WO2024231618A1 - Method for preparing a metal alloy - Google Patents

Abstract

The invention relates to a method for preparing a liquid metal bath of a metal alloy having a chemical composition comprising at least one first element (X1) and at least one second element (X2), the preparation method comprising a charging step (b) in which all or part of the variable metal waste is introduced continuously into a melting furnace, and is melted to give all or part of a liquid metal bath, and a measurement step (c) in which a composition of said liquid metal bath is measured continuously using a laser-induced plasma atomic emission spectrometry device (3) also called a LIBS device, so as to continuously measure at least a content of said first element (X1) and a content of said second element (X2) in the liquid metal bath.

Description

DESCRIPTION

TITLE: Process for the preparation of a metallic alloy

Technical field of the invention

The present invention relates to a method for preparing a metal alloy allowing the use of metal waste. The method is particularly interesting for the manufacture of aluminum alloy having a final composition comprising at least one chemical element of interest different from aluminum from aluminum waste.

State of the art

In the field of metallurgy, and in particular in the manufacture of aluminum alloys, it is known to prepare aluminum alloys by melting a primary aluminum obtained directly from bauxite to obtain a relatively pure liquid aluminum bath. In order to then prepare an alloy of precise composition, additives of chemical elements expected in the final composition are added to the previously obtained pure aluminum bath.

Once all the required additives have been added, a small amount of the molten metal bath is taken to form a test piece commonly called a "pawn", which is machined and prepared for laboratory analysis to determine if the composition of the molten metal bath is close to the expected composition of the aluminum alloy. If the composition is not close to that expected, then an adjustment of the composition can be made by adding new additives to the molten metal bath. Sometimes, when the composition is too far from the expected composition, the molten metal bath is drained from the furnace to start a new preparation process.

Although this method is satisfactory in that it allows the preparation of a bath of liquid aluminum alloy with a given composition, it first requires the use of pure materials, or those of known composition. Furthermore, it is always necessary to wait until the analysis of the pions is done to continue the preparation process, which involves a loss of time, and therefore of energy to maintain the liquid metal at temperature in the melting furnace.

An economically and environmentally advantageous solution for the supply of initial materials is to use scrap metal, and in the case of aluminium, aluminium waste. Indeed, the cost of purchasing aluminium waste is lower than the cost of producing pure aluminium, and reduces the CO2 footprint of manufacturing, and the reuse of waste allows aluminium waste to be disposed of. There are different sources of supply of metal waste that can be used for recycling. Depending on the source of supply, the composition of the metal waste may be more or less known. It is also possible to classify the sources of supply between so-called controlled sources and so-called mixed sources.

Controlled sources include aluminium waste whose composition is relatively known. For example, they correspond to waste from the transformation processes implemented by aluminium alloy manufacturers, such as plate feet or heads that are removed at the end of a casting process or cutting waste during the rolling stages. Controlled sources may also include waste produced by manufacturers of products made from aluminium (or "pre-consumer" scrap according to the dedicated Anglo-Saxon terminology). The particularity of all of this waste from controlled sources is that its composition generally corresponds to the composition of the alloy that was cast.

Mixed sources include aluminium waste with a more disparate composition. Indeed, this aluminium waste may, for example, correspond to aluminium waste that has been recovered following its use by the end user. In particular, it may correspond, for example, to waste from beverage containers also called UBC (Used Beverage Can according to the dedicated Anglo-Saxon terminology) or aluminium waste from the crushing of automobiles. Alternatively, this aluminium waste may correspond to waste of known composition but mixed with other waste of different types, called mixed metal waste. In particular, this may include mixed “pre-consumer” waste, or waste from casting processes that has been mixed. The particularity of all this mixed metal waste is that its composition is not constant depending on the source of supply. It can vary not only because it can come from different sources but also because there may be mixtures. This disparity in composition makes it difficult to use this waste in alloy production processes.

The ISRI institute for "Institute of Scrap Recycling Industries" (www.isri.org) provides technical definitions of metal scrap in its ISRI Scrap Specifications Circular. In particular, the Guidelines for Nonferrous Scrap: NF-2022 (edition 07/2022) section, which can be consulted for example on the site http://www.scrap2.org/specs/, presents different types of variable aluminum scrap. For example, the circular presents variable aluminum scrap called "Zorba" defined as crushed nonferrous scrap, which is mainly made up of aluminum. However, it is possible to find in the zorba copper, lead, magnesium, stainless steel, nickel, tin and zinc, in elemental or alloyed (solid) form. "Zorba" scrap can be better defined when its name is followed by a number, such as Zorba 90 which means that the material contains approximately 90% non-ferrous metals. Zorba is the result of typical, but not limited to, processing of automobile shredder residue (ASR) by known processes: first by ferrous separation in order to reduce or eliminate iron and/or large iron fasteners; after creating a mixed fraction of scrap and non-ferrous metals with a minimum iron content, the fraction can be separated in a non-ferrous metal separator, such as an eddy current separator. An eddy current separator separates the majority of non-ferrous metals from the other components. The result of this separation is a Zorba-type waste, a product of mixed non-ferrous metals.

Aluminum and magnesium are two specific components of Zorba produced by further processing virgin RBA to separate its components. Both aluminum and magnesium have commercial value – a value that increases if these metals are extracted from Zorba scrap. One such commercially valuable product is “Twitch,” which is an aluminum product derived from wet or dry separation of RBA, as defined by the Institute of Scrap Recycling Industries, Inc.

Twitch scrap can be obtained from an automobile at the end of its useful life after it has been shredded. To be classified as "Twitch", the material must be dry and contain no more than 1% free zinc, no more than 1% free magnesium and no more than 1% analytical iron. In addition, the material may not contain more than 2% total non-metallic materials, including no more than 1% rubber and plastic.

The use of mixed metal scrap, in particular the use of mixed aluminium scrap, may pose a number of problems if they are reused in a preparation process. Indeed, when preparing a liquid aluminium bath for preparing an aluminium alloy belonging to a given series, it is necessary to maintain the content of certain given chemical elements within a particular content range. For example, it may be necessary to ensure at least the presence of a first chemical element within a given content range, defined by a non-zero minimum value and a maximum value, and to limit the presence of a second chemical element as much as possible. If the content of said first chemical element in the variable aluminium scrap is too low, and/or if the content of said second chemical element in the variable aluminium scrap is too high compared to the given value range, it will be very difficult or even impossible to prepare a aluminum alloy corresponding to the targeted composition. In addition, even if the contents of the first and second chemical elements of the waste are suitable for the manufacture of the aluminum alloy, it is not easy to know exactly the composition of the alloy formed without resorting to a pin measurement.

US6784429 discloses a method and equipment and an in-situ method for measuring in real time the properties of liquids, and in particular liquid metal.

A report commissioned by the US Department of Energy, "In Situ, Real Time Measurement of Melt Constituents in the Aluminum, Glass and Steel Industries" by Robert De Saro et al. discloses the use of LIBS on an industrial scale.

In order to be able to use waste with a variable composition, it is known to sort the waste according to its chemical composition in order to reduce the uncertainty as to the composition. Document US20180297091 discloses in particular a method of solid analysis of mixtures of aluminum waste in order to determine the composition of the mixture in order to be able to use it during the alloy production stage. The aluminum waste is analyzed before being melted.

Document US9956609B1 discloses a method for using aluminum scrap that combines a solid-state analysis method for aluminum scrap mixtures to determine the composition of the mixture with continuous analysis of the liquid metal bath using a laser-induced plasma atomic emission spectrometry method, also known as "LIBS" for Laser Induced Breakdown Spectroscopy. Although these methods make it possible to prepare aluminum alloys from scrap, they require either the use of scrap with a known composition or the implementation of an upstream analysis step that eliminates a large portion of the mixed scrap, and which increases the production time of the aluminum alloy, which has obvious repercussions on the total cost of the manufacturing process.

Thus, there is a need to find a method that allows both the use of a maximum of mixed metal waste to carry out the preparation of an aluminum alloy of given composition, without carrying out a specific selection of the mixed metal waste prior to the preparation of the liquid metal bath, and by limiting the total time of implementation of the process to limit energy losses, and thus reduce the environmental and financial cost of the manufacturing process. Disclosure of the invention

The present invention aims to propose a solution which responds to all or part of the aforementioned problems.

This aim can be achieved by implementing a method for preparing a bath of liquid metal of a metal alloy having a chemical composition comprising at least one first element chosen from Cu, Mg, Si, Zn, Li, Mn, Zr, Cr, Fe, Ti, V, Ca, Be, Sc, Cd, Pb, Na and Ni, present in said chemical composition at a first content cl between a first target lower threshold Xlmin, and a first target upper threshold _Xlmax ; and at least one second element selected from Cu, Mg, Si, Zn, Li, Mn, Zr, Cr, Fe, Ti, V, Ca, Be, Sc, Cd, Pb, Na and Ni, present in said chemical composition at a second content c2, lower than a second target upper threshold X2 _max , the preparation method comprising: a) a provisioning step in which a quantity ml of variable metal waste is provided, said variable metal waste being characterized by an average charge content wl of said at least one first element between a first lower initial threshold Yl _min and a second upper initial threshold Yl _max , and such that Ylmax > Xl _max and (Ylmax- Ylmin)/wl > 0.1 > (Xl _max - Xl _min )/cl, preferably (Yl _max - Yl _min )/wl > 0.3 > (Xlmax - Xl _min )/cl; (b) a charging step in which all or part of said variable metal waste is introduced into a melting furnace, and is melted to obtain all or part of a bath of liquid metal; c) a measuring step in which a composition of said liquid metal bath is continuously measured using a laser-induced plasma atomic emission spectrometry device also called LIBS, so as to continuously measure at least a content of said first element and a content of said second element in the liquid metal bath, the introduction of said variable metal waste during the charging step being interrupted when said content of said first element measured in the liquid metal bath reaches a value Xl _maX LiBs such that 0.9* Xl _max < Xl _max uBs Xl _max , or when said content of said second element measured in the liquid metal bath reaches a value X2 _max iBs such that 0.9* X2 _max < X2 _max uBS< X2 _max , d) an adjustment step implemented if the content of said first element measured in the liquid metal bath during the measuring step is lower than the first target lower threshold Xlmin, in which a quantity m2 of first defined metal waste is introduced into the furnace of fusion, said first defined metal waste being characterized by a first average adjustment content vl in said first element XI between a lower adjustment threshold Zl _min which is strictly greater than first target lower threshold Xlmin, and an upper adjustment threshold Zl _ma x, and such that (ZI max" Zlmin)/vl <0.3; e) a dilution step implemented if the content of said first element measured in the liquid metal bath during the measurement step is strictly greater than the first target upper threshold Xl _ma x, or if the content of said second element measured in the liquid metal bath during the measurement step is strictly greater than the second target upper threshold X2 _max in which a quantity m4 of second defined metal waste is introduced into the melting furnace, said second defined metal waste being characterized by an average dilution content v2 of said first element strictly lower than the first target upper threshold, and/or being characterized by an average dilution content v3 of said second element strictly lower than the second target upper threshold (X2 _max ).

The provisions previously described and in particular steps a, b, c, d, and e make it possible to propose a preparation method for producing a liquid metal bath from variable metal waste and defined metal waste, without requiring a sorting step prior to the melting of the metals introduced. Thus, it is possible to obtain a liquid metal bath of precise composition from waste whose source is not controlled, partly coming from an external supplier, and whose composition is very variable.

The melting furnace can be a reverberatory furnace, a rotary furnace, an induction furnace, a chimney furnace or a sidewell furnace.

Furthermore, continuous measurement of the composition by a LIBS method makes it possible to reduce the time required to obtain the composition of the liquid metal bath, which makes it possible to reduce the duration of the process, and therefore to reduce the energy consumption associated with the melting of metals.

Preferably, the charging step (b) in which all or part of said variable metal waste is introduced into a melting furnace is carried out continuously.

The preparation process may further have one or more of the following characteristics, taken alone or in combination.

According to one embodiment, the dilution step (e) comprises the introduction of a quantity m4 of second defined metal waste into the melting furnace, said second defined metal waste being characterized by an average dilution content v2 of said first element between 0 and the first lower threshold.

According to one embodiment, the dilution step (e) comprises the introduction of a quantity m4 of second defined metal waste into the melting furnace, said second waste defined metallic elements being characterized by an average dilution content v3 in said second element strictly lower than the second upper target threshold.

According to one embodiment, the second content c2 is between 0 and the second target upper threshold X2 _max . Generally, the second content c2 does not correspond to a target value centered between 0 and X2 _max , however, it is possible that the second content c2 is substantially equal to X2 _max /2.

According to one embodiment, the first content cl is substantially equal to (Xl _max - Xl _min )/2. According to one embodiment, before the charging step (b), the melting furnace comprises a bath base, said bath base comprising liquid metal originating from a prior process, and/or first defined metal waste, and/or second defined metal waste, said bath base then forming at least part of the liquid metal bath.

According to one embodiment, the bath foot is obtained by the fusion of first defined metal waste and/or second defined metal waste.

According to one embodiment, (Yl _max -Yl _min )/wl > 0.2 and (Zl _max -Zl _min )/vl < 0.2, preferably (Y1 max" Yl _min )/wl > 0.3 and (ZI max" Zlmin)/Vl < 0.1.

According to one embodiment, Yl _min > Xl _max .

According to one embodiment, Ylmin < Xlmin-

According to one embodiment, 0.95* Xl _max < Xl _maxLiB s < 0.99*Xl _max or 0.95* X2 _max < X2 _maxLiB s < 0.99* X2 _max .

According to one embodiment, the loading step (b) comprises a regulation step taking into account the dissolution kinetics of the elements XI and/or X2.

According to one embodiment, the adjustment step (d) is implemented before the charging step (b).

According to one embodiment, the loading step (b) is carried out before the dilution step (e).

According to one embodiment, the measuring step (c) is implemented at any time, as soon as a bath of liquid metal is present in the melting furnace. For example, the measuring step (c) is implemented by measuring the composition of the bath base, in particular when it is melted.

It is also possible that the measuring step (c) is carried out several times during the preparation process. For example, the measuring step (c) may be interrupted when metal is introduced into the melting furnace during an adjustment step (d) and/or during a dilution step (e). The measurement step (c) can then be implemented again following this introduction.

According to one embodiment, the steps of loading (b), adjusting (d), and diluting (e) are implemented in any order.

According to one embodiment, during the adjustment step a quantity m3 of master alloys and addition metals containing said first element is introduced into the melting furnace.

According to one embodiment, the variable metal waste and/or the first defined metal waste, and/or the second defined metal waste are respectively variable aluminum waste, first defined aluminum waste and second defined aluminum waste.

According to one embodiment, the liquid metal bath is an aluminum alloy of the 2XXX, 3XXX, 5XXX, 6XXX, 7XXX, 8XXX series.

In one embodiment, the variable metal scrap is waste as defined by the ^Institute of Scrap Recycling Industries (ISRI) in ISRI Scrap Specifications Circular 2022 and Guidelines for Nonferrous Scrap: NF-2022.

In one embodiment, the variable metal scrap is waste as defined by the ^Institute of Scrap Recycling Industries (ISRI) in ISRI Scrap Specifications Circular 2022 and Guidelines for Nonferrous Scrap: NF-2022, and at least one subheading selected from Magnesium, Zinc, and Aluminum, Mixed Metals or Red Metals.

In one embodiment, the variable metal scrap is of the Twitch or Zorba type, as defined by the ^Institute of Scrap Recycling Industries (ISRI) in ISRI Scrap Specifications Circular 2022 and Guidelines for Nonferrous Scrap: NF-2022.

Description of figures

Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which:

[Fig. 1] Figure 1 is a schematic view of an example of the compositions of the alloys used in the preparation method according to one embodiment of the invention.

[Fig. 2] Figure 2 is a schematic view of certain steps of the preparation method according to one embodiment of the invention. [Fig. 3] Figure 3 is a schematic view of different contents of elements of interest in the example.

[Fig. 4] Figure 4 is a schematic view of the measurement step of the LIBS preparation process according to the example.

[Fig. 5] Figure 5 is a schematic view of the regulation stage during the charging stage.

Detailed description

In the figures and in the remainder of the description, the same references represent identical or similar elements. Furthermore, the different elements are not shown to scale so as to favor the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and can be combined with each other.

As illustrated in Figures 1 and 2, the invention relates to a method for preparing a liquid metal bath 10 of a metal alloy having a chemical composition comprising at least one first element XI selected from Cu, Mg, Si, Zn, Li, Mn, Zr, Cr, Fe, Ti, V, Ca, Be, Sc, Cd, Pb, Na and Ni, present in said chemical composition at a first content cl comprised between a first target lower threshold Xlmin, and a first target upper threshold Xl _ma x. In the particular case shown in Figure 1, the first content cl is substantially equal to (Xlmax - Xl _min )/2. The metal alloy also comprises at least one second element X2 selected from Cu, Mg, Si, Zn, Li, Mn, Zr, Cr, Fe, Ti, V, Ca, Be, Sc, Cd, Pb, Na and Ni, present in said chemical composition at a second content c2, lower than a second target upper threshold X2 _max . Generally speaking, the first element XI is strictly different from the second element X2. Generally speaking, and as shown in Figure 1, the second content c2 does not necessarily correspond to a target value centered between 0 and X2 _max , however, it is possible that the second content c2 is substantially equal to X2 _max /2.

The preparation method firstly comprises a provisioning step (a) in which a quantity ml of variable metal waste 13 is provided, said quantity ml being counted in kilograms. As illustrated in FIG. 1, the variable metal waste 13 corresponds to metal waste characterized by an average charge content wl of said at least one first element XI between a first lower initial threshold Yl _min and a second upper initial threshold Yl _ma x, and such that Yl _ma x > Xl _ma x, and such that (Ylmax- Ylmin)/wl > 0.1 > (Xl _ma x - Xl _min )/cl. Thus, the interval in which the average charge content wl falls is greater than the range of the first targeted content cl. In one embodiment, (Yl _ma x-Yl _min )/wl > 0.2, or even (Yl _ma x-Yl _min )/wl > 0.3. Preferably (Yl _ma x- Ylmin)/wl > 0.3 >(Xlmax - Xl _min )/cl. It is also possible that the average charge content wl is very far from the first content cl, and in particular that Ylmin > Xl _ma x, or that Ylmin < Xlmin. Unless otherwise stated, the definitions of the ISRI (Institute of Scrap Recycling Industries) “Scrap Specification Circular 2022” apply.

According to one embodiment, the variable metal scrap 13 is waste as defined by the Institute of Scrap Recycling Industries (ISRI) in the ISRI Scrap Specifications Circular 2022 and in the section Guidelines for Nonferrous Scrap: NF-2022. According to the invention, when the waste is aluminum, the term "scrap" can also be used to comply with the terminology EN12258-3; in this case, the term "aluminum scrap" or "scrap" is equivalent in the context of the present invention. Preferably, the variable metal scrap 13 is waste as defined in at least one subsection of Guidelines for Nonferrous Scrap: NF-2022, chosen from Magnesium, Zinc, and Aluminum, Mixed Metals or Red Metals. Even more preferably, the variable metal scrap 13 belongs to the Aluminum subsection, and corresponds in particular to Twitch or Zorba type waste. In particular, twitch is defined as waste or scrap of aluminum fragmented by automotive shredders. Twitch is derived from the separation device of wet or dry media, the material is dry and does not contain more than 1% maximum of free zinc, 1% maximum of free magnesium and 1% maximum of analytical iron. It does not contain more than 2% in total of non-metallic materials, of which not more than 1% is rubber and plastic. It is free from excessively oxidized materials, airbag cartridges or any sealed or pressurized article.

The provision step (a) may also comprise the provision of first defined metal waste 15. The first defined metal waste 15 is also metal waste, but is characterized by a first average adjustment content vl in said first element XI between a lower adjustment threshold Zl _min which is strictly greater than the first target lower threshold Xlmin, and an upper adjustment threshold Zlmax, and such that (Zl _max -Zlmin)/vl < 0.3. It may also be provided that (Yl _max -Yl _min )/wl > 0.2 and that (Zl _max -Zl _min )/vl < 0.2, and preferably that (Yl _max -Yl _min )/wl > 0.3 and that (Zl _max -Zl _min )/vl < 0.1. According to one embodiment, the variable metal waste 13 and the defined metal waste 15 are such that (Yl _ma x-Yl _min )/wl > (Zl _ma x-Zl _min )/vl. This means that the composition of the variable metal waste 13 is less well known than that of the defined metal waste 15, according to the invention.

In addition, the provision step (a) may comprise the provision of master alloys and addition metals containing said first element XI. Master alloys are understood to mean alloys intended only to be added to a mixture to rectify the composition and/or structure of the raw foundry product. Some master alloys may contain more than 50% of the main addition element. In other words, master alloys correspond to alloys whose composition is known. Finally, the provision step (a) may comprise the provision of second defined metal waste 17. These second defined metal waste 17 are characterised by an average dilution content v2 of said first element XI of between 0 and the first target lower threshold Xlmin- It is therefore well understood that second defined metal waste 17 may comprise a pure metal, free of first element XI. Alternatively, it is possible for the second defined metal waste 17 to be characterised by an average dilution content v2 of said first element XI of between 0 and the first target upper threshold Xl _ma x. Said second defined metal waste may also be characterised by an average dilution content v3 of said second element X2 strictly lower than the second target upper threshold X2 _M AX.

In general, the variable metal waste 13 and/or the first defined metal waste 15, and/or the second defined metal waste 17 are respectively variable aluminum waste, first defined aluminum waste and second defined aluminum waste. Thus, it is possible to use the preparation method to produce a liquid metal bath 10 corresponding to an aluminum alloy of the 2XXX, 3XXX, 5XXX, 6XXX, 7XXX, 8XXX series. In particular, the 2XXXX series corresponds to aluminum alloys comprising copper in given proportions, and the 6XXX series corresponds to aluminum alloys comprising silicon and magnesium in given proportions.

The preparation method then comprises a charging step (b) in which all or part of said variable metal waste 13 is introduced, preferably continuously into a melting furnace 1, and is melted to obtain all or part of a bath of liquid metal 10.

The melting furnace 1 may be a reverberatory furnace, a rotary furnace, an induction furnace, preferably a crucible induction furnace, a chimney furnace or a sidewell furnace. The reverberatory furnace is a type of furnace generally rectangular, covered with a refractory brick vault and a chimney, which reflects (or reverberates) the heat produced in a place independent of the hearth where the heating system is located. Rotary furnaces consist of a cylindrical casing, with a substantially horizontal axis, which ends in two structures, one at each end. The burner is located at one end and the outlet of the burnt gases is located at the other end, which generally passes through a heat recovery system to preheat the blown air before being evacuated by the chimney. The entire interior of the furnace is lined with a refractory material. The fuel may be gas. The induction furnace is preferably a crucible induction furnace. The heating is electromagnetic induction heating. A sidewell furnace is a furnace consisting of two chambers, the first chamber being used for loading and communicating with the second chamber. All these types of furnaces are well known to those skilled in the art. It is possible that before implementing the charging step (b), the melting furnace 1 already comprises a bath base 11 comprising liquid metal originating for example from a prior process, or from first defined metal waste 15, and/or from second defined metal waste 17.

To simplify the understanding of Figure 2, the different introductions into the melting furnace 1 are represented by layers, it is however well understood that once they are introduced, the materials are melted to form only one bath of liquid metal 10.

According to a variant in which the liquid metal bath 10 is a liquid aluminum alloy bath, it can be provided that during the charging step (b), the temperature prevailing in the melting chamber of the melting furnace 1 is set to a value between 800°C and 1000°C. In this way, it is possible to guarantee the melting of all the metallic elements constituting the variable metal waste 13 and the other waste introduced into the melting chamber. It is also possible to burn any organic residues which may have been introduced for example with the variable metal waste 13.

In parallel or not with the charging step (b), a measuring step (c) is implemented, in which a composition of said liquid metal bath 10 is continuously measured using a laser-induced plasma atomic emission spectrometry device 3 also called LIBS. This measuring step (c) is implemented so as to continuously measure at least a content of said first element XI and a content of said second element X2 in the liquid metal bath 10. It is therefore clearly understood that this measuring step (c) can be implemented continuously throughout the preparation process, but also punctually, and this before, after or during the charging step (b).

To implement the measuring step (c), the LIBS device 3 comprises a measuring probe 5 configured to incorporate argon bubbles into the liquid metal bath 10 so as to generate a plasma in said argon bubble; and to irradiate said plasma generated in said argon bubble by a laser to implement the laser-induced plasma atomic emission spectrometry method. Alternatively, it is possible to generate a plasma on the surface of the liquid metal bath 10 and to irradiate said plasma by the laser to implement the laser-induced plasma atomic emission spectrometry method.

As illustrated in FIG. 2, during the measuring step (c), the measuring probe 5 can be introduced into the liquid metal bath 10 inclined at a measuring angle measured relative to the surface of the liquid metal bath 10, said measuring angle being between 45° and 80°. Advantageously, the inclination of the measuring probe 5 makes it possible both to guarantee good evacuation of the argon bubbles from the measuring probe 5, while making it possible to carry out the measurement by laser-induced plasma atomic emission spectrometry. Advantageously, it may be provided that the measuring step (c) further comprises a determining step in which a temperature sensor measures the temperature of the liquid metal bath 10. In this way, it is possible to know the temperature of the liquid metal bath 10. For example, the LIBS device 3 may comprise the temperature sensor, so that the measurement of the composition of the liquid metal bath 10, and of the temperature of the liquid metal bath 10 are implemented simultaneously.

The measuring step (c) makes it possible to determine conditions for interrupting the introduction of the variable metal waste 13 during the charging step (b). Indeed, such an introduction is interrupted when said content of said first element XI measured in the liquid metal bath 10 reaches a value Xl _ma xLiBs such that 0.9* Xl _ma x < Xl _max uBs Xl _max or preferably 0.95* Xl _max < Xl _max uBs 0.99*Xl _max , or when said content of said second element X2 measured in the liquid metal bath 10 reaches a value X2 _max uBs such that 0.9* X2 _max <X2 _max iBs < X2 _max or preferably 0.95* X2 _max <X2 _max uBS < 0.99*X2 _max . Preferably, it may be provided that the introduction of waste is interrupted when Xl _max uBs = p * Xl _max and/or X2 axLiBs =p* X2 _max , with p being able to take a value among 0.90 or 0.91 or 0.92 or 0.93 or 0.94 or 0.95 or 0.96 or 0.97 or 0.98 or 0.99 or 1.

According to a preferred embodiment, the loading step (b) comprises a regulation step taking into account the dissolution kinetics of the elements XI and/or X2. The regulation based on the dissolution kinetics of the elements XI and/or X2 is possible thanks to the continuous LIBS measurement of the content of the elements XI and X2 in the liquid metal. It is possible to regulate the quantity of variable metal waste to be added without exceeding the value Xl _max uBs and/or X2 _maX LiBs from the composition measured by LIBS of the element XI and/or X2 at a time t. It is indeed possible to predict the dissolution of the element XI or X2 by taking into account the derivatives of the composition curve measured as a function of time. A principle of the regulation step is illustrated in FIG. 5.

The dissolution kinetics depends not only on the element considered, but also on the morphology of the variable metal waste considered (size, geometry), the temperature of the liquid metal, etc. Each dissolution kinetics is characterized by a function f linking the content XI (or X2) as a function of time and the quantity of variable metal waste added. The advantage of LIBS is the possibility of continuously measuring the composition. It is thus possible for a given type of variable metal waste and given melting conditions to know at any time the evolution of the composition as a function of the quantity added. The advantage of this regulation step is to be able to avoid the dilution step (e).

The preparation method also comprises an adjustment step (d) implemented if the content of said first element XI measured in the liquid metal bath 10 during the measurement step (c) is lower than the first target lower threshold Xlmin- In this case, a quantity m2 of first defined metal waste 15 is introduced into the melting furnace 1. During this step, it is also possible for a quantity m3 of master alloys and addition metals containing said first element XI to be introduced into the melting furnace 1, said quantities m2 and m3 being counted in kilograms. In this way, it is possible to adjust the composition of the liquid metal bath 10 from waste whose quantity is known more precisely. As previously specified, the adjustment step (d) can be implemented before the charging step b), for example to form the bath foot 11.

The preparation method may also comprise a dilution step (e) implemented if the content of said first element XI measured in the liquid metal bath 10 during the measurement step (c) is strictly greater than the first target upper threshold Xl _ma x, or if the content of said second element X2 measured in the liquid metal bath 10 during the measurement step (c) is strictly greater than the second target upper threshold X2 _max . In this case, a quantity m4 of second defined metal waste 17 is introduced into the melting furnace 1, said quantity m4 being counted in kilograms. Generally, the charging step (b) is implemented before the dilution step (e).

The previously described arrangements and in particular steps (a), (b), (c), (d), and (e) make it possible to propose a preparation method for producing a liquid metal bath 10 from variable and defined metal waste 13, without requiring a sorting step prior to the melting of the metals introduced. Thus, it is possible to obtain a liquid metal bath 10 of precise composition from waste partly coming from an external supplier, and the composition of which is very variable.

Furthermore, continuous measurement of the composition by a LIBS method makes it possible to reduce the time required to obtain the composition of the liquid metal bath 10, which makes it possible to reduce the duration of the process, and therefore to reduce the energy consumption associated with the melting of metals.

Following the preparation of the liquid metal bath 10, the preparation method may comprise a cleaning step in which a stirring device is introduced into the liquid metal bath 10 transferred into a holding enclosure (not shown), to stir said liquid metal bath 10 so as to extract gas possibly contained in the liquid metal bath 10. In this way, it is possible to prepare a liquid metal bath 10 ready to be cast.

This degreasing step may further comprise the addition of a grain refining agent, in particular titanium, said grain refining agent being configured to allow germination of solid aluminum alloy grains. Advantageously, the addition of a grain refining agent grain refining allows to obtain after casting the liquid aluminum bath, a solid aluminum alloy of better quality.

The preparation process and its implementation can be better understood on the basis of the example given below with reference to Figures 3 to 5, given as a non-limiting example.

Example of implementation:

For this example, the preparation method aims to prepare a bath of liquid metal 10 of an aluminum alloy having a chemical composition comprising silicon Si, and iron Fe as the first element XI. A Si content clsi equal to 0.95 wt% is targeted. As shown in Table 1, the target Si composition, clsi, can be comprised from 0.93 wt% corresponding to XIMIN si to 0.97 wt% corresponding to XIMAX SI. A Fe content elfe equal to 0.35 wt% is also targeted. As shown in Table 1, the target composition elfe is comprised from 0.30 wt% corresponding to XIMIN FE to 0.40 wt% corresponding to XIMAX Fe. The contents are expressed as a mass percentage, also noted wt% or weight%. Thus, and as illustrated in Table 1, it is possible to extract the value of the ratios (Xl _ma xi -XImin i)/cli. The target composition may also comprise a second element X2 corresponding to titanium Ti. Titanium may be present in said chemical composition at a second content c2ti, lower than a second target upper threshold X2 _max which is equal to 0.05 wt% in this example (Table 2).

[Table 1] - Target composition (in weight %) of the liquid metal bath to be prepared

Before proceeding with the charging step (b), a measuring step (c) was implemented in order to measure the composition of the bath foot (11) contained in the melting furnace 1, this bath foot 11 is made up of liquid metal originating from a previous process.

The measurement thus carried out makes it possible to obtain the composition of the liquid metal bath shown in Table 2. The bath base contains Si, Fe and Ti, the remainder being aluminium.

Une étape de mise à disposition (a) de déchets métalliques variables 13 est alors mise en oeuvre. Les déchets métalliques variable 13 sont caractérisés par la composition décrite dans le tableau 3 concernant les éléments Si, Fe et Ti respectivement (Ylsi, Ylfe, Y2). Il est possible d'extraire la valeur des ratios (Y_max i -Ymin i /w,). [Table 2] - Composition of the bath foot (by weight %)

A step of making available (a) variable metal waste 13 is then implemented. The variable metal waste 13 is characterized by the composition described in Table 3 concerning the elements Si, Fe and Ti respectively (Ylsi, Ylfe, Y2). It is possible to extract the value of the ratios (Y _max i -Ymin i /w,).

[Table 3] - Composition of variable metal waste (by weight %)

The graphical comparison between the variability of the metal composition (Ylsi, Ylfe, Y2) and that of the target (Xlsi, Xlfe, X2) is shown in Figure 3.

To manufacture a liquid metal bath 10 having a composition tending towards the target composition (Xlsi, Xlfe, X2), the measuring step (c) is implemented continuously and in real time using a LIBS sensor. FIG. 4 represents the composition of the liquid metal bath in each of the elements Si, Fe and Ti as a function of time during the measuring step (c).

As can be seen in Figure 4, the preparation process includes the following steps:

1. fusion and stabilization of the bath foot composition;

2. charging step (b) comprising the addition of variable metal waste 13;

3. achievement of the target composition by interrupting the charging step (b).

Figure 4 illustrates in particular the evolution of the composition of the elements Si, Fe, and Ti measured during measurement step (c) over time.

As can be seen in Figure 4, the charging step (b) is interrupted when the content of at least one of the elements (Si, Fe or Ti) has reached the limit 0.97*Xl _ma x. Here, it is the Si content that has reached the value of 0.94 wt% which is equal to 0.97*X _max si in the vicinity of a time of 40 min.

In this case, at the end of the interruption, the final composition obtained being included in the intervals defined in table 1, it is therefore not planned to implement an adjustment step (d), nor a dilution step (e).

Claims

1. Method for preparing a liquid metal bath (10) of a metal alloy having a chemical composition comprising at least one first element (XI) chosen from Cu, Mg, Si, Zn, Li, Mn, Zr, Cr, Fe, Ti, V, Ca, Be, Sc, Cd, Pb and Na present in said chemical composition at a first content cl between a first target lower threshold (Xl _min ), and a first target upper threshold (Xl _max ); and at least one second element (X2) selected from Cu, Mg, Si, Zn, Li, Mn, Zr, Cr, Fe, Ti, V, Ca, Be, Sc, Cd, Pb and Na present in said chemical composition at a second content c2, lower than a second target upper threshold (X2max), the preparation method comprising: a) a provision step (a) in which a quantity ml of variable metal waste (13) is provided, said variable metal waste (13) being characterized by an average charge content wl of said at least one first element (XI) between a first lower initial threshold (Yl _min ) and a second upper initial threshold (Ylmax), and such that Yl _max > Xl _max and (Yl _max - Yl _min )/wl > 0.1 > (Xlmax - Xl _min )/cl ; b) a charging step (b) in which all or part of said variable metal waste is introduced into a melting furnace (1), and is melted to obtain all or part of a bath of liquid metal (10); c) a measuring step (c) in which a composition of said liquid metal bath (10) is continuously measured using a laser-induced plasma atomic emission spectrometry device (3) also called LIBS, so as to continuously measure at least a content of said first element (XI) and a content of said second element (X2) in the liquid metal bath (10), the introduction of said variable metal waste (13) during the charging step (b) being interrupted when said content of said first element (XI) measured in the liquid metal bath (10) reaches a value Xl _max uBs such that 0.9* XI max — XlmaxLIBS < Xl _max , or when said content of said second element (X2) measured in the liquid metal bath (10) reaches a value X2 _m axLiBs such that 0.9* X2 _ma x < X2 _m axLiBs^ X2 _m a _X ; d) an adjustment step (d) implemented if the content of said first element (XI) measured in the liquid metal bath (10) during the measurement step (c) is lower than the first target lower threshold (Xlmin), in which a quantity m2 of first defined metal waste (15) is introduced into the melting furnace (1), said first defined metal waste (15) being characterized by a first average adjustment content vl of said first element (XI) between a lower adjustment threshold (Zlmin) which is strictly higher than the first target lower threshold (Xlmin), and an upper adjustment threshold (Zl _ma x), and such that (Zl _m ax-Zl _m in)/vl < e) a dilution step (e) implemented if the content of said first element (XI) measured in the liquid metal bath (10) during the measuring step (c) or (d) is strictly greater than the first target upper threshold (Xl _ma x), or if the content of said second element (X2) measured in the liquid metal bath (10) during the measuring step (c) is strictly greater than the second target upper threshold (X2 _max ) in which a quantity m4 of primary aluminium or second defined metal waste (17) is introduced into the melting furnace (1), said second defined metal waste (17) being characterised by an average dilution content v2 of said first element (XI) strictly lower than the first target upper threshold (Xl _max ), and/or being characterised by an average dilution content v3 of said second element (X2) strictly lower than the second target upper threshold (X2max). 2. Preparation method according to claim 1, wherein before the charging step (b), the melting furnace (1) comprises a bath foot (11), said bath foot (11) comprising liquid metal from a prior process, first defined metal waste (15), and/or second defined metal waste (17), said bath foot then forming at least part of the liquid metal bath. 3. Preparation process according to any one of claims 1 or 2, characterized in that (Ylmax-Ylmin)/wl > 0.2 and that (Zl _max -Zl _min )/vl < 0.2, and preferably in that (Yl _max -Ylmin)/wl > 0.3 and that (Zl _max -Zl _min )/vl < 0.1. 4. Preparation process according to any one of claims 2 or 3, characterized in that Ylmin > X1 max* 5. Preparation process according to any one of claims 1 to 3, characterized in that Ylmin < Xlmin. 6. Preparation process according to any one of claims 1 to 5, characterized in that 0.95* Xlmax < XlmaxLIBS < 0.99*Xl _max OR 0.95* X2max < X2 _maxLIBS < 0.99* X2max. 7. Preparation process according to any one of claims 1 to 6, characterized in that the loading step (b) comprises a regulation step taking into account the dissolution kinetics of the elements XI and/or X2. 8. Preparation method according to any one of claims 1 to 7, in which the adjustment step (d) is carried out before the charging step (b). 9. Preparation process according to any one of claims 1 to 8, in which the charging step (b) is carried out before the dilution step (e). 10. Preparation method according to any one of claims 1 to 9, in which the variable metal waste (13) and/or the first defined metal waste (15), and/or the second defined metal waste (17) are respectively variable aluminum waste, first defined aluminum waste and second defined aluminum waste, and wherein the liquid metal bath (10) is an aluminum alloy of the series 2XXX, 3XXX, 5XXX, 6XXX, 7XXX, 8XXX. 11. A preparation method according to claim 10, wherein the variable metal scrap (13) is of the Twitch or Zorba type, as defined by the ^Institute of Scrap Recycling Industries (ISRI) in the ISRI Scrap Specifications Circular 2022 and in the section Guidelines for Nonferrous Scrap: NF-2022.