Abstract:
Continuously cast ingots are spray-cooled by a fanned-out flow of water which has been accellerated by pressurized air with an original nozzle direction parallel to the surface of the ingot and transversely to the direction of ingot withdrawal. The arrangement avoids cooling impediment on account of the Leiden frost phenomenon.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to spray cooling of slab ingots produced by continuous casting. 
     It is common practice to spray water onto the casting as it emerges from the bottom of an open ended mold, and spray is continued for some distance along the withdrawal path, particularly as the casting is veered from a vertical orientation when leaving the mold to a horizontal orientation for further processing. Spray-cooling in one form or another is described e.g. in German Pat. Nos. 2,053,947 and 2,208,928 and also in a Handbook by E. Hermann &#34;Handbuch des Stranggiessens&#34; , Aluminum-Verlag Dusseldorf, pages 188,189. 
     It was found, however, that particularly in the mold-near zones of the ingot or casting, steam is developed extensively so that a steam layer tends to isolate the casting from the spray water to some extent, and water rarely comes into direct contact with the surface to be cooled. The production and effect of that steam layer is also known as the Leiden frost phenonemnon. 
     DESCRIPTION OF THE INVENTION 
     It is an object of the present invention to provide for cooling of an ingot as it emerges from a mold for continuous casting and in a manner that drastically diminishes the effect of the Leiden frost phenomenon. 
     It is a specific object of the present invention to spray cool a casting without incurring stagnating water between a withdrawal roll and the surface of the casting-ingot and elsewhere but in a manner which causes direct or rather even distribution of the cooling water on the ingot. 
     In accordance with the preferred embodiment of the invention, it is suggested to provide a cooling liquid for spray cooling of at least a total amount of 0.1 liters per kilogram steel to be cooled and to add a propellant gas at a minimum pressure of 2 bars, whereby both media are accellerated over a path of particular length prior to being emitted in fan-like jets originating between respective two rolls and, preferably, at a distance from the ingot closer than the roll axes. The gas preferably accelerates the coolant for a distance of at least 100 mm before being ejected by the nozzle. 
     The nozzle ends are bent off to extend parallel to the surface of the ingot, and the nozzles have oblique configuration to fan out the coolant rather widely. One will need plural nozzles, being differently oriented, but the bent off ends should extend transversely to the direction of casting. This way, one will obtain uniform coverage of the entire area between the lines of engagement of the ingot by two vertically spaced rolls. The amount of water stated above is used for the cooling region defined on the upper side of the ingot which in turn is defined by respective two vertically spaced lines of engagement with withdrawal rolls. The nozzeles are, however, provided on both sides of the ingot, so that it is possible to spray cooling medium onto both sides. 
     It was found that the fanned-out flow of air-accelerated water penetrates any steam layer that tends to form on the ingot surface, so that the Leidenfrost phenomenon is overcome. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which: 
     FIG. 1 is a section view taken e.g. in a horizontal plane through an ingot in the withdrawal path and showing somewhat schematically a portion of the spray equipment in accordance with the preferred embodiment; 
     FIG. 2 is an enlargement of a salient detail; and 
     FIG. 3 is a portion of a schematic longitudinal section view in a plane that includes the direction of the withdrawal path. 
    
    
     Proceeding now to the detailed description of the drawing, FIG. 1 shows a pair of rolls 6, 6a and is, for example, a vertical elevation in a horizontal plane with section taken through a slab ingot 7. The rolls are journalled in the usual manner, and the axes of the rolls have a particular distance from the ingot. The axes can be deemed to run through planes parallel to the surface of the ingot as can be seen also from FIG. 3. Each of the rolls is undivided and extends for more than the width of the slab ingot 7. 
     The figures show representatively spray nozzles 4; only three are shown in FIG. 1, more are provided on the same side, and a similar arrangement is provided on the other side of ingot 7, but on the same side of the horizontal plane as defined, for example, by the two rolls as depicted in FIG. 1. The nozzles 4 (particularly the tips of the smooth wall tubes that define these nozzles) are located closer to the ingot 7 than each of the axes of the withdrawal rolls as treated with reference to the same ingot surface. Moreover, the nozzle tips of a particular group considered are located e.g. underneath a plane as defined e.g. by a pair of oppositely positioned rolls above them. 
     Reference numeral 2 denotes the feeder input for cooling liquid such as water. That water is mixed with an injected gas, e.g. air under pressure of at least two bars. The water as fed is accelerated by the pressurized air as mixed therewith and in an acceleration path 3 serving also as distributor for the coolant. That path is at least 100 mm long, preferably about 400 mm. The distributor outlets are provided by the nozzle elements 4 having a construction shown in greater detail in FIG. 2. 
     Each of the nozzles 4 is a tube with an end portion extending parallel to the surface of ingot 7 and terminating in an obliquely cut end, forming a rather acute angle to the axis of the tube. That axis of each nozzle, of course, extends parallel to the surface of the ingot and in a direction transverse to the direction of casting. That latter direction runs at right angles to the planes of FIGS. 1 and 2. The nozzle tubes may have circular, elliptical, rectangular or trapezoidal cross-section. Therefore, the water-air mixture as ejected by the nozzle fans out rather broadly. The fan-out occurs in a horizontal plane as can be seen from FIG. 2 and also in a vertical plane as illustrated in FIG. 3. The latter fanning is particularly important if one considers that the nozzle is closer to the ingot than the axes of the two vertically arranged rolls. This way one obtains a rather uniform covering of the surface portion of the ingot as extending between the two lines of engagement with the two rolls of FIG. 3. 
     The total amount of spray water ejected against the ingot in such a space between two rolls on one side of the ingot is about 0.1 to 2.2 liters water per kilogram cast steel. The preferred range is from 0.15 to 0.3 liters water per kilogram steel. The amount of water thus sprayed is controlled by the amount of air as injected into the flow of water is fed to nozzle 4. 
     The entire cooling zone as it extends from the bottom of the mold is usually divided into several zones of different lengths. Assuming a slab ingot of 2000 by 200 mm of high tensile strength steel is cast, being identified by × 60 in accordance with API. Such a steel is used for making large pipes. If one uses an air pressure of 4 bar as propellant and for a normal casting speed, one will apply the following quantities of water: 
     Zone 1 -- 65 liter per minute 
     zone 2 -- 65 liter per minute 
     zone 3 -- 35 liter per minute 
     zone 4 -- 45 liter per minute 
     These are the four curved zones. The hozizontal zone (5) thereafter is cooled at a rate of 90 l/min. 
     The invention is not limited to the embodiments described above, but all changes and modifications thereof not consituting departures from the spirit and scope of the invention are intended to be included.