EP0437153A1 - Process and device for continuous casting of metal matrix composite bodies reinforced by refractory ceramic particles - Google Patents

Abstract

The invention relates to a process for continuous casting intended for shaping metal matrix composite bodies reinforced by refractory ceramic particles. It consists in casting the molten metal containing the ceramic particles in a mould closed off by a movable base and consisting of an upstream hot zone (1) made from an insulating material and a downstream cooled zone (3) in which the composite solidifies, whilst producing, inside this mould, an electromagnetic stirring action ensuring mixing movements in planes containing the casting axis. This invention applies in particular to the production of plates and billets made from composite based on aluminium alloy reinforced by silicon-carbide particles. <IMAGE>

Description

Field of the invention .

The invention relates to a process for the continuous casting of a liquid composite with a metal matrix reinforced by particles of a refractory ceramic material.

These refractory ceramic materials consist of non-metallic substances, having a melting temperature higher than that of the matrix in which they are incorporated, and which are unassailable or little attackable by the molten metal of the matrix.

These are, for example, graphite, carbides, oxides, nitrides, borides of metals or certain metalloids, but also compounds such as silicates, aluminosilicates, etc.

These materials can be in the form of long or short fibers or of particles or whiskers of suitable particle size. The invention relates to the manufacture of composites based on particles or whiskers.

• des procédés ressortissant de la métallurgie des poudres dans lesquels le métal mélangé aux particules est mis en forme,fritté,puis éventuellement filé ou forgé.
• des procédés ressortissant des techniques de fonderie dans lesquels les particules sont mélangées au métal en fusion.

The production of these particulate metal matrix composites can be done by two types of process:

• processes emerging from powder metallurgy in which the metal mixed with the particles is shaped, sintered, then optionally spun or forged.
• processes arising from foundry techniques in which the particles are mixed with the molten metal.

The invention relates to this second type and in particular to a process for the continuous casting of composites prepared according to a foundry technique.
The main problem encountered in the processes for the preparation of metal matrix composites (which will be referred to below as CMM) is that of wetting of ceramic particles with metal, wetting which conditions the compactness of CMMs and their homogeneity. that is to say, their characteristics of use.

• on met en oeuvre dans une poche de coulée une masse déterminée d'une dispersion homogène de particules dans un bain de métal liquide,cette dispersion,qualifiée d'initiale,ayant la composition du composite à fabriquer et étant soumise à un brassage.
• on alimente en continu et avec un débit déterminé,un ou plusieurs postes de coulée à partir de la poche dont on maintient le niveau constant par addition simultanée des particules à l'état solide et du métal à l'état liquide dans une proportion correspondant à celle du CMM à fabriquer,tout en maintenant le brassage.

Many methods have been proposed to solve this problem.
One of these methods was the subject of French patent application n ° 89-16000 filed on November 27, 1989 by the applicant. This request relates to a continuous manufacturing process of a CMM reinforced by particles of a material ceramic characterized in that:

• a specific mass of a homogeneous dispersion of particles in a liquid metal bath is used in a ladle, this dispersion, qualified as initial, having the composition of the composite to be manufactured and being subjected to stirring.
• one or more casting stations are fed continuously and with a determined flow rate from the ladle, the level of which is kept constant by simultaneous addition of particles in the solid state and of metal in the liquid state in a proportion corresponding to that of the CMM to be manufactured, while maintaining the mixing.

Statement of the invention

The continuous character of the development of the CMM exposed above lends itself particularly well to continuous casting. We can thus realize a continuous manufacturing line integrating the development of CMM and its casting into semi-finished products.

The object of the invention is to propose a method and a continuous casting equipment suitable for CMM casting, that is to say in which the stirring necessary for suspending the ceramic particles in the liquid matrix continues during the casting of the semi-finished product in the still liquid part of this semi-finished product that specialists call the "swamp".

However, the process of the invention is not limited to the casting of a liquid CMM obtained by the process of French patent application 89-16000; it applies to the pouring of any liquid CMM prepared by any process .

The process consists in creating an electromagnetic stirring which ensures mixing movements characterized by the fact that they are located in meridian planes containing the pouring axis. To be able to ensure this stirring in good conditions of suspension and dispersion of the particles, the stirred area must be sufficient. For this, it is necessary to precede the "ingot mold" part as can be encountered conventionally in a continuous casting by an upstream thermally insulated part. , which constitutes a hot zone and which has the effect of increasing the volume of the marsh.

Description of the invention .

FIG. 1 represents an exemplary embodiment of the invention.
The device intended for pouring, solidifying and extracting the CMM will be described successively, then the three types of electromagnetic devices intended to ensure the mixing of the metal.

FIG. 1 and the description of the casting, solidification and three types of electromagnetic stirring devices relate to a particular embodiment of the invention: that of vertical casting. Similar devices, having the same function are found in another embodiment of the invention: that of the horizontal casting.

• a) une partie chaude réalisée en matériau isolant thermique 1 qui renferme le métal liquide 2.Le matériau isolant est du type utilisé couramment en fonderie pour la confection de goulottes et de busettes.
• b) une partie froide reliée à la partie chaude de manière étanche au métal liquide.Cette partie froide comprend comme élément essentiel une lingotière 3 en métal conducteur de la chaleur refroidie extérieurement.Ce refroidissement peut être assuré par un film de fluide de refroidissement ,généralement de l'eau, 5 provenant d'une boite à eau 6,tel que représenté sur la figure 1.Il peut aussi être assuré directement par une chambre d'eau accolée de manière connue à la lingotière.Dans ce dernier cas,on formera de préférence des jets ou une lame d'eau au bas de l'ensemble chambre d'eau-lingotière qui viendront assurer par ruissellement le refroidissement direct du produit en cours de coulée..Cette lingotière peut être munie,à sa partie supérieure d'un anneau de graphite 4 jouant un rôle de lubrifiant vis-à-vis du métal coulé,en complément d'un agent de lubrification dont il s'avère parfois nécessaire de revêtir la paroi interne de la partie aval pour faciliter la coulée de certains métaux.Suivant une technique de l'art antérieur,il est aussi possible d'amener en continu par la lingotière un agent de lubrification qui traverse l'anneau de graphite et assure ainsi une lubrification en continu.Toujours dans la perspective de lubrifier en continu,on peut,au lieu d'utiliser un anneau de graphite,insérer dans la lingotière des crayons de graphite qui débouchent sur la face interne de la lingotière et sont connectés à leur autre extrêmité à une chambre où le lubrifiant est mis sous pression.
• c) le système d'extraction constitué d'un fond obturant la partie inférieure de la lingotière au démarrage,porté dans le cas d'une coulée verticale, par un plateau animé d'un mouvement régulier vertical et vers le bas,réglable selon les alliages et le format des produits coulés.Dans le cas de la coulée horizontale,ce système est porté soit par un tapis motorisé,soit par une table à rouleaux dont l'un est motorisé,un rouleau presseur venant garantir l'entrainement.

The casting, solidification and extraction device is similar to that used for continuous casting under load (or with enhancement) of metals and in particular of aluminum. It includes:

• a) a hot part made of thermal insulating material 1 which encloses the liquid metal 2. The insulating material is of the type commonly used in foundries for making trunking and nozzles.
• b) a cold part connected to the hot part in a sealed manner to the liquid metal. This cold part comprises as essential element an ingot mold 3 made of heat-conductive metal externally cooled. This cooling can be ensured by a film of cooling fluid, generally water, 5 coming from a water box 6, as shown in FIG. 1. It can also be provided directly by a water chamber adjoining the mold in a known manner. In the latter case, we will form preferably jets or a blade of water at the bottom of the water chamber-ingot mold which will ensure direct cooling of the product during casting. This ingot mold can be provided at its upper part with a graphite ring 4 acting as a lubricant with respect to the cast metal, in addition to a lubrication agent which it sometimes proves necessary to coat the internal wall of the downstream part to facilitate the casting of certain metals. Following a technique of the prior art, it is also possible to continuously supply by the ingot mold a lubricating agent which passes through the graphite ring and thus ensures continuous lubrication. perspective of continuous lubrication, you can, instead of using a graphite ring, insert graphite pencils into the ingot mold which open onto the internal face of the ingot mold and are connected at their other end to a chamber where the lubricant is put under pressure.
• c) the extraction system consisting of a bottom closing the lower part of the ingot mold at start-up, carried in the case of vertical casting, by a plate animated with a regular vertical and downward movement, adjustable according to the alloys and the format of the cast products. In the case of horizontal casting, this system is carried either by a motorized belt or by a roller table, one of which is motorized, a pressure roller coming to guarantee the drive.

After start-up, the already solidified product serves as a mold for the solidification of the metal fed continuously and one arrives at a state of equilibrium shown in FIG. 1:
From the ingot mold develops a solidified outer envelope while inside the cast product is established a solidification front 7 having the approximate shape shown in the figure. Below this front, the metal is completely solid above, in what is called the "swamp", there is a mixture of liquid and ceramic particles.

It is with a view to ensuring a better homogeneity of the distribution of the particles within the liquid metal that an electromagnetic mixing, causing movements in the marsh along meridian planes, is added.

The electromagnetic stirring device, the combination of which with the casting device constitutes the invention is preferably one of the three described below.

The first type consists in passing a single-phase electric current of frequency lower or equal to the industrial frequency within the ingot mold constituted, at least partially by an electrically conductive material. The wall of this ingot mold must then present on all its thickness and along at least one generator an electrical insulating insert on either side of which the current leads are fixed. ingot mold plays the role of a whorl and the current flowing through it generates a magnetic field which develops electromagnetic forces generating the desired movement. The internal wall of this ingot mold must be covered with an insulating film to avoid short circuits by the cast metal. The electromagnetic forces being a function of the current intensity, we will choose for the ingot mold a metal good conductor of the current. This can be, for example copper or aluminum or their alloys for the casting of aluminum.

We can also use assemblies of different materials in which the portion closest to the upstream part is made if not in insulating material at least with a less electrically conductive material such as stainless steel. In this case, the movement of the liquid is amplified.

The insulating film may consist of an oxide layer obtained by anodization in the case of aluminum, an enamel, or a fluocarbon resin. The thickness of this film depends on the tension of the wall of the ingot mold compared to the cast metal. An oxide thickness of 1 micrometer is suitable for a voltage of 100 volts.

In the case where the ingot mold is provided with a graphite ring, this ring can be divided into at least two sectors to avoid any Joule effect in an area which one wishes to cool and a reduction in energy which would limit movements metal.

In particular, one can use a ring having an insert placed opposite the insert of the ingot mold; in this case, one also avoids the Joule effect and one can then directly hoop the ring on the internal wall of the ingot mold without having need an intermediate insulating film.

The second type of brewing device (Figure 1) consists in placing at the outside of the ingot mold at least one metal coil 9 of axis substantially parallel to the axis of the mold in which a single-phase current of frequency less than or equal to the industrial frequency is passed. This coil, electrically insulated of the wall of the mold creates a magnetic field parallel to the axis of the mold which develops electromagnetic forces causing the stirring according to arrows 10 and 11. This stirring is more or less ample depending on the intensity of the current in the coil and according to other factors such as the composition and the structure of the ingot mold. As regards the composition, it is preferable to use a material having a resistivity greater than 5 microohm.cm, for example a non-magnetic stainless steel, titanium, or a ceramic with sufficient thermal conductivity, or a composite material such as stainless steel coated with a thin layer of aluminum. i concerns the structure, it is possible, in order to reduce the intensity necessary for stirring, to divide the mold according to its generators in at least two sectors separated from each other by an electrical insulator such as mica, these sectors being joined together by stainless steel pins and insulating dowels.
All these types of ingot molds can also be lined on their internal wall in the vicinity of the hot zone with a coaxial graphite ring preferably shared along its generators in at least two sections, this in order to improve the efficiency of the electric current. for brewing.

The turns surrounding the ingot mold are designed and mounted so as to adapt to any form of ingot mold and to optimize the current-force output and the distribution of forces in the metal in order to distribute the stirring over the entire section and the height of the mold and obtain the greatest possible homogeneity of the particles within the liquid metal. This is how the turns can be moved parallel to the axis of the mold or be formed by an assembly of removable elements capable of circumscribe molds of any section equidistantly, or at different distances.These assemblies are perfectly suited for rectangular sections.

It is also possible, according to the invention, to improve the efficiency of stirring by adding around the hot zone one or more turns traversed by an electric current and supplied in series or in parallel with those of the cold zone or by a current generator of intensity, frequency and / or phase different from those of the current supplying the turns of the cold zone.

In order to channel the magnetic field created by the coil (s), the cold zone can be surrounded by magnetic yoke elements formed from metal sheets isolated from one another and situated in planes passing through the axis of the mold.

The hot zone or at least its part closest to the cold zone can be surrounded by a sheath in which circulates a gas under pressure and chemically inert vis-à-vis the cast metal; it is then found that the cast product has a better surface condition.

The third type of mixing device consists of one or more inductors supplied with polyphase current surrounding the entire casting device, hot zone and cold zone. In principle, any type of current with n phases can be used; in practice we will obviously use the three-phase current: this is what is illustrated in figure 2. In this figure, six successive windings: A, B, C, D, E, F have been represented from top to bottom of the figure These windings are placed in planes perpendicular to the casting axis. They are supplied in a similar way to that of the supply of linear induction motors respectively by phases 1, -2, 3, -1, 2. , -3 so as to create an ascending, descending or periodically ascending then descending vertical sliding field, in the order in which the three phases are supplied. classic, we generally use a winding length which is a multiple of the pole pitch, the pole pitch being the length of the three windings of the elementary sequence 1, -2.3. This means in practice that we will use 6, 9, 12 , 15 .... windings but nothing in theory prohibits cutting a sequence in the middle. In addition, means are known to those skilled in the art of electrical engineering consisting in using particular windings at the ends in order to Eliminate side effects in linear motors. The interaction of this sliding field with the currents induced in the metal generates forces which generate movements in planes passing through the axis of the ingot mold and therefore of the cast product. are shown schematically in FIG. 2 by the arrows 10 and 11.

It is clear that these movements allow the entrainment of ceramic particles embedded in the still liquid metal towards the warmer upper part of the marsh, which ensures good homogenization of the ceramic particles.

• 1°) de façon classique avec des bobinages sous forme de galettes en fil de cuivre ou en tube de cuivre refroidi,les différentes galettes étant superposées et de préférence placées dans les encoches d'une culasse magnétique feuilletée 12 destinée à canaliser les lignes de force du champ magnétique.(figure 3 ).Les feuilles métalliques,isolées électriquement les unes des autres,sont situées dans des plans passant par l'axe du moule.Dans le cas où une chambre est accolée à la lingotière pour assurer le refroidissement de celle-ci,on peut placer les bobinages à l'intérieur de cette chambre.Ils sont alors efficacement refroidis.
• 2°) selon l'invention telle que représentée sur la figure 4:
  Le bobinage est constitué de disques minces d'épaisseur de l'ordre du mm en métal bon conducteur,du cuivre par exemple.Chaque disque 13 en forme d'anneau et muni d'une fente 14 constitue une spire du bobinage(figure 4a).Pour constituer le bobinage,on empile les disques en décalant deux disques successifs d'un angle donné.Une feuille d'isolant 15 est interposée entre deux disques de cuivre successifs sauf dans la zône entre les fentes de ces deux disques successifs.Il y a donc dans cette zône une plage de contact assurant la liaison électrique entre deux disques successifs et la continuité du bobinage.(figure 4b).

The three-phase inductors A to F described above can be produced in two ways:

• 1) in a conventional manner with coils in the form of wafers made of copper wire or of cooled copper tube, the different wafers being superimposed and preferably placed in the notches of a laminated magnetic yoke 12 intended to channel the lines of force of the magnetic field. (Figure 3). The metal sheets, electrically isolated from each other, are located in planes passing through the axis of the mold. In the case where a chamber is attached to the mold to cool the one You can place the coils inside this chamber and they are effectively cooled.
• 2) according to the invention as shown in FIG. 4:
  The winding is made up of thin discs with a thickness of the order of mm made of a good conductive metal, for example copper. Each disc 13 in the form of a ring and provided with a slot 14 constitutes a turn of the winding (FIG. 4a) .To constitute the winding, the discs are stacked by shifting two successive discs by a given angle. An insulating sheet 15 is interposed between two successive copper discs except in the area between the slots of these two successive discs. therefore has in this zone a contact pad ensuring the electrical connection between two successive discs and the continuity of the winding (FIG. 4b).

To ensure the cooling of the copper disks, two solutions have been devised according to the method of cooling the ingot mold.
In the case of cooling of the ingot mold by a film of water, the windings according to the invention described above are placed in an annular water chamber surrounding the upstream and downstream parts and leaving the passage for the water film at level of the ingot mold. A half-section of this chamber is shown in FIG. 5: The chamber consists of an inner wall, cylindrical or prismatic, depending on the shape of the cast product, preferably in insulating or weakly conductive material of the electricity, but in any case non-magnetic 16 and an external wall, also with cylindrical or prismatic internal surface, which may consist of a magnetic yoke 12.
The water chamber is closed at its upper and lower parts by two pieces 18 and 19 joined together by a threaded tie rod 20 whose role is also to ensure the tightening of the discs forming the winding by means of two nuts 21 and 22. Its central part, in contact with the copper discs is insulated.
A water inlet 23 and an outlet 24 are arranged respectively at the bottom and at the top of the chamber. The stacks of copper discs 13 and of insulator 15 are arranged inside the chamber. The copper discs and d insulation are drilled with holes, judiciously distributed to constitute the cooling conduits 25 and allow the passage of the tie rods.

If the ingot mold is cooled by a water chamber, we can take advantage of this solution by placing the coils directly in this chamber (Figure 6)
The internal wall of the chamber is in this case the ingot mold itself 26 which is coated upstream (hot part) with a thermally insulating material 27 and downstream (cold part) with a graphite ring 28. solid part 29 of the product during casting delimited by the front 30. The water which arrives at 31 serves not only to cool the windings 32 by means of the holes 33, and the ingot mold by passing through the gap 34, but also to form the blade of water 35 which trickles over the product 36. A valve 37 located on the output circuit 38 of the winding cooling makes it possible to control the respective quantities circulating in each of the passages. The rest of the technology is similar to what has been described for figure 5.

Example

• la lingotière était surmontée d'une zône chaude réalisée d'un anneau en matériau isolant MONALITE de hauteur 70 mm.
• la lingotière était entourée d'une spire alimentée sous une tension de 6,3 volts.
• la vitesse de coulée était de 200 mm/minute.

A 75 mm diameter billet of AS₇G₀ alloy _, 6 containing 15% by volume of SiC particles of approximately 10 micrometers was poured according to the method described above:

• the ingot mold was surmounted by a hot zone made of a ring in MONALITE insulating material, height 70 mm.
• the ingot mold was surrounded by a coil supplied with a voltage of 6.3 volts.
• the casting speed was 200 mm / minute.

Under these conditions, the billet obtained exhibited, with the exception of the extreme periphery, which is conventional in continuous casting of aluminum alloy, a homogeneous structure with good dispersion of the particles within the matrix, whereas '' in the absence of electromagnetic stirring according to the invention described, wide ranges of matrix without particles, these ranges up to 200 micrometers, have been observed.

A piece of this billet was peeled and then spun to form a bar with a diameter of 20 mm. In this bar were taken test pieces for mechanical tests which, after quenching and tempering (state T6) gave the following results:
Modulus of elasticity: 97 GPa
Yield strength at 0.2% elongation: 312 MPa
Breaking load: 374 MPa
Elongation at break: 6%

Claims (33)

Process for the production by continuous casting of semi-finished products in metal matrix composite reinforced by particles of refractory ceramic material into which the liquid metal containing the ceramic particles is poured into a mold closed at its downstream part by a movable bottom and consisting of two parts of the same axis:

an upstream part called the hot zone (1) whose wall is made of thermal insulating material at least on its internal face,
a downstream part, the ingot mold (3), the wall of which, made of thermal conductive material, is cooled by a cooling fluid (5) so as to cause it to form a solid crust and a solidification front ( 7) allowing the gradual extraction of the composite product using the movable bottom,
characterized in that:
is applied to the entire area located upstream of the solidification front and which contains the mixture of liquid metal and particles electromagnetic stirring ensuring mixing movements located in meridian planes containing the axis of the casting. A method according to claim 1 characterized in that the metal matrix is an aluminum alloy. Method according to one of claims 1 or 2 characterized in that the continuous casting takes place vertically. Method according to one of claims 1 or 2 characterized in that the continuous casting takes place horizontally. Method according to one of claims 1 to 4 characterized in that the liquid metallic composite which is poured into the continuous casting mold comes from a casting ladle fed simultaneously and continuously with liquid metal and solid ceramic particles in determined proportion, and in which an energetic mixing is practiced. Method according to one of claims 1 to 5 characterized in that the movement is obtained by passing a single-phase electric current of frequency less than or equal to the industrial frequency in the ingot mold whose wall has over its entire thickness and at least following a generator an insert made of an electrically insulating material on either side of which are fixed current leads, the mold being coated internally with an electrically insulating film. Method according to one of Claims 1 to 5, characterized in that the movement is obtained by means of at least one metal coil placed outside the mold whose axis is substantially parallel to the axis of the mold and traversed by a single-phase current of frequency lower or equal to the industrial frequency. A method according to claim 7 characterized in that one or more turns are parallel to the axis of the mold. Method according to claim 7, characterized in that the distance of the turn (s) is adjusted relative to the external wall of the mold. Method according to one of claims 1 to 4 characterized in that the electromagnetic stirring is obtained by a series of inductors consisting of annular coils having the axis of the mold axis, arranged around the hot and cold zones of the mold and supplied with polyphase current with a phase order such as established inside the mold a sliding field parallel to the axis of the mold moving in one direction or the other or alternately in one direction then in the other, generating electromagnetic forces which drive the liquid composite in movements in meridian planes passing through l axis of the mold and thus ensuring a homogeneous distribution of the particles within the liquid metal. Method according to one of Claims 1 to 10, characterized in that a gas is injected under pressure at the level of the cold zone. Device for the continuous casting of composite products with a metal matrix comprising a mold closed at its downstream part by a movable bottom and consisting of two parts with the same axis:
an upstream part, called hot zone (1) whose wall is made of thermal insulating material at least on its internal face
a downstream part, known as the cold zone (3) whose wall, made of thermal conductive material is cooled by a cooling fluid (5), a system for moving the movable base allowing the gradual extraction of the product characterized in that are arranged around the hot and cold zones of the mold, electromagnetic stirring means ensuring mixing movements located in meridian planes containing the pouring axis. Device according to claim 12 characterized in that the stirring means consists of the mold itself, the wall of which has over its entire thickness and along at least one generator an insert of material insulating electricity from both other of which are fixed current leads, said part being coated internally with an electrically insulating film. Device according to claim 13 characterized in that the internal wall of the mold is covered over its entire periphery and at least in the vicinity of the area hot of a graphite ring of the same axis as said zones. Device according to claim 14 characterized in that the graphite ring is divided along its generatrices in at least two sectors. Device according to claim 12 characterized in that the stirring means consists of at least one metal turn placed outside the mold whose axis is substantially parallel to the axis of the mold. Device according to claim 16 characterized in that the ingot mold consists of a material having a resistivity greater than 5 microohm.cm. Device according to claim 16 characterized in that the mold is divided along its generators into at least two sectors separated by an electrical insulator. Device according to claim 16 characterized in that the ingot mold is constituted by the assembly of different materials. Device according to one of claims 13 to 19 characterized in that the hot zone contains at least one metallic turn supplied with electric current; Device according to claim 20 characterized in that the turn is connected to the electrical supply of the cold zone. Device according to claim 12 characterized in that the stirring means consists of a series of inductors consisting of annular coils having the axis of the mold axis, arranged around the hot and cold zones of the mold and supplied with polyphase current with a order of the phases such that a sliding field is established inside the mold parallel to the axis of the moving mold alternately in one direction then in the other, generating electromagnetic forces located in meridian planes passing through the axis of the mold. Device according to claim 22 characterized in that the windings are supplied with three-phase current. Device according to either of Claims 22 and 23, characterized in that the total length of the windings is a multiple of the pole pitch. Device according to one of claims 12 to 24 characterized in that the cooling system of the downstream part consists of a film from a water box. Device according to one of claims 12 to 24 characterized in that the cooling system of the downstream part consists of a water chamber attached to the ingot mold and forming at its base jets or a layer of water coming to run on the product poured. Device according to one of claims 22 to 24 characterized in that the coils are produced in the form of superposed wafers of copper wire or of cooled copper tube. Device according to claim 27 characterized in that the wafers are placed in the notches of a laminated magnetic yoke formed of metal sheets isolated from each other and located in planes passing through the axis of the mold. Device according to one of Claims 22 to 24, characterized in that the windings consist of thin annular metal discs, preferably made of copper, each of them being provided with a radial slot, these discs being stacked with each successive disc. an offset of a given angle of the slot and with interposition between two adjacent discs of an insulating sheet except in the area between the slots of two neighboring discs so as to create a contact area between these two discs and thus ensure the continuity of the winding. Device according to Claim 29, characterized in that the coils thus formed are placed inside a chamber traversed by a circulation of water, of annular shape surrounding the casting mold, the inner cylindrical wall of which is an electrical insulator, provided with means for clamping the stack of copper discs and insulation sheets and in that these copper discs and insulation are pierced with aligned holes allowing the circulation of the cooling water. Device according to Claim 30, characterized in that the external cylindrical wall of the chamber consists of a magnetic yoke formed of metal sheets isolated from each other and situated in planes passing through the axis of the mold. Device according to claims 26 and 27 characterized in that to ensure their cooling the coils are placed inside the water chamber attached to the mold. Device according to one of Claims 29 to 31, characterized in that the chamber intended for cooling the stacks of copper discs and of insulation is constituted by the water chamber intended for cooling the cast product, the internal wall of which is the ingot mold itself coated upstream with a thermal insulating material.

Images