FIELD OF THE INVENTION
The present invention is directed to a submerged entry nozzle (SEN) that delivers a stream of molten steel from a tundish to a continuous casting mold, and in particular, to a SEN that improves the molten steel flow patterns and reduces turbulence within the continuous caster mold.
BACKGROUND OF THE INVENTION
There has been a continuing effort to improve steel flow circulation and reduce turbulence in a continuous casting mold receiving a stream of molten steel delivered through a SEN. One particular improvement is the development of a bifurcated port discharge end that enables better distribution of the molten steel delivered to the casting mold, for example as disclosed in Cahoon (U.S. Pat. No. 4,487,251) or Lee (U.S. Pat. No. 5,198,126).
However, although such bifurcated port nozzles improve molten steel flow patterns within casting molds, the past SEN designs fail to maintain a calm or still liquid reservoir of molten steel within the mold. For example, when it is necessary for operators to adjust the slide gate that controls the rate of molten steel draining from the tundish to the mold, such slide gate adjustments cause disruptive or erratic changes in the molten steel flow discharged from the bifurcated port into the caster mold. Such erratic changes make it difficult to maintain good flow control within the mold. Additionally, the steel flow fluctuations associated with slide gate adjustments may form eddies and/or vortexes within the molten steel reservoir and entrain mold powder and/or slag within the cast steel product.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved SEN that reduces steel flow fluctuations associated with slide gate adjustments.
It is another object of the present invention to provide a SEN that improves distribution flow patterns of molten steel delivered to a continuous casting mold under all cast steel flow rates.
It is still another object of the present invention to provide a SEN that reduces surface turbulence in the molten steel reservoir contained in a continuous casting mold.
In satisfaction of the foregoing objects and advantages, the present invention provides an improved submerged entry nozzle for use in a continuous casting machine. The improved SEN includes a connection end adapted to attach to a slide gate mechanism, a discharge end including a bifurcated port, a tapered bore extending between the connection end and the discharge end, and a flow control structure positioned proximate the bifurcated port. The flow control structure includes divergent flow control surfaces extending downward along opposite sides of a contiguous edge, each downwardly extending divergent flow control surface flaring in an outward direction toward a respective perimeter defining an outside edge of the bifurcated port and communicating therewith.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the preferred embodiment of the invention illustrated in the accompanying drawings, wherein:
FIG. 1 is a view of a continuous casting machine.
FIG. 2 is an elevation view of the submerged entry nozzle (SEN) of one embodiment of the present invention.
FIG. 3 is a top view taken along the lines 3—3 of FIG. 2.
FIG. 4 is a cross-section view taken along the lines 4—4 of FIG. 2.
FIG. 5 is an enlarged view of the bifurcated port end portion of FIG. 2.
FIG. 6 is a cross-section view taken along the lines 6—6 of FIG. 5.
FIG. 7 is a cross-section view taken along the lines 7—7 of FIG. 5.
FIG. 8 is an enlarged view showing another embodiment of a bifurcated port end portion in the SEN of the present invention.
FIG. 9 is a cross-section view taken along the lines 6—6 of FIG. 8.
FIG. 10 is a cross-section view taken along the lines 7—7 of FIG. 8.
FIG. 11 is a cross-section view taken along the lines 7—7 of FIG. 9.
FIG. 12A labeled prior art, is a cross-section showing a symmetrical molten steel flow through the bore of a SEN.
FIG. 12B labeled prior art, is a cross-section showing an asymmetrical molten steel flow through the bore of a SEN.
FIG. 12C labeled prior art, is a cross-section showing a different asymmetrical molten steel flow through the bore of a SEN.
FIG. 13A labeled prior art, is an elevation view showing the discharge of molten steel from the bifurcated port in FIG. 12A.
FIG. 13B labeled prior art, is an elevation view showing the discharge of molten steel from the bifurcated port in FIG. 12B.
FIG. 13C labeled prior art, is an elevation view showing the discharge of molten steel from the bifurcated port in FIG. 12C.
FIG. 14 is an isometric view that schematically illustrates the flow pattern in molten steel discharged from the present SEN invention.
FIG. 15 is a schematic view showing incoming steel moving through a caster mold.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The following detailed description is directed to preferred embodiments of the present invention for delivering a stream of molten steel from a tundish to a continuous casting mold. The invention comprises a submerged entry nozzle (SEN) having an improved bore and discharge end capable of delivering molten steel flow patterns that reduce surface turbulence within the reservoir of molten steel contained in the mold. Referring to FIG. 1, in a continuous casting operation, a ladle 1 delivers molten steel 2 from a steelmaking furnace (not shown) to the tundish 3 in a continuous casting machine 4. Tundish 3 provides an uninterrupted reservoir of molten steel supplied to a caster mold 5, the caster mold having a depth D and a width W represented by the direction arrow shown in FIG. 16. The continuous stream of molten steel delivered from tundish 3 to the caster mold 5 is controlled by a slide gate valve mechanism 6, and in the present invention, the molten steel is delivered to caster mold 5 through a submerged entry nozzle 7 comprising a refractory tube shroud attached to slide gate 6. The SEN 7 includes a connection end 8 adapted to couple to the slide gate mechanism 6, and a discharge end 9, that is immersed below the surface of the molten steel 10 contained in caster mold 5. Solidification of the cast molten steel begins within the caster mold. To promote solidification, cooling waters 11 are circulated through a copper alloy jacket 12 so that the molten steel is chilled and a solidified skin 13 is formed along the periphery of the cast steel product before it moves downstream through various roll racks and cooling sprays (not shown) that complete the continuous casting operation.
Casting machines may also include means to distribute mold powder compounds 14 onto the surface of the cast molten steel reservoir 10. Mold powders may be added either manually with rakes or by mechanical feeders 15 as shown in FIG. 1. On contact with the molten steel, the mold powder 14 melts forming a liquid slag that provides a lubricant between the mold walls 16 and the solidifying steel skin 13. In past SEN designs, whenever it became necessary to adjust the slide gate mechanism 6, the gate adjustment created fluctuations in the steel flow draining from the tundish. This caused erratic discharges of molten steel from the SEN into the caster mold 5. Such erratic discharge may create eddies and/or vortexes that tend to entrain mold powders 14 and/or slag within the cast steel product. Additionally, in such past SEN devices, slide gate adjustment and/or changes in cast flow rates, produce a preferential flow from one of the port openings that results in a higher discharge of steel from the SEN to one side of the caster mold 5. Such conditions create an increased possibility for shearing mold powder 14 from the coverage layer and entraining it into the cast steel product. The improved SEN device of the present invention is capable of dividing the incoming flow of liquid steel 2 from tundish 1 into substantially equal portions so that a similar volume and velocity of liquid steel 10 is discharged from each port opening into opposite sides of the caster mold 5 under all cast steel flow rates.
Referring to FIGS. 2-7, the improved SEN of the present invention provides a controlled molten steel flow stream that eliminates, or greatly reduces, erratic molten steel discharges associated with slide gate adjustments. The controlled flow stream eliminates eddies and/or vortexes associated with slide gate adjustments and thereby eliminates, or significantly reduces, entrainment of mold powders and slags within the cast steel product. The one embodiment of the present SEN invention comprises an elongated refractory tube 20 having a connection end 21 suited for attachment to a tundish slide gate mechanism, and a discharge end 22 having a bifurcated port defined by opposed discharge openings 23a and 23b that deliver a flow of molten steel 2 from the SEN into a caster mold. A bore 24 extends between a feed side opening 26 in connection end 21 and a terminus opening 29 communicating with discharge end 22. Bore 24 includes a tapered bore wall portion 25 extending along a length of the bore in a downward direction from a location proximate feed side opening 26 to the terminus opening 29, and the tapered bore wall portion 25 is angled toward a vertical bore wall portion 27 provided in bore 24. The tapered portion 25 may be further defined by a first tapered bore wall segment 25a proximate feed side opening 26 and angled toward the vertical bore wall portion at an angle θ, and a second tapered bore wall segment 25b extending between segment 25a and terminus opening 29. The second tapered bore wall segment 25b is angled toward the vertical bore wall portion 27 at an angle greater than θ (FIG. 2).
Discharge end 22 includes a chamber 30 shaped to generate a spiral flow of molten steel within chamber 30, and a flow control structure or diverter 31 positioned to receive an incoming stream of molten steel 2 from the SEN bore 24. Diverter 31 includes a knife-edge 32 angled in a downward direction from the vertical bore wall portion 27 to a location below terminus opening 29 so that it is positioned to receive incoming molten steel 2 from the second tapered bore wall segment 25b. The flow control structure or diverter 31 also includes divergent, concave shaped, flow control surfaces 33a and 33b that extend downward along opposite sides of the contiguous knife-edge 32. Surfaces 33a and 33b flare downward and outward from knife-edge 32 so that each surface 33a and 33b communicates with a perimeter that defines the opposed outside edges 23a and 23b of their respective bifurcated port. Discharge chamber 30 also includes a curved pad 34 positioned between and facially engaging the fan shaped surfaces 33a and 33b. Curved pad 34 comprises a substantially helical shape that spirals away from diverter 31 in an upward direction so that it tangentially engages terminus opening 29 proximate the intersection between opening 29 and the second tapered bore wall segment 25b.
Referring to FIGS. 8-11, another embodiment of the present SEN invention comprises an elongated refractory tube 60 having a connection end (not shown) suited for attachment to a tundish slide gate mechanism, and a discharge end 61 having a bifurcated port defined by opposed discharge openings 62a and 62b that deliver a flow of molten steel from the SEN into a caster mold. A bore 63 extends between a feed side opening in connection end (not shown) and a terminus opening 64 communicating with discharge end 61. Bore 63 includes a tapered bore wall portion 65 similar to FIG. 2, and the tapered bore wall portion is angled toward a vertical bore wall portion 66 provided in bore 63. Similar to the embodiment disclosed in FIG. 2, tapered portion 65 may include a first tapered bore wall segment 65a angled toward the vertical bore wall portion at an angle θ, and a second tapered bore wall segment 65b angled toward the vertical bore wall portion 27 at an angle greater than θ.
Discharge end 61 includes a discharge chamber 67 shaped to generate a spiral flow of molten steel within chamber 67, and a flow control structure or diverter 68 positioned to receive an incoming stream of molten steel from the SEN bore 63. Chamber 67 Diverter 68 includes a knife-edge 69 angled in a downward direction from the vertical bore wall portion 66 to a location below terminus opening 64 so that it is positioned to receive incoming molten steel from the second tapered bore wall segment 65b. The flow control structure or diverter 68 includes convex shaped flow control surfaces 70a and 70b that extend downward along opposite sides of the contiguous knife-edge 69. Surfaces 70a and 70b flare downward and outward from knife-edge 69 so that each surface 70a and 70b communicates with a respective chamfered edge 71a and 71b extending along at least a portion of the outside edges 62a and 62b defining the bifurcated port openings. Discharge chamber 67 also includes a curved pad 72 positioned between and facially engaging the fan shaped surfaces 70a and 70b. Curved pad 72 comprises a substantially helical shape that spirals away from diverter 68 in an upward direction so that it tangentially engages each chamfered edge 71a and 71b.
Referring to FIGS. 12A-12C, labeled Prior Art, a submerged entry nozzle 40 having a bore 41 and bifurcated discharge port 42, is shown draining steel 43 from a continuous caster tundish (not shown). The draining molten steel 43 is illustrated as a series of parallel dotted lines. In such past SEN devices, the draining molten steel 43 exhibits a continuously changing velocity gradient across the width or diameter of the SEN bore 41, the changing velocity gradient being effected by the position of slide gate and/or the adjusted size of the nozzle opening and/or cast steel flow rates. For example, FIG. 12A shows a substantially symmetrical velocity gradient 44 having a higher velocity concentration 45 along the central axis of the SEN bore. Such symmetrical velocity gradients typically occur when the slide gate is adjusted for a large nozzle opening that provides a higher cast steel flow rate draining from the tundish. On the other hand, when casting conditions require a reduced flow volume or flow rate, the sliding gate must be adjusted to stop down the nozzle opening size. This results in creating an asymmetrical velocity gradient 46 across bore 41 as illustrated in FIGS. 12B and 12C. Depending upon certain casting conditions, the particular slide gate mechanism, and upon the amount and shape of wear within bore 41, a higher velocity concentration 47 may occur along one side of the bore wall as shown in FIG. 12B, or along a different side of the bore wall shown as 48 in FIG. 12C. In either case, the high velocity gradient across the molten steel flow is a random occurrence and is substantially uncontrolled by steelmakers.
Consequently, referring to FIG. 13A labeled Prior Art, in the instance where the draining liquid steel has a symmetrical high velocity gradient (FIG. 12A); substantially equal amounts of steel are discharged at similar velocities from each port opening 42 into opposite sides of the caster mold. However, under such cast steel conditions, using SEN devices of the past, the discharged flow of molten steel 49 has a high velocity gradient 50 from the bottom to the top of the bifurcated port. In such instances, the low velocity portion of the gradient 51 is along the top of the port openings 42. This creates a reduced pressure at the top of opening 42 and causes an inward flow or backflow of molten metal 53 back into the SEN port. Such backflow creates eddies or vortexes that shear or draw mold powders and/or slag from the cover layer floating on the surface of the cast steel and back into the SEN. The foreign particles are discharged from the SEN and mixed into the molten steel contained within the caster mold where they form inclusions in the cast steel product.
Referring to FIGS. 13B and 13C, also labeled Prior Art, under certain casting conditions, for example when the slide gate setting causes an asymmetrical flow having a higher velocity concentration 47 along one side of the SEN bore as shown in FIG. 12B, the asymmetrical high velocity gradient causes a preferential flow 49a discharged from one of the port openings 42 rotating in either a clockwise 52a or counter clockwise 52b direction. When it becomes necessary to adjust the slide gate mechanism control the cast steel flow rate, there is a possibility that the changed gate setting will cause the asymmetrical flow pattern to suddenly flip/flop between the higher velocity concentration 47 shown in FIG. 12B and the different higher velocity concentration 48 shown in FIG. 12C. This sudden change in the flow pattern will cause an equally sudden change in rotation and preferential flow direction 49a of the molten steel discharge from opening 42 as shown in FIG. 13C. Such sudden direction and rotation changes in the molten steel discharge create turbulence within the caster mold and further increase the likelihood of mold powder shear and entrainment within the cast steel product. Additionally, the preferential flow discharge 49a results in one side of the caster mold being too active. This creates a turbulent cast steel surface where a quiet surface is desired to prevent mold powder and/or slag entrainment. Furthermore, the sudden flip/flop in the rotation and preferential flow direction causes a quiet/upset/quiet condition within the mold. It is always viewed as problematic by steelmakers when the steady state condition in a caster mold becomes unsettled.
Referring to FIG. 6, FIG. 9, and FIG. 14, reference numbers 80 show different positions “snapshots” of the same section of the molten steel flow as it drains through the SEN bore 24, or 63. The first tapered section 25a, 65a extends downward from a location proximate the bore feed side opening (FIG. 2) and gradually directs the downward draining steel, shown as a series of parallel phantom lines 81, toward the opposite bore wall portion 27, 66. The second tapered section 25b, 65b further narrows or restricts bore 24, 63 from the first tapered section through terminus opening 29, 64 that communicates with discharge chamber 30. The length of the tapered bore wall portion 25, 65 (FIG. 2) is shaped to create a gradual narrowing passageway that directs a concentrated flow of draining molten steel along a selected length of the bore wall, for example, in this instance the opposite bore wall 27, 66. This produces an increasing high velocity gradient across the draining molten steel as illustrated by a series of snapshots 80 of the molten steel as it drains downward through bore 24, 63. The tapered portion 25, 65 directs the draining steel in a predetermined downward flow path along the bore, and the steel flow exits terminus end 29, 69 as a concentrated steel stream 80′ having an angle tangential to the slope of the second tapered bore wall segment 25b, 65b. As shown in FIG. 14, the directed, angled steel stream 80′ always impacts upon diverter 31, 68 at the same location along knife-edge 32, 69, and the impacting steel stream 81′ is always divided into substantially equal discharge flows 80″ within discharge chamber 30, 67. Such predetermined flow control prevents the troublesome flip/flop changes and eliminates or reduces surface turbulence as discussed above.
Each divided molten steel flow 80″ follows the contour of its respective divergent flow control surface 33a, 70a and 33b, 70b, and at least a portion of the divided steel flow is directed along the shaped pad portions 34, 72 shown in FIGS. 6 and 9, the shaped pad portions providing a helical path that causes the divided steel flow to spiral within chamber 30, 67. The divided steel flows 80″ spiral in a direction perpendicular to the bifurcated port and along the periphery of each bifurcated port opening 23a, 62a and 23b, 62b where molten steel flows 82a and 82b are discharged from the SEN in opposite directions along the width W of caster mold 5 (FIG. 15). Referring to FIGS. 14 and 15, the swirling steel 80″ causes each discharge of incoming new steel 82a, 82b to have a high velocity gradient extending from the steel discharge periphery or circumference 83 toward its central axis or core 84, and the swirling steel at the periphery of the port openings 23a, 62a and 23b, 62b creates an equalized pressure zone 86 that eliminates the reduced pressure and back flow problems discussed above and shown in FIG. 13A.
Referring in particular to FIG. 15, the drawing shows a series of snapshots F1-F5 that schematically represent the same section of incoming new steel as it moves along the width of a caster mold. Water modeling tests reveal that, although the divided molten steel swirls within the SEN discharge chamber, there is only a slight rotation or no rotation in the incoming steel 82a, 82b after it enters the caster mold. Additionally, the high velocity gradient causes the incoming new steel to blossom or open into the substantially umbrella or mushroom like shapes shown at F1-F5. As the blossoming steel 82a, and 82b move in opposite directions along mold width W, the surface area of blossoming shape is increased so that the improved steel flow 82a, and 82b has a reduced volume to surface ratio as compared to the steel flow 49 generated by the SEN devices of the past (FIGS. 13A-13C). Accordingly, the larger surface area 82a and 82b dissipates energy faster than SEN devices of the past, and the improved energy dissipation provides a more quiet condition within the caster mold.
It should be understood that while this invention has been described as having a preferred embodiment, it is capable of further modifications, uses, and/or adaptations of the invention, following the general principle of the invention and including such departures from the present disclosure as have come within known or customary practice in the art to which the invention pertains, and as may be applied to the central features hereinbefore set forth, and fall within the scope of the invention of the limits of the appended claims. For example, while the detailed description is directed to a continuous casting operation, the improved flow control features of the present SEN device may be adapted for use outside the steelmaking art without departing from the scope of this invention. For example, the improved flow control features of the present invention may be adapted for use in liquid delivery systems used in non-ferrous metal industries, food and beverage industries, and municipal water service applications.
Patent Grant
6932250
