Drives help meet rubber mill safety standards

Published:  05 April, 2019

Ensuring rubber compounder mills capable of operating with bulk weighing up to three tons could stop within 1/6th of a revolution and reverse to meet European EN safety standards was going to be a challenge for materials specialist Clwyd Compounders.

The Wrexham, UK based company turned to Invertek Drives to see how its variable frequency drives (VFD) could help it meet the BS EN 1417:2014 Safety Standard for Rubber Mills.

The need for a solution was exacerbated by a move to a new bespoke manufacturing facility close to its existing site where it was founded in 1979. Its rubber mill and mixing machines had been previously exempted from the regulations but would have to meet the standard when they were moved and recommissioned.

“The EN standard is quite specific in that if a safety bar is pressed in an emergency, the mill rolls have to separate by 35mm within three seconds, and additionally the three-ton rolls must stop within 1/6th of a revolution. In addition, automatic reversal of the rolls has to occur within two seconds of the mill stopping,” said John Haywood, founder and chairman of Clwyd Compounders.

“Our mills vary in size, carrying a lot of bulk with 30kw to 250kw motors operating at speeds up to 1000rpm. The rolls themselves typically operate around 30RPM depending on the material. This means in an emergency situation, and to meet the EN standard, there is a lot of danger as you’re having to stop and then place them into reverse almost instantly.

“The mills must also shut down safely if the mains power supply is lost, which is something which had proved to be an extremely challenging case to handle in the past. The drive must be capable of recovering enough energy from the mill itself to accomplish a safe stopping condition within the allowed time.

“Additionally, some of the mills can go to a massive overload in short time periods and so we needed drives capable of handling this.”

The company’s internal team considered the problem and then met with Invertek’s technical team that helped identify a motor control solution using its Optidrive P2 VFDs.

Kes Beech, technical manager at Invertek Drives, said: “We were confident from the outset that the Fast Stop on Mains Loss feature of our Optidrive P2 along with the excellent motor control performance would ensure the machines would meet the safety standard requirements. Additionally, the Function Block programming would allow us to create a simple system for the automatic reversing.

“The more efficient control of the Optidrives will provide potential energy savings of over 20% by optimising motor start-up, running and stopping while also reducing wear and tear on the motors, reducing long-term maintenance costs and downtime.”

Available up to 250kW, the Optidrive P2 can also provide 150% overload for 60 seconds as standard. It also comes in IP20, IP55 and IP66 enclosures, making it ideal for industrial and heavy-duty environments, including outdoors.

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