Abstract:
In 2014 SMS group received the order to modernize Severstal’s fifty year-old four-stand tandem mill “1700” (TCM). The main aims were to increase the annual production capacity by 200,000 tons and to enlarge the product window and quality, focusing also on automotive grades. Furthermore, the modernization will prepare the mill for later coupling to a new pickling line (PL). On the one hand, improvement of the production is attained by new, stronger mill stands #1-#4 with a new AC drive system at the 1st mill stand, which are already prepared for later transformation into a continuously running PL-TCM. In addition, reduced off-gauge length, increased availability and higher automation level are required to improve the yield. On the other hand, the reduction of the gap time between two coils by automatic functions assists in reaching a higher production rate. New actuators have been implemented in the mill stands (hydraulic adjustment systems, work roll bending, CVC® plus shifting). Furthermore, a new field excitation control of the existing DC drives (Ward Leonard drive trains) and the new drive of mill stand #1 improve the dynamic behaviour of the mill. Based on this, a state-of-the-art thickness and flatness control was able to be introduced to the mill. Especially the flatness is controlled in the first and last stands by using SMS’ X-Shape® measurement and control system of the latest generation. Special automation features in L1, L2 and HMI support the improvements in quality and production rate. One of SMS’s special threading functions, called TRC®, reduces the off-gauge length per coil to less than 10 m. Part of this threading function is also a new, model-based Level 2 set-up system with an interface to the L3 system. The shutdown time was able to be limited to less than three months. Especially the phase between the first mechanical movement after erection and the first rolled coil was shortened to the record time of only 10 days.
