MOLTEN METAL IMPELLER

Abstract: An impeller (101) for a molten metal pump (32) has a cylindrical body (103) comprised of a refractory material. The cylindrical body includes generally coplanar top (105) and bottom surfaces. A central bore (111) is provided in the top surface to provide a point for mating with a shaft (109). A plurality of circumferentially spaced passages (115) extend from the top or bottom surface to a side wall (117) of the impeller, each of the passages being separate and preferably having an inlet opening which is equal to or less than the corresponding outlet opening in size. A recess (107) is optionally formed in the top or bottom surface, forming the initial inlet to the passages.

Description: MOLTEN METAL IMPELLER This application is a continuation-in-part of U.S. Serial No. 08/842,004 filed April 23, 1997. Background of the Invention This invention relates to molten metal pumps. More particularly, this invention relates to an impeller suited for use in a molten metal pump. The impeller of the present invention is particularly well suited to be used in molten aluminum and molten zinc pumps. In fact, throughout the specification, numerous references will be made to the use of the impeller in molten aluminum pumps, and certain prior art molten aluminum pumps will be discussed. However, it should be realized that the invention can be used in any pump utilized in refining or casting molten metals. In the processing of molten metals, it is often necessary to move molten metal from one place to another. When it is desired to remove molten metal from a vessel, a so called transfer pump is used. When it is desired to circulate molten metal within a vessel, a so called circulation pump is used. When it is desired to purify molten metal disposed within a vessel, a so called gas injection pump is used. In each of these types of pumps, a rotatable impeller is disposed within a pumping chamber in a vessel containing the molten metal. Rotation of the impeller within the pumping chamber draws in molten metal and expels it in a direction governed by the design of the pumping chamber. In each of the above referenced pumps, the pumping chamber is formed in a base member which is suspended within the molten metal by support posts or other means The impeller is supported for rotation in the base member by means of a rotatable shaft connected to a drive motor located atop a platform which is also supported by the posts Molten metal pump designers are generally concerned with efficiency, effectiveness and longevity For a given diameter impeller, efficiency is defined by the work output of the pump divided by the work input of the motor An equally important quality of effectiveness is defined as molten metal flow per impeller revolutions per minute A particularly troublesome aspect of molten metal pump operation is the degradation of the impeller Moreover, to operate in a high temperature, reactive molten metal environment, a refractory or graphite material is used from which to construct the impeller However, these materials are also prone to degradation when exposed to particles entrained in the molten metal More specifically, the molten metal may include pieces of the refractory lining of the molten metal furnace, undesirables from the metal feed stock and occlusions which develop via chemical reaction, all of which can cause damage to an impeller and pump housing if passed therethrough With regard to earlier impeller designs, U.S. Patent No. 3,048,384, herein incorporated by reference, displays a molten metal pump with a cup-like impeller having lateral openings in the sidewall for moving molten metal Although the impeller of this design adequately pumps molten metal, it is prone to clogging when particles are drawn into the pump. More specifically, because the inlet to the impeller makes up the entire central top surface area and extends downwardly the entire depth of the radial openings to the circular base, large particles can enter the impeller but cannot exit through the smaller radial openings Accordingly, a risk for catastrophic failure of the pump results if a large particle is jammed against the volute or the pumping chamber. In addition, small particles can slowly clog the radial openings and degrade the performance of the impeller by reducing the volume of molten metal that can be transferred In U S Patent No. 5,586,863, a significantly improved molten metal impeller design is provided. More specifically, an impeller comprised of a spherical base, a central hub and radially directed vanes is described This design achieves a significant advantage by providing a smaller inlet area than outlet area, which more readily passes particles without jamming and/or clogging However, this design is slightly disadvantaged in that molten metal flow between adjacent vanes is difficult to control Accordingly, an impeller having low clogging characteristics, yet also providing high effectiveness would be highly desirable in the art The current invention achieves these objectives Moreover, the current invention achieves a number of advantages in directional forced metal flow For example, the impeller of the current pump is not prone to clogging as in many of the prior impellers Accordingly, catastrophic failure is much less likely to occur and the effectiveness of operation does not degrade rapidly over time The design also achieves high strength by increasing the percentage of the body comprised of the refractory material. Furthermore, the impeller design can be prepared with relatively simple manufacturing processes. Therefore, the cost of production is low and accommodates a wide selection of materials, such as graphite or ceramics Summary of the Invention It is the primary object of this invention to provide a new and improved molten metal pump. It is a further object of this invention to provide a new and improved impeller for use in a molten metal pump. To achieve the foregoing objects and in accordance with the purpose of the invention as embodied and broadly described herein, the molten metal pump of this invention comprises a motor having an elongated drive shaft with first and second ends. The first end mates with the motor and the second end is attached to an impeller disposed in a pumping chamber. The impeller is comprised of a cylindrical body of a refractory material and includes generally coplanar top and bottom surfaces, with a first central bore in the top surface that mates with the shaft. A plurality of circumferentially spaced passages extend from the top surface to a sidewall of the impeller. Each of the passages provides a separate duct from an inlet opening at the top surface to an outlet opening at the sidewall In addition, preferably each inlet opening has a cross-sectional area which is the same as or less than it's corresponding outlet opening In a further preferred embodiment, the impeller is comprised of graphite In a particularly preferred form, the impeller includes at least two passages, and more preferably six passages Preferably, the impeller is provided with a bearing ring surrounding the edge of the bottom surface In a further preferred embodiment, the top surface of the impeller is formed of a ceramic material and the body of the impeller is graphite In an alternative form of the invention, the impeller has a cylindrical graphite or ceramic body with opposed top and bottom surfaces and a radial sidewall An annular recess is formed in the top or bottom surface, creating an outer ring and inner column In a top feed embodiment a bore is formed in the inner column to accommodate a shaft Preferably, the annular recess will extend to a depth between one-half the width of the recess and less than two-thirds, more preferably one half the overall height of the impeller body In a particularly preferred embodiment, the width and depth of the annular recess are approximately equal A plurality of passages extend from the sidewall and intersect the annular recess Preferably, the passages have a height and a width greater than the dimension of the recess radially between the inner column and the outer ring In this regard, any object or inclusion in the molten metal bath which is sufficiently small to enter the annular recess, will be easily passed through and out the passages in the sidewall In a preferred embodiment, the impeller will include four and more preferably six passages with a major portion of the passages disposed at a level below the annular recess, wherein the annular recess intersects only the top region of the passages For example, the annular recess will extend through the top half of the impeller height and the passages will be located predominantly in the lower half of the impeller height In a particularly preferred form of the invention, a ceramic cap member will be secured to the top outer ring of the impeller to protect the top surface and a bearing ring will be secured to the outer lower edge This form of the impeller has been found to effectively repel large objects in the molten metal bath away from the entry to the impeller, i e , the annular recess, without significant damage to the impeller or pump housing In an additional alternative embodiment, the impeller will include passages which are substantially straight bores passing from the top or bottom surface of the impeller to the sidewall Preferably the bores will be generally circular or oval in cross-section and will be angled at least 5° and more preferably about 45° from vertical Preferably, the bores will widen from the inlet to the outlet Furthermore, this straight bore embodiment can be combined with an annular recess, wherein each bore opens into the recess rather than the top or bottom surface Brief Description of the Drawings FIGURE 1 is a perspective view of the inventive impeller, FIGURE 2 is a top view of the inventive impeller, showing the passages in cross section, FIGURE 2A is a cross sectional view taken along lines A-A in FIG 2, FIGURE 3 is a top view of alternative embodiment of the inventive impeller, FIGURE 3A is a cross sectional view taken along lines A-A in FIG 3, FIGURE 4 is a cross-sectional view similar to that of Figures 2A, and 3A, of an alternative embodiment of the inventive impeller FIGURE 5 is a side elevation view of the inventive impeller secured to a drive shaft, partially in cross section, FIGURE 6 is an exploded view of a molten metal pump including the inventive impeller, FIGURE 7 is a perspective view of an alternative embodiment of the inventive impeller, 6 FIGURE 8 is a top view of the inventive impeller of Figure 7 (shaft removed), FIGURE 9 is a cross-sectional view of the inventive impeller of Figure 8, FIGURE 10 is a cross-section of the impeller of Figure 8 taken along lines B-B, FIGURE 11 is a cross-sectional view of the inventive impeller of Figure 7, FIGURE 12 is a top plan view of the ceramic cap member; FIGURE 13 is a top view of the straight bore embodiment of the inventive impeller; FIGURE 14 is a side elevation view of the impeller of Figure 13; and FIGURE 15 is a side elevation view of a bottom feed version of the impeller Detailed Description of the Invention Reference will not be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. While the invention will be described in connection with the preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents that may be included within the spirit and scope of the invention defined by the appended claims. This invention is directed to a new and improved impeller for use in molten metal pumps. In particular, the impeller is utilized in molten metal pumps to create a forced directional flow of molten zinc or molten aluminum. United States Patents 2,948,524; 5,078,572, 5,088,893; 5,330,328; 5,308,045 and 5,470,201 , herein incorporated by reference, describe a variety of molten metal pumps and environments in which the present impeller could be used. Referring now to Figures 1 , 2 and 2A, the inventive impeller 1 is a generally cylindrical shaped body of graphite or ceramic and includes an upper face 2 having a recess 4 to accommodate a shaft. The upper face 2 also includes inlets 5 to passages 6 which extend downwardly from the upper face and outwardly through a sidewall 8, to an outlet 9. A bearing ring 10 of a ceramic, such as silicon carbide, is provided surrounding the outer edge of a lower face 12. Figure 1 also shows an optional ceramic cap 13, which can be cemented to the top surface 2 of the impeller 1 to improve the wear characteristics of the device. With specific reference to Figures 2 and 2A, the passages 6 increase in diameter from the inlet 5 to the outlet 9. In this manner, any particle which can enter the impeller will also exit. Figures 3, 3A, and 4 depict an alternative embodiment of the impeller. Particularly, in Figures 2 and 2A, the passages have an increasing diameter throughout their length. In contrast, the impeller 14 of Figures 3 and 3A includes passages 15 having a first diameter portion in a downward direction 16 and a second wider diameter portion 18 in an outward direction. Nonetheless, an inlet 17 has a smaller diameter than an outlet 19. Figure 4 shows an impeller '14 wherein an inlet '17 and an outlet '19 have equivalent cross-sectional areas. Furthermore, the cross-sectional area of passages '15 are substantially equivalent in both the vertical component '16 and the horizontal component '18. Nonetheless, absent any constriction of the flow path, the passages provide a "tunnel" which will accommodate the flow-through of any particle which can fit into the inlet. Figure 5 is included to depict the inventive impeller 14 attached to a shaft 20. The shaft 20 is substantially encased in a protective sheath 21 , and includes a first end 22 which mates with a drive motor (see Fig. 5). The second end includes a tapered portion 24 which mates with the tapered walls of a central bore 26 in the impeller 14. The shaft is secured in the bore 26 by cement (not shown) and several dowels 28. A bearing ring 30 is also positioned on the shaft-cemented in place-to provide a wear surface. Figure 6 depicts the arrangement of the impeller 14 in a molten metal pump 32 Particularly a motor 34, is secured to a motor mount 36 A riser 38 (indicating this pump to be a transfer-style)through which molten metal is pumped is provided The riser 38 is attached to the motor mount 36 via a riser socket 40 A pair of refractory posts 42 are secured by a corresponding pair of post sockets 44, a rear support plate 46 and bolts 48 to the motor mount 36 At a second end, each of the posts 42, and the riser 38, are cemented into a base 50 The base 50 includes a pumping chamber 52, in which the impeller 14 is disposed The pumping chamber is constructed such that the impeller bearing ring 10 is adjacent the base bearing ring 54 The impeller is rotated within the pumping chamber via a shaft 59 secured to the motor by a threaded connection 60 pinned to a universal joint 62 Of course, the skilled artisan is aware of many various coupling designs such as, but not limited to, pinned connections and quadralobal drives which are all suitable for use in the present pump The novel impeller has a generally cylindrical shape and is formed of a refractory material such as graphite or a ceramic such as silicon carbide The cylindrical piece includes a cavity in its upper face suitable to accommodate a shaft The shaft, in turn, is joined to a motor to achieve rotation of the impeller The periphery of the upper face is machined to include a plurality of passages which extend downwardly and outwardly from the upper face to the sides of the cylindrical impeller In the preferred embodiment, six passages are formed and provide a large fluid volume area Importantly, the passages are formed such that they provide a "tunnel" at the upper face of the impeller which effectively provides entrainment of any particular particles entering the impeller and prevents lodging/jamming between the rotating impeller body and the pump casing Moreover, any inclusions which are too large to enter the passage will be thrown clear of the pump by centrifugal force, preventing catastrophic failure of the pump Furthermore, in the preferred embodiment of the impeller, any inclusions or scrap contained in the molten metal which is small enough to enter this dimension of the passage will of necessity be sized such that it can exit the impeller Referring now to Figures 7- 2, an alternative embodiment of the inventive impeller is depicted In this regard, the impeller 101 again includes a main body 103 having a generally cylindrical shape The cylindrical main body 103 includes a top surface 105 in which an annular recess 107 is formed A shaft 109 is secured within bore 111 formed within centrally located column 113, itself formed by annular recess 107. Four passages 115 enter from radial side wall 117 and intersect the annular recess 107. In this manner a plurality of passages are formed from the top surface 105 to the radial sidewall 117. In a particularly preferred embodiment, the impeller 101 includes a bearing ring 119 and a cap member 121 (see Figure 12), each comprised of a refractory, high strength material which protects the graphite or ceramic main body 103 from wear, e.g. silicon carbide. As most clearly seen in Figure 11 , the shaft assembly 109 is preferably provided with a diameter equivalent to that of the column 113 or, and as illustrated, is outfitted with a sheath member 123 to protect the shaft material and provide a consistent dimension with column 113 for effective mating of these two compounds. It has been found that the impeller design of Figures 7-11 is particularly effective in expelling large occlusions in the molten metal bath away from the impeller shaft arrangement and away from the pump housing. More particularly, it has been found that objects are flung away from the impeller and do not become trapped between the impeller and shaft of impeller and housing- -which otherwise results in excessive wear of the apparatus. Referring now to Figures 13-14, a further alternative embodiment of the present invention is depicted. Particularly, the inventive impeller 201 is shown comprised of planar top and bottom surfaces 203 and 205, respectively, and a generally circular in cross-section outer sidewall 207. The sidewall 207 does not extend fully to bottom surface 205, but rather a notch 209 is provided to which a bearing ring (not shown) can be affixed in the finished product. A 10 bore 210 is formed in the top surface 203 to accommodate a shaft (not shown) A plurality of passages 211 are provided The passages 21 1 are generally straight bores passing from an inlet 208 in the top surface 203 to an outlet 212 in the sidewall 207 The passages 211 generally have an oval cross- sectional shape and are inclined forwardly from vertical. Particularly, during operation of the pump, the impeller rotation is generally in a direction of arrow 213, from which the reference to forwardly inclined passages is derived Generally the forward incline will be at least 5°, and preferably about 45° as shown in the figures Of course, the passages are necessarily angled outwardly from inlet to outlet Finally, with reference to Figure 16, a bottom feed impeller 301 is displayed Moreover, the inlet 303 to the passages 305 is provided in the bottom surface 307 of the impeller 301. Therefore, a plurality of passages 305 are included in this embodiment with outlets 309 being positioned in the sidewall 311 and inlet 313 being provided in the bottom surface 307 It is also noted that each of the impeller embodiments of this invention, including (i) mated horizontal and vertical passages (Figures 1-5), (ii) the annular intake recess (Figures 7-12), and (iii) the straight bore passages (Figures 13-15), can be advantageously combined and can be used in both top and bottom inlet pumps Thus, it is apparent that there has been provided, in accordance with this invention, a molten metal impeller and pump that fully satisfies the objects, aims and advantages set forth above While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art In light of the foregoing description, accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the impended claims

Claims: 11 We claim 1 An impeller for a molten metal pump comprised of a generally cylindrical ceramic or graphite body, said cylindrical body having opposed top and bottom surfaces and a radial sidewall, an annular recess in said top surface forming an outer ring and an inner column, a bore formed in said inner column to accommodate a shaft, and a plurality of passages formed in said sidewall, said passages intersecting said annular recess. 2 The impeller of claim 1 further comprising at least four passages 3 The impeller of claim 1 wherein said annular recess has a depth less than one half of the overall height of said cylindrical body. 4 The impeller of claim 3 wherein said annular recess has a depth at least approximately one-half the width of the recess. 5. The impeller of claim 4 wherein the recess width and depth are approximately equal. 6. The impeller of claim 1 further comprising a cap member secured to said outer ring. 7. The impeller of claim 6 wherein said cap member includes a top surface which slants from a highest point adjacent the annular recess to a lowest point adjacent the radial sidewall. 8. The impeller of claim 1 further comprising a bearing ring secured to the outer edge of said bottom surface. 9. The impeller of claim 1 wherein a major portion of said 12 passages is disposed below the depth of said annular recess 10 The impeller of claim 1 wherein said passages have both a height and width equal to or greater than the width of said annular recess 1 1 A molten metal pump comprising a) an elongated shaft having first and second ends, b) a means for rotating said shaft about an axis and communication with said first end of said shaft, c) an impeller disposed adjacent said second end of said shaft d) a pumping chamber housing said impeller, said pumping chamber having an inlet opening through which molten metal can be drawn and an outlet opening through which molten metal can be discharged, and e) said impeller comprising a generally cylindrical body, said cylindrical body having opposed top and bottom surfaces and a radial sidewall, an annular recess in said top surface forming an outer ring and an inner column, said shaft secured to said inner column, and a plurality of passages formed in said sidewall intersecting said annular recess 12 The pump of claim 11 further comprising at least four passages 13 The pump of claim 11 wherein said annular recess has a depth less than one half of the overall height of said cylindrical body 14 The pump of claim 13 wherein said annular recess has a depth at least approximately one-half the width of the recess 15 The pump of claim 14 wherein the recess width and depth are approximately equal 13 16 The pump claim 11 further comprising a cap member secured to said outer ring 17 The pump of claim 11 further comprising a bearing ring secured to the outer edge of said bottom surface 18 The pump of claim 11 wherein a major portion of said passages is disposed below the depth of said annular recess. 19 The pump of claim 11 wherein said passages have both a height and width greater than the width of said annular recess 20 An impeller for a molten metal pump comprised of a generally cylindrical ceramic or graphite body, said cylindrical body having opposed top and bottom surfaces and a radial sidewall, an annular recess in said bottom surface forming an outer ring and an inner column, a means provided in said top surface to accommodate a shaft, and a plurality of passages formed in said sidewall, said passages intersecting said annular recess 21. An impeller for a molten metal pump having a cylindrical body comprised of a refractory material, said cylindrical body including opposed top and bottom surfaces, a means being provided in said top surface for mating with a shaft, a plurality of circumferentially spaced passages extending from said top or bottom surface to a sidewall of said impeller, each of said passages being separate and having an inlet opening in said top or bottom surface and an outlet opening in said sidewall. 22. An impeller for a molten metal pump comprised of a cylindrical refractory body, said cylindrical body having opposed top and bottom surfaces and a radial sidewall, said sidewall providing a substantial contiguous surface interrupted only by a plurality of passages extending from said top or 14 bottom surfaces to said sidewall, and a means for securing a shaft on said top surface 23 The impeller of claim 22 wherein said passages are substantially straight 24 The impeller of claim 23 wherein said passages are generally oval in cross-section 25 The impeller of claim 23 wherein said passages are inclined at least about 5° from vertical 26 The impeller of claim 23 wherein said passages are inclined about 45° from vertical

Inventors: BRIGHT MARK A, VILD CHRIS T, BRIGHT, MARK, A., VILD, CHRIS, T.
Applicants: METAULLICS SYSTEMS CO L P, METAULLICS SYSTEMS CO., L.P.
Application year: 1999
Main classification: F04D7
IPC codes: F04D7, F04D29