Fill tube with vitreous coating

Abstract

A fill tube for die casting machine includes a vitreous coating thereon effective to reduce or eliminate the flow of air through the gas permeable wall of the fill tube during die casting when air pressure is applied on the molten metal or alloy in the vessel.

I claim:  
     
         1 . A ceramic fill tube for a die casting machine wherein said fill tube includes a passage for conveying molten metal or alloy, said fill tube having a vitreous coating that reduces passage of a pressurizing gas present outside of said fill tube into said passage.  
     
     
         2 . The fill tube of  claim 1  wherein said vitreous coating is substantially gas impermeable.  
     
     
         3 . The fill tube of  claim 1  wherein said vitreous coating has a thickness of 0.001 to 0.004 inch.  
     
     
         4 . The fill tube of  claim 1  comprising a zirconia tube.  
     
     
         5 . A die casting machine having a vessel for holding a molten metal or alloy, a die cavity, and a ceramic fill tube disposed between said die cavity and said vessel and having a passage for conveying the molten metal or alloy from said vessel to said die cavity, said fill tube having a vitreous coating that reduces passage of a pressurizing gas present outside of said fill tube into said passage.  
     
     
         6 . The machine of  claim 5  wherein said vitreous coating is substantially gas impermeable.  
     
     
         7 . The machine of  claim 5  wherein said vitreous coating has a thickness of 0.001 to 0.004 inch.  
     
     
         8 . The machine of  claim 5  wherein said fill tube comprises a zirconia tube.  
     
     
         9 . A method of making a ceramic fill tube for a die casting machine wherein said fill tube includes a passage for conveying molten metal or alloy, comprising applying a glass-forming material on said fill tube and firing said fill tube at an elevated temperature to convert said material to a vitreous coating in-situ on said fill tube such that said vitreous coating reduces passage of a pressurizing gas present outside of said fill tube into said passage.  
     
     
         10 . The method of  claim 9  wherein said fill tube is dipped in said glass-forming material.  
     
     
         11 . The method of  claim 9  wherein after firing, said vitreous coating is substantially gas impermeable.  
     
     
         12 . The method of  claim 9  wherein said vitreous coating has a thickness of 0.001 to 0.004 inch.  
     
     
         13 . The method of  claim 9  wherein said fill tube comprises a zirconia tube.  
     
     
         14 . A method of die casting a melt comprising aluminum, comprising providing a pressurizing gas on said melt to force it to flow through a passage in a fill tube wherein said fill tube has a vitreous coating that reduces passage of said pressurizing gas present outside of said fill tube into said passage.  
     
     
         15 . The method of  claim 14  including gas pressurizing a chamber above said melt.  
     
     
         16 . The method of  claim 15  wherein said chamber is pressurized with air.  
     
     
         17 . The method of  claim 14  wherein an end of said fill tube is immersed in said melt and another end is communicated to said die cavity.  
     
     
         18 . The method of  claim 14  wherein said vitreous coating is provided on an exterior and/or interior surface of said fill tube.