Abstract:
A pump for processing molten metal having an enlarged tubular body which houses a centrifugal pump at its bottom end. The bottom end has a concave curved shape whose shape is a function of the particular type of vortex to be created for the application at hand. This curved portion of the body receives the ejected molten metal from the impeller and forms an uplifting axial vortex within the tubular section of the body. The pump is designed to cooperate synergistically with said body such that the uplifting axial vortex to climb up the inner wall of the body up to and out of an outlet formed in the upper end of the body. A radial vane impeller is formed in the back plate of the impeller. When the impeller is rotated, solid particles introduced into the body are accelerated radially by the back plate impeller into the vortex.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 12/604,000 filed Oct. 22, 2009 which claims priority of United States Provisional Patent Application filed Oct. 29, 2008 having Ser. No. 61/109,352. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to lifting molten metals and, more particularly, to a pump creating a vortex within a lift tube to elevate and mix molten metal. 
       BACKGROUND OF THE INVENTION 
       [0003]    A typical molten metal facility includes a furnace with a pump for moving molten metal. During the processing of molten metals, such as aluminum and zinc, the molten metal is normally continuously circulated through the furnace by a centrifugal circulation pump to equalize the temperature of the molten bath. These pumps contain a rotating impeller that draws in and accelerates the molten metal creating a laminar-type flow within the furnace. 
         [0004]    To transfer the molten metal out of the furnace, typically for casting the metal, a separate centrifugal transfer pump is used to elevate the metal up through a discharge conduit that runs up and out of the furnace. As shown in  FIG. 1 , a typical prior art transfer pump includes a base  5 , two to three support posts  6  (only one shown), a shaft-mounted impeller  7  located within a pumping chamber or volute  5   a  in the base  5 , a motor  8  and motor mount  9  which turn the impeller, bearings  10  that support the rotating impeller (and shaft), and a riser tube or conduit  11  located at the outlet of the base. The riser  11  is provided to allow the metal to lift upward over the sill edge of the furnace in order to transfer some of the molten metal  12  out of furnace into ladles or molds. 
         [0005]    A well-known problem with previous transfer pumps, however, is that the relatively narrow riser tube  11  becomes clogged as small droplets of the molten metal accumulate in the riser each time the pump stops transferring and the metal stops flowing through the riser. Initially, the metal accumulates in the porosity of the riser tube material (typically graphite or ceramic) and then continues to build upon the hardened metal/dross until a clog  13  occurs. As a result of this problem, furnace operators must frequently replace the transfer pump&#39;s riser tube as they are too narrow to effectively clean. This replacement typically requires the furnace to be shut down for an extended period to remove the clogged riser tube. 
         [0006]    Several treatments have been used to alleviate this riser-clogging in transfer pumps. Including impregnating, coating, and inert gas pressurization of the riser to reduce the build-up within the tube. Another method pump manufacturers employ is to simply increase the diameter of the riser to delay the blockage. These treatments have varying degrees of success, but still only delay the inevitable clogging of the riser. 
         [0007]    Another common operation in a molten metal facility is to add scrap metal, typically metal working remnants or chips, to the molten bath within a furnace. The heat of the bath melts the chips. Currently, the added chips are simply allowed to fall into the bath or may be mixed into the molten metal by a circulation pump. The current process(es), however, is not effective to fully immerse the solid chips into the molten bath resulting in a longer melt time. 
         [0008]    In view of the current inefficient use of molten metal transfer pumps, there is a need for a molten metal pump that overcomes all of the above-indicated drawbacks of prior transfer pumps. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a molten metal pump including an elongated body having an elongated straight tube that terminates in a curved bottom end whose curvature depends on a) the particular application; b) the total tangential velocity of the fluid exiting the impeller; and c) the particular specific speed of the pumping section, i.e., 
         [0000]    
       
         
           
             Ns 
             = 
             
               
                 
                   Q 
                 
                 × 
                 RPM 
               
               
                 Ho 
                 
                   3 
                   4 
                 
               
             
           
         
       
     
         [0010]    where Q is the flow in gallons per minute; Ho is the outlet head at rated flow; and RPM is the angular velocity of the impeller. 
         [0011]    A centrifugal impeller is seated in an inlet opening formed in the center of the bottom end. The curved shape of the body&#39;s bottom end provides a smooth upward transition for metal ejected from the impeller to the inner walls of the straight tube. The rotation of the impeller centered in the curved body&#39;s end results in the ejected flow of molten metal to create a vertical uplifting vortex which climbs the inner walls of the body to a outlet opening in an upper portion wall. 
         [0012]    It is an advantage of the present invention to provide a pump which creates a forced vertical uplifting vortex of molten metal within a vertical tube body of the pump to lift the whirling molten metal for transferring, mixing, and/or pre-melting applications. 
         [0013]    It is another advantage of the present invention that the particular curved shaped lifting cavity accommodates a large combination of flows and lifts as it has a relatively large internal diameter allowing the inner walls to be readily accessed for cleaning and removal of accumulated metal and dross. 
         [0014]    It is still another advantage of the present invention over prior art transfer-type pumps is that the present invention eliminates the support posts, riser tube, and one impeller bearing thereby reducing the complexity of the pump system and reducing the number of components subject to deterioration due to the molten metal environment and which must eventually be replaced. 
         [0015]    It is yet another advantage of the present invention to provide an impeller having a bottom plate with a plurality of radial vanes facing into the pump&#39;s tubular body. 
         [0016]    It is still yet another advantage of the present invention that the radial vanes of the bottom plate causes, when metal scrap chips are inserted into the pump&#39;s tubular cavity, the metal chips to be directed radially outwardly into the pump-generated uplifting vortex of molten metal. The rotational velocity of the impeller causes the chips to penetrate the surface of the vortex to fully immerse the chips within the molten metal at a force proportional to the square of the radial velocity, which indicates the wide range of melting capacity, i.e., the change in melting capacity, Δτ=fn(ΔT, Q, V 2 ), where Δτ is the time to melt; Q is the metal flow per pound of particles; V is the radial velocity; and ΔT is the difference in temperature (particles versus metal flow). 
         [0017]    These and other objects, features and advantages of the present invention will become apparent from the following description when viewed in accordance with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which: 
           [0019]      FIG. 1  is a side sectional view of a prior art transfer pump having a riser tube; 
           [0020]      FIG. 2  is a side sectional view of the present invention used in a transfer pump application; 
           [0021]      FIG. 3  is a side sectional view of the present invention used in either a mixing or pre-melting application; 
           [0022]      FIG. 4  is a side sectional view of an alternate embodiment of the present invention having an impeller with a plurality of radially extending vanes formed into the impeller&#39;s back plate; 
           [0023]      FIG. 5  is a top sectional view through line  5 - 5  in  FIG. 4  showing the radially accelerated metal particles penetrating the impeller induced vortex; and 
           [0024]      FIG. 6  is a side sectional view of another alternate embodiment of the present invention having a plurality of lifting vanes within the inner wall of the body. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring now to  FIG. 2 , the present invention is molten metal pump  20  which creates a forced vortex of accelerated molten metal within a vertical tube  22  in the pump to lift or raise the molten metal to an outlet  24  in the upper end of the pump. 
         [0026]    Pump  20  includes an elongated tubular pump body  26  having a substantially straight cylindrical inner tube wall  27  and a curved bottom end  28 . As will be discussed in greater detail below, the curvature of bottom end  28  is dependent on the particular application of the pump  20 : transfer, mixing, or pre-melting. An inlet opening  30  is formed in the center of the concave end  28 . A centrifugal impeller  32  is mounted within opening  30  and is rotated by an elongated output shaft  34  which runs concentrically down through the center of tube body  26 . Shaft  34  is driven by a conventional motor (not shown). Inlet opening  30  and the impeller&#39;s inlets are suspended above the furnace floor  36  to ensure an adequate amount of molten metal is pulled into pump  20 . 
         [0027]    Impeller  32  rotates on bearings  37  disposed between the impeller and body  26  to draw in molten metal from bath/matrix  12 , which is accelerated in both the radial and tangential direction and expels the accelerated molten metal out of the impeller and into bottom end  28  of the pump body. Impeller  32  is preferably a high velocity and/or high efficiency configuration to generate the molten metal lifting vortex within pump  20 . Two examples of such an impeller configuration include the type disclosed in my issued U.S. Pat. No. 7,326,028 entitled HIGH FLOW/DUAL INDUCER/HIGH EFFICIENCY IMPELLER FOR LIQUID APPLICATIONS INCLUDING MOLTEN METAL (“dual inducer impeller”) and my pending U.S. patent application Ser. No. 12/239,228 entitled HIGH FLOW/HIGH EFFICIENCY CENTRIFUGAL PUMP HAVING A TURBINE IMPELLER FOR LIQUID APPLICATIONS INCLUDING MOLTEN METAL (“turbine impeller”) which are both incorporated herein by reference. 
         [0028]    The pump body  26  is preferably formed from a material suitable for molten metal applications, such as a boron nitride impregnated alumina refractory material or equivalent. It should be appreciated that since most transfer-type molten metal pumps typically only need to lift the metal three to four feet vertically, the straight tube  27  of the pump body has a similar overall length/height. 
         [0029]    Tube  27  terminates in a curved shaped end  28 , that, at a low specific speed (Ns &lt;1500) and at low RPM, provides the contour necessary for the impeller to generate the vortex type required by the application at hand. 
         [0030]    As shown in  FIG. 2 , a transferring application is illustrated where the curved shape of end  28  has its focus proximate to its vertex. Further in this transferring application, the forced vortex  40  (i.e., where there is little to no shear in the fluid such that the fluid essentially rotates as a solid body) generated by the rotating impeller takes the shape of what I have termed a “super forced vortex”, where the vortex of fluid forms a near constant or uniform depth/thickness and the free surface  40   a  of the fluid has substantially the same shape as the underlying cavity  42  because the acceleration of the fluid increases at a constant rate with the radius at the point in consideration (defined by tube  27  and curved end  28 ) in pump body  26 . 
         [0031]    In the preferred embodiment of a transferring pump, body  26  includes an exit volute  44  in the upper end of the body. Exit volute  44  is a channel recessed in body  26  which redirects the whirling vortex  40  of molten metal out through outlet opening  24  and onto a conventional molten metal sluice  45  to move the exiting molten metal away from the furnace. 
         [0032]    The maximum lift, “Hmax”, (i.e., the maximum vertical distance a given pump  20  will elevate a given molten metal from the inlet of the impeller) will depend on: a) the internal diameter  27   a  of the pump body&#39;s tube; b) the impeller&#39;s outer diameter  30   a ; and c) the speed (in rpm) at which the impeller  32  is rotated. For optimum transfer lift the impeller&#39;s outer diameter  30   a  is preferably within the range of one-third to one-half the internal diameter  27   a  of the pump body tube  27 . The minimum lift, “Hmin”, is the vertical distance between the molten metal line  12   a  in the furnace and the height to the outlet opening  24 , which results in sufficient material exiting the pump  20  to maintain the desired vortex formed by the incoming/accelerating molten material. 
         [0000]    
       
         
           
             
               Ns 
               = 
               
                 
                   
                     Qo 
                   
                   × 
                   RPM 
                 
                 
                   
                     ( 
                     
                       
                         H 
                          
                         
                             
                         
                          
                         max 
                       
                       - 
                       
                         H 
                          
                         
                             
                         
                          
                         min 
                       
                     
                     ) 
                   
                   
                     3 
                     / 
                     4 
                   
                 
               
             
             , 
             
               
 
             
              
             where 
           
         
       
       
         
           
             
               H 
               
                 shut 
                  
                 
                     
                 
                  
                 off 
               
             
             = 
             
               k 
                
               
                 
                   V 
                   2 
                 
                 g 
               
             
           
         
       
     
         [0033]    where k=0.60-0.80 depending on the impeller type and 
         [0000]      ( H max− H min)&lt; Hs.o.&lt; 2( H max− H min)
 
         [0034]    Pump  20  further preferably includes an annular lid or splash protector  46  which substantially covers the upper open end of the tube body  26  while leaving a central opening to allow access for the drive shaft  34 . In one embodiment, pump  20  includes a gas injection tube or conduit  48 , which passes into cavity  42  to introduce a gas into the molten metal, such as injecting nitrogen gas to flux/clean molten aluminum and prevent the formation of aluminum oxide (Al 2 O 3 ). 
         [0035]    Referring now to  FIG. 3 , if the pump  20  is used as a metal mixer or pre-melter, chips or particles  50  of various materials are introduced into body  26  through the upper end. In one embodiment, the shape of cavity bottom  28  has a wider configuration than the transferring pump above, with the focus being as far as practicable from the curve vertex. In the mixing application, the height of the lifted metal should be maintained at a minimum to ensure proper dispersion of the particles  50  added for mixing with the metal matrix/bath  12 . This will depend on: a) the materials being mixed; b) the particles&#39; size; c) the wetability of the particles; d) the mixing speed (RPM); and e) the impeller configuration and tip velocity. In one embodiment of this mixing application, an “ordinary” forced vortex  40  is generated where the free surface  40   a  is parabolic resulting in a varying radial thickness or depth of the molten metal, which narrows as the flow rises up the tube walls  27  (Ns &gt;1500). That is, more molten metal can be found proximate to the lower end  28  in pump body  26  than at the upward end of the vertical tube. 
         [0036]    As shown in  FIG. 3 , while mixing, the flow out of the pump  20  returns the lifted molten metal to the furnace until the mixing is completed, then casting can start. Preferably, the outlet  24  is located proximate to the furnace metal line  12   a  to reduce turbulence and dross formation. 
         [0037]    If the riserless pump  20  is utilized as a pre-melting system (i.e., 300&lt;Ns&lt;1500) the conditions are similar to the mixing application described above, except the particles&#39;  50  residence time in the vortex  40  and the vortex&#39;s outlet flow should be such as to guarantee the complete melting of the material  50  added to the vortex to assure sufficient heat is available to cause the solid particles to melt without overcooling either the melting or the melted flow. 
         [0038]    In the mixing and pre-melting applications, the forced vortex  40  would be optimally generated by means of my dual inducer impeller or turbine impeller. These impellers generate a very balanced flow versus head performance curve assuring high melting flow and moderate to high recirculation (residence time). 
         [0039]    For optimum mixing or pre-melting applications the impeller outside diameter  30   a  is preferably within the range of one-fourth to one-third the internal diameter  27   a  of the pump body tube  27  to guarantee larger flows and longer residence times of the particles to be melted within or dispersed throughout the metal matrix/bath  12 . 
         [0040]    Referring now to  FIGS. 4 and 5  an alternate riserless pump  20 ′ having an impeller  32 ′ which is substantially the same as impeller  32  described above, except that impeller  32 ′ has a much thicker back plate portion  52  (i.e., the face of the impeller opposite to the surface bearing the molten metal inlets  35 ) than impeller  32 . Within the thickened back plate  52  is a plurality of spaced channels  54  which form a plurality of spaced mixing vanes  56  that extend radially outwardly from a central driveshaft mounting hub. These spaced vanes cooperatively form a second impeller which directs any material entering channels  54  in a substantially radial outward direction away from the impeller. As shown, when the impeller  32 ′ is inserted within inlet opening  30  of the pump body  26 , the inlets  54   a  of channels  54  are open to the internal cavity  42  facing in the opposite direction of lifting impeller inlets  35 , while the channel outlets  54   b  face toward the inner wall  27 . 
         [0041]    In another embodiment, the integrated second impeller formed within back plate  52  may be replaced with a separate second impeller mounted to the back plate of lifting impeller  32 . Like the integrated second impeller, this second impeller would include open channels  54  and vanes  56  substantially the same as those described above. 
         [0042]    In a mixing or pre-melting operation, solid particles  50  are introduced into cavity  42  through the upper end of the body  26 . As discussed above, when the impeller  32 ′ is turning at rated speed, the flow of molten metal exiting the impeller forms either a forced or super-forced vortex which travels up the body walls  27 . The solid particles  50  fall in the axial direction into the inlets  54   a  of the rotating channels  54  formed in the upper surface of back plate  52  and due to the radially extending vanes  56  are re-directed or thrown in a substantially radial direction out of channel outlets  54   b  into the vortex of molten metal. Importantly, the rotational speed of the impeller  32 ′ which is necessary to lift the molten metal up along walls  27  causes the particles  50  being ejected by the radial vanes  56  in the back plate to have sufficient velocity to fully penetrate into the liquid vortex, i.e., beyond the inward-facing surface  40   a  of the vortex, thereby allowing the molten material to fully engulf the solid particles  50  to maximize heating/melting efficiency. 
         [0043]    Although the riserless pump  20  has several applications, the general design remains substantially the same except only the lifting capability of the vortex  40  is utilized in the transfer application, while the lifting, mixing and recirculation capabilities are used in conjunction to achieve the ultimate requirements for mixing and pre-melting. The different applications require different curvatures at the body&#39;s end  28  generating curves from a) single point curvature to b) cubic or higher point curvatures. 
         [0044]    As shown in  FIG. 6 , for some of the stream-lining requirement in some cases/applications, axial flow curved vanes  60  can be formed inside body  26  proximate to the curved end  28  to enhance the fluid&#39;s guidance up and around the inner walls  27 . Vanes  60  have a general triangular cross-section, formed by grooves  64  starting at point  66  which is located aligned with the impeller&#39;s output and gradually decreasing in pitch height (groove depth) until the terminating portion of the groove  68  is substantially flush with the inner wall to form the helical guide vanes. The vanes  60  cooperate to define fluid channels  64  which guide the fluid ejected from the impeller outlet and wrap helically upward from the lower end  28 . In the preferred embodiment, vanes  60  define three complete turns or revolutions within the cavity  42 . In addition to helping in the formation of the uplifting vortex of molten metal, the channels  64  also increase the dwell time of any chips  50  that are flung by the impeller&#39;s mixing vanes  56  into the molten metal by limiting the upward movement to a desired angle/rate. 
         [0045]    From the foregoing description, one skilled in the art will readily recognize that the present invention is directed to an improved molten metal pump system that rotates the molten metal within an internal cavity creating an uplifting vertical vortex of molten metal along the vertical cavity wall, which rises up to an outlet at the upper end of the wall. While the present invention has been described with particular reference to various preferred embodiments, one skilled in the art will recognize from the foregoing discussion and accompanying drawing and claims that changes, modifications and variations can be made in the present invention without departing from the spirit and scope thereof.