Method for producing metal powders by means of gas atomization and production plant of metal powders according to such method

Abstract

A method for producing metal powders by gas atomization is provided, including providing a metal charge; melting the metal charge inside an electric-arc furnace, controlling its composition until a molten metal bath having a desired composition is obtained; tapping the bath from the furnace, collecting it inside a ladle; refining the bath under controlled atmosphere, vacuum, or overpressure condition; atomizing the refined bath by feeding it into a gas atomizer, inside which a molten metal bath flow is produced, and impinging the molten metal bath flow with an atomization inert gas stream for the atomization of the molten metal bath into metal powders; and extracting the obtained metal powders from the gas atomizer.

Claims

1. A method for producing metal powders by gas atomization, except for aluminium metal powders and titanium metal powders, the method comprising: a) providing a metal charge comprising at least one material selected from a group consisting of metal scraps, metal minerals, and metal powders; b) melting the metal charge inside an electric-arc furnace, controlling a composition of the metal charge until a molten metal bath having a desired composition is obtained; c) tapping the molten metal bath from the electric-arc furnace, collecting the molten metal bath inside at least one ladle; c1) refining the molten metal bath collected in the at least one ladle, until a refined molten metal bath is obtained, the refining step c1) being performed under controlled atmosphere or vacuum or overpressure condition, by introducing the at least one ladle, containing the molten metal bath tapped from the electric-arc furnace, into a closable refining chamber, inside which the controlled atmosphere or the vacuum or the overpressure condition is generated; d) atomizing the molten metal bath, tapped from the electric-arc furnace and refined, by feeding the molten metal bath into a gas atomizer, inside which a molten metal bath flow is produced, and impinging the molten metal bath flow with an atomization inert gas stream, for the atomization of the molten metal bath into metal powders; and e) extracting the obtained metal powders from the gas atomizer, wherein the atomizing step d) comprises: pouring the molten metal bath from the at least one ladle into the gas atomizer, wherein the gas atomizer comprises an upper closed chamber and a lower closed chamber, one vertically on the other, wherein the upper closed chamber houses a tundish, which is provided with heating means controllable from outside and, on a bottom thereof, with at least one outflow opening that communicates with the lower closed chamber, and wherein the lower closed chamber comprises at least one nozzle, which is fed with the atomization inert gas, and is associated with means for discharging the metal powder formed therein, wherein the molten metal bath is poured from the at least one ladle directly into the tundish through a feeding conduit that passes through the upper closed chamber, and making the molten metal bath contained in the tundish flow into the lower closed chamber through the at least one outflow opening so as to form the molten metal bath flow and, simultaneously, feeding the at least one nozzle with the inert gas so that the molten metal bath flow flowing out of the at least one outflow opening is impinged by the inert gas stream exiting from the at least one nozzle, the molten metal bath flow is thus atomized and solidified in a form of metal particles inside the lower closed chamber.

2. The method according to claim 1, wherein the refining step c1) comprises protecting the molten metal bath from oxidizing agents or contaminants.

3. The method according to claim 2, wherein the protecting the molten metal bath consists of forming a layer of protective slag, which is formed on the refined molten metal bath during the refining step c1).

4. The method according to claim 1, wherein, for at least a certain time of steady operation, the steps of melting a), atomizing d), and refining c1) are performed simultaneously.

5. The method according to claim 1, further comprising: f) classifying the obtained metal powders extracted from the gas atomizer based on a grain size thereof, by separating the obtained metal powders in at least one first fraction and one second fraction, wherein the obtained metal particles of the first fraction have a desired grain size and the obtained metal particles of the second fraction have a grain size different from the desired grain size; and g) recycling the second fraction of the obtained metal particles as material for the composition of the metal charge.

6. The method according to claim 1, wherein the feeding into the gas atomizer of the molten metal bath contained in the at least one ladle is performed by means of at least one discharge mouth that is obtained on a bottom of the at least one ladle and that is associated with closure means controllable from outside, the molten metal bath contained in the at least one ladle exiting from the at least one discharge mouth when the at least one discharge mouth is open, in a form of a vertical flow directed downwards.

7. The method according to claim 6, wherein the at least one discharge mouth of the at least one ladle, when the at least one discharge mouth is open, communicates with an end of the feeding conduit emerging out of the upper closed chamber.

8. The method according to claim 1, wherein at steady operation a filling level of the tundish is maintained at values greater than a minimum threshold value sufficient to ensure a continuity of flow of the molten metal bath from the tundish, the molten metal bath flowing from the tundish into the lower closed chamber through the at least one outflow opening being continuous, the gas atomizer operating uninterruptedly.

Description

(1) The characteristics and advantages of a method and a plant for the production of metal powders by means of gas atomization according to the present invention will become more apparent from the following description, which is to be understood as exemplifying and not limiting, with reference to the schematic attached drawing, wherein:

(2) FIG. 1 diagrammatically shows a production plant of metal powders by means of gas atomization according to the present invention.

(3) With reference to FIG. 1, a production plant 100 of metal powders according to the present invention is shown.

(4) The plant 100 comprises:

(5) a melting station 101 for melting a metal charge in the solid state until obtaining a molten metal bath,

(6) a refining station 102 (i.e. secondary metallurgy) for refining the molten metal bath produced in the melting station 101,

(7) an atomization station 103 for atomizing the metal bath melted and refined in the refining station 102, and

(8) one or more ladles 104 that can be moved between the melting station 101, the refining station 102 and the atomization station 103.

(9) The plant 100 may also comprise a classifying station 105 for classifying the metal powders produced in the atomization station 103 based on their grain size.

(10) The melting station 101 comprises an electric-arc furnace 106 (EAF), it itself known and for this reason not described in detail.

(11) The electric-arc furnace 106 comprises a shell 107 closed at the top by a roof 108 through which one or more electrodes 109 made of graphite are inserted in the shell 107. The electrodes 109 are supported at the upper end thereof external to the roof 108 by a support and movement system and are fed in alternating or direct current to generate, with the metal materials forming the charge in the shell 107 or with suitable anodes placed on the bottom of the shell 107, an electric arc which may be of the so-called “submerged” or “non-submerged” type in the metal charge in the shell 107.

(12) The electric-arc furnace 106 is provided with one or more feed openings that may be obtained in the walls of the shell 107 and/or in the roof 108 and/or be formed by the same upper end of the shell 107 once the roof 108 is removed, to feed therethrough the charge of metal materials, together with possible additives, to be melted.

(13) Feeding means of the metal materials and the additives forming the charge to be melted are operatively associated with such feed openings and may be configured to feed the materials in a continuous manner (such as for example, conveyor belts or of the vibration type or of the type known as Consteel® system) or a discontinuous manner (“batch”) with bucket charging or other known systems.

(14) Such feeding means are illustrated diagrammatically and are indicated with reference numeral 110 in the accompanying drawing.

(15) The shell 107 also has a slag opening or channel 111 through which the layer of slag, which during the melting of the metal charge is generated and kept above the metal bath, is extracted from the shell 107 and collected in specific vessel 112.

(16) The shell 107 also has a tapping opening 113 for tapping through it the molten metal bath that forms in the shell 107. The tapping opening 113 may have different shapes, such as for example a siphon, eccentric hole obtained on the bottom of the shell 107 or a spout, the shell 107 being supported by a tilting and inclining system.

(17) The electric-arc furnace 106 is then equipped with sampling and control systems of the metal bath that forms therein, and with systems for injecting additive materials required to control the composition of the metal bath that forms therein, such as for example lances of oxygen or other additive.

(18) The electric-arc furnace 106 and its operation are not further described, being of the type known to one skilled in the art.

(19) The refining station 102 comprises at least one refining chamber 114 of the type that can be closed and equipped with systems for refining and controlling the molten metal bath, such as for example lances 115 for injecting oxygen (when necessary, for the conduction of the secondary metallurgy process), probes 116 for controlling the temperature, feed conduits 117 for feeding additive materials, and is associated with a system for generating a controlled atmosphere and/or vacuum conditions (VOD decarburization-oxygen-vacuum) in it, such as for example a system 118 of the pump type for generating vacuum, and/or overpressure.

(20) Here too, the refining station 102 and its operation are not further described, being of the type known to one skilled in the art.

(21) The atomization station 103 comprises at least one gas atomizer 119 that in turn comprises an upper closed chamber 120, that is that can be closed, and a lower closed chamber 121, one vertically overlapping the other and separated from each other by a plate 122.

(22) The upper closed chamber 120 encloses therein a tundish 123 or hopper which is provided with heating means 124 that can be controlled from the outside of the upper closed chamber 120 and that are of the induction or electric resistance type.

(23) At least one outflow opening 125 is obtained on the bottom of the tundish 123, the opening communicating with the lower closed chamber 121 through at least one corresponding through opening 126 obtained in the plate 122. The outflow opening 125 is associated with occlusion means 127, for example of the stem type, that can be controlled from the outside of the upper closed chamber 120.

(24) A feeding conduit 140 is housed in the upper closed chamber 120 with an axial (lower) end leading into the tundish 123 and with the opposite axial (upper) end emerging out of the upper closed chamber 120. This feeding conduit 140 advantageously is made of ceramic material and is used for feeding the refined molten metal bath contained in the ladle 104 directly in the tundish 123, thus avoiding that it comes in contact with the ambient air so as to limit any risks of oxidation thereof, if necessary.

(25) The upper closed chamber 120 is connected to a vacuum generating system 128 of the pump type adapted to generate desired vacuum conditions therein.

(26) The lower closed chamber 121 comprises at least one nozzle 129 which is connected to feeding means 130 for feeding such nozzle 129 with an atomization inert gas of the argon, nitrogen or helium type.

(27) Advantageously, one or more nozzles 129 are obtained in the plate 122 close to the opening 126 communicating with the outflow opening 125.

(28) It is not excluded for other nozzles 129 to be provided inside the lower closed chamber 121.

(29) The bottom 121a of the lower closed chamber 121 advantageously is cone-shaped to collect therein metal powders that form, and is associated with discharging means 131, for example of the pneumatic type, for discharging metal powders.

(30) The discharging means 131 are connected with the classifying station 105 in which there are provided one or more separators 132, for example cyclone, sieve or other separators, for the separation of the metal powders in at least one first fraction and one second fraction, wherein the metal particles of the first fraction have a desired grain size and the metal particles of the second fraction have a grain size different from the desired one. The separator 132 is provided with an inlet associated with the discharging means 131, and with an outlet associated with collecting means of the two fractions of powders thus classified and separated. The plant 100 further comprises level sensors for detecting the filling level of the tundish 123 which are operatively connected with a control unit for keeping the value of the filling level of the tundish 123 above a predefinable minimum threshold value. Under steady operating conditions, maintaining the filling level of the tundish above a minimum threshold value allows to ensure a continuity of the flow of the molten metal bath that flows from the tundish 123 into the lower closed chamber 121 of the atomizer. This allows conducting the atomization with continuity and without interruptions, also during the execution of the melting and refining steps—which are conducted in separate stations from the atomization station 103—and during the pouring or topping up step.

(31) The upper closed chamber 120 and the lower closed chamber 121 are then equipped with known control systems, for example of the temperature or of other process parameters.

(32) Here too, the atomization station 103 and the separation station 105 and their operation are not further described, they being of the type immediately comprehensible to one skilled in the art.

(33) Advantageously, the conical bottom portion 121a of the lower closed chamber 121 is of the type that can be completely replaced with other similar and new portion, that is, in particular, if metal powders of different nature or quality are to be produced in sequence.

(34) Likewise, in case of production change, also the discharging means 131, the separator 132, the upper closed chamber 120, or at least the tundish 123 therein, and the relative feeding conduit 140 can be replaced with similar discharging means, separator, upper closed chamber, or tundish, and the relative feeding conduit all of new type.

(35) Each ladle 104 consists of a vessel covered internally with refractory material.

(36) In a preferred embodiment, each ladle 104 has, on the bottom thereof, a discharge mouth 134 conveniently calibrated and which is associated with closure means 135 that can be controlled from the outside.

(37) Advantageously, these closure means 135 are of the gate type controlled by a linear actuator.

(38) Advantageously, the ladle 104 is also at least partly heated, for example by induction or electrical resistance, and, in particular, it is heated close to or at the discharge mouth 134 thereof so as to ensure keeping the metal bath contained therein in the melted state and/or at the desired temperature conditions.

(39) When the ladle 104 is in the atomization station, it is supported above the upper closed chamber 120 in such a position whereby, when open, the discharge mouth 134 thereof is in communication with the upper end of the feeding conduit 140 which emerges outside the upper closed chamber 120 so as to pour the refined molten metal bath contained therein directly into the tundish 123.

(40) However, alternative embodiments of the ladle 104 are not excluded, which may be provided with other systems for transferring the molten metal contained therein into the tundish 123; for example, the ladle 104 could be provided with a transfer spout and be associated with a tilting system or a transfer siphon.

(41) The plant 100 comprises a plurality of ladles 104, each movable between the melting station 101, the refining station 102 (if present) and the atomization station 103, for collecting the molten metal bath tapped from the electric-arc furnace 106, containing the molten metal bath during the refining thereof inside the refining chamber 114 and pouring the refined molten metal bath into the tundish 123 by means of the feeding conduit 140, respectively.

(42) A removable cover 136 is applied at the top of the ladle 104.

(43) The plant 100 described above is configured to implement the production method of metal powders by means of gas atomization according to the present invention.

(44) The production method of metal powders by means of gas atomization according to the present invention comprises:

(45) a) providing a metal charge comprising at least one metal material selected from the group comprising metal scraps, metal minerals and metal powders;

(46) b) melting the metal charge inside the electric-arc furnace 106 controlling its composition until a molten metal bath having a desired composition is obtained;

(47) c) tapping the molten metal bath from the electric-arc furnace 106, collecting it inside at least one ladle 104;

(48) d) atomizing the molten metal bath tapped from the electric-arc furnace 106 by feeding the molten metal bath tapped from the electric-arc furnace 106 into a gas atomizer 119, inside which a molten metal bath flow is produced, and impinging such molten metal bath flow with an atomization inert gas stream for the atomization of the molten metal bath into metal powders;
e) extracting the thus obtained metal powders from the gas atomizer 119.

(49) The method according to the present invention further comprises, after said tapping step c) and before said atomizing step d), the step of:

(50) c1) refining the molten metal bath collected in the ladle 104, until obtaining a refined molten metal bath.

(51) If for example, ferrous or steel metal powders are to be produced, the refining step may provide a step of decarburization with methods and processes known to one skilled in the art, such as for example the VOD technique.

(52) At the end of the refining step, the metal bath contained by the ladle is isolated from the oxidizing agents by means of suitable protecting means. In one embodiment, a layer of protective slag isolating the refined molten metal bath with respect to the atmosphere of the environment outside the ladle is formed on the refined molten metal bath during and/or after the refining step.

(53) In particular, the atomization step d) comprises:

(54) pouring the refined molten metal bath directly from the ladle 104 into the gas atomizer 119, in which the refined molten metal bath is poured by the ladle 104 directly into the tundish 123 by means of the feeding conduit 140 that crosses the upper closed chamber 120,

(55) letting the refined molten metal bath contained in the tundish 123 flow into the lower closed chamber 121 through the at least one outflow opening 125 and, simultaneously, feeding the nozzles 129 with an atomization inert gas so that the molten metal flow flowing out of the outflow opening 125 is impinged by the inert gas stream coming out of the nozzles 129, thus atomizing and solidifying in the shape of metal particles inside the lower closed chamber 121,

(56) extracting the metal powders formed in the lower closed chamber 121, by means of the discharging means 131.

(57) From the above, it is immediately apparent that the method according to the present invention does not provide—but rather excludes—any step of solidifying the metal bath intermediate to the melting step b) of the raw materials in the electric-arc furnace 106 and to the atomization step d) in the gas atomizer 119. The molten metal bath tapped from the electric-arc furnace 106 indeed is collected in a ladle 104 that contains it during the refining step c1), at the end of which, except any stop times, it feeds it directly into the gas atomizer 119. In other words, no intermediate solidifying step is provided between the melting step b) of the raw materials and the atomization step d) of the refined molten metal bath, which has quite a different composition than the one of the raw materials (the latter partly consisting of metal scraps and metal minerals).

(58) The method according to the present invention also provides:

(59) e) classifying the metal powders extracted from the gas atomizer 119 and, in particular from the lower closed chamber 121 of it, based on the grain size thereof by separating them in at least one first fraction and one second fraction, wherein the metal particles of the first fraction have a desired grain size and the metal particles of the second fraction have a grain size different from the desired one, and advantageously

(60) f) recycling the second fraction of metal particles as materials for the composition of the metal charge that can be fed into the electric-arc furnace 106 for conducting a new production cycle.

(61) In greater detail, the method according to the present invention is provided for producing metal powders of iron, steel, nickel, chromium, cobalt, molybdenum and their alloys, but not aluminium or titanium metal powders.

(62) The metal materials forming the metal charge to be melted comprise at least one material selected from the group comprising metal scraps, metal minerals and metal powders. If, for example, metal powders of iron or steel are to be produced, as known, these metal materials (metal scraps and metal minerals) have a very variable composition rich with undesired elements in the final composition of the metal powders to be obtained, such as for example carbon, which may reach percentages that are even ten times higher than the ones of the final product. Such materials also have variable and any shapes and dimensions.

(63) Such materials are continuously and discontinuously fed in the desired proportions and quantities inside the electric-arc furnace 106 where they are melted by the radiation, convection and conduction heat that is generated inside the furnace and the molten metal bath formed therein due to the feeding of electric energy to the electrodes 109 with the formation of a submerged or non-submerged electric arc.

(64) During the running of the electric-arc furnace 106, the temperature, the volume and the composition of the molten metal bath formed therein are controlled and, when necessary, modified with interventions of the type known to one skilled in the art (such as, for example, adding raw materials, additives, oxygen, etc.) until obtaining a molten metal bath of desired volume, temperature and composition.

(65) In particular, during the melting step conducted in the electric-arc furnace 106, it is possible to intervene with known systems to modify and control the composition of the molten metal bath formed therein.

(66) The molten metal bath obtained is then tapped from the electric-arc furnace 106 and collected in a ladle 104.

(67) The molten metal bath collected in the ladle 104 is then refined (i.e. processes of so-called secondary metallurgy), such as for example decarburization by means of oxygen injection which advantageously is conducted under conditions of vacuum, controlled atmosphere or overpressure according to the needs, by introducing the ladle 104 into the refining chamber 114 where the desired conditions, for example vacuum, are created. This allows promoting the extraction of undesired gases, for example hydrogen, nitrogen or others, from the molten metal bath.

(68) During the refining step (secondary metallurgy), it is possible to periodically check the temperature of the molten metal bath and the composition thereof by analysing samples or the gases extracted from the closed refining chamber 114.

(69) Once the refining step is complete, before the conditions of vacuum or controlled atmosphere in the closed refining chamber 114 are removed, when necessary, suitable protecting means are implemented on the ladle 104 in order to avoid oxidation or contaminations.

(70) In a particular embodiment, it is possible to generate a layer of protective slag on the refined molten metal bath contained in the ladle 104 such as to isolate it from the atmosphere of the external environment.

(71) Air or an inert gas is blown into the closed refining chamber 114 and after removing the upper closure thereof, the ladle 104 is extracted therefrom and transported towards the atomization station 103.

(72) The ladle 104 containing the refined molten metal bath and/or covered by the layer of protection slag is arranged above and outside the upper closed chamber 120 of the atomizer 119 so that the discharge mouth 134 thereof communicates with the upper end of the feeding conduit 140. The level of opening of the discharge mouth 134 is controlled by the closure means 135. In particular, it is worth noting that the refined molten metal bath flows from the bottom of the ladle 104 in the form of a vertical flow directed downwards, which is channeled into the feeding conduit 140. Such flow is controlled in a simple and accurate manner by adjusting the level of opening of the discharge mouth 134 by means of the relative closure means 135.

(73) However, alternative embodiments are not excluded wherein the metal bath contained in the ladle 104 is fed into the atomizer 119 for example by means of a spout obtained in the ladle itself and an inclination system thereof or by means of siphons or the like.

(74) The refined molten metal bath is thus fed directly from the ladle 104 into the tundish 123 where it is kept at the desired atomization temperature due to the heating means 124. A controlled atmosphere of inert gas or vacuum conditions is produced inside the upper closed chamber 120, where the tundish 123 is located.

(75) The occlusion means 127 are controlled to free the outflow opening 125 when the desired filling level of the tundish 123 is reached: a flow of possibly refined molten metal flows from the tundish 123 into the lower closed chamber 121 where it is impinged by the stream formed by the jets of inert gas injected by means of the nozzles 129.

(76) In conditions of steady operation, the filling level of the tundish 123 is kept at values exceeding a predefinable minimum threshold value. Thereby, the molten metal bath flow that flows from the tundish 123 into the lower closed chamber 121 through the outflow opening 125 is continuous, that is it is continuous over time so that the atomizer operates uninterruptedly, also during the running of the melting and refining steps, which are performed in separate stations. The possibility of conducting the atomizer continuously while keeping the filling level of the tundish 123 above a minimum threshold is subsequent to: the fact that the melting b), refining c1) and atomization d) steps are conducted in separate stations and that therefore they may operate at steady operation at the same time; the fact that the refined molten metal bath contained in a ladle 104 is not poured therefrom directly into the true atomizer (i.e. the lower closed chamber 121 wherein the atomization occurs), rather into a tundish 123 that feeds the latter; the tundish 123 therefore acts as a “storage reservoir” or “tank” for feeding the lower closed chamber 121; the fact that there is provided a plurality of ladles 104 operating between the different melting, refining and atomization stations so as to ensure the continuity of the process.

(77) In a known manner, the molten metal flow is pulverized forming particles that take on a generally spherical shape and cool off by collecting on the bottom of the lower closed chamber 121, from where they are extracted by means of the discharging means 131.

(78) The metal powders thus formed and extracted are subjected to grain size classification with known technologies and systems, and are separated into at least two fractions: one of desired grain size and a scrap one.

(79) The latter advantageously is recycled as material for forming metal charge for feeding the electric-arc furnace 106 for conducting successive production cycles.

(80) In particular, it is known that the melting, refining and atomization steps occur—at least for a given time interval—at the same time at steady operation, each of them being conducted in a station that is separate and distinct from the others, respectively a melting station, a refining station and an atomization station.

(81) The method and the plant according to the present invention therefore have the advantage of being capable of conducting several production cycles at the same time and, although the times of each atomization cycle are substantially comparable with the ones according to the known technique, the overall productivity of the method and of the plant according to the present invention is at least double the one according to the known technique.

(82) Indeed, it is not necessary to wait for an atomization cycle to end before starting another one, the different steps wherein such cycle develops being capable of being conducted at the same time and separately from one another. As noted above, this, combined with the provision of the tundish acting as “storage reservoir” or “feed tank” of the refined molten metal bath to be atomized, among other things allows conducting the true atomization in a continuous manner, without any interruption.

(83) The conducting of the melting step of the metal charge in an electric-arc furnace melting station and the conducting of the refining step (decarburization) of the molten metal bath in a specific and separate refining station allow broadening the range of metal materials that can directly be used as “raw materials” for producing metal powders by gas atomization. The method and the plant according to the present invention indeed allow producing metal powders by gas atomization directly (that is without further intermediate solidification and re-melting steps) starting from metal materials in the liquid state such as metal scraps, metal minerals and the scrap metal powders themselves, also having significantly different composition than the one of the metal powders to be produced, in particular in terms of impurities, and variable and heterogeneous shapes and dimensions. It is also worth noting that it is not possible to use scrap metal powders as charging material in known atomization plants because the induction furnaces used in such known atomization plants are not capable of melting such raw materials due to how the plants are sized and conducted.

(84) The method and the plant according to the present invention therefore also allow using, as “raw materials” (i.e. inlet metal charge), less precious and costly metal materials than those normally used for producing metal powders by gas atomization. In particular, the method and the plant according to the present invention allow using metal materials as “raw materials”, such as metal scraps and metal minerals, having various and heterogeneous composition also containing increased percentages of impurities with respect to the composition of the metal powders to be obtained, in any case being it possible to control the composition of the metal bath during the conducting of the melting and refining steps to obtain metal powders of the desired composition and quality. This without it being necessary to conduct any intermediate solidification and successive re-melting step; indeed although they start from raw materials having a different composition (in particular in terms of impurities) from the one of the atomized powders obtained, the method and the plant according to the present invention provide for a single melting step and successive direct atomization of the refined molten metal bath without the same being subjected to further solidification and re-melting.

(85) The metal powders produced with the method and the plant according to the present invention can be used in particular with raw materials for additive production technologies (three-dimensional printing).

(86) The method and the plant according to the present invention also allow reducing the energy expenditure of the whole production cycle which is broken down into a single melting-refining-atomization cycle, while the methods and production plants of metal powders by gas atomization according to the known technique use “raw materials” (i.e. an inlet metal charge) that were already the subject of a preceding and separate melting-refining-forming/solidification cycle that is added to the melting-refining-atomization one conducted with them. Therefore, this results in a reduction of the pollutant emissions (carbon dioxide) into the atmosphere, to the greater protection of the environment. In a preferred embodiment, the method and the plant according to the present invention also allow optimally controlling the quality of the metal bath poured into the tundish that feeds the atomizer and the filling level of the tundish itself. The refined molten metal bath contained in the ladle indeed is no longer poured into the tundish by inclining the ladle itself, an operation that could result in the pouring of slag into the tundish and that is difficult to control. Contrarily, according to a preferred embodiment of the present invention, the metal bath contained in the ladle is poured into the tundish by means of a discharge mouth obtained on the bottom of the ladle itself, without the need to incline it, and thus controlling the level of opening thereof by means of the respective closure means. An increased control of the quality of the metal bath contained in the tundish and of the filling level of the latter allows controlling the parameters of the atomization process and therefore, the quality of the metal powders obtained therewith. The control of the filling level of the tundish also allows conducting the atomization in a continuous manner.

(87) Moreover, the atomization station according to the present plant is overall less bulky, in particular in height, and safer, since water cooling circuits are not provided close to molten metal baths.

(88) Finally, the method and the plant according to the present invention allow managing production changes in a relatively simple and quick manner while ensuring that metal powders of the desired quality are obtained.

(89) Should it indeed be necessary to produce metal powders of different quality or type, it is possible to use new ladles and rather than proceeding with long and demanding cleaning operations, completely replacing the portion of bottom of the lower closed chamber of the atomizer, together with the relative discharging means and separators, and the upper closed chamber, or at least the tundish therein contained, together with the relative feeding conduit. Thereby, any risk of contamination between the different metal powders is avoided.

(90) The invention thus conceived is susceptible to several modifications and variations, all falling within the invention; moreover, all the details can be replaced by technically equivalent elements. In practice, the materials used, as well as their dimensions, can be of any type according to technical requirements.