Schwermetall is a leading manufacturer of pre-rolled copper and copper alloy strips. Milling plays an essential part in the company’s production process, as it removes the rough oxide layer that forms on the strip during hot rolling. About half a millimeter is removed from the top and bottom of each strip, ensuring that the strips will gain a smooth, shiny surface during the subsequent cold rolling process.
The milling rolls contain around 200 cutter blades in total, and these lose their sharpness over time. To ensure that the cutter rolls can be safely changed, the motors have to be reliably shut down. The most radical approach is to completely cut off the power supply, but this means getting an electrician to come in and operate the feeder circuit breaker.
"Calling in an electrician only makes sense if we need electrical work doing in the plant," says Marcus Wätzmann, head of Schwermetall's technical office. "But we have to stop the line at least once a day to change milling cutter blades that have reached the end of their service life."
Switching off motor torque safely
The line does not need to be de-energized for this kind of planned maintenance, but it is vital to ensure that the milling machine will not start up unexpectedly. This is handled by Safe Torque Off (STO), a function built in to ABB DC drives as standard – a unique feature in this class of equipment.
The ABB DCS880 drives on Schwermetall’s milling line were installed when the line was upgraded at the end of 2019. The upgrade ensured that both the top and bottom milling rolls with their 550 kW DC drives achieved the required safety level, which guarantees the reliability of the safety function even if a single fault occurs in the system.
The system previously had two switches connected in series to safely switch the motor torque off, but the ABB Drives now have this capability built-in. The STO function provides the maximum Performance Level PL e or Safety Integrity Level SIL 3.
"This gives us the same safety level as before, but with less effort," Wätzmann explains. "Now, all it takes is one press of the shutdown button to ensure that it’s safe to work on the line."
ABB was responsible for the entire drive upgrade, from updating the electrical circuit diagrams to electrical disassembly, assembly and commissioning. As part of the project, the circuit breaker - which was expensive to operate and maintain – was replaced with a simple, maintenance-free contactor.
Customized solution speeds up rebuild
The milling line runs almost around the clock, and the upgrade has helped to streamline operations. The project was easily completed during Schwermetall’s annual Christmas shutdown, thanks to prefabricated mechanical solutions provided by ABB. Upgrading the drive cabinets involved adapting busbars, mechanical adapters, the size and orientation of the busbar connections, contact hazard protection, acrylic panels, and other components. However, the whole process was made quick and easy by the kit of standard, highly safety compliant products supplied by ABB. On request, ABB can take over the engineering work as a whole, including planning and implementation of upgrade projects in line with the customer's wishes.
Prior to the upgrade the milling machines were controlled by older drives that ABB had taken out of production a number of years previously.
"This was the first time we had used DCS880 drives at our plant, but we found the upgrade easy to manage and we only needed to assign one of our employees to supervise it," Marcus Wätzmann recalls. "Cooperation with ABB went very well. The project planning, management and implementation was extremely smooth."
He is pleased that ABB continues to develop drives for DC motors, which have proven themselves in many applications in heavy industry and are still in use. "In this respect, ABB has been more innovative than other drive manufacturers in recent years," he concludes.
Following the success of the milling line upgrade, Schwermetall has decided to upgrade a further six drives in other parts of its plant to ABB DCS880s.
Schwermetall Halbzeugwerk GmbH & Co. KG
Founded in 1972, Schwermetall is located in Stolberg, around 55 kilometers southwest of the city of Cologne. It is a leading manufacturer of pre-rolled copper and copper alloy strip, which is used in the manufacture of connectors, coins and many other types of product. Schwermetall is a joint venture of Aurubis AG and Wieland-Werke AG, and it has around 300 employees. Turnover averages EUR 370 million with production of some 200,000 tonnes per annum.