Mathematical modelling of the interrelated electric and mechanical systems of continuous sub-group of the rolling mill stands. Part 2. Study of dynamic loads in the universal mill stands

It was proposed to use the mathematical model considered in [1] for study of the repeated dynamical processes emerging within the electric and mechanical systems of the edging rolls of the universal mill stands at the strip gripping by rolls of the tandem horizontal stands. The analysis of the oscillograms representing transient processes of current and speeds of the electric drives of the horizontal and edging rolls installed at the universal stand No. 4 of the 2.000 mm wide-strip mill at OJSC Magnitogorsk Iron and Steel Works (OAO MMK) has helped to define reasons of the unallowable dynamical loads. The main reason is the incoordination of the speed of the strip leaving the edging stand rolls und linear rotation speed of the horizontal stand rolls. The paper provides results of the mathematical modelling of this dynamic mode under the starting conditions that correspond to the actual processes at the stand. To generalize the results, we compared designing and experimental data obtained at rolling of over 90 variable gauge strips. It has been proven that there is a (near-linear) dependence of current of the electric drive of the edging rolls on the related incoordination of the linear speeds of the edging and horizontal rolls. Based on this fact, it is justified to apply proportional control action on the speed of the electric drive of the horizontal rolls which provides dynamical load limitation. It has been shown that the relation of the linear speeds is greatly influenced by the steady-state error appearing in the electric drive with the proportional speed controller. The paper presents methods and technical solutions providing dynamic load limitation due to the coordination of the universal stand roll speeds and compensation of the speed control error by means of its increase before or immediately at the strip gripping.