Abstract:
A coupling has an opening and a protrusion extending downward from the opening. The protrusion has threads that are preferably positioned outside of the opening. A rotor shaft that connects to the coupling has an internal bore with threads that receives and retains the protrusion, such as by a threaded connection between the two, so the protrusion applies driving force to the shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a non-provisional of and claims priority to U.S. Provisional Application Ser. No. 62/020,332 entitled “Coupling and Rotor Shaft for Molten Metal Devices, filed on Jul. 2, 2014, the contents of which are incorporated herein in its entirety for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to couplings and rotor shafts that may be used in various devices, such as pumps, degassers and scrap melters used in molten metal. 
       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, that are released into molten metal. 
         [0004]    Known molten-metal pumps include a pump base (also called a housing or casing), one or more inlets (an inlet being an opening in the housing to allow molten metal to enter a pump chamber), a pump chamber, which is an open area formed within the housing, and a discharge, which is a channel or conduit of any structure or type communicating with the pump chamber (in an axial pump the chamber and discharge may be the same structure or different areas of the same structure) leading from the pump chamber to an outlet, which is an opening formed in the exterior of the housing through which molten metal exits the casing. An impeller, also called a rotor, is mounted in the pump chamber and is connected to a drive system. The drive system is typically an impeller shaft connected to one end of a drive shaft, the other end of the drive shaft being connected to a motor. Often, the impeller shaft is comprised of graphite, the motor shaft is comprised of steel, and the two are connected by a coupling. As the motor turns the drive shaft, the drive shaft turns the impeller and the impeller pushes molten metal out of the pump chamber, through the discharge, out of the outlet 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 impeller pushes molten metal out of the pump chamber. 
         [0005]    This application incorporates by reference the portions of the following publications that are not inconsistent with this disclosure: U.S. Pat. No. 4,598,899, issued Jul. 8, 1986, to Paul V. Cooper, U.S. Pat. No. 5,203,681, issued Apr. 20, 1993, to Paul V. Cooper, U.S. Pat. No. 5,308,045, issued May 3, 1994, by Paul V. Cooper, U.S. Pat. No. 5,662,725, issued Sep. 2, 1997, by Paul V. Cooper, U.S. Pat. No. 5,678,807, issued Oct. 21, 1997, by Paul V. Cooper, U.S. Pat. No. 6,027,685, issued Feb. 22, 2000, by Paul V. Cooper, U.S. Pat. No. 6,123,523, issued Sep. 26, 2000, by Paul V. Cooper, U.S. Pat. No. 6,303,074, issued Oct. 16, 2001, by Paul V. Cooper, U.S. Pat. No. 6,689,310, issued Feb. 10, 2004, by Paul V. Cooper, U.S. Pat. No. 6,723,276, issued Apr. 20, 2004, by Paul V. Cooper, U.S. Pat. No. 7,402,276, issued Jul. 22, 2008, by Paul V. Cooper, U.S. Pat. No. 7,507,367, issued Mar. 24, 2009, by Paul V. Cooper, U.S. Pat. No. 7,906,068, issued Mar. 15, 2011, by Paul V. Cooper, U.S. Pat. No. 8,075,837, issued Dec. 13, 2011, by Paul V. Cooper, U.S. Pat. No. 8,110,141, issued Feb. 7, 2012, by Paul V. Cooper, U.S. Pat. No. 8,178,037, issued May 15, 2012, by Paul V. Cooper, U.S. Pat. No. 8,361,379, issued Jan. 29, 2013, by Paul V. Cooper, U.S. Pat. No. 8,366,993, issued Feb. 5, 2013, by Paul V. Cooper, U.S. Pat. No. 8,409,495, issued Apr. 2, 2013, by Paul V. Cooper, U.S. Pat. No. 8,440,135, issued May 15, 2013, by Paul V. Cooper, U.S. Pat. No. 8,444,911, issued May 21, 2013, by Paul V. Cooper, U.S. Pat. No. 8,475,708, issued Jul. 2, 2013, by Paul V. Cooper, U.S. patent application No. 12/895,796, filed Sep. 30, 2010, by Paul V. Cooper, U.S. patent application Ser. No. 12/877,988, filed Sep. 8, 2010, by Paul V. Cooper, U.S. patent application Ser. No. 12/853,238, filed Aug. 9, 2010, by Paul V. Cooper, U.S. patent application Ser. No. 12/880,027, filed Sep. 10, 2010, by Paul V. Cooper, U.S. patent application Ser. No. 13/752,312, filed Jan. 28, 2013, by Paul V. Cooper, U.S. patent application Ser. No. 13/756,468, filed Jan. 31, 2013, by Paul V. Cooper, U.S. patent application Ser. No. 13/791,889, filed Mar. 8, 2013, by Paul V. Cooper, U.S. patent application Ser. No. 13/791,952, filed Mar. 9, 2013, by Paul V. Cooper, U.S. patent application Ser. No. 13/841,594, filed Mar. 15, 2013, by Paul V. Cooper, and U.S. patent application Ser. No. 14/027,237, filed Sep. 15, 2013, by Paul V. Cooper. 
         [0006]    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 the charging well where scrap metal is charged (i.e., added). 
         [0007]    Transfer pumps are generally used to transfer molten metal from the one structure to another structure such as a ladle or another furnace. 
         [0008]    Gas-release pumps, such as gas-injection pumps, circulate molten metal while introducing 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. 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. 
         [0009]    Gas-release pumps generally include a gas-transfer conduit having a first end that is connected to a gas source and a second end submerged in the molten metal bath. Gas is introduced into the first end 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 molten metal enters the pump chamber. 
         [0010]    Molten metal pump casings and rotors often 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 and outlet) 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 base, during pump operation. 
         [0011]    Generally, a degasser (also called a rotary degasser) includes (1) an impeller shaft having a first end, a second end and a passage for transferring gas, (2) an impeller, and (3) a drive source for rotating the impeller shaft and the impeller. The first end of the impeller shaft is connected to the drive source and to a gas source and the second end is connected to the connector of the impeller. 
         [0012]    The materials forming the 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. 
         [0013]    Generally a scrap melter includes an impeller affixed to an end of a drive shaft, and a drive source attached to the other end of the drive shaft for rotating the shaft and the impeller. The movement of the impeller draws molten metal and scrap metal downward into the molten metal bath in order to melt the scrap. A circulation pump is preferably used in conjunction with the scrap melter to circulate the molten metal in order to maintain a relatively constant temperature within the molten metal. 
         [0014]    Numerous rotor shaft to motor shaft couplings are known. A problem with the couplings, however, is that by applying driving force to the rotor shaft the rotor shaft tends to break at the location where the force is being applied. This is typically at the location where the coupling and rotor shaft are in contact, and the broken end of the rotor shaft must often be chiseled out of an opening in the coupling in which it is retained. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention helps to alleviate the afore-mentioned problems by providing a coupling and rotor shaft for use in a molten metal pump, a molten metal rotary degasser or a molten metal scrap melter. The coupling has a collar with a cavity open at the bottom and a protrusion extending out of the cavity. The protrusion is preferably threaded along at least part of its length, wherein the threaded portion(s) are preferably outside of the cavity. 
         [0016]    The rotor shaft preferably has a bore that receives the protrusion. Preferably the bore has internal threads that align with and receive the threads on the protrusion. Most preferably, there are no threads on the inner surface of the coupling opening or the outer surface of the rotor shaft. 
         [0017]    With such a structure, if the rotor shaft breaks, it tends to break where the threads of the rotor shaft bore align with the threads of the protrusion, which is below the opening in the coupling. As a consequence, the broken piece of rotor shaft can either be unthreaded or chiseled off of the protrusion, each of which is simpler than chiseling a broken end out of the coupling opening. 
         [0018]    The protrusion may have an internal passage for transferring gas therethrough and the rotor shaft passage may extend to the second end (or almost to the second end) to permit gas to be transferred therethrough. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0019]      FIG. 1  is a perspective view of a pump for pumping molten metal, which may include a coupling and rotor shaft according to aspects of the invention. 
           [0020]      FIG. 2  shows a rotary degasser, which may include a coupling and rotor shaft according to aspects of the invention. 
           [0021]      FIG. 3  shows a scrap melter, which may include a coupling and rotor shaft according to aspects of the invention. 
           [0022]      FIG. 4  is a side, cross-sectional view of a coupling that can be used in accordance with aspects of the invention. 
           [0023]      FIG. 5  is a partial side view of a rotor shaft that may be used according to aspects of the invention. 
           [0024]      FIG. 6  is a side view of a coupling that may be used in accordance with aspects of the invention. 
           [0025]      FIG. 7  is a side, perspective view of a coupling that may be used in accordance with aspects of the invention. 
           [0026]      FIG. 8  is a partial side view of the lower portion of the coupling shown in in  FIGS. 6 and 7 . 
           [0027]      FIG. 9  is a partial, cross-sectional side view of a rotor/coupling connection in accordance with aspects of the invention. 
           [0028]      FIG. 10  is a close-up view of Section G of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0029]    For any device described herein, any of the components that contact the molten metal are preferably formed by a material that can withstand the molten metal environment. Preferred materials are oxidation-resistant graphite and ceramics, such as silicon carbide. Oxidation-resistant graphite is most preferred because of its relatively low cost and ease of manufacturing. 
         [0030]    Referring now to the drawing where the purpose is to illustrate and describe different embodiments of the invention, and not to limit same,  FIG. 1  shows a molten metal pump  20  in accordance with an aspect of the present invention. Pump  20  is designed for operation in any environment in which molten metal is to be pumped or otherwise conveyed. Pump  20  can be any structure or device for pumping or otherwise conveying molten metal, such as the tangential-discharge pump disclosed in U.S. Pat. No. 5,203,681 to Cooper, or an axial pump having an axial, rather than tangential, discharge. Pump  20  has a pump base  24  submersible in a molten metal bath B. In this embodiment, pump base  24  includes a generally nonvolute pump chamber  26 , such as a cylindrical pump chamber or what has been called a “cut” volute although pump base  24  may have any shape pump chamber suitable of being used, such as a volute-shaped chamber. Chamber  26  may have only one opening, in either its top or bottom, since only one opening is required to introduce molten metal into pump chamber  26 , although chamber  26  may have an opening in both its top and bottom. Generally, pump chamber  24  has two coaxial openings of the same diameter and usually one is blocked by a flow blocking plate mounted on the bottom of, or formed as part of, rotor  100 . Base  24  further includes a tangential discharge  30  (although another type of discharge, such as an axial discharge, may be used) in fluid communication with chamber  26 . 
         [0031]    The invention is not limited to any particular type or configuration of pump base, or of even having a base. A pump, rotary degasser or scrap melter used with the invention could be of any size, design or configuration suitable for utilizing a rotor shaft and coupling according to the invention. 
         [0032]    In the embodiment shown, one or more support posts  34  connect base  24  to a superstructure  36  of pump  20  thus supporting superstructure  36 , although any structure or structures capable of supporting superstructure  36  may be used. Additionally, pump  20  could be constructed so there is no physical connection between the base and the superstructure, wherein the superstructure is independently supported, and/or there is no base. The motor, drive shaft and rotor could be suspended without a superstructure, wherein they are supported, directly or indirectly, to a structure independent of a pump base. 
         [0033]    A motor  40 , which can be any structure, system or device suitable for driving pump  20 , but is preferably an electric, hydraulic or pneumatic motor, is positioned on superstructure  36  and is connected to a drive shaft  42 . Drive shaft  42  can be any structure suitable for rotating the impeller  100 , and preferably comprises a motor shaft (not shown) that connects to rotor shaft  44 ′ via a coupling  500 , which is described further below. 
         [0034]    A rotor, also called an impeller,  100  is positioned at least partially within pump chamber  26 . Preferred rotor  100  is preferably imperforate, and any type or shape of impeller suitable for use in a molten metal pump, rotary degasser or scrap melter, respectively, may be used to practice aspects of the invention. Rotor  100  has a connecting portion  110  to connect to a second end  44 B′ of rotor drive shaft  44 ′. 
         [0035]      FIG. 2  shows a preferred gas-release device  200  according to the invention. Device  200  is designed to operate in a molten metal bath B contained within a vessel  1 . Device  200  is preferably a rotary degasser and includes a rotor shaft  44 , an impeller  300  and a drive source (not shown). Device  200  preferably also includes a coupling  500 . 
         [0036]      FIG. 3  shows a scrap melter utilizing a coupling  500  and rotor drive shaft  44 ′ in accordance with aspects of the invention. 
         [0037]    Turning to  FIG. 4 , coupling  500  includes a collar  502 , which as shown is circular with a flat top  504 , an annular outer side wall  506 , and a bottom edge  508 . Two slots  505  are preferably formed on either side of collar  502  so collar  502  may be easily gripped and turned by a wrench. A passage  509  may be formed in collar  502  to permit gas to transfer therethrough. A cavity  510  is formed within coupling  500  in order to receive a first end  38 A of rotor shaft  38 , described further below. In one embodiment the coupling  500  is made of steel, has a height of about 2.5″-3″ and an overall width of about 4½″-5½″. Cavity  510  has a depth D of about 1-1½″, and most preferably about 1¼″, a diameter of about 3″ next to bottom edge  508 , and an inner wall  512  that slopes inward at between 5° and 10°, and most preferably about 7°, until it terminates at upper cavity wall  514 . Inner wall  512  preferably is not threaded. 
         [0038]    A projection  600  extends downward from upper cavity wall  514 , through cavity  510  and projects outward therefrom. Projection  600  may be connected to collar  502  in any suitable manner, such as being threadingly received in an opening (not shown) or welded to collar  502 . In one embodiment, projection  600  is between 0.800 and 1.000 inches in diameter, and preferably about 0.875″ in diameter and extends outward from the bottom of cavity  510  (defined by where cavity  510  aligns with bottom edge  508 ) by between 2½″-3¾″, and preferably 3¼″. At the bottom end of projection  600  is preferably a chamfered end  602 , that in the embodiment shown is ¼″ long with a 45° chamfer. Projection  600  has an outer surface  604  with threads  606  that are preferably positioned outside of cavity  510 . An upper portion  605  of projection  600  is positioned in cavity  510 . As shown, the threads  606  preferably begin at a position about ½″ beneath the lower portion of cavity  510 , extend for about 1¼″, and are 1″ ACME threads, although any suitable length and type of thread may be used. Projection  600  may have an internal passage  509  therein for the passage of gas. 
         [0039]    Coupling  500  may also include one extended metal portion  650  above coupling Section  502 . The extended length of portion  650  reduces the cost of new and replacement rotor shafts (because they are shorter) and portion  650  is preferably between 4.5″ and 12″ in length. A top plate  660  mates with a known structure, such as a motor shaft with a rotary union, for driving the coupling  500  and injecting gas into it. Apertures  662  permit fasteners (not shown) to pass through and connect to a suitable driving structure, which is known in the art. 
         [0040]    As is illustrated in  FIGS. 2 and 5 , rotor shaft  38  has a first end  38 A, a second end  38 B, an outer surface  706  (that is preferably annular) and an inner passage  708  (which is optional depending upon the application) for transferring gas. Second end  38 B preferably has a structure, such as a threaded end, for connecting to an impeller, although any suitable connection may be used. Shaft  38  may be a unitary structure or may be a plurality of pieces connected together. 
         [0041]    First end  38 A is dimensioned to receive projection  600  and to fit into cavity  510 . First end  38 A as shown has a chamfered end  700  that is received in cavity  510  so that top surface  708  is against surface  514  when the rotor shaft  44  and coupling  500  are assembled. First end  38 A also has an opening  712  leading to inner passage  708 , which includes threads  714  that threadingly engage threads  606 . In this embodiment, inner passage  708  extends through, or essentially through, rotor shaft  38  to transfer gas to second end  38 B so that gas may be released into molten metal in any suitable manner. 
         [0042]    Rotor shaft  38  is connected to coupling  500  by aligning projection  600  with opening  712  and pushing projection into passage  708  until threads  606  meet threads  714 , and then screwing rotor shaft  38  onto projection  600 . Most preferably the respective threaded portions  606  and  714  are tightened in the same direction as the rotor shaft rotates during operation so that they do not loosen during operation. 
         [0043]    Having thus described different 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.