EP0502802A1 - Method and apparatus for continuous casting of thin wire from a metal melt - Google Patents

Abstract

The subject of the invention is a method for continuous casting of fine metal wire, in which a stream of metal melt (15), emerging from the nozzle of a vessel (8), is quenched (hardened) and solidified in a layer of cooling liquid (1), characterised in that the said liquid (1) flows over a stationary cylindrical or slightly frustoconical surface (3) with a substantially vertical axis, in that the reservoir (8) is given a rotational movement about the axis of the said surface so as to cause the end of the nozzle to move over a circular path which is concentric with the said surface, and in that the stream of metal (15) is ejected from the nozzle in a direction opposite to the direction of displacement of the nozzle. A further subject of the invention is an apparatus for implementing this method. <IMAGE>

Description

The invention relates to the manufacture of small diameter metal wires by quenching a jet of liquid metal in a layer of cooling liquid.

The last few years have seen the development of a casting process making it possible to obtain, directly from liquid metal, metallic filaments of indefinite length, of substantially circular section and of very small diameter, which can go down to around 80 µm. , and to which one can confer an amorphous structure, if the composition of the metal lends itself to it and if the conditions of cooling of the liquid metal are sufficiently violent (at least 10⁴ ° C / s). This process is described in particular in European Patent EP 39169. It consists in forming a jet of metal from a tank of liquid metal provided with heating means and an outlet nozzle whose diameter is equal to or slightly greater than the diameter of the desired filament. This metal jet then enters a layer of cooling liquid, such as water or an aqueous solution of a salt, which solidifies the jet into a metal wire. This layer of liquid is in movement in a direction transverse to that of the metal jet and flows on a solid surface itself in movement which entrains the liquid, and can be constituted by the interior of a drum rotating around a horizontal axis (European Patent EP 39169 already cited) or by a horizontal or concave portion of a grooved belt running in a loop (European Patent EP 89134). The wire is entrained in the cooling liquid, which preferably moves laminarly at a speed substantially equal to or slightly greater than the speed of ejection of the jet of liquid metal from the tank (of the order of 5 to 15 m / s). As it is poured, the wire is wound in the drum under the effect of centrifugal force, or is continuously removed from the cooling medium by suitable means to be picked up and possibly wound outside the casting machine.

Thanks to the high cooling speed which it can provide, this process makes it possible, if the metal is amorphizable, to obtain amorphous wires of uniform size having, among other properties, a very high tensile strength. We can thus cast amorphous wires in alloys based on various metals such as iron, copper, cobalt, gold, aluminum, etc.

The drawbacks of the devices implementing this method are however numerous. The drums with horizontal axis of rotation do not allow, in their simplest versions, to recover the wire in a continuous way and to lead it outside the installation, and to give this possibility leads to complicate very significantly the construction of the installation. In all cases, the size of the tank remains limited, as it must fit inside the drum. Unless the diameter of the drum is exaggeratedly increased, which makes it difficult to entrain the cooling liquid under the effect of centrifugal force, it is therefore hardly possible to treat quantities of metal exceeding a few kg at one time. As for installations using grooved belts, they allow the use of high-capacity liquid metal tanks, but are very bulky. In fact, the cooling liquid must generally travel several meters on the strip after it has been deposited before its turbulence is sufficiently dissipated to allow regular solidification of the metal.

A variant of this process, presented in Japanese Patent Application JP 60250859, consists in placing the cooling liquid in a fixed tank, in placing the liquid metal tank above this tank, in orienting the outlet nozzle of the jet of liquid metal so that the latter enters the cooling liquid at an angle less than or equal to 30 ° relative to its surface, and to impart to the reservoir a rotational movement around a vertical axis not passing through the nozzle output. thus describes a circular path above the tank, and the solidified wire is deposited at the bottom of the tank in the form of superimposed turns. However, it is not possible to recover the wire continuously.

The object of the invention is to propose a method of casting wire allowing continuous collection of the wire and not limiting the quantity of metal which it is possible to treat at one time to too small a value, as well as a device of simple design for its implementation.

To this end, the subject of the invention is a process for the continuous casting of fine metallic wire in which a jet of liquid metal leaving the nozzle of a reservoir is quenched and solidified in a layer of cooling liquid, characterized in that said fluid flows over a cylindrical or slightly frustoconical fixed surface with a substantially vertical axis, in that the tank imparts a rotational movement around the axis of said surface so as to move the end of the nozzle on a circular path concentric with said surface, and in that the metal jet is ejected from the nozzle in a direction making a right or obtuse angle with the tangent of the circular path.

The invention also relates to a device for continuously casting fine metallic wire comprising a reservoir containing a liquid metal provided with a nozzle, through which a jet of said liquid metal flows, oriented in the direction of a layer of cooling liquid. wherein said jet is quenched and solidified in the form of a wire, characterized in that it comprises a fixed cylindrical or slightly frustoconical surface of substantially vertical axis on which flows said layer of coolant, means for printing a rotational movement around the axis of said surface, and means for collecting said wire as it is formed, placed below said surface.

As will be understood, the invention consists in solidifying the jet of liquid metal in a film of coolant freely flowing over a cylindrical or slightly frustoconical surface. The wire thus solidified progressively descends along this surface in the form of turns, and, below the surface, is gripped by a device making it possible to evacuate it.

The invention will be better understood on reading the description which follows, referring to the single appended figure, showing the installation seen in frontal section and in perspective.

In the wire casting installation as shown in the single figure, the cooling medium in which the quenching and solidification of the liquid metal M takes place consists of a layer of liquid 1 trickling at a speed v on the upper surface 2 flat and horizontal of a fixed support 3. This support has any general shape, for example cylindrical as shown. Its essential characteristic is to have, in its central part, a recess 4 passing right through it, and produced in such a way that the surface 5 of the support 3 delimiting this recess is cylindrical, with a vertical XY axis. The liquid 1 flows from the upper surface 2 of the support to the cylindrical surface 5 and thus forms a layer of thickness e flowing at a speed v ′. The junction between the upper surface 2 of the support and the cylindrical surface 5 of the recess is preferably carried out without a sharp angle, in order to minimize the disturbances caused to the flow of the liquid 1 by the slope break. The liquid 1 is brought to the support 3 by means such as a hollow ferrule 6 connected to a liquid supply, not shown. This ferrule has an orifice 7 through which the liquid flows. This orifice describes a circle substantially concentric with the recess 4. Its dimensions and the flow rate of the liquid are calculated so as to form a layer of liquid 1 of regular thickness e of the order of 1 cm, and with a flow at relatively low speed v ′ in the recess 4 to prevent excessive turbulence from being established inside the layer 1.

• son diamètre terminal est égal ou très légèrement supérieur au diamètre désiré pour le fil 14, soit de l'ordre de 80 à 200 µm, afin de former un jet de métal liquide 15 cohérent possédant ce diamètre ;
• elle doit orienter le jet de métal liquide vers la couche de liquide refroidissant 1 ruisselant sur la surface cylindrique 5, et dans une direction opposée à la direction de déplacement de la busette ; par exemple, si, comme représenté sur la figure, la rotation du réservoir s'effectue dans le sens antihoraire, l'extrémité de la busette 12 doit être orientée vers l'arrière du plan de coupe ;
• son extrémité doit être située à une très faible distance (de l'ordre de 1 à quelques mm) de la surface de la couche de liquide refroidissant 1, pour assurer une bonne cohérence du jet de métal 15 au moment de sa pénétration dans le liquide.

Above the recess 4 is disposed a reservoir 8 containing the liquid metal M. This reservoir has a symmetry of revolution with respect to the axis XY, and may for example have a generally cylindrical shape as shown. It is coated internally with a refractory layer which is not very reactive with respect to the metal M, or is itself entirely made of this refractory. It is equipped with heating means, such as an induction coil 9, the electrical supply of which is not shown. These heating means make it possible to maintain the temperature of the liquid metal M which has been previously introduced into the tank at the desired level, or even also to ensure the melting of pieces of this metal themselves. The reservoir 8 also comprises means 10 for rotating it around the axis XY at an angular speed ω, and means 11 for introducing a neutral gas inside it. This gas protects the liquid metal M against atmospheric oxidation. It also makes it possible to put the tank under pressure so as to favor the ejection of the liquid metal and to regulate its outlet flow regardless of the quantity of metal which remains inside the tank 8. This outlet of the liquid metal from the tank 8 is effected by a nozzle 12 placed in the bottom 13 of the tank. This nozzle 12 must meet the following conditions:

• its terminal diameter is equal to or very slightly greater than the desired diameter for the wire 14, ie of the order of 80 to 200 μm, in order to form a jet of coherent liquid metal 15 having this diameter;
• it must direct the jet of liquid metal towards the layer of cooling liquid 1 trickling over the cylindrical surface 5, and in a direction opposite to the direction of movement of the nozzle; for example, if, as shown in the figure, the tank rotates counterclockwise, the end of the nozzle 12 must be oriented towards the rear of the cutting plane;
• its end must be located at a very short distance (of the order of 1 to a few mm) from the surface of the layer of cooling liquid 1, to ensure good consistency of the metal jet 15 at the time of its penetration into the liquid.

est aussi dans les limites de 1 à 1,5. la direction de pénétration du jet 15 dans le liquide refroidissant 1 doit également être optimisée, comme sur les installations classiques, où l'inclinaison du jet par rapport à la surface du liquide est très variable. Dans cette optimisation, on pourra être amené à tenir compte de la vitesse de chute v′ de la couche de liquide refroidissant 1.Usually, in direct wire casting installations, the cooling liquid is set in motion, while the tank is fixed, but the speed Vf of the jet of liquid metal, which is also the speed of the solidified wire, is made, and the speed Vl of the liquid are equal, or that Vl is slightly greater than Vf, in a ratio not exceeding 1.3 to 1.5. If Vf is greater than Vl, the jet and the wire are not entrained by the liquid, and there is an accumulation effect which results in an irregular thickness of the wire. If, on the contrary Vl is much greater than Vf the effect of driving the jet is too great and leads to its periodic break, which makes it impossible to obtain a continuous wire of great length. In the installation according to the invention, it is possible to neglect the rate of fall v ′ of the layer of cooling liquid 1 and to admit that it is fixed. The speed ratio to be taken into account for the adjustment of the installation is therefore the ratio between the speed of the metal jet 15 and the wire 14, and the linear speed Vb of the end of the nozzle 12, equal to ω R if R is the distance between the end of the nozzle 12 and the axis XY of rotation of the reservoir 8. These speeds are, for example, of the order of 5 to 15 m / s, as in conventional installations, and must be sufficient to guarantee a high solidification speed, especially if the formation of an amorphous wire is sought. Their report $$\frac{\text{Vb}}{\text{Vf}}$$

is also within the limits of 1 to 1.5. the direction of penetration of the jet 15 into the cooling liquid 1 must also be optimized, as in conventional installations, where the inclination of the jet relative to the surface of the liquid is very variable. In this optimization, it may be necessary to take account of the rate of fall v ′ of the layer of cooling liquid 1.

To form this layer 1, any liquid known for its cooling capacities can be used, for example water, aqueous saline solutions, or liquefied gases.

Under the effect of the centrifugal force and the direction initially imposed on the metal jet 15, the solidified wire 14 is pressed against the cylindrical surface 5. Under the effect of its weight and the thrust exerted on it by the descending layer of cooling liquid 1, the wire gradually descends along the surface 5 and thus forms turns. Below the support 3, these turns fall on each other and are deposited on a conveyor belt 16 moved by means smbolized by a pulley 17 and which evacuates the turns of wire as and when they are formed. The installation may also include means (not shown) for collecting the used cooling fluid and for returning this liquid to the supply circuit of the installation.

Compared to the usual solution consisting in using a fixed reservoir and a layer of liquid deposited on a mobile surface, an advantage of the invention is to cause the metal M to be centrifuged inside the reservoir. This centrifugation accentuates the separation between the metal and the non-metallic inclusions which it inevitably contains, and which ultimately rises to the surface of the metal M to form a layer of slag 18. This thus increases the quality of the wire, while by reducing the risks of clogging of the nozzle 12 by inclusions. Another advantage of this installation is that the metal tank 8 is not limited in size in the height direction. It is therefore possible to treat at once a quantity of metal as large as desired, provided that means for driving the tank in rotation with a suitable power. Finally, the solidified wire leaves the solidification zone on its own in the form of turns, and its evacuation and winding do not require complex installation. For this purpose, instead of a conveyor belt, it is possible to provide a gradually descending plate, or any other means making it possible to capture the end of the wire and to wind it on a mandrel.

As a variant, the surface 5 of the recess may not be strictly cylindrical, but slightly frustoconical. Such a shape allows better guidance and better formation of the turns, and makes it possible to reduce the speed v ′ of the layer of liquid 1, for a speed v equal to the outlet of the shell. This brings us closer to the conditions of solidification of the wire in conventional type installations. In addition, the distance between the nozzle 12 and the surface of the liquid layer 1 can be adjusted by simple vertical translation of the reservoir 8. The taper of the surface 5 should not, however, be so great as to hinder the descent of the turns of wire which could find themselves blocked inside the recess, which would make it necessary to interrupt the casting.

Likewise, provision can be made for continuously supplying the reservoir 8 with metal, either with already liquid metal, or with solid metal divided sufficiently finely for its complete melting to take place before it reaches the nozzle 12. can thus further reduce the limit on the quantity of wire that can be poured in a single operation. It is also possible to equip the reservoir 8 with several neighboring nozzles for casting multi-stranded wires, in a similar manner to that which is explained in the document JP 63273554. It is finally possible, in a known manner, to move the end of the nozzle 12 away from the liquid layer 1 more than a few mm, if it is possible to artificially maintain the coherence of the metal jet 15. This can be done by creating on the surface of the jet, in known manner, an oxide film, thanks to the limited oxidation of one of the metal components by air or by a suitable oxidizing atmosphere, as described for example in document EP 360104.

The invention applies to the casting of metallic wires of small diameter, for example steel, and makes it possible to obtain wires of amorphous structure if the solidification conditions are sufficiently violent and if the composition of the cast metal lends itself to it. .

Claims (5)

1) Process for the continuous casting of fine metallic wire in which a jet of liquid metal leaving the nozzle of a reservoir is quenched and solidified in a layer of cooling liquid, characterized in that said liquid trickles over a cylindrical or slightly fixed surface frusto-conical with a substantially vertical axis, in that the tank is given a rotational movement around the axis of said surface so as to cause the end of the nozzle to move on a circular path concentric with said surface, and that the metal jet is ejected from the nozzle in a direction opposite to the direction of movement of the nozzle. 2) Method according to claim 1, characterized in that the linear speed of displacement Vb of the end of the nozzle and the speed of the metal jet leaving the nozzle are in a ratio $$\frac{\text{Vb}}{\text{Vf}}$$

between approximately 1 and 1.5. 3) Device for continuous casting of fine metal wire comprising a reservoir (8) containing a liquid metal (M) provided with a nozzle (12) through which flows a jet (15) of said liquid metal (M) oriented in the direction a layer of cooling liquid (1) in which said jet (15) is soaked and solidified in the form of a wire (14), characterized in that it comprises a fixed cylindrical or slightly frustoconical surface (5) of substantially vertical axis (XY) on which said layer (1) of coolant flows, means (10) for imparting to said reservoir (8) a rotational movement around the axis (XY) of said surface, and means for collecting said wire (14) as it is formed, placed below said surface (5). 4) Device according to claim 3, characterized in that said means for collecting the metal wire (14) consist of a plate descending gradually. 5) Device according to claim 3, characterized in that said means for collecting the metal wire consist of a conveyor belt (16).

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