Impact pad, tundish and apparatus including the impact pad, and method of using same

Abstract

A tundish impact pad, a tundish containing the same, and a method of using and assembly containing the impact pad and tundish are provided. The tundish impact pad features a base having a base surface with a conical impact surface area establishing an apex, a sidewall, and a top wall extending inwardly relative to the sidewall to terminate at an inner edge establishing a mouth opening spaced above and centered relative to the apex. The top wall includes a lip sloping radially inwardly and downwardly towards the conical impact surface.

Claims

1. A tundish impact pad, comprising: a base having a base inner surface, the base inner surface comprising a conical impact surface area establishing an apex; a sidewall having a sidewall inner surface; a top wall extending inwardly relative to the sidewall to terminate at an inner edge establishing a mouth opening spaced above and centered relative to the apex, the top wall comprising a lip having a lip inner surface sloping radially inwardly and downwardly towards the conical impact surface area; and hemispherical protuberances on the lip inner surface.

2. The tundish impact pad of claim 1, wherein the sidewall inner surface is continuous and radially outward of the base inner surface, and wherein the inner surface of the tundish impact pad establishes a continuous annular chamber configured to reduce turbulence of an incoming ladle stream of molten liquid steel.

3. The tundish impact pad of claim 2, wherein: the base inner surface further comprises a first flat annular area between the conical impact surface area and the sidewall inner surface; the top wall comprises a second flat annular area extending between the sidewall inner surface and the lip inner surface; and the first and second flat annular areas are spaced apart from and extend in planes parallel to one another.

4. The tundish impact pad of claim 2, wherein the continuous annular chamber has a radius of curvature of about 30 mm.

5. The tundish impact pad of claim 1, wherein the conical impact surface area has an axis, passing through the apex, about which the conical impact surface area has rotational symmetry.

6. The tundish impact pad of claim 5, wherein the apex comprises a pointed apex, and wherein the conical impact surface area has a linear profile.

7. The tundish impact pad of claim 6, wherein the conical impact surface area has a cone angle, measured from a horizontal plane in which an outer perimeter of the conical impact surface area lies to an oblique plane in which the linear profile of the conical impact surface area lies, in a range of about 15 degrees to about 25 degrees.

8. The tundish impact pad of claim 1, wherein the lip inner surface has a downward lip angle, measured from a horizontal plane to the lip inner surface, in a range of about 20 degrees to about 25 degrees.

9. The tundish impact pad of claim 1, wherein the hemispherical protuberances are located annularly about the lip inner surface.

10. The tundish impact pad of claim 1, wherein: the apex is a pointed apex and the conical impact surface area has an axis, passing through the pointed apex, about which the conical impact surface area has a linear profile with rotational symmetry; the conical impact surface area has a cone angle, measured from a horizontal plane in which an outer perimeter of the conical impact surface area lies to an oblique plane in which the linear profile of the conical impact surface area lies, in a range of about 15 degrees to about 25 degrees; and the lip inner surface has a downward lip angle, measured from a horizontal plane to the lip inner surface, in a range of about 20 degrees to about 25 degrees.

11. The tundish impact pad of claim 10, wherein the sidewall inner surface is continuous and radially outward of the base surface, and wherein the inner surface of the tundish impact pad establishes continuous annular chamber configured to reduce turbulence of an incoming ladle stream of molten liquid steel.

12. The tundish impact pad of claim 11, wherein the continuous annular chamber has a radius of curvature of about 30 mm.

13. The tundish impact pad of claim 11, wherein: the base inner surface further comprises a first flat annular area between the conical impact surface area and the sidewall inner surface; the top wall comprises a second flat annular area extending between the sidewall inner surface and the lip inner surface; and the first and second flat annular areas are spaced apart from and extend in planes parallel to one another.

14. The tundish impact pad of claim 10, wherein the protuberances are located annularly about the lip inner surface.

15. An apparatus, comprising: a continuous caster tundish for containing a reservoir of molten metal having fluid flow generated by an incoming ladle stream; and a tundish impact pad within the continuous caster tundish, the tundish impact pad, comprising a base having a base inner surface, the base inner surface comprising a conical impact surface area establishing an apex; a sidewall having a sidewall inner surface; a top wall extending inwardly relative to the sidewall to terminate at an inner edge establishing a mouth opening spaced above and centered relative to the apex and positioned to receive the incoming ladle stream, the top wall comprising a lip having a lip inner surface sloping radially inwardly and downwardly towards the conical impact surface area; and hemispherical protuberances on the lip inner surface.

16. The apparatus of claim 15, wherein the protuberances are located about the lip inner surface.

17. The apparatus of claim 15, further comprising: a weir dividing a chamber of the tundish into a first compartment containing the tundish impact pad and a second compartment associated with an output port, the weir including a passage for communicating the first and second compartments with one another.

18. A strand casting method, comprising: feeding an incoming ladle stream of molten liquid steel into a continuous caster tundish, the continuous caster tundish containing a tundish impact pad comprising a base having a base inner surface, the base inner surface comprising a conical impact surface area establishing an apex; a sidewall having a sidewall inner surface; a top wall extending inwardly relative to the sidewall to terminate at an inner edge establishing a mouth opening spaced above and centered relative to the apex and positioned to receive the incoming ladle stream, the top wall comprising a lip having a lip inner surface sloping radially inwardly and downwardly towards the conical impact surface area; and hemispherical protuberances on the lip inner surface; impacting the incoming ladle stream of molten liquid steel against the conical impact surface area; and allowing the impacted molten liquid steel to discharge from the tundish impact pad through the mouth opening.

19. A tundish impact pad, comprising: a base having a base inner surface, the base inner surface comprising a conical impact surface area establishing an apex; a sidewall having a sidewall inner surface; a top wall extending inwardly relative to the sidewall to terminate at an inner edge establishing a mouth opening spaced above and centered relative to the apex, the top wall comprising a lip having a lip inner surface sloping radially inwardly and downwardly towards the conical impact surface area; and protuberances located on the lip inner surface.

20. The tundish impact pad of claim 19, wherein the protuberances are located annularly about the lip inner surface.

Description

BRIEF DESCRIPTION OF THE DRAWING(S)

(1) The accompanying drawings are incorporated in and constitute a part of the specification. The drawings, together with the general description given above and the detailed description of the exemplary embodiments and methods given below, serve to explain the principles of the invention. In such drawings:

(2) FIG. 1 is a longitudinal cross-sectional front perspective view of a single strand caster tundish including an impact pad according to an embodiment of the invention;

(3) FIG. 2 is a longitudinal cross-sectional front view of the single strand caster tundish of FIG. 1;

(4) FIG. 3 is a front perspective view of the impact pad of the embodiment illustrated in FIG. 1;

(5) FIG. 4 is a plan view of the impact pad of FIG. 3;

(6) FIG. 5 is a cross-sectional view taken along the line V-V of FIG. 4;

(7) FIG. 6 is a cut-away side perspective view of the impact pad of FIGS. 3-5;

(8) FIG. 7 is a cross-sectional end view taken from the view point of the arrow on the right side of FIGS. 1 and 2, showing the flow profile of incoming liquid steel introduced through a shroud centered above the impact pad;

(9) FIG. 8 is a cross-sectional view of an impact pad according to another embodiment of the invention;

(10) FIG. 9 is a bottom sectional view taken along line IX-IX of FIG. 8;

(11) FIGS. 10 and 11 are reproduced from U.S. Pat. No. Re. 35,685, wherein FIG. 10 is a longitudinal cross-sectional view of a water flow-model study tundish and FIG. 11 is a transverse cross-sectional view taken along line XI-XI of FIG. 10.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS AND EXEMPLARY METHODS

(12) Reference will now be made in detail to the exemplary embodiments and methods as illustrated in the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the drawings. It should be noted, however, that the invention in its broader aspects is not necessarily limited to the specific details, representative materials and methods, and illustrative examples shown and described in connection with the exemplary embodiments and methods.

(13) A tundish for a strand caster in accordance with an exemplary embodiment is generally designated by reference numeral 10 in FIGS. 1 and 2. Although a single-strand caster is shown therein, it should be understood that embodiments of the present invention may be practiced in connection with double-strand and other multiple-strand casters. An example of a multi-strand caster setup, albeit with a different impact pad, is shown in FIG. 10 of U.S. Pat. No. RE 35,685. The tundish 10 includes tundish end walls 12 and 14, tundish front and rear sidewalls (unnumbered), and a tundish floor 16 extending between and connected to (or integral with) the end walls 12, 14 and sidewalls. The tundish end walls 12, 14 and floor 16 collectively establish a chamber or reservoir 18 for receiving and holding a molten steel bath. A tundish impact pad 20 is located in the reservoir 18, for example, closer to the end wall 12 than to the end wall 14. Positioned above the tundish impact pad 20 is the lower part of a ladle shroud 22 for introducing an incoming ladle stream 24 (FIG. 7) of molten steel into the impact pad 20. The ladle shroud 22 is shown penetrating through the top of the molten steel bath, with the end of the ladle shroud 22 spaced above and centered coaxially with the tundish impact pad 20. The flow of molten steel and the structure and function of impact pad 20 are discussed in further detail below.

(14) The tundish 10 further includes a weir 26 dividing the tundish 10 into right and left (first and second) compartments 18a and 18b, respectively, with the impact pad 20 in the right compartment 18a on the tundish floor 16 in FIGS. 1 and 2. The bottom of the weir 26 includes a passage 26a for allowing fluid communication between the liquid steel in the left and right compartments 18a, 18b. A diffuser 28 is positioned on the tundish floor 16 in the right compartment 18a between the weir 26 and the tundish impact pad 20. A dam 30 having a plurality of upwardly sloping (from right to left in the direction of flow) cylindrical passages 30a rests on the tundish floor 16 in the left compartment 18b. On the opposite side of the darn 30 from the weir 26, a stopper rod 32 is aligned with an output port or tundish well block 34 through which liquid steel is discharged from the tundish 10. Upward and downward movement of the stopper rod 32 controls outflow of molten steel from the tundish 10 and into casts (not shown).

(15) The tundish impact pad 20 may be made of a material or materials suitable for the intended use in a caster tundish for molten steel processing. Typically, such material(s) have high impact and abrasion resistance, high hot strength and refractoriness, and good castability. Metals, ceramics, and sand with ceramic coatings are examples of suitable materials. As specific but non-limiting examples, low-moisture, high-alumina castable compositions such as Narcon 70 Castable and coarse high alumina low cement castable compositions such as Versaflow 70C Plus are refractory materials suitable for use as the tundish impact pad 20. According to product literature: Narcon 70 Castable contains (calcined basis) 26.9% silica (SiO.sub.2), 69.8% alumina (Al.sub.2O.sub.3), 1.7% titania (TiO.sub.2), 0.8% iron oxide (Fe.sub.2O.sub.3), 0.7% lime (CaO), and 0.1% alkali (Na.sub.2O); and Versaflow 70C Plus contains (calcined basis) 27.5% silica (SiO.sub.2), 67.3% alumina (Al.sub.2O.sub.3), 2.1% titania (TiO.sub.2), 1.2% iron oxide (Fe.sub.2O.sub.3), 1.6% lime (CaO), 0.1% magnesia (MgO), and 0.2% alkalis (Na.sub.2O+K.sub.2O). The body parts of the tundish impact pad 20 can be coated with an erosion resistant material to form erosion resistant coatings for receiving and coming into contact with the incoming ladle stream 24. The erosion resistant coatings may be made with medium emissivity materials (such as Zirconia, Yttria, Silicon Carbide), high reflectivity materials (such as aluminum and alumina), or high temperature, non-oxide lubricants (such as boron nitride).

(16) Referring to the embodiment shown in FIGS. 3-6, the tundish impact pad 20 includes a circular base 40 (relative to a plan or bottom view). The base 40 includes a top base surface having a conical impact surface area 42 and an adjoining, adjacent annular base surface area 44 concentrically surrounding the conical impact surface area 42. In the illustrated embodiment, the conical impact surface area 42 is not truncated. Optionally, the top of the conical impact surface area 42 may be slightly rounded while still retaining the conical shape. As best shown in FIG. 5, the conical impact surface area 42 extends upwardly to terminate at an apex or vertex 46. The conical impact surface area 42 has rotational symmetry about an imaginary axis Az (FIG. 5) passing through the apex 46. In the illustrated embodiments, the conical impact surface area 42 has a linear profile or cross section, as best shown in FIG. 5. The bottom of the linear profile of the conical impact surface area 42 terminates at an outer perimeter 48 adjacent to and contiguous with a radially inner edge of the annular base surface area 44. The top of the linear profile of the conical impact surface area 42 terminates at a point corresponding to the apex 46 that is coincident with the axis Az. The annular base surface area 44 may be at least partially flat and lie in a horizontal plane that is parallel to the bottom surface 40a of the base 40.

(17) The tundish impact pad 20 further includes a sidewall 50 having a sidewall inner surface 52 that continuously/endlessly circles on itself to appear as an annulus when viewed from above, as in FIG. 4. The sidewall 50 is shown having uniform thickness over its entire 360 degrees. The sidewall inner surface 52 is positioned concentrically outside of and generally perpendicular to the annular base surface area 44. As best shown in the cross-sectional view of FIG. 5, the sidewall inner surface 52 includes curved transition areas 54, 56 at its bottom and top, respectively. The curved transition areas 54, 56 may he symmetrical to one another. The ends of the lower curved transition area 54 are flush and contiguous with the annular base surface area 44 and the sidewall inner surface 52. The lower curved transition area 54 curves continuously between the base 40 and the sidewall inner surface 52.

(18) The tundish impact pad 20 still further includes a top wail 60 extending inwardly from the top transition area 56 and generally perpendicular to the sidewall 50 to terminate at an inner edge 62. The top transition area 56 is configured as a curvilinear undercut that curves continuously between and whose ends are flush and contiguous with the sidewall inner surface 52 and the top wall 60. A mouth opening 64 established by the inner edge 62 is spaced above and centered relative to the apex 46. In use, the mouth opening 64 is under and coaxial with the ladle shroud 22 to receive the incoming ladle stream 24. In the illustrated embodiments, the diameter of the mouth opening 64 is approximately equal to or less than the diameter of the outer perimeter 48 of the conical impact surface area 42.

(19) The top wall 60 includes a lip 66 angled inwardly and downwardly to terminate at the inner edge 62. The top wall 60 has a first lower surface area 60a that extends substantially horizontally and parallel to the bottom surface 40a and a second lower surface area (also referred to herein as a lower lip surface) 66a corresponding to the bottom of the lip 66. The lover lip surface 66a slopes radially inwardly and downwardly from the first lower surface area 60a towards the conical impact surface 42. As best shown in FIGS. 4 and 5, the first lower surface area 60a and the lower lip surface 66a interface at 60b.

(20) The base 40, side wall 50, and top wall 60 may be integral, that is a unitary piece or monolithic part. Alternatively, the base 40, the sidewall 50, the top wall 60 and/or other parts of the tundish 10 may be formed of separate pieces temporarily or permanently joined to one another. The conical impact surface area 42, the annular base surface area 44, the continuous sidewall inner surface 52, the curved transition surface areas 54, 56, and the lower surface areas 60a, 66a collectively establish a continuous annular chamber about axis Az that may be in the form of a torus.

(21) Referring to FIG. 7, liquid steel is introduced into the tundish 10 through the shroud or sprue 22 as the incoming ladle stream 24. It has been found that the ratio (D.sub.j/D.sub.m) of the diameter D.sub.j of the inner diameter of the shroud 22 to the diameter D.sub.m of the mouth opening 64 in a range of about 0.3 to about 0.4 provides particularly good results. The ladle shroud 22 and the mouth opening 64 are coaxially aligned with one another in the exemplary embodiment. The design of the exemplary embodiments described herein causes the incoming ladle stream 24 to impact against the conical impact surface area 42, which redirects the stream 24 radially outward towards the lower transition portion 54 and the sidewall inner surface 52. The shape of the continuous annular chamber forces the molten steel flow into a reversed direction back towards the incoming ladle stream 24 to reduce the turbulence and dissipate the energy of the molten steel before it flows from the impact pad 10. The reversed fluid flow is discharged upward through the mouth opening 64, then generally radially outward in all directions towards the walls of the tundish 10 as a substantially laminar flow. By providing a mouth opening 64 that is greater in diameter than the diameter of the shroud 22, an annular upward flow is created between the incoming ladle stream 24 and the inner edge 62.

(22) The molten steel exits the mouth opening 64 into the first compartment 18a. The continuous inflow of the incoming ladle stream and removal of molten steel through the outlet 34 causes the molten steel in compartment 18a to flow towards the weir 26 and through the weir passage 26a. After passing through the weir passage 28, the molten steel flows over the dam 30 and/or through the cylindrical passages 30a before being discharged through the output 34.

(23) The reversing of molten steel flow onto itself creates a self-braking effect. As a consequence, the outgoing flow of molten steel through the mouth opening 64 and into the first compartment 18a is less turbulent and has less energy. The above-described open-eye and splashing problems are thereby reduced significantly.

(24) In a particularly exemplary embodiment designed to suppress open-eye, the conical impact surface area 42 has a cone angle (FIG. 5), measured from a horizontal plane in which the outer perimeter 48 lies to an oblique plane in which the conical impact surface area 42 lies, in a range of about 15 degrees to about 25 degrees. In another particularly exemplary embodiment designed to suppress open-eye, the lip 66 has a downward lip angle theta (), measured from a horizontal plane to a plane in which the lower surface 66a of the lip 66 lies, in a range of about 20 degrees to about 25 degrees. In another particularly exemplary embodiment designed to suppress open-eye, the continuous annular chamber has a radius of curvature of about 30 mm. These exemplary embodiments may be practiced separately or together with one another in any combination. The impact chamber may be provided with a height that is equal to or greater than the inside diameter of the shroud to affect flow control.

(25) Computational fluid dynamics (CFD) simulations were performed on impact pads designed in accordance with the above parameters. The area average velocity, which is a measure of flow activity on the pouring side of the top surface of the steel bath, is calculated to be about 50% lower practicing an embodiment of the invention compared to a flat petal-shaped impact pad. The probability of open-eye formation is also calculated to be reduced by the same proportion. Using CFD analysis, in which velocities and areas are calculated for cells of a mesh and area average velocity, area average velocity is determined as follows:
area average velocity (m/s)=VA/A.

(26) Generally, it is found that higher area average velocities correspond to greater tundish flux entrainment and poorer quality steel, whereas lower area average velocities correspond to lesser tundish flux entrainment and higher quality steel. Thus, a decrease of about 50% area average velocity constitutes a significant decrease in tundish flux entrainment and leads to higher quality steel products. Without wishing to be bound by theory, it is believed that the improved quality obtained using exemplary embodiments described herein is attributable to one or more of the following: reduction of high velocity incoming flows and turbulence due to the self-braking effect; less splash during start-up and continuous operation; longer residence time of the molten steel in the reservoir; promotion of impurity and particle flotation; and more uniform reservoir temperature.

(27) FIGS. 8 and 9 illustrate an impact pad according to another exemplary embodiment. In the interest of brevity, the following description focuses on differences between the exemplary embodiment of FIGS. 8 and 9 and other exemplary embodiments described above. Like reference characters designate like or corresponding parts in the different exemplary embodiments.

(28) In the exemplary embodiment of FIGS. 8 and 9, protuberances 80 are distributed 360 degrees about the lower lip surface 66a. The protuberances 80 may be uniformly distributed, such as in a matrix pattern, or distributed randomly or otherwise. In the illustrated embodiment, the outer surfaces of the protuberances 80 have a hemispherical shape. However, the protuberances 80 may undertake alternative shapes. Moreover, the protuberances 80 may have identical or varying shapes relative to one another. It has been found that the protuberances 80, especially hemispherical protuberances, further decelerate the outgoing flow of liquid steel as it exits the impact pad 20 through the mouth opening 64. Additionally or alternatively, the protuberances 80 may be located elsewhere on the inner surface of the impact pad.

(29) The foregoing detailed description of the certain exemplary embodiments has been provided for the purpose of explaining the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. This description is not necessarily intended to be exhaustive or to limit the invention to the precise embodiments disclosed. The specification describes specific examples to accomplish a more general goal that may be accomplished in another way.

(30) No limitations from the specification are to be read into any claims unless those limitations are expressly included in the claims.