Abstract:
Method and apparatus for flowing molten metal substantially vertically into a mold by means of a feeder tube while concurrently impeding the flow of oxides that collect at the perimeter of the head of the feeder tube. This reduces inclusions in the molten metal and improves the quality of a molded component as the molten metal solidifies.

Description:
RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Application Ser. No. 60/839,853, entitled “Method and Apparatus for Filtered and Controlled Flow Metal Molding” by Stoyanov et al, and which was filed on Aug. 23, 2006. 
    
    
     BACKGROUND 
     In the past, metal molding relied on filling a cavity with molten metal and then allowing the metal to cool. A feeder tube is used to direct the molten metal into the cavity. Unfortunately, oxides form as a result of exposure of the molten metal to the material comprising the feeder tube. These oxides then find their way into the mold cavity along with the desired alloy. This causes an undesired effect in the resultant molded part in that the oxides weaken the final molded component. 
     Another problem that has not yet been addressed is that the flow of molten metal into the feeder tube is not controlled. Turbulent flow of the metal causes voids in the final molded part, again weakening its structural characteristics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Several alternative embodiments will hereinafter be described in conjunction with the appended drawings and figures, wherein like numerals denote like elements, and in which: 
         FIG. 1  is a flow diagram that depicts one example method for forming a casting; 
         FIG. 1A  is a pictorial representations of a molding machine that illustrates application of the present method; 
         FIG. 2  is a flow diagram that depicts one alternative method for impeding the flow of oxides that collect at the perimeter of the head of the feeder tube; 
         FIG. 3  is a flow diagram that depicts one alternative method for reducing inclusions in the molten metal; 
         FIG. 4  is a flow diagram that depicts an alternative method for filtering which substantially prevents introduction of impurities into a molten material; 
         FIG. 5  is a flow diagram that depicts an alternative variation of the present method that promotes recycling of excess material from a molded part; and 
         FIG. 6  is a pictorial diagram that illustrates one example embodiment of a filter; 
         FIGS. 6A and 6B  are pictorial diagrams that illustrate another illustrative embodiment of a filter. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a flow diagram that depicts one example method for forming a casting. According to this example method, the casting is formed by flowing molten metal substantially vertically into a mold by means of the feeder tube (step  5 ). The oxides that are collected at the perimeter of the head of the feeder tube are impeded in their flow (step  10 ) according to this example method. And inclusions in the molten metal are also reduced (step  15 ). The molten metal is then allowed to solidify (step  20 ). In one alternative example method, these process steps are accomplished in a manner where the chemistry of a molding material, for example an aluminum alloy, is not appreciably changed by the introduction of impurities to the molten metal. It can be appreciated that the present method may be applied in a vertical casting process that employees either vacuum, low-pressure or counter pressure molding. The scope of the claims appended hereto is to include this example method and variations thereof and an article of manufacture produced according to the teachings of the present method. 
       FIG. 1A  is a pictorial representation of a molding machine that illustrates application of the present method. In this example embodiment of a molding machine, the molding machine comprises an upper mold  70  and a lower mold  75 . A divider  80  projects into a mold cavity  85  from the upper mold  70 . The lower mold  75  is substantially concentric about a feeder tube  90 . In operation, molten metal is directed upwards  95  though the feeder tube into the mold cavity  85 . It should also be appreciated that, as the molten metal is directed outward  95  through the feeder tube  90 , contact between the molten metal and an inner surface  105  of the feeder tube induces the formation of oxides within the molten metal. The top portion of the feeder tube  90  is typically referred to as the head  110  of the feeder tube  90 . Generally, these oxides are more prevalent about the perimeter of the feeder tube as the molten metal flows upward there through. 
       FIG. 2  is a flow diagram that depicts one alternative method for impeding the flow of oxides that collect at the perimeter of the head of the feeder tube. According to this alternative method, the flow of oxides is impeded by filtering the molten metal proximate to the perimeter of the head of the feeder tube (step  25 ). Referring again to  FIG. 1A , one application of the present method provides for introducing a filter  100  on top of the feeder tube  90 . The filter  100  rests on a perimeter lip  91  of the feeder tube  90 . The filter  100  is held in place by the divider  80  as a divider and the upper mold  70  are collectively moved downward toward the bottom mold. 
       FIG. 3  is a flow diagram that depicts one alternative method for reducing inclusions in the molten metal. According to this alternative example method, inclusions in the molten metal are reduced by encouraging laminar flow of the molten metal by restricting the flow of the molten metal to a progressively smaller cross section as the molten metal proceeds into the mold (step  30 ). In one variation of the present method, this is accomplished by introducing a filter  100  having a substantially conical shape. This conical shape promotes yet another aspect of this alternative variation of the present method whereby the progressively smaller cross section impedes the entry of oxides into the mold cavity (step  35 ) formed between the upper mold  70  and bottom mold  75 . 
       FIG. 4  is a flow diagram that depicts an alternative method for filtering which substantially prevents introduction of impurities into a molten material. As already discussed, the method steps described herein, according to one variation of the present method, are accomplished in a manner whereby the chemistry of the molten material is not altered in any significant manner. As such, this variation of the present method provides for introducing a filter proximate to head of the feeder tube wherein the filter is made of a material that is inert relative to the molten metal (step  40 ). It should be appreciated that any material which is resistant to reaction with the molten material may be used. For example, a fiber material may be used. A fiberglass material may also be used. A wide variety of materials may be used so long as a filter itself maintains a shape when subjected to the temperatures involved in process of flowing molten metal through the feeder tube  90  into the mold cavity  85 . In one alternative method, the filtering is accomplished at a temperature of at least 800 C. 
       FIG. 5  is a flow diagram that depicts an alternative variation of the present method that promotes recycling of excess material from a molded part.  FIG. 1A  illustrates that the mold cavity  85  may have residual material  87  proximate to center of the mold cavity  85 . Accordingly, it will be highly beneficial to recycle this residual material  87 . According to prior art, any impurities found in the residual material would render it impractical, or economically infeasible to recover the residual material  87 . According to the present method, the excess material  87  is substantially free of impurities by virtue of the fact that, according to this variation of the present method, the filter  100  introduced at the head  110  of the feeder tube  90  comprises a material that is inert relative to the molten metal. But really, this variation of the present method provides for removing the excess material that includes the filter made of inert material from the casting (step  45 ). The excess material is then smelted (step  50 ). Through a process of degassing, the inert filter material is then separated from the excess material (step  55 ). 
       FIG. 6  is a pictorial diagram that illustrates one example embodiment of a filter. According to this example embodiment, a filter  100  comprises a mesh sheet that is stamped into a substantially conical shape having sloped sides  125  with a flat top section  120 . At the bottom perimeter of the conical shape, the mesh sheet is curled upward to form a rim  145 . When the filter  100  is used, the rim  145  is disposed on the periphery of a feeder tube included in a mold. In order to hold the filter in place, a force  130  is applied downward substantially at the center of the flat top section  120 . Due to the conical shape of the filter, the bottom perimeter of the filter will tend to expand (i.e. force  140 ). This expansion is resisted by the form of the rim  145 . Accordingly, upward force  135  is applied by the support of the perimeter of the feeder tube. In one alternative embodiment, the mesh sheet comprises a fiber material. In yet another alternative embodiment, the mesh sheet comprises a material that is inert relative to the material to be molded. In yet another alternative embodiment, the mesh sheet comprises a material that can withstand molding temperatures of at least 800 C without melting or otherwise losing much of its form, i.e. substantially maintains its shape in these operating temperatures. 
       FIGS. 6A and 6B  are pictorial diagrams that illustrate another illustrative embodiment of a filter. According to this example embodiment, a filter  100  comprises a mesh sheet formed into a substantially conical shape having sloped sides  125 . In order to hold the filter in place, a force  130  is applied downward substantially at the top of the filter. Due to the conical shape of the filter, the bottom perimeter of the filter will tend to expand (i.e. force  140 ) against the inside of the feeder tube included in a mold assembly. An upward force  135  is applied by the support of the perimeter of the feeder tube. In one alternative embodiment, the mesh sheet comprises a fiber material. In yet another alternative embodiment, the mesh sheet comprises a material that is inert relative to the material to be molded. In yet another alternative embodiment, the mesh sheet comprises a material that can withstand molding temperatures of at least 800 C without melting or otherwise losing much of its form, i.e. substantially maintains its shape in these operating temperatures. 
     While the present method and apparatus has been described in terms of several alternative and exemplary embodiments, it is contemplated that alternatives, modifications, permutations, and equivalents thereof will become apparent to those skilled in the art upon a reading of the specification and study of the drawings. It is therefore intended that the true spirit and scope of the claims appended hereto include all such alternatives, modifications, permutations, and equivalents.