FLOW CONTROL DEVICE

Abstract: A flow control device for the outlet (14) of a molten metal handling vessel (10) is provided for use towards the end of the pouring of molten metal through the outlet. The device (22) has a head portion (25) and a tail portion (26) with flow channels (25c) defined between the head and tail portions to reduce vortex effects in the molten metal (20), the tail portion (26) being contoured to fit into a correspondingly contoured entrance (19) to the outlet (14) with the flow channels (25c) leading into the outlet (14) and the device (22) being attached to a refractory positioning means (23) whereby it can be fitted into the outlet (14) during flow of the molten metal (20) through the outlet.

Description: FLOW CONTROL DEVICE This invention relates to a flow control device for the outlet of a molten metal handling vessel, e.g. a ladle or a tundish. It is particularly concerned to provide a device which limits the formation of vortexing effects during the discharge of the molten metal, e.g. molten steel from a tundish. For convenience the invention will be further described below with particular reference to the discharge of molten steel from a tundish although it will be appreciated that its application is not so limited. As steel empties through the discharge outlet in a tundish a vortex effect can commonly occur around the outlet. This is undesirable as it can cause the entrainment of slag or other impurities into the steel passing from the tundish. There has been a number of prior proposals to eliminate or reduce this unwanted vortex effect. For example international application PCT/ CA93/ 00529 describes a flow control device comprising a baffle plate and a plurality of dividers radially disposed to space the plate above an outlet nozzle of, e.g., a tundish. The radial dividers cause the steel to approach the nozzle outlet in several convergent radial streams whereby vortex entrainment can be eliminated. One problem with most prior proposals to reduce vortexing is that the proposed device has to be positioned in the, e.g., tundish prior to filling with molten steel and must then last for the life of the sequence of casting being employed. Even though it is possible to manufacture devices with such a life span, they are subject to considerable build up of oxides created by the complex flow with the result that the outlet flow area can be restricted, which can cause unwanted problems with the casting. The present invention aims to provide a flow control device that overcomes these deficiencies of the prior art. Accordingly in one aspect the invention provides a flow control device for the outlet of a molten metal handling vessel, the device having a head portion and a tail portion and flow channels defined between the head and tail portions to reduce vortex effects in the molten metal, the tail portion being contoured to fit into a correspondingly contoured entrance to the outlet with the flow channels leading into the outlet and the device being attached to a refractory positioning means whereby it can be fitted in the outlet during flow of the molten metal through the outlet. In another aspect the invention provides a method of controlling the flow of molten metal through an outlet from a vessel in which a flow control device having a head portion and a tail portion is positioned so that its tail portion fits into a correspondingly contoured entrance to the outlet whereby flow channels defined between the head and tail portions lead into the outlet, the fitting being effected during flow of the molten metal through the outlet by a refractory positioning means attached to the device. The refractory positioning means may be, for example, a refractory arm or shaft, e.g. a tube, which may be disposable, attached at one end to the flow control device, usually to its head and of sufficient length to be manoeuvred from above the surface of the molten metal, preferably from outside the vessel. The shaft may, if desired, be integrally formed with the head of the device. Most conveniently the flow control device is positioned in the outlet towards the end of the pouring of the metal through the outlet, whereby the aforesaid disadvantages of oxide build up may be avoided. Thus it may be inserted towards the end of the last "heat" being discharged in a sequence from a tundish. The device may be manually positioned in the outlet using the positioning means or a mechanical setting may be employed, if desired. The flow control device may be made from any refractory composition capable of withstanding the temperature and corrosive effects of the molten metal for at least short periods. Thus it may be disposable at the end of the pouring sequence from the vessel, i.e. dispensed with after a single use. Alternatively, if desired, it may be a recyclable unit manufactured, e.g. from isostatically pressed alumina graphite. A recyclable device should be removed from the vessel outlet immediately after the end of the pour, e.g. immediately after closure of a slide gate valve below the outlet. The contoured entrance to the outlet may be a contoured well plate or inner nozzle block which may also be made of any suitable refractory material and, if necessary, may be rebuilt after closure of the outlet at the end of the sequence. The flow control device may be of any suitable design having a head and tail portion as previously described. One suitable type is as disclosed in the aforementioned PCT/CA93/00529. Thus the head portion may comprise a baffle plate disposed in use above the nozzle outlet and the tail portion may comprise radial dividers disposed about the longitudinal axis of the outlet and supporting the baffle so as to space it from the outlet opening. Preferably the dividers define radial flow paths having a combined cross-sectional area at least as great as the cross-sectional area for flow through the nozzle. The dividers obstruct rotational forces in the molten metal so that it flows radially and horizontally towards the nozzle outlet where the flow paths meet. The metal then passes axially through the outlet. As indicated above, the invention is particularly useful in tundishes, particularly tundishes using slide gate control of the outlet. At the end of a casting sequence in conventional practice the quantity of steel left in the tundish after closure of the outlet is very variable as the main aim is to prevent slag passing through the outlet as this can cause severe quality problems. Conventionally one of two operations is frequently used at the end of the casting sequence, e.g. using a 70 ton twin strand tundish (which would have an operating depth of about 60 inches.) a) The tundish would be drained until the scale weight on tundish weighing scales shows a certain value. For safety, this may yield a skull in the range.30-50 ,000 lbs. b) A slag-floating device may be inserted at ladle shut- off and this is monitored to 14" or 15" height from the top of the tundish inner nozzle at which point the gate is shut. Typical skull weight is in the range of 15-20,000 lbs. The invention enables later shut off of the outlet to be employed. Yield improvement is improved even further when the tundish is equipped with a false bottom, thus increasing the height of the well area. In such instances skull weight may be reduced to about 3,000 to 5,000 lbs with no slag carry over. The device may be used on its own or in conjunction with tundish weighing scales or a slag-floating device. With such combined use, success rates for the procedure can approach or even reach 100%. Specific embodiments of the invention are now described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a section through a portion of a tundish in the region of its outlet at the beginning of pouring the last batch of steel of a sequence of pours; and Figure 2 is a similar view to Figure 1 at the end of pouring of that batch. In Figure 1 a tundish 10 has a base 11, sidewails 12 and a cover 13. An outlet 14 is provided through base 11 in a recessed region 11A defined by a higher false bottom region 1 IB of the base. Outlet 14 is defined by a conventional well nozzle 16 co¬ operating with a slide gate valve 17 to define an outlet passageway 18. A contoured well top plate 19 is fitted to overlie the tops of well block 15 and inner nozzle 16. The tundish contains molten steel 20 covered by a slag layer 21. This steel is the last batch of a sequence of "heats" passed through the tundish. The slide gate valve 17 is open and the steel is pouring out through passageway 18 in outlet 14. As the pouring continues, a flow control device 22 of the invention is positioned above the outlet 14 on a disposable attachment arm 23 through an aperture 24 in cover 13. Device 22 has a head portion 25 with a lower surface 25A of castellated outline and a tail portion 26 comprising four fins 26A contoured to converge away from head 25. The contouring of tail 26A corresponds to that of well top plate 19 into which the tail can be closely fitted - see Figure 2. In Figure 2, the flow control device 22 has been fitted into the entrance to outlet 14 defined by the contoured well top plate 19. The castellations of surface 25A of the device 22 now define gaps 25C through which the steel can continue to flow through the outlet as the slide gate valve 17 is still open. The slide gate valve 17 can be maintained open until the level of steel is very low because of the inhibition of vortex effects by device 22. Moreover, as can be seen in Figure 2, the steel remains only in the recessed region 11A of the base of the tundish before the valve 17 has to be closed. Thus on closing valve 17 at the end of the casting sequence, the amount of wasted steel not poured from the tundish is significantly reduced.

Claims: CLAIMS 1. A flow control device for the outlet of a molten metal handling vessel (10), characterised in that the device (22) has a head portion (25) and a tail portion (26) and flow channels (25c) defined between the head and tail portions to reduce vortex effects in the molten metal (20), the tail portion (26) being contoured to fit into a correspondingly contoured entrance (19) to the outlet (14) with the flow channels (25c) leading into the outlet (14) and the device (22) being attached to a refractory positioning means (23) whereby it can be fitted into the outlet (14) during flow of the molten metal (20) through the outlet (14). 2. A flow control device according to Claim 1, characterised in that it includes the refractory positioning means (23) as a disposable shaft. 3. A flow control device according to Claim 1 or 2, characterised in that the positioning means is a refractory tube (23) of sufficient length to enable the device (22) to be manoeuvred into the outlet (14) from outside the vessel (10). 4. A flow control device according to Claim 1 or 3, characterised in that the device (22) is a recyclable unit. 5. A flow control device according to Claim 4, characterised in that the device (22) is made of isostatically pressed alumina graphite. 6. A flow control device according to any preceding claim, characterised in that the head portion (25) has a lower surface (25 A) of castellated outline and the tail portion has fins (26A) contoured to converge away from the head (25). 7. A flow control device according to any one of Claims 1 to 5, characterised in that the head portion (25) comprises a baffle plate for disposition in use above the outlet (14) and the tail portion (26) comprises radial dividers disposed in use about the longitudinal axis of the outlet to support the baffle and space it from the outlet opening. 8. A method of controlling the flow of molten metal through an outlet from a vessel (10), characterised in that a flow control device (22) having a head portion (25) and a tail portion (26) is positioned so that its tail portion (26) fits into a correspondingly contoured entrance (19) to the outlet (14) whereby flow channels (25c) defined between the head and tail portions lead into the outlet (14), the fitting being effected during flow of the molten metal (20) through the outlet (14) by a refractory positioning means (23) attached to the device (22). 9. A method according to Claim 8, characterised in that the device (22) is positioned to fit into the entrance (19) to the outlet (14) towards the end of the last of a sequence of molten metal discharges from a tundish. 10. A method according to Claim 8 or 9, characterised in that the device (22) is manually positioned to fit into the entrance (19) to the outlet (14). 11. A method according to Claim 8, 9 or 10, characterised in that the device (22) is dispensed with after a single use. 12. A method according to Claim 8, 9 or 10, characterised in that the device is a recyclable unit and is removed from the outlet (14) immediately after the outlet (14) is closed to end the flow of molten metal (20) therethrough. 13. A method according to any one of Claims 8 to 12, characterised in that the head portion (25) of the device (22) comprises a baffle plate which is positioned above the outlet (14) and the tail portion (26) comprises radial dividers which are positioned about the longitudinal axis of the outlet (14) and support the baffle to space it from the outlet opening. 14. A method according to any one of Claims 8 to 13, characterised in that the vessel is a tundish and the device is used in conjunction with tundish weighing scales or a slag-floating device.

Inventors: DAINTON ALBERT EDWARD, DAINTON, ALBERT, EDWARD
Applicants: DAINTON ALBERT EDWARD, FOSECO INT, DAINTON, ALBERT, EDWARD, FOSECO INTERNATIONAL LIMITED
Application year: 1995
Main classification: B22D43
IPC codes: B22D11, B22D41, B22D43