Abstract: A centrifugal fan with single or double intake is provided with a fan impeller of a closed type which is formed of a rotating bladed wheel having at least a covering element. Blades of the fan impeller are flat and are backwardly inclined with respect to a direction of rotation of the fan impeller, and the covering element comprises along a direction of flow a frustoconical surface portion, a first curved surface portion and a second curved surface portion, wherein a radius of curvature of the first curved surface portion is smaller than a radius of curvature of the second curved surface portion.
Abstract: There is disclosed, in combination with an apparatus for the manufacture of a fan wheel having a plurality of inclined elongated blades cylindrically mounted to a pair of end rings and at least one disc centrally keyed onto the blades and carrying a fan wheel hub, a press for fixing the end rings, the disc and the blades to each other, and a blade feed conveyor belt for carrying the required number of blades, to be assembled on the fan wheel, spaced at a distance corresponding to the position of the blades when assembled on the fan wheel, and for feeding the blades to the press.