Abstract:
A molten metal pumping device is disclosed that comprises a pump base including at least one input port, a pump chamber, a chamber wall, and a discharge leading to an output port. A rotor is retained within the chamber and is connected to a rotor shaft. The rotor is a dual-flow (or mixed-flow) rotor, directing molten metal both into the chamber and out of the chamber, where it ultimately exits through the discharge. The dual-flow rotor has a recess to permit high amounts of molten metal to enter the pump chamber.

Description:
[0001]    This application claims priority to U.S. Provisional Application No. 61/247,509 entitled “Molten Metal Pump Rotor” which was invented by Paul V. Cooper and filed on Sep. 30, 2009. U.S. application Ser. No. 12/853,238 entitled “Quick Submergence Molten metal Pump,” filed on Aug. 9, 2010 is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to novel impellers that may be used in various devices, particularly pumps for pumping molten metal, and devices including the impellers (also called “rotors”). 
       BACKGROUND OF THE INVENTION 
       [0003]    As used herein, the term “molten metal” means any metal or combination of metals in liquid form, such as aluminum, copper, iron, zinc, and alloys thereof. The term “gas” means any gas or combination of gases, including argon, nitrogen, chlorine, fluorine, Freon, and helium, which may be released into molten metal. 
         [0004]    A reverbatory furnace is used to melt metal and retain the molten metal while the metal is in a molten state. The molten metal in the furnace is sometimes called the molten metal bath. Reverbatory furnaces usually include a chamber for retaining a molten metal pump and that chamber is sometimes referred to as the pump well. 
         [0005]    Known pumps for pumping molten metal (also called “molten-metal pumps”) include a pump base (also called a “base,” “housing” or “casing”) and a pump chamber (or “chamber” or “molten metal pump chamber”), which is an open area formed within the pump base. Such pumps also include one or more inlets in the pump base, an inlet being an opening to allow molten metal to enter the pump chamber. 
         [0006]    A discharge is formed in the pump base and is a channel or conduit that communicates with the molten metal pump chamber, and leads from the pump chamber to the molten metal bath. A tangential discharge is a discharge formed at a tangent to the pump chamber. The discharge may also be axial, in which case the pump is called an axial pump. In an axial pump the pump chamber and discharge may be the essentially the same structure (or different areas of the same structure) since the molten metal entering the chamber is expelled directly through (usually directly above or below) the chamber. 
         [0007]    A rotor, also called an impeller, is mounted in the pump chamber and is connected to a drive shaft. The drive shaft is typically a motor shaft coupled to a rotor shaft, wherein the motor shaft has two ends, one end being connected to a motor and the other end being coupled to the rotor shaft. The rotor shaft also has two ends, wherein one end is coupled to the motor shaft and the other end is connected to the rotor. Often, the rotor shaft is comprised of graphite, the motor shaft is comprised of steel, and the two are coupled by a coupling, which is usually comprised of steel. 
         [0008]    As the motor turns the drive shaft, the drive shaft turns the rotor and the rotor pushes molten metal out of the pump chamber, through the discharge, which may be an axial or tangential discharge, and into the molten metal bath. Most molten metal pumps are gravity fed, wherein gravity forces molten metal through the inlet and into the pump chamber as the rotor pushes molten metal out of the pump chamber. 
         [0009]    Molten metal pump casings and rotors usually, but not necessarily, employ a bearing system comprising ceramic rings wherein there are one or more rings on the rotor that align with rings in the pump chamber such as rings at the inlet (which is usually the opening in the housing at the top of the pump chamber and/or bottom of the pump chamber) when the rotor is placed in the pump chamber. The purpose of the bearing system is to reduce damage to the soft, graphite components, particularly the rotor and pump chamber wall, during pump operation. A known bearing system is described in U.S. Pat. No. 5,203,681 to Cooper, the disclosure of which is incorporated herein by reference. U.S. Pat. Nos. 5,951,243 and 6,093,000, each to Cooper, the disclosures of which are incorporated herein by reference, disclose, respectively, bearings that may be used with molten metal pumps and rigid coupling designs and a monolithic rotor. U.S. Pat. No. 2,948,524 to Sweeney et al., U.S. Pat. No. 4,169,584 to Mangalick, and U.S. Pat. No. 6,123,523 to Cooper (the disclosure of the afore-mentioned patent to Cooper is incorporated herein by reference) also disclose molten metal pump designs. U.S. Pat. No. 6,303,074 to Cooper, which is incorporated herein by reference, discloses a dual-flow rotor, wherein the rotor has at least one surface that pushes molten metal into the pump chamber. 
         [0010]    The materials forming the molten metal pump components that contact the molten metal bath should remain relatively stable in the bath. Structural refractory materials, such as graphite or ceramics, that are resistant to disintegration by corrosive attack from the molten metal may be used. As used herein “ceramics” or “ceramic” refers to any oxidized metal (including silicon) or carbon-based material, excluding graphite, capable of being used in the environment of a molten metal bath. “Graphite” means any type of graphite, whether or not chemically treated. Graphite is particularly suitable for being formed into pump components because it is (a) soft and relatively easy to machine, (b) not as brittle as ceramics and less prone to breakage, and (c) less expensive than ceramics. 
         [0011]    Three basic types of pumps for pumping molten metal, such as molten aluminum, are utilized: circulation pumps, transfer pumps and gas-release pumps. Circulation pumps are used to circulate the molten metal within a bath, thereby generally equalizing the temperature of the molten metal. Most often, circulation pumps are used in a reverbatory furnace having an external well. The well is usually an extension of a charging well where scrap metal is charged (i.e., added). 
         [0012]    Transfer pumps are generally used to transfer molten metal from the external well of a reverbatory furnace to a different location such as a launder, ladle, or another furnace. Examples of transfer pumps are disclosed in U.S. Pat. No. 6,345,964 B1 to Cooper, the disclosure of which is incorporated herein by reference, and U.S. Pat. No. 5,203,681. 
         [0013]    Gas-release pumps, such as gas-injection pumps, circulate molten metal while releasing a gas into the molten metal. In the purification of molten metals, particularly aluminum, it is frequently desired to remove dissolved gases such as hydrogen, or dissolved metals, such as magnesium, from the molten metal. As is known by those skilled in the art, the removing of dissolved gas is known as “degassing” while the removal of magnesium is known as “demagging.” Gas-release pumps may be used for either of these purposes or for any other application for which it is desirable to introduce gas into molten metal. Gas-release pumps generally include a gas-transfer conduit having a first end that is connected to a gas source and a second submerged in the molten metal bath. Gas is introduced into the first end of the gas-transfer conduit and is released from the second end into the molten metal. The gas may be released downstream of the pump chamber into either the pump discharge or a metal-transfer conduit extending from the discharge, or into a stream of molten metal exiting either the discharge or the metal-transfer conduit. Alternatively, gas may be released into the pump chamber or upstream of the pump chamber at a position where it enters the pump chamber. A system for releasing gas into a pump chamber is disclosed in U.S. Pat. No. 6,123,523 to Cooper. Furthermore, gas may be released into a stream of molten metal passing through a discharge or metal-transfer conduit wherein the position of a gas-release opening in the metal-transfer conduit enables pressure from the molten metal stream to assist in drawing gas into the molten metal stream. Such a structure and method is disclosed in U.S. application Ser. No. 10/773,101 entitled “System for Releasing Gas into Molten Metal”, invented by Paul V. Cooper, and filed on Feb. 4, 2004, the disclosure of which is incorporated herein by reference. 
         [0014]    Generally, a degasser (also called a rotary degasser) is used to remove gaseous impurities from molten metal. A degasser typically includes (1) an impeller shaft having a first end, a second end and a passage (or conduit) therethrough for transferring gas, (2) an impeller (also called a rotor), and (3) a drive source (which is typically a motor, such as a pneumatic motor) for rotating the impeller shaft and the impeller. The degasser impeller shaft is normally part of a drive shaft that includes the impeller shaft, a motor shaft and a coupling that couples the two shafts together. Gas is introduced into the motor shaft through a rotary union. Thus, the first end of the impeller shaft is connected to the drive source and to a gas source (preferably indirectly via the coupling and motor shaft). The second end of the impeller shaft is connected to the impeller, usually by a threaded connection. The gas is released from the end of the impeller shaft submersed in the molten metal bath, where it escapes under the impeller. Examples of rotary degassers are disclosed in U.S. Pat. No. 4,898,367 entitled “Dispersing Gas Into Molten Metal,” U.S. Pat. No. 5,678,807 entitled “Rotary Degassers,” and U.S. Pat. No. 6,689,310 to Cooper entitled “Molten Metal Degassing Device and Impellers Therefore,” the respective disclosures of which are incorporated herein by reference. 
       SUMMARY OF THE INVENTION 
       [0015]    The invention relates to rotors that can be used in molten metal devices, such as molten metal pumps, and to devices that include the rotors. A rotor according to the invention is dual-flow (or mixed-flow) meaning that it both directs (or pushes) molten metal into the pump chamber as it rotates, and directs (or pushes) the molten metal out of the pump chamber as it rotates. A rotor according to the invention has one or more vanes wherein each vane has a leading edge to direct molten metal into the pump chamber and a surface beneath the leading edge to direct molten metal out of the chamber. The leading edge preferably includes a downwardly-curved surface (also called a first surface) and the surface that directs molten metal outward (also called a second surface) preferably has a portion that has a downwardly-sloping, angled or curved portion that leads to a curved bottom. Alternatively, the second surface may be u-shaped or v-shaped or include a u-shaped or v-shaped portion. A rotor according to the invention also preferably includes a top surface and a recess formed in the top surface to allow large amounts of molten metal to enter the pump chamber. The recess in a preferred embodiment is an angled surface on the top of a vane of the rotor followed by a vertical surface that extends to the base of the rotor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a partial, cross-sectional side view of a pump including an impeller according to an aspect of the invention. 
           [0017]      FIG. 1   a  is a partial, cross-sectional view of a pump casing that includes an impeller according to one aspect of the invention. 
           [0018]      FIG. 2  is a side view of an impeller according to the invention. 
           [0019]      FIG. 3  is a different side view of the impeller of  FIG. 2 . 
           [0020]      FIG. 4  is a perspective side view of the impeller of  FIGS. 2 and 3 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0021]    Referring now to the figures, where the purpose is for describing a preferred embodiment of the invention and not for limiting same,  FIG. 1  shows a pumping device  10  submerged in a metallic bath B. Device  10  has a superstructure  20  and a base  50 . Superstructure  20  is positioned outside of bath B when device  10  is operating and generally comprises a mounting plate  24  that supports a motor mount  26 . A motor  28  is mounted to mount  26 . Motor  28  is preferably electric or pneumatic although, as used herein, the term motor refers to any device capable of rotating a rotor. 
         [0022]    Superstructure  20  is connected to base  50  by one or more support posts  30 . Preferably posts  30  extend through openings (not shown) in plate  24  and are secured by post clamps  32 , which are preferably bolted to the top surface (preferred) or lower surface of plate  24 . 
         [0023]    A rotor  100  is driven by a drive shaft  12  preferably comprised of a motor drive shaft connected to a rotor drive shaft  40 . The motor drive shaft has a first end (not shown) and a second end  36 , the first end being connected to motor  28 . The preferred structure for connecting the motor drive shaft to rotor drive shaft  40  is a coupling  38 . Coupling  38  has a first coupling member  90  attached to second end  36  of the motor drive shaft, and a second coupling member  180 . A rotor shaft  40  has a first end  42  and a second end  44 . First end  42  is connected to second end  36  of the motor shaft, preferably by coupling  38 , by connecting first end  42  to second coupling member  180 . The motor drive shaft drives coupling  38  which, in turn, drives rotor shaft  40 . Preferably, coupling  38  and first end  42  of rotor shaft  40  are connected without the use of connecting threads. 
         [0024]    Base  50 , and all of the components of device  10  exposed to the molten metal, are preferably formed from graphite or other material, such as ceramic, suitable for use in molten metal. Base  50  includes a top surface  54  and an input port (or inlet)  56 , preferably formed in top surface  54 . Alternatively, an inlet could be formed in the bottom surface or pump  10  could be a dual-inlet pump with inlets in both top surface  54  and the bottom surface. 
         [0025]    A pump chamber  58 , which is in communication with port  56 , is a cavity formed within housing  50 . Chamber  58  is partially defined by a chamber wall  59 . A discharge  60 , shown in  FIG. 1 , is preferably formed tangentially with, and is in fluid communication with, pump chamber  58 . Discharge  60  leads to an output port (or outlet)  62  formed in a side surface of housing  50 . Alternatively, the discharge may be formed in top surface  54  if the pump were a transfer pump, or the discharge may be the bottom or top opening of the pump chamber if the pump is an axial discharge pump. Base  50  preferably includes a wear ring (or bearing ring)  64  that is preferably made of ceramic and is cemented to the lower edge of chamber  58 . 
         [0026]    The rotor of the present invention may be used with any type of molten metal pump. As shown in  FIG. 1 , rotor  100  is imperforate, formed of solid graphite, is mounted in a circulation pump, is attached to and driven by shaft  40  and is preferably placed centrally within chamber  58 . Referring to  FIGS. 2-4 , rotor  100  preferably has three vanes  102 . Rotor  100  may, however, have any number of vanes and be formed of any material suitable for use in a molten metal environment. 
         [0027]    Rotor  100  further includes a connective portion  104 , which is preferably a threaded bore, but can be any structure capable of drivingly engaging rotor shaft  40 . It is most preferred that the outer surface of second end  44  of shaft  40  has tapered threads and bore  104  be threaded to receive the tapered threads. A flow blocking plate  106  is preferably formed of ceramic and is cemented to the base  108  of rotor  100 , but may be integrally formed with the rotor  100 . In the embodiment shown, plate  106  preferably rides against circular bearing ring  64  in pump chamber  58  and substantially blocks molten metal from entering or exiting through the bottom of chamber  58 . Alternatively, plate  106  could be replaced by a plurality of individual bearing pins mounted in the rotor, or the bearing ring could potentially be eliminated. In addition, the rotor could have a bearing surface integrally formed therein, such a bearing ring being either graphite or ceramic. Or, the bearing ring and/or bearing surface could be entirely eliminated, in which case the pump would preferably include a shaft or other device to keep the rotor centered in the pump housing. 
         [0028]    The preferred dimensions of rotor  100  will depend upon the size of the pump (because the size of the rotor varies with the size of the pump) and on manufacturer&#39;s specifications. The preferred proportions of rotor  100 , however, are shown in  FIGS. 2-4 . A rotor according to the invention should have a structure that directs flow into the pump chamber and a structure that directs flow out of the pump chamber. This is accomplished by providing at least one vane on the rotor that both directs molten metal into the chamber and out of the chamber. 
         [0029]    A vane, as shown, is a solid structure that extends outwardly from the hub of the rotor, and that is spaced apart from the other vanes. Preferably each vane  102  has the same configuration so only one vane  102  shall be described. Each vane  102  preferably includes a vertically-oriented portion  102 A and a substantially horizontally-extending portion  102 B. The respective vertical and horizontal orientation of the portions described herein is in reference to a rotor positioned in a standard pump having an input port in its top surface. The invention, however, covers any rotor for use in a molten-metal pump, whether the input port is formed in the top surface, bottom surface or a side surface. It will be therefore understood that the terms “horizontal” and “vertical” refer to the rotor when it is in the orientation shown in the Figures. 
         [0030]    In the preferred embodiment, portion  102 B (also called a projection or horizontally-extending projection) is positioned closer to inlet  56  than portion  102 A. This is because the molten metal in bath B outside of inlet  56  should first be directed into chamber  58  by portion  102 B before being directed outward by portion  102 A. Projection  102 B has a top surface  112  preferably substantially flush with inlet  56  and a bottom surface  114 . However, surface  112  and projection  102 B may be positioned outside or inside of inlet  56 . Projection  102 B further includes a downwardly-curved, leading surface (or first surface)  118 . As will be understood, surface  118  is curved such that, as rotor  100  turns (as shown it turns in a clockwise direction) surface  118  directs molten metal into pump chamber  58  (i.e., downward towards plate  106  in the embodiment shown). Any surface that functions to direct molten metal into chamber  54  can be used, but it is preferred that the downward curve of surface  118  forms a substantially 30 degree-60 degree, and most preferably, a 45 degree angle. Surface  118  could also be planar although a curved surface is preferred. Projection  102 B also preferably includes a lip  120 . Lip  120  is optional, and prevents too thin an edge from being formed when surface  118  is cut into projection  102 B. This reduces the likelihood of breakage during shipping or handling of rotor  100 , but is not related to the overall function of rotor  100  during operation of pump  10 . 
         [0031]    Portion  102 A extends from the back (or trailing portion) of projection  102 B to base  108 . Portion  102 A has a surface (the “second surface”)  132  that preferably has a downwardly-angled top portion  132 A (wherein the angle is preferably between 30 degrees and 60 degrees) and a curved bottom portion  132 B, so that it directs molten metal outward as rotor  100  rotates. Angled top portion  132 A may be substantially planar (as shown), curved or multi-faceted. Further, surface  132  may be u-shaped or v-shaped, or include a portion that is u-shaped or v-shaped. 
         [0032]    A recess  150  is formed in top surface  112  and includes an angled surface  134  and a vertical, cut-away portion  134 A. As shown, recess  150  begins at a position on surface  112  slightly forward of face  132 . The purpose of recess  150  is to reduce the area of top surface  112 , thereby creating a larger opening at inlet  56  when rotor  100  is positioned in pump chamber  58 . This allows more molten metal to enter pump chamber  58  for given time period thus enabling rotor  100  and pump  10  to move more molten metal per rotor revolution. Because pump  10  including rotor  100  can pump more metal per revolution of rotor  100 , pump  10  can, if desired, be operated at lower speeds. This decreases vibration and leads to longer life of the pump components. Therefore, if operated at a lower speed, pump  10  can achieve the same results as other molten metal pumps while requiring less maintenance, which saves money in parts, labor and reduced down time. Alternatively, pump  10  can be operated at the same speed as molten metal pumps utilizing conventional rotors, in which case it will generate a greater flow than such molten metal pumps. The cut-away portion  134 A helps to allow even more molten metal into the pump than previous designs. 
         [0033]    As shown, each vane  102  has a circumferential length L and the recess is at least 50% L and is preferably at least ⅔ L. The cut-away portion  134 A preferably reduces the length L by 10-25 percent of what it would be if the angled surface  134  continued without interruption to base  108  of rotor  100 . 
         [0034]    Having thus described some embodiments of the invention, other variations and embodiments that do not depart from the spirit of the invention will become apparent to those skilled in the art. The scope of the present invention is thus not limited to any particular embodiment, but is instead set forth in the appended claims and the legal equivalents thereof. Unless expressly stated in the written description or claims, the steps of any method recited in the claims may be performed in any order capable of yielding the desired result.