EP0077282A1 - Installation for the continuous treatment of liquid metals or liquid metal alloys in the form of magnesium or aluminium - Google Patents

Abstract

The invention relates to a device for the treatment of a stream of aluminum or magnesium-based liquid metal or alloy during its passage, comprising a ladle formed by an external metal casing, a refractory lining, a channel for the admission of the crude liquid metal at the rear, a nozzle for the casting of the treated liquid metal at the front, at least one internal partition leaving, with the bottom of the ladle, a space for the circulation of the liquid metal and defining a first rear compartment and at least one second front compartment opening into the casting nozzle. The ladle is fixed on a supporting cradle connected to an articulated frame relative to which the said cradle can rock forwards about a first horizontal axis passing through the casting nozzle, the articulated frame itself being connected to a fixed frame relative to which it can rock about the second horizontal axis. The first horizontal axis is approximately perpendicular to the stream of liquid metal. The second horizontal axis can be parallel or perpendicular to the first one and which includes a raisable cover, an immersion heater, an injector for agent for the treatment of the metal and a means 36 for alternately introducing and retracting the immersion heater and the injector.

Description

The present invention relates to a device for the treatment in passing of a stream of metal or liquid alloy based on aluminum or magnesium.

It is generally agreed to designate by the word "treatment" all the operations which a metal or a crude molten liquid alloy undergoes before its use in foundry, with a view to removing impurities and, in particular, dissolved gases and inclusions which would alter the properties of the cast products. These operations can be of a purely physical nature, such as filtration, or physicochemical, such as bringing them into contact with flows, or with an inert or active gas divided into very fine bubbles.

At present, the requirements of aeronautical construction, thin strips for boltages, thin sheets for electrolytic capacitors, fine wires for telephony or winding, oblige the producers of semi-finished products in metals and light alloys, to improve without quality ceases, especially since the display of analytical methods has shown that microscopic inclusions, previously considered negligible, could alter certain mechanical characteristics and increase scrap rates.

In what follows, we will agree to designate by "metal" or "liquid metal": unalloyed aluminum, unalloyed magnesium and alloys based on one or the other of these two metals.

Among the devices used for the treatment, in passing, of a stream of liquid metal, the most common are the "pockets", generally consisting of a metal container with refractory lining, whether or not provided with an external heating means , or integrated into the lining and, in most cases, divided into two compartments by a flat or circular partition. One or both of the compartments can be filled with a filtering substance often consisting of alumina granules. One of the compartments may include a means of injec tion of a gas or a mixture of inert gas (nitrogen, argon) and / or active gas (chlorine).

Mention may be made, as characteristic examples of the state of the art, of the patents US 2,840,463 (ALCOA), US 2,863,558 (ALCOA), US 3,010,712 (ALCOA), US 3,025,155 (ALCOA) ), US 3,039,864 (ALCOA), GB. 1,266,500 (BRITISH ALUMINUM C °), GB. 1367 069 (BRITISH ALUMINUM C °), US 3 870 511 (UNION CARBIDE), US 4 040 610 and US 4 047 938 (UNION CARBIDE).

However, the devices currently in use are not entirely satisfactory, both with regard to the final purity of the metal produced (content of hydrogen and of so-called "ultimate" inclusions, of the order of 5 micrometers or less), than in with regard to ease of use and handling: heating, scouring, rapid passage from an alloy to a non-alloy metal, or from an alloy to another type of alloy, emptying of pocket bottoms, change of bed filtering.

The object of the invention is a device for the treatment, in passing, of a stream of liquid metal, consisting of a pocket, comprising an external metal casing and an internal refractory lining, a chute for the entry of liquid metal at the rear and a pouring spout of the treated metal at the front, and at least one internal partition leaving with the bottom of the pocket, a space for the passage of liquid metal and delimiting a first rear compartment and at least a second front compartment opening onto the pouring spout, said pocket being fixed to a support cradle connected to an articulated frame with respect to which said cradle can tilt forward around a first horizontal axis passing substantially through the end of the spout casting, the articulated frame itself being connected to a fixed frame with respect to which said articulated frame can tilt around a second horizontal axis.

The first horizontal axis is substantially perpendicular to the direction of flow of the liquid metal in the pocket.

The second horizontal axis can be parallel or perpendicular to the first, which ensures rear or lateral tilting.

The device further comprises a means of internal heating in the pocket, removable and independent of the refractory lining. It may also be provided with means for injecting a liquid, solid, gaseous or vaporized treatment agent, and with means for alternately introducing and removing the internal heating means and the means for injecting the agent. treatment.

The internal lining comprises, in a conventional manner, a first heat-insulating layer with low thermal conductivity in contact with the external metal shell, and a refractory layer, chemically inert with respect to the metal and the treatment agents.

The bag can be provided, in the second compartment, with means for filtering the liquid metal.

It also includes a waterproof, removable cover, part of which is separable or movable to allow the removal of the dross formed during treatment.

• La figure 1 est une vue d'ensemble, en perspective de trois-quart avant, sur laquelle une colonne a été partiellement coupée pour la clarté du dessin.
• La figure 2 est une coupe verticale du dispositif de double basculement.
• La figure 3 est une vue en plan de la poche et du dispositif de double basculement.
• La figure 4 est une vue latérale, partiellement coupée.
• Les figures 5 et 6 représentent un injecteur rotatif qui peut être utilisé comme moyen d'injection d'un agent de traitement.

Figures 1 to 6 illustrate, but are not limited to, the device which is the subject of the invention:

• Figure 1 is an overall perspective view of three-quarter front, on which a column has been partially cut for clarity of the drawing.
• Figure 2 is a vertical section of the double tilting device.
• Figure 3 is a plan view of the pocket and the double tilt device.
• Figure 4 is a side view, partially cut away.
• Figures 5 and 6 show a rotary injector which can be used as a means of injecting a treatment agent.

Figure 1 shows the different elements constituting the entire device. The following figures show the construction details.

The platform (1) is a rigid element which constitutes the main fixed chassis. Preferably, it includes setting screws (2) for adjust the horizontality of the assembly. The pocket itself (3) is supported by the cradle (4) formed essentially of two arms on which the pocket (3) comes to bear by lugs (5). It is fixed by removable means such as bolts. Two screw stops (6) make it possible to adjust the horizontality of the pocket in the working position. The cradle (4) is articulated, relative to the articulated frame (7), on the two bearings (8) whose common axis (9) passes substantially through the pouring spout (10).

The chassis (7) is articulated by the two bearings (11) on two support elements (12) rigidly connected to the platform (1).

The axis of rotation (13) of the articulated frame (7) relative to the support elements (12) is horizontal and parallel to the axis of rotation of the cradle. This arrangement is not compulsory and the axis of rotation (13) of the articulated frame could also be perpendicular to the axis of rotation (9) of the cradle, owing to the fact that the two rotational movements are controlled, independently of one of the other, by a double system of pairs of jacks (14) and (15).

The first pair of jacks (14), which acts on the cradle (4), makes it possible to obtain a front tilting of the pocket in (3 '), (dotted line, FIG. 2), around an axis passing through the pouring spout (10). In this way, a complete emptying of the metal contained in the pocket is very quickly obtained. The slope of the front part (16) of the refractory lining (17) makes it possible to obtain this total emptying without raising the pocket to the vertical, which reduces the required stroke of the jack (14). The second pair of jacks (15), which acts on the articulated frame (7), makes it possible to obtain a rear tilting of the pocket to a substantially vertical position (3 "), (FIG. 2 in dotted lines). thus, in an uncluttered work area, since it is located outside the casting area, carefully clean the ladle, which is necessary when successively treating two incompatible metals or alloys and between which one wants to avoid any mixing, as well as at the end of casting, which guarantees, in all cases, the best possible quality of the treated metal. This tilting also makes it possible to inspect and possibly repair the internal lining (17) and the internal partition (18). The tilting of the articulated frame (7) could also, as indicated above, take place around a horizontal axis perpendicular to the front tilting axis (9). There would then be a lateral tilting, which would fulfill the same function and could be advantageous depending on the layout of the foundry workshop, if the lateral zone was more accessible than the rear zone of the treatment device.

The internal lining (17) supported by the metal carcass (19) is preferably made up of two parts: an external part in contact with the metal carcass, which is of low thermal conductivity and acts as an insulator, and a part internal, in contact with the liquid metal, which is refractory and chemically inert with respect to the liquid metal and the various treatment agents. The internal partition (18) delimits a first compartment (20) located at the rear of the pocket and a second compartment (21) located at the front, the terms "rear" and "front" being taken with respect to the direction of circulation of liquid metal which enters through the chute (22) and flows through the pouring spout (10). In the case shown, the inlet chute (22) is arranged on one side of the rear compartment. If the solution of lateral tilting of the pocket had been chosen, the chute could be arranged either laterally, and on the side opposite to the tilting, or at the rear of the pocket.

The connection between the pouring spout (10) and the flow channel (23) is effected by the usual means known to specialists in the foundry of light alloys.

The internal partition (18) is preferably made of a material which is heat conducive, for a reason which will be specified a little later. It is preferable that it be removable without damaging the lining (17).

In the case shown, there is only one internal partition. However, it is not excluded that the pocket, object of the invention, comprises several partitions arranged in baffles delimiting several compartments which the liquid metal passes through successively, each compartment provided same or different treatment: filtration, injection of inert or active gas, mixing with a flow, etc ...

The pocket (3) further comprises a cover (24) also constituted by a metal frame and a refractory and heat-resistant lining.

Preferably, the part (25) of the cover, which surmounts the rear of the pocket, is removable or liftable, for example by rotation about the axis (26). To facilitate the recovery of dross formed during treatment, the rear part (27) of the lining (17) is slightly inclined so that, the movable part (25) of the cover being raised, these dross are easily removed with a simple manual scraping tool, without disturbing the treatment.

The cover rests on the pocket in a substantially sealed manner, thanks to the seals (28). In this way, the evacuation of gaseous products possibly injected into the metal is carried out only by the inlet chute (22), which facilitates their capture.

The cover (24) is provided with an orifice (29) intended for the introduction into the pocket either of a heating means, or of a means of injection into the liquid metal of a treatment agent, the term "agent" designating any solid, liquid, gaseous or vaporized product used to treat the metal, in the sense defined above.

In the case of a large capacity pocket, the cover (24) may include two or more orifices (29) for the alternating introduction of several heating or injection means.

During the tilting operations of the pocket, the cover (24) is released, for example, by raising into position (24 ').

In the case shown, the cover is provided with a stirrup (30A) connected to a mechanical or hydraulic lifting device, of any known type, which finds its place in the lifting column (31) secured to the platform (1).

Given the well-known drawbacks of external heating devices or integrated into the internal lining, the device, object of the invention, was provided with internal heating by immersion heater, removable and independent of the internal lining, which had never was implemented in the foundry pockets existing to date. The active element of the immersion heater (32) is, for example, an electrical resistance protected by a sheath which is good conductor of heat, resistant to thermal shocks, waterproof and chemically resistant to molten metal.

In the case of a bag having a capacity of 600 kg of liquid aluminum, a 20 kW immersion heater provides preheating of the empty bag from 20 to 700 ° C. in about thirty hours, and maintaining the temperature of the pocket, full or empty, around 750 ° C with adequate regulation. It can also heat the metal at a speed of around 60 ° C / hour. Thanks to the good thermal conductivity of the partition (18), the heating also acts effectively on the second compartment (21).

The support of the immersion heater (32) which, moreover, ensures the passage and protection of the power cables and temperature sensors, comprises a conical sleeve (33), the conicity of which cooperates with the conicity of the orifice (29) of the cover, to ensure both precise positioning and a tight connection.

Similarly, the treatment agent injection device (34), whatever it may be, comprises a conical sleeve (33) which performs the same function.

In order to ensure rapid exchange between the immersion heater (32) and the injector (34), these two members are arranged on a manipulator (36) supported by the column (37). In the case shown, which is given only by way of non-limiting exemplary embodiment, the manipulator is connected to a mechanical or hydraulic lifting means, along the column (37) which can, when the manipulator ( 36) is in the high position (36 '), rotate around its axis to ensure the exchange and the return to the working position of the immersion heater (32) or of the injector (34).

The two columns (31) and (37) are preferably connected by an easily removable horizontal crosspiece (38) for possible removal of the pocket (3) by an external handling means such as a monorail hoist, overhead crane, etc.

The design of the device, object of the invention, ensures very great flexibility of use, while allowing the implementation and the combination of the various known processes for the ultimate purification of aluminum and alloys based on aluminum, magnesium and magnesium alloys.

It is perfectly suited to all gas injection devices, inert and / or active, fixed (porous or perforated injection rods) or rotary, such as those described, for example, in French patent application No. 80 22,193, which claims a rotary agitator whose lower end rests, when stationary, on a gas injection plug placed at the bottom of the bag and which, under the action of the pressure of the gas emitted by the plug is raised and, thus supported by a fluid bearing, can, under the effect of an external couple, freely rotate around its axis and let escape by the space which separates it from the stopper, a multitude of gas bubbles regularly dispersed , or, in French patent application No. 81 16 735, which claims a rotary device for dispersing gas (FIGS. 5 and 6), for the treatment of a bath of liquid metal contained in a container comprising a rotor ( 39) in the form of a cylinder fitted with paddles (40) plunging into the bath, connected a hollow drive shaft (41) for supplying gas. The rotor is pierced with pairs of channels (42), each pair comprises a channel (43) which is used for the passage of the liquid, and the other (44) for the passage of the gas, each of the couples opens separately at the same point (45 ) from the lateral surface of the cylinder so that a fine liquid-gas dispersion is formed there, which is then distributed in the bath by means of the vanes (40).

Similarly, the injector can be supplied with treatment agent, from the device claimed in French patent application no. 81 06 134 and which comprises a reservoir of halogenated product liquid at room temperature connected to the inlet at a metering micropump, the output of which flows on a vaporizer provided with a heating means, and connected to a source of inert gas, provided with a pressure and flow control means, and a connecting pipe between the vaporizer and the 'injector (34). The metal being treated in the first compartment can, in addition, and in a known manner, receive a cover of liquid or solid halogenated flux at the treatment temperature.

Similarly, the second compartment can receive different filtration devices such as: alumina beads of adequate particle size, or flux grains.

The holding in place and the exchange of such filtering beds based on solid flux grains can be carried out according to the interchangeable cartridge technique described in French patent 2,463,816 (SERVIMETAL). In such a case, the wall, or part of the wall of the cartridge can act as a partition between the first and the second compartment.

Filtration of the metal can also be obtained by the use of filter blocks in sintered flow, described in French patent 2,446,862 (SERVIMETAL).

EXAMPLE OF IMPLEMENTATION

Two treatment bags according to the invention were produced, in accordance with FIGS. 1 to 6.

The first has a capacity of 600 kg of liquid aluminum and is intended to process up to 10 tonnes / hour of metal. At this rate, the average duration of stay of the metal in the pocket is of the order of three and a half minutes. The injector used is the rotor with coupled channels, described above, rotating at 150 rpm (Figures 5 and 6). An argon-chlorine mixture containing 5% chlorine was injected, at a rate of 4 Nm 3 / hour for a flow rate of 6 tonnes / hour of metal to be treated.

The second has a capacity of 2,400 kg of liquid aluminum and can process up to 40 tonnes / hour of metal. It includes two rotary injectors with coupled channels, delivering a total of 16 Nm3 / hour of the same argon-chlorine mixture with 5% chlorine.

Tests were carried out on a 2014 alloy (designation Aluminum

Association and standard AFNOR A 02 102) having the following composition:

The assays of hydrogen on this metal gave the following results:

This level of 0.10 cm3 / 100 grams is currently considered as the desirable limit for particularly demanding uses such as aeronautical structures.

BENEFITS PROVIDED BY THE INVENTION

The processing bag, object of 1 .invention, has a number of decisive advantages over the bags currently in use.

• 1 - Vidange totale du métal contenu dans la poche, par simple basculement avant en fin de coulée, donc sans perte de métal et sans le moindre risque de mélange avec le métal de l'opération suivante .
• 2 - De la même façon : changement instantané de métal ou d'alliage sans aucune autre manoeuvre que le basculement avant, ce qui permet de travailler en coulées continues ou discontinues même avec des alliages successifs incompatibles entre eux.
• 3 - Facilité de décrassage en cours de traitement par la partie amovible du couvercle, ce qui est particulièrement utile dans les coulées continues de longue durée.
• 4 - Facilité de nettoyage en fin de traitement par basculement arrière (ou latéral, selon le cas) de la poche vide, ce qui permet d'éliminer tous résidus de crasses et de métal solidifié, qui risqueraient de polluer la charge suivante.
• 5 - Système de chauffage indépendant de la poche, ce qui autorise l'echange ou la réparation sans perturber les opérations en cours (l'échange du thermoplongeur demande moins d'une heure).
• 6 - Possibilité de surchauffer rapidement le métal en démarrage de coulée.
• 7 - Le chauffage interne permet d'utiliser une épaisseur importante de réfractaire et de calorifuge, Let d'obtenir ainsi une excellente isolation thermique de la cuve. Le gain d'énergie est très important, surtout le chauffage est piloté par une régulation précise.
• 8 - Pas de limitation dans le choix du type d'injecteur d'agent de traitement : tous les types, statiques ou rotatifs, actuellement connus, sont adaptables sans difficultés.
• 9 - Permutation rapide de l'injecteur et du thermoplongeur, ce qui permet d'utiliser la fonction voulue au moment voulu.
• 10- Enlèvement et remise en place rapides du couvercle, que ce soit pour inspection visuelle, décrassage, adjonction de flux, etc...
• 11- Peu de risque de corrosion par l'air et les agents de traitement du fait de la conception simple et du choix des matériaux.
• 12- Captage aisé des effluents gazeux à la goulotte d'entrée.

It offers the following possibilities:

• 1 - Total emptying of the metal contained in the pocket, by simple tilting before at the end of casting, therefore without loss of metal and without the slightest risk of mixing with the metal of the following operation.
• 2 - In the same way: instant change of metal or alloy without any other maneuver than the tilting before, which allows to work in continuous or discontinuous casting even with successive alloys incompatible with each other.
• 3 - Ease of scouring during treatment by the removable part of the cover, which is particularly useful in long-term continuous casting.
• 4 - Ease of cleaning at the end of treatment by tilting back (or lateral, as the case may be) the empty bag, which eliminates any residue of dirt and solidified metal, which could pollute the next load.
• 5 - Heating system independent of the pocket, which allows the exchange or repair without disturbing the operations in progress (the exchange of the immersion heater requires less than an hour).
• 6 - Possibility of quickly overheating the metal at the start of casting.
• 7 - Internal heating makes it possible to use a large thickness of refractory and heat-insulating, Let obtain an excellent thermal insulation of the tank. The energy gain is very important, especially the heating is controlled by precise regulation.
• 8 - No limitation in the choice of the type of treatment agent injector: all types, static or rotary, currently known, are adaptable without difficulty.
• 9 - Quick changeover of the injector and the immersion heater, which allows the desired function to be used at the desired time.
• 10- Quick removal and replacement of the cover, whether for visual inspection, scouring, addition of flux, etc ...
• 11- Little risk of corrosion by air and treatment agents due to the simple design and choice of materials.
• 12- Easy capture of gaseous effluents at the inlet chute.

It is not unnecessary to specify that the device, object of the invention, lends itself particularly well to full automation, all maneuvers of tilting front and rear, lifting and fitting the cover, lifting, swapping and laying the immersion heater and the injector, preheating, temperature maintenance, etc. which can be programmed, with the various safety features and prohibitions necessary, and centralized on a console placed at a distance, which also controls the hydraulic power station controlling the various tilting and raising / lowering cylinders for the cover, the immersion heater and the injector.

Finally, that the invention has been described as applicable to the treatment of aluminum, magnesium and alloys based on one or the other of these metals, its application to other metals or point point alloys comparable merger is not excluded. Thus zinc, lead, tin, copper and copper alloys such as bronzes and brasses, or cuproaluminiums can undergo purification and refining treatments in the device which is the subject of the present invention.

Claims (12)

1 / Device for the treatment, in passing, of a stream of metal or liquid alloy, based on aluminum or magnesium, comprising a pocket (3) constituted by an external metallic casing (19), an internal refractory lining ( 17), a chute (22) for the entry of the raw liquid metal at the rear, a spout (10) of the liquid metal treated at the front, and at least one internal partition (18) leaving, with the bottom of the pocket, a space for the circulation of liquid metal, and delimiting a first rear compartment (20) and at least a second front compartment (21) opening onto the pouring spout (10), characterized in that the pocket ( 3) is fixed on a support cradle (4) connected to an articulated frame (7) with respect to which said cradle can tilt forward around a first horizontal axis (9) passing through the pouring spout (10) , the articulated frame (7) being itself connected to a fixed frame (1) with respect to which it can tilt around a second horizontal axis (13). 2 / A processing device according to claim 1, characterized in that the first horizontal axis (9) is substantially perpendicular to the direction of flow of the metal in the pocket. 3 / A processing device according to claim 1, characterized in that the second horizontal axis (13) is parallel to the first axis (9). 4 / A processing device according to claim 1, characterized in that the second horizontal axis (13) is perpendicular to the first axis. 5 / A treatment device according to any one of claims 1 to 4, characterized in that it further comprises an immersion heater (32) for internal heating, removable and independent of the internal lining (17), fixed to a support (33). 6 / A treatment device according to any one of claims 1 to 5, characterized in that the internal partition (18) is made of a material which is a good thermal conductor. 7 / A treatment device according to any one of claims 1 to 6, characterized in that it further comprises at least one injector (34) of at least one liquid, solid, gaseous or vaporized treatment agent, and a means for supporting the injection means. 8 / A treatment device according to any one of claims 1 to 7, characterized in that it comprises means (36) for introducing and removing, alternately, the immersion heater and the injector. 9 / A treatment device according to any one of claims 1 to 8, characterized in that it comprises a cover (24) substantially sealed, provided with at least one orifice (29), whose shape and dimensions are adapted to the shape and dimensions of the support (33) of the immersion heater and of the support (35) of the injector so as to ensure precise positioning and a substantially sealed connection. 10 / A treatment device according to any one of claims 1 to 9, characterized in that it comprises a means for releasing the cover. 11 / A treatment device according to one of claims 9 or 10, characterized in that the cover (24) comprises above the rear part (27) of the first compartment, a part (25) movable or separable to allow the 'removal of dross formed during treatment. 12 / A treatment device according to any one of claims 1 to 11, characterized in that the second compartment comprises a means of filtration of the treated liquid metal.

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