Method of operating a batch type annealing furnace using a plasma heat source

The method of operating a batch-type annealing furnace of the type having a hearth floor, an inner box-like cover having a closed upper end and a sealable open bottom end adapted to rest about the floor and provide a treatment chamber to enclose the charge to be annealed, an outer box-like cover having a closed upper end and an open bottom end and a refractory lining therein and being adapted to rest surrounding said inner cover, comprising the steps:

• a. placing the charge on the hearth floor in a fixed position;
• b. placing appropriate temperature sensors proximate the charge;
• c. placing the inner cover over the charge;
• d. placing the covers so that the outer cover is over the inner cover;
• e. purging the chamber formed by the inner cover with an appropriate purging gas;
• f. heating a plasma gas with a plasma generator mounted proximate and external of said treatment chamber and directing such heated plasma gas through gas entry paths in said floor to said inner cover chamber to provide a temperature controlled annealing atmosphere for said charge;
• and
• g. sensing with said sensors the temperature within said chamber and using such sensed temperature to control the operation of said plasma generator to control the temperature of said chamber according to some predetermined time-temperature cycle.