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10/02/2010
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Paul Fanning looks at the application of carbon fibre driveshafts to large-span industrial applications.
 The benefits offered by carbon fibre driveshafts have long been known in the marine sector, where large, carbon fibre driveshafts for large, single spans have eliminated the need for intermediate bearing support and offered greater speed for large boats such as fast ferries. This is especially true in catamarans with two narrow hulls, each containing a staggered diesel engine. Naturally, long, but lightweight shaft lines are required, with the result all sizeable fast catamarans are now equipped with Carbon Fibre Tubes (CFT) for the power transmission between engine and gear and between gear and water jet.
The loss of weight (carbon fibre shafts are typically 70% lighter than solid steel) also means considerable savings in terms of fuel, while the removal of high-maintenance bearings has obvious benefits in terms of wear and tear and overall costs. Equally, carbon fibre's much higher critical speeds allow much longer spans between the bearings. What this means for the application is fewer bearings, fewer bearing pedestals, less power loss, less maintenance, less noise and easier installation.
However, the emphasis on the use of carbon fibre shafts in marine applications has tended to obscure their suitability for others. In fact, in many applications where there is a requirement for long-span drive shafts, carbon fibre may offer an answer.
Nigel Smith, sales manager for Centa, which has been at the forefront of this technology for some years, is enthusiastic about the possibilities. "Marine is the primary application for carbon fibre driveshafts, but it's not the only one," he says. "In Germany, for instance, you've got cooling towers with motor-driven fans in them. They've got a gearbox in the centre of the cooling tower, the fan going round inside and the motors outside. Traditionally, they've had a corrosion issue because the shaft is exposed to a considerable amount of water. As a result, they've used carbon fibre driveshafts, which don't have that problem."
Another instance where this technology has transferred to industry is in at least one pumping station, where there the pump is situated on the floor of the pumping house, but the motor is in the roof. The traditional method of connecting the motor to the pump would be to run a universal joint shaft all the way down the wall to another at the other end. Centa, however, has been able to span this with a single carbon fibre shaft from the pump straight up to the motor.
As well as delivering a lightweight and less cumbersome solution, this also offers considerable safety benefits, as Nigel Smith explains: "If there's a failure of the UJ shaft there's this thing flailing around on the end of the electric motor and it will destroy anything in its path. There are normally metal stairwells around the sides of these sites and it has been known for the shaft to flail the stairwell out. With the plastic carbon fibre shaft, if it breaks – which is unlikely in the first instance anyway - all you've got going around is that bit of plastic."
The use of carbon fibre driveshafts in this context is obviously far from traditional, but that doesn't alter their potential. Says Smith: "One of the things people really don't appreciate about carbon fibre is just how much torque you can transmit with it. The smallest shaft we've provided is 250 hp and the biggest we've built is 23mW. The biggest we've quoted for is 60mW."
This remains far from being a common industrial solution, however. "We haven't broken into that market yet by any means. We've supplied a couple of shafts, but it's certainly not a core application as yet… I don't think people are resistant to the idea as such, they just don't know. I don't think there's any resistance to the idea once it's presented to the right people."
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Author
Paul Fanning
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