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Magnetic measurements coupled with traditional VAR process measurements have enabled the characterization of the spatial distribution of electrical current through the furnace; a process variable that today’s VAR furnaces do not measure. This work presents data acquired by VARmetric, a high density magnetic sensor array, on an industrial VAR furnace processing Fe and Ni- based alloys. VARmetric is used to identify events which would go undetected through traditional process signal analysis, and importantly, can be used to distinguish between distinct arc modes, e.g. diffuse arcs, constricted arcs, and glows. This information facilitates a new method to assess the quality of an ingot in terms of the probability of segregation defects along the ingot axis. 

This work describes the utilization of applied transverse magnetic fields to influence the arc dynamics during laboratory and industrial VAR melting. The arc motion was monitored with VARmetricTM as an external sensing platform to inform the system on the resultant direction and magnitude of the arcs due to the applied transverse magnetic field. Electromagnetic coils were mounted outside of the VAR in order to produce the near-uniform transverse magnetic field inside the furnace. These fields interact with the arc in a precise and measurable way, providing a control mechanism for arc motions and distributions. Results are provided for conditions where the applied fields were chosen such that the resultant force forces the arcs into non-ideal distributions, replicating potential deleterious operating conditions that could lead to defects. Results at both laboratory and industrial scale are provided and, wherever possible, ingots were sectioned, and the resulting grain structures were analyzed for defects. 

This work describes the utilization of applied transverse magnetic fields to influence the arc dynamics during laboratory and industrial VAR melting. The arc motion was monitored with VARmetricTM as an external sensing platform to inform the system on the resultant direction and magnitude of the arcs due to the applied transverse magnetic field. Electromagnetic coils were mounted outside of the VAR in order to produce the near-uniform transverse magnetic field inside the furnace. These fields interact with the arc in a precise and measurable way, providing a control mechanism for arc motions and distributions. Results are provided for conditions where the applied fields were chosen such that the resultant force forces the arcs into non-ideal distributions, replicating potential deleterious operating conditions that could lead to defects. Results at both laboratory and industrial scale are provided and, wherever possible, ingots were sectioned, and the resulting grain structures were analyzed for defects. 

Magnetic measurements coupled with traditional VAR process measurements have enabled the characterization of the spatial distribution of electrical current through the furnace; a process variable that today’s VAR furnaces do not measure. This work presents data acquired by VARmetric, a high density magnetic sensor array, on an industrial VAR furnace processing Fe- and Ni- based alloys. VARmetric is used to identify events which would go undetected through traditional process signal analysis, and importantly, can be used to distinguish between distinct arc modes, e.g. diffuse arcs, constricted arcs, and glows. This information facilitates a new method to assess the quality of an ingot in terms of the probability of segregation defects along the ingot axis. 

Ampere Scientific’s VARmetricTM measurement system for Vacuum Arc Remelting (VAR) furnaces passively monitors the distribution of arcs over time during VAR in real time. The arc behavior is known to impact both product yield and quality and can pose potentially catastrophic operating conditions. Arc position sensing with VARmetricTM enables a new approach to control the heat input to the melt pool. Transverse external magnetic fields were applied to push the arcs via the Lorentz force while measuring the arc location to control the arc distribution over time. This has been tested on Ampere Scientific’s small-scale laboratory arc furnace with electromagnets used for control for up to 60 seconds while monitoring the arc location with VARmetricTM. The arc distributions were shown to be significantly different from the uncontrolled distributions with distinct thermal profiles at the melt pool. Alternatively, this type of control can be periodically applied to react to undesirable arc conditions. 

Ampere Scientific has previously developed and provided industrial validation of the VARmetricTM measurement system to measure the location of electric arcs during vacuum arc remelting (VAR) of high temperature specialty alloys. With the advent of VARmetricTM, it is nowpossible to continuously monitor and control arc distributions in order to tailor the heat flux that drives solidification during the VAR process. Laboratory experiments have applied transverse magnetic fields to generate specified Lorentz forces as a control mechanism across the arc gap in order to drive arc locations to predetermined distributions. This type of control makes it possible to react to undesirable arc conditions during VAR operations or to provide a continuous control to specify a thermal profile for heat input to the melt pool necessary for ensuring defect-free ingots. 

The behavior of vacuum arcs during VAR processing is known to impact product yield and contribute to ingot defects. For example, it has been shown that constricted arcs during the processing of segregation prone nickel-based alloys can lead to defects in ingots. Despite this knowledge, the role of arc distributions in VAR processing has not been considered in controlling the furnaces. In addition, computational models of the process have typically assumed that the arc provides an axisymmetric, Gaussian heat input to the ingot, while acknowledging that this is the biggest unknown variable. Here we present the theory behind VARmetricTM and present analyses of the spatio-temporal arc distributions measured on a production VAR furnace. We then use the measured axisymmetric arc distributions to provide updated boundary conditions for solidification of the ingot to investigate the implications of the changing distributions on solidification and the relationship between arc distributions and defects. 

Ampere Scientific’s VARmetricTM measurement system for Vacuum Arc Remelting (VAR) furnaces passively monitors the distribution of arcs over time during VAR in real time. The arc behavior is known to impact both product yield and quality and can pose potentially catastrophic operating conditions. Arc position sensing with VARmetricTM enables a new approach to control the heat input to the melt pool. Transverse external magnetic fields are applied to push the arcs via the Lorentz force using feedback of the arc location to control the arc. This has been tested on Ampere Scientific’s small-scale laboratory arc furnace with electromagnets used for control for up to 60 seconds while monitoring the arc location with VARmetricTM. The arc distributions are shown to be significantly different from the uncontrolled distributions with distinct thermal profiles at the melt pool. Alternatively, this type of control can be periodically applied to react to undesirable arc conditions.