US3468365A

US3468365A - Aluminum production apparatus

Info

Publication number: US3468365A
Application number: US665012A
Authority: US
Inventors: Paul H Scheffler Jr
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1967-09-01
Filing date: 1967-09-01
Publication date: 1969-09-23
Anticipated expiration: 1986-09-23

Description

Sept- 23, 1969 P. H. scHEFFLER, JR 3,468,355

ALUMINUM PRODUCTION APPARATUS Filed Sept. 1l 1967 United States Patent O U.S. Cl. 164-266 9 Claims ABSTRACT OF THE DISCLOSURE Apparatus for the continuous production of light metals such as aluminum including an electrolytic reduction cell for producing a liquid metal bath having a surface at an optimum distance below the cell electrode, an alloy holding furnace having upper and lower bath level limits, a conduit with pump for conveying metal to the alloy holding furnace and responsive to the liquid metal bath level in the electrolytic cell, and a conduit with a pump for conveying liquid metal to a casting mold.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to apparatus for the continuous production of a light metal from the ore-reduction stage to the ingot casting stage. More particularly, it pertains to apparatus for the continuous production of aluminum.

Description of the prior art In the production of lightweight metals such as aluminum, the present practice is to periodically siphon molten metal from the individual electrolytic reduction cells and then cast the metal into so-called pigs. After solidifying and cooling the pigs are stacked on pallets for shipment to processing plants. Aluminum pigs are usually melted in a remelting furnace and alloying materials are added. The furnace is then tapped into transportable crucibles from which ingots are poured by the direct-chill process. The ingots are the raw material for forging, rolling, extrusion, or drawing into the final product form.

All of the foregoing stages are batch type processes involving considerable manual labor and/ or manual control. Moreover, inasmuch as the electrolytic reduction cells, the remelting furnaces, and the ingot pouring proccesses are frequently located at separate places, there is a concomitant waste of time and heat.

From time to time attempts have been made to unite these separate processes into a continuous procedure in order to obtain the advantages of minimal manual handling as well as a savings of time and fuel costs.

One of the more basic problems limiting the operation on a continuous procedure basis is the removal of liquid metal from the electrolytic cells and conveying it to the holding furnaces where it is mixed with alloying materials. Similarly, there is a problem of conveying the liquid metal alloy from the holding furnace to the casting mold. Where the electrolytic cells, the holding furnace and the casting mold are preferably disposed on the same elevation, the molten metal cannot be conveniently flowed by ygravity from one stage to the next.

Associated with the foregoing is the procedure of forming the metal removed from the electrolytic cells into pellets of a convenient size and subsequently mixing them with pellets of other alloying elements such as copper, zinc, and magnesium in the holding furnace.

It has been found that the foregoing problems may be overcome in accordance with this invention by providing interconnecting conduits and pumps for conveying liquid metal between the several stages in the production of a lightweight metal such as aluminum.

ICC

Accordingly, it is a general object of this invention to provide an aluminum production apparatus having minimal operating costs and power consumption.

It is another object of this invention to provide aluminum production apparatus which is operative on a substantially continuous basis.

Finally, it is an object of this invention to satisfy the foregoing objects and desiderata in a simple and expedient manner.

SUMMARY OF THE INVENTION Briefly, the apparatus of the present invention comprises electrolytic cell means for producing a liquid metal bath, an alloy holding furnace having a bath level with upper and lower limits, and an alloy casting mold; first conduit means including a liquid metal pump for conveying metal from the metal bath in the electrolytic cell to the alloy holding furnace, second conduit means including a liquid metal pump for conveying metal from the metal bath in the holding furnace to the liquid metal casting mold, control means for maintaining an optimum level of crnetal bath in the electrolytic cell, the liquid metal pump being responsive to the control means for increasing and decreasing the rate of ow of metal in the first conduit means, and the liquid metal pump in the second conduit means `and being responsive to the upper and lower limits of the bath level in the casting mold for controlling the rate of ow of metal into the casting mold.

IBRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the nature and objects of this invention, reference is made to the drawings, in which:

FIGURE 1 is a diagrammatic View in accordance with the principles of this invention; and

FIG. 2 is a diagrammatic view of another embodiment in accordance with the principles of this invention.

Similar numerals refer to similar parts throughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Aluminum is generally produced by an electrolytic reduction process in which alumina is dissolved in molten cryolite from which molten aluminum is separated by electrolysis continuously from a molten solution of cryolite and alumina at about 1000 C. The electrolytic reduction normally takes place in large cells generally indicated at 1() in FIG. l which consists of a shell 12 lined with carbon 14 forming an inner cavity 16 containing the cryolite electrolyte 18.

A carbon anode 20 extends into the electrolyte 18 to introduce current which separates the metallic aluminum electrolytically and provides the heat to maintain a bath 22 of molten aluminum. During the electrolysis a gap 24 between the lower end of the electrode and the surface of the bath 22 must be maintained at a critical dimension in order to maintain optimum cell performance. Accordingly, as liquid metal 22 is withdrawn from the cell in a manner to be described below additional alumina must be added to the electrolyte 18 such as by an auger conveyor 26. The conveyor 26 consists of a cylindrical casing 28, a helical tin 30 snugly disposed within the casing, and a shaft 32 for rotating the fin within the casing. A variable speed motor 34 is provided for rotating the shaft. Alumina is introduced into the upper end of the casing 28 and enters the cell 10 as the tin 30 is rotated at the lower end of the casing 28.

Molten aluminum is `withdrawn from the cell 10 by a liquid metal pump 36 which is connected to the cell by a conduit 38 which extends from the -bottom of the cavity 16 to the lower end of the pump. The pump 36 has a variable speed and is composed of a ceramic rotor and housing to enable its handling of high temperature liquids and is more particularly described in copending application Ser. No. 610,935, tiled Jan. 23, 1967. The pump 36 is disposed within a shot tower chilling vessel 40 through which a flow of inert gas coolant 42 such as argon or nitrogen which is introduced at the upper open end of the vessel through a duct 44. The lower end of the vessel 40 is closed in a suitable manner such as by bottom wall members 46. The pump 36 is of the centrifugal type whereby liquid aluminum is dispersed radially from the upper end of the pump into the coolant 42 which causes the aluminum to solidify into solid pellets that settle on the bottom Wall members 46 of the vessel 40.

Although only one cell 10 is shown in the drawing, it is understood that a plurality of similar cells are usually provided and are connected by suitable means such as similar conduits 38 to the lower end of the pump 36. In addition, each conduit 38 may be provided with suitable closure means such as a freeze plug 48 to limit the flow of liquid aluminum from a particular cell for a given period of time to enable maintenance of the gap 24 between the anode 20 and the metal bath 22. Although the conduit 38 is suitably insulated to maintain a continuous liquid metal phase during operation of the pump 36, a portion of the conduit may -be uninsulated to permit the formation of the freeze plug 48 when necessary. Suitable melting means such as a resistance heater may be mounted on and around the conduit to melt the plug 48 when withdrawal of liquid metal 22 from the cell 10 is necessary.

The speed of the pump 36 is varied and matched with the speed of operation of the auger conveyor 26 by suitable means (not shown) to maintain an optimum level of the molten bath and thereby derive the optimum combination of conditions including the gap 24, amount of alumina added to the cell, and the amount of aluminum withdrawn from the cell. The pellets (not shown) are removed from the chilling vessel 40 by an auger conveyor 50, the lower end of which extends into the lower portion of the vessel 40 and the upper end of which empties into a hopper 52. The conveyor S is actuated by a motor 51 suiicient to keep the vessel 40 empty and the conveyor includes a casing 54 which serves as a conduit for the pellets and the greater portion of which is occupied by a rotatable helical fin 56.

As shown in FIG. 1, a holding furnace 58 is provided for the purpose of maintaining a metal bath 60' at about 1400 to 1500 F. The metal bath 60 serves as a reservoir for a casting mold generally indicated at 62. The furnace -58 is preferably operated with a liquid metal circulating system including a liquid metal pump 64, an outlet conduit 66, and a return conduit 68. In conjunction with the circulating system a plurality of bins or hoppers 70y for the storage of pellets of other metals, such as copper, zinc, and magnesium are provided with corresponding conduits 72 which communicate with the return conduit 68 for the addition of desired amounts of alloying elements. Each conduit 72 is provided with a valve 74 to enable the ,addition of measured amounts of the elements as required. Thus, the circulating system maintains a more homogeneous composition of the metal bath 60 and permits the addition of equivalent or different amounts of alloying elements and/ or aluminum from hopper 52 to the bath.

'Measured amounts of liquid metal 60 are withdrawn from the furnace S8 through a conduit 76 leading to the casting mold 62. For that purpose a variable speed pump 78, similar to the pump 36, is mounted in the conduit 76. The casting mold 62 may consist of any one of a variety type of molds. 'Ihe preferred mold shown in FIG. 1 is of a continuous casting type including an upper cylindrical shell 80 and a bottom wall `82 which is lowered as a liquid metal in the shell S0 solidiiies. For that purpose the bot- I 4 tom wall 82 is mounted on a shaft 84 and lowered in a conventional manner such as hydraulically.

The pump 78 is operated at a speed dependent upon the rate of solidication of the liquid metal 85 in the mold 62. The rate of solidication of the metal 8S controls the rate of movement of the shaft 84. The level of the metal bath 60 in the furnace 58 varies during the casting process in response to the rates of operation of the pump 78, the auger conveyor 50, and the shaft 84. But the necessity of adjusting these rates to a nearly perfect synchronization is minimized as the capacity of the furnace is increased.

The

conduits

66 and 76 are provided with conventional insulating means -to prevent solidication of the liquid metal in the conduits. However, short segments of these conduits are uninsulated to permit the formation of

freeze blocks

86 and 87, respectively, in a manner similar to the freeze block 48 in the conduit 38. The

freeze blocks

86 and 87 are eliminated by `the application of heat such as by the mounting of a resistance heater around the segment of the conduits Where the freeze blocks are formed.

Another embodiment of the invention is shown in FIG. 2 which differs from that of FIG. 1 in that it is an entirely liquid metal operation without Ithe formulation of aluminum pellets. Accordingly, all parts in FIG. 2 are similar to those of FIG. 1 except as described hereinbelow.

In FIG. 2, the conduit 38 extends from the cell 10 to an insulated liquid metal reservoir 86. A liquid metal pump 88 similar to the pumps 36 and 78 is provided in the conduit 38. The liquid metal reservoir 86 is suiliciently large to hold an adequate amount of liquid metal 89 which is conveyed by a pump 90 in an insulated conduit 91 to the furnace 58.

Alloying elements such as copper, zinc, or magnesium are added to the liquid metal 60 circulating through the conduit 68 in measured amounts through the valves 74. However, auger conveyors may be substituted for the valves 74.

It is understood that the above specification and drawings are merely exemplary and not in limitation of the Invention.

What is claimed is:

1. Apparatus for continuously processing molten metal comprising a metal reduction means for producing a liquid metal bath,

an alloy holding furnace having a bath level with upper and lower limits,

an alloy casting mold,

first conduit means for conveying metal from the metal bath 'm the reduction means to the alloy holding furnace,

second conduit means for conveying molten metal from the holding furnace to the liquid metal casting mold, control means for maintaining an optimum level of metal bath in the metal reduction means,

meter means in the rst conduit means for controlling the rate of flow of metal conveyed from the liquid metal bath to the alloy holding furnace,

means connected to the meter means and responsive to the control means and for increasing and decreasing the rate of flow of metal in the rst conduit means in response to a respective increase and decrease in the level of the bath, and

second meter means in the second conduits means for controlilng the rate of ow of metal conveyed from the alloy holding furnace to the casting mold and being responsive to the rate of solidifcation of metal in the casting mold.

2. The apparatus of claim 1 in which the metal reduction means is an electrolytic cell.

3. The apparatus of claim 1 in which the first conduit means comprises a liquid metal pump.

4. The apparatus ol" claim l in which the second couduit means comprises a liquid metal pump.

S. The apparatus of claim 1 in which the control means for maintaining rthe metal bath level in the reduction means comprises means for adding measured amounts of metal ore to the reduction means.

6. The apparatus of claim 1 in which the liquid metal pump in the first conduit is responsive to the level of the liquid metal bath in the reduction means.

7. The apparatus of claim 1 in which the liquid metal pump in the second conduit is responsive to the level of the liquid metal in the casting mold.

8. The apparatus of claim 2 in which the first and second conduit means each comprise a liquid metal pump, and

the control means for maintaining the metal bath level in the electrolyte cell comprises a means for adding measured amounts of metal ore to the cell.

9. The apparatus of claim 8 in which the means for adding measured amounts of metal ore to the cell and the meter means in the rst conduit comprise auger conveyors.

References Cited UNITED STATES PATENTS J. SPENCER OVERHOLSER, Primary Examiner V. RISING, Assistant Examiner U.S. C1. X.R. 164-155