Ultrasonic roll bite measurements in cold rolling – Roll stress and deformation

In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip flatness defects and thickness inhomogeneity. To control the process, several online measurements are usually carried out such as the rolling load, forward slip and strip tensions at each stand. Shape defects of the strip are usually evaluated after the last stand of a rolling mill thanks to a flatness measuring roll. However, none of these measurements is made within the roll bite itself due to the harsh conditions taking place in that area.

This paper presents a sensor capable of monitoring roll deformations as well as roll radial stresses in situ and in real time. The sensor emits ultrasonic pulses that reflect from the roll surface. The time-of-flight (ToF) of the pulses is recorded during the testing.

The sensor system was incorporated into a work roll and tested on a pilot rolling mill. Measurements were taken as steel strips were rolled under different strip elongation. Roll deformation and radial stresses obtained from the experimental data are in good agreement with numerical results computed with a cold rolling model developed in non-linear Finite Element software.