Abstract:
An impeller is provided having a first plate, a second plate, a plurality of blades being positioned between and connected to the first and second plates, and at least one brace member having first and second planes positioned between and connected to two blades such that the brace extends generally perpendicular from the first blade and extends from the second blade at an angle.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to impellers and more particularly to impellers of centrifugal fans for commercial and industrial use. 
       BACKGROUND OF THE INVENTION 
       [0002]    Centrifugal fans are used in a wide range of applications from commercial building ventilation to industrial dust-collection systems. The fan wheel, or impeller, can come in different designs depending on the chosen application. Conventional impellers can comprise a front plate, a back plate, and a plurality of blades positioned between and connected to the front and back plates. The impeller is operatively associated with a conventional driving means which rotates the impeller thereby creating centrifugal force in an radial direction relative to the impellers axis of rotation. Air enters through a side of the impeller and exits the impeller in the direction of the centrifugal force. In some impellers, the blades tend to be thicker and heavier than blades of other impeller designs, and can therefore be used in heavier duty applications in which the air being moved contains contaminants that can damage lighter weight impeller blades. Such impellers may include brace plates which are positioned between and connected to the blades. During operation, the blades have a tendency to flex in the direction of centrifugal force. The brace plates prevent the blades from flexing, which in turn causes the brace plates to flex in a direction generally perpendicular to the direction of centrifugal force and creating stress in the brace plate. Disadvantageously, high duty cycling and operation at higher temperatures have, at times, resulted in fatigue cracking in the brace plates. 
         [0003]    It would be highly desirable to provide an impeller that has heavy blades for use in applications with airborne contaminants, and that can also resist the stresses from high duty cycling that conventional impellers fail under while also providing satisfactory air performance capabilities thereby increasing the life cycle of the impeller. 
       SUMMARY 
       [0004]    An impeller is provided having a first plate, a second plate, a plurality of blades being positioned between and connected to the first and second plates, and at least one brace member having first and second planes positioned between and connected to two blades such that the brace extends generally perpendicular from the first blade and extends from the second blade at an angle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a perspective view of an embodiment of an impeller; 
           [0006]      FIG. 2  is a side view of the impeller of  FIG. 1 ; 
           [0007]      FIG. 3  is a sectional front view of the impeller of  FIG. 1 ; 
           [0008]      FIG. 4  is an enlarged view of two blades and a brace of the impeller of  FIG. 1 ; 
           [0009]      FIG. 5  is a front view of an embodiment of a brace; and 
           [0010]      FIG. 6  is a side view of an embodiment of the brace of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  illustrates a perspective view of an impeller, generally designated  10 . In this example, impeller  10  includes a generally circular back plate  12  having a tubular hub  14  at its center extending axially from the back plate  12 . The hub  14  is adapted to be attached to and operatively associated with a driving means (not shown). Impeller  10  also includes a generally annular front plate  16  and blades  18 . Blades  18  of the example impeller  10  are generally flat and rectangular in shape and are attached at one side to back plate  12  and at the opposite side to front plate  16 . Blades  18  are connected to back plate  12  and front plate  16  by conventional means such as welding and extend generally perpendicular to back plate  12  and front plate  16 . Blades  18  include a first end  20  and a second end  22 . Blades  18  are spaced apart and may be spaced equidistant from one another. In this example, blades  18  are inclined relative to the direction of rotation of the impeller  10  such that the first end  20  of each blade  18  is disposed further from the center of back plate  12  than the second end  22 . Blades  18  also include an outer surface  24  and an inner surface  26  as shown in  FIGS. 2-4 . 
         [0012]    The impeller  10  also includes braces  30  disposed between and connected to blades  18 .  FIGS. 5 and 6  illustrate an example of a brace  30 . In this example, braces  30  are generally triangular in shape and include a first plane  32  and a second plane  34  which are at an angle θ relative to each other. For instance, angle θ may be in the range of approximately 140 degrees to 160 degrees. In one example, the angle θ may selectively be 150 degrees. It is understood that angle θ could fall outside the range of 140 degrees to 160 degrees, although the brace  30  has been found to be most effective within this range. The first plane  32  has an edge  36  and the second plane  34  has an edge  38 . The angle between first plane  32  and second plane  34  may be created by any conventional means such as bending brace  30 , welding two pieces together to form brace  30  or any other known method. 
         [0013]    As shown in  FIGS. 3 and 4 , in this example, each brace  30  is positioned between and connected to a first and second of the blades  18 ,  18 ′ such that the edge  36  of the first plane  32  is flat against the inner surface  26  of the first blade  18  and brace  30  extends straight out from the inner surface  26  of the first blade  18  such that the first plane  32  is generally perpendicular to both the inner surface  26  of the first blade  18  and the outer surface  24  of the second blade  18 ′, while the edge  38  of the second plane  34  is at an angle Ω relative to the outer surface  24  of a second blade  18 ′. For instance, angle Ω may be in the range of approximately 20 degrees to 40 degrees. In one example, the angle Ω may selectively be 30 degrees. It is understood that angle Ω could fall outside the range of 20 degrees to 40 degrees, although the brace  30  has been found to be most effective within this range. Braces  30  may be connected to blades  18 ,  18 ′ by conventional means such as welding. 
         [0014]    During operation, impeller  10  is caused to be rotated by conventional driving means, and centrifugal force is created by the rotation of the impeller  10 . The direction of the centrifugal force is generally radial relative to the axis of rotation of the impeller  10 . Without braces  30 , the centrifugal force would act upon blades  18  and would cause blades  18  to bend or flex in the direction of the centrifugal force. Braces  30  serve to prevent or reduce blades  18  from bending or flexing in the direction of the centrifugal force, thereby creating a force on the braces  30  in a direction generally perpendicular to the direction of the centrifugal force. The design of brace  30  including the first plane  32  and the second plane  34  at an angle relative to one another advantageously provides a greater resistance to the stresses caused by the force on the braces  30 . 
         [0015]    Use of braces  30  results in greater overall resistance to the centrifugal force which caused blades to flex and braces to crack in conventional impeller designs. A finite element analysis utilizing computer simulation comparing an impeller design of the example set forth above and a conventional impeller having standard braces showed that the impeller design of the example set forth above had a 23% reduction in stress in the braces when compared to the conventional impeller at the same rotational velocity. With that reduction in stress, an impeller can provide higher cycling capabilities. 
         [0016]    The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The description was selected to best explain the principles of the invention and its practical application to enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention not be limited by the specification, but be defined by the claims set forth below.