Patent Publication Number: US-8529828-B2

Title: Molten metal pump components

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of, and claims priority under 38 U.S.C. §§119 and 120 to U.S. patent application Ser. No. 10/773,105 (Now U.S. Pat. No. 7,470,392), filed Feb. 4, 2004, by Paul V. Cooper which is a continuation application of and claims priority to U.S. patent application Ser. No. 10/619,405 (Now U.S. Pat. No. 7,507,367), filed on Jul. 14, 2003, by Paul V. Cooper, and U.S. patent application Ser. No. 10/620,318 (Now U.S. Pat. No. 7,731,891), filed on Jul. 14, 2003, by Paul V. Cooper both of which claim priority to U.S. Provisional Patent Application Ser. No. 60/395,471 filed Jul. 12, 2002. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to components used in molten metal pumps, particularly a rotor shaft, a rotor shaft coupling and a connective portion on a rotor to connect to a rotor shaft. The components are designed to facilitate connections while alleviating breakage of the components. 
     BACKGROUND OF THE INVENTION 
     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 are released into molten metal. 
     Known pumps for pumping molten metal (also called “molten-metal pumps”) include a pump base (also called a housing or casing), one or more inlets to allow molten metal to enter a pump chamber (an inlet is usually an opening in the pump base that communicates with the pump chamber), a pump chamber, which is an open area formed within the pump base, and a discharge, which is a channel or conduit communicating with the pump chamber (in an axial pump the pump chamber and discharge may be the same structure or different areas of the same structure) leading from the pump chamber to the molten metal bath in which the pump base is submerged. 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 these two shafts are coupled by a coupling, which is usually comprised of steel. 
     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. 
     Molten metal pump casings and rotors usually 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 top of the pump chamber and 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. As discussed in U.S. Pat. Nos. 5,591,243 and 6,093,000, each to Cooper, the disclosures of which are incorporated herein by reference, bearing rings can cause various operational and shipping problems and U.S. Pat. No. 6,093,000 discloses rigid coupling designs and a monolithic rotor to help alleviate this problem. Further, U.S. Pat. No. 2,948,524 to Sweeney et al., U.S. Pat. No. 4,169,584 to Mangalick, U.S. Pat. No. 5,203,681 to Cooper and U.S. Pat. No. 6,123,523 to Cooper (the disclosures of the afore-mentioned patents to Cooper, insofar as such disclosures are not inconsistent with the teachings of this application, are incorporated herein by reference) all disclose molten metal pumps. Furthermore, copending U.S. patent application Ser. No. 12/146,770 to Paul V. Cooper, filed on Jun. 26, 2008 and entitled “Pump With Rotating Inlet” discloses, among other things, a pump having an inlet and rotor structure (or other displacement structure) that rotate together as the pump operates in order to alleviate jamming. The disclosure of this copending application, insofar as such disclosures are not inconsistent with the teachings of this application, is incorporated herein by reference. 
     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. 
     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). 
     Transfer pumps are generally used to transfer molten metal from the external well of a reverbatory furnace to a different location such as a 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, insofar as such disclosures are not inconsistent with the teachings of this application, is incorporated herein by reference, and U.S. Pat. No. 5,203,681. 
     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 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. Another gas-release pump is disclosed in a co-pending U.S. Patent Application filed on Feb. 4, 2004 and entitled “System for Releasing Gas Into Molten Metal” to Paul V. Cooper, the disclosure of which that is not inconsistent with the teachings of this application is incorporated herein by reference. 
     A problem with known molten metal pumps is that machining the graphite components, such as the rotor and rotor shaft, can create weak points that may break during operation. For example, it is known to machine threads into an end of a rotor shaft in order for the end to be received in the threaded bore of a coupling so that the coupling (connected to a motor shaft at the end opposite the rotor shaft) can drive the rotor shaft. The threads formed in the end of the rotor shaft are typically pointed and create weak areas that can cause the rotor shaft to break during operation. A similar type of threaded connection is often used to connect the rotor shaft to the rotor. Further, it is known to machine an end of the rotor shaft to create opposing flat surfaces that are received in the coupling. Removing this material from the end of the rotor shaft also weakens the shaft and can cause breakage. 
     SUMMARY OF THE INVENTION 
     The present invention includes improved rotor shafts, and a coupling and rotor that can be used with one or more of the improved rotor shafts. One rotor shaft according to the invention has a first end for connecting to a coupling and a second end for connecting to a rotor. The first end has an outer surface, preferably having a generally annular outer wall, and a vertical keyway formed in the outer surface. The first end is received in a cavity of a coupling wherein the cavity includes a projection that is received at least partially in the keyway and the projection applies driving force to the rotor shaft as the coupling turns. 
     Another rotor shaft according to the invention has a second end including flat, shallow threads, rather than threads that end in a point (also referred to herein as “pointed threads”). This shaft is used with a rotor having a connective portion, wherein the connective portion is a bore that also includes flat, shallow threads and the second end of the rotor shaft is received in the connective portion. 
     A rotor shaft according to the invention may also have both a first end and a second end as described above. Further, a rotor shaft according to the invention may have a first end with shallow, flat threads that is used with a coupling having shallow, flat threads to receive the first end. 
     Also disclosed herein are a coupling and rotor that may be used with one or more rotor shafts according to the invention and pumps including one or more of the improved components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a perspective view of a pump for pumping molten metal. 
         FIG. 1   a  is a perspective view of the pump base of the pump of  FIG. 1 . 
         FIG. 2  is a side view of a rotor shaft according to the invention. 
         FIG. 3  is a perspective view of one end of the rotor shaft of  FIG. 2  showing a keyway. 
         FIG. 4  is side view of the end of the rotor shaft shown in  FIG. 3 . 
         FIG. 5  is a side view of the end of the rotor shaft shown in  FIGS. 3 and 4 , wherein the rotor shaft has been rotated to show a through bolt hole. 
         FIG. 6  is a side view of the end of the rotor shaft shown in  FIG. 2 , wherein the end is opposite the end shown in  FIGS. 3-5 . 
         FIG. 7  is a side view of a coupling according to the invention. 
         FIG. 8  is a bottom, perspective view of the coupling of  FIG. 7  as seen from the vantage of arrow A on  FIG. 7 . 
         FIG. 9  is a close up view of the coupling of  FIG. 8 . 
         FIG. 10  is a device that may be used as a rotor in the practice of the invention. 
         FIG. 11  is a cross-sectional view of the device of  FIG. 10  taken along line B-B. 
         FIG. 12  is a partial, perspective view of the cross-section of  FIG. 11 . 
         FIG. 13  is a partial, top view of the cross-section of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     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. During operation, Pump  20  is usually positioned in a molten metal bath B in a pump well, which is normally part of the open well of a reverbatory furnace. 
     The components of pump  20  that are exposed to the molten metal are preferably formed of structural refractory materials, which are resistant to degradation in the molten metal. Carbonaceous refractory materials, such as carbon of a dense or structural type, including graphite, graphitized carbon, clay-bonded graphite, carbon-bonded graphite, or the like have all been found to be most suitable because of cost and ease of machining. Such components may be made by mixing ground graphite with a fine clay binder, forming the non-coated component and baking, and may be glazed or unglazed. In addition, components made of carbonaceous refractory materials may be treated with one or more chemicals to make the components more resistant to oxidation. Oxidation and erosion treatments for graphite parts are practiced commercially, and graphite so treated can be obtained from sources known to those skilled in the art. 
     Pump  20  can be any structure or device for pumping or otherwise conveying molten metal, such as one of the pumps disclosed in U.S. Pat. No. 5,203,681 to Cooper, copending U.S. Patent Application to Cooper entitled “Pump with Rotating Inlet” or copending U.S. Patent Application to Cooper entitled “System for Releasing Gas Into Molten Metal.” The invention could also use an axial pump having an axial, rather than tangential, discharge. Preferred pump  20  has a pump base  24  for being submersed in a molten metal bath. Pump base  24  preferably 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, including a volute-shaped chamber. Chamber  26  may be constructed to have only one opening, either in its top or bottom, if a tangential discharge is used, since only one opening is required to introduce molten metal into pump chamber  26 . 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, a device or rotor  100 . (In the context of this application, “rotor” refers to any rotor that may be used to displace molten metal, and includes a device having a rotating inlet structure). 
     As shown in  FIG. 1   a , chamber  26  includes a top opening  28 , bottom opening  29 , and wall  31 . 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 . Base  24  has sides  112 ,  114 ,  116 ,  118  and  120  and a top surface  110 . The top portion of wall  31  is machined to receive a bearing surface, which is not yet mounted to wall  31  in this figure. The bearing surface is typically comprised of ceramic and cemented to wall  31 . 
     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. The motor, drive shaft and rotor could be suspended without a superstructure, wherein they are supported, directly or indirectly, to a structure independent of the pump base. 
     In the preferred embodiment, post clamps  35  secure posts  34  to superstructure  36 . A preferred post clamp and preferred support posts are disclosed in a copending application entitled “Support Post System For Molten Metal Pump,” invented by Paul V. Cooper, and filed on Feb. 4, 2004, the disclosure of which is incorporated herein by reference. However, any system or device for securing posts to superstructure  36  may be used. 
     A motor  40 , which can be any structure, system or device suitable for driving pump  20 , but is preferably an electric or pneumatic motor, is positioned on superstructure  36  and is connected to an end of a drive shaft  42 . A drive shaft  42  can be any structure suitable for rotating an impeller, and preferably comprises a motor shaft (not shown) coupled to a rotor shaft. The motor shaft has a first end and a second end, wherein the first end of the motor shaft connects to motor  40  and the second end of the motor shaft connects to the coupling. Rotor shaft  44  has a first end and a second end, wherein the first end is connected to the coupling and the second end is connected to device  100  or to an impeller according to the invention. 
     The preferred rotor is device  100  as disclosed in the previously-described copending application entitled “Pump with Rotating Inlet.” 
     Rotor shaft  44 , best seen in  FIGS. 1-6 , has an annular outer surface  46 , is preferably comprised of graphite, although any shape, size and material suitable for use in a molten metal pump may be used, has a first end  48  and a second end  50 . First end  48  preferably includes a vertically extending keyway  52  suitable for transferring driving force to rotor shaft  44 . Keyway  52  is preferably vertical, has a width of about ¾″ and a depth of about ⅜″ and a length of about 4″. Keyway  52  is preferably formed on a milling machine using a ¾″ diameter bit or tool. As used herein with respect to keyway  52 , the term “vertical” or “vertically-extending” means any keyway parallel to longitudinal axis Y of shaft  44  or having an angle up to 45 degrees from being parallel with axis Y. Moreover, any width, depth and length keyway may be used that is capable of supplying adequate rotational force to shaft  44 . Keyway  52 , however, should not have a depth greater than ÿ the diameter of shaft  44  nor should it have a width greater than about 3″, because keyway  52  should not significantly weaken shaft  44 . 
     Shaft  44  may also include multiple keyways, in which case the dimensions of each of the keyways need be sufficient to provide, in the aggregate, adequate driving force to rotor shaft  44 . Any rotor shaft described or claimed herein that has “a keyway” refers to a rotor shaft having at least one keyway. 
     A through-bolt hole  53  is included at end  48  of rotor shaft  44 . Hole  53  is preferably ½″ in diameter, although any suitable diameter may be used. The purpose of through-bolt hole  53  is to receive a bolt (not shown) that locates rotor shaft  44  in the proper location relative pump base  26  and any suitable structure that provides this function may be used. 
     Rotor shaft  44  has an optional ceramic sleeve  56 , which helps to prevent shaft  44  from being broken. 
     Shaft  44  also has a second end  50  that includes shallow, flat threads  54 . The preferred threads on shaft  54  (and the preferred threads on rotor  100 ) preferably have a width W of about 0.495″ and a height X of about 0.100″ and the grooves that receive the threads have a width W 1  of about 0.505″ and are about 0.005″-0.010″ deeper than the height X of the thread. The threads thus have a spacing of about one thread per inch. The threads preferably are flat, are not tapered outward and second end  50  preferably, but not necessarily, has a tapered portion that helps to properly locate end  50  in connective portion  110  of rotor  100 , do not end in a point, which further helps to alleviate breakage. 
     A preferred coupling  200  is made of steel, although any suitable material may be used, has a first coupling member  202  for receiving and being connected to an end of motor shaft  40  and member  202  may be any structure suitable for this purpose, although it is preferred that the connection is made using one or more set screws or bolts (not shown) that are threaded through openings  203 . A second coupling member  204  is preferably cylindrical and includes a cavity  206  for receiving first end  48  of rotor shaft  44 . Cavity  206  preferably has an annular inner wall  208  and apertures  210  though which a through bolt (not shown) is passed. A projection  212  is preferably steel and is dimensioned to be received at least partially in keyway  52  such that it can provide driving force to rotor shaft  44 . In this embodiment, projection  212  is a ¾″ diameter steel rod embedded approximately halfway in to annular wall  206 , and is about 3″-4″ in length. Projection  212  may be attached or connected to member  204  in any suitable manner, such as by welding. Projection  212  applies driving force to rotor shaft  44  as coupling  200  turns. 
     Rotor  100 , shown in  FIGS. 10-13 , has a connective portion  110  that includes a threaded bore  112  for receiving end  50 . Bore  112  includes flat, shallow threads  112  that mate with threads  54  of end  50 . Any rotor design, however, having a suitable connective portion may be utilized. Alternatively, a shaft according to the invention may have a first end including flat, shallow threads for connecting to a coupling. In that case, the coupling would have a cavity for receiving the first end of the rotor shaft wherein the cavity would include flat, shallow threads that would mate with the threads on the first end of the rotor shaft. Moreover, the first end of the rotor shaft may have a keyway and some threads. 
     Alternatively, a shaft according to the invention may have just a first end with flat, shallow threads, just a second end with flat, shallow threads or just a first end with a keyway, or a first end with flat, shallow threads and a second end with flat, shallow threads. 
     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 product.