| 摘要 |
Cylindrical drying rolls are provided over which a web is passed along with a support fabric. A throttling unit provided at short distance from opening nip in air blow box equipped at the side of fabric, divides negative pressure space formed between upper and lower sealing units into regions respectively of intensified and smaller negative pressures. The air blow box extends along the entire width of web. The air blowing device is arranged on that side of support fabric, which is away from the roll (10), mainly at the opening nip between the support fabric and the roll so that it extends from the nip to at least a short distance forward in support fabric travel direction. The sealing units include nozzles, or mechanical seals, being transversal with respect to web conveyance direction. The upper sealing unit (36) is a nozzle arranged in blow box, close to support fabric, for blowing air jets away from the negative pressure space formed between the support fabric and blow box. The lower sealing element is arranged close to support fabric or the roll (14) turning the support fabric at a distance from opening nip. A suction orifice (54) is provided between the upper sealing nozzle and throttling unit, and is connected to suction device to increase negative pressure in the region (34'). The upper sealing nozzle is arranged close to disengaging point (40) between drying roll and support fabric. The lower sealing nozzle is arranged close to closing nip between turn roll and support fabric, so that air jet from the lower nozzle is discharged from closing nip, from the region (34) and from the pocket (20) formed between the drying rolls. The throttling unit has convex surface which guides the air jets away from intensified negative pressure region, using the Coanda effect. A guide plate is arranged between throttling unit and closing nip, to prevent external ejection of air with the ejecting nozzle from reaching the closing nip. The throttling unit has air flow restriction unit extending across the web and mounted resiliently or pivotably in blow box in order to maintain intensified pressure in the region (34). The throttling unit extends to a distance to be at a distance of 10 mm from the support fabric. The region (34) has length 100-200 mm and upper and sealing nozzle is at a distance of about 70 mm from the disengaging point of support fabric. The throttling unit is at a distance of about 100 mm from the disengaging point. |
