20th International Forgemasters Meeting - IFM 2017

In recent years, the power generation industry has demanded forged parts of increasingly high quality to meet the requirements of increased operating temperatures and pressures. This has pushed metals suppliers to utilize Electro-slag Re-melt (ESR) technology to produce such large ingots. Single-phase, line frequency power supplies have traditionally been used to economically and reliably provide the melting power for these ESR furnaces. As long as the power supply line capacity was sufficiently large compared to the melt power requirement, the single-phase nature of the load was not a major concern. Likewise, the harmonic generation characteristic of saturable reactor power supply technology was also masked by a sufficiently robust power line. But, as ESR furnaces have grown in size, the unbalanced single-phase load and harmonic generation has become increasingly unacceptable. In addition, the use of line frequency power in melting requires ever higher voltages to overcome the inductive voltage drop component which decreases energy efficiency and poses a hazard to operators. The solution is to use a power supply that produces a low frequency output current from a three-phase AC source. Many technologies may be considered that meet this requirement. This paper will examine the use of an AC thyristor controlled cycloconverter to economically and reliably produce a variable low frequency current. Varying frequencies from DC up to 5 Hz can have a significant effect on pool depth and solidification structures, so the ability of this power supply to produce output frequencies up to 2.5 Hz is a major benefit. Detailed computational modeling of the effects of low frequency current on slag, melt pool dynamics including flow patterns, Lorentz forces, temperature distribution, pool depth, and the associated metallurgical effects will be discussed.