The Control System proposed for the automation of a Long Product Hot Rolling Mill can distinguish up to three types of controllers: Master Control System (MCS), Sequential Control System (SCS), and Technological Control Systems (TCS).
In a Long Product Hot Rolling Mill (Bar and Wire Rod Mill), there will exist at least a Master Control System. This system will be in charge of the generation and control of the speed and torque set-points of the main drives. Furthermore, it will manage the speed set-points of certain auxiliary drives, namely pinch rolls and roller tables. Among the functionalities carried out by the MSC are:
- Speed Master Reference.
- Running Modes Management.
- Rolling Speed Calculation.
- Inter-stand Tension reference.
MSC also realized standard calculations such as:
- Cascade Speed Control.
- Minimum Tension Control.
- Minimum Tension Control.
- Loop regulation in the final stands.
As far as the Sequential Control Systems (SCS) is concerned, the number of these systems will be the result of 1) the load of program to be handled, 2) the number of input/outputs to be treated, 3) the specific elements to be controlled, or any other reason that justifies the partition of the sequential operations. Roughly speaking, we can find the following SCS in a large Rolling Mill: Mill SCS (from the exit of the Reheating furnace up to the Cooling Bed), Evacuation SCS (from the exit of the Cooling Bed through the Cold Saw to the Piling Machines and the relation with the subsystems: binder, weighing station, etc.), Wire Rod SCS (if existing), Carrousel SCS related to the Wire Rod Outlet. Furthermore, SCS are also those systems specifically dedicated to tasks with very small cycle times, and therefore requiring their own hardware. For instance, start-stop shears, especially for high- speed outlets up to 32 m/sec.
- Crop and Chopping Shear Control.
- Cut-to-Length Shear Control.
- Continuity Control & Tracking.
- Simulation Rolling (ghost billet).
- Section Positioning in the Cooling Bed.
- Evacuation and Piling.
- Carrousel.
- Interface with other sub-systems: binding/tying machine and weighing stations.
- Emergency Sequences.
Finally, Technological Control Systems are in charge of those tasks directly influencing the process, i.e. Reheating Furnace regulation.
It is important to highlight that the hardware used for each one of the three systems mentioned above is the same. Furthermore, they three systems also share the same programming and diagnosis system. The difference is a mere question of hierarchy and task assignment.