Metal powder manufacturing equipment

Abstract

The present invention relates to an equipment for producing metal powder, the equipment comprises an atomization chamber having a top and a bottom, an atomization nozzle located at the top of the chamber through which liquid metal can flow, a gas atomizer adjacent to the nozzle and through which gas can be injected onto the liquid metal, an opening at the bottom of the atomization chamber for discharging metal powder, and a double-pipe heat exchanger comprising an inner pipe and an outer pipe, the two pipes being concentric, the inner pipe being connected to the opening at the bottom of the atomization chamber and the outer pipe being connected to the gas atomizer of the atomizer. The present invention also relates to a corresponding process.

Description

[Technical Field]

[0001] The present invention relates to a production installation for the production of metal powders by gas atomization, in particular steel powders for additive manufacturing. The invention also relates to a method for cooling metal particles at the outlet of a gas atomizer. [Background technology]

[0002] Demand for metal powders for additive manufacturing is increasing, and manufacturing processes must be adapted accordingly.

[0003] In particular, it is known to melt a metallic material and pour the molten metal into a tundish connected to an atomizer. The molten metal is forced through a nozzle in a chamber under a controlled atmosphere and struck by a jet of gas that atomizes the molten metal into fine metal droplets. The metal droplets solidify into fine particles that fall to the bottom of the chamber and accumulate there until the molten metal is completely atomized. The powder is then cooled in the atomizer until it reaches a temperature that allows it to come into contact with air without oxidizing too rapidly. The atomizer is then opened to collect the powder. This cooling process is lengthy and incompatible with the need to produce large quantities of metal powder. Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE INVENTION It is therefore an object of the present invention to remedy the drawbacks of prior art equipment and processes by providing an equipment in which the powder obtained can be cooled efficiently.

[0005] Also, the gas flow rate (m 3 The ratio of gas flow (kg / h) to metal flow rate (kg / h) is preferably maintained between 1 and 5, so that huge amounts of gas are required on an industrial scale to atomize the molten metal.

[0006] A further object of the present invention is to provide an installation in which gas is used efficiently. [Means for solving the problem]

[0007] To this end, a first subject of the invention is an installation for the production of metal powders, comprising: a gas atomizer comprising: an atomization chamber having a top and a bottom; an atomization nozzle disposed in the top of the chamber through which the liquid metal can flow; a gas atomizer adjacent to the nozzle through which a gas can be injected onto the liquid metal; and an opening in the bottom of the atomization chamber for discharging metal powder; a double-pipe heat exchanger comprising an inner pipe and an outer pipe, the two pipes being concentric, the inner pipe being connected to an opening at the bottom of the atomizing chamber, and the outer pipe being connected to a gas atomizer of the atomizer; The present invention relates to an installation for producing metal powder, comprising:

[0008] The installation according to the invention may also have the optional features listed below, considered individually or in combination: The facility also includes a classification station. The inner pipe is a pneumatic transport pipeline, the inner tube is provided with a transport gas inlet; a transport gas inlet disposed adjacent the opening at the bottom of the atomization chamber; the inner tube is connected to the opening at the bottom of the atomization chamber by a first end of a double-tube heat exchanger; The inner tube is connected to an inlet of the classification station by a second end of the double-tube heat exchanger; The inner tube is connected to an outlet of the classification station by a first end of a double-tube heat exchanger; The outer tube is connected to the gas atomizer by a first end of a double-tube heat exchanger; The outer tube is connected to the outlet of the classification station by a second end of the double-tube heat exchanger; The outer tube (10) is connected to a gas regulator, the atomizer further comprising a purge in the atomization chamber for purging the particle bed at the bottom of the atomization chamber; The outer tube is connected to the purge by a first end of the double-tube heat exchanger; The purge is connected to the transport gas inlet of the inner tube; the atomizer further comprising a gas extractor connected to the atomizing chamber; The gas extractor is connected to the gas atomizer; The gas extractor is connected to the outer tube by the second end of the double-tube heat exchanger.

[0009] A second subject of the invention is a method for cooling metal particles at the outlet of a gas atomizer, in which the gas used for atomization first comes into contact with the metal particles discharged from the atomizer in a double-tube heat exchanger comprising an inner tube and an outer tube, the two tubes being concentric.

[0010] The method according to the invention may also have the optional features listed below, considered individually or in combination: The gas used for atomization circulates in one direction inside the outer tube, while the metal particles discharged from the atomizer circulate in the other direction inside the inner tube. The gas used for atomization is recycled from a classification station that is part of a metal powder production facility and is equipped with a gas atomizer and a double-pipe heat exchanger; The gas used for atomization is recycled gas from the gas atomizer, The gas used to transport the metal particles in the inner pipe is a gas recycled from a classification station that is part of a metal powder production facility equipped with a gas atomizer and a double-pipe heat exchanger; The gas used to transport the metal particles in the inner tube is recycled gas from the gas atomizer.

[0011] As is apparent, the present invention is based on a double-pipe heat exchanger in which the metal particles discharged from the atomizer are cooled by the gas used for atomization. In this way, the particles are efficiently cooled during transport to the next equipment in the facility, while the gas is heated and can be sprayed onto the molten metal in the atomization chamber. As a result, the particles are cool enough for their handling in the next equipment, which can be, for example, a classification station. They also do not oxidize, so they are cool enough to be handled outside a protective atmosphere. The use of heated gas for atomization is also beneficial. The heated gas reduces the cooling rate, allowing the particles more time to solidify. As a result, surface tension can play its role for a longer period of time, forming rounder particles or even perfect spheres. Heated gas also results in a higher gas velocity at the exit of the gas atomizer. The gas jet more efficiently atomizes the molten metal, resulting in smaller particles. The particle size distribution shifts to a smaller range.

[0012] Other features and advantages of the present invention are explained in more detail in the following description of the invention.

[0013] The invention will be better understood from reading the following description, which is provided purely for illustrative purposes and is not intended to be limiting in any way. [Brief explanation of the drawings]

[0014] [Figure 1] This is an installation according to the present invention. [Figure 2] 1 is an installation according to a first variant of the invention; [Figure 3] 1 is an installation according to a second variant of the invention; [Figure 4] 1 is an installation according to a third variant of the invention. [Figure 5] 10 is an installation according to a fourth variant of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] It should be noted that the terms "lower", "beneath", "inward", "inward", "outward", "outwards", "upstream", and "downstream" used in this application refer to the locations and orientations of different components of the equipment when the equipment is installed in a plant.

[0016] Referring to FIG. 1, a metal powder manufacturing facility 1 is mainly composed of a gas atomizer 2 and a double-pipe heat exchanger 3.

[0017] The gas atomizer 2 is a device designed to atomize a stream of liquid metal into fine metal droplets by colliding it with a high-velocity gas. The gas atomizer 2 is primarily comprised of an atomization chamber 4 that is enclosed and maintained under a protective atmosphere. The chamber has an upper section, a lower section, a top, and a bottom.

[0018] The upper section of the atomization chamber is provided with an orifice, and a nozzle 5 is typically located centrally in the top of the chamber, through which the molten metal stream is extruded. The nozzle is adjacent to a gas atomizer 6 for injecting gas at high velocity into the liquid metal stream. The gas atomizer is preferably an annular slot located coaxially with the nozzle through which the pressurized gas flows. The gas atomizer is preferably coupled to a gas regulator 7 for controlling the flow and / or pressure of the gas prior to injection. The gas regulator may be a compressor, fan, pump, pipe reducer, or any suitable device.

[0019] The lower section of the atomization chamber is primarily a container for collecting the metal particles that fall from the upper section of the chamber. It is typically designed to facilitate the collection and discharge of the powder through an opening 8 located at the bottom of the chamber. It is therefore typically in the form of an inverted cone or an inverted frustum of a cone.

[0020] As mentioned above, the double-pipe heat exchanger is designed to cool the metal particles discharged from the atomizer while heating the gas used for atomization during transport. To this end, the double-pipe heat exchanger 3 comprises an inner pipe 9 for transporting the metal powder discharged from the atomization chamber and an outer pipe 10 for transporting the atomizing gas. These two pipes are concentric. This concentricity ensures efficient heat transfer between the metal powder and the atomizing gas.

[0021] The double-pipe heat exchanger has a first end 11 and a second end 12. The inner and outer pipes each have a first end flanking the first end of the heat exchanger and a second end flanking the second end of the heat exchanger.

[0022] At one of its ends, the inner tube 9 is connected to an opening 8 at the bottom of the atomization chamber. The way in which the connection and the opening are designed is not particularly limited in the context of the present invention. If the atomizer is operating continuously, the opening is designed so that metal powder can be continuously discharged from the atomizer without interrupting the atomization. The opening can be, for example, a control valve or a rotary valve.

[0023] The inner tube can be directly connected to the atomization chamber, in which case the metal particles flow directly from the atomization chamber into the inner tube. Alternatively, the inner tube can be indirectly connected to the atomization chamber, in which case the metal particles pass through other equipment(s) and / or chamber(s) of the atomizer as they exit the atomizer in the inner tube.

[0024] The inner pipe 9 is preferably a pneumatic conveying pipe, which facilitates the transport of the metal powder. Pneumatic conveying is a method of conveying powder in a dilute phase. The powder is diluted by gas and transported in the form of a cloud inside the inner pipe. The pneumatic conveying can be in a dense or dilute phase, depending on the ratio of metal powder (Kg) to gas (Kg).

[0025] According to one variant of the invention, transport in the inner pipe is provided by injecting gas at overpressure at the start of the inner pipe, i.e., at the side of the opening 8. The inner pipe is therefore equipped with a transport gas inlet 13. The transport gas inlet can be designed to admit fresh gas into the inner pipe. Alternatively, or in combination, the transport gas inlet can be designed to inject recycled gas into the inner pipe. In that case, the transport gas inlet is connected to other gas pipes of the installation and / or other gas regulators. Examples of such gas recycling are described below. Regardless of the design of the transport gas inlet, it is preferably coupled to a gas regulator to control the flow and / or pressure of the gas entering the inner pipe. The gas regulator can be a compressor, a fan, a pump, a pipe cross-section reduction device, or any suitable device.

[0026] In another variant of the invention, transport within the inner tube is provided by drawing gas through the end of the inner tube to create a vacuum, in which case the inner tube is provided with a gas outlet at its end, i.e., on the side opposite the opening 8. The gas outlet is connected to a blower or vacuum pump.

[0027] On the side of the inner tube opposite the opening 8, the inner tube is preferably connected to the equipment used in the next step of the process. The inner tube is preferably connected to a classification station 14.

[0028] At one of its ends, the outer tube 10 is connected to the gas atomizer 6 of the atomizer. This connection can be made through a gas conduit 15 which transports gas heated in a heat exchanger to the gas atomizer. A compressor can be arranged between the outer tube and the gas atomizer if the gas has to be compressed or further compressed before being injected into the molten metal stream.

[0029] At its other end, the outer tube 10 is provided with a cooling gas inlet 16. The cooling gas inlet can be designed to admit fresh gas into the outer tube. Alternatively, or in combination, the cooling gas inlet can be designed to inject recycled gas into the outer tube. In that case, the cooling gas inlet is connected to other gas pipes and / or other compressors of the facility. Examples of such gas recycling are described below. Regardless of the design of the cooling gas inlet, the cooling gas inlet is preferably coupled to a gas regulator to control the flow and / or pressure of the gas entering the outer tube. The gas regulator can be a compressor, a fan, a pump, a pipe cross-section reduction device, or any suitable device.

[0030] The respective and relative diameters of the inner and outer tubes are adjusted to suit the dimensions of the installation. In particular, they are adjusted so that the gas circulating in the outer tube 10 cools the metal particles circulating in the inner tube 9 to the desired temperature before they are discharged into the classification station 14. Preferably, meanwhile, the gas circulating in the outer tube 10 is heated to the temperature desired for atomization. Those skilled in the art can easily size the inner and outer tubes by knowing the desired temperature and particle flow to be discharged from the atomizer.

[0031] For efficiency reasons, it is most preferred that the gas and metal particles circulate in countercurrent. Thus, the inner tube 9 is connected by a first end of the heat exchanger 3 to an opening 8 in the bottom of the atomization chamber, and the outer tube 10 is connected by the same end of the heat exchanger to the gas atomizer 6 of the atomizer.

[0032] In particular, the transport gas inlet 13 of the inner tube is located adjacent to the atomizer opening 8 at a first end of the heat exchanger 3, and the cooling gas inlet 16 of the outer tube is located at a second end of the heat exchanger. In other words, the transport gas inlet and the cooling gas inlet are at opposite ends of the heat exchanger.

[0033] A first variant of the installation is described with reference to Figure 2. This variant differs from the one shown in Figure 1 in that the gas is recycled and the atomizer further comprises a purge 17 to facilitate the discharge of powder from the atomizer.

[0034] The purge 17 preferably comprises multiple purge nozzles located in the lower section of the atomizer. In particular, they are located above the portion of the atomizer where the metal powder accumulates. The purge nozzles are designed to allow gas to flow along the sidewalls of the atomizer, pushing the metal powder toward the opening 8 at the bottom of the atomizer. The purge nozzles can be part of a radial piping system located around the periphery of the chamber at a given distance from the bottom of the chamber. The purge nozzles can be part of multiple radial piping systems located around the periphery of the chamber at different distances from the bottom of the chamber. The purge nozzles are coupled to an auxiliary gas inlet 18. The auxiliary gas inlet can be designed to admit fresh gas to the purge. Alternatively, or in combination, the auxiliary gas inlet can be designed to inject recycled gas into the purge. In this case, the auxiliary gas inlet is connected to other gas pipes and / or other compressors in the facility. In this example, the auxiliary gas inlet 18 is connected to the outer tube 10 of the heat exchanger 3. In particular, the auxiliary gas inlet is connected to a gas conduit 15 that connects the outer tube to the gas atomizer. Regardless of the design of the auxiliary gas inlet, the auxiliary gas inlet is preferably coupled to a gas regulator to control the flow and / or pressure of gas entering the purge. The gas regulator can be a compressor, fan, pump, pipe cross-section reducer, or any suitable device.

[0035] The purge 17 can be coupled to a sensor to sense and control the gas pressure for efficient discharge of the metal powder through the opening while maintaining a possible pressure differential between the atomizer and the inner tube of the heat exchanger.

[0036] In the variant shown in Figure 2, the gas used for atomization and transport is also recycled: in particular, the gas used for transport and also used in the classification station 14 is reinjected into the outer tube 10 of the heat exchanger.

[0037] As shown in FIG. 2, the second end of the heat exchanger outer tube is connected to the classification station 14, specifically to a first separator 20, which forms the first stage of the classification station. The first separator can be a cyclone. In the first separator, a lower powder fraction (e.g., powder fraction less than 20 μm) is separated from a higher powder fraction (e.g., powder fraction greater than 20 μm). The lower powder fraction, along with the majority of the gas, passes through a first filter 21. The filter can be, for example, a bag filter or an electrostatic filter. Preferably, the electrostatic filter can withstand temperatures exceeding 150°C and / or avoid bag changes. The gas leaving the first filter is recycled. In particular, the gas leaving the first filter is reinjected into the heat exchanger outer tube 10. Therefore, the first filter 21 is connected, for example, via a filtered gas conduit 22 to the cooling gas inlet 16 of the outer tube. In particular, the first filter is connected to a gas regulator 23 coupled to the cooling gas inlet. The gas coming from the first filter can be cooled sufficiently during passage through the cyclone, filter and filtered gas conduit to be directly reinjected into the outer tube, or if not cooled sufficiently, a heat exchanger can be added between the filter and the outer tube, especially on the filtered gas conduit.

[0038] The higher powder fraction, for example the fraction above 20 μm, is preferably collected in a first collector 24. The first collector is preferably equipped with a bottom-opening valve 25, such as a butterfly valve, for discharging the powder. Discharge preferably takes place on a conveyor 26 connected to a classification system 27, which forms the second stage of the classification station.

[0039] The conveyor may include a conveyor gas inlet 28. The conveyor gas inlet may be designed to admit fresh gas into the conveyor. Alternatively, or in combination, the conveyor gas inlet may be designed to inject recycled gas into the conveyor. In that case, the conveyor gas inlet is connected to other gas lines and / or other compressors in the facility. Regardless of the conveyor gas inlet design, the conveyor gas inlet is preferably coupled to a gas regulator to control the flow and / or pressure of gas entering the conveyor. The gas regulator may be a compressor, fan, pump, pipe cross-section reducer, or any suitable device.

[0040] The classification system 27 comprises a series of classifiers or sieves. Each classifier 29 comprises a separation chamber 30, a bottom-opening valve 31, a collector 32, and a gas outlet 33. The characteristics of the separation chamber are optionally adapted to collect desired fractions of the powder. The separation chamber can be designed to sequentially collect portions of the fractions or grades of interest. Example grades are 20-60 μm, 60-150 μm, and 150-250 μm.

[0041] The powder coming from the conveyor 26 passes in turn through each classifier 29 of the classification system. A fraction of the powder is sieved and collected in a corresponding collector 32, while the remaining part of the powder is transported to the next classifier.

[0042] At the outlet of the classification system 27, the gas passes through a second filter 34. This filter can be, for example, a bag filter or an electrostatic filter. Preferably, the electrostatic filter can withstand temperatures exceeding 150°C and / or avoid bag changes. The gas leaving the second filter is recycled. In particular, the gas leaving the second filter is reinjected into the outer tube 10 of the double-tube heat exchanger. The outlet of the classification station is therefore connected to the outer tube. In particular, the second filter 34 is connected to the cooling gas inlet 16 of the outer tube, for example, via a second filtered gas conduit 35. In particular, the second filter is connected to a gas regulator 23 coupled to the cooling gas inlet 16. The gas coming from the second filter can be sufficiently cooled during its passage through the classification system and directly reinjected into the outer tube. If it is not sufficiently cooled, a heat exchanger can be added between the second filter and the outer tube, in particular on the second filtered gas conduit.

[0043] Optionally, gases from the different fractions obtained in the classification system are also captured and recycled within the outer tube.

[0044] A second variant of the installation is described with reference to Figure 3. This variant differs from the one shown in Figure 2 in that the auxiliary gas inlet 18 of the purge 17 is connected to the same gas source as the transport gas inlet 13 of the inner pipe. This connection is more efficient, since the purge is preferably carried out with low-pressure gas, as is the transport in the inner pipe.

[0045] In this variant, the atomizer further comprises a secondary gas atomizer 36 in its upper section, which is designed to inject gas in the vicinity of the nozzle to keep it clean. Since low-pressure gas is preferably used for the secondary gas atomizer, the secondary gas atomizer is preferably connected to the same gas source as the transport gas inlet 13 of the inner tube, as is the auxiliary gas inlet 18. The secondary gas atomizer is preferably coupled to a gas regulator 37 to control the flow and / or pressure of the gas entering the chamber. The gas regulator can be a compressor, a fan, a pump, a pipe cross-section reducer, or any suitable equipment.

[0046] 4 and 5, the atomizer may further comprise a gas extractor 38 to compensate for the gas injection through the gas atomizer, possibly through a purge. The gas extractor is preferably located in the upper section of the chamber so as not to interfere with the metal powder at the bottom of the chamber. The gas extractor may be in the form of a tube or tubes connected on one side to the chamber and on the other side to a dust removal means 39. The dust removal means remove the finest particles from the extracted gas. They may comprise an electric filter, a bag filter or a cyclone separator. Cyclone separators preferably have a relatively low pressure drop and therefore no moving parts.

[0047] Preferably, the gas extractor 38 is designed so that the extracted gas can be injected into the chamber and recirculated through the gas extractor. As a result, gas consumption is minimized. Therefore, the gas extractor is preferably connected to other parts of the installation, such as the gas atomizer, purge, secondary gas atomizer, cooling gas inlet of the outer tube of the heat exchanger, transport gas inlet of the inner tube, or a combination thereof. The connection can be in the form of an extracted gas conduit 40. In particular, the dust removal means 39 connected to the chamber on one side can be connected on the other side to the gas regulator 7 connected to the gas atomizer 6, or to the gas regulator 19 connected to the auxiliary gas inlet 18, or to the gas regulator 37 connected to the secondary gas atomizer 36, or to the gas regulator 23 connected to the cooling gas inlet 16, or to the gas regulator connected to the transport gas inlet 13, or a combination thereof. A filter can also be added to further purify the recirculated gas.

[0048] The extracted gas conduit 40 can be equipped with a heat exchanger 41 so that the gas can be cooled to a temperature at which it must be reused if the heat losses in the dedusting means 39 and in the connections are not sufficient.

[0049] The extraction gas conduit may also be provided with a gas inlet 42 in case any fresh gas must be introduced into the system, particularly to compensate for gas losses.

[0050] In a third variation shown in FIG. 4, the extraction gas conduit 40 is connected to a gas regulator 37 coupled to the secondary gas atomizer 36 and to a gas regulator 19 coupled to the auxiliary gas inlet 18.

[0051] In a third variant shown in Figure 4, the extraction gas conduit 40 is further connected to the transport gas inlet 13 of the inner tube 9 of the double-tube heat exchanger 3. As a result, the gas extracted from the chamber can be used to transport the metal powder in the inner tube.

[0052] In a fourth variant shown in Figure 5, the extraction gas conduit 40 is connected to the outer tube 10 of the double-pipe heat exchanger, in particular to the cooling gas inlet 16 of the outer tube, so that the gas extracted from the chamber can be used to cool the metal powder in the inner tube.

[0053] The fourth variant shown in FIG. 5 further differs from the previous variant in that the filtered gas conduit 22 coming from the first filter 21 of the classification station 14 and the second filtered gas conduit 35 leaving the classification station are connected to the transport gas inlet 13 of the inner tube 9 of the double-tube heat exchanger. The connection can be in the form of a third filtered gas conduit 43. The gas coming from the classification station and cooled during its passage can thus be used to transport the metal powder in the inner tube. If the gas is not cooled sufficiently, a heat exchanger can be added between the classification station and the inner tube, in particular on the third filtered gas conduit.

[0054] Other designs for gas recirculation are of course possible.

[0055] From a process point of view, the cooling of the powder discharged from the atomizer 2 is made possible thanks to a process in which the gas used for atomization first comes into contact with the metal particles discharged from the atomizer in a double-tube heat exchanger 3.

[0056] The metals to be atomized may be, in particular, steel, aluminum, copper, nickel, zinc, iron, alloys, including in particular carbon steel, alloy steel and stainless steel.

[0057] The metal can be supplied to the atomizer in solid form and melted in a tundish connected to the atomizer via a nozzle 5. It can also be melted in a previous step and poured into the tundish.

[0058] According to one variant of the invention, the molten metal to be atomized is steel obtained through a blast furnace route. In this case, pig iron is poured from a blast furnace and, optionally after being sent to a hot metal desulfurization station, is transported to a converter (or a basic oxygen furnace (BOF)). The molten iron is refined in the converter to form molten steel. The molten steel from the converter is then poured from the converter into a collection ladle and preferably transferred to a ladle metallurgical furnace (LMF). Thus, the molten steel can be refined in the LMF, in particular by deoxidation, and primary alloying of the molten steel can be carried out by adding iron alloys, silicide alloys, nitride alloys, pure metals, or mixtures thereof. In particular, in cases where demanding powder compositions must be produced, the molten steel can also be treated in a vacuum tank degasser (VTD), a vacuum oxygen decarburization (VOD) vessel, or a vacuum arc degasser (VAD). These devices make it possible, in particular, to further limit the hydrogen, nitrogen, sulfur, and / or carbon content.

[0059] The refined molten steel is then poured into multiple induction furnaces. Each induction furnace can be operated independently of the others, and in particular can be shut down for maintenance or repair while the others are still operating. Also, different amounts of ferrous alloys, scrap, direct reduced iron (DRI), silicide alloys, nitride alloys, or pure elements can be fed to each induction furnace.

[0060] The number of induction furnaces is adapted to the flow of liquid steel coming from the converter or refined liquid steel coming from the ladle metallurgy furnace and / or the desired flow of steel powder at the bottom of the atomizer.

[0061] In each induction furnace, alloying of the molten steel is carried out by adding iron alloys or silicide alloys or nitride alloys or pure metals or mixtures thereof to adjust the steel composition to that of the desired steel powder.

[0062] For each induction furnace, molten steel of the desired composition is then poured into a dedicated reservoir connected to at least one gas atomizer. By "dedicated," we mean that the reservoir is paired with a given induction furnace. However, multiple reservoirs can be dedicated to a given induction furnace. For clarity, each induction furnace has its own production stream with at least one reservoir connected to at least one gas atomizer. With such parallel, independent production streams, the process for producing steel powder is versatile and can easily be made continuous.

[0063] The reservoir is primarily a storage tank, which can be atmospherically controlled, can heat the molten steel, and can be pressurized.

[0064] The atmosphere in each dedicated reservoir is preferably argon, nitrogen or a mixture thereof to avoid oxidation of the molten steel.

[0065] The steel composition injected into each reservoir is heated above its liquidus temperature and maintained at this temperature. This heating prevents clogging of the atomizer nozzle. The reduced viscosity of the molten composition also helps to obtain powders with a proper particle size distribution and high sphericity without satellites.

[0066] Finally, when the dedicated reservoir is pressurized, molten steel can flow from the reservoir to at least one of the gas atomizers connected to the reservoir.

[0067] According to another variant of the invention, the metal to be atomized is steel obtained via an electric arc furnace route. In this case, raw materials such as scrap, metallic ores, and / or metal powders are fed into an electric arc furnace (EAF) and melted into a heated liquid metal at a controlled temperature, with impurities and inclusions removed as a separate liquid slag layer. The heated liquid metal is removed from the EAF into a ladle, preferably a passively heatable ladle, and transferred to a refining station, where it is preferably placed in an induction-heated refining holding vessel. There, a refining process, such as vacuum oxygen decarburization, is performed to remove carbon, hydrogen, oxygen, nitrogen, and other undesirable impurities from the liquid metal. The ladle with the refined liquid metal can then be transferred, under controlled vacuum and inert atmosphere, above a closed chamber containing a heated tundish of an atomizer. The ladle is connected to a feed conduit, and the heated tundish is then fed into the refined liquid metal through the feed conduit.

[0068] Alternatively, the ladle containing the purified liquid metal is transferred from the refining station to a separate induction-heated atomization holder vessel, which is positioned at the door of the atomizer station, which includes an injection zone with a heated tundish of a gas atomizer under controlled vacuum and inert atmosphere. The induction-heated atomization holder vessel is then introduced into a receiving zone where the vacuum and atmosphere are adjusted to one of the injection zones. The vessel is then introduced into the injection zone, and the liquid metal is poured into the heated tundish at a controlled rate and atomized by the atomizer.

[0069] In both variations, molten metal is maintained at atomization temperature in a tundish until it is forced through a nozzle 5 in a chamber 4 under a controlled atmosphere and struck by a jet of gas which atomizes it into fine metal droplets.

[0070] The metal powder formed in the atomization chamber is discharged from the atomizer in the inner tube 9 of the double-tube heat exchanger 3, preferably by purging the chamber. In the inner tube, the metal powder is transported to a classification station and simultaneously cooled. The pressure in the inner tube is preferably up to 5 bar, more preferably in the range of 3-5 bar.

[0071] The gas circulation in the outer tube 10 of the heat exchanger 3 is preferably adjusted so that the metal powder reaching the outlet of the inner tube or the inlet of the classification station is cooled to below 150°C. As a result, conventional screening equipment can be used as opposed to high-temperature resistant equipment. The pressure in the outer tube is preferably in the range of 20-20 bar. Preferably, the gas in the outer tube and the metal particles in the inner tube circulate in countercurrent.

[0072] The gas used to transport the powder in the double pipe heat exchanger is preferably also used during sieving of the powder. At the end of the sieving process, gas is preferably re-injected into the outer pipe 10 of the double pipe heat exchanger to cool the metal powder being transported in the inner pipe 9. Alternatively, gas is re-injected into the inner pipe 9 of the heat exchanger to transport the metal powder.

[0073] The gas injected into the chamber is preferably at least partially extracted from the chamber, then de-dusted and can be reused within the facility to inject a stream of molten metal, purge the chamber, clean a nozzle, cool the metal powder in a double-pipe heat exchanger, or transport the metal powder in a double-pipe heat exchanger.

Claims

1. An installation (1) for producing metal powder, comprising: a gas atomizer (2) comprising an atomization chamber (4) having a top and a bottom, an atomization nozzle (5) arranged in the top of the chamber and through which the liquid metal can flow, a gas atomizer (6) adjacent to the nozzle and through which a gas can be injected onto the liquid metal, and an opening (8) in the bottom of the atomization chamber for discharging the metal powder; a double-pipe heat exchanger (3) comprising an inner pipe (9) and an outer pipe (10), the two pipes being concentric, the inner pipe being connected to the opening (8) at the bottom of the atomization chamber, and the outer pipe being connected to the gas atomizer (6) of the atomizer; Equipped with The metal powder production facility (1) comprises an inner pipe (9) equipped with a transport gas inlet (13).

2. The system of claim 1 further comprising a classification station (14).

3. 3. The installation according to claim 1 or 2, wherein the inner pipe (9) is a pneumatic transport pipeline.

4. 2. The installation according to claim 1, wherein the transport gas inlet (13) is arranged adjacent to the opening (8) in the bottom of the atomization chamber.

5. 3. The installation according to claim 1 or 2, wherein the inner pipe (9) is connected to the opening (8) at the bottom of the atomizing chamber by a first end (11) of a double-pipe heat exchanger.

6. 3. The installation according to claim 2, wherein the inner pipe (9) is connected to the inlet of the classification station (14) by the second end (12) of the double-pipe heat exchanger.

7. 3. The installation according to claim 2, wherein the inner pipe (9) is connected to the outlet of the classification station (14) by a first end (11) of a double-pipe heat exchanger.

8. 3. The installation according to claim 1 or 2, wherein the outer pipe (10) is connected to the gas atomizer (6) by a first end (11) of a double-pipe heat exchanger.

9. 3. The installation according to claim 2, wherein the outer pipe (10) is connected to the outlet of the classification station (14) by the second end (12) of the double-pipe heat exchanger.

10. 3. The installation according to claim 1 or 2, wherein the outer pipe (10) is connected to a gas regulator.

11. 3. The installation according to claim 1 or 2, wherein the atomizer further comprises a purge (17) in the atomization chamber (4) for purging the particle bed at the bottom of the atomization chamber.

12. 12. The installation according to claim 11, wherein the outer pipe (10) is connected to the purge (17) by a first end (11) of the double-pipe heat exchanger.

13. 12. The installation according to claim 11, wherein the purge (17) is connected to the transport gas inlet (13) of the inner pipe (9).

14. 3. The installation according to claim 1 or 2, wherein the atomizer (2) further comprises a gas extractor (38) connected to the atomizing chamber (4).

15. 15. The installation according to claim 14, wherein the gas extractor (38) is connected to the gas atomizer (6).

16. 15. The installation according to claim 14, wherein the gas extractor (38) is connected to the outer pipe (10) by the second end (12) of the double-pipe heat exchanger.

17. A process for cooling metal particles at the outlet of a gas atomizer (2) provided in the equipment (1) according to claim 1, comprising: A process in which the gas used for atomization is first contacted with the metal particles discharged from the atomizer in a double-pipe heat exchanger (3).

18. 18. The process according to claim 17, wherein the gas used for atomization circulates in one direction in the outer tube (10) and the metal particles discharged from the atomizer circulate in the other direction in the inner tube (9).

19. 19. The process according to claim 17 or 18, wherein the gas used for atomization is recycled gas from a classification station (14) which is part of a metal powder production installation (1) comprising a gas atomizer (2) and a double-pipe heat exchanger (3).

20. 19. The process according to claim 17 or 18, wherein the gas used for atomization is recycled gas from the gas atomizer (2).

21. 19. The process according to claim 17 or 18, wherein the gas used to transport the metal particles in the inner tube (9) is a gas recycled from a classification station (14) which is part of a metal powder production installation (1) comprising a gas atomizer (2) and a double-tube heat exchanger (3).

22. 19. The process according to claim 17 or 18, wherein the gas used to transport the metal particles in the inner tube (9) is gas recycled from the gas atomizer.

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