Insulated bearings key to higher maintenance intervals 01 November 2009

Today's generation of trains can travel further, faster and with much longer maintenance intervals, largely as a result of developments with ac traction motors.

However, bearings specialist NSK makes the point that operators are now looking for maintenance-free running intervals of 2 million km for future trains, compared with the current 900,000km.

And the way to achieve that, says a company spokesperson, is to specify modern insulated rolling bearings.

"A major obstacle to achieving extended maintenance-free intervals is electrical erosion. This occurs when stray electric currents flow through motor bearings to earth. The result is damage to the bearing," he explains.

"The damage is usually in the form of craters on the bearing raceway and rolling element surfaces, resulting in premature bearing failure," he adds.

NSK, he says, has now developed a range of insulated bearings to combat the problem, using two new processes – one using ceramics, the other a PPS (polyphenylene sulphide) resin.

"The ceramic coating [mainly alumina over a bond coat to improve steel adhesion] is plasma sprayed onto the bearing outer ring. Then the bearings are coated with acrylic resin, which impregnates the pores of the ceramic coating and seals the surface."

The technologies are already being proven every day: NSK's bearings are in use on the latest generation Shinkansen Bullet trains.

But the other development concerns material specification and mechanical design of the bearings themselves. NSK cites both special tempering operations, that improve dimensional stability at high motor operating temperatures, and advances in cage manufacturing technology, which have enabled a one piece, rolling element guided cage to be used.

Brian Tinham

Related Companies
NSK Bearings Europe Ltd
NSK Europe Ltd

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