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Evraz NTMK at Nizhny Tagil Metal Works of Russia wanted to replace an old rail straightening machine with a modern and robust computer-controlled one. Increasing capacity and specification for the new higher grades of rail, this machine would be the largest of its kind in the world. Ancillary items to be supplied included hydraulic power packs, lubrication packs, an entry product manipulator, automatic roll change rigs and scale removal conveyors.
It consists of two machines in a series – a horizontal straightener with nine main roll drives and vertical straightener with eight main roll drives. The supplied drive system would control these main drive rolls, employing both speed and torque control.
Accurate positioning systems were required to set the rolls both axially and radially, in order to achieve the correct amount of bending and straightness without introducing residual stress. Fast changeover of roll position settings was important to increase productivity and reduce downtime between changes.
Iconsys chose Siemens Sinamics S120 inverter drives configured in a common DC bus arrangement to control the main drives. A 3200A incomer section supplied two 800kw Smart Line Modules, connected in parallel, to give a maximum DC bus current of 3400A.
A suite of cubicles housed the main drive inverters, all fed directly from the DC bus. The many auxiliary AC motors were controlled by direct online starters housed in a separate cubicle and started up prior to production, from dedicated screens on the HMI.
Overall control was by a Siemens S7 PLC system, whose main functions were to control the speed and torque set-points of the main drives, calculate theoretical set-points for the position loops and execute the position control loops.
Commissioned during a 2011 planned shutdown window, the new machine was successfully put into production on schedule. It’s achieving results which exceed those required for straightness, while also passing the equally important residual stress tests.
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