A measurement system for determining the positions of arcs during Vacuum arc remelting

It is has previously been shown that arcs can constrict during Vacuum arc remelting (VAR), and this constriction can lead to undesired defects in the material. This paper describes a novel measurement system capable of locating arcs in an existing industrial VAR furnace. The system is based on non-invasive magnetic field measurements and VAR specific forms of the Biot-Savart law which relate the measurements to the positions of arcs. Electromagnetic finite element modeling assists the analysis. The measurement system is applied to a commercial VAR furnace, and data are taken during production of titanium alloy. It is shown there exists arc distribution differences during this VAR operation and these differences are not apparent in the existing measurements used to control the furnace. It is also shown that there is more than one arc at an instant, and likely more arcs present at an instant than can be resolved with the number of sensors applied. Still, the described methodology can be extended to locating additional arcs by adding additional sensors.