Quick nozzle replacement system for atomizers

Abstract

The present invention provides a method for rapidly replacing a nozzle assembly suitable for use in a liquid metal atomization process in which liquid metal held in a liquid metal reservoir and exiting said metal reservoir through a reservoir opening is atomized by an atomization fluid to form a metal spray in an atomization tower. The present invention provides for the use of a sliding nozzle assembly system that allows replacement nozzles to be replaced in situ during manufacture.

Description

[Technical Field]

[0001] The present invention relates to the production of metal powders, in particular to the production of metal powders by atomization for additive manufacturing. The present invention also relates to equipment for producing steel powders, with a particular focus on nozzles used in the atomization process. [Background technology]

[0002] It is known to produce metal powder by atomizing molten steel. The molten metal is atomized into fine metal droplets by forcing it under pressure through a nozzle and impinging with a jet of fluid, which can be either a liquid (e.g., water) or a gas (e.g., nitrogen, argon, air, or any other suitable gas). The fluid impinges on the metal stream as it exits the nozzle, creating turbulence that results in the formation of droplets that then solidify in the form of metal powder. The powder is then collected for further processing.

[0003] Nozzles are a critical part of the atomization equipment and are subject to extreme conditions, so they can be subject to wear during production and can also become clogged during the process.

[0004] Nozzle wear and possible clogging are limiting factors for the length of the atomization run, which leads to productivity and cost problems. Summary of the Invention [Problem to be solved by the invention]

[0005] It is an object of the present invention to address the productivity issues discussed above by providing a nozzle assembly designed to be replaced without significantly reducing the productivity of pulverization and a method for changing nozzle systems during the continuous production of metal powder by pulverization. [Means for solving the problem]

[0006] The present invention provides an apparatus for quickly changing nozzle assemblies by using a sliding nozzle assembly system and providing a replacement nozzle that can be replaced in the field during manufacturing.

[0007] The object of the present invention is achieved by providing a nozzle changing device according to claim 1, which optionally comprises the features of claims 2 to 10.

[0008] The invention will now be described in detail with reference to the accompanying figures, illustrating by way of example without introducing any limitations, it being noted that for the sake of clarity the micronization tower is only shown in Figure 1 and not in the subsequent figures. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a micronization device. [Figure 2] FIG. 1 is a front perspective view of a nozzle changing device according to an embodiment of the present invention. [Figure 3a] 3a shows a bottom perspective view of a nozzle changing device according to an embodiment of the present invention, the support structure having no bottom plate in FIG. 3a, but this bottom plate is present in FIG. [Figure 3b] 3a shows a bottom perspective view of a nozzle changing device according to an embodiment of the present invention, the support structure having no bottom plate in FIG. 3a, but this bottom plate is present in FIG. [Figure 4] 3 is a front perspective cross-sectional view of a nozzle changing device according to an embodiment of the present invention, taken along axis II in FIG. 2. [Figure 5] FIG. 1 is a top perspective view of a nozzle assembly according to one embodiment of the present invention. [Figure 6] FIG. 1 is a bottom perspective view of a nozzle assembly according to one embodiment of the present invention. [Figure 7] 6 is a cross-sectional view of a nozzle assembly according to an embodiment of the present invention taken along axis II-II of FIG. 5. [Figure 8] 6 is a cross-sectional view of a nozzle assembly having an upper portion of a support structure according to an embodiment of the present invention, taken along axis II-II of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0010] In the following description and claims, the orientation of various parts is defined according to the normal orientation of a downward-flowing pulverizer, in which the liquid metal reservoir is located above the pulverization chamber and the heaviest fraction of the coarsest pulverized powder is collected at the bottom of the pulverization tower by the natural effect of gravity. Therefore, the directional terms "top," "up," "upper," "above," "bottom," "low," "lower," "below," etc., should be understood according to the typical configuration of the pulverizer. However, the present invention is applicable regardless of the actual installation orientation of the pulverizer, and the directional terms used in the present description and claims should simply be replaced with the functional orientation of the pulverizer. In the accompanying drawings, the top and bottom are indicated by the arrows "T" and "B," respectively.

[0011] "Substantially parallel" or "substantially perpendicular" means a direction that cannot deviate from the parallel or perpendicular direction by more than 15°.

[0012] The terms "upstream" and "downstream" refer to the relative position of two elements in a given direction, where an upstream element is located in front of a downstream element when moving in a given direction.

[0013] The term "enclosed" refers to a configuration in which one element (the enclosing element) completely covers or surrounds another element (the contained element).

[0014] The term "contiguous" when applied to surfaces defines two surfaces that touch each other over at least a portion of said surfaces. The term "contiguous" when applied to volumes defines two volumes that have a contiguous surface.

[0015] "Refractory" materials refer to materials that resist degradation by heat, pressure, or chemical attack and retain their strength and form at elevated temperatures.

[0016] The terms "high pressure" and "low pressure" refer to the amount of atomizing fluid pressure used in a given atomization process. The term "high pressure" refers to the pressure level required to supply to the atomizing fluid nozzle to reach the required atomizing fluid pressure exiting the atomizing fluid nozzle. The term "low pressure" refers to the pressure level required to supply to the atomizing fluid nozzle to reach a positive pressure at the outlet of the atomizing fluid nozzle.

[0017] Referring to FIG. 1, a general overview of a micronization apparatus 100 is first shown.

[0018] Molten metal 109, for example steel or aluminum or titanium or any other metal or metal alloy, is atomized into fine metal droplets by forcing it under pressure through nozzle 1 and by impinging it with a jet of fluid supplied from fluid supply 105 via supply circuit 106. The fluid hits the metal stream as it leaves nozzle 1 and enters atomization tower 102, creating turbulence that results in the formation of a spray 110 made of metal droplets, which then solidify in the form of metal powder. Said powder is then collected for further processing.

[0019] It should be noted that at this stage of the description, the term "nozzle" generally refers to the device through which the liquid metal enters the atomization tower. In the following description of the device according to the invention, the "nozzle" will be described in more detail and will include several different parts which together form a "nozzle assembly" and a "nozzle exchange device."

[0020] Molten metal 109 is held in a liquid metal reservoir 101 having a reservoir opening 104 at the bottom through which the liquid metal can flow into the nozzle 1. For example, the liquid metal reservoir is equipped with a channel 103 through which the liquid metal is forced to exit the reservoir 101 through the reservoir opening 104. This channel 103 can be equipped with an inductor to control the temperature of the liquid metal exiting through the reservoir opening 104.

[0021] The atomization tower 102 is typically filled with an inert gas to prevent the powder from oxidizing. The metal droplets are cooled as they fall into the atomization tower.

[0022] The atomization fluid can be a liquid or a gas. Generally speaking, gas atomization is advantageous for producing powder particles with high circularity. The particles are also less susceptible to oxidation than, for example, water atomization. On the other hand, liquid atomization, and especially water atomization, can provide a good cost / productivity / quality balance when the required particle size and shape for the above-mentioned applications allow.

[0023] In gas atomization, the preferred atomizing gas is argon or nitrogen. Helium can also be used, but due to its high thermal conductivity, significant superheating (above 300°C) is required to avoid clogging. Both gases increase melt viscosity more slowly than other gases, such as helium, which promotes the formation of smaller particle sizes. They also play a role in controlling chemical purity, avoiding unwanted impurities, and ensuring good powder morphology. Finer particles can be obtained with argon than with nitrogen, since the molar weight of nitrogen is 14.01 g / mol compared to 39.95 g / mol for argon. Meanwhile, the specific heat capacity of nitrogen is 1.04 J / (gK) compared to 0.52 for argon. Therefore, nitrogen increases the cooling rate of the particles. Argon may be preferred over nitrogen to avoid contamination of the composition with nitrogen and when the melt chemistry is reactive.

[0024] The gas flow influences the particle size distribution and microstructure of the metal powder. In particular, the faster the flow, the higher the cooling rate. Therefore, the gas-to-metal ratio, defined as the ratio of gas flow rate (kg / h) to metal flow rate (kg / h), is preferably kept between 1 and 5, more preferably between 1.5 and 3.

[0025] The outlet diameter of the liquid metal nozzle affects the flow rate of the molten metal, and therefore the grain size distribution and cooling rate. The maximum diameter is typically limited to 6 mm to limit the increase in average grain size and the decrease in cooling rate. A diameter of 2-3 mm is preferred to more precisely control the grain size distribution and promote the formation of the desired microstructure.

[0026] The metal powder obtained by micronization can be classified so that particles of a size better suited to the technology, especially additive manufacturing, are retained for subsequent use. For example, for additive manufacturing by powder bed fusion, a range of 15 to 50 μm is preferred. For additive manufacturing by laser metal deposition or direct metal deposition, a range of 45 to 150 μm is preferred.

[0027] The shape and size of the liquid metal nozzle outlet are important for ensuring the production of high-quality metal powder. However, during the atomization process, the nozzle outlet is subject to significant wear due to the liquid metal pressure at the nozzle outlet, the high temperatures imposed by the liquid metal (e.g., for steel, this temperature exceeds 1500°C), and possible chemical interactions between the liquid metal nozzle material and the liquid metal. To achieve a continuous atomization process with stable product quality, the liquid metal nozzle must be changed during operation. Because the atomization process relies on the liquid metal passing through the liquid metal nozzle, the nozzle change operation itself temporarily interrupts the atomization process. For this reason, this operation must be performed as quickly as possible. Furthermore, because the liquid metal is under pressure and exits through a reservoir opening, the flow of liquid metal must be managed during the nozzle change operation for safety and equipment protection purposes (especially the atomization tower, which could be damaged by a liquid metal leak).

[0028] 2-4 show a nozzle exchange device 30 according to one embodiment of the present invention, which allows nozzles to be moved in and out of place in a quick motion for quick exchange.

[0029] The nozzle changing device 30 comprises the following elements: at least one nozzle assembly 10 a support structure 20 intended to hold the nozzle assembly 10 a high-pressure atomization fluid supply 106 and distribution circuit 105 (not shown) suitable for supplying high-pressure atomization fluid for the atomization process; a mechanical device designed to move the nozzle assembly 10 within the support structure in a direction S generally parallel to the liquid metal reservoir opening 104. Said mechanical device is not shown in the accompanying drawings.

[0030] The support structure 20 is configured to allow the nozzle assembly 10 to move within said support structure 20 in a direction S generally parallel to the liquid metal reservoir opening 104, said support structure comprising: - an in-use section 20i corresponding to a portion of the support structure 20 designed to accommodate a nozzle assembly 10i having a liquid metal inlet effectively aligned with the reservoir opening. Referring to Figure 2, the in-use sections are roughly delimited by dotted lines i1 and i2. an inlet section 20e corresponding to the part of the support structure 20 located upstream of the active section 20i, taking into account the direction of movement S of the nozzle assembly;

[0031] The nozzle assembly 10 comprises a liquid metal inlet 41, a liquid metal outlet 42, and an atomizing fluid outlet 52, and is configured such that the liquid metal stream exiting the liquid metal outlet 42 is impinged by the atomizing fluid exiting the atomizing fluid outlet 52.

[0032] For clarity, the sliding direction S in the accompanying drawings is shown as a straight direction, and the overall shape of the support structure 20 is a linear, straight shape. However, it is also possible to practice the invention using a curved support structure 20 and an associated curved sliding direction S. Such a curved design may be desirable, for example, to design the support structure 20 to fit an allotted volume 20, or more generally, to reduce the overall space occupied by the nozzle changer 30.

[0033] 4-8, there is shown an example of a nozzle assembly 10 that can be used in a metal atomization process and that can be integrated into a support structure 20 to form a nozzle changer 30. The nozzle assembly 10 includes the following elements: an upper portion 11 designed to be located closest to the liquid metal reservoir during the pulverization process, said upper portion having an upper surface 12; a bottom 19 designed to be located closest to the micronization tower during the micronization process, said bottom having a bottom surface 18; - upstream and downstream surfaces joining said top and bottom surfaces and respectively located on the upstream and downstream sides of the nozzle assembly when considering the sliding direction S; - A liquid metal nozzle (40) having a liquid metal inlet (41) suitable for being aligned with the reservoir opening (104) and a liquid metal outlet (42) configured to pour out a liquid metal stream in the atomization tower, said liquid metal inlet (41) being located on the top surface (12) and said liquid metal outlet (42) being located on the bottom surface (18). an atomizing fluid nozzle (50) having at least one atomizing fluid inlet (51) and an atomizing fluid outlet (52) configured such that fluid flowing through the atomizing fluid outlet (52) impinges on the liquid metal stream flowing from the liquid metal outlet (42), said atomizing fluid outlet (52) being located on the bottom surface (18). The nozzle assembly 10 is adapted to be mounted to a support structure 20 in a configuration such that the nozzle assembly 10 can move within the support structure 20 in a direction S generally parallel to a liquid metal reservoir opening 104 .

[0034] 2, to replace a nozzle assembly 10 during manufacturing, a mechanical device, not shown, pushes the nozzle assembly 10 so that the in-use nozzle assembly 10i is pushed out of the in-use section 20i and replaced by the next in-line nozzle assembly 10n located in the inlet section 20e at a position closest to the in-use section 20i. This movement can be accomplished in a very short time, for example, less than 5 seconds, or even more preferentially less than 2 seconds or less than 1 second, so that the liquid metal flow is barely disturbed and the productivity loss associated with the nozzle replacement is very small.

[0035] In certain embodiments, the upstream surface 14 and the downstream surface 15 have complementary shapes to ensure a continuous upper surface 12 between two consecutive liquid metal nozzle inlets 41 of two nozzle assemblies 10 whose respective downstream and upstream surfaces are positioned opposite each other.

[0036] For clarity, all of the nozzle assemblies 10 shown in the accompanying figures have a substantially cubic shape. Their upstream and downstream surfaces 14 and 15 are flat, linear surfaces. However, other shapes can be used to implement the present invention. For example, it is possible to use curved surfaces for the upstream and downstream surfaces while maintaining the same radius of curvature to ensure the necessary geometric complementarity. This type of design can advantageously allow two consecutive nozzle assemblies within a support structure to rotate slightly even when pressed against each other. This can be advantageous when using support structures with a substantially nonlinear shape associated with a curved sliding direction S. Advantageously, the above-described design of the nozzle assembly 10 ensures that during a nozzle exchange operation, the active nozzle assembly 10i and the next in-line nozzle assembly 10n contact each other at their vertical sides, thereby ensuring that the nozzle assembly top surface 12 forms a continuous surface that blocks the metal flow during the nozzle exchange operation, preventing harmful liquid metal leakage within the pulverization tower. This means that the nozzle exchange operation may be performed without the need for a specific device, such as a stopper rod, to stop the metal flow. Furthermore, the nozzle changing device can even be used to intentionally temporarily stop the metal flow when it is necessary to do so for industrial reasons, such as when some operations need to be performed on the pulverization tower or there are production issues related to any of the equipment in the pulverization device. To temporarily stop the metal flow, the in-use nozzle assembly 10i is partially pushed out of the in-use section 20i and the next in-line nozzle assembly 10n is partially pushed inside the in-use section such that the reservoir opening is blocked by the top surface 12 of either or both of the in-use nozzle assembly 10i or the next in-line nozzle assembly 10n.

[0037] In a particular embodiment, as shown in FIGS. 5-8 , the atomizing fluid inlet 51 of the nozzle exchange assembly 10 is located in a different plane from the liquid metal inlet 41. Advantageously, this allows for independent management of the connections to the liquid metal inlet and the atomizing fluid inlet, each of which requires good airtightness for a smooth atomization process. For the nozzle 10i in use, the liquid metal inlet 41 needs to be precisely aligned with the reservoir opening 104. Meanwhile, the atomizing fluid inlet 51 needs to be fluid-tightly connected to the atomizing fluid supply 106 (especially since the atomizing fluid pressure can be very high). If both the liquid metal inlet and the atomizing fluid inlet are located in the same plane, there is no flexibility to independently adjust their positions or access them. However, if they are located in separate planes, it is possible to provide a quick-fit system for the atomizing fluid inlet 51, as shown in the accompanying figures, for example. The atomizing fluid inlet 51 can be easily accessed independently from the top surface 12 of the nozzle assembly.

[0038] According to a particular embodiment of the present invention, each nozzle assembly 1 has an even number of atomizing fluid inlets 51 forming at least one pair of atomizing fluid inlets, and for each said pair, the inlets are located in opposite, generally parallel planes on substantially opposite sides of the nozzle assembly 1. Advantageously, this configuration allows for better distribution of the atomizing fluid flow within the atomizing fluid nozzle 50.

[0039] According to certain embodiments of the invention as shown in Figures 5-8, the atomizing fluid outlet 52 is generally annular in shape. Advantageously, this allows for a homogenous atomizing fluid flow impinging on the liquid metal flow within the atomizing chamber.

[0040] According to a particular embodiment of the invention, as shown in FIGS. 5-8 , the top 11 of each nozzle assembly 10 comprises a top plate 13 made of a refractory material, said top plate 13 housing a portion of the liquid metal nozzle 40 located within the top 11. Advantageously, the use of a refractory material allows for good resistance to the high temperatures typically experienced by the apparatus during the atomization process, as well as good resistance to potential liquid metal flows that may impinge on said top plate 13 either during a nozzle exchange operation, when using the nozzle exchange apparatus to temporarily stop the liquid metal flow, or in the event of a parasitic liquid metal leak. Furthermore, the use of a design in which the top plate 13 houses the liquid metal nozzle 40 allows for easy maintenance and assembly of the top 11 and good hermeticity of said top, thus preventing damage to the nozzle assembly due to liquid metal leaks during a nozzle exchange operation, or the use of the nozzle assembly to temporarily stop the metal flow, or generally preventing damage during an atomization operation.

[0041] According to certain embodiments of the present invention, the portion of top plate 13 comprising upper surface 12 is surface treated to reduce its coefficient of friction. Advantageously, this allows nozzle assembly 10 to slide smoothly within support structure 20, minimizing wear on both nozzle assembly 10 and support structure 20 during a nozzle change operation.

[0042] According to a particular embodiment of the present invention, the top plate 13 is made of graphite, which is both a refractory material and a low coefficient of friction material, which can provide the above-mentioned advantages of good resistance to liquid metal and the general heat of the environment, as well as low wear on the nozzle assembly and support structure during nozzle replacement operations.

[0043] According to a specific embodiment of the present invention, as shown in FIGS. 5-8, the base 19 includes an atomizing fluid nozzle 50 designed to accommodate a portion of the liquid metal nozzle 40 located within the base 19. Advantageously, this allows for easy maintenance and assembly of the base 19 and good airtightness of the base. This design also allows for a nozzle assembly in which the atomizing fluid nozzle 50 can be reused after the nozzle is pushed out during use. In fact, it is possible to remove a used liquid metal nozzle 40 from the atomizing fluid nozzle 50, since the liquid metal nozzle is simply inserted into an interior provided to accommodate the volume of the atomizing fluid nozzle 50. This is advantageous in terms of maintenance and operating costs, since atomizing fluid nozzles are expensive devices. For example, the atomizing fluid nozzle 50 is made of stainless steel and, as mentioned above, is provided with a quick-fit inlet. For example, the atomizing fluid nozzle can be made of a top and bottom portion that are assembled together, for example, by screwing them together, as shown in FIG. 7. Advantageously, this allows for complex part designs while still using traditional part manufacturing processes such as casting, etc. This two-part construction can also advantageously lend itself to easy assembly of the liquid metal nozzle 40 and atomized fluid nozzle 50 prior to use and easy disassembly after use.

[0044] According to a particular embodiment of the invention, as shown in Figures 4 and 8, the support structure 20 comprises an upper portion 21 designed to be continuous with the upper surface 12 of the nozzle assembly 10, the active portion 21i of said upper portion comprising: an intermediate liquid metal nozzle 22 connected at its top side 23 to the reservoir opening 104 and configured at its bottom side 24 to be connected to the liquid metal inlet 41 of the nozzle assembly 10i in use; a top plate 25 housing the intermediate liquid metal nozzle 22;

[0045] In fact, this embodiment allows the nozzle through which the liquid metal flows to be separated into two separate parts: the intermediate nozzle 22, which is a non-movable part integrated in the support structure 20, and the liquid metal nozzle 40 of the nozzle assembly 10, which can be easily replaced during the atomization operation thanks to the nozzle exchange operation described above. Advantageously, this allows the most important part of the nozzle, the liquid metal outlet 42, to be easily exchanged, while avoiding contact between the movable part of the nozzle and the reservoir opening 104, which would result in wear of said reservoir opening and related parts of the liquid metal reservoir 101, such as the channel 103. Furthermore, the provision of a top plate 25 that houses the intermediate liquid metal nozzle 22 makes it possible to pull out and exchange the intermediate liquid metal nozzle 22 after the atomization operation has finished, ensuring good tightness and stability of the device.

[0046] According to a particular embodiment of the invention, the top plate 25 of the active section of the support structure is made of a refractory material, which advantageously allows good resistance to the high temperatures typically experienced by the device during the pulverization process, as well as to liquid metal flows that may result from parasitic liquid metal leaks.

[0047] According to certain embodiments of the present invention, the bottom surface 26 of the portion of the top plate 25 in the in-use section of the support structure is surface treated to reduce its coefficient of friction. Advantageously, this allows the nozzle assembly 10 to slide smoothly in the in-use section 20i within the support structure 20, minimizing wear on both the nozzle assembly 10 and the support structure 20 during a nozzle exchange operation.

[0048] According to a particular embodiment of the present invention, the top plate 25 of the in-use section of the support structure is made of graphite, which is both a refractory material and a low coefficient of friction material, which can provide the above-mentioned advantages of good resistance to liquid metal and the general heat of the environment, as well as low wear on the nozzle assembly and support structure during nozzle exchange operations.

[0049] According to a particular embodiment of the invention as shown in Figures 2 to 4, the support structure 20 further comprises a bottom 29 configured to support the bottom 19 of the nozzle assembly 10. Advantageously, this allows for better mechanical stability of the nozzle changing device as the nozzle assembly is supported from the bottom.

[0050] According to a particular embodiment of the present invention, the nozzle changing device 30 further comprises a low pressure fluid supply and distribution circuit (not shown in the accompanying figures), at least a next in-line nozzle assembly 10n has at least one of its atomizing fluid supply inlets connected to said low pressure fluid supply; In use the nozzle assembly 10i has at least one of its atomising fluid supply inlets connected to a high pressure atomising fluid supply.

[0051] By connecting the next in-line nozzle assembly 10n to the low-pressure fluid circuit, a positive pressure is ensured at the atomizing fluid outlet 52 of the next in-line nozzle assembly 10n. Advantageously, this generally protects the atomizing fluid outlet 52 and the atomizing fluid nozzle 50 from contamination by airborne metal powder particles that may be present in the atomizing tower. Indeed, it is known that very small diameter metal particles, e.g., metal particles having a diameter of less than 5 micrometers, fly around in the atomizing tower and are not easily captured by the appropriate equipment of the atomizing tower. These airborne particles can clog and damage the atomizing fluid nozzle, impairing its proper functioning while in use and making it more difficult to reuse in subsequent runs without cleaning or maintenance. Using low-pressure fluid to prevent metal powder contamination advantageously utilizes the existing fluid inlet 52, avoiding the waste of expensive high-pressure fluid for this purpose, and also ensuring that no negative interactions occur between the fluid exiting the next in-line nozzle assembly 10n and the high-pressure fluid exiting the nozzle assembly 10i during use.

[0052] According to a particular embodiment of the invention, the fluid used in the low pressure fluid supply and distribution circuit is the same fluid as the atomization fluid. Advantageously, this makes optimal use of the existing fluid inlet 52 and fluid circulation chamber of the atomization fluid nozzle 50, which are in fact configured for the flow of atomization fluid.

[0053] According to certain embodiments of the present invention, the low pressure fluid supply comprises at least a portion of recycled atomization fluid that has been recovered after being reduced in pressure due to use in the atomization process. Advantageously, using available used atomization fluid can provide cost and efficiency benefits.

[0054] According to certain embodiments of the present invention, at least the in-use nozzle assembly 20i and the next in-line nozzle assembly 20n are connected to both the high-pressure circuit and the low-pressure circuit, and the nozzle exchange apparatus 30 further comprises a valve system for each nozzle assembly to switch between the low-pressure circuit and the high-pressure circuit of each nozzle assembly. Advantageously, this allows the above-mentioned low-pressure fluid injection system to be implemented to prevent metal powder contamination without having to manage fluid supply connections when performing a nozzle exchange operation, and the fluid supply of the new in-use nozzle 10i is switched to the high-pressure fluid supply during the nozzle exchange operation by operating the valve system.

[0055] According to certain embodiments of the present invention, the nozzle exchange apparatus 30 further comprises a linear actuator designed to switch the fluid supply to the nozzle assembly fluid inlets 51 between high and low pressure circuits. Advantageously, this allows the same set of fluid inlets 51 to be used for connection to both high and low pressure fluid supplies, thereby simplifying the design and maintenance of the atomized fluid nozzle 50.

[0056] According to a particular embodiment of the invention, the nozzle changing device 30 further comprises a liquid metal nozzle wear detector, not shown in the accompanying figures, configured to monitor the level of material wear at the liquid metal nozzle outlet during use. Advantageously, this allows the nozzle changing operation to be carried out at the optimal time, thereby ensuring the most efficient use of the nozzle assembly during use, without reducing the quality and productivity of the pulverization process.

[0057] According to a particular embodiment of the invention, as shown in Figure 4, the nozzle changing device 30 further comprises a stopper rod 108 designed to block the liquid metal flow exiting through the reservoir opening 104. For example, the stopper rod is moved downwards to block the inlet of the channel 103 in order to stop the liquid metal flow. Advantageously, the presence of the stopper rod ensures the possibility to stop the metal flow when necessary, for example for operational reasons or to change the nozzle. This makes it possible to further prevent leakage of liquid metal during the nozzle changing operation.

[0058] According to a particular embodiment of the present invention, as shown in FIG. 4 , the stopper rod 108 contains a hollow volume 109 and further comprises a rod opening 110 through which pressure can be applied to the liquid metal below the stopper rod when the stopper rod 108 is used to stop the liquid metal flow, in order to push the liquid metal remaining below the stopper rod through the liquid metal outlet 42. Indeed, when the stopper rod is operated to stop the liquid metal flow, the portion of the liquid metal contained within the liquid metal nozzle 40 is no longer subjected to pressure coming from the liquid metal in the liquid metal reservoir 101. As a result, this causes the liquid metal to stop flowing through the liquid metal nozzle 40, which may lead to freezing of the metal within the liquid metal nozzle 40, making it impossible to use it again after the stopper rod is lifted. Furthermore, the liquid metal column can further solidify above the liquid metal nozzle 40 (e.g., in the intermediate nozzle 22 or in the reservoir opening 104). This would form a solid connection of solidified metal between the nozzle assembly 10 and the support structure or liquid metal reservoir, preventing sliding movement of the nozzle assembly 10 and thus effectively preventing the overall function of the nozzle exchange apparatus 30. To prevent this, the aforementioned hollow stopper rod 108 is advantageously used, which has a rod opening 110 through which pressure can be applied to the liquid metal below the stopper rod when the stopper rod 108 is used to stop the liquid metal flow, to force any liquid metal remaining below the stopper rod out through the liquid metal outlet 42. For example, a fluid can be sprayed through the rod opening 110 to apply pressure to the liquid metal column below the stopper rod to force the stopper rod out and prevent the harmful solidification described above. For example, the stopper rod can further include an inner rod that can slide downward within the hollow volume 109, thereby compressing the fluid within the hollow volume 109 and applying the pressure necessary to force out any liquid metal remaining below the stopper rod.

[0059] According to certain embodiments of the present invention, an upward pressure is applied to the bottom 19 of the nozzle assembly 10i during the atomization process, configured to counteract the downward pressure resulting from the liquid metal flow. Advantageously, this ensures that the nozzle assembly 10i is held firmly in place during the atomization process and does not move due to parasitic shear stresses, vibrations, or the like. Furthermore, it also protects the support structure. In fact, the downward pressure exerted by the liquid metal flow through the liquid metal nozzle 20 results in a downward pressure being exerted by the nozzle assembly 10i on the support structure 20 during use. If this pressure is not compensated for by intentionally applying a counter-upward pressure, the full load of the pressure will be borne by the support structure 20, potentially resulting in mechanical wear, warping, deformation, and subsequent maintenance issues. Such considerations are even more important given that atomization operations generate high temperatures, which expose the support structure to both high temperatures and high mechanical loads, potentially resulting in premature failure due to well-known phenomena such as creep.

[0060] The nozzle exchange operation implementing the above described device comprises the following steps: A / providing the aforementioned nozzle changing device; B / operating the mechanical device to actuate the movement of the nozzle assembly in the sliding direction S; C / pushing the in-use nozzle assembly out of the in-use section of the support structure and replacing it with the next in-line nozzle which becomes the new in-use nozzle; Equipped with.

[0061] The nozzle exchange operation optionally comprises the additional step of switching the fluid supply to the new in-use nozzle from a low pressure fluid supply to a high pressure atomizing fluid supply, said step being carried out by using a valve system, or a linear actuator, or any other system suitable for effecting rapid switching between said high pressure and low pressure fluid sources.

[0062] The nozzle replacement operation optionally includes the additional step of using information from a liquid metal nozzle wear detector configured to monitor the level of material wear at the liquid metal nozzle outlet during use to determine the appropriate moment to activate the nozzle replacement operation.

[0063] The nozzle exchange operation optionally comprises, before step B above, the additional step of moving a stopper rod to stop the liquid metal flow from reservoir opening 104.

[0064] The nozzle replacement operation optionally includes, before step B above, the additional step of applying pressure to the liquid metal below the stopper rod after the metal flow has stopped in order to force any liquid metal remaining below the stopper rod out through the liquid metal outlet 42.

[0065] The nozzle replacement operation optionally comprises the additional step, after step C above, of applying upward pressure to the bottom of the nozzle assembly during use.

Claims

1. 1. A nozzle changing device (30) suitable for use in a liquid metal atomization process in which liquid metal (109) held in a liquid metal reservoir (101) and exiting said liquid metal reservoir through a reservoir opening (104) is atomized by an atomization fluid to form a metal spray (110) in an atomization tower (102), comprising: a support structure (20), at least one nozzle assembly (10) mounted within said support structure (20), said nozzle assembly (10) comprising a liquid metal inlet (41), a liquid metal outlet (42) and an atomizing fluid outlet (52), said nozzle assembly (10) being configured such that a liquid metal stream exiting the liquid metal outlet (42) is impinged by an atomizing fluid exiting the atomizing fluid outlet (52); - a high pressure atomization fluid supply (105) and distribution circuit (106) suitable for supplying a high pressure atomization fluid suitable for atomization; a mechanical device designed to move the nozzle assembly (10) within the support structure (20) in a direction S parallel to the liquid metal reservoir opening (104); Equipped with The support structure (20) is configured to allow the nozzle assembly (10) to move within the support structure (20) in a direction S parallel to the liquid metal reservoir opening (104), and the support structure includes: - an in-use section (20i) corresponding to a portion of the support structure (20) designed to accommodate a nozzle assembly (10i) having a liquid metal inlet (21) effectively aligned with the reservoir opening (104); an inlet section (20e) corresponding to the part of the support structure (20) located upstream of the in-use section (20i), taking into account the direction of movement S of the nozzle assembly (10); A nozzle changing device (30) comprising:

2. a nozzle changing device comprising an in-use nozzle assembly (10i) and a next in-line nozzle assembly (10n), said in-use nozzle assembly (10i) having its liquid metal inlet (41) effectively aligned with a reservoir opening (104), said next in-line nozzle assembly (10n) being the nozzle assembly located in the inlet section (20e) at a position closest to the in-use section (20i); and said nozzle changing device further comprising a low-pressure fluid supply and distribution circuit; - at least the next in-line nozzle assembly (10n) has at least one fluid supply inlet (51) connected to said low pressure fluid supply; - in use the nozzle assembly (21i) has its fluid supply inlet (51) connected to the high pressure atomisation fluid circuit (106); The nozzle changing device (30) of claim 1.

3. 3. The nozzle changing device (30) of claim 2, wherein the fluid used in the low pressure fluid supply and distribution circuit is the same fluid as the atomization fluid.

4. 4. The nozzle changing apparatus (30) of claim 3, wherein the low pressure fluid supply contains at least a portion of recycled atomization fluid recovered after being reduced in pressure due to use in the atomization process.

5. 5. The nozzle exchange device (30) of claim 2, wherein at least the nozzle assembly (10i) in use and the next in-line nozzle assembly (10n) are connected to both the high-pressure circuit and the low-pressure circuit, and the nozzle exchange device (30) further comprises a valve system for each nozzle assembly (10) for switching between the low-pressure circuit and the high-pressure circuit of each nozzle assembly (10).

6. The nozzle changer (30) of any one of claims 2 to 4, further comprising a linear actuator designed to switch the fluid supply to the nozzle assembly fluid inlet (51) between a high pressure circuit and a low pressure circuit.

7. Nozzle changing apparatus (30) according to any one of the preceding claims, further comprising a liquid metal nozzle wear detector configured to monitor the level of material wear at the liquid metal nozzle outlet during use.

8. The nozzle changing device (30) of any one of claims 1 to 7, further comprising a stopper rod (108) designed to block the liquid metal flow exiting through the reservoir opening (104).

9. 9. The nozzle changing device (30) according to claim 8, wherein the stopper rod (108) has a hollow volume (109) therein and further comprises a rod opening (110) at a tip thereof, through which pressure can be applied to the liquid metal below the stopper rod to push the liquid metal remaining below the stopper rod out through the liquid metal outlet (42) when the stopper rod (108) is used to stop the liquid metal flow.

10. 10. The nozzle changing device (30) of any one of claims 1 to 9, wherein an upward pressure is applied to the bottom (19) of the nozzle assembly (10i) in use during the atomization process, said upward pressure being configured to counteract the downward pressure resulting from the liquid metal flow.

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