Abstract:
An apparatus for moving a stream of molten metal comprising a pumping member, a housing at least partially enclosing the pumping member, a power device seated on a support, a shaft connecting the power device and the pumping member. At least one post is disposed between the support and the housing. The post includes an elongated rod surrounded by a heat resistant outer member. The rod includes a first end connected to the support and a second end secured within a cavity in the housing.

Description:
This application claims benefit of provisional application No. 60/107,710 filed Nov. 9, 1998 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to apparatus for degassing, submerging, agitating and pumping molten metal. Particularly, this invention relates to mechanical apparatus for moving or pumping molten metal such as aluminum, zinc or magnesium. More particularly, this invention is related to a drive for such apparatus in which a motor is positioned above a molten metal bath and rotates a vertical shaft. The lower end of the shaft drives an impeller or a rotor to impart motion to the molten metal. The invention finds similar application in the construction of the post which supports the motor. 
     In the processing of molten metals, it is often necessary to pump molten metal from one place to another. When it is desired to remove 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 pumps, a rotatable impeller is submerged, typically within a pumping chamber, in the molten metal bath contained in the vessel. Additionally, the motor is suspended on a superstructure over the bath by posts connected to the base. Rotation of the impeller within the pumping chamber forces the molten metal as desired in a direction permitted by the pumping chamber design. The present invention relates to an improved design for each of these types of pumps. 
     Mechanical pumps for moving molten metal in a bath historically have a relatively short life because of the destructive effects of the molten metal environment on the material used to construct the pump. Moreover, most materials capable of long term operation in a molten metal bath have relatively poor strength which can result in mechanical failure. In this regard, the industry has typically relied on graphite, a material with adequate strength, temperature resistance and chemical resistance, to function for an acceptable period of time in the harsh molten metal environment. 
     While graphite is currently the most commonly used material, it presents certain difficulties to pump manufacturers. Particularly, mechanical pumps usually require a graphite pump housing submerged in the molten metal. However, the housing is somewhat buoyant in the metal bath because the graphite has a lower density than the metal. In order to prevent the pump housing from rising in the metal and to prevent unwanted lateral movement of the base, a series of vertical legs are positioned between the pump housing and an overhead structure which acts simultaneously to support the drive motor and locate the base. In addition to functioning as the intermediate member in the above roles, the legs, or posts as they are also called, must be strong enough to withstand the tensile stress created during installation and removal of the pump in the molten metal bath. 
     Similarly, the shaft connecting the impeller and the motor is constructed of graphite. Often, this shaft component experiences significant stress when occluding matter in the metal bath is encountered and sometimes trapped against the housing. Since graphite does not possess as high a strength as would be desired, it would be helpful to reinforce the leg and shaft components of the pump. 
     In addition, graphite can be difficult to work with because different stock may have different thermal expansion rates and/or different grain orientation. This may result in a post and base having divergent and conflicting thermal expansion rates in the molten metal environment. This problem is compounded by the fact that pump construction has historically required cementing the graphite post into a hole in the graphite base. This design provides no tolerance between the components to accommodate divergent thermal expansion. Unfortunately, this can lead to cracking of the base or the post. Accordingly, it would be desirable to have a molten metal pump wherein the mating of a post and a base is achieved in a manner which accommodates divergent thermal expansion tendencies. 
     The present invention is equally applicable to a variety of other apparatus used in processing molten metal. Moreover, in addition to pumps, molten metal scrap melting (i.e. submergence), degassing, and agitation equipment, typically rely on the rotation of an impeller/rotor submerged by a vertical shaft in a bath of molten metal. More specifically, a submergence device is used to help melt recycle materials. A major concern of the secondary metal industry is a generation of oxides and gasses which become entrained or dissolved into the molten metal during the melting of scrap metal. These impurities decrease the quality and value of the scrap metal which is ultimately marketable as end product. Accordingly, a degassing device is often used to remove these impurities. In the degasser, a hollow shaft is typically provided to facilitate the injection of gas down the shaft and out through the bores in an impeller/shaft rotor. Typically, the introduced gasses will chemically release the unwanted materials to form a precipitate or dross that can be separated from the remainder of the molten metal bath. 
     An example of a submergence device is described in U.S. Pat. No. 4,598,899, herein incorporated by reference. An exemplary degassing apparatus is described in U.S. Pat. No. 4,898,367, herein incorporated by reference. In both devices, a vertically oriented shaft having a impeller/rotor disposed at one end in the molten metal bath is employed. Similar problems arise in these apparatus wherein the components are usually constructed of graphite, and would benefit from an increase in strength. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a primary advantage of this invention to provide a new and improved molten metal pump. 
     It is a further advantage of this invention is to provide a new and improved post for a molten metal pump. 
     Another advantage of this invention is to provide a new and improved shaft for a molten metal pump, degasser or submergence device. 
     Yet another advantage of the subject invention is to provide a new and improved mechanism for joining of a pump post to a pump base. 
     A still further advantage of this invention is to provide a molten metal pump post or shaft having improved strength. 
     Another advantage of this invention is to provide a self-aligning post without a requirement for a cement joint. 
     Additional advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practicing the invention. The advantages of this invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     To achieve the foregoing advantages in accordance with the purpose of the invention, as embodied and broadly described herein, the molten metal pump of this invention comprises a pumping member (such as an impeller or rotor), at least partially enclosed within a housing. A power device is seated on a support above the housing and pumping member. A shaft connects the power device and the pumping member to provide rotation thereof. At least one, and preferably two to four posts, suspend the housing from the support. One or both of the post or shaft is comprised of an elongated rod surrounded by a heat resistant outer member. In the post embodiment, the rod includes a first end attached to the support (directly or via a coupling) and a second end disposed within a cavity in the housing. Alternatively, the rod can be used strictly for compressing the outer member, which is coupled to the support. In the shaft embodiment, the rod includes a first end secured to the power device (directly or via a coupling) and a second end disposed within a cavity in the pumping member. It is also noted that the shaft embodiment is further suited to use in submergence, degassing and agitation devices. 
     Preferably, the outer member is comprised of a graphite, refractory, or ceramic material and the housing is comprised of graphite. Preferably, the rod will be comprised of a heat resistant alloy. 
     In a particularly preferred form of the post embodiment, the rod is biased by a spring. Preferably, the outer member abuts a bottom surface of the support (or an intermediate coupling) and a top surface of the housing and the biasing force of the spring creates a compressive force on the outer member. 
     In a particularly preferred form of the invention, the outer member is comprised of a plurality of generally cylindrically shaped units, aligned along their longitudinal axis. The rod runs down a central bore of each unit to provide a stacked arrangement. Preferably, the lower most unit will include a circumferential protrusion shaped to mate with a recess formed in the top surface of the housing to create a fluid tight seal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention consists in the novel parts, construction, arrangements, combinations and improvements shown and described. The accompanying drawings, which are incorporated in and constitute a part of the specification illustrate one embodiment in the invention and, together with the description, serve to explain the principles of the invention. 
     Of the Drawings: 
     FIG. 1 is a front elevation view, partially in cross-section, of a molten metal pump in accord with the present invention; 
     FIG. 2 is a side elevation view, also partially in cross-section, of FIG. 1; 
     FIG. 3 is a front elevation view, partially in cross-section, of the rod of FIG. 1; 
     FIG. 4 is a front elevation view, in cross-section, of the inventive sheath of FIG. 1; 
     FIG. 5 is a front elevation view, in cross-section, of an alternative post embodiment; 
     FIGS. 6,  7  and  8  are front elevation views, in cross-section, of alternative post and base seating arrangements; 
     FIG. 9 is a front elevation view, in cross-section, of a segmented post design; 
     FIG. 10 is a front elevation view, in cross-section, of an alternative segmented sheath design; 
     FIG. 11 is an exploded side elevation view, in cross-section, of an alternative post/base joining arrangement; 
     FIG. 12 is an exploded view of section A of FIG. 11 showing the fluid tight joint; 
     FIGS. 13 and 14 provide alternative base and post joining mechanisms; 
     FIG. 15 is a top view of the base and post of FIG. 14 with their eccentric diameters aligned to allow insertion of post into base; 
     FIG. 16 is a top view of the base and post of FIGS. 14 and 15 with the post rotated to misaligned diameters to achieve a locking arrangement; and 
     FIG. 17 is a front elevation view, partially in cross-section, of a shaft impeller arrangement of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now 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 a 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 as may be included within the spirit and scope of the invention defined by the appended claims. 
     Referring now to FIGS. 1 and 2, molten metal transfer pump  1  is provided. The molten metal pump includes a base assembly  3  having a pumping chamber  5  with an impeller  7  disposed therein. Bearing rings  9  provide mating surfaces between the impeller  7  and the base assembly  3 . Rotation of the impeller  7  forces molten metal  11  through outlet  13  and up riser tube  15  for transport to another location. 
     Rotation of impeller  7  is achieved when motor  17  rotates shaft  19  by turning shaft coupling  21  provided therebetween. The motor is positioned above the base assembly  3  on a platform assembly  22  having an insulation layer  23 , a motor mount bracket  25  and a motor mount plate  26 . 
     Two post assemblies  27 , comprised of a rod  29  constructed of a heat resistant alloy material disposed within a refractory sheath  31  suspend the base assembly  3  below the platform  22 . Preferably, the rod will be constructed of an alloy such as MSA 2000 or MSA 20001 available from Metaullics Systems Co., L.P., 31935 Aurora Road, Solon, Ohio, 44139. The refractory sheath also includes a ceramic shield  33  for additional protection against oxidation. The lower end of rod  19  includes cap  35 . Cap  35  is disposed within a cavity  37  in base assembly  3 . A graphite or refractory plug  39  is cemented into the lowermost portion of the cavity to seal the area from molten metal. The upper end of the rod  29  extends through the insulation layer  23  and is secured with nut  41  to the motor mount plate  26 . A disc spring  43  or other compression spring is disposed between the motor mount platform  25  and insulation layer  23 . Preferably, an insulating washer (not shown) will be positioned between motor mount plate  26  and spring  43 . Tightening of nut  41  results in compression of the spring  43  and a bias on the rod  29  and sheath  31 . 
     Advantageously this assembly provides a high strength alloy rod connection between the base and motor mount. Of course, it also protects the otherwise degradable rod from the molten metal environment. A further advantage is that the thermal expansion mismatch resulting from divergent grain orientations in a graphite post and a graphite base is eliminated because a graphite post is not rigidly cemented into a hole in the base. Furthermore, the strength of the graphite sheath is increased because it is retained under compression as a result of being squeezed between a socket  45  and the upper surface of base assembly  3 . 
     Turning now to FIG. 3, a detailed depiction of rod  29  is provided. In this embodiment, cap member  35  is welded at weld lines  47  to the lower most end of the rod. Of course, other mechanisms of attachment, including but not limited to, threaded or swaged, are appropriate joining techniques. FIG. 4 provides a detailed cross-sectional view of the graphite sheath  31 . 
     Referring now to FIG. 5, an alternative post embodiment is depicted. In this embodiment, the post  101  again includes rod  103  protected from the molten metal environment by sheath  105 . Rod  103  passes through a bore/cavity  106  in a base member  107  and is retained by the cap  109  containing a snap ring  111  having corresponding retaining grooves  113  and  115  in the cap  109  and rod  103 , respectively. Again a disk spring  117  and nut  118  are provided, which in concert with the platform  119  create a bias on rod  103  and a compressive force on sheath  105 . 
     Turning now to FIGS. 6,  7 , and  8 , alterative post and base joining techniques are depicted. For example, in FIG. 6, rod  201  extends through base  205  and includes a threaded end  202  on which graphite cap  203  is secured. In FIG. 7, the embodiment of FIG. 6 is modified to include seal members  207  and  209  constructed of boron nitride, silicon carbide, or other suitable material. In FIG. 8, an alternative embodiment is depicted wherein a threaded bore  301  is provided in the end of graphite post  303  and a threaded graphite post  305  extends upwardly through base member  307  and is mated to the end of the post  303 . An advantage of each design is the ability to create a tension on the post to provide a self-alignment mechanism without the need for a structural use of cement. In this regard, a thermal expansion gap can be provided (see FIG. 11) where cement has been historically required. 
     Furthermore, the use of a protrusion  211  on the end cap post/bolt  203 / 205  in a combination with recesses  213  on the top and bottom surfaces of the base  205 / 307  create a fluid tight joint. Accordingly, molten metal does not enter this joint, allowing the post to be removed from the base if a rebuild of the pump is required. 
     It should be noted that while the present joining mechanisms in FIGS. 6 through 8 are generally depicted as coinciding to the utilization of a steel alloy rod, these mechanisms for joining a post to a base are equally applicable to a graphite post arrangement. Moreover, the arrangements depicted in FIGS. 6 through 8 can equally be considered as being constructed of all elements comprised of a combination of steel and graphite/ceramic or graphite/ceramic alone. The advantage provided by these assemblies is that there is no necessity for a cement joint between the post and the base which better accommodates thermal expansion mismatches. 
     Turning now to FIG. 9, an alternative embodiment of the present invention is provided wherein the post  401  includes a rod  403  and a sheath  405 . However, in this embodiment sheath  405  is comprised of the plurality of segmented units. This design is particularly desirable because of the relative ease of forming individual segmented units (A-E) as opposed to an elongated tube. Again, the post  401  is provided with a spring  407  and a metallic coupling unit  409 , which in combination with the motor mount (not shown) creates a compressive force on the sheath segments (A-E). A fluid tight seal is created between each of the individual units as a result of the compressive force, and, may be enhanced by the inclusion of a gasket material (not shown) therebetween. The lower most unit E includes a circumferential protrusion  411  which is seated in a recess  413  in the top surface of the base  415 . Accordingly, a fluid tight seal is achieved. As in any of the other designs herein, a bead of cement or sealant may be placed around the seated protrusion  411  to further protect against unwanted metal seepage. 
     Referring now to FIG. 10, an alternative embodiment of a segmented sheath  501  is depicted. In this embodiment, the end surfaces of the individual units A-E are cooperatively contoured to facilitate achieving an appropriate mating arrangement. In this regard, a verifiable seating arrangement is provided to assure a metal tight seal is formed between each individual segment. 
     Turning now to FIG. 11, a detailed view of an arrangement mating a graphite post to a graphite base is provided to demonstrate both the desired tolerance for thermal expansion and a desirable configuration for achieving a fluid tight seal. More particularly, graphite post  601  passes through a hole  603  in a base assembly  605 . Threaded graphite cap member  607  is attached to the lowermost portion of post  601 . At both of the top and bottom interface of post  601  and/or cap member  607  to the base assembly  605 , a cooperative protrusion  609  and recess  611  are provided to create a fluid tight if seal. Referring now to FIG. 12, the angled surfaces of the protrusion and recess are depicted. In this manner, a fluid tight mating surface achieved. The mating surfaces may be filled with a gasket material (not shown). A further advantage of the present invention is the tolerance provided by gap  613  for thermal expansion. 
     Referring now to FIGS. 13-16, alternative embodiments for securing a graphite shaft to a graphite base without cement are provided. Particularly, in FIG. 13, snap ring  701  is provided which is joined between corresponding grooves  702  and  703  and post  704  and base  705  respectively. 
     FIGS. 14,  15  and  16  depict a cam type locking mechanism which with post rotated (clockwise in this example) relative to the base until their relative eccentric diameters touch and displace the post slightly until any clearance between the previously concentric diameters is eliminated. This creates an efficient wedging together of the parts securing the post to the base. More specifically, post  801  is provided with a stepped end  803  having three different diameter sections  805 ,  807  and  809 . Base  811  includes a bore  813  which accommodates end  803  of post  801 . Base  813  includes three different diameter regions  815 ,  817  and  819 . Section  807  and region  817  are eccentric relative to corresponding sections  805  and  809  and regions  815  and  819 , respectively. In this manner, rotation of post  801  results in a wedging (see FIG. 16) of the respective sections and regions and an effective mating of the post  801  to base  811 . It should also be noted that this cam locking mechanism is equally suited to a shaft impeller assembly. 
     Referring now to FIG. 17, a shaft to impeller/rotor arrangement  901  is depicted. In short, the same design using a rod and sheath as shown and discussed with respect to FIG. 1 is employed. Particularly, an impeller  903  is secured to a rod  905 . Rod  905  includes cup  907  at a lower end, cap  907  being disposed within a recess  909  in impeller  903 . Preferably, cap  907  will include a jagged top surface (not shown) which mates with peaks and valleys (not shown) in the upper surface of recess  909 . This embodiment is suited to degassing, agitation, pumping and submergence apparatus. It should be noted that the degassing embodiment would most likely include a bore through the rod—or a sufficient gap between sheath and rod—to facilitate introduction of a reaction gas or other suitable agent. 
     Thus, it is apparent that there has been provided in accordance with the invention, a molten metal 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 like 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 appended claims.