Abstract:
A nozzle for transferring a flow of liquid metal between metallurgical vessels or molds comprising an entry portion for receiving the liquid metal. A flow regulator, such as a stopper rod, is movable from an open position to a closed position with respect to the entry portion for respectively permitting and prohibiting flow through the nozzle. The entry portion and the flow regulator define a control zone therebetween. A pressure modulator, downstream of the control zone, is adapted to minimize a pressure differential across the control zone. The pressure modulator constricts flow downstream of the control zone.

Description:
[0001]    This Application claims the benefit of U.S. Provisional Application Ser. No. 60/213,773, filed Jun. 23, 2000, the entire disclosure of which is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    During processing, liquid metals, and in particular liquid steel, flow from one vessel, such as a tundish, into another vessel, such as a mold, under the influence of gravity. A nozzle may guide and contain the flowing stream of liquid metal during passage from one vessel to another.  
           [0003]    Controlling the rate of flow of the liquid metal during processing is essential. To this end, a regulator or flow controller allowing adjustment of the rate of liquid metal flow is used. A common regulator is a stopper rod, although any type of flow regulator known to those skilled in the art can be used. Thus, a typical continuous steel casting process allows liquid metal to flow from a tundish into a mold, through a nozzle employing a stopper rod for flow regulation.  
           [0004]    Referring to FIG. 1, in such a typical continuous steel casting process, a tundish  15  is positioned directly above a mold  20  with a nozzle  25  connected to the tundish  15 . A nozzle  25  provides a conduit through which liquid metal  10  flows from the tundish  15  to the mold  20 . A stopper rod  30  in the tundish  15  controls the rate of flow through the nozzle  25 .  
           [0005]    [0005]FIG. 2 is a partial schematic view, drawn to an enlarged scale, of an entry portion and a lower portion  40   35  of a nozzle bore  45  of the nozzle  25  of FIG. 1. In FIG. 2, the entry portion  35  extends between points  1  and  2 . The lower portion  40  extends between points  2  and  3 . The entry portion  35  of the nozzle bore  45  is in fluid communication with liquid metal  10  contained in the tundish  15 . The lower portion  40  of the nozzle bore  45  is partially submerged in liquid metal  10  in the mold  20 .  
           [0006]    Returning back to FIG. 1, to regulate the liquid metal flow rate from the tundish  15  into the mold  20 , the stopper rod  30  is raised or lowered. For example, the flow of liquid metal  10  is stopped if the stopper rod  30  is lowered fully so that a nose  50  of the stopper rod  30  blocks the entry portion  35  of the nozzle bore  45 . As the stopper rod  30  is raised above the fully lowered position, liquid metal can flow through the nozzle  25 . The rate of flow through the nozzle  25  is controlled by adjustment of the position of the stopper rod  30 . As the stopper rod  30  is raised, the nose  50  of the stopper rod  30  is moved farther from the entry portion  35  of the nozzle bore  45 , which increases the open area between the stopper nose  50  and the nozzle  25  allowing a greater rate of flow.  
           [0007]    [0007]FIG. 3 shows another liquid metal flow system from the tundish  15  to the mold  20 . This system has a control zone  55  located between the nose  50  of the stopper rod  30  and the entry portion  35  of the nozzle bore  45 . The control zone  55  is the narrowest part of the open channel between the stopper nose  50  and the entry portion  35  of the nozzle bore  45 . Liquid metal  10  in the tundish  15  has a static pressure caused by gravity. If the stopper rod  30  does not block the entry of liquid metal  10  into the bore  45  of the nozzle, the pressure of liquid metal  10  in the tundish  15  forces liquid metal  10  to flow out of tundish  15  and into nozzle  25 .  
           [0008]    When the flow is less than the maximum, the characteristics of the open area of control zone  55  are primary factors in the regulation of the rate of flow into the nozzle  25  and subsequently into the mold  20 .  
           [0009]    [0009]FIG. 4 graphically shows changes in the pressure of liquid metal  10  flowing out of the tundish  15  through the control zone  55  and into the nozzle  25 . As shown in FIG. 3, point  60  represents a general location within the liquid metal  10  contained in the tundish  15  upstream of the control zone  55 . Point  65  represents a general location within the open bore  45  of the nozzle  25  downstream of the control zone  55 . As shown in FIG. 4, the general trend in the pressure of liquid metal  10  between points  60  and  65  is a sharp drop in pressure across the control zone  55 . The pressure at  60  is generally higher than atmospheric pressure. The pressure at  65  is generally less than atmospheric pressure, resulting in a partial vacuum.  
           [0010]    [0010]FIG. 5 illustrates a two-component nozzle, including an entry insert  70  and a main body  75 . The entry portion  35  of bore  45  extends from points  21  to  22  to  23 , and the lower portion  40  extends from points  23  to  24 .  
           [0011]    [0011]FIG. 6 illustrates a liquid metal flow system, from tundish  15  to mold  20  and incorporates the nozzle of FIG. 5. FIG. 7 illustrates the pressure trend from point  60  to point  65  in the system of FIG. 6. The pressure trend for the system of FIG. 6 basically is the same as that for FIG. 3, including a sharp drop in pressure across control zone  55 .  
           [0012]    In summary, the nozzles of FIGS. 1, 3 and  6  cause a sharp pressure drop across the respective control zones. This sharp pressure drop causes the flow regulation system to be overly sensitive. An overly sensitive flow regulation system tends to cause an operator to continually hunt, or move the regulator to achieve the correct position so as to adjust the size and/or geometry of the control zone for flow stabilization at a desired rate. Hunting for the proper flow regulation causes turbulence in the entry portion  35  and throughout the bore  45  of the nozzle  25 .  
           [0013]    Turbulence caused by hunting and also by the partial vacuum/low pressure generated downstream of the control zone accelerate erosion around the control zone. For example, erosion of a nose  50  of a stopper rod  30  and an entry portion  35  of a nozzle bore  45  can occur. The highest rate of erosion generally occurs immediately downstream of the control zone  55 . Erosion in and about the control zone  55  exacerbates difficulties associated with liquid metal flow rate regulation. Undesirable changes in the critical geometry of the control zone  55 , as a result of erosion, lead to unpredictable flow rate variances, which ultimately can result in the complete failure of a flow regulation system.  
           [0014]    Referring again to FIG. 5, for reducing erosion, hence improving flow regulation, in some nozzles the entry insert  70  is generally composed of an erosion-resistant refractory material. However, the addition of the entry insert  70  to the nozzle  40  does not affect the sharp pressure drop across control zone  55 , as shown in FIGS. 4 and 7. Thus, flow regulation for conventional nozzles remains overly sensitive to regulator movements, due to the size and shape of the control zone defined thereby, making flow rate stabilization difficult to achieve.  
           [0015]    Accordingly, a need exists for a nozzle that minimizes the pressure differential across a nozzle control zone, reducing the corrosive effects thereof and stabilizing the size and shape of the control zone, thereby reducing hunting and increasing flow stability.  
         SUMMARY OF THE INVENTION  
         [0016]    The present invention fulfills the above-described need by providing a nozzle with a minimal pressure differential across a nozzle control zone, reducing the corrosive effects thereof and stabilizing the size and shape of the control zone, thereby reducing hunting and increasing flow stability.  
           [0017]    To this end, the present invention includes a nozzle for controlling a flow of liquid metal including an entry portion for receiving the liquid metal. A regulator such as a stopper rod is movable from an open position to a closed position with respect to the entry portion for respectively permitting and prohibiting flow through the nozzle. The entry portion and the regulator define a control zone therebetween. A pressure modulator, downstream of the control zone, is adapted to minimize a pressure differential across the control zone. The pressure modulator constricts flow downstream of the control zone.  
           [0018]    The invention diminishes the sharp pressure drop across the control zone by modulating the pressure in the nozzle downstream of the control zone, reduces the turbulence of the flow immediately downstream of the control zone, and eliminates over-sensitivity of flow regulation. The nozzle of the present invention can reduce erosion in the region of the control zone and stabilize flow regulation, which improves flow control and mold level control during continuous casting.  
           [0019]    Other features and advantages of the present invention will become apparent from the following description of the invention, which refers to the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a schematic view of a liquid metal flow system incorporating a prior art continuous casting nozzle;  
         [0021]    [0021]FIG. 2 is a partial schematic view, drawn to an enlarged scale, of an entry portion and lower portion of the nozzle bore of the prior art nozzle of FIG. 1;  
         [0022]    [0022]FIG. 3 is a schematic view of a liquid metal flow system incorporating a second prior art continuous casting nozzle;  
         [0023]    [0023]FIG. 4 is a graphical view of the fluid pressure of liquid metal flowing through the embodiment of FIG. 3;  
         [0024]    [0024]FIG. 5 is a partial schematic view, drawn to an enlarged scale, of an alternative entry portion and lower portion of the nozzle bore of the prior art nozzle of FIG. 1;  
         [0025]    [0025]FIG. 6 is a schematic view of a liquid metal flow system incorporating the nozzle of FIG. 5;  
         [0026]    [0026]FIG. 7 is a graphical view of the fluid pressure of liquid metal flowing through the embodiment of FIG. 6;  
         [0027]    [0027]FIG. 8 is a schematic view of a liquid metal flow system incorporating a first embodiment of the continuous casting nozzle according to the present invention;  
         [0028]    [0028]FIG. 9 is a partial schematic view, drawn to an enlarged scale, of the entry portion, pressure modulator and lower portion of the embodiment of FIG. 8;  
         [0029]    [0029]FIG. 10 is a graphical view of the fluid pressure of liquid metal flowing through the embodiment of FIG. 8;  
         [0030]    FIGS.  11 - 16  are schematic views of alternative pressure modulators for the embodiments of FIGS. 8 and 9;  
         [0031]    [0031]FIG. 17 is a schematic view of a liquid metal flow system incorporating a second embodiment of the continuous casting nozzle according to present invention;  
         [0032]    [0032]FIG. 18 is a partial schematic view, drawn to an enlarged scale, of the entry portion, pressure modulator and lower portion of the embodiment of FIG. 17;  
         [0033]    [0033]FIG. 19 is a graphical view of the fluid pressure of liquid metal flowing through the embodiment of FIG. 17; and  
         [0034]    FIGS.  20 - 26  are partial schematic views of alternative entry portions and lower portions of the nozzle bore of the continuous casting nozzle of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0035]    [0035]FIGS. 8 and 9 show a first embodiment of the nozzle  100  of the present invention. FIG. 8 shows a liquid metal flow system, from a tundish  15  to a mold  20  that incorporates a nozzle  100 . FIG. 9 shows an enlarged view of the nozzle  100 .  
         [0036]    Referring to FIG. 9, nozzle  100  includes two components: a pressure modulator entry insert  105  and a main body  110 . The nozzle  100  has a bore  115  that is divided into three portions: an entry portion  120 , extending from point  121  to point  122 ; a pressure modulator portion  130 , extending from point  122  to point  123  to point  124  to point  125  to point  126 ; and a lower portion  140 , extending from point  126  to point  127 .  
         [0037]    The pressure modulator  130  generates sudden, strong flow compression. The compression minimizes the pressure differential across the control zone of nozzle  100 , as discussed below, reducing the corrosive effects thereof and stabilizing the size and shape of the control zone. This reduces hunting and increases flow stability.  
         [0038]    Referring to FIG. 8, the nozzle  100  has a control zones  55  located between the nose  50  of a stopper rod  30  and the entry portion  120  of the nozzle bore  115  on opposite sides of the nose  50 . One skilled in the art will appreciate that any known flow regulator can be used in place of the stopper rod  30 .  
         [0039]    Each control zone  55  is the narrowest part of the open channel between the entry portion  120  of the nozzle bore  115  and the stopper nose  50 . In general, each control zone  55  is located above the pressure modulator portion  130  and is defined by any structure capable of modifying the control zone  55  and regulating liquid metal flow into the pressure modulator portion  130 .  
         [0040]    The pressure modulation of nozzle  100  is effected using a constriction zone. The liquid metal system of FIG. 8 has a constriction zone  150  located downstream of the control zone  55  of the nozzle  100 . The constriction zone  150  is located across the narrow part of the nozzle bore  115 , defined by a pressure modulator insert  105 . If the stopper rod  30  does not block the entry portion  120  of the nozzle bore  115 , opening the control zone  55  to allow flow, the pressure of the liquid metal  10  caused by gravity in the tundish  15  causes liquid metal  10  to flow out of the tundish  15  and into the nozzle  100 . When the flow is less then the maximum, the characteristics of the open area of the control zone  55  are primary factors in flow rate regulation into the nozzle  100  and subsequently into the mold  20 .  
         [0041]    Changes in the pressure of the liquid metal  10  as it flows out of the tundish  15 , through the control zone  55 , and into the entry portion  120 , of the nozzle  100 , and then through the constriction zone  150  into the lower portion  140  thereof is illustrated schematically in FIG. 10. Point  60  represents a general location within the liquid metal contained in the tundish  15  upstream of the control zone  55 . Point  65  represents a general location within the open bore of the nozzle downstream of the control zone  55 , but upstream of the constriction zone  150  in the modulator portion  130  of nozzle bore  115 . Point  80  represents a general location within the open bore of the nozzle downstream of constriction zone  150  in lower portion  140  of nozzle bore  115 .  
         [0042]    As shown in FIG. 10, a small initial drop in pressure across the control zone  55  is followed by another drop in pressure across the constriction zone  150 . Points  60  and  65  in FIGS. 8, 10,  17  and  19  are analogous to points  60  and  65  in FIGS. 3, 4,  6  and  7 . Comparing FIG. 10 with FIGS. 4 and 7 demonstrates that the constriction zone  150  caused by the pressure modulator portion  130  reduces the magnitude of the pressure drop across the control zone  55 . Thus, the pressure at point  65  is modulated such that the pressure drop across the control zone  55  is reduced.  
         [0043]    Referring again to FIG. 9, pressure modulator  130  of nozzle  100  has design parameters A, B, L1 and L2. For simplicity, FIGS.  11 - 16  show wireform schematic views of various configurations derived from altering the foregoing parameters. “A” is the size of the constriction zone. “B” is the size of the open channel in pressure modulator portion  130  of the bore at or immediately upstream of the constriction zone. “L1” is the length of the pressure modulator above the constriction. “L2” is the length of the constriction zone. The region of the flow, which is upstream of the constriction, within the pressure modulator, is the pressure space. The constriction ratio is defined as B/A. The pressure space ratio is defined as L1/B. The relative constriction length ratio is defined as L2/A.  
         [0044]    The pressure at point  65  is influenced by the constriction ratio, the pressure space ratio and the relative constriction length ratio of the pressure modulator. To effectively influence and modulate the pressure at point  65 , flow separation in the pressure space must be minimized, and this generally requires the constriction ratio (B/A) to be greater than about 1.4, the pressure space ratio (L1/B) to be greater than about 0.7 and less than 8.0, and the relative constriction length ratio (L2/A) to be less than about 6.0.  
         [0045]    FIGS.  11 - 16  also show an angle Φ between the shelf of the constriction and the upstream nozzle bore. The magnitude of angle Φ may influence the efficiency of the flow constriction, and therefore the effectiveness of the pressure modulator. For acceptable efficiency, angle Φ should be less than about 135° and, preferably, ranges from about 80° to 100°.  
         [0046]    If angle Φ is too large, or too small, the pressure modulator is less able to effect sudden constriction of the flow or a strong pressure gradient, and thus is less able to modulate pressure. If the pressure modulator is unable to modulate pressure, then, as in prior art nozzles, the nozzle would not reduce the pressure differential across a nozzle control zone. A reduced pressure differential decreases corrosive effects and stabilizes the size and shape of the control zone, thereby reducing hunting and increasing flow stability.  
         [0047]    For example, if angle Φ is too small, when a nozzle is configured as in FIG. 13, where the walls of the pressure modulator upstream of the constriction expand toward the constriction zone, pressure modulation may suffer because within the pressure space severe flow separation can occur. Flow separation in the pressure space decreases the ability of the pressure modulator to modulate pressure. Similarly, if angle Φ is too small, when a nozzle is configured as in FIG. 15, severe flow separation can occur within the pressure space. Decreases in angle Φ increase the risk of flow separation.  
         [0048]    [0048]FIG. 16 also shows a radius R between the top shelf of the constriction and the upstream nozzle bore. Also, for acceptable efficiency and effectiveness, radius R must be less than (B−A)/2, and preferably less than (B−A)/4.  
         [0049]    The flow of liquid metal  10  enters into the pressure modulator proximate to the portion defining length L1, which has a general size B, such that the ratio L1/B ranges from about 0.7 to 8.0, a preferred range being from about 1.0 to 2.5. The flow is constricted at the shelf  135  of the pressure modulator portion  130 , the general size B reducing down to size A. The ratio of B/A should be greater than about 1.4 and, preferably ranges from about 1.7 to 2.5. As discussed above, the shelf defines angle Φ between the shelf and the upstream bore of the pressure modulator. Angle Φ must be less than about 135° and, preferably, ranges from about 80° to 100. The constriction of the pressure modulator has a length L2, where a ratio of L2/A is less than about 6.0, preferably ranging from about 0.3 to 0.5.  
         [0050]    [0050]FIG. 17 shows a second liquid metal flow system, from a tundish  15  to a mold  20 , that incorporates a second embodiment of the nozzle  200  according to the present invention. As shown in FIG. 18, nozzle  200  includes three components: an entry insert  203 , a pressure modulator insert  205  and a main body  210 . Like nozzle  100 , nozzle  200  has a bore  215  that is divided into three portions: an entry portion  220 , extending from point  221  to point  223 ; a pressure modulator portion  230 , extending from point  223  to point  227 ; and a lower portion  240 , extending from point  227  to point  228 . The entry insert  203  is separate from the pressure modulator insert  205  because each wears at different rates. The entry insert  203  and the pressure modulator insert  205  may be replaced independently as needed.  
         [0051]    Like the pressure modulator  130 , the pressure modulator  230  generates sudden, strong fluid compression, which minimizes the pressure differential across and corrosion of the control zone of the nozzle  200  and ultimately increases flow stability.  
         [0052]    The present invention also may assume the configurations of FIGS.  20 - 26 , all of which include nozzles  300 ,  400 ,  500 ,  600 ,  700 ,  800  and  900 , which provide for pressure modulation as described above. Each of the nozzles  300 ,  400 ,  500 ,  600 ,  700 ,  800  and  900  has three portions which correspond to the three portions of FIGS. 8 and 17: an entry portion  320 ,  420 ,  520 ,  620 ,  720 ,  820  or  920 ; a pressure modulator portion  330 ,  430 ,  530 ,  630 ,  730 ,  830  or  930 ; and a lower portion  340 ,  440 ,  540 ,  640 ,  740 ,  840  or  940 . FIGS.  20 - 23  show embodiments with post modulation lower portions of different configurations for various purposes. FIGS.  24 - 26  show embodiments with pre-modulation entry portions of different configurations for various purposes. So long as the pressure modulator is as described above, various post or pre-modulation configurations will obtain the beneficial effects provided thereby.  
         [0053]    Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. The present invention is not to be limited by the specific disclosure herein.