US3658311A

US3658311A - Apparatus for making powder metal

Info

Publication number: US3658311A
Application number: US12809A
Authority: US
Inventors: Vincent N Di Giambattista; Robert L Greene Jr
Original assignee: Kelsey Hayes Co
Current assignee: Kelsey Hayes Co
Priority date: 1970-02-19
Filing date: 1970-02-19
Publication date: 1972-04-25
Anticipated expiration: 1989-04-25
Also published as: SE373055B; FR2078853A5; DE2108050A1; NL7102265A; DE2108050B2; CH524416A; BE763223A; GB1304168A; CA937373A

Abstract

An apparatus for making metal powder of ultra high purity which comprises a vessel defining a main collection chamber filled with an inert gas which serves as a heat transfer medium for effecting a cooling and solidification of molten metal particles injected therein. The apparatus further includes heat transfer conduits for cooling and recirculating the heat transfer gas through the main collection chamber and a refrigerated secondary collection chamber in which further cooling of the spherical powder particles is attained. Suitable controls are provided to assure appropriate pressure levels within the apparatus, whereby metal powders of optimum properties are produced.

Description

United States Patent Di Giambattista et al.

[ 51 Apr.25,W72

[54] APPARATUS FOR MAKING POWDER METAL Mich. I [73] Assignee: Kelsey-Hayes Company 22 Filed: Feb. 19, 1910 [2]] App]. No.: 12,809

[52] US. Cl. ...266/34 R, 75/0.5 B, 26 4/12,

1 18/25 R [51] Int. Cl ..C2lc 7/00 [58] Field ofSearch ..24l/l6,l7;26 ,/5,11,12,

264/13, 14; 75/05 B, 0.5 AB, 0.5 BA, 0.5 BB, 0.5 BC, 0.5 C; 266/34 R; 18/25 R [56] References Cited UNITED STATES PATENTS 3,549,140 12/1970 Ingersoll ..266/ 3 4 R 3,457,336 7/l969 Harris ..264/l4 2,633,604 4/1953 Allenetal. ..264/l4 Primary Examiner-Gerald A. Dost Attorney-Harness, Dickey & Pierce ABSTRACT An apparatus for making metal powder of ultra high purity which comprises a vessel defining a main collection chamber filled with an inert gas which serves as a heat transfer medium for effecting a cooling and solidification of molten metal particles injected'therein. The apparatus further includes heat transfer conduits for cooling and recirculating the heat transfer gas through the main collection chamber and a refrigerated secondary collection chamber in which further cooling of the spherical powder particles is attained. Suitable controls are provided to assure appropriate pressure levels within the apparatus, whereby metal powders of optimum properties are produced.

9 Claims, 7 Drawing Figures PATENTEBAPR 25 1972 3,658,131 1 SHEET 2 OF 4 EEL- W715: 72/ A/ llzlkg f gi/z APPARATUS FOR MAKING POWDER METAL BACKGROUND OF THE INVENTION The adoption of powder metallurgical techniques for fabricating components suitable for use under high temperature conditions has occasioned an increasing demand for metallic powders of heat-resistant alloys which are of high purity, enabling subsequent compaction thereof into solid components approaching 100 percent theoretical density. The deleterious effects of impurities, and, particularly oxides, on the high temperature properties of parts fabricated from such metal powders requires such powders to be prepared and handled under substantially dry inert atmospheres. Convention-ally, heat-resistant metal alloy powders are produced by gas atomization of a molten mass ofthe metal alloy in a hermetically sealed chamber, which usually is filled with a suitable inert gas such as nitrogen, helium, argon, and mixtures thereof, for effecting a cooling and solidification of the particles without any appreciable contamination thereof. In such equipment, it is conventional to inject the molten atomized metal particles into the upper end of a vessel defining the collection chamber and the particles become progressively cooled and solidify during their gravitational drop to the bottom portion of the vessel where they are extracted in a manner so as to avoid any contamination.

There has been a continuing problem in the production of gas atomized metal powder employing inert gases as the heat transfer medium due to the fixed volume of gas present in the collection chamber which quickly becomes superheated upon initiation of the gas atomization process accompanied by a corresponding rise in pressure, necessitating a venting of the collection chamber to reduce the pressure. These foregoing factors result in a decrease in the density of the inert gas at-' mosphere present in the collection chamber with a corresponding reduction in the heat transfer efficiency. This condition is a dynamic one causing continuous changes in the atomization environment contributing to unstable gas atomization conditions with attendant nozzle fouling and fluctuations in the particle size of the atomized mass. In'some instances, still further problems are encountered such as a sintering and/or fusion of the molten particles, the production of hollow powder particles incorporating entrapped inert gas in the interior thereof, as well as excessive heat build up within the interior of the collection chamber. In view of the fore'going, it is conventional to limit the quantity of metal atomized in a single run to a relatively small amount to avoid one or more of the foregoing problems which seriously detracts from the efficiency of the gas atomization process.

In accordance with the apparatus comprising the present invention, substantially long runs, permitting the atomization of relatively large amounts of metal alloys, can be undertaken during which substantially stable conditions are maintained within the apparatus so as to assure optimum gas atomization of the melt and the attainment of metal powder particles within the desired size range and purity.

SUMMARY OF THE INVENTION The benefits and advantages of the present invention are achieved by an apparatus which comprises an elongated upright vessel defining a main or principal collection chamber which is formed at its upper end portion with a nozzle port through which atomized molten metal particles are discharged and at its lower end portion with an outlet port through which the solidified metal particles are extracted from the chamber. The principal collection chamber is filled with an inert gas for effecting a cooling and solidification of the metal particles during their travel from the nozzle port toward the outlet port. The heat absorbed by the inert gas is continuously extracted by cooling loops disposed in communication with the principal collection chamber, thereby preventing heat saturation of the gas and avoidance of pressure increases requiring excessive venting of the collection chamber. The apparatus further includes suitable deflection means within the collection chamber for intercepting and deflecting any molten metal which inadvertently may be discharged into the collection chamber, thereby avoiding a contamination and fouling of the components and previously formed powder. The apparatus further includes control means for continuously monitoring the pressure differential between the melt chamber and principal collection chamber and provides for a controlled flow and venting of inert gas into and out of the collection chamber to maintain optimum conditions. A secondary collection chamber disposed in communication with the outlet port of the vessel is further provided for receiving and effecting a further cooling of the powder particles in response to their contact with a refrigerated inclined ramp.

Still other benefits and advantages of the apparatus comprising the present invention will become apparent upon a reading of the description of the preferred embodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of an apparatus constructed in accordance with the preferred embodiments of the present invention;

FIG. 2 is a magnified fragmentary side elevational view of the principal collection chamber and melt chamber including sensing devices connected to suitable controls for regulating the pressure differential therebetween;

FIG. 3 is a fragmentary somewhat schematic view of a typical gas atomization nozzle arrangement suitable for use in ef fecting atomization of molten metal;

FIG. 4 is an enlarged fragmentary vertical sectional view of the lower portion of the main collection chamber illustrating the provision of a deflection cone above the outlet port thereof;

FIG. 5 is an enlarged fragmentary side elevational view of the secondary collection chamber shown in FIG. 1;

FIG. 6 is a transverse cross sectional view of the secondary collection chamber shown in FIG. 5 and taken along the line 66 thereof; and

FIG. 7 is a magnified vertical sectional view of one of the heat transfer loops on the main or principal collection chamber shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to the drawings and as may be best seen in FIGS. 1 and 2, the apparatus comprising the present invention is comprised of a series of interconnected vessels which define a vacuum melting chamber 10, a main collection chamber 12, a secondary collection chamber 14 and a collection box 16. The upper vessel defining the melting chamber 10 is adapted to be equipped with suitable heating devices for melting a crucible of the metal to be atomized and incorporates pouring devices for pouring the melt at a controlled rate into a suitable gas atomization assembly. The melting chamber 10 is adapted to be hermetically sealed in order that the heating of the metal charge to be atomized can be accomplished under vacuum or in the presence of a dry inert atmosphere so as to avoid any appreciable oxidation thereof.

The vessel defining the melting chamber 10 is connected by means of a suitable flange connection 18 to an upper section 20 of the elongated vessel defining the main collection chamber 12. A gas nozzle atomization assembly of any one of the various types well known in the art is adapted to be positioned at or adjacent to the flange connection 18 whereby the metal charge, upon atomization, is discharged into the upper end portion of the main collection chamber in the form of fine-sized molten droplets which become solidified during the course of their downward travel. Typical of the various atomization nozzle assemblies is the arrangement illustrated in FIG. 3 comprising a tundish 22 having a downwardly extending stem 24 which is formed with an orifice through which a molten metal stream 26 is discharged and becomes fragmentized or atomized upon coming in contact with one or a plurality of high pressure gas streams 28 discharged from a series of nozzles 30 disposed in circumferentially spaced converging relationship. During an atomization run, the molten metal in the tundish is continuously replenished by means of a suitable crucible 31. It will be appreciated that alternative gas atomization arrangements, as well as other means for effecting a fragmentation of the molten metal charge into droplets of the desired size, can be satisfactorily employed in lieu of the exemplary nozzle arrangement illustrated in FIG. 3.

The vessel defining the main collection chamber 12 is comprised of the upper section 20, an intermediate cylindrical section 32 and a lower conical section 34, which are secured together so as to provide a hermetically sealed chamber. The downward and outward taper of the walls of the upper conical section enables divergence of the atomized metal particles 'without contacting the side walls of the vessel while still in a molten state as they are injected into the main collection chamber at a point corresponding approximately to the position of the flange connection 18 defining a nozzle port. The molten metal particles are adapted to fall under the influence of gravity downwardly through the intermediate cylindrical section 32, during which travel they are progressively cooled and eventually solidify into spherical particles of the desired size range. The solidified metal particles eventually come in contact with the inner surfaces of a lower conical section 34 and are guided downwardly thereby toward a flanged outlet port 36, through which they are discharged into the secondary collection chamber 14. To avoid any adverse coreaction between the hot metal particles and the vessel defining the collection chamber, it is preferred to construct the

sections

20, 32, and 34 of a stainless-type steel which resists oxidation attack when exposed to an air atmosphere.

To further enhance a cooling of the atomized metal particles discharged from the main collection chamber, the lower conical section 34 is preferably cooled such as by means of a series of cooling coils 38 disposed in heat conductive contact with the exterior surfaces thereof for extracting heat therefrom by means of the circulation of a suitable heat transfer fluid through the cooling coils. For this purpose, conventional tap water, as well as any one of the well known fluid refrigerants, can be employed for cooling the lower end portion of the collection chamber.

In addition to the direct cooling of the walls of the collection chamber, such as by means of the cooling coils 38, a further extraction of heat from the inert gas atmosphere within the main collection chamber is achieved by two heat transfer loops as best seen in FIGS. 1 and 7, which extend longitudinally of the intermediate cylindrical section 32 and are disposed substantially diametrically opposite to each other. Each of the heat transfer loops is of an identical construction and operation and, therefore, a detailed description ofone will suffice. As shown in FIG. 1, a pair of flanged inlet ducts 40 are connected to the upper portion of the intermediate cylindrical section 32 and are disposed in communication with the interior of the main collection chamber in a region corresponding to the point at which the inert gas is at the highest temperature The inert gas atmosphere is adapted to be withdrawn through the two inlet ducts into a U-shaped conduit 42, as may be best seen in FIG. 7, which is provided with a conically shaped filter 44 for extracting extremely fine-sized metallic powder particles entrained in the gas. The filtered gas thereafter passes over the surfaces of a tubular heat exchanger bundle 46 which is connected by means of supply lines 48 to a source of cooling fluid, which may conveniently be water or any other of the well known refrigerants.

The withdrawal of the inert heat transfer gas from the upper portion of the main collection chamber, causing it to travel downwardly through the filter and heat exchanger bundle, is achieved by a suction blower assembly comprising a fan 50 and motor 52, which are axially mounted in the lower portion of the U-shaped conduit 42, as best seen in FIG. 7. The cooled and filtered gas discharged from the blower assembly passes downwardly and into outlet ducts 54, as shown in FIG. 1,

which are connected to the lower portion of the intermediate cylindrical section 32 and are disposed in communication with the main collection chamber into which the cooled gas is discharged. It will be apparent from the foregoing arrangement that the cooling loops effect a continuous circulation and cooling of the inert heat transfer gas in a direction countercurrent to the flow of the metal powder. The suction imparted by the blower assembly of each heat transfer loop serves to provide a reduction in the pressure of the inert gas in the upper portion of the main collection chamber, which serves to further promote stabilization of the metal stream 26 from the tundish and avoidance of erratic operation and/or fouling of the atomization nozzle assembly.

In accordance with a further preferred structural feature of the apparatus comprising the present invention, a foraminous deflection cone 56, as best seen in FIG. 4, is provided which is disposed in the lower end portion of the main collection chamber adjacent to the flanged outlet port 36. The deflection cone 56 is adapted to intercept and fragmentize and/or deflect a molten stream of metal moving downwardly as a result of an inadvertent malfunction of the gas nozzle atomization assembly, thereby averting molten metal from directly entering the secondary collection chamber 14, which might otherwise fuse with and agglomerate previously collected metal powder. The deflection cone 56 is formed so that during normal operation of the apparatus, the solidified metal particles pass through the apertures therein and downwardly into the secondary collection chamber. It will be further noted from the specific arrangement as illustrated in FIG. 1 that the nozzle port 18, in which the gas atomization assembly is adapted to be mounted, is disposed in direct vertical alignment with respect to the flanged outlet port 36, above which the deflection cone is disposed. The deflection cone can be positioned upwardly from the position as illustrated in FIG. 4 in a region of the main collection chamber at which the metal particles coming in contact therewith have sufficiently solidified so as not to become appreciably deformed upon striking the mesh of the deflection cone.

Upon passing through the deflection cone and outlet port 36 of the main collection chamber, the solidified metal particles enter the secondary collection chamber which is defined by an angularly inclined cylindrical vessel 58 which is provided with a flanged inlet port 60 in its upper end portion adapted to be sealingly connected to the flanged outlet port 36. The lower or right-hand end of the vessel 58, as viewed in FIGS. 1 and 5, is sealingly connected to a collection hopper 62 into which the cooled metallic powder is discharged. In accordance with a preferred construction, as shown in FIG. 5, the wall of the vessel 58 is provided with a port 64 over which a light 66 is sealingly positioned so as to illuminate the interior of the secondary collection chamber 14, enabling visual inspection of the collected powder through a suitable inspection port 68 provided in a flanged hatch 70 sealingly affixed to the upper end of the vessel 58.

As is best seen in FIGS. 5 and 6, a refrigerated plate 72 is disposed within the interior of the cylindrical vessel 58 and is correspondingly inclined downwardly toward the collection hopper 62. The upper portion of the plate is substantially flat and extends transversely of the cylindrical vessel 58 having the longitudinally extending edges thereof provided with a suitable resilient gasket 74 forming a seal so as to prevent passage of particles downwardly between the longitudinal side edges of the refrigerated plate. The refrigerated plate 72 extends for substantially the entire length of the cylindrical vessel 58 and is provided with a wear plate 76 at the upper end portion thereof disposed directly beneath the inlet port 60. The wear plate 76 is comprised of an abrasion-resistant material which resists the wear resulting from the impingement of the metal particles thereagainst. The refrigerated plate 72, as best seen in FIG. 6, is provided with a plurality of refrigeration conduits 78 disposed in direct heat transfer relationship with the underside thereof through which a suitable refrigerant is circulated as supplied from supply lines 80, which extend upwardly through the underside of the cylindrical vessel 58 through sealed ports.

In accordance with this arrangement, the solidified metal particles entering the secondary collection chamber first strike the upper surface of the wear plate 76 and thereafter roll downwardly along the upper surface of the refrigerated plate and in direct heat conductive contact therewith, effecting a further cooling of the metal particles. The cooled metal particles cascade off the lower edge of the refrigerated plate and are accumulated in the collection hopper 62 which is connected by means of a flexible bellows 82 to a flanged inlet port 84 on the upper surface of the collection box 16. The lower inner portion of the inlet port 84 is provided with a suitable removable flange or gate valve 86 which, upon opening, effects a discharge of the collected metal powder in the collection hopper so that it can be screened and classified, and thereafter packed in hermetically sealed containers prior to removal from the collection box. During the removal of the metal powder from the collection box, the removable flange 86 can be closed, thereby isolating the remainder of the system from the air atmosphere.

In accordance with the foregoing arrangement, gas atomization of the molten metal can be achieved providing substantially long runs without encountering overheating of the inert heat. exchange gas within the main collection chamber, thereby avoiding unstable conditions resulting in the production of metallic powder of less than optimum characteristics. In order to assure the maintenance of proper gas differentials between the melting chamber and main collection chamber and a venting and/or make-up of inert gas to maintain the proper pressure differential, a control system is provided for sensing the gas pressure present within the aforementioned chambers. As may be best seen in FIG. 2, the melting chamber is provided with a presettable high-pressure vent valve 88 which is adapted to discharge gas to the atmosphere whenever the internal pressure of the melting chamber exceeds a preset maximum limit. Ordinarily, the melting chamber is maintained under a positive pressure within the range of from about 2 to 3 psig. The actual pressure present in the melting chamber can be visually determined by means of a pressure gauge 90. In ad dition, the melting chamber is further provided with a pressure-sensing device 92 which may comprise a suitable pressure switch of the types well known in the art and which is electrically connected to a ratio relay 94, an inert gas fill valve 96 and a low pressure inert gas bleed-in valve 98. Similarly, the interior of the main collection chamber is provided with a pressure-sensing device 100, which is electrically connected to the ratio relay 94 and to an inert gas fill valve 102. The main collection chamber itself is disposed on communication with a venting system, as shown in FIG. 2, comprising a cyclone-type separator 104 which is connected at its outlet to a vacuum angle valve 106, the outlet of which is connected to an automatic pressure control valve 108, which is electrically connected to the ratio relay 94. The outlet side of the automatic pressure control valve is connected to the inlet side of a pressure control blower 110, imparting a suction pressure to the outlet side of the automatic pressure valve, effecting a withdrawal of the inert gas atmosphere from the main collection chamber, depending upon the position of the automatic control valve 108.

In operation, after the metal to be atomized has been charged into the melting chamber, the entire system is sealed and evacuated to a pressure preferably below 2 X l0' mm Hg. It is usually preferred to effect a melting of the metal charge while the system is under a vacuum whereafter prior to pouring, the system is backfilled with a suitable inert gas, such as argon, to a positive pressure of about 23 psig. This is accomplished by an actuation and opening of inert gas fill valves 96 and 102. At this point, immediately prior to pouring of the molten metal into the gas atomization assembly, the pressure in the melting chamber and main collection chamber is the same. Since a differential pressure between the melting chamber and main collection chamber is desirable to assure uniform operation of the atomization nozzle and stability of the metal stream being atomized, the ratio relay 94 is preset in order to provide a predetermined pressure difierential such as, for example, I to 2 psig between the melt chamber and main collection chamber.

Just prior to pouring, the pressure control blower 110 is energized and the vacuum angle valve 106 is opened, whereby inert gas is withdrawn from the main collection chamber at a rate dependent on the position of the automatic pressure control valve 108 as controlled by the ratio relay 94. Assuming that the initial backfilling of the melt chamber and main collection chamber was made to a pressure of 3 psig and the ratio relay was preset to provide a pressure differential of 2 psig, the venting system connnected to the main collection chamber will operate to withdraw inert gas from the main collection chamber so as to attain these preset conditions. At the same time that the pressure control blower is energized, pressurized inert gas is fed to the nozzles 30 (FIG. 3) of the atomization assembly and cooling fluid is circulated through the coil 38, heat transfer bundles 46 and refrigeration conduits 78, and the axial fan assemblies in the cooling loops are operating to circulate gas therethrough.

During initiation of the pour, the filling of the tundish 22 effects a sealing between the melting chamber 10 and main collection chamber 12, whereafter additional inert gas is bled into the melting chamber by the actuation of the inert gas bleed-in valve 98 to maintain the melt chamber at the desired preset level, such as 3 psig, during the entire run. During the continuance of the gas atomization of the melt, the increase in temperature of the gas in the main collection chamber, as well as the discharge of additional gas into the main collection chamber by the noules 30 of the gas atomizing assembly, tends to cause a pressure build-up in the main collection chamber which is continuously monitored by the pressuresensing device 100 which signals the ratio relay 94 which in turn adjusts the opening of the automatic pressure control valve 108, whereby the proper venting of the interior of the main collection chamber occurs. During the continuation of the atomization of the melt, the inert gas is continuously circulated through the two heat transfer loops disposed in communication with the interior of the main collection chamber, thereby minimizing pressure build-up and similarly minimizing the amount'of inert gas being vented, while at the same time assuring the maintenance of a reasonable density of the inert gas atmosphere so as to provide satisfactory cooling of the molten metal particles.

While it will be apparent that the invention herein disclosed is well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the spirit thereof.

We claim:

1. An apparatus for producing powdered metal comprising an elongated upright vessel defining a main collection chamber, said vessel formed at its upper portion with a melt chamber and a noule port through which atomized molten metal particles are discharged into said main chamber, said vessel formed at its lower portion with an outlet port through which solidified metal particles are discharged from said main chamber, said main chamber filled with an inert gas for extracting heat from the molten metal particles effecting a solidification thereof during the course of their travel from said nozzle port toward said outlet port, cooling means disposed in communication with said main chamber for extracting heat from said gas and recirculating the cooled said gas back to said main chamber, and pressure control means for controlling the pressure of the gas in said main collection chamber within a preselected range and at a pressure below that within said melt chamber disposed on the opposite side of said nozzle port.

2. The apparatus as defined in claim 1, wherein said cooling means are operative for withdrawing gas from the upper portion of said main collection chamber and for returning the cooled said gas to the lower portion of said main collection chamber.

3. The apparatus as defined in claim 1, wherein at least a portion of the surface of said vessel is disposed in heat exchange contact with a cooling medium for extracting heat from the vessel.

4. The apparatus as defined in claim 1, in which said nozzle port is disposed in vertical alignment above the said outlet ort. p 5. The apparatus as defined in claim 1, further including deflection means disposed in said main collection chamber beneath said nozzle port for intercepting and deflecting a molten metal stream inadvertently discharged through said nozzle port.

6. The apparatus as defined in claim 1, in which said cooling means comprises a conduit extending exteriorly of said vessel and having the ends thereof disposed in communication with the upper and lower portions, respectively, of said main collection chamber; heat exchanger means disposed in said conduit and adapted to extract heat from said gas passing in heat exchanging relationship relative thereto, and blower means for withdrawing gas from the upper portion of said main collection chamber into said conduit and relative to said heat exchanger means therein and thereafter for discharging the cooled said gas back into the lower portion of said chamber.

7. The apparatus as defined in claim 1, further including a second vessel defining a secondary collection chamber disposed in communication with said outlet port, said secondary collection chamber formed with a member having a downwardly inclined surface along which the metallic particles are adapted to travel in heat transfer contact therewith, and refrigeration means for extracting heat from said member.

8. The apparatus as defined in claim 7, further including a collection hopper disposed in communication with the outlet end of said secondary collection chamber for collecting the cooled metallic particles therefrom.

9. The apparatus as defined in claim 1, wherein said pressure control means include sensing means for sensing the pressure of said gas in said main collection chamber and in said melt chamber and adjustable valve means operable in response to said sensing means for controlling the quantity of said gas vented from said main collection chamber.

Claims

1. An apparatus for producing powdered metal comprising an elongated upright vessel defining a main collection chamber, said vessel formed at its upper portion with a melt chamber and a nozzle port through which atomized molten metal particles are discharged into said main chamber, said vessel formed at its lower portion with an outlet port through which solidified metal particles are discharged from said main chamber, said main chamber filled with an inert gas for extracting heat from the molten metal particles effecting a solidification thereof during the course of their travel from said nozzle port toward said outlet port, cooling means disposed in communication with said main chamber for extracting heat from said gas and recirculating the cooled said gas back to said main chamber, and pressure control means for controlling the pressure of the gas in said main collection chamber within a preselected range and at a pressure below that within said melt chamber disposed on the opposite side of said nozzle port.

4. The apparatus as defined in claim 1, in which said nozzle port is disposed in vertical alignment above the said outlet port.

5. The apparatus as defined in claim 1, further including deflection means disposed in said main collection chamber beneath said nozzle port for intercepting and deflecting a molten metal stream inadvertently discharged through said nozzle port.