EP1007247B1 - Method and device for continuous metal charge casting - Google Patents

Abstract

The invention concerns the adjustment of the linear distribution of an injected shearing fluid, during casting, through a slot (20) provided in the cooled metal body (1)-refractory riser block (14) interface of an ingot mold for continuous metal casting charge and emerging along said ingot inner periphery, the latter being provided with clamping means for adjusting the slot thickness. The invention is characterized in that it consists in "cold" injecting through said slot (20) a regulating inflammable fluid, which is ignited on its exit from the slot, and in acting on the clamping means (25, 26, 28, 29) such that the height of the flames (39) coming out of the slot (20) is substantially constant along the whole ingot inner periphery. The invention provides the advantage of an accurate and lasting adjustment of the injected flow rate without requiring the adjustment of the injection slot thickness. The invention is applicable to continuous steel charge casting in particular.

Description

The present invention relates to continuous casting in charge of metals, especially steel. It relates more specifically to the elements constitutive of the ingot mold of which it is a question of regulating their relative positioning during assembly of the assembly.

Continuous casting under load can be seen as an evolution of the classic continuous casting which is manifested by the fact that the meniscus (free surface of the cast metal) is pushed upwards relative to the level where the solidification of the metal begins against the cooled copper of the mold, while these two levels are almost confused in continuous casting classic. This originality is obtained by the installation, on the part in cooled copper of the ingot mold, of a joined extension of refractory material thermal insulation intended to contain the liquid metal poured and on the wall of which any consequent parasitic solidification must be avoided. Therefore, the solidification of the cast metal can start correctly on the edge upper part of this copper part. For this reason, an injection of a gas inert (argon for example) takes place according to the internal perimeter of the ingot mold between the copper part and the enhancement in the form of jets intended to shear any unwanted solidification veil which would tend to already form on contact with the refractory riser. We find described this type of provisions in document FR-A-2703609.

As provided for in patent application FR-A-2747061, we then have advantage that the bottom of the riser consists of a part in dense refractory with good mechanical resistance, such as Sialon®. This part will fulfill a role of transition zone between the cooled copper of the ingot mold and the fibrous heat-insulating refractory of the riser placed at the on it, which would degrade too quickly if placed directly on the contact of the upper edge of the cooled copper body, where the frank solidification of the cast metal. In return, the risk of parasitic premature solidifications on this intermediate part is increased, but remains without consequences thanks to the blowing of the shear gas at the interface with copper, which interrupts the downward spread of this unwanted process.

The shear gas flow is injected through a low slit thickness (barely a few tenths of a mm), which is achieved by compression. a cord of refractory fibrous material placed between the insert of Sialon and the copper body of the ingot mold. Using means of tightening, the cord is compressed until the slit thickness is obtained desired, which is calibrated using regulated shims.

Homogeneous distribution of gas flow around the interior of the mold is however necessary for the smooth running of the casting process. However, despite all the care that can be taken adjustment of the "cold" slit thickness (in the absence of cast metal), this good linear distribution is generally not correctly assured. On the one hand, local disparities in pressure losses at the copper-refractory interface, which are linked, among other things, to local variations in the micro-roughness of the two facing surfaces defining the injection slot. Furthermore, homogeneity is even less well ensured in "hot" operation (presence of cast metal) because phenomena of differential expansion of the materials present.

The object of the present invention is to allow a distribution homogeneous linear flow of shear gas injected at the interface "refractory riser-cooled metal body of the mold" in bypassing the adjustment of the thickness of the injection slot, and retaining this homogeneous "hot" distribution.

With this objective in view, the invention relates to a method of regulation of the injection, during casting, of a fluid through a slot injection at the interface "cooled metal body - extension refractory "of a continuous casting ingot mold in charge of metals and opening out around the inside periphery of this mold, the latter being provided with means for locally adjusting the thickness of the slot, process characterized in that, outside of the casting periods, through said slot a flammable fluid, which is ignited upon leaving the slot, and in that one intervenes on said adjustment means so such that the height of the flames emerging from the slit is substantially constant along the entire inside perimeter of the mold.

As will be understood, the very idea behind the invention is that we no longer look for a uniform slit thickness over the entire shear gas injection perimeter but uniformity of the distribution of the gas flow according to this perimeter, which is materialized by a curtain of flames, the height of which can be adjusted at any point.

• une ligne d'amenée d'un fluide dans ladite fente d'injection pourvue d'une vanne de réglage du débit et d'un sélecteur d'arrivée pouvant se connecter sur la sortie de sources différentes d'alimentation de fluides ;
• et des moyens de serrage élastique permettant de régler la largeur de la fente d'injection selon le périmètre intérieur de la lingotière.

The subject of the invention is also, a device for implementing the method and intended for a continuous casting ingot mold in charge of metals having, provided at the interface "refractory-cooled metallic body" raises an injection slot a fluid emerging along the inner periphery of the mold, device characterized in that it comprises:

• a line for supplying a fluid to said injection slot provided with a flow control valve and an inlet selector which can be connected to the outlet of different sources of fluid supply;
• and elastic clamping means making it possible to adjust the width of the injection slot according to the internal perimeter of the mold.

• la figure 1 montre schématiquement, vue en coupe verticale partielle, le haut d'une lingotière de coulée continue en charge d'acier en situation dite "à chaud", c'est-à-dire en cours de coulée, et équipée des moyens de réalisation de l'invention;
• la figure 2, analogue à la figure 1, montre la situation de la lingotière "à froid", c'est-à-dire vide de tout métal à couler, à un moment avant la coulée où s'effectuent les réglages de la distribution du débit de gaz de cisaillage conformément 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 with reference to the attached single drawing plate in which:

• FIG. 1 schematically shows, viewed in partial vertical section, the top of a continuous casting ingot mold loaded with steel in a so-called "hot" situation, that is to say during casting, and equipped with the means of carrying out the invention;
• Figure 2, similar to Figure 1, shows the situation of the mold "cold", that is to say empty of any metal to be poured, at a time before casting where the settings for the distribution are made the flow rate of shear gas according to the invention.

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

As we can see, the mold consists of two adjoining stages 1 and 14, distinguished from each other in the figures by the horizontal line A-A and at the interface of which is the gas injection slot 20 shearing.

The lower stage 1 constitutes the crystallizer. This is the part properly "active" of the mold, because this is where the solidification process of the cast metal by massive extraction of heat. This part, made of copper (more generally of copper alloy), energetically cooled by water circulation, has an interior passage 2 for the cast metal 3, in which the latter, in contact with the walls cold metal, will form a solidified crust 4. Once properly initiated, this solidification will continue gradually from the periphery toward the center of the poured product as it advances downward within the mold in the extraction direction indicated by arrow 5.

The crystallizer 1 is itself preferably formed of two sets superimposed: a main tubular body 6, extended from above by a auxiliary element 7, well adjusted and aligned internally with the body 6 so to offer the cast product a regular and continuous passage.

The main body 6 is conventionally constituted, in the case of the casting of elongated section products such as slabs, by four jointing plates assembled at right angles, or, in the case of casting blooms or billets, by a monolithic tubular element. In all the case, this body 6, the inner surface of which is intended to come into contact cast metal, is energetically cooled by circulation, against its face external, of a sheet of water channeled in a vertical passage 8 arranged at this effect thanks to a jacket 9 placed a short distance from said face. The shirt 9 has at its ends an upper opening 10 and a lower opening which connect passage 8 respectively with a high discharge chamber 10 and a chamber low introduction not visible in the figures.

The auxiliary element 7 is formed in turn by a ring cooled by an internal water circulation in a horizontal channel 12 arranged at proximity of the upper edge 13 on which the solidification of the cast metal. The essential role of ring 7 is precisely to protect thermally this edge 13, which will be very strongly stressed on the plane thermo-mechanical during casting, cooling it more efficiently what can the body's water cooling system do main tubular 6.

The upper stage 14 consists of an extension in material uncooled refractory, whose inner wall is also, and for reasons already explained, aligned with that of floor 1.

In terms of the casting process, we will limit ourselves here to recalling that the assembly "cooled metallic crystallizer 1 surmounted by the riser insulating refractory 14 "defines a calibrating passage for the cast metal 3, the upper portion 15 delimited by the extension constitutes a buffer zone of containment of hydrodynamic disturbances caused by the arrival (not shown) of the molten metal in the ingot mold, and the portion 16, which extends it downward, is the solidification zone of the metal sank.

• un manchon supérieur 17 en matériau réfractaire choisi pour ses qualités thermo-isolantes, car il s'agit d'éviter dans la zone 15 toute solidification parasite prématurée du métal coulé. On optera de préférence pour un réfractaire fibreux, par exemple le matériau commercialisé sous la dénomination A 120K par la firme KAPYROK;
• et un insert inférieur 18 en matériau réfractaire dense, choisi pour sa bonne tenue mécanique. Il s'agit là en effet de résister, au voisinage du cristallisoir 1, à l'érosion mécanique de la pointe de la croûte solide 4 sur l'arête 13 de l'anneau 7, alors que l'ensemble est soumis au mouvement d'oscillation vertical habituel nécessaire à l'opération de coulée, ainsi qu'aux sollicitations thermo-mécaniques d'une machine fonctionnant selon des cycles thermiques imposés par le caractère nécessairement séquentiel du processus de coulée lui-même. Un matériau tel que du SiAION (Sialon ®) avantageusement dopé au Nitrure de Bore, pourra convenir.

As we can see, this refractory riser 14 is also formed by two distinct overlapping contiguous elements:

• an upper sleeve 17 of refractory material chosen for its heat-insulating qualities, because it is a question of avoiding in zone 15 any premature parasitic solidification of the cast metal. We will preferably opt for a fibrous refractory, for example the material sold under the name A 120K by the firm KAPYROK;
• and a lower insert 18 made of dense refractory material, chosen for its good mechanical strength. This is in effect resisting, in the vicinity of the crystallizer 1, the mechanical erosion of the tip of the solid crust 4 on the edge 13 of the ring 7, while the assembly is subjected to the movement of he usual vertical oscillation necessary for the casting operation, as well as for the thermo-mechanical stresses of a machine operating according to thermal cycles imposed by the necessarily sequential nature of the casting process itself. A material such as SiAlON (Sialon ®) advantageously doped boron nitride, may be suitable.

The advantage of an extension 14 in two superimposed parts lies in effect in being able to improve the mechanical strength of the part bass 18 subject to a particularly harsh environment in this regard in the vicinity of the edge 13. In return, this resistant lower insert 18 is inevitably less insulating from heat than the upper sleeve 17 in fibrous refractory.

In contact with its inner wall, there is thus possible formation of a premature parasitic solidification veil of the cast metal. This veil is a important heterogeneity factor, see prohibitive, with regard to the process of controlled solidification which must take place in the crystallizer 1. It is for this reason that one has advantage, in accordance with an implementation preferred for pouring in charge as described in document FR-A-2 703 609 already mentioned, to inject an annular gas jet at the base of the enhances 14 in order to break any parasitic solidification veil born on insert 18 and thus allow a frank and regular start of the solidification of the cast metal in contact with the cooled metal ring 11.

To this end, a lost inert gas injection circuit (argon by example) is provided between the riser 14 and the crystallizer 7. This circuit includes an annular slot 20 formed at the interface "booster-crystallizer" opening onto the inner periphery of the mold. To his other end, the slot is connected to a distribution chamber 19 supplied with argon through a calibrated tubing 21, itself connected to a pressurized argon source 22.

As can be seen, a tiling 23 envelops it at a distance. 14 thus defining with it a closed box making it possible to limit the risk of oxidation of the liquid metal poured into the mold by air oxygen through refractory mass 17 inevitably somewhat porous.

A compressible bead 24 (made of fibrous refractory material by example) serves as a spacer for adjusting the thickness of slot 20. At this Indeed, a tightening crown 25 makes it possible to compress this cord using of elastic tightening nuts 28 screwed onto the free end threaded with tie rods 26 caught in anchor pads 27 fixed in the insert 7. The elasticity desired tightening can be obtained as seen by Belleville washers 29 stacked around tie rods 26 under the crown 25 and pertaining to an incoming return 30 of the tapping 23 provided for in its part higher. When the nuts 28 are screwed in, the inner periphery of the clamping ring 25 presses, via an O-ring of compression 32, on the upper face of the extension 14 coated for this purpose a mechanical protective plate 31.

In this case, the box surrounding the extension 14 is partially closed. upper opposite the clamping ring 25 by means of a plug annular 33 fixed under said crown and whose width is adjusted to ability to occupy opening left between return 30 and riser 17

An O-ring seal 34 is provided in a groove formed on the inside edge of the return 30 to allow the plug 33 to be able freely slide during adjustments. A vent 35, with a closable outlet not shown, is advantageously provided through the plug 33 and the crown 25 to allow the purge of the box as explained below.

As seen in Figure 1, during the pouring of metal 3, a flow of shear argon is blown into an ingot mold at the "enhances" interface 14 - crystallizer 1 "through the slot 20. The latter is then supplied by source 22 via a finish line comprising a "two-way" selector 36 followed by a flow adjustment member 37.

The "two-way" selector 36 has the function of being able to switch to choice on the argon 22 source used during casting, or on a source annex 38 containing a combustible flammable fluid which will inject through slot 20 during inter-flow periods in accordance with the invention. This flammable fluid is for example natural gas.

As illustrated in Figure 2, the "cold" situation is taken advantage of to start by adjusting the thickness of the slot 20 to a value of a few tenths of a mm, for example 0.2 mm, by compressing more or minus the spacer cord 24 using the crown 25 as previously stated. The selector 36 being in the position of the Figure 2, flammable fluid from the source 38 is then injected by the slot 20 at a flow rate, initially low, controlled by the regulating valve 37. This gas is ignited with air at the outlet of the slot 20. The latter is then used in the manner of a burner which produces on the inner periphery of the ingot mold a flame curtain 39 whose height can be variable according to the location as a function of the local flow of fuel leaving the slot directly above the location in question. Distribution of fluid flow flammable along this circumference is then adjusted by intervention on the clamping nuts 28 until the flame height 39 is slightly close constant over the entire perimeter when the opening of valve 37 is adjusted to allow a flame height of a few centimeters. Experience has shown that a flame height of 2 to 3 cm is sufficient to then ensure a satisfactory flow of argon shear through the slot 20 thus adjusted.

In this operation, we therefore no longer seek a thickness of constant slot 20 over the entire injection perimeter, but homogeneity linear of the shear gas flow according to this perimeter, homogeneity which materializes by a flame height. Note that the use of a elastic clamping 29-28,26, allows to keep in the presence of cast steel (fig. 1), the defined setting "cold" (fig. 2). The invention thus makes it possible to take into account the different expansions of the different materials involved in the manufacture of the mold.

Furthermore, it will also have been noted that a "rinsing" of the pipes and the watertight box surrounding the riser 14 east systematically performed by injecting argon, thanks to the purge system represented by the vent 35 which makes it possible to ensure the absence of traces of flammable fluid possibly remaining in the box.

In addition, the invention has the additional advantage of being able to ensure "cold" sealing of the complete injection circuit. For this, during injecting flammable fluid, a flame can be manually walked all along the circuit. The slightest possible leak is then immediately detected.

It goes without saying that the invention is not limited to the example described above, but presents multiple variants and equivalent of realization as long as its definition given by the claims is respected that follow. In particular, by the term "slit" used to describe the shear gas outlet injector in the mold, you should hear both a continuous slit along the perimeter, as well as a discontinuous slit, and therefore also a series of calibrated orifices distributed around the perimeter inside the mold and provided with means for adjusting the losses of charge at their level.

Claims (5)

1. Method for controlling the injection, in the course of casting, of a fluid by an injection aperture which is disposed at the "cooled metallic body (1)-refractory feeder bush (14)" interface of an ingot mould for continuous metal charge casting and opens out according to the interior circumference of said ingot mould, the latter being provided with means for regulating the thickness of the aperture, the method being characterised in that, outwith casting periods, a combustible fluid is injected through said aperture (20), which fluid is ignited upon its exit from the aperture, and in that said control means (25, 26, 28, 29) are acted upon in such a manner that the height of the flames (39) coming from the aperture (20) should be substantially constant according to the interior periphery of the ingot mould.
2. Method according to claim 1, characterised in that natural gas is used as the combustible fluid to be injected.
3. Method according to claim 1, characterised in that it is applied to an ingot mould for continuous steel charge casting.
4. Device for implementing the method according to claim 1 and intended for an ingot mould for continuous metal charge casting which presents, disposed at the "cooled metallic body-refractory feeder bush" interface, an injection aperture for a fluid which opens out according to the interior circumference of the ingot mould, the device being characterised in that it comprises:

   a supply line for a fluid into said injection aperture (20), which line is provided with a valve (37) for control of the discharge and with a front-end selector (36) which can be connected onto the discharge of different fluid supply sources (22, 38);

   and elastic clamping means (25, 26, 28, 29) which permit control of the width of the injection aperture (20) according to the interior periphery of the ingot mould.
5. Device according to claim 4, characterised in that it comprises means (35) for ensuring the purging of the fluid injection circuits of the ingot mould.

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