Verbesserung der Formtoleranzen kaltgewalzter Spaltbänder durch eine piezoelektrisch unterstützte Walzspaltregelung

Schätzler, Sven Matthias; Hirt, Gerhard (Thesis advisor); Abel, Dirk (Thesis advisor)

Aachen : RWTH Aachen University (2021, 2022)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2021

Abstract

This thesis describes improvement potential of thickness and width tolerances in the production of thin and very narrow (>20 mm) cold-rolled slit strip. These shape tolerances have a direct influence on the quality of the products made of them. The present thesis shows how an additional high-precision rolling process applied on a modified tandem cold rolling mill can improve the currently producible shape tolerances. In the beginning, the thesis is focusing on improving the thickness tolerances by means of a model-predictive strip thickness control concept developed in cooperation with the IRT of the RWTH Aachen University. This concept tries to compensate as many process disturbances of the rolled strip thickness as possible by continuously adjusting the roll gap with high precision and dynamics. This control concept uses, a self-designed strip thickness measuring device to be able to measure high-frequency strip thickness fluctuations. In addition, it uses various adaptation methods to take into account, for example, low-frequency, non-measurable process influences. Since conventional actuators for roll gap adjustment could no longer withstand these dynamic requirements at high rolling speeds, the suitability of piezoelectric actuators was examined in this thesis. At low rolling forces, as occur in the high-precision rolling of slit strips, piezoelectric actuators show superior dynamics compared to conventional actuators for roll gap adjustment. However, due to their short stroke length, they can only be used as a supplement to conventional actuators. Experimental investigations showed that even at the maximum system speed of 300 m/min, the piezoelectric-assisted actuating system can follow the target trajectory accurately. With this additional high-precision rolling pass, the existing thickness tolerances of 8 µm could be reduced by half. In an additional part of this dissertation, the concept of strip thickness control was extended in order to be able to similarly improve the width tolerance of a slit strip by flat rolling with piezoelectric-assisted roll gap adjustment. Considering that in flat rolling, the roll gap change required for the thickness control also changes the width of the rolled material. Consequently, in addition to the roll adjustment, a further influencing variable is necessarily required to set a defined strip width and thickness at the same time. Carried out Model-based FEM simulations showed that splitting a height reduction into two roll stands with different roll radii is suitable for this task. For the larger the work roll radius, the more material flows into the width of the strip during flat rolling. If more width is desired to improve the width tolerances, the roll stand with the larger work rolls can take over a higher part of the required total height reduction. Experimental verification confirmed that this method is suitable for influencing the width of such slit strip to the required extent. With this additional control system, the width tolerances were improved by more than 50% in case of 80% of the strip length. The results of this research can be used in industrial application for the production of even more precise cold-rolled slit strips.

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