Patent Application
20200023430
This invention relates to making thin metal strip and, more particularly, casting of thin metal strip by a twin cast roller.
In a twin cast roller, molten metal is introduced between a pair of laterally positioned casting rolls that are counter-rotated and cooled so that metal shells solidify on the moving roll surfaces and are brought together at a nip between them to produce a solidified strip product (delivered downwardly from the nip between the casting rolls). The term “nip” is used herein to refer to the general region where the casting rolls are closes together. The molten metal is delivered from a ladle into a smaller vessel or vessels from which the molten metal flows through delivery nozzles (also called the “core nozzles”) and form a casting pool of motel metal supported on the casting surfaces of the casting rolls and extending the length of the nip. This casting pool is locally confined by side plates or dams held in sliding engagement adjacent end portions of the casting rolls to confine the casting pool against outflow.
In prior systems, molten metal is delivered from a ladle to a moveable tundish. The molten metal is then transferred from the tundish to a transition piece (or distributor). The transition piece is independent of and opens into the delivery nozzle, delivering the molten metal to the delivery nozzle. Mechanical devices and/or robots are relied on for moving each of the ladle, tundish, transition piece, and delivery nozzle, independent of and relative to one another. In some examples, a delivery nozzle cannot be moved or accessed without independently and separately removing the tundish and/or transition piece. It, however, is necessary to move and/or access the delivery nozzle for repair, replacement, and/or reheating during and between casting. The necessary coordination between the each of the ladle, tundish, transition piece, and delivery nozzle creates inefficiencies which are overcome by the present disclosure, as discussed in greater detail below.
Two-piece delivery nozzles are most commonly used in such a configuration. A two-piece delivery nozzle is supported by means to allow adjustment between two halves. A central support structure is required to support the two separate moveable halves of a two-piece delivery nozzle. The separate halves of a two-piece delivery nozzle interrupt the flow of the molten metal, thereby, creating “dead zones” between the two halves in the casting pool. The two separate halves, and corresponding moving mechanisms, further require the two-piece delivery nozzle be supported independent of the transition piece, tundish, and ladle. By providing a unitary body, the uniform distribution nozzle of the present disclosure eliminates the dead zones created in the casting pool and removes the independent support structures required by a two-piece delivery nozzle.
A uniform distribution nozzle of the present disclosure improves the prior system by providing a delivery nozzle that may be attached or connected to a transition piece for movement therewith, thereby, reducing the number of mechanical devices, and/or robots, required for system set-up. The uniform distribution nozzle of the present disclosure improves the prior system by eliminating the need for two preheat furnaces, as required by two-piece delivery nozzle. The uniform distribution nozzle of the present disclosure improves the prior system by reducing the system set-up time and, thereby, reducing refractory heat loss within the system. The uniform distribution nozzle of the present disclosure improves the quality of the thin cast metal strip by eliminating the space between the two halves of a two-piece delivery nozzle, thereby, eliminating dead zones. The uniform distribution nozzle of the present disclosure improves the quality of the thin cast metal strip by increasing the head height of the molten metal within an internal casting pool and, thereby, absorbing kinetic energy within the molten metal prior to the molten metal exiting the uniform distribution nozzle. Finally, the uniform distribution nozzle of the present disclosure improves the quality of the thin cast metal strip by improving the application of controlled gases within the interior cavity and/or at the meniscus.
Presently disclosed is an elongated delivery nozzle for a twin roll caster, herein referred to as a uniform distribution nozzle. The uniform distribution nozzle is adapted to extend along and above a pair of casting rolls and to deliver metal from a transition piece to a location above a pair of casting rolls. The metal delivered from the uniform distribution nozzle forms a casting pool of molten metal supported by the pair of casting rolls.
In one example, the uniform distribution nozzle comprises:
(a) A unitary body formed of refractory and having a length configured to extend along a length of the casting pool. The unitary body extending in an axial direction of the pair of casting rolls. In one particular example, the body length extends at least 90% of the casting pool length.
(b) A top member arranged along a top side of the body. The top member includes a plurality of molten metal metering nozzles spaced apart along the length of the body.
(c) An interior cavity arranged within the body and below the top member. The interior cavity has a height extending from the top to a bottom of the body.
The body also includes a plurality of outlet ports arranged below the top member and extending from the interior cavity to an exterior of the uniform distribution nozzle. The interior cavity is configured to receive molten metal from the plurality of metering nozzles to form an interior molten metal pool. The interior cavity is also configured to discharge the molten metal from the uniform distribution nozzle through the plurality of outlet ports and into the casting pool during casting.
Also presently disclosed is a twin roll caster for continuously casting metal strip. The twin roll caster comprises:
(a) A pair of casting rolls laterally positioned to form a nip. The nip is formed between the pair of casting rolls and side dams to form a molten metal pool supported by the casting rolls between a pair of opposing side dams. The pair of casting rolls are adapted to counter rotate to form shells on the casting rolls brought together at the nip to cast metal strip downwardly from the nip.
(b) A uniform distribution nozzle adapted to extend along and above the pair of casting rolls and to deliver metal from a transition piece to a location above the pair of casting rolls. The metal delivered from the uniform distribution nozzle forms a casting pool of molten metal supported by the pair of casting rolls. The uniform distribution nozzle further comprises:
(c) A metal delivery system adapted to introduce molten metal through the uniform distribution nozzle downwardly converging toward the nip.
A method of casting metal strip is also disclosed. The method of casting metal strip comprising:
(a) Providing a pair of casting rolls laterally positioned to form a nip. The nip is formed between the pair of casting rolls and side dams to form a molten metal pool supported by the casting rolls between a pair of opposing side dams. The pair of casting rolls are adapted to counter rotate to form shells on the casting rolls brought together at the nip to cast metal strip downwardly from the nip.
(b) Providing a uniform distribution nozzle adapted to extend along and above the pair of casting rolls and to deliver metal from a transition piece to a location above the pair of casting rolls. The metal delivered from the uniform distribution nozzle forms a casting pool of molten metal supported by the pair of casting rolls. The uniform distribution nozzle further comprises:
(c) Delivering molten metal through the uniform distribution nozzle downwardly converging toward the nip. The molten metal is caused to flow from the plurality of metering nozzles of the uniform distribution nozzle and into the interior molten metal pool arranged in the interior cavity. The molten metal is additionally caused to flow from the interior molten metal pool, through the plurality of outlet ports, and into the casting pool.
(d) Counter rotating the casting rolls to deliver cast strip downwardly from the nip as casting proceeds.
The foregoing and other objects, features, and advantages of the examples will be apparent from the following more detailed descriptions of particular examples as illustrated in the accompanying drawings wherein like reference numbers represent like parts of the examples.
The invention may be more fully illustrated and explained with reference to the accompanying drawings in which:
The present disclosure is for an elongated delivery nozzle for a twin roll caster. The elongated delivery nozzle is herein referred to as a uniform distribution nozzle. The uniform distribution nozzle is arranged between a transition piece and a casting pool, where the casting pool is arranged above a nip and a pair of casting rolls. The transition piece may be a storage vessel, a tundish, or a conventional transition piece. Molten metal flows from a tundish into a transition piece and then into the uniform distribution nozzle. The molten metal is delivered from the uniform distribution nozzle to a casting pool supported by the casting surfaces of the casting rolls. In some examples of the present disclosure, the molten metal is molten steel for forming a thin cast steel strip.
In the present disclosure, the uniform distribution nozzle is a unitary delivery nozzle having a unitary body. The unitary body of the uniform distribution nozzle prevents dead zones, or areas formed within the casting pool which do not receive a consistent flow of molten metal. By example, a two-piece delivery nozzle has two halves which move relative one another by way of moving mechanisms positioned to opposite ends of the two-piece delivery nozzle. The two-piece delivery nozzle creates a gap in the flow of molten metal and in the casting pool. This gap forms the above-mentioned dead zones within the casting pool. Dead zones create undesirable ridges in the profile of thin cast metal strip. The unitary body of the uniform distribution nozzle reduces or eliminates these imperfections resulting from the dead zones by eliminating the dead zones.
The unitary body of the uniform distribution nozzle may be attached to or secured to the transition piece. By attaching the unitary body to the transition piece, the uniform distribution nozzle may be transported with the transition piece. This eliminates separate mechanical devices, and/or robots, required to move the uniform distribution nozzle and the transition piece independently. In comparison, the two-piece delivery nozzle of the prior system, and the corresponding moving mechanisms, are not and cannot be attached directly to the transition piece. Thereby, the two-piece delivery nozzle is moved independent of the transition piece using independent mechanical devices and/or robots. The two-piece delivery nozzle must also be independently supported, relative the transition piece, during casting. Ultimately, the uniform distribution nozzle of the present disclosure may be moved in combination with, and by the same means (e.g. robots, mechanical devices, etc.) as, the transition piece and, thereby reducing set-up time and equipment. Further, the uniform distribution nozzle is also maintained in cast position by the transition piece.
The unitary body of the uniform distribution nozzle of the present disclosure eliminates preheating using two preheat furnaces and also eliminates the need for robots to set metal refractories in casting position, as required by a two-piece delivery nozzle. Reduced set-up time, as mentioned above, reduces refractory heat loss before casting begins. Also, the simplified unitary body allows the uniform distribution nozzle of the present disclosure to be heated by a much simpler process. The uniform distribution nozzle of the present disclosure may be pre-heated in combination with the transition piece, to which it may be attached. Refractory heat loss is reduced since the uniform distribution nozzle of the present disclosure is partially submerged in the casting pool during casting. Refractory heat loss is also reduced since the uniform distribution nozzle of the present disclosure further comprises a top member (discussed in great detail below) which allows for a higher head level at an internal casting pool, the internal casting pool being within an interior cavity of the uniform distribution nozzle. All of these improvements account for a reduction in refractory heat loss and, thereby, an increased ability to maintain the heat of the uniform distribution nozzle of the present disclosure. In contrast, the two-piece delivery nozzle requires preheating, using two separate preheat furnaces, as a result of the complexity of the structure, refractory heat loss resulting from increased set-up time.
The uniform distribution nozzle of the present disclosure further comprises a top member. The top member provides a distribution means for delivering the molten metal from the transition piece into an interior cavity of the uniform distribution nozzle. The molten metal transfers through a plurality of molten metal metering nozzles positioned or formed in the top member into an interior cavity within the uniform distribution nozzle. The interior cavity formed within the uniform distribution nozzle of the present disclosure may be generally enclosed within the unitary body by way of the top member. An interior cavity that is generally enclosed means the interior cavity is enclosed with the exception of the plurality of molten metal metering nozzles, outlet ports, triple point outlet ports, and/or gas ports, each of which are described in greater detail below. By way of the internal head height, the kinetic energy generated by the transfer of the molten metal is absorbed by the internal pool of molten metal formed in the interior cavity. As a result, imperfections formed within the profile of the thin metal cast strip, resulting from the inability to control such kinetic energy, are greatly reduced or eliminated.
By generally enclosing the interior cavity, the control of gases around the molten metal is improved within the interior cavity and/or at the meniscus. The controlled gases may be added to the generally enclosed interior cavity independent of any controlled gases added at the meniscus. Such gases may be substantially insoluble within the molten metal. Such gases may be inert. One such controlled gas may be argon. By example, argon is not desired at the meniscus. Instead, argon may be applied within the interior cavity, independent of nitrogen, to eliminate nitrogen pick-up within the interior cavity. As a result, argon reduces or eliminates oxidation and nitrogen pick-up of the molten metal within the interior cavity. In contrast, nitrogen may be added at the meniscus of the casting pool, independent and separate from the argon, to enable proper heat transfer. Since the interior cavity is generally enclosed, the argon is captured within the head space between the internal pool of molten metal and the top member. The argon does not escape to offset the effects of the nitrogen applied at the meniscus and the nitrogen does not impact the effects of the argon applied within the interior cavity. Further, by way of generally enclosing the interior cavity, any influx of unwanted external gases is reduced or eliminated.
Referring now the drawings, there is illustrated in
The ladle 13 typically is of a conventional construction supported on a rotating turret 40. For metal delivery, the ladle 13 is positioned over a moveable tundish 14 in the casting position to delivery molten metal to the tundish. The movable tundish 14 may be positioned on a tundish car 66 capable of transferring the tundish from a heating station, where the tundish is preheated to near casting temperature, to the casting position. A tundish guide, such as rails, may be positioned beneath the tundish car 66 to enable moving the movable tundish 14 from the preheating station to the casting position.
The moveable tundish 14 may be fitted with a side gate, actuable by a servo mechanism, to allow molten metal to flow from the tundish 14 through the slide gate, and then through a refractory outlet shroud to a transition piece (or distributor) 16 in the casting position. From the transition piece 16, the molten metal flows from the transition piece 16 to the uniform distribution nozzle 17 positioned between the casting rolls 12 and the nip.
Referring to
The uniform distribution nozzle is a unitary body formed of refractory and having a length configured to extend along a length of the casting pool in an axial direction of the pair of casting rolls. The casting pool length is defined by the opposing side dams. In one example, the unitary body length extends at least 90% of the casting pool length. By providing a unitary body, the uniform distribution nozzle does not require a centrally located support, which is required in a two-piece delivery nozzle. The nozzle thus is unsupported between a pair of opposing end sections, or end portions, of the nozzle. The unitary body may also suspend from and be supported by the transition piece.
As illustrated by
As illustrated by
With particular reference to
The unitary body further comprises a plurality of outlet ports 130. The outlet ports 130 are arranged below the top member 100 and extend from the interior cavity 200 to an exterior of the uniform distribution nozzle 17. The interior cavity 200 receives molten metal from the plurality of metering nozzles 120 to form an internal molten metal pool 210. The molten metal 210 is then discharged from the uniform distribution nozzle 17 through the plurality of outlet ports 130 and into the casting pool 19 during casting. The outlet ports may, additionally or alternatively, be triple-point pouring outlets positioned to each end of the length of the uniform distribution nozzle. Triple-point pouring outlets properly feed molten metal to the triple point or the location where the casting rolls, side dam, and meniscus intersect. In one example, the unitary body includes a pair of end sections, or portions, where each end section is located at one end of the pair of opposing ends of the body length. A gap, into which each end section may extend, may be provided at each adjacent side dam 20. The gap is provide to accommodate side dam wear and corresponds to how much each side dam extends into the casting pool. Specifically, the length of the unitary body may be configured to provide a gap between each end section and an adjacent side dam of the twin roll caster when arranged within the twin roll caster during casting. In one example. the gap may be 25 mm to 30 mm. In yet another example, the gap may be 25 mm to 40 mm. Still, in yet another example, the gap may be up to 60 mm, or as wide as necessary to control snake eggs.
Each end section may include at least a pair of triple point outlet ports 140, separate and independent of the plurality of outlet ports. The triple point outlet ports 140 extend from the interior cavity 200 to the exterior of the uniform distribution nozzle at a location above the intended height of the casting pool. Each triple point outlet port is configured to discharge the molten metal contained in the interior cavity in a direction toward, in the vicinity of, and/or adjacent to a location where one of the casting rolls engages a side dam of the twin roll caster.
By way of combining a delivery nozzle with oscillating side dams, the above-mentioned unitary body has been facilitated. In particular, the employment of oscillating side dams has, at least in part, facilitated the unitary body since the lateral adjustment to the length of a two-piece delivery nozzle, to optimize triple point pouring, has been eliminated. This, however, does not mean that the uniform distribution nozzle having a unitary body is used only in combination with oscillating side dams. Examples of oscillating side dams are disclosed in United States Patent Application Publication No. 2017/0036266 A1 for “MULTIPLE PIECE CORE NOZZLE,” herein incorporated by reference.
In one example, the unitary body of the uniform distribution nozzle of the present disclosure also comprises end cavities 250. The end cavities 250 have triple point outlet ports 140 that are adapted to deliver molten metal to the casting pool to a “triple point” area or region. The formation of solid pieces known as “skulls” occur in the casting pool in the vicinity of the confining side plates or dams. The rate of heat loss from the casting pool is higher near the side dams in the “triple point region” due to conductive heat transfer through the side dams to the casting rolls. 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 causing defects in the cast strip. An increased flow of molten metal to these triple point regions near the side dams have been provided. See, U.S. Pat. Nos. 4,694,887 and 5,221,511, each of which are herein incorporated by reference. Increased heat input to these triple point regions has reduced formation of skulls. Each end section may comprise an end cavity that is open to the interior cavity of the uniform distribution nozzle. More specifically, each end cavity may be open to the interior cavity at a top side of a raised section separating the interior cavity and end cavity. The end cavity extends outwardly away from the interior cavity in a direction of the body length. Each cavity is adapted to receive molten metal through at least one of the plurality of metering nozzles of the top member and/or from the interior cavity. Molten metal is delivered to the casting pool through the triple point outlet ports 140 extending through the uniform distribution nozzle.
By generally enclosing the interior cavity, the head height of the molten metal retained internally within the uniform distribution nozzle may be adjusted, such as, by example, increased. In one example, the uniform distribution nozzle is configured to maintain an average head height of the internal molten metal pool within the interior cavity that is equal to or greater than 15 mm. By adjusting, such as reducing, the diameter, or opening dimension, of the outlet ports the head height of the molten metal within the interior cavity is impacted. Ultimately, the head height of the molten metal within the internal cavity absorbs kinetic energy formed by the transfer of the molten metal. The kinetic energy reduces as the depth of the internal molten metal increases, from top to bottom.
It is appreciated, however, that in one particular example at least one breather hole, or gas port, may be provided above the head height and extend through the uniform distribution nozzle and into the interior cavity to facilitate gas transfer. Specifically, the at least one breather hole is arranged above an intended maximum head height of an interior molten metal pool during casting operations. The breather hole permits or allows for a controlled influx of external gases, or gases outside the pool atmosphere or pool space. The controlled influx of external gases improves the flow of molten metal from the uniform distribution nozzle. However, the quantity and size of the breather holes are to be controlled and maintained for optimum results.
While the invention has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as illustrative and not restrictive in character, it being understood that only illustrative embodiments thereof have been shown and described, and that all changes and modifications that come within the spirit of the invention described by the following claims are desired to be protected. Additional features of the invention will become apparent to those skilled in the art upon consideration of the description. Modifications may be made without departing from the spirit and scope of the invention.
This application claims priority to, and the benefit of, U.S. Provisional Application No. 62/699,998 filed on Jul. 18, 2018 with the United States Patent Office, which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62699998 | Jul 2018 | US |
