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Retrofitted PLC future-proofs paper converting machine

23 October 2012

A large paper converting machine, located at Stora Enso’s UK Stowmarket facility, has been retrofitted with Siemens S7 PLCs to address issues of control system obsolescence and faltering performance.

The machine is now able to offer increased levels of production reliability. In addition, the PLC offers a future-proofed development platform.

The converting machine was experiencing increased levels of downtime. It handles 2m wide reels of paper, cuts and re-sizes it - for use in the printing and retail sectors. The increasing downtime periods posed an ongoing and potential risk to production as a result of the legacy plc processors used to control the machine. The PLCs were increasingly becoming unsupportable with the supply of spares proving problematic. As the control system aged so an increase in the number of downtime incidents began to occur, causing production issues for what is an extremely busy site.

To alleviate this problem, Stora Enso worked with Siemens solution partner, Underwoods and Tritec Systems, based in Basingstoke, to develop an upgrade solution that would eradicate the common causes of downtime for the machine, increase its reliability and set in place a solid platform for future control system developments. Together the team identified the best route forward and how the retrofit upgrade could be implemented without disruption to daily production levels.

Paul Ives is site manager at the Stora Enso Stowmarket site. He said: “With Tritec and Underwoods we agreed that the best solution was a conversion from the existing Siemens S5 controllers to the more advanced and fully supportable S7 controller. The old system was beginning to present us with spurious faults which would stop the machine and we could not afford to have production influenced in this way. We wanted a solution that would guarantee the machine’s reliability as well as take the opportunity to realize other benefits around production flexibility, diagnostic and error reporting and improved visibility on the machine’s status through the HMI.”

A major consideration of the conversion process was how to implement the changeover without interfering with the machine’s ongoing production requirements. With the machine handling up to 40,000 tonnes of material each year, it was vital that the changeover went smoothly.

Andy McKenzie from Tritec explains the implementation thinking. “To give the company peace of mind through the retrofit, we decided to phase in the conversion to the S7 controllers while at the same time continuing to operate the S5 controllers. By running them in tandem initially, we were able to ensure that if any problems did arise then we could simply switch back to the tried and trusted S5 solution. This reduced any risk for the company at a very important time and I’m pleased the say the conversion switch over went extremely smoothly.”

Ives and his team now have a fully supportable control system that among other things runs the DC motors that power the integral rotary knife which cuts the paper to requisite sizes. The S7 solution has introduced increased flexibility into the process to enable varying sheet sizes to be accommodated and cut on the machine. The old issue of reliability has also been eradicated.

Ives said: “We are delighted with the outcome of the conversion on the Jargenburg Paper Convertor. We now have a fully stable and supportable machine and done away with unnecessary downtime due to small, but time-consuming previous issues around input cards or racks. These have all disappeared and we are fully confident in the production prowess of the machine going forward. Indeed, we are planning further modifications to the machine such as converting the drive system to an AC drive system based upon the S7 technology. This would not have been previously possible. Again, such flexibility allied to the reliability and efficiency we are now experiencing has made the upgrade from S5 to S7 Siemens controllers an excellent decision for our business.”

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