Process for recycling aluminum from cooking containers with a container body made of aluminum

Abstract

The invention relates to a process for recycling aluminum from cooking containers having a container body made of aluminum, said process comprising the following steps: - a step of collecting the cooking containers, forming a raw material, - a step of selecting the raw material, to form a prepared raw material, - a step of melting the prepared raw material in a melting furnace. According to the invention, the collection step and the selection step are carried out in such a way that the prepared raw material comprises a mass proportion of at least 98% of cooking containers having a container body made of aluminum, and in such a way that the prepared raw material comprises a mass proportion of less than or equal to 50% of cooking containers having an induction heating element made of ferromagnetic material and assembled with the container body made of aluminum.

Description

Title of the invention: Process for recycling aluminum from cooking containers having a container body made of aluminum. Technical field

[0001] The present invention relates to the recycling of cooking containers comprising a container body made of aluminum.

[0002] The present invention relates more particularly to the step of selecting cooking containers and the step of melting the aluminum forming the body of the cooking containers. State of the art

[0003] Cooking vessels with a body made of aluminium are appreciated in particular for their heat diffusion properties.

[0004] Among these cooking vessels, the proportion of those compatible with induction heating is steadily increasing. Induction cooktops operate using a magnetic field system and require suitable cooking vessels. This magnetic field is generated at frequencies that necessitate the cooking vessel being made of a ferromagnetic material to generate eddy currents of sufficient intensity to provide adequate heating power. X8Crl7 (AISI 430) stainless steel can be used, for example, to form an induction heating element, such as a 0.5 or 0.6 mm thick disc attached to the outer surface of the base of the cooking vessel. This stainless steel contains approximately 16 to 18% chromium.

[0005] Furthermore, a significant proportion of cooking vessels have a handle or handles, and the handle or handles of the majority of these cooking vessels are attached to the body of the vessel by means of one or more screws made of steel. Thus, cooking vessels with a body made of aluminum contain a non-negligible proportion of iron or chromium.

[0006] Document WO2015110747 describes an example of a process for recycling cooking containers having a container body made of aluminum, which includes a step of grinding the cooking containers prior to sorting the materials. This recycling process makes it possible to obtain a food-grade wrought aluminum alloy.

[0007] However, recycling operations carried out according to the aforementioned process have shown that in the resulting shreds a significant proportion of aluminum remains assembled to steel, despite crushing. Sorting operations aimed at separating steel from aluminum, such as magnetic separation using an overband magnet or a magnetic pulley to exclude ferrous metals, or eddy current separation, which selects metals based on their conductivity, result in these crushed materials containing both aluminum and steel being included with the ferromagnetic fraction containing ferromagnetic elements, or with the ferrous fraction, and not with the aluminum fraction. These aluminum and steel crushed materials are then sorted with the steel, not the aluminum. This portion of aluminum is therefore not recovered within the aluminum stream, which, on the one hand, limits the recycling yield, and on the other hand, impacts the cost of the process due to the costs of collecting, transporting, and sorting this poorly recovered portion of aluminum.

[0008] The use of collections of cooking containers having a container body made of aluminium without going through a sorting step excluding the magnetic fraction containing ferromagnetic elements, nor through a sorting step excluding the ferrous fraction is therefore of interest, to increase the proportion of aluminium recycled, and to reduce the costs of the recycled aluminium obtained.

[0009] However, the use of this recycled aluminum for the manufacture of cooking containers requires compliance with food safety criteria, that is to say, suitability for contact with foodstuffs. Regulation (EC) No 1935 / 2004 of 27 October 2004 provides in Article 3 that materials and articles intended to come into contact with foodstuffs, including active and intelligent materials and articles, shall be manufactured in accordance with good manufacturing practices so that, under normal or foreseeable conditions of use, they do not release constituents into foodstuffs in quantities that could present a danger to human health, cause an unacceptable change in the composition of the foodstuff, or alter the organoleptic properties of the foodstuff.In the absence of specific legislation applicable to aluminium at the European Union level, national regulations apply, such as the French regulations concerning aluminium and its alloys. The decree of 27 August 1987 specifies a limit of 2% for iron content in the alloy composition.

[0010] It therefore appears necessary to control the iron content of the aluminum alloy obtained, in order to be able to consider the use of this recycled alloy in the manufacture of cooking containers having a container body made of aluminum.

[0011] However, the presence of iron in the metallic parts of cooking vessels other than the bodies of the vessels made of aluminum must be taken into account. Summary of the invention

[0012] An object of the invention aims to optimize the recycling of cooking containers comprising a container body made of aluminum, while preserving the ability of the aluminum alloy obtained to be reused in contact with food.

[0013] Another object of the invention aims to optimize the recycling of cooking containers comprising a container body made of aluminium, while preserving the ability of the aluminium alloy obtained to be shaped by stamping and / or flow forming.

[0014] Another object of the invention aims to optimize the recycling of cooking containers comprising a container body made of aluminum, while preserving the ability of the aluminum alloy obtained to be shaped by stamping and / or flow forming using the shaping processes and devices implemented with the aluminum alloys usually used for the manufacture of container bodies.

[0015] To this end, the invention relates to a process for recycling aluminum from cooking containers having a container body made of aluminum, said process comprising the following steps: - a stage of collecting cooking containers, forming a raw material, - a stage of selecting the raw material, to form a prepared raw material, - a melting step of the prepared raw material in a melting furnace, characterized in that the collection step and the selection step are carried out in such a way that the prepared raw material comprises a mass proportion of at least 98% of cooking vessels having an aluminum body, preferably at least 99% of cooking vessels having an aluminum body, even more preferably at least 99.5% of cooking vessels having an aluminum body, and in such a way that the prepared raw material comprises a mass proportion of less than or equal to 50% of cooking vessels having an induction heating element made of ferromagnetic material and assembled with the aluminum body.

[0016] While the proportion of iron in the total mass of cooking vessels appears to be much higher than the 2% level required to meet the food-grade suitability criterion, it has been observed that the proposed process makes it possible to obtain aluminum alloys with an iron content of less than 2%. It therefore appears possible to utilize a higher proportion of cooking vessels containing an induction heating element than the proportion of iron contained in the metallic components of said vessels. This process thus makes it possible to reliably obtain an aluminum alloy from cooking vessels that is suitable for reuse. Used in contact with food. It also significantly increases recycling efficiency by reintegrating the ferrous aluminum component into the process. In addition to the associated environmental benefits, this helps limit recycling costs by spreading collection, transport, and sorting expenses over a larger fraction of the material.

[0017] Among the aluminum alloys suitable for food contact used in the manufacture of cooking vessels, aluminum alloy type 3003 has a nominal iron content of 0.7%, aluminum alloy type 4007 has a maximum iron content of 1%. Another example is aluminum alloy type 8006, which is an aluminum alloy with 0.4% silicon, 0.3% copper, between 0.3 and 1% manganese, 0.1% magnesium and 0.1% zinc, and whose iron content is between 1.2 and 2%.

[0018] The prepared raw material may include a mass proportion of less than or equal to 30% of cooking vessels comprising an induction heating element made of ferromagnetic material and assembled with the vessel body made of aluminum.

[0019] Such a process makes it possible to obtain aluminum alloys with an iron content of less than 1.8%. These alloys prevent the formation of Al3Fe precipitates, which solidify first when the iron content exceeds 1.8% and are extremely brittle: the presence of such precipitates compromises the shaping of parts manufactured with these alloys. The alloys thus obtained make it possible to consider the shaping operations used for the manufacture of cooking vessels, in particular deep drawing or flow forming operations.

[0020] The prepared raw material may include a mass proportion of less than or equal to 14% of cooking vessels comprising an induction heating element made of ferromagnetic material and assembled with the vessel body made of aluminum.

[0021] Such a process makes it possible to obtain aluminum alloys with an iron content of less than 0.8%. Among the aluminum alloys suitable for food contact, type 3003 aluminum alloy with a nominal iron content of 0.7% is a standard in the field of cookware manufacturing. Cookware manufacturing processes, which involve surface treatment, forming, machining, or welding, are generally developed using this alloy.

[0022] The process may consist of carrying out the melting step by loading the melting furnace with at least 5 tonnes of prepared raw material, preferably between 8 and 15 tonnes of prepared raw material, and even more preferably between 10 and 12.5 tonnes of prepared raw material.

[0023] These provisions make it possible to optimize the aluminum melting operations.

[0024] The process may consist of carrying out the melting step for a duration of between 3 and 5 hours.

[0025] The process may consist of carrying out, for at least part of the prepared raw material, a disassembly of the induction heating elements made of ferromagnetic material.

[0026] These provisions make it possible to reduce the proportion of cooking vessels comprising an induction heating element made of ferromagnetic material and assembled with the vessel body made of aluminium before incorporating them into the melting furnace.

[0027] The process may consist of using, for at least part of the prepared raw material, cooking vessels having handles or grips attached to the body of the vessel, and of carrying out, for at least part of said cooking vessels, a disassembly of the handles or grips before the step of melting the prepared raw material.

[0028] Such a process makes it possible, in particular, to remove metal trim pieces present on handles or grips. Such a process also makes it possible to limit the amount of polymer material introduced into the melting furnace.

[0029] The process may consist of introducing the prepared raw material into the melting furnace in several loading stages including an initial loading stage and a subsequent loading stage, and of selecting the prepared raw material so that the iron content of the prepared raw material introduced during the initial loading stage is lower than the iron content of the prepared raw material introduced during the subsequent loading stage.

[0030] The process may consist of introducing the prepared raw material into the melting furnace in several loading stages comprising successively an initial loading stage, a subsequent loading stage, and at least one subsequent loading stage, and selecting the prepared raw material so that the iron content of the prepared raw material introduced during the initial loading stage is lower than the iron content of the prepared raw material introduced during the subsequent loading stage.

[0031] The process may consist of introducing the prepared raw material into the melting furnace in several loading stages including an initial loading stage and several subsequent loading stages, and of selecting the prepared raw material so that the iron content of the prepared raw material introduced during the initial loading stage is lower than the iron content of the prepared raw material introduced during the subsequent loading stages.

[0032] The selection step may include a selection of a portion of the raw material prepared for the initial loading step, said portion of prepared raw material having a proportion of non-magnetic fraction and / or non-ferrous fraction greater than the proportion of non-magnetic fraction and / or non-ferrous fraction contained in the whole of the prepared raw material used during the melting step.

[0033] The selection step may use magnetic separation to separate the non-magnetic fraction from the magnetic fraction, and / or eddy current separation to separate the non-ferrous fraction from the ferrous fraction. Magnetic separation can be performed on crushed raw material, but also on cooking vessels or pieces of cooking vessels. Eddy current separation is typically performed on crushed raw material.

[0034] The aims, aspects and advantages of the present invention will be better understood from the description given below of particular embodiments of the invention presented by way of non-limiting example.

[0035] The proposed aluminum recycling process relates to cooking containers having a container body made of aluminum. The cooking containers may have a handle or handles attached to the container body, or may not have them.

[0036] The proposed aluminum recycling process includes a step of collecting cooking containers, which may involve used cooking containers, but also production waste from cooking containers. This collection step makes it possible to obtain a raw material.

[0037] The proposed aluminum recycling process includes a raw material selection step to obtain a prepared raw material. If desired, sorting of cooking containers by LIBS (Laser-Induced Breakdown Spectroscopy) or LIPS (Laser-Induced Plasma Spectroscopy), or by X-ray fluorescence, can be considered to primarily select cooking containers with an aluminum body, or even to select the type of aluminum alloy.

[0038] If desired, the container bodies can be sorted by alloy type according to their embodiment: cast container body or deformation-formed container body. The proportion of cast container bodies can be defined in accordance with the teachings of document WO2015110747 to obtain a wrought aluminum alloy.

[0039] Generally, part of the collected cooking containers are of the type intended for induction heating, these cooking containers having an induction heating element made of ferromagnetic material and assembled with the container body made of aluminum.

[0040] Remelting the aluminum from the container bodies makes it possible to consider reusing this aluminum to make new container bodies.

[0041] The collection and sorting steps are carried out in such a way that the prepared raw material comprises at least 98% by mass of cooking containers with an aluminum body. Since the collection step uses raw material from a household waste collection, items other than cooking containers with an aluminum body may be collected, including cooking containers with a stainless steel body, or lids.

[0042] Preferably, this mass proportion of cooking containers comprising a container body made of aluminum is at least 99%, and even more preferably, this mass proportion of cooking containers comprising a container body made of aluminum is at least 99.5%.

[0043] This selection step may consist of using material from crushed container bodies and / or uncrushed container bodies. If desired, the container bodies may be sectioned, in particular by shearing.

[0044] The proposed process includes a step of melting the prepared raw material in a melting furnace. To optimize recycling operations, the melting step is carried out by loading the melting furnace with at least 5 tonnes of prepared raw material, preferably between 8 and 15 tonnes of prepared raw material, and even more preferably between 10 and 12.5 tonnes of prepared raw material.

[0045] The proposed process may then include a further refining step, for example by degassing, and / or with a reduction in magnesium content, and / or the addition of alloying elements. This further refining step may in particular include a transfer to a holding furnace, or the use of a continuous refining device.

[0046] Melting tests of cooking vessels carried out without crushing or separating the steel parts of the cooking vessels, such as induction heating elements or handle fixing screws, show a migration of iron generally contained in the steel constituting the induction heating elements. This remelting lasts approximately 4 hours, the time required to melt the entire metal charge. This contact time between the steel and the molten aluminum bath allows diffusion to occur and affect the composition of the molten aluminum bath.

[0047] Les Techniques de l'Ingénieur, reference M4663 V1, indicates that liquid aluminum at 700°C can solubilize 3% by mass of iron. The extent of this migration depends on the quantity of induction heating elements and screws introduced into the molten aluminum bath. The steel forming the ferromagnetic part of the containers of The steel in a cooking vessel is composed of approximately 79 to 81% iron. This steel makes up roughly 15% by weight of cookware compatible with induction heating. Therefore, the molten aluminum bath contains more than enough steel to become saturated with iron.

[0048] This migration also depends on the contact time between the molten aluminum and the iron. The load of a remelting furnace is typically 10 to 12 tons. For the same mixture of aluminum and iron, a small 4-ton pour will take much less time, given the mass to be heated, than a 12-ton pour, which typically takes 4 hours. In the 4-ton pour, the first pieces of aluminum that are melted therefore remain in contact with the steel components from the heating vessels for a much shorter time. Conversely, in a 12-ton pour, the first pieces of aluminum that are melted potentially remain in contact with the steel components from the heating vessels for 4 hours. However, remelting the aluminum in 4-ton batches is not an economically viable solution.Furthermore, from one collection to the next the proportion of steel is likely to change, and therefore the composition of the resulting aluminum alloy will be sensitive to the proportion of collected cooking containers that are compatible with induction heating.

[0049] The principle of the invention consists of controlling the quantity of steel contained in the melting bath to facilitate obtaining an aluminum alloy that can be used for the manufacture of cooking vessels.

[0050] Tests have shown that a threshold of approximately 50% of cooking vessels with an induction heating element assembled with the aluminum body must not be exceeded, otherwise the aluminum alloy obtained after remelting will lose its suitability for food contact. The ferromagnetic steel grid represents 15% by mass of cooking vessels with an induction heating element assembled with the aluminum body.

[0051] Limiting the proportion of cooking vessels with an induction heating element assembled with the aluminum body can be achieved by sorting the cooking vessels before the melting furnace, and / or by at least partially disassembling the steel parts of the cooking vessels, preferably the induction heating elements. A collection comprising 50% cooking vessels with an induction heating element assembled with the aluminum body has an iron content of 7.5%; however, aluminum ingots with an iron content of 2% have been obtained after casting. The furnace used for melting the aluminum is generally a gas furnace. The furnace is usually loaded in several stages of loading. A preliminary sorting of the prepared raw material can be carried out to limit the proportion of iron elements loaded into the furnace during the first stage of furnace loading, in order to obtain a bath base with low iron content.

[0052] Other tests have shown that incorporating 25 to 30% of cooking vessels comprising an induction heating element assembled with the body of the vessel made of aluminium corresponds to limiting the stainless steel content to 3% of the charge used for melting, and makes it possible to obtain alloys containing less than 1.8% iron, in particular alloys of type 4007, allowing a maximum iron content of 1%, such alloys being quite commonly used for the manufacture of cooking vessels, or even alloys of type 8050, allowing a high iron content (1.3%).

[0053] However, the use of such alloys to manufacture cooking vessels requires adaptations to the manufacturing processes, because these alloys have different contents of addition elements than those of a type 3003 aluminum alloy, or even addition elements of a different nature, and the formability and weldability of these alloys require adaptations to the production tools, in particular the geometry of these tools, or the cycle time of the operation.

[0054] Further tests have shown that limiting the number of cooking vessels with an induction heating element to 14% of the total number of cooking vessels involved in the melting process corresponds to limiting the stainless steel content to 2.1% of the charge used for melting. However, the resulting aluminum alloy has an iron content of 0.7%, which makes it possible to obtain, by remelting, an aluminum alloy close to a type 3003 alloy, commonly used in the cookware industry. These values ​​were obtained for a pour of 10 to 12 tonnes over approximately 4 hours in a rotary kiln.

[0055] The proposed method may consist of disassembling the induction heating elements made of ferromagnetic material for at least some of the cooking vessels, in order to increase the proportion of cooking vessels without such elements made of ferromagnetic material.

[0056] The proposed process may relate to cooking vessels having handles or grips attached to the body of the vessel. If desired, the handles or grips may be disassembled from at least some of said cooking vessels before the step of melting the material of the cooking vessels in the melting furnace.

[0057] The proposed method may relate to cooking vessels with screws used to attach handles or grips to the vessel bodies. Such screws are generally made of steel. However, the mass of these screws has a negligible influence on the composition of the molten metal bath, hence the interest in shrinkage The screws on the container bodies before their introduction into the melting furnace appear limited.

[0058] The proposed process may consist of introducing the prepared raw material into the melting furnace in several loading stages, and selecting the prepared raw material so that the iron content of the prepared raw material introduced during the first loading stage is lower than the iron content of the prepared raw material introduced during the other loading stage or at least one of the other loading stages. Magnetic separation of the prepared raw material may be carried out to obtain a non-magnetic fraction and a magnetic fraction, usually after a grinding operation. The non-magnetic fraction may then be used preferentially during the first loading stage, thereby limiting the time the iron-containing material remains in the melt pool, resulting in less iron solubilization and reducing the iron content in the melt pool.As an alternative or complement, eddy current separation of the prepared raw material can be carried out to obtain a non-ferrous fraction and a ferrous fraction, usually also after a grinding operation. The non-ferrous fraction can then be used preferentially during the first loading stage, which also limits the time the iron-containing material remains in the molten bath, resulting in less iron solubilization and a reduction in the iron content of the molten bath.

[0059] The proposed process thus makes it possible to better utilize the aluminium from container bodies for reuse in order to make new container bodies.

[0060] Various modifications and / or improvements obvious to a person skilled in the art may be made to the examples of embodiment of the invention described in this description without departing from the scope of the invention as defined by the attached claims.

Claims

Demands

1. A process for recycling aluminum from cooking vessels having a body made of aluminum, said process comprising the following steps: - a step of collecting cooking vessels, forming a raw material, - a step of selecting the raw material, to form a prepared raw material, - a step of melting the prepared raw material in a melting furnace, characterized in that the collection step and the selection step are carried out in such a way that the prepared raw material comprises a mass proportion of at least 98% of cooking vessels having a body made of aluminum, preferably at least 99% of cooking vessels having a body made of aluminum, and even more preferably at least 99.5% of cooking vessels having a body made of aluminum,and in such a way that the prepared raw material comprises a proportion by mass of less than or equal to 50% of cooking vessels having an induction heating element made of ferromagnetic material and assembled with the vessel body made of aluminum.

2. A method for recycling aluminum according to claim 1, characterized in that the prepared raw material comprises a mass proportion of less than or equal to 30% of cooking vessels comprising an induction heating element made of ferromagnetic material and assembled with the vessel body made of aluminum.

3. A process for recycling aluminum according to claim 1, characterized in that the prepared raw material comprises a mass proportion of less than or equal to 14% of cooking vessels comprising an induction heating element made of ferromagnetic material and assembled with the vessel body made of aluminum.

4. A process for recycling aluminum according to any one of claims 1 to 3, characterized in that it consists of carrying out the melting step by loading the melting furnace with at least 5 tonnes of raw material prepared, preferably between 8 and 15 tonnes of prepared raw material, preferably still between 10 and 12.5 tonnes of prepared raw material.

5. A method for recycling aluminum according to any one of claims 1 to 4, characterized in that it consists of carrying out the melting step for a period of between 3 and 5 hours.

6. A method for recycling aluminum according to any one of claims 1 to 5, characterized in that it consists of carrying out, for at least a part of the prepared raw material, a disassembly of the induction heating elements made of ferromagnetic material.

7. A method for recycling aluminum according to any one of claims 1 to 6, characterized in that it consists of using, for at least part of the prepared raw material, cooking containers having handles or grips attached to the body of the container, and of carrying out, for at least part of said cooking containers, a disassembly of the handles or grips before the step of melting the prepared raw material.

8. A method for recycling aluminum according to any one of claims 1 to 7, characterized in that it consists of introducing the prepared raw material into the melting furnace in several loading stages including an initial loading stage and a subsequent loading stage, and selecting the prepared raw material so that the iron content of the prepared raw material introduced during the initial loading stage is lower than the iron content of the prepared raw material introduced during the subsequent loading stage.

9. A method for recycling aluminum according to any one of claims 1 to 7, characterized in that it consists of introducing the prepared raw material into the melting furnace in several loading stages comprising successively an initial loading stage, a subsequent loading stage, and at least one further loading stage, and selecting the prepared raw material so that the iron content of the prepared raw material introduced during the initial loading stage is lower than the iron content of the prepared raw material introduced during the subsequent loading stage.

10. A process for recycling aluminum according to any one of claims 1 to 7, characterized in that it consists of introducing the raw material prepared in the melting furnace in several loading stages including an initial loading stage and several subsequent loading stages, and to select the prepared raw material so that the iron content of the prepared raw material introduced during the initial loading stage is lower than the iron content of the prepared raw material introduced during the subsequent loading stages.

11. A process for recycling aluminum according to any one of claims 8 to 10, characterized in that the selection step comprises a selection of a portion of the raw material prepared for the initial loading step, said portion of prepared raw material having a proportion of non-magnetic fraction and / or non-ferrous fraction greater than the proportion of non-magnetic fraction and / or non-ferrous fraction contained in the whole of the prepared raw material used in the melting step.

12. A method for recycling aluminum according to claim 11, characterized in that the selection step uses magnetization sorting to separate the non-magnetic fraction from the magnetic fraction, and / or eddy current sorting to separate the non-ferrous fraction from the ferrous fraction.