HIGH-throughput manufacturing processes producing millions of units per day often rely on sophisticated process equipment and control systems to help ensure uninterrupted production.
In such high-volume manufacturing applications, the effects of production stoppages can be crippling.
In particular, unscheduled downtime due to emergency stoppages and shutdowns, caused by breaches of safety systems, can impact the company’s bottom line in a matter of minutes.
Amcor Australia understands this complex issue and has responded by recently embarking on a safety upgrade at its Revesby facility.
The safety upgrade included a transition to Allen-Bradley control systems, and the redesign and replacement of the facility’s legacy safety control system architecture.
As the upgrade was to be implemented without impacting production, the company enlisted the local engineering firm, IGR Consulting to obtain a fast-tracked safety control solution.
A significant proportion of the manufacturer’s Australasian operation is devoted to the manufacture of aluminium beverage cans. Across Australia and NZ, the company produces over two billion beverage cans per year.
Its manufacturing facility in Revesby NSW is equipped to produce nearly two and a half million aluminium cans per day. The facility employs the ‘draw and wall iron’ (DWI) process to produce cans.
This production method involves forming shallow cups from aluminium sheet, and stretching or drawing the cup’s walls to form an open-ended can.
A combination of fast-moving precision machinery and sophisticated control systems is used to consistently manufacture large quantities of product. Rolled aluminium sheet is fed into a press, which cuts out discs and forms them into shallow cups using a ‘blank and draw’ die and ‘draw horn’.
These shallow cups are conveyed to one of the plant’s 11 aluminium can body makers, where a can-shaped mechanical ram forces each individual shallow cup through a series of circular dies.
This process elongates the cup’s wall and presses a dome shape into one end of the cup, forming an open-ended can.
The body maker’s ram moves up and back at high speed, forming up to 250 cans per minute. Each time the can-shaped ram retracts, the can is stripped off the ram head and dispatched into a bucket elevator which transports it to the trimming machines.
The trimming machine’s roll-cutters trim the can wall to a pre-determined height, leaving a smooth edge. A separate device is used to roll the freshly-cut edge to form a flange, suitable to receive a lid or closure.
The cans are then washed, etched, decorated, packed and shipped to various beverage manufactures.
Partially completed, the first stage of the site-wide safety and control upgrade is due for completion by mid-2008.
Prior to the in progress upgrade, the plant’s 11 body makers and trimming machines were controlled using individual conventional PLCs.
Each body maker/trimmer pair was equipped with its own PLC interlocked with a separate hard-wired safety control system.
A second PLC was employed at each machine pair to accommodate high-speed control applications. Engineering manager Chris Hilton said the safety upgrade provided the company with the opportunity to implement a more streamlined safety control solution.
“We needed a more user-friendly system with advanced diagnostic and troubleshooting capabilities.
“Our production schedule didn’t allow for a prolonged design and installation process,” he said.
IGR Consulting developed a new integrated safety and standard control solution, founded on the GuardLogix controller from Rockwell Automation.
Featuring two-processor safety architecture, the controller helps to provide integrated safety and conventional control within the one platform.
IGR consulting engineer Karl Schiesser said, “Both standard and safety control of each of the 11 body maker/trimmer pairs will now be managed by 11 individual controllers.
“The high-speed of the Logix platform means that the second PLC is no longer required. This integrated control architecture helps provide us with increased levels of safety functionality and enables easy system expansion.”
The controller is at the centre of the manufacturer’s new integrated ‘safety-plus-standard’ control solution: a seamless network of controllers, Category 4-compliant DeviceNet Safety communications and distributed I/O.
EtherNet/IP connectivity provides interlocking between machines, and links the controllers to the factory’s SCADA system.
Several InView message displays connected to the controllers via an RS232 serial port provide operators with detailed system diagnostics and allow straightforward monitoring.
The InView message displays are configured to help provide detailed system diagnostics. They allow on-site technicians to carry out fault analysis without having to directly access the program code.
Previously, access to the manufacturer’s 11 body makers and trimmers were guarded by three separate hard-wired pneumatic guarding systems, each incorporating a series of relays and pneumatic switches.
“If a guard was opened, the air was cut off and the pressure switch was tripped, activating the safety response,” Hilton said.
“On occasion, these pneumatic switches would fail in the open position, raise a ‘false alarm’ and cause the line to shut down.”
The legacy pneumatic safety system was replaced with a range of safety switches and devices wired back to local I/O, connected to the controllers via a DeviceNet Safety communications network.
With the integrated control system, troubleshooting false alarms and product jams is much easier. When the line shut down, a technician would have to visually inspect each machine-guard in the group to locate the breach.
“Now, the controller allows us to immediately pinpoint the tripped switch. This means our response time is quicker and downtime is minimised,” he said.
Programming and installation
The combination of distributed I/O and the DeviceNet Safety network helped to improve site installation and wiring time.
“Using an integrated control solution means, we don’t have to duplicate its safety and standard inputs,” Hilton said.
This means less wiring and less I/O. Local machine-mounted I/O and the use of a single communications network for both standard and safety communications also helps minimise wiring and streamlines installation.
The completely integrated nature of the system also provided Amcor with programming advantages.
“As the architecture is already set up, developing and expanding the system is uncomplicated,” said Hilton.
“We were able to develop both the standard and safety control system code concurrently. This was a real time saver.”
GuardLogix uses RSLogix 5000 programming software and allows users to program and manage their safety control system using familiar standard control methods.
“It actually provides us with real on-screen info–not a coded database hidden somewhere in systems like our previous PLCs.
With standard and safety control using the same [RSLogix 5000] programming environment, system configuration and troubleshooting are straightforward,” explained Hilton.
Rockwell Automation 03 9896 0300.