Patent EP-0620314-A2 (EP)
Inventor: VIRTA RAIMO
IPC: D21F5/04
Filed: 1994-03-31
Abstract: The invention concerns a method for ventilation of the pocket spaces (T) in a multi-cylinder dryer of a paper machine, in particular of a high-speed paper machine whose running speed is higher than 800 metres per minute, in the area of so-called twin-wire draw. In the twin-wire draw the drying cylinders (11,12) in the drying group have been arranged in two rows (R₁,R₂) placed one above the other, in which rows the successive cylinders (11,12) are placed in the upper row and in the lower row as interlocked and in each of which cylinder groups there are two drying wires (F₁,F₂), an upper wire (F₁) and a lower wire (F₂), by whose means the paper web (W) is pressed against the heated faces of drying cylinders, being guided by guide rolls placed in the gaps between the cylinders, in which the paper web (W) runs as free draws between the rows of cylinders. The pocket spaces (T) are formed in the area between the free draws of the web (W) and the upper wire (F₁) and its guide roll and the drying cylinder (12) in the lower row and, in a corresponding way, the adjacent pocket spaces (T) are formed in the area between the free draws of the web (W), the lower wire (F₂), its guide roll, and the drying cylinder (11) in the upper row. In the method, the pocket spaces (T) are ventilated by means of pumpings of air induced by the wire (F₁;F₂) in the multi-cylinder dryer, wherein, at the inlet side of the guide roll, the wire (F₁;F₂) pumps air into the pocket spaces (T) through the wire (F₁;F₂), and wherein the wire (F₁;F₂) pumps air out of the pocket spaces (T) at the outlet side of the guide roll of the wire (F₁;F₂). In the method, pumping-out through the wire (F₁;F₂) on its run at the outlet side from the guide roll to the following cylinder (11;12) is limited as compared with free pumping-in and pumping-out so as to control the pressure level and/or the flow status in the pocket spaces (T). The invention also concerns an apparatus for ventilation of a pocket space in a multi-cylinder dryer of a paper machine in the area of so-called twin-wire draw, in which, in the twin-wire draw, the drying cylinders (11,12) in the drying group have been arranged in two horizontal rows placed one above the other, in which the successive cylinders (11,12) are placed in the upper row and in the lower row as interlocked, and in each of which cylinder groups there are two drying wires (F₁,F₂), an upper wire (F₁) and a lower wire (F₂), by whose means the paper web (W) is pressed against the heated drying-cylinder faces, being guided by guide rolls placed in the gaps between the cylinders, in which the paper web (W) runs as free draws between the cylinder rows. The pocket space (T) is formed in the area between the free draws of the web (W) and the upper wire (F₁) and its guide roll and the drying cylinder (12) of the lower row (R₂), and, in a corresponding way, the adjacent pocket space (T) is formed in the area between the free draws of the web (W), the lower wire (F₂), its guide roll, and the drying cylinder (11) in the upper row. In the area of the run of the wire (F₁;F₂) from the guide roll to the following cylinder (11;12), an obstructing device (20) is fitted, which reduces the amount of air that escapes from the pocket space (T).