Abstract:
A nozzle, or porous plug, for use with molten metals is provided. The nozzle includes a connection port for connecting to a main gas line and a plurality of capillaries connected to the connection port. The capillaries are encased by refractory to protect them from the intense heat of the process. Typically, the nozzle is located at or near the bottom of a ladle and a gas is injected through the nozzle into the ladle. The gas flowing though the ladle agitates the molten metal and causes the impurities in the molten metal to form a slag. The nozzle allows the gas flow through the nozzle to be shut off during the process to allow additional slag to settle without the molten metal flowing into and plugging the capillaries.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims all of the benefits of, and priority to, U.S. Provisional Application Ser. No. 60/487,089 filed on Jul. 14, 2003. Application Ser. No. 60/487,089 is also titled Ladle Nozzle for Use with Molten Metals and is incorporated herein in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to a molten metal ladle nozzle apparatus and, more particularly, to a ladle nozzle, or porous plug, for use in the manufacture of chemical grade silicon metals.  
       BACKGROUND  
       [0003]     In the art of manufacturing chemical grade silicon metal a great deal of attention is paid to the reduction of the contaminants in the final product. Generally, raw materials are placed in an electric arc furnace where they are heated until they turn into raw molten silicon metal. Once a sufficient amount of silicon metal has been produced, the electric arc furnace is tapped and the raw molten silicon flows into a ladle. Impurities in the raw silicon metal are removed in the ladle during the manufacturing process to obtain a chemical grade silicon metal.  
         [0004]     There are currently two processes of manufacturing chemical grade silicon metal. The first method of manufacture uses sinking slag chemistry. In this method, the slag formed in the ladle is slightly denser then the molten silicon and, as a result, sinks to the bottom of the ladle. The chemical grade molten silicon is poured from the ladle and the remaining slag is removed from the ladle with a rack. The second method of manufacturing chemical grade silicon metal uses floating slag chemistry. In this method, the slag formed in the ladle is lighter then the molten silicon metal and floats on the top of the metal. The slag can be separated from the molten silicon metal with a variety of techniques, such as tapping the ladle from the bottom, blocking the slag with a damn, or skimming the slag off prior to pouring.  
         [0005]     In both manufacturing processes a gas mixture is injected into the ladle to mix the molten silicon metal and to separate the impurities from the molten silicon metal. Typically a nozzle or porous plug located at the bottom of the ladle is used to inject the gas mixture into the ladle. There are two types of porous plugs presently used in the manufacturing process. The first type of porous plug is made from a porous refractory body, and the second type of porous plug is made with either 9 or 12 copper tubes, or capillaries, having an inside diameter of 0.125″. The copper capillaries are encased in a refractory material to enable them to withstand the severe operating temperatures.  
         [0006]     Typically one element of the gas mixture injected into the ladle is oxygen. Injection of oxygen into the molten silicon metal removes impurities by forming slag through the process of oxidation. The slag is primarily composed of calcium and alumina. Injection of air, typically nitrogen, into the ladle agitates and stirs the molten silicon metal to ensure a uniform and consistent end product. The time required to produce chemical grade silicon metal is a function of the level of impurities in the tapped silicon metal and the volume flow of air into the process. To an extent the higher the flow of gas into the ladle, the shorter the process time for the batch. Porous plugs or nozzles made with porous refractory are disadvantageous because only a limited volume flow of gas can be introduced into the ladle through the porous plug. Limiting the flow directly increases the processing time.  
         [0007]     Nozzles using copper capillaries, having an inside diameter of 0.125″, immediately clog when the gas flow through the nozzle is shut off during the process. Back pressure created by the head of the molten metal, the constraints of the capillaries and piping system. The back pressure allows the molten silicon metal to flow into the nozzle capillaries when the gas flow is shut off. Once the molten metal enters the capillaries it cools down and plugs the capillaries.  
         [0008]     In addition, nozzles with copper capillaries tend to develop leaks, which inhibit the gas flow to into the ladle. One reason the nozzles develop leaks is the current construction. Currently the nozzles are made of copper tube and have either 9 or 12 capillary tubes with an inside diameter of 0.125″. The copper tubes are soldered to a cap, or gas inlet connection. During use the nozzles heat up and cool down causing the soldered joints to fail. As a result, gas flows through the failed joints and the proper volume of gas is not delivered through the nozzle into the ladle, resulting in inadequate agitation of the molten liquid, and a slower oxidation process.  
       SUMMARY  
       [0009]     A nozzle, or porous plug, for use with molten metals is provided. The nozzle includes a connection port for connecting to a main gas line and a plurality of capillaries connected to the connection port. The capillaries are encased by refractory to protect them from the intense heat of the process. Typically, the nozzle is located at or near the bottom of a ladle and a gas is injected through the nozzle into the ladle. The gas flowing though the ladle agitates the molten metal and causes the impurities in the molten metal to form a slag. The nozzle allows the gas flow through the nozzle to be shut off during the process to allow additional slag to settle without the molten metal flowing into and plugging the capillaries. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1A  is a sectional view of a ladle, in an upright position, with a nozzle.  
         [0011]      FIG. 1B  is a sectional of a ladle, in a tilted position, with a nozzle.  
         [0012]      FIG. 2  is a prospective view of a nozzle encased in refractory.  
         [0013]      FIG. 3  is a prospective view of a nozzle with nine ports encased in refractory.  
         [0014]      FIG. 4A  is a side view of a portion of a nozzle.  
         [0015]      FIG. 4B  is a cross sectional view of the portion of the embodiment of  FIG. 4 A .  
         [0016]      FIG. 4C  is an end view, looking down, of the embodiment of  FIG. 4A . 
     
    
     DETAILED DESCRIPTION  
       [0017]     The present invention relates generally to an apparatus and, more particularly, to a ladle nozzle, or porous plug, for use in the manufacture of chemical grade silicon metals. Illustrated in  FIGS. 1A and 1B  is a system  100  for use in manufacturing metal products, such as chemical grade silicon metal. The system  100  includes a ladle  105 , a nozzle  110  and a gas line  115 . A typical ladle  105  includes a steel shell that is lined with brick, or a refractory material. The brick lining serves to aid in retaining heat within the ladle  105  and increases the useful life of the ladle  105 . A nozzle or porous plug  110 , which will be described in more detail below, is inserted into an opening in the bottom of the ladle  105 . A gas line  115  is connected to the nozzle  110 . The gas line is configured to introduce gas mixture, such as oxygen and nitrogen into the ladle  105  through the nozzle  110 .  
         [0018]     A nozzle  110  is installed in the ladle  105  and connected to the gas line. The nozzle  110  configuration is selected based on the desired flow rate of the gas mixture  120 . The desired flow rate of the gas mixture  120 , typically between 20 and 55 cubic feet per minute, is determined based on the level of impurities in the molten silicon metal  125  and the desired process time for the batch of chemical grade silicon metal being manufactured. Typical process times range from approximately 40 to 75 minutes. A molten metal  125 , such as molten silicon metal, is tapped into the ladle  105 . A gas mixture  120 , such as oxygen and nitrogen, is forced into the ladle  105  under pressure. Preferably the pressure in the gas line is around 90 PSI and the gas line is capable of delivering a variable flow rate of 20 to 55 standard cubic feet per minute of the gas mixture  120 . The gas mixture  120  flows up from the bottom of the ladle  105  and agitates the molten liquid  125 . The agitation mixes the molten liquid  125  to ensure a uniform and consistent final product. In addition, through the process of oxidation, the oxygen in the gas mixture  120  reacts with the impurities in the molten silicon metal and creates a slag  130 . The resulting slag  130  is primarily composed of calcium and alumina.  
         [0019]     The manufacturing process described herein utilizes a sinking slag methodology of manufacturing chemical grade silicon metals, however, as should be readily understood by one skilled in the art, the nozzle and methods described herein apply to other applications and methodologies, such as floating slag chemistries, as well as with various types and mixtures of molten metals.  
         [0020]     The slag  130  formed in the sinking slag process is slightly heavier than the molten silicon metal  125  and, as a result, the slag  130  sinks to the bottom of the ladle  105 . The agitation of the molten silicon metal  125 , however, inhibits some of the slag  130  from sinking to the bottom of the ladle  105 . As a result, it is desirable to shut off the gas mixture  120  flow into the ladle  105  for a period of time, preferably 10 minutes, prior to tilting the ladle  105  and pouring the final product into molds (not shown). Shutting off the gas flow  120  allows additional slag to settle out of the molten silicon metal  125  providing for an end product with a lower level of impurities.  
         [0021]     Back pressure is created by the head of the molten metal, the components inside the nozzle and the piping system. In conventional nozzles, when the gas flow is turned off, the back pressure allows molten silicon metal to flow into the capillaries. After the molten silicon metal flows into the capillaries it solidifies and plugs the conventional nozzles. As a result, turning off the gas flow during the process using conventional nozzles, results in the required replacement of the nozzle between each batch.  
         [0022]     An embodiment of the present invention permits the gas flow to be turned off during the process without plugging the nozzle and requiring the nozzle to be changed after each batch. Reducing the inside diameter of the capillaries increases the surface tension across the opening of the capillaries. The back pressure, which allows the molten silicon metal to flow into the capillaries can be overcome with a sufficient surface tension. A range of inside diameters, smaller than 0.125″, increase the surface tension to an acceptable level to overcome the back pressure, preferably, the inside diameter is 0.082″. A nozzle utilizing a plurality of capillaries having an inside diameter of 0.082″ permits the use of standard size tubing or piping, allows sufficient flow rates to meet process time requirements and allows the gas flow to be shut off during the process permitting the slag to settle without the molten silicon metal entering the nozzle capillaries and plugging the nozzle.  
         [0023]     Illustrated in  FIG. 1B  is a typical method of removing the molten silicon metal  125  from the ladle  105 . The ladle  105  is tilted and poured out into molds, where the molten silicon metal  125  solidifies and is prepared for shipping. As the level of molten silicon metal  125  in the ladle  105  drops, the nozzle  110  becomes exposed. As soon as the end of the nozzle  110  becomes exposed, the gas flow  120  is turned back on to clear the end of the nozzle  110 . If the gas flow  120  is not turned on the molten silicon metal  125  quickly hardens forming a skull over the capillaries. Once the skull has formed, the nozzle  110  becomes plugged and needs to be replaced. Thus the life of the nozzle can be increased by turning on the air flow. The air flow can be turned on manually or automatically when the ladle  105  is tilted beyond a critical angle. The critical angle varies according to the ladle design and is defined generally as the angle of rotation that results in the nozzle being exposed to the atmosphere.  
         [0024]      FIG. 2  illustrates one view of a nozzle  110  in accordance with an embodiment of the present invention. The nozzle  110  includes a connection port  210  for connecting to a gas line. The connection port  210  has a plurality of capillaries, which will be discussed in more detail below, connected at one end. The capillaries extend from the connection port  210  to the end of the nozzle  110 . The capillaries (not shown) are encapsulated by a refractory material  205 , preferable a 3200° F. refractory material. The capillaries have an inside diameter that is sufficient to overcome the back pressure generated by the head of the molten metal and the gas line components. Preferably, the capillaries have an inside diameter of 0.082″.  
         [0025]     As illustrated in  FIG. 3 , the capillaries  305   a  through  305   i  extend from the connection port  210  ( FIG. 2 ) to the end of the nozzle  110 . Preferably, the refractory  205  is formed in a frusto-conical shape to facilitate insertion into the bottom of the ladle  105 . Other shapes, however, are contemplated and are within the spirit and scope of the present invention.  
         [0026]      FIGS. 4A, 4B  and  4 C illustrate a portion of the nozzle  400  in accordance with one embodiment. A connection port  410 , preferably made with a standard cap, is connected to a plurality of capillaries  405  and  407 . Preferably the connection port  410  is made of a standard 2″ or 3″ 150 lb. # 304 stainless steel cap, however, it should be obvious that the size of the cap can be increased or decreased depending on the desired volume of gas flow and other materials can be used. Preferably the capillaries  405 ,  407  are made of # 304 stainless pipe with an inside diameter of 0.082″. In one embodiment, holes are drilled in the cap and the capillaries are inserted into the holes. The capillaries are welded, preferably spray welded, to the cap. The use of stainless steel components and a spray welding technique greatly enhance the life of the nozzle. A bushing  415  is used to connect the nozzle to a gas line, not shown. The gas flows through the gas line (not shown), through the cap, through the capillaries and out of the nozzle.  
         [0027]     The capillaries  405  and  407  can be arranged in a plurality of orientations, preferably the capillaries are arranged to form an outer circle of capillaries  405 , and in an inner circle of capillaries  407 . Furthermore, the number and size of the capillaries  405  and  407  can be adjusted to accommodate a variety of required gas flow volumes and pressures. Different gas flow volumes and pressures are desired to accommodate different volumes of molten metal, different process times and different levels of impurities in the tapped molten metal. Preferably a variety of nozzles having different numbers of capillaries, such as 18, 15, 13, 11, and 9 capillaries, can be fabricated and stocked to accommodate flexibility during the manufacturing process.  
         [0028]     While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in some detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. As should be obvious, additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described herein. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant&#39;s general inventive concept.