Primary electrode arrangement for high temperature melting furnace

Abstract

.[.Prior art high temperature electric furnaces of the type using two or more, usually three, primary electrodes positioned around an electrically conducting central outlet brought the electrodes in through a side or bottom wall of the furnace at points below the melt line causing many problems. The present invention provides a primary electrode arrangement for such melting furnaces wherein the primary electrodes do not pass through the wall or bottom of the furnace below the melt line, but instead enter the furnace over the top of the melt line and then protrude through the top surface of the melt. The primary electrodes of the present invention are provided with means for preventing wear and deterioration at the interface between the top surface of the melt and the unmelted batch and/or the oxidizing air atmosphere surrounding the top of the furnace. The improved furnace of the present invention does not require the use of a purging neutral or reducing atmosphere to protect the primary electrodes..]. .Iadd.Rapid wear and deterioration of refractory metals forming primary electrodes which are disposed in a high temperature melting furnace are obviated by utilizing a plurality of fluid coolers. One of the coolers may be disposed about the periphery of each primary electrode such that it is located at the melt line of molten material filling the furnace. A second cooler may be provided in the interior of each primary electrode at least for the exposed portion of each primary electrode at and above the melt line. .Iaddend.

We claim: 
     
       1. In a melting furnace comprising: a. a vessel for containing molten material and unmelted batch on the surface of the molten material forming an interface,   b. an electrically conducting member located within said vessel, and   c. at least two electrically conducting primary electrodes made from a refractory metal highly susceptible to oxidation at elevated temperatures in an oxidizing atmosphere inside said vessel having their tips spaced radially about said electrically conducting member, the improvement comprising:   d. each primary electrode having a portion thereof exposed through the top surface of the molten material to the unmelted batch and other environment adjacent to the top surface of the molten material, and   .[.e. each primary electrode having means around its exterior surface located where said electrode passes through said interface for cooling the electrodes in this vicinity to a temperature below that at which the material used to form said electrodes would rapidly oxidize in an oxidizing atmosphere..].   .Iadd.e. each primary electrode having a first fluid cooling means around its exterior surface located where said electrode passes through said interface for cooling the electrodes in this vicinity to a temperature below that at which the material used to form said electrodes would rapidly oxidize in an oxidizing atmosphere and a second cooling means, located at the interior of said primary electrode and in that portion of said electrode extending out of and beyond the top surface of the melt, for maintaining the temperature of said electrode portion below a temperature at which the material used to make the electrode would rapidly oxidize in an oxidizing atmosphere. .Iaddend. .[.   
     
     
       2.  A melting furnace as defined in claim 1 wherein said cooling means is a fluid cooling means..]. .[.3. A furnace as defined in claim 2 wherein said primary electrodes are equipped with additional cooling means sufficient to maintain the temperature of said portion of the electrode extending out of and beyond the top surface of the melt below a temperature at which the material used to make the electrode would rapidly oxidize in an oxidizing 
     
     
        atmosphere..]. 4. A furnace as defined in claim .[.3.]. .Iadd.1 .Iaddend.wherein said primary electrodes are made from a refractory metal material selected from the group consisting of molybdenum, tantalum, 
     
     
        tungsten, and alloys thereof. 5. A furnace as defined in claim .[.2.]. .Iadd.1 .Iaddend.wherein each electrode comprises a generally horizontal electrode member extending out over an upper edge of the furnace and the melt therein a substantial distance, a generally vertical electrode member connected to said generally horizontal electrode member and extending from a point above said melt down through the upper surface of said melt and to 
     
     
        a point in said melt adjacent said electrically conducting member. 6. A furnace as defined in claim .[.2.]. .Iadd.1 .Iaddend.further comprising mounting means for each of said primary electrodes, said mounting means comprising means for moving the primary electrode such that the distance between a tip of said electrode and an outer opposing surface of said 
     
     
        electrically conducting member can be changed. 7. A furnace as defined in claim .[.7.]. .Iadd.6 .Iaddend.wherein said mounting means further comprises means for pivoting said electrode mounting means about a point on said electrode mounting means to adjust the parallelism between a surface of said electrode tip and the opposing outer surface of said 
     
     
        electrically conducting member. 8. A furnace as defined in claim .[.2.]. 
     
     
        .Iadd.1 .Iaddend.wherein there are three primary electrodes. 9. A furnace as defined in claim .[.2.]. .Iadd.1 .Iaddend.wherein the axis of that portion of the primary electrode extending from the electrode mounting 
     
     
        means and the tip of the electrode is essentially a straight line. 10. A furnace as defined in claim .[.2.]. .Iadd.1 .Iaddend.wherein said electrically conducting member is an outlet through which molten material passes to exit the furnace.