US2638630A - Production of metal powder - Google Patents

Description

Mgy 19, 1953 H. A GOLWYNNE PRODUCTION oF METAL POWDER 5 Sheets- Sheet 1 Filed Sept. 29, 1949 wm @k INVENTOR.

HENRY A. GOLWYNNE 'BY 17 '2, FTamwm ATTORNEYS N@ ww May 19, 1953 H. A. GOLWYNNE 2,638,630

PRODUCTION oF METAL POWDER Filed sept. 29, 1949 .5 srie'c-sheet 2 ATTORNEYS May 19, 1953 H. A. GOLWYNNE PRODUCTION OF METAL POWDER 5 Sheets-Sheet 3 Filed sept.- 29. 194s INVENTOR. HENRY A. GOLWYNNE mffmmmwmmw aw! Hull ATTORNEYS May 19, 1953 H, A. GoLwYNNE PRODUCTION oF METALv POWDER 5v Sheets-Sheet 4 Filed Sept. 29. 1949 'mvo A QN INVENTOR.

HENRY A. GoLwYNNE ATTORNEYS May 19;'1953 H. A. GoLwYNNE A2,638,630

PRoDUcTIoN oF METAL POWDER Filed Sept. 29AI 1949 5 Sheets-Sheet 5 INVENTOR. HENRY A. GLWYNNE BY 'EM/m, fammi/fm Pannmm ATTORNEYS Patented May 19, 1953 UNITED @PATENT o rfi-ICE "PRODUCTION "DF METAL yPOWDER Henryuolwynne, New York, N. Y.

Allplcaatitm September 29, 1949, Serial No.'11'8,621

20 Claims. -1

This invention relates 'to vthe production of metal powders and has forits object improvements inthe methodof producingmetalpowder. ,Amongthe methods of producing'metal; powder is that of atomizing'molten metal with ahlast of gas, freezing the *atomized 'metal-intofnely divided solid particles,'and'recovering the resulting metal powder. 'Most metals'have a 'marked kafiinity "for `.oxygen and nitrogen at elevated temperatures. metal powder from molten metal'byatomization with a gas because'the 'oxides and nitrides'formed b5/'the reaction of oxygen andnitrogenin'the gas with the atomizedVA metal tend'to vform at "or near and to contact aniithen-to'adhere'to the highly heated atomizing'nozzle*thus clogging or otherwise impairingiitsusefulness `Suchnotzles usually have a central outlet or discharge openin'through Whichthemolten'metal is 'forced and usually aiplurality ofports through which; streams of thegasare forced against the 'molten metal discharged from the outlet. Although a igreat deal of the oxide and nitride finds itsvvay into the vmetal vpowderproduced`y appreciable amounts contact the hot nozzle-and adhereltheretoasian Yaccretion orincrustation. 'This builds up around the ports, particularly, and even-the outlet, eventually, -so that'theybecoine smaller and smaller and clogged eventually. Asthis takes place'the size of the molten metal andgasstreamsisgrad- ,l

ually reduced, thus altering radically the conditions 4under -which the powder is Iformed. This aiects theparticle size-ofthe product as well'as 'the eciency of theoperation. The nozzles Imust 'be removed, repaired -or 'replaced fvrequernly.l

In the earlier attempts toprodnce'metallpowder by atomization, the gasemployed'for atomization andin the atomizing-chamber vwas air or steam. 4Air is highly oxidizing and nitrid-ing andstearn mildly oxidizing. lThey vhave been `discarded favor of sc-called inertor non-reacting gases, As we shall seeinertgases available commercially in quantities are not-truly inert,and\even-fi truly inert ether oxidizing andnitriding influences are inherent inthe operation. Inanyeventvarious g proposals'haveloeen advanced to atomize molten metal with `and in 4the presence of such inert f or non-reactiveatmospheres. For example, aatrickle Orstrearn-of molten-metal iss-blasted in'aeharnt-v bei; filled with inert gasythefatomized -metalvis f rozen linto 'nely divided solid particles and the resulting metal powder permitted to sett-leiat-thfe vbottom of `the chamber jfrom l which it isremoved periodically. Another-proposalis to spraymolten magnesium intoa- 'ohamberilled with cold Initro- This makes it diflicult to 'produce riods.

gen gas deemed to be comparatively inert to the magnesium. Magnesium, however, has a high affinity i or nitrogen, when either or both is heated, and itis'impossible to spray molten magnesium, which is necessarily highly heated, insuch a man- Iier W-ithout providing a zone, even though restricted in extent, conducive to the formation of an objectionable amount of magnesium nitride. As before the powder is removed periodically from the'bottom of the chamber.

Investigators in this el'd have been greatly troubled with the problem of producing a suinciently inert or non-reactive atmosphere in which to atomize the molten metal. As manufactured, the gas itself, for example helium, argon, etc., is not entirely inertbecause it usually contains a certain amount of impurities such as oxygen and. nitrogen. The inert gas must'be conducted into the chamber in which the molten metal is to be atomized and the powder formed. Since the 'chamberis initially lled with air, the air'n'iust be flushed out, or otherwise be'replaced, by the inert gas. `Sncegases, mix readily, the inert gas and-air promptly interni-ix. Inv spite of careful `precautions a residuum of air remains, and since the air isrich in :oxygen and nitrogen, the atmosphere as a Whole in the chamber isfcontami- Ihated to that extent.

The atomized metal reacts readily with the oxygen and nitrogen. vOxide and nitride incrustations thenforin on the nozzle -used toatomize the molten metal.

The discharge ports of the nozaflev are soon cloggedand the operation must Vloe stopped to clean or replace the nozzle.

--method of producing metal powder by atomizing molten metal witha :blast of'inert gas, metal powders may be 'produced steadily over prolongedV pe- 'Meta'l powders substantially uniform in quality land in yparticle size may be obtained. The operation maybe so conducted as to obtain metal `powders graded generally as to particle 4Inaccordance with oneaspect of the-invention, a confined circulatory system-including molten metal atomizing, metal powder forming and powder separatingzzones-is.lled initially with inert gas under pressurehigher than atmospheric to prevent. ingress ofvoutsideair. rilhe inert gas in the .system is puried with respect to such impurities asrvoxygenandnitrogen, after which-nieta 'powder is produced therein.

Air initially present in the circulatory system is replaced for the most part with inert gas. The inert gas is introduced in the system at a high point and the undesired air containing oxygen and nitrogen is withdrawn at a low point. The oxygen and nitrogen in the inert gas and in the residue of air remaining with the inert gas in the system are then eliminated.

The purification operation is advantageously conducted by causing the oxygen and nitrogen impurities in the gas to react with heated metal particles to form the oxide and nitride 'of the metal. Metal powder of the kind to be produced, or previously produced, is preferably employed because it is at hand. The gas may be withdrawn temporarily from the system, purified, and then returned to the system; the entire operation being a circulatory or cyclical 'one until all of the gas in the system has been in Contact with the heated metal for puriiication and has been returned to the system.

According to another aspect of the invention, the molten metal atomizing, metal powder forming and powder separating steps are conducted in the confined circulatory system filled with the purified inert gas as the gas is continuously circulated therethrough under pressure vhigher than atmospheric to prevent ingress of outside air. This is advantageously accomplished by blasting a nne stream of the molten metal circumferentially with a plurality of streams of heated inert gas in the metal powder forming zone filled with the circulating inert gas, the circulating gas being sufiiciently low in temperature promptly to freeze the atomized metal into nely divided particles. The circulating inert gas with metal powder suspended therein is passed from the powder forming zone to a powder-gas separating zone; metal powder is separated from the inert gas; the inert gas remains in the system to be'reused; and the metal powder so separated is withdrawn from the system.

To Iobtain the plurality of iine streams of inert gas to atomize the molten metal, it is advantageous to withdraw temporarily some of the inert gas from the systemy place it under substantial positive pressure, and return it to the system by atomizing the molten metal. The gas so withdrawn from the system is preferably preheated by placing it in heat-interchange relation- I ship with the body of molten metal to be atomized. The fine streams of heated inert gas are then forced under high pressure into the streamrof molten metal thus breaking it up into a myriad of fine droplets which are then enveloped in the cooler inert gas circulating through the system and frozen into solid particles. If cool gas were used to atomize the molten metal, at least in the atomizers conventionally employed, molten metal would tend to freeze and adhere to the discharge tip.

Another highly advantageous expedient is to place the source or body of molten metal to be atomized under substantial pressure with the inert gas so that molten metal may be forced as a stream into the atomizing zone. To this end some of the inert gas is withdrawn from the system, conducted lunder substantial positive `pressure to a confined space above the body of molten metal and used to force a stream of the molten metal to the atomizing zone.

In a presently preferred practice of the invention, the circulating inert gas with metal powder suspended therein is passed from the powder forming zone through a plurality of powder-gas separating zones, metal powder being separated from the inert gas in each zone and the metal powder so separated is withdrawn from the system at each zone.

The separation of the metal powder from the gas may be conducted in various ways. At the present time the gas with metal powder suspended therein is passed successively through a series of -cyclones so that the separation of the powder may take place by dry precipitation. This has the advantage that powder of graded particle size may be selectively separated in each cyclone; for example, ne particles in the iirst cyclone, finer particles in the next cyclone, and so on. The residue of dust remaining in the gas leaving the last cyclone is advantageously thrown down by wet precipitation, suc'h as by passing the gas througha bag lter wet with oil. As an additional precaution it is desirable to use a filter in the line going to the compressor.

As already indicated, improvements in the apparatus employed are necessary to obtain the advantages of the method. The apparatus for producing the metal powder comprises a conned circulatory system adapted to be filled with gas under pressure higher than atmospheric; a gasometer to hold surplus gas and to take care of expansion and contraction of the gas; a chamber for atomizing molten metal and chilling atomized metal into powder; a -blower for circulating the gas around the system; and a separator for separating the powder from the gas.

An atomizer for the molten metal extends at its discharge end into the chamber. The atomizer in turn connects with the bottom portion of a melting furnace and means are provided for exerting pressure inside the furnace so that molten metal at the bottom may be forced through the atomizer into the chamber. This pressure is preferably obtained with a compressor connected on the inlet side with the system for the withdrawal of some gas and on the outlet side with the interior of the melting furnace to place a layer of gas over the body of molten metal under sufcient pressure to force molten metal through the atomizer. The compressor preferably connects on the inlet side with the system beyond the place or places where the powder is separated from the gas so that substantially powder-free .gas may be passed by the compressor to the furnace.

Another advantageous arrangement is one adapted to use some of the gas in the system for atomizing the molten-metal. To this end the compressor, as before, connects on the inlet side with the system for the withdrawal of some gas and on the outlet side with a conduit in heatinterchange relationship with the furnace for melting the metal to be atomized, the discharge end of the conduit connecting with the atomizer for the molten metal so that the lmolten metal discharged from the atomizer may be blasted with gas preheated by the furnace. Also, as just described above for the furnace, the compressor preferably connects on the inlet side with the system 4beyond the place or places where the powder is separated from the gas so that substantially powder-free gas may be passed bythe compressor through the preheating conduit to the atomizer for atomizing the moltenmetal.

A combination of the features just described is highly desirable in practice. In other words, the compressor connects on its outlet side with the interior of the furnace as Well as with the atomizer, so that molten metal in the furnace may .be placed underpressure :by the as .aand thus be forced Afrom the furnace` .toiandthroueh the atomizerandso that thefinolten metal may be atomized by the gas from the compressor when itisy dischargedinto therchamber. The compressor .connects on the inlet Side with the System beyond the place where the powder :isseparated from the gas .so vthat substantially powder-.free gas may bepassed by the compressor to; the fur nace and to the .atomizer.

The invention is .adapted for the .production of a variety of-metal powders. The. metal to be converted into powderinay.be'essentially a Drimary metal -or a combination :of metals, `such as-alloys. As a practicalimatter .one-,of `.thedetermining factors-is, ofcourse, .the melting point of the metal. Thehigher `the melting point, .the more arethe diiiicultiesI encountered;-.partieularly as regards heating and wear vand `tear of the equipment. The invention .is .being .currently practiced in .the productionv otmagnesiurnpowder, and powders of alloys of magnesium, more particularly alloysof magnesium andfaluminum.

While various gases inert to thametal to be converted to powder may be used-asa practical matter the choice sinimers .down toone readily available at a relativelyilow cost. Forthis reason helium is now being used. Otherfinertgases, such as argon could,of course, beernployed.

The practice .of the ,invent-ion as described results in anunusuallystable and .eicient product. The .metal powder may be .stored without appearingtolose its eiectveness inzuse. In the case of magnesium, the .powder .remains highly effective after storage. .This is not true of conventional magnesiumpow'ders such as .are produced by grinding or attritional means. This may be due to the fact that such powders are produced in a relatively hot State due to the grinding or attritionalifrction, which vcausesthe exposed-surfaces of the particles'to react'with the surrounding gases and thus,"for .eXamplefto take on a coating'iof oxide. 'On the otherhand powder 'of kthe present invention 'is produced in a relatively cool atmosphere due to the large volumes of cool circulating inert gas=that envelop and chill the particlespromptly on formation, and carry them awaytfrom the atomizing `and powder forming'zones. There-islittle or no opportunity for an oxide'coating to form --on-the individual particles.

linl addition the metal powder 4of the invention is highly `activated thusmalrin-g lit -Very eiiicient in use. rThis appears tolbe due-totheenormous amount of surface 'area-offered by-a body of the product, far in lexcess of that lcaf-conventional metal powders. Metal vpowders as heretofore made aresolid andltherefore expose only an exterior surface. The powder-of'theinvention, on the other hand, is in the vform ofy hollow spherical particles. The interior surfaces andreXteriOr surfaces together provide an .enormous -amount of available surface for use. This is particularly important, for; example, in. theucase of magnesium powder used for flares. .Due to 'the .enormous amount` of available surface areaithelmagnesium powdermay be .burned inahighly intense instantaneous'. flash.

.Itis at present believed .that-.the particles are formedvv as the resultoi the marmer viirvrlu'on the inert gases .are employed. .As noted above, .a portion'of the ineringas is .withdrawn-vfromithe circulatory system and conductedto and over .the body of mol-ten metalzinfthe furnaceunderrsub- .stantialpositivepressure; in .order to. force molten metal from the urnace to .theiatomizen result of this step the molten metal becomes-'Saburatedzwith Y.the .feas fat :the prevailing [temperalturciand :pressure :in fthe :melting iurnace, Qausing a;.certain=.-a1nount.zoffthe.: sas tof go intofsolution in ithe.. molten imetal. 'When v.the molten metall is .fatomized .the resulting-:minute droplets arezpromptlyfrozenyby .the cool circulating inert gaszinto solid g: particles. .The chilling z eitect s isv so rapid 'that the gas :dissolved `the drnlets quickly :forced aoutzof. solution thus'. causing them toxexpandintofparticles.

.Theseiand- :otheryfeatures'ofzthe invention yWill be .better .undeistoodfhy referring :to the accomparuringfdrawings, taken .in .conjunction-.With the following; descriptiomin which:

:l is fa :diagrammatic flow sheet showing' the system asa whole;

Eig .2 .isa side elevation of the .purifier `shown in:Fig.f1;

.Eig. `Sgislafplan'view offene of the=trays in the purifier;

iFig. f4 :is a cross-section .zon ,theline "L -e4 of Fig;

x5 isa crosse-sectionalviewof Aone .ofthe melting urnacesishown inFig. .1;-

iFig. .6 iis 'anenlarged cross-sectional View .of the atomizer shown in:;Eig.:.5;

Tig. 7 a? longitudinalsection iofithe chamber shouminilfig. 1 :for atomizingmolten :metal and forming :metalv powder;

Figt iszatransverse ksectionyon line --.e .of Eign;

;Fig,.9 ..is an .enlarged Vside viewrof :one of `the powder-:gast separatorsf'showrrinlllig.'1;

Fig. ,10 is a similar .vieiv, .partly in section, of the f lower end-thereof; ...and

.Fig 11 is;a front elevation ofrtheesame.

Reference is made lto Fig. il for ran overall picture :of the: apparatus. Since .'pnriiication of the .gas in `the system -isiof initial importance, the ymain featuresfof rits sy-stein :or circuit will rst bezdescribed.

iincludes a .gasometer1i,.a conduit 2,.a main Vconduit f3, a branch conduit-Ara dustriilter 5, :a yconduit P16, a brancheondzui-t f1, aslter'ua branch conduit :-;9,.a.brar1ch conduit Ilka lter IJ, :fa phi-'anch .conduit 12, .a :compressor I3 .cone nected on .its .inlet or :suction :side with conduit S,:.af,conduit vtLccnneeting the :outlet orpressure side of the compressor, a filter I5, afconduit .113, a branch conduit :1:1reonnectingztheLinletof a purifier :t8 surrounded by a heating arurnace or chamber l li9 Lhaving :an rinlet 2 0. rfor the .introductionof heating :gasesfand fan outlet 2l .for y.the escape of spent gasesgandaconduit 2.2connectingnthe outleto'f the'purier-withzthe gasorneter. The latter oonduitrmayfof course, .connect the systemat any.v other .suitable point. mail@ some valves enclosure :members are indicated, `it .will -be clear-"that any suitable lnumber may .beeinployedat other pointsin the circuit. ln general, it will-be seenftha-tf-gas inayipass-f-rcm'themain systemby vway4 of the vgasoineterl and main conduit 3 to -and'through vdust lter5,one 'orboth filters 8 Vand I. l to and" through the ycorrrpressor, through filter "f5, purifier "I8 and backinto the system. "This cyclic operation maybe continued until all of .the gas in Vthe .system reaches .the desired purity. What has been'described may be ,regarded aspart .of the Kmain system, .o1-'indeed acirculating. system within the maincirculatingfsystem. When. all .of thegas` is purified, .it is y unnecessary `.to...continue with. .the ,purification operation and it may be shut-off until again needed.

The main system or circuit for producing the metal powder will now be traced. It includes a branch conduit 30 connecting main conduit 3 with a bonnet 3l at one end of a molten metal atomizing and powder forming chamber 32 for providing cool inert gas with which to freeze the atomized metal to powder. Another branch conduit 33 also connects main conduit 3 with the lower portion of the chamber in order to supply additional gas for keeping the newly formed metal powder in suspension, as will be described in more detail below. A branch conduit 34 similar to branch conduit 30, connects main conduit 3 with a bonnet 35 at the other end of the chamber. Conduit 36 connects the same or discharge end of the chamber with a blower 31, a conduit 38, a powder-gas separator 40, a conduit 4|, another powder-gas separator 42, a conduit 43, and a filter 44 which in turn connects main conduit 3. A branch conduit 45 connects the main conduit with a filter 46 and a conduit 41. Similarly a branch conduit 50 connects the main conduit with a filter and conduit 52. In practice it is customary to alternate use of filters 46 and 5|, so that while one is being cleaned or otherwise serviced, the other is used.

'Ihe next system or circuit to be traced is the one having to do with the use of gas to force a fine stream of molten metal to the atomizer and the use of gas to atomize the stream of molten metal. It includes conduit I6, from the outlet or pressure side of compressor I3 and a branch conduit 60 terminating in branch conduits 6| and 62. Branch 6| connects with a conduit 63 one end of which connects with the interior of a melting furnace 64 and the other end of which connects with the interior of chamber 32. A bonnet 65 connects the furnace to bonnet 3| of the atomizing and powder forming chamber.

A similar arrangement is provided for the other end of the chamber and includes a branch conduit connecting conduit I6 and terminating in branch conduits 1| and 12. Branch 1| connects with a conduit 13 one end of which connects with the interior of a melting furnace 'I4 and the other end of which connects with the interior of chamber 32. A bonnet connects the furnace to bonnet 35 of the atomizing and powder forming chamber.

Figs. 2, 3 and 4 show the purier in detail. It is cylindrical in form with a closed bottom 80 (see Fig. 2) resting on supports 8| on the bottom of the interior of the heating chamber. Superposed trays or baskets 82 rest on an inner flange support 83 integrally secured to the side wall of the purifier, the flange being located directly above inlet I1. An imperforate cover 85 is securable to the top of the purifier by means of a plurality of bolts 36 through an outer flange 81. All joints of the purifier are gas tight so that heating chamber gases cannot enter the purier and so that gases inside the purier cannot escape into the heating chamber.

The trays (see Figs. 3 and 4) are generally cylindrical in shape, being formed of a band of sheet metal 90 with a turned in bottom flange 9| and a similar turned in top flange 92. A circular piece of coarse mesh circular screen 94 rests on and is secured to the bottom flange. A circular piece of fine mesh screen 95 in turn rests on the coarse mesh screen, the latter serving as a firm support for the former. A relatively thin layer of finely divided metal particles 96,

y8 such as magnesium powder, if magnesium powder is to be produced, rests on the screen. A handle or bar 91 is secured to the underside of upper flange 92.

In preparing the purifier for use, the top of heating chamber I9 is removed, cover 85 of purier I8 is also removed and loaded trays or baskets B2are placed therein, one superposed on the other. In the case of the bottom tray, its bottom flange 9| rests on inner flange support 83. Lower flange 9| of the second tray will rest on upper iiange 92 of the rst tray, etc. The purier is provided with a suiiicient number of the loaded trays. Cover is then returned and bolted securely to outer flange B1 with bolts 86; after which the top of the purifier is returned.

Melting furnace 64 is shown in detail in Fig. 5. It rests on a dolly so that it may be wheeled into and away from operating position with respect to chamber 32. The furnace is formed of a rectangular heating chamber 9| surrounded by a metal casing 92 lined with refractory brick 93. The chamber is surmounted by a removable top 95. A plurality of spaced openings 91 are provided through the side walls near the bottom of the chamber into each of which is fitted an oil or gas burner 98. Three such burners are at present employed.

A stack 99 is mounted on the top for the escape of spent heating gases. A melting pot |00 rests on supports |0| at the bottom of the heating chamber. The top of the melting pot is provided with a removable cover |02 securable to an outer flange |03 by means of a plurality of bolts |04 to provide a non-leaking joint. A metal charging conduit |06 extends through the top of the heating chamber and communicates with the interior of the melting pot. It is secured to cover |02 by means of a plurality of bolts |01. A removable cover ||0 fits over the top of the charging conduit and can be screwed thereon to make a leak-proof joint. Branch conduit 93 for inert gas connects with the charging conduit above furnace top 95. A pyrometer ||2 extends through the top and cover |02 well into the interior of the melting pot. Branch conduit 62 for inert gas extends into heating chamber 9| and is spirally wound around the melting pot. The discharging end of the conduit extends into the interior passageway lill of bricklined furnace bonnet 65. A conduit ||5 for the passage of molten metal extends from near the bottom of the melting pot upwardly through its cover |02 and into passageway ||4 of furnace bonnet 65 where it connects with an atomizer H6 extending through end-cover ||1 into chamber bonnet 3|. The two bonnets are connectible with bolts ||9. The furnace bonnet is provided with an opening |20 in close proximity to the atomizer and is tted with a burner |22 adapted to supply heating gases at and around the atomizer.

Atomizer l I6 is shown in'more detail in Fig. 6. It is in a form of a main body portion |24 hollowed out at one end to receive the discharge end of conduit I5 from the melting pot and hollowed out at the other end to receive an atomizing nozzle |25 and to form a gas distributing chamber |26 around the nozzle. The tip end of the nozzle, with discharge outlet |28, extends through cap |29 screwed onto the other end of the main body portion. Conduit 62 for inert gas connects with a nipple |30 communicating with the gas distributing chamber. Cap |29 9,-' is: provided with a plurality ofl inclinedY circumferentially spaced" discharge ports |32 adapted to blast small `streams of preheated `inert-gas'against a stream oiv molten metal dischargedt through nozzle outletv lili? at a point. orarea |34a suit;-

able distance forward ofv the nozzle tip.

Figs. 'I and i show chamber 32: for atomizing molten metalandforming powder therefrom in more detail. tankv dividedlessentially into anupper compartment |40, Which is in the form offa trough, a lower compartment |41, which is essentially in the form of a duct; and two side compartments H52 and |43, which are separated from each other as Well as from the other two compartments. All of the compartments extend longitudinally of the chamber. The upper and lower compartments are tapered in reverse order. Thus, upper compartment lll!! hasits smallest cross-section at the right end of thetank, and its largest cross-section at the left end. The lower compartment or gas distributing duct i'i, on. the other hand, has its largest oros-section at the right end, Where the gas is shown to enter through conduit 33, and its smallest crosssection at the left end.

The compartments are obtained by the use of opposed pairs of overlapping plates to |53, top plates I6! to w8 and a pair of spaced side plates Hi' and W2. They are suitably, welded to the cylindrical walland to each other to provide an integral structure. Plates |53 to |58 are pitched or slanted atan angle, toward'the bottom of the trough, so that powder settling thereon will tend to slide down into the bottom or" the trough. Referring for a moment to Fig. 7, it will be seen that an overlying lip VM is welded to the head of the cylindrical tank at.. the right end to provide a slot '|15l between inlet conduit 33 and upper. compartment |40. Similar underlying lips |75 to IzBZ provide slots |85 to |9i. Upper plate |65 ofythe duct is spacedV above the bottoni of the tank to provide a `similar slot |92 at the left end of the tank, in direct communication with outlet conduit 3E. The overlying and underlying lips are sufficiently longto cause gas passing therethrough to sweep along the bottom of the upper compartment. In other words, gas going through slot |75 sweeps along the top of plate |68, gas passing through slot |85 sweeps across the top of plate |51, gas passing through slot |865 sweeps across the top of plate. |66, etc. A gas blow-oir |95 is provided along the. top of the tank. "in case of aneaplosion, the blowoi is opened to release explosive forces, thus saving the chamber from damage. An inlet |98 connects each side compartment with inlet con.- duit 33. An outlet I99'connects each side compartment with outlet 3.6. While the side. compartments are normally sealed from each other andthe other compartments, it is possible for leaks to develop at the welded joints. l't is therefore desirable to have an arangenient which Wi'li permit the side compartments to be cleared oi air and iilled with inert gas, and this can be done with the inlets and outlets referred to.

Figs, 9, 1G and 1lv show powder-gas separator M4' 'in some detail. Powder-gas separator i2 is advantageously oi the 'same general construction. Referring rst to, Fig. 9, the apparatus shown is in the form 4of a combination powder-gas separator and collector, ybeing speciiically a .conventional -cyclone Zdlivith an inlet 2.0i for. powdergas :and any outlet 262 for gas, .and `a .hopper '2263 integrally secured `to and depending from the It is in the forrnof` a cylindrical cyclone. The lowerendothehopper terminates in a laterally extending discharge conduit 205. ator near the .outletv end of which' is an upright relier"A chamber 296;. A, closure member 2M is pivotally sup-ported atrthe outlet.

Referring next to Fig. l0,` i-t` will be seen that relief-chamber. 2% provides `a substantial amount of 'free space-2m1- at its upper endfwhichextends 'a suitable distanceabove the'place where the chamber jointsl the conduit.. The top of the relief chamber is iittedwith ascrew.` cap 2| provided withv a plurality of circumferentially spaced handles 2 2.

ln. the specific construction shown they discharge-ou-tlet a convenient .angle fto cooperate with closure member 201:, which is in the form of an enclosed chute pivotally or hingedly con.- nected at 2i3fto a fixed support 2M.' The chute l'rasa` bottom 2.152 back 2|6; side Walls 2H' and 213, -a top Zillancit''a` discharge opening 22|). A.

piece off resilient gasket material 21212., such as rubber, isv integrally secured to the bottom ofthe chute-so-that it maybe-brought into sealingcontactiwitli the dischargeoutlet.

The discharge outlet is in the form ofa. pipe welded at its sidevtothe main `part of the conduit, the vupper end of the pipe being an extension which forms the relief chamber; The chute is integr ally secured at itsv ltop 219 Eto an outer collar 224' iitting looselyv around the lower endof the discharge conduit. rI'h-e upper'endo thecollar is integrally secured to the low-er endors, flexible sleeve 225 fitting loosely around the discharge conduit. This sleeve may be or rubberwand is adapted' to act like abellows. The upper` end of the flexible sleeve-is in turn integrally secu-redvr tothe discharge conduit. When the chute'is Imoved upwardly and downwardly, the lneri-ble sleeve yields sufficientlyto Vpermit the" discharge `outlet to be closed and opened.

A handle 228 issecuredfto the top oi the chute at its ldiscl'iarge er1-d` so that the operator may readiiy lower the lchute to 'open the discharge outlet and raise the chute 'to close the outlet. This is a manuali operation which may remain wholly in control of the operator.

If the operator, however, should -instinctively let. go of' the-handle in case ofire, or for any other reason, or should leave the scene, selfclosing means associated with the chute at once 'take care of such accntingency. The particular self-closing means disclosed include a Ypair of spring tensioning devicesZ-ll and 23 l" secured at their lower ends to the chuteand at their upper end to a iixedA support, in the instant construction `at the upper-portion or the relief chamber. A. turnbuckle is attached to each spring so that the springs may be placed under the proper amount of tension. When downward pressure is applied. lto the chute, such as by bearing Adown on handle 228., the springs yield suiiciently to permi'tthe chute to drop away angularly yfrom the discharge outlet. To make certain that the chute isno't .lowered unduly, for example, by the operator when excited, a chain 2M of ypredetermined length is fastened at its lower end to the chu-te and. at its upper end to a xed support. Theehain fixes and limits the amount of drop for the chute.. device ZBfwithaturnbuckle 238 is hooked Iat its lower end to lthe chute andat its upper end to a fixed support (not shown). When the chute is in its closedposition, thet-urnbuckle is tightened. Pressure on handle 22%.- will, therefore, not open the chute. This feature is particularly desirable- As a further precaution, a holdin-g` 11` if children or non-trained operators have access to the apparatus.

When, therefore, it is desired to discharge metal powder from the apparatus, the operator must deliberately loosen turnbuckle 238 in order to release holding device 236. He then 4applies downward pressure on handle 223, which causes chute 201 to move or open downwardly. Metal powder then moves by gravity from hopper 203 through conduit 205 and its discharge outlet into the chute, and downwardly through the chute out of its discharge opening 220 into a container 240.

If all goes well the handle is kept down until the desired amount of powder runs into the container. The handle is then lifted by the operator to close the discharge outlet and the holding device is again replaced. With the self-closing means in use, however, the operator need merely release the handle and spring-tensioning devices 233 and 23| will lift the chute into its closed position. As `already indicated this feature is particularly desirable in case of fire and if the operator should let go of the handle o-r leave the scene in fright. In case of fire this is precisely what he should do for safety.

In practicing the method ofthe presen-t invention, the apparatus may be operated as follows:

Since the circulatory system is initially filled with air, it is important that it be replaced with a suitable inert gas, such yas helium. Helium for -this `purpose is obtained commercially in cylinders. With an adequate supply of cylinders on hand, the helium is fed into the system at one or more high points and air is removed therefrom at one or more low points; for example, referring to Fig. 1, the helium may be fed into gasometer I and air may be withdrawn from conduit 36 in advance of blower 31. Whatever practice is followed a sufiicient amount of helium is lfed into the system to iiush out most of the air. Enough helium is thus used to `place the system under substantial positive pressure greater than atmospheric to keep outside air from seeping into the system. A manometer pressure of 2 Water has worked well.

Since helium and air are readily mi-scible, no matter what precautions are taken an appreciable amount of air will be in the system after the flushing operation; and since this residue of air and the helium contain objectionable amounts of oxygen and nitrogen, purifier I8 is placed in operation. As shown in Fig. l circulation of the helium through the system may be effected by the use of compressor I 3, as well as by blower 31, or both. In any event helium from the system is passed continuously and cyclically through the purifier. Heating gases, such as provided by oil or gas burners, are fed through inlet 2B into heating chamber I9, while spent heating gases escape from the heating chamber through outlet 2| to the open atmosphere. Impure helium from the system is forced by compressor I3 through conduit I4, filter I5, conduit Io and branch conduit I 1 into the purifier I3. The purified helium rises upwardly through conduit 22 and is returned to the main system.

As more particularly shown in Figs. 2, 3 and 4:, the impure helium passes upwardly through layers 35 of nely divided metal particles in superposed perforated trays 82. The heating gases applied externally to the purifier are adapted to heat the metal particles to a temperature sufiiciently high for the oxygen and nitrogen impurities to react therewith to form metal oxide and metal nitride. Assuming that magnesium powder is to be produced, the layers are formed preferably of magnesium powder, about IAL" to 1/2 deep; the depth being such that the helium may pass readily therethrough. The oxygen and nitrogen impurities react with the magnesium to form magnesium oxide and magnesium nitride which are retained in the layers on the trays. In the particular arrangement shown, the helium thus purified (see Fig. l) passes through conduit 22 into gasometer I where it mingles with helium stil1 to be purified.

Since the circulatory system is open, helium passes continuously through gasometer I, conduits 2, 3 and 4, filter 5, conduit 5, branch conduit 1, filter 8, branch conduit 3, branch conduit I, filter II, branch conduit I2, compres-- sor I3, conduit I4, filter I5, conduit I6, lbranch conduit I1, purifier I8, conduit 22, and again gasometer I. As this cyclic operation continues, helium is also forced by blower 31 through conduit 38, powder-gas separator 40, conduit 4I, powder-gas separator 42, conduit 43, filter 44, main conduit 3, branch conduit 45, filter 4B, conduit 41, as well as branch conduit 50, filter 5 I, conduit 52, main conduit 3, branch conduits 3D and 33 into and through chamber 32, inlets |98, side compartments I 42 and I 43, outlets |93, conduit 38, and back to blower 31.

In a similar manner compressor I3 also pulls some of the helium from main conduit 3 through branch conduit 4, dust lter 5, conduit B, branch conduit 1, lter 8, branch conduit 9, as well as branch conduit IIJ, filter II, branch conduit I2, conduit 6, the compressor itself, conduit I4, filter I 5, conduit I6 past branch conduit I1 to and through branch conduit 60, branch conduits 6I and 62 to furnace 64. As more clearly shown in Figs. 5 and 6, helium passing through conduit 6I goes into melting pot Ill. This helium may be passed through conduit 63 into chamber 32. The helium passing through branch conduit 52 moves through the coils surrounding the melting pot and is passed into and through atomizer IIS, after which it mingles with helium passing through chamber 32.

If furnace 14 is also placed in operating position with respect to chamber 32, its melting pot may .be flushed of air and filled with helium undergoing purificati-on in a manner similar to furnace 64. Helium is forced by the compressor through conduits I6 and 1I), and branch conduits 1I and 12. Helium passing through conduit 1I into the melting pot may be passed through conduit 13 into chamber 32. Helium passing through branch conduit 12 is passed through the coils around the melting pot and finally through the atomizer into chamber 32.

It will be clear from what has been said that if the impure helium in the system is circulated for a sufficiently long time, it will continue to pass through the purifier until substantially all of the objectionable oxygen and nitrogen are removed. Periodic tests are made, with an Orset tester, to determine the oxygen content of the helium. When it is sufficiently pure the valves in inlet I1 and outlet 22 are closed to cut-out the purifier circuit. It may be cut-in from time to time as needed. If all goes well, the purified helium may be retained in the system and used over a prolonged period of time.

With the circulatory system full of purified helium, it is ready for the actual metal powder producing operation. Referring for the moment to Fig. 5, which shows melting furnace S4 and its auxiliary equipmentv in 'more-f detail; cover.' 10i is removed from `char-ging. corlilui't' v 1%; Ingots' off metal to be converted' into metaly powder" are dropped into melting pot/lull; Arter. a 'suitable amount is placed therein the cover ifs'returned;k The apparatus is at present .beingu'sed't'o produce magnesium powder andalso magnesium-aluminum alloy powder. The inside dimensionsfof the pot are 24" diameter and@A Af charge' of aboutv 180 Vpounds-ol magnesiumiszthusxintroduced. Oil burnersfl are operatedsto heat,` the pot externally. untilits magnesiumcontent reaches a suitable molten temperature., fromv .1800?" to 1350 F. The burners-arekept in operation to maintain this temperature;

Pressure-gas conduit 61| is; openedi to admitl helium into the charge conduit-and'.topa-portion of the pot above the-level cfr themcltenzmagfnesium. Since the pressureegas. conduit conv municates with the compressor/the.mcltenzrnage nesium is placed undersufcient gas-ipressurel to: force a stream of magnesiumupwardly throughv molten-metal conduit Mil to. andthrough atornizerV IB into atomizing and powder: rormingzchamber 32. A pressure or JBZ-l5 poundsoper-squa'refinch is applied initially to 'the top of; the body of molten magnesium to start. itszipassage through; the conduit and the atomizen' After atomization of the .metal .is underway, theipressurc is reduced to 'about 5 pounds '.persquare inch. Helium under *adequateA pressure-.by thecompressoris passed throughV atomizingegasr conduit'` 62 ivi/here it is. heated in the coils around the meltingpot. The: preheated helium ispassed.y throught nipple- |3= (see Fig. 6) into gas .distributing chairiberv llt-Scofthe atomizer, from which it issues through discharge ports |32 of cap '|2S'in. a .plurality of streams or blasts and 'atomizes thene stream of molten magnesium discharged through nozzle outlet |23 at point or areailt a suitable-distance. forward of the nozzle tip. The pressure of the helium at the nozzlevaries somewhat according to its construction. A pressure in. the neighborhood of 60 pounds per square inch Works satisfactorily with the nozzles now emplcyecl.`

Returning for a moment to-Fig.'1, it' will be recalled that blower 3l causes the helium'to circulate continuously through the syste-m. Since chamber 32 is on the suction-sideor the-blower, the helium is inxeffect suckedthrough and from the chamber only to be forced or pushed: from the pressure side of the blower around the system. Relatively cool helium enters the chamber by" way of branch inlet conduits 36 and: lat the same end, adjacent melting furnace Sil- 'l-her atomized magnesium is promptlyenvfelopedand frozen into powder particles in the cool heliumA sweeping through upper comp-artm'entI HN! (see: Figs. 7 and 8).

While the newly formed particles of magnesium powder tend to remain inv Suspension. in: the helium as the helium.. passes through thecham.- ber to the blower, some of it also; tenclsftcf settle byfgravityonto'plates |51 to lxand'towardthe bottom 'or base of theV trougliof therupper.corn-Y partlnent. Additional'am'ountso relatiifelyncoel. helium are, therefore, introducedintonthezupper; compartment by way of. inletlconduit; Ac ccrding 'to a pre-'sent practice, the amount of helium entering the upper rcompartment `by way;l of inlet S'San'd lower compartment; 'orfductaV Mtl: substantially exceeds Vthat enteringloywvay for :inilet conduit Sil; Some ofl the h-eliumrom inlet.: 33 issues as a relatively Vsmallstream;throng- 11; slot I 'l 5T,- lthe Is'tre'ain being 'directed aiong.' theatopf oft plate |681T in', the-bottom of the trough. Airyr magnesium;l powder settling or tending tcy settle onthat' platevis, therefore, sweptw up and placed: in suspensionin.themain-and large currentl ofV gas or helium passing throughthe upperv compartnfuerit;v

In a similar-manner some heliumin lowercomp'artment or ducty IM passes as a stream-through siotfmffaloirg. the top of' plate Il ati the bottom of the trpugh.- of thev upper ycompartanentf. Similanstrteains lof helium'pass through slots |86 to ati the bottom of the troughl of the upper cornpartment arecontinuouslyswept with streams of heliumzunder. suirlc'ient'velocity to keep the powderfirom settling and. to keep it in suspension. additional; stream of helium passes through duct |92 into the discharge endof the upper-compartment; Some or. the helium thus introduced through the'` slots alsoQspreads to the side and.' sweepsacrosspl'atesfl 5|`to |58 to keep themclean ofripowder; The' mixture of gas and powder is under-'a great deal- 'or turbulence which inhibits settlin'gzor the powder. The powder laden gas 1- is inzeiTect suckedv fromthe upper compartment throughout-,ietf 3ft-and blown through conduit 33.

If melting furnimeiity must be shut down for some reason, such as for repairs, melting furnace 'M (see Fig. 1) isput in operation at the other end of. thechamber. In this case itis advisable to close inlet conduit Se anoto open 'inletwconduit 34. A'S before, anne stream orimolten .magnesium issuing from the nozzle ofv the atomizer is blasted with. helium 'and the atomized mag- 1. nesium` is promptly enveloped in the relatively coo1 helium gas entering the upper compartment by way of 'inlet conduit 3|! as well as by helium entering the chamber through inlet conduit 335.

'The force behind the line stream of molten metal issuingPv from the nozzle of the atomizer at either end or the chamber and the force of the helium used. to atomize the stream. of molten, magnesium is sui'cient to throw the Iatornized magnesium `'substantially across the `length of the chamber. tionthe directionuof the stream ofmolten.metal is in Ageneralconcurrent with the streamsV of'helium passed into and through theY chamber..` 0n the otherhand, when melting furnace M is in operation the direction of the stream 'of molten metalissuing from the nozzle is in general lcountercurrent to the helium entering the upper compartment by way of inlet conduit-Salani: concurrent: with the helium entering the chamber through inlet conduit 34. As a result of thesev contrary movements, at least initially, the helium is kept in a turbulent state. In anyevent' the suction force of the blower is suiiicient to draw the resulting po'wderegas mixture from the chamber. i

Still referring te Fig. l, the magnesium powder laden helium is -orced'by blower 3l through conduit: 38 yto powder-gas separator 40; Asshown in Figs` 9, 10 and lflY and asdescribed in some de- 6 1 tail above, the larger powder particles are sep arated sc'alectively from the helium and smaller particles in cyclonel'iB-'andzfall into hopper 2&3.' After asufcient supply of .powder has collected in Vtloeuhopper,.some of it withdrawn from time to time; care being taken not to break the powder seal'in 4discharge conduittiso that-air can enter the system.

Again returningrto' Fig. 1,7 the helium contain',-

ing .the smaller. particles of rnaegnesiunitpowder:is` forced. from. powderegas. separat-m'v @il through.

When melting furnace Al 4"' is in opera` conduit 4I to powder-gas separator 42. Since the separator operates like the other, the same procedure is followed in withdrawing powder. As already indicated one or more additional powdergas separators may be employed.

From the chamber to and through the powdergas separators the helium undergoes a substantial drop in temperature. As it leaves the last powder-gas separator in the series itv still contains some fines which should be removed before it reaches the compressor. To this end the helium leaving powder-gas separator 42 is passed through conduit 43 into dust-collector 44. In the present practice this is in the form of a plurality of filter bags, the specific device employed being a Dracoo dust collector. While a substantial amount of the dust is thus removed from the helium, some remains.

Helium leaving dust-collector 44 passes into main conduit 3 and is then diverted through branch conduit 45, filter 46 and conduit 41 back to main conduit 3. This is a wet lter, of the oil type, which needs to be cleaned from time to time. When cut-out of the circuit for that purpose, helium is diverted from main conduit 3 through branch conduit 58, a similar filter 5I and conduit 52 back to main conduit 3.

A substantial amount of the helium thus treated passes continuously through main conduit 3 and branch conduits 3Q, 33 and 34 back to chamber 32. Some of the thus treated helium is, however, diverted from main conduit 3 to the compressor. Additional steps are taken to remove further amounts of dust from this helium before it reaches the compressor. To this end the helium is diverted through conduit 4 into and through filter 5, which may be an oil filter similar to filters 46 and 5 I. Although the helium thus treated is substantially dust free, it usually contains some suspended oil and moisture, both of which contribute to the fire hazard. Helium leaving the lter enters conduit 6 and is diverted through branch conduit l, filter 3 and conduit 9 back to conduit 6 which connects the inlet or suction side of compressor i3. When filter 8 is cut-out for cleaning, helium leaving filter 5 is diverted from conduit 6 through branch conduit I0, filter I I, and conduit I2 back to conduit. Filters 8 and II are advantageously of the pot type containing a filter layer of steel wool or other suitable material, through which the helium is passed to abstract the suspended oil and moisture.

Since the helium may pick up some oil and moisture in the compressor, it is again filtered. Helium leaving the outlet or pressure side of the compressor is passed through conduit I4 and iilter I5. This lter may contain a filter layer of felt, for example, such as a Cuno iilter, which abstracts the oil and moisture as the helium passes therethrough. The helium thus treated for the removal of powder, fines, oil and moisture is passed through the remainder of the system, including the purifier when cut-in, the melting pots, and the atomizers, as already described.

Some losses of helium from the system are unavoidable, not only from minor leaks but also when charging the melting furnaces, etc. Replacement helium must, therefore, be added to the system. However, by keeing the system under positive pressure, ingress of air is for the most part avoided. Such oxygen and nitrogen as enter by replacement helium is so small compared with the total volume of helium in the system that their effect is of little consequence.vv

16 They react with the atomized magnesium or highly heated powder in the chamber and are quickly eliminated. That is, after the system is in metal powder producing operation, it acts to purify itself so far as the extremely small amounts of oxygen and nitrogen are concerned.

It will thus be seen that a conilned system may be provided in which an inert gas of high purity under positive pressure is continuously circulated while metal to be converted into powder is melted and atomized therein. Although the gas initially placed in the system is not satisfactory for the purpose, it may be so treated as to remove harmful impurities. After the gas is puried, it may be used over a long period of time to produce metal powder. While various inert or non-reactive gases may be employed, helium is especially suitable because of its availability. Metal powder may be produced from various metals and their alloys, such as magnesium, aluminum, zinc, cadmium, lead, etc. The principal limitation is the ability of the materials in the system economically to withstand the necessary wear and tear.

It will be clear to those skilled in this art that the practice of the invention lends itself readily to various modifications. The specic practice described is only by way of illustration. 1t is obvious, for example, that other compressors, puriers, furnaces, atomizers, separators, lters, etc., could be used and that the units making up the whole can be arranged in various ways. What is disclosed is a highly effective arrangement for producing metal powders in large quantities in an eflicient manner.

I claim:

l. In the method of producing metal powder by atomizing molten metal with a blast of inert gas, freezing the atomized metal into riely divided solid particles, and recovering the resulting metal powder, the improvement which comprises conducting the molten metal atomizing, metal powder-forming and powder-separating steps in successive zones therefor of a main confined circulatory system lled with gas inert to the metal, circulating the gas continuously therethrough under a pressure higher than atmospheric to prevent ingress of outside air, withdrawing continuously a relatively small portion of the inert gas from the main circulatory system beyond the powder-separating zone and in advance of the atomizing and powder-forming zones, compressing the gas so Withdrawn substantially to increase its pressure above that at any point in the main circulatory system, and atomizing the molten metal in the main circulatory system with at least a part of the compressed gas, the compressed gas being returned to and mixed with the gas in the main circulatory system.

2. Method according to claim 1, in which the circulating inert gas with the newly formed metal powder suspended therein is passed from the powder forming Zone through a plurality of powder-gas separating zones, metal powder is separated from the inert gas in each latter zone, and the metal powder so separated is withdrawn from the system at each latter zone.

3. Method according to claim 1, in which the inert gas so withdrawn is specially heated, a continuous ne stream of the molten metal is blasted circumferentially with a plurality of streams of the heated inert gas in a metal powder forming zone lled with the main body of circulating inert gas, the main body of gas being sufcently low in temperature promptly to freeze the atomized metal into nely divided particles, the main body of circulating inert gas with the newly yformed metal powder suspended therein is passed from the powder forming zone to a powder-gas separating zone, metal powder is separated from the mai-n body of inert gas, and the metal powder so separated iswithdrawn from the system.

4. Method according to claim 1, in which the main body of circulating inert gas with metal powder suspended therein is passed from the powder forming zone to a powder-gas separating zone, metal powder is separated from the main body of inert gas by dry precipitation, and the metal powder so separated is withdrawn from the system.

5. Method according to claim l, in which the main body of circulating inert gas with metal powder suspended therein is passed from the powder forming zone to a powder-gas separating zone, metal powder is separated from the main body of inert gas by wet precipitation, and the metal powder so separated is withdrawn from the system.

6. Method according to claim 1, in which the main body of circulating inert gas with metal powder suspended therein is passed from the powder `forming zone successively through a series of at least two powder gas separating zones, coarser metal powder being separated from the main body of inert gas in an earlier zone by dry precipitations, and finer metal powder being separated from the main body of inert gas in a later zone by wet precipitation.

'7. Method according to claim 1, in which sorne of the inert gas temporarily withdrawn from the system and compressed is heated before being used to atomize the molten metal.

8. Method according to claim 1, in which some of the inert gas withdrawn from the system and compressed is conducted while under substantial positive pressure to a conned space above a body of the molten metal to be atomized and used to force a stream of the molten metal to the atomizing zone.

9. Method according to claim l, in which the gas in the system is pured with respect to oxygen and nitrogen by passing it through a body of nely divided particles of heated metal adapted to react with the oxygen and nitrogen to form metal oxide and nitride.

10. Method according to claim 1, in which gas in the system contaminated with oxygen and nitrogen is withdrawn vfrom the system, passed through a body of heated metal powder adapted to react with the oxygen and nitrogen, and the purified inert gas is returned to the system.

11. Method according to claim 1, in which gas in the system contaminated with oxygen and nitrogen is passed through a plurality of thin beds of nely divided particles of heated metal adapted to react with the oxygen and nitrogen.

12. Method according to claim 1, in which gas initially in the system and contaminated with an objectionable amount of oxygen and nitrogen, is first passed through a body of finely divided particles of heated metal adapted to react with the oxygen and nitrogen until the gas is puried with respect to the oxygen and nitrogen, and the atomizing, metal powder forming and powder separating steps are then conducted in the presence of the inert gas so purified.

13. Method according to claim l, in which a fine stream of the molten metal is blasted with inert gas so `withdrawn in a metal powder' forming zone iilled with the main body of; circulate ing inert gas', the main body of circulating gas being' suificiently low in temperature promptly' to freeze the atoniized metai into finely divided soli-d particles, and a stream oi the inert gas withdrawn from the main body of gas is introduced at. the bottom of the powder forming. zone to help keep the newly forrriedfv particles of metal powder in suspension during their passagel to the powder separating zone.

14. Method according to claim 1, in which the inert gas so withdrawn is specially heated, a iine stream of the molten metal is blasted with the heated inert gas in a metal powder forming zone filled with the main body of circulating inert gas, the circulating gas being sufficiently low in temperature promptly to freeze the atomized metal into nely divided particles, a plurality of streams of inert gas from the main circulatory system is introduced at spaced intervals along the bottom of the powder forming `zone to help keep the newly formed particles of metal powder in suspension during their passage from the powder forming zone to the powder separating zone.

l5. Method according to claim l, in which a ne stream of the molten metal is blasted with the inert gas so withdrawn in one end of an elongated metal powder forming zone illed with the main body of circulating inert gas, the main body of circulating gas being sufficiently low in temperature promptly to freeze the atomized metal into finely divided particles, and a plurality of streams of inert gas from the main circulatory system is introduced along the bottom of the powder forming zone to help keep the newly formed particles of metal powder in suspension during their passage from the powder forming zone to the powder separating zone.

16. Method according to claim l, in which the inert gas so withdrawn is specially heated, a fine stream oi the molten metal is blasted circumferentially with a plurality of ne streams of the heated inert gas so withdrawn in one end of an elongated metal powder forming zone filled with the main body of circulating inert gas entering therein from the same end, the main body of circulating gas being suihciently low in temperature promptly to freeze the atomized metal into nely divided particles, introducing the main body of circulating inert gas in the powder forming zone at the same end so that the powder and gas may move concurrently through the powder forming zone, and a plurality of streams of inert gas from the main circulatory system is introduced along the bottom of the powder forming zone to help keep the newly formed particles of metal powder in suspension during their passage from the powder forming zone to the powder separating zone.

17. Method according to claim 1, in which the gas so Withdrawn from the main circulatory system is filtered to remove solids therefrom before it is compressed.

18. Method according to claim l, in which a portion of the gas so compressed is used to force the molten metal into the atomizing zone.

19. Method according to claim 1, in which a part of the withdrawn and compressed gas is puried with respect to oxygen and nitrogen by passing it through a body or" finely divided particles of heated metal adapted to react with 19 the oxygen and nitrogen to form metal oxide and nitride.

20. Method according to claim 1, in which the gas Withdrawn from the' main circulatory system for compression is filtered to remove solids therefrom before being compressed, and at least a part of the compressed ltered gas is purified with respect to oxygen and nitrogen by passing it through a body of finely divided particles of heated metal adapted to react with the oxygen and nitrogen to form oxide and nitride.

HENRY A. GOLWYNNE.

References Cited in the le of this patent UNITED STATES PATENTS Number Name l Date Nicol Sept. 7, 1920 Marx Jan. 18, 1927 Seastone July 26, 1932` Paddle 1 June 18, 1946 Burkhardt Sept. 28, 1946

Images