CA1311610C - Outlet and flow control device for metallurgical vessels and castingprocess - Google Patents

Abstract

OUTLET AND FLOW CONTROL DEVICE FOR
METALLURGICAL VESSELS AND CASTING PROCESS
ABSTRACT
A stopper (6), secured to the lower end of a stopper rod, carries a plug (13) having a radial throttle aperture (14) above which a frustoconical shut-off surface (16) is located in the said plug.
A further seal is provided by the annular surface of the plug (13) engaging in the outlet passage.
The stopper (6) may be rotated whereby the direction of flow of the emerging molten metal can be influenced.
This provides flow control and considerable resistance to wear. Moreover, the formation of vortices in the molten metal is largely prevented, thus avoiding the carrying along of slag.

Description

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SPECIFICATION
The invention relates to an outlet and flow control device for metallurgical vessels accommodating molten metals, the device comprising a casting outlet located at the bottom of the vessel and a stopper which cooperates with the casting outlet and is located at the lower end of a vertically mobile rod projecling into the interior of the vessel.
The invention also relates to a casting process.
~ umerous devices are already available for control-ling the discharge and 10w of molten metals from a vessel.
In the case of a very early system for casting steelor the like, use is made of a stopper mechanism in which the outlet aperture in the bottom oE the vessel is adapted to be closed off by a stopper located in the interior of the vessel, the stopper being secured to the lower end of a rod. By means of a system of levers adapted to be actuated from the outside, the stopper may be raised for pouring and may be lowered again to close the outlet. The disadvantage of this system is that flow control is unsatisfactory and considerable wear takes place as a result of the formation of deposits upon the stopper.
It has also already been proposed to use rotating ~; valves by means of which an eccentric inlet duct can be brought into communication with an outlet aperture by a rotating connection, but this requires very accurate machining ~nd grinding of the difficult spherical joint between the rotating and the stationary components. Furthermore, the rn/rm . . -: ' ~"' .
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molten metal tends to solidify in the inlet aperture.
Also known are sliding closures built onto the bottom of the vessel containing the molten metal, but the closure elements, which slide one upon the other under pre-load, are subject to considerable wear since movement of the adjustable parts must take place at the high temperatures of the molten metal. Another disadvantage is the high procure-ment and maintenance costs. Great accuracy in the machining of the slides, which are made of refractory material, is also required in order to achieve reliable sealing.
Another problem arising during the casting of molten metals i9 the need to prevent slag, and other non-metallic inclusions, from being carried along. Many attempts have been made to solve this problem. For example, it is known to use irl tundishes, partition-like displacement elements in order to promote ~eparation of non-metallic inclusions in the molten metal. It has been found, in the meanwhile, that the carrying along of non~metallic inclusions in the discharge area cannot be prevented by suction. Apart from this, building up the dams and weirs after each casting cycle is very costly and time-consuming.
It has also been proposed to keep the slag away from the outlet by injecting an inert gas, but this involves a relatively major technical effort and the results are ques-, ~tionable. It is also known to arrange, concentrically withthe discharge duct, a sensor based upon electromagnetism.
This makes it possible to evaluate the difference in measure-n/ rm , ~. . , ~

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--3--ments of molten metal and slag, so that, when slag is detec-ted, the casting process is halted. It is particularly diEficult to introduce such sensors in areas of wear in the outlet duct. Furthermore, a certain amount of slag has ~o pass through the duct before it can be detected.
There is also the requirement tha~ the molten metal shall, as far as possible, not come into contact with air.
Another problem is that in the case of tundishes comprising one inlet and several outlets, the temperature of the molten metal at different outlets varies and this is undesirable.
Even if there is only one outlet, some of the molten metal flows directly from the inlet to the outlet and will therefore be at a temperature higher than that of metal cir-culating for some time in dead areas.
Separating non-metallic inclusions may also raise problems if the period of residence in the metallurgical vessel is too short, or if the melt is highly turbulent, since such inclusions require a certain amount of time to rise to the surface of the melt.
It is the purpose of the invention to provide an ;outlet and a flow control device, and a casting process, which is of simple and inexpensive design; which can be relied upon to prevent the molten metal from breaking through the seal;
which permits constant, accurate control of the flow of molten metal; which largely prevents vortexing during casting; and " ~ which also prevents slag from being carried along as the metal rn/r~m , .. . . .

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is discharged.
The device according to the invention with which this purpose can be accomplished is characterized in that a stopper comprises, in its closed position, an, at least, approximately cylindrical plug which contains, at its peri-phery, at least, one radial throttle aperture which merges into a longitudinal bore, open at the bottom of the plug, the stopper comprising an expanded head and a first seal that is adapted to be closed by lowering the stopper, being formed between the head and the edge of a casting pipe, and the plug comprising, between its throttle aperture and the first seal located thereabove, an annular part which forms, together with the adjacent part of the bore, a second seal.
An outlet and flow control device of this kind, according to the invention, is comparatively simple to produce and the two consecutively acting seals provide good resis-tance to wear. The satisfactory flow characteristics also facilitate casting and ensure accurate metering of the flow of metal per unit of time during the casting process. There is also little vortexing.
The casting process according to the invention is characterized in that a predominantly horizontal direction of flow is imparted to the molten metal, at least in the area near the oatlet and the rotational position of the, at least approximately, horizontal outlet aperture or apertures may be varied continuously while the metal is being poured.
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influencing and smoothing the flow in the metallurgical vessel, reoxi~izing of the mol~en metal is prevented, and separation of non-metallic inclusions is promoted by smoothing the flow.
The enEorced, largely horizontal direction flow of near the outlet Erom the metallurgical vessel produces a smooth flow with no vortexing and thus no premature carrying along of slag. Since the horizontal casting outlet can be rotated during the casting process, it is possible to adapt flow conditions to the shape of the relevant vessel, to different levels in the bath, to the melting temperature, and to other parameters, from case to case or continuously. As a result of the smooth inlet flow through the pouring distributor, there are no rebound waves of molten metal from the bottom and this avoids flushing of the floating layer of slag preventing reoxidizing. The smooth flow also facilitates and accelerates the ascent of non-metalllc inclusions to the surface of the molten metal.
The drawing illustrates examples of embodiment of ; 20 the invention:
Figure 1 is a cross-section through the device together with the melting vessel;
; Figure 2 is a partial section through the stopper in its closed position projecting into the casting aperture Figure 3 is a section through the stopper in its open position ~; Figure 4 is a cross-section through a variant in the rn/rm ' 31~ 6~L~

direction of arrows IV-IV in Figure 5;
Figure 5 is a longitudinal section through the variant according to Figure 4 with a plurality of throttle apertures, Figure 6 is a cross-section through another variant with staggered throttle apertures producing a twist in the emerging molten metal;
Figure 7 is a longitudinal section through a vessel in the form of an intermediate receptacle with a pouring dis-tributor and a plurality o stoppers;
Figure 8 is a plan view of the intermediate recep-tacle according to Figure 7 showing the different rotational positions of the casting apertures in the plugs in cross-section:
Figure 9 is a cross-section through the intermediate receptacle according to Figure 7 with a sharper downward cross-sectional taper.
According to Figure l, an outlet aperture, with an outlet pipe 3 open at the bottom, is located in bottom 2 of a vessel l for the accommodation of molten metal. Projecting into bore 7 of outlet pipe 3 is a stopper 6 made of a refrac-tory material by means of which the flow of molten metal can be regulated.
A stopper rod 5 projects into neck 10 of the stop-per, the rod permitting the stopper to be moved vertically and to be rotated about its axis. Drive is by means of a mechanism 17 located externally of vessel l. The vertical ::
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drive may consist of a mechanical, motor-driven spindle ~3 or of a hydraulic or pneumatic lifting cylinder. A horizontal arm 23 is connected, above the edge of the vessel to a ver-tical guide element 9. The connections between the upper end of stopper rod 5 and arm 23, and between the lower end of the stopper rod and bell-like head 24 of the stopper, are in the form of ball joints. The stopper rod held in neck 10 has radial play. The rotary drive 17, used to rotate stopper 6 about its vertical axis, is connected to a drive-motor, not shown. This motor may be a servo- or stepping-motor by means of which the different rotational positions of stopper 6 may be programmed and reproduced. The change in the rotational position of the stopper may also be effected by a pneumatic or hydraulic drive.
Stopper 6 comprises a cylindrical plug 13 engaging ln bore 7 of outlet duct 4 and is provided with a horizontal, radial throttle aperture 14 which opens into a passage part 12 ; and merges into outlet duct 4. Since plug 13 is open radially only on one side, a predetermined flow direction is imparted to the emerging molten metal, as shown by line S in Figure 1.
In the area in front of the casting aperture, together with the bell-like stopper head 24, which is larger in diameter than plug 13, the most horizontal flow possible is sought in order to prevent vortexing of the molten metal and the sucking-in of slag from above. The direction of flow may also be varied, stepwise or continuously, during the cas-ting process, by rotating the stopper about its vertical axis.

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Lowering the stopper reduces the Elow cross-section of the throttle aperture, or shuts it off completely.
Stopper linkage 23 may be secured to upper ball joint 11 of stopper rod 5 automatically by means of a clamping device. This means that the stopper rod, which moves with play, and stopper 6, need not be accurately aligned prior to assembly. A neck 10, surrounding stopper rod 5, provides pro-tection from the mol~en metal~ Since the control forces pass through linkage 23 directly into the head of the stopper, the latter is protected from flexural forces arising from mis-alignment. The usual operations needed to align stopper 6 are eliminated and the stopper may also be used automatically even in hot metallurgical vessels. This results in a reduction in vessel turn-around times and thus a reduction in main~enance times.
The design of a variant of stopper 6 in the closed and open position is described hereinafter in conjunction with Figures 2 and 3. The stopper comprises a cylindrical or slightly conical plug projecting into bore 7 of casting pipe 3. Located in plug 13 -- in contrast to the design according to Figure 1 -- are several radial throttle aper~ures 14 dis-tributed uniormly around the periphery of the plug. The upper and lower areas of these apertures are wedge-shaped, whereas the central areas have parallel vertical lateral walls 18. The longitudinal axes of the said throttle apertures extend vertically, i.e. in the direction of movement of the stopper. This provides more advantageous control characteris~

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tics as compared with circular throttle apertures. Throttle apertures 14 open into the central lower open longitudinal bore part 15 of plug 13. Above the apertures, plug 13 merges into a frustoconical expansion 16 which forms a rustoconical shut-off surface having a central angle of between 75 and 105, preferably 90. Together with a fru~toconical counter-bore 18 of the same angle at the upper edge of bore 7, this forms a first annular seal 20. Located between the uppermost edge of throttle apertures 14 and frustoconical shut-off sur-face 16, on plug 13, is a closed cylindrical annular part 19 of width V (Figure 3). When stopper 6 is closed, i.e.
lowered, this annular part 19 provides, together with adjacent cylindrical bore 7, of matching diameter, a second seal 21.
The lowermost part of plug 13 is also in the form of an annular part 22 closed at the casing. Thus plug 13 remains guided in bore 7 even when throttle apertures 14 are fully open.
Since when stopper 6 is in the closed positionaccording to Figure 2, throttle apertures 14 are not in contact with the molten metal, there is no danger of the molten metal freezing in thi~ area. Above frustoconical expansion 16, stopper head 24 is expanded into the Eorm of a bell. This prevents, or greatly reduces, a discharge vortex in the interior of vessel 1, thus preventing slag inclusions ~Erom being carried along. When stopper 6 is closed, the approximately horizontal lower edge 26 of expanded stopper head 24 is relatively far away from horizontal surface 28 of rn/rm ~ .

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casting pipe 3, so that a relatively wide annular space 30 is provided for the molten metal in front of first seal 20. This relatively large mass of molten metal surrounding bore 7 reduces its cooling and counteracts any blockage. In addition to this, the design of stopper heaa 24 imparts an approximate-ly horizontal flow to the incoming molten metal, as indicated in Figure 3 by arrows A. This prevents a vertical vortex from forming in the molten metal, even if the ]evel thereof in the vessel is low. Slag is thus not drawn prematurely into the discharge. Furthermore, this annular space 30 may be flushed with argon or the like which may be fed to stopper 6 by thin supply lines 33 which may also be used to produce a control signal. As soon as the outlet end emerges from the molten metal, there is a drop in the pressure of gas in the supply line. This make~ it possible to shut off the casting flow before any slag is included therein.
Since two seals, acting consecutively, are provided, this reduces the risk of a breakthrough of molten metal, even if surface 16 or counterbore 18 of first seal 20 is damaged by wear.
Second seal 21 may also be kept free of incoming molten metal by injecting gas through passages 34.
Figures 4 and 5 illustrate a variant in which the throttle apertures in stopper 6 consist of a plurality of relatively small radial holes 14' around the periphery, arranged one above the other in axial rows. This provides ~ filtration of the molten metal. If upper holes 14' are : :
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blocked off, stopper 6 is raised so t'nat new, still open holes, are exposed for flow and filtration.
In the variant, according to Figure 6, ~wo throttle apertures 14" are arranged on opposite sides of plug 13 and are staggered in relation to the centreline so that they run approximately tangentially to longitudinal discharge opening 15. This imparts to the emerging molten metal a twist as shown by the arrow~. This prevents the formation of deposits upon the outlet, since lighter inclusions remain in the centre of the vortex.
Figures 7, 8 and 9 illustrate a variant in which vessel 1 is in the form of an intermediate receptacle with a pouring distributor 30 and several stoppers adapted to rotate independently of each other. In the case o such distributing vessels or intermediate receptacles with a plurality of cast-ing outlets, the problem is that the difference in the length of the paths travelled produces different temperatures in the molten metal, and this is undesirable. Immersing the pouring distributor 30 in the molten metal, and inlet aperture 32, below the level of the bath, which is directed, rotatable and predominantly horizontal, causes the molten metal to emerge appro~imately horizontally and produces a smooth flow approxi-mately in the direction of path T in Figures 7, ~ and 9. This flow is dependent upon inflow angle ~ of pouring distributor 30 and upon outflow angle ~ of stopper 6. The flow vectors of ~; the inlet and outlet produce a torque in the molten metal, as a result of which individual elements of the melt descend, : ~:
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from the hot layer near the surface, spirally to the colder layer near the bottom. The purpose of the spiral flow is to achieve paths of the same length for all throttle apertures 14 in order to avoid temperature differences. Flow paths T, shown diagrammatically in Figures 7, 8 and 9 cannot actually be maintained in practice, but since the part flows in the metal are thoroughly mixed, temperature distribution 'is satis-factory and dead areas are avoided. Figures 7 and 8 show only one half of such an intermediate receptacle.
The period of residence of the molten metal in vessel 1 may be influenced by the choice of angles~ and ~ .
The smooth flow provides an opportunity for non-metallic inclusions to ascend rapidly, by their own buoyancy, to the surface and into the layer of slag floating thereupon, so that they are not carried along by turbulence into the outlet duct. This also applies to slag. The substantially horizon-tal flow obtaining in the casting area of metallurgical vessel 1 eliminates vortices and premature carrying along of slag, and this improves the quality of the end proauct, reduces ?
scrap, and increases production.
Figure 9 shows a cross-section through the interme-diate receptacle from which it may be seen that the walls slope sharply, thus producing a preferred flow path.
Individual stoppers 6 according to Figures 7 to 9 correspond to those according to Figure 1 and may thus be raised, lowered and rotated as explained in connection with Figure 1. Individual or joint control may be effected by a :
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predetermined programme as a function of casting parameters such as temperature, throughput and analysis. Data-processing units may also be used for this purpose. Pouring distributor 30 may also be included in such a programmed control, i.e.
angle ~ and/or the height thereof may be varied. The throttle cross-sections in stopper 6 may also be adjusted individually by raising or lowering.

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Claims (21)

1. An outlet valve structure to control flow of a metallic melt, adapted for installation in the bottom (2) of a vessel (1) containing the melt, said valve structure comprising:
an essentially vertically positioned outlet pipe (3) having a vertical bore (7) therethrough;
a first sealing part (18) formed at an upper end portion of the vertical bore (7);
stopper means (6) comprising a plug (13), said plug (13) being formed with a second sealing part (16) dimensioned and shaped to fit against said first sealing part (18), said first and second sealing parts forming a first seal (20) for the melt;
a central longitudinal discharge opening (15) formed in said plug (13), said opening (15) having a lower open end discharging into said vertical bore (7);
at least one radially directed aperture (14) communicating with said discharge opening (15);
an operating rod (5) extending in vertical direction within, and outside of said vessel (1);
a hollow sleeve or stem (10) extending from said stopper means (6) and surrounding said operating rod, with radial play or clearance;
coupling link means (11) permitting limited relative deflection in a vertical and a horizontal plane located between the stopper means (6) and at least one end of the ycc/kb rod (5) to permit limited movement of the plug (13) with respect to the link means (11) and self alignment of said first seal (20); and an arm means (23) coupled to the upper end of the rod (5), said arm means being positioned outside of the upper portion of the vessel, said arm means selectively transferring vertical reciprocating and rotational movement to said rod to control, respectively and selectively, vertical reciprocation of the plug, (13) between the lowered position on said first seal (20) and a raised open position permitting communication between the interior of said melt containing vessel (1) and said radially directed aperture (14) and hence said discharge opening (15) and selective orientation of the radial position of said aperture with respect to said vessel.

2. The structure of claim 1 wherein said first seal comprises a frustoconical shut-off surface (16) formed on the plug (13) and a matching conical surface (18) formed at the upper end of the bore (7).

3. The structure of claim 1, wherein said link means (11) comprises at least one ball joint located at one of the ends of said operating rod (5), said at least one ball joint coupling the operating rod (5) with at least one of:
said stopper means (6) and said arm means (23).

4. The structure of claim 1, further including a second seal (21), said second seal comprising an annular cylindrical part (19) having a closed outer surface, and extending from said plug (13) into said vertical bore (7) and defining, between an uppermost portion of said radially directed aperture (14) and said first seal (20) a cylindrical plug second seal (21);
said first seal (20) opening first upon raising of said plug by said operating rod (5) to expose said radially directed aperture (14) to the interior of the vessel and hence permit melt to flow therethrough and through said longitudinal opening (15) and second seal opening subsequently to opening of said first seal.

5. The structure of claim 1, wherein said plug (13) is formed with a single, essentially horizontally directed aperture (14).

6. The structure of claim 1, wherein said at least one aperture comprises a plurality of substantially horizontally extending apertures (14') radially distributed around the periphery thereof.

7. The structure of claim 1, wherein said at least one aperture comprises a plurality of apertures (14') staggered axially along the length of the plug and communicating with said longitudinal discharge opening.

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8. The structure of claim 1, wherein said at least one aperture (14") extends tangentially from the outside of said plug (13) to said longitudinal discharge opening (15), terminating tangentially therein.

9. The structure of claim 1, wherein said at least one aperture (14) in cross-section, is formed with two essentially vertically extending side surfaces (35), and at least one end surface which is wedge, or roof-shaped, whereby said opening will be essentially, in cross-section, diamond shaped with essentially vertical sides (35).

10. The structure of claim 1, wherein said stopper means (6) is formed with an approximately bell or mushroom shaped lateral extension above the second sealing part (16).

11. The structure of claim 4, further including at least one gas passage (34) formed in the outlet pipe (3) and terminating in the vicinity of the second seal (21).

12. The structure of claim 1, further including drive means (M;17) coupled to said arm means (23) for transferring rotary movement to said stopper means (6).

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13. The structure of claim 1, wherein said vessel (1) comprises an intermediate receptacle;
a melt pouring distributor (30) located in said intermediate receptacle, said melt pouring distributor being formed with a plurality of essentially horizontally directed outlet apertures (32);
and drive means (8, 25', 36) are provided for, selectively, controlling at least one of: vertical position; horizontal position; rotary position;
of said pouring distributor (30) within the intermediate receptacle.

14. The structure of claim 1, wherein said stopper means (6) is formed with at least one through-passage (33) terminating in the vicinity of said second sealing part for injection of gas or powder therethrough.

15. An outlet valve structure for installation in the bottom (2) of a melt containing vessel (1) comprising an essentially vertical outlet pipe (3) having a vertical bore (7) therethrough;
a first sealing part (18) formed at the upper end of the vertical bore (7);
stopper means (6) comprising a plug (13), a second sealing part (16) arranged on said plug, dimensioned and shaped to fit against said first sealing part (18) for forming a first seal (20) for molten metal;

ycc/kb said plug (13) being formed with an essential longitudinal discharge opening (15), said opening having a lower end discharging into said vertical bore (7);
at least one essentially radially directed aperture (14) communicating with said discharge opening;
said plug (13) further comprising a cylindrical annular part (19) having a closed outer surface, and located between said at least one aperture (14) and said second sealing part (16), said cylindrical annular part (19) having an axial portion of predetermined dimension (V) which fits within the vertical bore (7) of said outer pipe (3) to form therewith a second seal (21);
an operating rod (5) extending in a vertical direction through said vessel and towards the outside thereof, said vertical rod being coupled to said stopper means (6);
a hollow sleeve or stem extending from said stopper means (6) and surrounding said rod, with radial play or clearance;
and a loose coupling means (11) permitting limited relative deflection in a vertical and horizontal plane between said rod (5) and said stopper means (6) coupling said stopper means and said rod, said rod controlling at least vertical reciprocation of the plug (13) between a lowered, closed position and a raised, open position, so that, upon movement between said open and closed positions, the first and second seals will consecutively ycc/kb effect sealing between the interior of said vessel and the outlet pipe.

16. The structure of claim 15, wherein said coupling means comprises a ball joint (11), the loose coupling protecting said plug (13) against flexure forces.

17. A process for selectively withdrawing, or inhibiting withdrawal of molten metal, forming a melt, from a vessel, wherein the vessel includes:
an outlet pipe having a vertical downwardly directed bore through which said melt can flow through gravity, and a first sealing part formed at an upper end of the vertical bore;
and wherein stopper means are provided, comprising a plug, the plug having a second sealing part arranged thereon, dimensioned and shaped to fit against said first sealing part to form a first seal for the molten metal;
said plug being formed with a central longitudinal discharge opening having a lower open end discharging into said vertical bore, and an essentially radially directed aperture means connecting said discharge opening with the interior of the vessel, said process comprising the steps of imparting to the molten metal a predominately horizontal direction of flow in the area near said outlet pipe, and varying the angular orientation of said flow with respect to said vessel by rotating the essentially ycc/kb radially directed aperture means within said plug, during flow of the melt through said aperture means, said opening, and said vertical bore.

18. The process of claim 17, including the step of introducing the molten metal into the vessel in an essentially horizontal direction but spaced vertically from said aperture means.

19. The process of claim 18, including the step or steps of varying continuously as a function of at least one predetermined command value, or a predetermined program at least one of: the vertical distance between the inflow of the melt and said aperture; the angle (.beta.) of inflow with respect to the vessel; the angle (.alpha.) of the outlet aperture means with respect to the vessel.

20. The process of claim 17, including the step of controlling the quantity per unit time of outflow of melt from said vessel through said aperture means and said discharge opening into said bore of said outlet pipe.

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