MOLTEN METAL PUMP ROTOR

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. 1a 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'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 102A and a substantially horizontally-extending portion 102B. 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 102B (also called a projection or horizontally-extending projection) is positioned closer to inlet 56 than portion 102A. This is because the molten metal in bath B outside of inlet 56 should first be directed into chamber 58 by portion 102B before being directed outward by portion 102A. Projection 102B has a top surface 112 preferably substantially flush with inlet 56 and a bottom surface 114. However, surface 112 and projection 102B may be positioned outside or inside of inlet 56. Projection 102B 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 102B 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 102B. 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 102A extends from the back (or trailing portion) of projection 102B to base 108. Portion 102A has a surface (the "second surface") 132 that preferably has a downwardly-angled top portion 132A (wherein the angle is preferably between 30 degrees and 60 degrees) and a curved bottom portion 132B, so that it directs molten metal outward as rotor 100 rotates. Angled top portion 132A 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 134A. 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 134A 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 2/3 L. The cut-away portion 134A 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.

Claims

1. A pump for pumping molten metal, the device comprising: (a) a superstructure; (b) a motor positioned on the superstructure; (c) a drive shaft having a first end and a second end, the first end being connected to the motor; (d) a pump base having an input port, a pump chamber, a chamber wall and a discharge leading to an output port; and (e) a rotor connected to the second end of the drive shaft, the rotor positioned in said pump chamber and having a vane including: (i) a first surface for moving molten metal into the pump chamber, the first surface having a downwardly-curved, leading portion; and (ii) a second surface for moving molten metal towards the chamber wall, the second surface being positioned farther from the inlet than the first surface and having a downwardly sloping portion.

2. The pump of claim 1 wherein the pump base includes a top surface and the output port is in the top surface, the device further including a metal-transfer conduit extending from said output port to the superstructure, and a clamp on the superstructure for securing the metal-transfer conduit.

3. The pump of claim 1 wherein the pump base includes a side surface and the output port is in the side surface, the device further including a gas-release device for releasing gas into a stream of molten metal generated by the device.

4. The pump of claim 3 wherein the gas-release device is connected to the discharge for the release of gas therein.

5. The pump of claim 3 which further includes a metal-transfer conduit extending from the discharge, the gas-release device being connected to the metal-transfer conduit for the release of gas therein.

6. The pump of claim 1 which includes a gas-release device for releasing gas directly into the pump chamber.

7. The pump of claim 1 wherein the rotor further includes a top surface and a recess juxtaposed the top surface for allowing molten metal to enter the pump chamber.

8. The pump of claim 7 wherein the recess comprises an angled surface formed next to the top surface and a vertical surface formed next to the angled surface.

9. The pump of claim 7 wherein the vane has a circumferential length and the recess comprises at least 50% of the length.

10. The pump of claim 9 wherein the recess comprises at least 2/3 or more of the length.

11. The pump of claim 9 wherein the rotor has a base and the vertical surface extends to the base.

12. The pump of claim 1 wherein the rotor includes a horizontally-extending projection, the projection including a leading edge, a top surface and a bottom surface, the first surface being formed on the bottom surface of the projection.

13. The pump of claim 12 wherein the projection has a width and a height and the second surface has a height, the height of the projection being no more than 1/2 the height of the second surface.

14. The pump of claim 12 wherein the second surface is the leading face of a vertical portion of the vane, the vertical portion having a width and including a trailing face, a recess being formed on the vane, the recess extending from the top surface of the projection to the trailing face of the vertical portion.

15. The pump of claim 14 wherein the width of the vertical portion is no greater than 1/2 the width of the projection.

16. The pump of claim 14 wherein the recess begins on the upper surface at a position forward of the second surface.

17. The pump of claim 8 wherein the angled surface is formed at a 30 degree -60 degree angle.

18. The pump of claim 7 wherein the top surface is flush with the inlet.

19. The pump of claim 1 wherein the second surface of the rotor is vertical.

20. The pump of claim 1 wherein the rotor vane is comprised of graphite.

21. The pump of claim 1 wherein the rotor is imperforate.

22. The pump of claim 1 wherein the rotor is imperforate wherein the rotor includes three vanes.

23. The pump of claim 1 that is a circulation pump.

24. A dual-flow rotor for directing molten metal into and out of a pump chamber, the rotor including a rotor vane comprising: (a) a first means for moving molten metal into the pump chamber; and (b) a second means for moving molten metal towards the chamber wall.

25. The rotor of claim 24 wherein: (a) the first means for moving molten metal into the pump chamber is a downwardly-curved surface on the leading portion of the vane; and (b) the second means for moving molten metal towards the chamber wall is a second surface beneath said curved surface.

26. The rotor of claim 25 wherein said second surface has a downwardly sloping portion.

27. The rotor of claim 24 wherein the vane further comprises a top surface and a recess means adjacent the top surface to allow molten metal to enter a pump chamber.

28. The rotor of claim 27 wherein the rotor further comprises multiple vanes and a recess between each of the vanes.

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