Vision-based strip-­steering control

The Electrics & Automation experts at Primetals Technologies, together with thyssenkrupp Steel Europe, have devised a new vision-based strip-steering control system for hot-strip mills. From the start of the development phase, the solution was intended to further improve strip quality by enabling even tighter tolerance levels for the strip profile and for strip flatness. Also, the buildup of camber was to be counteracted. The finalized solution met all expectations. During the pilot phase, nearly 18,000 coils were produced to statistically validate the effectiveness of the strip-steering control system. Results showed that with the steering control system turned on, the lateral displacement of the strip was dramatically reduced, whereas with the system switched off, the displacement strongly correlated with the evolved thickness wedge after the finishing mill (see comparison below for a visualization of the effect). Improvements were achieved for all products rolled in the testing mill, and for all material grades usually targeted.

While the complete strip-steering control system is complex and involves sophisticated control mechanisms, it could not function without a reliable sensor. Since operating conditions in a hot-strip mill are demanding (significant amounts of dust and splashes of cooling water), the sensor had to be able to withstand the challenges of its environment. The technology experts chose a custom-made optical sensor called the “ShapeMon” sensor—a combined camber and centerline measurement device with the ability to also measure the width of the strip. thyssenkrupp decided to keep the vision-based strip-­steering system in regular use at its Duisburg plant, based on the excellent results delivered by the solution.

Lateral displacement of the strip in successive stands, and thickness wedge of the rolled product without strip-steering control Photo: primetals.com
Lateral displacement of the strip in successive stands, and thickness wedge of the rolled product with active strip-steering control Photo: primetals.com