EP0993890B1 - Tubular continuous casting mould for metals - Google Patents

Abstract

PURPOSE: A mold design for a hot-top continuous casting device is provided to suit to add a sound or a vibration of supersonic waves to the mold, and to have the reliability needed to cast in many numbers. CONSTITUTION: A mold is equipped a side projection(18) located a metal unit(1) under an upper part(19) and integrally produced with the metal unit(1). A cooling channel(20) is processed between the upper part(19) and the projection(18), and closed by a collar(21). The collar is fixed in the metal unit(1) with two welding points generated by an electronic line. One of the welding points(22) is made in the upper part(19) of the metal unit(1), that is on a point processed the channel(20). The other welding point(23) is made on the upper face of the projection(18). The welding points(22,23) are received lower thermal and mechanical tension than existing welding points. And closer welding point(22) in a metal of high temperature is reduced the enduring mechanical tension by separating from emitters(25,26) more or less.

Description

The invention relates to the continuous casting of metals, such as steel. More specifically, it relates to cooled bottomless ingot molds, in which the solidification of the cast product, and even more precisely the tubular ingot molds, the cooled metal part is provided, on its upper edge, with a material extension refractory. This makes it possible to transfer the level of the surface of the liquid metal present in the ingot mold above the metal part of the ingot mold where the solidification of the cast product.

The continuous casting of steel is carried out conventionally by initiating the solidification of molten metal in a bottomless ingot mold whose walls are energetically cooled externally by circulation of a liquid such as water. This ingot mold is made of a material which is a good conductor of heat such as copper and its alloys. It can consist of an assembly of plates or a tubular part unique, defining an interior space corresponding to the desired shape for the product cast: of circular, square or rectangular cross section more or less elongated. In the case of pouring slightly elongated square or rectangular products, it is generally the solution of a single tubular part which is retained. This solution is mandatory for products with circular cross-section. A shirt of the ingot mold on its external face ensures cooling by circulation of water. To facilitate the extraction of the product from the ingot mold, the latter is printed vertical oscillations of low frequency (a few Hz) and of amplitude equal to a few mm, and the interface between the solidified metal and the ingot mold is lubricated. This lubrication is obtained using a fusible cover powder or an oil, which is deposited on the liquid metal surface and which infiltrates between the metal being solidified and the mold. Oil can also be brought to the interface through the wall metal of the mold.

On some casting machines, the tubular metal part of the mold is extended upwards by a tubular part of refractory material of the same internal dimensions, and the flow of metal entering and leaving the ingot mold is regulated so as to maintain the surface of the liquid metal present in the ingot mold inside this refractory enhancement. Under these conditions, the solidification of the metal is initiated by permanence at the junction between the refractory part and the metal part of the ingot mold, in other words where the metal first comes into contact with a cooled wall good conductor of heat. In this way, we make the initiation of solidification independent of fluctuations in the level of the surface of the liquid metal present in the ingot mold, and which are due in particular to the hydrodynamic disturbances caused by the jet of molten metal feeding the ingot mold. This improves the surface quality of the cast product. The casting installations thus equipped are called "continuous casting in charge ". On these machines, the lubrication of the solidified metal-ingot mold interface must imperatively be ensured by an injection of oil through the wall of the mold, since a covering powder or an oil deposited on the surface of the liquid metal does not could reach the solidified metal-ingot mold interface. Advantageously, as we sometimes do this also on conventional machines without risers, we superimpose to the vertical oscillations of the mold of the high frequency vibrations (for example 15 at 18 kHz) and low amplitude (a few µm) by means of sound or ultrasonic transmitters applied against the wall of the mold or a part attached to it. These vibrations improve the lubrication conditions of the metal-ingot interface.

According to one embodiment of such molds with refractory enhancement, the sound or ultrasonic emitters are fixed on a flange which is secured to the upper end portion of the metal part of the mold, where it replaces the liner that cools the rest of the mold height. A canal water circulation is provided between the mold and the collar so that the this portion of the mold can be cooled. This configuration provides said portion of the mold with independent cooling, which can be adjusted optimally so as to guarantee a good initiation of solidification of the product sank. In order to ensure good transmission of vibrations to the mold, it is essential that the connection between the ingot mold and the flange has at all points a high rigidity, which makes it inadvisable to use removable fixing means of a piece on the other. The best known method that can be used for this is probably the electron beam welding process.

Experience shows, however, that this conception of the ingot mold is not satisfactory. Indeed, we quickly observe the appearance of cracks in the welds which join the mold and the collar. These welds must therefore be regularly restored if you want to keep the ingot mold in working condition, hence a cost too high maintenance of the installation.

The object of the invention is to propose an ingot mold design for a machine of continuous casting under load adapted to the application to said vibration mold sound or ultrasonic and having all the necessary reliability for a large number of flows.

To this end, the invention relates to a tubular ingot mold for continuous casting in metal charge, having a cooled metal part intended to be fitted with transmitters sound or ultrasound imposing vibrations and to be surmounted by an enhancement refractory material, the upper end portion of said metal part being cooled by circulation of water in a channel formed on its external face and closed laterally by a collar which surrounds said upper terminal portion and is secured by welding, characterized in that said metal part has below from its upper end portion a lateral protuberance which is integrated therein manufacturing, and on the upper face of which said flange is fixed by welding.

As will be understood, the invention consists in shaping the upper end of the metal part of the mold so as to integrate a manufacturing lateral outgrowth. Below this outgrowth, the cooling of the part metal of the mold is ensured by the usual lining. Above this protrusion, the cooling of the metal part of the mold is ensured by a channel which is machined there and closed laterally by a flange welded to the upper face of the protrusion and at the upper edge of the mold.

• la figure 1 qui montre schématiquement, vue en coupe transversale, une lingotière pour coulée continue en charge conforme à l'art antérieur ;
• la figure 2 qui montre de la même façon une lingotière de coulée continue en charge selon l'invention.

The invention will be better understood on reading the description which follows, given with reference to the following appended figures:

• Figure 1 which shows schematically, in cross section, a mold for continuous casting under load according to the prior art;
• Figure 2 which similarly shows a continuous casting mold under load according to the invention.

In the figures, the same elements are designated by identical references.

• une partie métallique tubulaire 1, de section par exemple carrée, réalisée en un matériau bon conducteur de la chaleur tel que le cuivre ou un de ses alliages ;
• une collerette 2, qui entoure la portion terminale supérieure de la partie métallique tubulaire 1, réalisée en un matériau analogue à celui de ladite partie tubulaire 1 ; ces deux pièces sont solidarisées par une soudure 3 réalisée par un procédé utilisant un faisceau d'électrons ; elles sont usinées de manière à ménager entre elles un canal 4 dans lequel on peut faire circuler un fluide de refroidissement tel que de l'eau ; ce canal 4, dans la configuration représentée, est obturé par un couvercle métallique 5 qui est soudé, également par un procédé à faisceau d'électrons, à la partie tubulaire 1 et à la collerette 2 au moyen de soudures 6, 7 ;
• une rehausse en matériau réfractaire 8, de forme tubulaire, fixée sur le rebord supérieur 9 de la partie métallique 1, et dont l'espace intérieur 10 prolonge l'espace intérieur 11 de la partie métallique 1 ; ces espaces intérieurs 10, 11 sont destinés à renfermer le métal liquide en cours de solidification et définissent la forme du produit coulé ; conformément au principe de la coulée continue en charge, pour les raisons qui ont été précédemment exposées, la surface supérieure du métal liquide présent dans la lingotière est maintenue en permanence dans l'espace intérieur 10 de la rehausse réfractaire 8 ;
• une chemise 12 qui entoure la partie métallique 1 en dessous de la collerette 2 ; un espace 13 est ménagé entre la partie métallique 1 et la chemise 12, dans lequel on fait circuler de l'eau de refroidissement.

The mold for continuous casting under load according to the prior art represented in FIG. 1 conventionally and mainly comprises the following elements:

• a tubular metal part 1, of square section for example, made of a material which is a good conductor of heat such as copper or one of its alloys;
• a flange 2, which surrounds the upper end portion of the tubular metal part 1, made of a material similar to that of said tubular part 1; these two parts are joined by a weld 3 produced by a process using an electron beam; they are machined so as to form between them a channel 4 in which a cooling fluid such as water can be circulated; this channel 4, in the configuration shown, is closed by a metal cover 5 which is welded, also by an electron beam process, to the tubular part 1 and to the flange 2 by means of welds 6, 7;
• an extension in refractory material 8, of tubular shape, fixed on the upper rim 9 of the metal part 1, and whose interior space 10 extends the interior space 11 of the metal part 1; these interior spaces 10, 11 are intended to contain the liquid metal being solidified and define the shape of the cast product; in accordance with the principle of continuous casting under load, for the reasons which have been explained above, the upper surface of the liquid metal present in the ingot mold is permanently maintained in the interior space 10 of the refractory riser 8;
• a jacket 12 which surrounds the metal part 1 below the collar 2; a space 13 is provided between the metal part 1 and the jacket 12, in which cooling water is circulated.

Sound or ultrasonic emitters 14, 15 are applied against the flange 2, for the purpose of imparting vibrations to the metal part 1, for the reasons explained upper. The number of these transmitters is variable; in the case of a section ingot mold square or rectangular, we generally have at least one on each side of the mold. In the example shown, the emitters 14, 15 are applied to surfaces bevelled 16, 17 formed on the outer upper edge of the flange 1, so that the vibrations impressed on the metallic part 1 have both a horizontal component and a vertical component and that these vibrations are obtained using a single family transmitters (see in this regard patent EP 0 403 411). But other provisions of transmitters 14, 15 are conceivable, depending on the type of vibration that one wishes to impose on the metal part 1. By placing the transmitters 14, 15 against the upper face of the collar 2, we would impose purely vertical vibrations, and placing them against the lateral faces of the collar 2, purely horizontal vibrations would be imposed.

As we said, experience shows that this configuration according to the prior art is not satisfactory, in that the appearance of cracks in the welds 3, 6, 7. This appearance is explained by the intense stresses thermomechanical to which the welds are subjected, due to the proximity of the metal liquid and emitters 14, 15. They cause significant deformation of their constituent materials. This results in a plasticization of the welds, which eventually appear fatigue cracks.

The ingot mold according to the invention shown in Figure 2 is distinguished essentially from the ingot mold of the prior art shown in FIG. 1 in that its metal part 1 has a lateral protrusion 18, integrated in the manufacturing part metallic 1 and located below its upper end 19. Between this end upper 19 and the protrusion 18 is machined a cooling channel 20 closed by a collar 21. This collar is similar in its functions to collar 2 of FIG. 1, and is fixed to the metal part 1 by means of two welds made by a beam electron. One 22 of these welds is made at the upper end 19 of the metal part 1, therefore above the machining of the channel 20. The other weld 23 is made on the upper face 24 of the projection 18. As in the configuration of reference of FIG. 1, transmitters 14, 15 are fixed on the flange 21, for example on bevelled surfaces 23, 24

Compared to the configuration according to the prior art shown in Figure 1, the configuration according to the invention makes it possible to reduce to two instead of three the number of welds between the flange 21 and the metal part 1. On the other hand, these welds 22, 23 are subject to less thermal and mechanical stresses than welds 3, 6, 7 from the previous configuration. None found, like weld 6, nearby liquid metal or solidification present in the interior space 11 of the metal part 1. On the other hand, the weld 22, the closest to the hot metal, is distant from the transmitters 14, 15, which attenuates the mechanical stresses which it must support.

Preferably, the metallic tubular part 1 is produced by a process extrusion, which allows to provide at one of its ends a portion of large diameter. Once machined as indicated, this terminal portion forms the part upper of said tubular part 1, with its protrusion 18 and its channel 20. During this machining, it is preferable to make the junctions 27, 28 between the protrusion 18 and the vertical straight portion of the metallic tubular part 1 with a radius of curvature, and not with a sharp angle, to reduce the concentration of stresses at their level.

As in the ingot mold according to the prior art of FIG. 1, the placement of the transmitters 14, 15 on bevelled edges of the flange 21 is only one example. according to the orientation that is desired for the vibrations, the transmitters 14 can also be applied, 15 horizontally or vertically against the flange 21. Alternatively, the transmitters 14, 15 no longer on the collar 21, but on the protrusion 18.

Thanks to the invention, the accumulated deformations at the welds between the tubular metal part 1 of the mold and the flange 21 which closes the channel cooling can be limited, and the welds remain in the elastic range. The lifetime of the ingot mold can thus be considerably increased, up to reach a thousand flows.

To manufacture the tubular metal part 1 of the mold, it is also possible use any other process than extrusion, the main thing being that it leads to the realization of a single piece shaped as indicated.

By way of example, for an ingot mold intended for casting steel billets of 135 mm square section, the tubular metal part 1 of the mold can have a total height of 700 mm, and to be surmounted by a refractory riser 8 in height 200 mm. The collar 21 may have a height of 60 mm and an external dimension of 240 mm, and the protrusion 18 can have a thickness of 10 to 15 mm.

It is understood that in the above description, we have only mentioned the organs of the ingot mold directly linked to the problem posed and its resolution. In particular, not described and shown the organs which ensure the lubrication of the interface ingot mold-product, and which may, if necessary, comprise a cooled annular part fitted with an oil injection slot, inserted between the metal tubular part and the enhances refractory.

Claims (4)

1. Tubular mould for the hot-top continuous casting of metals, having a cooled metal part (1) intended to be provided with sound or ultrasound emitters (14,15) imposing vibrations on it and to be surmounted by a feed head (8) made of refractory material, the upper terminal portion of the said metal part (1) being cooled by water circulating in a channel (20) made on its external face and closed off laterally by a collar (21) which surrounds the said upper terminal portion and is fastened to it by welding, characterized in that the said metal part (1) includes, below its upper terminal portion, a lateral excrescence (18) which is manufactured integrally with it and to the upper face (24) of which excrescence the said collar (21) is fixed by welding.
2. Mould according to Claim 1, characterized in that its cooled metal part (1) is manufactured by an extrusion process followed by machining of its upper terminal portion and of the said excrescence (18).
3. Mould according to Claim 1 or 2, characterized in that the said emitters (14,15) are applied to the said collar (21).
4. Mould according to Claim 1 or 2, characterized in that the said emitters (14,15) are applied to the said excrescence (18).

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