The present invention relates to the protection of a stream of molten metal of substantially circular cross-section and of a mean diameter d, which flows vertically, over a height H, between an upper supply container and a lower receptacle, by means of a liquefied inert gas which is distributed by an apparatus comprising a phase-separating member of annular shape which surrounds the stream and which is intended to supply on the one hand the gaseous phase to form an atmosphere which envelops the upper part of the stream and on the other hand the liquid phase to form a substantially conical layer which converges towards the stream, which it meets at an angle .gamma..
At the present time protection of this kind is provided by means of installations which are equiped with phase separators of the kind described in French Patent specification No. 2,177,452. In their lower region, such separators have orifices from which the liquid phase emerges, the said phase flowing out in the form of a single layer. Experience has shown that such separators provide satisfactory protection for streams of small diameter (i.e. less than about 40 mm) which are released from a small height (i.e. less than about 900 millimeters) which is true of streams for casting billets or blooms between the tundish and the casting line. However, this protection ceases to be adequate as soon as the stream reaches a diameter greater than approximately 40 mm and a height greater than approximately 900 mm, which is the case with streams used in the continuous casting of slabs between the ladle and the tundish.
Studies made of the structure of the layer of liquid supplied by existing separators have shown that a spheroidalising effect arises from contact with the fast moving liquid metal, and as a result the liquefied gas does not flow along the stream of metal while forming a protective sheath but rebounds from the said stream and tends to break up into drops of greater or lesser size. These studies have also shown that corresponding to the angle of incidence i between the liquefied gas and metal, that is to say to the angle which the layer of liquid forms when it meets the stream of metal, is an angle of reflection r&lt;i. As a result, it drops are to be prevented from rebounding and adequate protection provided for the metal, the conditions under which the liquefied gas provides protection for the casting stream must be governed by the diameter d and the height H of the said stream.
Principally, the present invention has as an object the avoidance or minimisation of the drawbacks of known methods of protecting streams of metal so that satisfactory protection may be provided for such streams even when their diameter and height become considerable.