Bearing life?

[Ryland3210]

How about this, then:

 

Do tapered roller bearings necessarily have to slide to some degree -- all the time?

 

Not on the rolling surfaces. The spatial cones described by the inner and outer races both intersect at the same point along the axis of rotation. The rollers are tapered to match. However, retaining walls alongside the groove are places where sliding can take place. In a good design with adequate lubrication, this is not the long term cause of failure.

 

As Pete points out, absent adequate lubrication, there is the potential for scuffing caused by the sliding of ball retainers. Another cause of failure is spalling caused by extreme contact pressures caused by overloading. This is where the surface fails in compression, and pits form.

 

In theory, if the lubricant is free of particulate contamination, since the design fatigue life of bearings is infinite, failure comes down to overloading, contamination, and/or inadequate lubrication. Even with adequate lube, if spalling occurs, you can imagine what those fractured pieces of hardened steel will do to the balls and races to cause skidding and rapid failure.

 

Pete's certainly on the right track to make sure the lubrication is right, and cleanliness is vital.

 

Another factor to consider in high RPM applications: A bearing with the same ID and OD but with smaller balls will result in higher rotational velocity of the balls, and more revolutions per second of the balls around the outer race. Moreover, the contact pressure of the balls is increased. Therefore, bearing life will be reduced. For examply, in a pinch, I used a spare bearing on a 1750 RPM pump motor that was identical in overall dimensions, and of good Japanese manufacture, to replace a failed bearing. It lasted about three days! The next one, made in Taiwan (I only bought it because it was in stock) lasted one year. It had the right ball size, and probably decent steel, but the contact seals keeping the lubricant where it belonged failed-support to Pete's point.