Improving electric drive control system of cold plate leveler

Abstract

One of the main requirements to producing flat products is to ensure the flatness of the sheet within the strictly specified tolerances. The main flatness defects are longitudinal, central and edge waves that arise during deformation and cooling during thermomechanical rolling. The allowable limits of deviations for various rolled products of different thickness were listed for 5000 plate mill, PJSC “Magnitogorsk Iron and Steel Works” (PJSC «MMK»). It is noted that most of the defects occur due to the roll gap displacement in the rolling process or due to the thermal regime change when cooling. To eliminate these flatness defects, cold plate levelers are installed in the plate mill production lines. Strip flattening process in roll machines is considered and the characteristics of the nine-roll cold plate leveler at 5000 plate mill are given. The designed electric drive control system is considered. It was noted that its main drawback is that it limits the electric drive torque on all the rolls on one level regardless of the metal rigidity. The article considers the roll electric drives in the cold plate levelers as the interrelated controlled members. A control method is proposed, according to which the motor torques are distributed in accordance with the preset design loads. The automatic load control system was developed, which implements this method, simulation model for interrelated electromechanical systems of the cold plate levelers being developed. The load-balancing controller and its adjustment algorithm were considered. A comparative analysis of the electric drive torques for the design and the proposed settings has been carried out. Equality of motor torques was confirmed for the same load distribution factors. The experimental study results are presented and they confirm decrease in torque disagreements when implementing the developed control method. This provides reduction in electric drive overloads and, consequently, improves their reliability and service life. Uniform distribution of roll torques during deformation contributes to more accurate flattening in the straightening process which increases flatness and reduces the number of skipping the processed sheets.