Per: Philip J Lawlor (Primetals Technologies Limited, UK), martyna tulwin (Primetals Technologies Limited, UK), john n stevens (Primetals Technologies Limited, UK)
Abstract:
There are many installed cold single-stand or tandem mills, and all cold rolling producers face the challenge of extending their output and reducing the cost of production – new alloys, wider strip, heavier coils, higher throughput. This is necessary to achieve or maintain competitive advantage. Each mill line has its own limitations on maximum strip width and coil diameter, and torque available by stand. Changing these may need major investment. However, a line’s throughput is often held back by the time to change over from one coil to the next, or by the need to keep final coiling temperature low enough. These can be tackled on an existing line without huge investment.
Reducing the dead time between rolling one coil and the next will allow greater throughput in the line. Clever combinations of automation and minor equipment upgrades, with operator training, can reduce the overall time needed. This gives a shorter cycle to decelerate and tail out the strip, remove a spool or pup coil and replace it with a new entry coil, take out the finished coil and place a new empty spool, and thread and accelerate the next strip.
Maintaining the final coiling temperature below a certain limit, while keeping all mill stands running as close as possible to their speed or torque limits, optimises the line throughput. This is only possible by removing enough heat from the strip at the stand, or between mill-stands for tandem lines. Of course, increased rolling speeds will generate more heat in the strip and reduce the time to remove that heat. Therefore good design of cooling, for the work rolls and for the strip between stands on a tandem line, is crucial to achieving the best possible throughput. If this is combined with automation solutions, which can vary the reductions and rolling speed to keep the final coiling temperature within close limits, then the final properties of the cold rolled strip will be very consistent.
Achieving these aims needs a combination of skills; mechanical and fluids engineering, Level 1 and Level 2 automation expertise, metallurgical and process knowledge and thermodynamics. This paper discusses how to address these challenges and possible solutions to optimise existing asset utilisation.
