FR2521886A3 - Casting pipe for continuous casting mould - has side outlets co-operating with mould walls to produce melt rotation - Google Patents

Abstract

The molten metal bath in a continuous casting mould is rotated by using an immersed casting pipe which is oriented angularly around its longitudinal axis so that it delivers molten metal against the mould wall at such an angle that the metal deflected by the wall has a non-zero velocity component in the desired direction of rotation of metal in the mould. The casting pipe pref. has several side outlets which are either curved in the desired direction of metal rotation or are tangential to the bore of the pipe. The casting pipe is useful in conjunction with electromagnetic centrifugal continuous casting processes for casting round or rectangular section ingots and gives a horizontal circulation localised at the mould faces and a vertical secondary circulation localised at any mould corners.

Description

METHOD AND DEVICE FOR ROTATING LINGOTIERE
A FUSED METAL CONTINUOUSLY CAST.

 The present invention relates to the rotation of a molten metal, in particular steel, cast in a continuous casting ingot mold. It concerns in particular the continuous casting of long products (billets, blooms, ...).

 It is known that the continuous metal casting operation consists schematically in continuously pouring the molten metal from a reservoir, called a "distributor", into a bottomless mold that is energetically cooled, from the base of which is extracted, also continuously, a ingot still liquid at heart and which finishes to solidify thereafter.

The liquid metal is fed to the ingot mold either by free jet or by means of a vertical refractory tube mounted on the bottom of the distributor. This tube, usually called "submerged nozzle" opens below the level of the molten metal in the mold axially, or by lateral outlet passages distributed around the axis of the tube.

 I1 is known that a controlled mixing in an ingot mold, in particular the mixing putting the liquid metal in rotation around the idea neck axis, appreciably improves the quality of the products obtained, this as well from the point of view of the inclusional cleanliness as with regard to the solidification structure.

 Two rotary brewing techniques in an ingot mold currently exist in industrial operation.

 One, the first chronologically to have been developed, consists in putting in axial rotation a whole set of organs in contact with the cast product, including the ingot mold itself (Belgian patent nO 668.794 - SCEC). This technique, called "mechanical centrifugal continuous casting" is, by nature of application limited to fully vertical casting installations and only circular products. In addition, it is necessary to place between the distributor and the ingot mold a deflector device for the liquid metal (shoe, tube, ...) delivering a free jet of eccentric metal and strongly inclined vertically in the direction of rotation sought (patent Belgian aforementioned, French patent No. 2,118,867, etc.).

The second technique uses an inductor surrounding the flax and producing a rotating magnetic field which drives the liquid metal in its movement (French patents no. 2,779,500 - USINOR, no. 2,329,383, 2,391,014, 2,412,841 - IRSID , or US Patent No. 4,026,346
IRSID) .This process, usually referred to as electromagnetic centrifugal continuous casting "is now the subject, on the part of the French company ROTELEC SA, of worldwide marketing under the protected name" MAGNETOGYR process ". mechanical centrifugation process mentioned above, the advantage in particular of being free from the method of feeding the ingot mold in liquid metal and of being of general application to all types of casting machine, straight or curved, as well as long products of any size, circular or not.

 Another object of the present invention is to achieve a rotation of the liquid metal in a mold for continuous casting of long products.

 To this end, the subject of the invention is a process for rotating a molten metal in an ingot mold, in particular continuously cast steel for the production of long products, a method according to which the metal mold is supplied with melting according to the known practice of the submerged nozzle, said nozzle having one or more lateral passages for the exit of the liquid metal distributed around its axis, method characterized in that said nozzle is placed and it is oriented around its longitudinal axis so that the metal flows delivered by the outlet passage (s) meet the internal wall of the ingot mold with an angular incidence such that the flows after reflection on the wall have a non-zero component in the desired direction of rotation of the liquid metal in the ingot mold.

 As will be understood, the invention therefore consists in rotating the liquid metal in an ingot mold by jointly using the internal wall of the ingot mold and the energy, more precisely the momentum, of the liquid metal feed flows . These amounts of movement are vector quantities which are given non-orthogonal directions and preferably strongly inclined relative to the planes defining the internal surface of the ingot mold at the point of impact of the flows, so as to make the latter play a target. deflector deflecting metal flows, or at least a significant part thereof, in the direction in which one wishes to rotate the metal.

 In the case of cast products in a non-circular format, and particularly in a square or slightly elongated format, that is to say whose ratio of the largest side to the smallest does not exceed approximately 1.5, (billets and most common blooms), the invention can be implemented using a conventional submerged nozzle with radial outlet passages and centered on the casting axis. In these conditions, it suffices to angularly orient the nozzle on its axis so that each flow of metal delivered by the outlet passages meets the face of the ingot mold opposite at a place situated between a corner and the middle of the face.

 In general, whatever the format of the cast product, whether it is circular or not, the invention is preferably implemented using a nozzle specially designed for this purpose and constituting another object of the present. invention.

 This nozzle is characterized, compared to immersed nozzles of known type, in that, at least in their outlet section, the passages delivering the liquid metal into the ingot mold have their axis not concurrent with the longitudinal axis of the nozzle.

 In one embodiment, the nozzle is provided with outlet passages distributed around its axis of symmetry, and having a curvilinear profile, all curved in the same direction, which is that of the desired rotation of the liquid metal in the mold, of so as to give the whole a spiral configuration, which will be called "submerged nozzle with spiral flow".

 In another embodiment, these passages are rectilinear and open tangentially to the interior of the nozzle, the assembly thus obtained can be qualified as "immersed nozzle with tangential flow".

 These particular provisions, as will have been understood, have the primary purpose of ensuring the desired inclination of the flows of liquid metal with respect to the internal surface of the ingot mold. Furthermore, in the case of non-circular formats, they also make it possible to move the point of impact of the flow of liquid metal against the wall thereof as far as possible from the corner edge of the ingot mold, and thus to increase the distance of travel of the flows deflected by the ingot mold before meeting these corners, which is entirely favorable to the establishment of the desired rotational movement.

In order to illustrate what has just been said, an immersed nozzle with tangential flow in accordance with the invention is shown on the attached drawing boards, on which
FIG. 1 is an elevation view of the nozzle,
FIG. 2 shows, seen from above and in section along the plane AA of FIG. 1, the nozzle centered in a square ingot mold, in which the flows of liquid metal are symbolized by arrows,
FIG. 3 is a photograph of the wall speed map resulting from simulation tests on a hydraulic model carried out with the nozzle according to FIGS. 1 and 2 placed in a square ingot mold with translucent walls and supplied with water charged with reflective particles of the light,
FIG. 4 is a diagrammatic representation of FIG. 3 intended to show more clearly the organization of the movements of the liquid in the ingot mold,
- Fioure 5 is a view of the longitudinal section of the upper part of a continuous steel casting installation equipped with the Magnetogyr process and jointly using the process according to the invention, in accordance with a particular application of the latter.

 The nozzle 1, clearly visible in FIGS. 1 and 2, is a blind tube made of usual refractory material (for example made of silica). This tube defines an interior cavity 2 closed at its lower end and the upper open end of which is fitted against the drain orifice provided in the bottom of a distributor (which has not been shown so as not to overload these figures unnecessarily. ). The lower part of the nozzle, normally immersed in the molten metal cast in an ingot mold, is provided with lateral passages 3 for the exit of the flows of molten metal. Here, the passages 3 are four in number and are regularly distributed around the axis 4 of the nozzle. In accordance with one embodiment of the invention, these passages are rectilinear and formed in the thickness of the tube 1 in a tangential arrangement relative to the internal cavity 2. As can be seen in FIG. 2, the nozzle is centered on the axis of the square ingot mold 5, which merges with its own axis of symmetry 4.

 Furthermore, the angular position of the nozzle around its axis 4, is chosen so that the flows of liquid metal delivered into the mold (or, what amounts to the same thing, the axes of outlet passages, of which only one has been shown under the reference 6 in FIG. 2), meet the faces of the ingot mold 5 at points I situated substantially midway between the media M of each face and the neighboring corner stop C in the desired direction of rotation of the metal.

 This being the case, the "tangential" arrangement of the outlet passages 3 makes it possible to minimize the angle of intersection with axes 6 with the plane of the faces of the ingot mold situated opposite, and thus contributes to ensuring a maximum deflection effect of the flow of metal against the ingot mold in the desired direction of rotation. For greater clarity in the figure, the incident and reflected flows have been symbolized by arrow lines representing the most significant current lines of the rotation movement obtained.

I1 will no doubt already have been understood that, in the case of a square (or substantially square) ingot mold exemplified here, the respective roles of the angular offset of the nozzle around its axis and of the particular layout of the outlet passages in the thickness of the nozzle, are in fact of the same nature and complement and combine their effect to obtain the most effective rotational movement possible
For an action length IC of the deflected flow against the wall (length which is adjusted by the angular offset of the nozzle around its axis), the tangential arrangement of the passages 3 makes it possible, as we have said, to minimize the incidence has and therefore to increase the proportion of total metal flow deflected in the direction of rotation. Similarly, for a given incidence, this tangential arrangement of the passages provides a maximum action length IC and deviates therefore at best the effect of confining the metal flows through the corners of the mold.

The user will therefore have an interest in finding a length of action
Maximum CI together with minimum incidence. The antagonistic nature of these two criteria is however greatly attenuated by the use of a nozzle according to the invention.

 It will also be understood that, in all rigor, it is the criterion of the angle of incidence a which is predominant and that, in the case of an ingot mold of round format, only the tangential arrangement of the passages 3 allows '' simply satisfy them (i.e. in particular by keeping the nozzle centered in the mold).

 In FIGS. 3 and 4 below, we see from the front the overall rotational movement of the liquid which is established in the mold 5 fitted with the nozzle 1, according to the arrangements described above.

 These visualizations on a model (Figure 3) were made using a vertical light sheet which allows the stratification of the flows into distinct longitudinal planes, but the most representative of the type of flow created are, of course, those located in the immediate vicinity of the wall of the mold and which are shown here. For obvious reasons of symmetry, the configurations of the movements are identical with respect to each of the faces of the ingot mold, so that the view along one face (for example that of FIG. 3) is well representative of the centrifugation movement of whole cast metal.

 As can be seen, the current lines within the ingot mold materialized in FIG. 3 by the reflective particles of the light, and shown diagrammatically by the arrowed curves in FIG. 4, show an overall relative movement of the liquid metal in ingot mold around the casting axis.

A closer look makes it possible to discern in this overall movement two types of circulation
- a main horizontal circulation (arrows 7) generating the rotational movement, and located on the faces with the exception of the end zones corresponding to the corners of the ingotiber,
- a vertical secondary circulation located in the corners and having an inversion of direction substantially at the level of a horizontal plane P passing through the axes of the outlet passages 3. Below this plane, the liquid descends along the corners (arrows 9), above it goes up to the meniscus designated in 10 (arrows 11).

 Furthermore, the observation in plan from above the ingot mold also shows that the upward movements 11 in the corners combine with the horizontal circulation of the faces above the partition plane P to give the meniscus 10 a completely configuration characteristic of known electromagnetic centrifugation in a square ingot mold, namely four layers of wedges which join together approximately in the middle of the faces by forming rectilinear "valleys" descending tangentially towards a central circular area. The latter, consisting of a vortex in the case of electromagnetic centrifugation with an eccentric free jet, is occupied here by the plunging nozzle 1.

 For more details concerning the configuration of surface movements in a square ingot mold for electromagnetic centrifugal continuous casting, reference may advantageously be made to French patent No. 2,391,014 already cited.

 These hydraulic model simulation tests also made it possible to approach the phenomena observed quantitatively, much more easily than with molten steel poured on an industrial installation.

 Thus, in the case of the nozzle 1 with four outlet passages, placed axially in a square ingot mold 5 with a side of 120 mm, according to the angular arrangement illustrated in FIG. 2 (index a close to 600 and IC = HC / 2) and with a water flow in the mold of 2 m3 / h, the peripheral linear speed of the liquid measured at the meniscus 10 is between 0.3 and 0.4 m / second (i.e. a speed of rotation between 40 and Approx. 60 t / mm) depending on the immersion depth of the nozzle (18 and 12 cm respectively).

 It should be emphasized that, under the same experimental conditions, simulation tests of the "Magnetogyr" process on this hydraulic model in free-flow jet had been carried out in the past. These tests have shown that with a setting of the operating parameters representative of the industrial tests carried out thereafter and having led to good metallurgical results, that the peripheral linear speed induced at the meniscus was precisely between 0.3 and 0.4 m / s depending on the immersion depth (between 18 and 12 cm) of the upper end of the simulation mechanical stirrer used and rotating at around 450 rpm.

 The method according to the invention also advantageously combines with the "Magnetogyr" method. In such a combination, the rotating magnetic field is located in the lower part of the mold, or even immediately under the mold, while the means according to the invention act on the volume of cast metal present in the upper part of the mold. ingot mold, so that the overall rotary movement of the cast metal results from the combined actions of the magnetic field and the fluxes of the metal itself.

 This continuous casting method, which constitutes a particular application of the invention, finds a preferential and quite advantageous implementation in continuous casting installations provided with a regulation of the height level of the meniscus, including the detection means. occupy or clutter the upper part of the mold, for example Y-ray detection systems.

 In this case, in fact, the method according to the invention overcomes the fact that the electromagnetic inductor producing the rotating field cannot be placed, or extend, in the upper part of the mold.

 Figure 5 illustrates very schematically what has just been said.

This figure shows a distributor 13 placed above a boxed ingot mold 14 and supplying the latter with liquid steel using a submerged nozzle 1 according to the invention. The nozzle is centered on the casting axis 4 and has been attached at its upper end to the drain orifice 15 in the bottom of the distributor. Within the mold the cast metal forms a peripheral solidification dump 16 containing a core 17 still liquid and whose solidification will gradually end downstream of the mold in the direction of extraction indicated by the vertical arrow on the axis 4 .

 The ingot mold 14 of the usual type comprises a main element 5, generally made of copper or copper alloy in internal contact with the cast metal and energetically cooled externally by a blade of water.

ascending 18 laterally confined by a jacket 19.

 The latter defines with the outer envelope 20 of the mold a chamber 21 for discharging the cooling water.

 As can be seen, the chamber 21 contains on the one hand, in its lower part, a polyphase static electromagnetic inductor with rotating field 22 for the centrifugation of the liquid metal 17 according to the "Magn-togyr" process and, in its upper part d on the other hand, a meniscus level sensor 10 per beam Y, comprising a radioactive source 23 and, opposite with respect to the cast product, a counter 24 with an ionization chamber, the detection beam being represented by its envelope 25 in fine lines.

 At the level of the level detection system, open the passages 3 of the nozzle 1, the angular orientation of which on the axis 4 has been determined in accordance with the characteristics already explained of the invention, in order to centrifuge the metal in the upper part of the casting bar subjected directly to the action of the electromagnetic stirrer 22 and in the same direction as the latter.

 The method according to the invention can also be used, in combination with the known "Magnetogyr" method, according to a variant of the application described above and which consists in reversing the respective directions of mixing of the stirrer 22 and of the nozzle 1 on the liquid metal so as to mutually counteract their action in the upper part of the mold. It is thus possible, by an adequate adjustment of the stirrer, for example to centrifuge the metal in the lower part of the mold, while maintaining the upper part in a relatively calm state with a meniscus 10 which is substantially flat.

 Such a variant can be of decisive interest, precisely in the case of centrifugal continuous casting with submerged nozzle (French patent No. 2,412,841 already cited).

It is known, in fact, that the practice of continuous casting with a submerged nozzle is generally accompanied by a covering of the meniscus 10 with a powder, known as a "covering powder" having several functions: thermal insulation, chemical protection, mechanical lubrication, etc.
However, these functions can only be properly performed if the powder uniformly covers the meniscus, which can cause problems in continuous centrifugal casting due to the more or less pronounced concave shape that the meniscus takes. The variant application of the invention described above can constitute, as will be understood, an advantageous solution to this type of problem.

 It goes without saying that the invention cannot be limited to the examples described, but extends to multiple variants or equivalents and to numerous other applications insofar as the characteristics set out in the appended claims are respected.

 Thus, the number of nozzle outlet passages can be varied to a large extent. I1 remains however that in the case of casting non-circular formats, it is preferable to use a nozzle having a number of passages equal to the number of faces of the mold.

 Likewise, the rectilinear conformation of the passages, combined with an eccentricity of their axis to make them tangential to the internal cavity of the nozzle, may very well, as has already been said, be replaced by a spiral conformation, curved in the direction wanted rotation of the metal (this without prejudging however possible difficulties to overcome to manufacture a nozzle of this type).

 Likewise also, the lateral passages of the nozzle may have an inclination on the vertical so as to be oriented, in the direction of exit of the metal flows, either upwards or downwards.

 However, it seems that a horizontal arrangement of these passages makes it possible to achieve the best overall rotation efficiency, although an upward orientation can be retained if a concentration of the stirring action is sought at the level of the meniscus, or downwards, if on the contrary, a more localized action is sought in depth in the mold, for example in combination with an electromagnetic stirrer.

 Likewise, the application of the invention to a continuous casting installation in combination with an electromagnetic rotary stirring inductor described with reference to FIG. 5 is only a particular example of application of this type.

 Thus the electromagnetic inductor can be placed not only in or around the body of the mold, but also downstream of it. Likewise, several inductors can be used, being managed over the metallurgical height (depth of the well 17 of liquid metal) from the ingot mold, or from the outlet of the latter.

More generally, the invention can be combined with any means allowing the centrifugation of the metal during casting, and in particular with the specific means of mechanical centrifugal continuous casting mentioned at the beginning. In this case, the necessary implementation of a nozzle conforming to
The invention, because of the necessarily circular cast formats, can make it possible to advantageously replace the use of the "shoe", or of the eccentric and inclined free jet tube, intermediate between the distributor and the ingot mold and at the same time authorize, with a Simplified technology and easier implementation, mechanical centrifugal continuous casting of calm grades with aluminum for example, which so far does not seem to have already been carried out industrially.

Claims (13)

 10) A method for rotating a molten metal, especially steel, in a mold, continuously cast for the production of long products and according to which the mold is fed with molten metal according to the known practice of the submerged nozzle, said nozzle having at least one lateral passage for exit from the molten metal, process characterized in that lwon arranges the nozzle (1) and is oriented angularly around its longitudinal axis (4) so that the flow (6) of metal delivered by the outlet passage (3) meets the wall of the mold (5) with an angular incidence (a) such that the flux, after reflection on said wall, has a non-zero speed component in the desired direction of rotation of the liquid metal in an ingot mold.  20) Method according to claim 1, wherein the mold is of square or substantially square format, characterized in that the nozzle (1) is centered on the axis (4) of the mold (5) and in that the flow of metal delivered by each outlet passage of the nozzle meets the wall opposite the ingot mold at a place (I) located between the middle (H) of one face and the stop (C) of the neighboring corner in the direction of metal rotation.  30) Method according to claim 1, characterized in that one uses a nozzle (1) with several lateral outlet passages (3) regularly distributed around the axis (4) of the nozzle.  40) Method according to claims 2 and 3, characterized in that one uses a nozzle (1) having four lateral outlet passages (3).  50) Method according to claim 1, characterized in that it is implemented on a continuous casting installation of metals, in particular steel, equipped with means for the centrifugation of the cast metal.  60) Method according to claim 5, characterized in that at least one electromagnetic inductor (22) with magnetic field rotating around the casting axis (4) is used as the centrifugation means.  70) Method according to claim 6, characterized in that said inductor is disposed at the lower part of the mold (5).  80) Method according to claims 6 or 7, characterized in that the electromagnetic centrifugation is carried out in the same direction as the entrainment in rotation of the cast metal obtained by the reflection, on the internal wall of the mold, of the fluxes metal delivered by the lateral outlet passages of the nozzle.  90) Method according to claims 6 or 7, characterized in that the electromagnetic centrifugation is carried out in the opposite direction to that of the rotational driving of the cast metal obtained by the reflection, on the internal wall of the mold, of the fluxes of metal delivered by the lateral outlet passages of the nozzle.  100) Immersed nozzle for implementing the method according to any one of the norrientent claims and comprising at least one lateral pass (3) for exit from the molten metal, characterized in that said passage has, at least in its outlet section, an axis (6) not concurrent with the longitudinal axis (4) of the nozzle.  110) nozzle according to claim 10, characterized in that said passage has a curvilinear conformation, curved from inside the nozzle in the direction of rotation of the liquid metal.  120) nozzle according to claim 10, characterized in that said passage (3) has a rectilinear conformation and in that it opens tangentially into the volume defining the interior cavity (2) of the nozzle.  13) nozzle according to claims 10, 11 or 12, characterized in that it comprises several lateral passages (3) for output of the molten metal regularly distributed around the axis (4) of the nozzle.  140) Nozzle according to claim 13, characterized in that it comprises four lateral passages (3) for output of the molten metal regularly distributed around the axis (4) of the nozzle.