Patent Publication Number: US-2001000465-A1

Title: Pumps for pumping molten metal

Description:
RELATE BACK  
     1. This application is a continuation of co-pending application Ser. No. 09/245,005, filed Feb. 4, 2000, entitled “Pumps for Pumping Molten Metal.”  
    
    
     
       TECHNICAL FIELD  
       2. This invention relates to pumps for pumping molten metal. More particularly, this invention relates to molten metal pump bases.  
       BACKGROUND OF THE INVENTION  
       3. Pumps commonly used to pump molten metal include transfer pumps and discharge pumps as disclosed in the publication “H.T.S. Pump Equation for the Eighties” by High Temperature Systems, Inc., which is incorporated herein by reference in its entirety.  
       4. A transfer pump transfers molten metal out of one furnace to another furnace or into a ladle. In a transfer pump a tubular riser extends vertically upward from the base chamber to the motor mount and contains a passageway for molten metal. Support posts are also provided between the base and the motor mount.  
       5. A discharge pump transfers molten metal from one bath chamber through a submerged pipe to another bath chamber. Such a pump typically includes a shaft sleeve and support posts between the base and the motor mount, but has no riser.  
       6. As shown in FIG. 1, pumps which employ a base  11  may either be top feed pumps or bottom feed pumps depending, among other things, on the configuration of the base  11  and orientation of the impeller vanes  12  relative to the direction of shaft  17  rotation. Multiple impellers  13  and volute openings  14  may be used, as disclosed in U.S. Pat. No. 4,786,230 to Thut, issued Nov. 22, 1988, which is incorporated herein by reference in its entirety.  
       7. Pumps used for pumping molten metal typically include a motor carried by a motor mount, a shaft  17  connected to the motor at one end, and an impeller  13  connected to the other end of the shaft  17 . Such pumps may also include a base  11  with an impeller chamber  21 , the impeller  13  being rotatable in the impeller chamber  21 . Support members extend between the motor mount and the base  11  and may include a shaft sleeve  18  surrounding the shaft  17 , support posts (not shown), and an optional tubular riser  19 . As shown in FIG. 2, a spiral-shaped volute member  20  may be employed in the impeller chamber  21  to form a spiral-shaped volute opening  14  surrounding the impeller  13 . During pump operation, the volute opening  14  advantageously produces a higher molten metal outflow pressure than an impeller chamber  21  without a volute opening  14 . This is especially important with pumps employing a tubular riser  19  or for pumping high specific gravity molten metals such as zinc or lead. Molten metal is directed from the volute opening  14  to a molten metal outlet  22  or  25  with enough pressure to be expelled at an effective flow rate from the molten metal outlet  22  or  25 . In transfer pumps, the pressure created by the volute opening  14  is sufficient to push the molten metal to the outlet  22  and up the entire length of the vertically oriented tubular riser  19 . A disadvantage to the use of a separate volute member  20  is that the volute member  20  can become unattached within the impeller chamber  21  and move, thereby affecting molten metal flow through the pump.  
       8. Pumps may be designed with pump shaft bearings (not shown), impeller bearings (not shown) and with bearings  23  in the base  11  that surround the impeller to avoid damage of the shaft  17  and impeller  13  due to contact with the shaft sleeve  18  or base  11 . The shaft  17 , impeller  13 , and support members (not shown) for such pumps are immersed in molten metals such as aluminum, magnesium, zinc, lead, copper, iron and alloys thereof. The pump components that contact the molten metal are composed of a refractory material such as graphite or ceramic.  
       9. The typical base shown in FIGS. 1, 2 and  3  includes the impeller chamber  21 , and at least one molten metal inlet  26  and outlet opening  22  or  25 . The impeller chamber  21  houses the impeller  13  and generally includes the spiral-shaped volute member  20 . An egress channel  27  extends from the impeller chamber  21  toward the molten metal outlet  22  or  25 . The impeller chamber  21  of the base  11  may further contain upper (not shown) and/or lower annular bearing rings  23  to prevent damage to the pump components from direct contact of the impeller  13  with the base  11  during operation of the pump. The lower bearing ring  23 , for example, may be carried by an annular lower base portion  24  which is cemented to the base around its periphery and may be pinned in place. The lower portion of the impeller  13  is normally generally coplanar with the bottom portion of the base  11  and the bottom portion of the lower annular bearing ring  23 . The bearing ring  23 , volute member  20  and posts (not shown) are typically cemented in place.  
       10. A common problem during operation of molten metal pumps employing a base of this type is the frequency with which catastrophic failure occurs as a result of the volute member  20  and/or annular lower bearing  23  pushing through the bottom of the base. This can occur in top or bottom feed pumps and requires immediate repair. It is believed that the pressure load from the molten metal bath and the molten metal contained in the impeller chamber  21  on the volute member  20  and/or annular lower bearing  23  causes this failure. Repairs of this type are expensive and time consuming and require taking the equipment out of operation.  
       11. Manufacturing and construction of a base  11 , such as in a transfer pump, typically involves drilling openings through the top and bottom portions of the base  11  for the impeller  13 , drilling an opening at the top portion of the base  11  for receiving the shaft sleeve  18  and drilling an opening for a molten metal outlet  22  or  25 . If the pump is designed to have a lower annular bearing ring  23 , the lower base portion  24  is disposed in a lower opening  29 . The lower base portion  24  and the volute member  20  are separately manufactured. The lower base portion  24  is recessed to receive the annular bearing  23 . The volute member  20  is spiral-shaped and positioned in the impeller chamber  21  to form a volute opening  14 . Extending from the volute opening  14  is an egress channel  27  formed in the base  11 . The distal portion of the egress channel  27  extends to the molten metal outlet  22  or  25 . The bearing  23 , the lower base portion  24  and the volute member  20  are typically cemented into position. In order to complete the egress channel  27  of a transfer pump, labor intensive hammer and chisel work is required to remove the portion of the base shown as  30  in FIGS. 1 and 2 to enable the molten metal inlet  26  to be in communication with the molten metal outlet  22 .  
       SUMMARY OF THE INVENTION  
       12. The present invention is directed to a base of a nonmetallic pump for pumping molten metal of the type that receives an impeller carried on a motor driven shaft. In particular, the pump includes a motor fastened to a motor mount; a base having an impeller chamber, at least one molten metal inlet opening to the base; a molten metal outlet opening for the base; a shaft connected to the motor at one end; an impeller connected to the other end of the shaft and rotatable in the impeller chamber; and optional support structure located between the motor mount and the base. The base comprises a one-piece insert formed of nonmetallic heat-resistant material disposed in the impeller chamber. The insert comprises a generally circular bore in which the impeller is disposed, a wall extending so as to form a spiral-shaped volute opening around the bore and an egress channel that can extend from the volute opening toward the molten metal outlet opening. The insert may contain a recess surrounding the generally circular bore for receiving a generally annular bearing ring. The bearing ring is comprised of a refractory material, preferably one of silicon carbide and silicon nitride.  
       13. More specifically, the base includes a shell portion having an impeller opening and at least one molten metal outlet opening. The shell portion of the base is configured to receive the one-piece insert. The one-piece insert has a wall extending so as to form the spiral-shaped volute opening around the bore and an egress channel that upon assembly with the shell portion extends to the molten metal outlet opening. The egress channel is generally rectangular shaped and comprised of two elongated planar surfaces of the insert. The egress channel is dimensioned so as to extend to a vertically extending surface forming an opening in the base such that the molten metal inlet, volute opening, egress channel and molten metal outlet are in fluid communication with each other. No labor intensive, time-consuming hammer and chisel work is required to connect the egress channel with the molten metal outlet. The present base can be used in pumps for pumping molten metal such as the transfer pumps and discharge pumps described. In a preferred embodiment at least one pin is inserted through the base and into the insert.  
       14. Another embodiment of the invention is directed to a method of assembling a base of a nonmetallic pump for pumping molten metal comprising the steps of positioning a one-piece insert of nonmetallic heat-resistant material into an impeller chamber of the base. The insert comprises a generally circular bore that is configured and arranged to receive an impeller, a wall extending so as to form a spiral-shaped volute opening around the bore and an egress channel that extends outwardly from the volute opening. The egress channel of the insert is in connection (i.e., alignment) with the molten metal outlet opening of the base. The insert is fastened to the base. For example, at least one opening is drilled in the base into the insert and preferably to the impeller chamber. At least one fastener is then inserted into each opening in the base and insert. Cement may be applied between the base and the insert and also between the fastener and base. A generally annular bearing ring may be disposed and cemented into a recess around the impeller opening of the insert.  
       15. In another embodiment of the invention, a method of fabricating a nonmetallic heat-resistant base for a pump for pumping molten metal comprises the steps of forming a shell portion and an insert of nonmetallic heat-resistant material. The shell portion is formed by drilling an impeller chamber, a molten metal outlet opening and a lower opening for receiving the insert. A molten metal transfer conduit, such as a riser, is positioned in a recess formed about the molten metal outlet opening such that fluid communication can occur between the molten metal outlet opening and transfer conduit. The one-piece insert is positioned into the lower opening of the shell portion. The one-piece insert includes a generally circular bore which can receive an impeller, a wall extending so as to form a spiral-shaped volute opening around the bore, and an egress channel extending outwardly from said volute opening. The egress channel of the insert is aligned with the molten metal outlet opening of the shell portion. The insert may have a recess around the bore for receiving an annular bearing ring. The annular bearing ring is cemented in place. The insert is then fastened to the shell portion. Cement is applied between the insert and the base. At least one fastener is inserted into the base and the insert and cemented in place.  
       16. Another embodiment is directed to a method of fabricating a nonmetallic heat-resistant pump base for a pump for pumping molten metal comprising the steps of forming a pump base as a shell portion and forming a one-piece insert. The shell portion is formed by drilling a molten metal outlet opening, an impeller chamber and a upper opening of a size for receiving a one-piece insert. A molten metal transfer conduit, such as a riser, is positioned in a recess formed about the molten metal outlet opening such that fluid communication can occur between the molten metal outlet opening and transfer conduit. The one-piece insert formed includes a generally circular bore which can receive an impeller, a wall extending so as to form a spiral-shaped volute opening around the bore, and an egress channel extending outwardly from the volute opening. The one-piece insert is positioned in the upper opening of the shell portion so that the impeller opening of the shell is aligned with the impeller opening of the insert. The egress channel of the insert is then aligned with the molten metal outlet opening of the shell portion and the insert is then fastened to the shell portion.  
       17. The present base advantageously overcomes the catastrophic failure associated with volute member and lower annular bearing ring breakthrough of prior art pump bases. The one-piece insert comprises a wall extending so as to form a volute opening and egress channel and may carry a bearing ring, which eliminates the use of a separate volute member and a separate bearing ring to create the volute opening and protect against impact of the pump components. Moreover, the inventive base, by virtue of use of the one-piece insert, no longer requires labor intensive, time-consuming hammer and chisel work to connect the impeller chamber passageway with the molten metal outlet.  
       18. Other embodiments of the invention are contemplated to provide particular features and structural variants of the basic elements. The specific embodiments referred to, as well as possible variations and the various features and advantages of the invention will become better understood from the detailed description that follows, when considered in connection with the accompanying drawings.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     19.FIG. 1 is a vertical cross-sectional view showing a top feed pump constructed in accordance with the present invention;  
     20.FIG. 2 is a cross sectional view as seen from a plane taken along the lines  2 — 2  of FIG. 1 showing the pump base;  
     21.FIG. 3 is an exploded perspective view of the pump base of FIG. 1;  
     22.FIG. 4 is a cross-sectional view showing a pump constructed in accordance with the invention;  
     23.FIG. 5 is a cross-sectional view as seen from a plane taken along lines  5 — 5  of FIG. 4 showing a pump base;  
     24.FIG. 6 is an exploded perspective view of the pump base of FIG. 4;  
     25.FIG. 7 is a cross-sectional view of a pump employing a base constructed in accordance with the present invention; and  
     26.FIG. 8 is an exploded cross-sectional view of the pump of FIG. 7.  
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
     27. Referring now to the drawings and to FIG. 4 in particular, the illustrated pump is generally designated by reference numeral  10  and is shown as a top feed transfer pump. The pump  10  includes a motor  15  mounted to a motor mount  16 . The inventive base  60  has an impeller chamber  21  formed therein. A shaft  17  is connected to the motor  15  at one end. An impeller  13  is connected to the other end of the shaft and is rotatable in the impeller chamber  21 . A shaft sleeve  18  preferably surrounds the shaft  17 . The shaft sleeve  18  and an optional support post (not shown) are disposed between the motor mount  16  and the base  60 . The shaft sleeve  18  and the support post (not shown) have their lower ends fixed to the base  60 . A quick release clamp  31  is carried by the motor mount  16 . The quick release clamp  31  is of the type described in U.S. Pat. No. 5,716,195 to Thut, issued Feb. 10, 1998, which is incorporated herein by reference in its entirety. The clamp  31  releasably clamps corresponding upper end portions of the shaft sleeve  18  and the support posts (not shown). If only the shaft sleeve  18  is used without support posts, the shaft sleeve  18  may be fastened to the motor mount  16  in a manner known to those skilled in the art. The inventive base  60  shown in FIGS. 5 and 6 preferably includes a shell portion  32  and a one-piece insert  33 . However, other modifications and embodiments not shown are contemplated as part of the invention. For instance, the inventive base could include a ring, and an upper plate and lower plate respectively attached to the ring. Openings in the plates would correspond to the openings in the inventive base  60 . A selected one of the upper and lower plates would have an integrated wall extending portion so as to form a spiral-shaped volute opening  14  and egress channel  27 .  
     28. It should be apparent that the base  60  of the invention may be used with any construction of transfer and discharge pump of the types described. Although the invention has been shown used in a top-feed pump, it is also suitably used in a bottom feed pump. In a bottom feed pump construction, the impeller  13  is inverted from the orientation shown in FIG. 4 and molten metal enters through a lower opening in the base  60  and axially toward the impeller, after which it is directed radially. Moreover, more than one of the present impellers  13  may be used, such as in a dual volute impeller pump of the type described by U.S. Pat. No. 4,786,230 to Thut.  
     29. The motor mount or support  16  may comprise, for example, a flat mounting plate  34  and a motor support portion  35  supported by legs  36  on the mounting plate  34 . A hanger (not shown) may be attached to the motor mount for hoisting the pump  10  into and out of the furnace. Other suitable motor mount devices for mounting the motor above the molten metal bath will be apparent to one skilled in the art in view of this disclosure. The motor  15  is an air motor, electric motor or the like.  
     30. The shaft  17  is connected to the motor  15  by a coupling assembly  37  which is preferably constructed in the manner shown in U.S. Pat. No. 5,622,481 to Thut, issued Apr. 22, 1997, entitled “Shaft Coupling for a Molten Metal Pump,” the disclosure of which is incorporated herein by reference in its entirety. The motor mount  16  shown in FIG. 4 includes an opening in the mounting plate  34 , which permits connecting the motor  15  to the shaft  17  by the coupling assembly  37 .  
     31. The shaft sleeve  18  surrounds and contains the shaft  17 . The shaft sleeve  18  extends between the base  60  and the mounting plate  34  and is connected to the base  60  at a corresponding lower portion. The shaft sleeve  18  extends substantially perpendicular to the base  60 .  
     32. An impeller  13  is connected at the other end of the shaft  17  in the well-known manner, such as by engagement of exterior shaft threads  38  formed on the shaft  17  with corresponding interior threads of the impeller  13 . The impeller  13  includes a plurality of vanes  12 . An optional impeller bearing ring (not shown) may be used so as to surround an upper portion of the impeller  13  and is supported by the base  60 . There is an annular gap  57  between the annular bearing ring  23  and the impeller  13  or an optional impeller bearing (not shown) to allow for rotation of the impeller  13 . The annular bearing ring  23  is employed to prolong the life of the impeller  13  since during vibration the impeller  13  will not strike the base  60 , but rather the impeller will strike the upper (not shown) and/or lower annular bearing rings  23 . The invention is not limited to any particular impeller construction in this or in the following embodiments and may include vaned impellers, squirrel cage impellers or other impellers used in molten metal pumps. Preferred impeller designs are disclosed in U.S. Pat. No. 5,597,289 to Thut, issued Jan. 28, 1997 and in U.S. patent application Ser. No. 08/935,493 to Thut, which are both incorporated herein by reference in their entireties. As to a suitable squirrel cage impeller that may be used in the present invention, reference may be made to the squirrel cage impeller disclosed in the 08/935,493 application, with or without stirrer openings.  
     33. A particularly preferred embodiment of the invention uses the pump shown in FIGS. 4-6 with a bottom inlet (bottom feed) and an inverted squirrel cage impeller as impeller  13 , wherein a central opening of the impeller faces downwardly. Although the molten metal inlet openings  26  are unnecessary in this embodiment, the shaft sleeve  18  may include a plurality of smaller openings for relieving pressure therein. The pump shown in FIGS. 7 and 8 may also be used.  
     34. As illustrated in FIG. 6, the shell portion  32  of the base  60  includes a bore  39  for receiving the impeller  13 , a recess  41  (shown in FIG. 4) around the bore  39  for receiving the shaft sleeve  18 , and a lower opening  40 . In the case of a bottom feed pump the shaft sleeve  18  need not include the molten metal inlet opening  26 . The lower opening  40  is disposed in a lower surface of the base shell  32 . The insert  33  is received in the lower opening  40  and may have a recess  42  formed in a lower surface thereof for receiving the bearing ring  23 . The bearing ring  23  can be formed of silicon carbide, silicon nitride or other suitable material. The annular bearing ring  23  is cemented in place. The annular bearing ring  23  surrounds an optional impeller bearing (not shown) or the impeller  13 . The bearing  23  protects the impeller  13  from impact with the base  60 .  
     35. The one-piece insert  33  has a bore  43  formed in it for receiving the impeller  13 . As seen in FIG. 6, a wall  44  of the insert  33  extends so as to form a spiral-shaped volute opening  14  surrounding the impeller opening  43 . An egress channel  45  extends outwardly from the impeller opening  43  preferably up to an outlet opening  22  or  25  and has planar side surfaces S 1  and S 2 . The egress channel  45  is aligned with or extends to the molten metal outlet  22  or  25  as shown in FIG. 5 such that fluid communication exists between the molten metal inlet  26  and the molten metal outlet  22  or  25 . The egress channel  45  may extend into axial registry with a riser  19  as shown in FIG. 4, such as by extending at least to the line of reference L. A significant benefit of using a one-piece insert  33  including the volute opening  14  and egress channel  45  is that labor intensive and time-consuming hammer and chisel work are not required to connect the impeller chamber  21  with the molten metal outlet  22  or  25 . Moreover, the one-piece insert  33  has a large surface area for cementing to the shell portion  32 , which results in increased strength in the connection of the insert  33  to the base  60  thereby avoiding pushing of the volute opening  14  through the base  60  during operation.  
     36. The lower opening  40  of the shell portion  32  is sized so as to enable the one-piece insert  33  to be positioned in the impeller chamber  21 . The one-piece insert  33  is positioned in the impeller chamber  21  such that fluid communication exists between the molten metal inlet  26  and the molten metal outlet  22  or  25 . The one-piece insert  33  is positioned in the impeller chamber  21  defined by the shell portion  32  to provide fluid communication between the molten metal inlet  26  and the molten metal outlet  22  or  25 . The one-piece insert  33  is cemented in place in the shell  32 . Openings  46 ,  48  are made through the sidewall of the shell portion  32  of the base  60  and extend at least partially into the one-piece insert  33  of the base  60 . The openings  46  preferably extend all the way into the bore  40  of the insert  33 . Fasteners such as screws (not shown) or pins  47  with or without fastener portions are disposed through the shell  32  and insert  33  into the bore  40  where they may be trimmed flush with the insert  33 . Optionally, use of self-drilling screws may be possible. The pins  47  are preferably cemented in place.  
     37. Alternatively, the base components can be inverted as shown in the inventive base  70  of FIGS. 7 and 8. The shell portion  49  of the base  70  includes a bore  51  for receiving the impeller  13  and an upper opening  52  for receiving a one-piece insert  50 . The upper opening  52  is located in an upper surface of the base shell  49 . The one-piece insert  50  is received in the upper opening  52  of the shell  49  and may have a recess  53  formed in the upper surface thereof for receiving the shaft sleeve  18 . A lower portion of the shell  49  can be recessed at  54  to receive an annular bearing ring  23 . The bearing ring  23  can be formed of silicon carbide, silicon nitride or other suitable material. The bearing ring  23  is cemented in place. The annular bearing ring  23  may surround an optional bearing on the impeller (not shown) or the impeller  13 . The bearing  23  protects the impeller  13  from impact with the base  70 .  
     38. The upper opening  52  of the shell portion  49  enables the one-piece insert  50  to be positioned in the impeller chamber  21 . The one-piece insert  50  is positioned in the impeller chamber  21  defined by the shell portion  49  to provide fluid communication between the molten metal inlet  26  and the molten metal outlet  22  or  25  partially defined by the insert  50  and the shell portion  49 . The one-piece insert  50  is cemented in place in the shell  49 . The openings  46 ,  48  are made through the sidewall of the shell portion  49  of the base  70  and extend at least partially into the one-piece insert  50  of the base  70 . The openings  46 ,  48  preferably extend all the way into lower opening  55  of the insert  50 . The fasteners such as graphite pins  47  are disposed through the shell  49  and insert  50  into the lower opening  55  where they may then be trimmed flush with the insert  50  and are preferably cemented in place.  
     39. The one-piece insert  50  of the base  70  has a bore  56  for receiving the impeller  13 . The bore or impeller opening  56  of the one-piece insert  50  is aligned with the first opening  51  of the shell portion  49  of the base  70 . A wall (not shown) of the insert  50  extends so as to form a spiral-shaped volute opening  14  (as in FIG. 5) surrounding the impeller opening  56 . An egress channel  45  extends outwardly from the volute opening  14  preferably to the outlet opening  22  or  25 . The egress channel  45  is aligned with the molten metal outlet  22  or  25  as shown in FIG. 7 such that fluid communication exists between the molten metal inlet  26  and the molten metal outlet  22  or  25 . The egress channel  45  may extend into axial registry with the riser  19  as shown in FIG. 7.  
     40. Manufacturing and construction of the base  60  includes forming a shell portion  32  and an insert  33 . In forming the shell portion  32 , an impeller chamber  21 , a molten metal outlet opening  22  or  25 , an impeller opening  39  in an upper surface and a lower opening  40  for receiving the insert  33  are drilled into a block of nonmetallic heat resistant material such as graphite. A recess  58  is drilled around the molten metal outlet  22  for receiving a molten metal transfer conduit, such as a riser  19 . A recess  41  is drilled around the impeller opening  39  for receiving a shaft sleeve  18 . In forming the one piece insert  33 , a generally circular bore  43  which can receive an impeller  13  is drilled in a block of nonmetallic heat resistant material, such as graphite. The outer surface of the insert  33  is dimensioned so as to fit in the lower opening  40  of the shell portion  32 . A spiral-shaped volute opening  14  is drilled about the bore  43 . An egress channel  45  extending outwardly to a distance L 1  is drilled from the volute opening  14 . The one-piece insert  33  is positioned in the lower opening  40  of the shell portion. The egress channel  45  is aligned with the molten metal outlet opening  22  or  25  of the shell portion  32 . The insert  33  may have a recess  54  around the bore  43  for receiving an annular bearing ring  23 . The annular bearing ring  23  is cemented in place. The insert  33  is fastened to the shell portion  32 . Cement is applied between the insert  33  and the base  32 . At least one fastener  47  is inserted into an opening  46  in the shell portion  60  and an opening  48  in the insert and cemented in place.  
     41. Manufacturing and construction of the base  70  includes forming a shell portion  49  and an insert  50 . In forming the shell portion  49 , an impeller chamber  21 , a molten metal outlet opening  22  or  25 , an upper opening  52  for receiving the insert  50  and an impeller opening  51  in the lower surface are drilled into a block of nonmetallic heat resistant material such as graphite. The shell portion  50  may have a recess  54  around the impeller opening  51  for receiving an annular bearing ring  23 . The annular bearing ring  23  is cemented in the recess  54 . In forming the one piece insert  50 , a generally circular bore  56  which can receive an impeller  13  is drilled in a block of nonmetallic heat resistant material, such as graphite. A recess  53  is drilled in the upper surface of the insert  50  around the bore  56  for receiving a shaft sleeve  18 . The outer surface of the insert  50  is dimensioned to fit in the upper opening  52  of the shell portion  49 . A spiral-shaped volute opening  14  is drilled about the bore  56  in the lower surface of the insert  50 . An egress channel  45  extending outwardly to a distance L 2  is drilled from the volute opening  14 . The one-piece insert  50  is positioned in the upper opening  52  of the shell portion  49 . The egress channel  45  is aligned with the molten metal outlet opening  22  or  25  of the shell portion  49 . A recess  58  is drilled around the molten metal outlet  22  for receiving a molten metal transfer conduit, such as a riser  19 . The insert  33  is fastened to the shell portion  32 . Cement is applied between the insert  33  and the base  32 . At least one fastener  47  is inserted into an opening  46  in the shell portion  60  and an opening  48  in the insert and cemented in place.  
     42. Any suitable refractory cements may be used to cement the pins and insert in place. For instance, standard refractory cements such as those sold under the trade name SUPER CHIEF by North American Refractories, may be used.  
     43. In operation, the molten metal pump  10  is lowered into the molten metal and secured in place. The motor  15  is activated to rotate the shaft  17  via the coupling assembly  37 . Rotation of the shaft  17  rotates the impeller  13  in the molten metal. Centrifugal forces caused by rotation of the impeller  13  in the impeller chamber  21  cause molten metal to enter the pump through the inlet opening  26 , into the impeller chamber  21  and to the molten metal outlet  22  or  25 . In the impeller chamber  21 , molten metal is directed through the volute opening  14  to the egress channel  45  and through the molten metal outlet  22  or  25 . If molten metal is directed to the opening  22  it has enough pressure that it travels vertically through the riser  19 . Otherwise, in a discharge pump the molten metal leaves the base  60  or  70  through the outlet opening  25 .  
     44. The foregoing description of the preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments were chosen and described to provide the best illustration of the principles of the invention and its practical applications to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.