GB720956A - Improvements in or relating to centrifugal fan wheels - Google Patents

Abstract

720,956. Centrifugal fans. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. May 6, 1953 [June 21, 1952], No. 12570/53. Class 110 (1). In a centrifugal fan impeller comprising aerofoil blades attached at their ends to a back plate and a shroud plate, the blades comprise light-weight sponge-like (i.e. having a large number of interstices with air cells therein) cores within and adhesively bonded to outer skins of sheet metal, preferably aluminium. The impeller may be of the double-inlet type, in which case the back plate is the centre plate of the impeller. The core may be of a plastic composition which is poured into the blade through a hole in the back plate or shroud plate and is subsequently heated to cause it to foam and thus expand to press against and adhere to the inner surface of the blade skin. The plastic composition may be a mixture, such as tolylene diisocyanate plus alkyd resin, which generates its own heat. Alternatively, the heat may be applied externally, in which case the core may comprise pellets of nylon and phenolic rubber, or granular cork mixed with phenolic varnish. As a further alternative, the core is preformed, coated with an adhesive, and slid into an open end of a preformed blade. Or, the blade skin is wrapped around the preformed core with adhesive between them, the trailing edges of the blade skin being secured together in a lock seam. A suitable material for a preformed core is a foamed styrene. Or, a cellular or honeycomb texture may be provided by the use of resin impregnated paper or cloth, aluminium foil or cellular cellulose acetate. Holes 25, Fig. 9, can be pressed inwardly to assist in bonding the core 24 to the skin 23. The core may have a void within it, as shown in Figs. 4 and 8, where a hollow inner skin 26 of aerofoil shape is provided. In the modification shown in Fig. 13, a cellular core 38 is folded over an inner member 37 and then the outer skin 23 is folded around the core, and the trailing edges of the outer skin are joined together by a lock seam. Granular composition 39 is then poured into the vacant space at the trailing end, and heated. Alternatively, the voids may be formed by one or more hollow tubes 27, Fig. 11, passing longitudinally through the core. By expanding the ends of the tubes as shown, the blades are secured in place between the back plate 21 and shroud plate 20. In addition, the blade skin may be welded at 35 to the plates. Figs. 8, 9 and 10 show alternative ways of attaching the blades to the plates. Rivets are shown, but welding may be used instead at the connection to the blade skin. In Fig. 8, angle bars 30, 31 extend around the outside of the blade; and in Fig. 9, channel members 32, 33 are used. In Fig. 10, the use of W-shaped attachment members 34 avoids the use of blind riveting at the connection to the blade skin. Specification 488,781 is referred to.