EP0373133A3 - Method and device in the formation of a paper or board web - Google Patents

Abstract

Method and device for the formation of a paper or board web (W) out of a fibrous material in a wire part which consists of a lower-wire loop (20), which is horizontal at the initial end of its upper run, and of an upper-wire loop (10) jointly operative with said lower-­ wire loop. After the initial dewatering carried out in the single-­ wire dewatering zone (20a) through the lower wire (20), the fibre layer (W) is passed over a lower-wire (20) support system (30) constituting a direct extension of the single-wire zone (20a), in the area of which said support system (30) dewatering by the effect of gravity through the lower wire (20) is prevented. With web qualities of higher grammage, after the single-wire dewatering zone (20a), the web (W) is passed to an initial part of the twin-wire dewatering zone, which is determined by the above support system (30) placed inside the lower-wire loop (20) and by a suction and foil equipment (40) placed opposite to it inside the upper-wire loop (10). Dewatering is carried out within the initial part through the upper wire (10). When thinner web qualities are being produced, the suction and foil equipment (40) is placed apart from contact with the lower wire (20) placed facing it (Fig. 1). After the above web formation stages, there follows a twin-wire dewatering section, which takes place within an upward short sector (a) of a forming roll (16) fitted inside the upper-wire loop (10), whereupon the twin-wire forming zone is curved downwards, being guided by a forming shoe (26) with a relatively large curve radius (R).