Metal founding – Means to shape metallic material – Continuous or semicontinuous casting
Patent
1999-01-22
2000-08-29
Lin, Kuang Y.
Metal founding
Means to shape metallic material
Continuous or semicontinuous casting
164487, B22D 11049
Patent
active
061093351
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to the vertical hot-top continuous casting of metals, especially steel.
DESCRIPTION OF THE PRIOR ART
It is known that vertical hot-top continuous casting is essentially distinguished from conventional vertical continuous casting by the fact that sitting on top of the cooled mold body (generally made of copper or a copper alloy), which ensures that the cast metal undergoes peripheral solidification, is a feed head made of a refractory material containing a reservoir of molten metal maintained in the liquid state (FR-A-2,000,365). In this manner, the point in the copper body where the cast metal starts to solidify is decoupled from the point where the free surface of the molten metal in the feed head lies, whereas they are virtually coincident in conventional vertical continuous casting.
The aim is thus to be able to cast products of good quality at high extraction rates, since the solidification region is no longer disturbed by the normal turbulence in the flow of metal arriving in the mold, this turbulence being confined to the buffer volume within the feed head.
It is also known to apply an inert-gas purge, for example an argon purge, by injecting waste gas into the interface between the mold body and the feed head. Such an arrangement is described, for example, in Patent Application EP-A-620,062 in the name of the Applicant. This purge is intended to break the film of inhomogeneous spurious solidification which tends to form when the molten metal comes into contact with the wall of the refractory feed head. This creates conditions favourable to a cast metal starting to solidify in a sharp and uniform manner always at the same point in the mold, namely level with the upper edge of the cooled metal body at the end of the feed head.
The aforementioned document describes an injection technology shown in the appended FIG. 1. This essentially involves an peripheral slit (8) which emerges at the internal periphery of the mold, this slit being continuous or segmented. Flowing along the purge slit (8) is a stream of waste argon from an annular plenum chamber (13) made near the slit and allowing an identical gas pressure to be maintained at every point around the perimeter in said chamber. Low-pressure-drop inlets (12) connect this chamber (13) to the gas supply consisting of a box (10) attached to the mold.
In this type of configuration, the main pressure drop in the flow of injected gas occurs at the purge slit (8) and is intimately associated with the geometry of the latter, more particularly with the thickness of the slit. Should the surfaces facing each other (the upper face of the cooled metal body (1) of the mold and the lower face of the refractory feed head (2)) not be strictly parallel, a local variation in the thickness of the slit then results in a heterogeneous argon injection rate around the perimeter of the mold and therefore to possible surface defects on the cast product. Such lack of parallelism between the two facing surfaces occurs in particular when the perimeter, or the cross section, of the cast product is large (slabs or large blooms) and when differential thermal expansion effects, between the various materials present, occur, more particularly near the corners of the mold (which practically always occurs after a few minutes of casting).
SUMMARY OF THE INVENTION
The object of the present invention is to ensure that the purge gas injection rate is uniform and constant around the entire perimeter of the mold throughout the casting operation.
For this purpose, the subject of the invention is a mold for the vertical hot-top continuous casting of metals, especially steel, consisting of a cooled metal body which defines a passage for the cast product and on which sits a feed head made of a refractory, and a purge slit is made at the interface between said body and said feed head, a stream of waste inert gas being injected around the internal perimeter of the mold via said slit from a plenum chamber which is made near the slit and i
REFERENCES:
patent: 5320159 (1994-06-01), Schneider et al.
Jolivet Jean-Marc
Perrin Eric
Ascometal
Cole Thomas W.
Lin Kuang Y.
Societe Anonyme des Forges et Acieries
Sogepass
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