GB1420219A - Method of twin-wire web forming - Google Patents

Abstract

1420219 Web forming BELOIT CORP 15 Nov 1972 [15 Nov 1971] 35724/72 Heading D2A A vertical web forming machine comprises twin wires F1, F2 extending respectively round breast rolls 12, 13, then over stationary guides 15, 16 and round a couch roll 20, a headbox 11 being provided for feeding stock into the gap N-1 between the wires at the breast rolls and the guide 15 having a curved wire-engaging surface. The headbox 11 which has trailing flexible members therein may feed downwardly instead of upwardly as shown, the other members of the machine being disposed accordingly. The breast rolls may be open or solid and may be the same size or different sizes. The wires Fl, F2 extend over tensioning guide rolls 19, 19' and are synchronously driven by motors M1, M2 at a speed which may be that of the jet of stock from the headbox 11. The wires may be of bronze, steel, copper, plastics or fabric, or of a plurality of different materials, e.g. the wire F2 is of plastics such as acrylic or nylon and the wire Fl of bronze. The headbox 11 may be adjustable, e.g. by a hydraulic jack, to ensure that the jet of stock contacts one of the wires before the other end beyond the breast roll 13 to avoid pumping by the rolls. The radius of curvature of the wires throughout the forming zone is from 100 to 300 inches. The guide 15 comprises a plurality of closely spaced transversely disposed edges 15a having at least their wire-engaging portions formed of mirror-smooth ceramic or plastics material, and the guide may be subject to vacuum. The guide 16 is a suction box having a wire-engaging surface which is curved with a radius of curvature equal to or less than that of the guide 15. Doctors 12a, 13a, 17, 17a and 18 and an air doctor 18a are provided, and save-alls 5a collect water for re-use. The couch roll 20 has compartments 19, 21, 22 subject to successively decreasing amounts of vacuum less than that of the guide 16 which is subject to vacuum less than that of the guide 15. The radius of curvature of the roll 20 is 1/5 to 1/10 that of the surface of the guide 15, e.g. from 18 to 36 inches. The wire F2 carries the web to a pick-up felt PF extending round a suction roll 24 which can be moved away from the wire F2 if the web is damaged so that the web can be dumped by the wire F2 into a broke pit. The felt passes through a felt-only press nip FN-1 and a first web press nip WN-1 formed by rollers 25, 26, 27 which may be plain, blinddrilled, suction or grooved rolls and may be provided with doctors. In a second embodiment, Fig. 2 (not shown), the breast rolls are solid and are provided with doctors. A solid water-impermeable guide may be used in place of or in conjunction with the guide 15. A plurality of guides similar to the guide 16 may be provided or the guide 16 may be omitted. The couch roll may be a solid roll which may be the only roll driven by a motor. In a third embodiment, Fig. 3 (not shown), the headbox is adjustable to vary the thickness of the jet of stock, and the breast rolls are adjustable to vary the gap N-1. The guide 15 is pivotally mounted.