Induction heating apparatus and method

Induction heating apparatus comprising:

• a crucible having an open top end and a closed bottom end, with a substantially continuous side wall having a defined height between the top and bottom ends;
• an induction coil surrounding the crucible for generating an electromagnetic induction field;
• and
• a substantially continuous metallic shell comprising a substantially metallic wall disposed between the coil and the crucible for mechanically reinforcing the crucible, said shell surrounding and generally conforming to the crucible side wall and extending for at least a majority of the defined height of the crucible side wall from the bottom end to the top end, the shell having a bottom end corresponding to the bottom end of the crucible and a top end corresponding to the top end of the crucible, a portion of the shell adjacent the top end thereof and a portion of the shell adjacent the bottom end thereof having discrete physically integral and electrically isolated regions therein for limiting flow of induced electric current in the shell.

Induction heating vessel for use in induction heating apparatus including an induction coil surrounding at least a portion of said vessel, said vessel comprising:

• a refractory crucible having an open top end and a closed bottom end, with a substantially continuous side wall having a defined height between the top and bottom ends;
• a substantially continuous metallic shell surrounding and generally conforming to the continuous side wall and extending for at least a majority of the defined height of the side wall from the bottom end to the top end, said shell comprising a metallic wall disposed between said crucible and said coil for mechanically reinforcing said crucible, the shell having a bottom end corresponding to the bottom end of the crucible and a top end corresponding to the top end of the crucible, said bottom and top ends being respectively located opposite each other by a defined distance;
• a portion of the shell adjacent the top end thereof and a portion of the shell adjacent the bottom end thereof having discrete physically integral and electrically isolated regions therein for limiting flow of induced electric current in the shell, wherein the isolated regions of the shell are defined by a plurality of slits through the shell and extending from the top and bottom ends thereof so that the slits extending from the bottom of the shell extend toward the top end of the shell and the slits extending from the top of the shell extend toward the bottom end of the shell, the slits having a total length not exceeding half the defined distance between the respective opposite ends of the shell.

An induction vessel for melting a metal charge, said vessel being for use in induction heating apparatus including an induction coil surrounding at least a portion of said vessel, said vessel comprising:

• a substantially cylindrical refractory crucible having an open top end, a closed bottom end, and a substantially continuous side wall, said crucible being hollow to receive a metal charge to be melted;
• a substantially continuous metallic shell having two edges, a top end, and a bottom end, and conforming to the surface of said crucible side walls, the edges of said shell connected to and electrically insulated from each other at a line along the side wall of said crucible, said shell comprising a metallic wall between said crucible and said coil for mechanically reinforcing said crucible:
• electrically insulating means connecting said edges of said shell and forming a substantially physically continuous and electrically insulated tube;
• a circular metal bottom corresponding to the bottom end of said crucible, said bottom being connected by electrically insulating means to said shell, said shell and said bottom forming a closed vessel;
• and
• current reducing means integrally located on a portion of said shell adjacent the top end and the bottom end of said shell to reduce flow of induced electrical currents in the shell.

An induction vessel for melting a metal charge, said vessel being for use in induction heating apparatus including an induction coil surrounding at least a portion of said vessel, said vessel comprising:

• a substantially cylindrical refractory crucible having a predetermined shape and an open top end, a closed bottom end, and a substantially continuous side wall, said crucible being hollow to receive a metal charge to be melted;
• a substantially continuous metallic shell having two edges and conforming to the shape of said crucible side wall, the edges of said shell connected to an electrically insulated from each other at a line along the side wall of said crucible, said shell comprising a metallic wall between said crucible and said coil for mechanically reinforcing said crucible:
• electrically insulating means connecting the edges of said shell and forming a substantially physically continuous and electrically insulated tube;
• a circular metal bottom corresponding to the bottom end of said crucible, said bottom having a defined center, a defined radius and a circumference, said bottom being connected by electrically insulating means to said shell, said shell and said circular metal bottom forming a closed vessel wherein said circular metal bottom includes a plurality of slits therethrough each having a defined length and extending from the circumference of the bottom toward the center thereof, the length of said slits not exceeding forth percent of the radius of said circular metal bottom;
• and
• current reducing means integrally located on a portion of said shell adjacent the open top end and the closed bottom end of said shell to reduce flow of induced electrical currents in the shell.

An induction vessel for melting a metallic charge, said vessel being for use in induction heating apparatus including an induction coil surrounding at least a portion of said vessel, said vessel comprising:

• a refractory crucible having outer surfaces, an open top end, a closed bottom end and a substantially continuous side wall, said crucible being hollow to receive a metal charge;
• a substantially uniform and continuous thin metallic shell having an open top end and closed bottom end and conforming to the outer surfaces of said crucible, said shell comprising a metallic wall between said crucible and said coil for mechanically reinforcing said crucible, said continuous metallic shell having a side wall;
• lifting means on a portion of said shell adjacent the open top end of said shell;
• and
• discrete physically integral and electrically isolated regions located on a portion of said shell adjacent the open top end and closed bottom end of said shell for reducing flow of electric currents in said shell.