Abstract:
A method of installing an annular bearing element within a centrifugal pump utilizes a mechanical staking operation. The bearing element locates within a receptacle of a pump stage that is surrounded by a retaining wall. Once the bearing element is located within the retaining wall, the retaining wall is permanently deformed at various points against the bearing element. The bearing element, if of a hard wear resistant metal, may have flats for the circumferentially spaced apart deformations to locate within. The bearing element may be a thrust washer for transmitting downward thrust, or it may be a radial support bearing sleeve.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to centrifugal pump stages, and in particular to a method of attaching radial and axial support bearing elements. 
     BACKGROUND OF THE INVENTION 
     Centrifugal pumps for petroleum production are made up of a large number of stages. Each stage has an impeller that is rotated by a shaft driven by an electrical motor. Each impeller is located within a stationary diffuser. Each diffuser has passages that extend downstream and radially inward toward the shaft for receiving fluid from an upstream impeller and delivering the fluid to a downstream impeller. Each impeller has a central inlet and passages that extend outward in a downstream direction for delivering well fluid to a downstream diffuser. 
     The rotation of the impeller causes down thrust. Typically, each impeller is free to float axially on the shaft, and transmits the down thrust to its mating diffuser. Furthermore, thrust washers are located between the mating surfaces for handling the rotating sliding engagement between the impeller and the diffuser. 
     One type of thrust washer is made of phenolic material, which is not particularly hard. Another type, which is used for abrasive well fluid conditions, is of a hard, wear resistant metal such as tungsten carbide. The diffuser and impeller are cast of a metal such as Ni-Resist. Normally, the thrust washer is attached to the impeller for rotation therewith, such as by adhesive or by an interference fit. One problem with adhesive is that the bonding surface of the impeller must be very clean and free of oil. Also, the adhesive has to have time to cure. Further, in high temperature wells, the temperature may exceed that of the adhesive, causing it to deteriorate. If the thrust washer begins to spin relative to the impeller, damage to the impeller may occur. 
     An interference fit requires a high tolerance for the mating components. Also, it may not be as reliable as the adhesive because variations in the force fit installation. The differences in the coefficient of expansion of the impeller and a tungsten carbide thrust washer could cause the thrust washer to become loose at high temperatures. An interference fit required to hold a tungsten carbide thrust washer at high temperatures may be so large that the thrust washer fractures during assembly. 
     The diffuser has an internal bearing support that receives a bearing sleeve for engaging the rotating shaft. The bearing sleeve is typically installed in the bearing support by heat shrink and force fit techniques. In high temperature operations, the differences in thermal expansion of the bearing sleeve can cause the bearing sleeve to become loose and fall out or to spin in the bearing holder of the diffuser. Force fits may not be successful when the plastic deformation of the bearing holder material of the diffuser causes the bearing to become loose at high temperatures. An interference fit required to hold the bearing sleeve at high temperatures may be so large that the bearing fractures during assembly. 
     SUMMARY OF THE INVENTION 
     The bearing element for a centrifugal pump assembly is installed in a receptacle of a bearing holder, which may be a portion of an impeller or a portion of a diffuser. The receptacle has a retaining wall located adjacent the bearing element. The retaining wall is permanently deformed against the bearing element to prevent rotation. 
     The mechanical deformation involves staking or bending portions of the retaining wall inward. These deformed portions are spaced circumferentially apart from each other around the retaining wall. Recesses may be provided on the outer diameter of the bearing element for receiving the deflected portions of the retaining wall therein. The recesses may be flats that are circumferentially spaced around the bearing element. The flats may be in axial planes or, they may be inclined bevels located at the intersection of the sidewall with an end of the bearing element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial sectional view of a portion of a pump stage constructed in accordance with this invention. 
         FIG. 2  is an axial sectional view of the impeller of the pump stage of FIG.  1 . 
         FIG. 3  is a bottom view of the impeller of FIG.  1 . 
         FIG. 4  is a top view of a die used for staking the thrust washer to the impeller of FIG.  2 . 
         FIG. 5  is an axial sectional view of a die assembly that utilizes the die of FIG.  4 . 
         FIG. 6  is an enlarged sectional view of a portion of the assembly of  FIG. 5 , showing the staking operation being performed with the die assembly of FIG.  5 . 
         FIG. 7  is a sectional view of an alternate embodiment of a pump stage constructed in accordance with this invention. 
         FIG. 8  is a plan view of one of the thrust washers of the pump stage of FIG.  7 . 
         FIG. 9  is a partial sectional view of the pump stage of FIG.  7 . 
         FIG. 10  is a sectional view of the pump stage of  FIG. 11 , taken along the line  10 — 10  of FIG.  11 . 
         FIG. 11  is a sectional view of a third embodiment of a pump stage constructed in accordance with this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , pump stage  11  is part of a centrifugal pump stage of a pump that is particularly used for petroleum production. Normally, such a pump has a large number of pump stages  11 , each having an impeller  13  that has a hub  15  mounted to a shaft  17  for rotation therewith. In most pumps, impeller  13  is free to move small distances in axial directions on shaft  17 . Impeller  13  has a plurality of passages  19  that extend from an upstream inlet outward to the periphery of impeller  13 . A skirt  21  surrounds the central inlet and depends downward or in upstream direction. A retaining wall  23  extends downward from the lower or upstream side of impeller  13  concentric with the axis and spaced radially outward from skirt  21 . 
     Skirt  21  and retaining wall  23  define an annular receptacle for receiving an outer thrust washer  25 . A second or inner thrust washer  27  may be located on impeller  13 . Thrust washers  25 ,  27  are both secured in receptacles in a manner to cause them to rotate with impeller  13 . Because of the greater distance from the axis of shaft  17 , outer thrust washer  25  encounters more torque than inner thrust washer  27 . 
     Impeller  13  is rotatably carried within a diffuser  29  that is stationarily mounted in a housing (not shown). Diffuser  29  has fluid passages  31  that extend inward in a downstream direction for delivering fluid to the inlet of impeller  13  within skirt  21 . Skirt  21  slidingly engages the outlet of diffuser  29 . Diffuser  29  has an outer thrust surface  33  and an inner thrust surface  35 , both on the downstream end. Thrust surface  33  engages thrust washer  25 , while thrust surface  35  engages inner thrust washer  27 . 
     Referring to  FIG. 3 , retaining wall  23  has an inner side  37  and an outer side  39  that are joined by a rim  41 . Rim  41  is typically in a plane perpendicular to the axis of rotation of impeller  13 . After thrust washer  25  is placed in the receptacle next to retaining wall  23 , a plurality of deformed portions  43  are made in rim  41 . As can be seen in  FIG. 3 , deformed portions  43  enlarge the wall thickness of retaining wall  23  between inner side  37  and outer side  39 . Deformed portions  43  are spaced circumferentially around retaining wall  23  to mechanically stake or secure outer thrust washer  25  in place. Inner thrust washer  27  could be installed by the same manner, or it could be installed in a conventional manner, such as by adhesive. 
     Referring to  FIG. 5 , die assembly  45  is suitable for making the deformed portions  43  (FIG.  3 ), although other devices could also perform the staking operation. Die assembly  45  has a lower body  47  that rigidly supports an annular die  49 . Die  49  has a plurality of staking projections  51 , as shown in  FIG. 4 , which is a top view of die  49 . Each projection  51  is a sharp tooth-like member protruding from the upper surface of die  49 . 
     A lower support  53  is reciprocally carried within lower body  47 . Lower support  53  has a central cavity  54  and an annular upward facing rim  55 . Rim  55  is located radially inward a slight distance from die  49  for engaging thrust washer  25 . A plurality of coiled springs  57  bias lower support  53  upward. A fastener  59  extends axially through lower support  53  for retaining lower support  53  with lower body  47 , but allowing axial movement of lower support  53  relative to lower body  47 . A plunger  61  is located above or opposite lower body  47 . Plunger  61  is adapted to engage the downstream end of impeller  13  and may be hydraulically or mechanical driven. Plunger  61  has central passage  63  for receiving hub  15  of impeller  13 . 
     In the operation of die assembly  45 , impeller  13  is placed on die  49  with its wall  23  in contact with projections  51  and its skirt  21  located within cavity  54 . Lower support  53  will be in contact with outer thrust washer  25 . Plunger  61  is placed against the downstream end of impeller  13  with hub  15  located in passage  63 . Plunger  61  is stroked toward body  47 . As illustrated in  FIG. 6 , this causes projections  51  to embed into retaining wall rim  41 , radially deforming inner and outer sides  37 ,  39  (FIG.  3 ). This deformation also causes some deformation of thrust washer  25 , creating an interference fit. Springs  57  allow lower support  53  to move downward slightly as plunger  61  moves impeller  13  further toward die  49 . If a staking procedure is to be used with inner thrust washer  27 , a different die assembly would be required as it would need to pass through skirt  21  and engage the retaining wall surrounding inner thrust washer  27 . 
       FIG. 7  illustrates an alternate embodiment. Pump stage  65  is particularly to be used in abrasive applications, such as where well fluid has an appreciable content of sand. Impeller  67  rotates within diffuser  69 . An impeller thrust washer  71  is mounted to impeller  67  for transferring downward thrust to a diffuser thrust washer  73  that is stationarily mounted to diffuser  69 . Both thrust washers  71 ,  73  are preferably formed of a hard wear resistant material such as tungsten carbide. Thrust washers  71 ,  73  engage each other in rotating sliding contact. 
     Referring to  FIG. 9 , thrust washers  71 ,  73  are identical in this embodiment, each having an outer diameter containing a radially extending lip  75 . Also, lip  75  of each thrust washer  71 ,  73  has a plurality of flats  77 . In this embodiment, three flats  77  are shown spaced 120° from each other. Each flat  77  extends in an axial plane that is parallel with an axial plane that passes through the axis of thrust washer  71  or  73 . Lip  75  has a smaller radial dimension at each flat  77 , and if desired, could be substantially eliminated at each flat  77 . Impeller  67  as a cylindrical retaining wall  79  that receives lip  75  of thrust washer  71 . A skirt  81  depends from impeller  67 , surrounds the inlet of impeller  67 , and slidingly engages an outlet portion of diffuser  69 . 
     Deformed portions  83  are formed in the rim of retaining wall  79  adjacent each flat  77 . Deformed portions  83  bear against each flat  77  to prevent rotation of thrust washer  71 . Flats  77  avoid having to deform any portion of the tungsten carbide washer  71  to create an interference fit. The staking operation for deformed portions  83  may be as described in connection with the first embodiment. The plan view of  FIG. 8  discloses shallow recesses  87  formed in the mating surface of impeller thrust washer  71 . These recesses assist in lubrication and do not form a part of this invention. 
     Similarly, diffuser  69  has a retaining wall  85  that closely receives the lip of diffuser thrust washer  73 . It has deformed portions also that engage flats on the outer diameter of diffuser thrust washer  73 . The same procedure as described in connection with the first embodiment may be used for performing the staking operation. 
     Referring to  FIG. 11 , portions of two pump stages  89  are shown, these stages being a third alternate embodiment. Impellers  91 ,  93  are located within diffusers  95 ,  96 , respectively. Each diffuser  95 ,  96  has an outer wall or shell  97  that is stationarily mounted within a housing (not shown). Each diffuser has a central hub  99  that provides radial support for one of the impellers  91 ,  93 . Central hub  99  also receives down thrust from one of the impellers  91 ,  93 . Each diffuser  95 ,  96  has passages  101  that extend downstream and inward to an intake of one of the impellers  91 ,  93 . A central cavity  103  is formed within outer shell  97 . Fluid from upstream impeller  91  flows through central cavity  103  to diffuser passages  101  of downstream diffuser  96 . 
     Each diffuser  95 ,  96  also has an integral bearing support  107  formed in central cavity  103 . Bearing support  107  has an axial bore that serves as a receptacle to receive a stationary bearing sleeve  109 . Bearing sleeve  109  is fixed to bearing support  107  and receives within it a rotating bushing  111  that is mounted to shaft  112 . In an abrasion resistant pump, bearing sleeve  109  and bushing  111  may be made of a hard wear resistant material such as tungsten carbide. 
     To retain bearing sleeve  109  stationarily within bearing holder  107 , a plurality of flats or bevels  113  are formed on one end of bearing sleeve  109 , as shown in  FIG. 10 , and spaced circumferentially around the outer diameter of bearing sleeve  109 . Each bevel  113  is a flat surface that is inclined relative to an axial plane parallel to an axial plane passing through the axis of shaft  112 . Each bevel  113  joins an end surface  115  with an outer diameter  117  of bearing sleeve  111 . A plurality of circumferentially spaced-apart deformations  118  are located in one of the end surfaces  115  of bearing holder  107 , preferably the downstream end. Deformations  118  permanently deform a portion of bearing holder  107  into engagement with one of the bevels  113 . Deformations  118  may be formed generally in the same manner as described in connection with the first embodiment. Because of bevels  113 , no deformation of bearing sleeve  109  is required. Thrust washers  119  may be attached conventionally with adhesive, or they may be installed in a mechanical staking operation as in the other embodiments. 
     The invention has significant advantages. The mechanical staking operations avoids having to clean all oil from the impeller prior to securing a thrust washer. It avoids having to delay further manufacturing operations to allow the adhesive to cure. The circumferentially spaced apart deformations do not require high tolerances of the outer diameter of the thrust washer, unlike conventional force fits. As no glue is required, high temperature operations will not cause the adhesive to deteriorate. Mechanical staking also avoids the disadvantage of interference fits between two different materials that have different coefficients of expansion. 
     While the invention has been shown in only three of its forms. It should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.