Patent Application
20140044520
The present exemplary embodiment relates to a pump assembly to pump molten metal. It finds particular application in conjunction with a shaft and impeller assembly for variable pressure pumps for filling molds with molten metal, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
At times it is necessary to move metals in their liquid or molten form. Molten metal pumps are utilized to transfer or recirculate molten metal through a system of pipes or within a storage vessel. These pumps generally include a motor supported by a base member having a rotatable elongated shaft extending into a body of molten metal to rotate an impeller. The base member is submerged in the molten metal and includes a housing or pump chamber having the impeller located therein. The motor is supported by a platform that is rigidly attached to a plurality of structural posts or a central support tube that is attached to the base member. The plurality of structural posts and the rotatable elongated shaft extends from the motor and into the pump chamber submerged in the molten metal within which the impeller is rotated. Rotation of the impeller therein causes a directed flow of molten metal.
The impeller is mounted within the chamber in the base member and is supported by bearing rings to act as a wear resistant surface and allow smooth rotation therein. Additionally, a radial bearing surface can be provided on the elongated shaft or impeller to prevent excessive vibration of the pump assembly which could lead to inefficiency or even failure of pump components. These pumps have traditionally been referred to as centrifugal pumps.
Although centrifugal pumps operate satisfactorily to pump molten metal, they have never found acceptance as a means to fill molten metal molds. Rather, this task has been left to electromagnetic pumps, pressurized furnaces and ladeling. Known centrifugal pumps generally control a flow rate and pressure of molten metal by modulating the rotational rate of the impeller. However, this control mechanism experiences erratic control of the flow rate and pressure of molten metal when attempting to transfer molten metal into a mold such as a form mold. The erratic control of the flow of molten metal into the form mold is especially prevalent when attempting to fill a form mold for a complicated or intricately formed tool or part.
In one embodiment, the present disclosure relates to a molten metal pump assembly to fill molds with molten metal. The pump assembly comprises an elongated shaft connecting a motor to an impeller. The impeller is housed within a pump chamber of a base member such that rotation of the impeller draws molten metal into the chamber at an inlet and forces molten metal through an outlet of the chamber. The impeller includes a first radial edge spaced from a second radial edge such that the first radial edge is adjacent the elongated shaft. A bearing assembly surrounds the impeller within the chamber, the bearing assembly includes a first bearing adapted to support the rotation of the impeller at the first radial edge and a second bearing adapted to support the rotation of the impeller at the second radial edge. At least one bypass gap is interposed between one of the first and second bearings and the associated first and second radial edges. The bypass gap is operative to manipulate a flow rate and a head pressure of the molten metal. Molten metal leaks from the chamber through the bypass gap at a predetermined rate as the impeller is rotated such that a precise control of the flow rate is achieved.
In another embodiment of the present disclosure, a method of filling a mold with molten metal is provided. The method comprises rotating an impeller within a chamber. Molten metal is transferred through the impeller into the chamber. A predetermined portion of molten metal leaks through at least one bypass gap from the chamber to the base exterior. The leakage rate allows for precise tuning of a head pressure relative to a rotational speed of the impeller. An associated mold is filled with the molten metal and is controlled by a programmable control profile.
According to yet another embodiment of the present disclosure, a molten metal pump assembly to fill molds with molten metal is provided. The pump assembly comprises an elongated shaft connecting a motor to an impeller. The impeller is housed within a chamber of a base member such that rotation of the impeller draws molten metal into the chamber at an inlet and forces molten metal through an outlet of the chamber. The impeller includes a first radial edge adjacent to a first peripheral circumference spaced from a second radial edge adjacent to a second peripheral circumference such that the elongated shaft is rigidly attached to the first peripheral circumference.
A bearing assembly surrounds the impeller within the chamber and includes a first bearing adapted to support the rotation of the impeller at the first radial edge and a second bearing adapted to support the rotation of the impeller at the second radial edge. At least one bypass gap is provided at the second peripheral circumference to provide fluid communication between the chamber and a surrounding environment. The bypass gap is operative to allow a predetermined amount of molten metal leak from the chamber such that precise control of the flow rate and head pressure of the molten metal is provided at the outlet.
One aspect of the present disclosure is an assembly and method of use for a molten metal pump to fill complex molds such that the bypass gap allows for a more precise flow control.
It is to be understood that the detailed figures are for purposes of illustrating the exemplary embodiments only and are not intended to be limiting. Additionally, it will be appreciated that the drawings are not to scale and that portions of certain elements may be exaggerated for the purpose of clarity and ease of illustration.
With reference to
The elongated shaft 16 is rotated by the motor 14 and extends from the motor 14 and into the pump chamber 18 submerged in the molten metal 12 within which the impeller 22 is rotated. Rotation of the impeller 22 therein causes a directed flow of molten metal 12 through an associated metal delivery conduit (not shown) such as a riser, adapted for fluid metal flow. The riser for the metal delivery conduit system is connected to the outlet of the pump chamber 18 which is typically adjacent a side wall or top wall of the base member. These types of pumps are often referred to as transfer pumps. An example of one suitable transfer pump is shown in U.S. Pat. No. 5,947,705, the disclosure of which is herein incorporated by reference.
With reference to
The base member 20 defines the pump chamber 18 that receives the impeller 22. The base member 20 is configured to structurally receive the refractory posts 24 (optionally comprised of an elongated metal rod within a protective refractory sheath) within passages 31. Each passage 31 is adapted to receive the metal rod component of the refractory post 24 to rigidly attach to a motor mount 26. The motor mount 26 supports the motor 14 above the molten metal 12.
In one embodiment, the impeller 22 is configured with a first radial edge 32 that is axially spaced from a second radial edge 34. The first and second radial edges 32, 34 are located peripherally about 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 facially aligned with the first bearing ring 36 and the second radial edge 34 is facially aligned with the second bearing ring 38. The bearing rings are made of a material, such as silicon carbide, having frictional bearing properties at high temperatures to prevent cyclic failure due to high frictional forces. The bearings are adapted to support the rotation of the impeller 22 within the base member such that the pump assembly 10 is at least substantially prevented from vibrating. The radial edges of the impeller may similarly be comprised of a material such as silicon carbide. For example, the radial edges of the impeller 22 may be comprised of a silicon carbide bearing ring.
In one embodiment, the impeller 22 includes a first peripheral circumference 42 axially spaced from a second peripheral circumference 44. The elongated shaft 16 is attached to the impeller 22 at the first peripheral circumference 42. The second peripheral circumference 44 is spaced opposite from the first peripheral circumference 44 and aligned with a bottom portion 46 of the base member 20. The first radial edge 32 is adjacent to the first peripheral circumference 42 and the second radial edge 34 is adjacent to the second peripheral circumference 44.
In one embodiment, a bottom inlet 48 is provided in the second peripheral circumference 44. More particularly, the inlet comprises the annulus of a bird cage style of impeller 22. Of course, the inlet can be formed of vanes, bores, annulus (“bird cage”) or other assemblies known in the art. It is noted that a top feed pump assembly or a combination top and bottom feed pump assembly may also be used.
As will be apparent from the following discussion, a bored or bird cage impeller may be advantageous because they include a defined radial edge allowing a designed tolerance (or bypass gap) to be created with the pump chamber 18. An example of a bored impeller is provided by U.S. Pat. No. 6,464,458, the disclosure of which is herein incorporated by reference.
The rotation of the impeller 22 draws molten metal 12 into the inlet 48 and into the chamber 18 such that continued rotation of the impeller 22 causes molten metal 12 to be forced out of the pump chamber 18 to an outlet 50 of the base member 20.
With reference to
In one embodiment, the bypass gap 60 is interposed between a portion of the second bearing ring 38 and the second radial edge 34. For example, the bypass gap 60 is a radial space interposed between at least a portion of the second bearing 38 and the second radial edge 34 of the impeller 22. The radial space is of a designed tolerance that can be varied to allow for a predetermined leakage rate of the molten metal 12.
In this regard, it is noted that a lubrication gap 62 exists between the radial edge 32 of the impeller 22 and the bearing ring 36 disposed within the base 20. The lubrication gap is a space provided within which molten metal is retained to provide a low friction boundary. The lubrication gap can vary based upon the constituents of the relevant alloy. It is contemplated that the bypass gap will have a width (i.e. a distance between the impeller and the base) of at least about 1.2× the lubrication gap, or between about 1.5 and 6× the lubrication gap, or between about 2 and 4× the lubrication gap or any combination of such ranges.
It is also noted that a discontinuous gap width may be employed wherein relatively close tolerance regions are interspersed with relatively large bypass gap width regions.
For example, the bypass gap 60 may be a plurality of removable segmented teeth or posts that are radially positioned about the perimeter of the impeller 22 such that a plurality of teeth maintain contact with bearing ring 38 during rotation of the impeller 22 while radial spaces interposed between the teeth are configured to allow leakage of the molten metal 12 at a predetermined rate. In another embodiment, the bypass gap 60 may be provided by a plurality of apertures located through the first peripheral circumference 42 of the impeller to 22 allow fluid communication with the chamber 18 and an environment outside the base member. Further, it is contemplated that at least one bypass gap can also be provided downstream of the impeller 22 within the pump chamber 18 adjacent to outlet 50 or can even be located within the riser. This type of bypass gap can be comprised of a hole(s) drilled into a pump assembly component. In short, it is feasible to provide a molten metal pump that is functional in filling complex molds by providing a designed leakage path at any point in the pump assembly.
The bypass gap 60 is operative to manipulate a flow rate and a head pressure of the molten metal 12. The bypass gap 60 allows molten metal to leak from the pump chamber 18 to an environment outside of the base member 20 at a predetermined rate. The leakage of molten metal 12 from the pump chamber 18 during the operation of the pump assembly 10 allows an associated user to finely tune the flow rate or volumetric amount of molten metal 12 provided to an associated mold. The leakage rate of molten metal 12 through the bypass gap 60 improves the controllability of the transport of molten metal 12 and is at least in part, due to a viscosity coefficient of the molten metal 12. Namely, in one embodiment, as the viscosity of the molten metal 12 decreases, a size of the bypass gap 60 would also be decreased to get the optimal leakage rate of molten metal 12.
In one embodiment, the bypass gap 60 is provided by the second bearing ring 38 such that the second bearing ring 38 includes a larger inner diameter than the first bearing ring 36 in the bearing assembly 35. In this regard, there is a greater space between said radial edge 34 and second bearing ring 38. In another embodiment, the bypass gap 60 is provided by the impeller 22 such that the second radial edge 34 of the impeller 22 has a smaller diameter than the first radial edge 32. Here, the first radial edge 32 is abuttingly positioned and ratably supported at the first bearing ring 36 within the pump chamber 18 to form the relatively narrower lubrication gap while a bypass gap exists between the second bearing ring 38 and the second radial edge 34. Of course, a top side gap can be created by reversing the dimensions disclosed above.
In one embodiment, the pump assembly includes an ability to statically position molten metal 12 pumped through the outlet 50 and into a riser at approximately 1.5 feet of head pressure above a body of molten metal 12. In one embodiment the impeller rotates approximately 850-1000 rotations per minute such that molten metal is statically held at approximately 1.5 feet above the body of molten metal 12. The bypass gap 60 manipulates the volumetric flow rate and head pressure relationship of the pump 10 such that an increased amount of rotations per minute of the impeller 22 would allow the reduction of head pressure as the flow rate of molten metal 12 is increased. This relationship as schematically illustrated by the graph in
Precise control to the amount of molten metal 12 provided to an associated mold is achieved by positioning the bypass gap 60 between the bearing assembly 35 and the impeller 22. More particularly, in one embodiment, the motor 14 is operated by a programmable command rpm profile as illustrated by
With reference to
The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US12/34048 | 4/18/2012 | WO | 00 | 10/18/2013 |
| Number | Date | Country | |
|---|---|---|---|
| 61476433 | Apr 2011 | US |
