Abstract:
A graphite support leg for positioning an object, such as a pump, in a bath of molten metal. The leg is enclosed in a ceramic sleeve, and an inert material is disposed in a clearance between the leg and the sleeve to protect the leg from the heat of the molten metal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 09/130,937, filed Aug. 7, 1998 for “Advanced Motor Driven Impeller Pump for Moving Metal in a Bath of Molten Metal”, now U.S. Pat. No. 6,071,074. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention is related to a structure for supporting a pump or similar apparatus immersed below the metal level of a bath of molten metal, such as aluminum or zinc. 
     In my aforementioned co-pending patent application, I disclosed a vertical post or leg for supporting a pump immersed in a bath of molten metal beneath an overhead structure above the bath of molten metal. Certain pumps disclosed in my prior patent application are buoyant in a bath of molten metal because of their lower specific density. In order to locate the pump in a suitable position below the metal level, it is desirable to have one or more overhead support legs. I disclosed a support leg having a ceramic sleeve extending between the overhead structure and the pump. The ceramic sleeve material is resistant to the heat of the molten metal. An internal vertical graphite leg is disposed in the sleeve. The graphite leg has sufficient compressive strength to support the pump in the bath of molten metal but has a tendency to burn in the presence of heat and oxygen. I disclosed a means for protecting the graphite leg by providing an internal chamber around the graphite leg and in the ceramic sleeve. An inert gas, such as nitrogen, protects the graphite from burning. However, I have found in some cases it is unnecessary to have a gas filled chamber in the sleeve to protect the graphite. Further, I have found novel means for introducing an inert gas into the ceramic sleeve to prevent burning of the graphite. 
     SUMMARY OF THE INVENTION 
     The broad purpose of the present invention is to provide an improved vertical leg structure for supporting a pump immersed in a bath of molten metal beneath an overhead structure disposed above the molten metal. In the preferred embodiment of the invention a ceramic sleeve extends between the overhead structure and the pump housing. It has a sufficient height to hold the housing in the bath of molten metal. An internal leg of a graphite material is disposed in the sleeve to provide a vertical support between the overhead structure and the pump housing. 
     A slight clearance between the ceramic sleeve and the graphite leg forms a chamber which is filled in various ways by both, gaseous and non-gaseous but inert materials. The leg comprises a vertical ceramic sleeve housing and a vertical graphite leg that extends between the overhead supporting structure and the pump housing. The sleeve covers that portion of the graphite exposed to the heat of the molten metal and above the metal line where severe burning of the graphite would occur due to the oxygen present in air. 
     Still further objects and advantages of the invention will become readily apparent to those skilled in the art to which the invention pertains upon reference to the following detailed description. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views and in which: 
     FIG. 1 shows a ceramic sleeve shielding a leg disposed in an atmosphere containing an inert gas; 
     FIG. 2 is a view of an alternative means for connecting the lower end of the leg to the pump housing; 
     FIG. 3 is a view of another support leg in which the graphite is shielded by a inert gas; 
     FIG. 4 is a view as seen along lines  4 — 4  of FIG. 3; 
     FIG. 5 is a view in which the sleeve provides an inert chamber containing inert non-gaseous materials for protecting the graphite leg; 
     FIG. 6 is a view as seen along lines  6 — 6 ; 
     FIG. 7 is an enlarged fragmentary view of the inert chamber; and 
     FIG. 8 is still a further enlarged view showing the manner in which a nylon tape is wrapped around the leg to form a double chamber containing a porous cement. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a shielded leg  10  supporting a pump housing  12  beneath the metal level  14  of a bath of molten metal, such as aluminum or zinc. The upper end of the leg is connected to a cover plate  16 . 
     The cover plate has an opening  18 . An annular plate  20  is mounted on the underside of the cover plate and has a central opening  22  aligned with opening  18 . A fitting  24  has a gas-receiving passage  26  for receiving an inert gas, such as nitrogen, from a source of nitrogen  28  through conduit means  30 . 
     The pump housing has a frusto-conical opening  32  which extends between its upper and lower surfaces. A sleeve formed of a ceramic material that is resistant to the heat of the molten metal is mounted between mounting plate  20  and the top surface of the pump housing around opening  32 . Sleeve  34  has a cylindrical configuration and has its upper and lower ends seated against mounting plate  20  and the pump housing, respectively. 
     A graphite leg  36 , having a sufficient diameter to provide a structured support between cover plate  16  and pump housing  12 , has its upper end abutting the mounting plate and its lower end formed with a reduced frusto-conical exterior surface that is seated in opening  32 . The lower end  40  of the graphite leg is threaded for receiving a fastening nut  42 . 
     Mounting plate  20  is attached by fastener means  43  to the cover plate. 
     A cement, modified by adding boron nitrite or boronit paint (obtainable from Alphatech, Inc., Cadiz, Ky.) is coated between the outer surface of the graphite leg, in the areas of the thicker line  44 , and the ceramic sleeve, as well as between the lower end of the leg seated in opening  32 , and the upper end of the leg in contact with the cylindrical skirt  45  of the mounting plate to provide a seal between the ceramic sleeve and the graphite leg that prevents the penetration of the molten metal. 
     A Kawool gasket  48  is mounted between the upper end of the leg and the mounting plate. 
     The graphite leg material has sufficient porosity to impregnate with the inert gas and create a chamber of inert nitrogen gas that prevents a combustible gas from permeating inside the ceramic sleeve to burn the graphite leg. 
     Referring to FIG. 2, an alternative means for connecting leg  36  to pump housing  12  is illustrated in which the lower end of the leg has been enlarged to provide a frusto-conical outer surface at  50  that mates with a frusto-conical interior opening  52  in housing  12  to provide a simple disassemble and removal of a damaged leg eventuity. 
     The diameter of the leg is slightly smaller than the inner surface of the sleeve and of opening  52 . A suitable inert cement  56  occupies the space between the ceramic shield and the leg. 
     Referring back to FIG. 1, the graphite leg has an axial passage  58  connecting passage  24  so that the inert gas (nitrogen) can pass along the major length of the leg. The graphite is sufficiently porous to house the inert gas and prevent the entry of either air or molten metal inside the sleeve—leg chamber. 
     FIG. 3 illustrates another embodiment of the invention. In this case, cover plate  16  provides an overhead supporting structure above metal level  14 . Pump housing  12  is immersed in the bath of molten metal. Mounting plate  20  is disposed on the under side of the cover plate and connected by fitting  60  to a source of nitrogen under pressure  28  through conduit  30 . Ceramic sleeve  62  has its upper end in abutment with a Kawool gasket  64  on the underside of the mounting plate to create a sealed chamber between the ceramic sleeve and graphite leg. 
     The sleeve extends through a cylindrical opening  66  in the pump housing and is cemented by a suitable inert cement to the pump housing in the area indicated by heavy line  80 . Graphite leg  70  is housed inside the sleeve and has at its lower end an enlargement to engage and support the pump housing. The outer diameter generally corresponds to the inner diameter of the sleeve but allowing for any desirable (not necessary) refractory cement  80  to join the leg to the sleeve and for thermal expansion. The upper end of the sleeve also abuts gasket  64 . The lower end of the sleeve extends to the inner surface of the pump housing. 
     The graphite leg is formed with an external helical groove  68  which extends from its upper end to its lower end. Referring to FIG. 4, the groove has an upper end  72  in communication with a radial channel  74  in the leg. The inner end of channel  74  terminates with a vertical passage  76  which is connected to conduit  30 . Thus the nitrogen gas forms a helical shield around the vertical leg extending from its upper end to its lower end. A ceramic ring  78  is cemented to the sleeve to aid in preventing pump housing  12  from any vertical movement. 
     FIGS.  5 - 8  show still another embodiment of the invention in which a ceramic sleeve  100  has its lower end in abutment and sealed with the pump housing. The upper end of the sleeve extends above metal level  14  to a position adjacent mounting plate  20 . 
     A graphite leg  102  has its upper end in abutment with mounting plate  20  and its lower end seated in an opening  104  in the pump housing. The lower end of the leg has an annular groove  106 . The housing opening  104  has an annular groove  108 . The lower end of the leg is slightly smaller than the housing opening. Grooves  106  and  108  and the space between the lower end of the leg and the housing opening are filled with a cement in the area of the heavier line  110  to prevent any molten metal from entering the lower end of the ceramic sleeve, and to join the leg to the housing. 
     The leg has an outer diameter smaller than the inside diameter of the sleeve to provide a tubular chamber  112 . Preferably the chamber has a thickness, as illustrated in FIG. 7, filled with respectively, a mix of boron nitride paint and a suitable refractory cement coating  114 , a nylon tape  116  and outer layer  118 , also a mix of cement and boron nitride paint. The nylon tape is cemented by a combination of the refractory cement and boron nitride paint which constitutes inner and outer layers  114  and  118 . The nylon tape is wrapped in a helical wrapping as illustrated in FIG. 5 from the bottom of the cylindrical skirt  120  of the mounting plate  20  to the pump housing. When the cement mix has dried, an additional layer is applied over and around the helical tape to form layer  118 . Prior to the cement mix drying, this arrangement is then disposed inside the sleeve to form a gas-free environment between the leg and the sleeve now filled with inert materials that shield the graphite leg from burning gases. 
     FIG. 8 is an enlarged view of the manner in which the tape is wrapped. It is preferably wrapped in an overlapping arrangement as illustrated at  122 . Thus the nylon tape provides double cylindrical chambers of a ceramic low porosity cement which is both inert and non-wetting in aluminum. The boron nitride reduces the porosity of the cement and simultaneously increases the surface tension thereby eliminating the ability of molten aluminum or molten zinc to penetrate between the ceramic sleeve and the graphite leg.