EP1097762A1 - Ingot mould with large cross section for the continuous vertical load casting of metals - Google Patents

Abstract

A large sectioned ingot mould for the vertical continuous casting of metals comprises a cooled tubular metal element (9) and capped by a hot top (8) of thermal insulating refractory. The tubular element (9) is formed by an assembly of metal plates defining a measuring passage (12) for the cast metal, certain (14) of these plates termed as larger walls being backed with a rigidly fixed reinforcing counter plate (16). The ingot mould is characterised in that the upper part of each large wall (14) presents a recessed shoulder (23) with respect to the inner passage (12) for the cast metal in order to hold one (24) of the jaws of a clamping clip (22), of elongated form assuring a clamping continuously distributed along the said large wall (14), and being covered by the top of this latter and its associated counter plate (16) in contact with the other jaw (28) of the clip (22). A system (29, 30) for the regulation of the clamping of the plate (14) and counter plate (16) is provided on the clip (22). The shoulder (23) also provides a space left free by the clip (22) to receive the refractory hot top (8).

Description

The invention relates to continuous casting in charge of metals, in particular steel. More specifically, it relates to the casting of metals into format semi-finished products. elongated, such as slabs, thin slabs, etc., which are consequently poured into so-called "wide section" ingot molds.

Remember that a large section ingot mold is above all a bottomless metal tube arranged vertically and in which the cast steel will solidify on contact with the wall interior energetically cooled by intense water circulation. This tubular element, conventionally made of copper, or more generally of copper alloy, has a height ordinary of the order of a meter. However, it differs from other types of casting mold basically continues by the fact that it is not monolithic, but made up of four plates assembled at right angles: a pair of large plates, facing each other and intended to form the large faces of the poured slab, often much greater than a meter in width, and a pair of small side plates mounted to the right of the ends of the large plates to seal against the molten molten metal. Usually, for the sake of simplification of vocabulary, these plates are called large or small "walls", or, by analogy with the slab casting, large and small "faces".

Furthermore, in its current state of development, continuous casting known as "in charge" of metals can be considered, technically speaking, as an evolution of the process of classic continuous casting, evolution which shifts the starting point on the casting height the solidification of the metal in the mold from that, located above, where the free surface is located (or "meniscus") of the liquid metal in contact with the wall of the mold.

The first solidification, as we know, proceeds from a very sensitive physical mechanism, in at the same time that it represents an essential factor in the quality of the product obtained. Thanks to the distance in height of these two levels, which are confused, or almost confused in classic continuous casting, this solidification takes place in a hydrodynamically calm place, far from the always disturbed area that is the meniscus region. Concretely, this separation of the two levels is achieved by overcoming the cooled copper body of the ingot mold by an attached extension, not necessarily cooled, made of refractory material high heat insulating properties, well aligned internally with the mold and within which the color will maintain, during the entire duration of the casting operation, the meniscus cast steel, poured from a distributor located just above.

Continuous casting under load of this type, known for a long time in these principles, and described for example in EP-A-0620062, has still to date not encountered any industrial realization to the knowledge of the depositor. His more recent work on subject (see for example FR-A- 2747061 and FR-A-2747062) however showed all the interest provide an insert in material at the bottom of the insulating refractory riser dense refractory, therefore much more resistant mechanically than the usual insulating refractories. This insert must indeed be both good enough heat insulator to maintain in the liquid state, the molten steel that it will contain, like the enhancer, and present good mechanical resistance properties to preserve as long as possible the geometry of the upper edge of the copper wall on which it rests, precisely where will begin the solidification of the cast metal. We know that a material like SiAlON (R) responds fairly well to such opposing requirements. However, this type of material is expensive, in especially when it comes to conforming it into a ring hugging the inner periphery of the ingot mold. Its price can even become prohibitive for very long inserts, such as this is necessarily the case for large section molds.

In addition, and the work of the depositor also contributed to confirm it, it is important first of all for the success of the casting operation to strictly maintain an alignment of the SiAION insert with the large faces of the mold placed below within very narrow tolerances, of the order of ^1/10 mm. Such a requirement is all the more severe to comply with since the inevitable phenomena of hot differential expansion of the elements in contact with the molten metal are a major cause of misalignment. It should be noted in addition that such phenomena are all the more consequent as the mold is of large format, which is particularly the case, there too, for the casting of steel slabs (width which can conventionally reach or even exceed 2m ).

However, it turns out that the current technology of large section molds does not fill well this alignment requirement specific to continuous casting under load. The current technology of ingot molds is based schematically on the principle of the rigidity counterplate. Each large copper plate rests on a rigidity plate which is matched to it by attaching to it by assembly using tie rods anchored in the copper plate and distributed according to the height and according to the width of the plate with inter-pulling spacings of about twenty cm about. The robustness of such an assembly cannot be disputed. But, it induces in the course of casting, in other words "hot", a wave deformation of the copper plate between each pulling. Admittedly, this deformation, of a few tenths of a mm at most, is without real consequence in conventional continuous casting, but it is unacceptable in continuous casting in load due to the misalignment it creates between the copper plate and the riser refractory at their joint plane, where the first metal skin will be born solidified casting.

The purpose of the present invention is to provide a simple, reliable and economical response. to the aforementioned difficulties encountered with continuous casting in charge of wide products section.

To this end, the subject of the invention is a large section ingot mold for continuous casting. vertical in charge of metals, steel in particular, comprising a tubular body formed by assembling copper or copper alloy plates, cooled by circulation of a coolant, this cooled metallic tubular body being surmounted by a extension in heat-insulating refractory material aligned internally with it, and having, among the plates which constitute it, large plates each fixed on counter-plates of rigidity with the aid of distributed transverse tie rods, characterized in that the upper part of each of said large plates has a recessed shoulder relative to the plane of the large plate to offer grip to the jaw of an elongated clamp, which fixes thus the upper part of the large plate against the associated counter plate by covering this last from above and ensuring a continuous grip distributed over the width of the large plate, the base of the refractory riser coming to rest on the part of the shoulder left free by the jaw of the stirrup, the other jaw of the stirrup being provided with means for adjusting the clamping by pressing against the associated counterplate.

As will no doubt have been understood, the tie rods at the top of the mold are replaced by a clamping bracket, the jaw, therefore the bearing surface, can also be extended as desired along the upper edge of the large plates, or even continuous, in order to completely counteract the distortion of the upper edge of large copper plates, very sensitive place of the ingot mold for successful laden casting, as explained above. This stirrup covers each large plate from above and its associated counterplate. A recess set back from the upper edge of the large plate is thus provided to allow the jaw of the stirrup to take position in the shoulder as well formed on the top of the mold to press the heel of the copper plate and tighten it thereby rigidly against the base plate, on which the other jaw of the stirrup acts. This modification of the shape of the upper part of the large plates in accordance with the invention recalls a conformation in "femur head" with the difference however that the head offset is intended, not to articulate in a reception dome, but to serve as a hold for a blocking bracket against the counter plate.

The step being voluntarily larger than the bit of the stirrup it receives, the space thus left free on the shoulder in front of the jaw constitutes a centering housing for easy installation of a refractory riser.

It is therefore possible to produce the hard refractory insert much more easily than hitherto. "SiAION" provided at the base of the riser. Thus, this realization, by assembling sections juxtaposed (FR-A-2764533) whose alignment with each other guarantees the essential straightness of the whole assembly is executed, in accordance with a secondary object of the invention, from sections of refractory material each of which is taken hot in a metal shell which gives them the desired mechanical resistance and which is mounted by thread on a rigid guide rod up to the desired length (equal to maximum to the width of the large plate), and at the ends of which are provided elastic clamping means in order to keep the sections clamped together.

• la figure 1 montre, en coupe verticale, la partie haute d'une machine de coulée continue de brames pourvue d'une lingotière conforme à l'invention, vue de coté;
• les figures 2 montrent l'insert en réfractaire dur disposé à la base de la réhausse et constitué de tronçons jointifs assemblés, vu de dessus (fig.2a) et vu de face avant (fig. 2b).

The invention will in any case be well understood, and other aspects and advantages will appear more clearly in the light of the description which follows, given by way of example of embodiment and with reference to the plates of attached drawings in which:

• Figure 1 shows, in vertical section, the upper part of a continuous slab casting machine provided with an ingot mold according to the invention, side view;
• Figures 2 show the hard refractory insert disposed at the base of the riser and consisting of joined contiguous sections, seen from above (fig.2a) and seen from the front (fig. 2b).

Referring to FIG. 1, it can be seen that the head of a Continuous Casting machine in Vertical load of steel slabs present, in known manner and in the direction of extraction of the cast metal given by arrow F placed on the casting axis A (i.e. from top to bottom in the figure), a distributor 1 containing a bath of molten metal 2, which it distributes to a (or generally several) ingot mold 3 placed at a distance below by means of a nozzle immersed 4 by ingot mold and whose lateral outlet openings 5 of the metal open out to a ten cm below the free surface 6 of the liquid metal present in the mold. This is schematically composed of two superimposed stages 7 and 8 having respective functions distinct but complementary.

The lower stage 7 constitutes the main part of the mold, the crystallizer, of which the thermally active element 9 has the primary role of giving the cast metal a format with sufficient mechanical strength of the skin to avoid breakthroughs downstream. This element 9, a copper tube or more generally a copper alloy, is vigorously cooled by a water circulation in longitudinal channels 10 (shown in the background in the figure) hollowed out on its external face 11, and defines by its very smooth internal surface an internal passage 12 for cast metal.

The upper stage 8 is formed by an extension 13 made of uncooled refractory material, whose inner wall is aligned with that of element 9 of the crystallizer.

In terms of the casting process, the assembly "cooled metal tube 9 surmounted by the 8 "insulating refractory riser defines a calibrating passage for the cast metal, the portion of which upper within the extension constitutes a buffer zone for containment of disturbances hydrodynamics caused by the arrival of molten metal in the mold through the vents 5 of the nozzle 4, and the portion of which extends downward, is a zone of solidification of the cast metal.

This solidification, as we can see, is initiated from the first contact of the cast steel with the cold metal wall of the crystallizer 7, namely already on the upper edge 15 of the copper element 9, and continues downstream, forming a solid crust 13 whose thickness gradually increases from the periphery to the center as the poured product descends in the mold. At the end of the mold, the crust 13, one to two centimeters thick, is strong enough to withstand the ferrostatic pressure of the still liquid core. She then continues its centripetal growth until total solidification of the product poured under the effect water spray bars, not shown, located in the lower half of the machine. A once completely solidified, the product obtained is cut into sections of desired length (the slabs) and these slabs are then available for further processing (rolling, etc.)

In the case of the continuous casting of slabs which is exemplified here, the tubular element 9 is conventionally constituted by four plates (or walls) assembled at right angles: two large plates facing each other (of which only one, 14, is shown in the figure) and two small end plates, not visible in the figure, intended to close laterally so waterproof the casting space 12. These copper plates have a useful thickness of the order of centimeter in order to extract from the cast metal the high heat flux necessary for the solidification process. However, this is insufficient to safely provide resistance mechanical required, facing ferrostatic pressure and multiple constraints and efforts to which the assembled element 9 is subjected. Also, each large plate 14 is coupled to a thick steel counter plate 16 to which it is rigidly fixed. Conventionally, this fixing is carried out by tie rods 17 whose free end is screwed into inserts 15 embedded in counterbores provided for this purpose in the longitudinal ribs of large plates 14 delimiting the water circulation channels 10.

• un manchon supérieur 18 en matériau réfractaire peu dense, choisi pour ses qualités thermoisolantes car il s'agit de conserver à l'état liquide la masse de métal coulé présent au sein de la réhausse. On optera pour un réfractaire fibreux, par exemple le matériau commercialisé sous la dénomination A 120K par la firme KAPYROK. Au besoin, une résistance chauffante pourra être incorporée;
• et un élément inférieur 19, appelé "insert", en matériau réfractaire dur, choisi pour sa bonne tenue mécanique, donc dense. Il s'agit en effet de résister au mieux, en cet endroit voisin du cristallisoir 7, à l'érosion mécanique de la pointe supérieure de la croûte solide 13 sur l'arête en cuivre 20, alors que l'ensemble est soumis au mouvement d'oscillation vertical habituel nécessaire à la réussite de l'opération de coulée, ainsi qu'aux sollicitations thermo-mécaniques d'une machine fonctionnant par cycles thermiques imposés par le caractère nécessairement séquentiel du procédé de coulée lui -même. Un matériau tel que du SiAlON (Sialon (R)), avantageusement dopé au Nitrure de Bore, pourra parfaitement convenir.

As can be seen, the refractory riser 8 is also formed by two distinct superimposed elements:

• an upper sleeve 18 of sparse refractory material, chosen for its heat-insulating qualities because it involves keeping the mass of cast metal present within the riser in the liquid state. We will opt for a fibrous refractory, for example the material sold under the name A 120K by the firm KAPYROK. If necessary, a heating resistor can be incorporated;
• and a lower element 19, called "insert", made of hard refractory material, chosen for its good mechanical strength, therefore dense. It is indeed a question of resisting at best, in this place close to the crystallizer 7, the mechanical erosion of the upper point of the solid crust 13 on the copper ridge 20, while the assembly is subjected to movement of the usual vertical oscillation necessary for the success of the casting operation, as well as for the thermo-mechanical stresses of a machine operating by thermal cycles imposed by the necessarily sequential nature of the casting process itself. A material such as SiAlON (Sialon (R)), advantageously doped with boron nitride, may be perfectly suitable.

In return for this increased mechanical resistance, this lower insert 19 is inevitably less heat insulating than the upper sleeve 18. There is therefore, on contact of its inner wall aligned with that of the copper element 9, a risk of formation possible a premature parasitic solidification veil of the cast metal. This is why that it is advantageous, in accordance with an implementation of pouring under load already known by elsewhere (EP-A_0620062), to inject a gas at the base of the riser 8 in order to break the parasitic solidification veil possibly born above on the insert 19 and then allow a regular and frank start of solidification of the metal in contact with the copper element 9.

These reminders on the known practice being made, we will now describe in more detail the means of the invention.

Referring again to Figure 1, we see that the tie rods 17 normally located at the top of the bottom plate 16, have been replaced in their fixing function by a clamping bracket 22. This bracket comes to cover the top plate from above bottom 16 and the large copper face 9 paired and whose shape has been modified at this location to be able to offer grip easily to the caliper bit. The change of form, as regards the copper plate 9, consists, as can be seen, of a swaying of the upper part of so as to produce a shoulder 23 set back from the plane of the copper plate 9 for offer a grip on the passive jaw 24 of the stirrup 22 on the one hand, and on the other hand to offer a base 25 on which the refractory riser 8 is placed. As regards the bottom plate 16, the shape modification is more banal: on the "hot" side (towards the inside of the mold), it has a counterbore 26 cooperating with the shoulder 23 of the copper plate 9, on the other side, it includes a shrinkage shrinkage 27 in order to be able to engage in the clamping bracket 22 in providing a support surface for the active jaw 28.

As can be seen, this jaw 28 is qualified as active since it is provided with clamping means. easily accessible located on the "cold" side of the mold and made up, in the example considered, by a screw 29 engaged in a threaded barrel 30 passing through the jaw 28, the end free of the screw bearing on the bottom plate 16 to ensure the desired vise effect with the jaw passive 24 on the bottom plate-copper plate assembly located in the right-of-way.

A screw 31 for placing and removing the stirrup on the bottom plate is provided on the top, cooperating with an oblong passage light 32 to allow the necessary mobility play when tightening the side screw 29.

According to an essential characteristic of the invention, the stirrup 22 exerts its action of tightening, not locally, but all along each large plate of the mold, or less on a substantial portion of it. The tightening function must be exercised by sufficiently distributed so that the problems of local "hot" deformations of the wall of the mold encountered in conventional technology be abolished. For this purpose, the stirrup 22 is an elongated piece whose jaws 24 and 28 are continuously gripped over the entire length, the jaw active 28 being provided with a set of clamping screws 29 distributed over this length. We can thus have three or four stirrups juxtaposed one after the other depending on the width of the large face of the mold, or even a single stirrup that extends over this entire distance.

This embodiment also makes it possible to provide a housing for receiving the counterweight. refractory 8. The lower part thereof is then cut into "L" of shape corresponding to the passive jaw 24 to be able to automatically position itself during installation on the stirrup desired, well aligned with the copper wall 9. This advantage is found at the level of the insert in hard refractory 19 at the base of the riser. This insert 19, advantageously made of SiAlON, is not not in one piece over the entire width of the large plates 14, but made from elements juxtaposed kept joined together by tightening. We thus make a SiAlON bar of desired length much less expensive and much stronger than an equivalent monolithic bar that could be obtained commercially.

A clamping means integrated into the insert is visible in Figures 2. In these figures, only is shown, in partial view, a bar 33 constituting the insert as it appears on each large faces of the mold. Of course, the insert 19 goes around the inner periphery of the mold. It is therefore, once mounted, in the form of a rectangular frame whose the sides, small and large, are formed by rectilinear bars 33 conforming to that shown here, each of length equal to the width of the wall of the mold which receives it. As we sees, the bar 33 is formed by assembling contiguous contiguous links 34 maintained rigidly clamped together by a clamping means, preferably integrated into the bar itself. In the example described, this tightening means is a flange composed of a chassis frame with two sliding branches 44, 44 ′ associated with a tie rod crossing right through each link. This tie-rod comprises tightening nuts 36 screwed on its ends so to come, via the corresponding branch 44 of the chassis, compress a stack of Belleville washers 43 bearing on the free lateral faces of the two links 34 at the end. To allow the dimensional adjustment of the support frame of each bar 33, the two branches 44, 44 ′ of the chassis slide one on the other in its central zone by two bearing surfaces 46, 46 'provided with oblong lights for the passage of a locking screw 47 which is fixed a once the links 33 have been tightened by the nuts 36.

Preferably, the tie rod 35 is in an offset position towards the "cold" rear face of the bar. 33 in order to move away from its "hot" face 37 intended to come into contact with the molten metal, therefore more thermally stressed.

Such a clamping means is said to be "global action". Like a vice, it puts in compression mechanical all the links 34 by acting only on those located at the end of the bar. Of course, provision can be made to prestress each link individually to using the tie rod 35. For this, it is sufficient to have a threaded tie rod over its entire length is add intermediate nuts at the junction between two consecutive links.

In accordance with a particular provision of the invention, each link 34 comprises in fact two refractory portions: a body 38 crimped "hot" in a steel casing 39, and a head 40 which flourishes on the side of the "hot" face 37 of the insert while overflowing on both sides of the box 39. The lateral overhangs 41, 41 ′ are carefully surfaced to be able to apply tightly against each other from one link 34 to the next and do not offer joints 42 too wide into which the molten molten metal would infiltrate. We have an advantage, as shown in figure 2a, to conform in "tenon-mortise" 45 the contiguous front faces links 34 to promote their interlocking and, consequently, their mutual alignment as well as the sealing of the junction zones with regard to possible infiltration of liquid metal.

It goes without saying that the invention is not limited to the example described, but extends to multiple variants or equivalents insofar as its essential characteristics given in the appended claims are reproduced.

It should also be noted that if the invention was originally made specifically for casting slabs and other elongated formats, it nonetheless remains applicable to the pouring products of any format as far as, of course, such products can be cast using the continuous casting technique under load.

Likewise the invention applies to the continuous casting not only of steel, but all other continuously castable metal and in particular metals with a lower melting point than steel that are aluminum or copper.

Claims (6)

Large section ingot mold for vertical continuous casting in charge of metals including a metallic tubular element (9) cooled by circulation of a cooling fluid at its contact (10) and surmounted by an extension (8) of heat-insulating refractory material, internally aligned with it, said element (9) being formed by assembling plates metallic defining a calibrating passage (12) for the cast metal, some (14) of said plates, qualified as "large walls", each leaning against a counter plate of reinforcement (16) to which it is rigidly fixed, ingot mold characterized in that the part upper of each large wall (14) has a shoulder (23) set back relative to the internal passage (12) for the cast metal in order to provide a grip for one (24) of the jaws of a stirrup clamping (22), of elongated shape ensuring a continuous distributed grip along the width of said large wall (14), and from above covering the latter and its associated counter plate (16) engaged on the other jaw (28) of said stirrup, means for adjusting (29,30) the tightening of the plates (14) and counterplate (16) therebetween being provided on said stirrup (22), and in that said shoulder (23) provides a space left free by the stirrup (22) to receive in position the refractory riser (8). Continuous casting ingot mold according to claim 1, characterized in that the lower part of the refractory riser (8) is shaped as "L" cooperating with the top of the stirrup (22) on which said enhancement rests. Continuous casting ingot mold according to claim 1, characterized in that the base of the refractory riser (8) consists of a ring (19) of hard and smooth refractory material, the part relating to each large wall (14) is a straight bar formed by an assembly joined of elementary links (34) aligned one after the other and kept tight between them by clamping means (35,36) specific to said bar. Continuous casting ingot mold according to claim 3, characterized in that each link elementary (34) constituting a straight bar forming the refractory ring (19) present, in "hot" face (37), an opening (40) extending beyond the limits of a reinforcement box (39) who imprisons him. Continuous casting ingot mold according to claim 1, characterized in that the active jaw of the clamping bracket (22) provided with clamping adjustment means is the jaw (28) engaged on the reinforcement counterplate (16). Continuous casting ingot mold according to claim 1, characterized in that the means for fixing each large wall (14) to its associated reinforcement counterplate (16) and located outside the upper part of the tubular element (9) are constituted by tie rods (17) distributed in height and width over said large wall (14).

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