EP0943380A1 - Process and installation for continuous casting of metals - Google Patents

Abstract

The installation including a mold (2) with cooled walls and a top melt receiver (5) has an annular chamber (9) which surrounds the pouring pipe (81) from the melt receiver, and can be supplied with gas at a variable pressure. The gas pressure in the annular chamber (9) is controlled in such a way that the annular free melt surface (12) is maintained at a constant level.

Description

The invention relates to an installation of continuous casting of a metal product, in particular steel and also covers setting processes work of such an installation, allowing, in particular, to control the casting conditions.

We know that in a casting installation continuous, especially steel, metal in fusion is continuously poured into a shell or bottomless ingot mold with cooled walls which limit a casting cavity with a substantially axis vertical. Metal, for example steel, is usually brought steelworks into pockets and, to ensure the continuity of the casting it is first dumped into a called dispenser, in English, "tundish", consisting of a covered tank of refractory material and provided with an orifice casting by which a jet of molten metal is poured entering the upper opening of the mold which at the start of the casting, is closed at its part lower, so as to form a metal bath liquid.

Generally the walls of the mold are internally coated with copper and are cooled by circulating water so that it forms, along the internal faces limiting the pouring cavity, a solidified skin or crust of which the thickness gradually increases towards the bottom, which extracts, through the lower opening of outlet, a product with a liquid or pasty core, maintained by solidified skin. Solidification ends in the rest of the machine which, advantageously, can form a guiding corset of the product bringing it horizontally to facilitate cutting into products such as slabs, blooms or billets, depending on the profile and dimensions, in cross section, of the cavity casting.

The technique of continuous casting, in particular of steel, is exploited industrially for several decades and has been the subject many improvements, especially for simplify the operation of the casting machine and to improve the quality of the cast products.

It is particularly necessary to decrease the risk of breakthroughs that can occur in the ingot mold or immediately downstream of it, when the solidified crust has a low thickness. Indeed, such breakthroughs require stopping the machine when they are too important and, in any case, cause surface defects.

For this, it is necessary to control, as much as possible, the casting conditions and, in particular, formation of the solidified skin inside the ingot mold.

It has long been observed that performed better by now also as constant as possible the casting speed and the average level of the bath in the mold, sudden fluctuations in this level which can cause breakthroughs due to sticking of the skin. So we have developed means of automatic control which allow, in particular, to measure the level of bath in the mold and adjust the metal flow arriving in it, for example, by doing vary, by means of a stopper, the section of the dispenser outlet.

A particular problem arises, however, in so-called multiple casting installations, comprising several working casting lines simultaneously and fed at the same time from of the same distributor which can be provided with several pouring apertures each opening into a ingot mold. It is then difficult to settle simultaneously the flows in each of the orifices of out of the "tundish".

To resolve this problem, document DE-A-1.608.350 proposes to provide the "tundish" with only one outlet opening forming a single jet which opens out in an intermediate tank applied to all of the ingot molds and fitted with several each opening into an ingot mold. The steel bath level being the same for all ingot molds, these are fed to the same speed and you only need to control the flow of the single "tundish" outlet.

In a particular embodiment, each pouring opening is extended by a channel in refractory material that gets inside the ingot mold and thus limits an annular free space into which the lubricant is introduced. This one vaporizes on contact with metal and annular spaces are interconnected so as to be subject to the same pressure, this being limited by a valve dump. We thus determine the same conditions of casting in all working molds therefore simultaneously and at the same casting speed.

It follows, however, that one cannot individually control the casting conditions in each row.

Furthermore, it was found that avoid, as much as possible, the appearance of faults even superficial, on the surface of the product sunk because it is subsequently subjected to rolling operations which incorporate these defects in the metal and can diminish the qualities of the laminated product.

Such defects result, essentially, solidification conditions inside the ingot mold and, in particular, variations of level of the upper surface of the metal bath. Until now, in fact, it seemed necessary to subject the mold to periodic oscillations low amplitude to avoid sticking of the product and, in particular, to favor the introduction of a lubricant between the cooled face of the mold and the solidified crust. We note, however, the appearance of defects on the surface of the product and it has been established that these surface defects are mainly caused at the beginning of solidification, that is to say at the level of the free surface of the molten metal which is often referred to as term "meniscus", because of its shape.

Indeed, the edge area of this surface free which is in contact with the cooled wall of the ingot mold, solidifies instantly and contracts under the effect of cooling and phase change, from outside to inside of the product. The free surface thus presents, on its periphery, a convex shape that connects tangentially to the wall cooled from which the solidification process is propagated by conduction and radiation. As a result, the edge solidified metal peels inward in forming hardened parts commonly called "solidification horns".

As noted, oscillations tangentials are usually applied to the ingot mold to facilitate the descent of the metal and the introduction of a lubricant (powder fuse, or oil) between the cooled wall and the solidified surface of the metal.

Since the solidification horns follow the movement of the mold, the metal liquid that continues to be poured into it can fill, by overflow, the space between the wall and the horn. This overflow effect causes defects in surface and can even induce subcutaneous defects.

In addition, the oscillation of the mold promotes the introduction of lubricant into space between the cooled wall and the horn, increasing the bending of it, and this can cause deeper marks on the end product and even the trapping inclusions and gas bubbles at inside of the liquid steel.

Another difficulty comes from the conditions for introducing the metal into the ingot mold. As we indicated the metal spilled from the "tundish" forms a jet which falls into the inlet of the ingot mold. To avoid metal oxidation between the ingot mold and the "tundish", the outlet of this is usually extended by a tube of casting whose lower end is immersed in the metal bath contained in the mold. The jet of metal therefore penetrates at high speed into the bath existing and disturbs the free surface of the metal in increasing the risk of overflow. In addition, even if a pouring tube is used, the sealing cannot not be certain and the speed of the jet can cause air suction forming bubbles which, by the penetration of the jet, can get into the bath.

It is therefore desirable to master as much as possible the conditions for introducing the metal in the mold and the solidification process at the free surface of the bath.

To check the conditions of solidification at the meniscus, it has been proposed, a few years ago, to place above the ingot mold an uncooled feed tank into which the pouring nozzle opens. We avoid, in this way, the difficulties linked to the arrival of the metal in the bath whose free surface remains malleable. In addition, the flow of liquid metal which penetrates into the mold immediately distributes over the entire section of it and the start area solidification, in contact with the cooled walls, is placed clearly below the free surface. The solidified crust is therefore subject, from its formation, at the pressure of the metal which overcomes it and apply it against the wall.

Such a so-called "hot top" process has been described, by example in document FR-A-2,359,662 for the casting of non-ferrous metals and in document DE-C-3.330.844, for casting steel.

It was found, however, that difficulties may appear at the junction between the part upper refractory and lower cooled. Indeed, in this area of junction called "triple point" are on one side liquid steel and on the other two superimposed walls whose temperatures are very different, respectively, the temperature refractory wall which is located above the junction and, in below, the cooled wall of the mold. It is therefore difficult to obtain frank solidification at level of this junction area.

In the disposition of document DE-C-3.330.844, the lower part of the riser refractory fits into the inlet of the ingot mold so as to form a recess below from which the lubricant is introduced intended to facilitate extraction. This avoids the direct contact between the liquid metal and the point triple but the lubricant must be introduced under pressure and it's difficult to control conditions for early solidification, the crust solidified starting to form from the exit of the refractory riser. Moreover, this enhancement weighs down the mold and disturbs, for Consequently, the oscillating movements thereof.

The invention makes it possible to remedy the whole difficulties related to the conditions of introduction of the steel in the mold and in the process of solidification, thanks to a new provision which allows, in particular, to decrease or even to eliminate surface and subcutaneous defects which, usually occur early in the solidification.

• une lingotière comprenant des parois refroidies avec des faces internes qui limitent une cavité de coulée à axe sensiblement vertical ayant un orifice supérieur d'entrée du métal liquide et un orifice inférieur d'évacuation d'un produit qui sort de la lingotière à une vitesse d'extraction,
• des moyens d'introduction en continu du métal en fusion dans la lingotière pour la formation, à l'intérieur de celle-ci, d'un bain de métal se refroidissant progressivement par l'extérieur, le long des faces internes des parois de la lingotière pour former une croûte solidifiée dont l'épaisseur augmente progressivement vers le bas,
• lesdits moyens d'introduction comportant un récipient intermédiaire comprenant une chambre supérieure de réception d'un jet continu de métal liquide, placée au-dessus de la lingotière et dans laquelle le métal forme une surface libre, ladite chambre de réception étant prolongée vers le bas par un canal de liaison pénétrant à l'intérieur de la lingotière jusqu'à un orifice inférieur de sortie du métal, ledit canal de liaison étant limité par une paroi tubulaire séparée des faces internes des parois de la lingotière par un espace libre périphérique formant une chambre annulaire dans laquelle remonte le métal liquide sortant par l'orifice inférieur, jusqu'à une surface annulaire, ladite chambre annulaire étant fermée de tous côtés,
• des moyens d'introduction d'un gaz sous pression à l'intérieur de la chambre annulaire et,
• des moyens de régulation de la pression appliquée par le gaz sur la surface annulaire du métal.

To solve these problems, the subject of the invention is a continuous metal casting installation comprising:

• an ingot mold comprising cooled walls with internal faces which limit a casting cavity with a substantially vertical axis having an upper orifice for the entry of liquid metal and a lower orifice for discharging a product which leaves the ingot mold at a speed d 'extraction,
• means for continuously introducing the molten metal into the mold for the formation, inside thereof, of a metal bath gradually cooling from the outside, along the internal faces of the walls of the ingot mold to form a solidified crust whose thickness gradually increases towards the bottom,
• said introduction means comprising an intermediate container comprising an upper chamber for receiving a continuous jet of liquid metal, placed above the ingot mold and in which the metal forms a free surface, said reception chamber being extended downwards by a connecting channel penetrating inside the mold to a lower metal outlet orifice, said connecting channel being limited by a tubular wall separated from the internal faces of the walls of the mold by a peripheral free space forming a annular chamber in which the liquid metal exiting through the lower orifice rises to an annular surface, said annular chamber being closed on all sides,
• means for introducing a gas under pressure inside the annular chamber and,
• means for regulating the pressure applied by the gas to the annular surface of the metal.

As usual, a product of lubrication must be introduced along the walls cooled from the mold to lubricate them and avoid sticking. Advantageously, this product is introduced above the annular surface, at inside the annular chamber between the wall tubular connecting channel and the cooled wall of the ingot mold.

According to a preferred characteristic, the free space between the tubular wall of the connection and the cooled walls of the mold has a width over its entire periphery sufficient to avoid solidification of the surface of the metal in said free space.

Particularly advantageously, the connecting channel has an interior cross section sufficient for the metal flow speed liquid supplying the ingot mold is low, in particular between 3 and 6 times the speed of casting, which avoids turbulence in the ingot mold. Preferably, the cross section interior of the tubular extension is at least equal to 20% of the product cross section made.

In the case of slab casting, the cavity of casting has a cross section generally rectangular having two large faces and two small faces. According to another characteristic of the invention, the tubular wall of the connecting channel is then limited, at least in its engaged part in the mold, by two large faces substantially parallel to the large faces of the ingot mold.

In a first embodiment, the reception room includes a bottom opening into the connecting channel and provided, on a lower face, a bottom edge extending downward and externally surrounding the connecting channel so to rest on the upper edge of the ingot mold, via a seal sealing.

In another embodiment, the chamber receiver is fixed tightly on a frame support which is connected to the mold by a watertight bulkhead.

The receiving chamber support member can be connected to the mold using a bellows, especially when the mold is subjected to vertical oscillations.

According to another advantageous characteristic, the mold remains fixed and the annular chamber closed is supplied with gas at a pressure of value modulated so as to cause oscillations of the free surface of the liquid metal in space device between the ingot mold and the liaison.

Means for injecting a lubricant (fusible powder, or liquid oil) in the chamber closed ring are provided. These means of injection of lubricant may include a container storage, including a hopper, whose pressure is regulated so that the assembly is maintained at a zero pressure difference.

In a preferred embodiment, specially applicable to a casting mold slabs having two large faces and two small faces, the connecting channel can be provided with a solid block placed below the liquid metal inlet, between the faces of the canal parallel to the large faces of the ingot mold, to deflect the current of metal towards the two small faces of the mold.

According to another variant, the volume included between the connecting chamber and the means of distribution is closed, in particular by a bellows, and the flow of liquid metal between the distribution means and the connecting chamber takes place directly, without submerged nozzle.

The installation according to the invention can be implemented in different ways to control casting conditions and the invention covers also these various methods.

In a first embodiment, we regulates the gas pressure in the annular chamber of so as to constantly maintain the level of annular surface of the metal at a level substantially constant.

In particular, this pressure can be determined so that the surface tension of the meniscus, at the tip of the solidification horn, avoids any risk of liquid metal overflowing.

In another embodiment, we do periodically vary the gas pressure in the annular chamber between a lower value and a higher value, so that the level oscillates of the annular surface of the metal between a level higher and a lower level.

So we can remove the mechanical means or hydraulics used, until now, to animate the oscillation movement ingot mold and installation is therefore considerably simplified. In addition, variations in pressure can be easily controlled so as to determine the mode of variation in the level of the meniscus and, in particular, the negative stripping time.

In an implementation mode particularly simple, the gas pressure in the gas chamber is adjusted so that the level of the annular surface of the metal is maintained substantially at the lower outlet opening of the liaison, this level being kept constant, automatically, by a gas leak rate in the connecting channel.

But the invention will be better understood by the following description of some embodiments given by way of nonlimiting example with reference to the accompanying drawings.

Figure 1 is a schematic section vertical transverse of a casting installation continues at the ingot mold.

Figure 2 shows an example of a pressure regulation.

Figure 3 shows two variants of a free surface oscillation diagram of the liquid metal.

Figure 4 is a schematic section vertical illustrating the product supply ingot mold lubricant.

Figure 5 shows a variant of installation without submerged nozzle.

Figure 6 is a schematic section longitudinal vertical of a variant of the installation for conventional slab casting or medium.

Figure 7 is a view along line VII-VII in Figure 6.

Figure 8 shows, in schematic section vertical longitudinal, another variant of realization, with a separate support member for the raised linkage chamber.

Figure 9 is a section along line IX-IX in Figure 8.

Figure 10 shows, in schematic section vertical, another variant for the casting of slabs.

Figure 11 is a top view of the installation of figure 10.

Figure 12 is a cross-sectional view along line XII-XII of Figure 10.

Figure 13 is a schematic section transverse vertical of a line installation multiples according to the invention.

In Figure 1, there is shown schematically the upper part of a installation for continuous casting of a metal such as steel, comprising, as usual, a shell or ingot mold 2 with open bottom, limited by walls 4 generally having an internal face 41 coated with copper and defining a casting cavity with a substantially vertical axis, and whose cross section transverse corresponds to that of the product to be cast 3, for example, slab, bloom or billet.

The walls 4 are cooled externally by an envelope E of water or fluid circulation cooling. So it happens, along cooled walls 4, a solidified crust 30 of which the thickness gradually increases and is sufficient, at the outlet orifice 60 of the ingot mold to maintain the central part of the product which constitutes a liquid core becoming pasty and forming a well that gradually narrows downstream. The ingot mold 2 is followed by a zone of secondary cooling not shown on drawings, comprising at a level where the solidified metal is strong enough, means of extraction that pull the product down at a speed extraction.

The free surface of the bath is covered with a protective layer advantageously consisting of a product forming a lubrication layer which is driven by the metal to come between the solidified crust and the internal faces 41 of the ingot mold 2 so as to favor the extraction and avoid sticking.

The walls 4 of the mold are substantially vertical but can be curved to produce, from the start, a curved product likely to be brought horizontally in a guide corset and secondary cooling.

All these provisions are classic and need not be described in detail.

As usual, the molten metal is discharged by gravity from means of introduction D which, as shown in the other figures, usually include, a tank 7 called distributor or "tundish", coated internally of a refractory wall 7a, and supplied from ladles poured by liquid metal from the steelworks.

The metal is poured out through a hole in the bottom of the dispenser 7 and extended, generally, by a tube or nozzle intended for protect the metal jet 33 from oxidation.

Most often, the lower end of the distributor 7 drain nozzle enters inside the metal bath 3 formed in the ingot mold, so that the metal is protected from oxidation.

As indicated above, a disadvantage of this technique called the nozzle immersed lies in the fact that the metal jet arrives at high speed in the bath and disturbs the meniscus constituting the upper surface thereof.

To improve the conditions at the start of solidification, the installation is of the type known as "to feeder "or" hot top "in which the ingot mold 2 is surmounted by an intermediate container 1 forming an uncooled riser and therefore internally covered with ceramic or a product refractory, the upper part 5 of which constitutes a metal jet 33 receiving chamber from the distributor 7, which opens, through an orifice lower, in the mold 2. Thus, it is formed at inside the reception room 5 a bath metal M which spreads directly in the mold 2 so that the beginning of solidification along cooled walls 4 occurs at a level significantly lower than that of the upper surface 11 of the metal bath M in the receiving chamber 5.

As shown in Figure 1, the reception 5 rests directly, by a ledge lower 13, on the upper edge 6 of the mold 4 and is extended downwards by a connecting channel 8 limited by a tubular wall having a face 81 which has, in cross section, dimensions significantly smaller than those of the cavity casting 1, so as to penetrate with clearance inside of it to an outlet 82 placed inside the mold, below the upper edge 6 of the cooled walls 4.

The external face 81 of the connecting channel 8 is separated from the internal face of the cooled walls 4 of the mold 2 by a peripheral free space which surrounds him completely.

As usual, the metal spilled continues to descend along the walls 4 of the ingot mold 2 to exit from it in the form of a product 3 limited by a solidified skin 30 and the metal discharge rate from the distributor 7 is set according to the extraction speed of the product.

However, in the arrangement according to the invention, the ferrostatic pressure prevailing in the metal at the outlet orifice 82 of the connection 8 brings the metal back up inside peripheral space, up to level 12 constituting an annular surface separate from the free surface 11 of the metal bath M by a height ferrostatic h.

The reception room 5 is connected to the walls 4 of the mold 2 by a junction member waterproof J and thus form, above the space peripheral, an annular chamber 9 which is bounded inward by the outer wall 81 of the connecting channel 8, outwards through the wall interior 41 of the mold 2 and the junction J, upwards through the bottom of the receiving 5 and down through the surface 12 of the metal liquid which rises in the peripheral space. This annular chamber 9 is therefore closed on all sides and forms a sealed space.

The width d of the peripheral space 10 can be substantially constant but must be sufficient so that the metal remains liquid by forming a meniscus annular 12 between the two opposite faces, respectively 41 of the mold 2 and 81 of the channel liaison 8.

The installation also includes means 50 for introducing a gas under pressure to the interior of the annular chamber 9, by through an orifice 19 formed near the upper edge 6 of the mold 2. The gas introduced thus above the meniscus 12 is preferably a neutral gas with respect to metal, for example argon, nitrogen, helium or others.

The pressure of the gas introduced into the space annular 9 and applied to the annular surface 12 of metal is equal to the ferrostatic height h between the annular surface 12 and the free surface 11 of the bath M to which the pressure is applied atmospheric, the pressure in chamber 9 in front compensate for the weight of the metal column.

The section of the mold 2 depends obviously of the product to be poured. For the casting of slabs, the horizontal section of the mold 2 is rectangular, the large parallel faces of the ingot mold being perpendicular to the plane of the Figure 1. In this case, the connecting channel 8 has a contour also rectangular, with two large faces perpendicular to the plane of Figure 1 and parallel to the large faces of the mold 4.

In the embodiment of Figure 1, the reception chamber 5 is supported on the ingot mold 2 by a peripheral lower edge 13, protruding downward, which constitutes the organ of tight junction J, a flat seal 14, made of a material temperature resistant at this location, being disposed between the lower end of the rim 13 and the upper edge 6 of the mold 2.

The underside of the reception room 5 comprises, between the support flange 13 and the channel link 8, a transverse step 15 with a concave connecting surface 16 turned to the mold 2. The concave space above of the plane of the joint 14 contributes to the volume of the chamber closed 9.

So thanks to this particular arrangement of the riser 1, part of the metal spilled in the reception room 5 and down into the ingot mold 2 by the connecting channel 8, goes up in peripheral space 10 up to a level which corresponds to the pressure of the gas introduced into the annular chamber 9. This pressure therefore determines the height h between upper level 11 of the metal liquid in the receiving chamber 5 and the surface free 12 of the metal in the peripheral space 10.

By designating by ρ the density of the metal liquid and by g the acceleration of gravity, the pressure P of the gas introduced into chamber 9 is: P = ρgh.

As usual, the discharge rate metal from dispenser 7 should be adjusted to depending on the extraction speed of the product 3 at the out of the mold.

To this end, a regulation system allows to modify the flow rate of the metal jet 33 by acting on the position of a closing stopper rod distributor 7, based on a measurement of the level of the free surface of the metal in the mold, this measurement which can be carried out by known means.

Such a system, which acts only upstream, only keeps the metal at a level average and has a relatively short response time long which does not avoid disturbance in abrupt variation of the extraction speed.

The installation according to the invention is still equipped with the usual flow control systems spill from the dispenser but provides very important improvements to known systems until now. Indeed, the invention makes it possible to achieve very precise regulation of the level of ring meniscus and avoid the causes of disruption of the early solidification process recalled previously.

The installation is equipped with known means 51 location of the metal surface but these can be placed either like usually in the mold, either in the reception room 5, at the free surface 11 which, as we have seen, remains malleable and reacts immediately to variations in metal jet flow 33 leaving the distributor 7.

As shown schematically in Figure 1, the pressure of the gas introduced by the means 50 can be adjusted by a regulator 70 which receives the level information provided by the measurement system 51 but on which can also a setpoint 71 be displayed.

Thanks to such an arrangement, the pressure of the gas in annular chamber 9 can be set to every moment so as to immediately compensate for a variation of the ferrostatic height while maintaining the annular meniscus 12 at a given level.

Therefore, any variation, even significant, from the level of the surface 11 in the chamber 5 can be instantly offset by a change in the pressure in annular chamber 9 with low disturbance of the level of the annular surface 12.

For example, an abrupt decrease in the extraction speed results in an increase in level 11 in reception room 5 and a pressure increase in chamber 9, without notable disturbance of the level of the surface 12 of the metal that remains below the top edge 6 of cooled walls 4.

Conversely, a decrease in flow metal feed from distributor 7 results in a drop in level 11 in the reception 5 and a decrease in pressure in the room 9.

In practice, the dimensions of the room Annular 9 will be provided so that, taking into account volume of gas enclosed, the free surface 12 of the metal liquid rising in the peripheral space 10 can be maintained at the desired level.

Since the lower part of the canal of connection 8 plunges into the bath of liquid metal and is kept sufficiently far from the walls cooled 4 of the mold so that the surface 12 remains liquid, there is no possibility of contact, through metal, between cooled walls and the receiving chamber in refractory material. Indeed, the level of the meniscus 12 is always kept below the level of the junction 14 in the case where the introducer 1 is supported on the mold and this junction can even be deleted in the case of Figure 8 where the introduction member 1 is not connected to the mold only by a bellows.

In all cases, training is therefore avoided of a triple point and the difficulties encountered usually at this level.

Particularly advantageously, the cross section Si of the interior passage of the channel 8, while being weaker than the section Inner mold of mold 2 (or section of product), is sufficient for the speed of flow Vi of the liquid metal inside the link channel 8 is weak and corresponds to the flow necessary to maintain the extraction speed, taking into account the report of the sections. We thus avoid the strong turbulence which usually occurs occur at the outlet of the nozzle, when it opens directly into the ingot mold through an orifice immersed in the bath.

For example, the channel exit If section 8 may be in the range of 20 to 30% of the Sp section of the product. In practice, this leads to a slow speed of flow of steel, around 3 at 6 times the casting speed, i.e. 6 to 12 m / min then that usually the speed of metal at the outlet of the nozzle, can be of the order of 60 to 100 m / min.

The energy of jet penetration and agitation bath in the mold 2 is therefore reduced so very important, noticeably in the ratio of squares of penetration speeds. Consequently, the invention makes it possible to avoid or, at least, to reduce considerably, the directly related disturbances to this kinetic energy, which occur usually on the surface of the bath.

In addition, due to its weak impulse, the metal jet at the outlet of the connecting channel 8 is immediately braked by the liquid mass and, by density difference, goes up quickly in the peripheral space 10 according to the arrows F on the Fig. 1, which makes it possible to continuously heat the free surface 12 of the metal which therefore remains more easily liquid.

As usual, the metal poured into the ingot mold 2 solidifies superficially on contact cooled walls 4 thereof and forms a product 3 which is extracted through the outlet port 60 of the mold and which is limited by a crust solidified 30 whose thickness increases gradually from the level of the surface 12. The outer edge 31 of the latter, in the form of a meniscus, suddenly solidifies on contact with the wall 4 but, due to the rise in temperature which results from the permanent rise of the molten metal, this hardened edge 31 remains malleable. As a result, the skin solidified which descends along the mold can be immediately applied against wall 4 by the pressure prevailing in the liquid metal and which, at level of the surface 12, is proportional to the ferrostatic height h. This reduces the risk of solidification horn formation in the product sunk.

In the example shown in Figure 1, the introduction member 1 comprising the reception 5 and the connecting channel 8 rests on the ingot mold 2 and can therefore be submitted, with it, to vertical oscillations of limited amplitude, performed using mechanical means (not represented) and which favor the penetration of the lubricant between the solidified metal layer and the walls of the mold to avoid sticking.

However, to achieve a variation of the free surface level 12, it is not no more mechanical oscillation of the ingot mold 2 itself, because you can also use the regulation system 70 for modulating the pressure of the gas in the annular chamber 9 and thus vary the level of the annular meniscus 12.

By way of example, FIG. 3 gives two diagrams illustrating possible pressure modulations in chamber 9. On these diagrams the time is plotted on the abscissa and the gas pressure P, represented by the curves C ₁ in solid lines, is laid on the ordinate. The level N of the free surface 12, also plotted on the ordinate, is represented by the dashed curves C ₂ .

Figure 3a illustrates sinusoidal variations of the gas pressure in the chamber 9. An increase or decrease in the pressure determines a decrease or an increase in the level of the surface 12, with a certain delay which results, on the Figure 2, by a phase shift of the curves C ₁ and C ₂ .

Figure 3b illustrates variations in pressure in the form of triangular signals. We finds similar variations in level, also late phase shifted.

So by modulating the pressure in the chamber 9, it is possible to obtain, without moving the ingot mold 2, an oscillation of the free surface 12 allowing to sweep, on either side of a level medium, an area covered then discovered by steel liquid. When this area is discovered, the product lubricant introduced into chamber 9, fills the walls of the mold 2. During the period covered, the lubricant is trapped between the skin solid steel and the ingot wall, which allows flexible extraction of product 3 without risk lift-off.

In a particularly embodiment simple schematically shown in Figure 5, the pressure in the supply circuit 19 of the annular chamber 9 is regulated by a system with water column comprising two columns opening to different levels which can be linked alternatively to line 19 by a two-way valve positions ordered periodically depending on the pressure modulation diagram chosen.

The immersion depth a (Figure 1) of the connecting channel 8 of refractory material inside the mold 2 can be quite small. It must in fact be simply sufficient to keep the outlet orifice 82 of the connecting channel 8 below the surface 12 of the metal which depends on the pressure of the gas introduced by the means 50 inside the annular chamber. 9.

Figure 2 shows, by way of example, a regulation system.

Line 19 which leads to the part upper part of the mold 2, in the chamber ring 9, is connected to a supply circuit 50 in pressurized gas, preferably neutral with respect steel. The annular chamber 9 is also connected, by an outlet pipe 19 ', to a circuit discharge 52 on which is placed a valve 53 pressure regulator, supply pressure provided by circuit 50 being slightly greater than the desired pressure.

A pressure controller 72 compares a signal representative of supply pressure, supplied by a pressure transmitter 73, at a value of instructions which can be drawn up by a regulation 71 according to a signal supplied by the level 51 measuring device, but which can also be displayed manually.

The outer wall of the reception room 5 can also be provided with a cooling means 17 consisting, for example, of a shirt in which circulates a coolant, especially some water. The cooling means 17 allows avoid overheating of the liquid steel spilled in reception room 5 and, if necessary, form on the inner wall of the chamber receiving 5 a thin layer of solid metal which protects the refractory material of chamber 5 against wear and erosion, and reduces the risks inclusions by entrainment of particles of refractory.

It should be noted that the elevation of the level 11 liquid metal above the mold 2 allows a settling of the liquid metal in reception room 5, which also reduces the presence of inclusions and impurities in the metal driven in the mold 2.

The operation of the installation is following.

As usual, at the start of casting, the lower opening 60 of the mold 2 is closed by a false bar or dummy (not represented). Liquid metal is poured into the receiving chamber 5, passes through the connecting channel 8 and gradually fills the mold 2 until that the lower end of channel 8 is submerged in the liquid metal bath which goes back to level 12, by compressing the gas contained in the annular chamber 9 which is sealed.

By means of extraction cylinders not represented, the progress of the dummy for product advancement 3 limited by a solidified skin 30 which forms at contact of the cooled wall 4 of the mold 2 and whose thickness is increasing from top to bottom.

As indicated, when the mold 2 is supplied directly from the distributor 7 by a submerged nozzle, the pulse of the metal jet at the exit of it is such that the jet can penetrate deep enough into the metal already contained in the ingot mold by causing a reflow untimely. This risk is avoided thanks to the invention because, due to the large passage section of the connecting channel 8, the speed of the metal at the outlet 81 of it remains quite low.

In addition the loading of the resulting steel of the elevation of the raised reception room 5, promotes regularity of exchange and allows to increase the solid thickness at the outlet of the mold compared to a conventional arrangement. It results in solidification at the outlet of the mold is more important and that the risks of piercing solid skin are reduced.

The thickness solidified in the mold being larger and more regular, it is possible to sink faster at constant safety, or at constant casting speed to ensure safety increased against breakthroughs.

In addition, the jet pulse being quite weak at the output of link channel 8 it is possible to provide, above the lower opening 82, radially oriented orifices 29 which promote the rise of metal at high temperature in the annular space 10 without risk of deterioration of solidified skin 30.

We can thus reduce the height L of the walls of the mold for a given casting speed, or increase the casting speed for a height L given, these solutions can be optimized.

Primary settling can occur in the upper part of the reception chamber 5 and, therefore, outside the area of solidification. The steel that is solidified in the ingot mold 2 is therefore already decanted and purified from major inclusions. Thus, the settling which is usually produced in the mold is carried over in reception room 5 whose power elimination of inclusions is better thanks to increasing volume and at very low speed metal descent to the mold.

It should be noted that on its perimeter outside, the annular meniscus 12 is not in contact with the only cooled wall 4 of the mold. There is therefore no triple point and we avoid thus the resulting solidification problems habitually.

But the invention also presents other benefits.

For example, we know that the mold is usually with oscillating movements for favor the introduction of the lubricant between its wall cooled and the layer solidified. Thanks to the invention, it is possible to introduce the lubricant below the free surface 12 in the peripheral space 10, between the solidified layer metal and the wall of the mold and we can so consider not only removing the mechanical oscillations of the mold but, even, variations in level 12 of the share metal and else of an average level.

Thanks to the regulation, according to the invention, of the pressure in the annular chamber 9, so it's possible to keep the annular meniscus at a substantially constant level and, thus, to control solidification conditions at the meniscus avoiding the risk of overflow, generating superficial defects.

To introduce the fluid lubricant or powder, it is advantageous to use the arrangement shown in Figure 4 and comprising a container 21 constituted for example by a hopper tightly closed, and installed at a level higher than that of ingot mold 2 and chamber 5. The lower part of the container 21 is connected to the annular chamber 9 by the line 20 for injecting the lubricant, fitted with a non-return valve 22. The upper part of chamber 21 and annular chamber 9 are connected in parallel to a circuit 23 for supplying gas under pressure. The same pressure prevails in the container 21 and in the annular chamber 9 and it follows that the supply of lubricant of the mold 2 can be done by simple gravity. The container 21 is preferably mounted on a support 24 with interposition of load cells 25 allowing to follow the variation of the mass of lubricant in container 21 and fill up in good time.

As mentioned, a level variation of the free surface 11 of the metal in the reception 5 essentially results in a change in pressure in the annular chamber 9 but has little effect on the level of the free surface 12 of the metal in contact with the cooled wall 4 of the ingot mold 2, in annular space 10. By therefore, while in the facilities classics where the metal is poured directly into the ingot mold, we can only act on the flow steel feed from the distributor, the invention provides an additional means of very precise regulation of the level in the mold.

However, when performing a mechanical oscillation of the mold 2 with the organ introduction 1, this may affect the level of the free surface 12 insofar as the part submerged in the connecting channel 8 undergoes movement. To reduce this effect, we will therefore use preferably, a thin-walled connecting channel 8.

Note that the value of the amplitude of the oscillations becomes quite secondary because the whole surface 12 of the product (slab, bloom or billet) in the peripheral space 10 can be furnished with lubricant. The frequency of the oscillations can be reduced to avoid uncontrolled movements of the annular meniscus 12.

However, as we have seen, the invention allows to replace the mechanical oscillation of the mold by a simple modulation of the pressure above the annular meniscus to cause variation hydrostatic level of it and even allows to suppress the oscillations, the level of the meniscus annular 12 being kept substantially constant.

The invention therefore also covers various methods of implementing the installation that comes to be described.

In a first embodiment, the gas pressure in the annular chamber is regulated so as to permanently maintain the meniscus annular at a substantially constant level. This pressure acts, in particular, on the tension surface of the metal by reducing the risk of overflows.

In a second mode of implementation, we do periodically vary the gas pressure in the annular chamber between a lower value and a higher value, so that the annular meniscus between a higher level and a lower level.

But we can also supply the gas in the annular chamber 9 with a slight overpressure allowing the annular meniscus to be flush substantially at the level of the lower orifice 82 of outlet of the connecting channel 8. Thus, it can produce an inert gas leakage rate that rises along the walls of the connecting channel, the weak penetration speed avoiding entrainment of bubbles. In this way, the level of the meniscus is kept substantially constant.

In general, the invention allows ensure better surface regularity of the solid product, because the free surface 12 is not very agitated and kept under pressure, as well as good health subcutaneous thanks to the regularity of the skin 30. There further has a significant decrease in the segregation, low overheating casting in ingot mold appearing possible due to the free surface pressure 12.

As shown in Figure 4, the distributor 7 can be fitted with a jet protection nozzle 26 of liquid metal and the lower end of which is below the surface 11 of the liquid metal filling the reception room 5.

Figure 5 shows another mode of realization of the junction member J which, in this case, includes a bellows 18 surrounding the chamber reception 5 and the opening (s) 28 provided in the dispenser bottom 7. The upper part of the bellows 18 is tightly fixed to the bottom of the distributor 7. The lower part of this bellows 31 is tightly fixed to the mold 2 or to its envelope E. The interior volume of the bellows 18 is thus protected from the atmosphere so that the flow of liquid metal through the orifice 28 can be done directly, without the need to provide a submerged nozzle. This allows a casting faster, without creating disturbances in ingot mold 2 due to the presence of the organ intermediate 1.

The bellows 18 makes it possible to absorb the possible vertical oscillations of the mold 2 and of the reception chamber 5 relative to the distributor 7.

If no mechanical oscillation of the ingot mold 2 is not provided, we can then replace the bellows 18 by a rigid skirt ensuring, in the same way way, a tight closure of the interior space.

The interior space of the bellows 18 can be relative vacuum for degassing of the steel jet liquid exiting through the opening (s) 28. A pressure regulation inside the bellows 18 can be expected.

In Figures 6 and 7, there is shown in as an example, respectively in elevation and in cross section, an installation for the casting of rectangular section products called slabs.

The different elements already described in reference to the previous figures are designated by identical reference numbers, or augmented by number 100, their description not being repeated except for the modified parts.

In particular, the intermediate body introduction 1 includes an upper chamber of reception 105 resting, by a lower edge, on the chassis of the mold 2 and extended by a channel link 108 which enters the upper part of the mold.

As shown in Figure 7, the reception 105 forms an oblong section tank limited by two walls parallel to the long sides of the ingot mold and connecting by ends rounded.

However, to promote the distribution of metal flowing through the nozzle 26 opening at center of reception room 105, the canal link 108 is provided, in its central part, with a solid block 83 shown in top view and in half-section horizontal, respectively on the parts left and right of figure 7. This block 83 crosses transversely the connecting channel 8 below the outlet of the nozzle 26 and directs the metal in two currents symbolized by arrows F ', towards two orifices 84 with oblong section opening a little above of the lower opening 82 of the connecting channel 8. Thus, the metal spilled by the nozzle 26 is evenly distributed throughout the mold 2, the oblong sections 84 having sections sufficient to ensure relatively high speed low metal descent.

As previously mentioned, openings radial 29 ensure rapid diffusion metal in the annular space 10.

Figures 8 and 9 show, respectively longitudinal vertical section and horizontal section, another alternative embodiment, intended specially for a slab casting plant thin. Items identical or similar to elements already described in connection with Figures 1 to 6 are designated by the same reference numbers possibly increased by the number 200, their description not being repeated for the parts not modified.

Alternatively, the connecting chamber 205 is not no longer in direct support on the mold 2, but is maintained at a fixed level by a support frame 35 surrounding the upper part of the reception room 205 and connected by a waterproof bellows 237 to the ingot mold 2 to allow oscillations thereof. The support frame 35 may be constituted by a welded metal frame, with jacket cooling 117 in contact with the outer wall from reception room 105.

The transition between the upper part of the reception chamber 205 and the connecting channel 208 is gradually provided by a double game curvature to facilitate the descent of the metal into the ingot mold 2. The latter has a section horizontal transverse in rhombus or in spindle for facilitate the introduction of metal, the central part gradually narrowing to the orifice of outlet 60 of the mold 2 which presents the section desired rectangular, this one having a low width relative to its length.

Similarly, the introducer 1, at least in its lower part constituting the connecting channel 208, has a section transverse in analogous rhombus, by homothety, to that of the mold 2, so as to leave between the external wall 281 of the connecting channel 208 and the face internal of the mold, an annular space 10 of substantially constant width.

As in Figure 7, a block solid 283 is disposed in the connecting channel 208 to provide two elongated openings 284, the width gradually decreases towards the short sides of the mold, moving away from the axis of the nozzle 26.

In the embodiment of Figure 8, the annular chamber 9 is closed by the support frame 35 which rests directly on the ingot mold, the introduction member 1 oscillating therewith.

As previously stated, it is also possible to mount the introducer 1 on a fixed support, the support frame 35 being then connected to the mold by a bellows allowing the oscillations of it and closing so seals the annular chamber 9. However, the volume of enclosed gas is then larger and we increase so the possibilities of variations in the level of upper surface 12 of the metal in the annular space 10 depending on variations in surface level 11 of the metal in the receiving chamber 5.

Of course, the invention is not limited to details of the embodiments which have just been described, other variants that can be envisaged without departing from the protection framework defined by claims.

Thus, as shown in the figures 10 to 12, in the case of slab casting where the length of the casting cavity is much longer larger than its width, it can be interesting to provide an intermediate introduction device 1 including a 405 section receiving chamber analogous to that of the ingot mold and several channels 408 offset longitudinally and supplied each from a hole 438 in the bottom from reception room 405. As indicated in the Figure 12, each connecting channel 408 and constituted a tubular wall whose external diameter is determined so that there is a minimum distance d between the wall 481 and the longitudinal face 404 of sufficient ingot mold to avoid solidification metal in the narrowest part of space device 410.

For this reason, in the case shown on Figure 9 where a section ingot mold is used in diamond or in spindle for casting a slab thin it is possible to give to different channels connecting different sections, channels 408b placed in the central part being wider than the channels 408a placed at the ends.

In this way, it is possible to determine a practically uniform distribution of flow for introducing liquid steel into the mold 402.

According to another characteristic particularly advantageous, the arrangement according to the invention considerably facilitates the operation of a multi-line installation allowing to flow simultaneously, in parallel, several products.

Such an installation, represented schematically in Figure 13, includes several ingot molds 2, four in the example, which are arranged parallel to each other. According to the invention, these ingot molds 2a, 2b ... are associated to a single reception room 305 having a sufficient length to cover all four ingot molds and ensuring their metal supply liquid. This can be spilled from a distributor 7 by a single nozzle 26 opening substantially in the center of the receiving chamber 305.

The bottom of it is provided, in the axis of each ingot mold 2a, 2b ..., of an orifice 38 which leads into a connecting channel 308. In the example considered, reception room 305 therefore comprises four extensions each forming a channel of link 308a, 308b ..., plunging respectively into an associated ingot mold 2a, 2b ...

Liquid metal supply to the chamber reception 305 is provided by a single distributor 7 with a common level regulation for all four ingot molds 2a, 2b ..., in the reception room 305, which is provided with a level measuring device whose information is transmitted to the regulator associated with each line of casting.

Thus, the rate of introduction of the metal into each mold 2a, 2b ... automatically adjusts to extraction speed in the mold corresponding, the flow variations in each line being balanced by pressure adjustment above the corresponding annular meniscus, in order to maintain it at the desired level.

The speed of product extraction in each casting line can therefore be adjusted independently others.

Four shutters or cattails closure, not shown in the figure can be associated respectively with the four inlet ports 38 of the link channels 308 to close them in the event stop a line.

This multi-line arrangement can be advantageously applied to the casting of billets round or square.

The examples given above show that the invention is suitable for casting of all kinds of products, including blooms in the same conditions as billets, of conventional slabs thick, medium or thin.

But we can still note other advantages.

Regulation of the flow rate from dispenser 7 can be done more simple than in conventional casting, because a variation of flow has less influence on the process of solidification.

The tubular connecting channel 8, 108, 208, 308 between the reception room and the mold can be cleaned with argon or nitrogen at lower risk for ingot mold steel.

The upper level of the reception room 5, 105, 205, 305 can be cleaned by overflow intermittent (overflow) in a drain pan located next to the reception room for collect the overflow.

The equipment is simplified.

In some cases, the reception room can be fed directly from the pockets of casting, especially for slabs, with a pocket pressure feeding for example.

Casting speed can be increased to 8-10 m / min or more depending on the formats. It is, in fact, interesting to sink fast enough to warm up the free surface 12 in the peripheral space 10, this speed remaining, anyway, quite low so as not to disturb the metal bath, due to the large section of the outlet orifice 82.

Automatic start is safe since any deviation can be channeled by overflow.

In a multiple casting installation, thanks the possibility, according to the invention, of removing the means of oscillation of each ingot mold 2 and of individually set the feed rate of the metal as a function of the extraction speed in each line, the flow of billets, blooms, possibly twin slabs is greatly simplified.

The reference signs inserted after the technical characteristics mentioned in the claims are intended only to facilitate the understanding and limiting them in no way the scope.

Claims (21)

Continuous metal casting installation comprising: an ingot mold (2) comprising cooled walls (4) with internal faces (41) which limit a casting cavity with a substantially vertical axis having an upper orifice (6) for entering the molten metal and a lower orifice (60) d 'evacuation of a product (3) which leaves the ingot mold at an extraction speed, means (D) for continuously introducing the molten metal into the ingot mold (2) for the formation, inside the latter, of a metal bath (M) gradually cooling from the outside, along the internal faces (41) of the walls (4) of the mold (2) to form a solidified crust (30) whose thickness gradually increases downwards, said introduction means (D) comprising an intermediate container (1) comprising an upper chamber (5) for receiving a continuous jet (71) of liquid metal, placed above the ingot mold (2) and in which the metal forms a free surface (11), said receiving chamber (5) being extended downwards by a connecting channel (8) penetrating inside the ingot mold to a lower orifice (82) for leaving the metal , said connecting channel (8) being limited by a tubular wall (81) separated from the internal faces (41) of the walls (4) of the mold by a peripheral free space forming an annular chamber (9) in which the liquid metal rises exiting through the lower orifice (82), up to an annular surface (12), said annular chamber (9) being closed on all sides, means (19, 50) for introducing a gas under pressure inside the annular chamber (9) and, means (70) for regulating the pressure applied by the gas (9) to the annular surface (12) of the metal. Installation according to claim 1, characterized by the fact that it includes means (20) introduction, inside the chamber ring (9), a lubrication product. Installation according to one of the claims 1 and 2, characterized in that the free space (10) between the tubular wall (81) of the connecting channel (8) and the cooled walls (4) present, on all its periphery, a width sufficient to avoid the solidification of the upper surface (12) of the metal (M) in said free space (10). Installation according to one of the claims previous, characterized in that the section internal of the connecting channel (8) is sufficient to ensure the introduction of liquid metal into the ingot mold (2) with sufficient penetration speed slow so as not to disturb the bath deeply liquid metal. Installation according to claim 4, characterized by the fact that the cross section interior of the connecting channel (8,108,208,308) is such as the speed of penetration (Vi) of the metal liquid (M) in the mold (2) is between 3 and 6 times, approximately, the casting speed. Installation according to claim 4, characterized by the fact that the cross section interior (Si) of the connecting channel (8, 108, 208, 308) is at least 20% of the cross section (Sp) of the manufactured product. Installation according to one of the claims previous, in which the casting cavity has a cross section overall rectangular having two large faces and two small sides, characterized in that the tubular wall of the connecting channel (8, 108, 208, 308), is limited, at least in its part engaged in the mold (2), by two large substantially parallel faces the large faces of the mold (2). Installation according to one of the claims previous, characterized in that the chamber annular (9) is limited by a partition (13, 37) surrounding the connecting channel (8) and connected so waterproof, respectively to the receiving chamber (5) and to the cooled walls (4) of the mold (2). Installation according to claim 8, characterized by the fact that the receiving chamber (5) comprises a bottom (15) opening into the channel link (8) and provided, on a lower face, with a bottom edge (13) extending downwards and externally surrounding the connecting channel (8) of so as to rest on the upper edge (6) of the ingot mold, via a seal sealing (14). Installation according to one of Claims 1 to 8, characterized in that the receiving chamber (205) is tightly fixed, on a support frame (35,35a) which is connected to the ingot mold by a watertight bulkhead 37. Installation according to claim 10, characterized in that the partition (37) of sealed connection between the receiving chamber (5) and the mold (2) forms a bellows (37) allowing the vertical oscillations of the mold (2), the receiving chamber (5) being fixed. Installation according to one of previous claims, characterized in that that the gas supply means (19) of the closed annular chamber (9) are associated with means for controlling a variation in the pressure of the gas around medium pressure in the chamber annular (9), capable of causing oscillations in the level of the free surface (12) of the liquid metal around a medium level in space device (10) between the connecting channel (8) and the ingot mold (2). Installation according to one of previous claims, characterized in that that it comprises a container (21) for storing a lubricant placed above the mold (2) and having an outlet connected to a pipe inside the chamber ring (9) and a gas supply circuit (23) under pressure comprising a pipe (19) opening out in the annular chamber (9) and a pipe in bypass (19 ') opening into the container storage (21) for the introduction of gases to the same pressure above the metal surface (12) in the peripheral space (10) and above the product lubricant, so that it flows through simple gravity on said surface (12) of the metal liquid (M). Installation according to one of previous claims, characterized in that that the connecting channel is provided, in its part center of a solid block (32, 232) extending transversely below the metal inlet (26) poured into the receiving chamber (5), on a part only of the internal section of the connection (8), so as to deflect the stream of metal towards the two longitudinal end walls of the ingot mold (2). Installation according to one of previous claims, characterized in that that it includes a cooling means (17,18) of the walls of the reception chamber (5). Installation according to one of previous claims, characterized in that that the metal introduction member (1) is surrounded by a deformable partition (37) so connected waterproof, at its upper part by means of distribution (D) and at its lower part to the ingot mold (2) so as to form around the chamber reception (5), a sealed space allowing the free-flowing metal casting, said sealed space being filled with a gas at a regulated pressure. Installation according to one of previous claims comprising several lines casting each having an ingot mold (2a, 2b ...), and includes a common introducer (1) extending over all of the molds (2a, 2b ...) and comprising a single reception (305) having a bottom provided with a plurality orifices placed respectively in the axis of each ingot mold and each opening into an extension tubular of the receiving chamber (5) forming a connecting channel (308a, 308b ...) whose end lower enters the ingot mold (2a, 2b ...) corresponding, so as to form a chamber annular, characterized in that each chamber ring is connected to a power supply circuit gas under pressure provided with individual adjustment means pressure in each room for control individual casting conditions in each line. Installation according to one of previous claims, characterized in that that the gas introduced into the annular chamber (9) is a neutral gas for the cast metal. Method for checking the conditions of casting in a continuous casting installation of metal according to claim 1, characterized by you adjust the gas pressure in the chamber annular (9) so as to permanently maintain the level of the annular surface (12) of the metal at a substantially constant level. Method for checking the conditions of casting in a continuous casting installation of metal according to claim 1, characterized by causes the pressure to vary periodically gas in the annular chamber (9) between a value lower and higher value, so as to make oscillate the level of the annular surface (12) of the metal between a higher level and a level lower. Method for checking the conditions of casting in a continuous casting installation of metal according to claim 1, characterized by you adjust the gas pressure in the chamber annular (9) in order to maintain the level of the annular surface (12) of the metal substantially at level of the lower outlet of the connecting channel (8) with a gas leakage rate in said channel liaison.

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