Induction furnace for melting of metals, lining for an induction furnace and method for production of such lining.

Abstract

The present invention relates to an induction furnace for melting of metals that do not connect inductively in solid state. The induction furnace has a lining comprising a mixture of graphite and silicon carbide and has an electric conductivity higher than the electrical conductivity of the metal to be melted when metal is in solid state, but lower than the electrical conductivity of the metal to be melted when the metal is in molten state. The invention further relates to a lining for induction furnace and to a method for producing such lining.

1 . An induction furnace for melting metal where the metal does not connect inductively when the metal is in a solid state but does connect inductively when the metal is in a molten state, the furnace comprising:
 an outside housing having an inductive coil; and   a liner in the housing,   
       the liner comprising a mixture of graphite and silicon carbide, 
       the liner having an electrical conductivity higher than the electrical conductivity of a metal to be melted when the metal is in a solid state but lower than the electrical conductivity of the metal to be melted when the metal is in a molten state. 
     
     
         2 . The furnace of  claim 1 , wherein the liner comprises about 80 to about 20% by weight graphite and about 20 to about 80% by weight silicon carbide. 
     
     
         3 . The furnace of  claim 1 , wherein the liner comprises about 70 to about 30% by weight graphite and about 30 to about 70% by weight silicon carbide. 
     
     
         4 . A liner for an induction furnace for melting metal where the metal does not connect inductively when the metal is in a solid state but does connect inductively when the metal is in a molten state, the liner comprising:
 a mixture of graphite and silicon carbide,   
       the liner having an electrical conductivity higher than the electrical conductivity of a metal to be melted when the metal is in a solid state but lower than the electrical conductivity of the metal to be melted when the metal is in a molten state. 
     
     
         5 . The liner of  claim 4 , wherein the liner comprises about 80 to about 20% by weight graphite and about 20 to about 80% by weight silicon carbide. 
     
     
         6 . The liner of  claim 4 , wherein the liner comprises about 70 to about 30% by weight graphite and about 30 to about 70% by weight silicon carbide. 
     
     
         7 . A method for making a liner for an induction furnace for melting metal where the metal does not connect inductively when the metal is in a solid state but does connect inductively when the metal is in a molten state, the method comprising:
 mixing graphite particles, silicon carbide particles and a carbon based binder to form a mixture;   forming a green liner for an induction furnace from the mixture;   heating the green liner to a temperature above about 1100° C. to cure and bake the green liner and make a liner; and   adjusting the electrical conductivity of the liner so that the liner has a higher electrical conductivity than the electrical conductivity of the metal to be melted when the metal is in a solid state but lower than the electrical conductivity of the metal to be melted when the metal is in a molten state.   
     
     
         8 . The method of  claim 7 , wherein adjusting the electrical conductivity of the liner comprises regulating the ratio of graphite particles and silicon carbide particles in the mixture. 
     
     
         9 . The method of  claim 8 , wherein the mixture comprises about 80 to about 20% by weight graphite particles, about 20 to about 80% by weight silicon carbide particles and the carbon-based binder is present in an amount of about 10 to about 25% by weight based on the combined weight of graphite particles and silicon carbide particles in the mixture. 
     
     
         10 . The method of  claim 8 , wherein the mixture comprises about 70 to about 30% by weight graphite particles and about 30 to about 70% by weight silicon carbide particles and the carbon-based binder is present in an amount of about 11 to about 18% by weight based on the combined weight of graphite particles and silicon carbide particles in the mixture. 
     
     
         11 . The method of  claim 7 , wherein the carbon-based binder is selected from the group consisting of natural resins, synthetic resins and tar-based binders. 
     
     
         12 . The method of  claim 7 , wherein the carbon-based binder is selected from the group consisting of phenol formaldehyde resin and furfuryl alcohol. 
     
     
         13 . The method of  claim 7 , wherein the mixture further comprises a curing agent. 
     
     
         14 . The method of  claim 13 , wherein the curing agent is selected from the group consisting of hexamin and inorganic acids. 
     
     
         15 . The method of  claim 7 , wherein the binder is petroleum coke pitch or tar pitch. 
     
     
         16 . The method of  claim 7 , wherein the mixture further comprises silicon particles in an amount sufficient for carbon that form during heating from the binder, reacts with the silicon particles to SiC. 
     
     
         17 . The method of  claim 7 , wherein forming and heating are conducted outside an inductive furnace. 
     
     
         18 . The method of  claim 7 , wherein forming and heating are conducted inside an inductive furnace. 
     
     
         19 . A method for melting a metal in an induction furnace comprising:
 providing an induction furnace comprising:
 an outside housing having an inductive coil; and 
 a liner in the housing, 
 the liner comprising a mixture of graphite and silicon carbide, 
   the liner having an electrical conductivity higher than the electrical conductivity of a metal to be melted when the metal is in a solid state but lower than the electrical conductivity of the metal to be melted when the metal is in a molten state;   adding to the induction furnace a metal where the metal does not connect inductively when the metal is in a solid state and the induction coil is on but does not connect inductively when the metal is in a molten state and the induction coil is on;   supplying electrical energy to the induction coil to melt the metal; and   removing melted metal from the induction furnace.   
     
     
         20 . The method of  claim 19 , wherein removing comprises removing a substantial portion of the melted metal from the furnace and leaving a pool of melted metal in the furnace for the start of a second adding.