METHOD AND DEVICE IN A DRYER SECTION OF A FIBRE-WEB MACHINE, SUCH AS A PAPER OR BOARD MACHINE

摘要

A method in a dryer section of a fibre-web machine, in which dryer section at least one drying group employs single-wire draw in which a paper web (W) that is being dried runs on support of a drying wire (F) such that the drying wire (F) presses the web (W) on a drying cylinder (10) against heated cylinder surfaces, and the web (W) remains at the side of the outside curve of reversing cylinders (11) situated between drying cylinders (10, 12), and in which drying group a pocket space (T) is formed between two adjacent drying cylinders (10) and a reversing cylinder (11) situated between them, and the drying wire (F). In the method, a negative pressure is produced in at least one pocket space (T) of the drying group by means of a negative pressure component (20) placed in the pocket space (T) to create a pressure difference over the drying wire (F) and the web (W) for attaching the web (W) to the drying wire (F) such that the cross- direction shrinkage of the web (W) is controllable. In the method, the web (W) is passed from the drying cylinder (10) to the reversing cylinder (11) and from the reversing cylinder (11) to the next drying cylinder (12) as a short transfer, that in the method the tension of the drying wire (F) is maintained at a level of at least 3 kN/m to help to control the cross-direction shrinkage of the web (W), and that in the method the pocket space (T) is sealed by means of sealing members (25, 26) arranged in connection with the negative pressure component (20) and placed towards the surface of the adjacent drying cylinders (10, 12) to maintain the negative pressure in the pocket space (T). The invention also relates to a device in a dryer section of a fibre-web machine, in which dryer section a negative pressure component (20) is placed in at least one pocket space (T) of a drying group applying single-wire draw to produce a negative pressure effect in the pocket space such that a pressure difference is effective over the drying wire (F) and the web (W), and the drying cylinders (10, 12) and the reversing cylinder (1) of the drying group are placed with respect to one another in such a way that the transfer of the web (W) from the drying cylinder (10) to the reversing cylinder (11) and from the reversing cylinder (11) to the next drying cylinder (12) is short, and for confining an area of the negative pressure effect, seals (25, 26) of the negative pressure.