Patent Application
20190275584
The present invention relates to a refractory article known in the art as an “impact pad” for use in handling molten metals, especially steel. The invention particularly relates to an impact pad for placement in a tundish for reducing the effects of misalignment of an impinging stream of molten steel entering the tundish. The present invention finds particular utility in the continuous casting of steel.
Tundishes act as holding tanks for said molten metal, and especially for molten steel in commercial processes for the continuous casting of steel. In the continuous casting of steel, the molten steel fed to the tundish is generally high-grade steel that has been subjected to various steps for rendering it suitable for the particular casting application. Such steps normally involve, for example, one or more steps to control the levels of the various elements present in the steel, for example the level of carbon or other alloying ingredients, and the level of contaminants such as slag. The residence of the steel in the tundish provides a further opportunity for any entrained slag and other impurities to segregate and float to the surface where they can be, for example, absorbed into a special protective layer provided on the surface of the molten steel. Thus the tundish can be used to further “clean” the steel before it is fed to the mould for casting.
To optimize the ability of the tundish to continuously furnish a supply of clean steel to the mould, it is highly desirable to control and streamline the flow of steel through the tundish. Molten steel is normally fed to the tundish from a ladle via a shroud that protects the stream of steel from the surrounding atmosphere. The stream of molten steel from the ladle generally enters the tundish with considerable force, and this can generate considerable turbulence within the tundish itself. Any undue turbulence in the flow of molten steel through the tundish has a number of undesirable effects including, for example; preventing slag and other undesirable inclusions in the steel from agglomerating and floating to the surface; entraining into the molten steel a part of the protective crust that forms, or is specifically provided, on the surface of thereof; entraining gas into the molten steel; causing undue erosion of the refractory lining within the tundish; and generating an uneven flow of the molten steel to the casting mould.
In an effort to overcome these problems the industry has undertaken extensive research into various designs of impact pads for reducing turbulence in the tundish arising from the incoming stream of molten steel, and for optimizing the flow within the tundish to approximate ideal “plug flow” characteristics as nearly as possible of the molten steel as it traverses the tundish. In general, it has been found that the flow of molten steel through the tundish can often be improved using impact pads that have specially designed surfaces capable of redirecting and streamlining the flow of molten steel.
Plug flow behavior (i.e., passage of successive portions of steel through the tundish without significant mixing) requires direction of flow away from the tundish outlet after the molten steel recedes from the impact pad. The presence of a significant portion of flow from the impact pad to the tundish outlet, with a minimized residence time in the tundish, is known as “short-circuiting.” Impact pads disclosed in the prior art have generally been designed with particular attention to the upwardly directed component of the resulting flow. An increase in the residence time, and an increase in the uniformity of residence time, in the tundish corresponds to the minimization of mixing, and enables successive steel formulations to pass through the tundish with retention of their respective compositions.
In certain configurations of a tundish, such as in a tundish feeding multiple strands, it is difficult to produce an even residence time and temperature to all strands. This is particularly difficult if the ladle shroud feeding steel into the tundish is not vertical, or is not directing steel flow at the center of the tundish, in which case both an uneven thermal distribution and uneven residence time to the various strands may result. Large variation in the thermal distribution and residence time between strands can cause operational issues and increased defects in the steel product.
Impact pads disclosed in the prior art generally comprise a base against which a downwardly directed stream of molten steel impinges, and a vertical sidewall or sidewall elements that redirect the stream. They are fabricated from refractory materials capable of withstanding the corrosive and erosive effects of a stream of molten steel for their working lives. They are frequently shaped in the form of troughs or shallow boxes having, for example, square, rectangular, trapezoidal or circular bases.
Attaining the desired flow patterns requires that the incoming stream from the ladle encounters the impact pad at a specific location, generally the geometric center of the pad. However, exact control of an incoming ladle stream is difficult, and it is not unusual for an incoming stream to be slightly off center from its desired location. A misaligned stream may cause selective erosion of one of the walls of the impact pad, or may impact, and erode, the upper surface of an impact pad, leading to undesirable flow patterns and possibly exacerbating the problems the pad was intended to overcome.
It will be appreciated that the process of designing a new tundish impact pad which meets particular pre-determined criteria is extremely complex, since changing one aspect of the design of an impact pad generally has unforeseen ramifications on the flow dynamics of the entire tundish system.
It is an object of the present invention to provide an improved impact pad suitable for placement in a tundish for generating symmetric flow distribution of the flow of molten metal introduced therein.
The present invention provides a tundish impact pad formed from refractory material comprising a base having an impact surface which, in use, faces upwardly against a stream of molten metal entering a tundish, and a wall extending upwardly from the base around at least a part of the periphery of the impact surface. The wall comprises a plurality of adjacent wall portions. The base of the tundish impact pad has a centerline; the base may be symmetrically configured about the center line. The centerline may be a longitudinal line extending from one end of the largest horizontal dimension of the impact pad to the other end. The longitudinal center line may be nonhorizonal, having an angle of inclination or declination with respect to the horizontal plane. The longitudinal center line may comprise two segments or a plurality of segments, in which two segments, at least two segments or a plurality of segments are each nonhorizontal, or have an angle of inclination or declination with respect to the horizontal plane. The impact surface contains a planar portion or facet, extending from a wall portion towards the longitudinal center line, or to the longitudinal centerline, or towards the center of the impact surface. In certain embodiments, all lines in the facet have an inclination or declination with respect to all wall portions. In certain embodiments, the impact surface facet has an end proximal to the wall portion from which it extends and an end distal to the wall portion from which it extends, and the end distal to the wall portion terminates in a line parallel to the longitudinal center line. In certain embodiments, the impact surface facet has an end proximal to the wall portion and an end distal to the wall portion, and the end distal to the wall portion terminates in the longitudinal center line. In certain embodiments, the impact surface facet has an end proximal to the wall portion from which it extends and an end distal to the wall portion from which it extends, and the end distal to the wall portion terminates in a line parallel to the wall portion from which it extends. In certain embodiments, the impact surface facet may be described as not being contained in the horizontal plane. The impact surface facet may be nonhorizontal along a line of extent, perpendicular to the longitudinal center line, from the wall portion towards the longitudinal center line. The impact surface facet may also be described as having a nonzero angle with the horizontal between the wall portion and the longitudinal center line. The impact surface facet may also be described as either inclining or declining between the wall portion and the centerline. In certain embodiments, a line, or all lines, contained in the surface facet and extending perpendicularly from the wall portion have a nonzero angle of declination or inclination with respect to the horizontal plane, or can be characterized as not being contained in the horizontal plane. In certain embodiments, all lines contained in the surface facet and being perpendicular to lines extending perpendicularly from the wall portion have a nonzero angle of declination or inclination with respect to the horizontal plane, or can be characterized as not being contained in the horizontal plane. Certain embodiments of the invention contain an impact surface facet in which (a) all lines, contained in the surface facet and extending perpendicularly from the wall portion have a nonzero angle of declination or inclination with respect to the horizontal plane, or can be characterized as not being contained in the horizontal plane, and (b) all lines contained in the surface facet and being perpendicular to lines extending perpendicularly from the wall portion have a nonzero angle of declination or inclination with respect to the horizontal plane, or can be characterized as not being contained in the horizontal plane. Certain embodiments of the invention contain an impact surface facet in which (a) all lines, contained in the surface facet and extending in a perpendicular direction from the wall portion have a nonzero angle of declination or inclination with respect to the horizontal plane, or can be characterized as not being contained in the horizontal plane, and (b) all lines contained in the surface facet and parallel to the wall portion have a nonzero angle of declination or inclination with respect to the horizontal plane, or can be characterized as not being contained in the horizontal plane. In certain embodiments of the invention, impact surface facets in which (a) all lines, contained in the surface facet and extending perpendicularly from the wall portion have a nonzero angle of declination or inclination with respect to the horizontal plane, or can be characterized as not being contained in the horizontal plane, and (b) all lines contained in the surface facet and being perpendicular to lines extending perpendicularly from the wall portion have a nonzero angle of declination or inclination with respect to the horizontal plane, or can be characterized as not being contained in the horizontal plane, represent at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or the entirety of the impact surface of the invention. In certain embodiments, the impact surface facet is in contact with at least two wall portions, and is inclining or declining with respect to at least two of the wall portions with which it is in contact. In certain embodiments, the impact surface facet is in contact with at least two wall portions, and at least one line contained in the surface facet and extending in a perpendicular direction from each of the at least two wall portions has a nonzero angle of declination or inclination with respect to the horizontal plane. In certain embodiments, the impact surface facet is in contact with at least two wall portions, and all lines contained in the surface facet and extending in a perpendicular direction from one of the at least two wall portions have a nonzero angle of declination or inclination with respect to the horizontal plane.
In certain embodiments of the tundish impact pad, a facet having two ends and two sides extends from two adjacent wall portions; the impact surface facet has an end proximal to a first wall portion and an end distal to the first wall portion, and the end distal to the wall portion terminates in a line parallel to the centerline; the impact surface facet has a first side proximal to a second wall portion adjacent to the first wall portion and a second side distal to the second wall portion. The impact surface facet may be nonhorizontal along a line of extent extending perpendicularly from the first wall portion to the centerline, may be nonhorizontal along a line of extent extending perpendicularly from the first side to the second side, and may be nonhorizontal both from a line of extent extending perpendicularly from the first wall portion to the centerline, and along a line of extent from the first side to the second side. In certain embodiments, the second side of the impact surface facet is perpendicular to the centerline of the pad.
In certain embodiments of the invention, the impact surface of the base contains at least two impact surface facets, of which two impact surface facets extend towards each other from opposed wall portions. In certain embodiments, the opposed wall portions are parallel. Each of the two impact surface facets may extends towards the longitudinal center line; the facets may meet at the longitudinal center line, or be separated by an area containing the centerline. In certain embodiments of the invention, the two impact surface facets meet, and the line of intersection between the two impact surface facets is horizontal. In other embodiments of the invention, the line of intersection between the two impact surface facets is not horizontal, and has a lower end and an upper end. In certain embodiments of the invention, the line of intersection between the two impact surface facets is equidistant from two opposed walls.
In certain embodiments of the invention, the impact surface of the base contains a plurality of facets extending from respective wall portions towards the center of the impact surface, and all lines in the plurality of facets, or all lines contained in the plurality of surface facets and extending in a perpendicular direction from a wall portion, have an inclination or declination with respect to all wall portions, and the plurality of facets has an area of at least 35%, at least 30%, at least 35% at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or 100% of the area of the impact surface.
In certain embodiments of the invention, the impact surface of the base contains at least four impact surface facets; four impact surface facets meet at a base impact surface center point.
The base of the impact pad can be of any suitable shape, for example, polyhedral shapes having in the horizontal plane, for example, square, rectangular, trapezoidal, rhomboidal, hexagonal, octagonal or other polygonal geometries, or circular or elliptical geometries. In embodiments in which the base of the pad has a polyhedral shape, a plurality of wall portions may extend upwards from the base; each wall portion may extent upward from separate line segment constituting the polygon. In embodiments in which the base is rectangular, the impact pad may comprise two pairs of impact surface facets, wherein each impact surface facet extends inwardly from a pair of adjacent wall portions; the longitudinal center line may comprise a central peak or may comprise terminal peaks; and pairs of impact surface facets may intersect along a latitudinal line that may comprise a central peak or may comprise terminal peaks.
The wall may extend partially around the periphery of the base, or may extend around the entire periphery of the base. In certain embodiments wherein the wall extends around the entire periphery of the base, the wall has a uniform height. The wall may be vertical or have an angle in the range from, and including, 1 degree to, and including, 30 degrees from the vertical. In embodiments in which the pad is polygonal, a portion of the wall between two vertices may have a non-uniform height. For example, the portion of the wall may have a minimum height at the center of the portion of the wall.
One or more portions of the upper part of the wall may support one or more overhangs which project inwardly over the periphery of the base. The overhangs may be continuous around the periphery of the base, or may be discontinuous around the periphery of the base. In certain embodiments, inner surfaces of the overhang meeting at a vertex of the wall may be connected by a plane angle geometry, a radius geometry or a chamfer geometry.
One or more portions of the wall may contain ports. In certain embodiments, the impact surface may have an upper end and a lower end, and the ports may be provided at the lower end of the impact pad. In certain embodiments, one or more pairs of ports may be provided on faces of opposing wall portions adjacent to a wall portion located at the lower end of the impact surface. A port may be provided so that the bottom of the port has the same elevation as the portion of the impact surface in communication with the port.
Angles of declination or inclination, with respect to the horizontal plane, of impact surface facets as measured from a wall towards the centerline of the impact pad may range from and including 1 degree to and including 20 degrees, or from and including 1 degree to and including 15 degrees. The angle of declination or inclination, with respect to the horizontal plane, of the impact surface center line may range from and including 1 degree to and including 20 degrees, or from and including 1 degree to and including 15 degrees.
The percentage of the impact surface covered by impact surface facets having angles of declination or inclination, with respect to the horizontal plane, as measured both on a line perpendicular to a wall with which the facet is in communication and on a line parallel to the same wall, may range from and including 25% to and including 100%, from and including 30% to and including 100%, and from and including 40% to and including 100%,
In a first embodiment of the invention, two pairs of impact surface facets meet at a central vertical plane of the impact surface extending in the larger horizontal dimension of the impact pad, and at a central vertical plane of the impact surface extending in the smaller horizontal dimension of the impact pad. The impact pad has a rectangular geometry in the horizontal plane, with a pair of larger opposing wall portions and a pair of smaller opposing wall portions. Each facet has an angle of declination as it extends from a larger opposing wall portion. Each facet has an angle of inclination as it extends from a smaller opposing wall portion. The top of the wall is provided with an overhang that extends over the impact surface of the impact pad.
In a second embodiment of the invention, two pairs of impact surface facets meet at a central vertical plane of the impact surface extending in the larger horizontal dimension of the impact pad, and at a central vertical plane of the impact surface extending in the smaller horizontal dimension of the impact pad. The impact pad has a rectangular geometry in the horizontal plane, with a pair of larger opposing wall portions and a pair of smaller opposing wall portions. Each facet has an angle of declination as it extends from a larger opposing wall portion. Each facet has an angle of declination as it extends from a smaller opposing wall portion. The top of the wall is provided with an overhang that extends over the impact surface of the impact pad.
In a third embodiment of the invention, two pairs of impact surface facets meet at a central vertical plane of the impact surface extending in the larger horizontal dimension of the impact pad, and at a central vertical plane of the impact surface extending in the smaller horizontal dimension of the impact pad. The impact pad has a rectangular geometry in the horizontal plane, with a pair of larger opposing wall portions and a pair of smaller opposing wall portions. Each facet has an angle of inclination as it extends from a larger opposing wall portion. Each facet has an angle of inclination as it extends from a smaller opposing wall portion. The top of the wall is provided with an overhang that extends over the impact surface of the impact pad.
In a fourth embodiment of the invention, two pairs of impact surface facets meet at a central vertical plane of the impact surface extending in the larger horizontal dimension of the impact pad, and at a central vertical plane of the impact surface extending in the smaller horizontal dimension of the impact pad. The impact pad has a rectangular geometry in the horizontal plane, with a pair of larger opposing wall portions and a pair of smaller opposing wall portions. Each facet has an angle of inclination as it extends from a larger opposing wall portion. Each facet has an angle of declination as it extends from a smaller opposing wall portion. The top of the wall is provided with an overhang that extends over the impact surface of the impact pad. The smaller opposing wall portions have central height minima. The interior surfaces of portions of the overhang are joined by beveled segments, or join at right angles, or are joined by radii.
In a fifth embodiment of the invention, a pair of impact surface facets meet at a central vertical plane of the impact surface extending in the larger horizontal dimension of the impact pad. The impact pad has a rectangular geometry in the horizontal plane, with a pair of larger opposing wall portions and a pair of smaller opposing wall portions. One of the smaller opposing wall portions constitutes a front wall; the other of the smaller wall portions constitutes a back wall. Each facet has an angle of declination as it extends from a larger opposing wall portion. Each facet has an angle of declination as it extends from the front wall to the back wall. The larger opposing wall portions decrease in height as they extend from the back wall to the front wall. The top of the wall is provided with an overhang that extends over the impact surface of the impact pad. The interior surfaces of portions of the overhang are joined by beveled segments, or join at right angles, or are joined by radii.
In a sixth embodiment of the invention, a pair of impact surface facets meet at a central vertical plane of the impact surface extending in the larger horizontal dimension of the impact pad. The impact pad has a trapezoid geometry in the horizontal plane, with the smaller of the two parallel wall portions constituting a back wall and the larger of the two parallel wall portions constituting a front wall. One of the smaller opposing wall portions constitutes a front wall; the other of the smaller wall portions constitutes a back wall. Each of the pair of facets has an angle of declination as it extends towards the other facet from a nonparallel wall. Each facet has an angle of declination as it extends from the back wall to the front wall. The nonparallel wall portions decrease in height as they extend from the back wall to the front wall. The top of the wall is provided with an overhang that extends over the impact surface of the impact pad. The interior surfaces of portions of the overhang are joined by beveled segments, or join at right angles, or are joined by radii. Ports extend from the interior of the wall to the exterior of the wall; each of a pair of ports may extend through wall portions adjacent to the front wall at a location in the wall portion adjacent to the front wall.
The base itself can, if desired, be affixed to the base of a tundish using any suitable means, for example, using refractory cement, or by locating the base by means of corresponding elements formed in the surface of the refractory lining of the tundish and the underside of the impact pad. The impact pad may be embedded into the refractory base of the tundish. This can be achieved, for example, by placing the impact pad on the monolithic refractory lining of a tundish, placing a layer of cold cure or hot cure refractory power composition to surround the base and optionally part of the outer wall of the impact pad, and then curing the refractories to bind the impact pad in position in the tundish.
The wall extending upwardly from the base around at least a part of the periphery of the impact surface may be made from the same material as the base and may be integral therewith. At least one wall extending upwardly from the base around at least a part of the periphery of the impact surface may have a mirror image counterpart wall extending upwardly from the opposite peripheral part of the base.
In the case that the impact pad has a rectangular or trapezoidal-shaped base and is intended for so called “single strand” operation, the wall may extend around three sides of the base, with the fourth side having either no wall, or a relatively low wall.
If the wall of the impact pad is provided with an overhang, the upper surfaces of the overhang may be smooth surfaces. The upper surface can have a profile matching the profile of the under-surface if desired, e.g. to provide an overhang having a substantially uniform thickness at least in the portion occupied by the curved or sloping portion.
The junction between the wall and the impact surface (i.e. the upper surface of the base) can take the form of a sharp angle, e.g. a right angle, or an acute angle or an obtuse angle, or can be rounded or curved.
The impact pad according to the present invention can be made using the standard molding techniques well known in the art for forming refractory shaped articles. The impact pad can, if desired, be fabricated in two or more separate parts which can then be joined together to form the final article, or can be fabricated as a monolithic structure (i.e., formed in one piece as a single integral article).
The refractory material from which the impact pad is fabricated can be any suitable refractory material capable of withstanding the erosive and corrosive effects of a stream of molten metal throughout its working life. Examples of suitable materials are refractory concretes, for example concretes based on one or more particulate refractories, and one or more suitable binders. Refractories suitable for the manufacture of impact pads are well known in the art, for example alumina, magnesia and compounds or composites thereof. Similar suitable binders are well known in the art, for example, high alumina cement.
Impact pads in accordance with the present invention can be made for use with tundishes operating in single strand, two strand or multi strand mode. As is well known in the art, continuous casting steel processes operating in single strand and multi strand (delta tundish) modes generally employ impact pads having square, rectangular or trapezoidal cross section (in the horizontal plane) wherein one pair of opposite sides are provided with walls having equal height, a third side also having a wall, and the fourth side either having a lower wall or no wall. In the double (or sometime quadruple or six-fold) strand technologies, the impact pads generally have square or rectangular cross section wherein a first pair of opposite sides are provided with walls having equal height, and the second pair of opposite sides are also of equal height (which may be the same as, or different from the height of the first pair). In single strand and multiple strand operation the impact pad is generally positioned near one end of the tundish to one side of the area wherein the outlet(s) for the molten steel are situated, whereas in double strand operation the impact pad is generally positioned in the center of a rectangular tundish with two outlets situated on opposite sides of the impact pad (or in quadruple strand operation, two pairs of outlets situated on opposite sides, or in six-fold strand operation, three pairs of outlets situated on opposite sides).
Impact pads in accordance with the present invention can be used, for example, to provide symmetric flow patterns in tundishes for holding molten steel, and to minimize problems associated with non-vertical, or non-centered, introduction of molten metal into the impact pad.
The invention will now be described with reference to the accompanying drawings wherein:
Also contemplated is the use of an impact pad according to the invention, comprising (a) placing an impact pad according to the invention within a refractory vessel and arranging it so as to receive a flow of molten metal, and (b) directing the flow of molten metal into the interior of the impact pad. A method for reducing the effects of misalignment of an impinging stream of molten steel entering a refractory vessel comprises (a) placing an impact pad according to the invention within a refractory vessel and arranging it so as to receive a flow of molten metal, and (b) directing the flow of molten metal into the interior of the impact pad.
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.
This application is a U.S. national stage application, filed under 35 U.S.C. § 371, of International Application No. PCT/US17/45908, which was filed on Aug. 8, 2017, and which claims priority to U.S. Provisional Application Ser. No. 62/372,073, filed on Aug. 8, 2016, the contents of which are incorporated by reference into this specification.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US17/45908 | 8/8/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62372073 | Aug 2016 | US |
