Why cold rolling of electrical steels require a new generation of 20-high mills

The rapid growth of electric mobility, renewable energy systems, and high‑efficiency electrical equipment is driving demand for much thinner and higher‑performance electrical steels. As strip thickness requirements in Europe and North America are expected to fall from approx. 0.46 mm in 2023 to approx. 0.25 mm by 2030, producers face increasing pressure to deliver precise, energy‑efficient rolling performance while reducing CO₂ emissions. Combining advanced roll configurations, high‑precision mechatronics, and smart digital tools, SMS group’s 20-high mills meet the stringent rolling demands of both grain-oriented (GO) and non-grain-oriented (NGO) steels while supporting higher productivity, energy savings, and long‑term sustainability.

SMS group’s 20-high reversing mills meet these industry‑wide challenges with a rolling platform optimized for ultra‑thin electrical steels. Backed by more than nine decades of expertise, the system achieves the highest standards in thickness, flatness, and surface quality. 

The mills are designed to handle both GO and NGO steels — materials that demand precise control due to their magnetic performance characteristics. GO steels rely on a preferred grain direction for use in transformers, while NGO steels offer isotropic magnetic properties ideal for motors. SMS group’s 20-high platform covers both product types, making it a versatile solution for market needs. 

SMS group offers two specialized designs, which both represent highly adaptable rolling solutions tailored to modern electrical steel production.

• Mono Block – A compact, rigid mill stand ideal for extremely hard materials such as tool steel, stainless steel, and maraging steels. It enables up to 90% reduction through superior stiffness and high‑precision mechatronics.
• Split Block – A flexible design featuring upper and lower halves for improved accessibility, easier roll changes, and safe threading. It excels with brittle, high‑strength materials and supports stable rolling across diverse grades.

The performance of the 20-high reversing mill is rooted in its sophisticated roll arrangement, state‑of‑the‑art control systems, and high‑speed mechatronics. The roll assembly includes two ultra‑small work rolls, four axially shiftable first intermediate rolls, six second intermediate rolls, and eight backing bearing assemblies within a robust mill housing. This configuration allows the system to roll materials with yield strengths up to nearly 2,000 MPa and achieve strip thicknesses far below what is possible with 4‑ or 6‑high configurations. In addition, it ensures exceptional control over strip geometry, making it possible to roll ultra‑thin gauges while maintaining stable and uniform thickness and flatness.

Advanced control systems enhance operational efficiency of 20-high mills. They allow for precise management of rolling parameters, ensuring consistent product quality across various applications as well as safe threading and improving cooling. Such advantages are particularly crucial when working with brittle, high-strength materials that are susceptible to strip breakage.

Additionally, the rolling stands are equipped with hydraulic gap control and multi-axis dynamic crown adjustment. Combined with the axially shiftable intermediate roll system, this setup delivers superior strip flatness. The axial shifting of the intermediate rolls specifically reduces edge drop, alleviates forces at the strip edges. Upper block tilting in the Split Block design provides additional influence on wedge correction.

The mills support rolling speeds of up to 1,000 m/min, enabling high throughput while maintaining surface quality and strip stability.

SMS group complements its mechanical design with powerful digital intelligence. Our models enable stable, energy‑efficient rolling and consistently high strip quality across a wide variety of operating conditions. The X-Pact^® 20-high Mathematical Model is a self‑adapting, self‑optimizing model that dynamically calculates optimal setup values based on material behavior, mill status, and actuator responses, resulting in best possible thickness and flatness results and a high production flexibility.

Complementing this, X-Pact^® Mill Mining provides an AI‑based suite of tools that enhances rolling mill productivity by predicting thickness performance for each coil before it enters the mill, allowing pass schedules to be adjusted automatically to maximize output. Through its intuitive dashboard, plant owners gain a clear, real‑time overview of mill performance and can make strategic adjustments to increase throughput, with all productivity gains—whether measured in strip length or tonnage—captured and displayed as they occur. 

Robust safety functions are embedded directly in the high‑speed Level 1 control system to safeguard against incorrect predictions, such as those caused by erroneous PDI data, ensuring that AI‑driven optimization never compromises operational security. Beyond improving productivity, X-Pact^® Mill Mining also supports higher product quality by optimizing the achievement of target thickness over the full strip width. It enables target‑thickness offsets during setup and adjusts parameters in Level 1 automation as required, routinely achieving thickness performance that exceeds the minimum values needed to meet order tolerances.

By combining proven mechanics, advanced mechatronics, and digital intelligence, SMS group’s 20-high reversing mills enable producers to:

• Roll thinner electrical steels with superior magnetic performance
• Increase productivity through optimized pass schedules and high-speed rolling
• Improve product quality across thickness, flatness, and surface parameters
• Reduce energy consumption and CO₂ emissions, supporting decarbonization targets
• Enhance plant flexibility, enabling fast grade changes and reliable rolling of brittle or high-strength steels 

The implementation of a pilot plant for a renowned customer underscores the system’s readiness for real‑world deployment and its potential to help producers meet future market demands. As electrical steel requirements become more stringent and sustainability pressures rise, SMS group’s 20-high solutions position producers to compete successfully in a rapidly evolving industry.