EP1056559B1 - Ingot mould with multiple angles for loaded continuous casting of metallurgical product - Google Patents

Abstract

The invention concerns an ingot mould comprising in succession, in the direction for extracting the metallic product to be cast (7): a preheater (5) made of noncooled refractory material acting as reservoir for the melting metal to be cast and a standard cooled tubular metal element (6) for solidifying the metal. A slot (18) for injecting the shearing gas (for example Ar) is arranged between the preheater (5) and the metal clement (6) so as to emerge on the ingot mold internal periphery. The injection slot comprises means (17) for reducing the gas flow in each of the ingot mold angles, preferably formed by obstructing elements. The invention enables to reduce, even eliminate, defects encountered along the edges of the solidified cast products.

Description

The invention relates to a head of an ingot mold for continuous casting charge of a metallurgical product, such as a bloom, a billet or a steel slab.

In the case of the continuous casting of a metallurgical product, we a molten metal flows into an upper part or head of an ingot mold having a general vertical arrangement and out of which is extracted by the down a product solidified at the periphery.

The process known as "continuous casting under load", which in fact constitutes a improvement of the general continuous casting process is implemented in such a way that the meniscus (free surface of the cast metal) is carried over upstream of the level where the solidification of the metal inside begins of the mold head. To implement the continuous casting process under load, the usual copper tubular element of the ingot mold, cooled by internal circulation of cooling water, is overcome, so perfectly joined, by an uncooled refractory riser thermally insulating serving as a reserve of molten metal supplied by the jet of poured from a distributor located above at a short distance. Thanks to this new type of realization of the head this ingot mold, the metal meniscus liquid settles there, during casting, inside the refractory riser, while solidification of the metal only begins at the element cooled metallic tubular, which, as in conventional continuous casting size and shape of the cast product. In this way the eddies in the liquid metal due to the casting jet are limited to the interior of the riser. In the solidification space defined by the tubular copper element placed below, the flow of cast metal can thus be maintained in a relatively calm hydrodynamic state, which allows in particular to regularize the solidification profile of the steel in contact with the wall cooled in copper around the entire interior of the mold. However, to put implement such a method satisfactorily, it is necessary avoid premature solidification of the cast metal at the level of the riser in order to be able to ensure the start of solidification below. precisely at the point of contact with the cold copper wall.

For this, we have already proposed this household a gap of very small height (less than 1 mm and generally around 0.2 mm) between the refractory riser and the tubular element in copper and to produce, by through this slot, an injection of fluid, generally gas inert such as argon in the mold along its inner periphery. To ensure a gas flow at any point of the slot, it is supplied in pressurized gas via a distribution chamber which surrounds.

This gas injection shears the solidification veil heterogeneous parasite that could form above against the interior wall of the refractory riser and thus create the conditions favorable to a solid and regular start of solidification at the level of the copper element cooled just below.

In the case of non-circular ingot molds, in other words in the case ingot molds with a cooled tubular element of quadrangular shape (for casting slabs, or blooms or billets of square cross section, for example) or more generally pluriangular (casting of blanks already having the shape of the desired finished product), we could see on the products cast after solidification completes the presence of solidification defects along the edges, such as longitudinal cracks, exfoliations, etc ..., defects whose origin could be identified as a lack of metal solidified in these places already at the mold, so at the time even from the formation of solid skin.

The object of the present invention is precisely to propose a solution making it possible to reduce or even completely eliminate these defects solidification in the corners of the cast products obtained.

To this end, the invention relates to a mold for continuous casting in charge of molten metals, comprising a metallic tubular element cooled in quadrangular shape defining the shape and size of the product cast and in which the molten metal solidifies on contact with the wall metallic interior cooled, said cooled tubular element being surmounted by an uncooled extension in heat-insulating refractory material defining a reserve of molten metal to solidify, an injection slot of a shearing fluid (in particular an inert gas under pressure, such as argon preferably) according to the inner periphery of the mold being formed between the cooled metal element and the refractory riser, ingot mold characterized in that it is provided with means for reducing the flow of shearing fluid in the corners.

Preferably, these means are constituted by a constituent element an obstacle to the passage of gas through the injection slot and placed in each of the angles of the slot.

The invention results from the following considerations. To get an effect satisfactory shearing of the gas flow injected at the base of the riser, it it is necessary to maintain a gas flow all along the slit so that it there are no dead zones on which solidification fragments undesirable would therefore persist. Now even if we feed the slot from a peripheral distributor of pressurized gas, thus ensuring losses equal load and. Therefore. constant outgoing line flow over the entire slot length, however, no gas flow is obtained injected equal at every point of the perimeter of the cast product. We observe indeed an overflow of gas in the corners of the mold due to the fact that the slot of course being of the same rectangular shape as the mold, the interior of it is supplied with gas bidirectionally in its zones angle. This overflow in the angles is reflected in the vicinity of the slot, so especially in the upper part of the cooled copper element located just below by an overpressure which can cause detachment local of the solidified skin of the cold copper wall at the place of edges of the cast product. It is these detachments which, due to the collapse the cooling efficiency of the product in the corners which results, are responsible for disruptive phenomena of solidification of the “lack of solidified metal” type, which then materialize on the cast product obtained by solidification defects in the angles along edges.

In order to clearly understand the invention, we will now describe, at by way of nonlimiting example, with reference to the attached figures, a continuous casting ingot mold in charge of a shaped steel billet square according to the invention.

Figure 1 is a schematic half-view, in axial section, of the upper part of the mold. according to plan1-1 of figure 3.

Figure 2 is a schematic half-view in axial section of the part upper part of the mold, along plane 2-2 of figure 3.

FIG. 3 is a top view of the lower part of the mold, according to plan 3-3 of Figure 1 or Figure 2.

In Figure 1 and in Figure 2. we see the upper part of an ingot mold continuous casting under load generally designated by the item 1 which comprises a tubular element of cooled copper 6 extended towards the top, and in a tight way to avoid metal infiltration in fusion, by an extension 5 of non-cooled refractory material.

The cooled metallic element 6 and the refractory riser 5 delimit, in their internal part, an internal casting space 3 in which one realizes casting and solidifying a molten metal 4 such as steel. As can be seen in FIG. 3, the internal casting space 3 has a square cross section with rounded angles, the radius of which has voluntarily exaggeratedly enlarged to better show the constituent elements of the invention which will be specified again thereafter.

It will be noted that the cooled copper tubular element 6 constitutes the element main of the mold. It is he who, being energetically cooled by an internal circulation of water (which is established here in a space 2 that household a metal jacket 8 surrounding the element 6 from a distance, conventionally serves crystallizer, against the inner wall 11 of which solidifies the molten steel 7 by first forming a first skin 7 'from the first contact with cold copper 11. Then, as the poured product progresses down in the mold in the direction indicated by the arrow F, this skin, under the effect of intense caloric pumping due to cooling force of the copper element 6, thickens more and more. Solidification of the cast product 7 thus progresses from the periphery towards the central axis until complete solidification, which typically occurs at around ten meters below the mold, water spraying ramps are provided at this effect as a result of this to directly spray the surface of the product poured to cool.

As for the extension 5, a specific component of the so-called "in charge ", its essential function is to serve as a reserve 4 of molten metal. This metal arrives by a casting jet 12 from a distributor 14 placed a short distance above and brought by a nozzle 13 mounted on the distributor outlet. Reserve 4 constitutes a buffer mass, which has a determining role in terms of hydrodynamics by allowing often violent eddies of liquid metal due to the high amount of movement of the steel jet 12 to develop there freely and therefore to cushion. Thus, the liquid steel which then arrives in the crystallizer 6 to be there solidify is in a much calmer state and above all distant from the meniscus 15, whose agitation is often the source of solidification heterogeneities extreme skin in a conventional continuous casting mold. Below from reserve 4, the flow of molten metal approaches a "piston" type flow, that is to say without marked vector gradient speed in the section, which is extremely favorable for the good accomplishment of the solidification process.

The extension of refractory material 5 generally comprises - but not shown in the figures - a main upper part in one fibrous refractory material chosen for its heat-insulating qualities in order to keep the reserve of molten metal 4 in the liquid state, for example the material sold under the name A120K by the firm KAPYROK and a lower annular insert chosen from a dense refractory material, such as than SiAION ® to ensure better mechanical strength in the vicinity immediate of the cooled copper element 6 solicited by the start of solidification.

It will be observed that the extension is fixed in a well aligned position with the tubular element 6 by means of centering pins not shown and an assembly flange 9 with a tie 9 ', this flange bearing on a plate metal 5a covering the refractory part. A sheet metal box 10 is advantageously provided for the passage of the tie rods and to stiffen the mounting.

Despite the heat-insulating qualities of the refractory material used for the enhancement 5, parasitic solidification films 16 of cast metal more or less extensive may form on the inner wall of the extension. Even located around the edge, they can be harmful to the good solidification process in crystallizer 6 as long as these fragments 16 manage to extend to the level of the edge of the cooled element 6 where solidification begins. To break before this stage the possible unwanted solidification veil formed prematurely in the riser, practice at the base of the latter a peripheral injection of a shearing fluid. A gas will be used in this connection, and more preferably a chemically inert gas with respect to the cast metal, such as argon.

To this end, a slot 18, of small thickness, for example of the order of 0.2 mm, is provided between the extension 5 and the cooled copper element 6. This slot opens freely towards the inside of the mold and opens out its other end in a sealed annular chamber 19 formed in enhances it. This chamber 19, which runs along the slot 18 all along, serves well distribute the linear flow of gas to exit the slot. It is connected by a pipe 20 to an external source of pressurized gas 21. The slot 18 has an annular shape similar to the quadrangular shape of the mold, therefore that which takes the cast product 7 once solidified into skin within the copper element 6. In particular, it therefore has an outline at four angles, as shown in Figure 3, where the rounding of the angles has was deliberately exaggerated for the aforementioned reasons.

Because in the vicinity of each of the angles 3a, 3b, 3c and 3d of the ingot mold the shearing gas introduced into the casting space 3 is supplied from two sides at right angles to slot 18, bidirectional feeding and converging of the corner zones of the casting space 3 produces a gas blowing in these areas, leading to a risk of local removal metal cast from the copper wall 11 at the upper edge of this one, where the extreme skin is formed, and consequently, lacks of solidified metal, relative to the rest of the periphery, in the vicinity of the edges of the product cast during solidification within the copper element 6. because of the lack of effective cooling of the product in these places.

In order to avoid this gas overfeeding of the corner areas there are, according to the invention, in the corners of the slot 18 of the obstructing the passage of gas, as can be seen in the figures 2 and 3.

Obstruction elements 17. placed in corners of the gap 18, may consist of balls of fibrous refractory material flexible which, after tightening the extension against the top of the metal element 6, locally block the passage by crushing, outside to inside of the mold. Each of the obstructing elements 17 is then advantageously delimited towards the outside by the internal contour of the distribution chamber 19, inwards by an angle of the space of casting 3, and laterally by two straight sides converging in the direction of the casting space 3, making an angle α with the perpendicular to the flat internal surface of the casting space 3, at the corresponding end the rounded angle 3a (or 3b, 3c, 3d, respectively) of the casting space delimiting inwardly the obstruction element 17.

In the case where the rounded angle of the casting space of the mold has a radius close to 6.5 mm, the width of the obstruction element 17, in its smallest area, adjacent to an angle of the pouring space, should preferably be between 4 and 6.5 mm. If this width is less at 4 mm, it is difficult to remove the local gas overflow injected into the corner. In case the width is more than 6.5 mm, there is an area in the vicinity of the angle, where the linear flow rate of injected gas is zero.

Furthermore, the angle α between the rectilinear side of the obstruction element 17 and the perpendicular to the internal surface of the casting space will be advantageously between 0 and 45 °. Beyond these values of inclination of the sides of the obstruction element 17, the linear flow of gas injected, i.e. the flow rate per unit length of the interior contour of the ingot mold at the level of the slot 18 cancels in an area in the vicinity of the angles.

It has been determined that a value of the angle α close to 20 ° allows to obtain a constant linear flow rate according to the interior periphery of the mold, in the case of pouring rectangular or square products. In some cases, depending on the more or less complex form of the products to be poured, the two straight lateral sides of the blocking elements 17 can make angles α and α 'different with the perpendiculars to the planar internal surface of the internal casting space 3, at the ends of the angles.

By using blocking elements of the slot 18 presenting the geometric and dimensional characteristics given above, we can obtain a linear flow rate of inert gas in the internal casting space, at the level of the slot 18, perfectly constant. This removes the faults solidification observed along the edges of the product once solidified.

The invention is not limited to the embodiment which has been described. For example, as an obstruction to the slot 18, in its corner areas, different materials of refractory fibers. These elements can be completely impermeable to gas, or even slightly porous.

It is also possible to obstruct the slot 18 in its areas angle and suppress the gas flow in these areas by providing a slight increase in height of the extension 5 in the corner zones extending along the width of the slot 18, between the internal casting space 3 and the chamber distribution 19. This additional thickness can be achieved by machining, by example by milling, from the underside of the extension 5 adjacent to element 6. Conversely, the corner allowance may be provided on element 6, the upper face of which is turned towards the enhances 5. Preferably, the extra thickness area will have a shape similar to the shape of the blocking elements 17 as shown in Figure 3. This extra thickness may preferably be of the order of 0.2 mm.

It is also possible to partially obstruct the distribution chamber 19 in areas close to its angles, so as to limit or remove the power supply from the corner areas of the slot 18. The obstruction of the distribution chamber can be produced, for example, by introducing in the corner areas of the distribution chamber of the plugs traversed by channels in the direction of gas flow in the distribution chamber or caps with a certain porosity.

As long as the definition given by the claims is respected the invention applies to any multi-angle mold head continuous casting in charge of a metallurgical product, such as a billet, bloom or slab, preforms of shape already close to the product finished (beams, rails, various profiles, ...). Furthermore, it may apply both in the case of continuous steel casting and in the case of continuous casting of non-ferrous metals.

Claims (6)

1. Ingot mould for loaded continuous casting of molten metals comprising a multiple angled cooled tubular metal element (6) defining the shape and size of the casting and in which the molten metal (7) solidifies in contact with the cooled inner metal wall (11), the said cooled tubular element being surmounted by a higher uncooled part (5) in a heat-insulating refractory material defining a reserve of molten metal to be solidified, a slot (18) for injecting a shearing fluid along the inner periphery of the ingot mould being arranged between the said cooled metal element (6) and the said higher refractory part, the ingot mould being characterised in that it is provided with means (17) for reducing the flow of shearing fluid in the angles.
2. Ingot mould according to Claim 1, characterised in that the means of reducing the gas flow consist of elements (17) for local blocking of the passage in the slot (18).
3. Ingot mould according to Claim 2, characterised in that the blocking elements (17) each comprises a compressed fibrous refractory pad between the higher part (5) and the cooled tubular element (6) and each placed in an angled area (3a .... 3d) of the slot (18).
4. Ingot mould in accordance with any one of the Claims 2 and 3, characterised in that the elements (17) for blocking each of the said angle areas of the slot (18) have two straight sides between the distribution chamber (19) and an angle (3a, 3b, 3c, 3d) of an inner surface of the inner casting space (3) converging in the direction of the casting space (3) and each forming, with a perpendicular to the inner casting surface (3), in the vicinity of an angle (3a, 3b, 3c, 3d) of the surface of the inner casting space (3), an angle between 0° and 45°.
5. Ingot mould according to any one of the Claims 2, 3 and 4, and having rounded corners with a radius in the vicinity of 6.5 mm, characterised in that the blanking off elements (17) have one face turned opposite the casting space (3) of a width between 4 and 6.5 mm.
6. Ingot mould according to Claim 1, characterised in that the, means for reducing the gas flow are made up of elements for partially blocking the angles of the injection slot (18).

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