Patent Application
20160288203
(1) Field of the Invention
The present invention relates to nozzles for casting metal beams, such as H-beams and the like. The nozzle of the present invention allows a better control of the metal flow into a mould, yielding metal beams with low defects.
(2) Description of the Related Art
In 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
In some cases, two nozzles are used for a single mould in order to ensure optimal filling of the mould and thermal profile of the metal flowing into the mould. This solution may be used for simple rectangular profiles, such as in U.S. Pat. No. 3,931,850, but it is usually used for moulding complex shaped metal parts, such as H-shaped beams or similar. For example, JPH09122855 discloses a H-beam mould fed by two nozzles located at the intersections between each flange with web of the H-beam (note that the “flanges” refer to the two lateral elements of the “H” and the “web” refers to the middle element connecting both flanges; H-beams are also often referred to as I-beams, the two terms being used herein as synonyms). Using two nozzles for a single mould yields several drawbacks. First, the production costs are increased since two nozzles are required, instead of a single one. Second, the flow rates of the two nozzles must be well coordinated during casting, lest the overall metal feeding flow becomes uneven. This is not easy to achieve.
H-beam casting installations have been proposed comprising a single nozzle per mould, thus solving the drawbacks discussed above associated with the use of two nozzles as described, for example; in JPS58224050, JPH115144, and JPH05146858. In each of the foregoing documents, a single nozzle comprising an end outlet as well as front ports opening at the peripheral wall of the nozzle is positioned at the intersection between one flange only and the web of the H-mould. Because of its offset position with respect to the mould such nozzles have a more complex front ports design which openings are not distributed around the perimeter of the nozzle symmetrically with respect to a vertical plane as it would be the case in nozzles positioned symmetrically with respect to a mould. They comprise at least a first front port extending substantially parallel to the web, and opening towards the opposite flange of the H-mould. In order to ensure proper filling of the corners of the flange located on the nozzle side, the foregoing nozzles also comprise two front ports forming a Y with the first front port. The front ports usually extend downwards.
The size of the nozzle is limited by the clearance available at the intersection of the flange with the web of the H-mould, keeping in mind that contact between the nozzle and the mould walls should be avoided, lest solidified metal bridges would form between the nozzle and the cold mould walls. This has consequences on the flow rate achievable by such nozzles, which size of the peripheral wall is limited, thus limiting the size of the axial bore and front ports too. JPH09122855 proposes a pair of nozzles having a trianglular cross-sectional shape, with rounded corners, in order to optimize the clearance available at the intersection points between each flange and the web of the H-mould. Said nozzles are provided with an end outlet only, also triangular in shape, and comprise no front ports.
The flow profile and thermal profile of the molten metal filling the mould are of course of prime importance to ensure the production of flawless beams. Both flow and thermal profiles in H-beam moulds are very sensitive to the design of such single nozzles and, in particular, to the number, location, and design of the front ports. For example it is important to ensure a filling of the mould which is stable in time, that avoids as far as possible metal jets hitting a mould wall with excessive momentum, which creates uncontrolled turbulences and rapidly erodes the mould thus decreasing service life thereof. When vortices and turbulences are formed, cooling of the beam becomes more difficult to control and flaws appear.
It is an object of the present invention to provide a nozzle suitable for filling complex shaped moulds such as H-beams, T-beams, L-beams, C-beams, and the like, yielding enhanced control of the metal jets penetrating into such mould, resulting in smoother flow and thermal profiles and, ultimately, in metal beams with very low flaw concentrations. This and other advantages of the present invention are presented in the following sections.
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 submerged nozzle for casting steel, the nozzle having an exterior and comprising:
The expression “opening to the atmosphere” means opening to the atmosphere surrounding the exterior of the nozzle. If the nozzle front port is inserted in the cavity of a mould, the “atmosphere” refers to the space defined by the cavity of the mould surrounding said nozzle front port. A “front port” is used herein in its commonly accepted definition of a port channel in fluid communication with, and extending transverse from the axial bore and comprising an outlet opening at least partially at the nozzle peripheral wall. It includes ports opening partly at the second end of the nozzle, if they also open at the peripheral wall, such as the lower front port in
The “centroid” of a plane figure or two-dimensional shape is defined as the arithmetic mean (“average”) position of all the points in the shape. In other words, it is the point at which a cardboard cut-out of the region could be perfectly balanced on the tip of a pencil (assuming uniform density and a uniform gravitational field). In geometry the term “barycenter” of a two-dimensional figure is a synonym for “centroid”, and in physics, the “barycente?” and “centroid” form a single point for shapes of uniform density only.
Such geometry allows a substantially deeper penetration of a nozzle in the web direction of a complex shaped mould, such as a H-mould when said nozzle is positioned at the crossing point between a flange and the web of the mould. At the same time, it allows an elongation of the front port channel, which allows a more stable metal flow and a dissipation of momentum thereof as hitherto possible with traditional nozzles having concentric bore and peripheral wall.
The planar cut further comprises the outline of the bore, defined by the bore perimeter and by the bore centroid of the area defined by said bore perimeter. The bore centroid is preferably located at a distance to the outer peripheral wall on the side of the front port measured along the first transverse axis (Y) which is greater or equal to L1.
In order to further promote penetration of the nozzle in the web portion of a mould, it is preferred that the distance (H1) from wall to wall of the nozzle measured along a direction normal to the axis (Y) at a distance L/2 from the wall centroid (1x) on the side of the front port (35) is less than the dimension (H2) measured in the same direction at a distance L/2 from the wall centroid (1x) on the side opposite the front port (35); H1<H2. Actually, the wall perimeter is preferably either egg-shaped, with a positive curvature over the whole length of the wall perimeter or, alternatively, is preferably pear-shaped, with the curvature changing sign locally. The nozzle may have a prismatic geometry throughout the whole length of the elongated and outlet portions (1B, 1C), such that L1>L2 over the whole length of the nozzle. Alternatively, L1 may be substantially equal to L2 in an upstream portion of the nozzle, excluding the outlet portion, and the outer peripheral wall changing geometry in a downstream portion of the nozzle, including the outlet portion, such that L1>L2. Depending on the design of the nozzle, the latter embodiment may be useful for reducing the amount of refractory material required.
It is preferred that the outlet portion further comprises an end outlet opening at the second end of the nozzle. It is further preferred that the outlet portion further comprises at least one secondary front port extending transversally to both longitudinal axis (X1) and front port axis, from the bore to the peripheral wall of the outlet portion. It is more preferred that at least two such secondary front ports be provided, forming with the first front port a Y-shape. Better dissipation of the metal flow momentum is obtained when the outlet portion further comprises a second front port extending along an axis comprised within the half-plane defined by the longitudinal axis (X1) and the front port axis. Such second front port is located either above or below the first front port.
The first front port may extend normal to the longitudinal axis (X1) or downwards. In other words, the centroid of the front port outlet can be at the same distance from the nozzle second end as, or closer thereto than the centroid of the front port inlet.
The present invention also concerns a casting installation for casting metal beams comprising
The blank beam mould in the casting installation of the present invention may have a T-cross-section, an L-cross-section, an X-cross-section, a C-cross-section, or a H-cross-section. The blank beam mould preferably has a H-cross-section with the web of the H being defined by the first elongated portion, and the two lateral flanges being defined by the second elongated portion and a third elongated portion, both substantially normal to the second elongated portion, and wherein said submerged nozzle is positioned at the area intersecting a flange and the web of the H-beam cross-section. The casting installation of the present invention preferably comprises a single submerged nozzle per blank beam mould.
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:
As illustrated in
The nozzle further comprises a bore (50) extending parallel to the first longitudinal axis (X1) opening at said inlet orifice (18) and extending along the elongated portion (1B) of the nozzle and at least partly in the outlet portion (1C) of the nozzle whence it opens to the atmosphere at least through said first front port (35), which extends along a front port direction (Y1), transverse to said first longitudinal axis (X1) from a front port inlet (35i) joining the bore (50) to a front port outlet (35o) opening at the outer peripheral wall of the outlet portion of the nozzle.
Because a nozzle according to the present invention is particularly suitable for casting complex shapes, like H-beams, using a single nozzle per mould, which is located offset with respect to the plane of symmetry of the mould normal to the web, typically at the intersection of a flange (100f) and the web (100w) of the mould (100), the metal should not flow out of the nozzle front ports symmetrically with respect to a vertical plane passing by the longitudinal axis, X1. In particular, the first front port (35) is designed to extend, when in use, in a direction parallel to the mould web, and oriented away from the flange at which intersection with the web said nozzle is located. Because of the proximity of the outer wall (100f-out) of the mould flange located “behind” the nozzle front port (35) (cf.
In a planar cut of the nozzle outlet portion (1C) along a plane normal to the first direction (X1) passing through the front port inlet (35i), the following features can be identified:
It is essential that the distance (L1) from the wall centroid (1x) to the outer peripheral wall measured along the first transverse axis (Y) on the side of the front port (35) is greater than the same distance (L2) measured on the side opposite the front port (35); L1>L2. L1 is preferably at least 5% greater than L2, more preferably at least 10% greater than L2, most preferably at least 20% or even at least 40% greater than L2, wherein the percentage is calculated as (L1−L2)/L2×100. This geometry implies a thinning of the cross-sectional shape of the nozzle in the direction of the front port (35), such that it can better fit into the somewhat restricted area defined by the intersection between a first and a second elongated mould portions defining a beam profile having, e.g., a H-, L-, T-cross-section, or the like. The “thinning” of the nozzle cross-section at the level of the first front nozzle can also be expressed by defining the distance (H1) from wall to wall of the nozzle measured along a direction normal to the first transverse axis (Y) at a distance L2/2 from the wall centroid (1x) on the side of the front port (35), which must be less than the wall to wall distance (H2) measured in the same direction at a distance L2/2 from the wall centroid (1x) on the side opposite the front port (35); H1<H2.
In an egg-shaped cross-section, the curvature of the wall perimeter is positive over the whole length of the perimeter, which characterizes a convex shape. An egg-shaped cross-section as meant in the present invention comprises a “fat” end and a “lean” end and should not be confused with an elliptical cross-section, having two identical ends and which does not fall within the scope of the present invention. Indeed, the centroid of an ellipse is located at the intersection between major and minor diameters thereof, so that L1=L2 and H1=H2 in an ellipse. The wall perimeter of nozzles according to the present invention comprises at most one axis of symmetry, but never two as is the case of ellipses. The cross-sectional shape of nozzles according to the present invention having a convex cross-sectional perimeter is not restricted to egg-shapes and could be devoid of any axis of symmetry. However, an egg-shape or oval-shape (from ovum in Latin) symmetrical with respect to the first transverse axis (Y) is preferred.
Alternatively, the wall perimeter may comprise convex and concave portions, the latter being characterized by a negative curvature. A preferred embodiment of this type is a pear-shaped cross-section, symmetrical with respect to the first transverse axis, Y of the type illustrated in
It is clear that the wall perimeter may comprise straight sections, which are only singular embodiments of convex or concave curvatures, with an infinite radius and a zero-curvature. An example of such cross-sectional shape is illustrated in
As illustrated in
The peripheral wall may be characterized by L1>L2 only in the outlet portion (1C), in the greater part of the length of the nozzle, or over the whole length of the nozzle. In the former case, L1 may be equal to L2 in a portion of the nozzle upstream from the outlet portion (1C) (the terms “upstream” and “downstream” refer to the flow direction through the nozzle when in use, said flow starting from the nozzle inlet (18) and ending at the front port outlet (35o)). Any length of the elongated portion (1B) of the nozzle may be characterized by L1>L2 without departing from the scope of the present invention, as long as the portion of the nozzle which is inserted in the mould can fit in the corresponding space.
Since L1 and L2 are measured with respect to the wall centroid (1x) it is important to define said centroid properly. As discussed above, the “centroid” (1x) of an area is herein used in its traditional geometrical definition of the arithmetic mean (“average”) position of all the points in the area, which is equivalent to the barycenter of the area having homogeneous density (i.e., ignoring that the refractory density is higher than the bore density). For simple figures such as circles or ellipses, having two axes of symmetry the position of the centroid is easy to determine. For less regular geometries, however, having one or no axis of symmetry as is the case with the wall perimeter of nozzles according to the present invention, it is not always straightforward to calculate or determine geometrically the position of the centroid.
In
Besides the outer peripheral wall outline and the first transverse axis (Y) the planar cut further comprises the outline of the bore (50), defined by the bore perimeter (50P) and by the bore centroid (50x) of the area defined by said bore perimeter. The bore centroid (50x) is located at a distance, L′1 to the outer peripheral wall on the side of the front port (35) measured along the first transverse axis (Y) which is preferably greater or equal to L1 (L′1≧L1). The wall centroid (1x) and the bore centroid (50x) may be located at the same point (i.e., L′1=L1), preferably on the first transverse axis, Y. In this case, a nozzle according to the present invention characterized by L1>L2 has the advantage that the first front port (35) can be longer than in a traditional nozzle with L1=L2. The first front port length, LINV, can be even further prolonged if the centroid (50x) of the bore on such cut plane is offset with respect to the wall centroid (1x) such that the first transverse axis (Y) starting from said bore centroid (50x), passes through the wall centroid (1x) and extends until it reaches the wall perimeter (1P) (i.e., L1>L1). This is illustrated in
Extending the length of the first front port (35) has multiple advantages. First, it creates a substantially more stable metal melt flow out of the first front nozzle, jetting out at a relatively long distance along the mould web section and creating substantially less turbulences than shorter front ports. Second, as illustrated in
The front port direction (Y1) along which extends the first front port (35) may be normal to the first longitudinal axis, X1. This would correspond to a horizontal front port (35) as illustrated in
For a proper filling of complex shaped moulds, a single front port may not be sufficient. A nozzle according to the present invention may therefore further comprise an end outlet (37) opening at the second end of the nozzle (cf.
Further dissipation of the flow momentum and enhanced flow stability may be obtained by providing the nozzle with a second front port (36) extending along an axis comprised within the half-plane defined by the first longitudinal axis (X1) and the first transverse axis, Y. In other words, as illustrated in
A nozzle according to the present invention is advantageous in use with an installation for casting metal beams as illustrated in
The blank beam mould can have a T-, an L-, an X-, a C-, a H- or similar cross-section. In case of a H- or a C-cross-section, the web of the H or C being defined by the first elongated portion, and the two lateral flanges of the H or C being defined by the second elongated portion and a third elongated portion, both substantially normal to the first elongated portion. One single such submerged nozzle for each mould is sufficient and is preferably positioned at the area intersecting the web and a flange of the H- or C-beam cross-section. Similarly, in case of T-, L-, or X-cross-sections, a single nozzle can be used for each mould, and is preferably positioned at the intersecting area between the first and second elongated portions of the mould.
A nozzle according to the present invention permits a better control of the metal jet flowing out thereof into complex shaped moulds for producing beams and the like. With the greater length, LINV, of the first front port (35) than hitherto possible. This has the advantages of enhanced flow momentum dissipation as well as higher stability and lower velocity of the outpouring metal jet. This in turn prevents flow disruption at the radii of complex shaped moulds, as well as decreasing the formation of vortices and dead zone, responsible for many defects in cast beams. A nozzle according to the present invention also permits to increase the clearance between the outer peripheral wall of the outlet portion and the mould walls, thus reducing the risk of solidified metal bridges between the nozzle and the mould walls.
Numerous modifications and variations of the present invention are possible. It is, therefore, to be understood that within the scope of the following claims, the invention may be practiced otherwise than as specifically described
| Number | Date | Country | Kind |
|---|---|---|---|
| 13191871.6 | Nov 2013 | EP | regional |
| 13191876.5 | Nov 2013 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/074008 | 11/7/2014 | WO | 00 |
