Abstract:
A wear plate for use in a centrifugal pump is structured with at least one cutting element positioned at the inner bore of the wear plate, the cutting element or elements being positioned to impact the cutting edge of the vanes of an impeller and oriented in a direction relative to the rotation of the impeller so that the wear plate cutting element or elements can capture the solids in a processed fluid and hold them in place until the solids can be cut by the impeller vane or vanes, the wear plate cutting elements further being structured to be self-sharpening.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a non-provisional application claiming priority to provisional patent application Ser. No. 60/967,440 filed Sep. 4, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to centrifugal pumps, and relates specifically to a wear plate for a centrifugal pump having an inner bore edge structured for cutting solids. 
         [0004]    2. Description of Related Art 
         [0005]    Centrifugal pumps are structured with a pump casing in which an impeller is positioned for rotation. To maximize pump efficiency, the impeller is positioned in close proximity to the pump casing inner surface to provide minimal tolerances between the impeller and the pump casing. When such pumps are used to process fluids with a solids content, the solids tend to erode or wear the inner surface of the pump casing, thereby leading to reduced pump efficiencies. 
         [0006]    It is known in the pump industry to position a wear plate between the impeller and the inner surface of the pump casing so that the wear plate is subjected to the erosive effect of the solids. The wear plate can then be easily replaced when worn, rather than attempting to effect a repair or replacement of the pump casing. Certain types of centrifugal pumps are also configured with means for adjusting the position of the wear plate toward the impeller to decrease the gap therebetween as the wear plate becomes eroded. 
         [0007]    When centrifugal pumps having wear plates are used to process solids-entrained fluids, especially those containing stringy solids, the solids can become lodged around the smooth inner bore of the wear plate. The stringy solids tend to be pushed and rolled by the edge of the impeller without being cut. The accumulated solids then begin to cause excessive wear between the impeller and the wear plate and the gap between the impeller and wear plate increases, thereby reducing pump efficiency and allowing recirculation of fluid within the impeller. 
         [0008]    In recognition of the deleterious effects that solids have on the pump casing, it is known to provide a wear plate that is configured and positioned relative to the impeller to dislodge and direct solids away from the inlet opening or impeller. Examples of such wear plate designs are disclosed in U.S. Pat. No. 6,139,260 to Arbeus and U.S. Pat. No. 6,464,454 to Kotkaniemi. The wear plates of those inventions provide for an increased space between the wear plate and impeller, but the increased space has the resulting effect of reducing pump efficiencies. 
         [0009]    U.S. Pat. No. 7,037,069 to Arnold further discloses a wear plate for use in a centrifugal pump employing a single vane spiral-type impeller where the wear surface of the wear plate is provided with flow interrupters in the form of notches and recesses that are perpendicular to the axis or rotation, and/or that extend in a direction opposite to the direction of rotation of the impeller. The notches and recesses are provided to interrupt the flow of fluid along the vane of the impeller and to dislodge and clean solids from the impeller to move the solids toward the volute of the pump for discharge. The flow interrupters are positioned on the wear plate to remove solids from the impeller vane; however, they do not provide cutting or chopping of the solids. 
         [0010]    It is further known in chopper type centrifugal pumps to provide chopper plates with cutter bars or cutting elements that span the eye of the impeller to effect cutting of solids at the eye of the impeller. Such cutter bar arrangements can prove beneficial to effecting the reduction and processing of solids, but also may. result in solids, particularly stringy solids, from accumulating at the eye of the impeller. 
         [0011]    Thus, it would be advantageous to provide a means for cutting solids at the cutting edge of an impeller in centrifugal pumps that process solids-containing fluids, and to provide such means in a wear plate that can function to withstand the wear of processed solids. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    In accordance with the present invention, a wear plate for use in a centrifugal pump is structured with at least one cutting element, but most suitably a plurality of cutting elements, positioned at the inner bore of the wear plate. The cutting elements are positioned to impact the impeller and are oriented in a direction relative to the rotation of the impeller so that the cutting elements can capture the solids and hold them in place until they can be cut by the impeller blade or blades. 
         [0013]    Cutting elements on the wear plate of the present invention may be distributed or spaced evenly or unevenly about the inner bore of the wear plate and may have any shape, size, dimension or configuration which will effectively cause cutting of solids at the inner bore of the wear plate. By facilitating the cutting of solids at the inner bore of the wear plate, the solids are more quickly reduced for processing rather than being simply flushed into the impeller, as is the purpose of prior art wear plates. Additionally, the wear on the wear plate and impeller are reduced so that the pump operation life is not decreased. 
         [0014]    The cutting elements of the wear plate of the present invention are further configured with a wall, defined by the thickness of the wear plate and extending from the non-wear surface (i.e., that surface positioned away from the impeller) to the wear surface (i.e., that surface positioned adjacent the impellers, which is angled from the non-wear surface to the wear surface of the wear plate, thereby imbuing the cutting elements with a self-sharpening edge as the wear plate wears. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0015]    In the drawings, which illustrate what is currently considered to be the best mode for carrying out the present invention: 
           [0016]      FIG. 1  is a perspective view in partial cutaway of a conventional self-priming pump illustrating the relative positioning of the impeller and wear plate; 
           [0017]      FIG. 2  is a perspective view in partial cutaway of a self-priming pump illustrating the placement of the wear plate of the present invention; 
           [0018]      FIG. 3  is a perspective view of a prior art wear plate having a smooth inner bore; 
           [0019]      FIG. 4  is a perspective view of the wear plate of the present invention; 
           [0020]      FIG. 5  is a perspective view of the wearplate and impeller as viewed from the wear surface of the wear plate; 
           [0021]      FIG. 6  is a perspective view of the wear plate and impeller as viewed from the non-wear surface of the wear plate; 
           [0022]      FIG. 7  is a plan view of the non-wear surface of the wear plate of the present invention; 
           [0023]      FIG. 8  is an enlarged view of the cutting elements of the wear plate; 
           [0024]      FIG. 9  is a view in cross section of the radius of the wear plate shown in  FIG. 7 , taken at line  9 - 9 ; 
           [0025]      FIG. 10  is a perspective view of a prior art wear plate having a conical shaped wear surface; 
           [0026]      FIG. 11  is a perspective view of the prior art wear plate shown in  FIG. 10  illustrating the non-wear surface of the wear plate; 
           [0027]      FIG. 12  is a plan view of an alternative embodiment of the wear plate of the present invention, the wear plate being generally frustoconical in shape; 
           [0028]      FIG. 13  is a view in cross section of the wear plate shown in  FIG. 12  taken at line  13 - 13 ; 
           [0029]      FIG. 14  is a perspective view of the non-wear surface of the wear plate shown in  FIG. 12 ; 
           [0030]      FIG. 15  is a perspective view of the wear plate of  FIG. 12  shown in position adjacent an impeller; and 
           [0031]      FIG. 16  is a perspective view of the non-wear surface of the wear plate shown in  FIG. 15  illustrating the interaction between the wear plate and impeller. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    The wear plate of the present invention is adaptable for use in any type of centrifugal pump which employs or can employ a wear plate positioned between the impeller and the pump casing or another adjacent structure of the pump. The present invention is described herein with respect to a self-priming pump by way of example only. Those of skill in the art will understand, based on the present disclosure, how to adapt the present invention to other types of centrifugal pumps. 
         [0033]      FIG. 1  illustrates a conventional self-priming pump  10  which generally comprises a pump casing  12 , an inlet  14  and an outlet  16 . The impeller  18  is supported at the end of a bearing housing  20  and is connected to a drive shaft  22  for rotation. A clean out assembly  24  is axially aligned with the impeller  18  and comprises an end cover  26  and a supporting ring  28  that is spaced from the end cover  26  by a plurality of stanchions  30 . The supporting ring  28  provides a means for attachment of a wear plate  32 , which positions the wear plate adjacent the impeller  18 . 
         [0034]    As best seen in  FIG. 3 , the prior art wear plate  32  is generally configured as a flat plate having a thickness T extending between a non-wear surface  34  and an opposing wear surface  36  that is provided for orientation adjacent the impeller. The wear plate  32  is formed with an inner bore  38  that extends through the thickness of the flat plate and is provided with an inner circumferential edge  40  that surrounds the inner bore  38 . In the prior art wear plate  32 , the inner circumferential edge is smooth.  FIG. 3  also illustrates that-the wear plate  32  may be secured to the supporting ring  28  by bolts  44 . 
         [0035]    The wear plate  50  of the present invention is shown in  FIGS. 2 and 4 . In  FIG. 2 , where like parts of the pump are referred to by like reference numerals, the wear plate  50  of the present invention is likewise supported by a supporting ring  28  of a clean out assembly  24 , and is positioned adjacent the impeller  18 . 
         [0036]      FIG. 4  more clearly illustrates that the wear plate  50  of the present invention is formed, in this first embodiment, as a flat plate having a thickness T extending between a non-wear surface  52  and an opposing wear surface  54  that is provided for orientation adjacent an impeller. The wear plate  50  is provided with means for attachment of the wear plate  50  to the supporting ring  28  of the clean out assembly, such as bolts  56 . 
         [0037]    The wear plate  50  has an inner bore  58  formed through the center of the wear plate  50  and the inner bore  58  is formed with an inner circumferential edge  60 . The inner circumferential edge  60  of the wear plate  50  is formed with at least one or, as shown here, a plurality of cutting elements  62 . 
         [0038]    As illustrated in  FIGS. 5 and 6 , the cutting elements  62  are positioned to interact with the blade  66  or blades of the impeller  18  to produce a cutting action at the inner circumferential edge  60  of the wear plate  50 . The cutting action of solids at the inner bore  58  of the wear plate  50  assures that solids, particularly stringy materials, are processed to a smaller and/or more suitable form for movement by and through the impeller  18 . 
         [0039]    As best seen in  FIG. 7 , the cutting elements  62  are generally produced by forming notches  70  in the inner circumferential edge  60  of the inner bore  58 . The notches extend from the inner circumferential edge  60  toward the outer edge  74  of the wear plate  50 . Two adjacently-formed notches  70  produce a tooth  72 . As illustrated in  FIG. 7 , there may be more than one tooth  72  formed at the inner bore  58 ; however, a single tooth  72  may be formed in the inner bore  58 . Further, as illustrated in  FIG. 7 , the plurality of teeth  72  may be spaced evenly about the inner circumferential edge  60 . However, alternatively, the cutting elements  62  may be spaced unevenly about the inner circumferential edge  60 . 
         [0040]    The notches  70  formed in the inner circumferential edge  60  are preferably formed at a tangential angle to the inner circumferential edge  60  such that a center line  76  ( FIG. 7 ) of the notch  70  extends in the direction of rotation of the impeller, as shown in  FIG. 5 . The angle of the notches  70  facilitates the capture of solids material in the notch to enable cutting by the blade or blades  66  of the impeller  18 . 
         [0041]    As further illustrated in  FIGS. 7-9 , the notches  70  and teeth  72  are formed with a wall surface  80  that is defined by the thickness between the wear surface  54  and the oppositely-facing non-wear surface  52  of the wear plate  50 . The notches  70  are formed by cutting or machining through the thickness of the wear plate  50  at an angle to a plane  82 , formed through the thickness of the wear plate  50 , that is perpendicular to the planes of the wear surface  54  and non-wear surface  52  of the wear plate  50 . That is, the angle A of the wall  80  is directed toward the center  84  ( FIG. 7 ) of the wear plate  50  in a direction extending from the non-wear surface  52  to the wear surface  54  of the wear plate  50 . Notably, the center  84  of the wear plate  50 , when positioned in a pump, is co-axial with the rotational axis of the impeller. 
         [0042]    As best seen in  FIG. 8 , the angle A of the wall  80  of the notches  70  produces a tooth  72  having an edge  86  formed by the wear surface  54  which is greater than an edge  88  formed by the non-wear surface  52  of the wear plate  50 . Consequently, the cutting elements  62  or teeth  72  of the wear plate  50  are self-sharpening as the wear plate  50  becomes worn by its interaction with the impeller (it being understood in the art that the wear plate  50  is axially adjusted toward the impeller from time to time as the wear plate  50  becomes worn). 
         [0043]    The wear plate  50  described thus far, which is in the form of a flat plate, is suitable for use in smaller sizes, and certain types, of centrifugal pumps. In larger sizes or different types of centrifugal pumps, the wear plate may be formed in a generally frustoconical shape.  FIGS. 10 and 11  again illustrate a frustoconical wear plate  90  that is known in the prior art. The wear plate  90  has an inner bore  92  with a smooth inner circumferential edge  94 .  FIG. 10  illustrates the wear surface  96  of the frustoconical wear plate  90  and  FIG. 11  illustrates the non-wear surface  98 . 
         [0044]      FIGS. 12-14  illustrate a frustoconically-shaped embodiment of the wear plate  100  of the present invention where the inner bore  102  has an inner circumferential edge  104  that is formed with at least one cutting element  106 , or a plurality of cutting elements  106  as shown.  FIG. 12  illustrates the wear surface  108  of the wear plate  100  and  FIG. 14  illustrates the non-wear surface  110  of the wear plate  100 . The cutting elements  106  are formed in the manner previously described with respect to the flat plate embodiment illustrated in  FIGS. 7-9 , including the formation of the cutting elements to provide a self-sharpening capability. 
         [0045]      FIG. 15  further illustrates the frustoconically-shaped wear plate  100  of the present invention where the wear surface  108  is positioned adjacent an impeller  120  of a larger size pump.  FIG. 16  illustrates the non-wear surface  110  of the wear plate  100  and illustrates the interaction of the cutting elements  106  with the blades  122  of the impeller  120 .  FIGS. 15 and 16  illustrate the position and direction of the cutting elements relative to the direction of rotation of the impeller  120 , as denoted by arrow  126 . It can be appreciated from the view of  FIG. 16  that the notches  128  formed between the cutting elements  106  effectively trap solids therein for cutting by the leading edge  130  of the impeller blades  122  as the impeller rotates. 
         [0046]    The wear plate of the present invention can be adapted for use in any type of centrifugal pump having an impeller, and especially a pump that is used to process fluids which are laden with solids material. Thus, reference herein to specific details of the illustrated embodiments are by way of example only and not by way of limitation.