Abstract:
The present invention is directed to a molten metal transfer system. The system includes a pump having interchangeable low flow and high flow impellers and selective low flow and high flow transfer troughs.

Description:
BACKGROUND 
       [0001]    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. Die casting facilities are one example of a typical use of a molten metal transfer pump. Particularly, a molten metal transfer pump is used as one component in a die casting process to move molten metal from a furnace to a mold. 
         [0002]    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 . 
         [0003]    Currently, many metal die casting facilities employ a main hearth containing the majority of the molten metal. A transfer pump is located in a well adjacent the main hearth. The transfer pump draws molten metal from the well in which it resides and transfers it into a 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, ladle or the like. 
         [0004]    Aluminum production has been ongoing for over a century and is still going strong. One of the key factors in the success of aluminum is its recyclability. In fact, recycling has proven so valuable—both economically and ecologically—that recover and recycling has become its own industry, and a highly successful one at that. A common practice since the early 1900s, recycling was a low-profile activity until 1968 when recycling of aluminum beverage cans vaulted the industry into public consciousness. Forty years later, aluminum recycling is supported by a national infrastructure, and by a national mindset that recognizes the importance, value, and ease of aluminum recycling. The aluminum recycling industry has invested hundreds of millions of dollars developing a system of more than 10,000 recycling center nationwide. Sources for recycled aluminum include automobiles, windows and doors, appliances and other products. 
         [0005]    In many of these applications an aluminum recycling facility and/or a die cast facility may be required to provide cast aluminum in sizes varying from a few pounds to several thousand pounds. For example, aluminum can be cast into steel deoxidizer products. These aluminum cast products are used as an alloying agent in steel to facilitate deoxidation and also refine the grain. These products may take the form of various shapes, including shot, cone, star, or pyramid. Typically, these forms will provide an article which is less than about 100 lbs. in weight. Alternatively, aluminum is cast into T-bar and/or sow type products. Once cast, the T-bar and sow can be transported easily to a location where it will be remelted and cast into an end product. T-bar and sow products can weigh in excess of 100 lbs. 
       BRIEF DESCRIPTION 
       [0006]    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. 
         [0007]    According to a first embodiment, a molten metal pump is provided. The pump includes an elongated tube having a base end and a top end, a shaft disposed within the tube and an impeller rotatable by the shaft, the impeller is disposed proximate the base end, the base end includes an inlet and the top end includes an outlet, the outlet is in fluid communication with a pair of trough members. A first trough member has a first width and a second trough member has a second width. The second width is greater than the first width. 
         [0008]    According to a further embodiment, a metal casting operation is provided. The operation includes a molten metal pump configured for elevating a quantity of molten metal above a wall of a furnace. The pump is in fluid communication with at least two troughs, a first trough having a first volume and a second trough having a second volume greater than the first volume. A diverter is positioned to selectively permit molten metal to enter one of the first or second troughs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    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: 
           [0010]      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; 
           [0011]      FIG. 2  is a perspective view showing a molten metal transfer system including the pump disposed in a furnace bay; 
           [0012]      FIG. 3  is a perspective partially in cross-section view of the system of  FIG. 2 ; 
           [0013]      FIG. 4  is a side cross-sectional view of the system shown in  FIGS. 2 and 3 ; 
           [0014]      FIG. 5  is a perspective view of the pumping chamber; 
           [0015]      FIG. 6  is a top view of the pumping chamber; 
           [0016]      FIG. 7  is a view along the line A-A of  FIG. 6 ; 
           [0017]      FIG. 8  is a perspective view of the impeller top section; 
           [0018]      FIG. 9  is a perspective view of the assembled impeller; 
           [0019]      FIG. 10  is an alternative impeller design; 
           [0020]      FIG. 11  is an exploded view of the impeller of  FIG. 10 ; 
           [0021]      FIG. 12  is an alternative embodiment with an electric motor; 
           [0022]      FIG. 13  is a further alternative embodiment with an air motor; 
           [0023]      FIG. 14  is a perspective view of a high flow impeller, and; 
           [0024]      FIG. 15  is a schematic illustration of a cast house system providing high flow and low flow lines. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    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. 
         [0026]    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  39  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  43  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. 
         [0027]    Although depicted as a volute cavity  42 , 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. 
         [0028]    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. 
         [0029]    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 its interior diameter, alternatively at least about 1.4 times, greater than the impeller diameter. A range between about 1.4 and 2.0 may be particularly beneficial. 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 . 
         [0030]      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. 
         [0031]    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 . 
         [0032]    Referring now to  FIG. 12 , the pump assembly  100  has a metal frame  101  surrounding the top portion (cavity  142 ) of the refractory tube  41 , and includes a motor mount  102  which supports a motor  108 . 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  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  121  and/or a filter cap  122  are provided to protect against ingress of unwanted debris into the pump. In this embodiment, a compressible fiber blank 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 . 
         [0033]    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  207  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/or filter cap  219  are provided. 
         [0034]    The invention has many advantages in that its design creates a forced vortex, creating a smooth surface with little to no air intake. Accordingly, the vortex is non-violent and creates little or no dross. In addition, the forced vortex created by the system has a substantially constant angular velocity such that the column of rotating molten metal rotates as a solid body having very little turbulence. 
         [0035]    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. 
         [0036]    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. 
         [0037]    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. 
         [0038]    As stated previously, there are many situations which may require a molten metal processor to handle the molten metal (e.g. aluminum, zinc, silicon and/or magnesium) at varying speeds. In this regard, once a desired metal composition in its metal molten state has been attained within a furnace, it is desirable to transport the molten metal from the furnace to a casting location. The overflow transfer pump described in the preceding paragraphs provides such a device. By providing the overflow transfer pump with at least two troughs of varying dimension, divergent rates of molten metal flow can be provided. This can be desirable when, for example, a casting facility wants to cast a portion of the molten metal into relatively small size articles, deox cones for example, and cast a portion of the molten metal into a relatively large size article, sows for example. 
         [0039]    In certain applications, an aluminum manufacturer may desire the ability to provide molten metal at a rate of approximately 150 lbs. per minute or less for an application such as deox cone castings. The same manufacturer may also desire the ability to cast a large sow of aluminum which may require a flow rate of, for example, 1,000 lbs. per minute or more. The present embodiment provides a trough sufficiently large to accommodate at least a 1,000 lbs. per minute flow rate and a trough accommodating a flow rate of less than 150 lbs. per minute. In this regard, although the the large volume trough can accommodate a lesser flow, its dimensions create an excessive surface area of exposed molten metal resulting in undesirable oxidation. 
         [0040]    The apparatus can be further improved by providing a low flow impeller and a high flow impeller. A low flow impeller can be, for example, the type depicted in  FIGS. 8-11 , while a high flow impeller can be for, example, the type depicted in  FIG. 14 . More particularly, the impeller  400  of  FIG. 14  includes a bottom inlet design (as does the low flow version of  FIGS. 8-11 ) and includes outlet passages  401  in a sidewall  403 . In the  FIG. 14  embodiment, the outlet passages  401  are larger than the outlet passages of the low flow embodiment. Furthermore, the outlet passages  48  of the low flow impeller are narrow adjacent the impeller interior and wider adjacent the impeller exterior. This widening of the outlet passage can result in a decrease in the metal velocity passing therethrough. 
         [0041]    In contrast, the passages  401  of the high flow impeller are of a relatively larger constant dimension from impeller interior to the impeller exterior. In addition, high flow impeller  400  includes a plurality of pockets  405  disposed in the sidewall  403 . Pockets  405  have the effect of increasing the velocity of molten metal being discharged radially from the impeller. By increasing the velocity of the radial discharged molten metal, a higher speed vortex can be created within the pump body. 
         [0042]    A low flow impeller will be of a design capable of providing a maximum flow rate of less than 500 lbs. per minute at an RPM of  535 . A high flow impeller will be capable of providing a molten metal flow rate of at least 1,000 lbs. per minute at an RPM of  720 . 
         [0043]    The low flow impeller and the high flow impeller should have approximately the same exterior dimensions to facilitate the positioning thereof within the inlet to the pump base. The selection of either a low flow impeller or a high flow impeller based on the intended flow rate of molten metal is advantageous because pumps tend to operate most effectively at a turn down rate from full speed operation of about 3. Accordingly, a pump operating at a top end and providing 1,200 lbs. of molten metal per minute would provide effective operation down to about 400 lbs. per minute (turn down rate of 3). Such a pump is less effective for casting small pieces requiring, for example, less than 150 lbs. per minute of molten metal. Moreover, at such a large turn down rate, precise control of the pump and its rate of molten metal flow is not generally feasible. Accordingly, providing the present embodiment wherein both the impeller and a trough size are selected for optimal molten metal flow rates based on the size of casting to be formed provides an improved system. 
         [0044]    It may be desirable to provide the impeller as a component of a shaft and impeller assembly having a quick disconnect feature such as the Quad Drive Shaft Coupling available from Pyrotek, Inc. of Solon, Ohio, and/or as described in U.S. Pat. No. 6,358,467 or U.S. Pat. No. 5,092,821, which are herein incorporated by reference. In this manner, a cast house operator can rapidly change between a high flow operation using of the high flow impeller with selection of the large trough and a low flow impeller with diversion of the molten metal flow to the smaller trough. Diversion can be achieved by installation of a dam member into the deselected trough. In most situations the dam member can be placed at the entrance to the trough. 
         [0045]    It may be further desirable for the molten metal outlet and/or one or both of the troughs to be equipped with an apparatus for determining the molten metal level. For example, a laser can be utilized for determining molten metal levels. The laser can provide the molten metal level within either of the troughs to a processor controlling the rotational speed of the motor associated with the shaft and impeller assembly to provide real time control of the rate of operation of the pump which will allow the pump and associated molten metal flow to match the metal casting pace of the system. 
         [0046]    With reference now to  FIG. 15 , the trough arrangement of the present embodiment is depicted. Particularly, a molten metal pump casting system is depicted and includes a molten metal pump  301  disposed within a well of a furnace  305 . Pump  301  can be of the type depicted and described hereinabove or could alternatively be a transfer type described in U.S. Pat. No. 6,286,163, CA  2284985 , or U.S. Published Application 2008/0314548, each of which is herein incorporated by reference. 
         [0047]    In this embodiment, a pump outlet  307  is in fluid communication with a first trough member  309  and a second trough member  311 . Trough  309  can be in fluid communication with a deox caster  313 . The trough member  311  having a larger volume can be in fluid communication with a ladle device  315 . Trough member  311  can have a larger dimension(s) than trough member  309  to facilitate a higher volume of molten metal flow therethrough. Typically, one or both of the width and depth of the trough can be increased to add flow volume. Accordingly, the high flow trough  311  can have a width and/or depth greater than the width and/or depth of the low flow trough  309 . 
         [0048]    In select embodiments, the trough members  309  and  311  will be inclined in a direction towards the pump such that when not actively casting and upon cessation of impeller rotation, molten metal will flow backward into the pump and the furnace within which the pump resides. A slope of, for example, 2″ over a 24′ run can be suitable for this purpose. 
         [0049]    As stated previously, laser apparatus  317  can be provided to measure the height of molten metal within the outlet  307  or in either of the trough members  309  and  311  and provide molten metal levels to a controller  319  operating the pump motor and the associated impeller. In this manner, the rotational speed of the impeller can be adjusted to maintain a desired molten metal height within the trough as required to match the casting rate of the process being performed. 
         [0050]    Selection of either the low flow trough  309  or the high flow trough  311  can be performed via the utilization of a dam member  321 . Dam member  321  can be a door  323  secured by a hinge  325  at the intersection of trough members  309  and  311  and capable of rotating such that either of the trough member  309  and trough member  311  can be selectively closed to molten metal flow from the pump. The door  323  can be constructed of a refractory material such a s graphite or ceramic to provide longevity of service. 
         [0051]    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.