the stock discharge gap in a paper machine headbox, which is caused by thermal expansion due to the temperature of the stock and/or the pressure of the stock. This is achieved by ultrasonic transducers located close to the slice opening which obtain measurement results relating to the distance between the roof member and the apron beam member of the headbox. At least two such transducers, one preferably located close to a side wall of the discharge gap and the other preferably located midway between the side walls, give information about a possible difference between the measurement results caused by the deformation. This difference serves as a guide for adjusting the temperature of the apron beam member and/or the roof member in such a way that the deformation is reduced in magnitude or entirely eliminated.