Method for recycling aluminium from cooking vessels having a vessel body made of aluminium

Abstract

The invention relates to a method for recycling aluminium from cooking vessels having a vessel body made of aluminium, said method comprising the following steps: - a step of collecting the cooking vessels, forming an unprocessed raw material, - a step of selecting the unprocessed 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 at least 98% by mass of cooking vessels having a vessel body made of aluminium, and in such a way that the prepared raw material comprises no more than 50% by mass of cooking vessels having an induction-heatable member made from ferromagnetic material and assembled with the vessel body made of aluminium.

Description

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

[0001] The present invention relates to the recycling of cooking containers having 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 an aluminum body are particularly valued for their heat diffusion properties.

[0004] Among these cookware items, those compatible with induction heating represent an increasingly significant proportion. Induction cooktops operate using a magnetic field system and require suitable cookware. This magnetic field is generated at frequencies that necessitate the cookware containing a ferromagnetic material to generate eddy currents of sufficient intensity for adequate heating power. X8Cr17 (AISI 430) stainless steel can be used to create an induction heating element, for example, in the form of a 0.5 or 0.6 mm thick disc attached to the outer surface of the cookware's base. This stainless steel contains approximately 16 to 18% chromium.

[0005] Furthermore, a significant proportion of cooking vessels have a handle, and the handle(s) of most of these vessels are attached to the body with one or more steel screws. Thus, cooking vessels with an aluminum body contain a considerable amount of iron or chromium.

[0006] Document WO2015110747 describes an example of a recycling process for cooking containers with an aluminum body, which includes a step of grinding the cooking containers prior to sorting the materials. This recycling process yields a food-grade wrought aluminum alloy.

[0007] However, recycling operations carried out using the aforementioned process have shown that in the resulting shredded material, a significant proportion of aluminum remains bound to steel, despite the shredding process. 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 shredded 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 shredded materials are then sorted with the steel, and not with the aluminum.This portion of aluminum is therefore not recovered in the aluminum stream, which on the one hand limits the recycling yield, and on the other hand impacts the cost of the process because of the costs of collecting, transporting and sorting this poorly recovered portion of aluminum.

[0008] The use of collections of cooking containers with 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, meaning suitability for contact with foodstuffs. Regulation (EC) No 1935 / 2004 of 27 October 2004 stipulates in Article 3 that materials and articles intended to come into contact with food, including active and intelligent materials and articles, must be manufactured in accordance with good manufacturing practices so that, under normal or foreseeable conditions of use, they do not release constituents into food in quantities that could endanger human health, cause an unacceptable change in the composition of the food, or impair the organoleptic properties of the food.In the absence of specific legislation applicable to aluminum at the European Union level, national regulations apply, such as the French regulations concerning aluminum and its alloys. The decree of August 27, 1987, specifies a maximum iron content of 2% 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 with a container body made of aluminum.

[0011] However, the presence of iron in the metal parts of cooking containers other than the container bodies made of aluminum must be taken into account.

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

[0013] Another object of the invention aims to optimize the recycling of cooking containers having 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 having 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 vessels having a body made of aluminum, said process comprising the following steps: - a step of collecting the cooking vessels, forming a raw material, comprising cooking vessels having an induction heating element made of ferromagnetic material and assembled with the body of the vessel made of aluminum, - 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, given 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,preferably, at least 99.5% of the cooking vessels have an aluminum body, and the prepared raw material has a mass proportion of less than or equal to 50% of cooking vessels with 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% threshold required to meet food contact standards, 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 recover a higher proportion of cooking vessels containing an induction heating element than the proportion of iron contained in the metal components of said vessels. This process thus allows for the robust production of an aluminum alloy from cooking vessels that is suitable for reuse in food contact. It also significantly increases recycling efficiency by reintegrating the iron-containing aluminum into the process.In addition to the associated environmental benefit, this helps to limit the costs of this recycling by amortizing the costs of collection, transport and sorting over a larger fraction of material.

[0017] Among the aluminum alloys suitable for food contact used in the manufacture of cooking vessels, type 3003 aluminum alloy has a nominal iron content of 0.7%, while type 4007 aluminum alloy has a maximum iron content of 1%. Another example is type 8006 aluminum alloy, 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 an iron content 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 aluminium.

[0019] This process makes it possible to obtain aluminum alloys with an iron content of less than 1.8%. Such 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 in the manufacture of cooking vessels, particularly deep drawing or flow forming.

[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 aluminium.

[0021] This 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 manufacture of cookware. The manufacturing processes for cookware, which involve surface treatment, forming, machining, and 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 allow for the optimization of aluminum melting operations.

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

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

[0026] These provisions make it possible to reduce the proportion of cooking vessels with an induction heating element made of ferromagnetic material and assembled with the body of the vessel made of aluminum 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 melting stage of the prepared raw material.

[0028] This process allows, in particular, the removal of metal trim from handles or grips. It also reduces 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 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.

[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 stage can 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, as well as 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 applies to cooking containers with a body made of aluminum. These cooking containers may or may not have a handle or handles attached to the body.

[0036] The proposed aluminum recycling process includes a collection stage for cookware, which can include used cookware as well as production waste. This collection stage yields raw material. In sales of cookware with an aluminum body, the proportion of cookware compatible with induction heating exceeds 10% and can reach several tens of percent. The quantities of collected cookware used in the recycling process are measured in tons. These quantities therefore correspond to at least a thousand cookware items.Thus, due to the quantities of cooking containers collected, and the proportion of cooking containers compatible with induction heating among cooking containers with a container body made of aluminum, this collection stage includes cooking containers with an induction heating element made of ferromagnetic material and assembled with the container body made of aluminum.

[0037] The proposed aluminum recycling process includes a raw material selection step to obtain a prepared raw material. If desired, sorting of cooking vessels using LIBS (Laser-Induced Breakdown Spectroscopy) or LIPS (Laser-Induced Plasma Spectroscopy), or X-ray fluorescence, can be considered to primarily select cooking vessels 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 manufacturing process: cast container body or 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, some of the cooking containers collected are of the type intended for induction heating; these cooking containers have an induction heating element made of ferromagnetic material and are assembled with the container body made of aluminum.

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

[0041] The collection and sorting stages 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. In the collection stage, using 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 vessels having an aluminum body is at least 99%, and even more preferably, this mass proportion of cooking vessels having an aluminum body is at least 99.5%.

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

[0044] The proposed process includes a melting step of 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 notably involve transfer to a holding furnace, or the use of a continuous refining device.

[0046] Melting tests of cooking vessels, conducted without crushing or separating steel components such as induction heating elements or handle screws, revealed a migration of iron typically found in the steel of induction heating elements. This remelting process lasts approximately four 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.

[0047] The French engineering manual, Techniques de l'Ingénieur, reference M4663 V1, indicates that liquid aluminum at 700°C can dissolve 3% iron by mass. 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 cooking vessels is composed of approximately 79 to 81% iron. This steel constitutes roughly 15% by weight of cooking vessels compatible with induction heating. The molten aluminum bath therefore 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. A remelting furnace typically holds 10 to 12 tons. For the same aluminum-iron mixture, 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 melt 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 melt potentially remain in contact with the steel components from the heating vessels for 4 hours. However, remelting aluminum in 4-ton batches is not an economically viable solution.Furthermore, from one collection to another the proportion of steel is likely to change and therefore the composition of the aluminum alloy obtained will be sensitive to the proportion of cooking containers collected 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 the obtaining of 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 bonded to the aluminum body should 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 bonded to the aluminum body.

[0051] Limiting the proportion of cooking vessels containing an induction heating element bonded to the aluminum body can be achieved by sorting the vessels before they enter the melting furnace, and / or by at least partially disassembling the steel components of the cooking vessels, preferably the induction heating elements. A collection containing 50% cooking vessels with an induction heating element bonded to 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 aluminum melting is generally a gas furnace. The furnace is usually loaded in several stages.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 with an induction heating element assembled with the body of the vessel made of aluminum 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 content of additive elements than a 3003 type aluminum alloy, or even additive 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] Other tests have shown that limiting the number of cooking vessels with an induction heating element to 14% of the total number of vessels involved in the melting process corresponds to limiting the stainless steel content to 2.1% of the melting charge. However, the resulting aluminum alloy has an iron content of 0.7%, which allows for the production, through remelting, of an aluminum alloy similar to a type 3003 alloy, commonly used in the cookware industry. These values ​​were obtained for a casting of 10 to 12 tons over approximately 4 hours in a rotary kiln.

[0055] The proposed process 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 can be applied to cooking vessels with handles or grips attached to the body of the vessel. If desired, the handles or grips can be disassembled from at least some of these cooking vessels before the melting stage in the melting furnace.

[0057] The proposed method can be applied to cooking vessels with screws used to attach handles or knobs to the vessel bodies. Such screws are generally made of steel. However, the mass of these screws has a negligible impact on the composition of the molten metal bath, so the benefit of removing the screws from the vessel bodies before introducing them into the melting furnace appears limited.

[0058] The proposed process involves introducing the prepared raw material into the melting furnace in several loading stages, and selecting the raw material so that the iron content of the raw material introduced in the first loading stage is lower than the iron content of the raw material introduced in the subsequent loading stage(s). The prepared raw material can be separated by magnetization to obtain a non-magnetic fraction and a magnetic fraction, usually after a grinding operation. The non-magnetic fraction can then be used preferentially in the first loading stage, thus limiting the time the iron-containing material remains in the melt pool, resulting in less iron solubilization and a reduction in the iron content of the melt pool.As an alternative or complement, eddy current separation of the prepared raw material can be performed to obtain a non-ferrous 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 aluminum from container bodies for reuse in the production of 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

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, comprising cooking vessels having an induction heating element made of a ferromagnetic material and assembled with the body made of aluminum, - 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.preferably, at least 99.5% of the cooking vessels have an aluminum body, and the prepared raw material has a mass proportion of less than or equal to 50% of cooking vessels with an induction heating element made of ferromagnetic material and assembled with the aluminum body. Aluminum recycling process 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. Aluminum recycling process 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. Aluminum recycling process 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 prepared raw material, preferably between 8 and 15 tonnes of prepared raw material, more preferably between 10 and 12.5 tonnes of prepared raw material. A process 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. A process 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. 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. A process 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 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. A process 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. A process 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 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. 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 during the melting step. Aluminum recycling process 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.