Online Material Measurement of Tensile Strength and Yield Strength in Flat Steel Production: Understanding the EMG IMPOC System

EMG IMPOC: Background and Technology
EMG Automation GmbH introduced the Impulse Magnetic Process Online Controller (IMPOC) in the late 1990s as an innovative solution for online material testing in flat steel production. EMG IMPOC is predominantly used in continuous galvanizing and annealing lines to provide reliable online measurements of tensile and yield strength for ferromagnetic steel grades. Today, EMG IMPOC is widely regarded as a standard in online material properties measurement, with approximately 80 installations globally.

How EMG IMPOC Works
The EMG IMPOC system’s measuring principle is both sophisticated and user-friendly. It utilizes two identical sensors positioned on the upper and bottom side of the steel strip. Each measuring head consists of a magnetisation coil which is embedded in transformer oil for cooling and dissipating the heat to the environment or the cooling system via a heat sink, and a magnetic field probe for recording the measured values. The strip is periodically magnetised locally by the two magnetisation coils in pulses until saturation. (Structure: see figure).

The highly sensitive magnetic field sensors measure the gradient of the residual magnetic field strength (in A/m²) on both the top and bottom side of the strip. Averaging these measurements compensates for any vibrational influences on the strip. The resulting gradient (IMPOC raw value) correlates with the strip’s mechanical parameters tensile strength and yield strength.

Model Generation and Correlation Analysis
Generating absolute values for tensile and yield strength using the EMG IMPOC system involves a correlation analysis between the results of destructive testing and the EMG IMPOC raw value. Destructive tests are typically conducted at Continuous Annealing Lines (CAL) or Hot-Dip Galvanizing lines (HDGL). The correlation between the IMPOC raw values and the results from these tests is robust, showing a narrow band of deviation of ±5 % (see figure).

The models used for this correlation analysis are based on linear regression or more complex machine learning algorithms. To ensure statistical reliability, at minimum 300 data records are required for each regression group, which correspond to different material classes. A typical application might involve 10 to 15 regression models. The data necessary for regression analysis includes results from destructive testing, IMPOC raw values, sheet thickness, and optionally degree of skin-pass rolling, and sometimes yield degree.

Broad Application and Industry Impact
The versatility of the EMG IMPOC system allows it to be used in a wide range of production lines. Currently, about 80 systems are operational in HDGL , CAL, pickling lines, and pressing lines in the automotive industry. The broad application of the EMG IMPOC system underscores its reliability and effectiveness in maintaining the high standards required by today’s steel production.

Conclusion
The EMG IMPOC system represents a significant and established advancement in the continuous measurement of material properties in flat ferritic steel production. Its ability to provide real-time, accurate measurements of tensile and yield strength makes it an invaluable tool for industries that demand precision and consistency. As the demand for high-strength steels continues to grow, technologies like EMG IMPOC will play an increasingly critical role in ensuring that production standards are met with minimal deviation.

More Information
For more detailed information on how EMG IMPOC can enhance your production processes, visit the EMG website or contact the EMG sales and service team. Explore how this technology can be integrated into your operations to achieve the highest standards of quality and efficiency.

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