CASTING THIN STRIP AND DELIVERY NOZZLE THEREFOR
A method of casting metal strip and equipment therefor where an elongated metal delivery nozzle extending along in a continuous caster with at least one segment having a main portion adapted to deliver molten metal in the casting pool above the nip along the metal delivery nozzle and an end portion adjacent side dams having a reservoir portion with 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 the molten metal from the first pair of passages adjacent the side dams to inhibit formation of skulls during the formation of the cast strip during a casting campaign.
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This application is a continuation-in-part of, and claims priority to and the benefit of, U.S. patent application Ser. No. 13/464,188, filed May 4, 2012, which, in turn, claims priority to U.S. Provisional Patent Application No. 61/483,405, filed May 6, 2011, the disclosures of which are incorporated herein by reference.
BACKGROUND AND SUMMARY OF THE INVENTIONThis 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.
The invention is described in more detail in reference to the accompanying drawings in which:
Referring to
The disclosed method of casting metal strip may be performed upon a casting apparatus such as those illustrated in
Referring to
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
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
With reference to
In some embodiments, as shown in
Referring to
As shown in
As shown in
As shown in
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
As shown, in
Referring to
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
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
The reservoir portion 24 shown in
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.
Claims
1. 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 each side dam having a reservoir portion having a first pair and a 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 pairs 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 into the casting pool, and
- (d) counter rotating the casting rolls to deliver cast strip downwardly from the nip.
2. The method of casting metal strip as claimed in claim 1 having the first pair of passages and the second pair of passages such that the first and second pairs of passages are adapted to deliver molten metal outwardly from the reservoir portion of the delivery nozzle toward the side dam.
3. The method of casting metal strip as claimed in claim 1 where the second pair of passages is spaced longitudinally inward of 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.
4. The method of casting metal strip as claimed in claim 1 where the second pair of passages is 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.
5. The method of casting metal strip as claimed in claim 3 where the direction of flow from each of the first and second pairs of passages converge.
6. The method of casting metal strip as claimed in claim 4 where the direction of flow from each of the first and second pairs of passages converge.
7. The method of casting metal strip as claimed in claim 3 where the direction of flow from each of the first and second pairs of passages are substantially parallel.
8. The method of casting metal strip as claimed in claim 4 where the direction of flow from each of the first and second pairs of passages are substantially parallel.
9. The method of casting metal strip as claimed in claim 3 where the direction of flows from the first and second pairs of passages are directed toward the side dam.
10. The method of casting metal strip as claimed in claim 4 where the direction of flows from the first and second pairs of passages are directed toward the side dam.
11. The method of casting metal strip as claimed in claim 3 where the reservoir portion having a central passage adapted to deliver molten metal downwardly to the casting pool under the reservoir portion.
12. The method of casting metal strip as claimed in claim 4 where the reservoir portion having a central passage adapted to deliver molten metal downwardly to the casting pool under the reservoir portion.
13. The method of casting metal strip as claimed in claim 11 where the direction of flow from the central passage is downwardly toward the side dam.
14. The method of casting metal strip as claimed in claim 12 where the direction of flow from the central passage is downwardly toward the side dam.
15. The method of casting metal strip as claimed in claim 11 where the central passage having a diameter of between 4 mm and 8 mm.
16. The method of casting metal strip as claimed in claim 12 where the central passage having a diameter of between 4 mm and 8 mm.
17. The method of casting metal strip as claimed in claim 3 where the direction of flow from first pair of passages is different from the direction of flow from the second pair of passages.
18. The method of casting metal strip as claimed in claim 4 where the direction of flow from first pair of passages is different from the direction of flow from the second pair of passages.
19. The method of casting metal strip as claimed in claim 1 where the first and second pairs of passages have the same diameter.
20. The method of casting metal strip as claimed in claim 1 where the first and second pairs of passages have diameters of between 6 mm and 14 mm.
21. The method of casting metal strip as claimed in claim 1 where the first pair of passages has a cross-section smaller than a cross-section of the second pair of passages.
22. The method of casting metal strip as claimed in claim 1 where the first and second pairs of passages of the reservoir portion are shaped to control the velocity of molten metal through the passages.
23. The method of casting metal strip as claimed in claim 1 where the 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.
24. 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 form 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.
25. The metal delivery apparatus for casting metal strip as claimed in claim 24 having the first pair of passages and the second pair of passages such that the first and second pairs of passages are adapted to deliver molten metal outwardly from the reservoir portion of the delivery nozzle toward the side dam.
26. The metal delivery apparatus for casting metal strip as claimed in claim 24 where the second pair of passages is 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.
27. The metal delivery apparatus for casting metal strip as claimed in claim 24 where the second pair of passages is spaced laterally 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.
28. The metal delivery apparatus for casting metal strip as claimed in claim 26 where the direction of flow from each of the first and second pairs of passages converge.
29. The metal delivery apparatus for casting metal strip as claimed in claim 27 where the direction of flow from each of the first and second pairs of passages converge.
30. The metal delivery apparatus for casting metal strip as claimed in claim 26 where the direction of flow from each of the first and second pairs of passages are substantially parallel.
31. The metal delivery apparatus for casting metal strip as claimed in claim 27 where the direction of flow from each of the first and second pairs of passages are substantially parallel.
32. The metal delivery apparatus for casting metal strip as claimed in claim 26 where the direction of flow from each of the first and second pairs of passages are directed toward the side dam.
33. The metal delivery apparatus for casting metal strip as claimed in claim 27 where the direction of flow from each of the first and second pairs of passages are directed toward the side dam.
34. The metal delivery apparatus for casting metal strip as claimed in claim 26 where the reservoir portion having a central passage adapted to deliver molten metal downwardly to the casting pool under the reservoir portion.
35. The metal delivery apparatus for casting metal strip as claimed in claim 27 where the reservoir portion having a central passage adapted to deliver molten metal downwardly to the casting pool under the reservoir portion.
36. The metal delivery apparatus for casting metal strip as claimed in claim 34 where the direction of flow from the central passage is downwardly toward the side dam.
37. The metal delivery apparatus for casting metal strip as claimed in claim 35 where the direction of flow from the central passage is downwardly toward the side dam.
38. The metal delivery apparatus for casting metal strip as claimed in claim 34 where the central passage having a diameter of between 4 mm and 8 mm.
39. The metal delivery apparatus for casting metal strip as claimed in claim 35 where the central passage having a diameter of between 4 mm and 8 mm.
40. The metal delivery apparatus for casting metal strip as claimed in claim 26 where the direction of flow from the first pair of passages is different than the direction of flow from the second pair of passages.
41. The metal delivery apparatus for casting metal strip as claimed in claim 27 where the direction of flow from the first pair of passages is different than the direction of flow from the second pair of passages.
42. The metal delivery apparatus for casting metal strip as claimed in claim 24 where the first and second pairs of passages have the same diameter.
43. The metal delivery apparatus for casting metal strip as claimed in claim 24 where the first and second pairs of passages have diameters of between 6 mm and 14 mm.
44. The metal delivery apparatus for casting metal strip as claimed in claim 24 where the first pair of passages has a cross-section smaller than a cross-section of the second pair of passages.
45. The metal delivery apparatus for casting metal strip as claimed in claim 24 where the first and second passages of the reservoir portion are shaped to control the velocity of molten metal through the passages.
46. The metal delivery apparatus for casting metal strip as claimed in claim 24 where the 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 apparatus.
Type: Application
Filed: Nov 6, 2012
Publication Date: Apr 18, 2013
Applicant: NUCOR CORPORATION (Charlotte, NC)
Inventor: NUCOR CORPORATION (Charlotte, NC)
Application Number: 13/670,454
International Classification: B22D 11/06 (20060101);