Method and apparatus for reducing bubbles or gas pockets in a metal ingot using a continuous casting mold

Abstract

A method and apparatus are provided to cast a metal ingot using a continuous casting mold so that the ingot is essentially free of gas pockets which otherwise would result from gas bubbles being entrapped in the mushy zone and solid portion of the ingot during formation, wherein such bubbles may be caused by pouring molten metal into a molten liquid portion of the forming ingot and by impingement of a plasma plume of a plasma torch on the upper surface of the molten liquid portion.

1 . A method comprising the steps of:
 providing a segmented continuous casting mold comprising in alternating fashion a plurality of electrically conductive upwardly extending fingers and a plurality of electrically nonconductive high temperature insulation pieces;   withdrawing a metal ingot from the mold wherein the ingot comprises a solid portion, a mushy zone on top of the solid portion and a liquid portion on top of the mushy zone;   producing gas bubbles in the liquid portion by at least one of (a) pouring molten metal into the liquid portion and (b) heating the liquid portion with a plasma plume of a plasma torch; and   heating the liquid portion with an induction coil adjacent the mold whereby the liquid portion comprises a liquid metal head and a bubble zone such that the liquid metal head is on top of the mushy zone and essentially free of gas bubbles, and the bubble zone is on top of the liquid metal head and comprises gas bubbles.   
     
     
         2 . The method of  claim 1  further comprising the step of heating the liquid portion with a plasma plume of a plasma torch. 
     
     
         3 . The method of  claim 1  further comprising the step of pouring molten metal into the liquid portion. 
     
     
         4 . The method of  claim 3  wherein the step of pouring comprises pouring molten metal into the liquid portion from a hearth; wherein the hearth and mold are within an inert gas atmosphere. 
     
     
         5 . The method of  claim 4  further comprising the step of heating the liquid portion with a plasma plume of a plasma torch. 
     
     
         6 . The method of  claim 3  further comprising the step of preventing the pouring molten metal from contacting the tops of the fingers with a top member disposed directly above and adjacent the fingers. 
     
     
         7 . The method of  claim 1  further comprising the step of pouring molten material into the mold through a pouring passage defined by an annular top member disposed directly above and adjacent the fingers. 
     
     
         8 . The method of  claim 7  wherein the top member has a top surface, a bottom surface, an outer perimeter, and an inner perimeter which defines the pouring passage; and a gap is formed in the top member extending from the top surface to the bottom surface and from the outer perimeter to the inner perimeter. 
     
     
         9 . The method of  claim 8  further comprising an electrically non-conductive material in the gap. 
     
     
         10 . The method of  claim 7  further comprising the step of cooling the top member by moving a cooling liquid through a cooling passage formed in the top member. 
     
     
         11 . The method of  claim 7  wherein the top member entirely covers the tops of the fingers so that the tops of the fingers are not visible as viewed from above. 
     
     
         12 . The method of  claim 1  wherein the mold has a sidewall having an inner perimeter which defines a mold cavity in which the liquid portion is disposed; the inner perimeter defines a wider upper cavity portion and a narrower lower cavity portion and includes a step which extends inwardly from the wider upper cavity portion to the narrower lower cavity portion. 
     
     
         13 . The method of  claim 12  wherein the step angles inwardly and downwardly from the wider upper cavity portion to the narrower lower cavity portion. 
     
     
         14 . The method of  claim 12  wherein the fingers comprise respective upper segments which define the wider upper cavity portion and respective lower segments which define at least a portion the narrower lower cavity portion. 
     
     
         15 . The method of  claim 14  wherein the sidewall has a lower section; and the fingers are cantilevered upwardly from the lower section. 
     
     
         16 . The method of  claim 1  wherein the induction coil circumscribes the mold. 
     
     
         17 . The method of  claim 16  wherein the fingers have respective bottoms; and the induction coil has a bottom adjacent the bottoms of the fingers. 
     
     
         18 . The method of  claim 17  wherein the fingers have respective tops; and the induction coil has a top adjacent the tops of the fingers. 
     
     
         19 . A method comprising the steps of:
 providing a segmented continuous casting mold comprising in alternating fashion a plurality of electrically conductive upwardly extending fingers having respective tops and a plurality of electrically non-conductive high temperature insulation pieces;   withdrawing a metal ingot from the mold;   pouring molten metal into the mold atop the ingot;   preventing the pouring molten metal from contacting the tops of the fingers with a top member disposed directly above and adjacent the fingers; and   heating a portion of the ingot within the mold with an induction coil adjacent the mold.   
     
     
         20 . An apparatus comprising:
 a segmented continuous casting mold comprising in alternating fashion a plurality of electrically conductive upwardly extending fingers having respective tops and a plurality of electrically non-conductive high temperature insulation pieces;   a top member disposed directly above and adjacent the tops of the fingers and adapted to prevent pouring molten metal from contacting the tops of the fingers; and   an induction coil adjacent the mold.