ECO-FRIENDLY ALUMINUM ALLOY SCRAP RECYCLING PROCESS

Abstract

A process for remelting aluminum alloy-coated scrap in a cylindrical crucible induction furnace comprising the steps of supplying ground coated scrap, decladding, loading, remelting, and holding ground coated aluminum alloy scrap, such that at least 50% of the individual particles of the ground coated scrap have a particle size between 5 and 25 mm and a flatness of 10 mm or less, and wherein during the loading phase, the induction furnace is inerted and the inert gas outlet is located in the circular quarter-section of the furnace containing the delimited area where the scrap falls. (Shorthand figure: Fig. 3)

Description

Title of the invention: ECO-RESPONSIBLE ALUMINUM ALLOY SCRAP RECYCLING PROCESS Technical field

[0001] The invention relates to the remelting in an induction furnace of scrap coated with aluminum alloy, preferably scrap recovered from household aluminum packaging, typically used aluminum beverage cans. PREVIOUS ART

[0002] Aluminum recycling has the advantage of being economical and environmentally friendly. The production of secondary aluminum requires up to 95% less energy than primary aluminum and allows for the reduction of CO2 emissions. In an effort to improve the environmental impact of aluminum production, the aluminum industry is seeking to reduce the amount of CO2 emitted during the recycling stage during the scrap remelting stage.

[0003] In this text, the generic term "scrap" refers to raw materials for recycling, consisting of aluminum and / or aluminum alloy products resulting from the collection and / or recovery of metals produced at different stages of manufacture or products after use. Unless otherwise stated, reference is made to standard NF EN 12258-3 September 2003 which defines terms relating to aluminum and aluminum alloy scrap. "Coated scrap" refers to scrap composed of parts having any type of coating, for example paint, varnish, printing ink, plastic, paper, metal.

[0004] Aluminum alloy beverage cans consist of a can body and a lid; usually the can body is made of AA3104 alloy and the lid of AA5182 alloy. The can body and the lid are coated with an organic and / or inorganic coating such as a varnish and / or paint and / or organic material.

[0005] Used beverage cans, also called UBC (Used Beverage Can) made of aluminum belong to the category of coated scrap. Similarly, food packaging or aerosol cans made of aluminum alloys belong to the category of coated scrap. They are generally contaminated by the presence of varnish and / or paint and / or printing ink. It is also possible that these containers are contaminated by the possible presence of dust, sand, water, beverage residue or other pollution.

[0006] Among household packaging, we can cite used beverage cans, used food packaging, used aerosol cans. These types of products or any other aluminum alloy coated product can be collected. Usually, after collection, these products are compacted to form "bales" or "briquettes" which facilitate storage and transport. Compaction is also sometimes considered to facilitate submersion of scrap in remelting furnaces as in US application 4,159,907.

[0007] However, it is also possible to grind them. Scrap is obtained in divided form, consisting of individual entities. The grinding operation allows in particular to shred the products and to prevent liquid from still being present in the containers and thus avoid risks of explosion during the remelting operation. It is possible during this grinding step to carry out sorting to separate any contamination such as for example possible pieces of scrap metal, any other metal products not made of aluminum or aluminum alloy or plastic products.

[0008] The technology used in the profession for recycling coated products, particularly UBCs, usually uses a dedicated line consisting of cold preparation steps (shredder, magnetic sorting and air knife separator), hot removal in a decoater of inks, varnishes and other organic materials. The coated scrap is then remelted typically in a basin furnace (side-well furnace). A treatment of the metal by adding salt (3% to 5%) is necessary to remove the oxides contained in the liquid metal (R. Evans, G. Guest, “The aluminium decoating handbook”, Stein Atkinston Stordy, Gillespie Powers internet source). The metal is then transported to the foundry workshop to be cast. Another alternative is to carry out remelting in a rotary furnace. This solution requires a higher salt level than for the side-well furnace (10% to 15%).In this case, the combustion of organic materials and the remelting of the metal take place simultaneously in the furnace enclosure.

[0009] US 3,999,980 describes a method which does not require prior treatment in a “decoater” of UBCs. It is carried out in a scrap melting furnace under an inert atmosphere and compares it to typical processes using a molten salt.

[0010] Another alternative is remelting in a multi-chamber furnace ("Aluminium recycling" M. Schlesinger, CRC Press, (2007)). The coated scrap is loaded, preheated and deglazed in a separate chamber (vertical tunnel or horizontal ramp). The combustion of organic matter helps heat the installation. This is a salt-free process. This solution has the disadvantage of having to be carried out in a gas furnace, which is not suitable for reducing CO2 emissions.

[0011] One solution to reduce CO2 emissions is to use electric furnaces. Induction furnace technology is mentioned for UBC recycling in reference works (R. Evans, G. Guest, “The aluminium decoating handbook”, Stein Atkinston Stordy, Gillespie Powers internet source). The electric furnace Crucible induction has the advantage of good energy efficiency and generates little metal loss. The large-capacity electric channel furnace is sometimes used for remelting new manufacturing scrap or beverage cans after decoating (F. Herbulot - Recovery and recycling of aluminum - Engineering Techniques - March 2001). However, these types of furnaces have not experienced significant industrial growth. They require clean raw materials to avoid the progressive fouling of the crucible walls by oxides or the formation of oxides in the metal.

[0012] There is, with regard to the treatment of coated scrap in an induction furnace, a prejudice of the skilled person indicating that the recycling of coated scrap, in particular scrap recovered from used beverage cans, is not possible in an electric induction furnace on an industrial scale without the use of molten salts (Verran et al. Resources, Conservation and Recycling 52 (2008) 731-736). The molten salts act as a collector for the oxides and make it possible to form a pasty saline slag which separates from the liquid metal and floats on it. The presence of saline slag has the disadvantage of reducing the raw or net metal yield. The term "raw metal yield" (expressed in %) refers to the ratio between the mass of liquid metal actually removed from the furnace or cast to the mass of material charged to a furnace.The term "net metal yield" refers to the ratio between the mass of liquid metal actually discharged or poured to the net mass of metal charged into a furnace.

[0013] There is therefore a need for an economical and reliable solution allowing the use of induction furnaces without molten salts in the treatment of coated scrap, in particular scrap recovered from used aluminum beverage cans.

[0014] US2020 / 0255922 describes a method of treatment in an induction furnace under vacuum for recycling lithium aluminum alloy machining scrap. This method is carried out in batches, i.e. the lithium aluminum alloy scrap is placed in the furnace all at once to ensure vacuum operation. In order to increase the quantity of molten metal in the furnace, US2020 / 0255922 provides for a chip compaction step.

[0015] WO 2007 / 015013 describes a method of treatment in an induction furnace for recycling lithium aluminum alloy machining scrap. The lithium aluminum alloy scrap is loaded onto a liquid metal bath base so as to create a floating scrap mattress of controlled thickness on the surface of the liquid metal bed (loading step). This floating scrap mattress protects the liquid metal from oxidation and avoids the use of an inert atmosphere. This floating mattress consists of divided scrap of which at least one dimension is less than 1 mm and for which no dimension is greater than 25 mm. The density of the scrap is between 0.05 and preferably 0.1 to 0.7 t / m3 (tonne per cubic meter) and even more advantageously between 0.2 to 0.4 t / m3. The inventors have found that it It was not possible to obtain a good raw metal yield with coated scrap with these geometric considerations alone.

[0016] US 4,159,907 shows the disadvantage of the low density of scrap which tends to remain on the surface of the liquid aluminum and to oxidize and proposes to densify the scrap by compression to solve this problem. Other documents in the state of the art propose alternative solutions to the immersion of scrap in melting furnaces. US6,074,455 describes a method of rapid immersion of scrap in liquid aluminum by introducing it into the vortex created by a rotor. US 3,873,305 describes a method of melting beverage can scrap in which the scrap is forced to be submerged by the action of a rotating propeller. JP 10147822 describes a furnace used for melting beverage can scrap in which the scrap is mixed above the bath of liquid metal using specific equipment.These immersion solutions using mechanical means to immerse the scrap have the disadvantage of promoting oxidation of the bath which is not favorable for the raw metal yield.

[0017] The problem that the present invention seeks to solve is therefore to propose a method for recycling scrap coated with aluminum alloy, preferably recovered scrap from household aluminum packaging, typically used aluminum beverage cans, using an induction remelting furnace without using protective salts. Statement of the invention

[0018] The invention relates to a method for remelting scrap coated with aluminum alloy comprising the following steps:

[0019] (i) crushed coated scrap based on aluminum alloys is supplied, consisting of of individual entities, (ii) stripping said crushed coated scrap to obtain stripped scrap, (iii) preparing an initial bath base of liquid metal of a first composition in an induction furnace with a cylindrical crucible of internal radius R equipped with a cover operating at a given frequency, said induction furnace has a supply means allowing the supply of stripped scrap, (iv) the delaminated scrap is loaded into the induction furnace using the feed means directly onto the initial bath base to be melted, said delaminated scrap falls to the surface of the initial bath base in a delimited area and forms a bed of delaminated scrap floating on the surface of the initial bath base, (v) the floating bed of delamination scrap is remelted to form a bath of remelted liquid metal of second composition, (vi) the remelted liquid metal bath is kept in a liquid state.

[0020] An inert gas, typically argon gas, is injected above the surface of the liquid metal bath by at least one injection means. In step (iv), the surface area of ​​the delimited zone is less than or equal to a quarter of the cross-section of the surface of the liquid metal bath. At least one injection means is configured such that the inert gas outlet is located in the quarter circular section of the furnace containing said delimited zone.

[0021] According to the invention, at least 50% of the individual entities of the crushed coated scrap supplied in step i) has a particle size of between 5 and 25 mm, preferably between 8 and 25 mm, more preferably between 8 and 16 mm, the particle size being measured by sieving.

[0022] According to the invention, at least 50% of the individual entities of the crushed coated scrap supplied in step i) have a flatness of less than or equal to 10 mm, preferably less than or equal to 5 mm. The flatness is measured from an individual entity of crushed coated scrap placed on a flatness ruler such that the flatness of the entity corresponds to the maximum distance between the surface of the flatness ruler and the surface of the entity (see [Fig.l]).

[0023] Advantageously, the crushed coated scrap is obtained according to a method comprising a grinding step with a knife mill, equipped with a grid configured to adjust the particle size. According to the invention, the knife mill used is preferred because it allows a clean cut and avoids "crushing" the scrap, which leads to folding that is prohibitive for obtaining effective decoating and introduction of the scrap into the crucible induction furnace. Preferably, before the step of supplying crushed coated scrap, coated scrap is supplied, then is crushed in a knife mill. This consists of cutting the coated scrap between knives mounted on a rotating shaft and a row of fixed knives. The presence of a grid ensures particle size control at the outlet.

[0024] This preliminary grinding step in a knife mill corresponds to a process for remelting scrap coated with aluminum alloy comprising the following successive steps: - we supply scrap coated with aluminum alloys, preferably scrap recovered from household aluminum packaging, typically used aluminum drinks cans - The coated scrap is ground in a knife mill, equipped with a grid, to obtain ground coated scrap consisting of individual entities - the said crushed coated scrap is stripped to obtain stripped scrap, - an initial bath base of liquid metal of a first composition is prepared in a crucible induction furnace operating at a given frequency, folding ratio = R - the stripped scrap is loaded into the induction oven directly onto the initial bath base to be melted,

[0025] Advantageously at least 50% of the individual entities of the crushed coated scrap have a folding ratio (R) less than or equal to 0.6, where the folding ratio (R) of an individual feature is defined by the expression _ unfolded surface - folded surface |the folded surface is the .unfolded surface maximum area of ​​the orthogonal projection of the individual feature onto a plane and the unfolded area is the total area of ​​the same individual feature after being unfolded.

[0026] The folding ratio parameter makes it possible to account for the flatness, which is an essential parameter of the invention, but also for the “crumpled” appearance of the scrap, which is a characteristic influencing the metal yield during the remelting step.

[0027] Advantageously, the density of the crushed coated scrap supplied in step i) is between 0.2 and 0.4 t / m3.

[0028] Advantageously, the deglazed scrap obtained after step ii) is introduced into the induction furnace in step iv) at a temperature above 100°C, preferably at a temperature between 200°C and 450°C, more preferably between 300°C and 450°C, even more preferably between 400°C and 450°C.

[0029] Advantageously, no protective salt is used in the induction furnace.

[0030] Advantageously, the frequency of the induction furnace during steps iv) to v) is between 50 Hz and 150 Hz. This has the advantage of improving the submersion of scrap.

[0031] Advantageously, during step vi) at least two injection means, located in at least two quarter circular sections of the furnace, are used. This has the advantage of being able to reduce the quantity of inert gas used and inert the complete surface of the liquid metal bath. Advantageously, the at least two injection means are arranged in a crown. This has the advantage of being able to homogeneously inert the surface of the liquid metal bath.

[0032] Advantageously, at least four injection means are used and are located in each quarter circular section of the furnace.

[0033] Advantageously, the loading in step iv) is carried out discontinuously or continuously, preferably using a worm screw or a hopper or a vibrator system. Advantageously, the feeding means is provided with a weighing system in order to control the loaded weight.

[0034] Advantageously, the distance between the surface of the liquid metal bath and the inert gas outlet is less than or equal to 1 m, preferably 50 cm, even more preferably potentially 40 cm. This has the advantage of being able to inert effectively without excessive gas consumption.

[0035] Advantageously, the temperature of the liquid metal bath during step iv) is less than or equal to 750°C, preferably less than or equal to 730°C, or even preferably less than 710°C, and greater than 680°C.

[0036] Advantageously, the coated scrap supplied in step i) is mainly made from recovered scrap from household aluminum packaging, typically used aluminum beverage cans. That is to say, the crushed coated scrap is obtained from recovered scrap from household aluminum packaging, typically used aluminum beverage cans. FIGURES

[0037] [Fig. 1] [Fig. 1] represents the method for measuring the flatness of an individual entity of ground coated scrap.

[0038] [Fig.2] [Fig.2] represents the principles of the method for measuring the folding ratio R. Figures 2 a and 2 c represent respectively the appearance of an individual entity of supplied crushed coated scrap and the appearance of the same individual entity unfolded. [Fig.2] b represents the orthogonal projection of the individual entity 2 a giving a maximum surface area. [Fig.2] d represents the contour of the unfolded surface allowing the measurement of the unfolded surface area.

[0039] [Fig.3] [Fig.3] represents the appearance of the crushed coated scrap supplied according to the invention.

[0040] [Fig.4] [Fig.4] represents a diagram of a cylindrical crucible induction furnace with the stirring movements, containing an initial bath foot. [Fig.4] a is a front view and view 4b is a top view.

[0041] [Fig.5] [Fig.5] represents a diagram of an induction furnace during phase iv) of loading of scrap delamination of the process with the stirring movements. [Fig.5] a is a front view and view 5b is a top view.

[0042] [Fig.6] [Fig.6] represents a diagram of an induction furnace during phase v) of fusion of the delaminating scrap bed of the process. [Fig.6] a is a front view and view 6b is a top view.

[0043] [Fig.7] [Fig.7] represents a diagram of an induction furnace during phase vi) of maintenance of the process. [Fig.7] a is a front view and view 7b is a top view.

[0044] [Fig.8] [Fig.8] represents the appearance of the coated scrap crushed outside the invention obtained by a hammer milling process DETAILED DESCRIPTION OF THE INVENTION

[0045] The method according to the invention comprises six steps: firstly a step of supplying the crushed coated scrap, secondly a step of stripping the crushed coated scrap, thirdly a step of preparing a base of liquid metal bath in an induction furnace, fourthly the loading of the stripped scrap into the induction furnace, fifthly a step of remelting the stripped scrap to form a bath of liquid metal, sixthly a phase of maintaining the bath of liquid metal.

[0046] 1 / Supplying the crushed coated scrap

[0047] The coated scrap capable of being recycled by the method according to the present invention is in crushed form. It is important according to the invention that the coated scrap is crushed and supplied in divided form. The crushed coated scrap according to the invention consists of individual entities (1). They are of smaller dimensions compared to that of the initial waste such as beverage cans or food cans.

[0048] In the following, unless otherwise stated, the proportions in % of individual entities correspond to numerical % of individual entities.

[0049] It is advantageous for the individual entities of ground coated scrap to be substantially planar so that they can easily be superimposed on each other and easily immersed in the liquid metal bath. To measure the flatness, an individual entity of ground coated scrap 1 is placed on a flatness ruler 3. An individual entity of ground coated scrap can be inscribed in a fictitious volume defined by a length L, a width 1 and a height h, where the height h is the smallest dimension among the length and the width. The individual entity 1 is placed on the flatness ruler 3 in such a way that the height of the fictitious volume is substantially perpendicular to the surface of the flatness ruler. The flatness p of the entity corresponds to the maximum distance between the surface of the flatness ruler and the surface of the entity as placed on the flatness ruler (see [Fig. 1]).The flatness rule can be any flat surface, such as a measuring marble.

[0050] Advantageously at least 50% or 60% or 70% or 80% or 90% or 100% of the individual entities of the ground coated scrap have a flatness less than or equal to 10 mm or 5 mm. The inventors have found that the flatness of an individual entity of ground coated scrap is not modified by the stripping operation. The inventors believe that having a majority of individual entities of ground coated scrap having a flatness less than or equal to 10 mm or 5 mm promotes their arrangement in the form of stacked layers and improves their submersion in the liquid metal bath of the induction furnace.

[0051] The estimation of the percentage of individual entity of crushed coated scrap having a flatness less than or equal to 50 mm can be carried out on the whole of the scrap or on a part, typically on a number of individual entities at least equal to 20.

[0052] Advantageously, at least 50% or 60% or 70% or 80% or 90% or 100% of the individual entities of the crushed coated scrap have a particle size between 5 and 25 mm, preferably between 6 mm, or 7 mm or 8 mm or 10 mm, and 25 mm or 24 mm or 23 mm or 22 mm or 21 mm or 20 mm or 19 mm or 18 mm or 17 mm or 16 mm or 15 mm. Any combination of these values ​​is advantageously possible.

[0053] The particle size of the individual entities of the crushed coated scrap can be measured by sieving. To measure the particle size of the individual entities of the crushed coated scrap, a series of sieves nested inside each other can be used. The mesh sizes of the sieves decrease from top to bottom. The individual entities Individual constituents of the scrap are placed on the highest sieve and by vibration; the scrap is distributed on the different sieves according to their size. Square mesh sieves can be used by their opening; the nominal dimension of a sieve corresponds to the length of the side of the mesh (in mm). Seven sieves of size 35, 25, 16, 8, 4, 2, 1 mm can be used. The sieving time is preferably at least 10 minutes. The inventors have found that the particle size of the individual entities of the coated scrap is not modified by the stripping operation. A particle size of the individual entities between 1 and 25 mm allows an improvement in the submersion of the scrap in the liquid metal bath of the induction furnace.

[0054] The estimation of the percentage of individual entity of crushed coated scrap having a given particle size can be carried out on the whole of the scrap or on a part, typically on a number of individual entities at least equal to 20.

[0055] It is advantageous according to the invention that the majority of the individual entities of the crushed coated scrap have a folding ratio less than or equal to 0.6. Advantageously, at least 50% of the individual entities of the crushed coated scrap have a folding ratio (R) less than or equal to 0.6. Preferably, at least 60%, or 70% or 80% of the individual entities of the crushed coated scrap have a folding ratio (R) less than or equal to 0.6. The folding ratio of an individual entity is defined by equation 1.

[0056] [Math.l] folding ratio = R = folded surface - folded surface unfolded surface (equation 1)

[0057] Preferably, at least 50% or 60% or 70% or 80% or 90% or 100% of the entities individual pieces of the crushed coated scrap supplied in step i) has a folding ratio (R) less than or equal to 0.6, or 0.5, even more preferably less than or equal to 0.4.

[0058] The folding ratio of an individual entity of the crushed coated scrap quantifies the way in which this individual entity has been folded during the previous steps. The higher this ratio, the more the individual entity has been folded and is therefore compact or gathered, in particular in globular form. The lower the ratio, the more the individual entity is plane. The inventors found that it was necessary to have a folding ratio less than or equal to 0.6 to avoid the use of salts, called recycling flux, to separate the oxides from the liquid metal, during the remelting step in the crucible induction furnace.

[0059] The folded surface is the apparent surface of an individual entity of crushed coated scrap. The folded surface is defined as the maximum surface of the orthogonal projection onto a plane of the individual entity.

[0060] The unfolded surface area corresponds to the developed surface area of ​​an individual entity of crushed coated scrap. The unfolded surface area is defined as the total surface area of ​​the individual entity of crushed coated scrap after being unfolded. It should be noted that knowing the thickness and the mass and the average density of the individual entity, the unfolded surface area can easily be determined. The unfolded surface area can also be obtained by unfolding the individual entity.

[0061] For example, if we consider an individual entity of crushed coated scrap typically having the size of a postage stamp and having an unfolded surface area of ​​1 cm2, it has a folding ratio of 0.5 if this entity is folded in two. This same entity has a folding ratio of 0 if it has not been folded.

[0062] The inventors have found that the number of folds or surface coverings deteriorates the flatness of the individual entity. On the other hand, they have found that it is important that the coated scrap is folded back on itself as little as possible so that the coated surfaces are in direct contact with the atmosphere of the stripping oven and that consequently the exchanges of masses and heat on the surface of the scrap occurring during the stripping operation can take place as efficiently as possible.

[0063] The folding ratio can be measured as follows: an individual entity of crushed coated scrap (1, [Fig.2] a) is taken. A sheet of paper whose mass mo and surface area S0 are known is used. The outline of the individual entity is drawn on the sheet in such a way as to obtain the folded surface area (10, [Fig.2] b), ensuring that the individual entity has been placed on the sheet of paper in such a way as to have the projection of the maximum surface area of ​​the individual entity of coated scrap (10, [Fig.2] b). This gives the maximum surface area of ​​the orthogonal projection of the individual entity onto a plane. The outline is cut out and the piece mb is weighed. Once this step is completed, the same individual entity of crushed coated scrap (2, [Fig.2] c) is unfolded. A sheet of paper is taken again whose mass m'o and surface area S'0 are known. We draw the contours of the individual scrap entity thus unfolded (20, [Fig.2] d); the contours are cut out and m2 is weighed. The folding ratio (R) can be deduced according to equation 2.

[0064] [Math.2] (equation 2)

[0065] The unfolding operation can be done manually. During this operation, it is possible that pieces may come off. Each of the pieces must be taken into account in the measurement of the mass m2.

[0066] The estimation of the percentage of individual entity of crushed coated scrap having a folding ratio of less than 0.6 can be carried out on the whole of the scrap or on a part, typically on a number of individual entities at least equal to 20.

[0067] In the following, unless otherwise stated, the use of the expression "between ..and .." may be replaced by the expression "between .. and ..". In the following, unless otherwise stated, the expression of the style "the gain is between A and B" means that the gain is between A and B; the gain may take the value A or B; the limits A and B are included.

[0068] Advantageously, the density of the coated scrap is between 0.2 and 0.4 t / m3 (tonne per cubic meter). The density of the scrap is measured as follows: a cylindrical container with a capacity of 1 liter is filled with scrap, a vibration is produced in the form of small shocks so as to compact the scrap. The operation is repeated until the container is filled to the brim. The weight of the filled container from which the weight of the empty container is subtracted makes it possible to determine the density of the scrap.

[0069] The supply of crushed coated scrap having the geometric characteristics as defined above can be obtained using a method comprising a crushing step using a knife mill, equipped with a grid. In a knife mill, the coated scrap is cut between knives mounted on a rapidly rotating shaft and a fixed row of knives. The presence of a grid makes it possible to ensure particle size control at the outlet of the mill. Obtaining the desired particle size can be carried out separately on a dedicated tool. The grid is characterized by a mesh size. Preferably, the mesh size of the grid is less than or equal to 50 mm, 45 mm, 40 mm, 35 mm, 34 mm, 33 mm, 32 mm, 31 mm, 30 mm, 29 mm, 28 mm, 27 mm, 26 mm, 25 mm, 24 mm, 23 mm, 22 mm, 21 mm, 20 mm, 19 mm, 18 mm, 17 mm, 16 mm and greater than 15 mm.Below 15 mm, the particle size is too small, which forms too many fines, which are prohibitive for the remelting process. Above 50 mm, the particle size is too large, which does not allow a folding ratio of less than or equal to 0.6 to be obtained. The advantage of the knife mill is to obtain clean cuts and to avoid deformation. the scrap and it folds back on itself.

[0070] The supply of crushed coated scrap having the geometric characteristics as defined above can be obtained by using a low-density compaction process (used for the transport and handling of scrap to the recycling center), followed by a low-speed pre-crusher allowing the release of the unit UBCs from the compacted bales, followed by a crusher allowing the clean cutting of the scrap (knife crusher type). Compaction can be useful if the scrap has to be transported to the recycling center. However, care must be taken to ensure that compaction does not increase the apparent density of the compacted scrap, typically care must be taken to ensure that compaction does not increase the apparent density of the compacted scrap beyond a density of approximately 1400 kg / m3. This is referred to as low-density compaction.Indeed, if the compaction is too dense, it is not possible to individually release the scrap constituting the compacted packages (also called bales or bundles). The inventors found that it would be necessary to aim for a particle size of less than 5 mm to obtain the desired folding ratio with a technique other than knife grinding. This would then have the consequence of increasing the metal loss at the time of remelting.

[0071] Low-speed pre-crushing, which can also be called "unpacking", consists of breaking up the bales without changing the shape of the compacted individual scrap. This step is of course optional if the scrap has not been compacted.

[0072] The inventors have found that the use of hammer mills or centrifugal or impact grinding is not advantageous for obtaining the desired geometries.

[0073] 2 / Stripping stage

[0074] The crushed coated scrap thus supplied is then stripped. Stripping consists of heating the coated scrap to a temperature where moisture and organic matter (for example, paints, protective varnishes, lid seals and other smoke-producing materials) are eliminated, but without heating to too high a temperature to avoid melting the metal. Typically, the temperature is between 450°C and 540°C. The scrap is heated by heat transfer with the atmosphere of the furnace, preferably by the heated gas from the post-combustion of the fumes and which circulates in the stripping chamber. This operation makes it possible on the one hand to dry the scrap and on the other hand to eliminate organic matter. The organic matter can be converted into CO2 in a post-combustion unit to destroy organic molecules. This produces a dry, purified scrap, free of smoke-producing materials.

[0075] After sufficient time has elapsed, the scrap is removed from the decoating chamber.

[0076] The stripping operation can also be obtained chemically: the coated scrap The crushed material can be immersed in different baths allowing the dissolution of organic matter and followed by a drying operation.

[0077] The inventors have found that the stripping or drying operation does not modify the folding ratio, the flatness, the shape of the scrap. The clean scrap therefore has the same folding ratio, the same flatness, the same granulometry as the supplied crushed coated scrap. The density of the clean scrap is slightly modified compared to that of the coated scrap and remains between 0.2 and 0.4 t / m3.

[0078] The crushed coated scrap, before stripping, has an initial residual carbon quantity typically of at least 1.5% by weight. Advantageously, the scrap, after the stripping step, has a residual carbon quantity of less than 0.3% by weight, preferably less than 0.2% by weight, even more preferably less than 0.1% by weight. The residual carbon quantity in % by weight can be measured using a suitable instrument such as those supplied by the company LECO. The analysis consists of maintaining a given mass of scrap in a furnace after the stripping step at a temperature between 250°C and 550°C under an argon flow and converting the fumes into CO2 in a catalytic furnace. The carbon dosage is evaluated by dosing the proportion of CO2 via an infrared probe.

[0079] 3 / Preparation of an initial bath base of liquid metal in an induction furnace

[0080] A cylindrical crucible induction furnace 100 with an internal radius R is provided, equipped with a cover (170) operating at a given frequency ([Fig.4], 5, 6, 7). [Fig.4] b is a top view of the cylindrical induction furnace 100 showing the four quarter circular sections of the surface of the liquid bath (I, II, III, IV). The four quarter circular sections of the induction furnace (I', II', III', IV') which are superimposed on the four quarter circular sections of the surface of the liquid bath are also shown. The cylindrical crucible induction furnace is equipped with at least one injection means (160). This injection means makes it possible to inject gas in order to inert the atmosphere of the furnace. It is advantageous to have at least two injection means (160) in two separate quarter circular sections of the furnace. Preferably, at least one injection means (160) is arranged in each quarter circular section of the furnace (I', II', III', IV').Preferably, the injection means are arranged in a crown. They can be arranged on the walls of the furnace or on the furnace cover.

[0081] The crucible induction furnace is essentially composed of one or two induction coils cooled by circulation of heat transfer fluid 101, surrounding a refractory lining of rammed earth or a pre-baked refractory shell, forming the crucible 102 in which the metal mass to be melted is placed.

[0082] A liquid metal bath base 50 of a first composition is prepared ([Fig.4]) into which the clean scrap obtained after stripping and / or drying will be poured. The clean scrap obtained after stripping is poured onto the surface 52 of the metal bath liquid. The initial liquid metal bath base can be obtained from the clean scrap obtained after the stripping step or from massive waste, such as cutting scraps or cutting skeletons of thin or thick sheets, said massive waste being made of an alloy of composition compatible with the clean scrap, and preferably purer, the composition of which will not harm the final composition. Typically, the massive waste is aluminum alloys of the 3XXX series, typically an alloy of the AA3104 type. The liquid metal bath base can also be obtained by melting remelting ingots of an alloy of type Ixxx, 3xxx, 5xxx, 6xxx, 8xxx compatible with the clean scrap. In the case of successive castings, the liquid metal bath base can advantageously be made up of the remainder of the previous casting.

[0083] The volume of the bath base represents approximately 30% to 60% of the total volume of the induction furnace, typically half of the capacity of the induction furnace. If the volume of the bath base is too low, there is a risk that the bath base will not have sufficient heat capacity to remain in the liquid state and will solidify in the furnace. Operation with a bath base allows advantageous melting rates of 2 t / h to 4 t / h to be obtained.

[0084] 4 / and 5 / Step of loading the scrap obtained after step 3 and reflow

[0085] The step of loading ([Fig.5]) the clean scrap, obtained after stripping and / or drying, consists of introducing the stripped scrap using a feed means 150 allowing the feed of stripped scrap into the crucible induction furnace which previously contains a bath base. A cover (170) is used to cap the furnace and limit the quantity of inert gas used for inerting. The feed means is configured to pass through the cover 170. It is advantageous for the cover to be retractable or to have an opening 1700 allowing the feed means 150 to pass through. No protective salt is used in the induction furnace. The loading step is carried out continuously or semi-continuously. The scrap is loaded onto the liquid metal bath base by a suitable feed means 150, for example a screw screw or a hopper or a vibrator system.

[0086] An inert gas, typically argon, is used during this step to protect the liquid metal surface. The inert gas is injected above the surface of the liquid metal bath by at least one injection means 160.

[0087] The stripped scrap falls to the surface of the initial metal bath base in a delimited area (10) whose surface area is less than or equal to a quarter of the circular section of the surface of the liquid metal bath. Typically, the surface area of ​​the liquid metal bath is equal to irR2 where R is the inner radius of the cylindrical induction furnace. Thus according to the invention, the delimited area (10) is less than or equal to irR2 / 4. The surface area of ​​the retractable part of the cover or opening 1700 is approximately equal to the surface area of ​​the demarcated area.

[0088] It is advantageous to limit the delimited zone of scrap fall to less than a quarter of the circular section of the furnace to limit the consumption of inert gas. The inventors have found that it is advantageous to locate the injection of inert gas at the point where the scrap falls to obtain the best inerting while limiting the quantity of gas used. This has the effect of creating an overpressure at the zone of passage of the feed means through the cover and of reducing the quantity of air which could enter. By limiting the delimited zone to less than a quarter of the section of the surface of the liquid metal bath, and by making it correspond to less than a quarter of the section of the furnace ([Fig.4], I, II, III or IV), it is possible to locate the injection of inert gas. This makes the inerting more effective. The inert gas outlet is located in the quarter of the section of the furnace containing said delimited zone.

[0089] During the loading phase iv), the inert gas is injected into a single circular quarter-section of the induction furnace. This means that during phase iv), at least one injection means (160) located in this quarter-section injects inert gas and the other injection means arranged in the other circular quarter-sections do not inject gas. If other injection points were used in addition to the one used in the quarter-section of the furnace containing the delimited area, this would not provide any additional effect and would have the disadvantage of consuming more gas.

[0090] Depending on the volume to be inerted during phase iv), the flow rate of inert gas to be injected is to be adapted. Typically, if there is a single injection means, located in the quarter circular section of the furnace containing the delimited zone (10), the flow rate of inert gas, preferably the flow rate of argon, is between 12 and 18 Nm3 / h per m3 to be inerted during the loading phase iv). In the case where there are two injection means, located in the quarter circular section of the furnace containing the delimited zone (10), the flow rate of inert gas, preferably the flow rate of argon, is between 6 and 9 Nm3 / h per m3 to be inerted during the loading phase iv).

[0091] Advantageously, during the loading step, the stripped scrap, clean after stripping, is loaded at a temperature above 100°C for safety reasons in order to avoid any risk of explosion associated with the presence of residual moisture contained in the load. According to a preferred embodiment, to increase the melting rate and reduce energy consumption, the dried and stripped scrap is immediately loaded after stripping, at a scrap temperature of between 200°C and 450°C, preferably between 300°C and 450°C, even more preferably between 400°C and 450°C. In the case where the clean scrap is placed in the furnace at a temperature of between 300°C and 450°C, it is advantageous for the residence time of the clean scrap above the liquid metal bath to be short in order to limit their oxidation.

[0092] The inventors have found that it is advantageous for the bath to be covered by a floating bed of delamination scrap 4 on the surface of the liquid bath 52 ([Fig. 5]) for most of the duration of the loading step iv) and part of the duration of the remelting step v). The presence of a floating bed of scrap is ensured by regulating the scrap feed rate with the scrap remelting rate. This regulation can be done visually or with weighing means. The presence of a floating bed of delamination scrap makes it possible to protect the surface of the liquid metal bath from oxidation. Most of the duration of step iv) corresponds to a duration of at least 70% or 80% or 90% of the duration of step iv). The duration of step iv) is defined by the moment when loading of the scrap begins and the end of loading. The end of loading is defined by the moment when the quantity of molten metal in the induction furnace reaches its maximum filling level.

[0093] Advantageously, the thickness of the floating delaminar scrap bed is at least 300 mm, advantageously 1000 mm (t, [Fig.5]).

[0094] During the remelting phase, the floating bed of delacquered scrap allows the continuous supply of the liquid metal bath until it is completely dissolved. The loading phase iv) and the remelting phase v) overlap in time. Indeed, the inventors have found that it is advantageous for an individual entity of delacquered scrap to be maintained on the surface of the liquid metal bath for a period of at most 2 min, preferably between 30 s and 90 s, in order to avoid its oxidation. It is therefore important to encourage their submersion in the liquid metal bath.

[0095] Advantageously, the submersion of the scrap is improved by acting on the circulation velocity field of the liquid metal bath so as to obtain a descending velocity field 51 along the walls of the crucible (Figures 5, 6). This descending circulation velocity field results from electromagnetic forces, called Laplace forces, well known in the design of crucible induction furnaces. The descending velocity field along the walls of the crucible facilitates the submersion of the individual entities of delamination scrap present in the floating bed of delamination scrap. The inventors attribute the rapid submersion in the liquid metal bath to the particular shape of the individual entities used according to the invention. Indeed, due to their grain size and their flatness, they are organized in the form of stacked strata, like stacked cards arranged parallel along their largest face.This effectively protects the liquid metal bath and facilitates the introduction of individual entities into the liquid metal bath. These slide over each other and immerse along the wall of the crucible.

[0096] It is advantageous to promote a descending velocity field during the bath base preparation step, the loading step and the remelting step.

[0097] By the presence of inductive coils 101 at the periphery of the crucible 102, it is possible to obtain a descending velocity field 51, along the walls of the crucible allowing to improve the submersion of the scrap according to the invention. This descending velocity field 51 creates a vortex which facilitates the immersion of the scrap.

[0098] The creation of a vortex on the surface of the bath is not possible if a channel induction furnace is used. According to the inventors, a channel induction furnace does not provide favorable conditions for remelting scrap according to the invention: the absence of a vortex on the surface of the bath means that if the scrap according to the invention is introduced, they will pile up on top of each other, form an insulating blanket and will not be immersed in the bath of liquid metal. If the scrap is kept for a long time above the bath of liquid metal, the scrap can oxidize and reduce the metal yield.

[0099] The descending velocity field along the walls of the crucible is obtained by selecting the frequency of the induction furnace. Selecting a frequency of 50 Hz to 150 Hz, preferably 50 Hz to 70 Hz, typically about 60 Hz, makes it possible to obtain a descending velocity field. The inventors have found that this descending velocity field induces the formation of a dome on the upper surface of the liquid metal bath. This dome shape makes it possible to accelerate the melting of the scrap in the liquid. It is also possible to act on the power of the furnace to modify the descending velocity field. It is possible to adapt the frequency and / or the power of the furnace according to the filling level of the furnace as magneto-hydrodynamic calculations can show. The stacking of the individual entities of the deglazed scrap associated with a descending velocity field is particularly advantageous for the submersion of the scrap in the liquid metal and their immersion in the liquid metal.Advantageously, the power and frequency parameters of the oven are adapted according to the thickness of the deglazed scrap bed and the phase of the cycle (start, end of reflow, temperature rise and maintenance).

[0100] The inventors have found that for a density between 0.2 and 0.4 t / m3, the scrap is quickly submerged in the bath of liquid metal. This thus prevents oxidation of the scrap and makes it possible to maximize the metal yield during melting.

[0101] The melting of the scrap makes it possible to form a bath of liquid metal of a second composition. The second composition is generally different from the first composition but could also be identical if the scrap has the same composition as the initial bath base.

[0102] The remelting step consists of melting the scrap bed. The remelting step lasts for the entire time during which there is a floating scrap bed on the surface of the liquid metal bath. It is advantageous that during this remelting step, the feed means is removed so that there is no longer a passage zone 1700.

[0103] During the scrap bed remelting step (step v)), the same conditions inerting than those carried out during the loading phase iv) are preferably carried out. The inert gas is injected into a single quarter circular section of the induction furnace. The inventors have in fact noted that despite the vortex initiated by the descending velocity field, the majority of individual scrap entities tend to immerse themselves on the side of the delimited zone. This is why it is advantageous to maintain the inerting on the side of the delimited zone.

[0104] According to another preferred embodiment, it may be advantageous to gradually move from an inerting mode in a single quarter circular section to an inerting mode in at least two circular sections of the furnace at the end of the loading step iv).

[0105] During the loading period and after complete remelting of the scrap, the temperature of the liquid metal bath is less than or equal to 750°C, preferably less than or equal to 730°C or even preferably less than 710°C, and greater than 680°C. At the start of remelting the bath is typically at a temperature between 690°C and 710°C. Its temperature tends to increase during the remelting step.

[0106] 6 / Maintenance phase

[0107] At the end of the remelting step, the holding phase is followed. The purpose of this holding phase is to hold the liquid metal thus produced before transferring it to another furnace or casting it in the form of an intermediate product, such as a rolling plate, a spinning billet, a forging block or an ingot or a bowl in which a step of casting the liquid metal obtained by the melting process according to the invention is carried out.

[0108] During the holding step, it is advantageous for the surface of the liquid metal to continue to be inerted. According to the invention, it is advantageous to modify the inerting conditions with respect to the loading step iv). Preferably, during the holding step vi) at least two injection means are used and are located in at least two different circular quarter-sections of the furnace. Even more preferably, during the holding phase vi), at least four injection means are used and are located in each circular quarter-section of the furnace ([Fig.7]).

[0109] Depending on the volume to be inerted during phase vi), the flow rate of inert gas to be injected is to be adapted. Typically, it is preferable that if there are four injection means, located in each quarter of circular section of the furnace, the flow rate of inert gas, preferably the flow rate of argon, is between 6 and 10 Nm3 / h per m3 to be inerted during the holding phase vi).

[0110] During the holding phase, it is not necessary to create a descending velocity field. For this, the operating frequency of the furnace can be increased. Preferably, during the holding phase v) the frequency is between 100 Hz and 250 Hz. Preferably the frequency during phase iv) is lower than the frequency during the holding phase vi).

[0111] The invention also relates to a method for manufacturing an intermediate product such as a rolling plate, a spinning billet, a forging block or an ingot or a bowl in which a step of casting the liquid metal obtained by the melting method according to the invention is carried out.

[0112] Advantageously, before the casting step, the metal is degassed and / or filtered and / or treated so as to remove any oxides that may be present and / or reduce the hydrogen content and / or eliminate any undesirable impurities.

[0113] Example 1- Characteristics of crushed coated scrap

[0114] In this example, the coated scrap comes from used beverage cans (UBC). In this example, the grinding was carried out with a knife mill with a calibration grid smaller than 35 mm. [Fig. 3] represents the appearance of the scrap obtained in the knife mill which are representative of the scrap according to the invention. This scrap thus ground is characterized in such a way as to determine the folding ratio (Table 2), their particle size by sieving (Table 2), the flatness of the scrap by measuring the height (Table 3), their apparent density (Table 1).

[0115] 75% of the individual entities measured have a folding ratio lower than or equal to 0.6. 74% of the individual entities measured have a grain size between 8 and 25 mm. 100% of the individual entities measured have a height less than or equal to 10 mm.

[0116] [Tables 1] Scrap Crushing according to the invention % of individual entities having a folding ratio less than or equal to 0.6 75% % of individual entities having a particle size between 8 and 50 mm 74% % of individual entities having a height less than or equal to 15 mm 100% Apparent density (t / m3) 0.30

[0117] [Tables2] Proportion by folding ratio Folding ratio 0-0.2 0.2-0.4 0.4-0.6 0.6-0.8 0.8-1 % individual entity (measured number 25) 32% 4% 48% 12% 4%

[0118] [Tables3] proportion by sieve range (mm) Size < 1 1-2 2-4 4-8 8 - 16 16-25 >25 % individual entity (measured number approximately 250) 0.4% 0.9% 4.0% 20.4% 70.8% 3% 0%

[0119] [T ables 4] Proportion by flatness flatness (mm) 0-5 5-10 10-15 15-20 >20% individual entity (measured number 25) 72% 28% 0% 0% 0%

[0120] Example 2

[0121] The coated scrap crushed according to the invention characterized in the previous example was supplied and de-lacquered in an IDEX type de-lacquering furnace. The de-lacquering was carried out at a loading rate of 500 kg / h, a furnace rotation speed of 1 rpm, and a flue gas outlet temperature of 440°C to 540°C. These conditions made it possible to obtain a residual carbon varying from 0.1% -0.2%.

[0122] After de-lacquering, the de-lacquered scrap was introduced into a crucible induction furnace previously filled with a liquid bath base. The initial bath base was made from 3104 scrap, its volume is approximately 40% of the maximum capacity of the crucible. No protective salt was used. The de-lacquered scrap was introduced into the furnace at a temperature above 100°C, typically at a temperature of 200°C. The furnace frequency was set at 62 Hz. The furnace power was set at the start of the cycle at 50%. Selecting a frequency close to 60 Hz accelerates the submersion of the ground material into the liquid. A mattress of de-lacquered scrap was maintained on the surface of the liquid bath in order to reduce air penetration and protect the bath surface against oxidation. Argon blowing using a single injection method was carried out to reinforce the protection of the metal at a flow rate of 40 Nm3 / h, the volume to be inerted being approximately 2.8 m3.The loading of the deglazed scrap is carried out at a rate of approximately 4000 kg / h. Given the oxidation kinetics of the alloy in the temperature range measured in the mattress (220°C to 250°C), the deglazed scrap does not have time to oxidize on the surface of the bath. It does not stay there longer than 1 minute. The geometry of the individual scrap entities and their organization in layers facilitates their flow on the surface of the bath as well as along the . crucible.

[0123] At the end of the remelting phase, the metal was held for 30 minutes before being cast in the form of a bowl. During the holding phase, the surface of the metal was inerted using argon blowing carried out at four injection points, located in each quarter of the circular section of the furnace. The flow rate was 20 Nm3 / h for a volume to be inerted of 0.6 m3.

[0124] A net metal yield of 97.8% could be obtained using the process according to the invention. In particular, the net yield on the element Mg is 94%. The inventors believe that this excellent yield is made possible by the choice of the geometry of the individual entities of the crushed coated scrap, in particular the folding ratio, the particle size and the flatness.

[0125] Example 3 - Reference

[0126] For comparison, the folding ratio obtained on crushed coated scrap obtained by hammer grinding (see [Fig.8]) was determined according to the same principle as that described in Example 1.

[0127] In the same way as previously, the granulometry and the flatness were measured: it was noted that the majority of the scrap obtained with a hammer mill did not allow a majority of granulometry to be obtained between 5 and 25 mm (see table 5) and a flatness of less than 10 mm.

[0128] [Tables5] Proportion by sieve range (mm) Size < 1 1-2 2-4 4-8 8 - 16 16-25 >25 % individual entity (measured number approximately 250) 0.5% 0.8% 2.3% 7.9% 19.8% 18.8% 50%

[0129] [Tableauxô] Proportion by flatness (mm) p (mm) 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 % individual entity (measured number 25) 0 0 20 36 24 0 8 8 4

[0130] The folding ratio was measured on 25 samples. It is thus observed that the crushed scrap obtained by hammer grinding does not allow a folding ratio <0.6 to be obtained. (see table 7): 100% of the scrap has a folding ratio greater than 0.6.

[0131] The inventors consider that this is linked to the fact that knife grinding allows for a sharper cut and therefore prevents the scrap from folding back on itself.

[0132] [Tables?] Proportion by folding ratio Folding ratio 0-0.2 0.2-0.4 0.4-0.6 0.6-0.8 0.8-1 % individual entity (measured number 25) 0 0 0 68% 32%

Claims

Claims

1. A method of remelting aluminum alloy coated scrap comprising the following steps (i) crushed coated scrap based on aluminum alloys, consisting of individual entities (1), is supplied, (ii) stripping said crushed coated scrap to obtain stripped scrap, (iii) an initial bath base of liquid metal of a first composition is prepared in an induction furnace with a cylindrical crucible of internal radius R equipped with a cover (170) operating at a given frequency, said induction furnace has a feed means (150) allowing the feed of delaminated scrap, (iv) the delaminated scrap is loaded into the induction furnace using the feed means (150) directly onto the initial bath base, said delaminated scrap falls to the surface of the initial bath base in a delimited zone (10) and forms a floating bed of delaminated scrap (4) on the surface of the initial bath base, (v) the floating bed of delamination scrap is remelted to form a bath of remelted liquid metal of second composition, (vi) the remelted liquid metal bath is maintained in the liquid state, an inert gas, typically argon gas, is injected above the surface of the liquid metal bath by at least one injection means (160), characterized in that in step (iv) the surface area of ​​the delimited area (10) is less than or equal to a quarter of the section of the surface of the liquid metal bath, and that the at least one injection means (160) is configured such that the inert gas outlet is located in the quarter circular section of the furnace containing said delimited area, and in that at least 50% of the individual entities of the crushed coated scrap supplied in step i) have a particle size of between 5 and 25 mm, the particle size being measured by sieving, and a flatness (p) less than or equal to 10 mm, the flatness being measured from an individual entity of crushed coated scrap placed on a flatness rule such that the flatness of the entity corresponds to the maximum distance between the surface of the flatness rule and the surface of the entity.

2. A method of remelting coated scrap according to claim 1 characterized in that the crushed coated scrap supplied in step i) is obtained using a method comprising a grinding step using a knife mill, equipped with a grid configured to adjust the particle size.

3. A method of remelting coated scrap according to any one of claims 1 to 3 characterized in that at least 50% of the individual entities of the ground coated scrap supplied in step i) has a folding ratio (R) less than or equal to 0.6, where the folding ratio (R) of an individual entity is defined by the expression folding ratio = R = where the PUed surface is the maximum surface of the orthogonal projection of the individual entity onto a plane and the unfolded surface is the total surface of the same individual entity after being unfolded

4. Process for remelting coated aluminum scrap according to any one of claims 1 to 3, characterized in that the density of the crushed coated scrap supplied in step i) is between 0.2 and 0.4 t / m3.

5. Process for remelting coated scrap according to any one of claims 1 to 4, characterized in that the deglazed scrap obtained after step ii) is introduced into the induction furnace in step iv) at a temperature above 100°C, preferably at a temperature between 200°C and 450°C, more preferably between 300°C and 450°C, even more preferably between 400°C and 450°C.

6. Process for remelting coated scrap according to any one of claims 1 to 5, characterized in that the frequency of the induction furnace during steps iv) to v) is between 50 Hz and 150 Hz.

7. Method for remelting coated scrap according to any one of claims 1 to 6, characterized in that during step vi) at least two injection means (160) are used and located in at least two quarter circular sections of the furnace.

8. Method for remelting coated scrap according to claim 7 characterized in that the at least two injection means are arranged in a crown.

9. Method for remelting coated scrap according to claim 7 or 8 characterized in that during step vi) at least four means injection (160) are used and located in each quarter circular section of the furnace.

10. Process for remelting coated scrap according to any one of claims 1 to 9, characterized in that the loading in step iv) is carried out discontinuously or continuously, preferably using a worm screw or a hopper or a vibrator system.

11. A method of remelting coated scrap according to claim 10 characterized in that said feed means (150) is provided with a weighing system in order to control the weight loaded.

12. Process for remelting coated scrap according to any one of claims 1 to 11, characterized in that the distance between the surface of the liquid metal bath and the inert gas outlet is less than or equal to 1 m.

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