Abstract:
A method and an apparatus for preventing undesirable intensive cooling particularly of the strip edge areas of a cast strand resulting from running water emerging from the bottom opening of a secondary cooling chamber, wherein high-energy spray jets of a deflection medium are produced and directed against the emerging running water transversely of the strip edge areas of the cast strand, such that the running water is deflected from the strip edge areas and is discharged through outlet openings of the secondary cooling chamber arranged on both sides of the cast strand.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and an apparatus for preventing undesirable cooling particularly at the strip edge areas of a cast strand by means of the running water which emerges from the bottom opening of a secondary cooling chamber. 
     2. Description of the Related Art 
     In the operation of continuous casting plants for thin slabs it is known that running water emerges laterally next to the strand where the strand exits the secondary cooling chamber; this causes an undesired intensive undercooling of the strand edges. This effect is intensified as the casting size increases and as the casting speed increases. 
     In a continuous casting plant according to DE-OS 2 208 928, in which the strand is continuously pulled downwardly out of a water-cooled mold and is guided through a supporting and guiding device with rollers, a portion of the cooling device is formed by fan jet nozzles which are arranged parallel to the surface of the strand, i.e., parallel to the long side of the slab and at a distance therefrom, wherein the longitudinal axis of the cooling device extends parallel to the axes of the rollers. Moreover, in accordance with the known continuous casting plant, the fan jet nozzles are arranged in the area of a slab edge and are preferably arranged at both slab edges opposite each other and offset relative to each other. 
     In this known continuous casting plant with an arch-shaped supporting and guiding device for guiding the strand from an essentially vertical direction into an essentially horizontal direction, the cooling device is composed of fan jet nozzles in the area of deflection of the strand, i.e., along approximately ⅓ to ⅔ of the length of the supporting and guiding device. In particular, the cooling device is also at the bottom side of the slab composed of fan jet nozzles. 
     DE-AS 1 558 194 describes a method and an apparatus for cooling a cast strand in a secondary cooling zone. The cast strand is cooled in zones which are offset relative to each other transversely of the strand axis, such that the cooling effects in the zones of adjacent planes supplement each other over the strand surface transversely of the strand axis so as to achieve an approximately uniformly extending cooling effect. 
     DE-AS 1 289 956 discloses a secondary cooling device for continuous casting products with straight or flat surfaces. This cooling device is composed of a plurality of spray or dispersion nozzles arranged transversely of the strand axis. The spray nozzles have a flat characteristic of the impinging quantity of cooling medium and are arranged at such a distance from each adjacent nozzle that the nozzle sides overlap each other to such an extent that the cooling effect in the overlapping portion deviates only slightly from the cooling effect of the surface portions located outside of the overlapping portions. 
     None of the devices known in the art include effective means for preventing the running water from emerging laterally next to the strand and the attendant undesirable intensive cooling of the strip edge areas. 
     SUMMARY OF THE INVENTION 
     Staring from the prior art discussed above, it is the primary object of the present invention to provide a method and an apparatus for carrying out the method in which the emergence of running water from the secondary cooling chamber of a continuous casting plant laterally next to the strand and the attendant undesirable intensive undercooling of the strip edges are prevented. 
     In accordance with the present invention, in a method and an apparatus of the above-described type, high-energy spray jets of a deflection medium are produced and are directed preferably transversely of the strip edge areas against the running water outlet, such that the running water is deflected from the strip edge areas and is discharged through outlet openings of the secondary cooling chamber provided on both sides of the cast strand. 
     The solution according to the present invention of the object described above provides the advantage that an undesirable intensive cooling of the strip edge areas by the running water is suppressed. 
     By adjusting the process parameters, for example, adjustment of direction, energy content and number and throughput quantity of the individual nozzles, the effectiveness of the method according to the invention is optimized to the required extent and the existing conditions of the strand production of a thin slab casting plant are taken into consideration in an optimum manner. 
     In accordance with a further development of the method according to the invention, water or air or a water/air mixture are used as the deflect ion medium. This results in an even better adjustment of the process parameters to the existing production condition of a continuous casting plant. 
     The method according to the present invention further provides that spray jets with flat spray cones are produced. A spray jet of this configuration removes a minimum of heat from the strand, although it cannot be avoided that the deflection medium is also Partially sprayed onto the strand. 
     In accordance with another further development of the method according to the invention, partially overlapping rows of spraying cones are produced transversely on each side of an edge of the cast strand. This ensures that each side of an edge of the cast strand is completely covered with spray jets of the deflection medium. 
     In accordance with another further development of the method of the invention, the spray jets are sprayed preferably at an angle a against the travel direction of the running water. As a result, the deflection of the running water is optimized because the nozzles spray upwardly against the direction of flow of the running water. 
     In accordance with another advantageous embodiment of the invention, the deflection medium is sprayed against the edge areas of the cast strand at a relatively small distance upstream of the bottom opening of the secondary cooling chamber. This results in especially favorable process parameters for the deflection of the running water from the strip edge areas. 
     In accordance with another embodiment of the invention, several nozzles are arranged in a row so as to extend over the width of the strand, wherein individual pairs of nozzles of the rows of nozzles can be switched on or off depending on the changing width of the strand. This is an uncomplicated and advantageous way to provide changeable zones of strip edge areas to be sprayed transversely of the strand axis depending on the respective width of the strand. 
     Finally, the invention provides that the spray jets are sprayed essentially perpendicularly relative to the surface of the strip edge areas. This results in an optimum blocking effect of the emerging running water without the long sides of the strand being impinged in an undesired manner by the spray jets so that the strand edges are not subjected to an undesired cooling effect. 
     An apparatus for preventing an undesirable intensive cooling of the strip edge areas of a cast strand by the running water emerging from the bottom opening of a secondary chamber includes spray nozzles arranged in a row for producing high-energy spray jets directed against the running water outlet, wherein the spray nozzles are arranged at a relatively small distance upstream of the bottom opening of the secondary cooling chamber for the cast strand, and wherein the spray nozzles are combined in rows extending in the direction of the strand width and the spray nozzles are connected individually through throttle means to a feed line. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawing: 
     FIG. 1 is a schematic side view of a continuous casting plant with a spray apparatus according to the invention; 
     FIG. 2 is a sectional view taken along sectional plane II—II in FIG. 1 in the direction towards a cooling chamber bottom; 
     FIG. 3 is a side view of a strand emerging from the cooling chamber with a spray apparatus according to the invention; 
     FIG. 4 is a sectional view taken along sectional plane II—II of FIG. 1 showing the cooling chamber bottom with an arrangement of several spray nozzles and the pipe connections thereof; and 
     FIG. 5 is a sectional view taken along sectional plane II—II of FIG. 1 showing the cooling chamber bottom with spray nozzles arranged in rows. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The part of a continuous casting plant shown in FIG. 1 of the drawing with means for carrying out the method according to the invention is seen in a side view in such a way that the narrow side of the cast strand  6  is visible. 
     The schematic illustration of FIG. 1 shows at the top a mold  22  from which a cast strand  6  is pulled downwardly in accordance with the arrow  21 . The cast strand  6  travels through a strand guiding device  23  (shown only as a black box), arranged within a secondary cooling chamber  8 , also only shown as a black box. The schematic illustration of strand guiding device  23  and cooling chamber  8  without providing structural details was selected for reasons of clarity because it can be assumed that those skilled in the art will be familiar with the structural details of these elements. Provided in the lower portion of the secondary cooling chamber  8  is the bottom  20  thereof with the bottom opening  7  through which the strand  6  together with a flow of running water emerges downwardly. Arranged in the area of this outlet is a supply line  24  for the deflection medium emitted from the spray nozzle  17  in the form of spray jets  10 . This deflection medium may be water or air or a water/air mixture. 
     As seen in the top view of the cooling chamber bottom  20  shown in FIG. 2, the arrangement of spray nozzles  17  visible next to the bottom opening  7  of the cooling chamber  8  includes an upper nozzle row  25  and a lower nozzle row  26 . The individual partially overlapping spray cones  13  produced by the spray jets  10  of the upper and lower nozzle rows are aligned obliquely relative to the travel direction  21  of the cast strand  6  in the area closely above the cooling chamber bottom  20 . 
     This alignment of the rows  15  results in an at least partial overlapping of the spray jets  10  of the upper and lower nozzle rows  25 ,  26 . 
     As can further be seen in the side view of FIG. 3 in the direction towards the narrow side  16  of a cast strand  6 , the spray jets  10  of the upper or lower nozzle rows  25 ,  26  are aligned at an angle a relative to the travel direction of the running water  9 . This results in an optimum deflection of the running water  9 . 
     FIG. 3 of the drawing further shows the cooling chamber bottom  20  which is upwardly inclined towards the cast strand and the bottom opening  7 , wherein the bottom opening  7  is open adjacent the strand  6 . The purpose of the invention is to particularly prevent running water  9  from flowing through the area of the bottom opening  7 . This is achieved by the effect of the high-energy spray jets  10  which impinge on the flow of running water  9  in such a way that the running water is discharged through outlet openings  12  of the secondary cooling chamber  8  arranged on both sides of the cast strand  6 . 
     FIG. 4 is another sectional view of the cooling chamber  8  in the sectional plane II—II of FIG. 1 showing an arrangement of spray nozzles  17  in rows  15  for producing high-energy spray jets  10  at the strip edge areas  11  of the cast strand  6 . 
     The pipe connections of the spray nozzles  17  are formed by supply lines  24  which are individually connected to the side of the nozzle rows  15  to a throttle device  1  to  5  each, wherein these throttle devices  1  to  5 , in turn, are connected to a common feed line  18 . 
     FIG. 4 shows in detail that, with an arrangement of nozzles over the width of the strand  6  with several rows of nozzles  15  at the narrow side areas  16  of the strand  6 , individual pairs of nozzles  1 ,  1 ′;  2 ,  2 ′;  3 ,  3 ′; etc. of the nozzles rows  15  can be switched on or off in dependence on changing strand widths  19 . 
     For illustrating the different strand widths, FIG. 4 schematically shows the shortest strand with b and the greatest strand with B. In between, the strip edge areas  11  can be adapted in steps to the respective conditions. 
     Also in FIG. 4, the rows of nozzles are designated with reference numerals  15 , the spray jets with  10  and the strip edge areas with  16 . Any running water occurring at the narrow sides of the strand  6  is denoted by reference numeral  9 . The pipe connections of the supply lines are denoted by reference numeral  24 . It can also be seen that some lines  24  are shown in solid lines and other lines  24  are shown in dash-dot lines. The purpose of this is to indicate that pipe lines  24  or spray nozzles  17  can be switched on or off depending on the shorter width b or the greater width B of the cast strand  6 . 
     Finally, FIG. 4 also shows the bottom opening  7  in the cooling chamber bottom  20 . Denoted with reference number  17  are the variable width sections of the cast strand  6  which indicate a stepwise change of the strand width. 
     FIG. 5 of the drawing is also a top view on a larger scale taken along sectional plane II—II in FIG. 1 showing the structural elements of the apparatus of the present invention, i.e., the strand  6 , the bottom chamber  7 , the cooling chamber bottom  20 , the running water  9  whose discharge is to be prevented in the area of the strip edges  11 , as well as the arrangement of nozzle rows  15  with spray nozzles  17 . The supply lines to the nozzles  17  are in their totality denoted by reference numeral  24 . 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.