It is particularly concerned with the continuous casting of molten steel and, although not intended to be limited thereto, will for convenience be described below with specific reference to the continuous casting of steel.

In the continuous casting of molten metal it is a common practice to use a shroud to enclose molten metal as it flows from one vessel to another so as to exclude so far as possible air and other contaminants. For example, for the casting of steel, it is common practice to employ a shroud for the steel as it passes from a ladle to a tundish. This is an extremely important factor in the casting of clean steel as the shroud minimises oxygen and nitrogen pick up by the steel. Gaseous pick up, and the reactions of these gases with the steel, lead to the presence of undesirable inorganic inclusions in the cast steel and the amount of this contamination is an indication of the degree of cleanliness of the steel.

A variety of prior proposals have been made to reduce this contamination. Consider a conventional ladle shroud with a tapered upper portion which is connected to a correspondingly tapered or conical portion of the collector nozzle on the underside of a ladle. The stream of steel passing through the shroud creates a vacuum inside the shroud causing air to be sucked in through the junction between the shroud and nozzle. This air then reacts with the steel as described above with the formation of the undesired inorganic inclusions.

Although the gap through which the air can be sucked is very small when the ladle shroud is used for the first time, during use steel skulls form on the tapered portion of the shroud. These skulls have to be removed by oxygen lancing, which damages

the surface of the shroud and thereby widening the gap and resulting in increased air suction.

To prevent this ingress of air there have been a number of prior proposals. For example, a fibre gasket has been applied between the ladle shroud and the collector nozzle. Argon has been supplie above the ladle shroud to reduce so far as possible the amount of air in the gas sucked through the aforementioned gap.

Argon has also been supplie into the gap between the ladle shroud and the collector nozzle, for example through a porous material or via slots inserted horizontally or vertical into the tapered portion of the ladle shroud. Combinations of all these proposals are frequently used in practice.

These proposals have not, however, been entirely successful and it is an object of the present invention to provide an improved shroud/nozzle connection which can reduce air contact with the molten metal and provide a more stable environment in which continuous pressure monitoring of the argon supply and flow control can be better maintained.

Accordingly, in one aspect, the invention provides a disposable adapter for a tubular shroud for molten metal, the bore of the shroud having an upper tapered portion, the adapter being made of refractory material and having an external tapered shape to fit into the upper tapered portion of the shroud bore and being of size to cover substantially the surface of said upper tapered portion of the bore, the adapter being provided with means to provide gas flow channels from its outer surface into the tubular shroud.

The means to provide the gas flow channels may be, for example, grooves in the exterior surface of the adapter. The grooves may extend from a position adjacent the wider or upper end of the adapter to its lower edge so that an inert gas, usually argon, can be fed through the upper portion of a shroud into the grooves and then flow to the lower end of the adapter and then into the tubular portion of the shroud.

A molten metal stream flowing through the shroud is thereby shielded by the argon flow. Alternatively the gas flow channels may be provided by protrusions on the exterior surface of the adapter. In another embodiment the adapter may be gas permeable so that gas may flow through its wall and then into contact with molten metal flowing through the shroud.

The interior surface of the adapter should be of size and shape to receive as a close fit the collector or other nozzle of the vessel from which the molten metal is to be supplied to the shroud.

In another aspect the invention provides a molten metal handling vessel having an outlet nozzle, a tubular shroud attached to the outlet nozzle and leading to a receiving vessel, the outlet nozzle having a tapered outer surface and the bore of the tubular shroud having an upper portion having a correspondingly tapered surface, and a disposable adapter of refractory material positioned in the tapered upper portion of the shroud bore to be sandwiched between the outlet nozzle and the shroud, the adapter having a tapered shape to fit therebetween and being of size to cover substantially the surface of said tapered upper portion of the bore, the adapter being provided with means to provide gas flow channels from its outer surface into the tubular shroud.

The molten metal handling vessel may be, for example, a ladle and the receiving vessel a tundish for molten steel.

It will be appreciated that inert gas flow through the adapter channels, when provided by grooves on the exterior surface of the adapter, is unrestricted and unaffected by any skulling. In all instances the critical region of the interior tapered surface of the shroud bore is kept away from contact with the molten metal which comes into contact only with the interior surface of the adapter until it reaches the lower, tubular portion of the shroud. Less frequent lancing of skull leads to greatly

improved service life and a used adapter, being removable, can be removed and replace when necessary by a new one, e. g. on ladle changeover.

In addition to the above advantages, the invention also provides improved pressure control independent of the molten metal flow inside the shroud and the monitoring of the pressure of an inert gas supply is more consistently achievable. Thus the inert gas supply can be maintained at a level just sufficient for the operational requirements rather than in excess as is required in prior proposals and the gas supply can be independent of the flow rate of the molten metal.

Insulation may advantageously be applied to the external wall of the shroud in the region of the tubular bore adjacent to and below the adapter. This helps to maintain the molten metal inside the bore at a temperature to avoid skull build up and thereby ensures easier removal.

The adapter may be made from any suitable refractory material and so may be metallic or inorganic or a combination of both. For example, it may be an alumina-silicate, e. g. mullite, a magnesite-based material, a ceramic, a carbon-bonded refractory or a metal-ceramic composite. It may be made by any suitable shaping method, e. g. injection-moulding, pressing, vacuum-forming or slip casting, and firing where appropriate.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which : Figure 1 is a section through a shroud-nozzle connection incorporating an adapter of the invention ; Figure 2 is a section of a portion of the connection of Figure 1 showing a build up of steel skull on the adapter after use ;

Figure 3 is a section through a shroud after removal of a used adapter ; Figure 4 is an elevation of an adapter of the invention ; and Figure 5 is an end view in the direction of arrow C in Figure 4.

In Figure 1 a nozzle 10, e. g. a collector nozzle from a ladle (not shown) containing molten steel, is connected via a shroud 20 to, e. g., a tundish (not shown) positioned below the ladle. The lower portion 12 of the exterior surface 14 of the nozzle tapers in the direction of its lower end 16.

The upper portion of shroud 20 has an enlarged head 22 and an internal bore 24 tapering in the direction of a lower tubular bore 26. A recess 28 in head 22 is connected via a channel 30 through the head portion 22 to a connector 32 inserted partially into head 22. Recess 28 extends around the interior surface of bore 24.

The exterior wall of head portion 22 is encased in a steel shell 34 and a source (not shown) of an inert gas is connected to the connector 32 whereby the gas can flow in the direction of arrows B into the shroud 20. The gas flow is monitored in a conventional manner using pressure monitor 36.

The internal tapered surface 24 of shroud 20 is covered by a cone-shaped adapter 40 whose external surface is coextensive with the internal tapered surface 24. The degree of taper of surface 12 of nozzle 10, of internal surface 24 of shroud 20 and of the internal and external surfaces of adapter 40 are substantially the same so that the lower end 16 of the nozzle is a snug fit inside the upper end of head 22 of the nozzle with the adapter lying between them.

It will be noted that the tapered end portion 16 of the nozzle extends only partially into the tapered head portion of the shroud so that, in the absence of the adapter 40, steel flowing through the nozzle into the shroud, in the direction of arrows A,

would come into direct contact with surface 24 of the shroud below the nozzle.

However, this direct contact is prevented by adapter 40.

The exterior surface of the shroud beneath head 22 is provided with a sheath 38 of thermally-insulating material to help maintain the temperature of steel flowing through this region of the shroud and thereby prevent or discourage the formation of skull.

Adapter 40 has a series of grooves 42 spaced around its outer surface, each groove extending in that exterior surface from a position adjacent the level of recess 28 in the shroud head to the lower end 44 of the adapter. By this means the flow B of inert gas travels from recess 28 into the tubular bore 26 of the shroud.

In Figures 2 and 3 can be seen the effects of the invention. Steel skull 52 has built up on the internal surface of adapter 50 below nozzle 54 (Figure 2) whereas in Figure 3, where the used adapter has been removed from shroud 56, the internal tapered bore 58 of head 60 of the shroud is completely free of any deposits.

In Figures 4 and 5 an adapter 70 of the invention is shown in greater detail. It is cone-shaped, tapering from a wider upper end 72 to a narrower lower end 74.

Grooves 76 spaced around its outer surface extend downwardly from a position some way short of upper end 72 to its lower end 74 to provide the required gas channels.

It will be appreciated, as indicated above, that the grooves 76 may be replaced by or augmented by forming adapter 70 to have a gas-permeable structure.

In practice, the adapter may first be pressed onto the nozzle and the shroud then pressed onto the adapter or, alternatively, the adapter may first be inserted into the shroud and then attached to the nozzle.

After casting the adapter may be removed by hand or mechanically.