Patent Publication Number: US-2003221517-A1

Title: Article and method for treating molten metal bath

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001] (Not applicable)  
       STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT  
       [0002] (Not applicable)  
       TECHNICAL FIELD OF THE INVENTION  
       [0003] The invention relates to the production of metal products from molten metal, and more specifically, relates to an article of manufacture and method for treating a molten metal bath by introducing metallic particles into a molten metal mixture and, as a consequence, thereby enhancing the yield of metal products from the molten metal mixture.  
       BACKGROUND OF THE INVENTION  
       [0004] Metal products such as steel are typically produced in a process wherein a metallic substance such as iron ore is combined with other substances to create a molten mixture from which the desired metal product is produced. For example, steel is produced from a molten bath of iron and carbon. The bath typically contains substances other than the major desired metal-forming constituents. For example, other substances may be added to the mixture to produce a desired quality of finished metal product. As a further example, the bath may contain impurities that were included with the raw materials used to form the bath.  
       [0005] Slag is generally considered to be a fused substance that floats on top of a molten metal mixture. Slag is distinct from the molten metal, typically contains most of the impurities and other undesirable substances that are by products of the production process and is separated from the molten metal at some point in the production process. Typical undesirable substances found in slag and often to at least some extent in the bath are oxides of metals. For example, in the production of steel, iron oxide is an undesirable substance found in the slag and bath in general. What makes the iron oxide undesirable is that iron in this form cannot be subjected to the chemical reaction that produces steel. The iron must be freed from the oxygen in the compound to be useful, thereby increasing the yield of the process.  
       [0006] A means for breaking down oxide substances in a metal-making process such as steel-making is to place a substance in the slag and/or molten bath that will cause the oxide to release the metal, such as iron, in the oxide. A problem in attempting to add substances to a slag and molten metal bath is that the temperature of the slag and bath are so high that the additive is often substantially incinerated before it reaches the slag or the bath.  
       [0007] It can be appreciated that it would be useful to have a means for treating a molten metal bath so as to enhance the yield of the production process.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008] In accordance with a preferred embodiment of the invention, metallic particles are coated and then added to slag and a molten metal bath to treat the bath. The metallic particles selected are capable of causing iron or other desired metal to break free from its oxide and are coated with a refractory that prevents premature incineration.  
       [0009] In accordance with another aspect of a preferred embodiment of the invention, the metallic particles are aluminum particles.  
       [0010] In accordance with a further aspect of a preferred embodiment of the invention the refractory is an oxide or carbide.  
       [0011] In accordance with yet a further aspect of the invention, a binder is added to promote adherence of the refractory to the metallic particles.  
       [0012] Other advantages and objects of the present invention will be apparent from the following description, the accompanying drawings, and the appended claims. 
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
     [0013]FIG. 1 is a perspective illustration of a typical metallic particle in accordance with the teachings of a preferred embodiment of the invention;  
     [0014]FIG. 2 is a cross-sectional view of the metallic particle of FIG. 1 taken along line A-A; and  
     [0015]FIG. 3 is the cross-section view of FIG. 2 of a typical metallic particle that has been coated in accordance with the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION PREFERRED EMBODIMENTS OF THE INVENTION  
     [0016] Throughout the drawings, the same reference numerals are used to denote the same or like features of the invention.  
     [0017] The invention teaches an article and method for treating a molten metal bath in a metal producing process and an article of manufacture for treating the bath. The metal that is to be produced from the molten metal bath may for reference be considered the first metal in the teachings of the invention. In accordance with a teaching of the preferred embodiment initially discussed herein, the first metal is iron in a molten-iron bath with other ingredients (principally carbon) to make the iron-based product steel.  
     [0018] In order to free the first metal that is contained in the slag and that may also exist in the bath in the form of an oxide of the first metal, a second metal is added to the mixture. The second metal is selected for its ability to interact with the oxide of the first metal to take on the oxygen from the first metal oxide thereby freeing up the first metal and forming an oxide of the second metal. In the preferred embodiment wherein iron is the first metal, a suitable second metal having the properties described above is aluminum.  
     [0019] The second metal is added to the bath optimally in small particles to facilitate thorough interaction with the slag and bath admixture. Small particles of metal may take many forms including but not limited to shreds, grindings, chips, screenings, fines and irregularly shaped scraps. Referring now to FIG. 1, a typical particle  10  in shred form is depicted. Referring now to FIG. 2, the particle  10  is shown in cross-section taken along line A-A of FIG. 1.  
     [0020] The minute sizes of particles  10  used in accordance with the teachings of the invention promote interaction thereof with the first metal oxide. However, because the particles are so small combustion thereof is readily promoted. If the particles  10  combust before interaction in the admixture they are not effective in freeing the first metal from its oxide compound.  
     [0021] The particles  10  are coated with a refractory, typically produced as ceramic material, to inhibit premature incineration. FIG. 3 is an illustration of a coated particle  20  showing in the cross-sectional configuration of FIG. 2 the refractory coating  12  as applied to the particle  10 . Suitable refractory materials are metallic oxides and metallic carbides. Examples of suitable metallic oxides include calcium oxide, aluminum oxide, magnesium oxide, silicon dioxide, iron oxide, ferric oxide, zirconium dioxide and barium oxide. Examples of suitable metallic carbides include calcium carbide, silicon carbide and boron carbide. The invention teaches the use of a metallic oxide alone, or a metallic carbide alone, or a combination of a metallic oxide and a metallic carbide.  
     [0022] The invention further teaches the use of a binder to promote adhesion of the refractory to the particle. A suitable binder is cement. Preferred cements are portland concrete cement and calcium aluminate cement.  
     [0023] The refractory increases the mass and weight of the metallic particles  10 . The particles  10  are dropped into the bath from above. Heavier particles fall more quickly and are dispersed more thoroughly into the bath thereby lessening the possibility of premature combustion and incineration. The coated, weighted particles  20  mix more thoroughly and interact more readily. An optimum range of percentage weight of the refractory to the total weight of the coated particles is from about 2 percent to about 60 percent. The following are examples of suitable percentages by weight of components to treat a molten iron bath in accordance with the teachings of the invention:  
                                                          Example 1                   Metallic particles:   aluminum   50 -75%           Oxides:   calcium oxide or               aluminum oxide or               magnesium oxide   40-20%           Cement (binder)   portland   10%           Example 2           Metallic particles   aluminum   50%           Oxide   aluminum   25%           Carbide   calcium   20%           Cement   calcium aluminate    5%                      
 
     [0024] Minor changes may be made in the teachings of the invention described above without departing from the scope or spirit of the invention.