EP0142402A1 - Horizontal continuous casting installation for metals, especially for steel - Google Patents

Abstract

The installation comprises principally a metallurgical casting vessel (1), a horizontal continuous casting ingot mould (7) and a seal (11) connecting this ingot mould to this vessel, the seal (11) being an element made from refractory material formed from two contiguous parts (14) and (15) having between them a full cross-section difference. Moreover, the internal profile of the channel (10) made in the seal is of uniform shape, at least in the part of the seal (11) of smaller full cross-section, and the channel (10) is completely uninterrupted at the seal-ingot mould connection. Moreover, means are provided for cooling the part of smaller full cross-section (15). <IMAGE>

Description

The present invention relates to the continuous horizontal casting of metals or alloys, in particular steel.

The installations for horizontal continuous casting of steel essentially comprise a metallurgical casting container receiving the molten metal and provided at its lower part with a lateral outlet orifice situated opposite a bottomless mold, energetically cooled, arranged horizontally and whose format conditions that of the cast product. The passage of the liquid metal from the container to the ingot mold takes place by means of a seal constituted by a body axially hollowed out to allow the circulation of the metal, and having excellent refractory properties, for example silicon nitride.

Usually horizontal continuous casting installations are provided with a seal whose axial recess has a cross section smaller than that of the mold (see for example French patent n ° 2,077,534). This type of seal, including. 1 end engages in the manner of an insert in the inlet of the mold, thus creating a recess in the internal pipe of the passage of molten metal at the location of the joint-ingot mold. Given the importance of the heat exchange fluxes at this location, solidification already begins at the foot of the peeling in the mold, and thus ensures a good seal at the connection.

In order to facilitate the extraction of the product poured out of the mold, it is known to subject the product to a cyclic movement of longitudinal oscillations which consists in extracting a certain length of the product poured out of the mold, to be marked a downtime, possibly followed by a short push on the product in the opposite direction to the pouring, then to start again an extraction phase, and so on.

One of the essential problems encountered in the horizontal continuous casting installations mentioned above resides in the presence of skin defects in the solid product, these defects often being difficult to reconcile with current quality requirements.

Research into the causes of these defects has shown that the solidification of the metal against the above-mentioned setback takes place in two different main directions and at different speeds, thus creating zones of heterogeneous crystallization. As the formation of these zones is favored during the abovementioned stop and push phases, corresponding defects are found on the surface of the cast product, regularly spaced apart by a distance equal to the advancement step taken during the extraction phase product out of the mold.

The present invention aims to avoid these drawbacks. More specifically, the invention relates to a horizontal continuous casting installation allowing the control of the start of solidification in the joint and the obtaining of a homogeneous solid metal with good sealing conditions between the joint and the mold.

To this end, the subject of the invention is an installation for horizontal continuous casting of metals, in particular steel, mainly comprising: a casting container provided at its lower part with a lateral outlet orifice; a bottomless ingot mold, energetically cooled, arranged horizontally - or substantially horizontally - and whose internal format defines that of the cast product, said ingot mold having its inlet end facing the outlet orifice of the container; and a seal intended to ensure the tight connection between the outlet orifice of the container and the inlet of the ingot mold, said seal being provided with an internal channel for the passage of liquid metal from the outlet orifice of the container into the ingot mold, installation characterized in that said seal consists of a shaped piece of refractory material axially hollowed out to provide the internal channel, said piece being formed of two parts contiguous having between them a difference in solid cross sections, the part with the largest solid cross section being disposed opposite the outlet orifice of the container, in that means are provided for cooling the part with the smallest solid cross section, arranged opposite the inlet end of the ingot mold, in that the internal profile of the channel formed in the joint is of regular shape at least in the part of the joint with the smallest solid cross section, and in that the cross section right of the end of said channel, in the part of the smallest solid cross section of the joint, is equal to the internal cross section of the mold.

According to a variant, the end of the part with the smallest straight cross-section full of the seal is engaged in the inlet of the ingot mold so as to benefit from the cooling effect of the latter.

• - la figure 1 représente schématiquement une vue en coupe longitudinale d'une installation de coulée continue horizontale de l'acier selon l'invention,
• - la figure 2 est une représentation agrandie plus détaillée du joint montré sur la figure 1,
• - la figure 3 est une vue en coupe transversale selon le plan XX de la figure 2, montrant le joint en section droite.

The invention will be clearly understood and other characteristics will appear during the description which follows, given with reference to the accompanying drawing plates in which:

• FIG. 1 schematically represents a view in longitudinal section of a horizontal continuous steel casting installation according to the invention,
• FIG. 2 is a more detailed enlarged representation of the seal shown in FIG. 1,
• - Figure 3 is a cross-sectional view along the plane XX of Figure 2, showing the joint in cross section.

• - un récipient métallurgique de coulée 1 (ou répartiteur) dont la cuirasse métallique 2 est revêtue intérieurement d'un revêtement réfractaire 3. Ce récipient reçoit le métal en fusion 4 et comporte un orifice latéral de sortie 5 disposé à proximité de son fond, cet orifice étant ménagé dans une busette en matériau réfractaire 6 ;
• - une lingotière horizontale 7, en cuivre ou alliage de cuivre, ouverte à ses deux extrémités et adjacente à l'orifice de sortie 5 du récipient. Ce dernier ainsi que la lingotière, peuvent être de tout type connu ou à venir. La lingotière, dans le présent exemple, est entourée à faible distance par une chemise 8 de manière à définir entre eux un espace 9 pour le passage d'un fluide de refroidissement, généralement de l'eau, qui assure une extraction calorifique permettant d'obtenir, à la sortie de la lingotière, une solidification périphérique suffisante du produit coulé P.

In FIG. 1, the casting installation shown essentially comprises:

• - a metallurgical casting container 1 (or distributor), the metal breastplate 2 of which is internally coated with a refractory coating 3. This container receives the molten metal 4 and comprises a lateral outlet orifice 5 disposed near its bottom, this orifice being formed in a nozzle of refractory material 6;
• - A horizontal ingot mold 7, made of copper or copper alloy, open at its two ends and adjacent to the outlet orifice 5 of the container. The latter as well as the mold, can be of any known or future type. The mold, in the present example, is surrounded at a short distance by a jacket 8 so as to define between them a space 9 for the passage of a cooling fluid, generally water, which ensures a heat extraction allowing obtain, at the outlet of the mold, sufficient peripheral solidification of the cast product P.

The passage of the liquid metal from the container to the ingot mold takes place via a communication channel 10 connecting the orifice 5 of the container to the inlet of the ingot mold. This channel is formed in the seal 11 which, in this example, engages by its free end 12 in the inlet of the mold in the manner of an insert.

All the rest of the outer periphery of the seal 11 is wrapped in a thermal insulator 13 which is currently made of a fibrous material based on alumina and silica. In this example, the seal 11 is chosen from silicon nitride, well known for its good refractory qualities.

• - une partie 14 de grande section droite pleine que l'on convient d'appeler "tête" du joint,
• - et une partie 15 de faible section droite pleine que l'on convient d'appeler "nez" du joint.

Referring now to FIGS. 2 and 3, it can be seen that the seal 11 consists of a body of circular shape axially hollowed out to provide the passage channel 10. This body is composed of two well differentiated contiguous parts:

• a part 14 with a large solid cross section which should be called "head" of the joint,
• - And a part 15 of small solid cross section which should be called "nose" of the joint.

We saw with reference to the previous figure, that the end 12 of the nose could be engaged in the ingot of the ingot mold, this in order to benefit locally from an accelerated cooling by the cooling water of the ingot mold itself .

In accordance with a characteristic of the invention, the internal profile of the channel 10 formed in the joint 11 is uniform, at least in the part 15 of smaller solid cross section, and the internal cross section of the end 12 is equal to the internal cross section of the mold, so that the passage of the liquid metal has no discontinuity at the junction between the seal 11 and the mold 7.

In order to facilitate the extraction of the cast product, the internal profile of the channel 10 is slightly divergent in the direction of casting. The flaring of the channel 10 in the casting direction also makes it possible to compensate for any wear and tear which could occur on the walls of the channel 10. In the example described above, the channel 10 has a slope of 10%, as well as this is usually done.

According to a preferred variant of the invention and shown in Figure 2, the solid cross section of the nose of the seal decreases regularly away from the head of the seal. In addition, for practical reasons of construction which will be easily understood, the head and the nose of the seal are preferably separated by a zone 16 of abrupt variation of solid cross section.

We can very well envisage a sudden separation of the two parts of the joint, which would form an angle close to 90 ° in a longitudinal section, such as FIG. 2.

Unlike current devices for horizontal continuous casting, where one tries to obtain the start of solidification of the metal in the mold, the horizontal continuous casting installation according to the invention ensures the start of this solidification in the joint.

Indeed, the study of the heat exchanges in the joint according to the invention has shown that the density of extracted heat flux is very low in the head of the joint, then increases rapidly with the passage of zone 16 to be very high in the nose. In addition, in accordance with the invention, means are provided for cooling the part of the smallest solid cross section. As we saw earlier, in this example, these means may advantageously be constituted by the cooling device of the mold 7 itself. Consequently, the first deposit of solid metal is favored in the portion of the channel 10 located in the nose of the joint.

On the other hand, solidification is made impossible in the part of the channel 10 located in the head of the seal, where the heat exchange flow is made practically negligible due to the large mass of material constituting the seal at this location.

It is easy to understand that the results obtained are due in part to the structural characteristics of the joint, ie unlike the solid straight sections between the head 14 and the nose 15 and in part to the cooling means with which the nose 15 is provided. so define the joint in two parts in the following functional way: a "retarding" part of solidification (the head) turned towards the side of the pouring vessel, followed by an "accelerating" part of solidification (the nose) ) placed next to the mold.

In the case of a silicon nitride gasket, the dimensions of the gasket more particularly recommended are such that, the thickness AA 'of the end of the head 14 is equal to or greater than 15 mm, the thickness BB' of the end of the nose 15 is equal to or less than 5 mm and the total length AB of the joint, is preferably between 30 and 150 mm.

Indeed, silicon nitride while being an excellent refractory material, also has a low thermal conductivity, but which should not be neglected if one wishes to guarantee for sure the start of solidification in the nose of the joint.

In the example shown in Figure 2, the thickness AA 'is 24 mm, the thickness BB' is 2 mm and the total length AB of the joint is 40 mm, including 28 mm for the length of the head 14 of the joint and 12 mm for the length of the joint nose.

In addition, the results obtained are also due to the absence of discontinuity, or of detachment, in the part of the channel 10 in which the solidification of the metal is favored, namely in the nose of the joint and at the joint-ingot mold connection. .

Finally, the installation according to the invention ensures a regular start of the solidification of the molten metal, which has the main advantage, obtaining a homogeneous solid metal, free of the surface defects usually encountered.

According to a preferred variant, the head 14 of the joint, is, as can be seen in FIG. 1, wrapped in a thermal insulator 13 which, if necessary, contributes to avoiding an early initiation of solidification in this place.

As already said before, in accordance with an advantageous arrangement shown in FIG. 1, the nose 15 of the seal is introduced into the inlet of the mold. The cooling system of the mold is then judiciously used to generate a sufficiently large heat exchange flow in the terminal part of the seal nose to ensure the start of solidification. This arrangement makes it possible to obtain suddenly the desired result without having to use additional cooling means in the casting installation. In this case, as can be seen in FIG. 1, the inlet of the ingot mold is advantageously shaped as a funnel 17 which closely matches the external surface of the end 12 to ensure good thermal contact between them. That said, it remains of course possible to provide a specific cooling system for the seal nose which will be adjusted independently of that of the mold. In the same way, it is possible to reinforce the retarding power of solidification in the part 14 of larger solid cross section by providing the latter with a heating system in association or not with the insulating lining 13. It can be envisaged , for example, an inductive ring around the head 14 of the joint, or the use of a resistor embedded in the refractory of this part 14, or any other heating means having a localized action at the head of the joint. It will be understood that the installation of these heating means makes it possible, if desired, to reduce the thickness AA ′. The work carried out in this direction has shown that the thickness AA 'could then be reduced to 5 mm, without prejudice to the mechanical strength of the joint. These arrangements lead to the same results as those mentioned above, namely the beginning of the solidification of the metal in the nose 15 of the seal 11.

Consequently, in a continuous casting operation, the molten metal initially solidifies in the pipe formed in the joint, first in the nose of the joint where, once initiated, it continues regularly to become maximum in the mold where cooling is the most energetic. The joint according to the invention makes it possible to obtain a metal solidified homogeneously by virtue of the initial conditions for regular solidification of the cast product, and to avoid any infiltration of metal at the junction of the joint with the ingot mold.

In addition, the invention finds its application for the horizontal continuous casting of all metals and alloys.

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

In particular, if the end 12 of the seal is engaged in the inlet 17 of the mold, we will adopt, at least for this part 12, an external shape similar to that of the internal passage of the mold, for example a square shape for ingot molds in square format or a circular shape for ingot molds in round format.

Likewise, the length of the joint is in no way an essential or determining characteristic of the invention. Thus, the lower limit of 30 mm recommended for a silicon nitride gasket can be further reduced if a refractory material having a thermal conductivity less than that of silicon nitride, for example alumina.

Regarding the upper limit of 150 mm, recommended for the silicon nitride gasket, it is understood that it is advantageous if one wishes to equip the gasket n with a heating system for the head 14 or a autonomous nose cooling system 15, or of these two systems at the same time.

Furthermore, the refractory material constituting the seal is not necessarily silicon nitride. One can provide in an installation according to the invention, for example a boron nitride gasket which, while being a good refractory, has a thermal conductivity close to that of silicon nitride. One can also provide an alumina gasket which, on the other hand, has a thermal conductivity significantly lower than that of silicon nitride. Thus, in the case of an alumina joint, it is possible to reduce the thickness AA 'of the head of the joint up to 5 mm without prejudice to the retarding power of solidification of this part of the joint. in the case of an alumina seal, a thickness BB 'of the seal head not exceeding 1 or 2 mm is recommended if its cooling is ensured by the cooling system of the ingot mold. Depending on the thermal conductivity of the refractory material chosen for the joint, a person skilled in the art can easily determine the thicknesses of the parts of the largest solid cross section and of the smallest solid cross section in order to produce a joint according to the invention.

It is the same, moreover, for the size or the profile of the axial passage formed in the joint, while retaining that, in accordance with the invention, this axial passage must not have any format discontinuity with that of the mold, at least in the nose of the joint.

Claims (7)

1) Installation for horizontal continuous casting of metals, in particular steel, mainly comprising a casting container provided at its lower part with a lateral outlet orifice, a bottomless ingot mold, energetically cooled, arranged horizontally or substantially horizontally and whose the internal format defines that of the cast product, said ingot mold having its inlet end facing the outlet orifice of the container, and a seal intended to ensure the tight connection between the outlet orifice of the container and the inlet of the mold, said seal being provided with an internal channel for the passage of the liquid metal from the outlet orifice of the container into the mold, installation characterized in that said seal consists of a shaped part (11) made of material refractory axially hollowed out to provide the internal channel (10), said part being formed of two contiguous parts (14,15) having between them a difference in cross-sections d solid rites, the part (14) of larger solid cross section being disposed opposite the outlet orifice (5) of the pouring container (1), in that means are provided for cooling the part (15) of smaller solid cross section, disposed opposite the inlet end (17) of the mold (7), in that the internal profile of the channel (10) of the seal (11) is of regular shape, at least in the part (15) of smaller solid cross section, and in that the internal cross section of the end (12) of said part (15) of the joint is equal to the internal cross section of the mold (7). 2) horizontal continuous casting installation according to claim 1, characterized in that the end (12) of the part (15) of smaller straight cross section full of the seal (11) is engaged in the inlet of the mold (7 ). 3) horizontal continuous casting installation according to claim 1 or 2, characterized in that the thickness of the part (15) of smaller straight cross-section full of the joint (11) decreases regularly away from the part (14) Furthermore large full straight section. 4) horizontal continuous casting installation according to claims 1, 2 or 3, characterized in that the part (14) of larger cross section full of the joint (11) is provided with heating means. 5) horizontal continuous casting installation according to any one of claims 1 to 4, characterized in that the part (14) of larger cross section full of the joint (11) comprises an external thermal insulation (13). 6) horizontal continuous casting installation according to any one of claims 1 to 3, characterized in that the seal is made of alumina and in that the thicknesses of the parts of larger solid cross section (14) and smaller cross section solid (15) have values which are respectively greater than 5 mm and less than 2 mm. 7) horizontal continuous casting installation according to any one of claims 1 to 3, characterized in that the seal is made of boron nitride or silicon nitride and in that the thicknesses of the parts of larger solid cross section (14 ) and of smaller solid cross section (15) have values which are respectively greater than 15 mm and less than 5 mm.

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