WO2015113947A1

WO2015113947A1 - Torpedo ladle comprising a corrugated portion and use of a refractory module

Info

Publication number: WO2015113947A1
Application number: PCT/EP2015/051543
Authority: WO
Inventors: Martin Kreierhoff; Joachim SCHÜNTZEL
Original assignee: Vesuvius Crucible Company; Vesuvius Group
Priority date: 2014-01-28
Filing date: 2015-01-27
Publication date: 2015-08-06
Also published as: AR099214A1; TW201540392A; EP3099823A1

Abstract

The present invention concerns a torpedo ladle (1) for the transportation of molten metal, said torpedo ladle defining an inner cavity (3) and comprising: - an outer shell (1o) defining the outer surface of the torpedo ladle, and an inner liner (1i) comprising refractory bricks, defining the inner surface of the torpedo ladle, and - an opening (5) bringing in fluid communication the outer surface of the torpedo ladle with the inner surface thereof, said opening being located in the central portion of the torpedo ladle and facing upwards when the torpedo ladle is at its filling position, 6f; Characterized in that, the inner surface of the torpedo ladle comprises a corrugated portion (7) located opposite to, and in registry with the opening, the corrugation being characterized by crests (7c) and valleys (7v) extending parallel to the longitudinal axis, X1.

Description

TORPEDO LADLE COMPRISING A CORRUGATED PORTION AND USE OF

A REFRACTORY MODULE

[0001] Technical Field

The present invention relates to so-called torpedo ladles for the transportation of molten metal from a blast furnace to another site of a metal casting mill, for example for transporting pig iron from a blast furnace to a steel casting mill. In particular, it concerns a torpedo ladle provided with means for substantially reducing the erosion rate of the refractory bricks lining the interior of the torpedo ladle during filling thereof.

[0002] Background for the invention.

In metal forming processes, molten metal is transferred from one metallurgical vessel to another, to a mold or to a tool. For example, a ladle is generally filled with molten metal out of a furnace and transferred to a tundish through a ladle shroud. The molten metal can then be cast through a pouring nozzle from the tundish to a mold for forming slabs, billets, beams or ingots. Flow of molten metal out of a metallurgic vessel is driven by gravity through a nozzle system located at the bottom of said vessel.

[0003] In cases wherein the blast furnace is located at a remote location with respect to the next processing stage of the molten metal, large ladles of a capacity largely exceeding 100 t are used to transport the metal in the molten state from the blast furnace to the site where it must next be processed. Some versions are even coupled to special bogies so that they can be transported by either road or rail. Such large ladles generally define a cavity having a fusiform shape extending along a longitudinal axis, X1 , with a generally cylindrical central portion flanked by two generally frusto-conical end portions, as illustrated in Figure 1 (a). In the context of the present invention, a fusiform shape means a spindle-like shape that is wide in the middle and tapers at both ends. They can be tilted about said longitudinal axis, X1 , from a filling angular position, 6f, wherein they can be filled with molten metal, to a pouring position, θρ, wherein the molten metal contained therein can be discharged. Because of their shape, such ladles are often referred to as a "torpedo ladle", term which will be used throughout the present description to refer to such ladles.

[0004] During filling of such torpedo ladles from a blast furnace, molten metal is poured in a free falling jet into the torpedo ladle through an opening generally located in the central portion of the torpedo ladle. Molten metal falls freely from a tilted runner of a blast furnace from a substantial height through said opening, hitting the inner surface of the torpedo ladle opposite the opening, with considerable kinetic energy and flowing to fill the whole cavity formed by the inner surface of the torpedo ladle in a very turbulent flow. The first impact of the molten metal jet and following turbulent flow after bouncing and filling said cavity cause severe erosion of the refractory bricks lining the interior of the torpedo ladle, thus reducing considerably the service life of such vessels. The importance of the erosion problem of the lining material in torpedo ladles is discussed for example by Yoshito Isei, Tatsuro Honda, Kenichi Akahane, Hideyuki Takahashi, "DEVELOPMENT OF REFRACTORY THICKNESS METER FOR TORPEDO LADLE CAR", in XIX IMEKO World Congress Fundamental and Applied Metrology, September 6-1 1 , 2009, Lisbon, Portugal.

[0005] To increase the service life of torpedo ladles two solutions have to date been proposed applied alone or in combination: (a) thickening the refractory layer lining the impact region of the free falling molten metal jet upon filling the torpedo ladle, and/or (b) using harder materials for said impact region.

[0006] For example, US-A-3,661 ,374 discloses a torpedo ladle wherein the outer shell of the vessel diametrically opposite the opening is given a shape which is bulged outwardly as compared with the general shape of the remainder of the vessel. This is embodied in such a way that the refractory lining in the zone of this bulging out has an increased thickness. In other words, erosion rate is not decreased, but by increasing the thickness of the refractory bricks in registry with the opening, degradation thereof takes longer. A harder material is proposed in US-A1 -2010289195 teaching the use of a harder layer for the impact region formed of silicon nitride-alumina based material and JP-A-H04/319066 discloses an impact region made of a monolithic refractory slab devoid of any joints and encased in the surrounding refractory bricks in a comb-like pattern.

[0007] DE1 182679 discloses a torpedo ladle comprising an impact region made in a reinforced material and defined between two walls of a given height and extending substantially parallel to each other and substantially normal to the longitudinal axis, X1 , forming a trough. An example of such geometry is illustrated in Figure 8(a). Upon pouring molten metal into an empty torpedo ladle of this type, the metal will first hit the impact region made of a reinforced material, and rapidly fill in the trough defined between the two walls. Rapidly the pouring metal does not hit directly the impact region of the torpedo ladle, but impacts the pool of metal melt formed in the trough, which acts as a buffer, dissipating over the whole volume of the metal pool part of the kinetic energy of the impacting molten metal flow.

[0008] Combination of (a) thicker impact region with (b) harder material can be found in JP-A-H05/843 disclosing a moulded impact module made of heat treated stainless fibre reinforced refractory material containing 50-80 wt.% AI2O3, 5-30 wt.% S1O2, 5-20 wt.% SiC and 1-5 wt.% C.

[0009] The solutions proposed to date concentrate on increasing the durability of the impact region by using thicker plates and/or harder materials, but they fail to reduce the energy of the turbulent flow following the first impact as the molten metal fills the cavity of a torpedo ladle. It is true that the impact region is severely affected by erosion during filling of a torpedo ladle;

however, the present inventors have observed that other regions of the refractory lining, remote from the impact region undergo severe erosion during filling. As illustrated in Figure 5 (taken from http://www.corrosionlab.com/papers/erosion-corrosion/erosion-corrosion.htmJ, erosion is enhanced by a turbulent flow. Even with a laminar flow (cf. Figure 5(a)), erosion may be triggered by a surface defect of the refractory liner, provoking a local turbulence which applies shear stresses onto the surface defect which increases in size (Figure 5(b) &(c)), thus provoking stronger turbulence creating higher shear stresses onto the surface defect, thus accelerating the growth thereof (Figure 5(d)). It is known that erosion rate increases exponentially with increasing shear stress. Figure 6(a) is a graphical representation of a finite elements modelling (fern) of the erosion rate (= volume of material per unit time) calculated for a state of the art torpedo ladle at an early stage of a filling operation. As indicated in the scale, erosion rate increases with the darkness of the pattern. It can be seen that since the high impact energy of the free falling molten metal jet bouncing onto the impact region creates strong turbulence in the flow of the melt as it fills the cavity of the torpedo ladle, regions of high erosion rates appear in the frusto-conical end portions of the torpedo ladle, quite remote from the impact region, as identified by the dark regions in Figure 6(a).

[0010] Similary, Figure 9 is a graphical representation of a finite elements modelling (fern) of the magnitude of the shear stresses responsible for the erosion rate (= volume of material per unit time) calculated for a torpedo ladle of the type disclosed in DE1 182679 (cf. Figure 9(a)) and a torpedo ladle according to the present invention. It can be seen very clearly that the solution proposed in DE1 182679 is unable to reduce the magnitude of the shear stresses onto the torpedo walls at a distance from the impact region to a sufficiently low level to ensure a long service life of the torpedo walls.

[0011 ] There therefore remains a need in the art for increasing the service life of a torpedo ladle by increasing the durability of the refractory liner not only at the impact region, but also at other regions remote from the impact region and to date submitted to severe shear stresses during filling of the torpedo ladle. The present invention proposes a solution to this need. This and other advantages of the present invention are disclosed in more details in the following sections.

[0012] Summary of the invention.

The present invention is defined in the appended independent claims. Preferred embodiments are defined in the dependent claims. In particular, the present invention concerns a torpedo ladle for the transportation of molten metal, said torpedo ladle defining a cavity having a fusiform shape extending along a longitudinal axis, X1 , with a generally cylindrical central portion of inner diameter, Di, flanked by two generally frusto-conical end portions, said torpedo ladle being rotatable about said longitudinal axis, X1 , from a first angular position, 6f, referred to as filling position, to a second position, θρ, referred to as pouring position, and further comprising:

a) - an outer shell defining the outer surface of the torpedo ladle, and an inner liner comprising refractory bricks, defining the inner surface of the torpedo ladle,

b) an opening (5) bringing in fluid communication the outer surface of the torpedo ladle with the inner surface thereof, said opening being located in the central portion of the torpedo ladle and facing upwards when the torpedo ladle is at its filling position, 6f. The torpedo ladle of the invention is characterized in that, the inner surface of the torpedo ladle comprises a corrugated portion located opposite to, and in registry with the opening, the corrugation being characterized by crests and valleys extending parallel to the longitudinal axis, X1.

[0013] The expression "corrugated' (and derivations thereof) is used herein in its broadest sense as having a wavy surface, i.e., made of parallel ridges and grooves. The waveform of the corrugation can be smooth and rounded in shape, such as a sinusoidal wave, but it may also comprise sharp edges, such as in triangle waves or square waves and the like. Smooth waveforms are, however, preferred.

[0014] In a preferred embodiment, the crest to valley amplitude, A, of the corrugation is at least 2% of the inner diameter, Di, of the torpedo ladle, and preferably not more than 8% of the inner diameter, Di. The crest to valley amplitude, A, is defined as being the difference of altitude between a crest and a valley. For example, the crest to valley amplitude, A, of the corrugation may be comprised between 50 and 300 mm, preferably between 100 and 250 mm. The crest to crest distance, λ, of the corrugated portion is preferably comprised between π Di/ 20 and π Di/ 60, more preferably between π Di/ 25 and π Di/ 35. For example, the crest to crest distance, λ, of the corrugated portion may be comprised between 100 and 600 mm, preferably between 200 and 400 mm. The crest to valley amplitude, A, and crest to crest distance, λ, are not necessarily equal for all folds of the corrugated portion, and could be smaller at the edges of the portion than at the centre thereof (i.e. , directly opposite to the opening of the torpedo ladle.

[0015] In yet a preferred embodiment, the corrugated portion extends over an angular portion, a, of at least 90°, preferably at least 100°, more preferably 120°, in an orthogonal projection on a transverse plane, Π1 , normal to the longitudinal axis, X1 , and comprising a first transverse axis, X2, intersecting the longitudinal axis, X1 , and the centroid of the opening. Said angular portion, a, is preferably axis-symmetrical with respect to the first transverse axis, X2, and is of course located on the side of the inner surface opposite the opening with respect to the first longitudinal axis. The corrugated portion is preferably flanked on both sides by a hoop-wall extending substantially normal to the first longitudinal axis, X1 , and which are preferably parallel to one another. It is preferred that the top of each hoop-wall ends in an over-hanging protrusion extending partially over the corrugated portion. Such over-hanging protrusions and hoop walls contribute to maintaining the incoming flow of metal melt within the corrugated portion.

[0016] In an orthogonal projection on plane, Π1 , the hoop walls extend over an angular portion, β, of the inner wall of the torpedo ladle which is preferably larger than the angular portion, a, covered by the corrugated portion, and are preferably joined on either side of the first transverse axis, X2, above the level of the corrugated portion by a longitudinal buttress extending parallel to the longitudinal axis, and having an upstream surface facing the opening, which is slanted with an angle lower than 90°, preferably lower than 45° with respect to the inner surface of the torpedo ladle. In general it is preferred that the hoop walls be highest at the level of their intersection with the first transverse axis, X2, on an orthogonal projection on plane, Π1 .

[0017] Because the corrugated portion is submitted to intense erosive forces by the incoming flow of molten metal, it is preferred that the corrugated portion is made of, or is coated with a hard material comprising an aluminium oxide (e.g. fused or sintered) based refractory material comprising at least 92 wt.% AI2O3, preferably at least 96 wt.% AI2O3. Suitable materials the materials are CERCAST™ 955 or 966 (sold by the companies of the VESUVIUS group). [0018] The present invention also concerns the use of a pre-cast refractory module for producing a torpedo ladle according to any of the preceding claims, wherein said refractory module comprises a corrugated surface defined by crests and valleys extending parallel to each other along a longitudinal axis, X1 , and which can be laid onto and fixed to the inner surface of the cavity. The pre-cast module can be a monolithic pre-cast refractory module having the geometry of the corrugated portion as defined supra, and wherein the crests and valleys of the pre-cast refractory module are preferably flanked on either sides by a hoop-wall extending substantially normal to the first longitudinal axis, X1 , and parallel to one another. In an alternative embodiment, at least two partial pre-cast refractory modules are used, such that by assembling them inside the torpedo ladle, a corrugated portion as defined supra is obtained, preferably flanked on either sides by a hoop-wall extending substantially normal to the first longitudinal axis, X1 , and parallel to one another.

[0019] Brief description of the Figures

For a fuller understanding of the nature of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings in which: Figure 1 : represents a side cut view of a torpedo ladle (a) of the prior art, and (b) according to the present invention;

Figure 2: shows a perspective cut view of a torpedo ladle according to the present invention Figure 3: shows a cross-sectional cut view of a torpedo ladle according to the present invention Figure 4: shows a cross-sectional cut view of a torpedo ladle according to the present invention (a) in its filling position and (b) in its pouring position

Figure 5: schematically illustrates an erosion mechanism of a refractory lining by a flowing molten metal;

Figure 6: shows the graphical representation of a finite element modelling of the erosion rate during filling of a torpedo ladle (a) according to the prior art and corresponding to Figure 1 (a), and (b) according to the present invention and corresponding to Figure 1 (b)

Figure 7: shows two embodiments of pre-cast modules to be assembled inside the torpedo ladle to form the corrugated portion.

Figure 8: compares the finite element modelling of the shear stress generated during filling of a torpedo ladle (a) according to the prior art and corresponding to a torpedo ladle of the type described in DE1 182679, and (b) according to the present invention and corresponding to Figure 1 (b)

Figure 9: compares finite element modelling of the shear stress generated during filling of a torpedo ladle (a) of the type described in DE1 182679 and illustrated in Figure 8(a), and (b) according to the present invention and illustrated in Figures 1 (b) and 8(b).

[0020] Detailed description of the invention

As illustrated in Figure 1 , a torpedo ladle (1 ) for the transportation of molten metal, comprises an inner cavity (3) having a fusiform shape extending along a longitudinal axis, X1 , with a generally cylindrical central portion of inner diameter, Di, flanked by two generally frusto-conical end portions. This shape of the inner cavity is optimized for the rotation of the torpedo ladle about said longitudinal axis, from a first angular position, 6f, referred to a filling position, to a second position, θρ, referred to as pouring position as illustrated in Figure 4. A torpedo ladle further comprises:

(a) - an outer shell (1 o) defining the outer surface of the torpedo ladle, and an inner liner comprising refractory bricks, defining the inner surface (1 i) of the torpedo ladle, and

(b) - an opening (5) bringing in fluid communication the outer surface of the torpedo ladle with the inner surface thereof, said opening being located in the central portion of the torpedo ladle and facing upwards when the torpedo ladle is at its filling position, 6f.

[0021 ] A torpedo ladle according to the present invention differs from state of the art torpedo ladles in that the inner surface of the torpedo ladle comprises a corrugated portion (7) located opposite to, and in registry with the opening (5), the corrugation being characterized by crests and valleys extending parallel to the longitudinal axis, X1.

[0022] The corrugated portion (7) of the torpedo ladles according to the present invention permits to dissipate a substantial portion of the high kinetic energy with which a jet (9) of molten metal hits said corrugated portion during filling operation, by splitting said jet into smaller particles each time molten metal hits a corrugation of said portion and bounces to a next corrugation, as illustrated schematically in Figure 4(a). The molten metal is normally discharged from a blast furnace by running along a runner or tube which is tilted with respect to horizontal, and falls freely following an approximately parabolic trajectory until it hits an inner wall of the torpedo ladle, usually slightly offset with respect to a first transverse axis, X2, intersecting the longitudinal axis, X1 , and the centroid of the opening as shown in Figure 4(a). Because the corrugated portion follows the curvature of the inner surface of the torpedo ladle of inner diameter, Di, the molten metal after first hitting one area of the corrugated portion, provoking a first split of the jet into smaller particles, necessarily cascades down transversally to the crest and valleys of the corrugated portion until it reaches the lowest point of the corrugated portion and starts climbing up across the crests and valleys on the opposite side of the corrugated portion with respect to the first transverse axis, X2. This flow pattern dissipate a substantial portion of the kinetic energy of the flowing molten metal, allowing the metal to fill the rest of the torpedo ladle cavity (3) at lower velocity, thus generating substantially less shear stresses onto the refectory bricks lining the rest of the cavity. This results in a substantially longer service life of the refractory bricks as the erosion rate is thus reduced.

[0023] To optimize the energy dissipation of the molten metal jet, the crest to valley amplitude, A, of the corrugation is preferably at least 2% of the inner diameter, Di, of the torpedo ladle, and more preferably not more than 8% of the inner diameter, Di. For example a torpedo ladle capable of holding 400 t of steel typically has an inner diameter, Di, of the order of 3600 mm. The crest to valley amplitude, A, of the corrugation is therefore preferably comprised between 70 and 290 mm, more preferably between 140 and 220 mm. The amplitude, A, refers to the altitude difference separating the top of a crest and the bottom of an adjacent valley as indicated in Figure 3. A typical crest to valley amplitude, A, of the corrugation may be comprised between 50 and 300 mm, preferably between 100 and 250 mm. Corrugations shallower than 50 mm amplitude will generally be insufficient to substantially dissipate the energy of the molten metal jet (9). Corrugation amplitudes larger than 300 mm may lead to other problems of resistance of the corrugated portion, excessive volume occupied by said corrugated portion in the cavity, and the like.

[0024] Another important parameter of the corrugated portion is the crest to crest distance, λ, which is preferably comprised between π Di/ 20 and π Di/ 60, preferably between π Di/ 25 and π Di/ 35. A crest to crest distance, λ, is illustrated in Figure 3. For the 400 t capacity torpedo ladle of inner diameter, Di = 3600 mm discussed above, this represents a crest to crest distance, λ, of the order of 190 to 570 mm, preferably of about 300 to 450 mm. In general terms, the crest to crest distance, λ, of the corrugated portion of a torpedo ladle according to the present invention may be comprised between 100 and 600 mm, preferably between 200 and 400 mm.

[0025] The width, W, of the corrugated portion along the longitudinal direction, X1 , needs not extend over the whole length of the central portion of the torpedo ladle inner cavity, let alone over the whole length of the torpedo ladle. It is sufficient that the corrugated portion extends over the width spanned by the opening (5) in the longitudinal direction, X1 . The width, W, is preferably slightly larger than the opening, but it is not essential. Indeed, the molten metal jet (9) will always be substantially normal to the longitudinal axis, X1 , and, of course, centred on the opening (5).

[0026] The corrugated portion needs not extend over the whole circumference of the inner cavity. It only needs extend over an angular portion, a, over a plane normal to the longitudinal axis, X1 , including the impact area of the flowing molten metal jet and extending over a sufficient portion of the circumference to dissipate enough of the kinetic energy of said molten metal jet after its first impacting the corrugated portion. For example, the angular portion, a, can be of at least 90°, preferably at least 100°, more preferably 120°, such that said angular portion, a, is axis-symmetrical with respect to the first transverse axis, X2, and is located on the side of the inner surface opposite the opening with respect to the first longitudinal axis (in other words, on the bottom side of the cavity when the torpedo ladle is in its filling position). As illustrated in Figures 3 and 4(a), a corrugated portion spanning an angular portion of about 120° allows receiving the free falling molten metal jet and dissipating the kinetic energy thereof first by splitting the jet in smaller particles upon bouncing against the corrugated surface, and also by flowing transverse to the direction of the valleys and crest as the molten metal flows up the opposite side of the corrugated portion with respect to an axial plane defined by the longitudinal axis, X1 , and first transverse axis, X2.

[0027] In order to channel the flow along the hoop direction of the corrugated portion, it is preferred that the corrugated portion be flanked on either sides by a hoop-wall (7w) extending substantially normal to the first longitudinal axis, X1 , the two hoop walls being preferably parallel to one another. The hoop walls (7w) force the molten metal after first impacting the corrugated portion to flow across the successive crests and valleys of the corrugated portion thus dissipating yet more kinetic energy. In yet a preferred embodiment, the top of each hoop-wall (7w) ends in an over-hanging protrusion extending partially over the corrugated portion. Such overhanging protrusion retains splashing molten metal from flowing directly out of the corrugated portion into the rest of the cavity, causing turbulence and generating high shear stresses, responsible for a high erosion rate.

[0028] In an orthogonal projection on a plane, Π1 , normal to the longitudinal axis, X1 , and including the first transverse axis, X2, the hoop walls (7w) may extend up to or beyond the corrugated portion over an angular portion, β > a, of the inner wall of the torpedo ladle which can be larger than the angular portion, a, spanned by the corrugated portion (cf. Figures 1 (a), 2 to 4). The two hoop walls (7w) are preferably joined on either side of the first transverse axis, X2, above the level of the corrugated portion by a longitudinal buttress (7b) extending parallel to the longitudinal axis, and having an upstream surface facing the opening, which is slanted with an angle lower than 90°, preferably lower than 45° with respect to the inner surface of the torpedo ladle. The longitudinal buttress (7b) has a double function. First in case some molten metal hits the inner surface of the torpedo ladle higher than the first corrugation, the slanted upstream surface of the buttress may serve to break the hitting jet (9) and splitting it into smaller particles towards the corrugation. Second, the surface of the buttresses facing the corrugated portion partially retains the flow of molten metal within the corrugated portion.

[0029] In a preferred embodiment, the free edge of the hoop walls, optionally provided with an overhanging protrusion, form a circular arc offset along the direction of the first transverse axis, X2, with respect of the circular cross section of the central portion of the inner cavity (3), so that each of the hoop walls forms a crescent, being highest at the level of their intersection with the first transverse axis, X2, on an orthogonal projection on plane, Π1 , and lowest where they meet the longitudinal buttresses (7b) at each end of the hoop walls (cf. Figure 3).

[0030] Figure 6 compares the calculation by finite element modelling of the erosion rate of the refractory bricks lining the cavity (3) of a torpedo ladle (a) of the prior art, devoid of any corrugated portion, and (b) according to the present invention, at an early stage of the filling operation. As can be expected, it can be seen that the erosion rate is very high at the impact region of the free falling molten metal jet, confirming the observations of Isei et al (Op. Cit.). It is interesting, however, to observe that in the prior art torpedo ladle (Figure 6(a)), high erosion rates are measured far away from the impact region, at the two ends of the cavity, whilst the erosion rates measured in a torpedo ladle according to the present invention (Figure 6(b)) at these locations is negligible. The high erosion rate observed at the ends of the cavity of a torpedo ladle of the prior art demonstrates that reinforcing the impact region only, by thickening it and/or using wear resistant materials may increase the service life of the impact region, but not of the refractory bricks lining the ends of the torpedo ladle. Without wishing to be bound by any theory, it is believed that the high erosion rates measured at the ends of a torpedo ladle of the prior art are due to the still very high kinetic energy of the molten metal jet even after impacting and bouncing off the impact area, such that the bouncing jets smash against the ends of the cavity with still a high flow rate, generating high shear stresses and thus high erosion rates of the refractory lining at these locations.

[0031 ] By contrast, since a substantial fraction of the kinetic energy is being absorbed upon impact of the free falling jet of molten metal and the flow thereof along the corrugated portion (7), the molten metal fills the rest of the cavity of a torpedo ladle according to the present invention (Figure 6(b)) with a substantially lower velocity than observed in the absence of a corrugated portion (Figure 6(a)). The effects on the erosion rate of the surrounding refractory bricks is striking, with little to no dark areas observed in Figure 6(b) according to the present invention, in particular at the ends of the cavity so strongly solicited in the torpedo ladle of the prior art (Figure 6(a)).

[0032] The solution proposed in DE1 182679 of forming a trough defined by two parallel walls normal to the longitudinal axis, X1 , (cf. Figure 8(a)) absorbs only a fraction of the kinetic energy absorbed by the corrugated portion (7) of the present invention. Figure 9 compares the finite element modelling of the magnitude of the shear stresses generated at the torpedo walls by the flowing molten metal upon filling a torpedo ladle (a) of the type disclosed in DE1 182679 and (b) according to the present invention. It can be seen that much higher shear stresses (darker areas) are generated in a torpedo ladle according to DE1 182679 than in one according to the present invention, thus leading to a higher erosion rate in the former.

[0033] Because most of the kinetic energy of the free falling molten melt jet is absorbed upon impacting a relatively small area of the corrugated portion and thereafter by colliding with successive crests, the corrugated portion (7) is exposed to severe shear stresses. It may be advantageous that the corrugated portion be made of, or be coated with a hard material comprising wear resistant oxides such as aluminium oxide. Even if the corrugated portion is made of the same refractory material as the remaining bricks lining the cavity (3) of the torpedo ladle the present invention is still advantageous although the corrugated portion will be eroded as rapidly as a state of the art torpedo ladle, because the torpedo ladle of the present invention can be brought back to service very rapidly by simply replacing the corrugated portion, which is a very simple operation as is described below, and much quicker and economical than relining the inner walls of the whole cavity (3) with new refractory bricks.

[0034] The corrugated portion (7) can be built with refractory bricks inside the ladle shroud together with the lining of the cavity. This process is, however, long and labour intensive. It is more advantageous to use pre-cast refractory modules (7m) produced separately and thereafter fixed in their position inside the torpedo ladle when the inner walls of the cavity (3) are fully lined with refractory bricks. In a preferred embodiment, one such pre-cast refractory module forms the whole refractory portion and can be fixed at the bottom of the cavity in one piece. This, however, requires that the opening (3) of the torpedo ladle is large enough to allow the introduction therethrough of a monolithic module forming the whole of the corrugated portion. If the opening (3) is rectangular, as illustrated in Figure 2, it is possible to introduce such module with the free end of the corrugated portion aligned with a diagonal of the rectangular opening. The complexity of the introduction of such monolithic module can be compensated by the ease to fix it into place once inside the cavity. If a pre-programmed robot is used for this operation, very accurate trajectories can be programmed and applied in a reproducible manner.

[0035] Alternatively, if the opening (3) is not large enough to allow the introduction of a monolithic pre-cast module into the torpedo ladle, several partial pre-cast modules (7m) of smaller dimensions can be used instead and assembled inside the torpedo ladle to form the complete corrugated portion (7). Such pre-cast modules can have different geometries. For example, they may be in the shape of sections having the same width, W, as the corrugated portion but spanning a smaller angular portion as the corrugated portion, a, or as the hoop walls, β. For example, as shown in Figure 7(a) a partial pre-cast module (7m) having the full width, W, of the final corrugated portion is shown spanning only half the angular portion, β, spanned by the corrugated portion (7) and associated hoop walls (7w) when assembled in the torpedo ladle. Of course such pre-cast modules may span any fraction of the angular portion, β. Alternatively or additionally, a partial pre-cast module (7m) can span a width lower than the final width, W, spanned by the corrugated portion (7) once assembled in the torpedo ladle. Figure 7(b) shows an example of partial pre-cast module of half the width, W, and half the angular portion, β, spanned by the final corrugated portion and associated hoop walls once assembled in the torpedo ladle. Oder geometries of partial pre-cast modules (7m) can be envisaged. For example, the corrugated portion (7) can be pre-cast in one module or several partial modules, and the hoop walls can pre-cast as separate modules to be assembled with the corrugated portion module(s) in the torpedo ladle.

[0036] The use of pre-cast modules, the corrugated portion can be replaced very rapidly and simply in case of premature wear, whilst the surrounding refractory bricks are little affected by wear, thanks to the beneficial effect of the corrugated portion on the molten metal flow rate and associated shear stresses. This explains why the corrugated portion needs not necessarily be made of or coated with a wear resistant material. Indeed, compared with the laborious operation of re-lining the cavity of a torpedo ladle, installing a new corrugated portion is in comparison a routine operation. Of course, this operation requires the cooling of the torpedo ladle which is time consuming and imposes undesired thermal cycles to the refractory bricks. For this reason, it is preferred to reinforce the corrugated portion anyway by using a wear resistant material either as coating or as constitutive material.

[0037] As shown in Figure 4, a torpedo ladle according to the present invention is used in exactly the same way as any conventional torpedo ladle. It can be filled when at its filling angular position, 6f, as shown in Figure 4(a) and emptied when rotated upon the longitudinal axis, X1 , to its pouring position, θρ. The rotation angle from the filling position to the pouring position is comprised between 90 and 180°, preferably between 1 10 and 150°, typically about 120°.

Claims

Claims.

Torpedo ladle (1 ) for the transportation of molten metal, said torpedo ladle defining a cavity (3) having a fusiform shape extending along a longitudinal axis, X1 , with a generally cylindrical central portion of inner diameter, Di, flanked by two generally frusto- conical end portions, said torpedo ladle being rotatable about said longitudinal axis, from a first angular position, 6f, referred to a filling position, to a second position, θρ, referred to as pouring position, and further comprising:

- an outer shell (1 o) defining the outer surface of the torpedo ladle, and an inner liner comprising refractory bricks, defining the inner surface (1 i) of the torpedo ladle, and

- an opening (5) bringing in fluid communication the outer surface of the torpedo ladle with the inner surface thereof, said opening being located in the central portion of the torpedo ladle and facing upwards when the torpedo ladle is at its filling position, 6f; characterized in that, the inner surface of the torpedo ladle comprises a corrugated portion (7) located opposite to, and in registry with the opening, the corrugation being characterized by crests (7c) and valleys (7v) extending parallel to the longitudinal axis, X1 .

Torpedo ladle according to claim 1 , wherein the crest to valley amplitude, A, of the corrugation is at least 2% of the inner diameter, Di, of the torpedo ladle, and preferably not more than 8% of the inner diameter, Di.

Torpedo ladle according to claim 1 or 2, wherein the crest to valley amplitude, A, of the corrugation is comprised between 50 and 300 mm, preferably between 100 and 250 mm.

Torpedo ladle according to any one of the claims 1 to 3, wherein the crest to crest distance, λ, of the corrugated portion is comprised between π Di/ 20 and π Di/ 60, preferably between π Di/ 25 and π Di/ 35.

Torpedo ladle according to any one of the claims 1 to 4, wherein the crest to crest distance, λ, of the corrugated portion is comprised between 100 and 600 mm, preferably between 200 and 400 mm.

Torpedo ladle according to any one of the claims 1 to 5, wherein in an orthogonal projection on a transverse plane, Π1 , normal to the longitudinal axis, X1 , and comprising a first transverse axis, X2, intersecting the longitudinal axis, X1 , and the centroid of the opening, the corrugated portion extends over an angular portion, a, of at least 90°, preferably at least 100°, more preferably 120°, such that said angular portion, a, is axis- symmetrical with respect to the first transverse axis, X2, and is located on the side of the inner surface opposite the opening with respect to the first longitudinal axis.

Torpedo ladle according to any one of the claims 1 to 6, wherein the corrugated portion is flanked on both sides by a hoop-wall (7w) extending substantially normal to the first longitudinal axis, X1 , and which are preferably parallel to one another.

8. Torpedo ladle according to claim 7, wherein the top of each hoop-wall (7w) ends in an over-hanging protrusion extending partially over the corrugated portion.

9. Torpedo ladle according to claims 6 and either claim 7 or 8, wherein in an orthogonal projection on plane, Π1 , the hoop walls extend over an angular portion, β, of the inner wall of the torpedo ladle which is larger than the angular portion, a, covered by the corrugated portion, and are joined on either side of the first transverse axis, X2, above the level of the corrugated portion by a longitudinal buttress (7b) extending parallel to the longitudinal axis, and having an upstream surface facing the opening, which is slanted with an angle lower than 90°, preferably lower than 45° with respect to the inner surface of the torpedo ladle.

10. Torpedo ladle according to claims 6 and any one of the claims 7 to 9, wherein the hoop walls are highest at the level of their intersection with the first transverse axis, X2, on an orthogonal projection on plane, Π1.

1 1. Torpedo ladle according to any of the preceding claims, wherein the corrugated portion is made of, or is coated with a hard material comprising aluminium oxide.

12. Use of a pre-cast refractory module (7m) for producing a torpedo ladle according to any of the preceding claims, wherein said refractory module comprises a corrugated surface defined by crests (7c) and valleys (7v) extending parallel to each other along a longitudinal axis, X1 , and which can be laid onto and fixed to the inner surface (1 i) of the cavity (3).

13. Use according to claim 12, wherein a monolithic pre-cast refractory module (7m) having the geometry of the corrugated portion (7) as defined in claim 1 is used, and wherein the crests and valleys of the pre-cast refractory module are preferably flanked on either sides by a hoop-wall (7w) extending substantially normal to the first longitudinal axis, X1 , and parallel to one another.

14. Use according to claim 12, wherein at least two partial pre-cast refractory modules (7m) are used, such that by assembling them inside the torpedo ladle, a corrugated portion (7) as defined in claim 1 is obtained, preferably flanked on either sides by a hoop-wall

(7w) extending substantially normal to the first longitudinal axis, X1 , and parallel to one another