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INSOCOAT®
electrically insulated rolling bearings
Many bearing failures in electric motors and generators
are caused by flashovers.
The problem is more common than you might think. The reason flashovers
seldom get the blame is that the traces they leave are hard to see,
and even when the damage is visible the diagnosis is not always
obvious.
You have to examine the bearing closely to detect the signs: dulling
of the surface of the balls, or craters left by violent flashovers,
and fluting in the raceways.
Small cause, great effect
Flashovers occur because the shaft, as well as the inner ring of
the bearing, are charged by induction.
The risk of flashovers increases greatly if the motor has a frequency
converter, as more and more motors do nowadays. In a frequency controlled
induction motor, the shaft acts as an extra rotor bar. It only takes
a few volts of potential to produce a flashover, which means that
even very weak currents can cause damage.
But even though the problem may seem small, the consequences can
be disastrous: erosion of the balls, melting in the tracks and destruction
of grease. All of this causes noise and vibration, shortening the
life of the bearing.
This in turn can lead to unplanned stoppages - and expensive downtime.
Difficult to fix after the fact
To stop the current from taking short-cuts, the bearings or bearing
housings need to be insulated. Many electric motors still lack
such insulation. If you have an un insulated motor, you run a
great risk of suffering needless bearing failures. And to insulate
existing bearings is often a difficult solution. So what can you
do to protect your bearings? Here's the good news: SKF has
developed a simple but effective solution which we call
INSOCOAT®.
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