Siemens S7 plcs improve reliability for paper convertor

Stora Enso, publically traded and listed in Helsinki and Stockholm, operates global businesses in the paper, biomaterials, wood products and packaging industries. The paper converting machine in question is located at the company's UK Stowmarket facility - a site which deals with up to 100,000 tonnes of paper per annum. The converting machine that was experiencing increased levels of downtime handles 2m-wide reels of paper, cuts and re-sizes it - for example to A3 and A4 specification - for use in the printing and retail sectors.

The issue facing the site management team was the 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 a very busy site.

To alleviate this problem, Stora Enso worked with Siemens partner Underwoods and Tritec Systems to develop an upgrade 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 says: "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 realise 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: "In order to give the company peace of mind through the retrofit, we decided to phase in the conversion to the S7 controllers whilst 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 S5s. This vastly reduced any risk for the company at a very important time and I'm pleased the say the conversion switch over went extremely smoothly."

Increased flexibility

Paul 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 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.

Paul Ives comments: "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."

For more information about Siemens S7 plcs, please go to www.siemens.co.uk/.