Apparatus and process for heat treatment

Claim 2

Apparatus for batch-annealing a charge comprising: (a) a batch-annealing furnace; (b) a fan for circulating hot gas within said furnace; (c) an electric motor on which a load is exerted by said fan; (d) a load transducer for detecting an electrical load on said motor and capable of generating a load signal; (e) a load change detector responsive to said load signal and capable of generating a load change signal; (f) a frequency reference integrator responsive to said load change signal and capable of generating, storing and changing a reference signal responsive to said load change signal; and (g) an adjustable frequency drive responsive to said reference signal and capable of supplying a varying frequency alternating current power to said motor.

Claim 3

A process of batch-annealing a charge comprising the steps of: (a) increasing the temperature of a heat transfer gas within a batch-annealing furnace during heat-up of said charge; (b) circulating said heat transfer gas within said batch-annealing furnace with a fan driven by an electric motor; (c) sensing a change in the electrical load on said motor in response to a change in density of said heat transfer gas and generating a signal related thereto; (d) increasing the speed of said motor responsive to said signal to increase gas circulation within said furnace as the density of said gas decreases; (e) decreasing the temperature of said heat transfer gas within said furnace during cool-down of said charge; and (f) decreasing the speed of said motor responsive to said signal to decrease gas circulation within said furnace as the density of said gas increases.

Claim 4

A process of batch-annealing a charge comprising the steps of: (a) increasing the temperature of a heat transfer gas within a batch-annealing furnace during heat-up of said charge; (b) circulating said heat transfer gas within said batch-annealing furnace with a fan driven by an electric motor; (c) sensing a change in the electrical load on said motor in response to a change in density of said heat transfer gas and generating a signal related thereto; (d) increasing the speed of said motor responsive to said signal to increase gas circulation within said furnace as the density of said gas decreases; (e) decreasing the temperature of said heat transfer gas within said furnace during cool-down of said charge; and (f) decreasing the speed of said motor responsive to said signal to decrease gas circulation within said furnace as the density of said gas increases.