ALUMINUM CHARGE MELTING PROCESS USING AN INDUCTION FURNACE

Abstract

The invention relates to a process for melting an aluminum charge, comprising: supplying an aluminum charge (11, 12, 13) of which at least 15% by weight is in the form of a bowl of essentially cylindrical shape (11) of height h and maximum diameter d; loading said charge into a cylindrical induction furnace (10) of height H and maximum internal diameter D in which the direction of the height of said bowl is substantially parallel to the direction of the height of the furnace; melting said charge by induction to obtain a bath of liquid metal (2); optionally, refining said liquid metal to a fineness in which d is in the range of 0.7 D to 0.97 D and preferably in the range of 0.84 D to 0.92 D. Figure 1

Description

Description Title of the invention: METHOD FOR FUSION OF CHARGE ALUMINUM USING AN INDUCTION OVEN technical field

[0001] The invention relates to the melting of aluminum products and the manufacture of products intermediate aluminum alloy products, such as rolling plates, spinning billets or forging blocks, using an induction furnace. EARLIER ART

[0002] … The carbon footprint of aluminum manufacturing is much lower when the products are obtained by recycling existing raw materials only from primary aluminum obtained by electrolysis. It is therefore important to develop processes for economically and efficiently remelting materials first for recycling. In addition, induction ovens for which melting is electrically produced are favorable with regard to emissions carbon than gas ovens, especially when the electricity used is obtained without emissions.

[0003] The industrial efficiency of induction furnaces is, however, often lower than that gas furnaces due to their slower melting speed, limited size and the difficulty of loading the oven.

[0004] Patent EP1101830 describes a method for manufacturing an intermediate product, such as that a plate, billet or forging block, made of a specific aluminum alloy of The 7000 series is characterized in that it includes: - a) the supply of products to recycle such as scrap metal and machining offcuts of at least one second alloy of the series 7000 having a target content, in at least a second anti- element recrystallization such as Zr or Cr, exceeding the maximum acceptable content for the determined alloy; b) at least one refining step for scrap metal and offcuts, allowing the reduction of the content of this second anti-recrystallization element to a value lower than the maximum acceptable content in the determined alloy; c) the production of a batch of liquid metal from the pure metal obtained from the refining operation 3 d) the formation of the intermediate product (100) by pouring (40) the liquid metal.

[0005] Patent EP1913166 describes a process for melting aluminum alloy scrap containing lithium in which (i) scrap containing alloys of is supplied aluminum-lithium type (supply stage); (ii) an initial bed of liquid metal of a first composition (initial metal bed preparation step) liquid) in a melting furnace (iii) said scrap is loaded onto said initial bed of metal liquid so as to create on the surface of said bed of liquid metal a floating mattress of said scrap (loading step); (iv) said scrap mat is melted to obtain a bath of liquid metal of a second composition which may be equal to or different from the first composition (mat melting step); (v) liquid metal is taken (take-up step) from said bath of liquid metal of a second composition. US patent 6393044 describes an induction melting system that uses a crucible made of a material that has high electrical resistivity or high magnetic permeability and one or more induction coils formed from a wound cable made of several individually insulated copper conductors to form an induction furnace that, with its power supply, offers a compact design. Melting in induction furnaces is particularly useful for melting raw materials for recycling. The types of raw materials for recycling in aluminium and aluminium alloy (known in particular as "scrap") are described in the standard EN 12258-3. In many industries, the manufacturing processes for finished metal products through machining, processing, and cutting of intermediate products generate significant quantities of chips and machining scrap. This excess material is removed from intermediate products during manufacturing processes through turning, bar turning, planing, milling, surfacing, trimming, drilling, tapping, threading, sawing, boring, or finishing machining, or similar operations. This type of scrap includes both small pieces such as turnings and chips, and larger pieces such as shredded scrap, such as offcuts from cutting or shearing thin or thick sheets, profiles, plates, and billets. Other types of scrap commonly used in recycling processes are used packaging such as used beverage cans and used food packaging. Scrap can be in various forms such as prepared, bulk, crushed, granule-shaped, compacted, clean, coated, anodized, ground, intended for direct melting. Thus, in certain cases, scrap metal undergoes at least one initial transformation to make it suitable for direct melting, such as compaction (to produce, for example, "bricks") or melting (to produce remelting ingots such as "bowls"). This initial transformation can simplify the transport, handling, melting, and / or storage of scrap and chips, and contribute to improving the scrap by reducing oil residues and achieving a homogeneous composition. A remelting ingot is a metal cast in a shape suitable for remelting, possibly having undergone certain metallurgical treatments to rectify its composition and / or remove certain metallic or non-metallic impurities. A bowl is a remelting ingot typically weighing 500 kg. Bowls are usually in a generally rectangular shape and suitable for handling by forklifts. The problem that the present invention seeks to solve is to improve the productivity and energy efficiency of manufacturing processes comprising melting in a cylindrical induction furnace, particularly for processes using a significant proportion of recycled raw material. Description of the invention A first object of the invention is a process for melting an aluminum charge, characterized in that it comprises: the supply of an aluminium charge of which at least 15% by weight is in the form of a bowl of essentially cylindrical shape of height h and maximum diameter d; loading said load into a cylindrical induction furnace of height H and maximum internal diameter D in which the direction of the height of said bowl is substantially parallel to the direction of the height of the furnace; the melting of said charge by induction to obtain a bath of liquid metal; optionally the allocation of said liquid metal. in which d is in the range 0.7 D to 0.97 D. A second object of the invention is an essentially cylindrical aluminum bowl of height h and maximum diameter d adapted for melting by the process according to the invention. Another object of the invention is a method for manufacturing an intermediate product, such as a rolling plate, a spinning billet, a forging block, or an ingot or a bowl, characterized in that it comprises: - obtaining a bath of liquid metal optionally refined by the melting process according to the invention: - optionally the filtration and / or treatment of said liquid metal (2); - the formation of said intermediate product (100, 101) by pouring said liquid metal. Yet another object of the invention is a mold for casting a bowl according to the invention. FIGURES [Fig.1] Fig.1 illustrates a preferred embodiment of the process of the invention. [Fig.2] Fig.2 illustrates a bowl according to the invention. [Fig. 3a] Figure [Fig. 3a] illustrates another bowl according to the invention, and shows a top view and two cross-sectional views. [Fig.3b] Fig.3b illustrates another bowl according to the invention, and shows a perspective view. [Fig.4] Fig.4 illustrates one possible manipulation of bowls according to the invention. [Fig.5] Fig.5 illustrates a mold according to the invention. [Fig.6a] Fig.6a illustrates the loading of the example, with parallelepiped blocks. [Fig.6b], Fig.6b illustrates the loading with bowls according to the invention. [Fig.7] Fig.7 illustrates an embodiment of a process for manufacturing an intermediate product according to the invention. [Fig.8] The [Fig.8] is a cross-sectional view of a bowl according to an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION Unless otherwise specified, the definitions of standard EN 12258, in particular EN12258-1 and 12258-3, apply. The applicant found that, contrary to expectations, the use of bowls of essentially cylindrical shape of size adapted to the size of the oven makes it possible to significantly reduce the loading time and the melting time in a cylindrical induction oven. According to the invention, the process for melting an aluminum charge comprises: the supply of a load of aluminium; loading the load into an induction oven; the fusion of the charge. This process is illustrated by [Fig. 1]. In the present invention the term aluminium refers to pure aluminium as well as all aluminium alloys comprising at least 50% aluminium, such as in particular the alloys described in the Teal Sheets published by The Aluminium Association. At the supply stage, at least 15% by weight of the aluminum feed is in the form of a bowl of essentially cylindrical shape (11) of height h and maximum diameter d. Depending on the size of the bowl, one bowl may suffice to reach this minimum quantity, but generally several bowls are used, typically two, three, four, or more. Preferably, at least 25%, preferably at least 35%, or even at least 50%, at least 70%, or at least 90% by weight of the feed is in the form of a bowl of essentially cylindrical shape (11). According to the invention, the weight of the bowl(s) of essentially cylindrical shape is at least 100 kg, preferably- Preferably at least 300 kg, more preferably at least 400 kg, advantageously at least 500 kg. In one embodiment of the invention, the weight of the essentially cylindrical bowl(s) is at least 700 kg, advantageously at least 1000 kg, and preferably at least 1500 kg. Bowls weighing less than 700 kg, for example between 100 kg and 700 kg, can nevertheless be used alone or in combination with heavier bowls. The bowl is essentially cylindrical in shape, meaning that its form is primarily composed of one or more superimposed cylinders and / or truncated cones with the same axis of revolution, such that the maximum and minimum diameters of all the cylinders and / or truncated cones do not differ by more than 10%, preferably not by more than 7%, and preferably not by more than 5%. Thus, a section perpendicular to the axis of revolution of the essentially cylindrical shape is generally circular. Any section perpendicular to the axis of revolution of the essentially cylindrical shape may be a partially truncated circle, but the truncated portion represents less than 50% of the circular perimeter, and preferably less than 40%. The essentially cylindrical shape may have a central opening. The essentially cylindrical shape may have feet.The height h of the essentially cylindrical shape corresponds to the maximum dimension perpendicular to the maximum diameter, that is, along the axis of revolution. To supplement the feedstock, aluminum is used in other forms, including raw forms (12) such as ingots, billets, and plates, and processed forms (13) at various stages of manufacturing, such as strips, sheets, profiles, bars, tubes, wires, and forgings. This includes production scrap, particularly shredded scrap from cutting, shearing, or similar operations, as well as post-use products such as used beverage cans, used packaging, incinerator scrap, and turnings composed of grains, chips, shavings, and shavings produced by machining or other operations. When the scrap is coated, a decoating operation is advantageously performed to obtain decoated scrap. Preferably, the post-use scrap is ground.In one embodiment of the invention, at least 15% and preferably at least 30% or even 40% by weight of the load is in the form of processed products (13), preferably in highly divided form such as shredded scrap, turnings, used beverage cans or used packaging. The origin of aluminum, whatever its form, can be primary aluminum extracted from a metallic compound by reduction, or by decomposition of a metallic compound, or remelted metal, that is, metal that has already been solidified once. In one embodiment, the bowl according to the invention is obtained by primary metal casting. In another embodiment, the bowl according to the invention is obtained by casting remelted metal. Preferably, the bowl according to the invention is obtained by casting remelted metal comprising recovered scrap from post-use products. In one embodiment of the invention, at least 60% of the charge is derived from remelted metal, preferably from production scrap or recovered scrap. Preferably, the charge consists of suitably sorted alloys from the 2XXX, 3XXX, 4XXX, 5XXX, 6XXX, 7XXX, or 8XXX series. In an advantageous embodiment, the charge consists of 2XXX series alloys containing at least 0.5% by weight of lithium, such as, for example, AA2050, AA2196, or AA2198 alloys. In another advantageous embodiment, the charge consists of 3XXX series alloys containing at least 30% used beverage cans or used packaging. The charge is then loaded into a coreless crucible induction furnace of essentially cylindrical shape (10), hereafter referred to as a "cylindrical induction furnace," and known in English as a "coreless crucible induction furnace." The cylindrical induction furnace has a maximum internal diameter D, corresponding to the maximum internal diameter of the furnace crucible. The crucible may be removable or fixed.By essentially cylindrical shape, it is understood that its shape is mainly composed of one or more superimposed cylinders and / or truncated cones with the same axis of revolution, such that the maximum and minimum diameters of all the cylinders and / or truncated cones do not differ by more than 10%, preferably not by more than 7%, and preferably not by more than 5%. The maximum diameter d of the bowls according to the invention is adapted to the maximum internal diameter D of the oven; thus, d is in the range of 0.7D to 0.97D, and preferably in the range of 0.84D to 0.92D. The precise adaptation of the maximum diameter of the bowl according to the invention to the oven and its essentially cylindrical shape make it possible, in particular, to generate better inductive coupling with the coils of the induction oven and also to increase the charge density in the oven.Furthermore, it is preferable that the height h of the bowl be at most 50%, preferably at most 40% and preferably at most 30%, of the maximum diameter d to avoid metallurgical defects during the casting of the bowls. The bowl is loaded in such a way that its height is approximately parallel to the height of the oven. Advantageously, the bowls are loaded in a single operation regardless of the number of bowls being loaded. Advantageously, the essentially cylindrical bowl includes an opening in its center (111). The opening (111) allows, in particular, the insertion of a manipulator tool for example attached to a forklift or overhead crane. In one embodiment, the bowl according to the invention is loaded after the oven has been tilted horizontally. The bowl is tilted and loaded, for example, using a forklift. In this embodiment, it is advantageous to use a bowl whose circular perimeter has been truncated to ensure stability when it is tilted, its height h being then in a horizontal position. In this embodiment, when several bowls are loaded, it is advantageous for the bowls to be tilted and loaded, for example, using a manipulator tool attached to a forklift and inserted into the openings (111) in a single operation. It is advantageous in this embodiment to use identical bowls whose circular perimeter has been truncated to ensure stability when they are tilted. The oven is then tilted back to the vertical position for the introduction of other load elements such as scrap. In another embodiment, the bowl is inserted into the oven in a vertical position. The bowl can, for example, be manipulated using a suitable manipulator tool inserted into the opening (111) and placed inside the oven without touching the walls of the induction oven. If a circular opening, as illustrated in [Fig. 2], possibly beveled, is made, a pneumatic tool with an expanding mandrel can be used, for example. An oblong opening, as illustrated in Figure 3, can also be made. As illustrated in [Fig. 4], a manipulator tool (3) comprising a rectangular wedge (32) can be inserted into the oblong opening (111) and then pivoted using a rod (31) so as to be locked under the bowl. The assembly can then be easily manipulated using an overhead crane, the reverse operation being performed to remove the manipulator tool (3) when the bowls are positioned in the oven. In both cases it is possible to directly introduce a stack of bowls according to the invention, which makes the loading operation particularly fast, avoids the degradation of the crucible refractories and can be carried out by a single operator. In one embodiment, the furnace is first partially filled with production scrap and / or recovery scrap (13) and / or ingots (12), then the bowls according to the invention are introduced and again production scrap and / or recovery scrap are introduced, in particular in the remaining space between the bowls according to the invention and the walls of the furnace, the loading being finally completed with production scrap and / or recovery scrap and / or ingots. In another embodiment, bowls according to the invention are introduced first, then production scrap and / or recovered scrap are introduced, particularly in the remaining space between the bowls according to the invention and the walls of the furnace, the load finally being completed with production scrap and / or recovered scrap and / or ingots. It may be advantageous in one embodiment to not do not center the bowls according to the invention in the oven so as to facilitate the introduction of production scrap and / or recovery scrap. The inventors have observed that it is advantageous, for faster and less energy-intensive melting, for at least one bowl according to the invention to be positioned near the mid-height of the furnace. Thus, in an advantageous embodiment, the diameter h / 2 of the essentially cylindrical bowl, positioned at mid-height, is located at a distance from the bottom of the furnace, i.e., the bottom of the crucible, of between H / 2 - H / 4 and H / 2 + H / 4, and preferably between H / 2 - H / 5 and H / 2 + H / 5. The charge is then melted by induction to obtain a bath of liquid metal (2). Melting can be carried out under an inert atmosphere or in ambient air, with or without a lid. The power and frequency used are chosen according to the furnace used and the charge. Typically, the power is 40% to 100% of the maximum power and the frequency is 50 Hz to 400 Hz. The frequency is specifically adapted to the size of the induction furnace. It should be noted that in one embodiment the melting can be started before the complete introduction of the charge: once the charge is partially melted, in some cases the loading cycle can be resumed and, for example, scrap can be introduced using a clamp, a screw conveyor or by emptying a skip. Optionally, the alloying elements for fineness adjustment are then added to the furnace to achieve the desired composition. The alloying elements are generally added as high-strength aluminum alloys containing a single element, or as pure alloying metals. The various forms used to add alloying elements are known by the acronym "AMMA," which stands for "mother alloys and alloying metals." The invention also relates to a method for manufacturing an intermediate product (100, 101), such as a rolling plate, a spinning billet, a forging block (100) or an ingot or a bowl (101) in which a step of pouring the liquid metal obtained by the melting process according to the invention is carried out. This method is illustrated by [Fig. 7]. Optionally the cast metal can be transferred to a large furnace (102) in an intermediate way for example to group the liquid metal from several induction furnaces. Optionally, filtration and / or treatment steps of the liquid metal can be performed before casting. Typically, the liquid metal can be filtered through a filter medium in a "filtering ladle," or a so-called "treatment gas," which can be inert or reactive, can be introduced into the liquid metal bath in a "degassing ladle." In an advantageous variant of this embodiment, the process includes gas treatment of the metal to remove inclusions. The gas comprises chlorine preference, approximately, the rest being typically made up of nitrogen or argon. The liquid metal is then directed to a liquid metal solidification device (or "casting loom") to form an intermediate product such as a rolling plate (100), a spinning billet, a forging block, an ingot or a bowl (101). The process can also be semi-continuous, with only part of the liquid metal being taken for casting, a bath foot remaining in the furnace, and solid aluminum being introduced into the bath foot. The invention also relates to a predominantly cylindrical aluminum bowl adapted for melting in a cylindrical induction furnace. Preferably, the weight of the predominantly cylindrical bowl is at least 700 kg, and even more preferably at least 1000 kg or even at least 1500 kg. The bowl is essentially cylindrical in shape as defined. Any section perpendicular to the height of the essentially cylindrical shape may be a partially truncated circle, but the truncated portion represents less than 50% of the circular perimeter and preferably less than 40%. The essentially cylindrical shape may have a central opening. The essentially cylindrical shape may have feet. The height h of the essentially cylindrical shape corresponds to the maximum dimension perpendicular to the maximum diameter. Preferably, the bowl according to the invention has an opening in its center (111). In one embodiment, the opening is circular as illustrated in [Fig. 2], possibly beveled. In another embodiment, the opening is oblong as illustrated in Figure 3. Advantageously, the oblong opening is also beveled, as shown in particular in section BB of [Fig. 3].3a] in particular to facilitate the demolding of the bowl. The bevel angle is chosen to optimize the compromise between demolding and the amount of metal, advantageously the bevel angle is in the range of 15° to 50°, preferably in the range of 25° to 35°. In one embodiment, an oblong or circular groove (114) allows the vertical or horizontal passage of the handling tool with a clearance of at least 20mm for expansion. To facilitate handling, the bowl can be fitted with at least two feet (113). In one embodiment, the bowl has four feet. This allows the bowl to be handled with a forklift in all directions and cut in half without losing stability. The geometry of the bowls allows, in particular, for secure stacking of four stable heights, advantageously five or six stable heights, especially for bowls with four feet having four support points. In another embodiment without a foot and illustrated by [Fig.8] which represents a cross-section of the bowl, the bowl is provided with two notches (115) which allow it to be manipulated. Advantageously, the bowl is equipped with a collar (112). The collar provides a visual indication during the filling of the bowl mold and during its use. The absence of a collar alerts operators to insufficient filling of the mold and, if applicable, to the bowl's reduced strength. The collar also ensures a safe minimum handling height. The diameter at the collar can represent the maximum diameter. In one embodiment, the essentially cylindrical bowl is truncated at the ends by at least one diameter (114). In another embodiment, the diameter is truncated at the ends by two perpendicular diameters. The advantage of trunculating the diameter is twofold: firstly, it allows for vertical positioning of the bowls on their edge, thus facilitating insertion in the tilted furnace embodiment; and secondly, it facilitates horizontal positioning by placing the bowls against a frame at a 90° angle, thereby facilitating the insertion and removal of the handling system once the bowl is positioned in the furnace in the non-tilted furnace embodiment. It also facilitates the introduction of scrap into the furnace once the bowl is positioned. However, it is important that the shape remains essentially cylindrical to maximize inductive coupling with the induction furnace coils. The invention also relates to a mold (4) for casting a bowl according to the invention. An example of a mold according to the invention is illustrated in [Fig. 5]. The mold has a shape that allows for easy demolding of the bowls; in particular, the draft angles are adjusted, for example, by modeling using simulation tools known to those skilled in the art. Preferably, the mold according to the invention includes pockets (413) for forming the feet and allowing for turbulence-free pouring, which reduces oxide formation. Advantageously, the mold includes a central tip (411) for creating the opening (111). In an advantageous embodiment, the central tip (411) for creating the opening (111) is removable. Preferably, the central tip is hollowed out to improve cooling and prevent metallurgical defects such as porosity, blowholes, shrinkage cavities, and solidification cavities.Furthermore, it is preferable that the height h of the bowl be at most 50%, preferably at most 40%, and most preferably at most 30%, of the maximum diameter d to avoid metallurgical defects. Thus, the bowl according to the invention is preferably free from metallurgical defects such as porosity, blowholes, shrinkage cavities, and solidification cavities. The mold according to the invention is preferably made of cast iron, such as gray cast iron or spheroidal cast iron, or of cast steel. The bowl according to the invention has many advantages: First, it allows for improved inductive coupling in cylindrical crucible induction furnaces, thanks in particular to the overall cylindrical shape, which enables control of the distance to the wall. This reduces melting time by at least 15%, and preferably by at least 30%. Furthermore, the geometry improves the loss on ignition by at least 0.5%, and preferably by at least 1%. The geometry also improves the furnace filling rate by at least 15% and the loading time by at least 10%, thus increasing process productivity. The bowl geometry also prevents the arching effect, improving process safety. Since loading is easier, the risk of damage to the refractories is reduced, thus extending their lifespan. The mold according to the invention is advantageous because it allows for rapid demolding by turning, accelerated solidification by maximizing heat exchange, and the production of bowls free from defects. Examples Melting tests of various charges were carried out in a cylindrical induction furnace with a capacity of 500 kg and an internal diameter D of 500 mm. The melting of a parallelepiped block placed vertically in the center of the furnace was compared to the melting of cylindrical bowls according to the invention, with the same total mass of 100 kg as the parallelepiped block, a maximum diameter d of 384 mm, and placed at mid-height of the coil (Figure 6). The reference block was also centered with respect to the mid-height of the coil. A frequency of 385 Hz was used, and the power used corresponded to 50% of the furnace's nominal power. The test shows a 37% reduction in the melting time of bowls placed at mid-height of the inductors ([Fig. 6b]) compared to the parallelepiped block placed vertically ([Fig. 6a]). These tests were also used to calibrate a melting model.

Claims

Demands

1. A process for melting an aluminum charge, characterized in that it understand : the supply of a load of aluminium (11, 12, 13) of which at minus 15% by weight is in the form of a bowl, essentially cylindrical in shape lindrique (11) of height h and maximum diameter d; loading said load into a cylindrical induction furnace (10) of height H and maximum inner diameter D in which the direction the height of said bowl is substantially parallel to the direction of the oven height; the melting of said charge by induction to obtain a metal bath liquid (2); optionally the allocation of said liquid metal. in which d is in the range 0.7 D to 0.97 D and of preference in the range 0.84 D to 0.92 D.

2. Method according to claim ! in which the diameter positioned at halfway up (h / 2) of the essentially cylindrical bowl is located at a distance from the bottom of the oven between H / 2 — H / 4 and H / 2 + H / 4.

3. Method according to claim 1 or claim 2 wherein the bowl essentially cylindrical in shape, it has an opening in its center (111).

4. A method according to claim 3 wherein the bowl of essential shape- The cylindrical part is manipulated during the loading stage by a manipulator tool (3) inserted through said opening (111).

5. A method for manufacturing an intermediate product (100, 101), such as a rolling plate, spinning billet, forging block or ingot or a bowl characterized in that it comprises: obtaining a bath of liquid metal optionally finished to the required standard by the fusion process according to any one of claims 1 to 4; optionally the filtration and / or treatment of said liquid metal (2); the formation of said intermediate product (100, 101) by casting of said Liquid metal.

6. Bowl of essentially cylindrical shape made of aluminium of height h and of maximum diameter d suitable for melting by the process according to a any of the claims | to 4.

7. Bowl according to claim 6 having at least two feet (113).

8. Bowl according to claim 6 or claim 7 wherein the bowl of essentially cylindrical in shape, it is truncated at the ends by at least a diameter (114).

9. Mold (4) for casting a bowl according to any one of the claims instructions 6 to 8.

10. Mold according to claim 9 in which the central tip (411)° allowing the opening (111) is hollowed out.

11. Mold according to claim 10 in which the central tip (411)° allowing the opening (111) is removable.

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