Heavy duty and high precision don’t normally go hand in hand, but sometimes even the most brutal industrial process can require a level of precision that demands the use of advanced automation solutions.
In a recent project, Austrian specialist automation company, AT Equipment and Services GmbH, was tasked by its customer, A TEC Group, an Austrian engineering and technologies company with a focus on the optimization and efficiency improvement of cement plants, with the development of a precision control solution for two large permanent-magnet (PM) motors.
Deployed in a dual-chamber shredding unit, used to create alternative fuel from recycled waste for a treatment plant, the PM motors used were not a common product for this type of application due to their size. But what they do offer is more accurate speed control versus traditional induction motors – especially when a gearbox is not part of the equation.
AT Equipment and Services, based in upper Austria, has been developing industrial control solutions for over thirty years. For this project it had a choice of suppliers, but ultimately turned to Rockwell Automation because of its impressive Integrated Architecture® automation and safety solutions; and because of the easier integration of the drive solution within its engineering environment software, Studio 5000®.
The primary challenge in this application was the delivery of accurate speed control from such large PM motors without the use of gearboxes. This involved the deployment of numerous feedback loops and in-depth commission routines.
The shredder application uses chains rotating within a chamber to not only crush and batter the waste/recycled material into pieces, but also to score and roughen its surface in order to increase its surface area. This increased surface area not only helps with drying, but also improves combustion when the output material is ultimately burnt to generate heat.
Herwig Reischl, CEO of AT Equipment and Services, explains the challenge: “Similar shredders use rotating knives to cut the waste material, but they do not modify the surface area, hence the use of chains in this instance. But chain-based systems present their own issues due to friction – frictional heat gains can actually cause the material to melt and clump together. It is for this reason that precise speed control is required, especially here with the lack of gearboxes, not only to make the shredding process as effective as possible, but also to prevent too much heat being generated by the constant abrasion. If the chain runs too slowly, we can also see issues with clumping and hooking.”
Hannes Uttinger, from A TEC Group’s Process Department Alternative Fuel, explains the process: “In operation, the process starts with treated household or industrial waste, comprising mechanically sorted plastics, paper and organic materials. After sorting, cranes or loaders will load the input conveyors with material that is typically 200 to 300 mm in size. This material is then fed into the mill, which comprises two independent grinding chambers, where the material is crushed and abraded. After milling, the material is stored, before eventually being conveyed to a weighing system, prior to being fed into the kilns. In this application, the material is used as an alternative fuel for heat sources in cement plants, one of our core businesses, instead of using coal or oil, but it can also be used in power plants to generate steam. By using recycled materials, the process is more environmentally friendly and it outputs less CO2 and NOx versus coal or oil.”
At the heart of the new control and safety infrastructure is an Allen-Bradley® Compact GuardLogix® Safety Controller in combination with Allen-Bradley POINT I/O™ modules and an Allen-Bradley PanelView™ Plus 7 HMI.
The primary power control equipment comprises two Frame 8 (650 A) Allen-Bradley PowerFlex® 755 AC drives, which are used to drive the two PM motors. Secondary to these are PowerFlex 527 AC drives, which are used to control the screws and conveyors. Both sets of drives leverage the Rockwell Automation Premier Integration approach, which consolidates controller programming, device configuration and machine operation and maintenance activities into a single software environment. This helps simplify systems, and shorten design and configuration times. It also can give end users greater access to critical machine data to make better decisions and stay ahead of downtime issues.
“We were involved from the beginning of the project,” Reischl explains, “including the safety and risk analyses. Rockwell Automation offers very capable solutions from an automation and control perspective, but due to its integrated safety solution it really stands out. Other automation companies offer safety as part of a package, but the Rockwell Automation® components all work together especially effectively.
“We were also able to create safety reports based on SISTEMA,” he adds, “which is particularly easy to achieve with Rockwell Automation components, as data for its machinery safety products is available in the form of a library file to be used with the SISTEMA calculation tool.”
SISTEMA automates the calculation of the attained Performance Level from the safety-related parts of a machine’s control system to (EN) ISO 13849-1. By deploying the Rockwell Automation library data, machinery and system designers benefit from comprehensive time-saving support in the evaluation of safety to (EN) ISO 13849-1.
As well as the PowerFlex AC drives, which include integrated safety within the drives – both models now being available with Safety over EtherNet/IP™ – each chamber has an access point, which incorporates a Guardmaster® 442G Multifunctional Access Box. This integrated safeguarding solution is ideal for full-body applications where guard doors require a higher holding force, a greater tolerance to guard door misalignment and a means for exiting the safeguarded area in an emergency. A choice of operator controls and other options offer flexibility to meet a variety of applications.
AT Equipment and Services and its customer, A TEC, were able to reap multiple benefits by adopting a Rockwell Automation solution, with ease of integration being a key facet. As well as gaining a highly capable motor-control solution, the integrated safety hardware adds to the capabilities and with SISTEMA support, safety integration and calculations were made significantly simpler. Premier Integration of the drives into the engineering environment also streamlines the design, development and installation times.
“The Rockwell Automation team from Austria really helped us to work through the proposal to get the right components in place,” Reischl elaborates, “so we could commence with the detailed engineering element of the project. PM motors are a challenge and are not usual at this size. We needed precise rotational speed, which was achieved using the drives and encoder feedback. It was a challenge to commission, but we had a lot of help from the Rockwell Automation technical team.”
Uttinger concludes: “The shredder is working within its design parameters, thanks to the accurate speed control delivered by the Rockwell Automation drives, which is very impressive seeing as there are no gearboxes. The engineering teams worked very well together too. There were multiple parameters to consider and tying the drives and motors together to achieve the correct set points was vital. It took a while, but the ultimate success in this venture was down a proven range of controller products, coupled to good teamwork and effective technical interactions. We’ve had a great experience with Rockwell Automation and would certainly look to it favourably for future projects.”
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