IMPROVEMENTS RELATING TO VESSELS FOR CONTAINING LIQUID

Abstract: A vessel for holding a liquid, such as molten metal, has a valve (3) formed of at least two bodies, each providing abutting and mating surfaces. One of the bodies has a passage (11) leading from the interior of the vessel to its mating surface and the other has a passage (10) from its mating surface to the outside of the body. The second body (5) is rotatable with respect to the first body (4) by drive means positioned outside the vessel so that the passages can be brought into communication and can be disconnected from each other.

Description: IMPROVEMENTS RELATING TO VESSELS FOR CONTAINING LIQUID This invention relates to a vessel for containing liquid and which has a rotary valve for providing communication between the inside and outside of the vessel. A particular, but not sole, application of the invention is to a rotary valve on a vessel for holding molten metal. In continuous casting applications, molten steel flows from a ladle to a tundish and from the tundish to a casting mould. In such an application, during steady state operation, it is important that the flow of molten metal from the ladle to the tundish is essentially the same as from the tundish to the mould. At the present time, the flow of molten metal from a ladle or a tundish is controlled by a metering nozzle or a stopper rod or a sliding gate valve. Each of these control valves has its advantages and its limitations. A metering nozzle is a refractory brick with a specifically sized through orifice which, in use, only throttles the molten metal to the required flow rate at a known working depth of liquid. It is limited in that it tends to freeze at start up, it is prone to wear or blockage, it is totally dependent on the head of liquid above the outlet for control and it is difficult to fit a physical shroud, such as a submerged entry nozzle (SEN) , which prevents contaminating air coming in contact with the discharged liquid metal. A stopper rod mechanism comprises a refractory rod extending into the molten metal and engaging with a seating nozzle in the base of the vessel. It is limited in that such a refractory rod partially immersed in the molten metal can erode or deposits of alumina or solid metal can be deposited upon it. These factors can, on occasion, without notice, rapidly adversely increase or decrease the control gap between the stopper rod and its seating nozzle in™the vessel.- The support arm for the refractory stopper rod must be substantial in order to withstand deformation due to mechanical load arising from the weight of the stopper rod as well as loadings arising from the partial vacuum creating suction forces at the stopper rod/nozzle joint. Thermal deformation of the support arm can occur due to its location directly over the liquid metal in the vessel which also makes control relatively difficult. A stopper has a further drawback in that control of the flow is achieved by vertical movement of the rod to and from the nozzle varying the annulus between the rod and the nozzle, a small movement of the rod of typically less than 20 mm can change the flow from 0 to 100% making the mechanics of control difficult, particularly at low flow rates. At any head of liquid, the annulus between stopper rod and nozzle sets the flow rate whose characteristics are determined by the geometry of the stopper rod tip and the nozzle. Stopper rods require a force to be applied continuously to oppose the gravitational and hydro-dynamic pull on the stopper rod closing the control gap; under manual control this has been found to be very tiring whilst, when controlled automatically, the equipme t must be made to very high standards. It has been found to be very difficult to cast with stopper rods over extended periods, to obtain precise control at start of cast where a smaller than normal flow is required, as well as when casting small sections, such as billets of 150 mm square. ™ ' Sliding gate valves incorporating either linear or rotary motion are mounted to the underside of the outer shell of the vessel. The valve comprises a plate incorporating at least one hole sliding against one static plate or between two static plates also having holes therein. One hole moves across the other(s) creating a variable sized hole for controlling the flow of molten metal. This system requires that the plates are mechanically compressed together to ensure that the molten metal does not enter between the sliding plates. The passages through which the steel flows are often made larger than required to achieve the desired flow and to allow space for possible alumina build up, however, as the steel flows, it creates a partial vacuum in the exit region and this leads to air being sucked in between the plates and this can be detrimental in that the air may oxidise the metal. An expensive inert gas, such as argon, is often introduced to a sliding gate to minimise oxidation as well as to cool the loading mechanism which clamps the plates together. Sliding gates are prone to freezing when throttling to achieve low or at zero flow. Once flow is stopped it is sometimes impossible to re-open such a valve. Sliding gate mechanisms have been found to be difficult to manually control. A rotary valve is known which comprises a lower insert piece mounted in the base of a vessel and having" an outlet bore passing therethrough-from the inside to the outside of the vessel. An elongate shaft located above and pressed down on to the lower insert piece has a lower face which mates with the upper face of the lower insert piece. The shaft is rotatable relative to the insert piece about a generally vertical axis and the shaft has a side opening at its lower end which in at least one rotational position is capable of aligning with the top of the opening through the lower insert piece. When the vessel contains molten metal, the shaft, which is fitted above the insert piece, is in contact with the molten metal and the drive mechanism for the shaft is positioned above, and consequently heated by, the molten metal. Another application is to a vessel containing molten metal in which material is introduced into the molten metal from outside the vessel. In the treatment of liquid steel, for example, material transported by a gas or a gas per se is often added to the steel in order to adjust the composition and/or temperature. Thus, it is desirable for the vessel to have a valve through which the material can be introduced into the vessel. According to the present invention, a vessel for holding a liquid has a valve comprising a first body providing a mating surface against which a mating surface on a second body abuts; said second body being rotatable with respect to the first body; one of the bodies having a- passage therein which extends from said mating surface of the body to the outside of the vessel and the other body having a passage therein extending from the interior of the vessel to said mating "sur ace on the body; and drive means positioned outside the vessel and separated from the interior of the vessel by the wall of the vessel in driving relation with the second body for rotating the second body with respect to the first body to bring said passages in the first and second bodies into and out of communication with each other whilst the said mating surfaces are kept in abutting relation. The passages in the two bodies are such that, in at least one angular position of the second body, there is no communication between the passage in the second body and that in the first body and in at least one angular position there is a maximum degree of communication between the passages. The body which has the passage therein which extends from the interior of the vessel to the surface thereon may r in fact, have a plurality of such passages. At different angular positions, the passages are brought into communication with the passage in the other body. These passages can be used at different times, i.e. where large differences in flow are required or more as standby in case of blockage or severe erosion. The passage within both bodies is conveniently of rectangular cross-section in order to give a linear relationship between the flow and angle of rotation, but they can r of course, be of other cross-sections, if required. The mating surfaces on the two bodies can be held together in abutting relation by applying an external load to the second body or by the hydraulic pressure head of the liquid within the holding vessel acting on a portion of the second body to urge it into abutting relation with the first body. The two bodies need to be held together by an external force whilst initially filling the vessel to ensure that no fluid can penetrate the mating surfaces. The force required may be reduced once the required level has been achieved. The discharge from the valve can be via either the first or the second body. The first and second bodies may be pre-heated, continuously heated, pre-cooled or continuously cooled to suit the requirements of the liquid to be controlled. Typically, if the liquid is of molten metal, such as steel, then both bodies will be of refractory materials. In order to provide lubrication at the mating surfaces, at least one of the bodies should be graphite which can be in the form of alumina graphite, magnesia graphite, zirconia graphite, etc., the other may be made of another material, such as a high grade castable material. Composite materials may be used to minimise wear or reduce friction at the mating surfaces. Either or both bodies may include re- ~ inforcing members which can be made of materials such as steel, metallic or carbon fibres, etc. and may be sized to eliminate any buoyancy effect or give greater strength. In use, part of the mating surfaces of the two bodies may be in intimate contact with the liquid which will determine the amount of heating or cooling required during use. The valve may be used in conjunction with vessels whose attitude to their surroundings may vary from time to time, such as rotatable or tiltable holding vessels. When the valve is positioned in the bottom wall of the vessel, the top of the vessel can be closed off with a close fitting lid, and an inert or non-reacting gas can be introduced into the vessel to pressurise the contents which will have an undisturbed surface. Gaseous or liquid substances can be introduced into or around the mating surface on the two bodies or directly into any pertinent opening so as to minimise contamination by reducing or eliminating ingress of unwanted deleterious material, improving cleanliness as well as possibly improving sealing and lubrication. In the case of liquid steel, argon, nitrogen or carbon dioxide may be used. The mating surfaces on the two bodies are preferably shaped so that, during rotation prior to, or ■ during, use, the rotatable body will "bed" into the fixed body. The cross-sectional shape of the mating surfaces may be spherical, conical, paraboloid, ellipsoid or any cylindrical shape which would minimise work required when aligning the items during assembly. One of the bodies may be constructed to include a consumable/lubricating facing, such as flake graphite. The drive means needed to rotate the rotatable body, usually through 360°, may be operated manually, although any other type of non-manual drive can be employed. When liquid metal enters the vessel, it will normally be chilled by the cooler refractory material. It may be arranged for the first body to project above the refractory lining at the base of the vessel so that the mating surfaces will be above the lining of the vessel, that is, above the initial chill zone. This will minimise problems of frozen metal in the valve when it is operated, especially at start-up. The discharge body of the valve can be shaped to suit the connection of a discharge means, such as a submerged entry nozzle (S.E.N.). Relative rotational movement between the valve and the S.E.N. may be required in use. If the fluid is liquid steel, a material may be added at the valve/S.E.N. joint face that will liquefy to a highly viscous state which would eliminate/minimise ingress of contaminating air whilst also providing a lubricant. As mentioned above, the valve " may be u ' se " d to allow material to enter into the vessel. Furthermore, the valve may be used to discharge liquid from the vessel as well as to allow material to enter into the vessel. In one angular position of the second body, the passages in the first and second bodies communicate with each other to allow the liquid to discharge from the vessel whilst, at another angular position, other passages in the two bodies are in communication to allow material to pass through the valve into the vessel. The fixed body may include a porous element at the mating surface to allow gas through it and into the vessel via a passage in the rotating body. In use, the rotatable body may be rotated to a position as required to give the necessary flow. Alternatively, it may be rotated to that position and then circumferentially oscillated about that position, especially at start-up, in order to prevent freezing at the mating surfaces which are exposed to the liquid metal. In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figures 1 and 3 to 7 are sectional views of a rotary valve fitted in a vessel in accordance with alternative embodiments of the invention; -Figures 2A and 2B are sectional--side views-of ~ * " ~* parts of valves in accordance with alternative embodiments of the- invention; and Figures 8A and 8B are a sectional side view and a part sectional end elevation, respectively, of a still further embodiment of the invention. Referring to Figure 1, a holding vessel for molten metal comprises a metal outer shell 1 lined with refractory material 2. An outlet valve 3 is fitted into the base wall of the vessel. This valve comprises a first body 4 of refractory material fitted around an opening in the shell 1 and within an opening in the refractory material 2. The body 4 defines an opening therethrough and fitted within this opening is a second body 5 of refractory material. The body 5 has a part 6 which projects through the base wall of the vessel to the underside thereof. The body 4 provides a surface 7 against which a mating surface 8 on the body 5 abuts. In the arrangement shown in Figure 1, the mating surfaces are of conical form so that the surface 8 on the second body can mate with, and be supported against, the surface 7 of the first body. The surfaces are such that the body 5 can be rotated about its vertical longitudinal axis relative to the first body while the mating surfaces remain in abutting relation. The surfaces are such that when in use, as wear occurs, the surfaces will bed into each other to maintain or improve the mating relation between them. The body 5 has a passage 1-0- which- xtends- — axially through the part 6 which projects through the base of the vessel and this passage is directed internally to extend to the surface 8 of the body. A further passage 11 formed in the body 4 extends from the interior of the vessel to the surface 7 at a position where the two passages can be aligned to permit flow of molten metal from the interior through the passages to the exterior of the vessel. By rotating the second body with respect to the first body, the communication between the two passages can be varied from zero to cut off the flow of molten metal to maximum communication. In order to prevent/eliminate the ingress of contaminants, such as air, a gas port 12 is provided in the first body 4. This port extends to passage 11 and may, as shown, also extend to the mating surfaces; in use, gas, such as argon, is introduced into the port to flow into the molten metal as well as between the mating surfaces as required. A second gas port 9 may be provided in the first body which is coincident with a through hole 13 in the second body over a small part of its rotation. Reactants, such as gases, may be added to the molten metal through this port. The effort required to rotate the body 5 is imparted to the body via gear wheels 15, 15 and 17 from an electric motor 18 connected to the gear wheel 15 through a coupling 19.- The gear wheels -are mounted -in a housing 20 and the motor 18 is mounted on the outside of the housing. In turn, the housing is supported from the underside of the vessel by a plurality Of studs 21 extending downwardly from the base of the vessel and passing through apertured lugs 22 on the housing. Each stud has a spring 23 around it and engaging with the underside of the vessel and the upper side of the lug 22 and a further spring 24 engaging with the underside of the lug 22 and the upper side of a washer and a nut 25 on the lower end of the stud 21. The gear wheel 17 is fitted around the part 6 of the body 5 and is secured thereto by anchor members 17A. The gear wheel 17 has bearings 32 located within circular coaxial grooves formed in its upper and lower faces and fixed to appropriate locations within the housing 20. The body 5 is urged into its vertical position by forces applied to it by the hydraulic pressure head of the molten metal acting on its upper exposed face in the vessel and from the difference in loading resulting from the interaction of springs 23, 24 acting via lugs 22, the housing 20, the bearings 32 and the gear wheel 17. For normal working, the rating of the spring 23 will be greater than the sum of any upward load applied at the outlet end of the rotating body 5 and the rating of the spring 24. The embodiments shown in Figures 2A and 2B are very similar to that of Figure 1 except that the mating surfaces 34, 35 between the bodies-4 ^and- 5-are of concave/convex form with the body 5 contained within the body 4. In Figure 2A, body 4 provides the concave surface 34 to provide a self-aligning feature whereas, in Figure 2B, the concave surface 35 is on body 5. In the embodiment of the invention shown in Figure 3, the outlet valve 3A fitted into the base wall of the vessel comprises a first annular body 36 of refractory material fixed in the refractory material 2 and providing a convex surface 37. Mounted on this first body there is a second annular body 38 of refractory material. This second body provides a concave surface which abuts the convex surface 37 on the first body 36 and permits the second body 38 to be rotated with respect to the first body. A portion 38A of the second body 38 projects through the base wall of the vessel. A third refractory body 39 has a convex surface 39A which abuts against a concave surface 40 on the second body 38. The third body 39 has a portion 41 which projects through the body 38 to the underside of the vessel. The body 38 has a passsage 42 through it from the interior of the vessel to the surface 40. The body 39 has a passage 43 extending through it from the outer surface 39A to the outer end of the portion 41. The abutting surfaces between the three parts 36, 38 and 39 of the valve are such that the part 38 can be rotated with respect to the two other parts thus connecting the passages 42 and 43 together in a certain range of angular positions of the rotatable part 38 and disconnecting the passages in the other angular postions of the part 38. The part 38 is rotated by a drive mechanism similar to that shown in Figure 1 and coupled to the portion 38A of part 38. The portion 41 of the part 39 is connected to a plate 44 which is secured by bolts to the underside of the housing 20 with a separation to include springs 44A used to load and keep faces 39A and 40 together. In the arrangement shown in Figure 4, the mating surfaces 45, 46 between the bodies 47 and 48 are of part spherical form but do not extend to the interior of the holding vessel. The force urging the body 48 to the fixed body 47 at the mating surfaces is applied by springs 49 which surround the studs 21 projecting from the base of the vessel. The springs act between the nuts 25 on the studs and the underside of the lugs 22 on the housing 20. Figure 5 shows an embodiment of the invention which differs from the other embodiments in that the discharge is from the fixed body rather than the rotatable body, thus allowing attached S.E.N,s to remain stationary. The fixed body 54 provides a mating surface 56 against which a mating surface 57 of the rotatable body 55 abuts. The body 55 has a part 58 which extends through the base of the vessel. A drive mechanism of any convenient form, and which may be as shown in Figure 1, is employed to rotate the body 55 about its vertical axis. The fixed body 54 also has a part 59 which projects through the base of the vessel. A passage 60 in the fixed body 54 extends through the part 59 and terminates on the mating surface 56. A passage 61 in the movable body 55 extends from the upper surface thereof to the mating surface 57. A gas passage 12 extends axially of the body 55 and terminates at the mating surfaces. In use, the drive mechanism rotates the body 55 to connect and disconnect the passages 60 and 61. When the passages are in communication, molten metal can flow from the vessel through the passage 61 and into the passage 60 from which it is discharged from the vessel. A sliding gate valve 62 may be fitted to the outlet passage 60 of the valve. The gate valve is operated to control the flow of liquid from the vessel in addition to the control obtained by the valve. The arrangement shown in Figure 6 is similar to that shown in Figure 5 in that the liquid is discharged through a passage in the fixed refractory body 54. However, the rotatable body 65 has its longitudinal axis 66 inclined to the vertical. The bodies 54 and 65 have co-acting conical surfaces 67 and 68, respectively. A passage 61 in the body 65 has its axis vertical and, in one angular position of the body 65, the axis of the passage is aligned with the vertical axis of the passage 60 in the body 54 to form a linear passage which can be readily cleaned to remove any build-up within the passages. The body 65 is rotated about its longitudinal axis by a drive mechanism 69 which is mechanically coupled to its lower end. Although not shown in Figure 6, the drive mechanism is secured to the base wall of the vessel. The body 65 is urged into its seating with body 54 by springs 66A acting between the vessel shell 1 and drive extension 66B. The arrangement shown in Figure 7 is very similar to that shown in Figure 6 except that provision is made for urging the movable body towards the fixed body from above rather than below the base of the vessel. The movable body 65A has an upward extension 70 which projects out of the top of the vessel and its upper end is connected through a crosshead 71 to the piston rod 72 of a piston-cylinder device 73 which is pivoted to the outside of the shell 1. The piston- cylinder device is used to urge the body 65A downwardly on to the body 54. A valve having a three-piece construction is shown in Figures 8A and 8B. A fixed refractory body 80 is fixed in the base of the vessel and it has a vertical passage 81 extending therethrough. A second refractory body 82 having a vertical passage 83 therethrough is mounted in a cradle 84 with the passage 83 aligned with the passage 81. The cradle is mounted from the underside of the vessel by a plurality of studs 85 and springs * 86" rge the cradle towards the underside of the vessel. A rotatable body 88 is interposed between the fixed bodies 80 and 82. Body 88 has a frusto-conical portion 89 arranged with its axis horizontal and which mates with similar frusto-conical surfaces on the fixed bodies 80 and 82. A passage 90 extends through the portion 89 and, by rotating the body 88 about the longitudinal axis of the cylindrical portion, the passage 90 can be brought into communication with the passages 81 and 83 or it can be disconnected therefrom. The body 88 is rotated by a gear wheel 93 connected to a drive mechanism (not shown) located outside the vessel and in driving relation with one end of the body, the gear wheel being located on an extension 94 to the portion 89 which may only be included on one side of portion 89. In all embodiments of the invention, the degree of communication between the passages in the fixed and rotatable bodies can be varied from zero to maximum communication to thereby control the flow of liquid from the vessel. The mating surfaces remain hot in use so that there is little chance of freezing occurring between these surfaces. The mating surfaces "bed" into each other as wear takes place and the drive means is shielded from the heat of the molten metal in the vessel by the base of the vessel. The valve shown in the figures, other than Figure 7, and described in this specification can, if desired, be employed in combination with a stopper rod which controls a flow to the outlet passage of the valve. For example, with the embodiments of Figures 1, 2A and 2B, the passage 10 in the body extends also to the upper end of the body to form an additional opening (shown in broken lines in Figure 2A, fully in Figure 3) and the stopper rod 91 acts to control the flow of liquid through this additional opening. Where the rotary valve is used for coarse adjustment of the flow from the vessel, the stopper rod can be used for fine adjustment and vice versa. Similarly, a slide gate 62, as shown in Figure 5, may be used. The valve shown in Figure 6 includes a safety stop 92 which can be fixed in position between the refractory material 2 and the fixed body 54. The stop includes a part which overlies the movable body 65 and, if this body should break away from the drive mechanism at its lower end, it rises until it abuts the safety stop, thus limiting the opening through which the molten metal can flow from the vessel. The position and size of the safety stop 92 can be made to suit the valves shown in Figures 1, 2A, 2B, 3, 5 and 6.

Claims: Claims : 1. A vessel for holding a liquid having a valve comprising a first body providing a mating surface against which a mating surface on a second body abuts; said second body being rotatable with respect to the first body; one of the bodies having a passage therein which extends from said mating surface of the body to the outside of the vessel and the other body having a passage therein extending from the interior of the vessel to said mating surface on the body; and drive means positioned outside the vessel and separated from the interior of the vessel by the wall of the vessel in driving relation with the second body for rotating the second body with respect to the first body to bring said passages in the first and second bodies into and out of communication with each other whilst the said mating surfaces are kept in abutting relation. 2. A vessel as claimed in claim 1, in which the mating surfaces are of conical form". 3. A vessel as claimed in claim 1, in which one of the mating surfaces is of convex form and the other is of concave form. 4. A vessel as claimed in any preceding claim, in which the second body has an elongate part which extends through the base wall of the vessel to the outside thereof and the drive means is in driving relation with said elongate part. 5. A vessel as claimed in claim 4, in which the passage extending from the mating surface to the outside of the vessel is provided in the second body and part of the passage extends axially of said elongate part. 6. A vessel as claimed in claim 4, in which the first body also has an elongate part which extends through the base wall of the vessel to the outside thereof and the passage extending from the mating surface to the outside of the vessel is provided in the first body and part of the passage extends axially of said elongate part. 7. A vessel as claimed in claim 6, in which the longitudinal axis of the elongate part of the first body is substantially normal to the shell of the vessel through which it extends and the longitudinal axis of the second body is inclined to this normal. 8. A vessel as claimed in claim 7, in which means are provided outside the vessel for urging the mating surface on the second body into abutting relation with the mating surface on the first body. 9. A vessel as claimed in claim 1, in which the second body is arranged with its longitudinal axis substantially horizontal and its mating surface is urged against the mating surface on the first body by a third body positioned beneath the second body and urged towards the base wall of the vessel, said third body having a mating surface which abuts with the mating surface of the second body. 10. A vessel as claimed in any one of the claims 1 to 9, in which the drive means comprise an electric motor connected to the second member through gearing. 11. A vessel as claimed in claim 10, in which the gearing is mounted in a housing which is supported from the shell of the vessel. 12. A vessel as claimed in any preceding claim, in which each body is made of a refractory material to allow the vessel to contain molten metal. 13. A vessel as claimed in any preceding claim, in which at least one of the bodies includes graphite in its composition. 14. A valve for use with a vessel for holding liquid, said valve comprising a first body adapted to fit in an opening in a wall of the vessel and provide a mating surface against which a mating surface on a second body abuts; said second body being rotatable with respect to the first body; each of the bodies having at least one passage therein and drive means in driving relation with the second body for rotating the second body with respect to the first body to bring the passages in the bodies into and out of communication with each other; means for supporting the drive means from the outside of the vessel and means for urging the mating surfaces into abutting relation.

Inventors: PERRY ROBERT MAIDENS, PRESHAW DAVID ALAN, REYNOLDS TIMOTHY, PERRY, ROBERT, MAIDENS, PRESHAW, DAVID, ALAN, REYNOLDS, TIMOTHY
Applicants: DAVY DISTINGTON LTD, DAVY (DISTINGTON) LIMITED
Application year: 1988
Main classification: B22D41
IPC codes: B22D41