Patent Application
20200238373
The present invention relates to slab nozzles for casting slabs made of metal. In particular, it concerns slab nozzles having a specific design substantially enhancing their resistance to erosion during the continuous casting operation of slabs.
In continuous metal forming processes, metal melt is transferred from one metallurgical vessel to another, to a mould or to a tool. For example, as shown in
Slabs are continuously cast and therefore have an “infinite” length. Their cross-section can have a thickness to width aspect ratio, Tm/Wm; of the order of ¼ or more. Thin slabs are slabs of cross-section having a Tm/WM aspect ratio greater than “conventional” slabs which can have values of ⅛ and greater. Slab mould cavities obviously must reflect similar aspect ratios. Even if the inlet of slab moulds may locally have a funnel-like geometry to admit a downstream portion of a slab nozzle, said downstream portion of the slab nozzle cannot have a geometry of revolution, and must have a thickness to width aspect ratio T/W of at least 1.5 to fit in the cavity inlet of the mould. For thin slab nozzles, the thickness to width aspect ratio T/W must be at least 3.
As illustrated in
DE19505390 describes an immersed casting tube with a long and narrow cross section, having a flattened end section with outlet openings. The passage cross section of the tube within its end region is divided by a distributor into a row of channels. Below the broad pipe walls, as far as down as the exit openings, the channels (9) are open on one side.
WO2013004571, WO9814292, US2002063172, and CN103231048 relate to a submerged entry nozzle for guiding a stream of a metal melt from a tundish into a mould with multiple (three or four) front ports having different orientations and cross-sectional size ratios.
The present invention proposes a slab nozzle having a novel geometry which substantially enhances the service life thereof due to a much lighter and slower erosion of the outer wall of the downstream portion of the slab nozzle. This and other advantages of the present invention are presented in more detail in the following summary and descriptions.
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 slab nozzle for casting slabs made of metal, said slab nozzle having a geometry defined by an outer wall extending over a nozzle length, L, along a longitudinal axis, z, from an upstream end to a downstream end. The outer wall comprises a downstream portion extending along the longitudinal axis, z, from and including the downstream end, wherein
The slab nozzle further comprises a central bore opening at said inlet orifice, extending therefrom along the longitudinal axis, z, and intersecting the one or more front ports each opening at the one or more outlet port orifices.
The slab nozzle of the present invention is characterized in that, in a cut view or section of the slab nozzle along a transverse plane, P3, and, in certain configurations, in cut views or sections of the slab nozzle along any transverse plane, Pn, the outer wall of the slab nozzle is defined by an outer wall outline which comprises:
The system of axes, x, y, z, forms a coordinates system defining reference planes, Q1=(x,z), Q2=(y,z), and Q3=(x,y). The transverse plane, P3, is the plane normal to the longitudinal axis, z, and intersecting the one or more outlet port orifices, which distance, L3, to the downstream end is the largest. A transverse plane, Pn, is a plane normal to the longitudinal axis, z, and intersecting the longitudinal axis, z, at a distance, Ln, to the downstream end of not more than 60% of the nozzle length, L, preferably not more than 50% of L. All transverse planes, Pn, are parallel to the reference plane, Q3, and the transverse plane, P3, is a specific transverse plane, Pn.
In a particular configuration, in the cut view or section along a transverse plane, Pn, and, in particular, along the transverse plane, P3, the outer wall outline of the downstream portion is inscribed in a virtual rectangle of first and second edges parallel to the first transverse axis, x, and third and fourth edges parallel to the second transverse axis, y. The tight distance, dt, can be at least twice, or at least three times shorter than a flared distance, df, of the outer wall outline to the other two diagonally opposed corners of the virtual rectangle (2 dt≤df). The distance of the outer wall outline to a corner is defined as the distance between said corner and a point of the outline located closest to said corner. The tight distance, dt, may be not more than ten times, or not more than eight times shorter than the flared distance, df.
Another way of defining the geometry of the slab nozzle outline is by defining, on the one hand, a first and second tight areas, At, comprised between the outer wall outline and the edges of the virtual rectangle joining at the first and second diagonally opposed corners, respectively and, on the other hand, a first and second flared areas, Af, each of a first and second tight areas, At, comprised between the outer wall outline and the edges of the virtual rectangle joining at the other two diagonally opposed corners. The first and second tight area, At, each has an area of not more than 80%, or not more than 67%, or not more than 50% of an area of the first and second flared areas, At, (5 At ≤4 At).
With a slab nozzle according to the present invention and, in particular, having the foregoing geometries defined by tight and flared distances and/or by tight and flared areas, a stream of molten metal flowing towards the slab nozzle in a direction normal to the reference plane, Q2, will preferably flow through the gap formed between the slab nozzle and the slab mould which is on the side of the flared distance, df, and/or of the flared area, Af, and will be restricted on the side of the tight distance, dt, and/or of the tight area, At, thus creating a round-about effect, with two streams flowing in opposite directions on two opposite sides of the slab nozzle, thus avoiding any collision between the two streams within one such gap.
The central portion (Ax) of the outer wall outline may extend over at least 33%, or at least 50% of the width, W, of the first and second edges of the virtual rectangle, and may extend not more than 85%, or not more than 67% of the width, W, of the first and second edges of the virtual rectangle (33% W≤Ax≤85% W).
Protrusions can be distributed on the outer wall of the downstream portion of the slab nozzle. Protrusions allow the dissipation of the kinetic energy of a metal stream flowing through a gap. To further enhance the round-about effect, the protrusions are arranged on a first and second hindered portions of the outer wall of the downstream portion, said first and second hindered portions, corresponding to the portion of the outer wall outline in the cut along a plane, Pn, or, in particular, along the plane, P3, which is contained in the two diagonally opposed quarters of the virtual rectangle including the tight distance, dt, or the tight area, At.
The protrusions can have a multitude of geometries. For example, the protrusions may be in the form of circles, ellipses, straight or curved lines, chevrons, arcs of circles, polygons. The protrusions may protrude out of the surface of the outer wall of the downstream portion by at least 3 mm, or at least 4 mm, and may protrude by not more than 20 mm, or not more than 15 mm. If the protrusions are discrete protrusions, they may be distributed in a staggered arrangement on the outer wall of downstream portion of the slab nozzle, such as on the first and second hindered portions thereof.
The one or more front ports may flare out as they open at the corresponding outlet port orifices. A nozzle according to the present invention may contain a first and second front ports which open at a corresponding first and second outlet port orifices. The first and second front ports may be separated from one another by a divider extending in the central bore from the downstream end along the longitudinal axis, z, and dividing the bore into the first and second front ports. In a cut view or section of the thin slab nozzle along a transverse nozzle, Pn, and, in particular, along the transverse plane, P3, the first and second front ports may be defined by a first and second front ports outlines each comprising a lateral portion remote from the divider which is symmetrical solely with respect to the central point, c, and is may be substantially parallel to the corresponding first and second lateral portions (Ac1, Ac2) of the outer wall outline.
The present invention also concerns a metallurgic assembly for casting s15 metal slabs, said metallurgic assembly comprising:
A section of the metallurgic assembly along a transverse plane, Pm, and, in particular, along the transverse plane, P3, may comprise:
A transverse plane, Pm, Is a plane normal to the longitudinal axis, z, and intersecting the downstream portion of the nozzle slab, over at least 40%, preferably at least 50%, more preferably at least 75% of the inserted length, U. The transverse plane, P3, is a specific transverse plane, Pm, and are all parallel to the reference plane, Q3.
In the same cut view or section of the metallurgic assembly along a transverse plane, Pm, and, in particular, along the transverse plane, P3,
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:
The outer wall comprises a downstream portion extending along the longitudinal axis, z, from and including the downstream end, and comprises one or more outlet port orifices (51d). A slab nozzle generally comprises at least a first and second front ports (51) opening at a corresponding first and second outlet port orifices. The first and second front ports may be separated from one another by a divider (10) extending in the central bore from the downstream end along the longitudinal axis, z, as shown in
The downstream portion is defined by a width, W, measured along a first transverse axis, x, which is at least 1.5 times larger than a maximum thickness, Tx, of the downstream portion measured along a second transverse axis, y, wherein the first transverse axis, x, is normal to the longitudinal axis, z, and wherein the second transverse axis, y, is normal to both first transverse axis, x, and longitudinal axis, z. This W/Tx aspect ratio is required for inserting the downstream portion of the slab nozzle into the cavity of a slab mould, which is, of course, much wider than it is thick. For so-called thin slab nozzles, the WI Tx aspect ratio is at least 3, preferably at least 4 or 5.
The slab nozzle further comprises a central bore (50) opening at said inlet orifice (50u), extending therefrom along the longitudinal axis, z, and intersecting the one or more front ports (51) each opening at the one or more outlet port orifices. When the upstream end of the slab nozzle is coupled to the bottom floor of a metallurgic vessel (100), such as a tundish, the central bore of the slab nozzle is aligned and in fluid communication with an outlet (101) provided at the bottom floor of the tundish, such that the metal melt can flow out of the tundish through the outlet and through the central bore and flow out of the slab nozzle through the outlet port orifices.
The downstream portion of the slab nozzle is inserted in a cavity (110c) of a slab mould. The slab mould cavity has a width, Wm, measured along the first transverse axis, x, and a thickness, Tm, measured along the second transverse axis, y, which is constant for rectangular cavities (cf.
As illustrated in
The outer wall of a slab nozzle as seen by a stream of metal flowing towards the slab nozzle at the level of the outlet ports can be characterized by an outer wall outline of a cut view or section along a transverse plane, P3, wherein the transverse plane, P3, is the plane normal to the longitudinal axis, z, and intersecting the one or more outlet port orifices, which distance, L3, to the downstream end is the largest. Transverse plane P3 is therefore parallel to plane Q3=(x,y).
In conventional slab nozzles, as illustrated in
The gist of the present invention is to prevent two streams (70a, 70b) of molten metal from colliding in the narrow channels (111) formed on either side of a slab nozzle with the mould cavity wall. The principle is to create a round-about around the slab nozzle such that, like cars on a road, each opposite stream (70a, 70b) flows through its own channel (111) on one side only of the slab nozzle. As shown in
As illustrated in
It is important that the outer wall outline comprises lateral portions (Ac1, Ac2) having no axial symmetry with respect to the first transverse axis, x, in order to favour the flow of a stream of molten metal along one side of the outer wall of the slab nozzle, and to hinder the flow over the opposite side with respect to the axis, x. In one embodiment illustrated in
In order to keep the outer wall thickness substantially constant, it is preferred that, in the cut view or section of the thin slab nozzle along the transverse plane, P3, the first and second front ports are defined by a first and second front ports outlines each comprising a lateral portion remote from the divider which is symmetrical solely with respect to the central point, c, and may be substantially parallel to the corresponding first and second lateral portions (Ac1, Ac2) of the outer wall outline. In other words, it is advantageous that the same asymmetry be applied to the geometry of the front ports as to the outer wall, such that the nozzle wall has a substantially constant thickness. This way there is no risk of having a weak spot wherein the wall is too thin, or of wasting refractory material by unnecessarily locally increasing the thickness of the outer wall.
In the embodiment illustrated in
In a cut view or section along the transverse plane, P3, and advantageously along any transverse plane, Pn, the outer wall outline of the downstream portion is inscribed in a virtual rectangle of first and second edges parallel to the first transverse axis, x, and third and fourth edges parallel to the second transverse axis, y.
According to the embodiment illustrated in
Alternatively, or concomitantly, as illustrated in
As discussed supra, the round-about effect is obtained by forcing a stream of molten metal flowing towards a lateral profile of the slab nozzle to be deviated preferentially to a flowing side of the slab nozzle, rather than to the opposite, hindered side of the slab nozzle. This is achieved by facilitating flow through the flowing side of the slab nozzle by forming a broad funnel entrance at the flowing side and forming a narrow side of the funnel at the hindered side. By applying this geometry with a central symmetry at both lateral profiles of the slab nozzles, facing opposite flows of metal melt, each stream is deviated towards its own one-way street at one side of the slab nozzle (cf.
As shown in
The slab nozzle of the present invention is used in a metallurgic assembly for casting metal slabs as illustrated in
The cavity of the slab mould is defined by cavity walls extending along the longitudinal axis, z. In a cut view or section of the metallurgic assembly along the transverse plane, P3, the cavity wall is defined by a cavity wall outline 36 illustrated in
In one embodiment, Tmx=Tmc, defining a rectangular cavity wall outline, as shown in
In cases where the slab to be cast has a thickness substantially lower than the thickness, T, of the slab nozzle, the mould cavity may include a funnel shaped portion allowing the insertion of the downstream portion of the slab nozzle. This embodiment is illustrated in
A shown in
In a first side of the second transverse axis, y, there is a first tight gap between the cavity wall outline and the first lateral portions (Ac1) of the outer wall outline having a first tight gap width, Gt1, measured at a first side of the first transverse axis, x, along a segment, m, parallel to the second transverse axis, y, and passing by an intersection point between the first lateral portions (Ac1) of the outer wall outline and the first transverse axis, x. The first tight gap width, Gt1, is not more than half, or not more than a third of a first flared gap width, Gf1, of a first flared gap between the cavity wall outline and the first lateral portions (Ac1) of the outer wall outline measured at a second side of the first transverse axis, x, along the segment, m, (2 Gt1≤Gf1),
In a second, opposite side of the second transverse axis, y, there is a second tight gap between the cavity wall outline and the second lateral portions (Ac2) of the outer wall outline which is diagonally opposite to the first tight gap. The second tight gap has a second tight gap width, Gt2, measured at the second side of the first transverse axis, x, along a segment, n, parallel to the second transverse axis, y, and passing by an intersection point between the second lateral portions (Ac2) of the outer wall outline and the first transverse axis, x. The second tight gap width, Gt2, is not more than half, or not more than a third of a second flared gap width, Gf2, of a second flared gap between the cavity wall outline and the second lateral portions (Ac2) of the outer wall outline measured at the first side of the first transverse axis, x, along the segment, n, (2 Gt2≤Gf2).
Ignoring any movements of the slab nozzle with respect to the mould cavity during continuous casting operations, since the mould cavity is symmetrical at least with respect to the central point, c, the first tight width, Gt1, Is substantially equal to the second tight gap width, Gt2, (Gt1=Gt2), and Gt1 and Gt2 may be comprised between 10 and 70% of a maximum thickness, Tx, of the outer wall outline of the slab nozzle measured along the second transverse axis, y, (0.1 Tx≤Gt1≤0.7 Tx, with i=1 or 2). Similarly, the first flared gap width, Gf1, is substantially equal to the second flared gap width, Gf2, (Gf1=Gf2).
For example, a mould cavity may have a maximum thickness, Tmx=74−162 mm, depending on whether or not the mould cavity comprises a funnel shaped central cavity portion (i.e., whether Wmx is equal to or greater than 0). For such mould cavity, a thin slab nozzle can be used having a maximum thickness, Tx=60 mm, and the tight gap width, Gt1, Gt2, can be comprised between 6 and 42 mm, in general, about 25 mm. With a mould cavity having a maximum thickness, Tmx=156 to 251 mm, a slab nozzle can be used having a maximum thickness, Tx=130 mm. The tight gap width, Gt1, Gt2, can be comprised between 13 and 91 mm, in general, about 40 mm.
The geometries of the metallurgic assembly defined supra with respect to a cut along the transverse plane, P3, preferably also apply to any cut along any transverse plane, Pm, defined as a plane normal to the longitudinal axis, z, and intersecting the downstream portion of the nozzle slab, over at least 40%, or at least 50%, or at least 75% of the inserted length, U. The transverse planes, Pm, may intersect the downstream portion of the nozzle slab above the downstream end of the slab at least 1%, or at least 5% of the inserted length, Li, above the downstream end. For example, the following magnitudes defined with respect to the cut along plane, P3, also apply for cuts along a plane, Pm:
By preferentially deviating around the slab nozzle the two opposite converging molten metal streams flowing towards the two flanks of the slab nozzle, achieved by the specific geometry of the slab nozzle of the present invention, the impact or impinging area between the two opposite streams, normally located in the narrow channels between mould and slab nozzle is shifted away from the slab nozzle, and the turbulences thus created have substantially less impact on the erosion of the slab nozzle outer wall. The service life of the slab nozzle can thus be substantially prolonged. A slab nozzle according to the present invention can be used in any existing metallurgic installation and yield the foregoing advantages without any change in the rest of the installation. The round-about effect permits a substantial reduction of the erosion rate of the slab nozzle outer wall.
Various features and characteristics of the invention are described in this specification and illustrated in the drawings to provide an overall understanding of the invention. It is understood that the various features and characteristics described in this specification and illustrated in the drawings can be combined in any operable manner regardless of whether such features and characteristics are expressly described or illustrated in combination in this specification. The inventor and the Applicant expressly intend such combinations of features and characteristics to be included within the scope of this specification, and further intend the claiming of such combinations of features and characteristics to not add new matter to the application. As such, the claims can be amended to recite, in any combination, any features and characteristics expressly or inherently described in, or otherwise expressly or inherently supported by, this specification. Furthermore, the Applicant reserves the right to amend the claims to affirmatively disclaim features and characteristics that may be present in the prior art, even if those features and characteristics are not expressly described in this specification. Therefore, any such amendments will not add new matter to the specification or claims, and will comply with the written description requirement under 35 U.S.C. § 112(a). The invention described in this specification can comprise, consist of, or consist essentially of the various features and characteristics described in this specification.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17171047.8 | May 2017 | EP | regional |
This application is a U.S. national stage application, filed under 35 U.S.C. § 371, of International Application No. PCT/EP2018/062420, which was filed on May 14, 2018 and which claims priority to European Application No. EP 17171047.8, filed on May 15, 2017, the contents of which are incorporated by reference into this specification.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP18/62420 | 5/15/2018 | WO | 00 |
