Technical Field

The invention relates to the field of pumping molten metal and, in particular, to the pumping of molten metal which is reactive with the atmosphere. The in¬ vention is useful in those situations where it is not practical to replace the atmosphere with an inert gas.

In molten metal pumps of the type here improved, a displacement means (e.g., an impeller) is used below the surface of the liquid to force the molten metal up a riser tube to its destination. A motor is used to rotate the impeller. And because the motor is more efficiently located above the molten metal surface, an impeller shaft is used to communicate the rotational motion from the motor to the impeller. The impeller shaft therefore is part above and part below the molten metal surface. Typi¬ cally, metal and dross tend to adhere to the impeller shaft at the surface which, when the shaft is rotated, causes a turbulence in the liquid. This turbulence was found to cause an increase in the rate of reaction between the metal and the atmosphere resulting in excessive dross formation or appearance of metal/gas complexes.

Summary

It is an object of the invention to reduce dross form tion in reactive, molten metal systems.

More specifically, it is an object of the in¬ vention to reduce dross formation near a rotating or reciprocating shaft in a reactive, molten metal system.

In accordance with the objectives, the inven- tion is an apparatus for pumping a reactive molten metal and a method for pumping reactive molten metal without a buildup of reaction products.

The apparatus comprises molten metal pumping means including displacement means, a rotating or recip¬ rocating shaft for moving the displacement means, the means for driving the shaft, a fixed, protective housing surrounding the shaft in the region of the molten metal surface and means for admitting molten metal to the space between the protective housing and the shaft. Preferably, the apparatus also includes means for raising the gas pressure in the space between the shaft and the protective housing to lower the metal level therein.

The inventive method of reducing reaction near moving shafts in reactive molten metal baths comprises fixing a protective housing around the shaft and allowing molten metal to enter the space between the protective housing and the shaft. Preferably the method also com¬ prises applying a gas pressure to the space between the housing and the shaft to lower the metal level therein.

Brief Description of the Drawing

Figure 1 and Figure 2 are sectional elevation views of the inventive apparatus taken along planes per¬ pendicular to each other.

Figure 3 is a sectional view of the apparatus of Figure 1.

Figure 4 is a breakaway of alternative recipro- eating apparatus according to the invention.

Description of the Preferred Embodiments

An impeller-type embodiment pump apparatus is shown in Figures 1-3. The apparatus basically consists of three columns. One column contains the impeller 20, impeller shaft 4 and motor 21. The second column is a pump riser 5 for moving molten metal from the impeller to the top of the pump and the third column is merely a support post 6.

The apparatus shown is a centrifugal pump having an impeller 20 supported and rotated directly by impeller shaft 4. The impeller shaft is in turn rotated by motor

21 through an intermediate series of couplings. In parti- cular, the shaft of motor 21 is pinned to motor coupling 10 which is pinned to connecting shaft 12. Connecting shaft 12 is pinned to a universal joint 16 which supports the impeller shaft 4 through an impeller nipple 11. The connecting shaft 12 is rotatably located within bushing 14 and bearing housing 8 and is sealed with seal 15 and seal retainer 9. Housing 8 rests on a pump support plate 2.

Pump riser 5 has a channel 23 communicating with the impeller 20 through passage 24. Riser reducer 13 and riser tube 25 are connected at the top of the channel 23. Mounting sleeves 1 fix the pump riser 5 and the support post 6 to the pump support plate 2.

The bottom of pump riser 5 and the support post 6 are fixed in a lower support block 17. Impeller 20 is rotatable within the lower support block or pump housing 17 against bearing ring or rubbing seals 26.

The isolator assembly comprises a nonrotatable protective housing 3 fixed to the pump support plate 2 through a mounting sleeve 7. The protective housing is open at the bottom such that molten metal can enter the space between the isolator housing and the impeller shaft. An orifice 22 in the bearing housing (or optionally lo¬ cated through the pump support plate) is in gas communi¬ cation with the space between the isolator housing and the impeller such that an inert gas may be forced therein to lower the level of molten metal in the space.

The impeller is a cylindrical member with holes 27 in the periphery. The molten metal enters the impeller through the open bottom along the rotational axis and is forced at about 10 psig through the holes, into passage 24 and up the riser channel 23 and riser tube 25. Some metal

is also forced upwardly between the impeller and the seals.

Any reactive metals can utilize the invention. Iron, magnesium, aluminum, copper, lead, zinc and alloys 5 thereof are examples, though many others exist. Lower melting metals and alloys may utilize the inventive pump¬ ing apparatus made of steel parts. Lower melting metals or alloys which attack steel and the higher melting metals or alloys may utilize a pumping apparatus made of graphite 0 parts below the level of the melt. For example, a steel pump according to the invention could be used with lead or zinc. However, a pump with graphite parts below the surface should be used with aluminum because aluminum attacks most steels. The rubbing seals in either case most 5 effectively should be silicon carbide or equally hard material. The upper couplings can be made of metal.

Although somewhat effective by itself in pre¬ venting the large buildup of reaction products, the open-ended, nonrotatable protective housing is preferably 0 pressurized to lower the melt level. Without an over¬ pressure, the level inside would, of course, be sub¬ stantially equal to the level of the bath. An overpressure equal to the metallostatiσ head pressure of the melt in the annular space between the isolator housing and the shaft 5 would lower the level to the bottom of the isolator housing. A pressure of about 1-2 psig is typical with light metals. Argon or other nonreactive gas is desir¬ able. Preferably, the level of the melt inside the space is just above the bottom of the isolator housing.

30 The displacement means for moving molten metal up the riser can be a rotatable impeller, as shown, or could be a positive displacementpiston-type element which would require a reciprocating action by the piston and shaft to pump the metal. The latter are shown in Figure

354. The piston 31 is shown on shaft 32 and is guided into pump housing 33 by guide plate 34. The piston and shaft

are enclosed by protective housing 35 joined to the pump housing at the lower end. Protective housing has an orifice 36 for admitting molten metal in the space between the shaft and protective housing and into the chamber 37 through channel 38 on the upstroke. On the downstroke, piston 31 is sealed against the pump housing with seal 39 and molten metal is pumped out of the chamber 37 through hole 40 to a riser (not shown).

When the protective housing is extended to the lower support block or pump housing 17 of the centrifugal pump shown in Figure 1, the molten metal may enter the space between the protective housing and the shaft through the gap between the impeller and the lower support block. The seals are not adequate at the operating pressure to prevent such occurrence.