ON any factory floor, developing a manufacturing system that achieves both absolute safety and optimal production KPIs can be a challenge. This is all the more so when processing large heavy products at high throughput rates. Making all this happen within a fast-track engineering design/development timeframe calls for a fair measure of ingenuity, particularly in the area of safety control and automation.
Australian steel product manufacturer, Smorgon Steel , faced this challenge in a recent upgrade at its steel angle and channel plant.
Located at its Laverton North manufacturing facility on the outskirts of Melbourne, the plant annually produces 50,000 tonnes of steel angle and channel, in lengths of up to 15 metres. Historically, the steel lengths underwent a final straightening process at an independently-owned off-site straightening facility, four kilometres from the Smorgon site. So when the off-site facility ceased operations in March 2005, a challenge was presented to the steel manufacturing giant.
According to Smorgon Steel project electrical superintendent, Wayne Pearse, maintaining production was the company’s first priority.
“Smorgon has a market to supply and our customers come first,” said Pearse. The company was quickly convinced that relocating the entire straightening plant to the Laverton North site was the best choice.
While the key benefits were the significant savings to be made in transport costs, the core challenge was to ensure the relocation could be achieved within a tight timeframe with no impact on throughput.
As an interim measure, Smorgon Steel gained a six month extension on the off-site building lease, then manned it with its own workforce. Meanwhile, the design and development of the new on-site straightening facility began in earnest. The entire project, from conception to commissioning, had to be completed in just six months.
Let’s get it straight
THE off-site straightening facility relied heavily on forklifts and manual labour to manoeuvre the steel lengths in what was a materials handling operation of the highest order. Individual two tonne bundles of steel were delivered, unstrapped, de-bundled, orientated and straightened, and then repacked for transport without any automation or remote control.
According to Pearse, the combination of heavily-laden forklifts and personnel within a contained and busy work space represented an unacceptable safety risk to Smorgon Steel. There had to be a better way.
The company indeed determined that “better way”. In place of the “forklift plus manual handling” materials handling system, a network of chain conveyors, roller transition tables and overhead cranes would manipulate the heavy steel product as it passed through the straightening process.
Much of the entire process would be contained within three fenced “safety zones” to ensure personnel remained clear of potentially hazardous operations. An integral safety control system would permit remote control of the entire straightening, steel transport, de-bundling and bundling process from consoles located in “safe zones” outside the fenced areas.
Smorgon Steel’s site-wide culture of safety was a major factor in the design of the new straightening facility. Familiar “site-standard” safety isolation stations and gate-latching systems would be employed across the new plant.
The design process was an all-inclusive systematic one consisting of formalised hazard risk analyses, carried out by teams of Smorgon operators, technicians, engineers and its 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 would be applied plantwide, with Category 4 applied to emergency stop systems. External regulatory groups were also consulted.
“Smorgon worked with Worksafe Victoria to ensure all safety regulations were exceeded,” Pearse explained.
“We determined that the Category 3 requirements could be met in the three safety zones, by using double-block-and-bleed plus feedback on hydraulics and pneumatics, safe-off on the drives, and so on,” said Pearse. “Our design process provided a fundamental indication as to what was required control-wise and how it would operate.”
Fast-track to safety
WHILE the broad system concept design was established, the control platform itself remained a question. The traditional approach to safety control is to deploy a pair of linked controllers - a conventional PLC coupled with a dedicated safety controller. The design and development of the control system is typically carried out in two distinct stages: the PLC-based conventional control is first established as the system’s “foundation”, while the “safety” control aspect is retrofitted in the second stage.
While this approach had been used in safety control applications across Smorgon’s Laverton North site, the fast-track nature of the straightening plant project had Pearse assessing other options. A fully integrated safety and standard control platform would allow for faster implementation and flexibility.
Pearse reviewed Rockwell Automation ’s Allen-Bradley GuardLogix controller, part of the Logix family of Integrated Architecture control solutions.
The controller features a two-processor safety architecture that enables integrated safety and conventional control within the one platform. GuardLogix uses RSLogix 5000 programming software and allows users to program and manage their safety control system using familiar standard control methods.
Pearse had a GuardLogix-based trial system of his proposed control solution (which also incorporated Allen-Bradley drives, safety networks and I/O) connected, programmed and operating in his office in just two days, and in “run” mode within three hours. This fast deployment, coupled with the system’s performance under a series of harsh electrical tests, had Pearse convinced that GuardLogix was the ideal solution for this fast-tracked project.
“After I confirmed the GuardLogix’s TÜV certification, it was full steam ahead,” said Pearse.
THE GuardLogix controller forms the heart of a completely integrated “safety-plus-standard” control solution across the new straightening plant. The system comprises a seamless network of controller, drives, DeviceNet communications and distributed I/O.
The plant’s 19 variable speed drive applications (used to regulate the speed of the plant’s myriad of chain-driven transfer tables, cranes and so on) are founded on the Allen-Bradley PowerFlex 70 AC drive with “DriveGuard” option.
In addition, a distributed array of both Allen-Bradley Flex I/O and Safety I/O supports the facility’s distributed I/O requirements.
The drives on each of the 19 drives provided Pearse and his team with substantial savings in installation time, labour and valuable space within the plant’s main control panel.
DriveGuard consists of an electronics card internally mounted within the PowerFlex 70 drive that equips each drive with a “safe off” functionality compliant with Category 3. DriveGuard achieves this functionality without requiring the dual drive output safety contactors typically used in legacy Category 3 drive applications.
With 19 separate drives installed, the resultant space saving achieved in the plant’s main control panel and switchroom were substantial.
Both the drives and the distributed I/O are linked to the system’s GuardLogix heart via DeviceNet. Two separate DeviceNet networks - a conventional DeviceNet, plus a Category 4-compliant DeviceNet Safety - are employed for standard and safety communications respectively.
According to Pearse, the combination of distributed I/O and DeviceNet dramatically improved site installation and wiring time.
“While a single DeviceNet Safety network would have been sufficient, we chose to segregate the two so it was consistent with the remainder of our plant,” said Pearse.
A central control panel houses the GuardLogix processor along with the 19 drives, while the three plant floor consoles provide the operators local control of the facility and accommodate both the Safety and Flex I/O.
With Pearse’s project team able to develop both the standard and safety control system and code concurrently, the entire control system was successfully completed and commissioned within the tight project time frame.
“The completely integrated nature of GuardLogix gave us full access to our entire control system and, as the architecture is already set up, it provided an uncomplicated and flexible means of developing the system,” said Pearse.
“Also, with standard and safety control using the same [RSLogix 5000] programming environment, system configuration and troubleshooting times were reduced.”
Consistent safety and maintenance
MAINTAINING a consistent safety standard - both operationally and visually - was very important in the implementation of the new plant. It was Pearse’s aim to ensure that safety systems, such as gate-latching mechanisms and procedures, operated and appeared identical to those elsewhere across the facility.
“Diversifying safety procedures only causes confusion and ultimately accidents,” said Pearse.
Each of the three safety zones is equipped with one safety isolation station and at least one access gate to allow manual contact with the product. The control system ensures that all energy sources are isolated and the equipment has come to rest before any of the access gates can be opened.
Once isolated, an indicator on the access gate advises that the system is safe and enables the operator to open the gate. Entry is only permitted after the operator attaches a personal padlock to the gate and collects it on exit.
Each gate is fitted with an Allen-Bradley GuardMaster TLS-GD2 solenoid-operated safety latch, which provides the all-important Category 3-compliant latch element in the safety zone gate access control routines.
Maintaining the wellbeing of the straightening plant is made easier with the use of an Allen-Bradley PanelView Plus human-machine interface (HMI), which is linked to the GuardLogix via Ethernet/IP.
Mounted in the main PLC panel, the PanelView HMI has been configured by Pearse and his team to provide detailed system diagnostics, allowing technicians to carry out fault analysis without having to directly access the GuardLogix program code.
Further system support is provided by Rockwell Automation in the form of TechConnect, Rockwell Automation’s site-wide technical support for its hardware and software products.
A flexible future
WITH the new straightening facility operating perfectly since September 2005, Pearse envisages further applications for the GuardLogix solution on the Laverton North site.
“We have plans to implement a billet-yard access system with wireless connectivity to the overhead billet crane. GuardLogix will enable us to seamlessly incorporate this application into our control system - once again, we’ll be able to develop conventional and safety control concurrently,” said Pearse.
In addition to expanding the use of GuardLogix, bringing on-line access to Smorgon’s control system is a high priority for the company. “Internet connectivity for off-site diagnostic support is a must, considering our process runs 24 hours a day, five days a week,” said Pearse. “We already have the infrastructure in place enabling Internet access from on-site PCs, so off-site connectivity is the next logical step.”
The GuardLogix integrated safety control system has helped Smorgon Steel realise a two-pronged success: world-class operational safety and substantial savings in the freight costs that were associated with off-site straightening.
By leveraging Rockwell Automation’s Integrated Architecture and demonstrating ingenuity beyond the typical, Pearse and his team were able to optimise production, while ensuring the absolute safety on the Smorgon Steel factory floor.