Molten Metal Pumps

Abstract

A molten metal pump is provided having a base member defining a pumping chamber. The pumping chamber includes an opening in each of a top surface and a bottom surface of the base member. An impeller is disposed in the pumping chamber and is configured to draw molten metal through the opening in the bottom surface and discharge the molten metal through an outlet in the base member. A flow diverter is disposed above the opening in the top surface.

Description

Background Art

[0001] The present exemplary embodiment relates to an assembly for pumping molten metal. It is particularly suitable for filling a mold with molten metal at a variable pressure and will be described with particular reference thereto. However, it should be understood that the present exemplary embodiment is also applicable to other similar applications.

[0002] Sometimes it is necessary to move metal in liquid or molten form. Molten metal pumps can be used to transport molten metal through a system of pipes or troughs. These pumps often include a base member suspended below a motor in a pool of molten metal, wherein a rotatable, elongated shaft rotates an impeller in the base member. The impeller is mounted within a chamber formed in the base member. The impeller can be supported by bearing rings to allow for smooth rotation and act as a wear-resistant surface. The motor can be supported by a platform rigidly attached to at least one structural column from which the base member is suspended. Rotation of the impeller causes a directional flow of molten metal through an outlet in the base member, which can be used to fill a mold or other container.

[0003] While centrifugal pumps can operate satisfactorily to pump molten metal, they have only recently been accepted as a means of filling molds, particularly molds with complex geometries. An exemplary centrifugal pump for filling complex molds is described in U.S. Patent No. 9,970,442, incorporated herein by reference. While highly effective at efficiently filling complex molds, the centrifugal pumps referenced above have been found to sometimes generate undesirable turbulence at the surface of the molten metal pool. The present disclosure helps reduce this undesirable turbulence at the surface of the molten metal pool. Summary of the Invention

[0004] Various details of the present disclosure are summarized below to provide a basic understanding. This summary is not an extensive overview of the present disclosure and is neither intended to identify certain elements of the present disclosure nor to delineate the scope of the present disclosure. Instead, the primary purpose of this summary is to present some concepts of the present disclosure in a simplified form before the more detailed description presented below.

[0005] According to a first embodiment, a molten metal pump is provided having a base member defining a pumping chamber. The base member includes an opening in each of a top surface and a bottom surface, the opening being in fluid communication with the pumping chamber. At least one component extends between a motor frame and the base member. An impeller is disposed in the pumping chamber and is configured to draw molten metal through the opening in the bottom surface and discharge the molten metal through an outlet in the base member. A flow diverter is disposed above the opening in the top surface.

[0006] According to another embodiment, a method for pumping molten metal is described. The method includes providing a molten metal pump having a base member defining a pumping chamber. The base member includes an opening in a top surface and an opening in a bottom surface. The opening is in fluid communication with the pumping chamber. An impeller is disposed in the pumping chamber. When operating at 200 RPM or less, rotation of the impeller draws molten metal through the opening in the bottom surface and discharges the molten metal through an outlet in the base member. When operating at 500 RPM or more, the impeller also discharges the molten metal through the opening in the top surface. A diverter is disposed above the opening in the top surface to laterally direct the molten metal passing through the opening in the top surface.

[0007] According to a further embodiment, a molten metal pump is provided having a base member defining a pumping chamber. The base member includes an opening in a top surface and an opening in a bottom surface. The opening is in fluid communication with the pumping chamber. At least one post extends between the motor frame and the base member. An impeller is disposed in the pumping chamber and is configured to draw molten metal through the opening in the bottom surface and discharge the molten metal through an outlet in the base member. A flow divider is supported above the opening in the top surface by a spacer element in the form of a cylinder including a passageway therethrough. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following is a brief description of the drawings, which are presented for the purpose of illustrating the exemplary embodiments disclosed herein and not for the purpose of limiting the same.

[0009] FIG1 illustrates a cross-sectional view of a prior art molten metal pump for filling a mold with molten metal;

[0010] FIG2 illustrates a side view of a prior art pump assembly configured to controllably deliver molten metal to a mold, the pump assembly shown from a cross-sectional view of a holding furnace housing the pump assembly therein;

[0011] Figure 3 The molten metal pump of the present invention is illustrated; and

[0012] Figure 4 yes Figure 3 A partial cross-sectional view of the impeller area of ​​a pump assembly. DETAILED DESCRIPTION

[0013] A more complete understanding of the components, methods, and apparatus disclosed herein may be obtained by referring to the accompanying drawings, which are merely schematic representations for convenience and ease of illustrating the present disclosure and are not intended to indicate relative sizes and dimensions of the apparatus or its components and / or to define or limit the scope of the exemplary embodiments.

[0014] Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the specific structures of the embodiments selected for illustration in the drawings and are not intended to define or limit the scope of the present disclosure. In the following drawings and the following description, it should be understood that the same number names refer to components with the same functions.

[0015] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0016] As used herein, the terms about, approximately, and substantially are intended to encompass structural or numerical modifications that do not significantly affect the purpose of the element or number modified by such terms.

[0017] As used in the specification and claims, the term "comprising" may include the embodiments "consisting of" and "consisting essentially of." As used herein, the terms "comprising," "including," "having," "has," "may," "containing," and variations thereof are intended to act as open-ended transitional phrases, terms, or words requiring the presence of specified ingredients / steps and allowing the presence of other ingredients / steps. However, such descriptions should be construed as also describing a composition or method as "consisting of" and "consisting essentially of the recited ingredients / steps," allowing for the presence of only the specified ingredients / steps, and any impurities that may result therefrom, but excluding the other ingredients / steps.

[0018] Referring to Figure 1, elements of a molten metal pump assembly 10 suitable for use in the present disclosure are illustrated. As used herein, the term "molten metal" will be understood to refer to any metal that can be used for casting, dosing, or similar applications, such as aluminum, copper, iron, magnesium, and alloys thereof. The elongated shaft 16 has a cylindrical shape with its axis of rotation generally perpendicular to the base member 20. The elongated shaft has a proximal end 28 adapted to be attached to a motor via a coupling and a distal end 30 connected to an impeller 22. The impeller 22 is rotatably positioned within the pump chamber 18 such that operation of the motor rotates the elongated shaft 16, which in turn rotates the impeller 22 within the pump chamber 18.

[0019] The base member 20 defines a pump chamber 18 that receives an impeller 22. The base member 20 is configured to structurally receive refractory columns (elongated metal rods optionally included in a protective refractory jacket) within passageways 31. Each passageway 31 is adapted to receive a metal rod component of a refractory column for rigid attachment to the motor frame. The motor frame supports the motor above the molten metal pool and suspends the base member within the pool.

[0020] In one embodiment, the impeller 22 is configured with a first radial edge 32 axially spaced from a second radial edge 34. The first radial edge 32 and the second radial edge 34 surround the outer periphery of the circumference of the impeller 22. The pump chamber 18 includes a bearing assembly 35 having a first bearing ring 36 axially spaced from a second bearing ring 38. The first radial edge 32 is aligned with the first bearing ring 36 and the second radial edge 34 is aligned with the second bearing ring 38. The radial edges of the impeller can be composed of a material such as silicon carbide. For example, the radial edges of the impeller 22 can be bearing rings. At least one bearing can be adapted to support the rotation of the impeller 22 within the base member. The bearing rings 36, 38 can be made of a material such as silicon carbide, which has friction bearing properties at high temperatures to prevent cyclic failure. Generally speaking, all components of a pump for immersion in a pool of molten metal can be constructed of refractory materials such as graphite or ceramics (e.g., silicon carbide).

[0021] In one embodiment, impeller 22 includes a first peripheral circumference 42 axially spaced from a second peripheral circumference 44. Elongated shaft 16 is attached to impeller 22 at first peripheral circumference 42. Second peripheral circumference 44 is oppositely spaced from first peripheral circumference 42 and aligned with a bottom portion 46 of base member 20. First radial edge 32 is adjacent first peripheral circumference 42, and second radial edge 34 is adjacent second peripheral circumference 44.

[0022] The bottom inlet 48 is provided in the second outer peripheral circle 44. In this exemplary embodiment, the inlet comprises the annulus of a birdcage impeller. Of course, the impeller may be formed by blades, holes or other components known in the art.

[0023] Rotation of impeller 22 draws molten metal into inlet 48 and pump chamber 18. Continued rotation of impeller 22 forces molten metal from pump chamber 18 to outlet 50. The molten metal may be directed through outlet 50 to a piping assembly in fluid communication with a mold or other container.

[0024] In one embodiment, a bypass gap 62 is located between a portion of the first bearing ring 38 and the first radial edge 38. The bypass gap 62 is a radial space located between at least a portion of the first bearing ring 38 and the first radial edge 34. The bypass gap 62 is a space through which molten metal intentionally leaks from the pump chamber 18 of the base member 20. The bypass gap can be located at the top or bottom of the base member, but locating the bypass gap in the bottom surface may be preferred to direct the majority of the "leaking" molten metal to the bottom of the furnace.

[0025] A lubrication gap 60 is provided between the second radial edge 32 and the second bearing ring 36. The lubrication gap has a dimensioned space sized to primarily retain a molten metal layer that provides a low-friction boundary to support the rotation of the impeller and prevent wobble. The width of the lubrication gap may vary depending on the composition of the associated molten alloy.

[0026] It is contemplated that the width of the bypass gap (i.e., the distance between the impeller and the base and / or its bearing ring) will be at least about 1.2 times the lubrication gap, or between about 1.5 and 6 times the lubrication gap, or between about 2 and 4 times the lubrication gap, or any combination of these ranges.

[0027] Bypass gap 62 is operable to control the flow rate and discharge pressure of molten metal discharged from the pump. Bypass gap 62 allows molten metal to leak from pump chamber 18 to the environment external to base member 20 at a predetermined rate. During operation of pump assembly 10, leakage of molten metal from pump chamber 18 allows an operator to precisely adjust the flow rate or volume of molten metal provided to an associated mold. The leakage rate of molten metal through bypass gap 62 improves the controllability of molten metal delivery.

[0028] In one embodiment, the pump assembly includes the ability to statically position the molten metal being pumped through the outlet 50 and into the riser at a discharge pressure approximately 1.5 feet above the pool of molten metal in which the pump is located. In one embodiment, the impeller rotates at approximately 850 to 1000 revolutions per minute so that the molten metal is statically held approximately 1.5 feet above the pool of molten metal. The bypass clearance controls the volumetric flow rate and discharge pressure relationship of the pump so that an increase in the impeller's revolutions per minute will allow the discharge pressure to decrease as the flow rate of the molten metal increases.

[0029] A command RPM profile can be programmed into the controller to electrically communicate with the motor to rotate the impeller and force molten metal through the outlet and into the metal delivery conduit to the associated mold based on a desired volume fill rate established by the geometry of the associated mold.

[0030] 2, there is illustrated a centrifugal molten metal pump assembly 200 suitable for use in an exemplary environment of the present disclosure. Figure 3 and 4 The pump assembly detailed in FIG1 , as modified by the disclosure of FIG2 , is well suited for the environment and applications of FIG2 . Pump assembly 200 is shown from a side view immersed in a pool of molten metal 202 contained in a holding furnace 204. Each component of the pump, disposed below the molten metal line, may be formed from a refractory material such as graphite or ceramic.

[0031] The molten metal 202 can be maintained in a molten or liquid state by heating elements 206 disposed at any suitable location around the holding furnace 204. For example, the heating elements 206 can be disposed along the sides of the holding furnace 204 or below the holding furnace 204. In such a configuration, the molten metal 202 is heated to maintain the molten metal 202 in a liquid state. In some embodiments, the holding furnace can include a cover to create a closed environment.

[0032] The pump assembly 200 includes a motor 208 coupled to a rotatable elongated shaft 210. The motor 208 is configured to operate at a variable speed using a programmable controller 209. The programmable controller can be suitably programmed or otherwise configured to execute computer-executable instructions according to a programmable control profile stored in a computer-readable memory, such that the rotational speed of the impeller 212 varies according to the control profile.

[0033] Additionally or alternatively, the controller can be part of a feedback control system or closed-loop control system to monitor the filling state of the mold through sensors that can be located in the mold and configured to monitor the filling state of the mold. These sensors can be probes, or any similar monitoring mechanism capable of monitoring characteristics associated with filling the mold and sending feedback signals to the controller. In this case, the desired system output for filling the mold can be specified and can vary over time according to a programmable filling profile. In some embodiments, the controller is a proportional-integral-derivative (PID) controller suitable for feedback control systems. The controller can obtain the error (i.e., the difference) between the desired system output and the measured system output and adjust the command voltage to the motor 208 so as to operate the impeller at the desired rotational speed to maintain the desired system output.

[0034] 2 , an elongated shaft 210 is coupled to an impeller 212, which is located in a chamber or housing of a base member 214. The base member 214 is suspended by a plurality of refractory support columns 216 securely coupled to a platform 218 and immersed in the pool of molten metal 202. Alternatively, a central support tube may be used to suspend the base member, or support columns may be used in which elongated metal (e.g., steel) rods surrounded by a protective refractory jacket extend between the platform and the base member.

[0035] In some embodiments, elongated shaft 210 comprises a cylindrical, elongated orientation with an axis of rotation generally perpendicular to base member 214. Elongated shaft 210 includes a proximal end configured to couple to motor 208 and a distal end configured to couple to impeller 212. Elongated shaft 210 is configured to be rotated by motor 208 and extends from motor 208 into a chamber of base member 214, such that impeller 212 passes through elongated shaft 210 and rotates within the chamber of base member 214. Elongated shaft 210 includes plate 215 for degassing in top-feed pump designs. Generally, plate 215 does not meet the objectives of the present disclosure because, as a component of the shaft, plate 215 must have an outer diameter (OD) equal to or smaller than the diameter of the impeller to allow installation through the bottom of the pump base. A plate of this size is insufficient to cover / divert molten metal leaking from the top bearing. Therefore, it is desirable for the diverter plate to have an OD greater than the diameter of the impeller. Furthermore, because the plate 215 rotates with the shaft, it causes turbulence on the surface of the molten metal pool.

[0036] The rotation of the impeller 212 within the chamber causes a directional flow of the molten metal 202 by drawing the molten metal 202 into the chamber through the inlet of the base member 214 and forcing the molten metal 202 out of the chamber through the outlet of the base member 214. The outlet of the base member 214 can be disposed at any suitable location on the base member 214 and is typically adjacent to a side wall or top wall of the base member 214.

[0037] The outlet of the base member 214 can be coupled to a riser 220 for transferring the molten metal 202 to an associated delivery system and subsequently to the mold. The associated delivery system typically includes a piping system (or launder) adapted for fluid communication that also maintains the molten metal 202 at a desired temperature as it is transferred through the delivery system.

[0038] Now refer to Figure 3 and 4 , the molten metal pump 300 has been equipped with a diverter 302. Furthermore, it has been discovered that at low metal pool levels in the furnace and / or at high RPMs or pressures, unwanted slag may form on the surface of the molten metal pool. Without being bound by theory, it is believed that while some molten metal may pass through the lubrication gap during pump operation, the amount of molten metal passing through the lubrication gap increases at high impeller RPMs and during high-pressure mold filling. This increased molten metal discharge through the lubrication gap, particularly at low molten metal pool levels, may result in slag formation. The diverter 302 can help prevent this unwanted oxidation.

[0039] The pump 300 includes a base member 303 defining a pumping chamber 304. The pumping chamber 304 includes an opening 306 in a top surface 308 of the base member 303 and an opening 310 in a bottom surface 312 of the base member 303. At least one post can extend between the motor frame and the base member 303 and be received in a recess 314. An impeller 316 is disposed in the pumping chamber 304 and is configured to draw molten metal through the opening 310 in the bottom surface 312 and discharge the molten metal through an outlet 318 in the base member 303. The flow diverter 302 is disposed above the opening 306 in the top surface 308.

[0040] The molten metal pump may include a bypass gap 331 and a lubrication gap 319, as described with respect to FIG1 . A flow diverter 302 is used to interrupt the flow of molten metal exiting the opening 306 where the lubrication gap 319 is located. In addition, the flow diverter 302 can disperse the flow of molten metal exiting the lubrication gap 319 before it reaches the surface of the molten metal pool where the molten metal pump is located. Without the flow diverter, undesirable surface turbulence would occur in the molten metal pool, leading to unwanted oxidation of the molten metal.

[0041] The flow diverter is used to reduce turbulence in the pool of molten metal caused by the discharge of high-pressure molten metal through the lubrication gap (e.g., >10 psi). The flow diverter 302 includes a passage 322 through which an axis 324 extends. A spacer element 326 extends from the base member 303 and supports the flow diverter 302. The spacer element 326 can have a cylindrical body including a passage 330. The flow diverter 302 can include a curved lower surface 333 to help guide the flow of lubrication gap metal radially outward. The flow diverter 302 can be substantially disc-shaped. The flow diverter 302 can include a notch 332 in its radial edge to receive a post and / or lift.

[0042] In certain embodiments, the bottom surface of the flow divider 302 can include a channel 335 extending from an adjacent passage 322 to the peripheral edge. The channel can promote smooth flow of molten metal laterally across the bottom surface of the flow divider. In some embodiments, the channel 335 can be radially aligned with the passage 330 in the spacing element 326. Similarly, in selected embodiments, the arcuate lower surface 333 can be radially aligned to form a transition zone between the passage 330 and the channel 335.

[0043] Without being bound by theory, it is expected that when the pressure in the pumping chamber exceeds 5 PSI, or 10 PSI, or 15 PSI or more, the molten metal is discharged through the pump outlet, the bypass gap, and the opening in the top surface. Alternatively, this feature can be expressed by the following situation: the pressure in the pumping chamber is high enough to push the molten metal through the outlet and the bypass gap but not through the top surface because the size of the space between the impeller and the pumping chamber (i.e., the lubrication gap) is narrow enough to resist the flow of molten metal.

[0044] Another way to indicate when molten metal is being discharged in large quantities through the lubrication gap can be based on the impeller RPM. Furthermore, the pump can be operated at a first RPM and a second RPM. At the first RPM, no large quantities of molten metal are passing through the lubrication gap. At the second RPM, molten metal is discharged through each of the outlet, the bypass gap, and the opening in the top surface (e.g., the lubrication gap).

[0045] The exemplary embodiments have been described with reference to preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the foregoing detailed description. It is intended that the exemplary embodiments be interpreted as including all such modifications and alterations as fall within the scope of the appended claims or their equivalents.

Claims

1. A molten metal pump comprising a base member defining a pumping chamber, the base member including an opening in a top surface and an opening in a bottom surface, a bypass gap located at a top or bottom portion of the base member, the opening being in fluid communication with the pumping chamber, at least one post extending between a motor frame and the base member, a bottom feed impeller disposed in the pumping chamber and configured to draw molten metal through the opening in the bottom surface and discharge the molten metal through an outlet in the base member, and a flow diverter disposed above the opening in the top surface, wherein The flow diverter includes a passage through which a shaft extends, the shaft engaging the impeller at a first end and engaging the motor at a second end. The molten metal pump further includes a spacer element extending from the base member and supporting the flow diverter. The spacer element comprises a cylindrical body comprising at least one passage, The bottom surface of the flow diverter includes a channel extending from a passageway of the flow diverter to a peripheral edge, the channel being radially aligned with at least one passageway in the spacing element.

2. The molten metal pump of claim 1 including a bypass gap between a radial edge of the impeller and the opening in the bottom surface.

3. The molten metal pump of claim 2, comprising a lubrication gap between a radial edge of the impeller and the opening in the top surface.

4. The molten metal pump according to claim 1, wherein The flow diverter is substantially disc-shaped.

5. The molten metal pump according to claim 1, wherein A surface of the flow diverter facing the pumping chamber includes an arcuate surface.

6. The molten metal pump according to claim 4, wherein The flow splitter includes at least one notch in a radial edge, the at least one notch configured to receive a post.

7. The molten metal pump according to claim 1, wherein The impeller is in bottom feed configuration.

8. The molten metal pump according to claim 1, wherein Each of the base member, the impeller, and the diverter is composed of a refractory material.

9. A method of pumping molten metal, comprising providing a molten metal pump having a base member defining a pumping chamber, the base member including an opening in a top surface and an opening in a bottom surface, a bypass gap located at the top or bottom of the base member, the opening being in fluid communication with the pumping chamber, an impeller disposed in the pumping chamber, wherein when operating at 200 RPM or less, rotation of the impeller draws molten metal through the opening in the bottom surface and discharges the molten metal through an outlet in the base member, and when operating at 500 RPM or greater, rotation of the impeller also discharges the molten metal through the opening in the top surface, and wherein a flow diverter disposed above the opening in the top surface laterally directs molten metal passing through the opening in the top surface, The molten metal pump further includes a spacer element extending from the base member and supporting the diverter, The spacer element comprises a cylindrical body comprising at least one passage, The bottom surface of the flow diverter includes a channel extending from a passageway of the flow diverter to a peripheral edge, the channel being radially aligned with at least one passageway in the spacing element.

10. The method according to claim 9, wherein When the pressure in the pumping chamber reaches 5 PSI or higher, molten metal is discharged through the opening in the top surface.

11. The method of claim 9, performed to fill a mold.

12. A molten metal pump comprising a base member defining a pumping chamber, the base member including an opening in a top surface and an opening in a bottom surface, a bypass gap located at a top or bottom of the base member, the opening being in fluid communication with the pumping chamber, at least one post extending between a motor frame and the base member, an impeller disposed in the pumping chamber and configured to draw molten metal through the opening in the bottom surface and discharge the molten metal through an outlet in the base member, and a flow divider supported above the opening in the top surface by a spacer element secured to the base member, the spacer element comprising a cylinder including a passage therethrough. The bottom surface of the flow diverter includes a channel extending from the passageway of the flow diverter to a peripheral edge, the channel being radially aligned with the passageway in the spacing element.

13. The molten metal pump according to claim 12, wherein The spacer element is fixed to an inner surface of the opening in the top surface of the base member.

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