S-EMS
Strand electromagnetic stirring for billet and bloom casting
INTRODUCTION
S-EMS is Rotelec’s strand electromagnetic stirring solution for billet and bloom casters. Positioned below the mold or further down the strand but still above the mushy zone, it acts later than Mold EMS and is designed to improve the internal solidification pattern of the cast product.
Historically, strand stirring was the first EMS solution used to improve billet and bloom internal quality by reducing center porosity, generating equiaxed structure and limiting mini-ingot effects. Today, S-EMS is mainly used in special cases, large sections or multi-stage stirring configurations, often together with Mold EMS.
HOW IT WORKS
Billet and bloom strand stirrers use the same rotative stirring principle as Mold EMS. The stirrer acts like the stator of an AC motor fed by 3-phase electrical current, while the liquid steel behaves like the rotor and is put in rotation around its axis. The difference is not the physics of the stirrer, but the position in the process. Installed along the strand rather than in the mold, S-EMS acts on a liquid pool that is already further advanced in solidification.
At this position, the induced movement mixes higher-temperature liquid zones with lower-temperature liquid zones, helping reduce thermal unevenness inside the strand. The metallurgical effects include further superheat reduction, increased nucleation rate, redistribution of the solutes expelled from the solidification front, and reduction of shell-thickness differences with a delaying effect on the formation of solidification bridges near the point of closure of the liquid cone. The result is better internal homogenization and improved center quality in applications where a later stirring stage still has metallurgical leverage.
ROLE IN THE PROCESS AND PLANT INTEGRATION
S-EMS is most relevant when the metallurgical objective is not primarily surface quality, but internal structure improvement deeper in the strand. In most billet and bloom applications, Mold EMS remains the leading configuration because it improves both surface quality and internal quality more effectively in the majority of cases. S-EMS is therefore a targeted solution for special conditions, large sections or combined EMS configurations.
From a plant perspective, S-EMS follows the same integrated philosophy as the other billet and bloom EMS solutions: each strand keeps its own electrical supply, transformer and PLC, with dedicated cooling, protection logic and workshop testing before shipment. The final selection depends on section size, steel grade, casting speed and the exact metallurgical target.
For billet and bloom casters operating in domains where an additional stirring stage is required to improve internal quality, S-EMS offers a focused and technically robust solution. Contact Rotelec to assess whether a strand-stirring configuration, or a combined M+S approach, is the right fit for your caster conditions and product mix.
KEY BENEFITS
- Further superheat reduction by mixing higher-temperature liquid zones with lower-temperature liquid zones inside the strand.
- Increased nucleation rate thanks to the combined effect of columnar dendrite remelting and superheat reduction.
- Redistribution of the solutes expelled from the solidification front, improving internal homogenization.
- Reduction of shell-thickness differences and delayed formation of solidification bridges near liquid-pool closure, with less segregation and porosity.
- Improved internal structure and center soundness in specific casting domains, especially large sections or multi-stage stirring configurations.
- A valuable reinforcement stage when used in combination with Mold EMS, where additional internal-quality improvement is required beyond the mold position.
