This invention relates in general to air moving devices and in particular to centrifugal fans. 
Centrifugal fans include an impeller that rotates about an impeller axis.  The impeller draws air or another process gaseous fluid into the fan through an inlet that is parallel to an impeller axis.  The air is then delivered by the fan impeller in a direction perpendicular to the impeller axis.  The air stream delivered by the fan impeller enters a volute which collects and directs the air stream toward an outlet.  Centrifugal fans may have either a single or a double intake, that is, they can draw in air from only one side of the fan impeller or from two opposite sides of the impeller, respectively. 
The fan impeller is typically formed of a bladed rotating wheel consisting of a disk shaped base to which fan blades are secured.  For a fan with a single intake, the blades are arranged only on one side of the disk shaped base; however, for a fan with a double intake, the blades are arranged on both sides of the base.  The fan blades can be arranged in a radial direction or they can be inclined forwardly or backwardly with respect to a rotational direction of the fan impeller.  The fan blades often have a streamlined profile, but flat blades, that is, non-streamlined blades, are also known. 
Additionally, impellers of centrifugal fans can be of a closed or open type according to whether or not a covering element, commonly called an impeller covering, consisting of a circular frame fastened to a tip of the blades is provided.  Fan impellers provided with inclined blades are generally of the closed type in order to increase the bending strength of the blades. 
Impellers are typically formed by welding the fan blades to an impeller disc shaped base; however, it would be desirable if the impeller assembly could be simplified to reduce the cost and complexity of fabrication.