US2277268A - Metal treatment process and apparatus - Google Patents

Description

March 24, 1942. G. w. Gox-:RNER

METAL TREATMENT PROCESS AND APPARATUS FiledNOV. 6, 1940 I AN N HN ow 2 n E o H/// 2 H INVENTOR.

m. N m 7. W. m w U GY B A TTORNE Y.

Patented Mar. 24, -1942 l METAL vTREATMENT PROCESS AND APPARATUS Gustave W. Goerner, Bourne, Mass., assigner to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application November e, 1940, serial No. 364,569

(ci. :za-57) 12 Claims.

This invention relates to the treatment of nonferrous metals and more particularly to an improved method for purifying and casting nonierrous metals such as copper, copper alloys, and the like.

In the manufacture of copper to be used as electrical conductor. it is desired to substantially completely remove oxide from the metal in order to produce a product having maximum electrical v conductirity. For this purpose various deoxidizing reagents are commonly added to the copper prior to and during the casting operations. So dium or other alkali metal isl an excellent deoxidzer for this purpose; but is difficult to apply because of the relatively low boiling points of the alkali metals and their high chemical reactivity. Various methods of applying sodium for puricaton of copper have been proposed but heretofore none of these have been entirely satisfactory. l

A difficulty with prior methods for deoxidizing copper and other metals is that the purified metal becomes contaminated during the casting operations. For example, copper mayfbe completely deoxidized by adding sodium tothe melting crucible or to molten copper in the ladle, but some oxidation is liable to occur during the casting operation. Heretofore there has been no satisfactory method which will insure against such contamination.

An object of the present invention is to pro. vide an improved process and apparatus for purifying copper or other non-ferrous metal by means of treatment with an alkali metal. A further object is to provide such improved process and 2 apparatus by means of which copper may be completely deoxdized and cast into ingots or other molded articles under such conditions that the cast metal is completely protected from oxidation during the entire casting operation, so as to prevent any contamination of the deoxidized melt. Still other objects will be apparent from the following description of my invention.

The above stated objects may be obtained in` accordancewith the present invention by flowing a stream of the molten meta-l to be c ast through an oxygen-free atmosphere containing alkali metal vapor, directly into a suitable mold located in the same atmosphere, then transferring the filled mold into Ia bath of liquid alkali metal to cool the casting, removing the mold from the liquid alkali metal and thence transferring it to a point where the ingot o1' molded article may be removed from the mold. By this mode of operation the metal treated by passage through the alkali metal vapor is cast out of contact with the air and is protected from oxidizing iniiuences at all times until the casting has cooled sufliciently to be removed from the mold. This effectively prevents reoxidation or contamination of the puriiied melt. In practicing this invention I preferably provide a small amount of alkali metal in the mold prior tothe casting operation so that themetal cast into the mold becomes further treated by the alkali metal vapors formed by the heat of the melt passing into the mold. This supplements treatment obtained by passing the stream of metal through the alkali metal vapor and insures complete refinement.

My invention may be more clearly understood by reference to the appended drawing which illustrates one form of apparatus suitable for carrying out my process. Figure 1 is a vertical cross-section of the apparatus; Figure 2 is a section taken on plane A-A of Figure 1. In the upper part of the apparatus chamber l` is a large rectangular shaped container made with walls of a suitable refractory or heat resisting material. Partition 2 in this.l chamber together with vertical baffle 3 divides chamber I into two parts, namely a crucible or container I for the molten metal to, be cast and a vapor chamber 5. The crucible 4 is provided with a drainage opening 25 which is normally closed with fire clay brick 26. The crucible also is provided with suitable heating means not shownv in the drawin g, for example, conventional electrical resistance heaters or a reverberatory furnace built around and above the crucible. Batlle 6 is placed in' the vapor chamber 5 so as to prevent free fall of the liquid metal flowing from crucible 4 and to cause the metal to pass through the vapor chamber by a circuitous route. The top of the vapor chamber is closed by cover l which is made of steel and lined with refractory material.

Below chamber I there is arranged a steel tank 8 which is filled with liqtd alkali metal. Sealing baies 9 and l0 dip into the central portion of tank 8 to a .point below the surface of the liquid metal therein. Tank 8' is provided with heating means not shown, e. g. electrical resistance heaters,- to keep th'e alkali metal in liquid state. Inlet pipe 22 is provided for flowing molten alkali metal into tank 8. Pipe 22 is connected with an alkali metal supply tank not shown, and the supply tank and pipe connections to inlet 22. are provided with suitable heating devices to maintain the alkali metal in the liquid state. An alkali4 metal outlet pipe 23 similarly heated by means .not shown is provided to predetermine the level oi liquid in tank 8. A relief valve or safety valve 24 is connected to an exterior portion of outlet 23.

Tank 8 is enclosed by the walls of a mold conveyor chamber II. One end of chamber II is extended upwardly to form vertical elevator shaft I2. Shaft I2 is divided by vertical partition I3 which is an extension of an end wall of tank 8, to form vertical shafts I8 and I 8. Within the conveyor cham-ber and shafts I2, IB and I9 is arranged a. conventional chain conveyor 29 supported by pulley I4. Conveyor 2S is movable in the direction shown by the arrows, by application of power to drive shaft 21'. veyor 29 carries a series of ingot molds I5 each of which is suspended by projections located above its center of gravity and ending in bearings attached to conveyor chains, so that the mold is free to tilt or swing. 'I'ilting meansv I6 and Il are arranged at diierent points in the .circuit of the conveyor for the purpose of engaging with the molds as they pass and tilting them as shown in the drawing. At a convenient point near the bottom of shaft I9, an opening 20 is provided for discharge of molded articles into chute 2|. Opening 20 is provided with a door or cover not shown in the drawing.

The chain con- Y 'I'he apparatus is provided with a plurality of gas inlets 3U and gas outlets 3I. Inlets 30 are connected by means not shown to a source of nitrogen or other suitable inert gas which can be maintained under pressure as desired'. Outlets 3| which serve as vents are provided with conventional shut-off valves, not shown. If desired, outlets 3I.- can be connected to a common header or vent pipe, the latter being provided with a shut-off valve.

The conveyor chamber portion of the apparatus may be insulated by alayer 28 of insulating material, as desired, to conserve heat. .The temperature within the apparatus may then be regulated by suitable cooling ccilscarrying a heat exchange liquid. Such cooling coils or equivalent members may, for example, be located in the alkali metal tank 8, in the conveyor chamber, or

both. Heat thus conducted from the apparatus may be utilized for other useful operations.

In one method of practicing my invention by means of the above described apparatus, I first melt suicient copper in the crucible 4 to bring the level of the melt above the lower'edg'e of baille 3. At the same time, tank 8 is heated and lled with liquid sodium. Before filling tank 8, nitrogen is passed into the apparatus through nitrogen inlets 30 and out through outlets 3| until all of the air has been driven out and theentire apparatus is iilled with pure nitrogen. Outlets 30 are then closed and the apparatus is kept under a slight nitrogen pressure forthe remainder of the operation. The conveyor chain is then moved by rotating shaft 21 soA as to bring a mold I5 in position to receive molten metal ilowing from vapor chamber 5. A quantity of copper equal to the capacity of the mold then is added to the crucible either by adding solid' copper or molten copper ladled from another crucible. The addition of the copper to the crucible displaces an equal amount of the melt which ows over a depression in the upwardly projecting part of partition 2 and passes through the vapor chamber 5 over baille 6 and into mold I5. The conveyor then is again operated to bring the next mold into position. This movement causes the filled mold to be submerged in the liquid sodium in tank 8. which heats the sodium and causes the formation of sodium vapor which rises into vapor chamber 5. In coming into the llng position the second mold is caught by projection I5 which tilts the mold to a predetermined angle. so as to spill out substantially all or part of the liquid sodium which it carries from tank 8. Preferably projection I6 is so adjusted that the tilting of the mold removes the bulk of the liquid sodium but. leaves a small amount in the mold, for example, around 0.1 pound of sodium for a mold of 25 pounds of copper capacity. A second portion of copper then is added to the crucible and this time the displaced molten copper-passes through the sodium vapor in chamber 5 and thence into the mold. The sodium in the mold is vaporized and intimately mixed with the entering molten copper. The conveyor chain is then again movedto bring a third'mold into position and the process is repeated. As each mold is illled in succession and lowered into the sodium bath, sodium vapor is formed so .as to keep vapor chamber 5 continuously filled with sodium vapor. Excess vapor passes under baille 3, bubbling through the copper melt in the crucible thus causing, further purification of the copper.

As the molds pass out of tank 8 and upward through ,shaft I8, they come in contact with projection I1 which tilts -the molds so as to discharge any molten sodium in the upper part of the mold on the surface of the ingot. The discharged sodium falls back into tank 8. As each mold comes into position opposite the discharge opening 20, near the bottom of shaft I8. the door or sate is opened and the mold tilted sufficiently tc release the ingot. If desired, conventional means for automatically tipping the mold and releasing it into chute 2l may be provided. Alternatively, the ingot may be removed at this point by manual operation.

Obviously my invention is not conned to the particular apparatus and mode of operation illustrated .by the drawing and described above, since various modiilcations thereof will be apparent to those skilled in metallurgical operations. In general, my process consists in passing the molten copper through an atmosphere of sodium vapor directly into a mold and then contacting the mold with liquid sodium, whereby the liquid sodium is heated to generate sodium vapor. Various means of arranging the apparatus or accomplishing'this result will be apparent to the skilled -mechanic after having knowledge of my above described apparatus.

I claim: i

1. A process for casting a non-ferrous metal which comprises flowing a stream of the molten metal through an atmosphere oi an alkali metal vapor into a mold and then contacting the mold with a bath of liquid alkali metal.

2; A process for casting a non-ferrous metal which comprises flowing a stream oi' the molten metal through an atmosphere of sodiumvapor into a mold and then contacting the mold with a bath of liquid sodium.

3. A process for casting copper which comprises flowing a stream of molten copper through an atmosphere of sodium vapor into a mold and then contacting the mold with a bath of liquid 4. A process for casting copper whichl comprises lowing a stream of molten copper through an atmosphere of sodium vapor into a mold, then immersing the mold in a bath of liquid sodium, removing the mold from said bath, draining ott excess liquid alkali metal or sodium from the removing the mold from said bath', draining oi excess liquid sodium from the mold and further cooling the lled mold in an atmosphere of nitrogen.

l 6. An apparatus for casting non-ferrous metals v 4conducting molten metal from said rst-men tioned container through said.vapor chamber, at least one movable mold adapted to receive the `molten metal issuing from said vapor chamber and means for immersing said mold into liquid alkali metal in the lower container.

7. An apparatus for casting a non-ferrous metal comprising conveying means adapted to -move a mold into a vapor chamber containing an atmosphere of alkali metal vapor, means for ilowing a stream of molten metal'through said vapor chamber into-said mold and conveying means adapted to immerse said mold containing said molten metal into a bath of liquid alkali metal.

8. An apparatus according to claim 7 which has a passageway leading from the surface of said bath of alkali metal into said chamber and so` arranged that vapors caused by immersion of the hotA mold into said bath are conducted through said passageway into said chamber.

9. An apparatus according to claim 6 in which said vapor chamber is provided with baffles adapted to interrupt free fall of molten metal therethrough. i

10. An apparatus for casting non-ferrous metals comprising a container for the molten metal to be cast, a lower container for an alkali metal cooling bath located at a level below the rstl mentioned container, a vapor chamber arranged between the two above-mentioned containers and adapted to receive and confine vapors arising from the lower container.' means to substantially exclude air from said vapor chamber, means for conducting molten metal from said rstmen tioned contain-er through said vapor chamber, a plurality of molds arranged on an endless c one veyor adapted to bring the molds successively to: a mold filling position to receive molten metal flowing from said vapor chamber, thence t0 a position beneath the bath in said lower container, thence out of said lower container to a dischargel position and thence returning to said mold lling position.

1l. Apparatus according to claim' l0 in which said conveyor is arranged to lead the molds beneath the bath in said lower container for bringing the molds to said mold filling position, means for-tilting the molds leaving the bath before their arrival at said mold lling position, and means for tilting lled molds leaving said bath before arrival at the ingot discharging point.

l2. An apparatus for casting non-ferrous metals comprising a container for molten metal to be cast, a vapor chamber adjacent to said container, a baffle forming one wall of said vapor chamber and projecting into said container to a point below the melt level therein, means for discharging melt from said container into said vapor chamber, at least one baille arranged in said vapor chamber to prevent free fall of melt through the`- chamber, an opening for discharging melt from the bottom of said chamber, an open tank for liquid alkali metal located beneath said opening, bales extending from the bottom of said chamber into said tank arranged to-divert vapors evolved from liquid alkali metal in said tank into said chamber, an air-tight enclosure arranged about said tank, a vertical extension of said enclosure. divided by a vertical partition into' two vertical shafts, an. endless flexible conveyor arranged within said enclosure and carrying a plurality of molds, said conveyor being arranged to bring said molds successively to: a mold filling position to receive metal flowing from the opening in the bottom of the vapor chamber, thence to a point below the liquid alkali metal in said tank, thence upwardly through one of said shafts, thence downwardly through the other shaft to a point of ingot discharge, thence to the interior of said tankand thence upwardly to said mold filling position, means provided to tilt said molds leaving said tank before arriving at said lling position and means for tilting said molds while passing upwardly through the vertical shaft. A

GUSTAVE W; GOERNER.

CERTIFICATE oF CORRECTION. t patent No. 2,277,268. march 2h, 19142.

GUsTAvE w. GOERNER.

-It is hereby certified that error appears in tbe irinteci spe cifieation" of the above numbered patent requiring correction aus follows: 'Page 5, sec- -ond column, line'vl, claim 11, forthe-word "for" read --bef'orerm; and that the seid Letters Patent should be read with this correction therein that the same 'may conformto the'record of the case in the Patent Office.

.signed and sealed this 5th day of nay, A., D. 191m.

l Henry' van Arsdal'e (Seal) y Acting Commisioe'r of' Patents.

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