System for adjusting the equilibrium temperature of an inductively-heated susceptor

A system for inductively heating a workpiece, comprising:

• an induction coil configured to conduct an alternating current and generate a magnetic field in response to the alternating current, the magnetic field having flux lines oriented generally perpendicularly relative to a direction of the alternating current flowing through the induction coil;
• an upper susceptor face sheet and a lower susceptor face sheet inductively heated by the induction coil and configured to have a workpiece positioned therebetween, each one of the upper susceptor face sheet and the lower susceptor face sheet having opposing outer surfaces and an interior portion between the opposing outer surfaces and being formed of a ferromagnetic alloy having a Curie temperature and being inductively heatable to an equilibrium temperature approaching the Curie temperature in response to the magnetic field;
• and
• a current controller coupled to the induction coil and configured to adjust a frequency of the alternating current as a means to shift the equilibrium temperature of the upper susceptor face sheet and/or the lower susceptor face sheet, the current controller being configured, upon attainment of an initial magnetic permeability of the upper susceptor face sheet and the lower susceptor face sheet corresponding to a first equilibrium temperature in the upper susceptor face sheet and the lower susceptor face sheet relative to the Curie temperature, to increase the frequency of the alternating current to cause a reduction in the magnetic permeability of the upper susceptor face sheet and the lower susceptor face sheet resulting in, at a temperature below the Curie temperature, at least one of the upper susceptor face and the lower susceptor face sheet has a current density of 3-4×107 Ampere/meter2 adjacent to at least one of the opposing outer surfaces, a current density of 0-2×107 Ampere/meter2 in the interior portion, and a current density of 2-3×107 Ampere/meter2 between the interior portion and the at least one of the opposing outer surfaces, and a corresponding increase in the equilibrium temperature from the first equilibrium temperature of the upper susceptor face sheet and the lower susceptor face sheet to a second equilibrium temperature of the upper susceptor face sheet and the lower susceptor face sheet relative to the Curie temperature.

A system for inductively heating a workpiece, comprising:

• an induction coil configured to conduct an alternating current and generate a magnetic field in response to the alternating current, the magnetic field having flux lines oriented generally perpendicularly relative to a direction of the alternating current flowing through the induction coil;
• an upper susceptor face sheet and a lower susceptor face sheet inductively heated by the induction coil and configured to have a workpiece positioned therebetween, the upper susceptor face sheet and the lower susceptor face sheet being formed of a ferromagnetic alloy having a Curie temperature and being inductively heatable to an equilibrium temperature approaching the Curie temperature in response to the magnetic field;
• a current controller coupled to the induction coil and configured to adjust a frequency of the alternating current as a means to shift the equilibrium temperature of the upper susceptor face sheet and/or the lower susceptor face sheet, the current controller being configured, upon attainment of an initial magnetic permeability of the upper susceptor face sheet and the lower susceptor face sheet corresponding to a first equilibrium temperature in the upper susceptor face sheet and the lower susceptor face sheet relative to the Curie temperature, to increase the frequency of the alternating current to cause a reduction in the magnetic permeability of the upper susceptor face sheet and the lower susceptor face sheet resulting in an increase in a concentration of the alternating current to a current density in a range of 0-4×107 amps/meter2 along an outer surface of the upper susceptor face sheet and the lower susceptor face sheet and a corresponding increase in the equilibrium temperature from the first equilibrium temperature of the upper susceptor face sheet and the lower susceptor face sheet to a second equilibrium temperature of the upper susceptor face sheet and the lower susceptor face sheet relative to the Curie temperature;
• and
• the current controller is configured, upon attainment of the initial magnetic permeability of the upper susceptor face and the lower susceptor face sheet of 500, to reduce the magnetic permeability of the upper susceptor face and the lower susceptor face sheet to a magnetic permeability of 250 by increasing the frequency of the alternating current.