GB1222870A - Flexible fire resistant air duct - Google Patents

Abstract

1,222,870. Making composite tubes; skelping; corrugating. CRYO-THERM Inc. 22 Nov., 1968, No. 55481/68. Headings B3A and B3E. [Also in Division F2] A fire-resistant heating and air-conditioning duct is made by forming inner and outer concentrically arranged tubular members 29 and 30 from foils with an insulating material filling the annulus defined therebetween, at least one said member being formed of a metal foil, e.g. steel foil, having a melting point of at least 2000‹ F. Both foils constituting the inner and outer tubular members are preferably of steel foil having a thickness in the range of 0À0005 to 0À005 inch and advantageously between 0À001 and 0À003 inch. However, the inner foil tube may be an aluminium, plastics or impregnated paper foil. The insulating material may be a foamed or expanded plastics such as foamed urethane or polyvinyl chloride or expansible styrene beads. Alternatively, the insulant may be glass fibre batting. As shown, the duct may be formed by passing steel foil strips through skelping formers 14 and 20, and seam welding the lapped edges of the respective strips by means of a pulsed copper wheel electrode 17 and a spring-biased shoe electrode 25 respectively, a foaming plastics mix being applied by nozzle 22. Instead of welding the lapped edges of the respective strips, mechanical lock seams 33, 34, Fig. 5 (not shown) may be provided. In another embodiment, Figs. 2 and 3 (not shown), glass batting 37 and steel foil strip 44 are simultaneously wound over a helicallywound inner foil tube having a crimped or welded helical seam, the outer strip being welded by wheel 39. The walls of the duct may be circumferentially corrugated, Fig. 8 (not shown), by utilizing a foil strip which has been passed through coacting corrugating rollers 45, 46 of respectively convexly and concavelycurved form to impart a curvature to the strip, Fig. 6 (not shown). In a modification, Fig. 6a (not shown), the strip is left with plain margins 51, 52 to facilitate lapwelding or mechanical seam-locking. In the corrugated duct construction of Fig. 8 (not shown), axially-spaced rings 59 of activated charcoal are arranged in the expanded plastics insulation to absorb any smoke which may form in the event of ductoverheating. The uncorrugated duct of Fig. 9 is similarly provided with smoke interceptors and the outer surface of the foil may be coated with tin, plastics or zinc. In the embodiment of Fig. 10 (not shown), the foamed plastics insulant is provided with a helically-coiled spring reinforcement 62.