Electrode immersion depth determination and control in electroslag remelting furnace

1. A method of controlling an electroslag remelting furnace, the method comprising the steps of:

adjusting electrode drive speed by an amount proportional to the difference between a metric of electrode immersion depth calculated from at least impedance and temperature signals and a set point;

monitoring furnace signals comprising at least impedance and temperature signals;

identifying a corresponding magnitude of the impedance signal when the electrode tip is at a zero depth of immersion; and

calculating the metric of electrode immersion depth based upon a predetermined characterization of electrode immersion depth as a function of the furnace signals, comprising adjusting the impedance signal based upon the temperature signal.

2. The method of claim 1 wherein in the calculating step the function is a compound linear function.

3. The method of claim 2 wherein in the calculating step a point of intersection of two lines of the compound function corresponds to impedance at zero immersion depth.

4. The method of claim 3 wherein in the calculating step the function was predetermined based upon a bilinear regression of collected experimental data points as to corresponding impedance and electrode immersion depth.

5. The method of claim 4 wherein in the calculating step the point of intersection minimized a sum of squared errors in the bilinear regression.

6. The method of claim 1 wherein the adjusting based on temperature step adjusts according to an Arrhenius relationship.

7. The method of claim 1 wherein the furnace signal comprises a voltage signal.

8. The method of claim 6 wherein the furnace signal comprises a current signal.

9. An apparatus for controlling an electroslag remelting furnace, said apparatus comprising:

means for adjusting electrode drive speed by a predetermined amount if a metric of electrode immersion depth calculated from at least impedance and temperature signals differs from a set point by a predetermined maximum amount;

means for monitoring furnace signals comprising at least impedance and temperature signals; and

means for calculating the metric of electrode immersion depth based upon a predetermined characterization of electrode immersion depth as a function of the furnace signals, comprising adjusting said impedance signal based upon said temperature signal.

10. The apparatus of claim 9 wherein in said calculating means said function is a compound linear function.

11. The apparatus of claim 10 wherein in said calculating means a point of intersection of two lines of said compound function corresponds to impedance at zero immersion depth.

12. The apparatus of claim 11 wherein in said calculating means said function is predetermined based upon a bilinear regression of collected experimental data points as to corresponding furnace signal and electrode immersion depth.

13. The apparatus of claim 12 wherein in said calculating means said point of intersection minimizes a sum of squared errors in said bilinear regression.

14. The apparatus of claim 9 wherein said means for adjusting based upon temperature adjusts according to an Arrhenius relationship.

15. The apparatus of claim 9 wherein said furnace signal comprises at least a voltage signal.

16. The apparatus of claim 9 wherein said furnace signal comprises a current signal.