CONTINUOUS CASTING OF MOLTEN METAL

Abstract: A tundish sliding gate valve and nozzle change-over assembly for use in a continuous caster is disclosed. The assembly comprises a sliding gate valve (9) for controlling the flow of molten metal from a tundish to a continuous casting mould. The sliding gate valve (9) comprises upper and lower fixed plates (11, 13) and an intermediate sliding plate (15), each of the plates having apertures for molten metal. The assembly further comprises a change-over assembly connected to the lower plate (13) to support a nozzle (7) in the operative position and to move the nozzle (7) into and from the operative position. The change-over assembly comprises a means to bias a nozzle (7) against the sliding gate valve (9) so that there is a fluid tight seal and so that the biasing force is isolated from the upper plate (11) and the sliding plate (15) and therefore does not affect the operation of the sliding gate valve (9).

Description: CONTINUOUS CASTING OF MOLTEN METAL The present invention relates to continuous casting of molten metal and, in particular, to continuous casting of molten steel. In the continuous casting of molten steel the molten steel is usually transferred from a .tundish to a continuous casting mould. Usually, a tundish has an outlet nozzle which is arranged to bridge a gap. typically 50 cm, between the lower wall of the tundish and a continuous casting mould and to extend into the mould and a valve mechanism to control the flow of molten steel through the nozzle. In Europe, the preferred valve mechanism is a stopper rod located in the tundish, and in Australia and Japan the preferred valve mechanism is a sliding gate valve located below the tundish in the gap between the tundish and the mould. The nozzle tends to be susceptible to clogging, usually due to a build up of alumina on the inner wall, and it is necessary to regularly replace the nozzle during continuous casting in order to prevent disruption to continuous casting caused by clogging of the nozzle. International Industrial Engineering SPRL ("HE") has developed technology for changing a nozzle of a stopper rod controlled tundish without the change-over step itself causing disruption to the continuous casting. The basis of the technology is to force the upper surface of the nozzle upwardly against the lower surface of a tundish with sufficient force, typically 3-4 tonnes, to form a fluid tight seal between the surfaces and to slide the nozzle whilst in contact with the lower surface of the tundish into and out of register with the tundish opening. With such an arrangement, a nozzle can be replaced by locating a replacement nozzle adjacent an existing nozzle, lowering the stopper rod to stop the flow of molten metal through the nozzle, sliding the replacement nozzle into the operative position which simultaneously pushes the existing nozzle out of the operative position, and raising the stopper rod to allow molten steel to flow through the nozzle. It has been found that the HE technology can effect nozzle change-over in 2-3 seconds. For relatively slow continuous casting (up to 1.0 m/min) typically used in Europe a stopper rod provides adequate flow control. However, the HE technology is not suitable for use with a sliding gate valve controlled tundish which is required for high casting rates (above 1.0 m/min). In this regard, there are severe space constraints caused by the tundish and the mould and difficulties applying an upward force of 3-4 tonnes to the nozzle to form a fluid type seal with the sliding gate valve without adversely affecting the operation of the sliding gate valve. An object of the present invention is to provide an apparatus for changing over the nozzle of a sliding gate valve controlled tundish for use in continuous casting of molten steel without adversely disrupting the continuous casting. According to the present invention there is provided a tundish sliding gate valve and nozzle change-over assembly for use in transferring molten metal from a tundish to a continuous casting mould, the assembly comprising: (a) a sliding gate valve located below an outlet in the. tundish and operable to control the flow of molten metal from the tundish to the mould; and (b) a change-over assembly for supporting a tundish nozzle in an operative position with respect to the sliding gate valve to allow the transfer of molten metal from the tundish through the sliding gate valve and the nozzle to the mould and for moving the nozzle into and from the operative position, the change-over assembly comprising a means to bias together the sliding gate valve and the nozzle to form a fluid tight seal therebetween without the biasing force provided by the biasing means affecting the operation of the sliding gate valve. It is preferred that the change-over assembly further comprises a means to slide the nozzle in contact with the sliding gate valve to move the nozzle into the operative position and subsequently from the operative position when nozzle replacement is necessary against the resistance to sliding movement provided by the biasing force of the biasing means. It is preferred particularly that the sliding means is arranged to simultaneously move a replacement nozzle into the operative position as the nozzle is moved from the operative position. It is preferred that the sliding gate valve comprises an upper and a lower plate fixed together and a sliding plate located for sliding movement in a gap between the plates, each plate having an opening extending therethrough with the openings in the upper and lower plates being aligned vertically. With such an arrangement, it is preferred that the assembly further comprises a means to bias the upper and lower plates against the sliding plate to form fluid tight seals between the upper plate and the sliding plate and between the lower plate and the sliding plate. It is preferred particularly that the sliding gate valve further comprises a means to slide the sliding plate in the gap to move the opening in the sliding plate progressively into and from alignment with the opening in the upper and lower plates thereby to progressively open and close the flow of molten metal from the tundish to the mould. It is preferred that the biasing force is at least 3 tonnes. It is preferred that the biasing means is connected to the lower plate so that the biasing force is isolated from the upper plate and the sliding plate and therefore does not affect the operation of the sliding gate valve. It is preferred that the biasing means comprises a plurality of spring assemblies arranged in two parallel lines to define a path for moving the nozzle into and from the operative position, each spring assembly comprising a vertically extending spring means connected to the lower plate and an arm connected to the spring means to extend inwardly of the path to contact a downwardly facing surface of the nozzle so that the spring means causes the arm to apply an upwardly directed biasing force against the nozzle. It is particularly preferred that the spring means comprises a compression spring and the arm is pivotally connected to the lower plate at a point intermediate the ends of the arm so that the downwardly directed force of the compression spring translates to the upwardly directed biasing force applied by the arm against the nozzle. According to the present invention there is also provided a continuous casing apparatus for molten metal, comprising: (a) a continuous casting mould; (b) a tundish for retaining a supply of molten metal for continuous casting; (c) a nozzle for transferring molten metal from the tundish to the mould; and (d) the tundish sliding gate valve and nozzle change-over assembly described in the preceding paragraphs. The present invention is described further by way of example with reference to the accompanying drawings in which: Figure 1 is a vertical cross-section through a preferred embodiment of a tundish sliding gate valve and nozzle change-over assembly formed in accordance with the present invention; Figure 2 is a plan view along the line A-A in figure i; Figure 3 is a cross-section along the line C-C in figure 2. With reference to Figure 1, a preferred embodiment of a tundish sliding gate valve and nozzle change-over assembly (the "assembly") in accordance with the present invention is located in a gap G, typically 50 cm, between a lower surface S of a tundish 3 and the upper part of a continuous slab casting mould 5 and supports a nozzle 7 to extend into the mould 5. The assembly comprises a sliding gate valve, generally identified in figures 1 and 3 by the numeral 9. The sliding gate valve 9 comprises an upper plate 11 and a lower plate 13 which are fixed with respect to each other and a sliding plate 15 located for sliding movement in a gap between the upper and lower plates. Each of the upper, lower and sliding plates 11, 13, 15 has an opening therethrough, with the openings in the upper and lower plates 11, 13 being aligned vertically. In the arrangement shown in the figures, the opening in the sliding plate 15 is aligned with the openings in the upper and lower plates 11, 13 so that molten steel can flow from the tundish 3 through the nozzle 7 into the mould 5. The sliding gate valve 9 further comprises means (not shown) to slide the sliding plate 15 in the gap between the upper and lower plates 11, 13 to move the opening in the sliding plate 15 progressively into and from alignment with the openings in the upper and lower plates 11, 13 thereby to progressively open and close the flow of molten metal from the tundish 3 to the mould 5. With reference to Figures 2 and 3, the sliding gate valve 9 is connected by means of tension springs 17 to a quick nozzle change device frame 20 which in turn is bolted to the tundish 3. The springs 17 are connected at one end to the quick nozzle change device frame 20 and are operatively connected at the other end to the lower plate 13 and thereby bias the sliding gate valve 9 upwardly so that the upper surface 19 of the upper plate 11 contacts shoulders 20a of the quick nozzle change device frame 20 and the lower plate 13 is forced against the sliding plate 15 and the sliding plate 15 is forced against the upper plate 11. In this regard, the spring pressure is selected so that a fluid tight seal is formed between the lower surface of the upper plate 11 and the upper surface of the sliding plate 15 and between the lower surface of the sliding plate 15 and the upper surface of the lower plate 13. It can readily be appreciated that the use of tension springs 17 is illustrative of one means to bias together upper, lower and sliding plates 11, 13, 15. It is noted that in the preferred embodiment shown in the figures there is a gap G., between the upper surface 19 of the upper plate 11 and the lower surface 5 of the tundish 3 when the upper surface 19 is biased upwardly against the shoulders 20a and that in use refractory material is packed into the gap G . The assembly further comprises a change-over assembly for supporting the nozzle 7 in the operative position shown in the figures to allow the transfer of molten metal from the tundish 3 to the mould 5 and for moving the nozzle 7 into and from the operative position. The change-over assembly comprises two parallel lines of spring assemblies, generally identified by the numeral 22 in Figure 3, which define a path of movement of the nozzle 7 into and from the operative position. The spring assemblies 22 comprise compression springs 21 which, as can best be seen in Figure 3, are operatively connected at one end to the lower plate 13 of the sliding gate valve 9 and arms 23 which are operatively connected to the other end of the compression springs 21 and are arranged so that the free ends 24 of the arms 23 contact a downwardly facing surface 26 of the nozzle 7 to apply an upward force in the direction of the arrows Z in Figure 3 in response to the biasing force of the springs 21. In this regard, the change-over assembly further comprises pivot points 25 operatively coupled to each arm 23 so that the downward force of the compression springs 21 in the direction of the arrows D in Figure 3 causes the arms 23 to pivot about the pivot points 25 with the result that an upward force is applied to the nozzle 7 in the direction of the arrows Z in Figure 3. It can readily be appreciated that the effect of the arrangement is to bias together- the lower surface of the lower plate 13 and the upper surface of the nozzle 7 as indicated by the numeral 27 in Figure 3. In this regard, the spring pressure is selected so that a fluid tight seal is formed between the surfaces at 27. It can readily be appreciated that the arrangement of the compression springs 21, the arms 23 and the pivot points 25 is illustrative of one means to bias together the lower surface of the lower plate 13 and the upper surface of the nozzle 7. Significantly, it is noted that the connection of the compression springs 21 to the lower plate 13 of the sliding gate valve 9 and the positioning of the arms 23 to force the nozzle 7 upwardly in response to the action of the compression springs 21 is such that the upward force is isolated from the other components of the sliding gate valve 9 and therefore does not affect the operation of the sliding gate valve 9. In this regard, it is noted that, typically, upward forces in the order of 3-4 tonnes are required and if such forces were transferred to the sliding gate valve 9 the efficient operation of the sliding gate valve 9 would be seriously disrupted. The change-over assembly further comprises means (not shown) to slide the upper surface of the nozzle 7 in contact with the lower surface of the lower plate 13 of the sliding gate valve 9 to move the nozzle 7 initially into the operative position and subsequently from the operative position when nozzle replacement is necessary against the resistance to sliding movement provided by the biasing force of the biasing means. Whilst not shown in the figures, in the preferred embodiment, the assembly comprises guides to locate a replacement nozzle adjacent the existing nozzle 7 and a series of rams to move the replacement and existing nozzles to effect nozzle replacement. The nozzle change-over may be effected by closing the sliding gate valve 9 prior to actuating the rams. In such situations, it is preferable to slow the casting rate (typically to 0.6 m/min) to minimise the reduction in the level of molten steel in the mould 5. Alternatively, the nozzle change-over may be effected with the sliding gate valve 9 in the operative position shown in the figures. Many modifications may be made to the preferred embodiment described above without departing from the spirit and scope of the present invention.

Claims: CLAIMS : 1. A tundish sliding gate valve and nozzle change-over assembly for use in transferring molten metal from a tundish to a continuous casting mould, the assembly comprising: (a) a sliding gate valve located below an outlet in the tundish and operable to control the flow of molten metal from the tundish to the mould; and (b) a change-over assembly for supporting a tundish nozzle in an operative position with respect to the sliding gate valve to allow the transfer of molten metal from the tundish through the sliding gate valve and the nozzle to the mould and for moving the nozzle into and from the operative position, the change-over assembly comprising a means to bias together the sliding gate valve and the nozzle to form a fluid tight seal therebetween without the biasing force provided by the biasing means affecting the operation of the sliding gate valve. 2. The assembly defined in claim 1, further comprising a means to slide the nozzle in contact with the sliding gate valve to move the nozzle into the operative position and subsequently from the operative position when nozzle replacement is necessary against the resistance to sliding movement provided by the biasing force of the biasing means. 3. The assembly defined in claim 2, wherein the sliding means is arranged to simultaneously move a replacement nozzle into the operative position as the nozzle is moved from- the operative position. 4. The assembly defined in any one of the preceding claims, wherein the sliding gate valve comprises an upper and a lower plate fixed together and a sliding plate located for sliding movement in a gap between the plates, each plate having an opening extending therethrough with the openings in the upper and lower plates being aligned vertically. 5. The asembly defined in claim 4, further comprising a means to bias the upper and lower plates against the sliding plate to form fluid tight seals between the upper plate and the sliding plate and between the lower plate and the sliding plate. 6. The assembly defined in claim 4 or claim 5, wherein the sliding gate valve further comprises a means to slide the sliding plate in the gap to move the opening in the sliding plate progressively into and from alignment with the opening in the upper and lower plates thereby to progressively open and close the flow of molten metal from the tundish to the mould. 7. The assembly defined in any one of the preceding claims, wherein the biasing force is at least 3 tonnes. 8. The assembly defined in any one of the claims 4 to 6, wherein the biasing means is connected to the lower plate so that the biasing force is isolated from the upper plate and the sliding plate and therefore does not affect the operation of the sliding gate valve. 9. The assembly defined in claim 8, wherein the biasing means comprises a plurality of spring assemblies arranged in two parallel lines to define a path for moving the nozzle into and from the operative position, each spring assembly comprising a vertically extending spring means connected to the lower plate and an arm connected to the spring means to extend inwardly of the path to contact a downwardly facing surface of the nozzle so that the spring means causes the arm to apply an upwardly directed biasing force against the nozzle. 10. The assembly defined in claim 9, wherein the spring means comprises a compression spring and the arm is pivotally connected to the lower plate at a point intermediate the ends of the arm so that the downwardly directed force of the compression spring translates to the upwardly directed biasing force applied by the arm against the nozzle. 11. A continuous casting apparatus for molten metal, comprising: (a) a continuous casting mould; (b) a tundish for retaining a supply of molten metal for continuous casting; (c) a nozzle for transferring molten metal from the tundish to the mould; and (d) the tundish sliding gate valve and nozzle change-over assembly defined in any one of the preceding claims.

Inventors: POLLOCK RUSSEL WILLIAM, POLLOCK, RUSSEL, WILLIAM
Applicants: BROKEN HILL PTY CO LTD, THE BROKEN HILL PROPRIETARY COMPANY LIMITED
Application year: 1991
Main classification: B22D41
IPC codes: B22D11, B22D41