What is effective measurement in silicon steel production?

From power generation and distribution to EVs and home appliances: silicon steel is a critical enabler for society’s relentless electrification. Marko Sydänlammi, Global Product Manager – Flatness Systems for ABB, explains the importance of accurate measurement and control of key parameters including flatness, roll force and strip tension as well as strip position and width measurement, in ensuring that cold rolling mills meet exacting quality standards and satisfy growing demand for silicon steel products.

Silicon steel is an all-pervasive part of our global electrical infrastructure. Allowing smaller and more efficient components with lower energy losses, you’ll find it inside electrical motors, generators, transformers, and power supplies as well as actuators, relays, solenoids, and other electromechanical devices. 

Silicon steel is fundamental to the efficient generation, transmission, storage, and utilisation of electrical power. And as society pivots to an increased reliance on renewable sources of electricity, this specialised alloy plays a crucial role in securing our future energy security and sustainability.

Appetite for silicon steel across industrial, commercial and consumer applications is growing, with significant use by EV manufacturers. Demand is increasing faster than other types of steel production, with the global market for silicon steel projected to rise from $32 billion in 2024 to $50 billion by 2032, representing a compound growth rate of 5.6% during the period. And to satisfy rising customer need in a competitive market, silicon steel producers must maximise the quality, speed, cost-efficiency, and resilience of their operations.

Handle with care

After the initial hot rolling phase of silicon steel production, further cold rolling is carried out below its recrystallisation temperature, with the material fed between a series of rollers to meet the requirements of various customers. Cold rolling of flat metals such as steel is in itself a complex multi-stage process, with each step playing a critical role in determining the physical and electrical properties of the finished product for various applications.

Ensuring silicon steel’s quality and consistency during cold rolling demands precise monitoring and control of many parameters including rolling temperature, speed, strip position and width measurement, as well as flatness, roll force and tension of the steel strip as it passes through each rolling stage. Collectively, these factors have a profound effect on the electrical and mechanical properties of the finished product, determining its thickness and surface finish as well as the homogeneity of stress distribution patterns within the material itself.

To understand the importance of these factors, let’s look briefly at the various steps involved in silicon steel production, starting from initial preparation of the previously hot-rolled material that typically arrives at the cold rolling plant in coiled form.

Prior to further handling, the material is cleaned and conditioned to remove surface oxides or contaminants that may adversely affect quality of the final product. After this, the prepared silicon steel material is fed into the cold rolling mill where it undergoes a series of rolling passes to reduce its thickness and optimize a number of important quality properties.

During the cold rolling process, intermediate annealing stages will be performed between certain rolling passes. By heating the metal to a specific temperature and then cooling it slowly, the microstructure will be rejuvenated and the internal stresses relieved to improve formability.

After cold rolling to achieve the steel’s desired thickness, it may undergo further annealing to optimise its physical structure and magnetic properties such as permeability and core loss. Depending on its intended application, the steel may also be subjected to surface treatment processes such as coating to improve corrosion resistance and insulation properties.

Finishing operations such as cutting, slitting, or shearing are used to achieve the desired dimensions and shape before the finished material is inspected for quality control purposes. Lastly, the processed silicon steel is wound onto spools or coils and packaged for handling, transportation, and storage.

The mechanical and electrical properties of any steel are closely related to its grain structure. This is determined by several factors, notably the material’s temperature at various stages of the rolling process. While cold rolling typically occurs over a temperature range of 100-200°C, silicon steel production can push this well beyond 300°C. Silicon steel’s hardness and brittleness also increases the risk of small edge cracks forming as the material is worked, leading quickly to strip breakage.

Given the importance and variety of its end uses, it is vital to minimise the risk of allowing cracks or surface imperfections to form that could affect final quality and performance of silicon steel. Accurate measurement and control of key parameters including strip thickness, flatness, roll force, strip tension, strip position and width measurement during the cold rolling process is therefore critical to ensuring consistently high product quality.

A force for quality

Three key measurement technologies employed in cold rolling applications contribute directly to optimising the quality and reliability of silicon steel production.

Flatness systems such as ABB’s Stressometer technology are used to ensure that flatness of the silicon steel strip is maintained to within extremely tight tolerances during each rolling pass. Flatness directly influences uniformity of the steel’s magnetic properties. This is important in electrical transformer applications because minimising air gaps between adjacent layers of silicon steel boosts its performance by reducing undesirable eddy current losses.

Strips with low inner stress variations preserve silicon steel’s electrical and mechanical properties when wound onto coils or spools. Controlling flatness to tight tolerances helps steel producers maximise yield and minimise wastage of material to further improve the overall cost efficiency of production.

A high-performance flatness control system should be able to take several accurate measurements per linear meter of rolled strip as it passes rapidly through the mill. It should also ideally be able to visualise and control the stress distribution across the whole of the steel strip, including the material’s edges, tail and head ends.

From an overall production perspective, a control system should be quick and easy to fit, helping to minimize plant downtime during installation or upgrades. The system’s reliability and ability to handle a wide range of steel products while requiring a minimum of service contributes further to the plant efficiency and profitability.

Accurate strip tension measurement is similarly critical to ensuring material thickness and consistency during cold rolling. Maintaining accurate tension is key to achieving the steel’s desired magnetic properties and mechanical strength, while reducing the incidence of defects that can impact severely on production continuity and profitability.

Precisely controlling strip tension plays a vital role in preventing material defects such as buckling, slippage, or strip breaks.

Monitoring edge quality and controlling defects prevents damage during handling and processing, while precise control over strip width ensures that the finished material meets the precise dimensional requirements of downstream manufacturing operations. Stringent management of material thickness is also important from a cost efficiency perspective, since rolling a strip to the minimum permissible thickness ensures optimised material usage and reduced waste.

Roll force load cells may also play an essential role in silicon steel production, ensuring accurate measurement and control of roll force to maintain consistent deformation of the material at each rolling pass. Accurate control of roll force also helps ensure its uniform properties, while reducing the risks of costly damage to the material. Load cell data is also used for quality assurance purposes and provides valuable insights for mill operators to help with optimising parameters and enhancing the efficiency of cold rolling processes.

Satisfying demand, today and tomorrow

Accurate, reliable, and repeatable flatness control and measurement of roll force, strip tension, strip position and width are all crucial contributors to maximising consistent quality and profitability in silicon steel production.

ABB is a leader in flatness measurement and control, strip tension and roll force load cell solutions for cold rolling processes, with in-depth knowledge and experience gained from delivering more than 1000 customer projects worldwide. Our state-of-the-art solutions are engineered to address the demanding force and dimension measurement needs of today’s cold rolling plant operations, ensuring that production output can satisfy industry’s growing need for high quality silicon steel, now and in the future.