EP1007247A1 - 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

 PROCESS AND DEVICE FOR CONTINUOUS CASTING IN LOAD OF METALS

The present invention relates to continuous casting under load of metals, steel in particular. It relates more specifically to the constituent elements of the ingot mold which it is a question of meticulously adjusting their relative positioning during assembly of the assembly.

Continuous casting under load can be seen as an evolution of conventional 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. the cooled copper of the ingot mold, whereas these two levels are almost confused in conventional continuous casting. This originality is obtained by the installation, on the cooled copper part of the ingot mold, of a contiguous extension in heat-insulating refractory material intended to contain the molten liquid metal and on the wall of which any consequent parasitic solidification must be avoided. Consequently, the solidification of the cast metal can start correctly on the upper edge of this copper part. For this reason, an injection of an inert gas (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 the possible non-solidifying veil. desired which would tend to form already in contact with the refractory riser. This type of arrangement is described in document FR-A-9303871, the content of which is incorporated into the present document by reference.

As the Applicants have already shown (FR-A-96 04304), it is then advantageous for the bottom of the riser to consist of a dense refractory part with good mechanical resistance, such as Sialon®. This part will fulfill the role of transition zone between the cooled copper of the ingot mold and the fibrous heat-insulating refractory of the riser placed above, which would degrade too quickly if it was placed directly in contact with the upper edge of the body cooled in copper, where the solidification of the cast metal begins. 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 the copper, which interrupts the downward propagation of this undesirable process.

The flow of shear gas is injected through a thin slit (barely a few tenths of a mm is sufficient), which is produced by compression of a bead of fibrous refractory material placed between the Sialon insert and the body in copper from the ingot mold. Using tightening means, the cord is compressed until the desired slit thickness is obtained, which is calibrated using adjusted shims. A homogeneous distribution of the gas flow along the inside periphery of the ingot mold is however necessary for the smooth running of the casting process. However, despite all the care that can be taken in adjusting the thickness of the "cold" slit (in the absence of cast metal), this good linear distribution is generally not correctly ensured. On the one hand, local disparities in pressure drops at the copper-refractory interface cannot be taken into account, which are linked, among other things, to local variations in the micro-roughness of the two facing surfaces. screw defining the injection slot. In addition, homogeneity is even less ensured in "hot" operation (presence of the cast metal) due to phenomena of differential expansion of the materials present.

The object of the present invention is to allow a homogeneous linear distribution of the flow rate of shearing gas injected at the interface “refractory riser-cooled metal body of the ingot mold” by dispensing with the adjustment of the thickness of the slot. injection, and retaining this homogeneous "hot" distribution.

With this objective in view, the invention relates to a method of adjusting the injection, during casting, of a fluid (shearing) through an injection slot formed at the interface "body cooled metal - refractory enhancement "of a continuous casting ingot mold in charge of metals and opening out along the inner periphery of this ingot mold, the latter being provided with means for locally adjusting the thickness of the slot, process characterized in that, outside the casting periods, a flammable fluid is injected through said slit, which is ignited at its outlet from the slit, and in that one intervenes on said adjustment means so that the height of the flames leaving the slit is substantially constant according to the inside perimeter of the mold. As will be understood, the basic idea underlying the invention is that we no longer seek a uniform slit thickness over the entire perimeter of injection of the shear gas, but a uniform distribution of the gas flow according to this perimeter, which is materialized by a curtain of flames whose height is adjusted at all points. The subject of the invention is also a device for implementing the method, the definition of which is given in the claims appended to the end of this specification.

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:

- Figure 1 shows schematically, 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 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 shear gas flow distribution settings are made in accordance with the invention.

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

As can be seen, the ingot mold is composed of two contiguous stages 1 and 14, distinguished from one another in the figures by the horizontal line AA and at the interface of which is the slot 20 for injecting the gas of shearing. The lower stage 1 constitutes the crystallizer. This is the properly "active" part of the mold, because this is where the solidification process of the cast metal begins and progresses by massive extraction of heat. This part, made of copper (more generally of a copper alloy), energetically cooled by circulation of water, has an interior passage 2 for the cast metal 3, in which the latter, in contact with the cold metal walls, will form a solidified crust 4. Once correctly initiated, this solidification will continue progressively from the periphery towards the center of the cast product, as it advances downward within the mold in the direction of extraction indicated by arrow 5.

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

The main body 6 is conventionally constituted, in the case of the casting of elongated section products such as slabs, by four contiguous plates assembled at right angles, or, in the case of the casting of blooms or billets, by an element monolithic tubular. In all cases, this body 6, the inner surface of which is intended to come into contact with the cast metal, is vigorously cooled by circulation, against its external face, of a sheet of water channeled in a vertical passage 8 provided for this purpose. effect by a jacket 9 placed a short distance from said face. The jacket 9 has at its ends an upper opening 1 0 and a lower opening which put the passage 8 in communication respectively with an upper discharge chamber 10 and a lower introduction chamber 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 1 2 formed near the upper edge 1 3 on which will begin the solidification of the cast metal. The essential role of the ring 7 is precisely to thermally protect this edge 1 3, which will be very strongly stressed thermo-mechanically during casting, by cooling it more efficiently than can the blade cooling circuit d water from the main tubular body 6. The upper stage 14 is made up of an extension of uncooled refractory material, the inner wall of which is also, and for the reasons already explained, aligned with that of the stage 1.

In terms of the casting process, we will limit ourselves here to recalling that the assembly "cooled metallic crystallizer 1 surmounted by the insulating refractory riser 14" defines a calibrating passage for the cast metal 3, the upper portion 1 5 of which is delimited by the riser a buffer zone for confining hydrodynamic disturbances caused by the arrival (not shown) of the molten metal in the ingot mold, and of which the portion 1 6, which extends it downwards, is the solidification zone of the cast metal.

As can be seen, this refractory riser 14 is also formed by two separate overlapping joined elements:

- An upper sleeve 1 7 of refractory material chosen for its heat-insulating qualities, because it is a question of avoiding in zone 1 5 any premature parasitic solidification of the cast metal. Preferably, a fibrous refractory will be chosen, for example the material sold under the name A 120K by the company KAPYROK;

- And a lower insert 1 8 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 1 3 of the ring 7, while the assembly is subjected to movement 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 SiAION (Sialon (R)), advantageously doped with boron nitride, may be suitable.

The advantage of an extension 14 in two superimposed parts lies in fact in being able to improve the mechanical strength of the lower part 1 8 subjected to a particularly harsh environment in this regard in the vicinity of the edge 1 3. In return , this resistant lower insert 1 8 is inevitably less insulating from heat than the upper sleeve 17 in fibrous refractory.

In contact with its inner wall, there is thus possible the formation of a premature parasitic solidification veil of the cast metal. This veil is an important factor of heterogeneity, see prohibitive, with regard to the process of controlled solidification which must take place in the crystallizer 1. It is for this reason that it is advantageous, in accordance with a preferred implementation of pouring under load as described in the document FR-A-93 03871 already mentioned, to inject an annular gas jet at the base of the enhancement 14 in order to break the possible parasitic solidification veil born on the insert 1 8 and thus allow a frank and regular start of the solidification of the cast metal in contact with the cooled metal ring 1 1.

To this end, a lost inert gas injection circuit (argon for example) is provided between the riser 14 and the crystallizer 7. This circuit includes the outlet slot 20 formed at the interface "riser-crystallizer" , leading to the inner periphery of the mold. At its other end, the slit is connected to a distribution chamber 19 supplied with argon by a calibrated tubing 21, itself connected to a source of pressurized argon 22. As can be seen, a liner 23 remotely envelops the enhances

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 the oxygen of the air through the refractory mass 17 which is inevitably somewhat porous. A compressible bead 24 (made of refractory fibrous material for example) serves as a spacer for adjusting the thickness of the slot 20. For this purpose, a tightening ring 25 makes it possible to compress this bead using nuts 28 to elastic clamping screwed onto the threaded free end of tie rods 26 taken in anchor studs 27 fixed in the insert 7. The desired elasticity of the clamping can be obtained as seen by Belleville washers 29 stacked around the tie rods 26 under the crown 25 and relating to an incoming return 30 of the planting 23 provided for in its part superior. When the nuts 28 are screwed, the inner periphery of the tightening ring 25 presses, via a compression O-ring 32, on the upper face of the extension 14 coated for this purpose with a mechanical protective sheet 31. In this case, the box surrounding the riser 14 is closed at its upper part opposite the clamping ring 25 by means of an annular plug 33 fixed under said crown and the size of which is adjusted to be able to occupy the opening left between the return 30 and the sleeve 17.

An O-ring seal 34 is provided in a groove formed on the inner edge of the return 30 to allow the plug 33 to be able to slide freely during the 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 can be seen in FIG. 1, during the casting of the metal 3, a flow of argon shearing is blown into an ingot mold at the interface "enhancer 14 - crystallizer 1" through the slot 20. The latter is then supplied by the source 22 via an arrival line comprising a "two-way" selector 36 followed by a member 37 for adjusting the flow rate. The "two-way" selector 36 has the function of being able to switch, as desired, to the argon source 22 used during casting, or to an auxiliary source 38 containing a combustible inflammable fluid which will be injected through the slot 20 during the inter-flow periods in accordance with the invention. This flammable fluid is for example natural gas. As illustrated in FIG. 2, the "cold" situation is used to begin with 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 less the cord-spacer 24 using the clamping ring 25, as explained above. The selector 36 being in the position of FIG. 2, flammable fluid from the source 38 is then injected through the slot 20 at a flow rate, initially low, controlled by the adjustment valve 37. This gas is ignited at air at the outlet of slot 20. This is then used in the manner of a burner which produces on the inner periphery of the mold a curtain of flames 39 the height of which can be variable depending on the location as a function generally of the local flow of fuel coming out of the slot directly above the place considered. The distribution of the flammable fluid flow along this periphery is then adjusted by intervention on the clamping nuts 28 until the height of the flames 39 is almost constant over the entire perimeter when the opening of the valve 37 is adjusted. to allow a flame height of a few centimeters. Experience indeed shows 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 no longer seek a constant slit thickness 20 over the entire perimeter of injection, but a linear homogeneity of the flow of shear gas along this perimeter, homogeneity which materializes by a flame height. It will be noted that the use of an elastic clamping 29-28,26, makes it possible to keep, in the presence of cast steel (fig. 1), the setting defined "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 of the watertight box surrounding the riser 1 4 is systematically carried out by injecting the 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 the injection of the 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 has multiple variants and equivalent embodiments insofar as its definition given by the claims is respected. that follow. In particular, by the term "slit" used to qualify the shear gas outlet injector in the ingot mold, it is meant both a continuous slit along the perimeter, as well as a discontinuous slit, and therefore also a series of calibrated orifices distributed along the inner periphery of the mold and provided with means for adjusting the pressure drops at their level.

Claims

1) Method for adjusting the injection, during casting, of a fluid by an injection slot provided at the interface "cooled metal body (refractory D-raiser (14)") of a continuous casting mold in charge of metals and opening out along the inner periphery of said ingot mold, the latter being provided with means for adjusting the thickness of the slot, a process characterized in that, outside of the casting periods, injected through said slot ( 20) a flammable fluid, which is ignited at its outlet from the slot, and in that one intervenes on said adjustment means (25,26,28,29) in such a way that the height of the flames (39 ) coming out of the slot (20) is substantially constant along the inside perimeter of the mold. 2) Method according to claim 1, characterized in that natural gas is used as a flammable fluid to be injected. 3) Method according to claim 1, characterized in that it is applied to a mold for continuous casting in charge of steel. 4) Device for implementing the method according to claim 1, characterized in that it comprises: - a fluid supply line in said injection slot (20) provided with a valve (37) for adjusting the flow rate and an inlet selector (36) which can be connected to the source output different fluids supply (22, 38); - And elastic clamping means (25, 26, 28, 29) making it possible to adjust the width of the injection slot (20) according to the internal perimeter of the mold. 5) Device according to claim 4, characterized in that it comprises means (35) for purging the fluid injection circuits of the mold.