Controlling teeming streams

Abstract: Apparatus for constraining the flow of molten metal (3) from a tundish (4) to a mould (8) along the inner periphery of a tube (6) mounted between them. A vertically movable stopper rod (1) is seated at its lower end in a nozzle (5) at the entrance to the tube (6) the end being so designed as to cause an annular discharge of metal (3) into the tube (6) upon the stopper rod (1) lifting from its seating, gas being injected through the stopper whereby to generate a gaseous void within the interior of the tube (6) to promote the maintenance of the metal flow path of along the length of the inner periphery of the tube.

Description: This invention relates to the control of teeming streams, that is, the flow of molten metal from one receptacle to another, and particularly relates to controlling the flow of pattern within a tubular member mounted between the receptacles. United States specification 3954134 shows the teeming of molten metal from an upper to a lower receptacle through a tubular member with control through a stopper rod. Gas is injected into the teeming metal through the end of the stopper rod. However, in that invention the gas becomes intimately mixed with the molten metal in bubbles of less than 5 mm in size. In the current invention the molten metal flows through the tubular member in an annular flow, that is with a gas filled void in the centre of the tube and the metal flowing down the walls of the tube. It is an object of this invention to constrain the flow pattern in such a manner as, for example, to increase the surface to volume ratio to facilitate the removal of heat from the molten metal, and/or to influence or control the flow pattern of the molten metal issuing from the tubular member into the other receptacle. The invention provides apparatus for discharging molten metal from an upper to a lower receptacle through a tubular member, the flow from the receptacle being controlled by a stopper rod seating in a nozzle wherein the molten metal is induced to flow in an annular manner though a least the part of the tubular member proximate the upper receptacle by the shape of the end of the stopper rod and by the injection of gas under pressure through the end of the stopper rod into the centre of the annulus. The tubular member maybe adapted to remove heat from the molten metal passing therethrough and may do so by virtue of being an inwardly downward tapered water cooled tube. The tubular member may have an internal coating of a low conductivity refractory material. The inner surface of the tubular member may be profiled to promote turbulent peripheral flow or turbulent peripheral flow may be promoted in the tubular member by electro-magnetic force. Preferably the end of the stopper rod is formed with a dependent tip which extends into the nozzle and may have a circular or ovaloid cross section and may be necked to promote divergent flow. Arcuate fins may be provided adjacent the end of the stopper rod to promote a swirl in the discharging molten metal. As mentioned, this invention may be utilised to facilitate the removal of heat from the molten metal stream; this purpose may be enhanced by the provision of a definitive heat exchanger around the flow path through the tubular member - this might be in the form of a water cooled copper tube or e.g. of the type described and illustrated in our UK Patent No.2117687. In order that the invention may be fully understood some embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 illustrates the concept of this invention as applied to discharge of molten metal from a tundish to a mould in a continuous casting installation; Figure 2 illustrates a modification of Figure 1; Figures 3(a) to 3(c) illustrate different configurations of the stopper rod ends; Figure 4 graphically illustrates the balance to be achieved between the molten metal flow and the gas flow to ensure a stable peripheral flow through the pour tube; and Figure 5 graphically illustrates the manner in which stable peripheral flow can be recognised. Referring now to Figure 1, a stopper rod 1 with a shaped tip or end 2 is vertically movable to control the flow rate of molten metal 3 from a tundish 4 through a nozzle 5. An open-ended submerged entry 'pour' tube 6 depends from the nozzle area, feeding the molten stream to a liquid pool 7 within a continuous casting mould 8. Extending axially of the stopper rod 1 is a tube 9 through which an inert gas e.g. argon, is passed under pressure, creating a gaseous void within the tube, this pressure being measured at a tapping position 10 and the gas flow metered at 11. Both the flow rate and the pressure are controlled within defined limit whereby to promote a peripheral flow pattern of molten steel within the nozzle/submerged entry pour tube as depicted at 12 - additionally the gas flow rate must be controlled to avoid detrimental effects of excessive gas volume and flow patterns within the mould. Referring now to Figure 2 a similar arrangement is shown save for the utilisation of heat exchanger 13 intermediate the tundish and the pour tube - which latter component is now shown with a closed end and exit ports 14. The heat exchanger comprises a water cooled copper tube tapered, in the example shown, such that the smaller diameter is at the lower end, by this means any solidified shell formed within it will tend to move downwardly under gravity so as to maintain close contact with the inner wall and enhance heat transfer. The stopper rod end, by which an 'annular' discharge of molten metal is initially promoted, may, for example, be formed as shown in Figures 3(a) to 3(c). The 'tips' may either be integrally formed with the refractory stopper body or connected as separate items. In Figure 3(a) the tip is parallel whereas in Figure 3(b) it is 'necked'. In both instances essentially parallel flow is engendered; the tips may be of circular or an ovaloid cross-section. In Figure 3(c) in contrast a swirling flow path is promoted by the provision of arcuate fins 15. As mentioned, the gas flow rate through the system is closely monitored and the importance of this can be seen with reference to Figure 4 where, in particular, the achievement of a stable peripheral flow pattern is clearly dependent on the balance of molten metal and gas flow rates, lying as it does between conditions of uneven peripheral flow at low liquid and gas flow rates and non-peripheral flow at very high liquid throughput rates. It has been found in fact that the achievement of the required pattern of stable peripheral flow is characterised by a step change in the pressure within the supply line - see Figure 5 - this phenomenon thus being used as a reference to indicate that stable peripheral flow has been established. Although this invention has been described with reference to the particular embodiments illustrated it is to be understood that various changes may readily be made. For example, a smooth walled pour tube has been shown but this could be profiled, roughened or formed with protrusions, e.g. by sleeving, to enhance turbulence within the peripheral flow. Similar provision could be made within the separate heat exchanger shown in Figure 2 or indeed in the nozzle. This high degree of turbulence, together with high velocity, are desirable to maximise heat transfer coefficients and minimise shell formation and build-up which might lead to blockages. Alternatively, or additionally, electromagnetic means might be utilised to promote turbulent conditions. Additionally, shell formation may be reduced by the application of a low conductivity refractory coating material to the inner surfaces. Moreover it is not essential for the gas line to extend along the axis of the stopper rod, it may conveniently extend through the rod parallel to its axis emerging at the centre of the stopper tip or indeed in a plurality of orifices at the tip, e.g. for inducing peripheral flow.

Claims: Apparatus for discharging molten metal from an upper (4) to a lower receptacle (8) through a tubular member (6), the flow from the receptacle being controlled by a stopper rod (1) seating in a nozzle (5),the molten metal being induced to flow in an annular manner though at least the part of the tubular member proximate the upper receptacle, characterised in that the molten metal is induced to flow in the annular manner by the shape of the end (2) of the stopper rod and by the injection of gas under pressure through the end of the stopper rod into the centre of the annulus (12). Apparatus as claimed in claim 1 characterised in that the tubular member is adapted to remove heat (13) from the molten metal passing therethrough. Apparatus as claimed in claim 2 characterised in that the tubular member is so adapted by virtue of being an inwardly downward tapered water cooled tube. Apparatus as claimed in any preceding claim characterised in that the tubular member has an internal coating of a low conductivity refractory material. Apparatus as claimed in any preceding claim characterised in that the inner surface of the tubular member is profiled to promote turbulent peripheral flow. Apparatus as claimed in any one of claims 1-4 characterised in that turbulent peripheral flow is promoted in the tubular member by electro-magnetic force. Apparatus as claimed in any preceeding claim characterised in that the end of the stopper rod is formed with a dependent tip (2) which extends into the nozzle. Apparatus according to claim 9 characterised in that the tip is of circular or ovaloid cross section. Apparatus according to claim 7 of 8 characterised in that the tip is necked to promote a divergent flow. Apparatus according to any one of the preceeding claims characterised in that arcuate fins (15) are provided adjacent the end of the stopper rod to promote swirl in the discharging molten metal.

Inventors: SCHOLES ALAN, WIDDOWSON ROY, SCHOLES, ALAN, WIDDOWSON, ROY
Applicants: BRITISH STEEL PLC
Application year: 1990
Main classification: G05D9
IPC codes: B22D41