Centrifugal fan impellers with blades secured between plates

Claim 1

A fan impeller comprising a back plate, a front plate, and a plurality of metal blades lying between the front plate and the back plate wherein each blade is of channel section having a base and two sides, the base of each blade lying normal to the planes of the front plate and the back plate, one side of each blade lying along the back plate, the other side of each blade lying along the front plate, and both sides of each blade extending from the base in the direction of rotation of the impellers in use, the inside working surface defined by the base and sides of each blade being hardened to a minimum hardness of Rockwell C55, the working surface of the base of each blade being convexly curved in the longitudinal direction of the blade, and wherein two bars are provided for each blade fixedly attached to the surface of the base of the respective blade remote from sides of the blade and extending between the front and back plates, the bars being spaced apart along the base of the blade and extending perpendicular to the front plate and back plate, the front plate the back plate and the blades being retained in assembled relation solely by bolts passing through the plates and through bores formed in the bars, the bolts fixedly attaching the bars to the front plate and the back plate.