Safety control system for new straightening facility

Friday, 15 September, 2006



When Smorgon Steel's angle and channel plant in Laverton North, Melbourne, decided to bring the final straightening process in house instead of at a soon-to-close external facility, the steel manufacturing giant was faced with a mammoth challenge: a six-month time frame from concept to commissioning. All without impacting on current production levels. So the pressure was on.

The off-site facility had relied heavily on forklifts and manual labour to manoeuvre the steel lengths, but this method of materials handling was an unacceptable safety risk in Smorgon Steel's own contained and busy workplace. The project team decided instead on a network of chain conveyors, roller transition tables and overhead cranes to manipulate the product through the straightening process. In addition, they opted to contain much of the process within three fenced 'safety zones' to ensure personnel remained well clear of potentially hazardous operations.

A safety control system, permitting remote control of the entire straightening, transport, de-bundling and bundling process from consoles located in 'safe zones' outside the fenced areas, was another essential dictated by Smorgon Steel's site-wide culture of safety.

The systematic design process encompassed formalised hazard risk analyses carried out by teams of Smorgon operators, technicians, engineers and permanent on-site safety representatives. Working to the Australian Standard for machine guarding, AS4024, risk matrices were developed to identify the necessary system safety category. Category 3 was applied plant-wide, with category 4 applied to emergency stop systems. External regulatory groups, such as Worksafe Victoria, were consulted to ensure all safety regulations were exceeded.

While the broad system design concept was quickly established, the control platform initially remained in question. The tight project timeline did not allow for the traditional 'PLC control with dedicated safety control overlay' approach. The search was on for a fully integrated safety and standard control platform that would allow for faster implementation and flexibility.

With the release of the Allen-Bradley GuardLogix controller, which features a two-processor safety architecture enabling integrated safety and conventional control within the one platform, Smorgon Steel project electrical superintendent, Wayne Pearse was presented with a suitable option. Pearse had a trial system connected, programmed and operating in his office in just two days, and in 'run' mode within three hours.

The GuardLogix controller forms the heart of what is a complete integrated 'safety-plus-standard' control solution across the new straightening plant. The total system, based on Rockwell Automation's Integrated Architecture, comprises a seamless network of controller, drives, 'DeviceNet' communications network and distributed I/O.

A total of 19 variable speed drives (used to regulate the speed of chain-driven transfer tables, cranes and so on) are founded on the Allen-Bradley PowerFlex 70 AC variable speed drive with 'DriveGuard' option. In addition, a distributed array of both Allen-Bradley Flex I/O and Safety I/O supports the facility's I/O requirements. DriveGuard comprises an electronics card mounted within each PowerFlex 70 AC drive, equipping each drive with 'safe off' functionality compliant with Category 3.

Two separate DeviceNet networks, conventional plus a Category 3-compliant, are employed for standard and safety communications respectively. Although a single DeviceNet Safety network would have sufficed, the two were segregated for consistency with the rest of the plant.

A central control panel houses the GuardLogix processor along with the 19 PowerFlex 70 AC drives, while three plant floor consoles provide the operators with local control of the facility and accommodate both the Safety and Flex I/O.

With Pearse's project team able to develop the standard and safety control system and code concurrently, the entire control system was successfully completed and commissioned within the tight deadline.

The GuardLogix integrated safety control system has helped Smorgon Steel achieve world-class operational safety. By leveraging Rockwell Automation's Integrated Architecture and demonstrating ingenuity beyond the typical, Pearse and his team has been able to optimise production, while ensuring absolute safety on the Smorgon Steel factory floor.

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