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Methods for online measurement and control of section deviations during hot rolling of wire rod and bars

In the joint project PIREF, the metal forming group of the University of Duisburg-Essen has collaborated with the University of Applied Sciences Ruhr-West Mülheim (Ruhr), the University of Siegen, EMG Automation GmbH and SMS group GmbH to develop sensors, for an online measurement of material velocity and cross section as well as control models for the rolling process of wire rod and bars. The University of Duisburg-Essen provided a metal forming process model for the rolling process to assess the influencing parameters on the rolled section precision. A technique was found to segregate height- from width- influencing parameters from a measured cross-sectional area and actual roll gap. With this measuring technology and with help of the process model, rules for control of the rolling process to achieve close tolerances were obtained. The modelling was accompanied by rolling trials on a laboratory rolling mill at the University of Duisburg-Essen, where a typical Round-OvalRound pass sequence was used for validation of the rolling model concerning lateral spread, inlet and outlet velocity as well as rolling force and torque calculation. The present paper shows how the material flow and the distribution of the velocity in the roll gap can be described. In subsequent rolling of bar and rod in a continuous rolling mill the dimensions can be influenced by application of longitudinal stresses and screwdown. The application of stress can be achieved by an inter-stand velocity mismatch. With the developed models the necessary velocity mismatch can be calculated.