Method for sustainably recycling aluminium alloy scrap

Abstract

The invention relates to a method for remelting coated aluminium alloy scrap in an induction furnace having a cylindrical crucible, which comprises steps of supplying crushed coated scrap, delacquering, charging, remelting and holding the crushed coated aluminium alloy scrap, such that at least 50% of the individual entities of the crushed coated scrap have a particle size of between 5 and 25 mm, and a flatness of less than or equal to 10 mm, and wherein the induction furnace is inerted during the charging phase, and wherein the inert gas outlet is located in the quarter of the circular section of the furnace containing the delimited zone in which the scrap falls.

Description

[0001] DESCRIPTION

[0002] Title of the invention: ECO-RESPONSIBLE ALUMINUM ALLOY SCRAP RECYCLING PROCESS

[0003] TECHNICAL FIELD

[0004] 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.

[0005] PREVIOUS ART

[0006] Aluminum recycling has the advantage of being economical and environmentally friendly. Producing secondary aluminum requires up to 95% less energy than primary aluminum and reduces 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 process, during the scrap remelting stage.

[0007] 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 manufacturing 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 made up of parts having any type of coating, for example, paint, varnish, printing ink, plastic, paper, metal.

[0008] Aluminum alloy beverage cans consist of a can body and a lid; usually the can body is made of AA3104 alloy and the lid is made of AA5182 alloy. The can body and lid are coated with an organic and / or inorganic coating such as varnish and / or paint and / or organic material.

[0009] Used beverage cans, also known as UBC (Used Beverage Can), made of aluminum, fall into the coated scrap category. Similarly, food packaging or aerosol cans made of aluminum alloys fall into the coated scrap category. They are generally contaminated by the presence of varnish and / or paint and / or printing ink. These containers may also be contaminated by the possible presence of dust, sand, water, beverage residue, or other contaminants.

[0010] Examples of household packaging include used beverage cans, used food packaging, and used aerosol cans. These types of products, or any other aluminum alloy-coated product, can be collected. Typically, after collection, these products are compacted to form "bales" or "briquettes" that facilitate storage and transportation. Compaction is also sometimes considered to facilitate submersion of scrap in remelting furnaces, as in US application 4,159,907.

[0011] 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 avoid the liquid still being present in the containers and thus avoid risks of explosion during the remelting operation. It is possible during this grinding stage to carry out sorting to separate any contamination such as possible pieces of scrap metal, any other metal products not made of aluminum or aluminum alloy or plastic products.

[0012] 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 aluminum 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 content 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.

[0013] US 3,999,980 describes a method that does not require pre-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 molten salt.

[0014] Another alternative is multi-chamber remelting ("Aluminum 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 facility. This is a salt-free process. This solution has the disadvantage of having to be carried out in a gas-fired furnace, which is not suitable for reducing CO2 emissions.

[0015] 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 aluminum decoating handbook", Stein Atkinston Stordy, Gillespie Powers internet source). The electric crucible induction furnace 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.

[0016] 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). 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 gross or net metal yield. The term "gross metal yield" (expressed in %) is the ratio between the mass of liquid metal actually diverted or cast to the mass of material charged in a furnace. The term "net metal yield" is the ratio between the mass of liquid metal actually diverted or cast to the net mass of metal charged in a furnace.

[0017] 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.

[0018] US2020 / 0255922 describes a method of processing lithium aluminum alloy machining scrap in a vacuum induction furnace. This method is carried out in batch mode, meaning that the lithium aluminum alloy scrap is fed into the furnace in one go to ensure vacuum operation. In order to increase the amount of molten metal in the furnace, US2020 / 0255922 provides for a chip compaction step.

[0019] 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 and 0.4 t / m3. The inventors found that it was not possible to obtain a good raw metal yield with coated scrap with these geometric considerations alone.

[0020] 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 raw metal yield.

[0021] 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.

[0022] STATEMENT OF THE INVENTION

[0023] The invention relates to a method for remelting scrap coated with aluminum alloy comprising the following steps:

[0024] (i) crushed coated scrap based on aluminum alloys, consisting of individual entities, is supplied,

[0025] (ii) stripping said crushed coated scrap to obtain stripped scrap,

[0026] (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 operating at a given frequency, said induction furnace has a supply means allowing the supply of deglazed scrap,

[0027] (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,

[0028] (v) the floating bed of delamination scrap is remelted to form a bath of remelted liquid metal of second composition,

[0029] (vi) the remelted liquid metal bath is kept in a liquid state.

[0030] An inert gas, typically argon gas, is injected above the surface of the liquid metal bath by at least one injection means.

[0031] 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.

[0032] 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.

[0033] 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 10 and 25 mm, more preferably between 8 and 25 mm, the particle size being measured by sieving.

[0034] 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. 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 Figure 1).

[0035] Advantageously, the crushed coated scrap is obtained according to a method comprising a step of crushing with a knife mill, equipped with a grid configured to adjust the particle size such that the grid has a mesh size of less than 50 mm. According to the invention, it is preferable for the mesh size of the grid to be less than or equal to 45 mm, preferably 35 mm, and even more preferably 25 mm. The mesh size is chosen in order to obtain the particle size and flatness required for the invention. According to the invention, the knife mill used is preferred because it allows a clean cut and avoids "creasing" the scrap, which results in folding which 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 involves cutting the coated scrap between knives mounted on a rotating shaft and a row of fixed knives. The knives can be V-shaped or straight. The presence of a grid ensures particle size control at the outlet. This preliminary grinding step in a knife mill corresponds to a process for remelting aluminum alloy coated scrap comprising the following successive steps: aluminum alloy-based coated scrap is supplied, preferably scrap recovered from aluminum household packaging, typically used aluminum beverage cans.

[0036] Said coated scrap is ground in a knife mill, provided with a grid, such that the grid has a mesh size of less than 50 mm, to obtain ground coated scrap consisting of individual entities, said ground coated scrap is de-lacquered to obtain de-lacquered scrap, an initial bath base of liquid metal of a first composition is prepared in a crucible induction furnace operating at a given frequency, the de-lacquered scrap is loaded into the induction furnace directly onto the initial bath base to be melted,

[0037] 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 less than or equal to 0.4, where the folding ratio (R) of an individual entity is defined by the expression unfolded surface — folded surface folding ratio = R = - - - , , , , - unfolded surface where the folded 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.

[0038] The bending ratio parameter makes it possible to account for flatness, which is an essential parameter for the invention, but also for the “crumpled” appearance of the scrap, which is a characteristic influencing the metal yield during the remelting stage.

[0039] Advantageously, the density of the crushed coated scrap supplied in step i) is between 0.2 and 0.4 t / m3.

[0040] Advantageously, the stripped 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.

[0041] Advantageously, no protective salt is used in the induction furnace.

[0042] 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 the scrap. 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.

[0043] Advantageously, at least four injection means are used and are located in each quarter circular section of the furnace

[0044] Advantageously, the loading in step iv) is carried out discontinuously or continuously, preferably using a screw feeder or a hopper or a vibrator system. Advantageously, the feeding means is provided with a weighing system in order to control the loaded weight.

[0045] 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 40 cm. This has the advantage of being able to inert effectively without excessive gas consumption.

[0046] 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.

[0047] Advantageously, the coated scrap supplied in step i) is made mainly from scrap recovered from household aluminum packaging, typically used aluminum beverage cans. That is to say, the crushed coated scrap is obtained from scrap recovered from household aluminum packaging, typically used aluminum beverage cans.

[0048] FIGURES

[0049] [Fig. 1] Figure 1 represents the method for measuring the flatness of an individual entity of ground coated scrap.

[0050] [Fig. 2] Figure 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. Figure 2 b represents the orthogonal projection of the individual entity 2 a giving a maximum surface area. Figure 2 d represents the contour of the unfolded surface allowing the measurement of the unfolded surface area.

[0051] [Fig. 3] Figure 3 shows the appearance of the coated scrap ground supplied according to the invention. [Fig. 4] Figure 4 shows a diagram of a cylindrical crucible induction furnace with stirring movements, containing an initial bath foot. Figure 4a is a front view and view 4b is a top view.

[0052] [Fig.5] Figure 5 shows a diagram of an induction furnace during phase iv) of loading the process with deglazed scrap with stirring movements. Figure 5a is a front view and view 5b is a top view.

[0053] [Fig.6] Figure 6 shows a diagram of an induction furnace during phase v) of melting the deglazed scrap bed of the process. Figure 6a is a front view and view 6b is a top view.

[0054] [Fig.7] Figure 7 shows a diagram of an induction furnace during the process maintenance phase vi). Figure 7a is a front view and view 7b is a top view.

[0055] [Fig. 8] Figure 8 represents the appearance of the coated scrap crushed outside the invention obtained by a hammer crushing process.

[0056] [Fig. 9] Figure 9 shows the appearance of the crushed coated scrap obtained in Example 4 by a knife grinding process.

[0057] DETAILED DESCRIPTION OF THE INVENTION

[0058] 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, loading 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.

[0059] 1 / Supply of crushed coated scrap

[0060] The coated scrap that can be 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 smaller in size compared to the initial waste such as beverage cans or food cans.

[0061] In the following, unless otherwise stated, the proportions in % of individual entities correspond to numerical % of individual entities. It is advantageous for the individual entities of ground coated scrap to be substantially flat 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 I and a height h, where the height h is the smaller 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 feature is the maximum distance between the surface of the flatness rule and the surface of the feature as placed on the flatness rule (see Figure 1). The flatness rule can be any flat surface, such as a measuring marble.

[0062] 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.

[0063] The estimation of the percentage of individual entities 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.

[0064] 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 of between 5 and 25 mm, preferably between 10 and 25 mm. Preferably 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 of 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.

[0065] 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 nested sieves can be used. The mesh sizes of the sieves decrease from top to bottom. The individual entities constituting the scrap are placed on the highest sieve and, by vibration, the scrap is distributed over the different sieves according to their size. Sieves with square or round meshes can be used by their opening; the nominal size of a sieve corresponds to the length of the side of the mesh or its diameter (in mm). Seven sieves of sizes 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 delacquering operation.A particle size of the individual entities between 1 and 25 mm, preferably between 5 and 25 mm, allows an improvement in the submersion of the scrap in the liquid metal bath of the induction furnace.

[0066] 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, preferably at least 200, typically around 10 kg.

[0067] 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. unfolded surface - folded surface folding ratio = R = unfolded surface

[0068] (Equation 1)

[0069] Preferably, at least 50% or 60% or 70% or 80% or 90% or 100% of the individual entities 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.

[0070] The bend ratio of an individual entity of the ground coated scrap quantifies how this individual entity was bent during the previous steps. The higher this ratio, the more the individual entity was bent and is therefore compact or gathered, in particular in globular form. The lower the ratio, the more the individual entity is flat. The inventors found that it was necessary to have a bend ratio less than or equal to 0.6 to avoid the use of salts, called recycle flux, to separate the oxides from the liquid metal, during the remelting step in the crucible induction furnace. The bent surface is the apparent surface of an individual entity of ground coated scrap. The bent surface is defined as the maximum surface of the orthogonal projection onto a plane of the individual entity.

[0071] 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 be easily determined. The unfolded surface area can also be obtained by unfolding the individual entity.

[0072] For example, if we consider an individual entity of crushed coated scrap typically the size of a postage stamp and having an unfolded surface area of ​​1 cm 2 , 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.

[0073] The inventors found that the number of folds or surface overlaps deteriorates the flatness of the individual entity. On the other hand, they found that it is important that the coated scrap be folded as little as possible on itself so that the coated surfaces are in direct contact with the atmosphere of the stripping oven and that consequently the exchanges of mass and heat on the surface of the scrap occurring during the stripping operation can take place as efficiently as possible.

[0074] The folding ratio can be measured as follows: take an individual entity of crushed coated scrap (1, Figure 2 a). Use a sheet of paper whose mass mo and surface area So are known. Draw the outline of the individual entity on the sheet in such a way as to obtain the folded surface area (10, Figure 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, Figure 2 b). This gives the maximum surface area of ​​the orthogonal projection of the individual entity onto a plane. Cut out the outline and weigh the piece mi. Once this step is completed, unfold the same individual entity of crushed coated scrap (2, Figure 2 c). Take another sheet of paper whose mass m'o and surface area S'o are known.The contours of the individual scrap-coated entity thus unfolded are drawn (20, Figure 2 d); the contours are cut out and m2 is weighed. The folding ratio (R) can be deduced according to equation 2.

[0075] (Equation 2) 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 mass m2.

[0076] 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.

[0077] 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 can take the value A or B; the limits A and B are included.

[0078] Advantageously, the density of the coated scrap is between 0.2 and 0.4 t / m 3 (ton per cubic meter). The density of 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, subtracted from the weight of the empty container, is used to determine the density of the scrap.

[0079] The supply of crushed coated scrap having the geometric characteristics as defined above can be obtained using a process comprising a grinding step using a knife mill, equipped with a grid. The mesh of the grid is advantageously less than or equal to 50 mm so as to obtain the desired particle size and flatness as well as the density. 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 ensures particle size control at the mill outlet. 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 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 the desired flatness or density to be obtained. The advantage of the knife shredder is that it produces clean cuts, avoids deforming the scrap, and ensures that it folds back on itself. Advantageously, the shredder's rotation speed is between 70 rpm and 120 rpm, although it is possible to go to higher speeds.

[0080] The supply of crushed coated scrap with 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-shredder allowing the release of 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 called 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 metal loss at the time of remelting.

[0081] 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.

[0082] The inventors found that the use of hammer mills or centrifugal or impact grinding is not advantageous for obtaining the desired geometries.

[0083] 2 / Stripping stage

[0084] The crushed coated scrap thus supplied is then stripped. Stripping consists of heating the coated scrap to a temperature where moisture and organic matter (e.g., 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 furnace atmosphere, preferably by the heated gas from the post-combustion of the fumes and which circulates in the stripping chamber. This operation allows on the one hand to dry the scrap and on the other hand to eliminate organic matter. Organic matter can be converted into CO2 in a post-combustion unit to destroy organic molecules. This produces dry, purified scrap, free of smoke-producing materials.

[0085] After sufficient time has elapsed, the scrap is removed from the decoating chamber.

[0086] The stripping operation can also be achieved chemically: the crushed coated scrap can be immersed in different baths allowing the dissolution of organic matter and followed by a drying operation.

[0087] The inventors found that the stripping or drying operation does not change the folding ratio, flatness, or shape of the scrap. The clean scrap therefore has the same folding ratio, flatness, and grain size 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 / m 3 .

[0088] 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 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.

[0089] 3 / Preparation of an initial bath of liquid metal in an induction furnace

[0090] A cylindrical crucible induction furnace 100 with an internal radius R is provided, equipped with a cover (170) operating at a given frequency (Figure 4, 5, 6, 7). Figure 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 (T, 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. The crucible induction furnace essentially consists 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.

[0091] A liquid metal bath base 50 of a first composition is prepared (figure 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 liquid metal bath. 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 lxxx, 3xxx, 5xxx, 6xxx, 8xxx compatible with clean scrap.In the case of successive castings, the base of the liquid metal bath can advantageously be made up of the remainder of the previous casting.

[0092] 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 thermal capacity to remain in a 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 achieved.

[0093] 4 / and 5 / Step of loading the scrap obtained after step 3 and reflow

[0094] The step of loading (figure 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 conveyor or a hopper or a vibrator system.

[0095] 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.

[0096] 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 a circular section of the surface of the liquid metal bath. Typically, the surface area of ​​the liquid metal bath is equal to nR 2 where R is the inner radius of the cylindrical induction furnace. Thus, according to the invention, the delimited zone (10) is less than or equal to nR 2 / 4. The surface area of ​​the retractable part of the cover or opening 1700 is approximately equal to the surface area of ​​the delimited area.

[0097] It is advantageous to limit the delimited area of ​​scrap fall to less than a quarter of the circular section of the furnace to limit the consumption of inert gas. The inventors found that it was advantageous to localize 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 area where the feed means passes through the cover and reducing the quantity of air that could enter. By limiting the delimited area 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 (Figure 4, 1, II, III or IV), it is possible to localize the injection of inert gas. This makes inerting more efficient. The inert gas outlet is located in the quarter of the section of the furnace containing said delimited area.

[0098] 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 located 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.

[0099] Depending on the volume to be inerted during phase iv), the flow rate of inert gas to be injected must 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 Nm 3 / h per m 3to 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 Nm 3 / h per m 3 to be inerted during the loading phase iv).

[0100] 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.

[0101] 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 (Figure 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 is started 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.

[0102] Advantageously, the thickness of the floating delaminated scrap bed is at least 300 mm, advantageously 1000 mm (t, figure 5).

[0103] During the remelting phase, the floating bed of de-lacquered scrap allows the continuous feeding of the liquid metal bath until its complete dissolution. 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 de-lacquered scrap to be kept 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.

[0104] 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 flatness, they are organized in the form of stacked layers, like stacked cards arranged parallel along their largest face.This effectively protects the molten metal bath and facilitates the introduction of individual entities into the molten metal bath. These slide over each other and immerse along the wall of the crucible.

[0105] It is advantageous to promote a descending velocity field during the bath foot development step, the loading step and the reflow step.

[0106] 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 making it possible 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.

[0107] Creating 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 liquid metal bath. If the scrap is kept for a long time above the liquid metal bath, the scrap can oxidize and reduce the metal yield.

[0108] The downward 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 around 60 Hz, allows a downward velocity field to be obtained. The inventors have found that this downward velocity field induces the formation of a dome on the upper surface of the liquid metal bath. This dome shape accelerates the melting of the scrap in the liquid. It is also possible to act on the power of the furnace to modify the downward 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 magnetohydrodynamic calculations can show. The stacking of the individual entities of the deglazed scrap associated with a downward velocity field is particularly advantageous for the submersion of the scrap in the liquid metal and their immersion in the liquid metal.Advantageously, the oven's power and frequency parameters 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).

[0109] The inventors 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 prevents oxidation of the scrap and maximizes metal yield during melting.

[0110] Melting the scrap allows the formation of a liquid metal bath 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.

[0111] 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 if during this remelting step, the feed means is removed so that there is no longer a passage zone 1700.

[0112] During the scrap bed remelting step (step v)), the same inerting conditions as those operated 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 indeed observed 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 inerting on the side of the delimited zone.

[0113] According to another preferred embodiment, it may be advantageous to gradually switch 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).

[0114] 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 stage.

[0115] 6 / Maintenance phase

[0116] 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 into which a casting step of the liquid metal obtained by the melting process according to the invention is carried out.

[0117] 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 compared 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 (Figure 7).

[0118] Depending on the volume to be inerted during phase vi), the flow rate of inert gas to be injected must be adapted. Typically, it is preferable that if there are four injection means, located in each quarter of the circular section of the furnace, the flow rate of inert gas, preferably the flow rate of argon, is between 6 and 10 Nm 3 / h per m 3to be inerted during the maintenance phase vi).

[0119] 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 holding phase v) the frequency is between 100 Hz and 250 Hz. Preferably the frequency during phase iv) is lower than the frequency during holding phase vi).

[0120] 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.

[0121] Advantageously, before the casting step, the metal is degassed and / or filtered and / or treated so as to remove any oxides present and / or reduce the hydrogen content and / or eliminate any undesirable impurities.

[0122] Example 1- Characteristics of crushed coated scrap

[0123] 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 less than 35 mm. Figure 3 represents the appearance of the scrap obtained in the knife mill which is 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). 75% of the individual entities measured have a folding ratio less than or equal to 0.6. 74% of the individual entities measured have a particle size between 8 and 25 mm. 100% of the individual entities measured have a height less than or equal to 10 mm. [Table 1]

[0124] [Table 2]

[0125] [Table 3]

[0126] [Table 4] Example 2

[0127] The coated scrap ground 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%.

[0128] 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 50% at the beginning of the cycle. Selecting a frequency close to 60 Hz accelerates the submersion of the ground material in the liquid. A mattress of de-lacquered scrap was maintained on the surface of the liquid bath to reduce air penetration and protect the bath surface from 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 m 3. 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.

[0129] 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 Nm 3 / h for a volume to be inerted of 0.6 m 3 .

[0130] 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. Example 3 - Reference

[0131] For comparison, the folding ratio obtained on crushed coated scrap obtained by hammer milling (see figure 8) was determined according to the same principle as that described in example 1. In the same way as previously, the particle size and flatness were measured: it can be seen that the majority of scrap obtained with a hammer mill does not allow a particle size of between 5 and 25 mm to be obtained (see table 5) and a flatness of less than 10 mm.

[0132] [Table 5]

[0133] [Table 6]

[0134] The folding ratio was measured on 25 samples. It can be seen 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.

[0135] The inventors believe that this is due to the fact that knife grinding allows for a sharper cut and therefore prevents the scrap from folding back on itself.

[0136] [Table 7] Example 4 - Grinding parameters

[0137] Crushing tests were carried out on coated scrap with shredders equipped with knives and a grid. The grid consists of holes of diameter D. The diameter of the holes in the grid, which corresponds to the grid mesh, was varied between 25 mm and 50 mm. For all cases, each hole in the grid was separated from its nearest neighbor by approximately 15 - 20 mm. The rotation speed was varied between approximately 80 rpm and approximately 163 rpm. Depending on the case, the knives have V-shaped blades or straight blades. The operating conditions are summarized in Table 8

[0138] [Table 8]

[0139] For each case, the particle size and flatness of the shredded scrap were measured (Tables 9 and 10). It can be seen that using a grid with a diameter of less than 50 mm makes it possible to obtain shredded scrap such that 50% of the shredded scrap has a particle size between 5 and 25 mm and a flatness of less than 10 mm. It can be seen that increasing the rotation speed of the knife shredder drum tends to obtain a finer particle size and lower flatness. However, the inventors found that increasing the rotation speed tends to form more fines, which can be unfavorable for the remelting process. The shape of the knives, V-shaped or straight, can influence the morphology of the shredded scrap. According to the inventors, both types of knife shape are suitable.

[0140] The folding ratio (Table 11) and the density (Table 12) were measured for each of the tests A, B and C. It is found that the density is less than 0.2 t / m3 in the case of knife grinding using a 50 mm grid while it is between 0.2 and 0.4 t / m3 according to grinding conditions considered by the invention. In all cases, at least 50% of the individual entities have a folding ratio less than 0.6. Figure 9 illustrates the appearance of scrap A, B, C. [Table 9]

[0141] [Table 10] [Table 11]

[0142] [Table 12]

Claims

CLAIMS 1. A process for 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 supply means (150) allowing the supply of deglazed 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 during step (iv) the surface of the delimited zone (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 zone, and in that 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, the particle size being measured by sieving, and a flatness (p) of less than or equal to 10 mm,the flatness being measured from an individual feature of ground coated scrap placed on a flatness ruler such that the flatness of the feature corresponds to the maximum distance between the surface of the flatness ruler and the surface of the feature., Tl ?. Process for remelting coated scrap according to claim 1 characterized in that the crushed coated scrap supplied in step i) is obtained using a process comprising a grinding step using a knife mill, equipped with a grid configured to adjust the particle size and such that the mesh size of the grid is less than 50 mm, preferably less than or equal to 45 mm.

3. A method of remelting coated scrap according to any one of claims 1 to 2 characterized in that at least 50% of the individual entities of the crushed 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 unfolded surface — folded surface folding ratio = R = - - - , , , , - unfolded surface where the folded 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. Process 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. Process for remelting coated scrap according to claim 7 or 8 characterized in that during step vi) at least four injection means (160) are used and located in each quarter of 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. Method for remelting coated scrap according to claim 10 characterized in that said feeding means (150) is provided with a weighing system in order to control the loaded weight.

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.

Images