EP0904170B1 - Bimaterial ingot mould for the continuous vertical casting of metals - Google Patents

Abstract

PCT No. PCT/FR97/00545 Sec. 371 Date Jan. 25, 1999 Sec. 102(e) Date Jan. 25, 1999 PCT Filed Mar. 27, 1997 PCT Pub. No. WO97/37791 PCT Pub. Date Oct. 16, 1997The mold includes a cooled copper body 4 on top of which sits a refractory feed head 9 which itself consists of two separate components-a thermally insulating upper bush 16 and a bottom annulus 17 made of a stronger and more compact refractory which is surrounded by a crimping ring 18 narrower than the annulus, so that an edge of the annulus extends beyond each side of the ring. As the lower inner edge of the bottom annulus becomes worn due to an erosive flow of molten metal, the working life of the annulus may be extended in two ways. First, the annulus may be removed between casting operations and its bottom surface may be faced. Second, after the facing operations have rendered the bottom surface flush with the crimping ring 18, the annulus may then be inverted so that the lower inner edge is replaced with the upper inner edge.

Description

The invention relates to Continuous Casting in Vertical Load of metals, and steel in particular.

It is known that Continuous Casting in Vertical Load is distinguished on the essentials of the Classic Vertical Straight Flow by the fact that the ingot mold body, of copper or copper alloy, vigorously cooled by circulation of water and defining a passage for the cast metal which it ensures peripheral solidification in contact with its wall, is overcome by an extension in heat-insulating refractory material intended to contain in the liquid state a volume of cast metal delivered by the distributor placed above (BF 2,000 365).

Thus, thanks to a "bi-material" ingot mold of this type, move away the free surface of the cast metal (the meniscus), which is then at the within the enhancement, from where necessarily the solidification of the metal cast in contact with the cold wall, namely the upper edge of the copper element.

The aim is thus to continuously pour better semi-finished products. quality and with high extraction speeds, or even higher than Classic Continuous Casting, because all hydrodynamic turbulence caused by the arrival of molten metal in the mold are indeed confined to the refractory riser so that below the solidification can begin and continue in an environment calm in which the cast steel progresses towards the exit of the ingot mold without significant velocity gradient in the section (so-called type flow "piston").

It has been envisaged, as described in FR-A-2690099, to design the refractory extension itself, in two separate superimposed parts. An upper part, the sleeve, made of highly insulating refractory material thermally, therefore generally in fibrous refractory and fairly little dense to prevent parasitic solidification on the inner wall of the sleeve by cooling the metal cast at its contact, and a smaller lower part aligned internally with the mold body, the ring, made of compact refractory material with good mechanical strength to resist erosion mechanics caused by the proximity of the nascent solidification point on the upper edge of the copper body in contact with the end of the enhances. An example of a compact refractory material which may be suitable for this effect is SiAION (or Sialon®).

Other materials may also be suitable, but they all have the disadvantage of being expensive in use because, even very resistant, they eventually wear out, which necessarily leads to the replacement of the ring used by a new ring sooner or later.

The aim of the present invention is to propose a solution which allows a very significant extension of the life of a ring refractory of this type, in order to make affordable the operating cost of a Continuous Load Casting machine, linked to the renewal of this ring.

To this end, the invention relates to a bi-material ingot mold for the Continuous casting in vertical load of metals, such as steel, comprising a metal body (copper or copper alloy) energetically cooled and defining a passage for the cast metal which it ensures, in contact with its inner wall, a peripheral solidification, and an extension in heat-insulating refractory material surmounting the body cooled metal intended to contain molten metal in the liquid state poured from a distributor placed above, an ingot mold characterized in that the extension is made up of two distinct refractory parts superimposed: an upper sleeve of refractory material having good thermal insulating properties and a lower material ring refractory with good mechanical properties and aligned internally with the mold body, and in that the ring is crimped in a reinforcing means of height less than that of the ring.

In the case of the casting of long products which will be considered only thereafter, this reinforcing means is advantageously constituted by a crimping ring, preferably in steel, surrounding the ring.

As will be understood, the invention therefore consists in crimping the ring in hard refractory (in SiAION), -which otherwise would risk cracking, or even burst after only a few pours - by a reinforcement ring, in steel for example, which covers only the middle part of the periphery of the ring, in order to let a free portion of it protrude above and below the reinforcement ring.

Thanks to such an assembly, the lower edge of the ring in contact with the cast metal can be easily restored by surfacing the turned side towards the cooled metal body if degradation or spalling of the ring is noted.

In addition, taking into account the possible symmetry of the mounting, after that the successive uses have exhausted the capacities of regeneration from the underside of the ring, it is easy to turn it over reversing upper face and lower face for a new series of flows. We thus manage to double the service life of the ring as a compact refractory and therefore halving its influence in the cost of operating the casting machine.

• la figure 1 montre schématiquement, en coupe verticale, le haut d'une machine de Coulée Continue en Charge Verticale pour la coulée de billettes d'acier.
• la figure 2 montre, en coupe verticale partielle, le détail de la partie supérieure d'une lingotière de Coulée Continue en Charge Verticale, conforme à l'invention.

The invention will 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 with reference to the single sheet of drawings appended in which:

• Figure 1 shows schematically, in vertical section, the top of a Continuous Casting Machine with Vertical Load for the casting of steel billets.
• FIG. 2 shows, in partial vertical section, the detail of the upper part of a mold for continuous casting under vertical load, in accordance with the invention.

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

Referring to the general view of Figure 1, we see that the upper part of a Continuous Casting machine with Vertical Load the steel is made up, in the direction of extraction of the metal to be produced, i.e. from top to bottom in the figure, a distributor 1 (or "tundish") containing a bath of molten metal 2, which it distributes to one (or more) ingot mold 3 placed below by means of one (or more) orifice extended outlet by a guide nozzle 20.

The mold comprises, as can be seen, a tubular body in copper 4 energetically cooled by circulation of water along its face outside. Conventionally, a steel jacket 5 is provided for channel this circulation and communicates at its ends with a introduction chamber 6 and with an evacuation chamber 7, delimited by a mantle 8 surrounding the cooled metal body 4 at a distance.

The latter is surmounted by an extension 9 made of refractory material uncooled, the inner wall of which is preferably aligned with that of the body 4.

In terms of the casting process, the assembly, "metallic body cooled 4 preceded by the 9 "insulating refractory riser, defines a passage for cast metal, the upper part of which in the riser is a containment zone 12 of the hydrodynamic disturbances caused by the arrival of the jet 11 of molten metal in the ingot mold, and the part of which lower, which extends it, is a zone 13 for solidification of the cast metal. This solidification, as we can see, is initiated from the first contact of the steel cast with the inner wall of the body of cooled copper 4, namely on the upper edge 14 thereof, and continues downstream forming a solid crust 15 whose thickness increases from the periphery towards the center. AT leaving the mold, the crust 15, slightly more than a centimeter, is strong enough to withstand ferrostatic pressure of the still liquid heart and continues its centripetal growth until total solidification of the cast semi-finished product 10 under the effect of the ramps not shown water sprinkler located in the lower half of the machine. Once completely solidified, the semi-finished product is cut into sections of desired width (billets, blooms or slabs, depending on the format of the casting section) and these sections are then available for further processing (rolling, etc.).

• un élément supérieur, le manchon 16, en matériau réfractaire choisi pour ses qualités thermo-isolantes, car il s'agit d'éviter toute solidification parasite prématurée du métal coulé dans la zone de turbulence 12. On optera pour un réfractaire fibreux à base d'alumine, par exemple le matériau commercialisé sous la dénomination A 120K par la firme française KAPYROK s.a..
• et un élément inférieur, l'anneau 17, en matériau réfractaire choisi pour sa bonne tenue mécanique, car il s'agit de résister au mieux, au voisinage du cristallisoir 4, à l'érosion mécanique de la pointe supérieure de la croûte solide 15 sur l'arête 14 alors que l'ensemble est soumis à un mouvement d'oscillation vertical qui, comme on le sait, est nécessaire à la réussite de l'opération de coulée, aux sollicitations thermo-mécaniques d'une machine fonctionnant par cycles thermiques rythmés par le caractère nécessairement séquentiel du procédé de coulée.

Referring now more particularly to FIG. 2, it can be seen that the refractory riser 9 is itself formed by stacking two separate elements:

• an upper element, the sleeve 16, made of refractory material chosen for its heat-insulating qualities, because it is a question of avoiding any premature parasitic solidification of the metal poured into the turbulence zone 12. We will opt for a fibrous refractory based on alumina, for example the material sold under the name A 120K by the French firm KAPYROK sa.
• and a lower element, the ring 17, made of refractory material chosen for its good mechanical strength, because it is a question of resisting as best as possible, in the vicinity of the crystallizer 4, against mechanical erosion of the upper tip of the solid crust 15 on the edge 14 while the assembly is subjected to a vertical oscillation movement which, as is known, is necessary for the success of the casting operation, to the thermo-mechanical stresses of a machine operating in cycles thermal rhythmic by the necessarily sequential nature of the casting process.

This ring 17, for example made of SiAlON, doped with boron nitride of preferably, as marketed by the company VESUVIUS under the reference 531, is set in a metal ring 18 by mounting to hot in the workshop. This avoids the risk of cracking and bursting the ring which can appear, if not after a low number of flows, or even after each pour. According to the invention, this ring crimping is dimensioned in width and placed around the ring of so as to let the latter exceed on either side of the limits of the Ring.

To fix the ideas, we could for example circle a ring 17 of three centimeters in height using a two 18 steel ring centimeters and a half wide placed around the edge of the ring in position central (and preferably symmetrical) so as to allow it to protrude the ring of the ring on a distance of two and a half millimeters apart and other.

As we said, this provision allows, in case of degradation or flaking, to restore by surfacing the face 19 of the ring turned in gaze of the metallic body 4. Ordinarily, a surfacing operation consumes in thickness from 0.1 to 0.2 mm of material.

And, once you have reached the end of possible successive surfacing, flush with the ring 18 therefore, it is easy to turn the ring over and thus place in the same situation as the initial situation for a new series of castings before having to change the used ring for a new ring.

It goes without saying that the invention is not limited to the example described above. but extends to multiple variants or equivalents to the extent where the essential characteristics thereof are met, given in the appended claims.

In particular, by "ring" within the meaning of this specification, it is necessary hear not only a continuous strapping that can be put in place around a ring 17 of circular shape in the case of casting Continuous Vertical of long products (blooms, billets), but also any means of clamping ensuring the refractory ring mechanical reinforcement allowing it to better resist significant thermo-mechanical stresses that it undergoes due to the cyclical nature of the operations of casting.

In the case of continuous casting of flat or large products elongated section, slabs in particular, and using a ring refractory no longer continuous around the periphery of the mold, but formed a juxtaposition of segments for example, this reinforcement means may then advantageously consist of a U-shaped flange compressing by its ends, the end faces of each segment, the current central part on the outside of the segment.

Furthermore, although preferred, the arrangement shown in the figures revealing an alignment between the extension and the metal body cooled, is not essential for the implementation of the invention.

Claims (4)

1. Two-material mould for the hot-top continuous casting of metals, such as steel, comprising a metal body (4), which is vigorously cooled and defines a passage for the metal (2) to be cast which, on contact with its internal wall, undergoes peripheral solidification (15), and a feed head (9) made of a thermally insulating refractory which sits on top of the metal body (4) and is intended to contain, in the liquid state, the molten metal introduced into the mould, the said feed head (9) being formed by two stacked internally-aligned separate refractory components - an upper bush (16) made of a refractory chosen for its good thermal insulation properties and a lower annulus (17) made of a refractory chosen for its good mechanical strength properties - which mould is characterized in that the said lower annulus (17) is crimped into a reinforcing means (18) whose height is less than that of the said annulus.
2. Mould according to Claim 1, characterized in that the reinforcing means (18) is in a central position, centred with respect to the height of the annulus (17).
3. Mould according to Claim 1 or 2, characterized in that the reinforcing means is a crimping ring (18) surrounding an annulus of circular shape.
4. Mould according to Claim 1 or 2, characterized in that the reinforcing means consists of a U-clamp, the ends of which compress the abutting faces of a segment of an annulus consisting of the juxtaposition of several segments.

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