WO2009146527A1

WO2009146527A1 - Method and apparatus for removal of cooling water from ingots by means of water jets

Info

Publication number: WO2009146527A1
Application number: PCT/CA2009/000726
Authority: WO
Inventors: Eric W. Reeves; Randy Womack; Wayne J. Fenton; Jeff Mcdermott; Jim Boorman
Original assignee: Novelis Inc.
Priority date: 2008-06-06
Filing date: 2009-05-28
Publication date: 2009-12-10
Also published as: CA2725614A1; JP2011526205A; EP2293892A1; US20090301683A1; KR20110022659A; CN102083569A

Abstract

The exemplary embodiments relate to the removal of cooling water used to cool the surface of an ingot as it is formed during casting. The cooling water is removed from the surface by directing jets of water onto the surface at an angle, and with a momentum, that causes the cooling water to be stripped from the surface when contacted with the jets, and to follow a path that prevents the cooling water from again coming into contact with the ingot surface at a position beyond the point of removal. The apparatus for this includes nozzles to create the water jets, and equipment for supplying water under sufficient pressure and rate of flow to the nozzles.

Description

METHOD AND APPARATUS FOR REMOVAL OF COOLING WATER FROM INGOTS BY MEANS OF WATER JETS

TECHNICAL FIELD

This invention relates to casting of metal ingots. More particularly, the invention relates to the cooling of such ingots as they emerge from a casting apparatus by the application and removal of cooling water to the outer surfaces of the ingots.

BACKGROUND ART

There are various techniques for casting metal ingots, such as direct chill (DC) casting (a technique that includes electromagnetic casting (EMC)), hot top technologies for the production of rolling slab ingots, forging ingots, extrusion ingots (billets), etc. These various casting techniques may involve the application of cooling media to the external surface of the ingots as they emerge from the mold to ensure ingot surface solidification and to reduce the likelihood of molten metal bleedout from the interior of the ingot before the ingot becomes fully solid. Frequently, the ingots are cast vertically, but horizontal casting is also practiced as, for example, in horizontal direct chill casting (HDC). In the case of vertical direct chill casting, in particular, cooling water is directed onto the outer surface of the ingot around the bottom of the mold and the cooling water flows down the sides of the ingot.

For some purposes, it is desirable to remove the cooling water from the surface of the ingot at a certain distance from the mold exit. This reduces the rate of cooling of the ingot from that point on because the surface becomes air cooled rather than water cooled. As shown, for example, in U.S. patent 4,237,961 to Zinniger on December 9, 1980, the cooling water may be removed by means of physical wipers or squeegee- like devices that contact the metal surface, but the surface of the ingot is still hot and wiper devices may quickly become degraded, especially if there is an instance of molten metal bleed-out that brings molten metal into contact with the elastomeric material of the wiper or the metal of the supporting structure. It may also be difficult to employ mechanical wipers of this kind at an early stage in the casting process. The geometry of the butt (bottom) of the ingot makes mechanical wiping schemes difficult, especially in the case of thin ingots. For example, in DC casting, during the initial fill, start down, primary and secondary curl, metal sometimes dribbles or bleeds out of the mold and the molten metal may collect on the wiper and burn the elastomeric contact material prior to its being able to wipe the ingot. Therefore, the wiper is not usually deployed until after the incidence of butt-curl, i.e. only after the ingot has emerged by 10 to 14 inches. Wipers which mechanically engage the ingot cannot be engaged prior to final curl, so again the first 10 to 14 inches of the ingot is substantially cooled prior to any water being removed. After wiper engagement, the dissimilar temperatures between the butt portion and run portion generates varied metallurgical structures and stresses which can result in further processing problems or the formation of scrap while casting, preheating and rolling.

It is known to remove cooling water by means of jets of gas, such as compressed air, that blow the cooling water from the cast metal, for example as disclosed in US patent 2,705,353 to Zeigler which issued on April 5, 1955. However, compressed air wipers are costly to install and use because of inefficiencies involved in pressurizing compressible gases. US patent 5,685,359 to Wagstaff et al. shows coolant spray holes with overlapping spray patterns for use in direct secondary cooling, but the spray holes are not used for coolant water removal.

US patent 5,431 ,214 to Ohatake et al. mentions cooling water jets, but again such jets are not used for coolant water removal.

There is a need for improved ways of removing surface cooling water from such ingots. DISCLOSURE OF THE INVENTION

An exemplary embodiment of the invention provides a method of removing cooling water from a surface of a metal ingot, wherein the cooling water streams over the surface in a casting direction. The method involves directing one or more water sprays onto the surface of the ingot at an angle and rate of flow effective to cause the cooling water streaming over the surface to separate from the surface as the cooling water encounters the sprays. Preferably, enough of the cooling water is removed to allow natural film boiling to occur, thereby removing all of the cooling water within a short distance of the water sprays.

Another exemplary embodiment provides an apparatus for removing cooling water from a surface of a metal ingot, wherein the cooling water streams over the surface in a casting direction. The apparatus includes one or more nozzles adapted to direct water sprays onto the surface, the nozzles being positioned and angled such that the water sprays are effective in use to cause the cooling water streaming over the surface to separate from the surface as the cooling water encounters the sprays. The apparatus also includes one or more conduits for supplying water to the nozzles, and pressurizing apparatus for pressurizing water supplied to the nozzles.

According to these exemplary embodiments, water jets or sprays are used to remove cooling water from the surface of an ingot as it is being cast. The apparatus for producing the water jets is economical to provide and operate given that the removal medium is water (which may be taken from the same source as the water used for cooling the ingot). The apparatus and method may be used early during casting operations and close to the outlet of the casting mold as the jets are not affected by molten metal bleed out and they follow any variations in the profile of the ingot as it is being produced. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail in the following with reference to the accompanying drawings, in which:

Fig. 1 is a vertical cross-section of a known direct chill casting mold provided with a mechanical wiper for removal of cooling water;

Fig. 2 is a horizontal cross-section of an ingot being cast by DC casting showing an exemplary embodiment of apparatus for removing cooling water;

Fig. 3 is an enlargement of part of the apparatus of Fig. 2, showing water jets in action;

Fig. 4 is a vertical section of part of the apparatus of Fig. 2 prior to activation of the water jets;

Fig. 5 is the same view as Fig. 4 but showing the apparatus following activation of the water jets; Fig. 6 is a vertical cross-section similar to that of Fig. 5 but showing an exemplary embodiment that makes use of a scupper to remove cooling water;

Fig. 7 is a horizontal cross-section of an alternative exemplary embodiment that makes use of a corrugated shield wall to form channels for cooling water stripped from the ingot surface.

Figs 8 to 10 illustrate alternative embodiments making use of narrow cylindrical water jets to remove cooling water from an ingot; and

Fig. 11 is a cross-section illustrating an exemplary embodiment applied to horizontal DC casting.

BEST MODES FOR CARRYING OUT THE INVENTION

The exemplary embodiments of the present invention may be used with apparatus of many kinds that employ streams of water to cool a newly-formed metal ingot, e.g. an ingot of a non-ferrous or light metal, such as an ingot of an aluminum, magnesium or copper alloy. However, the exemplary embodiments are especially suitable for use with DC casting apparatus and one form of such apparatus is shown in Fig. 1 and is briefly described below so that the preferred and exemplary embodiments may be better understood, although it is to be noted that the present invention is not limited to equipment of this kind.

Fig. 1 is a vertical cross-section of a direct chill casting mold producing a metal ingot and showing a known arrangement for removing cooling water from the outer surface of the ingot. This apparatus is disclosed in U.S. patent publication no. 2007/0102136 to Wagstaff et al., published on May 10, 2007 (the disclosure of which is specifically incorporated herein by this reference). The mold is indicated generally at 10 and it is provided with an open upper entrance 11 and an open lower exit 12. Molten metal is introduced into the entrance of the mold as indicated by arrow 13. The mold includes a primary cooling channel 14 filled with recirculating cooling water 15 that cools the inner wall of the mold. The molten metal cools adjacent to the mold wall and forms an embryonic ingot 16 that emerges from the mold. The embryonic ingot has a molten metal sump 17 surrounded by a solid metal shell 18 which increases in thickness as the ingot descends until full solidification occurs at a point remote from the exit 12 of the mold to form a fully solid ingot 19. Streams or jets of cooling water 20 are poured onto the surface of the ingot from the channel 14 adjacent to the lower exit 12 of the mold to help to form and maintain the solid outer shell 18 around the molten metal sump. The water streams down along the sides of the embryonic ingot, but is removed by a mechanical wiper 21 positioned at a distance X from the exit of the mold. The cooling water 20 removed in this way forms streams 22 spaced from the ingot 19 that have no further cooling effect. The wiper is in the form of an annulus made of a soft flexible or elastomeric material that physically contacts the outer surface of the ingot to wipe away the cooling water. The wiper is held in a rigid holder (not shown) made of metal or the like. In the apparatus of Fig. 1 , distance X is made such as to allow the ingot to "self homogenize". Of course, there are other reasons why the cooling water may be removed at a predetermined distance from the mold, so the exemplary embodiments are not limited to this one purpose.

In preferred exemplary embodiments of the present invention, a mechanical wiper of the kind shown at 21 may be replaced by a series of water jets that remove the cooling water from the surface of the ingot. This is shown by way of example in Figs. 2 to 11 of the accompanying drawings. Fig. 2 shows a horizontal cross-section of an ingot at a distance below a direct chill casting mold where cooling water is to be removed. The ingot 19 (or embryonic ingot 16) having a downwardly streaming surface layer of cooling water 20 is completely surrounded at a narrow horizontal spacing by a short solid vertical wall 25 (made, for example, of a metal such as aluminum or stainless steel) that extends downwardly from a bottom wall 26 of a direct chill casting mold 10 (see Figs. 4 and 5). The wall 25 is not essential, but acts as a shield to prevent water from spraying onto any other ingots that may be cast at the same time in adjacent areas. The wall 25 is penetrated by a number of holes or slots 27 all positioned at the same vertical height in the illustrated embodiment. An elongated nozzle 28 extends through each slot from outside the wall and terminates a short distance from the outer surface 29 of the ingot. As best seen in Fig. 2, the nozzles 28 on each side of the ingot 19 are connected to a manifold 30 that supplies water under pressure to the nozzles, and the manifolds are connected together in series by high pressure flexible hoses 31 , 32 and 33. The first manifold in the series is connected by a flexible high pressure hose 34 to an apparatus 35, e.g. a pump, for supplying water under pressure. When supplied with water under pressure in this way, the nozzles each spray a jet 36 (Fig. 3) of water towards the surface 29 of the ingot. It will be noted that each of the nozzles forms a jet 36 having the shape of a flat fan of water. Thus, the jets 36 are generally flat in vertical side view but expand outwardly in plan view, so that they extend vertically by a much smaller distance than they extend horizontally. The fan shaped jets 36 are preferably partially overlapping, as shown. The angle at the apex of the water jets (as shown in the plan view of Fig. 3) is preferably at least 65°, and may be 72°, or more. The nozzles are preferably spaced from each other (and/or from the ingot) by distances effective to provide an overlap of the water jets of 1 - 2 inches at the ingot surface 29. While this arrangement is particularly preferred, it will be noted from later embodiments that nozzles producing water jets of other shapes may alternatively be employed, e.g. cylindrical jets, and that overlap of the jets may not always be necessary.

The manifolds 30 may be of any size and shape, but are preferably square in cross-section (e.g. of 1!4 inches per side) and the nozzles 28 are preferably arranged at intervals of up to about 5 inches from each other, although this may be varied to suit particular molds and spacing arrangements. For standard DC casting equipment, the manifolds 30 may be, for example, 1720 mm long (long side of ingot) and 560 mm long (short side of ingot). The pressure of the water supplied to the nozzles 28 should be adequate for the removal of most or all of the coolant water from the surface of the ingot and is preferably at least 80 psi up to about 150 psi, and more preferably is in the range of 100 -120 psi, to give a rate of flow at each nozzle of at least 0.4 gallons per minute per linear inch of distance around the mold circumference (gpm/in) up to about 1.5 gpm/in, (ideally in the range of 0.6 - 1.0 gpm/in). The mold discharge flow rate (flow rate relating to the overall water discharge from the mold in advance of the wipers) is preferably at least 0.6 gpm/in up to about 1.5 gpm/in, and is preferably in the range of 0.7 - 1.0 gpm/in. The high pressure hoses 31 , 32, 33 and 34 are preferably attached to the manifolds by quick release fittings so that they may be easily disconnected and re-connected to allow the replacement of one or more of the manifolds if they become blocked or otherwise require attention. Moreover, the manifolds 30 are preferably supported on equipment (not shown) that allows them to be moved closer to or further away from the ingot 19, and/or closer to or further away from the casting mold. Also, it is desirable to make the nozzles rotatable about a horizontal axis to make it possible to adjust the angle of spray relative to the ingot surface, as circumstances dictate. The action of the jets is best shown in Figs. 4 and 5, which are detailed vertical sectional views in the region of the bottom wall 26 of the casting mold 10. The manifolds 30 have been omitted from these drawings for the sake of simplicity but are positioned immediately outside the walls 25. Fig. 4 shows the situation before the jets are started.

Nozzles 28 extend through the vertical wall 25 and face the surface 29 of the ingot 19 emerging from an exit 12 of the casting mold. Cooling water 20 is streamed onto the surface 29 from apertures in the bottom of channel 14 of the mold and the water streams in a continuous layer downwardly along the outer surface of the ingot (as represented by arrow A). Without operating the water jets, the cooling water streams down the ingot in this way until it reaches the bottom of the ingot or a water collection pool. As shown in Fig. 5, in order to remove the cooling water at distance X from the bottom of the mold, the nozzles 28 are supplied with water under pressure to create flat fan-shaped jets 36 of water that contact the surface 29 of the ingot. When the jets have sufficient momentum (volume of water and rate of flow), and a suitable angle g relative to the surface 29 (preferably in the range of 65 to 75°, and more preferably 68 to 72°) with a component of movement countercurrent to the direction of flow of the cooling water 20, they strip the cooling water 20 from the ingot surface and force it to adopt an upward flow 40 (as indicated by arrow B) after leaving the ingot surface 29. This means that the nozzles 28 are preferably angled upwardly from the horizontal (when the streams 20 flow downwardly) at an angle of 15 to 25°, and more preferably 19 to 22°, although the most effective angle may be determined in particular situations by trial and experimentation. The overlap of the jets further helps to remove the streaming water from the ingot because the momentum created by the water in the overlap region helps to cause the streaming water to spray away from the ingot with an "interactive fountain" effect. Ideally, sufficient cooling water is removed in this way to leave just a thin residual film that quickly dries off due to the high temperature of the ingot. Preferably, the upward flow 40 of cooling water is caused to bounce off the bottom wall 26 of the casting mold without impacting the junction between the ingot and the mold and entering the mold cavity, and is then caused to run down the inside surface 42 of the vertical wall 25 (as indicated by arrow C) so that there is no further contact between the cooling water and the surface 29 of the ingot beyond distance X. The cooling water is thus stripped from the surface without any direct contact from mechanical parts of the apparatus.

It should be noted that sufficient cooling water should be stripped from the surface 29 to achieve a desired reduction of cooling of the ingot beyond distance X. Ideally, all or substantially all of the cooling water is removed in this way, but this is not always essential (or perhaps possible) because small amounts of cooling water remain beyond distance X. However, these residual amounts normally disappear quickly or even instantly due to evaporation caused by the heat of the ingot. Also, according to the cooling effect desired in any particular case, a small amount of residual cooling water may be acceptable, even if it does not disperse immediately by evaporation. Preferably, at least 90% of the volume of the cooling water above point X, more preferably at least 95%, and even more preferably at least 99%, is removed by the water jets themselves to leave just a sub-film that is quickly or even substantially instantly removed by evaporation.

The spacing of the nozzles from the ingot is preferably optimized according to the following considerations. The closer the nozzles are positioned to the ingot, the higher will be the momentum of the water in the jets as they contact the ingot surface, but the more at risk the nozzles will be from damage if molten metal bleeds out of the mold or ingot during the casting operation. Also, the closer the nozzles are positioned to the ingot, the greater the number of nozzles will be required in order to provide a constant line of impacting water around the entire periphery of the ingot. Therefore, the spacing of the nozzles from the ingot should be made as far as possible without causing the momentum of the water in the jets to diminish to a point below their effectiveness for stripping cooling water from the ingot.

The distance X at which the water jets are applied to the ingot surface depends on the reason for the desired water stripping operation. As noted above, the water stripping may be required for "in-situ homogenization", in which case the distance X is one that allows the temperature of the ingot to rise to the homogenization range following water stripping. Cooling water removal may alternatively be carried out for stress relief within the ingot. In the case of more conventional wiping used with hard alloys, a greater distance X is employed and a flash boiling effect of any residual cooling water may not be so important.

It should also be noted that the distance X may, in some cases, be chosen to differ on different sides of the ingot. The short sides of the ingot (ingot ends) may have a jet contact point that is higher (closer to the mold) than that required for the long faces of the ingot (rolling faces). Also, thinner ingots may have water contact points that are higher than those required for thicker ingots. However, the rate of flow and pressure of the water jets would normally be the same on all sides of the ingot, unless the streaming water is acted upon by a different force on different sides of the ingot (e.g. gravity in the case of horizontal direct chill casting). In such a case, the flow rate and/or pressure would be varied on different sides of the ingot to achieve the desired degree of water stripping from each ingot face.

The ideal angle of the nozzles to produce the cooling water stripping effect can be determined by manually adjusting the angle of the jets (e.g. by rotating the manifolds 30) and observing the results. This may be done in a preliminary run of the casting apparatus and then maintained at the same angle for all subsequent casting runs of the same characteristics. It should be noted that the exemplary embodiments of the present invention may be especially effective when used with the means of cooling water application disclosed in U.S. patent 5,685,359 to Wagstaff mentioned above. This means of cooling employs a split jet/dual jet arrangement for ingot cooling purposes at the exit of the casting mold. For reasons of safety, performance and maintenance, the hoses and manifolds through which the water passes will need filters, shut off valves and other conventional equipment. For example, a 50 mesh filter may be provided to protect the nozzles from blockage. Such a filter may be provided on the supply side of the apparatus 35 for supplying the water under pressure in order to minimize loss of performance of the apparatus. The apparatus 35 may be a pump capable of generating for example 150 psi or more of water pressure and a rate of water flow of 115 gallons per minute or more. Suitable pumps may be obtained, for example, from Pioneer Pump Inc., of 310 South Sequoia Parkway, Canby, OR 97013, U.S.A. (e.g. model SC32C10). The same water that is used for cooling may be employed for the nozzles, or it may be supplied from a different source. The water may be substantially pure, but may contain various additives, such as ethylene glycol. When the water contains such additives, it must of course be supplied from a source different from the cooling water. The water may also contain unintentional additives, particularly if recycled cooling stream water is used. The water is generally at ambient temperature when fed to the nozzles.

The nozzles 28 are preferably capable of delivering about 0.8 to 1.0 (or even 1.5 or more) gallons of water per minute over an arc of at least 65° (preferably 72°) at a pressure of 120 psi. Such nozzles may be obtained, for example, from Spraying Systems Co. of P.O. Box 7900, Wheaton, Illinois 60189-7900, U.S.A. The nozzles are preferably used with extenders to allow them to project sufficiently through the shield wall 25 to avoid interruption by contact with the reverse flow of cooling water streaming along the inner surface of the wall.

An alternative embodiment is shown in Fig. 6. In this embodiment, the underside 26 of the mold 10 is provided with a scupper 50 to collect the cooling water 20 stripped from the ingot 19 before it descends down wall 25 to the level of the nozzles 28. This avoids the possibility that the stripped cooling water may interrupt or adversely affect the operation of the nozzles 28 or the shape or power of the water jets 36. Water collected in the scupper 50 flows to the ends of the mold and is allowed to pour away from the ingot or is removed through suitable channels (not shown). Another alternative arrangement is shown in Fig. 7 which makes use of a shield wall 25 having a corrugated shape in plan view. The nozzles 28 project through the wall 25 at positions where the wall is closest to the surface 29 of the ingot 19. After curling back away from the ingot in the manner shown in Fig. 5, cooling water 20 stripped from the mold by the jets 36 tends to stream into the vertical channels 52 formed between the points of the wall 25 closest to the ingot. This directs the cooling water away from the nozzles 28 and water jets 36, thereby minimizing any likelihood of interference with the jets.

Figs. 8 to 10 show embodiments where narrow cylindrical water jets are used instead of the fan shaped jets of the above embodiments. In Fig. 8, the jets 36 (which are upwardly angled as in previous embodiments) penetrate the layer of cooling water 20 to the surface 29 of the ingot 19 and then spread out to separate the cooling water from the ingot surface. In the case of Fig. 9, after contacting the ingot 19, the jets 36 spread sufficiently to contact each other and form a combined "interactive fountain" 54 between the positions of the nozzles. This effect is created by adjusting the pressure and flow rates of the nozzles sufficiently. The cooling water layer becomes completely separated from the ingot.

In the case of Fig. 10, the effect shown in Fig. 9 is accentuated by angling the nozzles towards each other to maximize the separation of the cooling water from the ingot surface.

Fig. 11 shows an exemplary embodiment of the invention applied to horizontal DC casting. In horizontal direct chill casting apparatus, the positions of the nozzles may have to be adjusted to allow the water wiping jets to contact the top surface of the ingot at a different distance from the casting mold relative to the bottom surface of the ingot. In addition, in the illustrated embodiment, a scupper 50 is used at the upper side of the ingot to collect and remove cooling water 20 stripped from the ingot. Without such a means of collecting and removing the stripped cooling water, it would fall back on the ingot and adversely affect the cooling characteristics of the ingot. At the lower side of the ingot, cooling water 20 may fall naturally from the ingot 19 as shown, or alternatively a series of water jets may also be applied to remove the cooling water at a distinct distance from the mold. However, a scupper such as the one 50 used at the upper side of the mold, will not be needed at the lower side of the mold because cooling water stripped from the ingot will anyway stream away from the ingot under the action of gravity. As in the embodiment of Fig. 6, the scupper 50 removes the collected cooling water to the ends of the mold and disposes of it without allowing it to come into contact with the ingot or the nozzles.

While the embodiments described above are preferred, various modifications and alternatives are possible. As already noted, the exemplary embodiments may be employed with various kinds of casting apparatus, not just the DC casting apparatus of Fig. 1. Moreover, the invention is suitable for use with metals of various kinds, particularly alloys of aluminum, magnesium and copper. Use with the casting of aluminum alloys is particularly preferred.

Claims

CLAIMS:

1. A method of removing cooling water from a surface of a metal ingot, wherein said cooling water streams over said surface in a casting direction, the method comprising: directing one or more water sprays onto said surface at an angle and rate of flow effective to cause said cooling water streaming over said surface to separate from said surface as said cooling water encounters said one or more water sprays.

2. A method according to claim 1 , wherein said water sprays are directed onto said surface at an angle within a range of 65 to 75 degrees in a direction countercurrent to said streaming direction.

3. A method according to claim 1 or claim 2, wherein said water sprays each have a rate of flow of up to about 1 gallon per minute.

4. A method according to claim 1 , claim 2 or claim 3, wherein said water sprays made generally flat and fan shaped.

5. A method according to claim 4, wherein said fan shaped sprays are positioned close to one another so that the sprays overlap where the sprays contact the ingot.

6. A method according to claim 4, wherein said water sprays are positioned close to each other so that the amount by which said sprays overlap is in the range of 1 to 2 inches.

7. A method according to claim 4, wherein said sprays each extend over an arc of at least 65 degrees.

8. A method according to any one of claims 1 to 7, wherein said nozzles are separated from each other by a distance of up to 5 inches.

9. A method according to any one of claims 1 to 8, wherein said cooling water removed from said surface by said sprays, and water from said sprays after contact with said surface, is constrained to follow a path remote from said surface of the ingot.

10. A method according to any one of claims 1 to 9, wherein said cooling water removed from said surface, and water from said sprays after contact with said surface, is maintained out of contact with said surface but confined to a region surrounding said ingot.

11. A method according to any one of claims 1 to 10 applied to an ingot emerging from a direct chill casting mold provided with orifices applying said cooling water to said surface of said ingot, wherein said sprays are all directed onto said surface at a predetermined distance from said direct chill casting mold.

12. A method according to claim 11 , wherein said ingot is generally rectangular and has four sides, and wherein said sprays are directed onto all said four sides of said ingot at said predetermined distance from said direct chill casting mold.

13. A method according to claim 11 , wherein said direct chill casting mold is orientated for vertical casting.

14. Apparatus for removing cooling water from a surface of a metal ingot, wherein said cooling water streams over said surface in a casting direction, said apparatus comprising: one or more nozzles adapted to direct water sprays onto said surface, said nozzles being positioned and angled such that said water sprays are effective in use to cause said cooling water streaming over said surface to separate from said surface as said cooling water encounters said sprays; one or more conduits for supplying water to said nozzles; and pressurizing apparatus for pressurizing water supplied to said nozzles.

15. An apparatus according to claim 14, wherein said one or more nozzles are orientated at an angle to said surface within a range of 65 to 75 degrees in a direction countercurrent to said streaming direction.

16. An apparatus according to claim 14 or claim 15, wherein said water sprays are rated for a flow of up to about 1.5 gallons per minute.

17. An apparatus according to claim 14 claim, claim 15 or claim 16, wherein said nozzles are configured to generate water sprays that are generally flat and fan shaped.

18. An apparatus according to any one of claims 14 to 17, wherein said nozzles are positioned close to one another so that the sprays overlap where the sprays contact the ingot.

19. An apparatus according to claim 18, wherein said nozzles are positioned close to each other so that the amount by which said sprays overlap is in the range of 1 to 2 inches.

20. An apparatus according to claim 17 or claim 18, wherein the nozzles are configured such that the fan shaped sprays each extend over an arc of at least 65 degrees.

21. An apparatus according to any one of claims 14 to 20, wherein said nozzles are separated from each other by a distance of up to 5 inches.

22. An apparatus according to any one of claims 14 to 21 , wherein said nozzles are configured such that said cooling water removed from said surface by said sprays, and water from said sprays after contact with said surface, is constrained to follow a path remote from said surface of the ingot.

23. An apparatus according to any one of claims 14 to 22, wherein said nozzles are configured such that said cooling water removed from said surface, and water from said sprays after contact with said surface, is maintained out of contact with said surface but confined to a region surrounding said ingot.

24. An apparatus according to any one of claims 14 to 23 including a direct chill casting mold for producing said ingot, said mold being provided with orifices applying said cooling water to said surface of said ingot, wherein said nozzles are positioned at a predetermined distance from an outlet of said direct chill casting mold.

25. An apparatus according to claim 24, wherein said ingot is generally rectangular and has four sides, and wherein said nozzles are positioned on all said four sides of said ingot at said predetermined distance from said direct chill casting mold.

26. An apparatus according to claim 24, wherein said direct chill casting mold is orientated for vertical casting.