Patent ID: 8011115
Filing Date: 2011-09-06
Classification: D21F,Y10T

Abstract:
1. A method of drying a web in a dryer section of a paper or board machine comprising the steps of: passing the paper web through at least one single-wire draw dryer group in which the paper web runs supported on a drying wire such that the drying wire presses the paper web against a heated cylinder surface of a first heated drying cylinder; traversing the web from the first drying cylinder on an outside surface of the drying wire to a cylinder surface of a reversing roll along a first transfer length of less than 1000 mm, so the drying wire engages said reversing roll cylinder surface overlain by the paper web, and further transferring the web from the reversing roll to a second heated cylinder surface of a second drying cylinder along a second transfer length of less than 1000 mm and supported by the drying wire which presses the web onto the second heated cylinder surface, wherein the first drying cylinder, the second drying cylinder and the reversing roll positioned between the first drying cylinder and the second drying cylinder form together with the drying wire a pocket space therebetween; enhancing the runnability of the web by using a negative pressure component placed in the pocket space to produce a negative pressure in the pocket space to create a negative pressure difference over the drying wire and the paper web for attaching the paper web to the drying wire such that the cross-direction shrinkage of the web is controlled; maintaining a tension in the drying wire at a level of at least 3 kN/m to help to control the cross-direction shrinkage of the web; and sealing the pocket space with a first mechanical seal mounted to the negative pressure component extending towards the surface of the adjacent first drying cylinder and a second mechanical seal mounted to the negative pressure component extending towards the surface of the adjacent second drying cylinder to maintain the negative pressure in the pocket space.