US1930195A - Electrolytic aluminum reduction - Google Patents

Description

Oct. 10, 1933. EIGENHEER 1,930,195

ELECTROLYTIC ALUMINUM REDUCTION Filed July 10, 1931 2 Sheets- Sheet 1 INVENTOR KmaaL W W, NW4 Wi 41 A TTORNE Y8,

Oct 10, 1933. K, EIGENHEER 1,930,195

ELECTROLYTIC ALUMINUM REDUCTION INVENTOR Y KW 21- 1111. B

A TTORNE Y5,

I Patented Oct. 10, 1933 PATENT OFFICE.

' UNITED .srArss' Aluminium Industrie Aktiengesellscliaft,

Neuhausen, Switzerland; a joint-stock commay of Switzerland Application July 10, 1931, Serial No. 549,885,

and in Germany July 31, 1930 7 Claims. (Oi. 204-20) This invention relates to electrolytic aluminum reduction, and more especially to an improved apparatus therefor wherein the molten metal in the lower stratum of the furnace may be separated and withdrawn or scooped from the furnace in a novel and improved manner.

It is known that during the aluminum electrolysis in a fluoride bath according to the process of Hrou'lt the liquid aluminum sinks and collects on the cathode bottom under the fluoride electrolyte, which has a lower specific weight than the molten metal. Thealuminum has to be removed periodically. This can be carried out in different ways.

.In several plants the liquid aluminum is run off through a tap hole in the side of the furnace. This method offers numerous disadvantages relating to the working with the fumace and to its construction.

It is more suitable to ladle out the metal through the top of the furnace. This method is carried out for instance in the following way: At first a carbon anode is removed from the furnace. After that a receiver made of cast iron is placed into the furnace on the spot which be-.

came free. The receiver has a hole on the bottom. As soon as it is placed into the furnace,

' electrolyte and liquid metal flow upwards into the receiver, in which separation is made of the bath material carried out, and then the metal is scm'o'ia'ed out with a ladle. This ladling offers also disadvantages. Chiefly the working over the hot furnace is toilsome and lengthy. Fur-.

thermore the aluminum can become contaminated by little quantities of iron dissolved from the ladle and principally from the receiver.

According to the invention these disadvantages are avoided by scooping out of the receiver and consequently out of the furnace the liquid aluminum by means of a mechanically actuated scooping apparatus, which acts in a funnel-like receiver, and scoops the metal in a continuous stream and has for instance the form of a screw pump. Thereby is saved a great deal of trouble and of time.

The apparatus is suitably operated by a compressed air motor, which is more resistant to the heat than an electric motor. The air which comes out of the motor is advantageously used for the cooling of the apparatus.

In the drawings Fig. 1 is an elevation partly in central section of apparatus for withdrawing molten aluminum embodying the invention; and 65 Fig. 2 is a diagrammatic section showing a complete reduction system with the invention included.

Fig. 1 shows an example of a scooping apparatus used for carrying out the novel method. A scooping screw 2, which is rotated by the compressed air motor 3, is located in a conical receiver 1. The liquid aluminum flows through the bottom hole 4 into the receiver, is raised by means of the scooping screw up to the spout 5 and flows thereout. The expanded air which comes out .65 of the motor is conducted through the'driving shaft 6 into the scooping screw, ascends again in the screw and finally escapes, after having carried out its cooling action.

Fig. 2 illustrates the scooping process with the above described apparatus. It shows a furnace for the electrolytic production of aluminum, with the positive electric conductor '7, the anodes 8 and the iron cathode connection 9 molded in the bottom; the number 10 designates the refractory 7i lining, 11 the molten aluminum and 12 the molten cryolite electrolyte. The scooping apparatus is placed in a part of the furnace where previously a carbon electrode has been removed in order to provide a space for the receiver. It may rest on the bottom or be suspended as shown in any desired manner- The screw 2, which-is turned by the compressed air motor 3, scoops the aluminum, which flows into the receiver 1 through the bottom hole 4, up to'the spout 5; the metal runs 8 then through the channel 13 into a wheeled re-' ceiver 14.

The flow of cooling air from the air motor 3 may be substantially as follows, it being understood that due to expansion of air passing. through the motor it is discharged at a much lower temperature than when compressed. A coupling 18 conducts compressed air from a suitable supply to an inlet 19 which feeds the motor, the air being discharged by an outlet 20 and this cooled air conducted by a pipe 21 to a casing 22 constituting part of the support of the motor. The cooled air is received within the casing and therefrom passes through an aperture 23 into the central space 24 within the extension 25 of the rotary shaft of the motor. From the cavity 24 the air flows downwardly through a central bore 26 formed in the interior sleeve 2'7 of the shaft 6 of the lifting screw 2. At its lower end the central passage 26 delivers into a cavity 28 formed in the screw, so that the cool air is brought directly to this cavity, assisting greatly to prevent undue heating of the screw. From the cavity 28 the air may flow upwardly through the annular passage 29 between the inner sleeve .110

- 27 and the outer sleeve 30 of the shaft 6. Near advantages of the present invention. Many mattors of method, operation, arrangement and construction may be variously modified without departing from the principles of the invention, and

it is not intended to limit the invention to such matters except to the extent set forth in the appended claims.

what is claimed is:

1. An electrolytic aluminum reduction apparatus'of the kind comprising a cathode vessel to contain a lower stratum of molten aluminum and resting thereon a lighter upper stratum of molten electrolyte, with anodes mounted above and dipping into the upper stratum, characterized by means for separating and withdrawing molten aluminum from thelower stratum of the vessel comprising a walled uuct mounted above and extending downwardly through the upper electrolyte stratum and having its open lower end immersed in the lower stratum, whereby only molten aluminum and no electrolyte may enter the duct, the duct having a liquid outlet above the cathode vessel for the lateral discharge of separated molten aluminum, and a driven lifting means adapted to maintain an upward current of molten aluminum inliquid form through the duct and outlet.

2. Apparatus as in claim 1 and wherein the lifting means is a mechanically movable device submerged in the molten aluminum in the lower part of the duct.

3. Apparatus as in claim 1 and wherein the lifting means is a mechanically movable device submerged in the molten aluminum in the lower partof the duct, with means for flowing cooling medium through it to prevent overheating.

4. Apparatus as in claim 1 and wherein the duct has a contracted lower inlet end and flares upwardly therefrom, and the lifting means is a rotary screw device extending into submerged position in the lower part of the duct.

5. Apparatus as in claim 1 and wherein the duct has a contracted lower inlet end and flares upwardly therefrom, and the lifting means is a rotary screw device extending into submerged position in the lower part of the duct, both the screw device and duct being tapered downwardly.

6. In the art of electrolytic aluminum reduction, the method of removal of molten aluminum from the lower stratum in the reduction cell, which consists in mechanically forcing the upflow of the molten metal into and through a walled passage dipped into such lower stratum, afl'ording discharge of the metal in a continuous liquid stream.

'7. The method of claim 6 and wherein the forcing of upflow is by a revolving screw lift action.

KONRAD EIGENHEER.

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