Abstract:
The present invention is directed to a molten metal pump comprising an elongated pumping chamber tube with a base end and an open top end. A shaft extends into the tube and rotates an impeller therein, the impeller rotates proximate the base end. The tube has a diameter at least 1.1 times the diameter of the impeller. The pumping chamber tube preferably has a length at least three times the height of the impeller. The base end includes an inlet and the top end includes a tangential outlet. Rotation of the impeller draws molten metal into the pumping chamber and creates a rotating equilibrium vortex that rises up the walls of the pumping chamber. The rotating vortex adjacent the top end exists the device cia the tangential outlet.

Description:
BACKGROUND 
     Pumps for pumping molten metal are used in furnaces in the production of metal articles. Common functions of pumps are circulation of molten metal in the furnace or transfer of molten metal to remote locations along transfer conduits or risers that extend from a base of the pump to the remote location. 
     Currently, many metal die casting facilities employ a main hearth containing the majority of the molten metal. Solid bars of metal may be periodically melted in the main hearth. A transfer pump is located in a separate well adjacent the main hearth. The transfer pump draws molten metal from the well in which it resides and transfers it into a ladle or conduit and from there to die casters that form the metal articles. The present invention relates to pumps used to transfer molten metal from a furnace to a die casting machine, ingot mould, DC caster or the like. 
     A traditional molten metal transfer pump is described in U.S. Pat. No. 6,286,163, the disclosure of which is herein incorporated by reference. Referring to  FIG. 1 , the molten metal pump is indicated generally by the reference numeral  10 . The pump  10  is adapted to be immersed in molten metal contained within a vessel  12 . The vessel  12  can be any container containing molten metal, although the vessel  12  as illustrated is an external well of a reverberatory furnace  13 . The pump  10  has a base member  14  within which an impeller (not shown) is disposed. The impeller includes an opening along its bottom or top surface that defines a fluid inlet for the pump  10 . The impeller is supported for rotation within the base member  14  by means of an elongate, rotatable shaft  18 . The upper end of the shaft  18  is connected to a motor  20 . The base member  14  includes an outlet passageway connected to a riser  24 . A flanged pipe  26  is connected to the upper end of the riser  24  for discharging molten metal into a spout or other conduit (not shown). The pump  10  thus described is so-called transfer pump, that is, it transfers molten metal from the vessel  12  to a location outside of the vessel  12 . 
     Another exemplary transfer pump is described in CA 2284985. The pump consists of two main parts, an upper tube portion which is suspended above the molten magnesium bath during operation and lower tube portion which is immersed in the bath. A motor is positioned at the top of the upper portion. A coupling attaches an auger shaft to the motor. The coupling holds the weight of the auger shaft and positions it in place inside the tube. The auger shaft is centered within the internal diameter of the two portions, running the length of both, and is held in position by a set of guide bearings. The lower portion is comprised of a cylindrical casing in which the auger is located and aligned. Several inlet holes are located in the walls of the cylindrical casing. A second set of inlet holes in the cylindrical casing are located near the base of the pump. These inlet holes permit the surrounding molten metal to enter the pump. 
     The auger comprises a shaft, upon which are welded flutes. The pitch of the flutes preferably varies between 2 to 4 inches. The auger acts like a positive displacement pump. The rotation of the auger shaft by the motor supplies a steady force to the molten magnesium, forcing the molten liquid to the bottom of the pump and out of an elbow shaped connector located at the outlet end of the cylindrical casing at the base of the pump. The molten magnesium displaced to the bottom of the pump is downwardly forced out through the connector by means of the rotation of the auger. The connector is attached to a heated transfer tube which will convey the molten magnesium from the holding furnace to the die of a casting machine. 
     A further alternative transfer pump is described in U.S. Published Application 2008/0314548. The system comprises at least (1) a vessel for retaining molten metal, (2) a dividing wall (or overflow wall) within the vessel, the dividing wall having a height H 1  and dividing the vessel into a least a first chamber and a second chamber, and (3) a molten metal pump in the vessel, preferably in the first chamber. The second chamber has a wall or opening with a height H 2  that is lower than height H 1  and the second chamber is juxtaposed another structure, such as a ladle or lauder, into which it is desired to transfer molten metal from the vessel. The pump (either a transfer, circulation or gas-release pump) is submerged in the first chamber (preferably) and pumps molten metal from the first chamber past the dividing wall and into the second chamber causing the level of molten metal in the second chamber to rise. When the level of molten metal in the second chamber exceeds height H 2 , molten metal flows out of the second chamber and into another structure. If a circulation pump, which is most preferred, or a gas-release pump were utilized, the molten metal would be pumped through the pump discharge and through an opening in the dividing wall wherein the opening is preferably completely below the surface of the molten metal in the first chamber. 
     BRIEF DESCRIPTION 
     Various details of the present disclosure are hereinafter summarized to provide a basic understanding. This summary is not an extensive overview of the disclosure, and is intended neither to identify certain elements of the disclosure, nor to delineate the scope thereof. Rather, the primary purpose of this summary is to present some concepts of the disclosure in a simplified form prior to the more detailed description that is presented hereinafter. 
     According to one embodiment of this disclosure, a molten metal pump comprising an elongated tube having a base end and a top end is provided. A shaft extends into the tube and rotates an impeller proximate the base end. The tube has a diameter at least 1.1 times the diameter of the impeller. The tube has a length at least three times the height of the impeller. The base end includes an inlet and the top end includes an outlet. 
     According to an alternative embodiment, a molten metal pump comprised of an elongated refractory body is provided. The refractory body includes an inlet region having an inlet region diameter, a vortex region having a vortex region diameter, and an outlet region having an outlet region diameter. The outlet region diameter is greater than the vortex region diameter which is greater than the inlet region diameter. An impeller is disposed in or adjacent the inlet. A shaft extends through the vortex region and the outlet region and includes a first end engaging the impeller and a second end adapted to engage a motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following description and drawings set forth certain illustrative implementations of the disclosure in detail, which are indicative of several exemplary ways in which the various principles of the disclosure may be carried out. The illustrated examples, however, are not exhaustive of the many possible embodiments of the disclosure. Other objects, advantages and novel features of the disclosure will be set forth in the following detail description of the disclosure when considered in conjunction with the drawings, in which: 
         FIG. 1  is a schematic view of a prior art system including a furnace, a melting bay and an adjacent bay containing a transfer pump; 
         FIG. 2  is a perspective view showing a molten metal transfer system including the pump disposed in a furnace bay; 
         FIG. 3  is a perspective partially in cross-section view of the system of  FIG. 2 ; 
         FIG. 4  is a side cross-sectional view of the system shown in  FIGS. 2 and 3 ; 
         FIG. 5  is a perspective view of the pumping chamber; 
         FIG. 6  is a top view of the pumping chamber; 
         FIG. 7  is a view along the line A-A of  FIG. 6 ; 
         FIG. 8  is a perspective view of the impeller top section; 
         FIG. 9  is a perspective view of the assembled impeller; 
         FIG. 10  is an alternative impeller design; 
         FIG. 11  is an exploded view of the impeller of  FIG. 10 ; 
         FIG. 12  is an alternative embodiment with an electric motor; and 
         FIG. 13  is a further alternative embodiment with an air motor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One or more embodiments or implementations are hereinafter described in conjunction with the drawings, where like reference numerals are used to refer like elements throughout, and where the various features are not necessary drawn to scale. 
     With reference to  FIGS. 2-4 , the molten metal pump  30  of the present invention is depicted in association with a furnace  28 . Pump  30  is suspended via metallic framing  32  which rests on the walls of the furnace bay  34 . A motor  35  rotates a shaft  36  and the appended impeller  38 . A refractory body  40  forms an elongated generally cylindrical pump chamber or tube  41 . The refractory body can be formed, for example, from fused silica, silicon carbide or combinations thereof. Body  40  includes an inlet  43  which receives impeller  38 . Preferably, bearing rings  45  are provided to facilitate even wear and rotation of the impeller  38  therein. In operation, molten metal is drawn into the impeller through the inlet (arrows) and forced upwardly within tube  41  in the shape of a forced (“equilibrium”) vortex. At a top of the tube  41  a volute shaped chamber  42  is provided to direct the molten metal vortex created by rotation of the impeller outwardly into trough  44 . Trough  44  can be joined/mated with additional trough members or tubing to direct the molten metal to its desired location such as a casting apparatus, a ladle or other mechanism as known to those skilled in the art. 
     Although depicted as a volute cavity, an alternative mechanism could be utilized to divert the rotating molten metal vortex into the trough. In fact, a tangential outlet extending from even a cylindrical cavity will achieve molten metal flow. However, a diverter such as a wing extending into the flow pattern or other element which directs the molten metal into the trough may be preferred. 
     In addition, in certain environments, it may be desirable to form the base of the tube into a general bell shape, rather than flat. This design may produce a deeper vortex and allow the device to have improved function as a scrap submergence unit. 
     Turning now to  FIGS. 5-7 , the tube  41  is shown in greater detail.  FIG. 5  shows a perspective view of the refractory body.  FIG. 6  shows a top view of the volute design and  FIG. 7  a cross-sectional view of the elongated generally cylindrical pumping chamber. These views show the general design parameters where the tube  41  is at least 1.1 times greater in diameter, preferably at least about 1.5 times, and most preferably, at least about 2.0 times greater than the impeller diameter. However, for higher density metals, such as zinc, it may be desirable that the impeller diameter relative to pumping chamber diameter be at the lower range of 1.1 to 1.3. In addition, it can be seen that the tube  41  is significantly greater in length than the impeller is in height. Preferably, the tube length (height) is at least three times, more preferably at least 10 times, greater than a height of the impeller. Without being bound by theory, it is believed that these dimensions facilitate formation of a desirable forced (“equilibrium”) vortex of molten metal as shown by line  47  in  FIG. 7 . 
       FIGS. 8 and 9  depict the impeller  38  which includes top section  46  having vanes  48  supplying the induced molten metal flow and a hub  50  for mating with the shaft  36 . In its assembled condition, impeller  38  is mated via screws or bolts to an inlet guide section  52  having a hollow central portion  54  and bearing rings  56 . The impeller can be constructed of graphite or other suitable refractory material. It is envisioned that any traditional molten metal impeller design would be functional in the present overflow vortex transfer system. 
     Referring now to  FIGS. 10 and 11 , an alternative impeller design is depicted. In this embodiment, the impeller top section  62  includes bores  64  in the vanes  65  which receive posts  66  to facilitate proper registration of the components and increase the mating strength. In addition, the inlet guide section  68  has been extended relative to the prior design to include bearing rings  56  and added alignment element  70 . Particularly, alignment element  70  is received within a the cooperatively shaped inlet  43 . 
     Referring now to  FIG. 12 , the pump assembly  100  has a metal frame  101  surrounding the top portion (outlet chamber) of the refractory tube  41 , and includes a motor mount  102  which is secured to the pump assembly  100 . The motor mount assembly  102  is secured to together via hex bolts  103 , flat washers  104 , lock washers  105  and hex nut  106 . Motor adaptor assembly  107  joins electric motor  108  to the motor mount  102 . Particularly, hex bolts  109 , lock washers  110 , hex nuts  111  provide the mating between electric motor adaptor assembly  107  and electric motor  108 . A hanger  112  is provided to facilitate the lifting of the assembly. Hanger  112  is secured to the motor via hex bolts  113  and flat washers  114 . Heat break coupling assembly  115  mates the motor drive shaft to the shaft and impeller assembly  116 . A mounting support assembly  117  including hex bolts  118 , bevel washer  119  and hex nut  120  is provided to secure the assembly to the furnace. A strainer  123  and a filter cap  122  are provided to protect against ingress of unwanted debris into the pump. In this embodiment, a compressible fiber blank  127  can be disposed between the steel frame and the refractory bowl to accommodate variations in thermal expansion rates. Furthermore, in this embodiment the outlet chamber is provided with an overflow notch  123  to safely return molten metal to the furnace in the event of a downstream obstruction which blocks primary outlet trough  124 . Overflow notch  123  has a shallower depth than primary outlet trough  124 . 
     Referring now to  FIG. 13 , an overflow pump with an air motor option is depicted. Particularly, a metal frame  201  surrounds tube  41  and is mated to a motor mount assembly  202  via hex bolts  203 , flat washers  204 , lock washers  205  and hex nuts  206 . Motor adapter assembly  207  facilitates mounting of the air motor  208  thereto. Air motor  208  includes a muffler  209  and is secured to the air motor adapter assembly  207  via hex bolts  210 , and lock washers  211 . A heat break coupling  212  mates the drive shaft of the air motor  208  to shaft and impeller assembly  213 . Mounting support assembly  214  is provided to secure the unit to the refractory furnace. Particularly, hex bolts  215 , bevel washers  216  and hex nuts  217  provide securement thereof. In addition, strainer  218  and filter cap  219  are provided. 
     The invention has many advantages in that its design creates an equilibrium vortex at a low impeller RPM, creating a smooth surface with lithe to no air intake. Accordingly, the vortex is non-violent and creates little or no dross. Moreover, the present pump creates a forced vortex having a constant angular velocity such that the column of rotating molten metal rotates as a solid body having very little turbulence. 
     Other advantages include the elimination of the riser component in traditional molten metal pumps which can be fragile and prone to clogging and damage. In addition, the design provides a very small footprint relative to the traditional transfer pump base and has the ability to locate the impeller very close to the bay bottom, allowing for very low metal draw down. As a result of the small footprint. The device is suitable for current refractory furnace designs and will not require significant modification thereto. 
     The pump has excellent flow tunability, its open design structure provides for simple and easily cleaning access. Advantageously, only shaft and impeller replacement parts will generally be required. In fact is generally self-cleaning wherein dross formation in the riser is eliminated because the metal level is high. Generally, a lower torque motor, such as an air motor, will be sufficient because of the low torque experienced. 
     Optional additions to the design include the location of a filter at the base of the inlet of the pumping chamber. It is further envisioned that the pump would be suitable for use in molten zinc environments where a very long, pull (e.g. 14 ft.) is required. Such a design may preferably include the addition of a bearing mechanism at a location on the rotating shaft intermediate the motor and impeller. Furthermore, in a zinc application, the entire construction could be manufactured from metal, such as steel or stainless steel, including the pumping chamber tube, and optionally the shaft and impeller. 
     The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.