EP0153205B1 - Process and device for elaborating metallic and semi-metallic thin strip - Google Patents

Abstract

The invention relates to the preparation of especially metallic or semi-metallic bands or sheets, particularly with a microcrystalline or amorphous structure. According to this process, an electrically conductive molten material is made to flow from a tank through a nozzle, to form a strip of substantially rectangular cross-section, which is subsequently solidified. According to the invention, the form of the strip of liquid material is stabilized, after it has been shaped and before solidification, as a result of a mechanical surface effect induced by an alternating magnetic field.

Description

The present invention relates to methods and devices for the preparation of ribbons according to the preambles of the independent claims 1 and 11, and more particularly of thin metallic or semi-metallic ribbons, in particular such ribbons having a microcrystalline or amorphous structure.

The simplest method for manufacturing such thin metallic ribbons consists in projecting a jet of liquid metal onto a mobile substrate such as the surface of a metallic roller rotating at a circumferential speed greater than 10 m / second. This process is designated by the English expression "meit-spinning". The major problem to be solved concerns the shape stability of the jet during its impact and its solidification on the substrate due to the relatively high impact speed, notably increased by the acceleration of gravity. It is moreover impossible to produce by this method ribbons of width greater than 1 cm.

A process is known which is described in particular in document FR-A 2 368 324 (7 731 659). According to this method, the liquid metal is made to flow through a slit whose width varies from 0.2 to 1 mm and whose length can be several centimeters. This slot is placed at a distance from the mobile substrate which is less than 1 mm, and most often of the order of 0.1 mm, which overcomes the drawback of the first method mentioned above since the substrate on which the metal solidifies is at a very short distance from the slot through which the liquid metal flows. However, this method also has serious drawbacks: it requires very specific and very severe conditions with regard to the machining and the surface condition of the lips delimiting the slot. These lips are subject to significant wear due to the ripple effect which is exerted on the metal in the immediate vicinity of these lips. Furthermore, it is also necessary for the wheel which constitutes the substrate on which the metal solidifies to have very tight dimensional tolerances in order to be able to obtain a strip of roughly constant thickness, since this is the distance between the lips and this substrate which partly determines the thickness of the ribbon.

Document FR-A 2 525 508 describes a process according to which a jet of liquid metal of circular section is deformed by application of a magnetic field, until it takes the form of a ribbon or a blade parallel to this. field. However, this process requires a minimum forming time during which the magnetic field must act on the initial section of the metal, against the surface tension of the liquid, to deform this section until the desired final shape is obtained.

During this time, the liquid metal is subjected to the action of gravity, so that the formed blade reaches its useful width outside the zone of the magnetic field precisely when the maximum stabilizing action of the field would be necessary to maintain it in l 'state. In addition, the blade thus formed can only have a limited width taking into account the rapid decrease of the magnetic fields in the air.

• a) une instabilité due aux vitesses différentes du fluide constituant la lame et de l'atmosphère ambiante. Cette instabilité (Kelvin-Helmoltz) qui se développe très rapidement se manifeste par une série de rides parallèles, surtout perpendiculaires à la direction de l'écoulement qui conduisent à une modulation d'épaisseur dans le sens de la longueur de la lame.
• b) une instabilité due aux perturbations engendrées au niveau de la sortie du nez de la busette d'où s'écoule le fluide. Ces perturbations n'ont pas de direction privilégiée et dépendent de la géométrie de la busette.
• c) une instabilité due à la tension superficielle et à l'accélération gravitationnelle qui tend à réduire la largeur de la lame et à lui redonner une section circulaire. Cette instabilité se développe beaucoup moins rapidement que la précédente et se traduit par l'apparition de fuseaux successifs avec une rotation de 90° à chaque noeud (Fig. 7). Les rides sont parallèles au bord de la lame et les modulations d'épaisseur se trouvent dans une direction perpendiculaire à la vitesse du jet.

It should be noted that three types of physical problems interfere with precise control of the consistency of the liquid blade in thickness and in width during its flow in the air:

• a) instability due to the different speeds of the fluid constituting the blade and the ambient atmosphere. This instability (Kelvin-Helmoltz) which develops very quickly is manifested by a series of parallel wrinkles, especially perpendicular to the direction of the flow which lead to a modulation of thickness in the direction of the length of the blade.
• b) instability due to disturbances generated at the outlet of the nozzle nose from which the fluid flows. These disturbances have no preferred direction and depend on the geometry of the nozzle.
• c) instability due to surface tension and gravitational acceleration which tends to reduce the width of the blade and restore it to a circular section. This instability develops much less quickly than the previous one and results in the appearance of successive spindles with a rotation of 90 ° at each node (Fig. 7). The wrinkles are parallel to the edge of the blade and the thickness modulations are in a direction perpendicular to the speed of the jet.

Finally, a publication JP-A-57-17781 is known, on which the preambles of claims 1 and 11 are based, which subjects a metal strip formed on a heat exchanger substrate to the action of a magnetic field created in a zone close to the solidification point of the metal. This magnetic field has a direction perpendicular to the direction of advancement of the metal blade and the field lines pass through it. It is clearly indicated and explained that the aim is to increase the viscosity by braking action on the fluid particles, which imposes a low frequency continuous or alternating field penetrating the mass of the fluid flow.

Now, precisely, this type of field penetrating the metallic flow vein exerts an almost zero stabilizing action on the shape instabilities which have been defined previously under a, b and c and which the present invention aims precisely to combat in the formation of 'a metal strip to be projected onto the heat exchange substrate.

None of the known methods therefore makes it possible to obtain, without placing the crucible at a distance of less than 1 mm from the mobile substrate, a wide ribbon with regular dimensions. The purpose of this invention is precisely to provide an original process and device allowing the production of such a product while freeing itself from the constraints which, in the second process, analyze se above, relate to the production of the lips of the slot and the wear of the latter.

To this end, the subject of the invention is mainly a process for producing, from an electroconductive material in the form of an infusion, a ribbon, of the type in which a flow is made from a reservoir, through nozzle, a molten material, to form a blade of substantially rectangular cross section which is subjected before solidification to an alternating magnetic field producing a stabilizing effect characterized in that one exerts on the surface of at least one large face of the blade a force of pressure using the alternating magnetic field by positioning on the same side of the blade at least two poles of opposite polarity of an inductor, the field lines of the first pole being directed perpendicularly towards the blade, extending then in a direction parallel to the blade towards the second pole, then being reoriented perpendicularly to said blade in the direction of said second pole, and finally channeled to the first pole, to form a loop.

• - les lignes de champ parallèles à la lame s'étendent suivant une direction parallèle à la direction de déplacement de la lame, éventuellement en combinaison avec des lignes de champ s'étendant perpendiculairement à ladite direction de déplacement de la lame;
• - la buse a une section droite en forme de fente sensiblement rectangulaire;
• - la buse a une section droite sensiblement circulaire et la veine métallique liquide sensiblement cylindrique est préformée en forme de lame par l'action d'au moins deux champs magnétiques incidents opposés, en regard l'un de l'autre, disposés de chaque côté de la veine et la stabilisation est réalisée par un bouclage du champ tel que décrit ci-dessus;
• - une lame de grande largeur est obtenue par coalescence de lames individuelles plus étroites le long de leurs bords longitudinaux;
• - la solidification de la lame est réalisée par mise en contact de la lame stabilisée avec un substrat mobile.

According to other characteristics:

• the field lines parallel to the blade extend in a direction parallel to the direction of movement of the blade, possibly in combination with field lines extending perpendicular to said direction of movement of the blade;
• - The nozzle has a cross section in the form of a substantially rectangular slot;
• - The nozzle has a substantially circular cross section and the substantially cylindrical liquid metallic vein is preformed in the form of a blade by the action of at least two opposite incident magnetic fields, facing one another, arranged on each side. vein and stabilization is achieved by looping the field as described above;
• - a very wide blade is obtained by coalescence of narrower individual blades along their longitudinal edges;
• - The solidification of the blade is carried out by bringing the stabilized blade into contact with a mobile substrate.

The invention also relates to a device for implementing the method as defined above, of the type comprising a reservoir containing a molten material and comprising at its lower part a nozzle for the flow of this material, means for forming a blade and solidifying the latter, arranged downstream of the tank, electromagnetic means arranged in an area situated between the means for forming the blade and the solidifying means, these electromagnetic means being adapted to exert on at least one face of the blade a stabilizing effect, characterized in that the electromagnetic means comprise at least two induction coils, with parallel axes, perpendicular to the plane of the blade, these two coils being arranged on the same side of the blade, a U-shaped ferrite core housed between the coils so that each branch of the U enters the coils, these coils being supplied with alternating current so that the opposite ends of the blade of the branches of the ferrite core constitute poles of opposite signs.

• - les moyens électromagnétiques comprennent deux autres bobines d'induction d'axes parallèles, perpendiculaires au plan de la lame disposées sur l'autre face de la lame de manière symétrique des premières bobines par rapport au plan de la lame et un deuxième noyau de ferrite en forme de U logé entre les bobines de telle manière que chaque branche de U pénètrent dans lesdites autres bobines, les polarités dès extrémités en vis-à-vis des branches des noyaux de ferrite étant les mêmes;
• - les bobines d'induction situées d'un même côté de la lame sont disposées l'une au-dessus de l'autre parallèlement à la direction de déplacement de la lame;
• - les bobines d'induction situées d'un même côté de la lame sont disposées l'une à côté. de l'autre perpendiculairement à ladite direction de déplacement de la lame;
• - le dispositif comprend un réseau de bobines d'induction disposées parallèlement et perpendiculairement à la direction de déplacement de la lame et dont les pôles adjacents en regard de la lame ont des polarités alternées.
• - la buse a une section droite en forme de fente sensiblement rectangulaire,
• - la buse a une section droite sensiblement circulaire et la veine métallique liquide sensiblement cylindrique est préformée en forme de lame par passage entre les bobines supérieure des paires de bobines disposées verticalement définies ci-dessus, la stabilisation étant réalisée par le passage entre les bobines situées à un niveau inférieur,
• - les bobines sont alimentées par un courant alternatif à haute fréquence, compris entre 3 et 3000 kHz environ,
• - l'intensité du champ magnétique est comprise entre 1 et 1000 millitesla environ,
• - les moyens de solidification comprennent par exemple un substrat mobile sur lequel on dépose le matériau, sous forme de deux bandes sans fin comportant deux brins parallèles, en regard, délimitant entre eux un intervalle situé dans l'alignement de la buse et de la lame sortant de cette buse, les deux brins se déplaçant dans la même direction que ladite lame.

According to other characteristics:

• - the electromagnetic means comprise two other induction coils with parallel axes, perpendicular to the plane of the blade arranged on the other face of the blade symmetrically with the first coils with respect to the plane of the blade and a second ferrite core U-shaped housed between the coils in such a way that each U-shaped branch enters said other coils, the polarities from the ends facing the branches of the ferrite cores being the same;
• - The induction coils located on the same side of the blade are arranged one above the other parallel to the direction of movement of the blade;
• - the induction coils located on the same side of the blade are arranged one beside. on the other perpendicular to said direction of movement of the blade;
• - The device comprises a network of induction coils arranged parallel and perpendicular to the direction of movement of the blade and whose adjacent poles facing the blade have alternating polarities.
• the nozzle has a cross section in the form of a substantially rectangular slot,
• - The nozzle has a substantially circular cross section and the substantially cylindrical liquid metallic vein is preformed in the form of a blade by passage between the upper coils of the pairs of coils arranged vertically defined above, the stabilization being achieved by the passage between the coils located at a lower level,
• - the coils are supplied by a high frequency alternating current, between 3 and 3000 kHz approximately,
• - the intensity of the magnetic field is between 1 and 1000 millitesla approximately,
• the solidification means comprise, for example, a mobile substrate on which the material is deposited, in the form of two endless bands comprising two parallel strands, facing each other, delimiting between them an interval situated in alignment with the nozzle and the blade leaving this nozzle, the two strands moving in the same direction as said blade.

• la Fig. 1 est une vue schématique en perspective d'un dispositif selon l'invention,
• la Fig. 2 est une vue partielle en perspective d'une variante,
• la Fig. 3A est une vue schématique en perspective du dispositif de la présente invention dans un mode de réalisation de la seconde variante dans lequel la stabilisation est réalisée par un bouclage vertical du champ magnétique,
• la Fig. 3B est une vue schématique en élévation des inducteurs 3A vus depuis la lame et illustrant les lignes du champ,
• la Fig. 4 est une vue schématique de la disposition des pôles des noyaux de ferrite en regard de la lame dans un mode de réalisation de la seconde variante dans lequel la stabilisation est obtenue par un bouclage magnétique combiné vertical et horizontal,
• la Fig. 5 est une représentation schématique d'une troisième variante dans laquelle une lame de grande largeur est réalisée par coalescence de lames individuelles plus étroites le long de leurs bords longitudinaux, les lames individuelles étant coulées à partir de buse à section circulaire, puis préformées et stabilisées selon la variante des Fig. 3 et 4,
• la Fig. 6 est une vue schématique illustrant un mode de mise en contact avec le substrat mobile,
• la Fig. 7 illustre un phénomène de modification physique d'une lame métallique formée par effet de la tension superficielle.

The invention will be described below with reference to the appended drawings given solely by way of example and in which:

• Fig. 1 is a schematic perspective view of a device according to the invention,
• Fig. 2 is a partial perspective view of a variant,
• Fig. 3A is a schematic perspective view of the device of the present invention in an embodiment of the second variant in which stabilization is achieved by vertical looping of the magnetic field,
• Fig. 3B is a schematic elevation view of the inductors 3A seen from the blade and illustrating the lines of the field,
• Fig. 4 is a schematic view of the arrangement of the poles of the ferrite cores facing the blade in an embodiment of the second variant in which the stabilization is obtained by a combined vertical and horizontal magnetic loop,
• Fig. 5 is a schematic representation of a third variant in which a very wide blade is produced by coalescence of narrower individual blades along their longitudinal edges, the individual blades being cast from a nozzle of circular section, then preformed and stabilized according to the variant of FIGS. 3 and 4,
• Fig. 6 is a schematic view illustrating a method of contacting the mobile substrate,
• Fig. 7 illustrates a phenomenon of physical modification of a metal blade formed by the effect of surface tension.

It should be noted before defining the inductors according to the present invention, capable of providing an adequate geometry of the magnetic fields, that the effect of an alternating magnetic field of given frequency on the stability of a plate of liquid electroconductive material is to oppose disturbances which would tend to separate the faces of the blade from their geometric position of plane and parallel jet. This stabilizing effect is selective with respect to disturbances insofar as only the waves whose wrinkles are perpendicular to the direction of the magnetic field are reduced, since it is zero for disturbances whose wrinkles are parallel to the magnetic field. Finally, it should be noted that this effect is all the more important the higher the frequency of the alternating magnetic field.

The frequency of the alternating magnetic fields used to reduce the instabilities of the blade must be such that the depth of penetration into the material constituting the liquid blade is as small as possible so as to obtain a mechanical effect located on the surface of the blade where they appear disturbances. The electrical conductivity of metals and semi-metals in the liquid state places the frequency range between 3 kHz and 3000 kHz.

The invention will be described below with reference to the manufacture of metallic, semi-metallic or amorphous ribbons, but is not limited thereto and relates to any manufacture of a ribbon from an electroconductive material.

In the diagram of FIG. 1 shows a device comprising a reservoir 11 which can contain a metallic or semi-metallic molten material. This tank is surrounded by heating means 12, for example, induction. This reservoir ends at its lower part with at least one nozzle in the form of a slot 13 whose cross section corresponds to the shape of the liquid blade that it is desired to obtain. In the example chosen, this slot may have a rectangular shape, with a width of 0.7 mm and a length of 20 mm.

Below this nozzle and at a distance which can be between 1 and 15 mm and preferably between 2 and 10 mm, there is a wheel 14 which can be driven in rotation and whose width is greater than the length of the slot 13. The surface 15 of this wheel constitutes a substrate on which the metal blade will cool very quickly. The distance between the outlet of the slot and the surface of the substrate is greater than the width of the slot and preferably greater than 1 mm. The surface of the substrate is provided so as to allow easy detachment of the solidified tape 16. It can be cooled by any suitable means (not shown) and driven with a speed of rotation such that its tangential speed at the point of reception of the molten material is compatible with that of the flow of the blade and can be of the order of 20 m per second.

In the zone included between the nozzle 13 and the receiving wheel 14, means are arranged making it possible to generate in this zone an alternating magnetic field exerting a mechanical stabilizing effect on the faces of the blade 17 of liquid material leaving the nozzle. These means comprise, in the example chosen, two coaxial coils 18 made of an electrically conductive material, for example copper, the axis of these coils being arranged parallel to the slot 13, and consequently parallel to the blade 17 and orthogonally to the longitudinal axis of the latter. The axis of the coils is even preferably contained in the plane of this blade. Both coils can be cooled, as is known in the art. A core of ferrite or equivalent material 19 which can also be cooled, is placed inside each coil coaxially to concentrate the intensity of the magnetic field towards the liquid material leaving the slot.

The coils are supplied by alternating currents of appropriate frequency, in such a way. that the ends 19a opposite the blade 17 of the opposite ferrite cores 19 are opposite poles.

For example, the two coils can be supplied with alternating currents having a frequency between 3 and 3000 kHz, for example of the order of 400 kHz, the intensity of the field produced being between 1 and 1000 millitesla.

In this example, the width of the ribbon obtained corresponds to that of the slot, ie 20 mm and its thickness is approximately 0.07 mm. It is obtained from a rectangular slot of 20.0 x 0.6 mm by contacting a substrate in the form of a wheel whose tangential speed is 20 m / s.

In the variant of FIG. 2, use is made of a pair of induction coils 28 and ferrite cores 29 arranged inside these coils. The coils are coaxial and have their common axis per pendulum to the plane of the blade 27 leaving the nozzle. The ferrite cores have a rectangular cross-section and have their ends arranged a few millimeters from the liquid metal blade.

In this case, the coils are supplied by alternating currents such that the ends 29a opposite the blade of the opposite ferrite cores are similar poles, that is to say, either both of the north poles, or both south poles.

For example, the two field coils can be supplied with alternating current with a frequency of 500 kHz. The intensity of the field can be between 1 and 1000 millitesla. The nozzle slot can have a length of the order of 45 mm and a width of 0.7 mm. The distance between the outlet of the nozzle and the substrate can be of the order of 10 mm. In this case, assuming that the speed of this substrate, in a direction perpendicular to the direction of arrival of the liquid blade is 15 m per second, we obtain a ribbon of width 45 mm and thickness of the order 0.1 mm.

In the embodiment of FIG. 3A, a blade 31 of preformed liquid metallic material is sent between a first pair of coaxial induction coils 32a, 32b placed on either side of the blade 31, so that their common axis is perpendicular to the plane of the blade.

A second pair of coaxial induction coils 33a, 33b, parallel to the first pair of coils 32a, 32b is arranged on the same vertical line and below the coils 32. A ferrite core 34a in the shape of a U is housed between the coils 32a and 33a located on the same side of the blade so that each branch of the U, respectively 35a. and 36a, enters the coils 32a and 33a

The coils 32a and 33a are supplied by alternating currents so that the opposite ends of the blade of the branches 35a and 36a of the ferrite 34a are opposite poles.

In the case of FIG. 3A, the end of the branch 35a is a north pole and the incident magnetic field lines coming from this pole are directed perpendicularly to the blade, then looped by first following a direction parallel to the blade going towards the branch 36a which is a south pole, opposite which they are reoriented perpendicular to the blade 31 and finally channeled by the U-shaped ferrite 34a to the north pole 35a.

As in the previous variants, the alternating supply current is a high frequency current similar to that previously mentioned.

On the other side of the blade, a ferrite core 34b similar to the U-shaped core 34a is inserted between the coils 32b and 33b which are supplied in such a way that the poles of the ends 35a, 35b or 36a, 36b of ferrite opposite the blade of the same pair 32a, 32b or 33a, 33b, are similar poles. In the case of FIG. 3A, 35a and 35b are north poles and 36a and 36b are south poles.

The appearance of the field lines shown diagrammatically for the same face of the blade in FIG. 3B explains the stabilizing action of the field created: the numerous field lines straight and parallel to the axis of the blade make it possible to reduce the greatest instability (Kelvin-Helmotz) due to speed; the more curved field lines reduce the other types of instability thanks to their inclination.

It is obviously possible to associate in the same vertical direction more than two induction coils to obtain a field loop over a greater length arranged vertically.

The looping which has just been explained previously for a vertical direction can, according to another embodiment of this variant, be carried out horizontally with a ferrite of similar structure in the form of U and an opposition of the poles at each end of the branches of the U next to the blade.

According to the embodiment of FIG. 4, which schematically only represents the alternation of the poles opposite the same face of the blade, a combination of vertical and horizontal looping of the magnetic field is carried out which offers the maximum stabilizing effect of the blade in all the directions of the plan. The alternation of the poles in the horizontal direction and the vertical direction is such that two adjacent poles are always opposite.

The basic configuration of FIG. 3A can be translated in a direction parallel to the blade, as described above, when the width of the latter becomes very large. By respecting the opposition of the directions of the magnetic fields created by the successive coils, it is possible to obtain an isotropic stabilizing effect, as shown in Figure 4. Indeed, the arrangement of the coils allows a diversification of the direction of the lines of fields and thus allows the stabilization of waves from different directions. This stabilization technique knows no limits as to the width of the blade to be stabilized.

In the case of the embodiment of FIG. 4, the ferrite core has the form of a mesh network analogous to a grid on each apex of the meshes from which branches extend extending close to the blade and carrying an inductor coil suitably supplied.

In addition to the stabilizing effect created by such inductors, there is an electromagnetic forming effect of electrically conductive materials. The variation of the modulus of the magnetic field over time generates currents induced on the surface of the material which interact with this field to give rise to (Laplace forces); the latter can be decomposed into two distinct forces whose ratio is proportional to the square root of the frequency (f). The greater f, the more the effect will be a pressure force on the surface of the material; the lower f, the more ef- will force a stirring force inside the liquid material. We therefore use alternating magnetic fields at high frequencies, created by inductors of geometry defined above to obtain an electromagnetic forming effect.

Thanks to this embodiment which makes it possible to widen the stabilization zone while retaining an all the more intense magnetic field, it is possible to coalesce at least two individual blades 51 and 52 shown in FIG. 5, along their common longitudinal edge 53 to obtain a blade of greater width perfectly stabilized.

This embodiment also allows the creation of a very wide blade from cylindrical jets 54 and 55 from nozzles of circular section, by preforming the blade between the induction coils greater than 32a and 32b in FIG. 3A, before stabilization. This stabilization can be obtained between a single pair of coils or between other pairs of coils placed below and next to it according to a repetitive diagram of the type described in FIG. 4.

dans laquelle µ∘ = perméabilité magnétique du vide. cr = conductivité électrique du matériau liquide. f = fréquence du courant dans les bobines d'induction.In the case of a cylindrical jet flowing between the pairs of inductors, the magnetic field created by the coils in opposition tends to repel the metal and therefore to form it in a regular blade. Note the importance of the frequency and therefore of the skin thickness 8 (depth of the action of the Laplace force within the electrically conductive material) as a function of the thickness e of the liquid plate to be formed. 8 is defined by the expression:

in which µ∘ = magnetic permeability of the vacuum. cr = electrical conductivity of the liquid material. f = frequency of the current in the induction coils.

To obtain the results according to the present invention 8 must be of the order of e and preferably <e / 2.

The blade thus formed is then stabilized by the phenomenon described above. The advantage of such an inductor lies in the fact that the coils are always very close to the metal, which is very important due to the rapid decrease in the intensity of the magnetic field in the air. A micrometric adjustment device can be associated with the two half-inductors thus allowing the approach of the latter near the blade or the slight offset relative to the formed blade thus acting as guide of the blade relative to a point of impact given.

It is possible to start from several cylindrical jets which, flowing through identical inductors, deform under the action of the magnetic field until forming juxtaposed blades which coalesce to give only one single stable blade and regular (fig. 5). Indeed, at the point of coalescence, the velocities of the fluid particles not being parallel, it follows the creation of a protuberance on the surface of the blade. This type of inductor overcomes this drawback by stabilizing the blade regularly. This forming technique also knows no limits as to the width of the blade to be stabilized.

The embodiment of FIG. 6 comprises a reservoir or crucible 61 surrounded by an induction heating device 62 and ending at its lower part by a nozzle 63 delimiting a slot of substantially rectangular shape.

The magnetic device making it possible to stabilize the shape of the liquid blade leaving this reservoir can be as described above and shown in FIG. 3A. The essential originality of this third embodiment concerns the cooling substrate. The latter is here produced in the form of two conveyor belts 64 passing over drive rollers 65a and over return rollers 65b and 65c. These two strips have two vertical strands 64a included here between the return rollers 65b, 65c and which are arranged face to face, in the extension of the slot of the nozzle 3. These two strands are therefore parallel to the liquid blade 67 leaving the nozzle and move in the same direction as this blade. The latter is thus received between the two receiving bands while being effectively maintained and the solidified tape 66 is easily extracted from the lower part of the device. Of course, the conveyor belts acting as a cooling substrate can be cooled by suitable means, not shown.

In this embodiment, the tape can have improved dimensional stability, taking into account the guiding between the two adjacent strips 64a.

• - les lèvres de la buse à partir de laquelle s'écoule le matériau liquide ne sont pas soumises aux mêmes contraintes que dans le procédé dans lequel le substrat de refroidissement se trouve très proche de la sortie de la fente, de sorte que dans le dispositif suivant l'invention, la buse peut être réalisée de façon plus simple et moins coûteuse. De plus, elle a une durée de vie bien supérieure, car elle est soumise à un érosion bien plus faible.
• Les risques d'obturation de cette buse sont également sensiblement réduits,
• - par ailleurs, la stabilité dimensionnelle de la lame liquide est assurée de façon efficacè, ce qui permet d'obtenir un ruban de dimension régulière, tant en épaisseur qu'en largeur,
• - ce résultat est obtenu par des moyens relativement simples et en maintenant la distance entre la sortie de la buse et le substrat récepteur à une valeur suffisamment faible pour que la lame liquide parvienne sur la surface de refroidissement avec une vitesse faible et en tout état de cause suffisamment faible pour ne pas engendrer de perturbation,
• - le procédé suivant l'invention permet également d'obtenir des rubans métalliques minces présentant une grande largeur et ce de façon stable et régulière.

The proposed process and device respond well to the objectives sought:

• - the lips of the nozzle from which the liquid material flows are not subjected to the same stresses as in the process in which the cooling substrate is very close to the outlet of the slot, so that in the device according to the invention, the nozzle can be produced in a simpler and less costly manner. In addition, it has a much longer lifespan, because it is subject to much lower erosion.
• The risks of blockage of this nozzle are also significantly reduced,
• - moreover, the dimensional stability of the liquid blade is efficiently ensured, which makes it possible to obtain a ribbon of regular size, both in thickness and in width,
• this result is obtained by relatively simple means and by maintaining the distance between the outlet of the nozzle and the receiving substrate at a value low enough for the liquid blade to reach the cooling surface with a low speed and in any state of cause low enough not to cause disturbance,
• - The process according to the invention also makes it possible to obtain thin metallic ribbons having a large width and this in a stable and regular manner.

Claims (20)

1. A process for the production of a ribbon from a molten electrically conductive material, of the kind wherein a molten material is caused to flow from a reservoir (11; 21; 61) through a nozzle (13; 23; 63) to form a strip of substantially rectangular cross-section, whereafter the strip is subjected prior to solidification to an alternating magnetic field producing a stabilizing effect, characterized in that a pressure is exerted on the surface of at least one major face of the strip by means of the alternating magnetic field, by positioning on the same side of the strip at least two poles of opposite polarity of an inductor, the field lines of the first pole being directed perpendicu- lartowardsthe strip, then extending in a direction parallel with the strip towards the second pole and then being reoriented perpendicularly to the strip in the direction of the second pole and finally channelled as far as the first pole, to form a loop.

2. A process according to claim 1, characterized in that the magnetic field lines induced by the poles are directed in the direction of forward movement of the strip.

3. A process according to claims 1 or 2, characterized in that the magnetic field lines induced by the poles are directed in a direction substantially perpendicular to the direction of forward movement of the strip.

4. A process according to any of the preceding claims, characterized in that a cross-section in the form of a substantially rectangular slot is selected for the nozzle.

5. A process according to any of claims 1 to 3, characterized in that a circular corss-section is selected for the nozzle and the substantially cylindrical liquid metal jet emerging from the nozzle is shaped into the form of a stirp by means of at least two facing opposite incident magnetic fields disposed on each side of the jet.

6. A process according to any of claims 1 to 5, characterized in that a strip of very large width is obtained by the coalescence of narrower individual strips along their longitudinal edges.

7. A process according to any of the preceding claims, characterized in that a frequency of between 3 and 3000 kHz approximately is selected for the alternating magnetic field.

8. A process according to any of the preceding claims, characterized in that an intensity of between 1 and 1000 millitesla approximately is selected for the magnetic field.

9. A process for the production of a metallic or semi-metallic ribbon according to any of the preceding claims, characterized in that solidification is performed by contacting the stabilized strip with a mobile substrate (14, 64).

10. An apparatus for the performance of the process according to any of the preceding claims, of the kind comprising a reservoir (11; 21; 61) containing a molten material and comprising in its lower part a nozzle (13; 23; 63) for the flow of the material, means disposed downstream of the reservoir for the formation and solidification of a strip, and electromagnetic means disposed in a zone between the means for the formation of the strip and the means for its solidification, the electromagnetic means being adapted to exert a stabilizing effect on at least one face of the strip, characterized in that the electromagnetic means comprise at least two induction coils (32a, 33a) of parallel axes perpendicular to the plane of the strip, the two coils being disposed on the same side of the strip, a U-shaped ferrite core (34a) being so disposed between the coils (32a, 33a) that each arm of the V (35a, 36a) enters the coils (32a, 33a), the coils being so supplied with alternating current that the ends of the arms (35a, 36a) of the ferrite core (34a) facing the strip form poles of opposite signs.

11. An apparatus according to claim 10, characterized in that the electromagnetic means comprise two other induction coils (32b, 33b) of parallel axes perpendicular to the plane of the strip, such coils being disposed on the other face of the strip (31) symmetrically of the first coils (32a, 33a) in relation to the plane of the strip and a second U-shaped ferrite core (34b) so disposed between the coils (32b, 33b) that each arm of the U enters the other coils (32b, 33b), the polarities of the ends opposite the arms (35a, 35b; 36a, 36b) of the ferrite cores (34a, 34b) being identical.

12. An apparatus according to one of claims 10, 11 and 12, characterized in that the induction coils (32a, 33a; 32b, 33b) situated on the same side of the strip (31) are disposed one above the other parallel with the direction of forward movement of the strip.

13. An apparatus according to one of claims 10 to 12, characterized in that the induction coils (32a, 33a; 32b, 33b) situated on the same side of the strip (31) are disposed one beside the other perpendicularly to the direction of forward movement of the strip.

14. An apparatus according to claims 12 and 13, characterized in that it comprises a network of induction coils disposed respectively parallel with and perpendicular to the direction of forward movement of the strip, their adjacent poles opposite the strip having alternating polarities.

15. An apparatus according to any of claims 10 to 14, characterized in that the nozzle has a cross-section in the form of a substantially rectangular slot.

16. An apparatus according to any of claims 10 to 14, characterized in that the nozzle has a substantially circular cross-section and the substantially cylindrical liquid metal jet is preshaped into the form of a strip by passing between coils disposed at a higher level (32a, 32b) of the apparatus, stabilization being obtained by passage between coils (33a, 33b) situated at a lower level.

17. An apparatus according to claims 10 to 16, characterized in that the cores (34a, 34b) of ferrite or a similar material extend over substantially the whole length of the strip (31).

18. An apparatus according to any of claims 10 to 17, characterized in that the coils are supplied with a high frequency alternating current of between 3 and 3000 kHz approximately.

19. An apparatus according to any of claims 10 to 18, characterized in that the intensity of the magnetic field is between 1 and 1000 millitesla approximately.

20. An apparatus according to claim 10, characterized in that the solidifying means comprise a mobile substrate on which the material is deposited in the form of two endless bands (64) comprising two parallel facing strands (64a) which bound between themselves a gap lying in the alignment of the nozzle (63) and the strip (67) emerging from the nozzle, the two strands (64a) moving in the same direction as the strip.

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