Abstract:
According to another embodiment, a molten metal impeller comprised of a generally cylindrical body including a plurality of passages extending from a top surface to a side wall and a cap member secured to a top surface of the body. The cap member is shaped cooperatively to overlay the cylindrical body. The cap member includes a first side seated on the top surface and a second opposed side. The top surface includes one of a notch or a protrusion and the first side of the cap member includes one of a notch or a protrusion oriented to mate with the notch or protrusion of the body.

Description:
The present application is a continuation-in-part filing based on U.S. Ser. No. 13/176,254 filed Jul. 5, 2011, which claims priority to U.S. Provisional Patent Application No. 61/361,075 filed on Jul. 2, 2010, which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure is directed to a molten metal impeller having improved metal flow properties. According to one embodiment, a protective flow inducing cap member for a molten metal pump impeller is provided. 
     This disclosure generally relates to molten metal pumps. More particularly, this disclosure relates to an impeller suited for use in a molten metal pump. The impeller is particularly well suited to be used in molten aluminum pumps. However, it should be realized that the impeller can be used in any pump employed 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. 
     An exemplary pump in which the impeller of this disclosure can operate is depicted in  FIG. 1 .  FIG. 1  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 . 
     Obviously, there is a desire to increase the efficiency of a molten metal impeller. Improving the flow of metal into the impeller is one mechanism by which this is achieved. It is a further desire to limit the degradation of the impeller. Moreover, to operate in a high temperature, reactive molten metal environment, a graphite material is typically used to construct the impeller. Graphite is 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. 
     BRIEF DESCRIPTION 
     According to one embodiment, a molten metal impeller is provided. It includes a generally cylindrical graphite body having a plurality of passages extending from a top surface to a side wall. A hub is formed in the center of the graphite body. A ceramic cap member is secured to the top surface of the graphite body. The cap member is comprised of a ring forming a central passage shaped cooperatively to overlap the hub and a plurality of vanes extending radially from the ring to an outer rim. The rim has a height between adjacent vanes which increases in the direction of intended impeller rotation. The rim also has a height which decreases from its radially outer most edge to an inner most edge. 
     According to a further embodiment, a molten metal impeller comprised of a graphite body having a central hub disposed upon a generally disk shaped base and at least two vanes extending from the hub is provided. A ceramic cap member engages a top surface of the graphite body. The cap member has a central ring sized to overlay the hub and wings extending therefrom. The wings are shaped to cooperatively overlay the vanes. Each wing includes a terminal end with a vane engaging edge and an opposed chamfered edge. 
     According to a further embodiment, a molten metal impeller comprised of a generally cylindrical graphite body is provided. The graphite body includes a plurality of vanes defining passages extending from a first surface to a side wall. A ceramic cap member is secured to the first surface. The cap member is comprised of a plurality of vanes corresponding to the plurality of graphite body vanes and a rim. The rim includes a plurality of segments between adjacent vanes wherein the segments have a height profile which increases in the direction of intended impeller rotation. 
     According to an additional embodiment, a molten metal impeller is provided. The impeller is comprised of a graphite body having an at least substantially cylindrical sidewall and opposed top and bottom end walls. At least one of the end walls forms an inlet comprised of multiple passages extending to the sidewall. The passages are defined by a plurality of radially extending vanes and a peripheral rim. The vanes have a terminal portion intersecting the rim. The terminal portions are canted in the intended direction of impeller rotation. In addition, the sections of rim between the vanes include a surface which slopes downward away from the direction of intended impeller rotation. 
     According to another embodiment, a molten metal impeller comprised of a generally cylindrical body including a plurality of passages extending from a top surface to a side wall is provided. A cap member is secured to a top surface of the body. The cap member is shaped cooperatively to overlay the body. The cap member includes a first side seated on the top surface and a second opposed side. The top surface includes one of a recess or a protrusion and the first side of the cap member includes one of a recess or a protrusion oriented to cooperatively mate with the recess or protrusion of the body. 
     According to a still further embodiment, an impeller having an intended direction of rotation and comprised of a body having an at least substantially cylindrical base is provided. A hub is disposed on a first side of the base, and a plurality of vanes extend from the base and the hub. The vanes include a free end adjacent a periphery of the impeller and a cap receiving side opposed to the base. The cap receiving side has a receiving surface having a recessed leading edge in the intended direction of rotation and a raised trailing edge. A cap member having a ring sized to overlay the hub and a plurality of fingers extending from the ring and configured to overlay the vanes is secured to the body. The fingers include a raised leading edge mating with the recessed leading edge of the vane and a recessed trailing edge mating with the raised trailing edge of the vane. 
     According to an additional embodiment, an impeller having an intended direction of rotation and comprised of a body having a base and a plurality of vanes extending from the base is provided. The vanes include a cap receiving side opposed to a side extending from the base. The cap receiving side has a receiving surface including a recessed leading edge in the intended direction of rotation and a raised trailing edge. A cap member having a plurality of fingers configured to overlay the vanes is provided. At least one finger includes a surface having a projection mating with the recessed leading edge of the associated receiving surface and a recessed trailing edge mating with the projecting trailing edge of the associated receiving surface. 
     A further embodiment is directed to a molten metal pump comprised of a motor, and an associated shaft. The shaft is attached to the impeller described in the preceding paragraphs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In accordance with one aspect of the present exemplary embodiment: 
         FIG. 1  is a perspective view of a prior art molten metal pump; 
         FIG. 2  is an perspective view of the present impeller; 
         FIG. 3  is a perspective view of the cap member removed from the impeller of  FIG. 2 ; 
         FIG. 4  is a cross-section taken along lines A-A of  FIG. 3 ; 
         FIG. 5  is a side elevation view of the cap member of  FIG. 3 ; 
         FIG. 6  is a perspective view of an alternative impeller embodiment; 
         FIG. 7  is a perspective view of an alternative impeller embodiment; 
         FIG. 8  is a cross section view of vane of the impeller of  FIG. 7 ; and 
         FIG. 9  is an exploded view of the impeller of  FIG. 7  (without bearing ring). 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the representative embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in connection with the selected embodiments, it will be understood that it is not intended to limit the invention to those 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. 
     A new and improved impeller for use in molten metal pumps is disclosed. In particular, the impeller is utilized in molten metal pumps to create a forced directional flow of molten zinc or molten aluminum. U.S. Pat. Nos. 2,948,524; 5,078,572, 5,088,893; 5,330,328; 5,308,045, 5,470,201 and 6,464,458 herein incorporated by reference, describe a variety of molten metal pumps and environments in which the present impeller could be used. 
     Referring now to  FIGS. 2-5 , impeller  100  is depicted. Impeller  100  includes three main components; a graphite body  102 , a top cap  104 , and a bearing ring  106 . A hub  108  is centrally formed in the graphite body  102  to receive a shaft. Although indicated as cylindrical in shape, the hub and corresponding top cap passage could be formed to have flat surfaces for mating with a cooperatively shaped shaft. It is further envisioned that the present embodiment is functional with an impeller which connects to a shaft via a mechanism other than a hub. For example, a threaded post could extend from the impeller body and be received within a threaded bore of a shaft. The present disclosure contemplates use with the myriad of shaft impeller connections available to the skilled artisan. 
     Graphite body  102  is generally cylindrically shaped and includes a plurality of passages  112  extending from an upper surface  110  to side wall  111 . Four or more passages are typically present. Cap  104  is secured (for example via cement) to upper surface  110 . Although reference is made to passages originating in a top surface, it is noted that bottom feed impellers can similarly benefit from the present disclosure. Accordingly, contemplated within this disclosure are impellers having either top or bottom surface passages or both. Similarly, it is envisioned that the cap can be secured to either or both top and bottom surfaces. 
     With reference to  FIG. 4 , the cement joinder of the cap member  104  to the graphite body  102  can be enhanced by including cooperative grooves  130  in the mounting surfaces of each (not shown in the graphite body). Moreover, in this manner a cement channel is formed that extends into the top cap  104  and into the graphite body  102 . In addition, in certain environments, it may be desirable to extend a pin between the cap member  104  and the graphite body  102 . 
     Cap member  104  can be shaped to generally match the outline shape of graphite body  102 . Cap member  104  further has a top surface  114  profile which encourages induction of fluid. Referring now to  FIGS. 3 and 5 , vanes  116  extend radially from a central ring  118  to an outer rim  120 . Rim  120  include segments between adjacent vanes having a height profile which slopes downwardly from H 1  to H 2  between adjacent vanes  116 . H 1  is greater than H 2  such that the terminal portion of vanes  116  have a higher leading edge  122  than trailing edge  124  to create a scooping action in the direction of intended rotation  126 . In certain embodiments, the ratio of H 1 :H 2  is at least 4:3. Furthermore, the leading edge  122  may be forwardly canted (in the direction of intended impeller rotation  126 ) relative to the portion of vane  116  between central ring  118  and outer rim  120 . Trailing edge  124  can also be forwardly canted. In addition, top surface  114  includes a flow inducing surface  127  which slants downwardly from its peripheral edge  128  to its inner edge  129  adjacent passages  112 , effectively funneling molten metal therein. Moreover, there is an incline in surface  127  relative to the planar orientation of the cap member  104 . In an exemplary embodiment the incline is at least 5 degrees. 
     Referring now to  FIG. 6 , an open top impeller  200  is depicted. In this embodiment, the impeller includes four blades  204  which reside upon a disk shaped base  206  and extend from hub  208 . Cap  210  is shaped to mate with and overlay the vanes and includes a passage  212  providing access to hub  208  which accommodates a shaft. The cap member includes chamfered radial edges  214 , provided to facilitate the placement of the impeller within the pump housing. Moreover, referring again to  FIG. 1 , during installation, the impeller is typically installed via insertion through the lower opening of the pump housing. Given the hardness of the material forming the cap member, sharp edges thereon at the radial surface would increase the likelihood of chipping and/or otherwise damaging the pump housing during the installation step. The chamfer allows proper registration of the impeller within the pump housing without causing chipping damage. A preferred chamfer forms an angle relative to the planar surface  216  of the cap member of between about 20 and 60° or about 30 and 50°. 
     Referring now to  FIGS. 7-9 , an alternative impeller embodiment is depicted. Particularly, impeller  300  is comprised of a main body  301  having a substantially cylindrical base  302  from which a hub  304  extends. A plurality of vanes  306  extend from the base  302  and the hub  304 . Hub  304  is provided to receive a shaft connected to a motor to provide rotation of the impeller  300 . Impeller  300  has an intended direction of rotation depicted by arrow  305 . Impeller base  301  can further include a groove  332  formed to receive a bearing ring  324 . 
     The impeller  300  further comprises a cap member  308  which overlays the main body  301 . Cap member  308  can be secured to the main body  301  by cement or other adhesive joinder. Cement in cooperating grooves  330  and  331  can form a cement channel extending in body  301  and cap member  308 . 
     Cap member  308  includes a ring  310  which overlays hub  304  and fingers  312  which overlay vanes  306 . Each vane/finger  306 / 312  has a leading edge  307 / 313  and a trailing edge  314 / 315 . The leading edge  307  of vane  306  is provided with a recess  316  receiving a projection  318  on the leading edge  313  of finger  312 . The trailing edge  315  of finger  312  is provided with a recess  320  receiving a projection  322  on the trailing edge  314  of vane  306 . 
     In certain embodiments, the transition between recess and projection can be formed at substantially a right angle such that a vertical interface  321  exists between the cap member  308  and the main body  301 . The interface  321  can provide an effective energy transfer plane between the cap member  308  and the main body  301  to improve energy transfer between the cap member and the larger mass of the impeller body resulting from the impact of particulate in a molten metal environment. A groove  330 / 331  may be formed in the vane  306  and finger  312 , respectively, in the vicinity of the interface  321 , which receives cement and improves the joinder of the components. 
     According to certain embodiments, the cap member can be formed of a higher density material than the impeller body. For example, the cap member can be formed of a ceramic and the impeller body formed of a graphite. 
     The cooperative recesses and projections of the fingers and the vanes can extend any suitable length, although the greater the extension along the vertical interface, the more advantageous the design may become. Accordingly, the recesses/projections can extend the full length of the vanes/fingers. Furthermore, it is noted that although described in association with a cylindrical impeller body typically utilized in a pumping chamber, it is also contemplated that the described cap impeller mating arrangement can be used with non-cylindrical designs utilized in degassing, submergence and pump environments wherein a traditional base is not employed. 
     The present design has been found particularly effective in high rock inclusive molten metal environments. Particularly, the high strength cap member has been found to provide increased strength. In general, in each embodiment, the cap member can be comprised of a fine grain refractory material, such as silicon carbide. Preferably, the material has a suitable coefficient of thermal match to graphite, for example, no more than a three to one difference. In this regard, SiC having a 2.2×10 −6  in/in/° F. and graphite having a 7×10 −7  in/in/° F. are sufficiently compatible. Furthermore, it is noted that the grain size of the fine grain refractory is preferably not too fine (for example larger than 3 microns may be desirable; although if a mixture of particle sizes is employed it is feasible even smaller sized particles could be present provided larger sized particles are also present such that for example an average particle size layer greater than  3  micros is achieved) to allow cement to suitably grip the material. 
     In addition, it is noted that although much of the present disclosure has focused on the use of a ceramic cap member to provide the improved flow in combination with protection of the graphite body, the disclosure also contemplates an impeller without the ceramic cap. Moreover, the improved flow design can be machined directly into the surface of the graphite body of the impeller. For environments that have little or no entrained particles, the requirement for a cap is diminished, yet the desire to retain the improved flow of the present inlet shaping remains. 
     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.