US2840463A

US2840463A - Degassing and purifying molten aluminous metal

Info

Publication number: US2840463A
Application number: US429438A
Authority: US
Inventors: Philip T Stroup; Kenneth J Brondyke
Original assignee: Aluminum Company of America
Current assignee: Howmet Aerospace Inc
Priority date: 1954-05-13
Filing date: 1954-05-13
Publication date: 1958-06-24
Anticipated expiration: 1975-06-24

Description

June 24 1953 P.'r.` sTRouP ErAl. 2,840,463

' DEsAssIN-c Aun PURIFYING u'oursN Awumous METAL v I Filed nay v'13. 1954 'r4 INVENToRs 38 frog/rey DEGASSING AND PU'RIFYnsG MoLruN ALUivnNoUs METAL Philip T. Stroup, New Kensington, and Kenneth J. Brondyke, Uakmont, Pa., assignors to Aluminum Company of America, Pittsburgh, Pa., Ya corporation of Pennsylvania Application May 1,3, 1954,1seria1 No. 429,438

1s claims. (ci. vs -6s) This invention relates to removing dissolved or sorbed gas and other impurities from molten aluminum` and aluminum Ibase alloys and is concerned with both the process and apparatus for accomplishing this purpose. For the sake of convenience both 'aluminum and aluminum base alloys will be referred to as aluminous metal.

It is well known that aluminousv metal absorbs'various gases either directly from the air or from the solids placed in Vcontact with the liquid metal or` by the reaction of certain chemical compounds with aluminum. Hydro- .'gen appears to composev the major portion of the ga'spoccurring in aluminous metal and is regarded as being 'chiey'responsible for the defectsassociated with gas` in the metal. It is further well recognized that the amount ofk gas which can be held by molten metal varies with the .temperature,kthe capacity tol hold gas diminishing with "the temperatureand hence some gas is released as the liquid metalcools. Of greater importance is the fact that as the molten metal solidiiies ya relatively large proportion of the gas heldbyrthe metal is expelled with the resultant formation of bubbles or other voids in the cast product. Such' discontinuities are objectionable both from the standpoint of reducing the strength of the metal and the surface appearance, if the voids-are at the surface. For these and other reasons an'eiort is usually made to minimize the absorption yof gas by careful melting 'and metal transfer practices.

' To remove gas which has been absorbed inthe course of melting, various vtreatments have been, proposed and used. One of ,the0 most obviousr methods proposed has been that of creating a vacuum above the molten metal Ibath and extracting anygas which diffuses through the metal; This kind of treatment isldiicult and expensive tofoperate 44on'fa commercial scale and requires a long exposure to remove substantially all of the'gas. In addition, such treatment does not remove any solid impurities dispersed throughout the metal bath,

Anothermethod which has been used from time to time has consisted of introducin'gvinto the melt small amounts ofscertain solid halides which either react with aluminumto form an aluminum halide vaporv or which merely vaporize without reaction. Zinc chloride is an example of the first type and aluminum chloride is repres entative of the second kind ofsubstance. Suchtreatments are usually carried out in a furnace or in an open ladle, and do not remove much of the gas vunlessV large quantities of the halides are employed. The large volume of fumes resulting from the treatment create a difficult disposal problem.A f

An alternative practice which has been widely rused in the melting and purification ofv aluminous metal is that yof bubbling gaseous chlorine through the metal shortly before the metal is cast. This treatment is also carried out in a furnace or in 'a'ladle with the generation of a large amountA of fume. To reduce the gas content of the metal to a low value it is usuallynecessary to introduce a large quantity of chlorine over an extended period of time.` This means that one unit of metal holding equipsome solid impurities.

calcium impurity, content offa melt is lowered by ex-v ICC 2 ment is tied up for a long time and hence a large ynumber of units are required to process the output of but :arfew melting furnaces. As ran illustration of the quantityy .of chlorine that is consumed, itis knot uncommon to introduce 30 pounds ofy chlorine in a 5000 pound melt over a period of 20 minutes to bring'about a reduction-in gas content of the melt. The chlorine tluxigtreatment is' therefore a costly operation. .n

One of the objects of this invention is to provide method for rapidly removing ,substantiallyv all fof` the Agas held by an aluminous metal melt. Anothenobjeet'is" to reduce the sodium impurity content of 'a melt as it is being degassed. A further vobject is to provide a method for effectively degassing a stream o'f aluminous metal delivered from a melting furnace to a m-old or other receptacle. Still another object is toprovide a method for adding certain alloying elements simultaneously with the degassing treatment. Another object Vis to provide `a degassing unit which is adapted to. handle a relatively large volume of molten metal in a short time. Y y

These and other objects and advantages are achieved by the invention described hereinbelow,y the examples given to illustrate the principles of the invention and not as limitations thereof. Y

lt has been discovered that molten aluminous metal can be degassed quickly, effectively and economically by passing metalin a finely divided form through an inactive atm-osphere containing aluminum chloride in vapor form as the essential active component, of the atmosphere. By mean-s of the same treatment the sodium impurity content ofl the melt can also be reduced. To bring about the rapid degassing and-purification vof the melt it is necessary to provide an extremely large surface areawith respect to the volume in orderto expose the maximum area of the metal to the aluminum chloride vapor. In referring to an inactive atmosphere it isY to be understood that this means an atmosphere which doesv not increase the gas content of the molten metal when incontact therewith. Such an atmosphere may contain nitrogen, helium or similar gases, or dry air or even air with a' slight moisture content but in no case does it contain hydrogen or compounds yielding hydrogen in an amount suicient to introduce that element into the melt wherebythe gas content is increased. j l

As mentioned above the treatment not only reduces the gas content of the molten metal but it `serves to remove For example, the sodium and posure to the aluminum chloride atmosphere. In addition it serves to disengage suspended oxide particles dispersed in the molten metal. Such non-volatile impurities collect on the surface ofthe melt in the degassing unit.

rThe degassing and purification can be accomplished Y by subdividing thel metal into droplets or'very 'thin streams Whichpass through a chamber filled with the' aluminum chloride-containing atmosphere. `A Also, to obtain the desired rapid action it is imperative that a current of aluminum chloride` vapor pass through to the space wherein the treatment iseffected.A The constant movement of aluminumy chloride through theAV chamber sweeps away the gas released fromthe molten vmetal and transports it from `the treating chamber while at the same time reabsorption of gas is prevented. Lastly, ac-

cording to this'invention therdegassed and purilied metal y is immediately discharged from the treating chamber and transferred to suitablevmolds or other receptacles before any substantial re-gassing occurs. j A j The apparatus for carrying out the process is simple, compact vand does not include any moving parts. "It is therefore easy to maintain and to replace any wornout parts. The apparatus can be conveniently constructed inLV the form of a small unit Which'is adapted to "handle a Y onntheA practically all aluminum chloride fumes are c ondensedand/there/is `no pollution of the adjacent at rnorspllgi-ev lnewhole apparatusjoperates at atmospheric pr and thus avoids expensive" pumping equipment to evacuate, the treating chamber. i

, "A better" understanding ofthe invention will be gained bvnreferrins whe accompanying drawings wherein:

1 Fig: 1 ,is an unit;Y

elevationlin `section of a .simple degassing j Figl is a`n`elev`ation, partially in section, of a modilieldffrm vfapparatus: `and 1 Y t 1'F`g.1"4 ismatop plan view ofthe `unit shown in Fig. 3.

u Referring tolFigL" 1, `steel shell 10 lined `with refractory `12 forms thebaseand side walls` of chamber 14 wherein the degassing and purication treatment is conducted. The1ftop`1of`the chamber-is enclosed by the perforated plate 22d-which forms the, bottom of distributing basin 270 Iwhich inturnis supported on the .bottom tlange 28.\;In operation the basinis filled with: molten metal thus preventing access ofair 'to the treating chamber. The basin `20 restson top tlange116 of the vertical wall of the cham- Aber (and `affseal `18, such as `asbestos rope, is provided between that flange and the bottom flange 28 of the basin gto maintain a gas tight joint. Y

` `Immediately adjoining the treating chamber 14 is disl charge well l0` which is in communication with the chamber through opening 38. t Theshell 24 of the well is also lined with refractory 12. Discharge fromthe well is eectedfbymeans `of spout 42 mounted in the outer wall pd The"aluminum'` chloride vapor toprovide the desired In tmosplrere is supplied `to theV chamber from an external 4source throughinlet pipe 30 and'complementary'opening `32 refractory lining andthe outgoing aluminum chloridewaporis discharged through aperture `36` and `pipeoA to. a` condenser or :other suitable means for fre- .ivins ,the halide vapori molten metalto` be degassed is brought to the apparatus by trough 44. 1 The basin 20 tlled toa level .of 48distributes.the molten charge to thetreating cham- .ber.,j Ihebasefplate 22 provided with holes V26 serves subdivide the melt into` the form `of droplets 50 which descend `through the chamber to the pool of metal 52.

; VFigfZYis'zi` top` planiview of the` unitshown inFig. l; y

;When the metal level in lthe chamber and discharge well s2 a *rises above. he bttomof spout 42 a discharge 0f desassedmetaloccurs. d j j I The modification of Fig.11 appearing in Fig. 3 relai.;- i toganother method of supplying aluminum chloride vapor` Here ngaseous' chlorine is ini to, the 1. treating chamber. 'troducedy below` ,the surface .of `,the metal pool 52 by meansof the long downwardly extending tube 70. By `this arrangement a `gas tight seal is provided where the tube passes throughplate 22. Other means of introducing chlorine, such `as a horizontal` perforated pipe neat the` lloor ofl the degassing chamber can fbe "used. `Upon `contact;between` 4the chlorine and the aluminum, aluminumchloridevapor is formed .which together with anyrllnlacted chlorine rise through the metal in the form of bubbles 72." The aluminum chloride leaves the chamber` through aperture `and pipe 62 Aand passes into condenser `64' cooled with waterl coils 68. Any uncondensed aluminum chloride and gases associated :therewith can escape` through vent 66..` Itwill be appreciated that the systems 'shown in both Figsyl' and `3 operate at substantially: atmospheric pressure,` it beingfnecessary to provide only sucient pressure to drive the aluminum chloride through the degassingchamber.l l.

l Before startingjoperation of the degassing unit the api t paratus should be preheated to insure `absolute dryness as wellas to bring itupto a temperature such that the -a molten charge in a furnace or in a ladle.

metal has started through the unit it has been found that it is unnecessary to supplement the heat derived from the molten metal to maintain the desired temperature. Prior to introducing the aluminum chloride atmosphere or gaseous chlorine the chamber should be lled with molten metal to a depth indicated at 5,6 to seal the chamber fromY the discharge well and thus prevent access of the outside atmosphere or other gases to the chamber during the period of degassing and purification. When the molten metal seal has been thus effected the aluminum chloride or gaseous chlorine may be introduced and the metal level permitted to rise to level 58 just above the bottom of spout 42 in the discharge well. To maintain a uniform flow of metal through the unit it is desirable to keep the metal level in the distributing basin 20 at a substantially constant depth. The Vflow can be varied, of course, by changing the depth of the pool of metal in basin 20. Also, itis sometimes desirable to block off a portion of the perforations 26 where a marked reduction in metal `flow is demanded.

' Several factorsare important to the successful operation of the `process and construction of the apparatus.

`First, the degassing and purification treatment must be conducted in a confined space out` of contact with the air in the melting room. The atmosphere in the conlined space must contain aluminum chloride as the essential component for it is this compound which appears to create the condition prerequisite to escape of gas from andV reaction with impurities in the subdivided molten metal. If desiredthe aluminum chloride may be diluted with such bases as dry air, nitrogen or helium but in any case the aluminum chloride should not be less than the quantity necessary Ato effect degassingand purification. Where the aluminum chloride is generated by a reaction between `chlorine and aluminum no evidence has been observed of chlorine escaping from the treating chamber. It is possible that some chlorine may escape from thepool of metal but if this occurs, the `chlorine probably reacts with the metal droplets. d. If chlorineis` used,- only a relatively small amount is required `for producing the amount of aluminum chloride essential to the degassing and purification operation. As( a result the amount of metal consumed to from the chloride is so small asto be insignificant. Also, thedquantity of chlorine consumed to achieve substantial'degassing is extremely small as compared tothe priory conventional practice of `bubbling chlorine through Furthermore, it is possible to dilute the chlorine with ya gas such as dry air, nitrogen or helium but obviously enough chlorine must be supplied to generate an adequateamount ,of aluminum chloride. VAnother factor to be taken into account in the suocessful degassing and purification treatment is that of maintaining `a Iflow of` aluminum chloride through the treating chamber. In the absence of a flow of the chloride anydegassing action shortly comes to ahalt as the ability of the, chloride vapor to carryfaway the gas is quickly lost. Moreover, a static atmosphere does not provide the proper condition for the continuous treatment of a large volume of metal. Although the rate of flow of aluminum chloride is not highly critical, nevertheless for most degassing treatments Ait` is preferable to maintain a flow of 1 to 20 pounds per hour. In any given case itrwill be necessary for those skilled in the art to make minor adjustments,` in order to use the least amount of chlorine without sacrificing the benefits of theY invention;

`Instead of providing aluminum` chloride from an external'source, the solid `halide may be placed in the conned space either in contact with the molten metal or in close proximity thereto. `In both cases the heat from the molten metal serves to vaporize `the halide. To obtain a Acontinuous flow of, aluminum chloride through the space, itis necessary'to introduce the solid chloride l reither continuously or vlfrom time vto time, This may involve some operating difiiculties whichare'not present only when a gas vapor vis introduced into the c haniber.

The aluminum chloridey may be provided w in other waysthan those mentioned above. For example, decomposiable metal halides may be introduced into the treating chamber in solid or vapor form which react with the molten aluminum., Suchl halidesas the chlorides of zinc, boron or titanium maybe used. In addition, organic chlorides may be employed.

A third factor in the successful degassing and purif cation of aluminous metal is that of subdividing the molten metal into sufficiently small droplets or streams which will permit almost instantaneous escape of any n dissolved or sorbed gas and reaction with any sodium or calcium impurity. One very effective means of accomplishing this result is to pass metal through a perforated platey as villustrated in the accompanying figures. .1 Instead of forming droplets, the liquid metalA can be subdivided into very thin streams depending `upon the size ofthe hole and pressure exerted on :the metal in contactwith ,the plate. Care must be taken ito avoid making the perforations in the plate so small that they can easily Abecome clogged. It is also desirable` to space the, holes r'far enough apart to maintain the individualvlines of drops or streams of metal. The simplest way of passing the subdivided metal through the chamber is that of allowing the droplets or streams to descend undef-.the inuence of gravity. However, `it is also possible to project the metal into the chamber in the form of a spray and accomplish the same result. In .view of the simplicity of the foregoing gravity fiow method this is generally preferred in large scale operations.

Y Another factor is that of providing a suicient distance for the subdivided metal to travel through the aluminum chloride containing atmosphere. If the metal droplets or streams move at a high velocity, the distance through the atmosphere should be greater than where the velocity is low. A distance sufficient to accommodate gravitational velocity is ordinarily satisfactory. LWhile in theory a greater distance and longer exposure of the metal to the aluminum chloride might be more effective lin degassing the metal, this has not proved to be necessary in practical operation. Where the metal drops from a perforated plate a distance of 5 to 8 inches from the plate to the surface of the metal 'pool is adequate. It is to be understood, of course, that it is not harmful to employ a greater fall in this or similar forms of degassing units but this is not imperative from the lstandpoint of effective degassing. fall of 5 to 8 inches it has been possible to effectively treat as much as 30,000 pounds of metal per hour. An even higher flow rate canbe used if enough fresh aluminum chloride `is provided.

The size of the droplets or streams of metal are also important. For rapid and effective treatment there must be a large surface area per unit volume of metal. Generally speaking in a gravity system such as that shown in Figs. l and 3 the holes in the perforated plate shoulddbeof sufficient size to permita free ow ofthe metal without becoming clogged, and yet not so large as to prevent adequate exposureV of the metal to the atmosphere. It has been found that holes of a diameter between Y0.113 and 0.116 inch produce adequate sub-A division of the metal. In addition, the number of holes must be taken into account in treating a predetermined volume of metal within a specified period of time. It has been found, for example, that a plate 10 inches in diameter containing 100 holes 0.166 inch in diameter In units providing for a l 6 y for example, within the range of l250 to l400 Fl, 'rvit maybe higher.

The process and apparatus herein described is effective in degassing and purifying both aluminum and aluminum base alloys. Neither the aluminum chloride nor the chlorine have any appreciable effect upon the amount of most of the common alloying elements present in thealloys. If there is a reaction the reduction in quantity is too small to b e significant. If magnesium is present, however, it will react with both the chloride and chlorine to form magnesium chloride. In spite of the reaction the flow of metal through the unit is rapid enough that only a very small portion is affected, and generally, this is negligible in respect to the limits specified for the element in the alloy and hence none need be added to compensate for the loss.

The presence of the magnesium chloride in the treating chamber has been found to be distinctly beneficial in the degassing operation even though at first it might be regarded as an undesirable by-product. It appears to supplement the action of the aluminum chloride as the droplets or thin streams of metal pass through it on their way to the pool of metal in the bottom of the chamber. The liquid magnesium chloride, of course, floats on top of the molten `metal because of its much lower density. Also, for the same reason it does not become entrapped with the metal discharged from the chamber. After continued operation of the unit too much magnesium chloride may accumulate with the result that the operation must be stopped andthechloride be removed.k

As mentioned hereinabove, the treatment o f-molten aluminous metal with an aluminum chloride atmosphere notv only serves to degas the metal but it reduces any sodium or calcium impurity content of themolten metal.

While chlorine has been referred to as the gas for re acting with aluminum to generate aluminum chloride it is possible to employ it incombinaion with decomposable halides of elements which are to be` alloyed with aluminum. The halides are preferably vaporized and admixed `with the chlorine. It has been found that a small amount of boron or titanium can be conveniently added to an aluminous metal by using a mixture of chlorine and vaporous boron chloride or titanium chloride; The intraduction of these alloying elements shortly beforethe metal is cast appears to have a greater beneficial eect in refining the grain size of the resultant castings, than where the elements are added at an early vstage of melting.

The process and apparatus which have been described can be used in single or multiple stages to effect removal of gas and sodium and/or calcium from molten aluminousmetal. `The single stage operation lwhichy has been referred to liereinaboveis ordinarilyeffectivelin degassing aluminous metal melts. However, where the kgas content must be brought to a very low value or kit is particularly difficult to extract gas from the alloy, it may be desirable to use two units in tandem. .y The ksame considerations apply to ,the removal of sodium and c alcium impurities. ln the tandem arrangement the Vdischargefrom one unit flows through the second unit. `If desired, still ,another degas'sing unit ,could ,be added.v

1 ber is lined with any` suitable refractory such as alumina,

graphiteor silicon carbide which does not react with `molten aluminum orY aluminum chloride. It is desirable `that thefrefractory notonly resist attack by the molten `metal but that it be resistant to spalling during heating `and cooling. `The perforatedplate, if one is used, may

`be made` of a strong lasbestos board, silicon carbide,

`graphite or even cast iron. It is often necessary to discard theplate after` a period of use because the holes .become worn `and `hence a relatively cheap plate material should be used. Y

As to the design of the apparatus, the aluminum chloride may be introduced to the chamber through an opening `in the vertical wall Vor through a tube passing through the r perforated plateor other cover of the chamber. Likewise, `the aluminum chloride vapor may be withdrawn through suitable openings in the walls or cover `of the chamber. Also, it is to be understood that the metal may be withdrawn through a tap hole'in the `bottom of the chamber instead of through the discharge well shown Vin the `tigures. The means for supplying metal to the basin and ofreceiving itfrom theunit are conventional. n 4 `As examples of the `effectiveness of our method and apparatus the following examples may be cited.

In one series of tests `involving the simultaneous casting of four ingots of `an aluminum-2.5% magnesium- 0.25% chromium alloyin continuous ingot casting units the molten metal wassupplied from a melting furnace at a rate of 22,500 pounds per hour. A degassing unit of the ltypeillustrated in Figs. 3 and `i was placedr in the transfer lineto treat all of the metal coming from the ,furnace. Gaseus chlorinewwas introduced into the molten metal at the rate of 20 pounds per hour with the resultant production of both aluminum and` magnesium chloridesf A small amount of the latterwas removed from the `unit after each casting operation. YSamples of the metal were taken before it entered the degassing unit Aand after it has passed `throughthe unit for the purpose ofidetermining the `density of `the metal which in turn `indicates the gas content. Thevdensity `determinations -were made by thev modified Pfeiffer vacuum method described in the publication, Foseco Foundry Practice, No. 102, November 1950, pages 481 and 482 under a pressure of 2 to 3 mm. The densitiesof different runs of the alloy are givenbelow in Table I. f

Tamar- Denmarof rs1-2.5% Mfg-0.25% Cr alloy Density (g./cc.)

Run No.

` Before De- After Degassiug gassiug In a seconditest;involvingv casting the Ysame type of ingot but using an alloy having a nominal composition `of aluminum-5.6% zinc, 2.5% magnesium, 1.3% copper, 05%, @temine the fOllQWing alle were. @eine Density (g./cc.)

Run N0.

Before Dc- Atter Degassing gasslng The normal density of the gas-free alloy is 2.7 to 2.75 and hence it is apparent that the degassing treatment was highly effective in removing gas from the metal.

In a third test made on an .Al-0.7% magnesium-0.4% silicon alloy whichwas cast in tilt molds to produce extrusion ingots, 8 inchesin diameter Aand 27 inches long, the metal was treated at a rate of 4,000 pounds per hour with 5 pounds of chlorine per hour. Again, both alumi- 4num and magnesium chlorides were generated. The following density values were obtained under the foregoing conditions, as shown by the vacuum test method wherein the pressure was 2 to 3 mm.

Table 111.-Densiry of A1u.7% Mg-0.4% si alloy Density (g./cc.)

Run No.

Before D0- gassing After Degassng v v 1. 2 Vz.

Acontent of commercially pure aluminum and an alloy containing 2% magnesium.A In these tests 6,000 pounds per hour of metal were passed through-the degassing unit and 5 pounds of chlorine per hour were introduced into the molten metal to form aluminum chloride. The' results of the tests are given in Table IV.

Table I V.-Sodum content 0f metal Percent Sodium Metal Treated Before De- After Dey gassing gasslng Commercial Aluminum s 0. 005 0.002 Alf-2% Mg 0. 004 0. 002

Although the sodium was not completely removed by the degassing process the amount was considerably reduced. Such a reduction is important in cases where a `maximum sodium impurity value is specified for a given alloy. Itis thuspossible to obtain both a gas-free and `a low sodium content metal by the invention herein de- The effect of introducing boron trichloride along with gaseous chlorine is to be seen in the following two examples where commercially pure aluminum was treated. 4In the tirst` case a mixture of 7.9 Vpounds of chlorine and metal is given in Table V below.

Table V.-Addirn of boron to aluminum Percent Boron Run N o. n Before De- Aftery Degassing gassing 1 o. oo o. 002 2 0. 000 0. 004

It was noted that the metal treated with the mixture of chlorine and boron trichloride was thoroughly degassed. In addition, the boron trichloride reacted with the aluminum to lave a small quantity of boron. Such a quantity is of importance where grain refinement of the casting is desired.

Having thus described our invention and certain embodiments thereof, we claim:

l. The method of degassing `and purifying molten aluminous metal preliminary to casting the same comprising filling a confined space at substantially atmospheric pressure with an atmosphere containing aluminum chloride as the essential degassing component, introducing more aluminum chloride to said space while simultaneously withdrawing previously introduced aluminum chloride whereby a continuously changing atmosphere is provided in said space at substantially atmospheric pressure, subdividing the molten metal as it Venters the confined space containing said atmosphere, passing said subdivided liquid metal through the atmosphere whereby the gas content of the metal is reduced and the metal is purified without substantial change in the aluminum -content of the melt, collecting the treated liquid metal and thereafter discharging it while molten from said confined space.

2. The method of continuously degassing and purifying molten aluminous metal preliminary to casting the same comprising filling a confined space at substantially atmospheric pressure with a mixture of an inactive gas and aluminum chloride as the essential degassing component, introducing more of the gas and aluminum chloride to said space while simultaneously withdrawing previously introduced gas and aluminum chloride whereby a continuously changing atmosphere is provided in said space at substantially atmospheric pressure, subdividing the stream of molten metal at the top of said confined spacecontaining said gas and aluminum chloriderand allowing it to drop through the said gaseous mixture without substantial change in the aluminum content of the melt, collecting the subdivided liquid metal at the bottom of said confined space and thereafter discharging the treated liquid metal therefrom. n

3. The method of degassing and purifying molten aluminous metal preliminary to casting the same comprising filling a confined space at substantially atmospheric pressure with aluminum chloride vapor, introducing more aluminum chloride while simultaneously withdrawing Vp reviously introduced chloride vapor whereby a continuously changing atmosphere is provided in said confined Vspace at substantially vatmospheric pressure, subdividing the molten metal as it enters the confined space containing said aluminum chloride vapor, passing said subdivided liquid metal through the aluminum chloride vapor whereby the metal is degassed and purified without substantial change in the aluminum content of the melt, collecting the treated liquid metal and thereafter discharging it while molten from said confined space;

4. The method of simultaneously degassing and purifying an aluminous metal melt and adding an alloying lenient theretopby, decomposition'Y of a halide of said element preliminary to castingthe'alloy comprising'fillir'g a confined space at substantially atmospheric pressure with anratmosphere containing aluminum chloride as the essential degassing component and lthe vaporofa decomposable halide of the element to be added'to the melt, iri- Y space.

5. The method of simultaneously degassing and purifying an aluminous metal melt and adding boron thereto preliminary to casting the alloy comprising filling a confined space at substantially atmospheric pressure with an atmosphere consisting of aluminum chloride and boron trichloride vapors, introducing morev aluminum chloride and boron trichloride vapor while simultaneously withdrawing previously introduced aluminum chloride whereby a continuously changing atmosphere is provided in lsaid space at substantially atmospheric pressure, subdividing the molten metal as it enters the confined space ycontaining said atmosphere, passing said subdivided liquid metal through said atmosphere whereby the metal is degassed, purified and boron added thereto without substantial change in the aluminum content of the melt', collecting said treated liquid metal and thereafter discharging it while molten from said confined space.

6. The method of `degassing and purifying molten aluminous metal preliminary to casting the same comprising initially partially filling a confined space with sufficient molten metal to form a pool therein, introducing gaseous chlorine below the surface of said pool of metal whereby aluminum chloride in Vapor form is generated, filling said confined space above the pool of molten metal with an atmosphere at substantially atmospheric pressure containing said aluminum chloride as the essential degassing component, continuing the introduction of gaseous chlorine while simultaneously withdrawing aluminum chloride fromV said space whereby a continuously changing atmosphere is provided in said confined space at substantially atmospheric pressure, the rate of introduction of chlorine only being sufficient to form additional aluminum chloride to replace that withdrawn from said confined space, subdividing the remainder of the molten metal to be treated as it enters said confined space, passing said subdivided liquid metal through said flowing atmosphere without substantial change in the aluminum content of the melt, collecting said subdivided metal in said molten metal pool and thereafter discharging said treated liquid metal from said confined space.

7. The method of degassing and purifying molten aluminous metal preliminary to casting the same comprising initially partially filling a confined space with sufiicient molten metal to form a pool therein, introducing a gaseous mixture of chlorine and an inactive gas below the surface of said pool of metal whereby aluminum chloride in vapor form is generated, filling said confined space above said pool of molten metal with a mixture of aluminum chloride and said inactive gas at substantially atv mospheric pressure, continuing the introduction lof said 11 molten metal torbe treated as it enters said confined space, passingaid subdivided liquid metal through `said flow- `ing'atmosphere `without substantialchange in the aluminum content of the melt,.collecting said subdivided metal gaseous chlorine and decomposable metalhalide in vapor form `below the` surface of said pool of molten metal whereby aluminum chloride in vapor form is generated, andthe metal halide is decomposed leaving the metal portionalloyed with the melt, `filling said confined space above the pool of molten metal with an atmosphere at substantially atmospheric pressure `containing said aluminum chloride `as the essential degassing component, con- `tiuuingthe.introduction ofthe mixture of chlorine `and halide while simultaneously `withdrawing aluminum chloride `from said space whereby a continuously changing atmosphere is `providedkrin` said confined spaceltat substantially atmosphericpressure, the rate of 'introduction of chlorine and metal halide vapor only being sufficient to form additional aluminum chloride to substantially `replace that withdrawn from said confined space, subdividing the remainder of the molten metal to be treated as `it enters said confined space, `passing said subdivided liquid metal through said flowing atmosphere without substantial change `in the aluminum content of the melt, collecting said subdivided metal in a pool at the bottom of said confined space and thereafter discharging said treated liquid metal from-said confined space. f

9. The method of degassingand purifying molten aluminous metal `while adding boron thereto by decomposition of boron trichloride preliminary to casting the ,alloy comprising initially partially filling Va conned space withusufficient molten metal to form a pool therein, introducing a mixture` of gaseous chloride and .boron trichloride vaporbelow the surface of said pool of molten metal `whereby aluminum chloride inrvapor form is generated and the boron trichloride is decomposed leaving boron in said melt, filling `said confined space above the pool of molten metal with` an atmosphere at substantially atrnospheric pressure consisting ofsaidvaluminum chloride and any unreacted chlorine and boron trichloride, continuing `the introductionof chlorine and boron trichloride ,while simultaneously withdrawing aluminum chloride from said space ywhereby a continuously changing atmosphere is provided in said confined space at substantially` atmospheric` pressure, the rate of introduction of said chlorine and boron trichloride only being sufficient to form additional aluminum chloride to `substantially replacerthat withdrawn' from said confined space, subdividing the remainderof the molten metal tobe treated as itenters said confined space, passing said subdivided liquid metal through` said flowing atmosphere Withoutl substantial change in the aluminum content of the melt, collecting said subdivided `metal in a pool at the bottom of said `confined space and` thereafter discharging saidtreatedV liquid metal from saidtconfined space.

l0.` The method of degassing and purifying a molten aluminumbase alloy containing magnesium preliminary to casting the alloy comprising filling a confined space atsubstantially atmospheric pressure with anatmosphere containing aluminum chloride ras the essential degassing component, introducing more aluminum chloride :to `said `space while simultaneously withdrawing previouslyintrouduced aluminum. chloride whereby `a continuously chang- `ing atmosphere `is provided in said space at substantially atmospheric pressure, subdividing the molten metal as it `:enters said confined space, passing said subdivided liquid lmetal through said atmosphere without substantial change in the aluminum content of the melt, collecting said subdivided liquid metal in a pool at the bottom of said confined space,lforming a layer of molten magnesium chloride on top of the body of said collected liquid metal, and thereafter discharging said treated liquid metal from said confined space. Y

ll. The method of degassing and purifying a molten aluminum base alloy containing magnesium preliminary to casting the alloy comprising partially filling a confined space with sufficient molten metal to form a pool therein, introducingY gaseous chlorine below the surface of said pool whereby aluminum chloride vapor is generated and liquid magnesium chloride is formed, filling said confined space above the poolofmolten metal with an atmosphere at` substantially atmospheric pressure containing said aluminum chloride as the essential degassing component, continuing the introduction of gaseous chlorine while simultaneously withdrawing aluminum chloride from said space whereby a continuously changing atmosphere is provided in said confined space at substantially atmospheric pressure, the rate of introduction of chlorine only being sufiicient to form additional aluminum chloride without substantial change in the aluminum content of the melt to replace that withdrawn from said confined space and to form additional magnesium chloride, forming a layer of molten magnesium chloride on top of said pool of metal subdividing the remainder ofthe molten alloy `to be treated as it enters said confined space, passing the prising a metal treating chamber having atop, side walls and a floor, the top consisting of a shallow open top receptacle for receiving the molten metal and dispersive .means in the base of said receptacle for forming droplets ber, means for introducing gas or vapor to said chamber at not less than atmospheric pressure and means for receiving said gas or vapor discharged from said chamber.

1,3. ApparatusV for degassing and purifying molten aluminous metal at substantially atmospheric pressure comprisinga metal treating chamber having a top, side walls and a floor, the top consisting of a shallow open top receptacleifor receiving the molten metal and dispersive means in the base of said receptaclefor forming droplets Vor thin streams of molten metal, said receptacle being removable but scalable to the side walls of said chamber, the `floor of said chamber providing acomplete bottom closure thereof, a discharge well juxtaposed laterally of said chamber andicommunicating` therewith through at least one A.aperture in the side wall adjacent the bottom thereof whereby the molten metal collected in the lower portion of thechamber flows into the discharge well and fills it to substantially the same level as that in the chamber, an openin'gin the sidewall of the chamber above the level of the pool of molten metal accumulating therein and communicating with means for introducing gas or `vapor at a pressure not less than atmospheric pressure and a second opening in the side wall above the level of the molten metal communicating with condensing means for receiving said -gas or vapor.

14. Apparatus for degassing and purifying molten aluminous metal at substantially atmospheric pressure comprising a metal treating` chamber having a top, side Walls and a oor, the top consisting of a shallow open top receptacle for receiving the molten metal and dispersive means in the base of said receptacle for forming droplets or then streams of molten metal, said receptacle being removable but scalable to the side Walls of said chamber, the loor of said chamber providing a complete bottom closure of the -base thereof, a discharge well juxtaposed laterally of said chamber and communicating therewith through at least one aperture in the side wall adjacent the bottom thereof whereby the molten metal collected in the lower portion of the chamber flows into the discharge well and fills it to substantially the same level as that in the chamber, a tube entering the treating chamber and terminating adjacent the oor thereof, said tube being adapted to pass chlorine into the pool of molten metal accumulating in the bottom portion ofthe treating chamber and an opening in the upper portion of the chamber connected to a condenser for receiving aluminum chloride.

15. Apparatus for degassing and purifying molten aluminous metal at substantially atmospheric pressure comprising a metal treating chamber having a top, side walls and a floor, the top consisting of a shallow open top basin for receiving the molten metal, the base of said basin being perforated to discharge the metal in the form of droplets or thin streams, said basin being removable but sealable to the side wall-sof said chamber, the oor of said chamber providing a complete bottom closure there- CII of, a discharge well juxtaposed laterally of said chamber, the floor of which is an extension of the chamber oor, at least one aperture at the base of the side wall for discharge of the molten metal from the chamber to the discharge well, Esaid aperture being of such size that it allows a free tlow of metal therethrough and extends to a height such that it is completely covered by the molten metal accumulating in the chamber and discharge well, an opening in the wall of said chamber above the level of the pool of molten metal accumulating therein connected to pressure source of gas or vapor capable of introducing said gas or vapor into the chamber at not less than atmospheric pressure, and a second opening in the side Wall of said chamber also above the level of the molten metal pool connected to a condenser for receiving said gas or vapor.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No., 2,840,463, June 24, 1958 Philip To Stroup et al.,

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below..

Column 2, line 23, after "givem insert serving n; column 3, lines 14 and 15, for "modifield" read L== modified m; oolumn A, line 3l, for "bases" read -kgases ma; line 44, for #fromn read form m; column 5, line 65j, for n0,116? read m 0,166 n; column '7, line 38, for Gaseus read -l Gaseous uw; column 9, line 21, for lllave" read 4leave m; column l2, line 2, strike out "liquidf oolumn 13, line 4, for "then" read thin M,

Signed and sealed this 26th day of August 1958.,

(SEAL) Attest:

KAEEEIAMEE ROBERT C. WATSON Attesting Ocer Commissioner of Patents

Claims

1. THE METHOD OF DEGASSING AND PURIFYING MOLTEN ALUMINOUS METAL PRELIMINARY TO CASTING THE SAME COMPRISING FILLING A CONFINED SPACE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE WITH AN ATMOSPHERE CONTAINING ALUMIUM CHLORIDE AS THE ESSENTIAL DEGASSING COMPONENT, INTRODUCING MORE ALUMINUM CHLORIDE TO SAID SPACE WHILE SIMULTANEOUSLY WITHDRAWING PREVIOUSLY INTRODUCED ALUMINUM CHLORIDE WHEREBY A CONTINUOUSLY CHANGING ATMOSPHERE IS PROVIDED IN SAID SPACE AT SUBSTANTIALLY ATMOSPHERIC IS PROVIDED DIVIDING THE MOLTEN METAL AS IT ENTERS THE CONFINED SPACE CONTAINING SAID ATMOSPHERE, PASSING SAID SUBDIVIDED LIQUID METAL THROUGH THE ATMOSPHERE WHEREBY THE GAS CONTENT OF THE METAL IS REDUCED AND THE METAL IS PURIFIED WITHOUT SUBSTANTIAL CHANGE IN THE ALUMINUM CONTENT OF THE MELT, COLLECTING THE TREATED LIQUID METAL AND THEREAFTER DISCHARGING IT WHILE MOLTEN FROM SAID CONFINED SPACE.