Innovative gearboxes delivers savings for wastewater plant 24 April 2014

Planetary gearboxes offer increased reliability and efficiency, alongside reduced size and weight, compared to conventional alternatives – and site managers at sewage treatment works with ageing plant should consider them.

So says Jim Norton, technical manager at transmissions specialist Brevini.

"Typical efficiencies of the planetary unit are 98% per stage, ensuring that the energy being generated is not being consumed by mechanical losses," he advises.

That efficiency, which is retained even at very low speeds, he observes, can be useful, especially when compared, for example, to worm gears where efficiency is commonly 50%.

"Planetary gearboxes are designed for arduous, continuous applications," he continues.

"They have inherent advantages over conventional helical gearbox designs, because there is an equilibrium of forces on individual gears – so the planet-carrier is in charge of transmitting torque only."

Norton makes the point that conventional helical gearboxes employ a system of bearing-supported gear-carrying shafts where forces are concentrated. Planetary gearboxes have a complete gear system that is in-line, so there are no high torsional loads on the bearings and gear elements.

He gives the example of powering bridges that are fitted to settlement and thickener tanks.

"Whether a central drive system for a full bridge, or a peripheral drive for a half bridge, the load from the scrapers and thickener fences is unrelenting, and the drive must perform at speeds as low as 0.05 rpm, 24 hours a day, 365 days a year."

To drive the scrapers through the settled solids could require anywhere from 1,000—50,000 Nm, depending upon the tank size and the process, he notes.

"By using a planetary arrangement, there are no lubrication problems arising from the drive operating at such low speeds – a condition that can reduce the reliability of conventional gear units."

And he says that Brevini Power Transmission can design and engineer modern planetary solutions that may be fitted as direct replacements for failed gearboxes with no additional engineering required to the bridge.

Brian Tinham

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Brevini UK Ltd

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