Patent ID: 8532158
Filing Date: 2013-09-10
Classification: F27B,F27D,H05B

Abstract:
1. A method of melting a crucible batch of a transition material by gradually adding a solid or semi-solid charge of the transition material to a molten heel of the transition material in a crucible having a plurality of induction coils surrounding the exterior of the crucible, each one of the plurality of induction coils exclusively surrounding one of a plurality of partial interior volumes of the crucible, the lowest one of the plurality of partial interior volumes comprising a bottom interior volume and the highest one of the plurality of partial interior volumes comprising a top interior volume of the crucible, at least one intermediate interior volume comprising at least one of the plurality of partial interior volumes, each of the at least one intermediate interior volumes sequentially disposed between the bottom interior volume and the top interior volume, each one of the plurality of induction coils connected to the output of a separate ac power source, the method comprising the steps of: loading the molten heel of the transition material into at least a bottom portion of the bottom interior volume and adjusting the output of the separate ac power source connected to the one of the plurality of induction coils surrounding the bottom interior volume to a melting frequency and a melting power level to keep the molten heel of the transition material at least at the minimum melting temperature of the transition material; sequentially adding the solid or semi-solid charge of the transition material into at least a portion of each of the next highest one of the at least one intermediate volume above the bottom interior volume while adjusting the output of the separate ac power source connected to the one of the plurality of induction coils surrounding the next highest one of the at least one intermediate volume to which the solid or semi-solid charge of the transition material is sequentially added to the melting frequency and the melting power level while synchronizing the phase of an output voltage of the separate ac power source connected to the one of the plurality of induction coils surrounding the next highest one of the at least one intermediate volume to which the solid or semi-solid charge of the transition material is sequentially added with the phase of the output voltage of the separate ac power source connected to the one of the plurality of induction coils surrounding the bottom interior volume; and simultaneously adding the solid or semi-solid charge of the transition material into at least a top portion of the top interior volume of the crucible subsequent to sequentially adding the solid or semi-solid charge of the transition material into the at least one intermediate volume below the top interior volume to form the crucible batch of a molten transition material and adjusting the output of the separate ac power source connected to the one of the plurality of induction coils surrounding the top interior volume to the melting frequency and the melting power level while synchronizing the phase of the output voltage of the separate ac power source connected to the one of the plurality of induction coils surrounding the top interior volume with the phase of the output voltage of the separate ac source connected to the one of the plurality of induction coils surrounding the bottom interior volume; and simultaneously reducing the output of each one of the separate ac power sources to a stirring frequency and a stirring power level while phase shifting the output voltages of each of the separate ac power sources to induce a unidirectional electromagnetic stirring of the crucible batch of the molten transition material in the crucible, the stirring frequency being lower than the melting frequency, and the stirring power level being lower than the melting power level.