US2638626A - Apparatus for the production of metal powder - Google Patents

Description

May 19, 1953 H. A. GOLWYNNE 2,538,626

APPARATUS FOR THE PRODUCTION OF METAL POWDER Filed Sept. 29, 1949 5 Sheets-Sheet l CHAMBER BLOWER GASOMETER Q Q? a Z O: D U.

II 3 I IN V EN TOR.

HENRY A. GOLWYN NE 8? ATTORNEYS SEPA ATOR S'EPARATOR May 19, 1953 H.,A. GOLWYNNE v APPARATUS FOR THE PRODUCTION OF METAL POWDER Filed Sept. 29. 1949 5 Sheets-Sheet 2 v INVENTOR. HENRY AVQOLWYNNE I BY EMA/Iii, d/Mwkdo l l wfitmmm ATTORNEYS H. A. GOLWYNNE APPARATUS FOR THE PRODUCTION OF METAL POWDER Filed Sept. 29, 1949 May 19, 1953 5 Sheets-Sheet 3 u. -iiff.

} INVENTOR. HENRY A. GOLWYNNE I ATTORNEYS May 19, 1953 H. A. GOLWYNNE APPARATUS FOR THE PRODUCTION OF METAL POWDER Filed Sept. 29, 1949 5 Sheets-Sheet 4 INVENTOR.

HENRY A. GOLWYNNE ATTORNEYS May 19, 1953 H. A. GOLWYNNE APPARATUS FOR THE PRODUCTION OF METAL POWDER Filed Sept. 29, 1949 5 Sheets-Sheet 5 INVENTOR.

HENRY A. GOLWYNNE 7 a/mi? fol/much (ri or FEW ATTORNEYS Patented May 19, 1953 UNITED STATES patent OFFICE APPARATUS FOR THE PRODUCTION or METAL rownsa 21 Claims.

This invention relates to the production of metal powders and has for its object improvements in the apparatus for producing metal powder.

Among the methods of producing metal powder is that of atomizing molten metal with a blast of gas, freezing the atomized metal into finely divided solid particles, and recovering the resulting metal powder. Most metals have a marked afiinity for oxygen and nitrogen at elevated temperatures. This makes it difficult to produce metal powder from molten metal by atomization with a gas because the oxides and nitrides formed by the reaction of oxygen and nitrogen in the gas with the atomized metal tend to form at or near and to contact and then to adhere to the highl heated atomizing nozzle, thus clogging or otherwise impairing usefulness. Such nozzles usually have a central outlet or discharge opening through which the molten metal is forced and usually aplurality of portsthrough which streams of the gas are forced against the molten metal discharged from the outlet. Although a great deal of the oxide and nitride finds its way into the metal powder produced, appreciable amounts contact the hot nozzle and adhere thereto as an accretion or incrustation. This builds up around the ports, particularly, and even the outlet, eventually, so that they become smaller and smaller and clogged eventually. As this takes place the size of the molten metal and gas streams is gradually reduced, thus altering radically the conditions under which the powder is formed. This affects the particle size of the product as well as the efiiciency of the operation. The nozzles must be removed, repaired or replaced frequently.

In the earlier attempts to produce metal powder by atomization, the gas employed for atomization and in the atomizing chamber was air or steam. Air is highly oxidizing and nitriding and steam mildly oxidizing. They have been discarded in favor of so-called inert or non-reacting gases. As we shall see inert gases available commercially in quantities are not truly inert and even if truly inert other oxidizing and nitriding influences are inherent in the operation. In any event various proposals have been advanced to atomize molten metal with I and in the presence of such inert or nomreactive atmospheres. For example, a trickle or stream of molten metal is blasted in a chamber filled with inert gas; the atomized metal is frozen into finely divided solid particles; and the resulting metal powder is permitted to settle at the bottom of the chamber from which it is removed periodically. Another proposal is to spray molten magnesium into a chamber filled with cold nitrogen gas deemed to be oompara ti-vely inert .to the magnesium. Magnesium, however, has a high afifinity for nitrogen, when either or both is heated, and it is impossible to spray molten magnesium, which is necessarily highly heated, in such a manner without 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 thisfield have been greatly troubled with the problem of producing :a suifl'ciently 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 inert because it usually contains arcertain amount of impurities such as oxygen and nitrogen. The inert gas must be conducted into the chamber in which the molten metal isto' be atomizedand the powder formed. Since the chamber isinitially filled with air, the air must be flushed out, or otherwise be replaced, by the inert gas. Since gases mix readily, the inertgas and air-promptly intermix. In spite of careful precautions a residuum of air remains,:and since the air is rich in oxygen and nitrogen, the atmosphere as a whole in thechamher is contaminated to that extent. The atomized metal reacts readily with the oxygen and nitrogen. Oxide and'nitride incrustations then form on the nozzle used to atomize the molten metal. "The discharge ports of the nozzle are soon clogged and the operation must be stopped to clean or replace the nozzle.

M investigations have led to the discovery that difiiculties and disadvantages of the type discussed may for-the most part readily be overcome. With certain-important improvements in the method of and apparatus ior producing metal powder by atomizing molten metal with a blast ofjinert gas, metal powders may be produced steadily over prolonged periods. Metal powders substantially uniform in quality and in particle size maybe obtained. The operation may be so conducted as to obtain metal powders, graded generall as to particle size.

In accordance withone aspect of the invention, a confined circulatory system-includfa min an p wder separating zonesfis filled initially with inert gas under pressure higher than atmospheric to prevent ingress of outside air. The inert gas in the system is purified with respect to such impurities as oxygen and nitrogen, after which metal powder is produced therein.

Air initially present in the circulatory system is replaced for the most part with inert gas. The inert gas in 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 purification 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 higher than atmospheric to prevent ingress of outside air. This is advantageously accomplished by blasting a fine 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 suificiently low in temperature promptly to freeze the atomized metal into finely 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 obtain the plurality of fine streams of inert gas to atomize the molten metal, it is advantageous to withdraw temporarily some of the inert gas from the system, 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 relationship with the body of molten metal to be atomized. The fine streams of heated inert gas are then forced under high pressure into the stream of 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 th atomizing zone. To this end some of the inert gas is withdrawn from the system, conducted under substantial positive pressure to a confined space above the body of 4 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 sys tem at each zone.

The separation of the metal powder from the gas may be conducted in various way. 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, fine particles in the first 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, such as by passing the gas through a bag filter 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. In accordance with the invention, the apparatus for producing the metal powder comprises a confined 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 pressureis 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 sufficient 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 molten 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 beyond the place or places where the powder is separated from the gas so that substantially powder-free gas may be passed by the 2&38326 compressor through the preheating conduit to t'heatomizer for atomizing the molten metal.

A combination of the features just described is highly desirable in practice. In other words, the compressor connects on its outlet side with th interior of the furnace as well as with the atomizer, so that molten metal in the furnace may be placed under pressure by the gas and thus be forced from the furnace to and through the atomizer and so that the molten metal may be atomized by the gas fromthe compressor when it is discharged into the chamber. The compressor connects on the 'mlet side with the system beyond the place where the powder is separated from the gas so that substantially powder-free gas may be passed by the compressor to the furnace and to the atomizer.

Th invention is adapted for the production of a variety of metal powders. The metal to be converted into powder may be essentially a primary metal or a combination of metals, .such as alloys. As a practical matter one of the determining factors is, of course, the melting point of the metal. The higher the melting point, the more are the difficulties encountered; particularly as regards heating and wear and tear of the equipment. The invention is being currently practiced in the production of magnesium powder, and powders of alloys of magnesium, more particularly alloys of magnesium and aluminum.

While various gases inert to the metal to be converted to powder may be used, .as a practical matter the choice simmers down .to one readily available at a relatively low cost. For this reason helium isnow being used. Other inert gases, such as argon could, of course, be employed.

The practice of the invention as .described results in an unusually stable and enicient prodnot. The metal powder may be stored without appearing to lose its effectiveness in use. In the case of magnesium, the powder remains highly effective after storage. This is not true of conventional magnesium powders 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 attritional friction, which causes the exposed surfaces of the particles to react with the surrounding gases and thus, for example, to take on a coating of oxide. On the other hand, powder of the present invention is produced in a relatively cool atmosphere due to the large volumes of cool circulating inert gas that envelopand chill. the particles promptly on formation, and carry them away from the atomizing and powder forming cones. There is little or no opportunity for an oxide coating to form on the individual particles.

In addition the metal powder of the invention is highly activated thus making it very efficient in use. This appears to be due to the enormous amount of surface area offered by a body of the product, far in excess of that of conventional metal powders. Metal powders as heretofore made are solid and therefore expose only an exterior surface. The powder cf the invention, on the other hand, is in the form of hollow spherical particles. The interior surfacesand exterior surfaces together provide an enormous amount of available surface for use. This is particularly important, for example, in the case of magnesium powder used for flares. Due to the enormous amount of available surface area the magnesium powder may be burned in a highly .intense instantaneous flash.

It is at present believedthat the hollow spherical particles are formed as the resultof the vmanner in which the inert gases are employed. As noted above, a portion of theinert gas is withdrawn from the circulatory system-and conducted to and over the body-of molten metal in the furnace under substantial positive pressure, in order to force molten metal from the furnace to the atomizer. As a result )Of this step the molten metal becomes saturated with the gas at the prevailing temperature and pressure in the melting furnace, causing a certain amount of the gas to go into solution in the molten metal. Then the molten metal is atomized, the resulting minute droplets are promptly frozen .by the cool circulatin inert gas into solid particles. The chilling effect is so rapid that the gas dissolved in the droplets is quickly forced out of solution thus causing them to expand into hollow spherical particles.

These and other features of the invention will be better understood by referring to the accompanying drawings, taken in conjunction with the following description, in which:

Fig. 1 is a diagrammatic flow sheet showing the system as a whole;

Fig. 2 is a side elevation of the purifier shown in Fi 1;

Fig. 3 is a plan view of one of the trays in the purifier;

Fig. 4 is a cross-section on the line 4-4 of Fig. 3;

Fig. -5 is a cross-sectional view of one of the melting furnaces shown in Fig. 1;

Fig. -6 .is an enlarged cross-sectional view of the atomizer shown in Fig. 5;

Fig. 7 is .a longitudinal section of the chamber shown in Fig. 1 for atomizing molten metal and forming metal powder; I

Fig. 8 is a transverse section on the line 8& of Fig. 7;

Fig. 9 is an'enlargecl side View of one of the powder gas separators shown in Fig. 1;

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

Fig. 11 is a front elevation of the same.

Reference is made to Fig. 1 for an overall picture of the apparatus. Since purification of the gas in the system is of initial importance, the main features of its system or circuit will first be described.

This includes a gascmeter l, a conduit 2, a main conduit 3, a branch conduit d, a dust filter 5, a conduit 6, a branch conduit 1 a filter 8, a branch conduit 9, a branch conduit Ill, a filter I I, a branch conduit 12, a compressor is connected on its inlet or suction side with conduit 6, a conduit M connecting the outlet or pressure side of the compressor, a filter l5, a conduit [-6, a branch conduit H connecting the inlet of a purifier l8 surrounded by a heating furnace or chamber I9 having an inlet 29 for the introduction of heating gases and an outlet 2| for the escape of spent gases, and a conduit -22 connecting the outlet of the purifier with the gasometer. The latter conduit may, of course, connect the system at any other suitable point. While some valves or closure members are indicated, it will be clear that any suitable number maybe employed at other points in the circuit. In general, it will be seen that gas may pass from the main system by way of the gasometer and main conduit 3 to and through dust filter 5, one or both filters *3 and i I, to and through the compressor, through filter l5, u ifier wand back. into th system. This cyclic operation may be continued until all of the gas in the system reaches the desired purity. What has been described may be regarded as part of the main system, or indeed a circulating system within the main circulating system. When all of the gas is purified, it is 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 3| 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 ll, 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 5| and conduit 52. In practice it is customary to alternate use of filters 45 and 5|, so that while one is being cleaned or otherwise serviced, the other is used.

The 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 as to atomize the stream of molten meal. It includes conduit I6, from the outlet or pressure side of compressor I3 and a branch conduit 60 terminating in branch conduits BI and 62. Branch GI 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 I connecting conduit i6 and terminating in branch conduits H and I2. Branch I connects with a conduit I3 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 15 connects the furnace to bonnet 35 of the atomizing and powder forming chamber.

Figs. 2, 3 and 4 show the purifier in detail. It is cylindrical in form with a closed bottom 80 (see Fig. 2) resting on supports 0i 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 H. An imperforate cover 05 is securable to the top of the purifier by means of a plurality of bolts 06 through an outer flange 81. All joints of the purifier are gas tight so that heating chamber gases cannot enter the purifier and so that gases inside the purifier cannot escape into the heating chamber.

The trays (see Figs. 3 and 4) are generally cylindrical in shape, being formed on a band of sheet metal 90 with a turned in bottom flange SI and a similar turned in top flange 02. 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 05 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, 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 of purifier I8 is also removed and loaded trays or baskets 82 are placed therein, one superposed on the other. In the case of the bottom tray, its bottom flange 9I rests on inner flange support 83. Lower flange SI of the second tray will rest on upper flange 92 of the first tray, etc. The purifier is provided with a sufficient number of the loaded trays. Cover 85 is then returned and bolted securely to outer flange 81 with bolts 86; after which the top of the purifier is returned.

Melting furnace G4 is shown in detail in Fig. 5. It rests on a dolly 90 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 01 surrounded by a metal Casing 02 lined with refractory brick 93. The chamber is surmounted by a removable top 95. A plurality of spaced opening 9! 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 I00 rests on supports [III at the bottom of the heating chamber. The top of the melting pot is provided with a removable cover I 02 securable to an outer flange I03 by means of a lurality of bolts I04 to provide a non-leaking joint. A metal charging conduit I06 extends through the top of the heating chamber and communicates with the interior of the melting pot. It is secured to cover I02 by means of a plurality of bolts I01. A removable cover IIO fits over the top of the charging conduit and can be screwed thereon to make a leak-proof joint. Branch conduit 03 for inert gas connects with the charging conduit above furnace top 95. A pyrometer I I2 extends through the top and cover I02 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 I I4 of brick-lined furnace bonnet 65. A conduit I I5 for the passage of molten metal extends from near the bottom of the melting pot upwardly through its cover I02 and into passageway II4 of furnace bonnet 65 where it connects with an atomizer I I6 extending through end-cover II'I into chamber bonnet 3|. The two bonnets are connectible with bolts I I9. The furnace bonnet is provided with an opening I20 in close proximity to the atomizer and is fitted with a burner I22 adapted to supply heating gases at and around the atomizer.

Atomizer I I6 is shown in more detail in Fig. 6. It is in the form of a main body portion I24 hollowed out at one end to receive the discharge end of conduit I I5 from the melting pot and hollowed out at the other end to receive an atomizing nozzle I25 and to form a gas distributing chamber I26 around the nozzle. The tip end of the nozzle, with discharge outlet I28, extends through cap sesame I29 screwed onto the other end of the main body portion. Conduit 62' for inert gas connects with a nipple I30 communicating with the gas distributing chamber. Cap I29 is provided with a plurality of inclined circumferen'tially spaced discharge ports 1 32 adapted to blast small streams of pre-heated inert gas against a stream oi molten metal discharged through nozzle outlet I28 at a point or area I34 a suitable distance forward of the nozzle tip.

Figs. '7 and 8 show chamber 32 for atomizin'g molten metal and forming powder therefrom in more detail. It is in the form of a cylindrical tank divided essentially into an uppercompartment Hit, which is in the form of a trough, a lower compartment l l'l', which is essentially in the form of a duct; and two side compartments M2 and MS, 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 Hit" has itssmallest cross-section at the right end of the tank, and its largest cross-section at the left end. The lower'compartment or gas distributing. duct Hil', on the other hand, has its largest cross-section at the right end, wherethe gas is'shownto enter through conduit 33, and its smallest cross-section at the left end.

The compartments are obtained by the use of opposed pairs of overlapping plates I5! to I56, top plates Isl to 568 and apair of spacedside'plates ill and H2. They are suitably welded" to' the cylindrical wall and to each other to provide an integral structure. Plates 5! to ['58 are pitched or slanted at an angle, toward the bottom of the trough, so that powder settling thereon will" tend to slide downinto'the'bottom of thetrough. Re ferring for a moment to Fig. 7-, it will be seen' that an overlying lip El i is welded to the-headof the cylindrical tank at the-right end to provide'a'slot iltbetween inlet conduit 33 and upper comparte ment Mil. Similar underlying lips [16" to m2- provide slots its to Isl. Upper plate 1'6! of the duct is spaced above the bottom of the tank to provide a similar slot 92 at the left end of the tank, in direct communication with outlet conduit The overlying andunderlying lips are sufhcien'tly long to cause gas passing therethrough to sweep along thebottomof the upper compartment. in other words, gas going through slot l'lii sweeps along the top of plate W8", gas passing through slot 585 sweeps across'the'top'of plate Hi7, gas passing through slot I86 sweeps across thetop or" plate I68, etc;

A gas blow-off E95 is provided-along the top'o the tank. In case of an explosion, the blow-off is opened to release explosive forces, thussaving the chamber from damage. An inlet ltdconnects each side compartment with inlet conduit 33. An outlet E99 connects each side compartment with outlet '36. While the side con'rpartments are normally sealed from each other and the other compartments, it is possible for leaks to develop at the welded joints. It is therefore desirable to have an arrangement which will p'ermit the side compartments'to be cleared of. air and filled with inert gas, and this can be done with the inlet and outlets referred to:

Figs. 9, 10 and 11 show powder-gas separator is in some detail. Powder-gasseparator 62 is advantageously of the same general construction.

Referring first to Fig. 9,,the apparatus shown is in the form" of a combination powder-gas separator and collector, being specifically a conventional' cyclone 2%, with an inlet ecu for powdergas and an outlet 202 for gas, and a hopper 293 integrally secured to and depending from the cyclone. The lower end of the hopper terminates in a laterally extending discharge conduit 295 at or near the outlet end of which is an upright relief chamber are. A closure member 26? is pivotally supported at the outlet.

Referring next to Fig. 10, it will be seen that relief. chamber 286 provides a substantial amount of free space 2E6 at its upper end which extends a suitable distance above the place where the chamber joins the conduit. The top of the relief chamber is' fitted with a screw cap 2!] provided with a plurality of circumferentially spaced. handles 2 It.

In the specific construction shown the discharge outlet is at a convenient angle to cooperate with closure member 2671, which is in the form of an enclosed chute pivotally or hingedly connected at 2 it to a fixed support Z'Hi. The chute has a bottom 2th, back 256, side walls 217 and 2l8', a top H9 and a discharge opening 220'. A piece of resilient gasket material 222, such as rubber, is integrally secured to the bottom of the chute so that it may be brought into sealing contact with the discharge outlet.

The discharge outlet is in the form of a pipe welded at its side to the main part of the conduit, the upper end of the pipe being an extension which forms the relief chamber. The chute is integrally secured at its top 2H) to an outer collar 224 fitting loosely around the lower end of the discharge conduit. The upper end of the collar is integrally secured to the lower end of a flexible sleeve 225 fitting loosely around the discharge conduit. This sleeve ma be of rubber and'is adapted to act like a bellows. The upper end of the flexible sleeve is in turn integrally'secured to the discharge conduit. When the chute is moved upwardly and downwardly, the flexible sleeve yields sufiiciently to permit the discharge outlet to be closed and opened.

A'handle 228'is-secured to the top of the chute at its discharge end so that the operator may readily lower the chute to open the discharge outlet and raise the chute to close the outlet. This is a. manual operation which may remain Whollyin control of the operator.

If the operator, however, should instinctively let go of the handle in case of fire, or for any other reason, or should leave the scene, selfclosing means associated with the chute at once take care of such a contingency. The particular self-closing means disclosed include a pair of spring tensioning devices 230' and 23! secured at their lower ends to the chute and at their upper end to a fixed support, in the instant construction at the upper portion of 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 to the chute, such as by bearing down on handle 228, the springs yield suliicientl to permit the chute to drop away angularly from the discharge outlet. To make certain that the chute is not lowered unduly, for example, by the operator when excited, a chain 234 of predetermined length is fastened at its lower end to the chute and at its upper end to a fixed support. The chain fixes and'limitsthe amount of drop for the chute. As a further precautionaholding device 236 with aturnbuckle 238 ishooked at its lower end to the chute and at its upper end to 11 a fixed support (not shown). When the chute is in its closed position, the turnbuckle is tightened. Pressure on handle 228 will, therefore, not open the chute. This feature is particularly desirable 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 applies downward pressure on handle 228, which causes chute 207 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 230 and 23I 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 or leave the scene in fright. In case of fire this is precisely what he should do for safety.

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 as 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 fed into the system to flush out most of the air. Enough helium is thus used to place the system under substantial positive pressure greate1- 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 miscible, 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. 1 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 28 into heating chamber I3, while spent heating gases escape from the heating chamber through outlet 2I to the open atmosphere. Impure helium from the system is forced by compressor i3 through conduit I4, filter I5, conduit I6 and branch conduit II into the purifier I8. 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 95 of finely divided metal particles in superposed perforated trays 82. The heating gases applied externally to the purifier are adapted to 12 heat the metal particles to a temperature surficiently high for the oxygen and nitrogen impuri ties 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 A,, to 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. 1) passes through conduit 22 into gasometer I where it mingles with helium still to be purified.

Since the circulatory system is open, helium passes continuously through gasometer I, conduits 2, 3 and 4, filter 5, conduit Ii, branch conduit I, filter 3, branch conduit 9, branch conduit I0, filter II, branch conduit I2, compressor I3, conduit I4, filter I5, conduit I6, branch conduit II, 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 43, conduit 41, as well as branch conduit 50, filter 5I, conduit 52, main conduit 3, branch conduits 33 and 33 into and through chamber 32, inlets I93, side compartments I42 and I43, outlets I33, conduit 36, 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 filter 5, conduit 6, branch conduit I, filter 8, branch conduit 9, as well as branch conduit III, filter II, branch conduit I2, conduit 6, the compressor itself, conduit I4, filter I5, conduit I6, past branch conduit II to and through branch conduit 63, branch conduits BI and 62 to furnace 64. As more clearly shown in Figs. 5 and 6, helium passing through conduit 6i goes into melting pot I03. This helium may be passed through conduit 63 into chamber 32. The helium passing through branch conduit 32 moves through the coils surrounding the melting pot and is passed into and through atomizer H3, after which it mingles with helium passing through chamber 32.

If furnace I4 is also placed in operating position with respect to chamber 32, its melting pot may be flushed of air and filled with helium undergoing purification in a manner similar to furnace 64. Helium is forced by the compressor through conduits I6 and I0, and branch conduits II and I2. Helium passing through conduit II into the melting pot may be passed through conduit I3 into chamber 32. Helium passing through branch conduit 72 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 sufiiciently pure the valves in inlet II and outlet 22 are closed to cut-out the purifier circuit. It may be cutin 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 area-cas helium, it is ready for the actual metat powder producing operation. Referring. for tnemoment to Fig. 5, which shows melting: furnace 64 and its auxiliary equipment in more detail, cover H is removedirom charging conduit r166. ingots. of metal to be converted into metal powderare dropped into melting pot limi. After a suit:- able amount is placed therein the cover isv re.--. turned. The apparatus is at present being. used; to produce magnesium powder and also magnesium-aluminum alloyv powder. The inside di-: mensions oi the pot are 24" in diameter and 42" high. A charge of about 180 pounds of mag nesium isv thus introduced. Oil burners 98: are. operated to heat the pot externally until its:magnesium content reaches a suitable molten tom-'- perature, from 1300" to 1350 F; The burners. are kept in operation to. maintain this temperature.

Pressure-gas conduit 6| is opened to admit helium into the charge. conduit and top portion of the pot above the level of the molten. magnesium. Since the pressure-gas conduit communicates with the compressor the molten magnesium is placed under sufiicient gas pressureto. force a stream of magnesium upwardly through molten-metal conduit I I to andthrough' atomizer I [6 into atomizing and powder forming chamber 32. A pressure of l2-15 pounds persquare inch is applied initially to the topof the body of molten magnesium to: start its passagethrough the conduit and the atomizer. After atomization of the metal is underway the pressure is reducedv to about 5- pounds per square inch. Helium under adequate pressure by the compressor is passed through atomizing-gas conduit 62 whereit is heated in the coils around the melting pot. The preheatedv helium is passed through nipple [30 (see Fig. 6) into gas distributing chamber I26 of the atomizer, from which it issues through discharge ports [32 of cap I29 in a plurality of streams and blastsor atomizes the fine stream ofv molten magnesiumdischarged through nozzle outlet 23 at point or area I34 a suitable distanceiorward ofthenozzle tip. The pressure of the helium atv the nozzle varies somewhat according. to. its construction. A pressure in the neighborhood: of 60pounds per square inch Works satisfactorily with the-nozzles now employed.

Returning for a moment; to Fig. 1, it will be:

recalled that blower 31- causes the helium; to circulate continuously through. thesystem. Sincechamber 32 is on the suctionside. of. theblower, the helium is in effect sucked through and fromthe chamber only to be. forced or pushed front frozen into powder particles. in: the coolhelium-- sweeping through upper. compartment I40 (see- Figs. 7 and8).

While the newly formed particles of magnesiumpowder tend to remain in suspension in the heliumas the heliumpasses throughthe chamber to the blower, some of it also tends t'o'settlebyv gravity onto plates Fit. to I58. and toward the bottom or base of the trough of the upper compartment. Additional amounts of relatively cool helium are, therefore, introduced intd the upper compartment by way of. inletconduit 33'; Accordin to .a present: practice... the. amount of'. helium.

The

stream being directed along the top of plate 16.8:

in the bottom of the trough. Any magnesium powder settling or tending to settle on. that plate:

is, therefore, swept up and placed in suspension in the. main. and large current of gas of helium.

passing through the upper compartment.

In a similar manner some: helium in lower compartment or duct Ml. passes as a stream through. slot. I85 along the top of plate. iii-l at the bottomof the trough of theupper compartment. Similar streams of helium pass through slots I381 to l9l,. so that plates I66, I65, I6 1, W3, [.62 andv IGI at:

the bottom of the trough. of the upper compartment are continuously swept with streams of.

helium under sufficient velocity to keep the powder. from" settling and: to keep it in suspension.

An additional stream of helium passes through.

duct I92 into the: discharge end: of the upper compartment. duced: through the slots also spreads to. the side and sweeps. across plates 15! to iEB to keep them clean of powder. The mixture of gas and powder is under a great deal of turbulence which inhibits settling of the powder. gas is-in efiect. sucked. from the upper compartment throughv outlet 36 and blown through conduit 38.

If melting furnace 64: must be shut down for some reasons, such asior repairs, melting furnace Mi (see Fig. 1') is put in operation at the other end: of the chamber. In this case it is advisable to close inlet conduit 30 and: to openinlet conduit 34'. Asbefore, a finestreamof molten magnesium issuing from. thenozzle of the atomizer is. blasted with helium and the atomized magnesium. is promptly enveloped in the relatively cool helium gas entering theupper compartment byway of inlet conduit 341 as well as by helium entering the chamber throughinlet conduit 33.

The force behind the fine stream of molten 7 metal issuing from the nozzle of the atomizer at either end of; the chamber and the force of the heliumv used to atomizew the stream of molten magnesium. is. suificient to throw the atomized magnesium. substantially across the length of the chamber; When melting furnace 64 is in operation the direction of the streamofmolten metal is in. general concurrent with the streams of helium passed into and through the chamber. On the other hand, when melting. furnace-M is. in

operation the direction of the stream of molten metal: issuing from the. nozzle is. in general counter'current to thehelium entering the upper compartment by way of inlet conduit 33 but con-- current with the helium entering the. chamber through inlet conduit 35.

is kept in a. turbulent state. Inany event the suction force of the bloweris sufficient to draw tail above, the larger powder particles are separated. selectively from the helium and smaller particles-inoyclo'ne ZOO-and fall into-hopper 293. After asufiicient supplyof powder has collectedintheihopper, some ofit is'wi-thdrawn from'ti-me entering the upper t t. byway. f: inl t. to time; care being taken not to break thepowder Some of theheliu-m. thus. intro! The powder laden.

As a result of these contrary movements, at least initially, the helium:

seal in discharge conduit 205 so that air cannot enter the system.

Again returning to Fig. l, the helium containing the smaller particles of magnesium powder is forced from powder-gas separator 40 through conduit 4| 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 it still contains some fines which should be removed before it reaches the compressor. To this end the helium leaving the 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 Dracco 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 4'! back to main conduit 3. This is a wet filter, 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 50, a similar filter 5| 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 30, 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|. 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 filter enters conduit 6 and is diverted through branch conduit 1, filter 8 and conduit 9 back to conduit 6 which connects the inlet or suction side of compressor l3. When filter 8 is cut-out for cleaning, helium leaving filter 5 is diverted from conduit 6 through branch conduit [0, filter l l, and conduit 62 back to conduit 6. Filters 8 and H 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 filter I5. This filter may contain a filter layer of felt, for example, such as a Cuno filter, 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. placement helium must, therefore, be added to the system. However, by keeping 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. 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 confined 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 purified, 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 specific practice described is only by way of illustration. It is obvious, for example, that other compressors, purifiers, furnaces, atomizers, separators, filters, etc., could be used and that the units making up the whole can be arranged in various ways. Wat is disclosed is a highly effective arrangement for producing metal powders in large quantities in an efficient manner,

I claim:

1. In apparatus for producing metal powder from a body of molten metal, the improvement comprising a main circulatory system of connectlng conduits adapted to be filled with gas under pressure higher than atmospheric, a gasometer connecting the main circulatory system to hold surplus gas and to take care of contraction and expansion of the gas, a chamber in the system to receive atomized molten metal and to chill the atomized metal into powder, a furnace with amelting pot for melting and holding the body of molten metal, an atomizer in the system for the molten metal connecting the melting pot of the furnace and the chamber, a by-pass conduit connecting the main circulatory system and the atomizer for the passage of some of the gas, a portion of the by-pass conduit being in heat-exchange relationship with the furnace to heat the gas going to the atomizer, a filter to remove metal powder from the gas before it reaches the atomizer, a compressor in the by-pass conduit to increase the pressure of the gas going to the atomizer in the system, a blower above that in the main circulatory system for circulating the gas around the main circulatory system, and a separator in the main circulatory system for separating the powder from the gas.

2. Apparatus according to claim 1, in which the filter is located in the main criculating system forward of the separator and rearward of the by-pass conduit.

3. Apparatus according to claim 1, in which the filter is located in the by-pass conduit rearward of the compressor.

17 '4. Apparatus according to claim 1, in which the filter is located in the bypass conduit forward of the compressor.

5. Apparatus according to claim 1, in which the by-p-ass conduit is divided into two branches in advance of the furnace, one branch connecting the atomizer and the other branch connecting the interior of the melting pot.

6. Apparatus according to claim 1, in which the filter is located in the main circulating system forward of the separatorv and rearward of the by-pass conduitjand the by-pass conduit is divided into two branches in advance of the fur nace, one'branch'being in heat-exchange relationship with the furnace and connecting the atomizer and the other branch connecting the interior of the melting pot.

'7. Apparatus according to claim 1, in which the filter is located in the by-pass conduit rearward of the compressor; and the by-pass conduit is divided into two branches in advance of the furnace, one branch being in heat-exchange relationship with the furnace and connecting the atomizer and the other branch connecting the interior of the melting pot.

8. Apparatus according to claim 1, in which the main circulatory system is provided with a plurality of separators in the form of cyclones connected in series so that the gas may be passed successively through the separators and the powder may be separated from the gas by dry precipitation.

9. Apparatus according to claim 1, in which another by-pass conduit connects the first bypass conduit forward of the compressor with the main circulatory system, and the second by-pass conduit includes a purifier for the gas forced therethrough by the compressor.

10. Apparatus according to claim 1, in which another by-pass conduit connects the first bypass conduit forward of the compressor with the main circulatory system; the second by-pass conduit includes a purifier provided with a perforated container adapted to hold finely divided heated metal particles through which the gas may be passed by the compressor for purification with respect to such impurities as oxygen and nitrogen on its way back to the main circulatory system.

11. In apparatus for producing metal powder from a body of molten metal, the improvement comprising a main circulatory system adapted to be filled with gas under pressure higher than atmospheric, a gasometer connecting the main circulatory system to hold surplus gas and to take care of expansion and contraction of the gas, a chamber to receive atomized molten metal and to chill the atomized metal into powder, a furnace with a melting pot for melting and holding the body of molten metal, an atomizer for the molten metal connecting the melting pot of the furnace and the chamber, a blower for circulating the gas around the main circulatory system, a separator in the main circulatory system for separating the powder from the gas, a by-pass conduit connecting the main circulatory system at two spaced points for the passage of the gas therethrough, and a purifier for the gas in the by-pass conduit for purifying the gas on its way back to the main circulatory system.

12. Apparatus according to claim 11, in which the purifier is provided with a perforated container adapted to hold finely divided heated metal particles through which the gas may be passed for purification with respect to such impurities as oxygen and nitrogen on its way back to the main circulatory system.

13. In apparatus for producing metal powder by atomizing a body of molten metal into very finely-divided particles and freezing the particles intofpowder with a gas inert to the metal, the main body of gas being jconfined in amain cir culatory system under pressure higher than atmospheric pressure to prevent ingress ofjoutside air; the improvement comprising a heating chamber, a melting pot for metal to' be atomized within the heating chamber, an atomizing chamber forming a part of the main circulatory system, an atomizer positioned to spray molten metal into said atomizing chamber, a conduit for molten metal extending from the bottom portion of the melting pot to the atomizer, a by-pass line through" which a portion of the main body of gas can be withdrawn from the main circulatory system, a compressor in the by-pass line for withdrawing a portion of the gas from the main circulatory system and increasing its pressure, said by-pass line including a conduit system connecting the outlet of the compressor with the atomizer and having a portion thereof extending through the heating chamber, whereby gas withdrawn from the main circulatory system and compressed and passed through said conduit system is preheated before reaching the atomizer.

14. Apparatus according to claim 13 in which a furnace bonnet communicates with the heating chamber as an extension thereof and the atomizer is located at least in part in the bonnet so that it may be maintained at an elevated temperature.

15. Apparatus according to claim 14 in which heating means are provided in the bonnet for supplying extra heat to the atomizer to maintain it at an elevated temperature.

16. Apparatus according to claim 13 in which the conduit system of the by-pass line also includes conduit means connecting the outlet of the compressor with the upper portion of the melting pot, whereby molten metal in the melt ing pot can be placed under pressure to cause it to fiow through the conduit extending from the bottom of the melting pot to the atomizer.

17. Apparatus according to claim 16 in which a closeable metal charging conduit extends from the melting pot to the exterior of the heating chamber and the conduit means from the compressor to the upper portion of the melting pot includes said metal charging conduit.

18. Apparatus according to claim 13 in which a filter is positioned in the by-pass line to remove solids from the gas withdrawn from the main circulatory system before it reaches the atomizer.

19. In apparatus for producing metal powder by atomizing a body of molten metal into very finely-divided particles and freezing the particles into powder with a gas inert to the metal, the main body of gas being confined in a main circulatory system under pressure higher than atmospheric pressure to prevent ingress of outside air; the improvement comprising a heating chamber, a melting pot for metal to be atomized within the heating chamber, an atomizing chamber forming a part of the main circulatory system, an atomizer located at a level above the bottom of the melting pot and positioned to spray molten metal into said atomizing chamber, a conduit for molten metal extending from the bottom portion of the melting pot to the atomizer, a conduit extending from the exterior of ing from the bottom portion of the melting pot 5 tqthe atom'mer, a by-pass line from the main circulatory system connected with the atomizer,

whereby a, portion of the main body of circulate gas may be Withdrawn and used for the atomization of molten metal discharged from the m atomizer! a portion of said by-pass line extending, through the heating chamber exteriorly of the, melting pot, whereby gas withdrawn through raid lily-pass line for atomization of molten metal pre-heated before. reaching the atomizer.

2.0. Apparatus according to claim 19 in which bite-ting means are provided for heating the atomizer to maintain it at an elevated temperature.

20 21. Apparatus according to claim 19 in which a g -pressure-r leas conduit connects the top portion of the melting pot nd the atomizing chamber so that gas within the melting pot under a pressure higher than that in the. atomizing chamber may pass to said atomizing chamher to reduce the gas pressure in the melting pot.

HENRY A. GOLWYNNE.

References Cited. in the file of this patent UNITED STATES PATENTS Number Name Date 1,356,780 Nicol Oct 26, 1920- 15/ 1,61%566 Marx -v Jan. 21 1927 1,869 0215 Seastone sr July 26, 1932 2,402,441 Paddle June 18,, 1946 2,450,081 Burkhardt Sept. 28, 1948

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