Patent ID: 6092304
Filing Date: 2000-07-25
Classification: B65H,D21F,F26B

Abstract:
A blow box intended to be used in a plant for drying a material web (1), such as a web of papermaking pulp being advanced through said plant, said blow box having an elongate, essentially right-angled parallel-epipedon shape including an essentially horizontal upper box wall (3) and being intended to be placed, jointly with a plurality of identical blow boxes, below the material web (1) for the purpose of holding the material web floating, i.e. suspended in the air, in a well-defined position above the upper blow box wall (3) by means of air streams that are being blown out of the box while simultaneously drying the material web, said blow box being designed to be placed below the material web (1) in a manner ensuring that the longitudinal centre line (C) of the upper box wall (3) extends transversely of the direction of advancement (P1) of the web (1), the upper well (3) of said blow box being formed with a plurality of essentially circular nozzle orifices (5), and with a plurality of so-called eyelid perforations (6), each one of said perforations consisting of a slit (7) extending in parallel with said centre line (C) and of a depression (8) formed in the upper box wall (3) adjacent the slit, at one side of the latter, said eyelid perforations (6) being arranged in two rows extending in parallel with and on either side of the centre line (C), said nozzle orifices being arranged in rows (9a, 9b, 10a, 10b), likewise extending in parallel with and on either side of said centre line (C), the eyelid perforations in one row being so displaced in the longitudinal direction of the blow box relatively to the eyelid perforations of the other row that the eyelid perforations of both rows together form a zigzag pattern, the eyelid perforations (6) of both rows being oriented in such a manner as to cause air to exit essentially in parallel with the upper box wall (3), towards said centre line (C), and essentially perpendicularly thereto, and the nozzle orifices (5) being directed in such a manner as to cause air to exit essentially at right angles to the upper box wall (3), characterised in that the slits (7) of the eyelid perforations (6) in both rows are equally spaced from said centre line (C), that said centre line (C) intersects the depressions (8) of the eyelid perforations (6) in both rows, that the nozzle orifices (5) are arranged in respectively a first and a second pair of rows (9a, 9b and 10a, 10b, respectively), the two rows of each pair being positioned on either side of and spaced equally from said centre line (C), that the distance of the rows (9a, 9b) of the first pair to said centre line (C) is smaller than the distance of the rows (10a, 10b) of the second pair to said line, that for each eyelid perforation (6) there is a corresponding nozzle orifice (5) in the row (9a or 9b) of the first pair of nozzle orifices that is positioned on the same side of said centre line (C) as a slit (7) of the associated eyelid perforation (6), and also a corresponding nozzle orifice (5) in the row (10a, 10b) of the second pair that is positioned on the opposite side of said centre line (C), each eyelid perforation (6) and its two corresponding nozzle orifices (5) being essentially in alignment in the crosswise direction of the blow box, and in that the upper box wall (3) has a shallow continuous arcuate shape across its entire width.