Aluminum alloy sorting process

Abstract

A first object of the invention is a method for sorting a mixture of at least two different types of aluminum alloy by heating such that each different type of aluminum alloy is colored to such an extent that said different types of aluminum alloy are distinguishable from one another by their color, no chemical reagent being used to color the different aluminum alloys. Another object of the invention is a device for carrying out the method according to the invention. (Short figure: Fig. 1)

Description

Title of the invention: Method for sorting aluminum alloys FIELD OF INVENTION

[0001] The field of the invention is that of sorting processes for aluminium alloys in the context of recycling. STATE OF THE ART

[0002] Aluminium alloys are increasingly used in automotive construction to reduce vehicle weight and thus decrease fuel consumption and greenhouse gas emissions.

[0003] It is also necessary to reduce greenhouse gas emissions during the production of said alloys. This reduction can be achieved by recycling aluminum alloy scraps and waste, thereby reducing or even eliminating the use of primary aluminum produced by electrolysis and / or the addition of alloying elements.

[0004] The best electrolysis plants, which use hydroelectricity, have a carbon footprint of 4 tonnes of CO2 equivalent (CO2 eq) per tonne of aluminum alloy foundry plate, taking into account the use of a carbon anode. The carbon footprint of one tonne of aluminum alloy foundry plate obtained solely from scrap and waste is 0.5 t of CO2 eq per tonne of foundry plate. The term “CO2 equivalent” is a unit of measurement created by the IPCC (Intergovernmental Panel on Climate Change). This indicator is used to quantify the impact of various greenhouse gases (methane, nitrous oxide, etc.) on the environment, using carbon dioxide (CO2), the main greenhouse gas, as a reference. This index has become essential in the fight against climate change.

[0005] There is therefore a high demand for aluminum scrap. However, recycled products are generally mixed. Using a mixture directly in a foundry too often requires diluting the aluminum scrap mixture with Ixxx alloy ingots produced by electrolysis and adding missing elements to obtain the desired alloy. This increases the carbon footprint. Sorting aluminum scrap reduces the carbon footprint because it allows the use of sorted scrap close to the desired composition. Processes exist for sorting different materials, for example, ferrous metals from aluminum alloys based on their magnetic properties. However, it remains difficult to separate the different types of aluminum alloys from each other.

[0006] Application WO 97 / 05969 discloses a sequential sorting process where each part is analyzed by laser-induced plasma spectrometry (LIBS) or X-ray fluorescence (XRF) which requires heavy investment.

[0007] Application EP0861910 discloses a chemical treatment for aluminum alloys for their separation. This treatment includes treatment with a chemical agent that allows different types of alloys to be distinguished based on their color. However, this treatment is an acid or basic pickling process that oxidizes a surface layer of the metal to be recycled and produces waste that also requires recycling. PROBLEM INSTALLATION

[0008] The problem to be solved is to sort different types of aluminum alloy using an economical, rapid and environmentally friendly process, preferably one that does not require the use of chemicals. OBJECT OF THE INVENTION

[0009] A first object of the invention is a method for sorting a mixture of aluminum scrap comprising at least two different types of aluminum alloy, comprising: a. a heating step at a predetermined temperature above 90°C and for a predetermined duration so that at least one of the two different types of aluminum alloy is colored, b. a sorting step using a device to distinguish the color of at least two different types of aluminium alloy to obtain at least one enriched batch preferably pure to at least 80% in one of the at least two types of aluminium alloy and any residue of the mixture.

[0010] Another object of the invention is a machine for sorting a mixture of aluminum scrap comprising at least two different types of aluminum alloy according to the invention, comprising: A furnace, preferably continuous, which heats the at least two different types of aluminum alloy to a predetermined temperature and for a predetermined duration; A device for distinguishing the color of the at least two different types of aluminum alloy, preferably by the parameter b* measured according to ISO 7724 / 11:1984; A device comprising means for sorting the at least two different types of aluminum alloy; A conveying means, preferably a flat conveying means such as a belt, which conveys the different types of aluminum alloy, preferably through the oven preferably continuous, then in front of the device allowing the colour to be distinguished. DESCRIPTION OF FIGURES

[0011] [Fig. 1]: This figure shows the difference in color obtained between 5xxx alloys and 6xxx after heating. [Fig. 2]: This figure shows the variation of the parameter b* as a function of heating. [Fig. 3]: This figure shows the variation of the parameter b* as a function of heating. [Fig. 4]: This figure shows the sorting obtained by heating DESCRIPTION OF THE INVENTION

[0012] Unless otherwise stated, all aluminum alloys referred to below are designated according to the rules and designations defined by the Aluminum Association in the Registration Record Series that it publishes regularly. Unless otherwise stated, compositions are expressed as % by mass. The expression 1.4 Cu means that the copper content expressed as % by mass is 1.4%. The alloy groups, also called series, are defined in EN 573-1 (2005). DETAILED DESCRIPTION

[0013] The invention is based on the applicant's observation that it is entirely possible to sort a mixture of aluminum scrap comprising at least two different types of aluminum alloy. Aluminum scrap is defined according to EN 12258-1 (2012) and is known in English as "scrap".

[0014] In one embodiment, the scraps are new scraps according to EN 12258-1 (2012). In the recycling industry vocabulary, the mixture of aluminum scraps is also referred to as "pre-consumer scrap". In one embodiment, the aluminum scraps are pre-painted scraps. In one embodiment, if the scraps are painted, the paint is removed by any method known to a person skilled in the art.

[0015] An aluminum alloy is an alloy in which aluminum is the most important element in the chemical composition. The different types of aluminum alloys include the aluminum alloy series defined in the aforementioned EN 573-1 (2005). These different series are therefore the 1xxx series, defined by alloys with an aluminum content of at least 99.00%; the 2xxxx series, defined by alloys with the highest average percentage of alloying element being Cu; the 3xxxx series, defined by alloys with the highest average percentage of alloying element being Mn; the 4xxxx series, defined by alloys with the highest average percentage of alloying element being Si; the 5xxxx series, defined by alloys with the highest average percentage of alloying element being Mg; and the 6xxxx series, defined by alloys with the highest average percentage of alloying element being... The high-grade aluminum alloy is Mg2Si, the 7xxxx series is defined by alloys whose highest average percentage of added element is Zn, and the 8xxxx series is defined by alloys whose highest average percentage of added element is not one of those mentioned above. The different types of aluminum alloys include one or more alloys defined within these series of EN 573-1 (2005). For example, and not limited to, a first type of alloy might include alloys AA5754, AA5182, and a second type of alloy might include alloys AA6016, AA6005, etc. The different types of aluminum alloys might also include alloys not standardized by EN 573-1 (2005). Preferably, there is a difference in at least one element, other than aluminum, between the at least different types of aluminum alloys. Preferably it is Mg.There is a difference in an element between two different types of aluminum alloys if the minimum content of that element in one is greater than the maximum in the other. For example, the process can separate alloys AA5754 and AA5182 on the one hand, and alloys AA6016 and AA6005 on the other.

[0016] The scrap mixture, comprising at least two different types of aluminum alloy, is heated to a predetermined temperature above 90°C for a predetermined duration. This heating causes the diffusion of the alloying elements, which form an oxide on the surface and change the color of at least one of the two different types of aluminum alloy. The heating is determined such that the at least two different types of aluminum alloy are distinguishable by their color, which forms the basis for their separation by sorting. Heating to a predetermined temperature above 90°C, preferably 100°C, and more preferably 150°C, is advantageous because it eliminates the need to use a chemical reagent to color the at least two types of aluminum alloy. Increasing the temperature accelerates the process.

[0017] A device allows the color of at least two different types of aluminum alloy to be distinguished after heating and then sorted to obtain at least one batch enriched, preferably to at least 80%, in one of the at least two types of aluminum alloy and any residue of the mixture. Enriched to at least 80% or pure to at least 80% of the type of aluminum alloy means that the enriched batch contains at least 80% pieces, by number, of that type of alloy. The color can be distinguished by a means known to those skilled in the art, such as a camera or a digital camera and their equivalents. The device includes means, for example, but not limited to, mechanical means or a compressed air jet, known to those skilled in the art, for sorting at least two different types of aluminum alloy and obtaining at least one batch enriched in one of the at least two types of aluminum alloy and any residue of the mixture.

[0018] When a batch is enriched, its composition is closer to that of at least one of the at least two types of aluminum alloys than the composition of the mixture. The composition of the mixture is the composition obtained by its remelting. It can also be calculated as the mass-weighted average composition of each component of the mixture. The same applies to the enriched batch. With respect to the elements that constitute the composition of the mixture and one of the at least two types of aluminum alloy, the enrichment of the batch relative to the mixture ensures that at least one element has either been enriched to approach the minimum target content of one of the at least two types of aluminum alloy, or depleted to approach the maximum target content of one of the at least two types of aluminum alloy.If sorting aims to separate at least two series of aluminum alloys, enrichment aims either to increase the content of the element that defines a series or to decrease the content of at least one of the other elements that is not the series-defining element. For example, enriching with alloy 5xxx increases the Mg content. Enriching with alloy 5xxxx also decreases the content of at least one element that is not Mg, with the exception of aluminum.

[0019] Enriching the batch is advantageous because when the batch is melted to produce a rolling plate, an extrusion or forging billet, a casting, powder for additive manufacturing, or any other semi-finished product known to those skilled in the art, it reduces the amount of the element or other aluminum alloys that need to be added to obtain the desired composition of one of the at least two types of aluminum alloys. For example, if an element is in excess in the batch relative to the desired composition of one of the at least two types of aluminum alloys, it is necessary to dilute the batch by adding ingot of an alloy from the Ixxx series. For example, if an element is insufficient in the batch, it is necessary to add more. A 100% or approximately 100% pure batch requires no additions to obtain one of the at least two types of aluminum alloys.For a batch that is 100% -X% pure in one of at least two types of aluminium alloys, it is necessary to add one or more elements and / or an alloy from the Ixxxx series to obtain the composition of the desired alloy type.

[0020] In one embodiment, the batch is at least 80% pure, preferably at least 90%, more preferably at least 95%, and more preferably around 100%. Increasing the purity reduces the purchase costs of the additives. Increasing the purity also reduces the carbon footprint because the additives rarely come from a recycling process but rather from electrolysis in the case of the ingot into an alloy of the Ixxxx series, or from processes using ores known to those skilled in the art for elements other than aluminum.

[0021] In one embodiment, no chemical reagents are used to color the at least two different types of aluminum alloys. Not using chemical reagents is advantageous because, on the one hand, it is generally more environmentally friendly, and on the other hand, the resulting chemical waste, with its associated carbon footprint, would then need to be treated. Furthermore, some chemical reagents oxidize a portion of the at least two different types of aluminum alloys. Another advantageous technical effect of the method is that the separation is independent of the shape of the fragments. Indeed, metal separation processes, for example, eddy current processes, are shape-dependent because the trajectory depends on the weight and the induced force. However, the force induced by the eddy current depends on the surface area exposed to the magnetic field and the thickness.

[0022] In one embodiment, the sorting step makes it possible to obtain at least two enriched batches, preferably at least 80% pure, of at least two types of aluminum alloy and any residual mixture. Obtaining at least two enriched batches is advantageous because factories often manufacture parts from different alloys without having implemented a segregation of scraps during production based on their composition. Preferably, the batches are at least 90% pure, and even more preferably, approximately 100% pure.

[0023] In one embodiment, the quantity of any residual material is at most 20% by number of pieces in the mixture, preferably at most 10%, and more preferably at most 5%. Reducing the quantity of residual material is economically advantageous because it allows for better closed-loop recycling of at least two different types of aluminum alloy. Closed-loop recycling is advantageous because it is not necessary to add other elements or ingots of a 1000 series alloy to compensate for the quantity of residual material.

[0024] In one embodiment, the criterion for distinguishing by color is the parameter b* measured according to ISO 7724 / 1 1:1984, which can be used on a camera or digital camera or any equivalent device. The parameter b* allows for good contrast between at least two different types of aluminum alloy.

[0025] In one embodiment, the difference in Mg content between the at least two different types of aluminum alloy is at least 0.05% by mass of aluminum, preferably 0.5%, more preferably 1.0%, more preferably 1.5%, more preferably 2.0%. The process is advantageous for separating alloys based on their Mg content because this element diffuses very easily under the effect of temperature, which makes it possible to reduce the temperature and / or the heating time. A greater difference in Mg increases the color contrast.

[0026] In one embodiment, the different types of aluminum alloys are selected from the 5XXX series and the 6XXXX series alloys, preferably AA5754 and AA5182 for the 5XXX series, and AA6016 and AA6005 for the 6XXX series. In one embodiment, the different types of aluminum alloys are sourced from scrap, preferably from stamping and / or forming, and / or from production rejects prior to painting, preferably from vehicle parts production, before the parts are assembled onto the vehicle body. Separating 5XXX alloys from 6XXX alloys is advantageous because they are often mixed in automotive plants. Indeed, 6XXX series alloys are used to make the body panels of vehicle openings, and 5XXX series alloys are used to make the lining of vehicle openings.Therefore, the lining and skin sheets are sometimes stamped simultaneously for flow reasons in the factories, and production scraps are then mixed together. AA5754, AA5182, AA6016, and AA6005 are alloys known to vehicle manufacturers for their mechanical and surface properties used in openings.

[0027] A high heating temperature induces surface oxidation, which is disadvantageous due to the resulting metal loss. A high temperature makes the process difficult to control because it is necessary to precisely control the predetermined temperature. A maximum predetermined temperature is preferably 500°C, more preferably 450°C. A low temperature implies a long heating time for sufficient color development, which degrades the productivity of industrial operations. A minimum predetermined temperature is preferably 200°C, more preferably 250°C.

[0028] In one embodiment, the predetermined duration is a maximum of 160 minutes, preferably 100 minutes, or more preferably 60 minutes. In another embodiment, the predetermined duration is a minimum of 3 minutes, preferably 4 minutes.

[0029] A predetermined temperature above 400°C is advantageous for obtaining a rapid process. A predetermined temperature below 400°C, preferably 350°C, is advantageous because it consumes less energy and allows for a more robust process in the event of variability in the control of the predetermined duration.

[0030] In one embodiment, the equivalent duration at a temperature of 300°C of the predetermined duration at the predetermined temperature ToC, calculated according to the formula: duration 30- f ___Àl^avecune ilU CC eq predetermined duration^PI 'HT 5+273 "300+273 J activation energy Q of 37615 J / mol and R=8.314 J / mol, the equivalent duration of The duration at 300°C is at least 20 minutes, preferably 25 minutes and / or at most 60 minutes, preferably 50 minutes, more preferably 40 minutes, more preferably 33 minutes. This duration is a compromise between duration and color distinction.

[0031] In one embodiment, the predetermined temperature and predetermined duration are determined by the method comprising the following steps: 1. Sampling of at least two samples of at least two different types of aluminum alloy, 2. Exposure of each of the at least two samples to at least two heatings that differ at least in duration and / or temperature, 3. Determination of the predetermined temperature and predetermined duration, using the temperature and duration of heating that produced the strongest contrast between the at least two types of aluminum alloys.

[0032] Advantageously, it is preferable to have identified the at least two samples, either by knowing their traceability or by measuring their composition using methods known to a person skilled in the art. This allows for a more precise determination of the predetermined temperature and duration. Advantageously, this method can be repeated to determine the temperature and duration of heating by selecting them from a narrower range in order to choose the heating method that produces the best contrast (dichotomy method).

[0033] In one embodiment of the method for determining the predetermined temperature and predetermined duration, the contrast is measured by the ratio of the parameters b* between the different types of aluminum alloy which have been heated by the same temperature for the same duration, the parameters b* being measured according to ISO 7724 / 1 1:1984.

[0034] The machine for sorting a mixture of at least two different types of aluminum alloy according to the invention comprises a preferably continuous furnace. A continuous furnace is advantageous compared to a static furnace, also known as a batch furnace. Indeed, a static furnace heats a batch of at least two different types of aluminum alloy. However, for productivity reasons, this batch is large, which leads to temperature heterogeneity during heating, making it difficult to precisely control the predetermined temperature and duration. A continuous furnace allows for better control of the predetermined temperature and duration.

[0035] A flat conveying means, such as a belt, is advantageous because it allows the spreading of at least two different types of aluminum alloy. This allows for homogeneous heating when it passes through a furnace, preferably a continuous one. On the other hand, this allows the color-distinguishing device to measure each of the at least two different types of aluminum alloy by spreading them out. The color-distinguishing device can be a digital camera, a digital photo camera, or any equivalent device.

[0036] Advantageously, the machine does not include means for chemically treating at least two different types of aluminum alloy. EXAMPLES

[0037] Mixed production scraps of AA5754, AA5182, AA6016, AA6005 originating from production scraps of parts whose traceability was known either as 5xxxx or as 6xxxx.

[0038] Samples were prepared and subjected to different heating conditions according to the conditions in Table 1. The color of the samples was then quantified according to ISO 7724 / 1 1:1984 on a part of each sample.

[0039] Fig. 1 shows the difference in color that can be obtained between samples in alloy 5xxx and alloy 6xxx. The b* axis corresponds to blue / yellow.

[0040] Figure 2 shows that the best contrast measured over the tested durations and temperatures, by calculating the ratio of the b* values, is obtained at a temperature of 450°C for a duration of 5 minutes. Figure 2 shows that the best contrast measured by calculating the ratio of the b* values ​​is obtained at a temperature of 400°C for a duration of 10 minutes. Figure 2 shows that the best contrast measured by calculating the ratio of the b* values ​​is obtained at a temperature of 300°C for a duration of 30 minutes.

[0041] Figure 3 shows all the values ​​obtained. The method makes it possible to separate the alloy groups for each of the tested temperatures despite the variability of the tested durations.

[0042] [Tables 1] TfC) Alliage Durée (min] r .25 sxxx 0 1,89 25 SXXX 1.,.57 SCO 5XXX 5 355 300 SXXX 1S 5,47 300 5XXX 30 S,77 300 5XXX SD 4,14 300 SXXX .120 4,9 300 sxxx 1395 5,85 300 sxxx 5 2,68 300 sxxx 15 3,18 300 sxxx.. 30 2,07 300 sxxx SG 2,04 309 sxxx 120 2,88 300 sxxx 1355 2,15 400 5XXX 5- S,35 400 5XXX 10 S,77 400 5XXX 20 5,18 400 5XXX 3G 5,17 400 SXXX SD 8,2 400 sxxx 230 S,15 400 sxxx 5 2,02 400 sxxx 1D 2,13 400 sxxx 20 2,35 400 sxxx 30 2,22 400 sxxx SG 3,74 400 sxxx. 230 4,2S 450 sxxx 5 3, 75 450 5XXX lû 7,6 450 5XXX 20 5.7 450 5XXX 30 7,7 450 5XXX SC 8,13 450 5XXX S7SQ 3,7S 450 sxxx S 2,32 450 sxxx 10 2,64 450 sxxx 20 4,01 450 sxxx. 30 4,87 450 sxxx so 3,7 450 sxxx 5760 7,72

[0043] The remaining mixture was then exposed to a temperature of 400°C for 15 minutes. The color of the samples was then quantified according to ISO 7724 / 11:1984. The results obtained are shown in Table 2. The alloy column corresponds to known traceability. Column b* corresponds to the color measurement. It is then possible to classify each piece according to the color according to the expected requirement.

[0044] If the expected requirement is to obtain a pure sorting result in 5xxxx and 6xxxx, then the scraps whose b* is less than or equal to 3.1 must be classified in 6xxx, and those scraps whose b* is greater than or equal to 4.6 must be classified in 5xxx. This results in a residue of 10 pieces out of 60, or 17%.

[0045] If the purity requirement is lower, it is possible to avoid having residue by choosing a value b* of 4 as the sorting criterion. We then obtain two batches whose purity is 97% in number of pieces.

[0046] Fig. 4 shows the distribution of b* values ​​as a function of the alloy.

[0047] [Tables2] Alliage b* Tri 1 Tri 2 Alliage b* Tes 1 Tri .2 Alliage b* Tri 1 Tri 2 Gxxx 0,46 6xxx 6xxx 5xxx 3.15 résidu 6xxx Sxxx 5.03 Exxx 5xxx tox 0,S9 6xxx 6xxk Sxxx 3.22 résidu 6xxx 5xxx 5. H Sxxx 5xxx 6xxx 0 86 6xxx 6xxx 3,45 résidu 5 xxx 5,34 Bxxx 5xxx 6xxx 1,1 bxxx 5xxx 6xxx ,3.54 résidu Gxxk 5xxx 5.7 5xxx 5xxx Sxxx 1,.52 6xxx 6xxx 6xxx 3 57 résidu Bxxx 5xxx 5,72 5xxx 5xxx 6xxx 1,55 6xxx 6xxx 6xxx 37 résidu 6xxx 5nx 5.73 5xxx 5xxx 6xxx 1,58 6xxx ■S.xxx Gxxx 3.72 résidu 6xxx 5xxx 5.96 5xxx 5xxx Gxxx 1,63 6xxx Sxxx 5xxx 5,97 5xxx 5xxx 6xxx 1,77 5xxx Gxxx Sxxx 4,5 résidu 5xxx 5xxx 6,02 5xxx Sxxx 8xxx 1.81 Gxxx 6xxx 5xxx 4,54 résidu 5xxx 5xxx 6,17 5xxx 5xxx 6xxx 1,81 6xxx 6xxx 6xxx 4.54 résidu 5xxx 5xxx 6,26 Sxxx 5xxx 6xxx 1,92 6xxx 5xxx 6,76 5xxx 5xxx Bxxx 1.99 6xxx 6xxx 5xxx 6,78 Exxx 5xxx Sxxx 2,15 Gxxx 6xxx 6,84 5xxx 5xxx 6xxx 22 6xxx 5xxx 6,92 Bxxx 5xxx Gxxk 2,24 bxxx 5xxx 6xxx 7.07 5xxx 5xxx Sxxx 226 6xxx 6XXX 5xxx 7,07 5xxx 5xx.x Gxxx 2,28 6xxx 6xxx 5xxx 725 5xxx 5xxx 5xxx 2.3 6xxx ■Sxxx 5xxx 7 26 5xxx 5xxx Gxxx 2,36 6xxx Sxxx 5xxx 727 Exxx 5xxx 6xxx 2,38 5xxx Gxxx Sxxx 7,31 5xxx Sxxx 8xxx S Gxxx 6xxx Sxxx 7.36 5xxx 5xxx 6xxx 2,89 Sxxx Sxxx Sxxx 7.8 5xxx Sxxx 5xxx 7,93 5xxx . 5xxx 5xxx 8,9 Exxx 5xxx 5xxx 9,02 5xxx 5xxx 5xxx 19.12 5xxx 5xxx.

Claims

Demands

1. A method for sorting a mixture of aluminum scrap comprising at least two different types of aluminum alloy, comprising: a. a heating step at a predetermined temperature above 90°C and for a predetermined time so that at least one of the two different types of aluminum alloy is colored, b. a sorting step using a device to distinguish the color of the at least two different types of aluminum alloy to obtain at least one enriched batch preferably pure to at least 80% in one of the at least two types of aluminum alloy and any residue of the mixture.

2. The process according to claim 1 characterized in that the sorting step makes it possible to obtain at least two enriched batches, preferably pure at least 80%, of at least two types of aluminum alloy and a possible residue of the mixture.

3. A process according to any one of the preceding claims characterized in that no chemical reagent is used to color the at least two different types of aluminum alloys.

4. A process according to any one of the preceding claims characterized in that the quantity of any residue of the mixture is at most 20% by number of parts of the mixture, preferably at most 10%, more preferably at most 5%.

5. A method according to any one of the preceding claims characterized in that the criterion for distinguishing by color is the parameter b* measured according to ISO 7724 / 1 1:1984.

6. A process according to any one of the preceding claims characterized in that the difference in Mg content between at least two different types of aluminum alloys is at least 0.05% by mass of aluminum, preferably 0.5%, more preferably 1.0%, more preferably 1.5%, more preferably 2.0%.

7. The method according to claim 2 characterized in that the different types of aluminium alloys are chosen from the alloys of the 5XXX series and the 6XXX series, preferably AA5754, AA5182, AA6016, AA6005.

8. A method according to any one of the preceding claims characterized in that the different types of aluminum alloy come from stamping and / or forming scraps, and / or production scraps before preparation for painting, preferably from vehicle parts production, before the parts are assembled on the vehicle body.

9. A method according to any one of the preceding claims characterized in that the minimum of the predetermined temperature is 200°C, preferably 250°C and / or the maximum of the predetermined temperature is 500°C, preferably 450°C and / or the maximum of the predetermined duration is 160 minutes, preferably 100 minutes, more preferably 60 minutes and / or the minimum of the predetermined duration is 3 minutes, preferably 4 minutes.

10. A method according to any one of the preceding claims characterized in that the minimum of the predetermined temperature is 400°C.

11. A method according to any one of claims 1 to 7 characterized in that the maximum of the predetermined temperature is 400°C, preferably 350°C,

12. A method according to any one of the preceding claims, characterized in that the equivalent time at a temperature of 300°C of the predetermined time at the predetermined temperature T0C, calculated according to the formula: time - (---!--- ---—11 dt^vec an auree eq - j predetermined time exp | R. T -c^213 300+273 J | activation energy Q of 37615 J / mol and R=8.314 J / mol, the time is at least 20 minutes, preferably 25 minutes and / or at most 60 minutes, preferably 50 minutes, more preferably 40 minutes, more preferably 33 minutes,

13. A method according to any one of the preceding claims, characterized in that the predetermined temperature and predetermined duration are determined by a method comprising the following steps:

1. Taking at least two samples of at least two different types of aluminum alloy, 2. Exposure of each of the at least two samples to at least two heatings that differ at least in duration and / or temperature, 3. Determination of the predetermined temperature and predetermined duration with the temperature and duration of heating which gave the strongest contrast between the at least two types of aluminium alloys, preferably the contrast being measured by the ratio of the parameters b*, the parameters b* being measured according to ISO 7724 / 1 1:1984.

14. Machine for sorting a mixture of aluminum scrap according to any one of the preceding claims comprising at least two different types of aluminum alloy according to any one of the preceding claims comprising: A furnace, preferably continuous, which heats at least two different types of aluminum alloy to a predetermined temperature and a predetermined duration; A device for distinguishing the color of at least two different types of aluminum alloy, preferably by the parameter b* measured according to ISO 7724 / 1 1:1984; A device comprising means for sorting at least two different types of aluminum alloy; A conveying means, preferably a flat conveying means such as a belt, which conveys the different types of aluminum alloy, preferably through the preferably continuous furnace, and then past the device for distinguishing the color.

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