US3702631A

US3702631A - Apparatus for continuous casting of metal ingots

Info

Publication number: US3702631A
Application number: US126550A
Authority: US
Inventors: Felix Antoine Sergerie
Original assignee: Alcan Research and Development Ltd
Current assignee: Alcan Research and Development Ltd
Priority date: 1971-03-22
Filing date: 1971-03-22
Publication date: 1972-11-14
Anticipated expiration: 1989-11-14
Also published as: AU4019872A; CA966632A

Abstract

In continuous casting of metal ingots by delivering molten metal to an open-ended mold while withdrawing cast ingot continuously from the open mold end and while directing liquid coolant onto the ingot surface emerging from the mold, the extremity of the ingot is supported by a stool that initially closes the mold open end and moves progressively away from the mold as the ingot is cast. The stool is provided with one or more drainage passages which are closed while the stool is in its initial position but open as the stool moves away from the mold to release fluid that may accumulate between the ingot extremity and the stool. The passages are defined by sliding portions of the stool that initially are held in passage-closing position, but are released for movement to passage-opening position when the stool moves away from the mold.

Description

' [72 I Inventor:

' United States Patent Sergerie I 1 APPARATUS FOR CONTINUOUS CASTING OF METAL INGOTS Felix Antoine Sergei-1e, Arvida, Quebec, Canada [73] Assignee: Alcan Research and Development Limited, Montreal, Quebec, Canada 22 Filed: March22, 1971 21 Appl.No.: 126,550

[52] US. Cl. ..164/274, 164/283, 164/281 [51] Int. Cl. ..B22d 11/08 [58] Field of Search ..164/89, 126, 128, 348, 82, 164/274, 88, 273, 276, 282, 87, 136, 363,

Monndt ..164/282 X Nov. 14, 1972 Primary Examiner-J. Spencer Overholser Assistant Examiner-John S. Brown Attorney-Christopher C. Dunham, P. E. l-lenninger, Lester W. Clark, Robert S. Dunham, Gerald W. Griffin, Thomas F. Moran, Howard J. Churchill, R. Bradlee Boal, Robert Scobey and Henry T. Burke [57] ABSTRACT In continuous casting of metal ingots by delivering molten metal to an open-ended mold while withdrawing cast ingot continuously from the open mold end and while directing liquid coolant onto the ingot surface emerging from the mold, the extremity of the ingot is supported by a stool that initially closes the mold open end and moves progressively away from the mold as the ingot is cast. The stool is provided with one or more drainage passages which are closed while the stool is in its initial position but open as the stool moves away from the mold to release fluid that may accumulate between the ingot extremity and the stool. The passages are defined by sliding portions of the stool that initially are held in passage-closing position, but are released for movement to passage-opening position when the stool moves away from the mold.

13 Claims, 3 Drawing Figures APPARATUS FOR CONTINUOUS CASTING OF METAL INGOTS BACKGROUND OF THE INVENTION This invention relates to the continuous casting of metal ingots, and in a specific sense is directed to new and improved procedures and apparatus for so-called direct chill casting of ingots. By way of illustration, the

invention will be particularly described with reference to the casting of aluminum ingots, it being understood that the term aluminum as herein employed embraces pure aluminum metal and alloys thereof.

In a typical example of present-day practice, the continuous direct chill casting of an aluminum ingot is effected in a shallow open-ended axially vertical mold which is initially closed at its lower end by a downwardly movable platform or stool. The ingot is surrounded by a cooling jacket through which a coolant fluid such as water is continuously circulated to provide external chilling of the mold wall. Molten aluminum is introduced to the upper end of the chilled mold, and as this molten metal solidifies in a region adjacent the periphery of the mold, the stool is moved downwardly. With effectively continuous downward movement of the stool and correspondingly continuous supply of molten aluminum to the mold, there is produced an ingot of desired length.

The ingot emerging from the lower end of the mold is externally solid but is still molten in its central portion; in other words, the pool ofmolten aluminum within the mold extends downwardly into the central portion of the downwardly moving ingot for some distance below the mold as a sump of molten metal having a progressively decreasing cross section as the ingot solidifies inwardly until its core portion becomes completely solid. As an important feature of the direct chill casting process, continuously supplied coolant fluid such as water is brought into direct contact with the outer surface of the advancing ingot below the mold. This direct chilling of the ingot surface serves both to maintain the peripheral portion of the ingot in solid state and to promote internal solidification of the ingot.

In the initial stages of the casting operation, the butt of the ingot resting against the stool tends to shrink away from the stool at both ends owing to contraction incident to solidification and cooling. Frequently, the upper face of the stool is dished or concave to aid in retaining the initial portion of the cast ingot during solidification. Thus, very commonly, as'the ingot begins its descent from the mold, a gap or space forms, between the ingot and the stool, in which fluid can collect. The liquid coolant (e.g., water), directed against the ingot surface in streams or jets, tends to collect in this space or cavity.

Such accumulation of stagnant liquid between the butt of the ingot and the stool especially at the initial stage of casting is highly undesirable. Heat from the solidifying ingot evaporates the trapped water, causing a build-up of steam pressure beneath the ingot, and as this steam from time to time escapes, the ingot is subjected to shocks and vibrations in a vertical direction. Especially within the first few inches of travel of an ingot butt below the mold, the vibrations or bumps imparted to the ingot by entrapped and escaping steam between ingot and stool cause disturbance of the molten metal meniscus in the mold, and produce in the cast ingot structural defects such as surface cracks and so called cold shuts for as much as 12 inches to 18 inches above the butt. These defects are not readily removable; hence it is ofien necessary to cut off as scrap an uneconomically long portion of the ingot or (if the ingot is rolled into slab transversely of its long axis) it may be necessary to shear an unusually wide edge portion of the slab to remove slab defects resulting from the aforementioned structural flaws in the ingot butt.

The defects described above are encountered particularly often in the casting of large ingots, e. g., of aluminum-magnesium alloys, having a rectangular cross section (that is, cast in rectangular molds) and adapted for rolling into sheet. However, like problems may be encountered in the casting of other types of ingots as well.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate or minimize the incidence of vertical vibrations or bumps resulting from entrapment of fluid betweeningot butt and stool in the continuous direct chill casting of metal (e.g., aluminum) ingots, and thereby to eliminate or minimize the creation of structural defects in the ingot butt portion by such bumps or vibrations. Another object is to provide procedures and apparatus for preventing accumulation of fluid between an ingot butt and stool, such as might cause the aforementioned bumps and vibrations.

To these and other ends the present invention broadly contemplates improvements in procedures and apparatus for continuously casting a metal ingot in a mold having a wall laterally defining a casting zone with an open outlet end, i.e., in casting operations of the type wherein molten metal is in effect continuously delivered by suitable means into the casting zone of the mold, and wherein a stool, initially closing the outlet end of the mold and supporting the extremity of the ingot being cast, is moved away from the mold outlet end for effecting continuous advance of the ingot from the mold during casting, and wherein coolant liquid is directed by suitable means onto the surface of the ingot emerging from the mold.

The improvement in accordance with the invention broadly comprises the provision of one or more drain passages in the stool, for conducting fluid away from a locality defined between the stool and the ingot butt, and means for closing the drain passage or passages while the stool is in its initial mold-closing position, such means being openable for pennitting discharge of fluid through the passage or passages as the stool moves away from the mold outlet end so that coolant liquid entering the locality between the ingot butt and the stool is discharged therefrom through the passage or passages. In a procedural sense, then, the invention contemplates the step of opening a drain passage or passages in the stool as the stool advances away from the mold outlet end for discharging any fluid that may collect or become entrapped between the stool and the ingot butt.

As a particular feature of the invention, the stool may comprise a portion fixed in relation to a supporting movable platform, and one or more additional portions slidably movable in relation to the first-mentioned portion to open passages for discharge of fluid between the ingot butt and the stool. The sliding portion or portions are so arranged that when they are in a first position they close the drain passages of the stool and cooperate with the fixed portion of the stool to support the solidifying ingot butt and to close off the outlet end of the mold with which the stool is used. For example, the sliding portions may be formed to engage and be retained by structure disposed in adjacent and essentially stationary relation to the mold when the stool is in mold-closing position. Advance of the stool away from the mold then releases the sliding portions which move as by the force of gravity to positions in which the drain passages are open to release fluid from between the ingot and the stool.

As thus embodied, the invention incorporates means for opening one or more drain passages in the stool in response to movement of the stool away from the mold. Thereby, water from the coolant streams impinging on the ingot surface just below the mold and collecting in the space formed between the contracting ingot butt and the stool is drained away (as liquid and/or steam) so that steam pressure cannot accumulate between the ingot and stool to cause bumping of the ingot.

Further features and advantages of the invention will be apparent from the detailed description hereinbelow set forth, together with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a simplified sectional elevational view of a continuous casting apparatus embodying the present invention in a particular form;

FIG. 2 is an enlarged sectional elevational view of the stool in the casting apparatus of FIG. 1 at a stage in the casting operation after the stool has moved away from the mold; and

PK]. 3 is an end view of the stool, taken as along the line 3 3 of FIG. 2.

DETAILED DESCRIPTION Referring to the drawing, there is shown in FIG. 1 a form of apparatus for continuously casting aluminum ingots, including an axially vertical mold (open at its lower end) to which molten aluminum metal 11 is supplied for casting an ingot 12. The mold l0, fabricated of a metal suitably resistant to deterioration under the conditions for casting aluminum, has a vertical inner wall 14 which defines an axially vertical casting zone 14a of desired horizontal cross section (e.g., circular, square, or rectangular), it being understood that this mold wall configuration determines the cross-sectional shape of the produced ingot; merely by way of specific illustration, reference will be made herein to a mold which is rectangular, i.e., in cross section, for producing an ingot of corresponding rectangular cross section.

Surrounding the outer surface of the mold wall 14 is a cooling jacket 15 shown for simplicity as formed of further wall portions cooperating with the wall 14 to define and enclose an annular chamber 15a completely laterally surrounding the casting zone. This enclosed chamber is supplied by suitable means (not shown) with a cooling fluid such as water for chilling the mold wall 14, and is preferably kept continuously filled with a flowing or circulating body of fluid, designated 16.

At the start of the casting operation, the lower end of the casting zone 14a is closed by a stool 18 which is carried on a platform 19 that is in turn supported on a hydraulic ram 20. As molten aluminum in the casting zone solidifies around the lower portion of the periphery of that zone, the stool 18 and platform 19 are drawn slowly vertically downward by operation of the hydraulic ram 20. The solidifying base of the ingot being cast, resting on the stool, then begins to emerge from the lower end of the casting zone.

The mold apparatus is arranged to direct a spray or stream of cooling fluid such as water onto the emerging solidified ingot surface immediately below the casting zone. Thus, as shown, there may be provided a slit 22 in the lower wall of the cooling jacket 15, extending entirely around the mold periphery, and oriented to direct water from the chamber 15a of the cooling jacket onto the surface of the emerging ingot. This spray of water, striking the ingot surface, acts to enhance the cooling and consequent solidification of the ingot as it moves downwardly away from the mold. In this arrangement, water is continuously supplied to the chamber and is continuously discharged through the slit 22 onto the ingot surface so that there is a continuous flow of coolant fluid for removing heat from the solidifying metal.

Molten aluminum is supplied to the mold from a body or source shown as contained in a launder 26 positioned at a level above the mold and communicating therewith through an axially vertical dip tube 28 that extends downwardly from the launder into the casting zone 14a in coaxial relation to that zone. The lower end of dip tube 28 opens at a level in the casting zone somewhat beneath the level of the molten aluminum pool therein. A filter, baffle or the like may be positioned at or adjacent the lower end of dip tube 28 within the mold for filtering and/or directing the supply of molten aluminum as the molten metal enters the mold. For example, in FIG. 1 there is shown a floattype baffle 30, buoyantly supported in the molten aluminum pool 11 in surrounding relation to the outlet end of the dip tube for directing the major flow of metal laterally (toward the side walls of the mold) and for controlling the level of molten metal in the mold by effectively closing off the lower end of the dip tube incident to rise of molten metal above a desired maximum level in the mold.

The foregoing structures are broadly conventional and their operation, for continuously casting an aluminum ingot, will be familiar to those skilled in the art. The present invention, as embodied in the illustrated casting apparatus, is directed to improvements in the structure of the stool 18 for preventing accumulation of fluid between the stool and the butt end of the ingot resting thereon. As embodied in procedures that may be performed with the apparatus of FIG. 1, the invention resides in steps for effecting discharge of fluid that may accumulate between the ingot butt end and the stool, all as now to be described.

In accordance with the invention, in its illustrated embodiment, the stool 18 is made in three parts: a central body 34 fixed on the platform 19, and two side members 35 respectively extending along opposite sides of the central body and laterally slidable in relation to the central body. The upper surfaces of these three stool portions together constitute the support surtending completely around the periphery of the stool (i.e., when the members 35 are in positions abutting the .body 34, as hereinafter further described) so as to give the ingot-supporting surface a dished or concave contour which aids in supporting the solidifying butt of the ingot at the start of the casting operation.

Each of the members 35 is slidable in a generally horizontal direction toward and away from abutting engagement with the central stool body 34. When the members 35 abut the body 34, as shown in FIG. 1, they cooperate with that body to form a continuous, unapertured stool-supporting surface; the stool rim then formed by rim portions 36 is dimensioned to fit closely within the lower end of the mold casting zone. However, when they are moved away from the central body, the spaces then opened between the members 35 and the central body (as shown in FIG. 2) constitute drain passages 38 for discharge of any fluid that may have collected on the upper surface of the stool. To aid in such drainage, the upper surface 34a of the stool central body 34 may be pitched or cambered so as to cause flow of liquid from surface 34a into the passages 38.

The two side members 35 are mounted on outwardly sloping side portions of the fixed stool body 34, in such manner that a space or passage 39 for fluid flow is defined between the downwardly facing surface of each member 35 and the upwardly facing surface of the sub jacent portion of body 34. As best seen in FIG. 3, each member 35 is slidably supported at its ends by outwardly sloping flanges 40 formed integrally with and projecting upwardly from the subjacent portion of the stool body 34. In addition, each member 35 has one or more centrally disposed lugs 42 which project downwardly from its lower surface into a guide channel 43 formed in thesubjacent portion of the body 34. The flanges 40 support the members 35 in upwardly spaced relation to the underlying portion of body 34 so as to define the desired fluid passages 39, while permitting the above-described outward sliding movement of the members 35 in relation to body 34. The lugs 42 in cooperation with the channels 43 prevent movement of the members 35 in directions transverse to the desired direction of movement. In addition, stop means such as washers 44 are mounted by screws 45 at the outer ends of the channels 43 for engaging the. lugs 42 to arrest, and thus limit outward movement of, the members 35 at a position at which the members 35 are sufficiently spaced from body 34 to open the passages 38 as described.

Fixedly mounted on the outwardly facing side surface of each member 35 is an outwardly projecting element 47 which is adapted to be engaged by a springloaded arm 48 when the stool is in position closing the lower end of the mold and the members 35 are disposed in abutting relation to the body 34. Two such arms 48 are mounted on respectively opposite sides of the path of downward travel of the stool, in essentially stationary relation to the mold immediately below the lower end of the mold, for engagement with the elements 47 of the two members 35 respectively, to retain the members 35 in their initial passage-closing positions so long as the stool remains at the lower end of the mold. As the stool moves downwardly away from the mold, however, the elements 47 of the members 35 are carried downwardly out of engagement with their respectively associated arms 48 (which may, as shown, bear rollers 49 at their ends engaging the elements 47), releasing the members 35 for outward sliding movement to open the passages 38.-Except when restrained by the arms 48, the members 35 tend to move to their passage-opening positions under the force of gravity (i.e., until arrested by stop washers 44) owing to the outward and downward slope of the flanges 40 on which they rest. It will be understood that the arms 48 are only illustrative of means for restraining the members 35 in passage-closing position and releasing the members for movement to passage-opening position in response to descent of the stool. Alternatively, for example, such retention (and release) of the members 35 may be effected by engagement of the rim portions 36 of members 35 with the wall of the mold itself.

Thus in response to downward movement of the stool away from the mold, outward sliding movement of the members 35 opens the passages 38 so as to drain off any fluid collected on the upper surface of the stool. The passages 38, defined between the inner side surfaces of the members 35 and the facing side surfaces of the central stool body 34, communicate with the passages 39 defined between the lower surfaces of members 35 and the subjacent surfaces of body 34 to provide a continuous path for flow of fluid from the upper surface of the stool to the exterior.

The operation of the described apparatus, and performance of the inethod of the invention therewith, may now be readily understood. With the stool in its initial position shown in FIG. 1 closing the lower end of the mold, and with the members 35 in their innermost positions as also shown in FIG. 1, molten metal is introduced to the mold, a suitable flow of coolant being circulated through and below the mold. The effect of the coolant is to solidify the peripheral portions of the molten metal in the mold. As solidification proceeds, the butt of the ingot being formed contracts upwardly away from the stool surface on which it rests, so that a gap or space (shown at 50in FIG. 2) is defined between the central portion of the butt and the stool.

Until the stool begins to move downwardly, the sliding members 35, being at their innermost positions, close the passages 38 so that liquid cannot flow downwardly therethrough. This initial closing of the passages 38 serves to prevent leakage of molten aluminum through those passages at the start of the casting operation. However, such leakage is no longer a problem once the butt has solidified.

The descending motion of the stool is now initiated, and as the projecting elements 47 of the sliding side members 35 move below the arms 48 (i.e., as, or shortly after, the stool rim 36 clears the lower end of the mold and descends into a region in which coolant discharged onto the side surface of the stool and of the descending ingot, tends to flow into the space 50 formed between the contracting ingot butt and the stool. If this liquid were permitted to accumulate, it would vaporize owing to the heat of the solidifying ingot, and intermittently escaping steam from this space 50 would tend to cause undesired vertical vibrations damaging to the structure of the butt portion of the ingot being formed. The opening of the passages 38 as the stool moves downwardly away from the mold, however, drains the space 50; i.e., any liquid and/or steam that may enter or tend to collect in the space 50 flows downwardly and outwardly through the passages 38 and 39 defined between the members 35 and the stool central body 34, so that there can be no significant build-up of pressure in the space 50 beneath the ingot.

It has been found that the practice of the invention enables casting of ingots, e. g., aluminum ingots of large rectangular .cross section, which are substantially or entirely free of the types of butt defects associated with bumping or vertical vibrations such as result from build-up of fluid pressure between butt and stool. In conjunction with such practice of the invention, further reduction in intensity of vertical vibrations may be attained by reducing the volume of coolant (e.g., water) impinging on the ingot surface below the mold; for example, a pulsed discharge of water onto the ingot may be used to provide such control of volume.

It is to be understood that the invention is not limited to the features and embodiments hereinabove specifically set forth but may be carried out in other ways without departure from its spirit.

I claim:

1. Apparatus for continuously casting a metal ingot including a. a mold having a wall laterally defining a casting zone with an open outlet end;

b. means for delivering molten metal into said casting zone;

0. means including a stool for closing the outlet end of said mold, said stool being positioned and adapted to support the extremity of an ingot being cast in said zone and being movable away from said mold outlet end for effecting continuous advance of the ingot from the mold during casting; and

d. means for directing coolant liquid onto the surface of the ingot emerging from the outlet end of said mold;

wherein the improvement comprises e. said stool having at least one drain passage for conducting fluid away from a locality defined between said stool and said ingot extremity; and

f. means for initially closing said one drain passage and for opening said one passage to permit discharge of fluid therethrough after initial formation of the ingot extremity.

2. Apparatus as defined in claim 1, wherein said passage-closing means comprises means for opening said one passage in response to movement of said stool away from said mold outlet end.

3. Apparatus as defined in claim 2, wherein said passage-closing means comprises a member carried by said stool and movable between a passage-closing position and a passage-opening position, said member being retained in passage-closing position when said stool is in position closing said mold outlet end, and being released, for movement to passage-opening position, upon movement of said stool away from said mold.

4. Apparatus as defined in claim 3, wherein said passage-closing means further comprises structure, positioned to engage said member when said stool is in mold-closing position and adapted to remain essentially stationary during movement of said stool away from said mold-closing position, for retaining said member in passage-closing position when said stool is in moldclosing position, said member being released by disengagement from said structure for movement to passageopening position upon movement of said stool away from said mold.

5. Apparatus as defined in claim 4, wherein said stool includes a first ingot-engaging portion movable in the direction of advance of the ingot from the mold, and wherein said member comprises a second ingot-engaging portion of said stool, laterally movable relative to said first portion between a first position in which said second portion abuts said first portion, and a second position in which said second portion is spaced from said first portion to define between said first and second portions said one drain passage.

6. Apparatus for continuously casting a metal ingot including a. a mold having a wall laterally defining an axially vertical casting zone with an open lower end;

b. means for delivering molten metal into an upper region of said casting zone;

c. means including a stool for closing the lower end of said mold, said stool being positioned and adapted to support the extremity of an ingot being cast in said zone and being movable downwardly away from said mold lower end for effecting continuous downward advance of the ingot from the mold during casting; and

. means for directing coolant liquid onto the surface of the ingot emerging from the lower end of said mold;

f. means for closing said one drain passage while said stool is in position closing said mold lower end, said passage-closing means being adapted to open as said stool moves downwardly away from said mold lower end so that coolant liquid entering said locality between said ingot extremity and said stool is discharged therefrom through said one passage.

7. Apparatus as defined in claim 6, wherein said passage-closing means comprises a member cooperating with said stool in supporting the extremity of said ingot, said member being supported by said stool and slidable in a direction transverse to the path of advance of said ingot between a position in which said member closes a drain passage and a position in which said member opens said passage, said member being retained in passage-closing position when said stool is in mold-closing position and being released, for movement to passage-opening position, upon descent of said stool from said mold.

8. Apparatus as defined in claim 7, including a second passagetopening member identical to said firstmentioned member but disposed on an opposite side of the stool, both said members being disposed to engage portions of the extremity of said'ingot and to cooperate with said stool in supporting said ingot extremity, and said members, when moved to their passage-opening positions, cooperating with said stool to define drain passages between said members and said stool on opposite sides of said stool.

9. Apparatus as defined in claim 8, wherein said stool has a pitched upper surface for promoting flow of fluid into said last-mentioned passages.

10. Apparatus as defined in claim 8, wherein said stool and said members have upwardly projecting rim portions cooperatively defining a dished surface in which said ingot extremity rests.

11. Apparatus as defined in claim 8, wherein said passage-closing means further comprises structure, positioned to engage said members when said stool is in mold-closing position and adapted to remain essentially stationary during descent of said stool, for retaining said members in passage-closing position when said stool is in mold-closing position, said members being released by disengagement from said structure for movement to passage-opening position upon descent of said stool from said mold.

12. In continuous casting apparatus, in combination with an open-ended mold for receiving in molten form the material to be cast, a stool for closing the outlet end of the mold, positioned and adapted to support the extremity of a body being cast in the mold and movable away from the mold for effecting continuous advance of the body from the mold during casting, said stool having at least one drain passage for removing fluid from between the extremity of the body and the stool, said stool having a surface facing the interior of said mold for contact with said extremity of said body, and said passage opening through said surface inwardly of the periphery thereof.

13. Apparatus as defined in claim 12, including means supported by and carried with said stool for initially closing said one passage prior to introduction of molten material to said mold to prevent fiow of said molten material into the passage.

Claims

1. Apparatus for continuously casting a metal ingot including a. a mold having a wall laterally defining a casting zone with an open outlet end; b. means for delivering molten metal into said casting zone; c. means including a stool for closing the outlet end of said mold, said stool being positioned and adapted to support the extremity of an ingot being cast in said zone and being movable away from said mold outlet end for effecting continuous advance of the ingot from the mold during casting; and d. means for directing coolanT liquid onto the surface of the ingot emerging from the outlet end of said mold; wherein the improvement comprises e. said stool having at least one drain passage for conducting fluid away from a locality defined between said stool and said ingot extremity; and f. means for initially closing said one drain passage and for opening said one passage to permit discharge of fluid therethrough after initial formation of the ingot extremity.

4. Apparatus as defined in claim 3, wherein said passage-closing means further comprises structure, positioned to engage said member when said stool is in mold-closing position and adapted to remain essentially stationary during movement of said stool away from said mold-closing position, for retaining said member in passage-closing position when said stool is in mold-closing position, said member being released by disengagement from said structure for movement to passage-opening position upon movement of said stool away from said mold.

6. Apparatus for continuously casting a metal ingot including a. a mold having a wall laterally defining an axially vertical casting zone with an open lower end; b. means for delivering molten metal into an upper region of said casting zone; c. means including a stool for closing the lower end of said mold, said stool being positioned and adapted to support the extremity of an ingot being cast in said zone and being movable downwardly away from said mold lower end for effecting continuous downward advance of the ingot from the mold during casting; and d. means for directing coolant liquid onto the surface of the ingot emerging from the lower end of said mold; wherein the improvement comprises e. said stool having at least one drain passage for conducting fluid away from a locality defined between said stool and said ingot extremity; and f. means for closing said one drain passage while said stool is in position closing said mold lower end, said passage-closing means being adapted to open as said stool moves downwardly away from said mold lower end so that coolant liquid entering said locality between said ingot extremity and said stool is discharged therefrom through said one passage.

8. Apparatus as defined in claim 7, including a second pasSage-opening member identical to said first-mentioned member but disposed on an opposite side of the stool, both said members being disposed to engage portions of the extremity of said ingot and to cooperate with said stool in supporting said ingot extremity, and said members, when moved to their passage-opening positions, cooperating with said stool to define drain passages between said members and said stool on opposite sides of said stool.

13. Apparatus as defined in claim 12, including means supported by and carried with said stool for initially closing said one passage prior to introduction of molten material to said mold to prevent flow of said molten material into the passage.