US1896201A - Process of separating oxides and gases from molten aluminum and aluminium alloys - Google Patents

Description

. 7, 1933. R. STERNER-RAINER 0 PROCESS OF SEPARATING OXIDES AND GASES FROM MOLTEN ALUMINIUM AND ALUMINIUM ALLOYS Filed Jan. 14, 1932 Pure Hyena Comprc'sl' 7 a Waz'de orllecomposablz Chloride erda Bzflu orc'de I lmlenzorl m% o p at? Patented Feb. 7, 1933 I UNITED mm PATENT oFrIcr-i ROLAND s'ranxna-nmu, OI HEILBBONH-ON-TIIE-N Im', onmmr, ABIIGI'OBTQ mm LUBOI: MBPOB-LTION, O! NEW YORK, Y A CORPORATION 01 m YORK rnocrss or smm'rme oxmlis m easns' m1 tom-air ALUIINIUI m ummmnr Annexe 7 Application and January 14,1932, sex-m Io.

Various reports have been published on attempts aiming at separating gases and oxides from aluminium alloys y passing a current of chlorine gas throu h the metal while in the molten state. It as also been roposed to erform the purifying process By means 0 chlorides, such as boron trichloride, vanadium chloride, titanium tetra-' chloride. While the treatment with chlorine in many cases was not successful, the chlorides named are so expensive that they cannot be used per se in practice. Chloride of zinc which has been used for purifying molten aluminium for a long time past has remained the most suitable chloride and the only one in practical use up to the present time. Yet the purification by means of zinc chloride is not entirely perfect. Moreover it cannot be used for alloys which "are to remain free from zinc, for instance silumin '(Si 13%, Al remainder), piston alloys, or aluminium alloys resisting corrosion, not only because by tie treatment with zinc chloride these metals will be contaminated with zinc, but especially because the alloy recovered from the residues contains so much zinc that it cannot be used for-the same purpose.

The object of the present invention is a process for separating gases as well as oxides from aluminium and aluminium alloys while in the molten state. For carrying on this process, those chlorides are added to the metal bath that vaporize at or shortly above the melting point of aluminium or the aluminium alloys, for instance, at temperatures from GOO-800. A portion of these chlorides suffer a thermal decompositionat these temperatures, the compound v(1C1, for instance decomposing into gaseous chlorine on the one hand and carbon on the other hand. The selection of the chloride is therefore to be made with the idea that: gaseous products will result, since the aim of the process requires that bubbles be formed in the melt by 680,085, and in Germany January 17, 1981.

the gases produced, so that in this way the impurities contained in the melt and in particular the unmelted impurities are removed. It has been found, however, that the treatment with chlorides alone which has already been proposed, is not suflicient to produce a comp ete removal of the impurities contained in t e melt and particularly of any gases which may be dissolved'in the melt. For this purpose, the invention provides for the combination of the addition of chlorides with the addition of volatile fluorides.- Suitable volatile fluorides are bifluoride of alkali metals and ammonium bifluoride. If a mixture of these substances, i. e., volatile or decom sable chlorides and volatile fluorides oft e group consisting of alkali metal and ammonium ifluorides are brou ht to ether in the melt, the result is a puri ed an gasfree metal which when cast yields dense castings. In this manner a urification of the molten metal can easily be attained to such an extent, that perfect castings can be made at only small expenditures. Of the chlorides which answer these requirements, first of all those mentionedabove are to be considered, i. e. boron trichloride, vanadium chloride, titanium tetrachloride, and zinc chloride.

Also carbon tetrachloride, antimony pentachloride, silicon chloride, manganous chloride and chlorides of tin and iron may be applied for carrying out the process according to the invention. Most of these chlorides are known to have been used separately for the purpose of purifying metals, particularly for separating gases from molten aluminium; however the present invention does not relate to using such chlorides separately, but to u'sing-themin combination with alkali bifluorides.

Carbon tetrachloride was found to be suitable agent for separatingv oxides from the molten metals; it was however found, 00

that, in using this agent a significant separation of gases only took place, if there was taken a large amount, i. e. 415 cm.'/kg. of metal treated or if the metal was treated a longer time for instance 20 mintues .with this material. If however carbon tetrachloride is used jointly with alkali bifluoride, especially immersing-bell, until the reaction had ceased.

with ammonium-bifluoride, it will be found that both gases and oxides can be completely separated even from a highly contaminated and oxidized melt of aluminium in a short time with a small amount of the flux. In

place of carbon tetrachloride, antimony pentachloride or manganous chloride or an analogous compound of chlorine may be used with almost equally good success. These agents too, if used separately, effectuate up to a certain degree a separation of oxides, but only if the are used jointly with alkali bifluoride wi l a good separation of both oxides and gases be attained.

The action of the aforesaid mixtures upon the metallic melts will however be considerably increased, if silicon chloride is added to these mixtures. Though silicon chloride alone has ave strong purifying and degasifying effect-,1t evolves by its action hydrochloric acid fumes in such a quantity, that, when used by itself, it will raise practical difliculties. If however it is added to the aforesaid a cuts the action of the latter can be increase by the silicon chloride, without hydrochloric acid vapours being evolved to such an extent as to be noxious.

The small amount of purifying agents required in carrying out the process according to the invention deserves particular notice.

To prove this, a few examples may be disparticular case was pressed into the molten metal at the same temperature by means of an About 200-300 g. of metal were treated in each case. Of the total of this treated metal asample of 100 g. was at once allowed to cool down in vacuo in a pre-heated crucible, while another sample was taken 10 minutes later, during which waiting-time the melt in the furnace was constantly kept up at its temperature. This second sample was then 'metal. 4

The following results were obtained:

Comparative teats carried out with K. S. Seawateralloy of the oompoemon Ha 2-87,, Mar 1.3%, St 0.2%. At remainder at 850' 0. temperature of treatment namlm ranoeot No. Aaentuaed Time the Great number of abt. W7 0! the vm The name Without treatment Wlthout treatment 0.1 carbon tetrachlo- 0.1 carbm tetrachlo- 1% aiitlmmy pmtlehlo- 1% ahtlmany pentachloli lddmm blfluorldo..

1% sodium blfluorlde..

At moo.

AM 10 min. At once. 10

After 10 8 min. At once.

After 10 6 min. At once. 6

After 10 The mln. At once.

After 10 min.

The results of these tests unmistakably show, that in employing the proposed agents individually, the effect is far inferior'to that attained by usin a mixture of carbon tetrachloride and so ium bifluoride. Naturally the molten metals are, in practice, not treated in vacuo. Yet these tests show, that even under such severe conditions it is possible to attain the positive absence of pores, and therefore the positive absence of gas in the molten metal by treatment in accordance with the invention.

The small amount of the agent required allows now, also to employ in practice those chlorides hitherto considered to be too expensive, such as vanadium chloride, boron trichloride and titanium tetrachloride. In doing this the particular advantage is attained, that a minute quantity of thetitanium, or the vanadium contained in the salt forms an allo with the aluminium, causing a finer grain 1n the casting. Simultaneously the MS]! of an absolute purification of the treated metal causing coarse crystals in the castings is hereby avoided.

The finally mentioned chlorides of iron, tin, or zinc, naturally may only be employed in such cases, in which the entrance of zinc, tin, or iron into the alloy are of no detrimental influence. When for example it is intended to purify 'an aluminium-sandcasting alloy containing zinc one-may use zinc chloride in admixture with carbon tetrachloride or antiinony pentachloride and alkalibifluorid'e, because the individual action of zinc chloride is not so intensive as that of its mixtures mentioned. Herewith however an appreciable savin in the working expenses is attained, zinc c oride being obtainable at a low price.

A suitable re ration for -a bath of molten alu iiiinium only is composed as follows:

This preparation is filled into an aluminof the ha is to be treated, and is charged with one tube g ium tube of about 20-25 g. capacity. The metal which ma .have been considerably overheated is coo ed down to'750" C.. The

,immersin device is chosen to'suit the shape containing the molten metal which perevery 20 kg. of metal. It is then immersed into the metal bath and removed when the reaction has ceased. During the sub- 7 sequent waiting time of 10 minutes the temperature should drop to 730 C. Then the dross is skimmed off and' the metal is taken out of the furnace and cast. i

For an alloy of the composition Si 13% Al 23 remainder the following mixture has been found suitable:

' Per cent Carbon tetrachloride 50 Ammonium bifluoride 10 Boron trichloride 5 Antimony pentachloride 10 Manganous chloride Infusorial earth; 10

German alloy is suitably purified with the following mixture:

' Percent Carbon tetrachloride 50 Ammonium bifluoride 10 Zincchloride 4 Infusorial earth 10 For American alloy containing Cu 8% Al remainder, Y-alloy containing Cu 4%, N1 2%, Ng 1.5%, A1 remainder, and similar al loys, for example, the following mixture may be used:

Ifthe separation ofgases and oxides is intended for example'from an allo of alumin- 5 ium containing about 0.5% antimony, 1.4%

manganese, 2% magnesium, so as to attain a good castibility, it is sufiicient to use 1 to 2 per thousand of the weight of the alloy of the above named salts.

7 The chlorides which occur in the liquid cause the latter can be ground to an exceed state are preferably allowedto be soaked up by inert material before'they are applied. Besides charcoal powder, infusorial earth is particularly suitable for this purpose, be-

l en-cent in ly fine wder and possesses a good abso ptivity lf the chlorides are not in the li uid state infusorial earth is also a suitable admixture, because it has a saving efiect upon the consumption of material, causing the more volatile chlorides not tobe released before a certain time of their action has elapsed. Therefore the action u n the molten metal is more intensive and on r lasting, if the chlorides are mixed with infusorial earth or soaked into it. Similar to the action of infusorial earth, though not quite as favourable, is that of asbestos wool.

Since a satisfactory effect of the purifying material can only be attained if the chlorine as liberated or formed from the chlorides 18 caused to penetrate into the whole mass of the molten metal, it has been found desirable to use a special device for introduoin the material into the molten metal. This evice is shown in the accompanying drawin In the fi ure (1) denotes a semicircular be provide with holes (2) at the side to allow the escape of gases, and in the centre of it a pointed plungin rod (3). The point 34) of the plunging rot? is provided wi h bear s 5 to allow a firm fastening of the shell 7 which is preferably an aluminium tube, fil ed with the purifying material (6). The other end of the plun ng rod is bent at a right angle and provi ed with the handle (8) so as to allow the workmen calmly and steadily to insert the purifying material without being spattered or molested by the rising fumes.

The bell which is firmly connected with the plunging rod serves the purpose of preventing the chemicals from rising u and of allowing the. evolved gases to be istributed in the molten metal and to escape.

In case of metal baths being shallow, it is advisable to unite a plurality of these bells with each other, forming an aggregate which is simultaneously charged and introduced into the metal.

After the reaction has taken place and after a short waiting-time the slags are taken OK and the metal maybe cast.

I claim:

1. A process for removing oxides and gases from molten aluminium and aluminium alloys which com rises treating the molten metal with a purifying agent consisting of a chloride which produces a gaseous product at the temperature of treatment and a volatile fluoride of the group consisting of alkali 3. A process for removing oxides and gases from molten aluminium and alumimum alloys which comprises treating the molten metal with a purifying aglentpf the group consisting of carbon tetrac loride, antimony pentachloride, manganous chloride, zinc chloride and silicon tetrachloride and ammonium bifluoride.

at the temperature of treatment and a volatilefluoride of the group consisting of alkali metal and ammonium bifluorides together with a chloride of ametal which alloys with the molten metal causing a finer grain in the cast metal.

6. A process for removing oxides and gases from molten aluminium and aluminium alloys which comprises treating the molten metal with a urifying agent consisting of a chloride which produces a gaseous product at the temperature of treatment and a volatile fluoride of the group consisting of alkali metal. and ammonium bifluorides together with a chloride of a metal selected from the group consistin of vanadium and titanium.

7. A process or removing oxides and gases from molten aluminium and aluminium alloys which comprises treating the molten metal with a urifying agent consisting of carbon tetrachlhride, a chloride of the group consisting of antimon pentachloride, manganous chloride, zinc c loride and silicon tetrachloride and a volatile fluoride of the group consisting of alkali metal and ammonium b1- 8. A process for removing oxidesand gases from molten aluminum and aluminum alloys which comprises treating the molten -metal with a purifying agent consistin of a chloride which produces a gaseous pr uct at the temperature of treatment and a volatile fluoride of the grou consisting of alkali metal and ammonium-bi uorides, said purifying agent being associated with an inert absorptlve material.

9. A process for removing oxides and gasesfrom molten aluminium and aluminium alloys which com rises treating the molten metal with a uri ying agent consisting of a chloride whic produces a gaseous product.

at the temperature of treatment and a volatile fluoride of the group consisting of alkali metal and ammonium bifluorides, said purifying agent being associated with infusorial' 10. A composition for removing I oxides and gases from molten aluminium and aluminium alloys comprising-a chloride which produces a gaseous product at the temperature of the molten metal and a volatile fluo-' ride of the group consisting of alkali metal chloride, antimony pentac oride, man anous chloride, zinc chloride, silicon tetrach oride, and ammonium bifluoride.

13. A composition for removing oxides and gases from molten aluminium and aluminium alloys comprising carbon tetrachloride and ammonium bifluoride.

.14.- A composition for removing oxides and gases from molten aluminium and aluminium alloys comprising a chloride which produces a gaseous product at the temperature of the molten metal and a volatile fluoride of the grou consisting of alkali metal and ammonium ifluorides, together with a chloride of a metal which alloys with the molten metal causing a finer grain in the cast metal.

15. A composition for removing oxides and gases from molten aluminium and aluminium alloys comprising a chloride which produces a gaseous product at the temperature of the molten metal and a volatile fluoride of the group consisting of alkali metal and ammonium bifluorides, together with a chloride of a metal selected from the group consisting'of vanadium and titanium.

' 16. A composition for removing oxides and gases from molten aluminium and aluminium alloys comprising carbon tetrachloride, a chloride of the group consisting of antimony pentachloride, manganous chloride, zinc chloride and silicon tetrachloride, and a volatile fluoride of the group consistof alkali metal and ammonium bifluor- 1 es.

17. A composition for removing oxides and gases from molten aluminium and aluminium alloys comprising a chloride which produces a gaseous product at the temperature of the molten metal, and a volatile fluoride of the group consisting of alkali metal and ammonium bifluorides, said purifying agent being associated with an inert absorptive material.

18. A composition for removing oxides and gases from molten aluminium and aluminium alloys comprising a chloride which produces a gaseous product at the temperature of the molten metal, and a volatile fluoride of the group consisting of alkali metal and ammonium bifluorides, said purifying agent being associated with infusorial earth.

In testimony whereof, I afiix my signature.

ROLAND STERNER-RAINER.

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