Developments and Benefits from Optical Flatness Measurement in Strip Processing Lines

Flatness measurement using shape-rolls has been used in cold rolling mills for a long time. The benefit is obvious since the measured flatness profile can be used directly to control roll bending, tilt and cooling profile. It was therefore integrated in the mill control system at an early stage to control the strip shape against a target I-unit profile. However, since the flatness is also affected by coiling and in down-stream processing lines, there is a need for measurement in a number of places in a steel mill. A shape roll requires high tension and is a large capital investment and there is therefore a need for alternatives. Whereas shape rolls are more or less standard in a cold rolling mill, very few are installed in processing lines today. Instead, optical gauges which measure manifest flatness (flatness not hidden by tension) can be attractive alternatives. It is, however, important to understand under which conditions an optical gauge will give a reliable measurement result and how the measured data can be used to improve productivity, yield and strip quality.