BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to making thin strip and, more particularly, casting of thin strip by a twin roll caster.
It is known to cast metal strip by continuous casting in a twin roll caster. Molten metal is introduced between a pair of counter-rotating horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between the casting rolls to produce a solidified strip product delivered downwardly from the nip. The term “nip” is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel or tundish/distributor, from which it flows through a metal delivery nozzle located above the nip, which directs the molten metal to form a casting pool supported on the casting surfaces of the rolls above the nip. This casting pool may be confined at the ends of the casting rolls by side plates or dams held in sliding engagement adjacent the ends of the rolls.
In casting thin strip by twin roll casting, the metal delivery nozzles receive molten metal from the movable tundish and deposit the molten metal in the casting pool in a desired flow pattern. Previously, various designs have been proposed for delivery nozzles involving a lower portion submerged in the casting pool during a casting campaign, and having side openings through which the molten metal is capable of flowing laterally into the casting pool outwardly toward the casting surfaces of the rolls. Examples of such metal delivery nozzles are disclosed in Japanese Patent No. 09-103855 and U.S. Pat. No. 6,012,508. In prior art metal delivery nozzles, there has been a tendency to produce thin cast strip that contains defects from uneven solidification at the chilled casting surfaces of the rolls.
In the past, the formation of pieces of solid metal known as “skulls” in the casting pool in the vicinity of the confining side plates or dams have been observed. These skulls become “snake-eggs” in the cast strip when swallowed and passed through the nip into the cast strip. The rate of heat loss from the casting pool is higher near the interface between side dams and the casting rolls (called the “triple point region”) due to conductive heat transfer through the side dams to the casting roll ends. This localized heat loss near the side dams has a tendency to form skulls of solid metal in that region, which can grow to a considerable size and fall between the casting rolls and cause defects in the cast strip. An increased flow of molten metal to these regions near the side dams and meniscus of the casting pool have been provided by separate direct flows of molten metal to these regions. Examples of such proposals may be seen in U.S. Pat. No. 4,694,887 and in U.S. Pat. No. 5,221,511. Increased heat input to these regions has inhibited formation of skulls.
Nevertheless, we have continued to observe skulls in the triple point region and also deeper into the casting pool adjacent the side dams. It was thought that such formation of skulls was near the meniscus of the casting pool as the shells were initially formed. We have now discovered that such skulls can also form deeper in the casting pool as the shells continue to form while the shells move toward the nip. We have found that the formation of skulls can be substantially reduced by providing molten metal through first and second pairs of passages from a reservoir portion of the metal delivery nozzle, the first pair of passages adapted to deliver the molten metal into the casting pool adjacent the side dams and the second pair of passages adapted to deliver molten metal into the casting pool adjacent molten metal delivered from the first pair of passages.
Disclosed is a method of casting thin strip with continuous casting apparatus having an improved delivery nozzle therefor. Disclosed is a method of casting metal strip comprising:
(a) assembling a pair of casting rolls laterally disposed to form a nip between them and between side dams adapted to maintain a molten metal pool supported by the casting rolls,
(b) assembling an elongated metal delivery nozzle extending along and above the nip with at least one segment having a main portion adapted to deliver molten metal in the casting pool along the metal delivery nozzle and an end portion adjacent side dams having a reservoir portion having a first pair of passages and second pair of passages adapted to deliver molten metal into a molten metal pool adjacent the side dams while shells are forming on the casting rolls, the first pair of passages adapted to deliver molten metal into the casting pool adjacent the side dams and the second pair of passages adapted to deliver molten metal into the casting pool adjacent molten metal delivered from the first pair of passages,
(c) introducing molten metal through the elongated metal delivery nozzle to form a casting pool of molten metal supported on the casting rolls above the nip, and through the first and second pairs of passages in the reservoir portion in the end portions of the elongated metal delivery nozzle into the casting pool, and
(d) counter rotating the casting rolls to deliver cast strip downwardly from the nip.
In embodiments, the first and second pairs of passages may be adapted to deliver molten metal outwardly from the reservoir portion of the delivery nozzle toward the side dam. Additionally, the direction of flow of the first and second pairs of passages may be substantially parallel.
Also disclosed is a metal delivery apparatus for casting metal strip comprising at least one elongated segment having a main portion adapted to deliver molten metal in the casting pool along the metal delivery nozzle and an end portion adjacent side dams having a reservoir portion having first and second pairs of passages adapted to deliver molten metal into a molten metal pool adjacent the side dams while shells are forming on the casting rolls, the first pair of passages adapted to deliver molten metal into the casting pool adjacent the side dams and the second pair of passages adapted to deliver molten metal into the casting pool adjacent molten metal delivered from the first pair of passages.
In some embodiments of the disclosed method and apparatus, the second pair of passages may be spaced longitudinally inward of the first pair of passages in the reservoir portion, the direction of flow from the first and second pairs of passages directed to below the reservoir portion. The longitudinal direction herein defined as the direction of the longitudinal, or longest, dimension of the casting nozzle. The first and second pairs of passages may be substantially parallel, providing a substantially parallel direction of flow from each passage. The direction of flow from the first pair of passages may be parallel to the direction of flow from the second pair of passages. Alternatively, the first pair of passages may have a different direction of flow from the second pair of passages, such that the direction of flow from each half of the pairs of passages may converge, or diverge. Additionally, or alternatively, the direction of flow from the first and second pairs of the passages in the reservoir portion may be directed toward the side dam.
In other embodiments, the second pair of passages may be spaced laterally inward of the first pair of passages in the reservoir portion, the direction of flow from each pair of passages directed to converge below the reservoir portion. The lateral direction herein defined as the direction of the shortest dimension of the casting delivery nozzle. The direction of flow from each passage of the first pair of passages may converge. Similarly, the direction of flow from each passage of the second pair of passages may converge. Additionally, or alternatively, the direction of flow from the first and second pairs of the passages in the reservoir portion may be directed toward the side dam.
In further embodiments, the direction of flow from the first pair of passages may be different than the direction of flow from the second pair of passages. By way of example, in some embodiments, the direction of flow from the first passages of the first and second pairs of passages may diverge, and the direction of flow from the second passages of the first and second pairs of passages may diverge. Alternatively, the direction of flow from the first passages of the first and second pairs of passages may converge, and the direction of flow from second passages of the first and second pairs of passages may converge. As herein used, the direction of flow refers to the direction of the molten metal travels when it leaves the passages of the reservoir portion. Once the molten metal interacts with the metal casting pool, the direction in which the molten metal travels may change. In any embodiment the direction of flow of the first and second pairs of passages may be substantially downward. Alternatively, the direction of flow from the first and second pairs of passages may be directed toward the side dams.
In some embodiments, the reservoir portion may additionally have a central passage adapted to deliver molten metal downwardly to the casting pool under the reservoir portion. The central passage may be disposed between the first passages of the first and second pairs of passages and the second passages of the first and second pairs of passages. The central passage may be arranged laterally in line with the first or second pairs of passages. Alternatively the central passage may off-set laterally and/or longitudinally from the first and/or second pairs of passages. The central passage may be substantially horizontal. Alternatively the central passage may be adapted to deliver molten metal downwardly to the casting pool under the reservoir portion toward the side dam. The central passage may have a diameter between 4 mm and 8 mm.
The diameter of the first and second pairs of passages may be the same, or substantially similar. In some embodiments, the first and second pairs of passages have diameters of between 6 mm and 14 mm. In further embodiments, the cross-section of the first pair of passages is less than the cross-section of the second pair of passages. The passages may have any cross-sectional shape. In preferred embodiments, the passages may have a circular or oval cross-sectional shapes. In other embodiments, the passages may have a square shape, hexagonal shape, or any polygonal shape.
The first and second pairs of passages may be shaped to control the velocity of the molten metal. For example, the entry port for a passage may have a smaller cross-section than the exit port for the passage, reducing the velocity of the molten metal as it flows through the passage. Conversely, the entry port of the passage may have a larger cross-section than the entry port for the passage, increasing the velocity of the molten metal as it flows through the passage.
The exit ports of the first passages of the first and second pairs of passages and the exit ports of the second passages of the first and second pairs of passages, of the reservoir portion, may be between 4 and 30 millimeters apart, between edge portions of the passages. The entry ports of the passages may have the same distance of separation as the exit ports, or they may have a different distance of separation. The passages themselves may be generally 7 to 12 millimeters in diameter. In some embodiments the first and second pairs of passages may have a cross-section of 10 millimeters. In other embodiments, the first and second passages may be of different diameter as desired to deliver the molten metal into the casting pool at the desired location adjacent the side dams.
The method may include assembling an elongated metal delivery nozzle having a reservoir portion, where reservoir portion in the end portion of each segment has longitudinally extending weirs adjacent the side walls of the inner trough adapted to allow molten metal to flow over the weirs between the reservoir portion and the main portion of the metal delivery nozzle.
The metal delivery apparatus for casting metal strip may have dual first and second passages in each reservoir portion of the metal delivery nozzle. The first and second passages of the reservoir portion also may be shaped to control the molten metal flow through the passages by increasing or decreasing the velocity of molten metal through the passage, and, in turn, control the kinetic energy of the molten metal exiting the passage to direct the molten metal shallow or deep into the casting pool as explained in more detail below.
Various aspects of the invention will be apparent from the following detailed description, drawings, and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in more detail in reference to the accompanying drawings in which:
FIG. 1
a illustrates a cross-sectional end view of a portion of twin roll strip caster with an assembled metal delivery nozzle;
FIG. 1
b is an enlarged view of a portion of twin roll strip caster similar to FIG. 1a except showing a trough with a concave upper surface;
FIG. 2 is a plan view of a segment of a metal delivery nozzle for use in the twin roll caster shown in FIG. 1a;
FIG. 3 is a cross-sectional side view taken along line 3-3 of the segment of the metal delivery nozzle shown in FIG. 2;
FIG. 4 is an enlarged side view of the reservoir portion of a segment of the metal delivery nozzle shown in FIG. 3.
FIG. 5 is an enlarged side view of an alternative embodiment of a reservoir portion of a segment of the metal delivery nozzle shown in FIG. 3.
FIG. 6 is a cross-sectional transverse taken along line 6-6 of the segment of the metal delivery nozzle shown in FIG. 2;
FIG. 7 is a cross-sectional transverse of an alternative embodiment of the reservoir portion shown in FIG. 6;
FIG. 8
a illustrates a cross-sectional end view of a portion of twin roll strip caster with an assembled metal delivery nozzle having an alternative embodiment of the reservoir portion of a segment of the metal delivery nozzle;
FIG. 8
b is an enlarged view of a portion of twin roll strip caster similar to FIG. 8a except showing a trough with a concave upper surface;
FIG. 9 is a plan view of a segment of a metal delivery nozzle for use in the twin roll caster shown in FIG. 8a;
FIG. 10 is a cross-sectional side view taken along line 10-10 of the segment of the metal delivery nozzle shown in FIG. 9;
FIG. 11 is a cross-sectional transverse taken along line 11-11 of the segment of the metal delivery nozzle shown in FIG. 9;
FIG. 12 is a cross-sectional transverse of an alternative embodiment of the reservoir portion shown in FIG. 11;
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 1A and 1B, the metal strip casting apparatus 2 includes a metal delivery nozzle 10 located below a tundish 4 and above a pair of casting rolls 6. The casting rolls 6 are laterally positioned with a nip 9 formed between them. The tundish 4 receives molten metal from a ladle (not shown) and delivers the molten metal to a delivery nozzle 10. A shroud 5 may extend from the tundish 4 and into the delivery nozzle 10, for the purpose of transferring molten metal into the delivery nozzle 10. In the alternative, the tundish 4 may transfer molten metal to the delivery nozzle 10 via a hole in the bottom of the tundish 4. Below and around the lower portions of the delivery nozzle 10, a casting pool 8 having a surface 8A is formed and supported on the casting surfaces 7 of the casting rolls 6 adjacent the nip 9. The casting pool 8 is constrained at the ends of the casting rolls 6 and side dams or plates (not shown) positioned against the ends of the casting rolls. The side dams and their location in relation to the casting rolls 6 and the casting pool 8 are described, for example, in U.S. Pat. No. 7,556,084 granted Jul. 7, 2009, and in United States Publication No. 2009/0283240 published Nov. 19, 2009, which are incorporated herein by reference. The delivery nozzle 10 controls molten metal flow through passages 16 into the casting pool 8. Generally, the delivery nozzle 10 extends into the casting pool 8 during the casting campaign as shown in FIGS. 1A and 1B. A gas seal 11 may be maintained between the casting plates 50 and the casting surfaces 7 of the casting rolls 6 and, in some embodiments, to maintain an inert atmosphere of nitrogen and/or argon above the casting pool 8 by blowing such gas into the space above the casting pool 8.
FIG. 1B, shows an enlarged view of a portion of the twin roll caster 2 similar to FIG. 1a except showing a trough 14 having a concave upper surface. A first pair of passages 22 is shown, adapted to deliver molten metal into a molten metal pool 8 adjacent the side dams. The rate of heat loss from the casting pool 8 is higher at the triple-point-region, the intersection between the side dam, casting rolls 6, and the melt pool 8, due to conductive heat transfer through the side dams to the ends of the casting rolls 6. The localized heat loss has a tendency to form skulls of solid metal in that region, which can grow and fall between the casting rolls 6, causing defects in the cast strip. Increasing the flow of molten metal to the triple point regions near the side dams, and deeper in the casting pool, reduces skull formation. The first pair of passages 22 in the reservoir portion 24 of the metal delivery nozzle 10 provides an increased flow of molten metal into the casting pool 8 to or near the triple point region. Additionally, not shown, are a second pair of passages in the reservoir portion 24 of the metal delivery nozzle 10 adapted to provide molten metal to the casting pool 8 at a different location, to inhibit the formation of skulls, as shown in FIG. 4.
The disclosed method of casting metal strip may be performed upon a casting apparatus such as those illustrated in FIGS. 1a and 1b. A pair of casting rolls 6 may be assembled, laterally disposed to form a nip 9 between them and between side dams adapted to maintain a molten metal pool 8 supported by the casting rolls 6. An elongated metal delivery nozzle 10 extending along and above the nip 9 may be assembled.
Referring to FIG. 2, the delivery nozzle 10 may have at least one segment 13 (one shown), adapted to deliver molten metal into the casting pool 8 along the metal delivery nozzle 10. Each delivery nozzle segment 13 having opposing side walls 15 and an upward opening inner trough 14, which extends lengthwise along the segment 13 in the longitudinal direction of the delivery nozzle 10. In the embodiment shown, the side walls 15 are joined to the inner trough 14 to form shoulder portions 30, and the passages 16 are in the form of holes 31 extending through the shoulder portions 30 along each side of the inner trough 14. The molten metal flows from the inner trough 14 through the holes 31 to the side outlets 20. In this embodiment, the shoulder portions 30 provide the structural support to the delivery nozzle segment 13 when loaded with molten metal during a casting campaign. As a result, the flow of molten metal from the side outlets 20 into the casting pool 8 can be provided laterally more evenly along the delivery nozzle segment 13.
The pair of delivery nozzle segments 13 may be assembled lengthwise with the end walls 19, in abutting relation, and end walls 18 forming the ends of delivery nozzle 10. Alternatively, delivery nozzle 10 may comprise a single delivery nozzle segment 13, or more than two segments 13, that include all the features of, and effectively functions as the assembled pair of segments 13 as described herein. Each delivery nozzle segment 13 may be made of any refractory material, such as alumina graphite. As shown in FIG. 1, each delivery nozzle segment 13 includes mounting flanges 27 that extend outward from side walls 15, either continuously or, intermittently, as desired, to mount delivery nozzle segments 13 assembled forming the delivery nozzle 10 of the casting apparatus 2.
In operation, molten metal is poured through a shroud 5 into the inner trough 14 of mounted delivery nozzle segments 13. Several shrouds 5 may be provided along the length of the delivery nozzle segments 13. The molten metal flows from the inner trough 14 into and through passages 16 into the side outlets 20. The side outlets 20 direct the flow of molten metal to discharge the molten metal laterally into the casting pool 8 in the direction of the meniscus between the surface 8A of the casting pool 8 and the casting surfaces 7 of the casting rolls 6. Since the passages 16 and side outlets 20 extend along both sides of the delivery nozzle segments 13, a relatively uniform flow of molten metal can be provided along the length of the metal delivery nozzle segments 13.
Referring to FIG. 3, a segment 13 of an elongated metal delivery nozzle 10 is assembled along and above the nip 9 (see FIG. 1). The segment 13 has a main portion adapted to deliver molten metal in the casting pool 8 along the metal delivery nozzle 10. The segment 13 may have an end portion 18 adjacent each side dam (not shown) having a reservoir portion 24. The reservoir portion 24 has a first pair of passages 22 and a second pair of passages 23 spaced longitudinally inward of the first pair of passages 22, in the reservoir portion 24. The first pair of passages 22 and the second pair of passages 23 adapted to deliver molten metal into a molten metal pool 8 adjacent the side dams (not shown) while shells are forming on the casting rolls 2. The first pair of passages 22 adapted to deliver molten metal into the casting pool 8 adjacent the side dams and the second pair of passages 23 adapted to deliver molten metal into the casting pool 8 adjacent molten metal delivered from the first pair of passages 22. The direction of flows from the first pair of passages 22 and the second pair of passages 23 are directed to below the reservoir portion 24. In the embodiment shown in FIG. 3 the first pair of passages 22 and the second pair of passages 23 are adapted to delivery molten metal outwardly from the reservoir portion 24 of the delivery nozzle segment 13, toward the side dam.
With reference to FIGS. 1 through 3. In operation, molten metal may be introduced through the elongated metal delivery nozzle 10 to form a casting pool 8 supported on the casting rolls 6 above the nip 9, and through the first and second pairs of passages in the reservoir portion 24 in the end portions 18 of the casting nozzle 10 into the casting pool 8. Additionally, the casting rolls 6 are counter-rotated to deliver cast strip downwardly from the nip 9.
FIG. 4 illustrates an enlarged view of the reservoir portion 24 at the end of the casting nozzle segment 13. The reservoir portion 24, in this embodiment, has a first pair of passages 22 disposed in the reservoir portion 24 adapted to deliver molten metal outwardly below the reservoir portion 24 toward the side dam (not shown). Additionally, the reservoir portion 24 comprises a second pair of passages 23 spaced longitudinally inward of the first pair of passages 22, adapted to deliver molten metal outwardly below the reservoir portion 24 toward the side dam, adjacent the molten metal delivered from the first pair of passages 22. The angle of the first and second pairs of passages may be any desired angle adapted to deliver molten metal downwardly from the reservoir 24. In some embodiments, the first and second pairs of passages may be angled between 20 and 60 degrees to the vertical to achieve a desired direction of flow from the first and second pairs of passages.
In some embodiments, as shown in FIG. 4, the reservoir portion may further comprise a central passage 40 disposed laterally inward of the first and second pairs of passages, and disposed longitudinally inward of the second pair of passages 23. The central passage 40 may be arranged such that the direction of flow from the central passage 40 may be substantially downward from the reservoir. Alternatively the central passage 40 may be arranged to have an angle of between 0 and 50 degrees from the vertical, adapted to deliver molten metal to a desired location in the molten metal pool 8, under the reservoir portion, toward the side dam. The central passage 40 may have a cross-section up to 8 millimeters. In other embodiments the central passage 40 may have a cross-section between 6 and 14 millimeters. The central passage 40 may have the same or different cross-section as the first and/or second pairs of passages.
FIG. 5 illustrates an alternative embodiment of the reservoir portion 24. The reservoir portion may comprise a first pair of passages 22 and a second pair of passages 23 adapted to deliver molten metal downwardly to the molten metal pool 8 near the side dam. The first pair of passages 22 may be arranged having a different angle than the second pair of passages 23. In some embodiments the difference between the angle of the first and second pairs of passages may be between 0 degrees and 90 degrees. In other embodiments, the difference between the angle of the first and second pairs of passages may be between 0 degrees and 20 degrees. Consequently, the direction of flow 52 of the first pair of passages 22 and the direction of flow 53 of the second pair of passages 23 converge below the reservoir portion 24. In alternative embodiments, the first and second pairs of passages may be arranged such that the direction of flow 52 from the first pair of passages 22 may be parallel to, or diverge from, the direction of flow 53 from the second pair of passages 23.
Referring to FIGS. 3-5. The region of casting pool 8 below the reservoir 24 at the end portion 18 near the intersection of the casting rolls 6 and the side dams is the area where skulls are more likely to form because of the different heat gradient adjacent a side dam. To compensate, molten metal is directed through first passages 22 and second passages 23 from the reservoir 24, which is positioned transverse to the end portion 18 of the delivery nozzle segment 13 as shown in FIGS. 2 through 5. A weir 25 is also provided in the segment 13 to separate the flow of molten metal in the reservoir 24 providing a constant head while allowing the flow of molten metal from the inner trough 14 to flow concurrently into the holes 31 in the main body of the metal delivery nozzle 10.
As shown in FIG. 6, the first pair of passages 22 and second pair of passages 23, spaced longitudinally inward of the first pair of passages 22 (not shown), are provided slanted, such that the entry ports 35 are further apart than the exit ports 36, so that the first and second pairs of passages are adapted to converge in the lateral direction and deliver the molten metal into the triple point adjacent the side dams. The first pair of passages 22 is adapted to deliver molten metal adjacent the side dams below the reservoir portion 24 into the casting pool 8, and the second pair of passages 23 are adapted to deliver molten metal into the casting pool 8 adjacent molten metal delivered from the first pair of passages 22. This allows shells to form on the casting surfaces 7 of the casting rolls 6 without substantial washing by the molten metal from first and second pairs of passages 22 and 23, respectively, during a casting campaign. In other embodiments, the first and second pair of passages may not be slanted in the lateral direction and may delivery molten metal to the molten metal pool 8 downwardly and outwardly toward the side dam.
As shown in FIG. 4, the first pair of passages 22 and the second pair of passages 23 may be substantially parallel in the longitudinal direction. The first and second pairs of passages 22 and 23, respectively, may have a cross-section to provide a desired amount of molten metal to the molten metal pool 8 below the reservoir 24, to a desire location while shells form on the surfaces 7 of the casting rolls 6. In some embodiments, the first and second pairs of passages may have the same diameter, and may have a cross-section between 7 to 12 millimeters in diameter, or between 6 and 14 millimeters. In other embodiments, the first and second pairs of passages may have different cross-sections, for example, the cross-section of the first pair of passages 22 may be less than the cross-section of the second pair of passages 23.
As shown in FIG. 6, the first and second pairs of passages 22 and 23 (not shown), respectively, may be provided in pairs on both sides of the reservoir 24 adapted to deliver molten metal to the molten metal pool 8 on either side of the side dams near the casting rolls. The reservoir 24 may further comprise a central passage 40, spaced between each pair of passages. The central passage 40 may be slanted such that the exit port 42 of the central passage 40 may be arranged closer the side dam in comparison to the entry port 41.
FIG. 7 shows a reservoir portion, similar to the reservoir portion of FIG. 6, except the first and second pairs of passages are shaped to control the velocity of the molten metal through the passages. In FIG. 7, the first pair of passages 22 are shown having an entry port 35 and an exit port 36. The first pair of passages 22 are shaped so that the entry port 35 has a smaller diameter than the exit port 36. The exit port 36 having a larger diameter than the entry port 35 increases the cross-sectional area for the molten metal as it travels through the first pair of passages 22 and, in turn, reduces the velocity of the molten metal. Thus, the kinetic energy of the molten metal exiting the first pair of passages 22 at exit port 36 is reduced, further inhibiting the washing of shells from the casting roll surface 7, allowing the shells to form and develop during casting.
In alternative embodiments, the first and/or second pairs of passages may be shaped to the exit port 36 is smaller than the entry port 35. The exit port 36 having a smaller diameter than the entry port 35 reduces the cross-sectional area for the molten metal as it travels through the pairs of passages and causes the velocity of the molten metal to increase as it flows through the passages. Thus, the kinetic energy of the molten metal exiting the passages at the exit port 36 is increased. The first and second pairs of passages may have a similar shape, both pairs of passages adapted to effect the velocity of the molten metal travelling through the passages in a similar way. Alternatively, the first and second pairs of passages may be shaped differently, to have different effects on the velocity of the molten metal traveling through the passages. Furthermore, the central passage 40 may be shaped such that the cross-section of the entry port 41 of the central passage 40 may be smaller than the cross-section of the exit port 42 of the central passage 40, such that the velocity of the molten metal decreases as it travels through the central passage 40. Alternatively, the central passage may be configured where the exit port 42 has a small cross-section than the entry port 41. In further embodiments, the central passage 40 may have a similarly sized exit port 42 and entry port 41.
Referring to FIG. 8a, illustrated is a cross-sectional end view of a portion of a twin roll strip caster 2 with an assembled delivery nozzle 10. FIG. 8b is an enlarged view of a portion of the twin roll strip caster 2 similar to FIG. 8a except showing a trough 14 with a concave upper surface. The twin roll strip casters 2 shown in FIGS. 8a and 8b are similar to the twin roll strip caster 2 shown in FIGS. 1a and 1b except that the reservoir portion 24 has a first pair of passages 22 and a second pair of passages 23, where the second pair of passages 23 is spaced laterally inward of the first pair of passages 22 in the reservoir portion 24, the direction of flow from each pair of passages directed to converge below the reservoir portion 24.
FIG. 9 is a plan view of a segment 13 of a metal delivery nozzle 10 for use in the twin roll caster 2 as shown in FIGS. 8a and 8b. The segment 13 of the metal delivery nozzle 10 shown in FIG. 9 is similar to that shown in FIG. 2 except, the reservoir portion 24 comprises a second pair of passages 23 spaced laterally inward of the first pair of passages 22. The delivery nozzle 10 illustrated comprises two segments 13 (one shown), with each delivery nozzle segment 13 having opposing side walls 15 and an upward opening inner trough 14, which extend lengthwise along the segment 13 in the longitudinal direction of the delivery nozzle 10. In this embodiment, the side walls 15 are joined to the inner trough 14 to form shoulder portions 30, and the passages 16 are in the form of holes 31 extending through the shoulder portions 30 along each side of the inner trough 14. The molten metal flows from the inner trough 14 through the holes 31 to the side outlets 20. In this embodiment, the shoulder portions 30 provide the structural support to the delivery nozzle segment 13 when loaded with molten metal during a casting campaign. As a result, the flow of molten metal from the side outlets 20 into the casting pool 8 can be provided laterally more evenly along the delivery nozzle segment 13.
As shown, in FIG. 10, the inner trough 14 of each delivery nozzle segment 13 may extend into the end portions 18 underneath a reservoir 24 to further extend the relatively uniform flow of molten metal into the casting pool 8 along the length of the segment 13. In other embodiments, as shown in FIG. 3, the inner trough 14 extends to the end wall 18 of the segment 13 of the delivery nozzle 10. Such embodiments may provide for simpler fabrication of the delivery nozzle segment 13.
Referring to FIGS. 9 and 10, the assembly of the reservoir 24 is shown at the end portion 18 of the delivery nozzle segment 13 adjacent the ends of the casting rolls 6. The region of casting pool 8 below the reservoir 24 at the end portion 18 near the intersection of the casting rolls 6 and the side dams is the area where skulls are more likely to form because of the different heat gradient adjacent a side dam. To compensate, molten metal is directed through the first pair of passages 22 and the second pair passages 23 from the reservoir 24, which is positioned transverse to the end portion 18 of the delivery nozzle segment 13 as shown in FIG. 9. The shape of the reservoir 24, having the second pair of passages 23 spaced laterally inward of the first pair of passages 22, the direction of flow from each pair of passages directed to converge below the reservoir portion 24, is shown in FIGS. 11 and 12. The reservoir portion has a bottom portion 26 shaped to cause the molten metal to flow into first pair of passages 22 and the second pair of passages 23. A weir 25 is also provided in the segment 13 to separate the flow of molten metal in the reservoir 24 providing a constant head while allowing the flow of molten metal from the inner trough 14 concurrently into the passages 16 in the main body of the metal delivery nozzle 10. The first and second pair of passages may be arranged to have a similar angle in the lateral direction of the casting nozzle 10. Alternatively, the first and second pair of passages may be arranged to have different angles, as desired, in the lateral direction, providing different directions of flow in the lateral direction. Furthermore, the first and second pairs of passages may be arranged such that each passage of each pair of passages have directions of flow which diverge below the reservoir portion 24.
In other embodiments, the first and second pairs of passages, 22 and 23, respectively, may be arranged such that the directions of flow from each passage do not converge below the reservoir portion. For example the first pair of passages and second pair of passages may be arranged such that the direction of flows from each passage is substantially downward. Alternatively, the first and second pairs of passages may be adapted such that the directions of flow diverge. In some embodiments, the direction of flow from the passages on each side of the reservoir portion 24 may converge below the reservoir portion. Additionally, or in the alternative, the direction of flow from each passage of each pair of passages may diverge below the reservoir portion.
As shown in FIG. 11, the first pair of passages 22 and the second pair passages 23 are provided slanted to deliver the molten metal toward the triple point region adjacent the side dams. The first pair of passages 22 may be adapted to deliver molten metal into the casting pool 8 adjacent the side dams, and the second pair of passages 23 may be adapted to deliver molten metal into the casting pool 8 adjacent the molten metal delivered from the first pair of passages 22, while allowing shells to form on the casting surfaces 7 of the casting rolls 6 without substantial washing by the molten metal from first and second pairs of passages 22 and 23, respectively, during a casting campaign. The first pair of passages 22 and the second pair of passages 23 may be between 5 and 30 millimeters apart between near wall portions of the passages as shown in FIG. 11. The passages of the first pair of passages 22 and the second pair of passages 23, on each side of the reservoir 24 may be substantially parallel to each other. In other embodiments, the first pair of passages 22 and the second pair of passages 23 may be arranged different angles, providing different directions of flow of the molten metal into the molten metal pool 8, to direct the molten metal into the molten metal pool 8, as desired.
The first and second pairs passages 22 and 23, respectively, may have the same diameter, the cross-section of the first and second pairs of passages may be between 6 to 14 millimeters in diameter, or, alternatively between 7 and 12 millimeters in diameter. In other embodiments the first and second pairs of passages may be have a different cross-section, as desired, to deliver the molten metal into the casting pool 8 at the desired location as the shells move through and are formed in the casting pool 8. The first pair of passages 22 may have a small cross-section than the second pair of passages 23.
Referring to FIG. 12, an alternative embodiment of the reservoir 24 of a delivery nozzle segment 13 is shown that is otherwise the same as that shown in FIG. 8a. The first pair of passages 22 and the second pair of passages 23, spaced laterally inward of the first pair of passages 22, are provided slanted to deliver the molten metal into the desired area adjacent the side dams. The passages of first pair of passages 22 are shown having an entry port 35 and an exit port 36 and the passages second pair of passages 23 are shown having an entry port 37 and an exit port 38. The first pair of passages 22 are shaped so that the entry port 35 has a smaller cross-section than the exit port 36. The exit port 36 having a larger cross-section than the entry port 35 increases the cross-sectional area for the molten metal as it travels through the first pair of passages 22 and, in turn, reduces the velocity of the molten metal. Thus, the kinetic energy of the molten metal exiting the first passages 22 at exit port 36 is reduced and the molten metal is directed into the casting pool 8 near the region adjacent the side dams, inhibiting the washing of shells from the casting roll surface 7, allowing the shells to form and develop during casting.
The reservoir portion 24 shown in FIGS. 11 and 12 may further comprise a central passage, as shown in, and discussed in relation to, FIGS. 6 and 7. The central passage may be adapted to deliver molten metal downwardly under the reservoir portion. In other embodiments the central passage may be adapted to deliver molten metal outwardly toward the side dam, under the reservoir portion. In any embodiment the reservoir portion 24 may not comprise a central passage. Alternatively, the reservoir portion 24 may comprise one or more central passages, adapted to delivery molten metal to the molten metal pool 8 below the reservoir portion 24.
In any embodiment, the cross-section of the first pair of passages 22, the second pair of passages 23 and the central passage or passages 40 may be the same, or may be all different. Each cross-section may have any shape. For example, the passages may have a circular shape, an oval shape, a hexagonal shape, or any polygonal shape.
It should be understood that the above described apparatus and method of casting thin strip are the presently contemplated best modes of embodying the invention. Other details in the assembly and operation of the casting method and metal delivery nozzle therefor, are described by reference to U.S. Pat. No. 8,047,264 which is incorporated herein by reference. It is to be understood that these and other embodiments may be made, and performed, within the scope of the following claims. In each embodiment of the delivery nozzle, the nozzle insert dissipates a substantial part of the kinetic energy built up in the molten metal by reason of movement through the delivery system from the metal distributor to the delivery nozzle, and the resistance to movement of the molten metal from the inner trough through the passages to the side outlets further reducing the kinetic energy in the molten metal from the molten metal before reaching the casting pool. As a result, a more uniform and more quiescent flow of molten metal is provided to the casting pool for the formation of the cast strip.
While the principle and mode of operation of this invention have been explained and illustrated with regard to particular embodiments, it must be understood, however, that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.
Patent Application
20130092343
