Steelmakers today are operating in a fundamentally different environment than even a decade ago. Product portfolios are broader, quality requirements are tighter, and production planning is increasingly dynamic. In response, slab casting is evolving away from static, single‑purpose operation toward more flexible and agile production concepts. This evolution is placing new demands on how mold flow is controlled.

Modern thin to medium slab casters must support frequent changes in steel grade, slab geometry and casting strategy, often within the same production sequence. Under these conditions, productivity is no longer defined by maximum output alone. Increasingly, it is about maintaining stable operation and predictable quality while retaining the freedom to adapt.

From turbulence control to agile production

At its core, continuous slab casting is about controlling how liquid steel transforms into a solid product. Conditions near the meniscus – where steel first begins to solidify – play a decisive role in determining surface quality, cleanliness and downstream performance.

“Casting generally poses a number of different challenges, but the idea is always the same,” explains Martin Sedén, Technology Lead for Product Development at ABB’s Metallurgy business unit. “You want to transform liquid steel into solid steel in a controlled way so that the material becomes strong, homogeneous and free from defects.”

Over time, electromagnetic flow control technologies have evolved to address the very different flow regimes encountered across slab formats. In thin slab casting, the dominant challenge has typically been excessive turbulence and high surface velocities. Here, electromagnetic braking (EMBR) has been used to dampen the steel jets exiting the submerged entry nozzle, stabilize the meniscus and reduce the risk of mold powder entrapment. In thick slab casting, the situation is often different. Flow velocities can be low, and the risk shifts toward insufficient motion, poor temperature homogenization and uneven shell growth.

ABB’s Flow Control Mold (FC Mold) was developed to address this by combining electromagnetic stirring and braking, enabling both flow stabilization and controlled acceleration in the mold. Thin to medium slab casting sits between these two regimes and can exhibit characteristics of both, depending on grade, casting speed, nozzle configuration and operating mode.

“Medium slab casting is where you need the full toolbox,” Sedén notes. “You may need strong braking in one situation and controlled stirring in another – and increasingly, you need to be able to move between those conditions without destabilizing the process.”

Why compact caster concepts raise the bar for flow control

This requirement for adaptability is one of the drivers behind compact, flexible casting concepts such as SMS group’s CSP® Nexus. Designed to support thin to medium slab formats with high energy efficiency and a broad grade mix, CSP® Nexus widens the operating window that mold flow control must accommodate.

“The big change is that you are rarely optimizing for one steady condition,” says Sedén. “You are also designing to handle transitions – between grades, between quality‑sensitive and more throughput‑oriented operation. That fundamentally changes what mold flow control has to deliver.”

For ABB and SMS group, this shift has also influenced how development work is carried out. “Working with SMS group at an earlier stage allows us to align electromagnetic flow control much more closely with the caster design,” Sedén explains. “That matters when you are going for flexibility rather than a single, fixed casting practice.”

Co‑developing FC Mold X for CSP® Nexus

Within this closer collaboration, ABB and SMS group jointly developed FC Mold X – a mold flow control system created specifically for SMS group’s CSP® Nexus caster concept and aligned with its flexible operating philosophy.

“With CSP® Nexus, we set out to design a casting concept that supports flexible production without compromising stability,” says Jochen Wans, Vice President of Casting Slab at SMS group. “That required mold flow control to be considered as part of the caster architecture from the beginning. Co‑developing FC Mold X with ABB allowed us to align electromagnetic flow control directly with the operating philosophy of Nexus.”

Technically, FC Mold X applies three electromagnetic fields to enable different flow control functions in the mold:

• Lower DC braking field dampens and stabilizes flow below the submerged entry nozzle
• Upper DC stabilizing field reduces fluctuations at the meniscus
• Upper AC stirring field controls meniscus flow speed

Together, these functions allow flow behavior to be adapted across a wide range of casting conditions.  “You need to be able to calm the flow when surface quality is critical, and you also need to be able to introduce controlled motion when homogeneity demands it,” Sedén adds.

Making flexibility physical: adjustable positioning with the SMS manipulator

A defining feature of FC Mold X is its manipulator‑based installation, fully integrated into the CSP® Nexus concept. The electromagnetic coils are mounted externally and can be retracted during mold change, enabling efficient handling with no added weight on the mold.

FC Mold X is designed to adapt to different casting practices by adjusting the vertical positioning of the coils. This is achieved using an SMS robot manipulator that moves the magnetic units to their optimal position for the selected operating mode.

“Positioning is critical,” Sedén explains. “The molten steel enters through the submerged entry nozzle, and different nozzle designs and casting practices can change the flow pattern and even the meniscus level. Being able to adjust the position of the braking and stirring fields lets us match the flow control to what is actually happening in the mold.”

Technical versatility through multiple operating modes

To support both quality‑critical and throughput‑oriented production, different flow control strategies are required depending on casting conditions. High-throughput operation typically prioritizes braking to stabilize flow.  Surface-sensitive grades demand more controlled flow behavior through combined stirring and stabilization. These different needs are reflected in FC Mold X’s operating modes, with transitions handled automatically by ABB’s FC Mold Control system, which integrates easily into existing electrical and automation systems:

• Braking mode is typically used for high-throughput conditions where stronger damping of flow is required. For higher casting speeds, the lower coil can be lifted to increase the braking effect on the steel jet.
• Dual braking mode, using upper and lower DC fields, provides an additional configuration for very high casting speeds, facilitating stable flow behavior across varying conditions.
• Combi mode supports surface‑defect‑sensitive grades at moderate casting speeds.  Upper and lower coils work together with simultaneous AC and DC magnetic fields to control flow and stabilize penetration depth and meniscus behavior.

Across all modes, the objective is not to maximize any single parameter, but to provide the ability to select the most appropriate flow control strategy for each grade and production target while maintaining stable solidification conditions.

This flexibility is also reflected in how mold flow control capability can be introduced and extended over time. For high-throughput production, braking functionality may be the initial priority. As production requirements evolve toward more surface-sensitive grades or wider operating windows, additional stirring and stabilization capability can be added to support more advanced flow control strategies. 

Expertise behind the collaboration

FC Mold X builds on decades of experience in electromagnetic braking and stirring, including advanced or ‘smart’ stirring concepts, combined with closer integration between ABB’s metallurgy specialists and SMS group’s continuous casting plant experts.

“When you work this closely, you stop thinking in terms of interfaces and start thinking in terms of outcomes,” says Sedén. “You solve problems together, and that helps translate metallurgical know‑how into practical, reliable solutions on the caster.”

Supporting flexible operation in modern slab casting

As continuous slab casting keeps evolving toward greater flexibility and responsiveness, mold flow control is becoming a more central lever for achieving stable operation and high output quality across a wider range of conditions.

By co‑developing FC Mold X specifically for the CSP® Nexus concept, ABB and SMS group demonstrate how electromagnetic flow control can be designed into the caster architecture itself. This enables stable operation under changing conditions while also allowing flow control capability to expand over time with evolving production requirements.