CA2216577A1 - Limiting ingress of gas to continuous caster - Google Patents

Abstract

Ingress of gas such as air through the joint of a pour tube (8) and tube holder (7) of a continuous caster, or a similar interface of a slide gate valve (5, 6, 7), is prevented or inhibited by passing an inert gas into a channel (16, 21, 22, 27, 64) around the orifice and at the interface through which air is likely to enter, the gas is evenly distributed within the channel over the entire configuration of a porous refractory insert (17, 23, 24, 28, 65) which contacts the interface in the channel; the porous refractory insert assures evendistribution of the gas to the desired location in the interface, thus providinga positive pressure of inert gas to inhibit the entry of ambient gas.

Description

CA 02216~77 1997-10-10 W O 97/04901 PCT~US96/11471 --LIMITING INGRESS OF GAS TO CONTINUOUS CASTER--Technical Field This invention relates to valves used in the continuous casting of metal, especially steel. In particular, it relates to delivery systems for inert yas to the mating surfaces of sliding gate valves and stopper rod flow control valves or systems to effect a seal by generating a positive pressure of gas between the mating surfaces to inhibit the entry of ambient gases such as air which could degrade the quality of the metal being cast and to help minimize the entry of molten metal to the interface. The invention involves the use of a porous refractory insert in a channel around or partially around the valve opening, occupying only part of the channel so that the gas can be evenly distributed in the circumferential recess ~ehind (upstream from) the porous refractory. The porous refractory insert evenly distributes the flow of inert gas between the contacting surfaces which are moved in contact with each other such as the contacting surfaces of the slide plate and the tube holder and/or the slide plate and the top plate, the tube holder and the nozzle, and other similar interfaced surfaces which slide or move with respect to each other.
A similar construction is used for the prevention of the ingress of air and other gases such as sealing gas ~ into contact with molten metal at the top of a pouring tube where it is fixed to a tube holder. The ~ 35 invention is useful in any substantially flat interface, made by parts movable or stationary, which form a conduit for liquid metal near the input of a CA 02216~77 1997-10-10 W O 97/04901 PCT~US96/11471 continuous caster.
'R~ uud of the Invention In the continuous casting of metal, and steel in particular, molten metal is poured from a ladle o~
1tllnc~ h through a valve, commonly a slide valve, through a refractory nozzle and into the tube which is partially immersed in the incipient continuous ingot in order to insulate the molten steel from air and other gases. The tube is fixed to a tube holder, which contacts the under side of a slide valve. The presen~ invention addresses the control of the ingress of undesirable gases (the aspiration of air) through the joint between the tube and the tube holder, and also through the substantially flat interfaces of the slide valves. Sliding gate valves and stopper-rod ~alves with on-line pouring tube change capability have been found to be quite practical and are widely used. There is still room for improvement, however, in the control of the seepage of gas through the mating surfaces of the valve. Such slide valves and stopper rod valves obviously operate under difficult conditions; they are directly contacted with molten metal which has a tendency to splash and freeze.
Having movable components, they are subject to some wear, and, since they comprise two or more joints of wide surface areas, gases such as air are likely to find fissures and cracks through the interfaces to the flowing metal where pressures are almost always less than the ambient pressures outside the unit; such gases can cause unwanted reactions with the molten steel.

Prior to the present invention, the joint between the tube holder and the tube itself was commonly simply W O 97/04901 PCT~US96/11471 mortared. A circumferential steel shroud or shell frequently is used to cover the joint, but such a shell is generally more effective for strengthening - the structure than for providing a gas seal. Cracks ~ 5 inevitably develop in the mortar, and the mortared and shrouded joint frequently permits the negative pressures inside the tube to cause the aspiration of air through the joint. A primary problem caused by air is the oxidation of aluminum present in the steel.
The formation of alumina at this stage of steel production is highly undesirable.

In US Patent 3,887,117, Fehling describes a U-shaped channel to be placed in the slide or the complementary stationary part of the valve. The U-shaped channel is ground into the refractory of the unit and inert gas is fed to it from an outside source. The inert gas provides a positive pressure with respect to the atmosphere outside the valve. This kind of construction is subject to the possibility of molten metal finding its way into the channel and blocking the p~Cc~ge of gas.

Russo, in US Patent 5,100,034, purports to improve upon Fehling by inserting porous refractory in a similar channel. But Russo feeds his gas to one portion only of the refractory, thus requiring the gas to pass through the refractory before entering an open space leading to the fissures to be sealed. This configuration leads to considerable variation in gas pressure in different areas of the unit; also the refractory cannot physically block the spillage of molten metal into the ch~n~el.

In US Patent 4,576,317, Wenger discloses an CA 02216~77 1997-10-10 W O 97/04901 PCT~US96tl1471 im~Lo~ement on the Fehling '117 concept, by providing a second U-~h~peA ch~nnel in the complementary slide surface, dimensioned so that the channels will overlap in certain positions. A vacuum is drawn on the channels.

It should be kept in mind in considering the construction of devices for feeding inert gas to the contacting surfaces in slide gate valves that it is generally more convenient to feed the gas through the stationary portions of the valve than through the moving slide; however, the present invention is not so limited.

~ummary of the Invention The present invention employs a particular assembly for f~i ng inert gas into the joint between the mating faces of the tube and tube holder. In the interior of the tube holder mating surface, I employ a circumferential chAnn~l in which a porous refractory element is placed without occupying the entire depth of the channel, thus providing a circumferential feed passage for the introduction of gas at a more or less equal pressure contacting the porous refractory throughout the channel. Inert sealing gas is fed from outside the shroud, through the tube holder wall, preferably in response to a signal representing the difference in pressure between the circumferential feed passage and the outside ambient pressure. The inert sealing gas is thus able to displace air which may find its way into the joint.

I do not employ mortar on the entire mating surfaces of the joint, as has commonly been the case in the CA 02216~77 1997-10-10 W O 97/04901 PCT~US96/11471 past. Rather, a preferred joint is designed to provide a mortar shelf on the interior surface of the tube and a complementary overhang on the interior surface of the tube holder; the shelf and overhang are maintained approximately one to six millimeters apart when the remaining flat surfaces of the joint are placed together, thus providing room for a circumferentially mortared area. At the interior terminus of the shelf, the tube is cut circumferentially at an upward angle so the mortar will tend not to be spilled into the remainder of the 3oint; to further assure that it will not, I employ a relief groove at the high end of the circumferential upward angled cut. The purpose of the relief groove in the mortared variation of my invention is to minimize the possibility of mortar and/or steel ~inding its way into the main joint.

In addition, my preferred assembly requires that the flat portions of the mating joint surfaces be ground flat, i.e. within a tolerance of .00125cm to .03cm --that is, the surface preferably should not vary more than about .03 cm throughout its area. Should the circumferential porous refractory project beyond the flat surface of the joint, it should also be ground to effect flush, firm contact around the circumference of the main portion of the joint.

Thus my invention is seen to comprise a circumferential porous refractory placed on the tube holder joint surface, spaced from the interior wall of the tube holder and its exterior wall, and being in contact with a gas feed channel throughout its circumference. The gas feed channel is in turn connected to a source of inert gas, preferably fed in CA 02216~77 1997-10-10 response to a signal which is a function of the difference between the ambient outside pressure and the pressure at the internal wall of the tube and/or the circumferential gas feed passage.
My invention includes an apparatus and method for feeding inert gas into the interface of movable member and stationary members of a gate valve such as used to control the pouring of molten steel into a continuous caster. In the case of the stopper-rod valve, the movable member is the tube holder or submerged nozzle and the stationary member is the tlln~ h nozzle or an intermediate plate, depending on the particular construction. A preferred form of the invention involves the use of a channel, preferably generally U-shaped, in the surface of the slide, and another ~-h~nnel, also preferably generally U-shaped, in the mating surface of at least one of the stationary portions of the valve. Each of the channels is partially filled with a porous refractory insert, in such a way that the outer surface of the refractory is level with the respective mating surface, leaving an unoccupied area of the channel deeper into the slide or stationary portion, so that an open area or passage is provided over the entire internal surface of the porous refractory insert. This open area or passage in the ~hAnn~- is connected to a duct for a source of inert gas, which is then provided at pressures which are equal over the entire internal surface of the porous refractory insert. For conveying the gas from one element to another, i.e. from the stationary portion of the valve to the slide plate, open channels are provided in position so that, when they are juxtaposed, gas can pass freely from one to the other.

CA 02216~77 1997-10-10 Detailed Description of the Drawings Figure la is a side elevational view of the upper region of a typical prior art commercial continuous caster for steel, showing the placement of the commonly used slide gate valve. Figures 2, 3, 4, 5, and 6 are directed to this type of valve.

Figures lb and lc show prior art stopper rod arrangements to which my invention is also applicable.

Figure 2 is a simplified side sectional view of a slide gate valve, showing the top plate, the slide plate, and the tube holder, together with a preferred configuration of my gas delivery system.

Figure 3a is a simplified overhead view of the upper surface of the tube holder, showing only the features of the upper surface.
Figure 3b is a simplified view of the under side of the slide plate, showing only the surface features.
This under side of the slide plate will slide on the tube holder surface of Figure 3a.
Figure~ 3c, 3d, and 3e show the relatio~h;p of the features of Figures 3a and 3b as the slide plate is moved leftward into the "fully closed" or "entry"
position (3c), the "throttle" or working position (3d), and the "exit" position (3e).

Figure 4a is a simplified overhead view of the top plate, showing only the features on the under side.

Figure 4b is a simplified overhead view of the top of CA 022l6~77 l997-lO-lO

the slide plate, showing only the features relevant to the top surface.

Figure~ 4c, 4d, and 4e show the relationship of the S features of Figures 4a and 4b as the slide plate is moved leftward underneath the top plate into the "fully closed" or "entry" position (4c), the "throttle" or working position (4d), and the "exit"
position (4e). Figures 5 and 6 show variation of the slide plate incorporating my invention.

Figure 7~ is an enlarged (compared to Figure 1) side sectional view of a typical prior art joint between a pour tube and tube holder. Figure 7b is a more highly~
enlarged detail of another prior art variation of the joint showing mortar on the outside of the tube.

Figure 8a is a side sectional view of a pour tube and tube holder joint of my invention, showing the circumferential porous refractory, and the circumferential gas feed passage. Figure 8b illustrates the sealed fit of the porous refractory in the circumferential channel.

Figure ga is side sectional view of a different embodiment of my invention, which includes a mortar shelf and a mortar relief groove. Figure 9b shows the preferred extremity of the mortar placement in the joint.
Figure 10 illustrates that my invention may be used with no mortar in the joint.

Referring now to Figure la, this more or less conventional assembly includes a ~l~n~ h 2 having a CA 02216~77 1997-10-10 W O 97/04901 PCT~US96/11471 refractory lining 1 contA;n;ng liquid steel 3 for forming into a continuous slab. Control of the flow of steel through refractory nozzle 4 (which is secured by well block 20) is by a sliding gate valve ~ 5 comprising top plate 5 and slide plate 6 as is known in the art. Top plate 5 may be secured to mounting plate 51. Directly beneath the slide plate 6 is tube holder 7 and fixed directly beneath it is pour tube 8.
In operation, pour tube 8 passes directly through slag layer 9 on the top of the incipient slab 11, which is formed from molten steel 10 deposited near the top of the incipient slab 11 while being exposed to as little atmosphere as possible. Water-cooled copper mold 12 solidifies the steel sufficiently so that by the time it exits mold 12 at its bottom, it has formed a hard shell 13 strong enough to contain the still molten steel 10 in its center. Copper mold 12 is reinforced by a steel envelope 14 around it. The rate of passage of molten steel 3 through the slide plate 6 is controlled so as to simultaneously (1) prevent an overflow of mold 12 (2) maintain a constant molten metal level and (3) keep up with the solidification and production rates of the slab 11.

Figure lb illustrates a variation of the prior art to which the present invention is also applicable. In this variation, the submerged entry nozzle 47 passes through slag layer 9 as in Figure la, but there is no slide plate 6 (Figure la); rather, flow of metal is stopped by the insertion, by manipulator 45, of stopper 44 into refractory nozzle 4. Refractory nozzle 4 may be ~uLLo~lded by mortar 54. Submerged entry nozzle 47 may then be replaced by moving it horizontally, maint~;n;ng contact with fixed plate 46 at interface 48, which retains molten metal in passage CA 022l6~77 l997-lO-lO

52. A new submerged entry nozzle 47 follows horizontally, also maint~;ning contact with fixed plate 46 at interface 48. As will be seen hereafter, the movement of the submerged entry nozzle 47 across interface 48 is exactly comparable for our purposes to the movement of the upper surface of slide plate 6 with respect to the under side of top plate 5 as depicted in Figures 4a-4e. That is, the gas delivery system of Figures 4a-4e can be applied exactly to the variation of Figure lb.

In Figure lc, another variation is shown in which the refractory nozzle 4 is combined with the shell of tlln~; ~h 2 to form an integral nozzle/top plate 50, forming an interface 49 directly with tube holder 53.
Tube holder 53 may be replaced in a manner similar to the replacement of submerged entry nozzle 47 in Figure lb -- that is, it is moved horizontally, keeping it in contact with nozzle/top plate 50 at interface 49 while stopper 44 halts the flow of metal. Again, the upper surface of tube holder 53 can be comparable to the upper surface of slide plate 6 as illustrated in Figures 4a-4e and the under surface of nozzle/top plate 50; both may be equipped with a gas delivery system exactly as described in Figures 4a-4e.

In Figure 2, top plate 5 is seen to have an orifice 15 and a gas delivery channel 16, the lower part of which is filled with a porous refractory 17, leaving a passage 18 connecting with a gas duct 19 which is in turn connected to a source of inert gas, not shown, under pressure. Slide plate 6 has an orifice 31 and gas delivery channels 21 and 22 similar to gas delivery channel 16, also only partly filled with refractory shapes 23 and 24, forming passages 25 and CA 02216~77 1997-10-10 26. The top of tube holder 7 also has a gas delivery channel 27 partly filled with refractory 28 and forming a passage 29. Passage Z9 is connected to gas supply duct 30 in a manner similar to that of passage 18 and duct 19 on the top plate 5. Persons skilled in the art may recognize that the gas introduction through ducts 19 and 30 is contemplated in this embodiment only in the stationary parts, the top plate S and the tube holder 7. In principle, however, it is not necessary that gas introduction should only take place through a stationary part; rather, one may envision, for example, through the use of flexible tubing and the like, that the introduction could be in t~e slide plate 6, as is illustrated in Figure 6.
The porous refractory I use for the channel insert may be any of the porous refractories known in the art, such as porous zirconia refractories or high-alumina porous refractory. In practice typically varying from one-quarter inch thick to three quarters inch thick, they should preferably provide no more than about 2 psi pressure drop (and in any event no more than about 4 psi pressure drop) when a st~n~rd inert gas such as argon is flowing through the insert at about 35 st~n~rd cubic feet per hour. The refractory may be formed in place in the ch~nnel or prefabricated and set into the çh~nn~l with a sealant suitable for the conditions of pressure, temperature and wear; such sealants are known in the art.
- The series of Figures 3a-3e are described specifically with respect to the configurations of Figures la and 2, although, as will appear, in principle they are equally appropriate for the configurations of Figures lb and lc.

CA 02216~77 1997-10-10 W O 97/04901 PCTrUS96/11471 Figure 3a is a simplified overhead view of the top surface of tube holder 7, defining an orifice 32 within refractory insert 34 and showing gas delivery channel 27 and gas transfer channel 35. Gas delivery c-h~nnel 27 may be seen to be generally U-shaped, as is preferred. Refractory 28, seen in Figure 2 partially filling gas delivery channel 27, is not illustrated in Figure 3. Duct 30 connects gas transfer channel 35 and gas delivery channel 27, and receives gas from an outside source not shown.

The slide plate 6 in Figure 3b is viewed from above in a simplified manner showing only features directly relevant to its lower surface which will interface with tube holder 7. Slide plate 6 has gas transfer channel 36 and gas delivery channel 22 on its lower surface. Gas transfer channel 36 is connected to gas delivery channel 22 by duct 33. As will be seen in Figure~ 3c, 3d, and 3e, the dimensions of gas transfer channel 36 coordinate with the dimensions of gas transfer channel 35 on tube holder 7 (Figure 3a) so a connection may be made to pass gas originating in duct 33 (Figure 3a) and passed into gas transfer channel 35 of tube holder 7 to gas transfer channel 36 of slide plate 6. This is illustrated further in Figures 3c, 3d, and 3e.

In Figure 3c, the features of Figure 3~ have been ~uxtaposed on those of Figure 3a to illustrate the relative positions of gas delivery channel 27 and gas transfer 35 of tube holder 7 with respect to gas delivery channel 22 and gas transfer channel 36 of slide plate 6. Figure 3c is the first of the series 3c, 3d, and 3e showing the typical movement of the slide plate 6 over tube holder 7. The slide plate 6 CA 02216~77 1997-10-10 W O 97/04901 PCT~US96/11471 moves from right to left, as depicted. When it reaches the "entry" or "fully closed" position of ~ Figure 3c, meaning there is not yet an overlap of orifice 31 and orifice 32, the gas transfer channels 35 and 36 have begun to overlap, permitting inert gas to travel from duct 30 through gas transfer channels 35 and 36 into duct 33 and further to gas delivery channel 22 of slide plate 6, while gas continues to fill gas delivery channel 27 in tube joint 7. The reader may observe that passages 26 and 29, and refractory inserts 24 and 28 are not shown, for the sake of simplicity, in Figure 3; gas flow mentioned in the gas delivery channels 22 and 27 is confined to passages 26 and 29.
It may be observed that gas transfer channels 35 and 36 are somewhat removed from orifices 31 and 32. This is preferred because gas transfer channels 35 and 36 do not contain porous refractory inserts as do gas delivery channels 22 and 27; placement as far as practical from the molten metal is recommended to minimize the incidence of metal deposition. In addition, the gas transfer channels are linearly aligned with the sliding direction of the mating surfaces. This preferred form of interface further minimizes the possibility of deposition in these channels.

Figure 3d shows the slide plate 6 having moved further to the left on tube holder 7 than shown in Figure 3c, ~ e.g. to the "throttle" position, or a position for normal or typical operation in which orifices 31 and 32 are overlapping but not concentric. Here there is more of an overlap of gas transfer channels 35 and 36 than was seen in Figure 3c. Typically, gas flow will CA 02216~77 1997-10-10 W O 97/04901 PCT~US96/11471 be maintained at a high rate in this position to overcome the negative gas pressure induced by the flow of metal through orifices 31 and 32.

~n termination of operation the slide plate 6 is typically moved further to the left (as depicted)~ at least to the "exit" position of Figure 3e, where it will be seen orifices 31 and 32 no longer overlap and the flow of liquid steel 3 ceases. Gas transfer channels 35 and 36 may still overlap as shown but gas *low may be shut off at the operators~ discretion.

As mentioned previously with respect to Figures 3a-3e, the series 4a-4e is described specifically for the configuration of Figure la but the principle of operation is applicable to the "quick tube change"
structures of Figures lb and lc.

In Figure 4a, a simplified overhead view shows the top plate S having a generally U-shaped gas delivery ch~nnel 16 in its lower surface around orifice 15.
Gas delivery channel 16 is connected to gas transfer channel 37 through duct 40. Gas delivery channel 16 is fed with inert gas from duct 39 from an outside source not shown. As with the gas delivery channels Z7 and 22 in Figures 3a and 3b, the porous refractory inserts (illustrated in Figure 2 - see refractory inserts 17, 23, 24, and 28) are present but not illustrated in Figure 4 for the sake of simplicity.
The gas flows from duct 39 into passage 18 of gas delivery rh~nnel 16 (which contains refractory insert 17 -- see Figure 2) and thence through duct 40 to gas transfer ch~nn~l 37, which does not contain porous refractory.

CA 02216~77 1997-10-10 The top surface of slide plate 6 is illustrated in Figure 4b, showing gas delivery ch~nnel 21 connected to gas transfer ch;~nn~l 38 through duct 41.

In the "fully closed" or "entry" position of Figure 4c, the slide plate 6 has been moved leftward (as depicted and corresponding to Figure 3c) but orifice 31 does not yet overlap orifice 15 of top plate 5.
However, communication has been established between gas transfer channels 37 and 38 by reason of their overlapping positions, so that gas can flow from top plate 5 into the gas delivery channel 21 of slide plate 6. In Figur2 4d, the "throttle" position, metal may flow through orifices 31 and 15; inert gas flowing into gas delivery channels 16 and 21 and through porous refractory inserts 17 and 23 (see Figure 2) provides a positive pressure in the interface of top plate 5 and slide plate 6, while a similar effect takes place at the interface of slide plate 6 and tube holder 7, as shown in Figure 3d (see also refractory inserts 24 and 28 in Figure 2). The positive inert gas pressure prevents air and other ambient gases from entering the tube holder orifice 32 where it could damage the relatively reactive molten steel.

Figure 4e shows the "exit" relationship of the gas delivery channels 16 and 21 and gas transport channels 37 and 38 as the slide plate 6 is moved leftward on termination of operation. The juxtaposition of top plate 5 and slide plate 6 shown in Figures 4c, 4d, and 4e may be contemplated as superimposed on top of corresponding juxtaposition of slide plate 6 on tube 7 illustrated in Figures 3c, 3d, and 3e.

CA 022l6~77 l997-lO-lO

My invention includes the slide plate represented in perspective in Figure 5, which shows the gas transfer channels 21 and 22, refractory insert 23, and gas transfer ~h~nnl~l c 36 and 38. This embodiment shows an H--ChAr~l internal duct 42 which permits the flow of gas from either of the gas transfer channels 36 or 38 to both of the gas de:Livery ~-hAnnels 21 and 22. Duct 42 may be replaced by a simple duct connecting gas transfer channel 38 to gas delivery duct 21 and/or a simple duct connecting gas transfer channel 36 to gas delivery channel 22. In other words, for whatever reason, one may have separate gas delivery systems on the top and bottom of the slide plate; my invention includes such embodiments so long as a refractory insert 23 or 24 is present.

In Figure 6, a variation of the slide plate 6 is shown having no gas transfer channels because it has its own gas supply system represented by T-shaped duct 43 which serves to supply inert gas from an outside source not shown to the passages 25 and 26 of gas delivery ::hAnne~.C 21 and 22.

Figure 7a shows a conventional joint 60 of a tube holder 7 and a pour tube 8. They are joined by a layer of mortar 61 and enclosed by a steel shroud 62.
The mortar tends to develop cracks and otherwise permit the passage of gases into the interior 63 of the tube, and the shroud 62 is typically not made to be gas tight; accordingly gases can easily pass underneath it and gain access to the joint 60. In Figure 7b, a variation is shown in which mortar 61 extends only part way into the joint 60, but also is employed on the outside of tube 8. This variation also illustrates the commonly used ring 78 surrounding CA 022l6~77 l997-lO-lO

the entire tube 8 and the weld strip 79 which serves as a seal between the ring 78 and the shroud 62.
Typically, tight contact of the ring 78 and the tube 8 is assured by holding the ring 78 under compression while the weld strip 79 is secured.

In Figure 8a, an embodiment of my invention is illustrated, in which circumferential channel 64 is made in the tube holder 7 and partially filled lo throughout its circumferential ~orm with porous refractory 65, leaving a circumferential gas passage 6~. Circumferential gas passage 66 is connected through at least one duct 67 to a source 68 of inert gas such as argon or other suitable gas. Flow of the gas into gas passage 66 from source 68 is controlled in a known manner as a function of the difference between the gas pressure in gas passage 66, measured by pressure transducer 69 and the outside ambient pressure. The pressure difference is generally about 2 to about 5 psi, and is preferably maintained at at least about 3 psi to provide a pressure barrier in the joint -- that is, between mating surfaces 73 and 74 --against ambient gas; pressure drop in duct 67 will vary d~psn~;ng on its length and internal diameter, but may be expected to be less than one-half psi and more likely about 0.2 psi. Mortar 70 fills the space between circumferential shoulder 71 on pour tube 8 and complementary circumferential rim 72 on tube holder 7.
The mating surface 73 of tube holder 7 and mating surface 74 of pour tube 8 are preferably ground flat within a tolerance of 0.00125cm to 0.03cm. Figure 8b provides the detail particularly of sealant 77 between ~ porous refractory 65 and channel 64. The sealant should be a high temperature resistant sealant and serves to prevent the passage of gas from CA 02216~77 1997-10-10 circumferential gas passage 66 into the joint below mating surface 73 without going through refractory 65.

A preferred variation of my invention is shown in Figure 9~. In this version, it is seen that a circumferential shelf 75 is formed on the top of the pour tube 8 and a complementary overhang 76 is formed on the lower terminus of the tube holder 7. Behind the overhang 76 -- that is, concentrically external therefrom, a mortar relief groove 77 in the form of a deeper recess is provided to allow for spillage of mortar 70 during placement of the tube holder 7 on the tube 8. Circumferential ~hAn~el 64 containing porous refractory 65 is similar to that in Figures 8a and 8b, and is also connected through circumferential gas passage 66 and duct 67 to gas source 68. As in the Figure 8 embodiment, the flow of inert gas to channel 64 may be controlled as a function of pressure in gas passage 66 and ambient external pressures as determined by transducer 69. In any event, the effect of the open circumferential gas passage 66 is to provide a gas feed pressure substantially evenly around the circumferential ch~nnel 64. Preferably, care is taken during mortaring not to have an excess of mortar which could find its way into the horizontal portion of the joint (mating surface 74). This is further illustrated in Figure 9b, in which it will be seen that mortar 70 has been carefully placed so as not to extend onto the horizontal area of mating surface 74 as the mating surfaces 73 and 74 of tube holder 7 and pour tube 8 are brought together.

In Figure 10, tube holder 7 and pour tube 8 form a mortarless joint at mating surfaces 73 and 74 which CA 022l6~77 l997-lO-lO

W O 97/0490~ PCTrUS96/11471 have been ground flat to a tolerance of <0.03cm.
Channel 64 is formed in tube holder 7 as in the other figures and partially filled with porous refractory 65, leaving circumferential gas passage 66 available to conduct gas from duct 67 with even pressure on the upper surface of porous refractory 65, thus assuring its even distribution. In this configuration also, an optional centering ring 80 surrounds and reinforces the assembly, and metal b~ g 81 also is tightly fixed to the circumference of the upper portion of the tube 8. To prevent the ingress of ambient gas such as air from outside the assembly through the joint, an inert gas such as argon is fed to gas passage 66 from source 68 at such a rate as to maintain a pressure difference between the ambient outside pressure and pressure in the channel 64 of at least 3 pounds per square inch tO.21 kg/cm2).

Persons skilled in the art will realize that my invention minimizes the possibility of destruction of the seal between mating surfaces 73 and 74 by the migration of pieces of mortar; also my invention tends to assure that if any gas is drawn into interior 63 through joint 60 (between mating surfaces 73 and 74 and through mortar 70), the gas is far more likely to be gas from source 68 than external air which may have seeped into joint 60 from behind shroud 62. The distribution of inert gas around gas passage 66 assures that inert gas will be available with sufficient pressure to any point in the circumference - of porous refractory 65.

- The porous refractory 65 I use for the channel inserts may be any of the porous refractories known in the art, such as porous zirconia refractories or high-CA 02216~77 1997-10-10 alumina porous refractory. In practice typically varying from one-quarter inch thick to three quarters inch thick, they should preferably provide no more than about 2 psi pressure drop (and in any event no more than about 4 psi pressure drop) when a st~n~rd inert gas such as argon is flowing through the insert at about 35 st~n~d cubic feet per hour. The refractory may be formed in place in the channel or prefabricated and set into the channel with a sealant as illustrated in Figure 8b.

My invention thus includes a slide plate adapted to deliver inert gas as described, a slide gate valve having gas delivery systems as described, and apparatus for delivering molten steel to the top of a continuous caster including a tundish and a flow-directing means below it, each of the tlln~;.ch and the flow-directing means having substantially flat surfaces forming an interface in at least one of which is built a gas delivery channel including a porous refractory insert ext~n~;ng throughout its length and having a depth ext~n~;ng from said substantially flat surface to partially fill said channel (preferably about half the depth of the ch~nnel, or about one-fourth to about three-fourths the depth); where gas delivery channels are on both surfaces, the surfaces may also have gas transfer channels for delivering gas from a source on or near one surface to a passage in a channel on the other surface.

Claims (6)

1. Molten metal delivery apparatus for a continuous caster, said molten metal delivery apparatus having an upper molten metal conducting element which comprises a tube holder and a lower molten metal conducting element which comprises a tube, said upper molten metal conducting element and said lower molten metal conducting element each having an opening therethrough for guiding the substantially downward flow of molten metal, each of said molten metal conducting elements having a substantially flat surface for interfacing with the other to form an interface, wherein the flow of metal in said elements tends to create a negative pressure which draws gas through said interface, characterized in that the said substantially flat surface of at least one of said molten metal conducting elements has a gas delivery channel for delivering inert gas to said interface, said gas delivery channel being partially filled, on the side of said channel nearest said substantially flat surface, with a porous refractory, said substantially flat surfaces of both said molten metal conducting elements having been ground to a flatness having a tolerance of 0.03 centimeter.

2. Apparatus of claim 1 wherein both said molten metal conducting elements contain gas delivery channels partially filled with porous refractory.

3. Apparatus of claim 1 wherein the top of said upper molten metal conducting element has a circumferential shelf extending to the opening for guiding downward flow of molten metal therethrough and said lower molten metal conducting element has a complementary overhang with a mortar relief groove in the form of a deeper recess, and mortar between said circumferential shelf and complementary overhang which does not extend to the area between the substantially flat surfaces of the upper and lower molten metal conducting elements.

4. A slide gate valve for a continuous caster comprising a stationary element and a slide plate, each of said stationary element and said slide plate having an orifice therethrough for conducting flowing metal and a working surface in contact with the other, each of said working surfaces having gas delivery channels therein for conducting inert gas, each of said gas delivery channels being partially filled with porous refractory inserts substantially even with said working surface while defining a gas passage inward of said refractory, each of said working surfaces including a gas transfer channel not having porous refractory therein for conducting gas from one gas transfer channel to the other, said gas transfer channels being proportioned and dimensioned so that when said orifices are aligned, said gas delivery channels will be connected to said gas transfer channels and gas may pass from one gas transfer channel to another.

5. Apparatus of claim 4 wherein said gas transfer channels extend lengthwise in the direction of sliding movement of said slide plate, and further comprising a duct connected to said gas delivery channels and said gas transfer channels, and a source for supplying inert gas to said duct, delivery and transfer channels.

6. A tube assembly for use in continuous casting of metal comprising (a) an elongated, generally cylindrical pour tube having an axial opening therethrough, said pour tube being generally vertically oriented and having a generally flat upper terminus, (b) a tube holder having an axial opening therethrough, said tube holder being fixed on top of said tube, having a generally flat lower terminus adapted to mate with said upper terminus of said pour tube, and having a circumferential channel in said flat lower terminus, (c) gas supply means connecting said circumferential channel with a source of inert gas, (d) a porous refractory partially filling said circumferential channel throughout its circumference, leaving said circumferential channel partially open throughout its circumference and in connection with said gas supply means, whereby to form a gas feed passage to provide feed gas pressure substantially evenly around said circumferential channel in contact with said porous refractory, and (e) means for feeding inert gas from said source of inert gas to said circumferential channel and controlling the flow of inert gas as a function of the difference between the pressure in said circumferential channel and ambient pressure outside said tube assembly, said flow of inert gas being controlled so as to maintain said pressure difference within a range of 2 to 5 psi.