US2371105A - Atomization process - Google Patents

Description

Mai-ch a, 19215.

,R. LEPSOE ATOMIZATION PROCES/S',

Filed Sept. 21, 1943 j-nvevflor- Baler-7' Lep aoa.

Patented Mar. 6, 1945 oFricE 2,371,105 'A'roMnzArroN rnoo'sss Robert Lepsoe, Trail, British (Joiumbia,

The Consolidated i Company oi Canada, Quebec, Canada, a corporation of assignor to smelting Montreal, Canada Application September 21, 1943, Serial m.

In @anada September 22, 1942 11 Claims.

This invention relates to a method and apparatus for the production of finely divided metal @da, t r and Limite (or. se er) powder and is particularly directed to the pro I duction of the metal powders of magnesium and magnesium alloys.

Processes for the production of metal in powder form by subjecting a stream of the molten gas under relatively high pressure impinged thereon are relativelywell known and have been and are being used for the production of the metal powders of a number of metals.

In general, the methods of the prior artemploy a bath of. molten metal maintained at or above The surface of into small globules which are simultaneously converted into solid form and carried as finely divided particles, by the force of the blast, into a collection chamber.

It is known that the sium and. magnesium subjecting a relatively metal powders of magnealloys can be produced by thin stream of the molten metal to the disintegrating action of a-jet of atomizing gas impinged, under relatively high pressure, on the stream of metal. However, in the actual production of the metal powders of magnesium and magnesium alloys on a, commercial scale, there are a number of difficulties which are not present'in the. production of the powders sium nitride, and when th nitrogen contains small quantities'ofoxygen, as such p eas-water vapour, as is usual in commercial supplies of nitrogen, it is found that oxygen reacts with the v to provide a method, and

in the final product. For-inin the lower magnesium, causing it to burn and to magnesium oxide. locally and thereby increases the dangers of fire and explosion, due to oxidation and nitridingl In the course of the reaction between the magne sium and the nitrogen, there isdanger or fire and explosion in addition to the contamination of the product with highly undesirable impurities;

A still further diihcuity, in the production or the metal powders of magnesiumiand magnesium alloys, resides in the presence, in the final product, of particles or the flux used to protect the surface of the molten bath from the action ofthe gases, particularly air, to which it isezposed.

, The principal object of the present invention is apparatus for carrying out the method, by which the metal powders of magnesium and magnesium alloys can be produced without danger of fire or explosion.

A'further object of I a method and apparatus for the production of the metal powders of magnesium and magnesium alloys of a substantially uniform particle size and of a high degree of purity. I

One of the principal features of the invention resides in thelmanner in which a relatively thin stream of molten metal, uncontaminated with fiux, is withdrawn from a bath of molten magnesium or magnesium alloy,

through a'passageway in'a porous sleeve or nozzle impregnated with a flux whereby the exposed surface of the'stream of metal, in passing through the nozzle, is in contact with the flux impregnating the nozzle and becomes coated with an flux, and the stream of molten metal is, in sheet, sheathed or enclosed in an extremely thin him of flux, whereaiter a jet of pressure is impinged on the stream of metal thereby disintegrating the molten metal into :finely divided particles which are carried, by the force of the blast, into a collection chamber. The thin film of fiuxin which the stream of metal is en-v closed serves to protect the stream of molten metal from reaction with the gas in the powder chamber, and the danger of fire and the formation of compounds undesirable in the final product are avoided.

A further and preferred feature of the invention resides in the use of a flux which is of higher specific gravity than that of'the bath of molten metal. The flux is in the form of a molten layer part of the vessel below the bath of molten metal, and surrounds the lower portion of the porous nozzlein the pot, whereby the flux is absorbed into the pores of the nozzle. As the This reaction raises the temperature the invention is to provide extremely thin film of gas under relatively high to the method of operation,

fer to taper the sleeve 1 nozzle 8 is tapered correspondingly so that the nozzle fits snugly and tightly into the sleeve.

when metal P sses through the nozzle, it becomes, coated with a thin film of flux-with the resultthat the stream of metal issuing from. the nozzle is effectively sheathed in a thin, uniform flux film. As the upper part of the nozzle extends above the layer of flux into the bath of molten metal, the metal stream issuing from the nozzle contains no lumps or particles offiux but, due

is provided with a protective film of fiux. The pores of the nozzle remain method.

A still further featureof theinventlon resides in the design of apparatus suitable for carrying out the method and producing thereby metal powders of magnesium and magnesium alloys of substantially uniformly sized particles of high purity. 1

The manner in which I attain the above and other objects of this invention may be understood from the following description and accompanying drawing in which is illustrated a cross sectional side elevation of a preferred form of apparatus suitable for carrying out the method.

.Like reference characters refer to like parts throughout the specification and drawing. I t

The numeral l indicates a furnacesetting preferably formed of insulating material such as fire brick. A metal pot or vessel 2 is received within the furnace setting, being carried on the walls of the setting by outwardly extending lugs 3. The vessel 2 may be heated in any one of several ways such as by oil or coal firing or by electricity. I prefer to provide electrical heating elements 4 between the outer walls of the vessel 2- and the furnace setting. The elements to a source of electrical energy through the leads 5 and 6.

The bottom of the pot 2 is drilled to form an opening approximately at the centre thereof into which is welded a downwardly extending sleeve tory nozzle 8, preferably graphite, is fitted snugly into the sleeve 1. The nozzle 8 extends upwardly a short distance into the body of the pot and extends downwardly approximately flush with or slightly below the bottom of slightly inwardly and the The nozzle 8 is drilled, preferably centrally, throughout its length to form a relatively narrow channel '9 which forms a passageway for the stream of molten metal. The fu nace I, the pot 2, and the heating elements 4,

The powder chamber II is of standard design,

through which the let 14 extends horizontally and a hopper-likecollection chamber I! at the end remote from the jet H wherein the metal powder is accumulated.- A door 13 is provided in the base of the collection chamber I! through which the metal powder may be removed. An opening 1 I5 is provided in the uppermost wall of the collection chamber throughwhich the gases may be withdrawn therefrom. A further opening is formed in the upper wall of the powder chamber above the inwardly extending end of jet ll. The opening is of sufficient size to fitting relationship, the tapered lower end of nozzle 8. I

The portable furnace unit,'comprising the pot 2,"is placed at the end of the powder chamber the stream of metal' I which is preferably tapered. A porous, refracthe sleeve 1. I prereceive, in snug constantly impreghated with flux during the operation of the relatively simple. The unit is placed in position on the upper wall of the powder chamber above I the jet l4 and with the sleeve 1 in line with the opening directly above the atomizing jet.- The pot Iis then heated to a temperature above the.

melting temperature of the magnesium or magnesium alloy. While the pot is heating, the porous nozzle 8 may be fitted into position in sleeve 1, in which position the lower end of the nozzle may extend through the aforesaid opening a short distance into the powder chamber.

, When the pot has been heated to its predetermined temperature, the flux is introduced into the pot, forming a layer of molten flux, indi- ,cated by the numeral H, in the bottom thereof.

4 are connected The depth of the layer of fiux is such that its upper surface is below the upper end of nozzle 8. A stopper attached to a rod (not shown) is inserted in the passageway in the nozzle and the pot is filled with magnesium or a magnesium alloy, indicated by the numeral I8. Powdered flux may be sprinkled over the surface of the molten bath to form a thin, film .of flux over the surface and thereby prevent exposure of the surface ,of the molten metal to the atmosphere. Before the molten metal is allowed to flow through the nozzle, the powder collecting system is thoroughly flushed with atomizing gas to remove all air. This may be done while the pot is being heated. The stopper may then heremoved and, at the same time, the pressure of being provided with an opening at one. end

the atomizing gas, flowing through jet I4, may

be raised to the desired operating pressure. The atomizing gas, under relatively high pressure, impinges on the stream of molten metal leaving the nozzle 8, thereby disintegrating the stream of metal into small globules whichsubstantially instantaneously solidfyinto finely divided'particles which are carried, by the force of the blast, into collection chamber.

The metal powder collected in chamber I! may be removed periodically through clean-out door l3 provided for that purpose. The gas in the chamber ll-I2 passes out through opening l5 and is passed through suitable dust collecting apparatus (not shown) to separate the entrained metal powder particles, after which it may be re-compressed and returned to the process.

The'molten metal in pot 2 may be maintained at a substantially constant level by the continuousor intermittent addition, of. metal thereto. Referring to the details of the .process, the porous nozzle O'may be formed of any one of a number of refractory materials capable of selfimpregnation with the flux m which 'it is partially immersed. Very satisfactoryresults have been obtained from the use of graphite which is wettable by the flux but which is not reactive therewith or with the metal with which it is in contact.

The flux preferably has 'a higher specific gravity than that of the molten metal. It has been found that fluxes of lower specific gravity, such as lithium chloride, may evaporate, leaving the surface of the metal exposed to the atmosphere, with resultant oxidation.' Another disadvantage of a lighter flux, is that it'will oxidize, forming a above the layer of flux,

' with the flux. As the stream product heavier than the metal, which settles through the bath of metal thereby contaminating the molten stream withdrawn through the nozzle and deleteriously affecting the fluidity of the bath.

'Satisfactory results in the operation of the method may be obtained from any one of a number of fluxes, the composition of which may vary over a relatively wide range. In general, the flux is preferably composed of magnesium chloride,'in combination with other chlorides or fluorides other than those which will so afi'ect the surface tensionof the flux that its protective properties are diminished. It has been found that most satisfactory results are obtained from the use of a flux composed of from 50% to 60% magnesium chloride and from 50% to'l0% sodium chloride. A flux of this composition is maintaining a low of sumciently high specific gravity that it remains as a layer in the bottom of the vessel in contact with the lower portion of the nozzle in the pot,and yet forms an extremely thin film over the surface of the bath of metal which protects the surface from the oxidizing action of the atmosphere. In the operation of the method, it has been found that there is a consumption of about one pound of flux for each ton of molten metal atomized.

The gas impinged on the stream of molten metal leaving the nozzle 8 and used to disintegrate the molten metal into finely divided particles is preferably, nitrogen, carbon dioxide or mixtures thereof, containing as little free oxygen as-possible, although it has been found that air can be used for short periods. An appreciable saving is effected by recirculating the exit gas from the collection chamber.

In the operation of the method, the upper end of the nozzle '8 extends into the bath of metal and the stream'of metal, contaminated with particles of or other foreign inatteri The therefore, is not entrained flux lower portion of the nozzle ln'the pot is immersed in the flux and, consequently, the pores of the nozzle are constantly maintained impregnated of molten metal flows through the channel 9, the surface of the stream in contact with the wall of the channel acquires anextremely thin film of flux so that, in effect, the stream of molten metal is enclosed in the thin film of flux.

The thin film of flux which of molten metal issuing from it possible to the nozzle 8 makes overcome the difilcultles hitherto associated with the production of the metal powders of magnesium and magnesiumalloys. Ordinarily, magnesium will react readily with nitrogen or carbon dioxide at temperatures above the melting point of magnesium to form magnesium nitride ormagnesium oxide with the attendant danger of fire and contamination of the final product with undesirable compounds. The thin encloses the stream zle B at temperatures lower than would be pos sible without the flux, thereby permitting operation of the method at lower temperatures, if desired. A lower temperature lessens the rate of oxidation of metal in the pot and also assists in temperature in the collection chamber.

The metal powders of magnesium-aluminum alloys can be produced successfully by the method and apparatus described hereinabove. As the percentage of aluminum in the alloy is increased, the specific gravity of the molten metal approaches that of the preferred magnesium chloride sodium chloride. flux until, in a magnesium-aluminum alloy containing about 50% aluminum, the flux would be lighter than the molten metal and would float on the surface of the metal in the pot. There is, of course, less danger of fire when treating magnesium alloys or high aluminum content but it has been round that by impregnating the nozzle with flux prior to commencing operations, adequate protection is provided until the supply of flux is depleted,

thereby eliminating the danger of fire and obtalning the improved product described hereinabove.

v prises passing a stream of molten metal through till film of flux enclosing the stream of metal prevents contact between the atomizing gas and the molten metal with the result that the dangers of fire and explosion are avoided and no undesirable compounds are formed which would contaminatefthe final product. 'It has been found in continuous operationof the method that magnesium metal heated to temperaturesas high as 100 centigrade degrees above its melting pointvcan 'be atomized with nitrogen, carbon'dioxide, or

mixtures thereo,f,without danger of, fire and without the formation of compounds undesirable in the final product.

a porous nozzle impregnated with a flux comprising magnesium chloride, and thereafter disintegrating the stream of metal by the action of a jet of atomizing gas under relatively high pressure impinged thereon. s

2. The method of producing the metal powders of magnesium and magnesium alloys which comprises enclosing a stream of the molten metal in a thin film of flux comprising magnesium chloride and thereafter disintegrating the stream of metal by the action of a jet. ofatomizing gas under relatively high pressure impinged thereon.

3. .The method of producing the metal powders of magnesium and magnesium alloys which comprises maintaining, in separate layers in a vessel, a bath of molten metal and a molten flux comprising magnesium chloride, withdrawing a stream of molten metal from. a portion of the bath remote from the flux and passing the stream ol metal through a porous nozzle in contact with said flux, whereby the pores of said nozzle are impregnated with said flux and the passing through said nozzle becomes coated with a thin film of said flux, and thereafter disintegrating the stream of metal by the action of a Jet of an atomizing gas under relatively high pressure impinged thereon.

4. The-method of producing the metal'powderg of magnesium and magnesium alloys which com.

prises maintaining, in separate layers in'a vessel, a bath of molten metal and a magnesium comes coated with a thin film of said flux, and

thereafter distintegrating the stream of metal by the action of a jet of an atomizin gas under relatively high pressure impinged thereon.

5. The method of producing the metal powders of magnesium and magnesium alloys which comprises maintaining, in separate layers in a vessel, a bath of molten metal and a molten flux comprising magnesium chloride and being of greater specific gravity than said metal, withdrawing a stream of molten metal from a portion of the bath remote from the flux and passing the stream of metal through a porous nozzle in contact wtih said flux, whereby the pores of said nozzle are impregnated with said flux and the surface of the stream of metal passing through said nozzle becomes coated with a thin film of said metal by the action of a jet or an atomizing gas, under relatively high pressure, impinged thereon.

6. The method of producing the metal powders of magnesium and magnesium alloys which comprises maintaining, in separate layers in a vessel, a bath of molten metal and a magnesium chloride-sodium chloride flux, withdrawing a stream of molten metal from aportion of the bath remote from the flux and passing the stream of metal through a porous nozzle in contact with said fiu'x whereby the pores of said nozzle are impregnated with said flux and the surface of the stream of metal passing through said nozzle becomes coated with a thin film of said fiux,'and thereafter disintegrating the stream of molten metal bythe action of an atomizing gas, selected from the group consisting of nitrogen, carbon dimetal by the action of an atomizing gas, under relativ ely high pressure, impinged thereon,

8. Apparatus for the production of metallic powders which comprises a pot, and means for flux, and thereafter disintegrating the stream of heating said pot, an opening in the base of said pot, a porous, graphite nozzle fitted into said opening'and exten'ding upwardly. into said pot, a

passageway extending through said' nozzle, 9. layer of molten flux in' the lower part of said pot, and a layer of molten metal above said fiux, said nozzle extending through said flux into the bath of metal, whereby the'pores of said nozzle are impregnated with said flux and the stream of metal, is withdrawn from a portion of the bath remote from said flux and means for disintegrating the stream of metal issuing from the passageway in said nozzle.

9.- Apparatus for the production of metallic powders which comprises a pot, and means for heating said pot, an opening in said pot and a porous refractory nozzle fitted into said opening and extending into said pot, a passageway extending through said nozzle,'a bath of molten metal and a layer of molten fiux in said pot, said nozzle extending through said flux into the bath of metal whereby the-pores of said nozzle are impregnated by said flux and the stream of metal is withdrawn from a portion of the bath remote from said flux, and means for disintegrating the stream of metal issuing from the passageway in said nozzle.

10. Apparatus for the production of metal powders which comprises a pot, and means for heating said pot, an opening in the base of said pot, a layer of molten flux in the lower part of said pot, and a layer of molten metal above said flux, a porous nozzle wettable by said flux fitted into said opening and extending upwardly through said fiux into the bath of metal, whereby the pores of said nozzle are impregnated with said fiux and the stream of metal is withdrawn from a portion of the bath remote from said flux, and means for disintegrating the stream of metal issuing from the passageway in the nozzle;

11. The method of reducing explosion and fire hazards in the production of metal powders of magnesium and magnesium alloys which comprises passing a stream of molten metal through a porous refractory nozzle impregnated with a fiux comprising magnesium chloride whereby the surface of the stream of molten metal becomes coated with a thin film of fiux, and thereafter disintegrating the stream of molten metal by the action of an atomizing gas, under relatively high pressure, impinged thereon.

ROBERT LEPSOE.

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