Tundish stopper rod for continuous molten metal casting

Abstract

Stopper rods (22) for the continuous casting of molten metal have a stopper rod body (22-3), and a stopper rod tip (22-1) at a lower end of the stopper rod body. The stopper rod tip defines a frustoconically shaped exterior surface (22-1a) which terminates in a recessed nose (22-1b). The recessed nose is most preferably a curvilinear surface (e.g., a spherical segment), but non-curvilinear surfaces (e.g., prismatic, pyramidal, triangular, and quadrangular surfaces) may alternatively be employed. The frustoconically shaped exterior surface (22-1a) of the stopper rod tip most preferably forms an angle θ with respect to a horizontal plane which is sufficiently great so as to increase the velocity of the flowing molten metal to reduce the boundary layer thickness thereof adjacent the nozzle and stopper rod tip surfaces so as to minimize the deposition of inclusions thereon. Preferably the angle θ is greater than 70°.

Description

[0001] This application is a continuation-in-part (CIP) of copending U.S. application Ser. No. 11 / 120,181 filed May 3, 2005, the entire content of which is expressly incorporated hereinto by reference.FIELD OF THE INVENTION [0002] The present invention relates generally to the casting of molten metal, such as steel, copper, aluminium and alloys thereof. More specifically, the present invention relates to stopper rods for regulating the flow rate of molten metal discharged from a tundish during a continuous casting operation. BACKGROUND AND SUMMARY OF THE INVENTION [0003] The continuous casting of molten metal involves providing an available source of molten metal in a suitable vessel, for example, a tundish or ladle, which is located physically above a mould in the continuous casting apparatus. When using a tundish as the vessel for holding the molten metal, a flow of molten metal is discharged therefrom into the mould via a tundish discharge nozzle at a flow rate which is suitable ...

AI Technical Summary

Benefits of technology

The present invention provides a stopper rod for continuous molten metal casting that minimizes the deposition of inclusions onto the stopper rod tip, which can lead to nozzle clogging and slab defects. The stopper rod has a geometric profile that increases the velocity of the flowing molten metal and reduces the boundary layer thickness, thereby minimizing the deposition of inclusions. The recessed nose of the stopper rod tip is formed by a frustoconically shaped exterior surface that terminates in a recessed curve. The technical effect of the invention is to improve the cleanliness of the molten metal flow and to provide a wider range of flow rate control of the molten metal flow discharged from the tundish.

Problems solved by technology

One problem associated with controlling molten metal flow is that so-called inclusions (e.g., contaminants in the molten metal such as oxidized particles of the metal being cast) are typically present in the molten metal as it is discharged from the tundish through the nozzle.

Over time, therefore, the geometry of the orifice are defined between the tundish nozzle and the stopper rod tip may change due to continual deposit of inclusions thereby eventually detrimentally affecting the stopper rod's flow control characteristics.

A flow condition like this brings about downstream flow instability causing an incomplete useage of a port area in a SEN.

In other words, separation phenomena may bring about instability in the internal walls of a SEN and its ports promoting flow fluctuations, meniscus oscillations of bath in the mould and out of control turbulent spikes of velocity.

All those phenomena induce severe slab defects.

Then just at the tip a stagnant zone is formed and any inclusion that touches that area loses momentum and can be easily trapped on the ceramic surface of the tip becoming, with time, into a clogging problem.

Moreover, rounded tips enhance boundary layer thickness in zones upstream the tip and these are prone for inclusions trapping increasing danger of nozzle clogging.

That is, the geometric profile of the stopper rod tip does not create molten metal flow profiles which would make it difficult to exercise physical displacement of the stopper rod tip relative to the tundish nozzle.

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