EP0989918B1 - Ingot mould head for continuous vertical load casting of elongated flat metal products - Google Patents

Abstract

In this type of mold, a feed head (23) made of thermally insulating refractory fits on top of the cooled copper crystallizer (7) being internally aligned with it in order to define a passage for the cast metal, with interposition between the two of an insert (24) made of dense refractory having mechanical strength properties. This insert (24) consists of bars, each bar (29) being formed by a rigid assembly of aligned and juxtaposed contiguous elements (30) kept clamped against each other by a clamp incorporated into the bar, such as a cross-tie (31) associated with compression pads (33), and positioning and aligning the bar on the crystallizer (7) are provided and consist of a battery of spring pushers (38), which battery is associated with a positioning stop (39) on the crystallizer against which the bar (29) presses.

Description

The invention relates to continuous casting in charge of metals, especially steel. It relates more precisely to the casting in charge of elongated products, especially large sections, such as slabs, more commonly called "flat products".

In its current state of development, the casting continues in load can be considered as an evolution of the casting process classic continuous, which aims to offset the height of the mold the place where solidification of the cast metal begins by contact with the inside face of the wall in cooled copper, from the place, located above, where is the free surface of the poured liquid metal (the "meniscus"). The first solidification, as we know, proceeds from a very physical mechanism sensitive, at the same time that it constitutes an essential factor of quality of the product obtained. Thanks to the separation of the levels specific to the casting continues in charge, this solidification takes place in a calm place on the plan of hydrodynamics, far from the always disturbed area that is the region meniscus. Schematically, this separation of the two levels is made by overcoming the cooled copper body of the mold with a uncooled added extension made of refractory material with properties high thermal insulation (a kind of weight), well aligned internally with the ingot mold and within which the color will place and maintain the meniscus of the cast steel, spilled from a distributor arranged above.

Continuous casting under load of this type, known since long in these principles, and described for example in FR-A-2 009 365, to date has not yet obtained industrial production at the knowledge of depositors. Their own work done more recently on the subject (see for example FR-A-2 747 061 and FR-A-2 747 062) have shown all the advantage of providing between the insulating refractory riser and the ingot mold in cooled copper which supports it, an insert also in refractory, but dense material therefore much more mechanically resistant than the usual insulating refractories, which are usually fibrous. This insert must indeed be both good enough insulator from the heat to maintain the molten steel in the liquid state that it will contain at like the enhancer, and have good resistance properties mechanical to preserve the geometry of the the upper edge of the copper wall on which it rests, there precisely where solidification of the cast metal begins. We know that material like SiAION® responds fairly well to this type of requirement opposite.

However, this type of material is expensive, especially when it it is to conform it into a ring hugging the inner periphery of the ingot mold. Its price can even become prohibitive for large inserts length, as is the case with molds with a large perimeter of solidification which are necessarily the ingot molds for the casting of large section products, such as slabs. Furthermore, and the work of depositors have also confirmed this, it is important for the success of the casting operation to keep the SiAION insert aligned with the ingot mold within very narrow margins of tolerance (0.1 mm maximum). Such a requirement is all the more severe to meet in the species that the inevitable phenomena of hot differential expansion different parts in contact with the molten metal are a major cause of misalignment. It should also be noted that such phenomena are all the more significant as the mold is large format, which is particularly the case here, too, of slab casting of steel (width which can conventionally reach or even exceed 1800 mm).

The aim of the present invention is to provide a simple answer, reliable, and economical to the aforementioned difficulties encountered with casting of large section products.

To this end, the invention relates to a mold head for the vertical continuous casting in charge of metals, steel in particular, comprising an extension of heat-insulating refractory material which overcomes the cooled metal crystallizer of the mold (usually in copper or copper alloy) by being internally aligned with it, and comprising, between the enhancer and the crystallizer, an insert of material dense refractory with mechanical resistance properties (SiAION for example) and shaped into a ring so that it can match the inner periphery of the mold, characterized in that said insert is consisting of bars, each bar being formed from a rigid assembly of juxtaposed and aligned contiguous elements, maintained clamped together by a clamping means integrated into said bar, and in this that means for aligning said bar with the body of the mold are provided and constituted by a pusher associated with a stop positioning on the cooled copper body and against which is supported by said assembly subjected for this purpose to the action of the pusher which tends to push it permanently towards the inside of the mold.

Several assemblies of this type abutted one after the other others with suitable connection angles (generally right angles because the products cast continuously are usually rectangular section) will form an insert in its final geometry wanted to marry the periphery of the mold.

In a preferred embodiment of the invention, the means of integrated clamping consists of a transverse threaded tie rod in the long direction associated with clamping nuts (more generally clamping pads) provided at least in abutment on the free front face of the elements located at each end of the assembly. Advantageously, the tie rod is placed in an eccentric position towards the "cold" side of the assembly, that is to say its rear face opposite to the front "hot" face intended to be contacting the molten metal to be cast.

More preferably, intermediate clamp nuts are also provided for abutment against the internal front faces of the different elements so as to put in mechanical compression each elements in the long sense.

In accordance with another advantageous embodiment of the invention, the assembly of constituent elements of the insert is provided, in addition to the aforementioned overall clamping means, mechanical stiffening means of the "cold" side

As will no doubt have already been understood, the invention consists, in its essential characteristics, to build a long straight bar of compact refractory (which will be assumed to be SiAION thereafter for fix ideas) from elements, possibly identical, in any case surfaced if necessary to allow their watertight junction, of course, and placed end to end one after the other over a distance corresponding to the desired length for the bar, then combined into a whole made rigid using clean clamping means designed to ensure also a mechanical reinforcement of the assembly. We thus realize a SiAION rod of desired length much less expensive and much more solid than an equivalent monolithic bar that one could get in trade. Consequently, this increased solidity makes it possible to retain rustic yet precise and reliable alignment solutions, such as "stop + push", which could not be applied to organs fragile or brittle.

• la figure 1 est une vue en coupe verticale de la tête d'une machine de coulée continue de brames d'acier selon l'invention, faite suivant le plan médian perpendiculaire aux grandes faces de la lingotière;
• la figure 2 est une vue en coupe du dessus selon le plan de coupe A-A de la figure 1.

The invention will be well understood and other aspects and advantages will appear even more clearly in the light of the following description given by way of non-limiting example of embodiment and with reference to the single sheet of drawings in which:

• Figure 1 is a vertical sectional view of the head of a continuous steel slab casting machine according to the invention, taken along the median plane perpendicular to the large faces of the mold;
• FIG. 2 is a sectional view from above along the section plane AA of FIG. 1.

Referring to the general view of Figure 1, we see that the head of a Continuous Casting machine with Vertical Load of steel slabs has, in the direction of extraction of the metal to be produced Pl, i.e. top to bottom in the figure, a distributor 1 containing a metal bath 2, which it distributes to one (or more) ingot mold 3 placed below by means of one (or more) submerged nozzle 4, the gills lateral outlet 5 of the metal lead to a dozen cm below the free surface 6 (or "meniscus") of the liquid metal present in the ingot mold 3.

This ingot mold comprises, as can be seen, two stages 7 and 8.

The lower stage 7 constitutes the crystallizer, also called "body" of the mold. This body in copper, or more generally in an alloy of copper, cooled by water circulation has an interior passage 9 for the cast metal, in which the latter in contact with the metal walls will gradually solidify from the periphery towards the center at as the PI cast progresses downward within the ingot mold.

The crystallizer 7 itself is preferably formed of two parts superimposed: a main part 10, extended from above by a accessory part 11 well adjusted and aligned internally with the part low 10 to offer the cast product a regular and continuous passage.

The lower part 10 is conventionally formed in the case of the continuous slab casting by four plates (or walls) assembled at right angle: two large walls 12 and 12 'facing each other and two small end walls, not visible in the figure. These four walls, the inner face of which is intended to come into contact with metal sunk, are energetically cooled by circulation of water along their outer face. Conventionally, a steel liner 13 is provided for short distance from each plate 12, 12 ′, for channeling a blade of water 14 preferably vertical circulation. The shirt 13 has at its ends of passages 15 and 15 ′ which bring the sheet of water 14 into communication with an introduction chamber 16 and with a chamber outlet 17 located above, delimited by an external partition 18 placed at a distance behind the shirt 13.

The added upper part 11 forms a ring cooled by a internal water circulation in a channel 19 arranged as close as possible to its upper edge 20 on which the solidification of the metal will be initiated sunk. The role of ring 11 is precisely to protect well thermally this edge 20 which will be very thermo-mechanically stressed during casting by cooling it so significantly more efficient than the cooling system can do with water blade 14 of the main part 10 with assembled plates. The ring cooled 11 is surfaced at its base so as to match the surface well upper part of the tubular assembly 10 on which it rests, and thus avoid any risk of molten metal infiltration.

The upper stage 8 is formed by an extension of material uncooled refractory, including the inner wall, for the same reasons as previously, is preferably aligned with that of the body of the crystallizer 7 (and in any case, not indented).

In terms of the casting process, the "metallic crystallizer" assembly cooled 7 surmounted by the insulating refractory riser 8 "defines a calibrating passage for the cast metal PI, the upper portion of which 21 at within the riser constitutes a buffer zone for the containment of hydrodynamic disturbances caused by the arrival of molten metal in the mold through the openings 5 of the nozzle 4, and the portion 9, which extends it downward, is a solidification zone of the cast metal.

This solidification, as we can see, is initiated from the first contact of steel cast with the cold metal wall of the crystallizer 7, namely on the upper edge 20 of the copper ring 11, and continues towards downstream by forming a solid crust 22 whose thickness increases by periphery towards the center. At the exit of the mold, the thick crust 22 a little over a centimeter, is strong enough to withstand the ferrostatic pressure of the still liquid heart and continues to grow centripetal until total solidification of the PI cast product under the effect of water spray bars, not shown, located in the lower half of the machine. Once completely solidified, the product obtained is cut in sections of desired length (the slabs) which are then available for further processing (rolling, etc.)

• un manchon supérieur 23 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 21. On optera pour un réfractaire fibreux, par exemple le matériau commercialisé sous la dénomination A 120K par la firme KAPYROK.
• et un élément inférieur 24, appelé "insert", en matériau réfractaire choisi pour sa bonne tenue mécanique, donc dense, car il s'agit de résister au mieux, au voisinage du cristallisoir 7, à l'érosion mécanique de la pointe supérieure de la croûte solide 22 sur l'arête 20 de l'anneau métallique refroidi 11, 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, this refractory riser 8 is also formed by two distinct superposed elements:

• an upper sleeve 23 made of refractory material chosen for its heat-insulating qualities, since this involves avoiding any premature parasitic solidification of the metal poured into the turbulence zone 21. We will opt for a fibrous refractory, for example the material sold under the name A 120K by the firm KAPYROK.
• and a lower element 24, called an "insert", made of refractory material chosen for its good mechanical strength, therefore dense, because it is a question of resisting as best as possible, in the vicinity of the crystallizer 7, against the mechanical erosion of the upper tip of the solid crust 22 on the edge 20 of the cooled metal ring 11, while the assembly is subjected to the usual vertical oscillation movement necessary for the success of the casting operation as well as to the thermo-mechanical stresses d '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.

The advantage of an extension 8 in two superimposed parts 23, 24 lies in being able to improve the mechanical strength of the part bass subject to erosion caused by the movements of "back and forth" of the solidification point of the cast metal printed by the oscillations vertical of the mold. In return, this resistant lower insert 24 is inevitably less heat insulating than the sleeve upper 23. There is therefore, in contact with its inner wall aligned with that of the cooled ring 11, possible formation of a solidification veil premature parasite of the cast metal. This veil is a factor of heterogeneity important with regard to the controlled solidification process which must have place in the crystallizer 7.

It is for this reason that it is advantageous, in accordance with a implementation of load casting already known elsewhere (FR-A-2 703 609), to breathe a gas curtain at the base of the riser 8 into the purpose of breaking the parasitic solidification veil born on the insert 24 and then allow a regular and frank start of the solidification of the metal poured in contact with the cooled ring 11. For this purpose, an injection circuit lost inert gas (argon for example) is provided between the riser 8 and the crystallizer 7. This circuit comprises an annular slot 25 formed at the enhanced interface - crystallizer and opening at one end to the inside circumference of the mold and connected at its other end to a distribution chamber 26 supplied with argon by a tube calibrated 27, itself connected to a source of argon not represented by by means of a pressure vessel 28 enveloping the riser 8. This arrangement has the advantage of avoiding any risk of oxidation of the liquid metal poured into the mold by the oxygen in the air through of the insulating refractory mass 23 which is inevitably somewhat permeable.

According to the invention, the SiAION 24 insert is, not in one piece, but made from juxtaposed contiguous elements held rigidly clamped together by a clamping means integrated in the insert. An embodiment is visible in Figure 2, which shows a bar constituting the insert as it appears on each of the large faces of the mold. Of course, the insert goes around the periphery inside of the mold. It therefore presents, once mounted, in the form a rectangular frame whose sides, small or large, are formed by rectilinear bars in accordance with that, 29, shown in FIG. 2.

As can be seen, a bar 29 is formed by assembly juxtaposed contiguous elements 30 rigidly held together by a clamping means integrated into the bar itself. In the example described, this tightening means specific to the bar is a compound flange of a tie 31 crossing right through each element passing in a passage 32 provided for this purpose in each of them, this tie rod, threaded at less at its ends protruding from the assembly, is associated with nuts clamp 33 screwed on these ends so as to bear on the free front faces of the elements 30 at the end. Such a clamping means is said to be "global action" because, like a vice, it puts in compression mechanical all the elements by acting only on the elements at the end of the bar. Of course, one can also provide for prestress each element individually using tie rod 31. It it is enough to have a threaded tie rod over its entire length and add intermediate nuts at the junction between two elements 30.

It is advantageous, as shown in Figure 2, to conform the faces frontal contiguous elements 30 to promote their nesting and by consequently their alignment as well as the sealing of the zones of junction with regard to possible infiltration of molten liquid metal counts given the ferrostatic pressure in the mold at the height level where insert 24 is located.

Preferably, the tie rod is in an offset position towards the "cold" side of the bar (towards the bottom of the figure). As opposed to the "hot" side intended to come into contact with molten metal, we call it "cold face" the side of the insert opposite to it and therefore the least stressed thermally. The offset of the location of the tie rod 32 towards this cold face is intended to prevent the tie rod, generally made of steel, from overheating by being too close to the hot face, which would consequence a possible decohesion of the whole following excessive differential expansion phenomena.

Such preferential compression of the cold face is of other interest. As the refractory insert 24 is by destination a transition piece between the cooled metallic crystallizer 7 and the insulating refractory sleeve 23 it's necessarily a bad conductor of heat. So we will always have a thermal gradient significant between its warm side and its cold side. So it will always be also the site of significant differential expansion phenomena in its thickness. Compression prestressing preferential of its cold face will thus help to counteract the inclinations subsequent cracks, which otherwise could be caused by its pulling during expansion of the hot face in contact with metal in fusion.

The offset of the tightening tie 31 still has the advantage additional to be able to reduce the thickness of the insert 24 if necessary, by example during hot face reconditioning operations after use.

In accordance with a preferred embodiment, means of stiffening of the cold side of the bar are provided. To avoid everything risk of buckling, which would give the bar a "banana" shape due of the "cantilever" effect of tightening by the eccentric tie rod 31, we have advantage to stiffen the cold side of the bar 29. This function can be simply provided by a shell 34 better visible in Figure 2. This shell in the shape of "L" at slightly acute angle, is made of spring steel: the bottom plate 35 is applied tightly against the cold face of the bar while being held there elastically by its side cheek 36 anchored in the material of the insert 24 using its folded edge 37 engaged in a notch provided for this purpose on the lateral face (here the upper face) of the bar.

The correct positioning of the bar 29 within the mold consists in allowing its hot face 36 to come flush with the internal surface of the mold and this in a very regular manner over its entire length, which can reach and even exceed 1.5 m, depending on the width of the poured slab. In accordance with an essential characteristic of the invention, this result is achieved by means of alignment of the bar, consisting in permanently pushing it elastically towards the inside of the ingot mold against a retainer secured to the upper copper ring 11 of the 7. In concrete terms, such means can be simply constituted, on the one hand, by a battery of springs 38 placed facing the cold face of the bar and on which the springs act by taking their fixed support on the partition of the casing 28 , and, on the other hand, by a stop stop 39 come by machining of the upper face of the cooled ring 11. In the example described, this stop is in the form of a tongue so as to constitute at the same time a partition delimiting the chamber 26 for distributing the flow of argon opening onto the inner periphery of the ingot mold just below the refractory insert 24.
Of course, the underside of the bar 29 must also be machined in correspondence in order to provide a shoulder 40 visible in the view of FIG. 1 coming to cooperate with the stop 39.

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

Thus, there is no limitation in the number or length of unitary elements 30 constituting a bar 29, and which can by elsewhere be all of the same length or not. Likewise, if we estimate it preferable to a single bar, several bars such as 24 can be placed end to end to occupy the width of a large face of the mold.

Furthermore, it is not essential that the tightening tie crosses the elements 30. It is indeed possible, subject compatible space in this location of the mold, to provide a external tie along the cold side of the bar and provided at its ends of two jaws in the manner of a classic clamp.

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

Likewise the invention applies to continuous casting not only steel, but any other metal capable of being cast continuously and in particular metals with a lower melting point than steel such as aluminum or copper.

Claims (7)

1. Mould head for the vertical hot-top continuous casting of metals, particularly steel, comprising a feed head (8) made of a thermally insulating refractory, which fits on the cooled metal crystallizer (7) of the mould, being internally aligned with the latter in order to define a continuous and uniform passage for the cast metal, and comprising, between the feed head and the crystallizer, an insert (24) made of a dense refractory material having mechanical strength properties and shaped in the form of a ring so as to be able to match the internal periphery of the mould (3), which mould head is characterized in that the said insert (24) consists of bars, each bar (29) being formed from a rigid assembly of juxtaposed and aligned contiguous elements (30) which are kept clamped against each other by a clamping means (31, 33) incorporated into the said bar and in that means for positioning and aligning the said bar with the crystallizer (7) of the mould are provided and consist of a battery of pushers (38) which is associated with a positioning stop (39) made on the said crystallizer, against which stop is pressed the bar (29) subjected for this purpose to the action of the pushers (38) which permanently tend to push it back towards the inside of the mould.
2. Mould head for vertical hot-top continuous casting according to Claim 1, characterized in that the clamping means consists of a tie (31) associated with compression pads (33) which bear at least on the front end faces of the bar (29).
3. Mould head for vertical hot-top continuous casting according to Claim 2, characterized in that the tie (31) passes through the elements (30) making up the bar (29) which has a passage (32) for this purpose.
4. Mould head for vertical hot-top continuous casting according to Claim 3, characterized in that the passage (32) made in the bar (29) for fitting the tie (31) is offset towards the "cold" face of the bar.
5. Mould head for vertical hot-top continuous casting according to Claim 3, characterized in that intermediate compression pads are present on the tie (31) in the junction regions of the elements (30).
6. Mould head for vertical hot-top continuous casting according to Claim 1, characterized in that means (34) for stiffening the "cold" face of the bar are provided.
7. Mould head for vertical hot-top continuous casting according to Claim 6, characterized in that the said stiffening means consist of a metal shell profiled in the form of a "L" whose bottom plate (35) is pressed elastically against the "cold" face of the bar.

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