Precision measurements in a steel plant

Heißer Rohstahl auf dem Fließband.
© Photo Fraunhofer FHR

Hot crude steel on the production line.

Fertige Stahlbänder bereit zur Auslieferung.
© Photo shutterstock

Manufactured coil ready for delivery.

The extreme working conditions that prevail in steel plants pose a special challenge for the precision measurement techniques in quality control. In that regard, they are the perfect environment for robust radar systems.

Radar technique for highly exacting requirements

Hot and cold rolling are particularly important in the area of steel production as they greatly influence the quality of the final product which is delivered in the form of rolled metal coil. Due to their robustness, radar systems are a meaningful addition to existing measuring techniques. The framework conditions for precise measurement systems in steel plants are, however, anything but optimal: dirt, steam, vibrations and temperature fluctuations make it difficult to use sensitive measuring equipment. Parallel to this, the requirements on the system are very high. These include 24/7 operation, high failure safety and measurement precision to within a few hundred micrometers. Radar systems are characterized by the fact that they use electromagnetic waves that are capable of providing authentic measurements even under conditions of poor visibility. For this reason, a lot of systems that are used for safety-related applications are based on radar technology, whether for people screening, surveillance of airspace to prevent collisions or for driver assistance systems in modern vehicles.

This provides great motivation for the development of radar sensors for the steel industry. Here, the measurement tasks are very diverse. They facilitate the measurement of the belt width, but are also suitable for the determination of the material thickness of the running belt or, in combination with a control system, can also make sure that the belt stays in the middle of the guide roller. The high-precision measurements are carried out remotely, also at distances of up to several meters at high belt speeds of between 4 and 20 meters per second. To meet the speed requirements in plants, the evaluation processes are carried out on modern FPGAs. This ensures that the systems can meet the real-time processing requirements of the plants. In hot rolling mills, the visibility conditions are particularly poor due to the extensive utilization of cooling agents. Radar systems can play out their strengths in these conditions and are capable of achieving excellent results. The measurement dynamics of the in-house developed radar systems play a decisive role in this respect. Depending on the application, the dynamic range of the operating system lies between 60 dB and 90 dB. This means that the distance to the edge of the belt can be detected even in cases where only one-millionth of the emitted transmission power is reflected back to the radar. One further advantage it that the radar beams are hardly influenced by the spray mist.

Precision through innovative techniques

This level of precision can not be achieved with simple standard techniques. For this reason, coordinated algorithms for high resolution were specially developed and implemented for the frequency-modulated radar techniques along with new in-line calibration techniques. The capacity of modern radar sensors was demonstrated in various plants and installations over the last years. At the beginning, there were a number of hurdles to overcome. The implementation of the laboratory measurements in the real working environment revealed problems and challenges that required extensive technological adaptations. Mechanical constructions had to be hardened to suit the raw environmental conditions and special hard- and software interfaces had to be developed for continuous operation. The adaptations vary in the respective plants. This ensures that each plant receives a tailored solution. The final result is a robust, universally applicable radar sensor which can be used to control cold as well as hot rolling processes.

The implementation in real products took place in cooperation with industrial partners who specialize in the integration of measurement techniques in industrial plants for steel production. The aim is to keep a close eye on the product and accompany and support our customers from the initial idea up to the completion of the product. A new round has now commenced in the competition to produce the best system. In the past, systems were built with discrete components. The new generation of radar systems, however, will be entirely built on a single chip using cost-effective SiGe technology. This opens the door for the development of complex multichannel systems for steel production and paves the way for a completely new generation of measurement systems.