Abstract:
Apparatus for moving a stream of molten metal in a bath of molten metal, includes a pump disposed in the met. The pump has a lower inlet opening with a strainer and a slinger rib to prevent the entry of debris that exceeds a predetermined diameter from passing through the pump.

Description:
This application is a division of application Ser. No. 09/130937, filed Aug. 7, 1998, pending. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention is related to mechanical pumps for moving or pumping metal such as aluminum or zinc in a bath of molten metal, and more particularly to such a pump in which a motor supported above the bath drives a vertical stainless steel shaft. The lower end of the shaft drives the impeller to create a stream of molten metal. A ceramic sleeve shields the stainless steel shaft to protect it from the corrosive effects of the heated molten metal, as well as forming a loose fit with the shaft to accommodate differences in the thermal expansion characteristics between the ceramic and the stainless steel. 
     Mechanical power driven pumps for moving metal in a bath of molten metal conventionally have a relatively short life because of the destructive effects of the molten metal on the pump components. If the pump shaft connecting the motor to an impeller is formed of any steel to provide sufficient torque to move the impeller in the molten metal, the steel has a short life because it is chemically attacked by the molten metal. If the steel shaft is shielded by a protective coating of a ceramic material, then the different thermal expansion characteristics of the steel and the ceramic causes the ceramic to shatter in a relatively short time. 
     A shaft made of graphite alone will burn at the metal surface. A shaft made of ceramic alone does not have sufficient tensile, torque or impact strength to overcome the stresses normally encountered when pumping molten metal. 
     A pump housing submerged in molten metal and made of graphite or ceramic material to withstand the heat, tends to rise in the metal bath because the ceramic has a lower density than the metal. In order to prevent the pump housing from rising in the metal, it is desirable to mount a series of vertical legs between the pump housing and an overhead supporting structure. In addition the legs (or posts as they are also called) should be strong enough to overcome the tensile stresses created during installation and subsequent removal of the pump in the molten metal bath. Such legs experience problems similar to that of an unshielded pumping shaft, that is, if they are made of an uncoated steel they have a short life because the steel is attacked by the molten metal. If they are made entirely of graphite, the legs will bum at the metal interface. If a leg is made entirely of a ceramic material having good heat resistant characteristics, it has insufficient tensile strength to ensure a long life. 
     SUMMARY OF THE INVENTION 
     The broad purpose of the present invention is to provide a shielded stainless steel driving shaft for a centrifugal impeller-type pump immersed in a molten metal bath. 
     Another object of the invention is to provide an improved stainless steel leg (post) for supporting and preventing the pump housing from rising in the molten metal. 
     Still another object of the invention is to provide an improved static inlet filter configuration for an impeller pump immersed in a molten metal bath. 
     Still another object of the invention is to provide a ceramic shield surrounding a graphite leg and forming an inert gas chamber around the leg. An inert gas is delivered to the gas chamber to provide an oxygen-free environment around those graphite components of the leg that may tend to burn at the temperatures of the surface of the molten metal bath. 
     Still another object of the invention is to provide a dynamic filter for the inlet opening of the impeller of a pump mounted in a molten metal bath. The filter rotates with the impeller without interfering with the pumping vanes. Slinger ribs provided on the dynamic filter deflect debris attempting to enter the strainer apertures to prevent their passage into the pump housing. 
     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 is a longitudinal sectional view of an impeller pump immersed in a bath of molten metal and illustrating the preferred embodiment of the invention; 
     FIG. 2 is an enlarged view of the tongue carried on the lower end of the driving shaft for rotating the impeller; 
     FIG. 3 is a view as seen along lines  3 — 3  of FIG. 2; 
     FIG. 4 is a longitudinal sectional view of an impeller pump immersed in a bath of molten metal and illustrating a graphite quill shaft design with an external ceramic shield protection; 
     FIG. 5 is a view of an unshielded leg used for connecting a pump housing to an overhead structure; 
     FIG. 6 is a view illustrating a split ring employed for connecting the lower end of the leg to the pump housing; 
     FIG. 7 is an enlarged view as seen along lines  7 — 7  of FIG. 5; 
     FIG. 8 is a view of another arrangement for connecting the support leg to the pump housing; 
     FIG. 8A is a view of a graphite leg for supporting the pump housing, utilizing graphite cement for connecting the lower end of the leg to the pump housing; 
     FIG. 9 is a view as seen along lines  9 — 9  of FIG. 8A; 
     FIG. 10 is a view of a quill-shaft, ceramic support leg for the pump housing; 
     FIG. 11 is a view of another form of a quill-shaft, ceramic support leg for the pump housing; 
     FIG. 11A is a view of another form of a quill-shaft ceramic or graphite support leg for the pump housing; 
     FIG. 12 is an enlarged fragmentary view of a graphite inert quill-shaft support leg for the pump, having an oxygen-free chamber to eliminate oxidation of the graphite components; 
     FIG. 13 is a sectional view of a dynamic strainer for the pump; 
     FIG. 14 is a bottom view of FIG. 13; and 
     FIG. 15 is an enlarged view of the internal pumping vanes of the embodiment of FIG.  13 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, FIG. 1 illustrates a preferred impeller pump  10  having a lower pumping end disposed in a bath of molten metal  12  such as aluminum. The bath has a top metal level  14 . Typically the bath operates at a temperature not in excess of 1800° F. The bath is contained by a pot having a floor  16 . An electrically driven motor  80  is supported in any suitable location above the pump cover plate  18 , and is connected by a coupling  22  to a stainless steel pumping or driving shaft  24 . The shaft is supported in an opening  26  in the pump cover plate. The shaft has a sufficient length that the upper end is supported above cover plate  18  and its lower end is disposed in the bath of molten metal  12 . 
     A pump housing assembly  28  includes a housing  30  and a vane-type pumping member  32  disposed in the housing. The shaft is drivingly connected to the pumping member to rotate it in the housing in order to produce a stream of molten metal that enters the housing adjacent the floor of the pot through an inlet opening  34 , into a pumping chamber  36  and toward an outlet opening  38  in the direction of arrows  40 . 
     The pumping member includes a ceramic impeller  33  which carries pumping vanes  44 . Bearing means  46  carried in a shoulder  48  of the housing  30  engage a ceramic end driver  42  cemented to a vertical outer tubular ceramic shield  50 . The lower end of the end driver  42  is closed off and fits into pumping member  32 . The upper end of the shield extends upwardly through cover plate  18 . End driver  42 , after cementing, forms a single integral part of shaft assembly  20  together with shield  50 , tubular spacer shield  52 , steel driving shaft  24  and tongue  58 . 
     Inner ceramic tubular shield  52  is cemented to the inside of the outer shield  50 . The upper end of the inner shield is flush with the upper end of the outer shield. The inner tubular shield is shorter than the outer shield to form an annular shoulder  54 . 
     The lower end of the drive shaft  24  is threaded at  56  as illustrated in FIG.  1 . The threaded end  56  extends below shoulder  54 . A stainless steel tongue  58  is threadably mounted on threaded end  56  and seated on shoulder  54  in a manner that will be described. 
     Referring to FIG. 2, the inside bottom of the outer shield forms a chamber  60 . Tongue  58  is disposed in the chamber. Cement  62  is disposed in the chamber and has a socket  64  generally corresponding to the configuration of the tongue but slightly larger to provide for a clearance between the tongue and the socket to allow for thermal expansion differences. 
     As can be seen in FIG. 2, the bore  76  of the spacer shield  52  is larger than the diameter of the shaft  24  to provide a clearance which permits the shaft to expand in response to heat without creating an expansion tensile stress on the spacer shield  52 . Similarly, the tongue has a clearance that permits it to expand in response to heat without creating an expansion interference stress with the cement. The clearance between the driving structure (shaft) and the socket is formed by the steps of forming the outer tubular shield with a lower blind end, disposing a cement in the blind end of the outer tubular shield to form a socket having a configuration similar to but larger than that of the driving structure; disposing a wax that turns to a gas when exposed to the heat in a bath of molten metal, in the socket; disposing the driving structure in the wax; telescopically inserting the inner tubular shield and the outer tubular shield to engage the driving structure, and cementing the inner tubular shield to the outer tubular shield to form a unitary tubular shield around the shaft. 
     Referring to FIG. 1, coupling  22  forms the connection between the motor shaft and the shield assembly  20  that rotates pumping member  32  with impeller vanes  44 . torque from the shaft is transmitted through the tongue to the body of cement to outer tubular shield  50  to the end driver  42 , that is through the lower end of the shaft to the impeller. The shaft has a sufficient torque characteristic for driving the impeller in molten metal. 
     The inner spacer shield is located to form an annular air chamber  76  between the shaft and the inner shield along its full length. The air chamber has a size chosen to permit the stainless steel shaft to fully expand in the bath of molten metal without applying any expansion pressure on the ceramic shield. The shaft is then fully shielded by heat-resistant and molten metal resistant ceramic. 
     FIG. 4 illustrates a modified impeller pump  10 ′. 
     Bearing means  46  carried in a shoulder  48  of the housing  30  engage an inner graphite sleeve-like shield  50 ′. The lower end of shield  50 ′ is closed off and fits into pumping member  32 . The upper end of shield  50 ′ extends upwardly through cover plate  18 . Inner shield  50 ′ is cemented to a protective ceramic sleeve  78 ′ to form a single integral part of shaft assembly  20  together with, spacer shield  52 , steel driving shaft  24  and tongue  58 . 
     FIGS. 5-6 show various forms of an unshielded vertical leg that can be mounted between the pump housing  30  and cover plate  18  in order to lock the pump legs to the pump housing without the use of load-carrying cements, eliminating the need for large clearances between the legs and post sockets. Graphite cement is used only as a sealant to prevent molten metal penetration. 
     Graphite leg  120  has an upper end fastened to the cover plate by a threaded fastener  122 . The lower end of the leg is received in a cylindrical socket  124  in the pump housing. The leg&#39;s lower end has an annular enlargement  126  which is bottomed in the socket. The leg has an annular groove  128  above the enlargement for receiving a close fitting split ring  130 . The socket also has an annular groove  132  for receiving the split ring. 
     In this embodiment of the invention, the lower end of the leg is inserted into the socket by squeezing the split ring into groove  128 . Once the split ring is disposed in the socket, the shaft is pushed down until the split ring snaps into groove  132  thereby being disposed in both the groove in the leg and the groove in the socket, locking the leg in position. 
     FIG. 6 illustrates another embodiment of the invention in which a vertical leg  140  has an annular groove  142  for receiving a close fitting split ring  144 . The pump housing  30  has a socket  146 . The upper edge of the socket is chamfered as at  148  in such a manner that as the leg is inserted into the socket, the chamfered edge squeeze the split ring into the groove  142 . The leg is moved further into the socket until the split ring is partially expanded into the annular groove  150  in the socket. The split ring is disposed in both the socket of the leg and the groove of the socket thereby locking the leg to the housing. 
     In FIG. 8, housing  30  has a generally cylindrical socket with a radial groove  162 . The upper wall of the groove is adjacent a chamfered lip  164 . Split ring  166  is placed in groove  162 . When leg  168  is pushed into socket  160 , ring  166  will expand, then snap into groove  170 . 
     FIGS. 8A and 9 illustrate another version of a leg-housing locking device. Leg  171  has a groove  178  connected by means of passage  174  to an opening  180  located above the upper surface of housing  182 . Housing  182  has a socket  172  with an annular groove  176 . After leg  171  is inserted in housing socket  172 , graphite cement is injected under pressure in opening  180  and via passage  174  fills the cavity generated by grooves  176  and  178  in the housing and leg respectively, thus, preventing, after hardening, any axial displacement of the leg with respect to the housing. 
     FIG. 10 illustrates a shielded upright quill leg for supporting pump housing  30  beneath a cover plate  18 . An opening  181  is formed in housing  30 . An outer ceramic tubular shield  183  is formed with a length sufficient so that its lower blind end extends below the inside surface of the wall of housing  30 . The upper end abuts cover plate  18 . 
     An inner ceramic tubular shield  188  is disposed inside the outer shield and cemented along the length and around the inner shield in the area  190  (indicated by the heavier line). The lower end of the inner shield extends above the bottom of the outer shield. The upper end of the outer shield is located by an annular mounting member  192  that is attached to the cover plate. The lower end of the outer shield is threaded at  194  to receive a locking nut  196  which is screwed up to abut the inside surface of the housing. 
     A stainless steel leg  198  is disposed in the inner shield. The lower end of the stainless steel leg has a radial enlargement  200  which has a diameter less than the inner diameter of the outer shield but greater than the inner diameter of the inner shield so that it abuts the lower edge of the inner shield. Leg  198  is located so as to form an annular chamber  201  between the leg and the inner shield to permit the leg to thermally expand when it is disposed in the molten metal bath, without imposing an expansion stress on the shields. 
     The upper end of the leg is threaded at  202  for receiving a locking nut  204  and bevel washer  206  in order to lock the leg in position when it has been properly located within the ceramic shield. 
     FIG. 11 illustrates a slightly modified version of the shielded leg of FIG.  10 . In this case a tubular shield  210  comprises inner and outer ceramic shields similar to those illustrated in FIG. 10, and an internal stainless steel leg. The lower end of the outer shield has an enlargement  212  sequestered inside a corresponding similar enlargement in the housing instead of using nut  196  with the threaded configuration. 
     FIG. 11A illustrates a quill leg that is identical to that of FIG. 11 except that it has been cemented to pump housing  30  in accordance with common post-cementing procedures known by a person skilled in the art. 
     FIG. 12 illustrates another version of a shielded leg  220  for supporting pump housing  30  beneath cover plate  18 . This particular design utilizes graphite components in combination with a ceramic outer sleeve to protect the graphite outer shield. Although the graphite components of the leg are protected by the heat resistant ceramic shield, in some cases the air chamber between them or air leakage provides sufficient oxygen to allow the support leg components to bum. 
     In this case, a stainless steel leg  222  has an enlargement  224  carried at its lower end mounted within an inner graphite tubular shield  226 . The enlargement is seated against the lower end of the inner shield. The upper end of the leg is threaded at  228  to engage a fastening nut  230  and bevel washers  232  in such a manner that by tightening on nut  230 , enlargement  224  firmly seats graphite shield  226  in position against the bottom of the cover plate to form a gas chamber  234  around leg  222 . 
     An intermediate tubular graphite shield  236  telescopically receives the inner shield and has its internal surface cemented to the inner shield. 
     Leg  222  has a longitudinal gas passage  242  that extends from its upper end down to its lower end and also radially out through an opening  244  into chamber  234 . 
     The inner shield, in turn, has a small passage  246  which communicates with a passage  248  in shield  236 . 
     An outer ceramic tubular shield  250  encloses both of the graphite shields and has an internal annular chamber  252  in communication with passage  248 . Chamber  252  is filled with molten metal resistant cement. A source of nitrogen  254  is connected to passage  242  to form an oxygen-free atmosphere around the leg as well as an oxygen-free atmosphere along and around the graphite shields exposed to the metal level to prevent the graphite shields from burning. 
     FIGS. 13-15 illustrate a combination dynamic filter and pumping vane member  300  that may be substituted for the pumping member  32  illustrated in FIG.  1 . Pumping vane member  300  has an opening  302  for receiving the lower threaded end of pumping shaft  42 . A nut  303  attaches the body to the pumping member  300 . Pumping member  300  thus rotates with driving shaft  24 . 
     The pumping member has an internal chamber  304  with outlet opening means  306  and an apertured bottom strainer plate  308 . The strainer plate has an annular outer series of openings  310  and an inner series of openings  312 . The inner series of openings are in a bottom horizontal portion of the strainer plate while the outer inlet openings are in a frusto-conical wall. 
     Referring to FIG. 15, the pumping member has a series of pumping vanes  314  which are curved to form openings each having a width A in such a manner that as the pumping member is rotated, the pumping vanes draw the liquid metal through the inlet openings and then push the liquid metal out through the outlet opening means  306 . Strainer openings  310  and  312  have a maximum diameter B that is smaller than the larger openings A between the vanes. Thus the strainer openings prevent debris having a size larger than strainer openings B from entering into the pumping chamber thereby preventing any clogging of the vane openings. 
     A series of inner linear radial slinger bars  320  and outer radial slinger bars  322  are mounted on the strainer plate between adjacent strainer openings to strike any relatively large debris attempting to enter the strainer openings before they reach the vane openings. The slinger vanes strike the debris thereby permitting the pump to be located closely adjacent the bottom of the molten metal pot thereby permitting a stream of inlet liquid metal to be generated at a lower level in the pot. 
     Thus, it is to be understood that several variations have been described of an improved impeller-type pump useful in molten metal baths as well as several variations of shielded legs for supporting the pump in the molten metal bath.