Fluid sprinkling – spraying – and diffusing – Unitary plural outlet means – Having interior filter or guide
Reexamination Certificate
2000-11-30
2002-10-22
Douglas, Lisa A. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Unitary plural outlet means
Having interior filter or guide
C239S590500
Reexamination Certificate
active
06467704
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a nozzle for guiding molten metal, for example molten steel. More particularly, the invention relates to a so-called submerged entry nozzle, sometimes also known as a casting nozzle, used in the continuous casting process for producing steel. The invention also relates to a method of guiding molten metal using the nozzle.
In the continuous casting steelmaking process, molten steel from a ladle is poured into a large vessel known as a tundish. The tundish has one or more outlets through which the molten steel flows from the tundish into one or more respective moulds in which the molten steel cools and solidifies to form continuously cast solid lengths of the metal. A submerged entry nozzle, which has the general form of an elongate conduit (it generally has the appearance of a rigid pipe or tube) is located between the tundish and each mould, and guides molten steel flowing through it from the tundish to the mould.
The main functions of the ideal submerged entry nozzle are as follows. Firstly, the nozzle serves to prevent the molten steel from coming into contact with air as it flows from the tundish into the mould, since air would cause oxidation of the steel, which is undesirable. Secondly, it is highly desirable for the nozzle to introduce the molten steel into the mould in as smooth and non-turbulent a manner as possible, since turbulence in the mould causes the flux on the surface of the molten steel in the mould to become dragged down into the steel (known as “entrainment”), thereby generating impurities in the cast steel. Turbulence in the mould also disrupts the lubrication of the sides of the mould: one of the functions of the mould flux (apart from preventing the surface of the steel from coming into contact with air) is to lubricate the sides of the mould to prevent the steel adhering and solidifying to the mould and to prevent the consequent formation of surface defects in the cast steel. Minimizing the turbulence by means of the submerged entry nozzle is therefore important for this purpose also. Additionally, turbulence can cause stress on the mould itself, risking damage to the mould. Furthermore, turbulence in the mould can also cause uneven heat distribution in the mould, consequently causing uneven soldification of the steel and also causing variations in the quality and composition of the steel being cast. This latter problem also relates to a third main function of the submerged entry nozzle, which is to introduce the molten steel into the mould in an even manner, in order to achieve even solidified shell formation (the steel solidifies most quickly in the regions closest to the mould walls) and even quality and composition of the cast steel. A fourth function of an ideal submerged entry nozzle is to reduce or eliminate the occurrence of oscillations in the standing wave in the meniscus of steel in the mould. The introduction of molten steel into the mould generally creates a standing wave at the surface of the steel, and any irregularities or oscillations in the flow of the steel entering the mould can give rise to oscillations in the standing wave. Such oscillations can have a similar effect to turbulence in the mould, causing entrainment of mould flux into the steel being cast, disrupting the effective lubrication of the sides of the mould by the mould flux, and adversely affecting the heat distribution in the mould.
It will be appreciated that designing and manufacturing a submerged entry nozzle which performs all of the above functions as well as possible is an extremely challenging task. Not only must the nozzle be designed and manufactured to withstand the forces and temperatures associated with fast flowing molten steel, but the need for turbulence suppression combined with the need for even distribution of the molten steel in the mould create extremely complex problems in fluid dynamics.
U.S. Pat. No. 5,785,880 discloses nozzles in which the bottom outlet is divided into two ports by means of a flow divider. This design of nozzle is claimed to diffuse and decelerate the molten steel flow, and is also claimed to provide a generally uniform flow velocity distribution along the length and width of the outlet ports. This design of nozzle, it is claimed, has the consequence of reducing the size of oscillations in the standing wave in the meniscus of steel in the mould.
U.S. Pat. No. 5,944,261, which is a continuation-in-part of U.S. Pat. No. 5,785,880, discloses a submerged entry nozzle in which each of the two outlet ports is itself divided into two by means of a baffle, in such a way that the largest proportion of the molten steel flow throughput exits the nozzle via the two central ports. The particular shape and positioning of the baffles is claimed to diffuse the central streams and to cause recombination of the central streams with their respective outer streams upon exiting the nozzle. The consequence of this is claimed to be a reduction in the velocity of the molten steel exiting the nozzle, and a reduction in the turbulence created in the mould.
U.S. Pat. No. 6,027,051, which is a continuation-in-part of U.S. Pat. No. 5,944,261, discloses a variation on the design disclosed in U.S. Pat. No. 5,944,261, in which it is claimed that the effective discharge angle of the outer streams of molten steel varies depending upon the flow throughput. It is claimed that this has the effect of providing a smooth, quiescent, meniscus, over a range of flow throughputs.
One of the conclusions which will be most readily drawn from a consideration of the above patents is that seemingly minor, or even seemingly insignificant, changes in the design of a submerged entry nozzle can have dramatic effects upon the flow pattern of the molten steel flowing through, and out of, the nozzle. This is a consequence of the chaotic nature of fluid dynamics, in which small design changes to a conduit transporting a fluid can have profound effects upon the fluid flow pattern, and can even alter the nature of the fluid flow entirely.
The present invention seeks to provide a submerged entry nozzle which performs, as well as possible, the main functions of the ideal nozzle referred to above. The invention seeks to achieve this objective in a way which is entirely contrary to the teaching of the patents mentioned above, as will be explained below.
According to a first aspect, the invention provides a nozzle for guiding molten metal flowing from a vessel into a mould, the nozzle comprising a conduit which is elongate along an axis which is oriented substantially vertically during use, the nozzle having at least one upper inlet, at least two lower outlets which are inclined to the axis, and at least one lower outlet located generally axially between the inclined outlets, the minimum combined cross-sectional area of the inclined outlets being at least twice as great as the minimum combined cross-sectional area of the one or more generally axially located outlets.
The first aspect of the invention has the advantage that because the minimum combined cross-sectional area of the inclined outlets is at least twice as great as the minimum combined cross-sectional area of the one or more generally axially located outlets, the proportion of all of the molten metal flowing through the nozzle which flows out of the inclined outlets is generally significantly greater than the proportion which flows out of the generally axially located outlets. Preferably, at least 55% of the total molten metal flow exits the inclined exits and no more than 45% of the total molten metal flow exits the generally axially located outlets; more preferably, at least 60% of the total flow exits the inclined exits and no more than 40% of the total flow exits the generally axially located outlets. Because of the inclination to the vertical, of the inclined outlets, the downward vertical component of the velocity of the molten metal exiting such outlets is smaller than would be the case for vertically oriented outlets.
This has the effect of reducing the
Khurana Shuchi P.
Sahai Yogeshwar
Douglas Lisa A.
Foseco International Limited
Nixon & Vanderhye
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